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 cubani te (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 G Pa 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 tran sition from a magnetically ordered phase at low pressure to a nonmagne tic or paramagnetic phase at high-pressure. The change in magnetic beh aviour at the structural transition may be attributed to a reduction o f the Fe-S-Fe superexchange angle formed by edge-sharing octahedra. oc curring in the high-pressure phase. The non-magnetic or paramagnetic m etallic phase at high pressure is retained upon decompression to ambie nt pressure-temperature conditions, indicative of substantial hysteres is associated with the pressure driven orthorhombic-->hexagonal struct ural transition. The pressure evolution of both the Fe-57 Mossbauer hy perfine interaction parameters and resistance behaviour is consistent with the transition from mixed-valence character in the low pressure o rthorhombic structure to that of extended-electron delocalization in t he hexagonal phase at high-pressure.