Values of the deviation from stoichiometry, and of the cation tracer diffusion coefficients, were obtained experimentally. They were all measured at 1200C, as a function of O activity, in compositions which covered essentially all of the spinel phase stability region at this temperature. All of the deviation versus O activity curves were S-shaped. From the activity-dependence of the deviation from stoichiometry (tables 50 to 52), it was deduced that cation vacancies were the majority point defects at high activities, while cation interstitials predominated at low activities. All of the diffusivity versus activity plots, for various cationic compositions, exhibited a distinct minimum; which indicated that the high-temperature diffusion process was governed by cation vacancies at high activities and by interstitials at low activities. By combining information on point defects and cation tracer diffusion, the mean mobilities of cations and the cation diffusion mechanism in this system were deduced.

F.H.Lu, S.Tinkler, R.Dieckmann: Solid State Ionics, 1993, 62[1-2], 39-52

Table 47

Diffusivity of Mn in (Co,Fe)O as a Function of O Activity

continued

Table 47 (continued)

Diffusivity of Mn in (Co,Fe)O as a Function of O Activity