Local environment in Ba2In2−xWxO5+3x/2 oxide ion conductors

The actual oxygen environment of the tungsten dopant in the Ba2In2−xWxO5+3x/2 solid solution was revealed by combining X-ray absorption spectroscopy at the tungsten LI and LIII edges and at the indium LI edge. Whatever the substitution ratio, the tungsten atoms exhibit a regular octahedral environment. When the substitution ratio increases, the oxygen vacancies are progressively filled until their total occupancy for x=2/3. For x⩾0.3, the perovskite structure is stabilised; the tungsten atoms are randomly distributed in the structure. Although X-ray diffraction revealed a cubic symmetry for these compositions, a local distortion of the indium environment is observed when a tungsten atom is in its surrounding.

Evolution of the XANES signal of Ba2In2−xWxO5+x type compounds with x=0.1 (orthorhombic), x=2/3 (cubic) and of BaWO4, Bi2WO6 and WO3 references, in which tungsten has, respectively, a tetrahedral, distorted octahedral and quasi-regular octahedral environment.Text3Figure optionsDownload full-size imageDownload as PowerPoint slide