POINT-DEFECTS AND CATION TRACER DIFFUSION IN (CO, FE, MN)3-DELTA-O4 SPINELS .1. MIXED SPINELS (COXFE2YMNY)3-DELTA-O4

Point defects causing a deviation from stoichiometry, delta, in (Co, Fe, Mn)3-deltaO4 have been investigated by thermogravimetric measurements. Delta was measured at 1200-degrees-C as a function of oxygen activity, a(O2), and cationic composition. The obtained delta versus log10a(O2) curves are S-shaped for all cationic compositions investigated. The observed oxygen activity dependences suggest that two different types of point defects, cation vacancies and cation interstitials, occur as majority defects. Furthermore, cation tracer diffusion in these spinels has been studied at 1200-degrees-C as a function of oxygen activity and cationic composition by simultaneously using different radioactive isotopes, Co-60, Fe-59, and Mn-54. Cation tracer diffusion coefficients as a function of oxygen activity in general show a minimum indicating that two types of point defects, cation vacancies and cation interstitials, contribute to the cation tracer diffusion.