METHODS, COMPOSITIONS AND SYSTEMS FOR SOLID-STATE BAROCALORIC APPLICATIONS
20240230171 ยท 2024-07-11
Inventors
Cpc classification
Y02B30/00
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
C07C211/15
CHEMISTRY; METALLURGY
F03G7/0614
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
C07C217/08
CHEMISTRY; METALLURGY
F25B23/00
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
C07C211/63
CHEMISTRY; METALLURGY
C07C229/08
CHEMISTRY; METALLURGY
C09K5/02
CHEMISTRY; METALLURGY
C07C211/27
CHEMISTRY; METALLURGY
International classification
F25B23/00
MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
C07C217/08
CHEMISTRY; METALLURGY
C07C211/63
CHEMISTRY; METALLURGY
C07C229/08
CHEMISTRY; METALLURGY
C07C215/08
CHEMISTRY; METALLURGY
C07C211/15
CHEMISTRY; METALLURGY
Abstract
The invention provides methods, compositions, and systems for barocaloric applications such as cooling, heating, and energy storage.
Claims
1. A method of heating or cooling employing a barocaloric cycle comprising: a) providing heat energy to a composition comprising an organic layer comprising optionally substituted C.sub.>3 alkyl chains, wherein the organic layer is in a disordered state and wherein the organic layer is between first and second inorganic layers or comprises a head group capable of hydrogen bonding, halogen bonding, and/or electrostatic interaction with a counterion; b) applying compression to the composition to induce the organic layer to undergo an exothermic phase transition to an ordered state, releasing latent heat; c) removing the latent heat while the composition is compressed; and d) removing the compression to allow the composition to revert to the disordered state.
2. The method of claim 1, wherein the composition comprises first and second inorganic layers separated by the organic layer.
3. The method of claim 1, wherein the compression is hydrostatic or mechanical and/or the latent heat is removed by a heat sink.
4. The method of claim 1 or claim 2, wherein the organic layer comprises a C.sub.>3 alkyl ammonium species.
5. The method of claim 4, wherein the C.sub.>3 alkyl ammonium species is selected from: ##STR00021##
6. The method of any one of claims 1-5, wherein the organic layer is an organic bilayer.
7. The method of any one of claims 1-6, wherein the organic layer comprises a compound of formula (C.sub.nH.sub.2n+1)(C.sub.mH.sub.2m+1)NH.sub.2X, wherein n is 1-3 or 4-36 and m is 4-36; and wherein X is a monoanionic species.
8. The method of claim 6, wherein the monoanionic species is a halide and/or wherein n=m and n=4-36 or wherein n=1-3 and m=4-36.
9. The method of any one of claims 1-6, wherein the composition is a 2D perovskite.
10. The method of claim 7, wherein the 2D perovskite comprises a transition metal halide.
11. The method of claim 10, wherein the 2D perovskite comprises Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Rh, Pd, Cd, Re, Pt, or Hg.
12. The method of claim 11, wherein the 2D perovskite comprises a tetrahedral or octahedral transition metal complex.
13. The method of claim 12, wherein the halide of the transition metal halide is F, Cl, Br, or I.
14. The method of claim 13, wherein the transition metal halide comprises a monovalent metal cation and a trivalent metal cation.
15. The method of any one of claims 9-14, wherein the 2D perovskite is of formula [(R.sup.1).sub.x(R.sup.2).sub.1?x].sub.2MX.sub.yX.sub.4?y, wherein R.sup.1 and R.sup.2 are independently optionally substituted alkylammonium species, wherein X and X are different halides, wherein x is between 0-1, wherein y is 0-4, wherein M is a transition metal; and wherein if y=0 or 4, R.sup.1?R.sup.2 and x?0 or 1.
16. The method of any one of claims 1-15, wherein the organic layer comprises two different molecular structures.
17. The method of any one of claims 1-6, wherein the first and second inorganic layers comprise a silicate.
18. The method of any one of claims 1-6, wherein the composition comprises a metal alkyl phosphonate salt.
19. The method of any one of claims 1-6, wherein the composition comprises a compound of the following table: TABLE-US-00031 Type Chemical Formula 2-D perovskite (OA).sub.2MnCl.sub.4 (OA).sub.2MnCl.sub.4 (NA).sub.2MnCl.sub.4 (NA).sub.2CuCl.sub.4 (DA).sub.2CuCl.sub.4 Mixed 2D perovskites (NA).sub.2CuCl.sub.3Br (NA).sub.2CuCl.sub.2Br.sub.2 (NA).sub.2CuClBr.sub.3 (DA).sub.2CuCl.sub.3Br (DA).sub.2CuCl.sub.2Br.sub.2 (DA).sub.2CuClBr.sub.3 [(NA).sub.0.75(DA).sub.0.25].sub.2CuCl.sub.4 [(NA).sub.0.5(DA).sub.0.5].sub.2CuCl.sub.4 [(NA).sub.0.25(DA).sub.0.75].sub.2CuCl.sub.4 [(NA).sub.0.25(UA).sub.0.75].sub.2CuCl.sub.4 [(NA).sub.0.5(UA).sub.0.5].sub.2CuCl.sub.4 [(NA).sub.0.5(DA).sub.0.5].sub.2CuCl.sub.2Br.sub.2 Di-n-alkyl ammonium salt (n-C.sub.6H.sub.13).sub.2NH.sub.2Br (n-C.sub.8H.sub.17).sub.2NH.sub.2Cl (n-C.sub.6H.sub.13).sub.2NH.sub.2Cl (n-C.sub.6H.sub.13).sub.2NH.sub.2I (n-C.sub.8H.sub.17).sub.2NH.sub.2Br (n-C.sub.12H.sub.25).sub.2NH.sub.2Cl (n-C.sub.8H.sub.17).sub.2NH.sub.2I (n-C.sub.10H.sub.21).sub.2NH.sub.2Cl (n-C.sub.10H.sub.21).sub.2NH.sub.2Br (n-C.sub.10H.sub.21).sub.2NH.sub.2I (n-C.sub.12H.sub.25).sub.2NH.sub.2Br (n-C.sub.18H.sub.37).sub.2NH.sub.2Cl (n-C.sub.18H.sub.37).sub.2NH.sub.2Br (n-C.sub.12H.sub.25)(CH.sub.3)NH.sub.2Br (n-C.sub.12H.sub.25)(CH.sub.3)NH.sub.2Cl Intercalation compound FeOClC.sub.14H.sub.29NH.sub.2.sup.g (first-row transition metal) Ni(CN).sub.2C.sub.12H.sub.25NH.sub.2.sup.h Ni(CN).sub.2C.sub.12H.sub.25NH.sub.2.sup.h intercalated between (C.sub.18H.sub.37).sub.3NH.sup.+ montmorillonite (smectite) Self-Assembled Monolayer (C.sub.18H.sub.37).sub.4N.sup.+ Self-Assembled Monolayer Layered metallo- Mg(O.sub.3PC.sub.22H.sub.45) alkylphosphonate
20. The method of any one of claims 1-19, wherein the compression results from a pressure change of less than 500 bar.
21. The method of claim 20, wherein the compression results in a reversible entropy change of more than 200 J kg.sup.?1 K.sup.?1.
22. The method claim 1, wherein the compression is provided using a pressure transmitting medium (PTM).
23. The method of claim 22, further comprising providing a gas to the PTM that induces a change in a thermal property of the composition.
24. The method of claim 23, wherein the change in thermal property is a lowering of a phase transition temperature and/or a barocaloric effect inversion.
25. The method of claim 24, further comprising removing the gas from the PTM.
26. The method of any one of claims 23-25, wherein the gas is an inert gas that permeates into a free volume of the organic layer.
27. The method of claim 26, wherein the permeated gas interacts with the composition.
28. The method of claim 27, wherein permeation and interaction of the gas with the composition together induce a lowering of a phase transition and/or a barocaloric effect inversion.
29. The method of any one of claims 23-28, wherein the gas is nitrogen, argon, krypton, xenon, methane, ethane, propane, butane, sulfur hexafluoride, or carbon dioxide.
30. A method of storing thermal energy comprising: a) providing a composition comprising an organic layer comprising optionally substituted C.sub.>3 alkyl chains at a first temperature and a first pressure, wherein the composition is in an ordered state and wherein the organic layer is between first and second inorganic layers or comprises a head group capable of hydrogen bonding, halogen bonding, and/or electrostatic interaction with a counterion; and b) reducing compression on the composition to a second pressure to induce a phase transition in the composition to a disordered state, thereby storing energy.
31. The method of claim 30, further comprising increasing compression on the composition to apply a third pressure to revert the composition to an ordered state and release heat energy.
32. The method of claim 30 or 31, wherein the composition comprises first and second inorganic layers separated by the organic layer.
33. The method of any one of claims 30-32, wherein the compression is hydrostatic or mechanical.
34. The method of any one of claims 30-33, wherein the organic layer comprises a C.sub.>3 alkyl ammonium species.
35. The method of claim 34, wherein the C.sub.>3 alkyl ammonium species is selected from: ##STR00022##
36. The method of any one of claims 30-35, wherein the organic layer is an organic bilayer.
37. The method of any one of claims 30-36, wherein the organic layer comprises a compound of formula (C.sub.nH.sub.2n+1)(C.sub.mH.sub.2m+1)NH.sub.2X, wherein n is 1-3 or 4-36 and m is 4-36; and wherein X is a monoanionic species.
38. The method of claim 37, wherein the monoanionic species is a halide and/or wherein n=m and n=4-36 or wherein n=1-3 and m=4-36.
39. The method of any one of claims 30-36, wherein the composition is a 2D perovskite.
40. The method of claim 39, wherein the 2D perovskite comprises a transition metal halide.
41. The method of claim 39, wherein the 2D perovskite comprises Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Rh, Pd, Cd, Re, Pt, or Hg.
42. The method of claim 39, wherein the 2D perovskite comprises a tetrahedral or octahedral transition metal complex.
43. The method of claim 40, wherein the halide of the transition metal halide is F, Cl, Br, or I.
44. The method of claim 40, wherein the transition metal halide comprises a monovalent metal cation and a trivalent metal cation.
45. The method of any one of claims 40-44, wherein the 2D perovskite is of formula [(R.sup.1).sub.x(R.sup.2).sub.1?x].sub.2MX.sub.yX.sub.4?y, wherein R.sup.1 and R.sup.2 are independently optionally substituted alkylammonium species, wherein X and X are different halides, wherein x is between 0-1, wherein y is 0-4, wherein M is a transition metal; and wherein if y=0 or 4, R.sup.1?R.sup.2 and x?0 or 1.
46. The method of any one of claims 30-45, wherein the organic layer comprises two different molecular structures.
47. The method of any one of claims 30-36, wherein the inorganic layer comprises a silicate.
48. The method of any one of claims 30-36, wherein the composition comprises a metal alkyl phosphonate salt.
49. The method of any one of claims 30-36, wherein the composition comprises a compound of the following table: TABLE-US-00032 Type Chemical Formula 2-D perovskite (OA).sub.2MnCl.sub.4 (OA).sub.2MnCl.sub.4 (NA).sub.2MnCl.sub.4 (NA).sub.2CuCl.sub.4 (DA).sub.2CuCl.sub.4 Mixed 2D perovskites (NA).sub.2CuCl.sub.3Br (NA).sub.2CuCl.sub.2Br.sub.2 (NA).sub.2CuClBr.sub.3 (DA).sub.2CuCl.sub.3Br (DA).sub.2CuCl.sub.2Br.sub.2 (DA).sub.2CuClBr.sub.3 [(NA).sub.0.75(DA).sub.0.25].sub.2CuCl.sub.4 [(NA).sub.0.5(DA).sub.0.5].sub.2CuCl.sub.4 [(NA).sub.0.25(DA).sub.0.75].sub.2CuCl.sub.4 [(NA).sub.0.25(UA).sub.0.75].sub.2CuCl.sub.4 [(NA).sub.0.5(UA).sub.0.5].sub.2CuCl.sub.4 [(NA).sub.0.5(DA).sub.0.5].sub.2CuCl.sub.2Br.sub.2 Di-n-alkyl ammonium (n-C.sub.6H.sub.13).sub.2NH.sub.2Br salt (n-C.sub.6H.sub.13).sub.2NH.sub.2Cl (n-C.sub.6H.sub.13).sub.2NH.sub.2I (n-C.sub.8H.sub.17).sub.2NH.sub.2Cl (n-C.sub.8H.sub.17).sub.2NH.sub.2Br (n-C.sub.8H.sub.17).sub.2NH.sub.2I (n-C.sub.10H.sub.21).sub.2NH.sub.2Cl (n-C.sub.10H.sub.21).sub.2NH.sub.2Br (n-C.sub.10H.sub.21).sub.2NH.sub.2I (n-C.sub.12H.sub.25).sub.2NH.sub.2Cl (n-C.sub.12H.sub.25).sub.2NH.sub.2Br (n-C.sub.18H.sub.37).sub.2NH.sub.2Cl (n-C.sub.18H.sub.37).sub.2NH.sub.2Br (n-C.sub.12H.sub.25)(CH.sub.3)NH.sub.2Br (n-C.sub.12H.sub.25)(CH.sub.3)NH.sub.2Cl Intercalation compound FeOClC.sub.14H.sub.29NH.sub.2 (first-row transition metal) Ni(CN).sub.2C.sub.12H.sub.25NH.sub.2 Ni(CN).sub.2C.sub.12H.sub.25NH.sub.2 intercalated between (C.sub.18H.sub.37).sub.3NH.sup.+ montmorillonite (smectite) Self-Assembled Monolayer (C.sub.18H.sub.37).sub.4N.sup.+ Self-Assembled Monolayer Layered metallo- Mg(O.sub.3PC.sub.22H.sub.45) alkylphosphonate
50. The method claim 30, wherein the compression is provided using a pressure transmitting medium (PTM) and further comprising providing a gas to the PTM that induces a change in a thermal property of the composition.
51. The method of claim 50, wherein the gas is an inert gas that permeates into a free volume of the organic layer.
52. The method of claim 51, wherein the permeated gas interacts with the composition.
53. The method of claim 52, wherein permeation into and interaction of the gas with the composition together induce a lowering of a phase transition and/or a barocaloric effect inversion.
54. The method of any one of claims 50-53, wherein the gas is nitrogen, argon, krypton, xenon, methane, ethane, propane, butane, sulfur hexafluoride, or carbon dioxide.
55. The method of any one of claims 50-54, wherein the change in thermal property is a lowering of a phase transition temperature and/or a barocaloric effect inversion.
56. A 2D perovskite composition comprising: a) first and second layers of a transition metal halide; and b) an organic layer comprising a C.sub.>3 alkyl ammonium species selected from: ##STR00023##
57. A 2D perovskite composition having formula [(R.sup.1).sub.x(R.sup.2).sub.1?x].sub.2MX.sub.yX.sub.4?y, wherein R.sup.1 and R.sup.2 are independently optionally substituted alkylammonium species, wherein X and X are different halides, wherein x is between 0-1, wherein y is 0-4, wherein M is a transition metal; and wherein if y=0 or 4, R.sup.1?R.sup.2 and x?0 or 1.
58. The 2D perovskite composition of claim 57, wherein R.sup.1 and R.sup.2 are independently alkylammonium species of formula C.sub.nH.sub.2n+1NH.sub.3.sup.+, wherein n>3.
59. The 2D perovskite composition of claim 57, wherein the composition has a formula selected from: (NA).sub.2CuCl.sub.3Br; (NA).sub.2CuCl.sub.2Br.sub.2; (NA).sub.2CuClBr.sub.3; (DA).sub.2CuCl.sub.3Br; (DA).sub.2CuCl.sub.2Br.sub.2; (DA).sub.2CuClBr.sub.3; [(NA).sub.0.75(DA).sub.0.25].sub.2CuCl.sub.4; [(NA).sub.0.5(DA).sub.0.5]2CuCl.sub.4; [(NA).sub.0.25(DA).sub.0.75]2CuCl.sub.4; [(NA).sub.0.25(UA).sub.0.75].sub.2CuCl.sub.4; [(NA).sub.0.5(UA).sub.0.5].sub.2CuCl.sub.4; or [(NA).sub.0.5(DA).sub.0.5].sub.2CuCl.sub.2Br.sub.2; wherein DA=decylammonium, NA=nonylammonium, and UA=undecylammonium.
60. The 2D perovskite composition of claim 57, wherein R.sup.1 and R.sup.2 are independently alkylammonium species selected from: ##STR00024##
61. The 2D perovskite composition of any one of claims 57-60, wherein X is Cl and X is Br.
62. A barocaloric system comprising: a) a composition comprising an organic layer comprising optionally substituted C.sub.>3 alkyl chains, wherein the organic layer is between first and second inorganic layers or comprises a head group capable of hydrogen bonding, halogen bonding, and/or electrostatic interaction with a counterion; and b) a source of compression.
