Theoretical study on the phase stability, elasticity, hardness and electronic structures of Ni–P compounds

A systematic investigation concerned with phase stability, elastic properties, hardness and relevant electronic structure of Ni–P compounds (Ni3P, Ni12P5, Ni2P, Ni5P4, NiP, NiP2 and NiP3) was carried out using first principles calculations. The calculated results show that the Ni–P compounds have strong hardness, ranging from 7.80–14.54 GPa. Also, the hardness values gradually increase with the P content. Electronic structure analysis shows that the strong Ni–P and part of P–P hybrid orbitals play important roles in the hardness of these compounds. The calculated elastic constants indicated that the Ni3P, Ni12P5 and NiP2 phases are significantly anisotropic, the NiP and Ni2P exhibit some anisotropy, while the Ni5P4 and NiP3 show a relatively isotropic character. At last, the properties of these Ni–P compounds including lattice constants, thermodynamic stability, elastic constants Cij, bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio ν have been calculated.