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Abstract
In spinels, the cations are distributed over sites with octahedral and tetrahedral coordination, respectively. In crystals with a significant temperature dependence of the cation distribution, the kinetics of the cation exchange can be studied by means of temperature-jump relaxation experiments. An analysis is reported for the kinetics of the cation exchange between the tetrahedral and octahedral sublattices of spinels. Several microscopic models for the cation exchange which involve direct exchange, a vacancy mechanism, and an interstitial mechanism are discussed and compared to experimental data. These data were obtained by means of optical spectroscopy for the relaxation of the cation distribution in NiAl2O4 after temperature-jumps in the temperature range between 720 and 890°C.