PROCESS FOR PREPARING A TRANSITION METAL PHOSPHATE

Abstract

The present invention is directed to a process for preparing a transition metal phosphate comprising mixing a transition metal oxide with a hypophosphite compound and heating the mixture under inert gas conditions.

Claims

1.-10. (canceled)

11. A process for preparing a transition metal phosphate comprising: a) preparing a mixture of a particulate transition metal oxide with an at least stoichiometric amount of a particulate hypophosphite compound, b) heating the mixture obtained in step a), optionally under inert gas conditions, to a temperature range between the melting point and the decomposition temperature of the hypophosphite compound, wherein the ratio of the weight amount of the hypophosphite compound to the weight amount of the transition metal oxide is in the range of 2:1 to 10:1, and wherein the hypophosphite compound is (NH.sub.4)H.sub.2PO.sub.2.

12. Process according to claim 11, wherein the heating step b) is carried out up to a temperature in the range between 200? C. and 600? C.

13. Process according to claim 11, whereby the heating of step b) is carried out at gradually increasing temperature.

14. Process according to claim 11, whereby the heating step is carried out for 30 to 600 minutes.

15. Process according to claim 11, wherein the process further comprises: purifying the product obtained in step b), and optionally drying the obtained product.

16. Process according to claim 11, wherein the transition metal oxide is a first-row transition metal oxide or alternatively another early transition metal oxide.

17. Transition metal phosphate obtainable by the process according to claim 11, wherein the metal oxide is selected from Ti, V, Cr, Mn and Fe oxides and mixtures thereof.

18. Titanium(III/IV)phosphate compound obtainable by the process according to claim 11, wherein TiO.sub.2 is used as transition metal oxide and wherein the heating step b) is carried out up to a temperature of less than 500? C.

19. A method comprising performing an organochemical reaction or a reaction in an electrochemical device in the presence of a catalyst, wherein the catalyst is a titanium(III/IV)phosphate compound according to claim 18.

Description

[0038] The present invention is further illustrated by the attached Figures and the Experimental part. As shown in the Figures:

[0039] FIG. 1 illustrates the general synthesis procedure for the preparation of TMPs, starting from a solid mixture of ammonium hypophosphite and metal oxide.

[0040] FIG. 2 shows the XRD patterns of two novel titanium phosphate phases (a) Ti(III)P, b) Ti(IV)P) and c) Ti(PO.sub.3).sub.3 synthesized by the conversion of d) TiO.sub.2 (P25) in a melt of ammonium hypophosphite. Lines indicate the positions of the main reflections of the TiO.sub.2 compound.

[0041] FIG. 3 shows a Raman spectrum of Ti(III)p, which reveals a strong signal (764 cm.sup.?1) in a range (box) characteristic for inorganic pyrophosphate compounds.

[0042] FIG. 4 shows TG-DSC curves of the Ti(III)p.fwdarw.Ti(IV)p phase transformation.

[0043] FIG. 5 shows TG curve of Ti(III)p.fwdarw.Ti(IV)p phase transformation and associated mass signals of hydrogen (m/z 2), ammonia (m/z 17) and water (m/z 17, 18). The mass signals have been recorded from mass spectra of the exhaust gas of the TG/DSC instrument.

[0044] FIG. 6 shows a .sup.31P MAS NMR spectra of Ti(IV)p prepared via phase transformation from the Ti(III)p compound phase. The Ti(III)p samples were prepared at different batches of 1 g, 5 g and 10 g.

[0045] FIG. 7 shows the XRD patterns of phases obtained with increasing hypophosphite weight ratios from 1/1 up to 1/10. The vertical lines indicate the positions of the main reflections of the TiO.sub.2 compound.

[0046] FIG. 8 shows the XPS spectra of a) Ti(III)p, b) Ti(PO.sub.3).sub.3, c) Ti(IV)p and d) phosphated Ti(III/IV) oxide synthesized from a mixture of TiO.sub.2 and NH.sub.4H.sub.2PO.sub.2 with a weight ratio of 1/2.

