Local atomic and electronic structure of tungsten ions in AWO 4 crystals of scheelite and wolframite types

Abstract

X-ray absorption spectroscopy was used to study the local atomic and electronic structure of tungsten ions in polycrystalline scheelite CaWO 4 and wolframite-type ZnWO 4 and NiWO 4. The W L 1- and L 3-edges X-ray absorption near edge structure (XANES) signals suggest tetrahedral coordination of tungsten ions in CaWO 4 and strongly distorted octahedral coordination in ZnWO 4 and NiWO 4. Accurate analysis of the W L 3-edge extended X-ray absorption fine structure (EXAFS) signals by the regularization procedure was performed to reconstruct the radial distribution functions within the first coordination shell around tungsten atoms in AWO 4 crystals and polycrystalline WO 3, which was utilized for comparison. For the local environment around tungsten atoms in CaWO 4, we found very good agreement with known crystallographic data, suggesting the presence of four oxygen atoms at ∼1.79 A ̊ . The results obtained for ZnWO 4 and NiWO 4 show similarity of their local atomic structures: the oxygen atoms forming [WO 6] octahedra can be divided into two groups — four atoms at 1.84±0.01 A ̊ and two atoms at 2.13±0.01 A ̊ .