63. The system of claim 62, further comprising first and second inorganic layers separated by the organic bilayer.
64. The system of claim 62, wherein the organic layer includes a compound of formula (C.sub.nH.sub.2n+1)(C.sub.mH.sub.2m+1)NH.sub.2X, wherein n is 1-3 or 4-36 and m=4-36; and wherein X is a monoanionic species.
65. The system of claim 64, wherein the monoanionic species is a halide and/or wherein n=m and n=4-36 or wherein n=1-3 and m=4-36.
66. The system of any one of claims 62-65, wherein the source of compression is hydrostatic or mechanical.
67. The system of any one of claims 62-66, further comprising a heat sink.
68. A barocaloric system comprising: a) a composition comprising an organic layer comprising optionally substituted C.sub.>3 alkyl chains; b) a pressure transmitting medium comprising one or more gases, wherein at least one gas of the one or more gases induces a change in a thermal property of the organic layer; and c) a source of compression.
69. The system of claim 68, wherein the at least one gas is an inert gas that is able to permeate a free volume of the organic layer.
70. The system of claim 69, wherein the permeated gas interacts with the composition.
71. The system of claim 70, wherein an extent of permeation and interaction of the at least one gas with the composition together induce a lowering of a phase transition and/or a barocaloric effect inversion.
72. The system of any one of claims 68-71, wherein the change in thermal property is a lowering of a phase transition temperature and/or a barocaloric effect inversion.
73. The system of any one of claims 68-72, further comprising a pump for controlling the amount of the at least one gas.
74. The system of any one of claims 68-73, further comprising a heat sink.
75. The system of claim 72, wherein the change in thermal property comprises the barocaloric effect inversion, further comprising a second organic layer that does not undergo the barocaloric effect inversion.
76. The system of any one of claims 68-75, wherein the at least one gas is nitrogen, argon, krypton, xenon, methane, ethane, propane, butane, sulfur hexafluoride, or carbon dioxide.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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DETAILED DESCRIPTION OF THE INVENTION
[0087] Barocaloric effectsthermal changes driven by hydrostatic pressureoffer particularly simple and energy-efficient ways to achieve solid-state cooling. As first-order phase transitions involve a latent heat, large barocaloric effects are expected to occur near the phase transition temperature when the first-order transition is induced by applied hydrostatic pressure. To exhibit a large barocaloric effect, a material must meet the following three requirements: 1) first-order phase transition with large latent heat (G.sub.tr), large entropy change (?S.sub.tr), and transition temperature T.sub.tr close to a desired operational temperature; 2) high sensitivity of the phase transition to applied pressure (i.e., high barocaloric coefficient ?T.sub.tr/?P); and, 3) low thermal hysteresis. As cooling devices operate cyclically, the barocaloric effects must be driven reversibly upon a sequence of application and removal of external pressure; therefore, thermal hysteresis dramatically affects the cooling performance, determining the minimum pressure needed to achieve reversible barocaloric effects (p.sub.rev). Usually, p.sub.rev is proportional to the thermal hysteresis width. Since it is practically beneficial to have low operating pressure (p.sub.rev), identifying barocaloric materials with low thermal hysteresis is highly desirable. Note, additionally, that for a first-order phase transition, the barocaloric coefficient can be calculated using the Clausius-Clapeyron relation ?T.sub.tr/?P=?V.sub.tr/?S.sub.tr where ?V.sub.tr=volume change of the phase transition. Thus, a material must have a high ?V.sub.tr/?S.sub.tr to have a high barocaloric coefficient.
[0088] The invention provides highly generalizable approaches to realizing a new class of materials that display colossalyet tunablebarocaloric effects at relatively low operating pressures. Specifically, this invention describes the use of reversible, solid-solid, order-disorder phase transitions, e.g., in layered, two-dimensional (2D) organic-inorganic hybrid materials for barocaloric cooling (
[0089] The propensity for confined chain melting to drive large barocaloric effect is based on: (i) the wide range of organic phase-change materials that undergo phase transitions near ambient temperature with a large volume change (?V.sub.tr), latent heat (Q.sub.tr), and entropy change (?S.sub.tr); (ii) the organic phase-change materials, when templated with inorganic substances, remain solid-state during the phase change, exhibiting reversible, solid-solid phase transitions with all beneficial phase-change properties (i.e., high ?V.sub.tr, Q.sub.tr, ?S.sub.tr) retained. Unlike magnetocaloric, electrocaloric, and elastocaloric effects, the barocaloric effect is not system-selective and in principle can be observed in any materials, as the free energy of a system always depends on pressure. In summary, this invention reports that order-disorder transition of normal, branched, or functionalized organic chainson or within inorganic structural templatescan be used as a new mechanism to achieve large barocaloric effects relevant to solid-state cooling.
[0090] Layered materials such as two-dimensional (2-D) metal-halide perovskites of the form (R-NH.sub.3).sub.2MX.sub.4 (R=C.sub.nH.sub.2n+1; n>3 (e.g., >4); M=Mn, Fe, Cu, Cd, Pb; X=F, Cl, Br, or I) can undergo chain-melting transitions in the solid state. In these compounds, sheets of corner-sharing MX.sub.6 octahedra create anionic pockets-defined by the axial halides of four adjacent metal centersthat template the arrangement of bilayers of alkylammonium cations through charge-assisted hydrogen bonds. When long-chained hydrocarbon molecules (n>3, e.g., >4) are incorporated, many layered perovskites undergo thermally induced, first-order phase transitions between ordered and disordered states driven by what is effectively a partial melting transition of the hydrocarbon bilayers. As such 2-D perovskites can serve as a highly tunable solid-state platform to leverage the large changes in entropy and enthalpy that accompany hydrocarbon chain-melting transitions for barocaloric cooling (
[0091] In one embodiment, this invention describes barocaloric effects in 2D hybrid perovskites, with a general chemical formula of (R-NH.sub.3).sub.2MX.sub.4, which contain layers of first-row transition metal halides [MX.sub.4].sup.2? (M=Mn, Fe, Co, Cu, Zn; X=Cl, Br, or I) connected by bilayers of ammonium cations (R-NH.sub.3.sup.+).
[0092] In these compounds, organic bilayers are confined by metal-halide inorganic layers. Inorganic layers can assemble (and confine organic layers) via, e.g., hydrogen bonds (e.g., between R-NH.sub.3.sup.+ . . . X.sup.? groups), electrostatic attraction, or a combination thereof. Van der Waals interactions between R groups (see, e.g.,
[0093] Many 2D perovskites with long-chain organic molecules (R=C.sub.nH.sub.2n+1, n>4) are known to undergo thermally-induced, reversible, solid-solid phase transitions near room temperature (20-90? C.) due to the ordering and disordering the organic molecules. As these solid-solid transitions are often accompanied by a large latent heat (>60 kJ kg.sup.?1) and entropy change (>200 J kg.sup.?1 K.sup.?1), layered hybrid perovskites may be employed as solid-solid phase-change materials for passive thermal management and thermal energy storage.
[0094] The main phase transition of these compounds involves disordering of organic chains, often referred to as a chain-melting transition. The mechanism for chain meltingdefined as the rapid diffusion of a kink (one or more gauche bonds) up and down along the CC bonds within an organic chainhas been extensively studied at ambient pressure by various structural, thermal, and spectroscopic techniques, including powder and single-crystal X-ray diffraction, differential scanning calorimetry, dielectric measurements, and infrared and Raman spectroscopies. The dynamics of the ammonium chains have been further investigated at ambient pressure by solid-state NMR techniques and inelastic neutron scattering. In the low-temperature, ordered phase, the confined chains are tilted because their cross-sectional area is less than the area of the halide square (?5?5 ?.sup.2) afforded by the 2D inorganic lattice.
[0095] In the high-temperature, disordered phase, the chains are disordered and effectively occupy the whole cross-sectional area available to them. This results in a large expansion of the interlayer spacing. As the intralayer distances are essentially unchanged due to the robust inorganic templates, this directly leads to large increase in volume (?V.sub.tr/V.sub.0=7-10%). These studies show that the large latent heat, entropy change, and volume change of main phase transition observed in the organic-inorganic hybrid materials originate from confined chain melting process.
[0096] A representative layered perovskite (C.sub.10H.sub.21NH.sub.3).sub.2MnCl.sub.4 undergoes solid-solid, reversible phase transition near room temperature (35? C.) with large entropy change (e.g., ?221 J kg.sup.?1 K.sup.?1) and volume expansion (e.g., ?7.3%). Based on thermodynamics calculations (Clausius-Clapeyron relation), we identified that the phase transition is expected to be highly sensitive to applied pressure (e.g., ?T.sub.tr/?P?28 K kbar.sup.?1). As such, inducing the disorder-to-order transition by adiabatically applying pressure is expected to result in adiabatic temperature increase, e.g., (?T.sub.ad) of ?30 K. Taken together, this analysis suggested that (C.sub.10H.sub.21NH.sub.3).sub.2MnCl.sub.4 should exhibit colossal barocaloric effect.
[0097] To experimentally confirm the existence of large barocaloric effects in layered perovskites, we measured powder X-ray diffraction (PXRD) patterns as a function of temperature and applied pressure for the 2D layered perovskites (C.sub.10H.sub.21NH.sub.3).sub.2MnCl.sub.4 to evaluate the pressure dependence of the transition temperature (T.sub.tr) between ordered and disordered phases of this material. As the thermally induced order-disorder phase transition leads to a clear shift in powder diffractions peak positions (
[0098] The class of existing and potential 2D layered perovskites provide access to a tremendous structural and chemical diversity through the judicious selection of the inorganic and organic moieties that constitute each material. As such, we may control the confined chain melting in these materials leading to not only colossal but also highly tunable barocaloric effects. Indeed, the thermodynamics and kinetics of these pressure-induced phase transitions are controllable, e.g., by modifying: 1) the molecular interactions between the inorganic layers, 2) the flexibility of the organic chains, and 3) the free volume within the organic bilayers.
[0099] For instance, we have synthesized a series of new layered perovskitescontaining Cu, Mn, and Fe metal centers ligated to Cl.sup.? anionswith organic molecules incorporated as bilayers between the metal-chloride sheets that include oxygen-substituted alkyl chains (C.sub.3OC.sub.4), functionalized phenylalkylamines (C.sub.4Ph and C.sub.6Ph), alkyl chains incorporating an ester group (C.sub.nCOOC.sub.2; n=9, 10, 11), and alkyl chains functionalized with alcohols (C.sub.nOH; n=5, 6, 8) that create hydrogen bonding networks within the bilayers (see, e.g.,
TABLE-US-00003 ?S.sub.transition ?S.sub.transition Compound T.sub.tr (K) (J kg.sup.?1 K.sup.-1) (J L.sup.?1 K.sup.-1) Q.sub.tr (kJ L.sup.?1) C OC.sub.4
)
Mn 287 219.7 263.6 73.9 Simple hydrocarbon chains C.sub.11
Mn 308 220.7 264.8 82.1 C.sub.10(COO)C.sub.2
(COO)C.sub.2
F
)
F
)
OC.sub.4)
Cu 243 130.7 183.0 44.5 Functionalized chains C
OH
Ar).sub.2Cu 338 62.7 70.8 23.9 C
OH
OAr)
Cu 396 134 162 64 C
OH
OH).sub.2Cu 309 105.9 148.3 45.8 C
OC.sub.4OH
OH)
Cu 341 145.8 204.1 69.6 C
OC
OH
OH)
Mn 342 223.8 305.0 104.2 C
OPh
indicates data missing or illegible when filed
[0100] Table 1 shows a library of long-chain ammonium cations incorporated into layered perovskites. Structures of long-chain ammonium cations studied in our laboratory (left) and thermal properties of layered perovskites incorporating the ammonium cation chains (right). T.sub.tr, transition temperature; ?S.sub.transition, entropy of phase transition; Q.sub.tr, latent heat of phase transition. (R).sub.2M denotes layered perovskite (R-NH.sub.3).sub.2MCl.sub.4.
[0101] These newly synthesized 2D hybrid perovskites exhibit reversible, thermally-induced phase transitions driven by chain melting. Most notably, the synthetic modifications of the organic chain enabled the tuning of transition temperature between ?30? C. to 120? C. without compromising beneficial thermodynamic properties (e.g., large latent heat and entropy change). These results demonstrate that the barocaloric properties of layered perovskites can be readily tuned through synthetic modifications. Barocaloric effects of the functionalized perovskites synthesized in our laboratory are summarized in Table 5.
[0102] In addition, we have synthesized compositionally engineered mixed halide 2D metal-halide perovskites, e.g., replacing allor a portionof Cl anions with Br anions for mixed-halide systems, e.g., having formula [(R.sup.1).sub.x(R.sup.2).sub.1?x].sub.2MX.sub.yX.sup.4?y, where R.sup.1 and R.sup.2 are long chain alkylammonium species(e.g., C.sub.nH.sub.2n+1NH.sub.3.sup.+, where n>3, e.g., >4, e.g., NA or DA) and where X and X are different halides, e.g., selected from Cl, Br, or I, e.g., (R-NH.sub.3).sub.2MCl.sub.4?yBr.sub.y (0<y?4), e.g., where M is a transition metal (e.g., Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Rh, Pd, Cd, Re, Pt, or Hg) and R is NA or DA. Mixed halide compounds may also be double mixed, e.g., containing two halides (e.g., Cl and Br) and two different alkylammonium species. The different alkylammonium species may be in non-integer ratios, relative to the metal center (e.g., [(NA).sub.0.75(DA).sub.0.25].sub.2CuCl.sub.4, [(NA).sub.0.5(DA).sub.0.5].sub.2CuCl.sub.4, or [(NA).sub.0.25(DA).sub.0.75].sub.2CuCl.sub.4, [(NA).sub.0.25(UA).sub.0.75].sub.2CuCl.sub.4, [(NA).sub.0.5(UA).sub.0.5].sub.2CuCl.sub.4, or [(NA).sub.0.5(DA).sub.0.5].sub.2CuCl.sub.2Br.sub.2). In compounds of the formula [(R.sup.1).sub.x(R.sup.2).sub.1?x].sub.2MX.sub.yX.sub.4?y, y may be 0-4 (e.g., 0, 1, 2, 3, or 4) and x may be between 0-1, e.g., about 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or 0.95. Thermal and structural data on the mixed 2D metal-halide perovskite materials in shown in Tables 21-25. Some mixed 2D metal-halide perovskite materials are compared to non-mixed 2D metal-halide perovskite materials in
[0103] In addition, additional functionalized layered perovskites may be formed by (i) combining two different modifications in a single chain (e.g., C.sub.3OC.sub.4OH) (ii) fluorinating the chain, (iii) synthesizing layered halide double perovskites of the form (R-NH.sub.3).sub.4MMX.sub.8 where M is a monovalent cation such as Na.sup.+ and M is a trivalent cation such as Fe.sup.3+, X=Cl.sup., Br.sup.. In some embodiments, one or more Cl, Br, or I halides may be replaced by F. In addition, additional functionalized layered perovskites may be formed from non-halide anions, e.g., CN.sup., HCOO.sup., N.sub.3.sup., N(CN).sub.2.sup., BF.sub.4.sup., BH.sub.4.sup., PF.sub.6.sup., SCN.sup., OCN.sup.. Incorporation of the larger anions can increase the pocket size for cations (e.g., the alkylammonium species), thus relatively larger cations e.g., the largest cations of Table 1, or even dialkylammonium cations described herein.
[0104] In addition to synthetic tunability and chemical diversity, layered halide perovskites display a number of other properties that are advantageous for practical solid-state cooling. First, the soft nature and high solution processability of layered halide perovskites enables thin films to be easily fabricated. The high processability not only presents rich opportunities for the design of miniaturized cooling devices but may also allow the invention to take advantage of microscopic mechanisms for barocaloric effects across various length scales (from bulk powders to thin films to atomically thin layers) and materials forms (from single crystals to microcrystalline powders to thin films). Second, phase transitions in appropriately designed layered perovskites display small thermal hysteresis (<4 K). Thus, reversible barocaloric effects can be achieved at small operating pressure prev. Given that these layered perovskites display high barocaloric coefficients (>20 K kbar.sup.?1), this suggests that colossal reversible barocaloric effects can be realized at easily accessible pressures (<100 bar) (
[0105] For comparison, organic plastic crystalsanother class of colossal barocaloric materialsrequire relatively high operating pressure of 500-1,000 bar for reversible barocaloric effects. These two featureshigh processability and low operating pressureallow various device architectures with minimal design constraints.
