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 42), by using the radioactive isotopes, 54Mn. 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 39
Diffusion of 59Fe in [CoxFe2(1-x)/3Mn(1-x)/3]3-dO4
as a Function of O Activity at 1200C
O Activity | x | D (cm2/s) |
2.09 x 10-1 | 0 | 6.46 x 10-9 |
2.69 x 10-3 | 0 | 3.47 x 10-10 |
2.30 x 10-6 | 0 | 1.86 x 10-10 |
4.00 x 10-7 | 0 | 5.13 x 10-10 |
2.09 x 10-1 | 0.1 | 8.13 x 10-10 |
4.57 x 10-2 | 0.1 | 2.82 x 10-10 |
7.41 x 10-3 | 0.1 | 8.71 x 10-11 |
4.27 x 10-5 | 0.1 | 6.31 x 10-11 |
1.38 x 10-5 | 0.1 | 1.10 x 10-10 |
1.80 x 10-6 | 0.1 | 3.72 x 10-10 |
8.91 x 10-1 | 0.2 | 1.74 x 10-10 |
2.09 x 10-1 | 0.2 | 6.92 x 10-11 |
1.18 x 10-3 | 0.2 | 3.63 x 10-11 |
1.41 x 10-4 | 0.2 | 1.32 x 10-10 |
8.91 x 10-1 | 0.333 | 2.69 x 10-11 |
2.09 x 10-1 | 0.333 | 3.24 x 10-11 |
3.55 x 10-2 | 0.333 | 7.08 x 10-11 |
1.23 x 10-2 | 0.333 | 1.29 x 10-10 |