Tennantite: multi-temperature crystal structure, phase transition and electronic structure of synthetic CuAsS.

The structure of synthetic tennantite CuAsS was investigated at various temperatures in the 90-293 K range. It crystallizes in space group I{\overline 4}3m. No structural transformation was observed in this temperature range. The structures were refined in anharmonic approximation for atomic displacements and electron density maps were refined using the maximum entropy method. Both approaches indicate a noticeable static disorder of the copper atoms in the triangular sulfur coordination and neighbouring site at high temperatures, whereas these split copper sites are well defined at lower temperatures. One particle potential is used to describe the behaviour of atoms at these copper sites. Such behaviour may be the structural reason for changes in magnetic properties.