[0047] FIG. 9 shows the reaction pathways for the preparation of novel and known titanium phosphate phases starting from TiO.sub.2 converted in a melt of ammonium hypophosphite.

[0048] FIG. 10 shows XRD patterns of TMPs synthesized by reductive phosphatization of metal oxides in a melt of ammonium hypophosphite: a) V(PO.sub.3).sub.3 (obtained at 500? C.), b) Mn.sub.2(P.sub.4O.sub.12) (obtained at 500? C.), c) Cr(NH.sub.4)HP.sub.3O.sub.10 (obtained at 300? C.) (additional reflections belonging to the Cr.sub.2O.sub.3 compound phase (lines), d) Cr(PO.sub.3).sub.3 (obtained at 500? C.), e) Fe(II)p (obtained at 300?), f) Fe.sub.2(P.sub.4O.sub.12) (obtained at 500? C.).

[0049] FIG. 11 shows the .sup.57Fe Mossbauer spectrum of Fe(II)p recorded at 80 K showing two Mossbauer sites with isomer shifts characteristic for Fe(II) species.

EXPERIMENTAL PART

Characterization Methods

Powder X-Ray Diffraction (XRD)

[0050] XRD patterns were measured on Stoe STADI P (Debye-Scherrer) transmission and STADI P reflection (Bragg-Brentano) geometry using 0.5 mm borosilicate capillaries for transmission measurements. The transmission diffractometer was equipped with a primary germanium monochromator, the reflection instrument was equipped with an energy-dispersive PIN diode detector. Both instruments were operated with Cu K.sub.? radiation.

Raman Spectrometry

[0051] The Raman data was recorded on an InVia spectroscope (Renishaw Ltd, UK) with an excitation wavelength of 785 nm; the laser power was tuned to 30 mW. A 1200 grating/mm grid assured a spectra resolution of 1 cm.sup.?1. All spectra were collected with 10 s per step and three repetitions.

Thermogravimetric Analysis and Mass Spectrometry

[0052] TG/DSC measurements have been performed with a Netzsch STA 449 thermobalance attached to a Netzsch Aeolos mass spectrometer. Measurements have been performed under argon atmosphere using a heating rate of 10? C./min.

X-Ray Photoelectron Spectroscopy

[0053] XPS measurements were performed with a spectrometer from SPECS GmbH equipped with a PHOIBOS 150 1D-DLD hemispherical energy analyser. The monochromatized Al K.sub.?, X-ray source (E=1486.6 eV) was operated at 15 kV and 200 W. For measuring high-resolution scans, the pass energy was set to 20 eV. The medium area mode was used as lens mode. The base pressure during the experiment in the analysis chamber was 5?10.sup.?10 mbar. To account charging effects, all spectra are referred to C 1s at 284.5 eV.

MAS NMR Spectroscopy

[0054] The .sup.31P MAS NMR spectra were recorded on a Bruker Avance III HD 500WB spectrometer using a double-bearing MAS probe (DVT BL4) at a resonance frequency of 202.5 MHz. The spectra were measured by applying single ?/2-pulses (3.0 ?s) with a recycle delay of 600 s (4 or 8 scans) at several spinning rates between 3 and 12? kHz. High-power proton decoupling (spinal64) was applied. The chemical shifts are given with respect to 85% aqueous H.sub.3PO.sub.4 using solid NH.sub.4H.sub.2PO.sub.4 as secondary reference (?=0.81 ppm).

