Stability, Mechanical Properties and Anisotropic Elastic Properties of GaxMgy Compounds

The stability, mechanical properties and anisotropic properties of sound velocities of Ga2Mg5, GaMg2, GaMg, O-Ga2Mg, H-Ga2Mg and Ga5Mg2 are investigated systematically by the first-principles calculation. The cohesive energy and formation enthalpy are obtained and used to estimate the stability of the Ga-Mg binary compounds. GaMg compound is the most stable and has the lowest formation enthalpy as -0.162eV/atom of those GaxMgy compounds. The elastic constants of single crystal, hardness, bulk, shear, Young's modulus and Poisson's ratio of the polycrystalline crystal are obtained and used to estimate the mechanical properties. Ga5Mg2 and H-Ga2Mg have the lager bulk, shear and Young’s modulus and corresponding B/G is low. H-Ga2Mg is harder than the other compounds from the results of Poisson’s ratio. The anisotropic mechanical properties are discussed using the anisotropic index, two-dimensional planar projections on different planes of the bulk and Young's modulus. The Young's modulus of H-Ga2Mg shows the strongly anisotropy of mechanical properties and GaMg2 has the weakest anisotropy among all the compounds.

本研究通过第一性原理计算（first-principles calculation），系统探究了Ga₂Mg₅、GaMg₂、GaMg、O-Ga₂Mg、H-Ga₂Mg及Ga₅Mg₂的稳定性、力学性能与声速各向异性特性。通过计算得到结合能（cohesive energy）与形成焓（formation enthalpy），并以此评估Ga-Mg二元化合物的结构稳定性。在所有GaₓMgᵧ化合物中，GaMg相最为稳定，其形成焓最低，为-0.162 eV/原子。本研究获取了单晶弹性常数（elastic constants）、多晶硬度、体积模量（bulk modulus）、剪切模量（shear modulus）、杨氏模量（Young's modulus）与泊松比（Poisson's ratio），以此表征其力学性能。Ga₅Mg₂与H-Ga₂Mg具有更高的体积模量、剪切模量与杨氏模量，且其B/G比值较低。根据泊松比计算结果，H-Ga₂Mg的硬度高于其余化合物。通过各向异性指数（anisotropic index）、体积模量与杨氏模量的不同平面二维投影，对各向异性力学性能展开讨论。H-Ga₂Mg的杨氏模量表现出极强的力学各向异性，而GaMg₂则是所有化合物中各向异性最弱的相。