First-principles Study On The Mechanical, Electronic And Thermal Properties Of Ni₃X（X=Pt,Mo,V,Sn） Under Pressure

Intermetallic compound has good potential for high-temperature structural material, forthe advantages such as small specific gravity, good high-temperature resistance and oxidationresistance, and so on. So it has a good application foreground in aerospace, automobile,chemical industry and other field. However, the practical application of intermetalliccompound is confined because of its drawbacks such as poor plasticity at room temperatureand low breaking tenacity. Hence, it’s of great significance to have a study on improving theroom-temperature plasticity or its essence of brittleness and inherent properties. Therefore,four common intermetallic compounds (Ni3Pt, Ni3Mo, Ni3V and Ni3Sn) have been studied inthis paper.This article focuses on the Ni3X(X=Pt, Mo, V, Sn) intermetallic compounds, and thefirst-principles plane-wave pseudopotential method based on the density functional theory isadopted. Using the principles of quantum mechanics and CASTEP code, with thequasi-harmonic Debye model, we calculate the parameters such as lattice constant, cellvolume, elastic constants, elastic modulus, Poisson’s coefficient, the density of states,population analysis, thermal expansion, heat capacity, Debye temperature, and so on. Byanalysing these parameters, we investigate the mechanical, electronic and thermal propertiesof Ni3X(X=Pt, Mo, V, Sn) with pressure ranges from0to30GPa, and the results are asfollowed:The calculated results within the GGA-PBE agree better with the other research resultsthan the results computed by the LDA-CA-PZ. So, the GGA-PBE is eventually adopted inthis work. Our calculated equilibrium lattice constants of Ni3X(X=Pt, Mo, V, Sn) are consistent with the experimental data and other theoretical values, indicating that theproposed computational methodology used in this paper is available and the calculated resultsare reliable. In the range of0-30GPa, the cell volumes of Ni3X(X=Pt, Mo, V, Sn) decreasewith pressure increasing.Under zero pressure, the elastic constants of Ni3X(X=Pt, Mo, V, Sn) all satisfy theircorresponding elastic stability criterion, suggesting that Ni3X(X=Pt, Mo, V, Sn) intermetalliccompounds are all mechanically stable. In the range of0-30GPa, the bulk modulus B, shearmodulus G and Young’s modulus E of Ni3X(X=Pt, Mo, V, Sn) intermetallic compoundsincrease with pressure going up, manifesting that pressure can improve their hardness. Thevalues of B/G of Ni3X(X=Pt, Mo, V, Sn) are larger than1.75, showing they are ductilematerials. The values of B/G and Poisson’s coefficient ν of Ni3X(X=Pt, V, Sn) are allincreasing with enhanced pressure, demonstrating pressure can improve the ductility andplasticity of Ni3X(X=Pt, V, Sn). The values of B/G and Poisson’s coefficient ν of Ni3Mofirstly increase but then decrease with the increasing pressure, which means the ductility andplasticity of Ni3Mo can be improved by proper pressure but will be decreased by excesspressure. The metallicity of Ni3X(X=Pt, Mo, V, Sn) compounds decreases with pressureenhanced.We also analyze the density of states of Ni3X(X=Pt, Mo, V, Sn) and study thedistribution of bonding electrons. In the range of0-30GPa, the curves of the density of stateshave no sharp changes, meaning that the structures of Ni3X(X=Pt, Mo, V, Sn) intermetalliccompounds remain stable and no structural phase transition have occured. The values of N(EF)(the density of states at the Fermi level) decrease with pressure rising up, which suggests thatthe hardness of Ni3X(X=Pt, Mo, V, Sn) have been improved by pressure. Moreover, thecharge transfer and bonding characteristics of Ni3X(X=Pt, Mo, V, Sn) have also beeninvestigated.Finally, the thermal properties of Ni3X(X=Pt, Mo, V, Sn) intermetallic compounds arestudied in the range of0-30GPa and0-1000K. The cell volumes V, thermal expansioncoefficient α and heat capacity C of Ni3X(X=Pt, Mo, V, Sn) intermetallic compounds increase with the increasing pressure and temperature. The bulk modulus B and Debye temperature ΘDof Ni3X(X=Pt, Mo, V, Sn) increase with the increasing pressure but decrease with theincreasing temperature.