[en] Vanadium phosphates can be easily obtained via the reaction of phosphoric acid with vanadium alkoxides. Well crystallized vanadium phosphate VOPO₄,2H₂O is rapidly precipitated at room temperature from alkoxide precursors. Large anisotropic particles are obtained allowing the deposition of transparent thin films with a marked preferred orientation. Adding water results in longer precipitation times and less anisotropic morphologies. Tertiary alkoxides exhibit a much lower reactivity giving rise to amorphous phases related to the VOPO₄ structure in which some organic groups have not been removed

[en] Alkali metal and ammonium heteropolyvanadophosphate(HPA) catalysts supported on silica and an active carbon fibre felt (KF-felt) were prepared, and isopropanol decomposition over the catalysts was examined as a test reaction. All the alkali metal: HPA-silica catalysts worked stably at 300 - 400⁰C, but the ammonium:HPA catalysts were deactivated above 300 - 320⁰C. The activity of the KF-felt-supported catalysts was several times higher than that of the silica-supported catalysts. Both the activity and stability of ammonium:HPA catalysts were greatly improved by the use of the silica-coated KF-felt as the carrier. 8 refs.; 12 figs.; 1 table

[en] The effect of both composition and creation of the crystalline phase in (V₂O₅)_1-x(P₂O₅), glasses, where x=0.10, 0.15, 0.20 and 0.25, on both I-V characteristic curves and ac conductivity are studied in the temperature range 303-473 K. The I-V characteristics show non-linear behaviour below and beyond a turnover point (switching point) characterizing these glasses. This turnover point is shifted towards lower voltage and higher current as the vanadium, the ambient temperature or the degree of crystallinity in the glass were increased. The results are interpreted according to the Poole-Frenkel emission of electrons under high field between filled V⁴⁺ and empty V⁵⁺ sites in the region below the turnover point. The conduction in the negative-resistance region (beyond the turnover point) is discussed according to the hopping of electrons between filled and empty sites under high field, joule heating and self-generation of ac signal. The frequency dependence of the ac conductivity satisfies the power law relation, σ(ω)≅ω⁸, which explains the quantum-mechanical hopping of single electrons in the disordered matrix

[en] A new monophosphate of tetravalent vanadium was isolated and its structure has been determined from a single crystal X-ray diffraction study. It crystallizes in the space group P2₁/c with a=5.187(1), b=7.959(2), c=17.187(2)A. The framework is very similar to that observed for Ag(VO)₂(PO₄)₂ and can be described from V₄O₂₀ octahedral units sharing their corners with monophosphates group. This framework delimits tunnels running along a where the cadmium ions are located. In fact, this phosphate belongs to a structural series A(VO)₂(PO₄)₂ with A=Ba, Pb, Ag, Cd and derives from the barium phase by a strong distortion of the framework changing the coordination of a part of vanadium atoms from pyramidal to octahedral. The structural evolution of these phosphates is discussed; the amazing flexibility of the coordination of the interpolated A cations is emphasized

[en] The research area is located in the northern part of Beishan area, Gansu province and rich in uranium resources with Hongliuhe uranium deposit, Fangshankou uranium-vanadium phosphate deposit and lot of radioactive abnormal lies. By collecting and collating the data of predecessors, we studied the characteristics of typical uranium deposits and analyzed the uranium mineralization conditions, established a geophysical-mathematical prediction model for the carbonaceous-siliceous-argillaceous type uranium deposits. With the results of field work, two uranium prospects was predicted in Hongliuhe-Fangshankou area. (authors)

[en] The structure of a new tetravalent phosphate has been determined by single crystal X-ray diffractometry. Although it presents a structure close to that of LiVPO₅, this oxide exhibits a different symmetry. Monoclinic cell parameters are given. The host lattice [VPO₅]_∞ is described as [VO₃]∞] octahedral chains linked together through PO₄ tetrahedra. The geometry of the octahedral chains is intermediate between that of hexagonal tungsten bronze and ReO₃-type structure

[en] Mechanochemically coating over-lithiated layered oxide with the multi-functional VOPO₄ is studied by using that VOPO₄ is capable of accommodating lithium ions that are reversibly inserted/extracted at 3.8 V vs. Li/Li⁺ and exerts a surface-stabilizing effect. The impregnation with VOPO₄ relieves the characteristic irreversible problems of over-lithiated layered oxide, since the initial fully delithiated structure of VOPO₄ provides extra lithium storage sites and thus compensates for the unavoidable loss of irreversible charging capacity of VOPO₄ during the first cycle. Interestingly, VOPO₄ loadings below 1 wt. % improves cycleability, whereas higher loadings result in unfavorable kinetic hindrance. Additionally, VOPO₄-coated samples exhibit enhanced thermal stability due to featuring reduced decomposition exothermicity and increase thermal runaway onset temperature.

[en] IR absorption spectra of α-VOPO₄, VPO₄, V₄(P₂O₇)₃, (VO)₂P₂O₇ in the range of 400-4000 cm^-1 are considered. An empirical correlation equation is proposed to determine absorption frequencies of metal-oxygen bounds in phosphates of multivalent metals. The equation describes satisfactorily the dependence of maximum frequency of oscillations of the M³⁺-O bond on cation mass, bond length and ionization potential

[en] The valence-band and core-level x-ray photoelectron spectroscopy (XPS) of vanadium phosphates are reported, and the valence-band spectra interpreted by various calculation models. The spectral interpretation of the vanadium phosphates is used to show that an oxide-free vanadium phosphate film corresponding to VO(H₂PO₄)₂ can be prepared on vanadium metal. Three types of vanadium phosphate were investigated to provide an understanding of the XPS data for vanadium phosphates, and to demonstrate the differences between these phosphates and vanadium oxides. The three phosphates formed, VO(H₂PO₄)₂, VOHPO₄.0.5H₂O, and VOPO₄·2H₂O were prepared by reaction of vanadium with phosphoric acid under a variety of conditions. The article focuses upon the valence-band region which shows significant differences between different types of vanadium phosphates as well as clear differences between the phosphates on the one hand and oxides on the other hand. The valence-band spectra are effectively interpreted by the multiple scattered-wave Xα calculations and band structure calculations

[en] An in situ polymerization assisted fast sol–gel method was introduced to synthesize high performance Li₃V₂PO₄/C (LVP/C) cathode material. The crystal structure, surface morphology and electrochemical performances of the LVP/C samples sintered at different temperatures were investigated. The composite sintered at 750 °C exhibits the highest specific discharge capacity of 119.02 mAh g⁻¹ (440.35 Wh g⁻¹) at 10 C rate. The Li⁺ diffusion coefficient ranges from 10⁻⁶ to 10⁻⁸ cm² s⁻¹ based on different scanning rates and the electronic conductivity is about 10⁻⁵ S cm⁻¹. For comparison, an ex situ polymerization method was also employed to obtain the LVP/C composite. A novel charge/discharge testing mode was designed to investigate the electrochemical behavior of the as-prepared LVP/C composite for practical application in electric vehicle cells. The obtained high power density and the special testing mode prove the LVP/C composite would be a promising candidate for the electric vehicle application and deserves further investigation