Synthesis of Ni-B Compounds by High-Pressure and High-Temperature Method.

Nickel borides are promising multifunctional materials for high hardness and excellent properties in catalysis and magnetism. However, it is still a blank of intrinsic properties in Ni-B compounds, because crystallization of the single phases of Ni-B compounds with micro-size is a challenge. In this work, single phases of Ni 2 B ( I 4 /mcm ), α-Ni 4 B 3 ( Pnma ), β-Ni 4 B 3 ( C 2 /c ), and NiB ( Cmcm ) are synthesized by high pressure and high temperature (HPHT). The results indicate that synthesizing α-Ni 4 B 3 and β-Ni 4 B 3 requires more energy than Ni 2 B and NiB. The growth process of Ni-B compounds is that Ni covers B to form Ni-B compounds under HPHT, which also makes the slight excess of B necessary. So, generating homogeneous distribution of starting materials and increasing the interdiffusion between Ni and B are two keys to synthesize well crystallized and purer samples by HPHT. This work uncovers the growth process of Ni-B compounds, which is significant to guide the synthesis of highly crystalline transition metal borides (TMBs) in the future.