Mossbauer Spectroscopy

[0055] Mossbauer spectra were recorded on a conventional spectrometer with alternating constant acceleration of the ?-source. The minimum experimental line width of the instrument was 0.24 mm/s (full width at half-height). The sample temperature was maintained constant in an Oxford Instruments Variox cryostat, whereas the .sup.57Co/Rh source (0.9 GBq) was kept at room temperature. The detector was a Si-Drift diode (150 mm.sup.2 SDD CUBE) of an AXAS-M1 system from Ketek GmbH. The spectrometer was calibrated by recording the M?ssbauer spectrum of 25 ?m alpha-Fe foil at room temperature. As the center of the six-line pattern was taken as zero velocity, isomer shifts are quoted relative to iron metal at 300K. The zero-field spectra were simulated with Lorentzians by using the program mf SL (by EB).

General Synthetic Procedure

[0056] The general synthetic procedure of TMPs is illustrated in FIG. 1. In a typical preparation, metal oxide powder (e.g. TiO.sub.2, V.sub.2O.sub.5, Cr.sub.2O.sub.3, MnO.sub.2, Fe.sub.2O.sub.3) is mixed with a surplus of ammonium hypophosphite (NH.sub.4H.sub.2PO.sub.2) with weight ratios up to 1/10 (1 part metal oxide powder, 10 parts ammonium hypophosphite) and heated for 2 h in a tube furnace under argon flow. Finally, the sample is cooled down and washed with de-ionized water until pH 6 is achieved for removing excess phosphates from the crystalline material.

[0057] The process of the present invention was tested for a series of first row transition metals (Ti, V, Cr, Mn, Fe) under low (300? C.) and high (500? C.) temperature conditions. The results, listed in Table 1, indicate that low temperature conditions tend to form ammonium TMPs, while higher temperatures lead to the formation of ammonium-free TMPs with condensed metaphosphate structures. In almost all cases, the reaction was accompanied by a reduction of the transition metal.

TABLE-US-00001 TABLE 1 TMP product phases and oxidation states for the conversion of first row transition metal oxides with ammonium hypophosphite at 300? C. and 500? C. Compound Product (300? C.) Product (500? C.) TM oxide Valence TMP Valence TMP Valence TiO.sub.2 4+ Ti(III)p 3+ Ti(PO.sub.3).sub.3 3+ V.sub.2O.sub.5 5+ V(PO.sub.3).sub.3 3+ V(PO.sub.3).sub.3 3+ Cr.sub.2O.sub.3 3+ Cr(NH.sub.4)HP.sub.3O.sub.10 3+ Cr(PO.sub.3).sub.3 3+ MnO.sub.2 4+ Mn.sub.2(P.sub.4O.sub.12) 2+ Fe.sub.2O.sub.3 3+ Fe(II)p 2+ Fe.sub.2(P.sub.4O.sub.12) 2+

[0058] In a typical reaction, the metal oxide powder (e.g. TiO.sub.2, V.sub.2O.sub.5, Cr.sub.2O.sub.3, MnO.sub.2 or Fe.sub.2O.sub.3) is mixed with a surplus of hypophosphite (NH.sub.4H.sub.2PO.sub.2) and heated briefly in a tube furnace under inert gas flow. Then the melt is cooled down and washed with water to yield the pure TMPs. The process window of the method is determined by the temperature and time between the melting point and the thermal decomposition of the hypophosphite compound. Therefore, the heating rate of the process is of significant importance. The hypophosphite melt mediates the reaction with the dispersed or dissolved metal oxides. Due to the thermodynamic instability of the hypophosphite anion, the disproportionation into phosphane gas and phosphates limits the reaction. The phosphane acts as spectators under the presented reaction conditions. Excess phosphate compounds, formed on the crystal surfaces, can easily be removed by washing with water. Formation of metal phosphides via reaction of phosphane and metal oxides, as often described in the prior art, was not observed under the reaction conditions used here.

