COORDINATION AND VALENCE OF NIOBIUM IN TIO2 NBO2 SOLID-SOLUTIONS THROUGH X-RAY ABSORPTION-SPECTROSCOPY

The coordination and valence of niobium in TiO2{single bond}NbO2 solid solutions, NbxTi1-xO2 (for 0.1 ≤ x ≤ 1.0), were studied by Nb K-edge X-ray absorption spectroscopy (XAS) as a function of Nb composition, x. Ten single-phase compositions in the NbxTi1-xO2 solid solution with the rutile structure were examined: x = 0.1, 0.2, 0.32, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0. Analysis of X-ray absorption near edge structure (XANES) data shows that the position of the preedge absorption shifts to higher energy with decreasing Nb concentration, indicating that the ratio of Nb5+ to Nb4+ is larger at low Nb concentrations than at high ones. The extended X-ray absorption fine structure (EXAFS) analysis indicates that the average Nb{single bond}O interatomic distance increases nearly linearly with increasing Nb concentration. This structural modification of the oxygen environment about niobium suggests that an increasing fraction of Nb ions (i.e., Nb5+) occupy tetrahedral interstitial sites with decreasing Nb composition. © 1991 Academic Press, Inc.