[0106] The confined chain melting described herein is a general mechanism to achieve colossal barocaloric effects because large latent heat, entropy change, and volume expansionprerequisites to colossal barocaloric effectscan simultaneously emerge when long-chain molecules are forced to undergo large conformational changes in confined space. Note that the analysis and experiments described in this invention are readily applicable to other types of layered materials beyond hybrid perovskites. Any organic and inorganic materials that can be assembled into layers of organic material between layers of inorganic material are suitable to be used in the invention. Alternatively or in addition, organometallic materials including a layer-forming inorganic component and an organic component including long, optionally substituted alkyl chains may be used, for example, the following barocaloric materials: di-n-alkylammonium salts (e.g., compounds of formula (C.sub.nH.sub.2n+1).sub.2NH.sub.2X (n>3 (e.g., >4, e.g., C.sub.4-36 alkyl chains) or compounds of formula (C.sub.nH.sub.2n+1)(C.sub.mH.sub.2m+1)NH.sub.2X, where n is 1-3 or 4-36 and m is 4-36, e.g., where n=m, or where n=1-3 (e.g., 1) and m=4-36 (e.g., 6, 8, 10, or 12); where X is a monoanionic species, e.g., a halide (e.g., F, Cl, Br, or I) or a non-halide anion, such as NO.sub.3, ClO.sub.3, ClO.sub.4, H.sub.2PO.sub.4, HSO.sub.4, CN.sup., HCOO.sup., N.sub.3.sup., N(CN).sub.2.sup., BF.sub.4.sup., BH.sub.4.sup., PF.sub.6.sup., SCN.sup., or OCN.sup.), see
[0107] Chain-melting phase transitions and their pressure sensitivity (dT.sub.tr/dP), discussed here in the context of barocaloric cooling (using the 2-D perovskites as proof-of-concept examples), offer a new mechanism to realize highly efficient and tunable thermal energy storage, whereby application of hydrostatic pressure can be used to tune the storage temperature, T.sub.stor, and release temperature, T.sub.rel (
[0108] The material properties required for efficient PT-TES are similar to those required for efficient barocaloric cooling. Materials for PT-TES should undergo solid-state phase transitions with high thermal changes (?S.sub.tr), high sensitivity to pressure (dT.sub.tr/dP), and small hysteresis (?T.sub.hys), because the temperature span of the PT-TES operation (?T.sub.span), defined here as the difference between T.sub.rel and T.sub.stor, is calculated by, ?T.sub.span=(dT.sub.tr/dP)??P??T.sub.hys. Note that PT-TES materials will benefit from having large ?T.sub.span and small ?P, and materials with high dT.sub.tr/dP and low ?T.sub.hys, as well as large ?S.sub.tr and ?H.sub.tr, will be suitable for this. Another difference is, unlike barocaloric cooling (which requires phase transition temperatures near or below ambient temperature), thermal energy storage materials are needed across a broad temperature range. In this context, compositions of the invention, e.g., the two-dimensional metal-halide perovskitesfirst highlighted here in the context of barocaloric cooling due to their large thermal changes (?S.sub.tr and ?H.sub.tr), high pressure sensitivity (dT.sub.tr/dP), and small hysteresis (?T.sub.hys)provide a versatile platform to achieve efficient the PT-TES in the broad temperature range, as their transition temperatures and sensitivity to pressure can be readily manipulated by changing the length of hydrocarbon chains to cover a wide temperature range (from 250 K to 400 K) (Tables 2 to 5). Layered compounds of the invention, e.g., with long-chain hydrocarbons, will be highly competitive PT-TES materials, due to their beneficial phase-change properties, synthetic tunability, and pressure dependence, similar to those of the 2-D perovskites (Table 20) exemplified herein.
[0109] As shown in
Effect of Pressure Transmitting Medium
[0110] The invention also includes methods of enhancing barocaloric cycles based on the properties of the pressure-transmitting medium. The pressure transmitting medium (PTM) can affect the properties of the phase transitions of the barocaloric cycles in materials including long-chain hydrocarbons. The effects include inverse barocaloric effects for compounds (e.g., with long-chain hydrocarbons) that undergo reversible chain-melting transitions. Gaseous PTMs may induce changes in thermal properties of materials with long alkyl chains (e.g., those of the invention) by permeating into and interacting with the materials of the composition, e.g., by permeating into free volume in the organic layer. Gases that can permeate into the composition are preferably inert gases that can also interact with the composition at the microscopic level (e.g., non-covalently interact, e.g., via Van der Waal's-type interactions, e.g., via dispersion forces). Both the extent of permeation (e.g., amount of gas molecules in the free volume/interacting with the composition) and degree and nature of interaction (e.g., strength of interaction, e.g., determined by a molecule or atom's size, shape, polarizability, etc.) can determine the effect of the PTM on thermal transitions of the composition. Exemplary PTM gases include nitrogen, argon, krypton, xenon, methane, ethane, propane, butane, sulfur hexafluoride, or carbon dioxide. Gases that permeate and interact sufficiently with the composition (e.g., argon into (NA).sub.2CuBr.sub.4)) can cause the barocaloric effect of the composition to be inverted.
[0111] In our recent studies, we discovered that the pressure sensitivity (dT/dP) of chain-melting transitions in representative 2-D perovskites(DA).sub.2MnCl.sub.4 and (NA).sub.2CuBr.sub.4depends on the identity of pressure-transmitting medium (PTM). Specifically, as shown in
[0112] These results fully confirm the validity of this phenomenon and establish that (NA).sub.2CuBr.sub.4and other related barocaloric compounds (e.g., with long-chain hydrocarbons), e.g., those described herein, more broadlydisplays highly reversible, giant inverse barocaloric effects under a pressure-transmitting medium that can interact with hydrocarbon chains (and the lattice).
[0113] Most inverse barocaloric effects arise from a decrease in volume upon increase in a degree of freedom (during thermally-induced phase transitions). The mechanism described herein is unique for the following reasons. First, the material (i.e., the host lattice, e.g., a barocaloric material of the invention) still undergoes a volume expansion upon the thermally-induced order-to-disorder transition, and the inverse barocaloric effect is entirely driven by the permeation and absorption of the PTM into the lattice. Second, the magnitude of inverse barocaloric effects can be tuned via judicious selection of pressure medium. As shown in
Methods
[0114] Methods of the invention may include providing heat energy (e.g., from a room, an AC system, heat transfer medium, heat pump, heat sink, etc.) to a composition of the invention (e.g., a 2D perovskite). The heat energy may cause alkyl chains in the composition to undergo a phase transition (e.g., from an ordered to a disordered state, e.g., in a thermal energy storage system) or there may be no phase transition until pressure is applied (e.g., in a barocaloric cooling system). Methods may be for refrigeration or heating.
[0115] In a barocaloric cooling system or method, providing compression to the composition releases latent heat in the composition, which may be removed, e.g., via a heat sink, e.g., a high surface area, high conductivity medium in thermal contact with the composition which may be itself cooled by, e.g., a fan. Removal of the heat is performed while the composition is still compressed, and removal of the compression allows the composition to return to a disordered state, cooling the composition as the endothermic transition occurs. At this point the cycle may be repeated with input of new heat energy.
[0116] In a barocaloric thermal energy storage system heat energy is provided to a composition of the invention causing it to undergo a phase transition to a disordered state. The disordered state is then modified by the application of compression in order to change the temperature at which heat is released.
[0117] Methods of the invention may also include selecting or otherwise controlling the pressure transmitting medium to modulate the barocaloric cycle. For example, selecting a gas (e.g., a high polarizability gas) that sufficiently permeates and interacts with the composition at the microscopic level as the PTM to change the temperature of phase transitions in the barocaloric material, or to induce inverse barocaloric effects such as described herein. Methods may include modulating the barocaloric cycle by altering a ratio of polarizable and on-polarizable gases used as a mixed in a PTM. Methods may include selecting a gas as the PTM that does not interact, or minimally interacts, with the composition (e.g., He), e.g., to not induce changes in thermal properties, or to revert changes caused by an interacting gas.
Systems and Additional Components
[0118] Systems of the invention may include components to provide compressive force to the composition, e.g., pumps, pistons, actuators (e.g., mechanical, hydraulic, or pneumatic, etc., actuators), presses (e.g., mechanical, hydraulic, or pneumatic, etc., presses), piezoelectric actuators, levers, etc. Systems may also include components to transfer or remove heat energy, e.g., pumps, heat sinks, thermoelectrics, fans, chiller pumps, etc. A system of the invention may also include a power source, e.g., to power the source of compressive force, the cooling or heat transfer components, etc. Systems of the invention may include a pressure transmitting medium (PTM), e.g., a gas. The PTM may be a non- or minimally-interacting gas (e.g., a low polarizability gas, e.g., He) or a polarizable gas (e.g., N.sub.2, Ar, Kr, Xe, methane, ethane, propane, butane, sulfur hexafluoride, or carbon dioxide). Systems of the invention may include a pump for controlling a pressure transmitting medium (e.g., a mixture of gases), such as pumps, gas reservoirs (e.g., tanks, cylinders, etc.), pressure sensors, actuators, valves, etc. The PTM may not be a gas, for example, the PTM may be an oil, e.g., a fluorocarbon oil, silicone oil, etc.).
EXAMPLES
[0119] The 2-D perovskite (DA).sub.2MnCl.sub.4 (DA=decylammonium) was selected as a barocaloric material because of its large phase-transition entropy (?S.sub.tr=230 J kg.sup.?1 K.sup.?1) and enthalpy (?H.sub.tr=71 kJ kg.sup.?1), near-ambient phase transition temperature (T.sub.tr=310 K), and lightweight, nontoxic elemental composition. At ambient temperature and pressure, (DA).sub.2MnCl.sub.4 adopts an ordered monoclinic structure (low-temperature, LT, phase) with bilayers of hydrocarbon chainseach of which contain a single gauche CC bond (C2-C3) and seven trans CC bondsaligned parallel to one another and tilted 48.3(1)? with respect to the MnCl plane (
[0120] Differential scanning calorimetry (DSC) measurements (
[0121] To directly evaluate the pressure dependence of the phase transition temperature, isobaric DSC experiments were performed under applied hydrostatic pressures of up to 150 bar using He as the pressure-transmitting medium. The phase transition shifts to higher temperatures as the pressure is increased, with a measured dT.sub.tr/dP of 22.1?0.7 K kbar.sup.?1 during heating and 20.6?0.8 K kbar.sup.?1 during cooling (
[0122] To investigate the origin of the different experimental and predicted barocaloric coefficients, we used helium pycnometry to directly measure the volume change of (DA).sub.2MnCl.sub.4 during the phase transition (
[0123] Under the cyclic operating conditions of a barocaloric cooling system, the lowest possible operating pressure is set by the pressure that must be applied to induce a reversible entropy change, P.sub.rev, when cycling to and from ambient pressure. For a conventional barocaloric effect, P.sub.rev corresponds to the pressure at which the onset temperature of the exothermic phase transition is equal to the onset temperature of the endothermic phase transition at 1 bar. As such, P.sub.rev is proportional to the thermal hysteresis at 1 bar and inversely proportional to the barocaloric coefficient for the exothermic transition, with P.sub.rev=?T.sub.hys/(dT.sub.tr/dP).sub.cooling (16). Owing to its low ?T.sub.hys and high dT.sub.tr/dP, (DA).sub.2MnCl.sub.4 has a predicted P.sub.rev of just 66 bar.
[0124] This low P.sub.rev was further confirmed by calculating the isothermal entropy changes (?S.sub.it). To do so, we first obtained isobaric entropy changes (?S.sub.ib) associated with the chain-melting transition as a function of temperature and pressure by integrating the HP-DSC heat flow signal, Q, obtained at a scan rate of {dot over (T)} over the temperature range from T.sub.i to T.sub.f:
[0125] ?S.sub.it curves were then calculated as the difference between ?S.sub.ib at ambient pressure and ?S.sub.ib at elevated pressure, with ?S.sub.ib values obtained from heating data corresponding to the disordering transition induced by a decrease in pressure (?S.sub.it>0) and ?S.sub.ib values from cooling data corresponding to the ordering transition induced by an increase in pressure (?S.sub.it<0). Excitingly, these ?S.sub.it curves show that a non-zero reversible entropy change can be induced below 80 bar, and the full entropy of the phase transition can be induced irreversibly by applying a pressure of just 100 bar (
[0126] Although quasi-direct methods of calculating isothermal changes-as well as adiabatic ones-from isobaric experiments are commonly used to evaluate barocaloric materials due to the challenge of maintaining isothermalityor adiabaticityduring direct variable pressure measurements, we performed quasi-isothermal HP-DSC experiments to more directly evaluate P.sub.rev by measuring pressure, rather than thermal, hysteresis. Specifically, we measured heat flow signals while cycling the pressure between 1 bar and 150 bar at 311 K. Note that isothermality is maintained until the phase transition onset pressure, which allows us to accurately determine pressure hysteresis. By comparing the onset pressures for compression-induced exotherms and decompression-induced endotherms, we were able to directly measure a pressure hysteresis for (DA).sub.2MnCl.sub.4 of 70 bar, which is in excellent agreement with the predicted value of 73 bar at 311 K (
[0127] In an effort to target barocaloric materials with large reversible entropy changes at even lower pressures, we searched for a 2-D perovskite that undergoes a chain-melting transition with a thermal hysteresis of less than 1 K. Unlike (DA).sub.2MnCl.sub.4, however, the total entropy of the chain-melting transition in most 2-D perovskites is partitioned across one or more minorlower entropyphase transitions in addition to the principal transition (
[0128] Since Br anions can be more readily accommodated within Cu, rather than Mn, 2-D perovskites, we targeted a (C.sub.nH.sub.2n+1NH.sub.3).sub.2CuBr.sub.4 compound with alkylammonium cations of appropriate length to place the chain-melting temperature near ambient temperature. We found that the new 2-D perovskite (NA).sub.2CuBr.sub.4 (NA=nonylammonium) undergoes a chain melting transition at 303 K with a high ?S.sub.tr (78 J kg.sup.?1 K.sup.?1), hysteresis of only 0.4 K, and no minor phase transitions within at least 60 K of the principal transition (
[0129] Isobaric HP-DSC experiments confirmed that (NA).sub.2CuBr.sub.4 features a high barocaloric coefficient with dT.sub.tr/dP of 26.9?0.4 K kbar.sup.?1 and 26.5?0.5 K kbar.sup.?1 during heating and cooling, respectively (
[0130] To provide additional insight into the structural and chemical factors that influence barocaloric effects in 2-D perovskites, we used X-ray crystallography and IR spectroscopy to compare the nature of the chain-melting transition in (NA).sub.2CuBr.sub.4 and (DA).sub.2MnCl.sub.4. In particular, we hypothesized that the increased size of the halide pocket in (NA).sub.2CuBr.sub.4 (30.5 ?.sup.2) relative to (DA).sub.2MnCl.sub.4 (26.3 ?.sup.2)coupled with weaker NH . . . Br hydrogen bonds at the organic-inorganic interfacewould lead to more conformational disorder in the LT phase of the Cu compound. This would reduce the entropy difference between the LT and HT phases and explain the 56% lower molar entropy change of (NA).sub.2CuBr.sub.4, as well as the lower entropy changes generally observed across longer-chain (C.sub.nH.sub.2n+1NH.sub.3).sub.2CuBr.sub.4 (n=11-16) compounds compared to (C.sub.nH.sub.2n+1NH.sub.3).sub.2MCl.sub.4 (M=Mn, Cu, Cd) compounds of the same lengths (Tables 2 to 4).
[0131] As anticipated, the atoms in the NA chains of (NA).sub.2CuBr.sub.4 have much larger atomic displacement parameters in the LT phase than those in the DA chains of the LT phase of (DA).sub.2MnCl.sub.4 (
[0132] Although conformational disorder in the LT phase leads to a decreased entropy change, it also likely contributes to the enhanced reversibility of the (NA).sub.2CuBr.sub.4 chain-melting transition through two primary effects. First, the higher degree of disorder in the alkylammonium chains in the LT phase-along with the softer nature of Br anionsshould make the (NA).sub.2CuBr.sub.4 lattice more compressible than the (DA).sub.2MnCl.sub.4 lattice. Since the barocaloric coefficient dT.sub.tr/dP of a solid tends to increase with increasing compressibility (43, 44), this would be expected to make the phase transition in (NA).sub.2CuBr.sub.4 more sensitive to pressure. Indeed, dT.sub.tr/dP for the transition to the LT phase of (NA).sub.2CuBr.sub.4 is 29% higher than for (DA).sub.2MnCl.sub.4. Second, the presence of certain configurational degrees of freedom, such as gt.sub.2n+1g kinks, in both the LT and HT phases should render the two phases more compatible, lowering both isobaric and isothermal hysteresis. In any case, both compounds display, near room temperature, large and reversible barocaloric cooling, represented by their materials properties T.sub.tr, ?S.sub.tr, and P.sub.rev, and are highly competitive with other leading barocaloric materials (
[0133] In addition to its influence on operating pressure, hysteresis, which leads to dissipative heat losses, adversely impacts the second-law efficiency and coefficient of performance (COP) of any caloric cooling cycle. The impact of hysteresis on efficiency can be quantified by calculating the idealized thermodynamic efficiency, ?, of a caloric materialrelative to the Carnot efficiencyusing a simple material model that integrates the dissipative losses in a Carnot-like cycle:
[0134] Based on this model, caloric materials with ?T.sub.hys/?T.sub.ad,max of less than 10% will have second-law efficiencies competitive with those of conventional vapor compression-based systems (?85%). Excitingly, (DA).sub.2MnCl.sub.4 and (NA).sub.2CuBr.sub.4 display second-law efficiencies of 88 and 93%, while the values found in most barocaloric compounds range between 40 and 65% (Table 19), either because of large ?T.sub.hys or a low ?S.sub.tr that leads to a small ?T.sub.ad,max. Additionally, both compounds display the largest values of barocaloric strengththe reversible isothermal entropy change ?S.sub.it,rev normalized by the driving pressurethan have been realized for barocaloric materials (Table 19).