[0059] A representative example is the reaction of titanium(IV) oxide (P25) and ammonium hypophosphite, resulting in novel and known crystalline titanium(III) phosphate compounds. At 300? C. an unknown crystalline ammonium titanium(III) phosphate compound, denoted as Ti(III)p, is formed from the melt as illustrated by the respective XRD pattern in FIG. 2a. The product is a pyrophosphate as evidenced by Raman spectroscopy (FIG. 3). Increasing the reaction temperature to 500? C. yields known titanium(III) trimetaphosphate, Ti(PO.sub.3).sub.3 (FIG. 2c). In this structure the isolated TiO.sub.6 octahedral are linked through infinite chains of PO.sub.4 tetrahedra.

Synthesis of Ti(III)p at 300? C.

[0060] The synthesis of Ti(III)p was performed from a dry mixture of TiO.sub.2 (P 25, Degussa, phase mixture of anatase and rutile, ?99.5%) and NH.sub.4(H.sub.2PO.sub.2) (Fluka, ?97.0%) with a weight ratio of 1/10. The synthesis was tested for batches in a range between 1 g and 10 g without any technical complications or deviations of the product crystallinity and purity. The mixture was filled in a ceramic crucible and heated in a tube furnace at 300? C. for 2 h under Ar flow (100 mL/min). A heating ramp of 10? C./min was used up to 250? C. which then was decreased to 2? C./min up to 300? C. Finally, the sample was cooled down and washed with de-ionized water until pH 6 was achieved in the effluent. The powdery product was dried in air at 80? C.

[0061] Up to 200? C. the compound mixture keeps a powdery form before ammonium hypophosphite starts to melt at 215? C. Partial thermal decomposition of the ammonium hypophosphite into phosphane and ammonium phosphate starts at temperatures above 230? C. Above 245? C. the hypophosphite starts to react with titanium oxide as indicated by a deep purple coloration of the melt which is characteristic for the formation of titanium(III) species. Finally, the melt solidifies after the whole ammonium hypophosphite has reacted or decomposed. Both decomposition products were tested for their reactivity with TiO.sub.2 under the relevant reaction conditions and did not show any significant reaction.

[0062] The thermal decomposition of ammonium hypophosphite causes the formation of gaseous phosphane (PH.sub.3, CAS: 7803-51-2) which is known as a strong respiratory poison. Therefore, the preparation of TMPs by the presented molten salt method has to be implemented exclusively in closed systems under continuous inert gas flow.

[0063] FIG. 3 shows a Raman spectrum of Ti(III)p, which reveals a strong signal (764 cm.sup.?1) in a range (box) which has been identified to be characteristic for inorganic pyrophosphate compounds.

Synthesis of Ti(IV)p at 500? C.

[0064] Ti(III)p obtained via the synthetic procedure described above was filled in a ceramic crucible and thermally treated at 500? C. under Ar flow (100 mL/min) for 4 h using a heating rate of 10? C./min. Finally, the resulting white-yellowish powder was washed with de-ionized water and dried in air at 80? C. for 12 h. The phase transformation was tested for batches ranging from 100 mg to 1 g without any deviations of the product crystallinity and purity.

[0065] TG (thermogravimetry)/DSC (differential scanning calorimetry) performed under Argon atmosphere with a heating rate of 10? C./min reveals a single step mass loss between 300 and 500? C. The mass loss of 7 wt % is accompanied by two endothermic signals (FIG. 4) indicating the release of ammonia, hydrogen and water during the phase transformation (FIG. 5). Due to the high thermal stability of Ti(IV)p, no further transformations occur. The thermal decomposition of the ammonium cation causes the release of ammonia, while the protons are reduced to hydrogen during the oxidation of Ti(III) to Ti(IV) as illustrated in FIG. 5.

[0066] FIG. 6 shows .sup.31P MAS NMR spectra of three Ti(IV)p samples, which were prepared via phase transformation from the presented Ti(III)p compound phase. The Ti(III)p compound material was synthesized in different batches of 1 g, 5 g and 10 g (FIG. 6 a-c). The signals around ?30 ppm can be attributed to the pyrophosphate units of the crystalline Ti(IV)p samples. Spectra a) and b) show two small signals between 0 and ?10 ppm which are characteristic for free ortho- and pyrophosphates which are not part of the crystal structure. The .sup.31P MAS NMR spectra of Ti(IV)p show no additional phases and low amounts of amorphous parts, which indicates also a good purity of the Ti(III)p compound material. Upscaling without losses in crystallinity and a high purity are features of the presented molten salt method.

