SELF-DIFFUSION OF MANGANESE IN NONSTOICHIOMETRIC MANGANOUS SULFIDE

Self-diffusion of manganese in nonstoichiometric manganous sulphide, M n1+/-yS, has been studied as a function of temperature (1073-1373) K a nd 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 bee n shown that at very low sulfur pressures, close to the Mn/MnS phase b oundary, self-diffusion of cations in metal excess Mn1+yS proceeds by an interstitial mechanism, consisting of pushing a cation from its nor mal lattice site into neighboring interstitial position. At higher sul fur activities, on the other hand, cation self-diffusion in metal-defi cit Me1-yS proceeds by a simple vacancy mechanism, consisting of Mn2ions jumping from the lattice sites into neighboring vacancies. It has bees demonstrated that not only the temperature and pressure dependen ce 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 man ganese sulfidation and evaporation kinetics. This agreement clearly in dicates that both these methods can successfully be utilized in studyi ng the transport properties of transition-metal sulfides and oxides.