Phase relations, and mechanical and electronic properties of nickel borides, carbides, and nitrides from ab initio calculations.

Based on density functional theory and the crystal structure prediction methods, USPEX and AIRSS, stable intermediate compounds in the Ni-X (X = B, C, and N) systems and their structures were determined in the pressure range of 0-400 GPa. It was found that in the Ni-B system, in addition to the known ambient-pressure phases, the new nickel boride, Ni 2 B 3 - Immm , stabilizes above 202 GPa. In the Ni-C system, Ni 3 C- Pnma was shown to be the only stable nickel carbide which stabilizes above 53 GPa. In the Ni-N system, four new phases, Ni 6 N- R 3̄, Ni 3 N- Cmcm , Ni 7 N 3 - Pbca , and NiN 2 - Pa 3̄, were predicted. For the new predicted phases enriched by a light-element, Ni 2 B 3 - Immm and NiN 2 - Pa 3̄, mechanical and electronic properties have been studied.