Synthesis of Ti(PO.sub.3).sub.3 at 500? C.

[0067] The procedure used for the synthesis of Ti(PO.sub.3).sub.3 is similar to that described for Ti(III)P with a difference in heating rate and temperature. A mixture of TiO.sub.2 (P 25, Degussa) and NH.sub.4(H.sub.2PO.sub.2) (Fluka, ?97.0%) with a weight ratio of 1/10 was filled in a ceramic crucible and heated in a tube furnace at 500? C. for 2 h under Ar flow (100 mL/min) using a heating rate of 10? C./min. Finally, the sample was cooled down and washed with de-ionized water until pH 6 was achieved. The powdery product was dried at 80? C. in air. The synthesis was tested for batches ranging from 1 g to 5 g without any technical complications or deviations of the product crystallinity and purity.

Influence of the Amount of Hypophosphite

[0068] The formation of a melt by using an excess of hypophosphite is beneficial for complete conversion of the TiO.sub.2 and high crystallinity of the product. Syntheses of Ti(PO.sub.3).sub.3 with increasing weight ratios of hypophosphite compound result in different phase compositions as documented by the XRD patterns in FIG. 7. Lower ratios of the hypophosphite compound (1/1-1/2) are apparently not sufficient to convert the TiO.sub.2 quantitatively. However, also these conditions cause partial reduction and the formation of stable titanium(III) oxide species on the surfaces of the titania particles as indicated by the characteristic black coloration and confirmed by XPS spectra (FIG. 8d). Unknown intermediate phases are formed by increasing hypophosphite ratios (1/3-1/5 in FIG. 7) before phase pure Ti(PO.sub.3).sub.3 is yielded from the melt (ratio ?1/6 in FIG. 7). In a proposed redox reaction mechanism, the compounds can be considered as oxygen donor and acceptor pairs. While the hypophosphite acts as oxygen acceptor to form stable phosphate compounds, the metal oxide donates oxygen atoms under reductive conditions. Provided that sufficient hypophosphite is available, all oxygen of the metal oxide will be consumed and the reduced cations are free to form crystalline TMP phases.

Low-Valent Titanium (III) Phosphates

[0069] Reports on low-valent titanium(III) phosphates are rather rare in the prior art, likely due to their strong tendency to oxidize in presence of an oxidant, such as air. XPS spectra show the presence of two different titanium species on the crystal surfaces of Ti(III)p and Ti(PO.sub.3).sub.3 as shown in FIG. 8 a) and b). They can be attributed to Ti(III) and Ti(IV) indicating that the Ti(IV) species exist on the on the crystal surface in both compounds, likely as the result of oxidation of Ti(III) on the surface by ambient air. XPS analysis probes surface-near regions of the particles, thus, the Ti(IV) signal is caused by surface species. Crystalline Ti(PO.sub.3).sub.3 is known to be a pure Ti(III) compound.

Thermal Stability

[0070] The bulk of the novel Ti(III)p compound offers a good thermal and chemical stability as indicated by XRD data. It is longtime-stable in acidic aqueous solution even at elevated temperature (H.sub.3PO.sub.4, pH=1, 80? C., 72 h) and also thermally stable in air up to 250? C. At higher temperature the material undergoes a phase transformation to a known titanium(IV) pyrophosphate (TiP.sub.2O.sub.7). Under non-oxidative conditions, thermal treatment of Ti(III)p yields to another novel crystalline Ti(IV) phosphate, denoted as Ti(IV)p, showing exclusively the Ti(IV) species (FIG. 8c). TG-MS monitoring (FIG. 4 and FIG. 5) reveals that the phase transformations are accompanied by release of ammonia, hydrogen and water. The XRD pattern of the novel Ti(IV)p is presented in FIG. 2b. Reproducibility and purity of the novel crystalline diamagnetic Ti(IV)p compound was confirmed by .sup.31P MAS NMR spectra (FIG. 6) showing no additional crystalline or significant amorphous parts in the product.

