Self-diffusion of manganese in nonstoichiometric manganous sulphide

Self-diffusion of manganese in nonstoichiometric manganous sulphide, Mn1+/-yS, has been studied as a function of temperature (1073-1373) K and sulfur activity (10-(11)-10(3)) Pa using radioactive Mn-54 isotope as a tracer. In agreement with the defect model of Mn1+/-yS it has been shown that at very low sulfur pressures, close to the Mn/MnS phase boundary, self-diffusion of cations in metal excess Mn1+yS 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 Me1-yS proceeds by a simple vacancy mechanism, consisting of Mn2+ ions jumping from the lattice sites into neighboring vacancies. It has bees demonstrated that not only the temperature and pressure dependence of cation selfdiffusion 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.