XAFS ANALYSIS OF THE LOW-SYMMETRY OCTAHEDRAL MOLYBDENUM AND TUNGSTEN-OXIDES

Comparative XAFS analysis of the main isostructural crystalline phases of W(Mo)O-3 oxides and W(Mo)O-3.nH(2)O hydrates has been done at the W L(3) and Mo K edges. These compounds have (1) 3D perovskite-type (PT) structure (m-WO3); (2) 2D PT structure (WO3.H2O and MoO3.nH(2)O (n = 1,2)); (3) 2D hexagonal-type structure (WO3.1/3H(2)O) and (4) 2D double layered structure (alpha-MoO3). The detailed analysis of X-ray absorption fine structure (XAFS) in the low-symmetry structures shows that in order to simulate the experimental spectrum, it is sufficient to take into account single-scattering contributions in the range from 1.7 to similar to 5.0 Angstrom and a number of multiple-scattering paths from nearly linear atomic chains in the first and second shells. The results obtained by XAFS are only in partial agreement with known X-ray diffraction data (XRD). The strong deviation of the short-range order, detected by XAFS, from the one, given by XRD, has been found in W(Mo)O-3.nH(2)O.