On the Defect Structure and Transport Properties of NiS2
Because of considerable experimental difficulties, the defect structure of NiS2 has not been elucidated so far. The first step in these investigations was to explain which sublattice of this compound is predominantly disordered. In order to solve this problem, the mechanism of sulphidation of NiS to NiS2 has been studied using marker technique. These experiments have been carried out at temperatures 823-923 K in sulphur vapors under pressure 103 105 Pa. It has been found that the predominant defects in NiS2 occur in cation sublattice. The problem then arised whether these defects are cation vacancies or interstitial cations. This phenomenon could have been explained in studying the kinetics of NiS sulphidation as a function of sulphur activity. It has been found that the parabolic rate constant of this reaction increases with sulphur activity, strongly suggesting that cation vacancies, and not cation interstitials, are the prevailing defects. If, namely, interstitial cations would prevail, the sulphidation rate would be virtually pressure independent.
I. Bezverkhyy, S. Chevalier and O. Politano
Z. Grzesik et al., "On the Defect Structure and Transport Properties of NiS2", Defect and Diffusion Forum, Vols. 323-325, pp. 315-320, 2012