Reaction Pathways

[0071] Overall, the conversion of TiO.sub.2 with ammonium hypophosphite offers reaction pathways to several known titanium phosphate compounds as well as two novel phases as sketched in FIG. 9. As representative example, the reduction of Ti(IV) to Ti(III) shows the reductive feature and variability of the hypophosphite route.

[0072] Formation of low-valent phosphates, as reported here for the titanium compounds, is observed also for other transition metal compounds (see below). In the prior art, low oxidation states of TMPs are generally reported to be accessible by using metal powders or low-valent titanium compounds as compounds. In comparison, the new route offers the possibility to direct the oxidation state of the transition metal via the hypophosphite, which results in quite moderate reaction conditions.

Synthesis of V(PO.sub.3).sub.3 at 300? C.

[0073] The synthesis of V(PO.sub.3).sub.3 was performed from a mixture of 0.2 g V.sub.2O.sub.5 (Merck, ?99%) and 2 g NH.sub.4(H.sub.2PO.sub.2) (Fluka, ?97.0%). The mixture was filled in a ceramic crucible and heated in a tube furnace at 300? C. for 2 h under Ar flow (100 mL/min). A heating ramp of 10? C./min was used up to 250? C. which then was decreased to 2? C./min up to 300? C. Finally, the sample was cooled down and washed with de-ionized water until pH 6 was achieved. An additional washing step with ethanol was performed to avoid partial dissolution of the product by residual washing water during the drying process. The powdery product was dried in air at 80? C.

Synthesis of V(PO.sub.3).sub.3 at 500? C.

[0074] The procedure used for the synthesis of V(PO.sub.3).sub.3 at 500? C. is similar to those described above for 300? C. The synthesis was performed from a mixture of 1 g V.sub.2O.sub.5 (Merck, ?99%) and 10 g NH.sub.4(H.sub.2PO.sub.2) (Fluka, ?97.0%). The mixture was filled in a ceramic crucible and heated in a tube furnace at 500? C. for 10 h under Ar flow (100 ml/min). A heating ramp of 10? C./min was used up to 250? C. which then was decreased to 2? C./min up to 500? C. Finally, the sample was cooled down and washed with de-ionized water until pH 6 was achieved in the effluent. An additional washing step with ethanol was carried out to avoid partial dissolution of the product by residual washing water during the drying process. The powdery product was dried in air at 80? C. FIG. 10a shows the XRD pattern of V(PO.sub.3).sub.3.

Synthesis of Cr(NH.sub.4)HP.sub.3O.sub.10 at 300? C.

[0075] The synthesis of Cr(NH.sub.4)HP.sub.3O.sub.10 was performed from a mixture of 0.5 g Cr.sub.2O.sub.3 (Merck, ?98%) and 5 g NH.sub.4(H.sub.2PO.sub.2) (Fluka, ?97.0%). The mixture was filled in a ceramic crucible and heated in a tube furnace at 300? C. for 10 h under Ar flow (100 ml/min). A heating ramp of 10? C./min was used up to 250? C. which then was decreased to 2? C./min up to 300? C. Finally, the sample was cooled down and washed with de-ionized water until pH 6 was achieved in the effluent. An additional washing step with ethanol was carried out to avoid partial dissolution of the product by residual washing water during the drying process. The powdery product was dried at 80? C. in a ventilation oven over night and used for analysis. FIG. 10c shows the XRD pattern of Cr(NH.sub.4)HP.sub.3O.sub.10 and additional reflections belonging to the Cr.sub.2O.sub.3 compound phase.

