A new high-pressure polymorph of NiSb2

A new polymorph of NiSb₂ was obtained under high-pressure/temperature condition of 6 GPa and 550–650°C. The crystal structure is orthorhombic with the space group Pbca (No. 61), isostructural with the low-temperature form of NiAs₂ (pararammelsbergite). The crystallographic parameters were refined by the Rietveld analysis of the powder X-ray diffraction data (a=0.62866(2) nm, b=0.63643(2) nm, c=1.23670(3) nm, Z=8). The structure can be regarded as an intermediate structure between the marcasite-type and the pyrite-type. The pararammelsbergite-type NiSb₂ is a high-pressure form of NiSb₂ and the density is slightly higher than that of ambient pressure form with the marcasite-type structure.