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[en] Methods of microdiffraction, micro-probe analyses and X-ray photoelectron spectroscopy have been applied to conduct electron-microscopic study of dark-green and black carnotite. The data obtained permit to conclude that different-valent state of vanadium in the mineral is the main reason for unusual dark-areen and black colour of carnotite. In the case of green carnotite the ratio V4+:V5+ makes up 27:73 and for black one the ratio V4+:V5+ equals 56:44. Dark colour in uranium vanadates is associated with presence of V4+ in their composition
[en] Bismuth vanadate (BiVO4) has emerged as one of the most promising photoanode materials for solar fuel production. Oxygen vacancies play a pivotal role in the photoelectrochemical efficiency, yet their electronic nature and contribution to n-type conductivity are still under debate. Using first-principles calculations, we show that oxygen vacancies in BiVO4 have two distinguishable geometric configurations characterized by either undercoordinated, reduced VIVO3 and BiIIO7 subunits or a VIV–O–VIV/V bridge (split vacancy), quenching the oxygen vacancy site. While both configurations have similar energies in the bulk, the (001) subsurface acts like an energetic sink that stabilizes the split oxygen vacancy by ~1 eV. In conclusion, the barrierless creation of a bridging V2O7 unit allows for partial electron delocalization throughout the near-surface region, consistent with recent experimental observations indicating that BiVO4(001) is an electron-rich surface.
[en] Highlights: • Elastic properties of vanadate and V2O5-contained glasses were predicted. • Prediction has been carried out on the basis of Makishima–Mackenzie's theory. • Correlation between elastic moduli and compositional parameters was studied. • Dissociation energy was evaluated in terms of V–O and P–O single bond strength. • Good agreement between theoretical and experimental elastic moduli was achieved.
[en] The vanadium-molybdenum mixed oxide bronzes of composition K0.23(V5.35Mo0.65)O15 and K0.32(V5.48Mo0.52)O15 have a monoclinic structure with s.g. C2/m, Z=2, and unit-cell dimensions a=15.436(2), b=3.6527(5), c=10.150(1) A, β=108.604(3)o and a=15.452(2), b=3.6502(5), c=10.142(1) A, β=109.168(3)o, respectively, as determined by single-crystal X-ray diffraction. These compounds show the β-Na x V6O15 tunnel structure, which is isostructural with bannermanite, natural sodium-potassium vanadate. Structure refinements from diffracted intensities collected in the 2-38oθ range converged to final R=5.58% and 7.48% for the two crystals, respectively. The V atoms are distributed on three different crystallographic sites. Partial substitution of V with Mo occurs in only one of these positions. Oxygen atoms involved in vanadyl groups point toward the tunnels. The K ions in the tunnels are coordinated by seven oxygen atoms. The alkali metal content in these crystals is much lower than the solubility limit found for the analogous Na containing compound. - Graphical abstract: Perspective view of the crystal structure of K x V6-y Mo y O15 along . This vanadium-molybdenum mixed bronze assumes the β-Na x V6O15 (bannermanite-type) structure, in which Mo(VI) substitutes for V only in the V2 position. The alkali metal content in the studied crystals is much lower than the solubility limit found for the analogous Na containing compounds
[en] The output beam parameters of the disk laser were investigated at different pump powers of nine-beam spatially periodic pumping and different resonator lengths. It was realized that a super-mode lasing regime and the values of thermally-induced distortions of an active disk were measured. The diffraction-limited output beam parameters came from the total aperture of all the lasing spots. An explanation of the in-phase super-mode lasing conditions was proposed, and the limits of its operation were defined. (letter)
[en] Main regularities of production of calcium pyrovanadate from NaVO3 solution, calcium methavanadate and calcium decavanadate from technical vanadium pentoxide were determined. Conditions of production of calcium vanadate compounds from technical vanadium pentoxide were established. The flowsheet of calcium methavanadate and decavanadate production is considered to be the most snitable, because it enables to save ∼ 40% alkali
[en] Lithium and sodium insertion into the layered host materials KV3O8 and K3V5O14 has been studied. KV3O8 has a very high stoichiometric capacity for lithium insertion and good cycling properties, which make it an interesting material for use in secondary lithium cells. K3V5O14, which has a very open structure, inserts lithium and sodium ions at unusually low potentials, probably due to inadequate shielding of coulombic guest-guest interactions. (author). 7 refs.; 4 figs
[en] Complete text of publication follows. In this paper, we have examined and analyzed the effects of systematic lead ions intercalation on vanadate-tellurate glasses and glass ceramics with interesting results. Glass formation and structural properties of the lead-vanadate-tellurate glasses of compositions xPbO · (100-x)[6TeO2 · V2O5], x=0-100mol%, are reported for the first time. Our studies on structural properties of (1-x)TeO2 · xV2O5 glass system (with x=0.3 and 0.4) show the sample with x=0.4 is more thermodynamic stability than their analogue with x=0.3. The present study provides interesting information concerning devitrification behavior of these vanadate-tellurate vitreous systems. We propose a possible structural model of building blocks for the formation of continuous random (1-x)TeO2 · V2O5 glass network used by DFT calculations. Comparing the theoretical and experimental IR spectral characteristic features, we conclude that the performance of the method/basis sets used on the prediction of the structural data and vibrational modes is good. Influence of lead ions on structural behavior in vanadate-tellurate glasses has been investigated using infrared spectroscopy and DFT calculations. The presented observations in these mechanisms show that the lead ions have an affinity pronounced towards [TeO3] structural units yielding the deformation of the Te-O-Te linkages and pursuant to the intercalation of [PbOn] entities in the [TeOn] and [VOn] chain network.