Structural, mechanical and electronic properties of binary Ni-B compounds under pressure

The novel structures of binary of Ni-B compounds containing different amounts of boron have been systemically studied by the unbiased structure search techniques. Three previously unreported crystal structures of NiB2, NiB3, and NiB4, crystallizing in space groups P-3m1, P63/mmc, and Cmc2(1) respectively, are determined. We found that the stoichiometries of NiB2, NiB3, and NiB4 are thermodynamic and dynamical stable at ambient pressure. The P63/mmc-NiB3 exhibits the highest bulk modulus and shear modulus, and the smallest Poisson's ratio of Cmc2(1)-NiB4. The calculated density of states shows that the considered compounds are all metallic. We hope that these findings will contribute to experimental work on the synthesis of this technologically important material.