LAUSR

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 Ni2B (I4/mcm), α-Ni4B3 (Pnma), β-Ni4B3 (C2/c), and NiB (Cmcm) are synthesized by high pressure and high temperature (HPHT). The results indicate that synthesizing α-Ni4B3 and β-Ni4B3 requires more energy than Ni2B 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.