Abstract
The kinetics of cation reequilibration have been studied theoretically and experimentally in complex oxides after an external perturbation of equilibrium by temperature jumps. A general kinetic model for cation redistribution amongst non-equivalent sites in complex oxides is derived based on a local homogeneous point defect mechanism involving cation vacancies. Temperature-jump optical relaxation spectroscopy has been established to investigate cation kinetic processes in spinels and olivines. The kinetic model satisfactorily describes the experimental absorbance relaxation kinetics in cobalt containing olivines and in nickel containing spinels. It is found that the kinetics of cation redistribution in complex oxides shows a strong temperature- and compositiondependence. Activation energies for cation redistribution in Co-Mg olivines are found to range between 200 and 220 kJ/㏖ whereas an energy barrier of about 230 kJ/mol is observed in the case of nickel gallate spinel.
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