Preparation of CoGe₂-type NiSn₂at 10 GPa

An unprecedented NiSn2 intermetallic with CoGe2-type crystal structure has been recovered (at ambient conditions) after high-pressure high-temperature treatment of a Ni33Sn67 precursor alloy at 10 GPa and 400 °C. The orthorhombic structure with Aeam space group symmetry is pseudotetragonal. Based on the evaluation of powder X-ray diffraction data, lattice parameters of a = b = 6.2818 Å and c = 11.8960 Å have been determined. Complicated line broadening and results of a further microstructure analysis, however, imply a defective character of the crystal structure. First-principles calculations with different model structures and a comparison with structural trends in the literature suggest that at the high-pressure high-temperature conditions a CuAl2-type crystal structure might be stable, which transforms to the recovered CoGe2-type crystal structure upon cooling or the release of pressure.