Materials of the form, (CoxFezMn2z)3-δO4, were considered, where x + 3z = 1. The deviation from stoichiometry, , was measured at 1200C as a function of O activity and composition by using thermogravimetric measurements. The  versus log[activity] curves were basically S-shaped for all of the cationic compositions which were investigated. This suggested that 2 predominant types of point defect (cation vacancies and cation interstitials) were present. Cation tracer diffusion in the spinels was investigated at 1200C, as a function of O activity and composition (table 37), by using the radioactive isotope, 60Co. The cation tracer diffusion coefficients, as a function of O activity, tended to exhibit a minimum. This again indicated that 2 types of point defect (cation vacancies and cation interstitials) contributed to cation tracer diffusion.

F.H.Lu, R.Dieckmann: Solid State Ionics, 1993, 59[1-2], 71-82

Table 37

Diffusivity of Co in (CoxFezMn2z)3-δO4 at 1200C