Self-diffusion of manganese in nonstoichiometric manganous sulphide

Self-diffusion of manganese in nonstoichiometric manganous sulphide, ${\mathrm{Mn}}_{1\ifmmode\pm\else\textpm\fi{}y}\mathrm{S},$ has been studied as a function of temperature (1073\char21{}1373) K and sulfur activity ${(10}^{\ensuremath{-}11}\char21{}{10}^{3})\mathrm{Pa}$ using radioactive ${}^{54}\mathrm{Mn}$ isotope as a tracer. In agreement with the defect model of ${\mathrm{Mn}}_{1\ifmmode\pm\else\textpm\fi{}\mathrm{y}}\mathrm{S}$ it has been shown that at very low sulfur pressures, close to the Mn/MnS phase boundary, self-diffusion of cations in metal excess ${\mathrm{Mn}}_{1+y}\mathrm{S}$ proceeds by an interstitial mechanism, consisting of pushing a cation from its normal lattice site into neighboring interstitial position. At higher sulfur activities, on the other hand, cation self-diffusion in metal-deficit ${\mathrm{Me}}_{1\ensuremath{-}y}\mathrm{S}$ proceeds by a simple vacancy mechanism, consisting of ${\mathrm{Mn}}^{2+}$ ions jumping from the lattice sites into neighboring vacancies. It has been demonstrated that not only the temperature and pressure dependence of cation self-diffusion in metal-excess and metal-deficit manganous sulphide, but also absolute values of self-diffusion coefficients of this process are in excellent agreement with those calculated from manganese sulfidation and evaporation kinetics. This agreement clearly indicates that both these methods can successfully be utilized in studying the transport properties of transition-metal sulfides and oxides.

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