Ambient and High Pressure CuNiSb₂: Metal-Ordered and Metal-Disordered NiAs-Type Derivative Pnictides

The mineral Zlatogorite, CuNiSb₂, was synthesized in the laboratory for the first time by annealing elements at ambient pressure (CuNiSb₂-AP). Rietveld refinement of synchrotron powder X-ray diffraction data indicates that CuNiSb₂-AP crystallizes in the NiAs-derived structure (P3m1, #164) with Cu and Ni ordering. The structure consists of alternate NiSb₆ and CuSb₆ octahedral layers via face-sharing. The formation of such structure instead of metal disordered NiAs-type structure (P6₃/mmc, #194) is validated by the lower energy of the ordered phase by first-principle calculations. Interatomic crystal orbital Hamilton population, electron localization function, and charge density analysis reveal strong Ni-Sb, Cu-Sb, and Cu-Ni bonding and long weak Sb-Sb interactions in CuNiSb₂-AP. The magnetic measurement indicates that CuNiSb₂-AP is Pauli paramagnetic. First-principle calculations and experimental electrical resistivity measurements reveal that CuNiSb₂-AP is a metal. The low Seebeck coefficient and large thermal conductivity suggest that CuNiSb₂ is not a potential thermoelectric material. Single crystals were grown by chemical vapor transport. The high pressure sample (CuNiSb₂-8 GPa) was prepared by pressing CuNiSb₂-AP at 700 °C and 8 GPa. However, the structures of single crystal and CuNiSb₂-8 GPa are best fit with a disordered metal structure in the P3m1 space group, corroborated by transmission electron microscopy.