Point defects and cation tracer diffusion in (CrFe1 − )3 − O4 spinels

Abstract

The deviation from stoichiometry, δ, in (CrxFe1−x)3−δO4 was measured by thermogravimetry at 1200 °C as a function of oxygen activity, aO2, and cationic composition, x. Moreover, cation tracer diffusion coefficients, DMe∗, for Me = Co, Cr, Fe and Mn, were experimentally determined using radioactive isotopes, Co-60, Cr-51, Fe-59 and Mn-54. δ versus log aO2 plots for different x displayed S-shaped curves. The experimental data suggested that cation vacancies and cation interstitials were the majority defects at high and low oxygen activities, respectively. V-shaped curves were observed in DMe∗ versus log aO2 plots. The observed oxygen activity dependence indicated that the diffusion of Co, Cr, Fe and Mn in (CrxFe1− x)3−δO4 at high oxygen activities is governed by cation vacancies and at low oxygen activities by cation interstitials. Mean cation mobilities were derived by combining non-stoichiometry and cation diffusion information.