Structure and planar faults in the defective NiAs-type compound Ni₁₇S₁₈

Abstract

Nickel sulphide, NitTS,s, is a vacancy-ordered superstructure 3a-3a-3c of the NiAs type. Its structure was solved using a microtwinned model with two types of domains with respective space groups P3121 and P3221; a = 10.290 (2), c = 15.993 (3) (A), R = 6.4% for 1122 reflections. The microtwinning mechanism corresponds to a glide vector (a-b)/3 in the substructure which is studied using Cowley's theory [Cowley (1976). Acta Cryst. A32, 83-87, 88-91]. The analysis of the diffuse streaks leads to a very weak fault rate (ct = 0.003). The in-plane hexagonal Ni-Ni correlations are discussed.