Synthesis of Cr(PO.sub.3).sub.3 at 500? C.

[0076] The synthesis of Cr(PO.sub.3).sub.3 was performed from a mixture of 0.2 g Cr.sub.2O.sub.3 (Merck, ?98%) and 2 g NH.sub.4(H.sub.2PO.sub.2) (Fluka, ?97.0%). The mixture was filled in a ceramic crucible and heated in a tube furnace at 500? C. for 4 h under Ar flow (100 ml/min) with a heating ramp of 5? C./min. Finally, the sample was cooled down and washed with de-ionized water until pH 6 was achieved in the effluent. An additional washing step with ethanol was carried out to avoid partial dissolution of the product by residual washing water during the drying process. The powdery product was dried at 80? C. in a ventilation oven over night and used for analysis. FIG. 10d shows the XRD pattern of Cr(PO.sub.3).sub.3 as well as an additional phase which could not be attributed to a known chromium phosphate or oxide phase.

Synthesis of Mn.sub.2(P.sub.4O.sub.12) at 500? C.

[0077] The synthesis of Mn.sub.2(P.sub.4O.sub.12) was performed from a mixture of 0.2 g MnO.sub.2 (Merck, ?99.0%) and 1 g NH.sub.4(H.sub.2PO.sub.2) (Fluka, ?97.0%). The mixture was filled in a ceramic crucible and heated in a tube furnace at 500? C. for 4 h under Ar flow (100 ml/min) with a heating ramp of 10? C./min. Finally, the sample was cooled down and washed with de-ionized water until pH 6 was achieved in the effluent. The powdery product was dried in air at 80? C. FIG. 10b shows the XRD pattern of Mn.sub.2(P.sub.4O.sub.12).

Synthesis of Fe(II)p at 300? C.

[0078] The synthesis of the novel Fe(II)p compound was performed from a mixture of 0.5 g Fe.sub.2O.sub.3 (Riedel-de-Haen, ?97%) and 5 g NH.sub.4(H.sub.2PO.sub.2) (Fluka, ?97%). The mixture was filled in a ceramic crucible and heated in a tube furnace at 300? C. for 10 h under Ar flow (100 ml/min). A heating ramp of 10? C./min was used up to 250? C. which was then decreased to 2? C./min up to 300? C. Finally, the sample was cooled down and washed with de-ionized water until pH 6 was achieved in the effluent. The powdery product was dried in air at 80? C. over night. FIG. 10e shows the XRD pattern of the novel iron(II) phosphate phase (Fe(II)p).

[0079] FIG. 11 shows the .sup.57Fe M?ssbauer spectrum of Fe(II)p. Two different Mossbauer signals with isomer shifts in a range expected for Fe(II) high spin species are illustrated. While the quadrupole splitting of first component (green line) is similar to that observed in LiFePO.sub.4, the smaller quadrupole splitting of the second component (blue line) is quite small for Fe(II) high spin species. The sharp resonance signals of the spectrum indicate that the sample contains no significant amorphous parts of iron phosphate.

Synthesis of Fe.sub.2(P.sub.4O.sub.12) at 500? C.

[0080] The synthesis of Fe.sub.2(P.sub.4O.sub.12) was performed from a mixture of 0.2 g Fe.sub.2O.sub.3 (Riedel-de-Haen, ?97%) and 2 g NH.sub.4(H.sub.2PO.sub.2) (Fluka, ?97%). The mixture was filled in a ceramic crucible and heated in a tube furnace at 500? C. for 10 h under Ar flow (100 ml/min) with a heating ramp of 10? C./min. Finally, the sample was cooled down and washed with de-ionized water until pH 6 was achieved in the effluent. The powdery product was dried in air at 80? C. over night. FIG. 10f shows the XRD pattern of Fe.sub.2(P.sub.4O.sub.12).