High temperature neutron diffraction studies of phase transformations in NiCr2S4
High temperature structural transformations in NiCr2S4 have been investigated by neutron powder diffraction in situ. At 835(5) °C, NiCr2S4 undergoes an order–disorder transition from the monoclinic Cr3S4 structure to a hexagonal cation-deficient NiAs structure. Above the transition temperature, cation vacancies, which at room temperature are ordered in every second cation layer, become statistically distributed between all cation layers. Prior to this structural transition, intralayer disordering of vacancies occurs within the half-occupied layer. This is not sufficiently complete to cause the change to trigonal symmetry which has been reported for binary sulfides.