First-principles investigations on structural, elastic, thermodynamic and electronic properties of Ni3X (X = Al, Ga and Ge) under pressure

The structural, elastic, thermodynamic and electronic properties of L12-ordered intermetallic compounds Ni3X (X = Al, Ga and Ge) under pressure range from 0 to 50 GPa with a step of 10 GPa have been investigated using first-principles method based on density functional theory (DFT). The calculated structural parameters of Ni3X at zero pressure and zero temperature are consistent with the experimental data. The results of bulk modulus B, shear modulus G, Youngʹs modulus E, Poissonʹs ratio v, anisotropy index AU and Debye temperature ΘD increase with the increase of external pressure. In addition, the Debye temperature of these compounds gradually reduce as the order of Ni3Al > Ni3Ga > Ni3Ge. The ratio of shear modulus to bulk modulus G/B shows that the three binary compounds are ductile materials, and the ductility of Ni3Al and Ni3Ga can be improved with pressure going up, while Ni3Ge is opposite. Finally, the pressure-dependent behavior of density of states, Mulliken charge and bond length are analyzed to explore the physical origin of the pressure effect on the structural, elastic and thermodynamic properties of Ni3X.