[0135] These results highlight exciting opportunities to exploit the tunability of 2-D perovskites to independently manipulate phase-change hysteresis, entropy, and sensitivity to pressure for improved barocaloric performance. For instance, it should be possible to realize chain-melting transitions with even higher entropy changes through functionalization of the organic bilayerssuch as by introducing aromatic groups or hydrogen bond donor-acceptor pairsand even lower hysteresis through modification of the organic-inorganic interfacesuch as by incorporating mixtures of different halide anions or introducing defectsor through leveraging multicaloric effects. In addition, the anisotropic nature of the chain-melting transition in (DA).sub.2MnCl.sub.4 and (NA).sub.2CuBr.sub.4wherein an increase in interlayer spacing along a single direction accounts for ?80% of the volume change-suggests that uniaxial stress, which can be readily applied through mechanical actuation, may be able to drive large elastocaloric effects in 2-D perovskites.
[0136] The results and materials discussed herein were obtained according to the following methods.
EXPERIMENTAL METHODS
[0137] All manipulations were conducted in air unless otherwise noted. Anhydrous diethyl ether was obtained from a Pure Process Technology anhydrous solvent system. Anhydrous methanol and ethanol were purchased from a commercial vendor and used as received. All other reagents were purchased from commercial vendors and used as received. Single crystal diffraction data was collected using a Bruker D8, SMART APEX II, or APEX DUO instrument. IR spectra were obtained on a Bruker ALPHA II Platinum ATR with a variable temperature stage. Thermogravimetric analysis (TGA) experiments were performed using a TA Instruments TGA550. Abbreviation used: DA=decylammonium, (C.sub.10H.sub.21NH.sub.3).sub.2MnCl.sub.4=(DA).sub.2MnCl.sub.4, (NA)=nonylammonium, (C.sub.9H.sub.19NH.sub.3).sub.2CuBr.sub.4=(NA).sub.2CuBr.sub.4.
Synthesis of Two-Dimensional Perovskites
[0138] (DA).sub.2MnCl.sub.4.Math.: Decylamine (?99.0%) and hydrochloric acid (HCl) solution (37 wt %) were purchased from Sigma Aldrich and used without further purification. C.sub.10H.sub.21NH.sub.3Cl was first synthesized by adding HCl solution (550 ?L, 6.6 mmol) into decylamine (1.1 mL, 5.5 mmol) in ca. 5 mL ethanol in a cold-water bath. After evaporating the solvent at reduced pressure, the resulting white powder of (DA)Cl was washed with diethyl ether and vacuum dried at room temperature for a day. Crystalline powders of (DA).sub.2MnCl.sub.4 were prepared by the cooling of an ethanol solution containing a stoichiometric quantity of the manganese(II) chloride and (DA)Cl, as previously reported (e.g., in M. R. Ciajolo, et al., Comparative Studies of Layer Structures: The Crystal Structure of Bis(Monodecylammonium)tetrachloromanganate(II). Gazzetta Chimica Italiana. 106, 807 (1976), and H. Arend, et al., Layer perovskites of the (C.sub.nH.sub.2n+1NH.sub.3).sub.2MX.sub.4 and NH.sub.3(CH.sub.2).sub.mNH.sub.3MX.sub.4 families with M=Cd, Cu, Fe, Mn or Pd and X=Cl or Br: Importance, solubilities and simple growth techniques. J. Cryst. Growth. 43, 213-223 (1978)). (DA)Cl (96.9 mg, 0.5 mmol) was dissolved in 4.0 mL of ethanol. After several minutes of stirring, MnCl.sub.2.Math.4H.sub.2O (49.5 mg, 0.25 mmol) was added to the solution, and the solution was heated to 65? C. After the cooling this solution to room temperature at a rate of 4 K h.sup.?1, pale pink crystals were obtained. The crystals were filtered and washed with diethyl ether (5?10 mL) and held at reduced pressure for 6 h to afford 45.2 g (35.2% yield) of product. Crystals suitable for structure determination were obtained by slow cooling at a rate of 2 K h.sup.?1.
[0139] (NA).sub.2CuBr.sub.4: Nonylamine (?99.5%) and hydrobromic acid (HBr) solution (48 wt %, 8.8 M) were purchased from Sigma Aldrich and used without further purification. C.sub.9H.sub.19NH.sub.3Br was first synthesized by adding HBr solution (545 ?L, 4.8 mmol) into nonylamine (733 ?L, 4.0 mmol) in ca. 5 mL ethanol in a cold-water bath. The solvent was removed at reduced pressure to yield colorless powder of (NA)Br. The powder was washed with diethyl ether and vacuum dried at room temperature for a day. CuBr.sub.2 (402 mg, 1.8 mmol) and C.sub.9H.sub.19NH.sub.3Br (807 mg, 3.6 mol) were dissolved in 2 mL of ethanol. The solution was slowly cooled from 65? C. to room temperature at a rate of 4 K h.sup.?1. The saturated solution was then stored at below ambient temperature (5? C.) for 1 hour. The resulting dark purple precipitate was filtered and washed with diethyl ether (5?10 mL). The dark purple crystalline powder was held at reduced pressure for 12 h to remove moisture. Crystals suitable for structure determination was obtained by slow evaporation of a 1-mL solution of (NA).sub.2CuBr.sub.4 (202 mg, 0.3 mmol) in methanol. Anal. Calcd. for (C.sub.9H.sub.19NH.sub.3).sub.2CuBr.sub.4: C: 32.19%, H: 6.60%, N: 4.17%, Br: 47.58%, Found: C: 31.84%, H: 6.69%, N: 4.43%, Br: 47.76%.
Differential Scanning Calorimetry (DSC)
[0140] DSC at ambient pressure: A Discovery 2500 DSC with an RCS 90 cooling system (TA Instruments) was used to measure the transition temperatures and gravimetric enthalpies for all compounds. The DSC baseline and cell thermal parameters were calibrated using sapphire discs. The temperature and cell constant were calibrated using an indium standard. All DSC samples were prepared in air using 3-15 mg of sample and were hermetically sealed in aluminum pans (purchased from TA instruments). The sample was scanned under a dynamic flow of N.sub.2 (50 mL min.sup.?1). An empty, hermetically sealed aluminum pan we used as a reference.
[0141] Determination of T.sub.tr and gravimetric ?H.sub.tr and ?S.sub.tr: Transition temperatures, T.sub.tr, and enthalpies of transition, ?H.sub.tr, were determined using the TA Instrument TRIOS or Netzsch Proteus software. Peaks were selected for analysis by defining a temperature range containing the peak of interest. The lower bound and upper bounds of the temperature range were chosen to encompass the phase transition, which starts with a deviation from the baseline and ends with a return to baseline.
[0142] Prior to determination of T.sub.tr or ?H.sub.tr, a baseline, which models the heat flow in the absence of transition, must be generated to approximate the baseline in the transition region in the absence of a transition. A baseline is generated within the defined temperature range using various option that determine the slope of the lower and higher temperature limits and shape of the baseline. When possible, baselines were generated using mutual tangent slopes at both the upper and lower temperature limits with a sigmoidal baseline, which we found to produce most physically reasonable baselines.
[0143] The extrapolated onset temperature was reported as the transition temperature, as is standard in DSC data analysis, because the onset temperatureunlike the peak temperatureis relatively independent of experimental parameters like the heating rate or sample mass. The onset temperature is determined by identifying the region of the onset melting peak that has the highest slope, defining a tangent to that region, and then extending the tangent to the generated baseline. The intersection between the baseline and the tangent is the onset temperature. Endotherms were integrated between the upper and lower temperature limits with the baseline subtracted to provide ?H.sub.tr, and ?S.sub.tr was calculated through ?S.sub.tr=?H.sub.tr/t.sub.tr. If physically reasonable limits were chosen, the onset transition temperatures and ?H.sub.tr did not depend strongly on the choice of the temperature limits, and such variations were within the error of the measurements, which is estimated to be <0.5% for T.sub.tr and <2% for ?H.sub.tr. Note that volumetric ?H.sub.tr were calculated from gravimetric quantities using crystallographic densities at ambient temperature.
[0144] DSC at applied hydrostatic pressure: High-pressure DSC measurements at the pressure range between 1 to 150 bar were carried out in a DSC 204 HP Phoenix? (Netzsch). The temperature and heat flow were calibrated at each pressure using an indium standard. The temperature and cell constant were calibrated at each pressure using an indium standard. Helium gas was used as a pressure-transmitting medium. All DSC samples were prepared in air using 3-10 mg of sample and were sealed in aluminum pans (purchased from Netzsch) with a pierced lid. An empty, aluminum pan with a pinhole was used as a reference. All measurements were carried out in a dynamic gas environment with a 50 ml min.sup.?1 He. Otherwise noted, heating and cooling rates of 2 K min.sup.?1 were used during isobaric measurements.
[0145] During the pressure cycling experiments, heat flow signals were measured over time under the repeated application and removal of a hydrostatic pressure of 150 bar at 311 K for (DA).sub.2MnCl.sub.4 and 307 K for (NA).sub.2CuBr.sub.4. The pressure linearly increased at a rate of 6 bar min.sup.?1 and asymptotically decreased at an average rate of 13 bar min.sup.?1. During the pressure change, quasi-isothermal conditions were maintained, where a small change in temperature (<1 K) induced by gas compression and decompression is compensated by external thermal control measures. The pressurization and depressurization processes are associated with average temperature fluctuations of 0.3 K and 0.7 K, respectively. To distinguish the heat flow signals associated with pressure-induced phase transitions of samples from those associated with compression and decompression of pressure transmitting medium (He gas), (C.sub.12H.sub.25NH.sub.3).sub.2MnCl.sub.4, prepared from the previously reported procedure (G. F. Needham, et al., J. Phys. Chem. 88, 674-680 (1984), was used as a blank sample because it undergoes transitions at temperatures (T.sub.tr, major=331 K and T.sub.tr,minor=335 K) well above the set temperatures for (DA).sub.2MnCl4 and (NA).sub.2CuBr.sub.4. The heat flow signals measured from the blank during the pressure change at the set temperature were modeled as a baseline for the sample data. By subtracting the features in the heat flow associated with the gas compression and decompression from the sample data, we were able to determine the onset pressure associated with the pressure-induced transitions during compression and decompression processes. Because maintaining isothermal conditions becomes challenging once the phase transition is induced and both pressure and temperature change drive the endothermic and exothermic transitions to completion, we did not integrate the heat flow signals and focused only on using the information to determine the onset pressures for transitions.
[0146] On the barocaloric effects outside the transition: We note that the ?S.sub.it values obtained through our HP-DSC experiments do not include the contributions from the additional barocaloric effects (?S.sub.+) that arise from each phase. This additional contribution can be estimated through ?S.sub.+=?[(?V/?T).sub.p=0]?P, where ?P and (?V/?T).sub.p=0 denote a driving pressure and a thermal expansion at the ambient pressure, respectively. Note that the isothermal entropy contribution is derived from the Maxwell relation (?V/?T).sub.p=?(?V/?P).sub.T with an assumption that the volume expansion is independent of pressure. The ?S.sub.+ values are estimated to be ?3 and ?4 J kg.sup.?1 K.sup.?1 at the ordered and disordered phases, respectively, under 150 bar driving pressures. Although these values are small in comparison with ?S.sub.tr, these contributions can be large at higher driving pressure, such as ?# at 400 bar, because of large thermal expansion coefficients (?10.sup.?4 K.sup.?1)
Helium Pycnometry
[0147] Sample density was determined using an InstruQuest Inc. ?-ThermoPyc variable temperature He pycnometer. In a typical measurement, ca. 150 mg of crystalline sample were transferred to the sample holder, and the sample mass obtained. The holder was then placed in the instrument test chamber and the headspace evacuated and refilled five times to obtain a pure He atmosphere. The sample was then cycled multiple times through the order-disorder transition with the chamber volume determined every 2-5? C. away from the transition and every 0.5-1.0? C. close to the transition. For each point, the temperature was fully equilibrated with a standard deviation of no more than 0.2? C. prior to volume measurement. At each temperature, the chamber volume was measured five times to obtain good statistics. Sample volume was then determined by subtracting the average observed chamber volume from the volume of the empty sample holder which had been measured previously. The sample mass was redetermined after the measurement and found to have decreased by no more than 0.5 mg, likely due to loss of adsorbed water. Uncertainties of the reported densities were determined by propagation of the standard deviations of the empty and filled chamber volumes and the sample mass.
X-Ray Crystallography
[0148] X-ray diffraction analyses were performed on a single crystal coated with Paratone-N oil and mounted on a MiTeGen microloops, at different temperatures (100 to 335 K) controlled by an Oxford Cryostreams nitrogen flow apparatus. Crystals were mounted at 270 K, and 270 K data sets were collected. Crystals were then cooled to 100 K for 100 K data collection. After 100 K data sets, high-temperature data sets were collected, 330 K for (DA).sub.2MnCl.sub.4 and 335 K for (NA).sub.2CuBr.sub.4. The temperature was manipulated at a rate of 60 K h.sup.?1. The intensities of the reflections were primarily collected by a Bruker D8 diffractometer with CMOS area detector (Mok? radiation, ?=0.71073 ?). The collection method involved 0.5? scans in ? at 23? in 2?? with a detector distance at 9 cm for (DA).sub.2MnCl.sub.4 and 8 cm for (NA).sub.2CuBr.sub.4. Data integration down to 0.84 ? resolution was carried out using SAINT V8.37A with reflection spot size optimization (9). Most crystals were either single or merohedrally twinned and absorption corrections were made with the program SADABS. All single crystal structures were solved by the Intrinsic Phasing methods and refined by least-squares methods again F.sup.2 using SHELXT-2014 and SHELXL-2018 with OLEX 2 interface. Thermal parameters were refined anisotropically for all non-hydrogen atoms. Hydrogen atoms were placed geometrically and refined using a riding model for all structures. Crystal data as well as details of data collection and refinement are summarized in Tables 15 and 16, and geometric parameters are shown in Tables 10 to 14.
[0149] Notes on data quality, twining, and disorders: The phase transition from low-temperature phase to high-temperature (HT) phase during heating often resulted in fracturing and twining of the crystals, giving rise to the decay of crystal quality. Due to the large thermal motions of the long alkyl ammonium cations, the geometric parameters calculated for the HT phase structures should be treated as estimates, as pointed out in the literature.
Synchrotron In Situ Powder X-Ray Diffraction (PXRD) Studies
[0150] Powder X-ray diffraction data for (DA).sub.2MnCl.sub.4 and (NA).sub.2CuBr.sub.4 were collected on beamline 17-BM-B at the Advanced Photon Source (APS) at Argonne National Laboratory. All X-ray wavelengths were between 0.24 ? and 0.45 ?, and are specified for each experiment in the relevant figures and tables. For variable temperature and pressure experiments, approximately 10 mg of samples was loaded into a sapphire capillary (1.524 mm?1.07 mm?50.8 mm, Saint-Gobain Crystals). Each capillary was attached to a custom-designed flow cell equipped with a gas valve, which was mounted onto the goniometer head and connected to a syringe pump that the applied the hydrostatic pressure of Helium (80-360 bar). Sample temperature was controlled by an Oxford Cryostream (Oxford Cryostream 800+). Prior to measurement, samples were evacuated by flowing ambient pressure of He gas for 10 minutes and annealed by heating 20 K above T.sub.tr and cooling back to ambient temperature, at a rate of 6 K min.sup.?1 in the cryostream. The internal sample temperature was monitored via a K-type thermocouple (TC) that maintained the thermal contact with the powder sample within the capillary. Otherwise noted, the samples were heated and cooled by the cryostream at a rate of 6 K min.sup.?1, which resulted in the rate of ca. 3 K min.sup.?1 in the TC temperature due to the temperature gradient. Diffraction patterns were analyzed using the software TOPAS-R (Bruker AXS, version 3.0, 2005). Diffraction patterns at select temperature were indexed, and Le Bail refinements were performed to extract unit cell parameters.
