The deviation from stoichiometry, and the cation tracer diffusion coefficients, were measured as a function of O activity for various compositions of (CoxMn1-x)3-δO4 at 1200C. All of the  versus log[activity] plots tended to be S-shaped. The O activity-dependence suggested that cation vacancies were the predominant point defects at high O activities, while cation interstitials prevailed at low activities. All of the log[diffusivity] versus log[activity] curves were V-shaped. This indicated that cation vacancies and cation interstitials governed high-temperature cation diffusion at high and low O activities, respectively. By combining the non-stoichiometry and diffusion data, the mean mobilities of cations which diffused via various point defects were determined. At high O activities, the prevalent cation diffusion mechanism was a vacancy diffusion process. The diffusion mechanism which prevailed at low O activities was expected to be an interstitialcy diffusion process.

F.H.Lu, R.Dieckmann: Solid State Ionics, 1993, 67, 145-55