Deviations from stoichiometry and chemical diffusion in metal-deficit samples were studied at 973 to 1273K, for S activities of 0.1 to 10000Pa, by using a microthermogravimetric technique. It was found that the non-stoichiometry was a function of temperature and the equilibrium S pressure; thus indicating that the cation vacancies did not interact, were fully ionized and were randomly distributed throughout the crystal lattice. Re-equilibration-rate measurements of non-stoichiometry showed that the vacancy diffusivity (a direct measure of defect mobility) did not depend upon their concentration and could be described by:

D (cm2/s) = 1.97 x 10-2 exp[-83.4(kJ/mol)/RT]

These results were used to deduce the diffusivity of cations:

D (cm2/s) = 6.0 x 10-4 exp[-142.0(kJ/mol)/RT] PS1/6

where PS was the S pressure.

Nonstoichiometry and Self-Diffusion in α-MnS. S.Mrowec, Z.Grzesik: Solid State Phenomena, 2000, 72, 69-78. See also: Solid State Ionics, 2001, 143[1], 25-9 and Solid State Ionics, 2001, 141-142, 493-8