Conformational Disorder in Two-Dimensional Metal-Halide Perovskites
[0151] Conformational entropy: For an alkylammonium chain C.sub.nH.sub.2n+1NH.sub.3.sup.+, there are n-2 rotatable CC bonds that can contribute to formation of different conformers. Note that the conformation of alkylammonium chains can be described through a sequence of dihedral angles often referred to as Hoffmann's notation, with the terms g.sup.+, g.sup.?, and t denoting dihedral angles of approximately +60 (gauche), ?60 (gauche), and 180? (trans), respectively. In principle, each CC bond should be able to equally access these three rotameric states that correspond to local energy minima, and the change in solid-state configurational entropy can be described as ?S.sub.configuration=R In W, where W is the ratio between the number of configurations in the disordered and ordered chains (That is, W=N.sub.disorder/N.sub.order). Thus, the entropy change associated with the conformational disordering of an alkylammonium chain can be estimated as R In 3.sup.n?2.
[0152] However, depending on how chains are packed and how neighboring chains influence one another in each phase, the average number of accessible rotameric states for each CC bonddefined as the chain flexibility number ?can deviate from 3. Note that, in linear organic molecules, the flexibility number depends on the energetic difference between each conformer and a flexibility number of 2.85 has been used to predict the melting thermodynamics. In two-dimensional perovskites, a few structural featuressteric restrictions (imposed by halide pockets and neighboring chains), correlations between torsions, and residual degrees of freedom present in CC bonds in the ordered phasecan partially limit conformational degrees of freedom, reducing the number of CC bonds associated with the chain melting processes by a restriction parameter ?. The number of accessible conformations at the disordered phase can then be approximated as (?).sup.n?2??, which includes the conformers arising from kink {gtg} formation and cooperative torsion along the chain axis. Here, we assume that the two parameters ? and ? are independent. Note that the entropy change associated with a reorientational motion (flipping) of the entire alkylammonium chains between two energetically equivalent orientations within the metal-halide pocket can be accounted for by adding the term R In 2. This chain-flipping can occur as an isolated minor transition or be coupled to the major order-disorder transition. In addition to the flipping, the major conformation disordering can be often distributed across multiple, successive transitions, and the total number of structural transitions of a compound is here referred to as m. The contributions from both flipping (?S.sub.flipping) and chain melting (?S.sub.melting) to the total entropy change, ?S.sub.total, are multiplied by 2, because 2 mole of C.sub.nH.sub.2n+1NH.sub.3.sup.+ chains are present in 1 mole of perovskite. The contribution from any change in entropy associated with the MX.sub.6 octahedra is assumed to be negligible. Thus, the total difference in entropy associated m structural transitions in 2-D perovskites between low-temperature (LT) ordered and high-temperature (HT) disordered phases can be expressed through the following relationship:
?S.sub.total=?.sub.i=1.sup.m?S.sub.tr,i=?S.sub.flipping+?S.sub.melting=2RIn2+2RIn(?).sup.n?2??(1)
[0153] By fitting ?S.sub.total as a function of chain length n, we were able to determine the flexibility number ? and the restriction parameter ? for two-dimensional perovskite (C.sub.nH.sub.2n+1NH.sub.3).sub.2MX.sub.4 (M=Mn, Cu, Cd; X=Cl, Br). ?S.sub.total values are tabulated in Tables 2 to 4, and fitting parameters are summarized in Table 6. With the expectations that odd and even chain lengths should exhibit different thermodynamic trends, odd-numbered and even-numbered analogs were fit separately. We note that, somewhat surprisingly, the structural origins of odd-even effects of the phase-change thermodynamics in 2-D perovskites are not fully understood and require further investigations.
[0154] (DA).sub.2MnCl.sub.4: From the fitting parameters (?=3.0 and ?=2.1, R.sup.2>0.99) for (C.sub.nH.sub.2n+1NH.sub.3).sub.2MnCl.sub.4, (n=8-15), we can estimate that each decylammonium chain can access 3.sup.5.9 (?650) distinct configurations as a result of conformational disorder at the HT phase. In addition, the total entropy change associated with the single-step transition at 310 K can be calculated as ?S.sub.total,calc=?S.sub.flipping+?S.sub.melting=2R In 2+2R In (3).sup.5.9=119 J K.sup.?1 mol.sup.?1, which agrees with the experimentally measured ?S.sub.total,exp of 118 J K.sup.?1 mol.sup.?1. This estimation is further supported by the single-crystal structure of (DA).sub.2MnCl.sub.4 at the HT phase (330 K), where each alkylammonium chain is disordered over two energetically equivalent positions and has a conformation with six CC dihedral angles of 150-166? that deviate from the ideal trans dihedral angle of 180? and two CC dihedral angles (C1-C2, 174?; C3-C4, 180?) close to the trans angle. (Table 13). This deviation may indicate fast trans-gauche rotations around CC bonds and/or cooperative torsion along the chain axis. It is worth emphasizing that the chain length dependence of ?S.sub.total does not display a pronounced odd-even effect in 2-D MnCl perovskites.
[0155] We also note that the conformational disordering is likely to be associated with the formation of one {gtg} kink per chain (on average) near the chain ends and the most probable conformer is {t.sub.4gtgt}, as suggested by incoherent neutron scattering experiments and intramolecular energy calculations. At higher temperature, some chains could adopt energetically less stable forms, in which the kink defects are located near the polar head groups, such as {t.sub.3gtgt)} and {t.sub.2gt.sub.3gt}. These proposed conformers are shown in the conceptual illustration in
[0156] The single-crystal structure at the HT phase also supports the proposed model that formation of kink is favored near the chain ends. In
[0157] (NA).sub.2CuBr.sub.4: We note that the transition entropy of (NA).sub.2CuBr.sub.4 is about 48% and 56% of ?S.sub.total of (C.sub.9).sub.2MnCl.sub.4 and (C.sub.9).sub.2CuCl.sub.4, respectively. This trend is also observed in the previously reported thermal data of (C.sub.n).sub.2CuBr.sub.4 (n=11-16), which shows that the transition entropies of 2-D CuBr perovskites are only 40-60% of those reported in CuCl and MnCl analogs. Fitting ?S.sub.total with chain length n results in ?=2.1 and 2.2 and ?=5.1 and 5.5, for odd-numbered and even-numbered chains, respectively (Table 6). The lower value of ? and higher value of ?, compared to those obtained from MnCl and CuCl series, indicate that the difference in solid-state conformational entropy between LT and HT phases is smaller in (Cn).sub.2CuBr.sub.4, and the difference likely originates from the smaller difference in the flexibility of the chain and the number of newly rotating CC bonds.
[0158] The LT phase crystal structure indicates that the smaller difference in solid-state entropy between LT and HT phase may result from the higher degree of disorder present in the nonylammonium chains at the LT phase. In the LT phase, each of the two chain conformations (chain A with C1-C2 gauche bond and chain B with C2-C3 gauche bond) is modeled with two-part disorder (Table 14). Note that the atomic positions in chain A and chain B were refined to 35/65% and 53/47% occupancies, respectively. The analysis on the chain conformations shows that (i) the chains are distorted near the methyl ends with C7-C8 dihedral angles of and +159?/?170? in chain A (Part 1/Part 2) and +164?/?164? in chain B and (ii) the chain A displays additional distortion in the C3-C4 bond (?159?/+169?). These results illustrate that configurational disorder is present in the LT phase of (NA).sub.2CuBr.sub.4. In addition, the chains also display U.sub.equiv values higher than those in decylammonium chain of (DA).sub.2MnCl.sub.4 at the LT phase, whereas the U.sub.equiv values at the HT phase were similar in both compounds (
[0159] Comparison with 2-D CdCl and CuCl perovskites. Although the chain length dependences of ?S.sub.total in 2-D CdCl and CuCl perovskites exhibit similar trends to that observed in the MnCl series, with ??3 and ??2, the trends slightly deviate from linearity and/or display pronounced odd-even effects. Even with the same chain length, these analogs display different phase transition behaviors, depending on the identity of metals. For example, unlike (C.sub.10).sub.2MnCl.sub.4, both (C.sub.10).sub.2CuCl.sub.4 and (C.sub.10).sub.2CdCl4 display two-step transitions, and the major transition in (C.sub.10).sub.2CuCl.sub.4 is followed by a minor transition, whereas the major transition in (C.sub.10).sub.2CdCl4 is preceded by a minor transition. These compounds also display differences in chain conformations at room temperature: (C.sub.10).sub.2MnCl.sub.4 with B conformer (C2-C3 gauche), (C.sub.10).sub.2CdCl.sub.4 with both A conformer (C1-C2 gauche) and B conformer), and (C.sub.10).sub.2CuCl.sub.4 with A, B, and all trans {t.sub.8} conformers. As expected, these changes translate to the most probable conformational disorder at the HT phase. Overall, these observations indicate that (i) the trends in thermodynamics of chain melting transitions are sensitive to chain packing and metals and (ii) the stepwise conformational disordering transitions observed in most compounds are complex. To fully describe the trends and the impact of the phase transition behaviors on barocaloric effects, detailed investigations into the structural changes and microscopic motions associated with each transition are required, both at ambient and applied pressures.
[0160] Comparison with melting of n-alkane: For the melting transition of n-alkane and solid-solid transitions of 2-D metal-halide perovskites and related systems, the relationships among transition entropy (?S.sub.tr), chain length (n), and temperature of transition (T.sub.tr) have been investigated, where ?S.sub.total normalized by chain length n is fit with T.sub.tr. Although this approach, often referred to as SnT analysis, can provide insights into the trends in series of 2-D perovskites and related compounds, we did not include the temperature of transition as a fitting parameter because most 2-D perovskites undergo stepwise transitions and the nature of molecular motions associated with each transition is not fully understood. However, both approaches provide similar insights into the conformational degrees of freedom of alkylammonium chains of 2-D perovskites during the phase transition. For example, the SnT analysis indicates that the total transition entropy increases by 9.1 J K.sup.?1 mol.sup.?1 per carbon in (C.sub.n).sub.2MnCl.sub.4 (n=7, 11-17) and 13.5 J K.sup.?1 mol.sup.?1 per carbon in n-alkane. The chain length dependence of 9.1 J K.sup.?1 mol.sup.?1 in 2-D MnCl perovskites can be translated to the flexibility number of 3, which agrees with our analysis. As previously pointed out, the ratio between the chain length dependences of ?S.sub.total in (C.sub.n).sub.2MnCl.sub.4 and n-alkane is 2:3 and correlates to the ratio between their dimensionalities. This interesting relationship is supported by a theoretical prediction based on kink-block transitions, where the melting entropy of alkyl chains confined in two-dimensional layers was shown to exhibit similar chain length dependence of 9.1 J K.sup.?1 mol.sup.?1. We also note that this value is close to the pressure dependences of melting transitions of n-decane (21 K kbar.sup.?1) and n-nonane (20 K kbar.sup.?1) (29). (nonane, with a dTdP solid-solid transition also similar).
[0161] Notes on dynamics: In addition to the kink formation (gauche defect), the cooperative torsion along the chains is coupled to the overall molecular motion at the HT phase. According to incoherent neutron scattering experiments, molecular motion corresponding to kink formation and cooperative torsion occurs over 1-5 ps timescale. However, due to the relatively low Q-values explored in the measurements, overall molecular motions, cooperative torsions, and kink formations were not accurately distinguishable. We also note that further studies are needed to fully model the microscopic details of the chain melting processes, both for fast motions (e.g., kink motion within a chain) and slow processes (e.g., the formation of clusters with similar chain conformations), at ambient and applied pressures.
[0162] Differences in phase transition behaviors between (DA).sub.2MnCl.sub.4 and (DA).sub.2CdCl.sub.4: First of all, their transition behaviors are qualitatively similar, with the chains at HT phase adopting approximately one kink conformation per chain. Neutron scattering experiments indicates, however, that the diffusion of kink, which was previously observed in (C.sub.10).sub.2CdCl.sub.4 with ?1000 ps time scale by proton NMR and .sup.35Cl and .sup.14N quadrupole resonance spectroscopies, is unlikely to occur in (C10).sub.2MnCl.sub.4, because no cooperative conformational interconversion within a chain with a time scale greater than 20 ps was observed. This indicates that, unlike in (C.sub.10).sub.2CdCl.sub.4, in (C.sub.10).sub.2MnCl.sub.4, some kink formations are energetically more dominant. For the diffusion of the kinks to occur, several conformers with similar energies need to be in equilibrium. From the spectroscopic studies, it was revealed that (DA).sub.2CdCl.sub.4 does have multiple conformers with similar energy levels. We also note that vibrational studies revealed that {tgtttgtt} is the most probable conformer in (C.sub.10).sub.2CdCl.sub.4, which is more flexible in the middle of the chain and does not have an end-gauche conformation.
Infrared Spectroscopy Analysis
[0163] Note that the IR signals used for conformational analysis are summarized in Tables 7 and 8.
[0164] CH stretching: In the compounds containing long alkyl chains, shifts in CH stretching peaks to higher wavenumbers are correlated with an increase in the number of gauche CC bonds, a change in chain packing, and presence of order-disorder transitions. For example, in the melting transitions of n-alkanes, v.sub.symmetric(CH) and v.sub.anti-symmetric(CH) shift from 2920 to 2928 cm.sup.?1 and 2850 to 2856 cm.sup.?1, respectively. 2-D perovskites also display similar trend, with the shifts ?v of 2-3 cm.sup.?1. The temperature dependence of these peaks can be either abrupt or gradual depending on metal and chain packing. Overall, this feature provides indirect evidence on the changes in the disorder in 2-D perovskites.
[0165] CH.sub.2 rocking and bending: For well-ordered chains in a monoclinic or orthorhombic lattice, CH.sub.2 rocking and bending bands split into doublets near 720 and 1470 cm.sup.?1, respectively, because of the factor group splitting that arises from directional intermolecular interactions between the chains. Generally, these features have been observed across materials with long hydrocarbon chains, including n-alkanes, layered silver thiolates, and 2-D metal-halide perovskites. The frequencies, shapes, and separations of these signals are correlated with orientations between neighboring chains and conformational disorder within the chain. In 2-D perovskites, the disappearance of the splitting can be used to determine if the chain undergoes conformational disordering, because it is correlated with the emergence of CH.sub.2 wagging bands specific to defect conformations (e.g., gtg kink) and indicative of the re-orientational motion of whole chain. However, we note that understanding specific microscopic motions associated with these features requires further investigations.
[0166] CH.sub.2 wagging: CH.sub.2 wagging bands, which provide insights into vibrational modes localized on a few CH.sub.2 units pinned in specific conformation sequences, are weakly coupled with the host lattice and independent of chain length. Thus, they provide characteristic signals of specific conformational defects. In 2-D perovskites, these modes are readily mixed with internal modes of chain end (CH.sub.3) and head (NH.sub.3.sup.+), and this coupling enhances the intensity of some CH.sub.2 wagging modes. Through normal-mode calculations on (C.sub.10).sub.2CdCl.sub.4 and related compounds, the key peaks have been assigned. These signals appear at 1310 cm.sup.?1 (in-plane, two CH.sub.2 units, kink), a shoulder near 1370 cm.sup.?1 (out-of-plane, two CH.sub.2 units, kink), 1350 cm.sup.?1 (gg conformation), 1340 cm.sup.?1 (tg conformation near the chain end). The kink refers to gt.sub.2n+1g-type conformational defects.
[0167] NH.sub.3 and CH.sub.3 bending: In 2-D M-Cl perovskites, the signal from NH.sub.3 symmetric bending modes appears around 1490 cm.sup.?1 at the LT phase and are often split into doublet due to the crystal field effect. The degree of the peak splitting highly depends on the identity of metals, with MnCl and CdCl perovskites displaying very small and often negligible splitting and CuCl perovskites showing clear doublet (1492-1480 cm.sup.?1). At the HT phase, the peak splitting disappears, often accompanied by noticeable broadening, and this indicates the reorientational motion of the polar head within the halide pocket. The NH.sub.3 antisymmetric bending mode is associated with a strong singlet peak near 1580 cm.sup.?1 and red-shifts by 6-8 cm.sup.?1, as a compound undergoes a structural transition. This feature can be correlated with the decrease in the strength of NH . . . Cl hydrogen bond. As these features are associated with the onset of chain melting transitions, vibrational spectra from NH.sub.3 bending can provide insights into the motions of chains within the halide pocket. The CH.sub.3 symmetrical bending mode, which appears near 1376 cm.sup.?1 at the LT phase, blue-shifts (?v?3 cm.sup.?1) as the chains undergo structural transitions. This feature is correlated with the change in inter-lamellar interactions within the organic bilayers.
