NANOPARTICLES FOR THE USE AS PINNING CENTERS IN SUPERCONDUCTORS

Abstract

The present invention is in the field of nanoparticles, their preparation and their use as pinning centers in superconductors. In particular the present invention relates to nanoparticles comprising an oxide of Sr, Ba, Y, La, Ti, Zr, Hf, Nb, or Ta, wherein the nanoparticles have a weight average diameter of 1 to 30 nm and wherein an organic compound of general formula (I), (II) or (III) or an organic compound containing at least two carboxylic acid groups on the surface of the nanoparticles (I) (II) (III) wherein a is 0 to 5, b and c are independent of each other 1 to 14, n is 1 to 5, f is 0 to 5, p and q are independent of each other 1 to 14, and e and f are independent of each other 0 to 12.

##STR00001##

Claims

1. Nanoparticles, comprising: an oxide of Sr, Ba, Y, La, Ti, Zr, Hf, Nb, or Ta, wherein: the nanoparticles have a weight average diameter of 1 to 30 nm, and an organic compound of general formula (I), (II) or (III) or an organic compound containing at least two carboxylic acid groups is on the surface of the nanoparticles, ##STR00004## wherein: a is 0 to 5; b and c are independent of each other 1 to 14; n is 1 to 5; r is 0 to 5; p and q are independent of each other 1 to 14; and e and f are independent of each other 0 to 12.

2. The nanoparticles according to claim 1, wherein the nanoparticles comprise ZrO.sub.2, HfO.sub.2 or Ta.sub.2O.sub.5.

3. The nanoparticles according to claim 1, wherein the organic compound containing at least two carboxylic acid groups is a compound of general formula (IV): ##STR00005## wherein: R.sup.1 and R.sup.2 are independent of each other H, OH, or COOH; and m is 1 to 12.

4. The nanoparticles according to claim 1, wherein a trialkyl phosphorous oxide or a fatty acid is additionally on the surface of the nanoparticles.

5. The nanoparticles according to claim 1, wherein the nanoparticles are crystalline.

6. The nanoparticles according to claim 1, wherein the nanoparticles have a dispersity of particle size distribution D.sub.90/D.sub.50 measured by dynamic light scattering of 1.2 or less.

7. A process for producing the nanoparticles of claim 1, the process comprising: (i) precipitating nanoparticles comprising the oxide of Sr, Ba, Y, La, Ti, Zr, Hf, Nb, or Ta from a suspension comprising a non-polar solvent, wherein the nanoparticles have a weight average diameter of 1 to 30 nm; and (ii) adding an alcohol and the organic compound of general formula (I), (II) or (III) or the organic compound containing at least two carboxylic acid groups to the precipitated nanoparticles to precipitated nanoparticles, to obtain the nanoparticles.

8. The process according to claim 7, wherein the suspension comprising a non-polar solvent and nanoparticles is produced by a condensation or esterification reaction comprising a soluble precursor in the presence of a surfactant.

9. An ink for the preparation of a high temperature superconductor, the ink comprising: (a) an yttrium or rare earth metal-containing compound; (b) an alkaline earth metal-containing compound; (c) a transition metal-containing compound; (d) an alcohol; and (e) the nanoparticles of claim 1.

10. The ink according to claim 9, wherein the alcohol is a mixture of methanol and C.sub.2 to C.sub.12 alcohols.

11. The ink according to claim, wherein at least one of the rare earth metal-containing compound or the yttrium-containing compound, the alkaline earth metal-containing compound and the transition metal-containing compound contains fluorine.

12. The ink according to claim 9, comprising the nanoparticles at a concentration at which a molar ratio of metal in the nanoparticles to the yttrium-containing compound or the rare earth metal-containing compound is 1 to 30%.

13. A superconductor, comprising the nanoparticles of claim 1 as pinning centers in the superconductors.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0076] FIG. 1 shows a SAXS measurement of stabilized ZrO2 particles in an YBCO ink.

EXAMPLES

Example 1

Nanoparticle Synthesis

Example 1.1

ZrO.SUB.2 .Nanoparticles

[0077] 20 mmol (7.8 g) of zirconium(IV) isopropoxide propanol complex (Zr[OCH(CH.sub.3).sub.2].sub.4. (CH.sub.3).sub.2CHOH) and 25 mmol (5.83 g) of zirconium(IV) chloride were added to 100 g of purified and degassed trioctylphosphine oxide (TOPO, purified by vacuum distillation) at 60 C. in an argon atmosphere. The temperature of the reaction mixture was raised slowly to 340 C. and held at this temperature for 2 h with vigorous stirring. During this thermal treatment, the initial light yellow solution changed to light green. The reaction mixture was then cooled to 60 C., and 500 ml of acetone was added to precipitate zirconia nanoparticles. The precipitate was retrieved by centrifugation and washed several times with acetone and redispersed in 110 ml toluene. The particle size of the nanoparticles measured by high resolution transmission electron microscopy was 2 to 3 nm. An XRD with peak assignment to crystal planes is depicted in FIG. 1.

