Structural investigation of cooperite (PtS) crystals

Abstract

The single-crystal structure of cooperite, a natural platinum sulfide PtS, is studied by X-ray diffraction supported by high-resolution scanning transmission electron microscopy and X-ray spectrum microanalysis. It is found that, in addition to the main reflections corresponding to the known tetragonal cell (a = 3.47 and c = 6.11 Å; space group P4₂/mmc), many weak reflections with intensities I ≤ 60σ(I) are clearly observed. These reflections fit the tetragonal cell (space group I4/mmm) with doubled parameters. In structures with small (P4₂/mmc) and large (I4/mmm) cells, the S atoms occupy statistically two special positions. It is shown that the chemical composition of the cooperite crystals deviates from the stoichiometric composition: sulfur-deficient specimens predominate.