[0168] Comparison of vibrational spectra related to chain conformations: IR spectra of (DA).sub.2MnCl.sub.4 and (NA).sub.2CuBr.sub.4 are summarized in
[0169] For symmetric CH stretching peaks, both compounds display blue-shifts (?2 cm.sup.?1) after the transitions, which supports that the phase transition introduces disorder in the alkylammonium chains (
[0170] Both compounds show pronounced differences in the progression of CH.sub.2 wagging bands, as shown in
[0171] Taken together, these results indicates that (i) the differences in conformations of and local environments around the chains in (NA).sub.2CuBr.sub.4 is smaller than those in (DA).sub.2MnCl.sub.4 and (ii) a noticeable degree of conformational disorder is present in (NA).sub.2CuBr.sub.4 at the LT phase. These results, qualitatively, agree with our interpretations of single-crystal structures at the HT phase. Although the trends we observed from both compounds are consistent with those measured in other 2-D metal-halide perovskites as shown in Table 8, we note that accurate assignments and quantitative interpretation of IR spectra, particularly of CH.sub.2 wagging bands, are challenging, because the signals are relatively weak, coupled with the internal modes of chain end and head, and sensitive to the positions and diffusion of the defects, with the relationships among these factors not well understood. For accurate assignments of chain conformations, particularly those for (NA).sub.2CuBr.sub.4, further investigations using normal-mode calculations and other complementary spectroscopic techniques, such as Raman or sum frequency generation vibrational spectroscopy, will be required.
[0172] Chemical origin of the difference in the solid-state disorder between (NA).sub.2CuBr.sub.4 and (DA).sub.2MnCl.sub.4: The difference in the disorder between the two compounds may arise from the difference in the size of metal-halide pocket and the strength of NH . . . X (X=Cl, Br) hydrogen-bond interactions within the pocket. In particular, comparisons of IR spectra associated with NH.sub.3 bending modes provide useful insights into how the charge-assisted H-bond interactions differ between the two compounds. As shown in
[0173] Collectively, these results illustrate that, for (NA).sub.2CuBr.sub.4, the weaker NH . . . Br hydrogen bonds, in combination with a larger area provided for each chain (from incorporation of larger Br ions and presence of Jahn-Teller distortion), result in the increased degrees of freedom of chains in (NA).sub.2CuBr.sub.4 at the LT phase, which contributes to the difference in the chain disorder between LT and HT phase smaller than the difference in (DA).sub.2MnCl.sub.4. We also hypothesize that the smaller thermal hysteresis observed in (NA).sub.2CuBr.sub.4 may arise from this enhancement in the conformational degrees of freedom, as it may lower the energy barrier associated with the formation of nucleation sites (i.e., clusters with similar chain conformations). The structure-property relationship between the two compounds provides insights into how conformational disorder in the 2-D perovskites can be controlled through chemical manipulations of the organic-inorganic interfaces.
Data tables
[0174]
TABLE-US-00004 TABLE 2 Summary of previous reported chain melting transitions in representative two-dimensional (C.sub.nH.sub.2n+1NH.sub.3).sub.2MnCl.sub.4 perovskites. ?H ?H ?S ?S Chemical T.sub.tr.sup.c (kJ (kJ (J mol.sup.?1 (J kg.sup.?1 Formula.sup.a Type.sup.b (K) mol.sup.?1) kg.sup.?1) K.sup.?1) K.sup.?1) (C.sub.6).sub.2MnCl.sub.4 minor 206 5 13 26 64 major 291 10 25 37 93 total 15 38 63 157 (C.sub.7).sub.2MnCl.sub.4 major 250 17 39 68 159 minor 314 10 24 33 76 total 27 63 101 235 (C.sub.8).sub.2MnCl.sub.4 major 274 19 42 70 153 minor 302 4 10 14 32 total 24 52 84 185 (C.sub.9).sub.2MnCl.sub.4 major 291 26 53 89 183 minor 294 2 5 8 16 total 28 58 97 199 287.sup.e 31 63 107 220 (C.sub.10).sub.2MnCl.sub.4 308 35 68 113 221 310 37 72 118 230 (C.sub.11).sub.2MnCl.sub.4 major 317 40 74 126 234 minor 321 4 8 13 25 total 44 82 140 258 316.sup.e 46 86 147 271 (C.sub.12).sub.2MnCl.sub.4 major 331 48 84 145 254 minor 335 6 10 18 31 total 54 94 162 285 (C.sub.13).sub.2MnCl.sub.4 major 331 52 87 158 264 minor 343 8 13 22 37 total 60 100 180 301 (C.sub.14).sub.2MnCl.sub.4 major 345 58 92 167 268 minor 357 9 15 26 41 total 67 107 193 309 (C.sub.15).sub.2MnCl.sub.4 major 340 63 96 184 282 minor 362 10 16 28 44 total 73 112 213 325 (C.sub.16).sub.2MnCl.sub.4 major 346 60 88 172 253 minor 364 12 17 32 46 total 71 104 204 299 .sup.aC.sub.n = C.sub.nH.sub.2n+1NH.sub.3. .sup.bWhen a compound displays multiple transitions, the transition with the highest ?S was labeled as a major transition. .sup.cThe temperature of transition measured during the first heating scans are tabulated here. .sup.dThis compound was synthesized and characterized for the completeness of the series. .sup.eClosely spaced transitions were not resolved. .sup.fThese compounds was synthesized and characterized by DSC at a slow scan rate (0.5 K/min) to resolve major and minor transitions. .sup.gThe difference between the previously reported value are within experimental uncertainties; however, the higher T.sub.tr reported here may represent the higher purity of the sample, because some of the long-chain amines used in the previous literature have been shown to contain impurities, such as amines with different chain lengths (n ? 2), which typically give rise to lowering of T.sub.tr (up to 4-5 K), ?H and ?S.
TABLE-US-00005 TABLE 3 Summary of previous reported chain melting transitions in representative two-dimensional (C.sub.nH.sub.2n+1NH.sub.3).sub.2 CuX.sub.4 perovskites (X = Cl, Br). ?S ?S Chemical T.sub.tr.sup.c ?H ?H (J mol.sup.?1 (J kg.sup.?1 Formula.sup.a Type.sup.b (K) (kJ mol.sup.?1) (kJ kg.sup.?1) K.sup.?1) K.sup.?1) (C.sub.8).sub.2CuCl.sub.4 major 269 18 39 68 146 minor 303 5 11 16 35 total 23 50 84 181 (C.sub.9).sub.2CuCl.sub.4 major 294 23 46 78 158 minor 303 5 9 15 31 total total 28 56 93 189 (C.sub.10).sub.2CuCl.sub.4 major 309 35 67 113 216 minor 312 5 9 15 28 total 39 75 128 244 (C.sub.11).sub.2CuCl.sub.4 major .sup.317.sup.e 36 65 112 204 minor 327 6 11 18 33 total 42 76 130 237 (C.sub.12).sub.2CuCl.sub.4 major 328 40 69 121 210 minor 334 8 14 25 43 total 48 83 146 253 (C.sub.13).sub.2CuCl.sub.4 major .sup.333.sup.e 48 80 145 239 minor 344 10 16 29 48 total 58 96 174 287 (C.sub.14).sub.2CuCl.sub.4 major 334 50 61 150 237 minor 356 11 83 31 48 total 61 144 181 285 (C.sub.15).sub.2CuCl.sub.4 major 343 54 82 158 238 minor 358 12 18 33 50 total 66 100 191 288 (C.sub.16).sub.2CuCl.sub.4 major 345 36 52 103 150 minor 354 8 12 23 33 minor 360 14 20 39 56 total 58 83 165 239 (C.sub.9).sub.2CuBr.sub.4 303 16 24 52 78 (C.sub.11).sub.2CuBr.sub.4 major 328 19 26 59 80 minor 340 1 1 1 2 total total 20 27 60 82 (C.sub.12).sub.2CuBr.sub.4 337 22 29 64 85 (C.sub.13).sub.2CuBr.sub.4 344 30 38 86 109 (C.sub.14).sub.2CuBr.sub.4 348 28 34 80 98 (C.sub.15).sub.2CuBr.sub.4 354 39 46 110 131 (C.sub.16).sub.2CuBr.sub.4 major 343 2 2 4 5 minor 357 37 43 105 120 total total 39 45 109 125 .sup.aC.sub.n = C.sub.nH.sub.2n+1NH.sub.3. .sup.bWhen a compound displays multiple transitions, the transition with the highest ?S was labeled as a major transition. .sup.cThe temperature of transition measured during the first heating scans are tabulated here. These minor transitions were not resolved in the initial reports. Note that reported full DSC traces of (C.sub.n).sub.2CuCl.sub.4 (n = 2-14), are reported without integrated thermodynamic values.
TABLE-US-00006 TABLE 4 Summary of previous reported chain melting transitions in representative two-dimensional (C.sub.nH.sub.2n+1NH.sub.3).sub.2CdCl.sub.4 and (C.sub.nH.sub.2n+1 NH.sub.3).sub.2PbI.sub.4 perovskites. ?S ?S Chemical T.sub.tr.sup.c ?H ?H (J mol.sup.?1 (J kg.sup.?1 Formula.sup.a Type.sup.b (K) (kJ mol.sup.?1) (kJ kg.sup.?1) K.sup.?1) K.sup.?1) (C.sub.7).sub.2CdCl.sub.4 major 250 18 36 71 147 minor 317 5 10 16 33 total 23 47 87 180 (C.sub.8).sub.2CdCl.sub.4 major 269 15 28 54 105 minor 308 5 10 17 32 total 20 38 71 138 (C.sub.10).sub.2CdCl.sub.4 minor 308 8 14 25 44 major 313 30 52 95 166 total 38 66 120 210 (C.sub.12).sub.2CdCl.sub.4 minor 332 11 17 33 52 major 334 44 69 130 208 total 54 87 163 260 (C.sub.14).sub.2CdCl.sub.4 major 345 40 58 115 168 minor 351 23 34 66 96 total 63 92 181 264 (C.sub.16).sub.2CdCl.sub.4 major 345 40 55 117 158 minor 352 8 10 22 30 minor 356 32 43 88 120 80 108 227 308 (C.sub.7).sub.2PbI.sub.4 minor 271 7 7 25 26 major 286 8 9 29 31 minor 310 3 3 9 10 total 18 19 63 67 (C.sub.8).sub.2PbI.sub.4 minor 252 15 15 58 59 major 311 21 22 68 70 total 36 37 126 129 (C.sub.9).sub.2PbI.sub.4 minor 252 7 7 28 28 major 314 24 24 75 75 total 31 31 104 103 (C.sub.10).sub.2PbI.sub.4 minor 259 10 10 39 38 minor 284 8 8 30 29 major 337 32 31 96 93 total 51 49 165 160 (C.sub.12).sub.2PbI.sub.4 minor 315 11 10 35 32 major 350 44 41 126 116 total 55 51 161 148 (C.sub.14).sub.2PbI.sub.4 minor 329 11 9 32 28 major 360 55 48 152 133 total 65 57 184 161 (C.sub.16).sub.2PbI.sub.4 minor 340 12 10 34 28 major 369 63 52 170 142 total 74 62 204 170 .sup.aC.sub.n = C.sub.nH.sub.2n+1NH.sub.3. .sup.bWhen a compound displays multiple transitions, the transition with the highest ?S was labeled as a major transition. .sup.cThe temperature of transition measured during the first heating scans are tabulated here. Note that 2-D Pb-I perovskites have partially interdigitated organic bilayers.
TABLE-US-00007 TABLE 5 Estimated barocaloric coefficients of representative two- dimensional MCl perovskites (M = Mn and Cu). Note that chain-melting phase transitions of these compounds are also expected to be sensitive to pressure, with minor transitions particularly more sensitive than major transitions. Estimated ?S.sub.tr Chemical T.sub.tr ?d ?V.sub.tr.sup.b (J K.sup.?1 dT.sub.tr/dP.sup.c Formula.sup.a Type (K) (?) (cm.sup.3 kg.sup.?1) kg.sup.?1) (K kbar.sup.?1) (C.sub.12).sub.2MnCl.sub.4 major 331 29.7 to 61.7 254 24.3 31.9; 2.2 (7.4%) minor 335 31.9 to 8.4 31 27.1 32.2; 0.3 (0.9%) (C.sub.14).sub.2MnCl.sub.4 major 345 33.3 to 56.1 268 20.9 35.5; 2.2 (6.6%) minor 357 35.5 to 23.0 41 56.0 36.4; 0.9 (2.5%) (C.sub.10).sub.2CuCl.sub.4 major 309 25.2 to 57.1 216 26.4 27.0; 1.8 (7.1%) minor 312 27.0 to 19.0 28 68.0 27.6; 0.6 (2.2%) (C.sub.12).sub.2CuCl.sub.4 major 328 28.8 to 43.0 210 20.5 30.3; 1.5 (5.2%) minor 334 30.3 to 22.9 43 53.3 31.1; 0.8 (2.6%) (C.sub.14).sub.2CuCl.sub.4 major 334 32.9 to 41.8 237 17.6 34.5; 1.6 (4.9%) minor 356 34.5 to 26.1 48 54.4 35.5; 1.0 (2.9%) .sup.aC.sub.n = C.sub.nH.sub.2n+1NH.sub.3. .sup.bNote that the specific volume of each phase was estimated using the relationship, V = dA.sub.c ? M.sub.w/N.sub.A, where A.sub.c is the area of metal-halide sheet per chain, d is the interlayer distance, M.sub.w is the molecular weight, and N.sub.A is Avogadro's number. We used this estimation because the unit cell parameters of intermediate phases were often not available. The reported mean values of A.sub.c are 26.5 ?.sup.2 and 27.5 ?.sup.2 for MnCl and CuCl perovskites, respectively. Note that this approach is likely to overestimate the volume change. .sup.cBarocaloric coefficients were calculated through the Clausius-Clapeyron equation (dT.sub.tr/dP = ?V.sub.tr/?S.sub.tr).
TABLE-US-00008 TABLE 6 The linear relationship between chain length and total change in entropy (?S.sub.total) in chain-melting transition of 2-D perovskites. Restriction Area per Chain y- Flexibility parameter chain Compound.sup.a length Slope intercept R.sup.2 number ? ? (?.sup.2) (C.sub.n).sub.2MnCl.sub.4 odd 19.4 ?75.3 0.995 3.2 2.5 26.5 even 18.5 ?63.7 0.994 3.0 2.1 (C.sub.n).sub.2CdCl.sub.4 even 18.7 ?71.4 0.976 3.1 2.4 27.7 (C.sub.n).sub.2CuCl.sub.4 odd 16.9 ?55.8 0.960 2.8 2.0 27.5 even 15.5 ?35.2 0.965 2.5 1.0 (C.sub.n).sub.2CuBr.sub.4 odd 12.5 ?77.2 0.999 2.1 5.1 30.3 even 11.3 ?73.2 0.946 2.0 5.5 .sup.aC.sub.n = C.sub.nH.sub.2n+1NH.sub.3.
TABLE-US-00009 TABLE 7 Summary of characteristic infrared signals of (DA).sub.2MnCl.sub.4 and (NA).sub.2CuBr.sub.4. Mode.sup.a (DA).sub.2MnCl.sub.4 (DA).sub.2MnCl.sub.4 (NA).sub.2CuBr.sub.4 (NA).sub.2CuBr.sub.4 Structure (cm.sup.?1) LT band (cm.sup.?1) HT band (cm.sup.?1) LT band (cm.sup.?1) HT band (cm.sup.?1) Alkyl chain v.sub.as(CH) 2919 2919 2919 2920 (C.sub.nH.sub.2n+1NH.sub.3.sup.+) v.sub.s(CH) 2850 2852 2851 2853 v(CH.sub.2).sub.rocking 727-720 721 722 722 doublet singlet singlet singlet v(CH.sub.2).sub.bending 1472-1463 1464 1467 1468 doublet singlet shoulders shoulders (~1440, ~1455) (~1440, ~1455) v(CH.sub.2).sub.wagging band progression 1306 1306 two units, ~1310 (broadening) in-plane (shoulder, contribute 1312 ~1310 (kink) to broadening) (new peak) v(CH.sub.2).sub.wagging band progression 1360 not detected two units, ~1367 (shoulder) out-of-plane ~1360 (kink) v(CH.sub.2).sub.wagging not detected not detected not detected not detected single unit ~1350 (gg) (CH.sub.2).sub.wagging not detected not detected 1340 not detected single unit ~1340 (tg, chain end) v.sub.s(CH.sub.3).sub.bending 1375 1379 1378 1379 ~1376 Polar head v.sub.s(NH.sub.3).sub.bending 1496 1496 1480 1480 (C.sub.nH.sub.2n+1NH.sub.3.sup.+) narrow broad v.sub.as(NH.sub.3).sub.bending 1585 1579 1569-1572 1569 narrow broad doublet singlet .sup.av.sub.s and v.sub.as refer to symmetric and anti-symmetric modes, respectively. .sup.bprevious reports on CdCl and MnCl analogs revealed that the peak near 1337 cm.sup.?1 does not depend on chain conformation (20, 37).
