Low-temperature structural distortion in CuS

The crystal structure of CuS has been studied by powder X-ray and neutron diffraction methods between 6 and 730 K. At room temperature the hexagonal structure was confirmed. At low temperature (∼55 K) a second order phase transition takes place with a space group change from P63/mmc to the “translationengleiche” subgroup Cmcm. This orthorhombic distortion causes only small, but significant changes in the Cu —S and S–S bonding distances. The most pronounced changes occur for the Cu – Cu distances, indicating metal – metal bond formation to be the main cause of the transition.