A new high-pressure polymorph of NiSb2

A new polymorph of NiSb2 was obtained under high-pressure/temperature condi tion of 6 GPa and 550-650 degreesC. The crystal structure is orthorhombic w ith the space group Phca (No. 61). isostructural with the low-temperature f orm of NiAs2 (pararammelsbergite). The crystallographic parameters were ref ined by the Rietveld analysis of the powder X-ray diffraction data (a = 0.6 2866(2) nm, b-0.63643(2) nm, c = 1.23670(3) nm, Z = 8). The structure can b e regarded as an intermediate structure between the marcasite-type and the pyrite-type. The pararammelsbergite-type NiSb2 is a high-pressure form of N iSb2 and the density is slightly higher than that of ambient pressure form with the marcasite-type structure. (C) 2000 Elsevier Science Ltd. All right s reserved.