THE MECHANISM OF CATION EQUILIBRATION IN NICKEL ALUMINATE SPINEL, NIAL2O4

In spinels, the cations are distributed over sites with octahedral and tetrahedral coordination, respectively. In crystals possessing a noti ceable temperature dependence of the cation distribution, the kinetics of the cation exchange can be studied by means of temperature-jump re laxation experiments. In situ experiments of this type are reported fo r a series of nickel aluminate spinels, NiAl2O4, containing different amounts of cation vacancies. Various microscopic models are discussed for the mechanism of cation exchange between the sublattices. Experime ntal results for the composition dependent kinetics favour a vacancy m echanism.