Structural Stability, Elasticity, Thermodynamics and Electronic Structures of L12-Type Ni3X (X=Al, Ti, V, Nb) Phases Under External Pressure Condition

Abstract

In this paper, the impacts of external pressure on structural stability, elasticity, thermodynamics and relevant electronic structures of L12-type Ni3X (X=Al, Ti, V, Nb) phases were investigated using the first-principles methods. The lattice parameters(a,b,c) and volume(V) of the Ni3X phases decrease with increasing pressure. however, the elastic constants(Cij ), bulk modulus(B), shear modulus(G), and Young's modulus (E) increase. The calculated elastic constants indicate that the mechanical stability and ductility of Ni3X phases enhance with increasing pressure. The mechanical anisotropy of Ni3X phases are enhanced by the raised pressure. Electronic analysis shows that increase pressure makes Ni-d-orbital and X(X=Al, Ti, V, Nb) -d-orbital hybridization stronger and electron transfer increases. The sequence in regard to electron aggregation strength is Ni3Ti>Ni3Nb>Ni3V>Ni3Al. It is more directly reflected in the charge density difference maps. This is consistent with the analysis results of the enthalpy of formation(ΔH) and Debye temperature (ΘD).