Determination by X-ray diffraction of interstitial concentrations of vanadium ions in disordered VOx

Abstract

Integrated intensities were measured from VOx single crystals with x = 0.80, 0.94, 1.01, 1.11 and 1.25. A least-squares refinement was carried out for the scale factor and the isotropic temperature factors of vanadium and oxygen ions for each composition, for a range of interstitial vanadium contents. The R values after the refinement were 0.04-0.05. There are vanadium ions at tetrahedral interstitial sites, the concentration of which changes from 0-0.5% to 3% with composition x; this confirms quantitatively previous studies which employed dynamical electron diffraction effects. The temperature factors of vanadium (BV) and oxygen (BO) increase with x; BV = 1.02-1.38 A2 and BO = 0.58-1.24 A2. The composition dependence of the overall temperature factor is similar to that of the lattice parameter. The 002 structure factor for electrons U002 and the critical voltage Ec at which the second-order Kikuchi line disappears were calculated for VO0.82 and VO1.20, using the individual temperature factors determined by this study. The 002 structure factors measured by the critical-voltage and the intersecting-Kikuchi-line method [Watanabe, Andersson, Gjonnes & Terasaki (1974). Acta Cryst. A30, 772-776] were in agreement within less than 2%. The results support the idea that the ionic state of the cation lies between neutral and singly ionized.