Example 1.2

HfO.SUB.2 .Nanoparticles

[0078] Under vigorous stirring, 0.5 ml of dibenzyl ether was added to 0.4 mmol of hafnium-IV-chloride in a 10 ml microwave vial. Then quickly 4 ml of benzyl alcohol was added, yielding a clear and colorless solution after 5 minutes of stirring. The solution was subjected to microwave heating with the following temperature settings: 5 minutes at 60 C. and 3 hours at 210 C. After synthesis the phase separated mixture was transferred to a plastic centrifugation tube and 3 ml of diethyl ether were added. After mild centrifugation (2000 rpm, 2 min) two clear and transparent phases were observed. The organic (top) phase was removed and ethanol was added to the aqueous (bottom) phase yielding 2 ml of a clear suspension. The particles were precipitated and washed once with diethyl ether. Finally the particles were redispersed in chloroform and typically 0.2 mmol of oleic acid was added to the milky suspension. Under stirring, oleylamine was added until a colorless and transparent suspension was obtained which is usually about 0.15 mmol (i.e., 50 L). The particle size of the nanoparticles measured by high resolution transmission electron microscopy was 4 to 5 nm.

Example 2

[0079] To 1 ml of the ZrO2 dispersion of example 1.1 7-8 ml acetone were added in a centrifuge vial. The ZrO.sub.2 dispersion had a concentration of about 0.18 mol/l with regard to the zirconium. The precipitate was centrifuged for 15 min at 4000 rpm in a lab centrifuge. The supernatant solution was discarded. The precipitate was redispersed in 1 ml toluene, precipitated by adding 7-8 ml acetone and centrifuged. After the supernatant solution was discarded, 100 l of a methanol solution containing compound la at a concentration of 350 g/I was added. Ia is a compound of general formula (I) in which a=0, b=6, c=5, n=2-3. The mixture was shaken in a lab shaking device for 2 min, whereupon a clear suspension formed. Then 900 l of a methanol solution containing yttrium propionate (0.24 mol/l), barium trifluoroacetate (0.32 mol/l), and copper propionate (0.54 mol/l) was added (YBCO solution). The concentration of the YBCO solution is given as the concentration of the sum of yttrium, barium and copper in table 1.

Example 3

[0080] Ca. 15 mg of the organic compound given in table 1 were added to 100 l of a nanoparticle dispersion in toluene at the concentration given in table 1. The mixture was shaken on a lab shaking device for 2 minutes to form a clear suspension. Then the toluene was removed by heating to 110-120 C. while decanol was added to replace the toluene. The obtained decanol solution was added to an YBCO solution as in example 2.

Example 4

[0081] The procedure according to example 2 is followed with the difference that instead of the compound Ia the compound IIa is used. Compound IIa is a compound of general formula (II) in which f=3, p=10, q=8.

Example 5

[0082] The procedure according to example 2 is followed with the difference that instead of the compound Ia the compound IIIa is used. Compound IIIa is a compound of general formula (III) in which e=0 and f=5-6.

Example 6

Comparative Example 100 l of a nanoparticle dispersion in toluene was added to 900 l of an YBCO solution described in example 2.

[0083]

TABLE-US-00001 TABLE 1 Results from the examples. YBCO Organic compound Nanoparticle solution Amount c in c in Obtained Example Type in mg Oxide mol/l mol/l dispersion 2.1 Ia 35 ZrO.sub.2 0.18 1.10 clear 2.2 Ia 15 ZrO.sub.2 0.18 1.10 clear 2.3 Ia 35 ZrO.sub.2 0.18 1.10 clear 3.1 Ia 35 ZrO.sub.2 0.18 1.10 clear 3.2 Ia 35 ZrO.sub.2 0.18 1.10 clear 3.3 Ia 35 HfO.sub.2 0.08 1.10 clear 4.1 IIa 21 ZrO.sub.2 0.18 1.10 clear 4.2 IIa 21 HfO.sub.2 0.08 1.10 clear 5.1 IIIa 24 ZrO.sub.2 0.08 1.10 clear 5.2 IIIa 24 HfO.sub.2 0.08 1.10 clear 6.1 Oleic acid ZrO.sub.2 0.18 1.10 precipitate 6.2 TOPO HfO.sub.2 0.08 1.10 precipitate

[0084] The YBCO solution containing the stabilized particles according to example 1.1 were subjected to small angle X-ray scattering (SAXS). The result was analyzed via Guinier theory. A particle size of 2.1 nm was measured indicating that the nanoparticles are non-aggregated.