TABLE-US-00010 TABLE 8 Summary of characteristic infrared signals of representative 2-D perovskites. Mode.sup.a Structure (cm.sup.?1) (C.sub.10).sub.2CdCl.sub.4 (C.sub.9).sub.2CuCl.sub.4 (C.sub.10).sub.2CuCl.sub.4 (C.sub.12).sub.2CuCl.sub.4 (C.sub.14).sub.2MnCl.sub.4 Alkyl chain v.sub.as(CH) not not not 2919 .fwdarw. not (C.sub.nH.sub.2n+1NH.sub.3.sup.+) ~2920 discussed discussed discussed 2923 discussed increase v.sub.s(CH) 2851 .fwdarw. 2852 .fwdarw. not 2850 .fwdarw. not ~2850 2853 2854 discussed 2852 discussed increase increase increase v(CH.sub.2).sub.rocking 728-720 727-722 730-725 730-725 729-719 doublet to doublet to doublet to doublet to doublet to singlet singlet singlet singlet singlet v(CH.sub.2).sub.bending ~1460 1471-1466 1472-1467 1472-1467 1475-1463 doublet to doublet to doublet to doublet to doublet to singlet singlet singlet singlet singlet v(CH.sub.2).sub.wagging 1306 1310 1308 1310 1305 two units, in- broad broad broad broad broad plane ~1310 (kink.sup.b) v(CH.sub.2).sub.wagging not 1364 1367 1367 two units, detected shoulder shoulder shoulder out-of-plane ~1360 (kink.sup.b) v(CH.sub.2).sub.wagging not not not not not single unit detected detected detected detected detected ~1350 (gg) (CH.sub.2).sub.wagging not 1340 1341 1342 not single unit detected detected ~1340 (tg, chain end) v.sub.s(CH.sub.3).sub.bending .sup.1376.sup.a not 1376 .fwdarw. 1377 .fwdarw. 1375 .fwdarw. ~1376 discussed 1378 1379 1379 increase increase increase Polar head v.sub.s(NH.sub.3).sub.bending ~1488 1491-1479 1492-1480 1492-1480 ~1496 (C.sub.nH.sub.2n+1NH.sub.3.sub.
TABLE-US-00011 TABLE 9 Comparison of predicted and experimentally determined barocaloric coefficients (dT.sub.tr/dP). Note that the barocaloric coefficient were estimated using the Clausius-Clapeyron equation dT.sub.tr/dP = ?V.sub.tr/?S.sub.tr, with ?V.sub.tr determined through powder X-ray diffraction or Helium pycnometry, and ?S.sub.tr measured at ambient pressure. ?S.sub.tr values for (DA).sub.2MnCl.sub.4 and (NA).sub.2CuBr.sub.4 were 230 and 78 J K.sup.?1 kg.sup.?1, respectively. PXRD.sup.a He pycnometry HP-DSC ?V ?V dT.sub.tr/dP dT.sub.tr/dP (cm.sup.3 dT.sub.tr/dP (cm.sup.3 kg.sup.?1) (K kbar.sup.?1) (K kbar.sup.?1) Compound kg.sup.?1) (K kbar.sup.?1) heating cooling heating cooling heating cooling (DA).sub.2MnCl.sub.4 65.07 28.3 linear 54.7 53.06 23.8 23.1 22.1 ? 0.7 20.6 ? 0.8 (7.95%) fit (6.60%) (6.38%) nearest 49.3 ? 3.4 47.5 ? 5.8 21.4 ? 1.5 20.7 ? 2.5 points (5.9%) (5.7%) (NA).sub.2CuBr.sub.4 24.93 32 linear 19.32 19.25 24.8 24.7 26.9 ? 0.4 26.5 ? 0.5 (3.95%) fit (3.1%) (3.1%) nearest 20.0 ? 1.9 19.7 ? 2.4 25.6 ? 2.4 25.3 ? 3.0 points (3.2%) (3.1%) .sup.aPXRD data was obtained during cooling and the volume change was obtained through linear fit away from the transition.
TABLE-US-00012 TABLE 10 Selected geometric parameters of (DA).sub.2MnCl.sub.4 at 100 K, 270 K, and 330 K. Temperature (K) 100 K 270 K 330 K Space Group P
TABLE-US-00013 TABLE 11 Selected geometric parameters of (NA).sub.2CuBr.sub.4 at 100 K, 270 K, and 335 K. Temperature (K) 100 K 270 K 335 K Space Group P
TABLE-US-00014 TABLE 12 Donor-acceptor (NCl) distances and bond angles for LT and HT phases in (DA).sub.2MnCl.sub.4 and (NA).sub.2CuBr.sub.4. Tilt of NH.sub.3 HA DA ?(DHA) group Compound T (K) NHX (?) (?) (?) Occupancy (?).sup.a (DA).sub.2MnCl.sub.4 270 Equatorial 2.4213(34) 3.291(37) 166.12(44) 61.4 Axial 1 2.4668(14) 3.3310(75) 164.12(42) (16) Axial 2 2.3544(15) 3.226(66) 165.2(26) 330 Equatorial 2.6051(17) 3.384(20) 146.53(74) 67.66 Axial 1 2.7753(4) 3.622(29) 158.8(17) (92) Axial 2 2.7215(22) 3.3332(84) 127.02(52) (NA).sub.2CuBr.sub.4 270 Equatorial 2.7385(5) 3.5262(45) 148.22(31) Chain A 50.682 Axial 1 3.0803(7) 3.9226(54) 158.73(35) Part 1 (0.35) (60) Axial 2 2.7546(6) 3.4350(48) 134.20(31) Equatorial 2.5836(6) 3.431(5) 159.52(31) Chain A 57.37 Axial 1 2.6022(6) 3.4350(48) 156.18(31) Part 2 (0.65) (39) Axial 2 2.9046(7) 3.7516(55) 159.55(35) Equatorial 2.6289(6) 3.4424(55) 152.25(31) Chain B 54.76 Axial 1 2.5648(6) 3.3696(49) 150.76(31) Part 1 (0.53) (41) Axial 2 2.7882(7) 3.6367(55) 159.92(35) Equatorial 2.6929(6) 3.5496(50) 161.86(31) Chain B 81.09 Axial 1 2.7716(6) 3.3696(49) 125.71(31) Part 2 (0.47) (88) Axial 2 3.3243(7) 4.0423(54) 139.38(35) 335 Equatorial 2.6419(12) 3.506(21) 162.449(3) 70.7 Axial 1 3.1158(5) 3.9023(25) 147.952(4) (15) Axial 2 3.1905(10) 3.8858(25) 136.106(1) .sup.athe tilt angle is defined as the angle between a line connecting the atoms N and C and a plane through the metal atoms of the inorganic layers.
TABLE-US-00015 TABLE 13 Tabulation of dihedral angle ? of alkylammonium chains at 100K, 270K, and 330K for (DA).sub.2MnCl.sub.4. Atoms ? (?) Occupancy Atoms ? (?) Occupancy T (K) Part 1.sup.a Part 1 Part 1 Part 2.sup.a Part 2 Part 2 100 N1-C1-C2-C3 179.6 (10) 0.504(13) N1A-C1A-C2A-C3A 178.2 (10) 0.496(13) C1-C2-C3-C4 ?68 (2) 0.504(13) C1A-C2A-C3A-C4A .sup.70 (2) 0.496(13) C2-C3-C4-C5 ?178.2 (13).sup. 0.504(13) C2A-C3A-C4A-C5A 177.5 (14) 0.496(13) C3-C4-C5-C6 178.0 (14) 0.504(13) C3A-C4A-C5A-C6A ?178.4 (15) 0.496(13) C4-C5-C6-C7 ?179.7 (15).sup. 0.504(13) C4A-C5A-C6A-C7A ?179.3 (16) 0.496(13) C5-C6-C7-C8 178.6 (14) 0.504(13) C5A-C6A-C7A-C8A ?179.3 (15) 0.496(13) C6-C7-C8-C9 178.4 (15) 0.504(13) C6A-C7A-C8A-C9A 177.7 (16) 0.496(13) C7-C8-C9-C10 175.9 (17) 0.504(13) C7A-C8A-C9A-C10A 179.3 (17) 0.496(13) 270 N1-C1-C2-C3 174 (3) C1-C2-C3-C4 ?65 (5) C2-C3-C4-C5 179 (3) C3-C4-C5-C6 177 (4) C4-C5-C6-C7 ?175 (5) C5-C6-C7-C8 180 (5) C6-C7-C8-C9 ?174 (5) C7-C8-C9-C10 ?169 (8) 330 N1-C1-C2-C3 174 (3) C1-C2-C3-C4 ?166 (3) C2-C3-C4-C5 ?180 (3) C3-C4-C5-C6 163 (4) C4-C5-C6-C7 154 (4) C5-C6-C7-C8 160 (4) C6-C7-C8-C9 165 (5) C7-C8-C9-C10 ?151 (5) .sup.aPart 1 and part 2 refer to the sets of disordered positions of the alkylammonium chains conformer B (C2-C3 gauche bond)
TABLE-US-00016 TABLE 14 Tabulation of dihedral angle ? of alkylammonium chains at 100K, 270K, and 335K for (NA).sub.2CuBr.sub.4. Atoms ? (?) Occupancy Atoms ? (?) Occupancy T (K) Part 1.sup.a Part 1 Part 1 Part 2.sup.a Part 2 Part 2 100 N1-C1-C2-C3 ?175.0 (6).sup. C1-C2-C3-C4 ?65.7 (9).sup. C2-C3-C4-C5 ?177.4 (7).sup. C3-C4-C5-C6 178.8 (7).sup. C4-C5-C6-C7 179.9 (6).sup. C5-C6-C7-C8 179.0 (7).sup. C6-C7-C8-C9 177.9 (7).sup. N2-C11-C12-C13 70.0 (7) C11-C12-C13-C14 ?177.6 (6).sup. C12-C13-C14-C15 174.1 (6).sup. C13-C14-C15-C16 178.6 (6).sup. C14-C15-C16-C17 ?179.5 (6).sup. C15-C16-C17-C18 ?175.1 (6).sup. C16-C17-C18-C19 ?177.3 (7).sup. 270 N1-C1-C2-C3 ?173.0 (17).sup. 0.528(9) N1A-C1A-C2A-C3A 172 (2) 0.472(9) C1-C2-C3-C4 ?39 (3) 0.528(9) C1A-C2A-C3A-C4A ?178 (3) 0.472(9) C2-C3-C4-C5 ?176 (3) 0.528(9) C2A-C3A-C4A-C5A 174 (3) 0.472(9) C3-C4-C5-C6 178 (3) 0.528(9) C3A-C4A-C5A-C6A 180 (4) 0.472(9) C4-C5-C6-C7 178 (4) 0.528(9) C4A-C5A-C6A-C7A 173 (4) 0.472(9) C5-C6-C7-C8 168 (4) 0.528(9) C5A-C6A-C7A-C8A ?174 (4) 0.472(9) C6-C7-C8-C9 164 (4) 0.528(9) C6A-C7A-C8A-C9A ?164 (4) 0.472(9) N2-C11-C12-C13 ?67 (5) 0.350(15) N2A-C11A-C12A-C13A 77 (2) 0.650(15) C11-C12-C13-C14 173 (4) 0.350(15) C11A-C12A-C13A-C14A ?176.9 (19).sup. 0.650(15) C12-C13-C14-C15 ?159 (5) 0.350(15) C12A-C13A-C14A-C15A 169 (2) 0.650(15) C13-C14-C15-C16 ?175 (5) 0.350(15) C13A-C14A-C15A-C16A ?180 (2) 0.650(15) C14-C15-C16-C17 ?173 (6) 0.350(15) C14A-C15A-C16A-C17A 175 (3) 0.650(15) C15-C16-C17-C18 ?177 (6) 0.350(15) C15A-C16A-C17A-C18A 176 (3) 0.650(15) C16-C17-C18-C19 159 (6) 0.350(15) C16A-C17A-C18A-C19A ?170 (3) 0.650(15) 335 N1-C1-C2-C3 156 (3) C1-C2-C3-C4 44 (7) C2-C3-C4-C5 156 (4) C3-C4-C5-C6 ?128 (8) C4-C5-C6-C7 160 (7) C5-C6-C7-C8 174 (6) C6-C7-C8-C9 ?142 (10) .sup.aPart 1 and part 2 refer to the sets of disordered positions of the alkylammonium chains conformer conformers A (C1-C2 gauche) and B (C2-C3 gauche bond)
TABLE-US-00017 TABLE 15 Crystallographic data for (DA).sub.2MnCl.sub.4 collected at 100 K, 270 K, and 330 K. (DA).sub.2MnCl.sub.4 (DA).sub.2MnCl.sub.4 (DA).sub.2MnCl.sub.4 Formula C.sub.20H.sub.48Cl.sub.4MnN.sub.2 C.sub.20H.sub.48Cl.sub.4MnN.sub.2 C.sub.20H.sub.48Cl.sub.4MnN.sub.2 Temperature (K) 100 (2) 270 (2) 330 (2) Crystal System Triclinic Monoclinic Orthorhombic Space Group P
TABLE-US-00018 TABLE 16 Crystallographic data for (NA).sub.2CuBr.sub.4 collected at 100 K, 270 K, and 335 K. (NA).sub.2CuBr.sub.4 (NA).sub.2CuBr.sub.4 (NA).sub.2CuBr.sub.4 Formula C.sub.18H.sub.44Br.sub.4CuN.sub.2 C.sub.18H.sub.44Br.sub.4CuN.sub.2 C.sub.18H.sub.44Br.sub.4CuN.sub.2 Temperature (K) 100 (2) 270 (2) 335 (2) Crystal System Triclinic Triclinic Orthorhombic Space Group P
TABLE-US-00019 TABLE 17 Comparison of crystallographic unit cell data for ordered phase of (DA).sub.2MnCl.sub.4. (DA).sub.2MnCl.sub.4 (DA).sub.2MnCl.sub.4 (DA).sub.2MnCl.sub.4 experimental experimental reported (1) Formula C.sub.20H.sub.48Cl.sub.4MnN.sub.2 C.sub.20H.sub.48Cl.sub.4MnN.sub.2 C.sub.20H.sub.48Cl.sub.4MnN.sub.2 Temperature (K) 100 (2) 270 (2) 298 (3) Crystal system Triclinic Monoclinic Monoclinic Space Group P
TABLE-US-00020 TABLE 18 Phase-change properties and barocaloric effects of representative barocaloric materials. ?S.sub.tr.sup.c dT.sub.tr/dP dT.sub.tr/dP ?S.sub.it, rev.sup.f Chemical (J kg.sup.?1 heating cooling ?T.sub.hys.sup.d P.sub.rev.sup.e (J kg.sup.?1 ?P.sup.f Type Formula.sup.a T.sub.tr.sup.b K.sup.?1) (K kbar.sup.?1) (K kbar.sup.?1) (K) (bar) K.sup.?1) (bar) Ref 2-D perovskite (DA).sub.2MnCl.sub.4 310 230 22.1 20.6 1.4 66 75 150 This (NA).sub.2CuBr.sub.4 303 78 26.9 26.5 0.4 16 68 150 work 3-D hybrid [(CH.sub.3).sub.4N][Mn(N.sub.3).sub.3] 305 80 12.sup.g.sup. 7 583 70 900 (59) perovskite [TPrA][Mn(dca).sub.3] 330 43 .sup.23.1.sup.g 0.9 39 31 70 (60) [TPrA][Cd(dca).sub.3] 386 16 .sup.38.2.sup.g 1.4 37 11.5 70 (61) Organic (CH.sub.3).sub.2C(CH.sub.2OH).sub.2 314 389 11.3 9.3 14 1505 445 2500 (62, 63) plastic (CH.sub.3)C(CH.sub.2OH).sub.3 354 485 7.9 9.4 3.7 394 490 2400 (64) crystal (CH.sub.3).sub.3C(CH.sub.2OH) 232 204 22.sup. 11.9 20.3 1706 290 2600 (64) C.sub.60 259 27 16.7 17.2 3 174 32 (42) 1000 (4100) (65) Inorganic (NH.sub.4).sub.2SO.sub.4 222 65 ?5.7 ?4.5 1 175 60 1000 (66) AgI 420 64 ?14.sup. ?12.8 25 1786 60 1000 (67) Fe.sub.49Rh.sub.51 310 13 5.4 6.4 10 1563 13 2500 (68) Ni.sub.0.85Fe.sub.0.15S.sup.h 303 53 ?7.5 11.5 1533 (69) Spin Fe.sub.3(bntrz).sub.6(tcnset).sub.6 318 80 25.sup. 25.sup. 2 80 80 (120) 550 (2600) (70) crossover [FeL.sub.2](BF.sub.4).sub.2.sup.h, i 262 86 10.sup.j 10.sup.j 4 400 (71) complex .sup.aDA = decylammonium; NA = nonylammonium; TPrA = tetrapropylammonium; bntrz = 4-(benzyl)-1,2,4-triazole; tcnset = 1,1,3,3-tetracyano-2-thioethylepropenide; L = 2,6-di(pyrazol-1-yl)pyridine. .sup.bTransition temperatures measured during heating are tabulated here. .sup.cEntropy of transition ?S.sub.tr measured at ambient pressure are tabulated here. .sup.d?T.sub.hys refers to the difference between T.sub.tr, heating and T.sub.tr, cooling at ambient pressure. .sup.eP.sub.rev is calculated through P.sub.rev = ?T.sub.hys/|dT.sub.tr/dP|, and dT.sub.tr/dP values for exothermic and endothermic transitions are used for conventional and inverse barocaloric materials, respectively. Note that inverse barocaloric materials refer to the compounds with dT.sub.tr/dP < 0. .sup.fThe reversible isothermal entropy changes, ?S.sub.it, rev, at the driving pressure ?P are tabulated here. Note that these values were derived from quasi-direct measurements. At high pressure (typically above 1 kbar), the additional entropy change outside of the transition, ?S.sub.+, plays a role and contributes to ?S.sub.it values, leading to ?S.sub.it to higher than ?S.sub.tr. The ?S.sub.it measured at higher pressures are shown in the parentheses. .sup.gdT.sub.tr/dP values were averaged from heating and cooling data. .sup.hOnly irreversible ?S.sub.it value is reported (Ni.sub.0.85Fe.sub.0.15S, 53 J kg.sup.?1 K.sup.?1 at 1000 bar; [FeL.sub.2](BF.sub.4).sub.2, 68 J kg.sup.?1 K.sup.?1 at 430 bar). .sup.ian irreversible phase transitions occur at the pressure above 4900 bar. .sup.jdT.sub.tr/dP values obtained at a pressure range < 2 kbar values are shown. Note that (dT.sub.tr/dP).sub.heating and (dT.sub.tr/dP).sub.cooling were obtained from calorimetry and SQUID magnetometry, respectively.
