EXAFS Study of Molten V₂O₆

The coordination numbers of cations are usually not more than 4 in oxide glasses such as GeO₂, SiO₂, As₂O₃, P₂O₆, B₂O₃, and so on. Though V₂O₅ crystals have a layer structure consisted of VO₆ pyramids, V₂O₅ is successfully transformed into a noncrystalline solid from the melt by use of the splat-quenching technique. Therefore, it is significant to examine the coodination number of the vanadium atoms in molten V₂O₅. The EXAFS (extended X-ray absorption fine structure) of the vanadium atoms above its K-absorption edge has been measured for molten V₂O₅ at 750°C using the crystalline V₂O₅ as a reference material. By the Fourier transform, the V-O bond lengthes were determined to be 1.60 and 1.90Å in crystalline state and 1.80Å in molten state. The results of the former were in good agreements with those obtained through the crystal structure analysis. The coodination number, bond length, and Debye-Waller factor in molten state were further examined by least-squares calculation, using the coefficients of the phase shift and amplitude functions estimated from EXAFS spectrum of the crystal. By the parameter fitting method, the V-O bond length was determined to be 1.818±0.003Å and the coordination number of the vanadium atoms was found to be 4. 8±0.2. On the other hand, the mean V-O bond length and the coodination number of the vanadium atoms are 1.828 Å and 5.0 in the crystal, respectively. The results of EXAFS analysis showed that the values in the melt are close to those in the crystal.