Abstract
The mechanical, electronic and thermodynamic properties of Ni-X compounds (NiTi, Ni3Ti, NiAl, Ni3Al and Ni3Si) under different pressures and temperatures were investigated with the first-principles calculation. The predicted lattice constants of Ni-X compounds were in good accordance with the available experimental and theoretical values at zero pressure. All the compounds were mechanically stable with the pressure increasing up to 50 GPa, the bulk modulus B, shear modulus G and Young's modulus E increased with increasing the pressure, elucidating the resistance to volume deformation, shear deformation and the enhanced stiffness of the five compounds under various pressure ranging from 0 to 50 GPa. There was no trend for the ductility, micro-hardness and anisotropy among the compounds. The slight changes of total density of states (TDOS) curves supported the point of view that no structural variations and phase transformation occurred under pressure. In addition, the thermodynamic properties, such as Debye temperature Theta(D), bulk modulus B, linear thermal expansion coefficient alpha and heat capacity C-v, C-p were calculated with the quasi-harmonic Debye approximation. At constant temperature, the B and Theta(D) increased for Ni-X compounds when the pressure was increased. Besides, alpha, C-v and C-p increased exponentially when T < 300 K. With increasing the temperature, the alpha and C-p showed the modest linear increase and the C-v tended to approach to the Dulong-Petit limit at high temperature regions.