60.
The chemical composition, defect structure, and diffusion in nickel sulfide -Ni
3S
2 have been investigated in H
2S-H
2 mixtures containing between 1 and 65% H
2S between 560 and 700°C. Gravimetric, density, and X-ray studies were carried out. In the thermodynamically stable compound the ratio of Ni/S varied between 1.3 and 1.75. The X-ray examination showed a step change in the lattice parameter at the Ni/S ratio 1.4. A linear dependence of the density values (between 5.5 and 6.2 g/cm
3) on the composition was observed. On the basis of the chemical composition and density measurements the number of nickel and sulfur atoms in 1 cm
3 were determined. It has been shown that the Ni
3S
2 phase is defected in both anion and cation sublattices and that its chemical formula may be described as follows: Ni
3±yS
2x, where y 2x. It has been found that in the mixture containing 10% H
2S the process of defect formation is determined by their diffusion in the sulfide. The temperature dependence of the diffusion coefficient is described by the equation D = 13.15 exp(-30,000/RT) cm
2/sec. No dependence of D on the sulfur partial pressure was observed, but this may be due to the relatively large uncertainties in the measurement of the diffusion coefficients.
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