Effects of Cation Vacancies of the Diffusion of Nickel Ions in Defective Spinels

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Abstract
In order to clarify the influence of composition-dependent cation vacancies in defective spinels on the diffusion, the diffusion rates of Ni2+ in several kinds of defective spinels (MgO·xAl2O3, where x=1.1,1.2,1.3,1.4 and 1.5) and a perfect spinel (MgO·Al2O3) were measured by the use of an electron probe micro-analyzer, and the diffusion coefficients were obtained. The diffusion coefficients were found to be linear to the concentrations of the composition-dependent vacancies. The so-called activation energies which were calculated from the Arrhenius plot were about 70 kcal/mol for the defective spinels and 106 kcal/mol for the perfect spinel. It may be concluded that composition-dependent cation vacancies govern the diffusion of cations in the defective spinel, while temperature-dependent vacancies probably predominate in the perfect spinel.