Tracer diffusion and defect structure in Ga-doped CoO

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Abstract
Cation tracer diffusion coefficients for Co and Ga have been measured in Ga-doped CoO, (Co1-uGauO, as a function of the dopant fraction (0≤u≤0.03), the oxygen activity (-7≤logao 2 ≤ -0.67), and the temperature (1100°C≤T≤1350°C). For both diffusion coefficients a nonlinear dependence on the dopant fraction and a strong influence of the dopant Ga on the aO 1 dependence of the diffusion coefficients were found. The experimental observations are modelled in terms of a defect model involving solute-vacancy pairs in two charge states and triplets composed of two Ga ions and a cation vacancy. By fitting the experimental data we find a binding energy for neutral pairs, {Ga. V′}x, which is small compared to the thermal energy, while the binding energy for singly charged pairs, {Ga. V″}′, is about 0.5 eV. The binding energy for the triplets, {Ga.V″ Ga.}x, decreases with rising temperature from 1.1 eV at 1100°C to 0.76 eV at 1350°C. The mobility for free vacancies is about 50% larger for V″ than for V′.

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