High-pressure metallization and electronic-magnetic properties of hexagonal cubanite (CuFe2S3)

Fe-57 Mossbauer studies at room temperature and temperature-dependent resistance studies have been performed on a natural specimen of cubanite (CuFe2S3) in a diamond-anvil cell at pressures up to similar to 10 GPa. An insulator-metal phase transition occurs in the range 3.4-5.8 GPa coinciding with a previously observed structural transition from an orthorhombic to a hexagonal NiAs (B8) structure. The room temperature data shows that the metallization process concurs with a gradual transition from a magnetically ordered phase at low pressure to a nonmagnetic or paramagnetic phase at high-pressure. The change in magnetic behaviour at the structural transition may be attributed to a reduction of the Fe-S-Fe superexchange angle formed by edge-sharing octahedra. occurring in the high-pressure phase. The non-magnetic or paramagnetic metallic phase at high pressure is retained upon decompression to ambient pressure-temperature conditions, indicative of substantial hysteresis associated with the pressure driven orthorhombic-->hexagonal structural transition. The pressure evolution of both the Fe-57 Mossbauer hyperfine interaction parameters and resistance behaviour is consistent with the transition from mixed-valence character in the low pressure orthorhombic structure to that of extended-electron delocalization in the hexagonal phase at high-pressure.