TABLE-US-00021 TABLE 19 Barocaloric effects and predicted thermodynamic efficiencies for selected barocaloric materials including two of the invention ((DA).sub.2MnCl.sub.4 and (NA).sub.2CuBr.sub.4). ?S.sub.it, rev/?P.sup.c ?T.sub.hys/ Chemical (J kg.sup.?1 K.sup.?1 ?T.sub.ad, max.sup.d ?T.sub.ad, max.sup.e ?.sup.f Formula.sup.a T.sub.tr.sup.b kbar.sup.?1) (K) (%) (%) (DA).sub.2MnCl.sub.4 310 500 42.sup.g 3.3 89 (NA).sub.2CuBr.sub.4 303 453 21.sup.h 1.9 93 [TPrA][Mn(dca).sub.3] 330 436 5.sup.i 15.8 61 (CH.sub.3).sub.2C(CH.sub.2OH).sub.2 314 178 45.sup.j 31.1 45 C.sub.60 259 32 20.sup.k 15.0 63 (NH.sub.4).sub.2SO.sub.4 222 60 8.sup.l 12.5 67 Ni.sub.0.85Fe.sub.0.15S.sup.h 303 30.sup.m 38.3 40 Fe.sub.3(bntrz).sub.6(tcnset).sub.6 318 145 35.sup.n 5.7 81 .sup.aDA = decylammonium; NA = nonylammonium; TPrA = tetrapropylammonium; bntrz = 4-(benzyl)-1,2,4-triazole; tcnset = 1,1,3,3-tetracyano-2-thioethylepropenide. .sup.bTransition temperatures measured during heating are tabulated here. .sup.cThe reversible isothermal entropy change ?S.sub.it, rev normalized by the driving pressure, often referred to as barocaloric strength, are tabulated here. Note that the barocaloric strength values were maximized by choosing the smallest ?P values that can capture the full entropy of the transition. .sup.dMaximum adiabatic temperature changes tabulated here were predicted by indirect methods, with ?T.sub.ad, max = T?S.sub.it/c.sub.p, or, by quasi-direct methods. .sup.e?T.sub.hys values measured at ambient pressure were used. .sup.fThe second-law efficiency ?, which corresponds to coefficient of performance (COP) of material with hysteresis normalized by COP of Carnot cycle, is estimated using the equation
TABLE-US-00022 TABLE 20 Phase-change properties and barocaloric effects of compounds with long-chain hydrocarbons. ?S.sub.tr.sup.c d T.sub.tr/d P.sup.d ? T.sub.hys.sup.d Type Chemical Formula.sup.a T.sub.tr.sup.b (J kg.sup.?1 K.sup.?1) (K kbar.sup.?1) (K) 2-D perovskite (OA).sub.2MnCl.sub.4.sup.e 274 153 13 3.0 major (OA).sub.2MnCl.sub.4.sup.e 303 33 40 0.7 minor (NA).sub.2MnCl.sub.4.sup.e 291 183 20 2.2 major Di-n-alkyl ammonium (n-C.sub.6H.sub.13).sub.2NH.sub.2Br 292 291 .sup.34.sup.e 4.7 salt.sup.f (n-C.sub.8H.sub.17).sub.2NH.sub.2Cl 294 343 (n-C.sub.8H.sub.17).sub.2NH.sub.2Br 302 247 (n-C.sub.12H.sub.25).sub.2NH.sub.2Cl 338 379 (n-C.sub.12H.sub.25).sub.2NH.sub.2Br 345 327 (n-C.sub.18H.sub.37).sub.2NH.sub.2Cl 366 411 (n-C.sub.18H.sub.37).sub.2NH.sub.2Br 370 379 Intercalation compound FeOClC.sub.14H.sub.29NH.sub.2.sup.g 323 93 (first-row transition Ni(CN).sub.2C.sub.12H.sub.25NH.sub.2.sup.h 327 214 metal) major Ni(CN).sub.2C.sub.12H.sub.25NH.sub.2.sup.h 363 41 minor intercalated between (C.sub.18H.sub.37).sub.3NH.sup.+i 324 83 montmorillonite Self-Assembled (smectite) Monolayer (C.sub.18H.sub.37).sub.4N.sup.+i 310 63 Self-Assembled Monolayer Layered metallo- Mg(O.sub.3PC.sub.22H.sub.45).sup.j 290- 682 alkylphosphonate 330 .sup.aDA = decylammonium; NA = nonylammonium. .sup.bTransition temperatures measured during heating are tabulated here. .sup.cEntropy of transition ?S.sub.tr measured at ambient pressure are tabulated here. The literature values are associated with large uncertainty. .sup.dBarocaloric coefficients tabulated here were measured through high-pressure differential calorimetry under Helium gas environment. Thermal hysteresis were measured at ambient pressure. .sup.ePhase-change properties, including the change in volume, was previously reported. .sup.fCompounds listed here are predicted to display large barocaloric effects, due to high ?S.sub.tr and large volume change (?V.sub.tr)of ~7%. .sup.gPredicted to display large inverse barocaloric effects due to ?V.sub.tr, = ?7%. .sup.hPredicted to display large barocaloric effects due to large ?V.sub.tr ~11%. However, the reversibility of the major transition requires further investigation. .sup.iPredicted to display large barocaloric effects due to large ?V.sub.tr of 2% and 5% for (C.sub.18H.sub.37).sub.3NH.sup.+ and (C.sub.18H.sub.37).sub.4N.sup.+, respectively. .sup.jFour successive transitions occur at a temperature range between 290 K and 330 K, with a major transition around 305 K. The total entropy change is tabulated here. To probe reversibility and volume change, further investigations are required.
TABLE-US-00023 TABLE 21 Summary of both gravimetric and molar thermodynamic properties of the phase transition in mixed-halide 2-D perovskites. The transition temperatures listed are heating values for the principal transition, and the molar values were calculated based on the intended halide ratios. ?S ?S Chemical T.sub.tr ?H ?H (J mol.sup.?1 (J kg.sup.?1 Formula (K) (kJ mol.sup.?1) (kJ kg.sup.?1) K.sup.?1) K.sup.?1) (NA).sub.2CuCl.sub.4 295 26.8 51.7 86.1 174.3 (NA).sub.2CuCl.sub.3Br 290 24 44.6 82.3 153.0 (NA).sub.2CuCl.sub.2Br.sub.2 286 17.9 30.8 62.5 107.2 (NA).sub.2CuClBr.sub.3 292 16.4 26.1 56.1 89.5 (NA).sub.2CuBr.sub.4 302 15 22.3 49.6 73.9 (DA).sub.2CuCl.sub.4 309 34.5 66.2 111.4 213.5 (DA).sub.2CuCl.sub.3Br 308 25.6 45.3 83.3 147.1 (DA).sub.2CuCl.sub.2Br.sub.2 307 25.2 41.2 82.0 134.2 (DA).sub.2CuClBr.sub.3 309 19.8 30.2 64.2 97.9 (DA).sub.2CuBr.sub.4 317 18.1 25.9 57.3 81.9
TABLE-US-00024 TABLE 22 Summary of both gravimetric and molar thermodynamic properties of the phase transition in mixed-cation 2-D perovskites. ?H ?H ?S ?S T.sub.tr (kJ (kJ (J mol.sup.?1 (J kg.sup.?1 Chemical Formula (K) mol.sup.?1) kg.sup.?1) K.sup.?1) K.sup.?1) (NA).sub.2CuCl.sub.4 295 26.8 54.3 86.1 174.3 [(NA).sub.0.75(DA).sub.0.25].sub.2CuCl.sub.4 290 19.0 44.6 65.5 130.7 [(NA).sub.0.5(DA).sub.0.5].sub.2CuCl.sub.4 291 22.0 43.2 75.6 148.9 [(NA).sub.0.25(DA).sub.0.75].sub.2CuCl.sub.4 297 21.7 26.1 72.9 141.6 (DA).sub.2CuCl.sub.4 309 34.5 22.3 111.4 213.5 [(NA).sub.0.5(UA).sub.0.5].sub.2CuCl.sub.4 282 20.6 39.4 72.8 139.4
TABLE-US-00025 TABLE 23 Summary of thermodynamic properties of the phase transition in compositionally engineered 2-D perovskites with promising barocaloric potentials. ?H ?H ?S ?S T.sub.tr (kJ (kJ (J mol.sup.?1 (J kg.sup.?1 Chemical Formula (K) mol.sup.?1) kg.sup.?1) K.sup.?1) K.sup.?1) (DA).sub.2CuCl.sub.3Br 308 25.6 45.3 83.3 147.1 (DA).sub.2CuCl.sub.2Br.sub.2 307 25.2 41.2 82.0 134.2 (NA.sub.0.5DA.sub.0.5)CuCl.sub.4 291 22.0 43.2 75.6 148.9 (NA.sub.0.5UA.sub.0.5).sub.2CuCl.sub.4 282 20.6 39.4 72.8 139.4 (NA.sub.0.5DA.sub.0.5).sub.2CuCl.sub.2Br.sub.2 285 18.2 31.45 64.0 111.5
TABLE-US-00026 TABLE 24 Summary of thermodynamic trends for the five compounds identified as promising barocaloric materials. ?T.sub.hys is defined here as the difference between the peak transition temperature upon heating and the peak transition temperature upon cooling. T.sub.tr ?H ?S dT/dP P.sub.rev, ad ?T.sub.hys Chemical Formula (K) (kJ kg.sup.?1) (J kg.sup.?1 K.sup.?1) (K kbar.sup.?1) (bar) (K) (DA).sub.2CuCl.sub.3Br 308 45.3 147.1 24.3 151 2.3 (DA).sub.2CuCl.sub.2Br.sub.2 307 41.2 134.2 25.8 129 2.3 (NA.sub.0.5DA.sub.0.5).sub.2CuCl.sub.4 291 43.2 148.9 22.4 166 1.6 (NA.sub.0.5UA.sub.0.5).sub.2CuCl.sub.4 282 39.4 139.4 25.1 176 2.2 (NA.sub.0.5DA.sub.0.5).sub.2CuCl.sub.2Br.sub.2 285 31.45 111.5 24.1 161 2.6
TABLE-US-00027 TABLE 25 Summary of barocaloric properties for mixed halide and mixed cation perovskites. Here, ?P is defined as the operating pressure required to achieve the maximum adiabatic temperature change, and is calculated as ? T.sub.ad, max/(dT/d P). Note that c.sub.p for the low temperature phase is used for the calculations. T.sub.tr ?S c.sub.p dT/dP P.sub.rev, ad ?T.sub.bys ?T.sub.ad, max ?P Chemical Formula (K) (J kg.sup.?1 K.sup.?1) (J g.sup.?1 K.sup.?1) (K kbar.sup.?1) (bar) (K) (K) (bar) (DA).sub.2CuCl.sub.3Br 308 147 1.50 24.3 151 2.3 27 1103 (DA).sub.2CuCl.sub.2Br.sub.2 307 134 1.41 25.8 129 2.3 26 989 (NA.sub.0.5DA.sub.0.5).sub.2CuCl.sub.4 291 149 1.50 22.4 166 1.6 26 1163 (NA.sub.0.5UA.sub.0.5).sub.2CuCl.sub.4 282 139 1.51 25.1 176 2.2 23 915 (NA.sub.0.5DA.sub.0.5).sub.2CuCl.sub.2Br.sub.2 285 112 1.34 24.1 161 2.6 21 866
TABLE-US-00028 TABLE 26 Phase-change properties of newly synthesized symmetric dialkylammonium salts. Preliminary characterizations through high-pressure differential scanning calorimetry (HP-DSC) in our lab or the Clausius-Clapeyron equation (dT.sub.tr/dP = ?V.sub.tr/?S.sub.tr) indicate that these candidate compounds are all expected to display high pressure sensitivity (dT.sub.tr/dP) between 10-30K kbar.sup.?1. Note that the temperature of transition measured during the first heating scans are tabulated here. ?S.sub.tr ?S.sub.tr T.sub.tr (J kg.sup.?1 (J mol.sup.?1 dT.sub.tr/dP (? C.) K.sup.?1) ?S.sub.tr K.sup.?1) (K kbar.sup.?1) major ?T.sub.hys major (J L.sup.?1 per chain major Candidates (minor) (? C.) (minor) K.sup.?1) (total) (minor) (C.sub.12H.sub.25)(CH.sub.3)NH.sub.2Br 69.6 1.4 300 351 84 23.1 22.2 (C.sub.12H.sub.25)(CH.sub.3)NH.sub.2Cl 61.1 (58.6); 2.5 350 363 83 23.1 (36).sup. 58.6 (48.1) (10.5) (14) (15) 24.5 (42.7) ?S T.sub.tr ?H (J K.sup.?1 dT/dP Chemical Formula (K) (kJ kg.sup.?1) kg.sup.?1) (K kbar.sup.?1) (C.sub.6H.sub.13).sub.2NH.sub.2Cl 277 59.5 215 (C.sub.8H.sub.17).sub.2NH.sub.2Cl 292 105.5 361 (C.sub.10H.sub.21).sub.2NH.sub.2Cl 321 125.0 390 (C.sub.6H.sub.13).sub.2NH.sub.2Br 295 88.3 308 22-27 (C.sub.8H.sub.17).sub.2NH.sub.2Br 301 80.1 266 (C.sub.10H.sub.21).sub.2NH.sub.2Br 377 103.7 317 (C.sub.6H.sub.33).sub.2NH.sub.2I 284 56.6 199 16-25 (C.sub.8H.sub.17).sub.2NH.sub.2I 285 47.7 167 (C.sub.10H.sub.21).sub.2NH.sub.2I 317 81.0 256
[0175] Table 27. Phase-change properties of newly synthesized asymmetric dialkylammonium salts. Preliminary characterizations through high-pressure differential scanning calorimetry (HP-DSC) indicate that these candidate compounds all display high pressure sensitivity (dT.sub.tr/dP) between 20-30 K kbar.sup.?1.
TABLE-US-00029 TABLE 28 Unit cell parameters for (C.sub.nH.sub.2n+1).sub.2NH.sub.2Br (n = 6, 8, 10) from single-crystal X-ray diffraction at ambient pressure. Space Compound T (K) a (?) b (?) c (?) ? (?) ? (?) ? (?) V (?.sup.3) Group (C.sub.6H.sub.13).sub.2NH.sub.2Br 100 26.267(2) 5.3453(3) 10.7542(6) 90 98.299(1) 90 1494.14 C2/c (C.sub.8H.sub.17).sub.2NH.sub.2Br 100 5.372(2) 33.568(1) 5.279(2) 90 90 90 951.895 P2.sub.12.sub.12 (C.sub.10H.sub.21).sub.2NH.sub.2Br 100 5.3475(4) 39.886(3) 5.2758(4) 90 90 90 1125.28 P2.sub.12.sub.12
TABLE-US-00030 TABLE 29 Unit cell parameters for (C.sub.12H.sub.25)N(CH.sub.3)H.sub.2X (X = Cl, Br) from single-crystal X-ray diffraction at ambient pressure at 100K. Space Compound a (?) b (?) c (?) ? (?) ? (?) ? (?) V (?.sup.3) Group (C.sub.12H.sub.25)(CH.sub.3)NH.sub.2Cl 4.8858(3) 5.2510(2) 29.585(1) 93.453(4) 94.633(4) 90.810(4) 755.012 P
[0176] Other embodiments are in the claims.