Chemical diffusion and defect mobility in non-stoichiometric manganous sulphide Original Research Article

The chemical diffusion coefficient, , in metal-deficit manganous sulphide, Mn1−yS, has been determined as a function of temperature (700–1273 K) and sulphur activity (104–10−1 Pa) from re-equilibration kinetics. It has been found that does not depend on p(S2) and can be described as a function of temperature by the following empirical equation. Recalculation of these results into the defect (vacancy) diffusion coefficient, DV, the direct measure of defect mobility, showed that this coefficient is also pressure independent and can be described by the following relationship. These results may be considered as the first experimental proof that the mobility of cation vacancies in metal-deficit manganous sulphide does not depend on their concentration. Using this relationship and non-stoichiometry data reported by Rau [H.Rau, J. Phys. Chem. Solids, 39 (1978) 3339] the self-diffusion coefficient of cations in Mn1−yS has been calculated as a function of temperature and sulphur activity: The result of these calculations, being in good agreement with recent self-diffusion data obtained with direct tracer methods, clearly indicates that chemical diffusion measurements may offer important information on transport properties of non-stoichiometric metal sulphides.