The cation tracer diffusion coefficient of Co was measured in (Co1-xGax)O as a function of dopant fraction, x, (0 to 0.03), log[O2 activity] (-7 to -0.67) and temperature (1100 to 1350C). For both diffusion coefficients, a non-linear dependence upon dopant fraction and a large effect of the Ga dopant upon the activity-dependence of the diffusion coefficients were found. The experimental observations were modelled in terms of a defect model which involved solute-vacancy pairs in 2 charge states, and triplets which comprised two Ga ions and a cation vacancy. By fitting the experimental data (table 55), a binding energy for neutral pairs, {Ga.V'}x, was found which was small in comparison to the thermal energy, whereas the binding energy for singly-charged pairs, {Ga.V"}', was equal to about 0.5eV. The binding energy for the triplets, {Ga.V"Ga.}x, decreased from 1.1eV at 1100C to 0.76eV at 1350C. The mobility of free vacancies was some 50% larger for V" than for V'.

R.Schmackpfeffer, M.Martin: Philosophical Magazine A, 1993, 68[4], 747-65

Table 54

Diffusion of 60Co in CoO

Table 55

Diffusion Parameters for Co in (Co1-xGax)O at 1100 to 1350C