Mg_(8)Sn_(4-x)M_(x)结构稳定性与弹性常数的第一性原理计算

First⁃principles calculations on the structural stability and elastic constant of Mg_(8)Sn_(4-x)M_(x)

利用基于密度泛函理论的CASTEP软件构建Mg_(8)Sn_(4-x)M_(x)(M=Al、Cu;x=0、1或2)晶体结构模型,采用第一性原理计算其晶格常数、结构稳定性和弹性常数,并分析不同量的M原子固溶于Mg_(2)Sn后体系的电子特性、弹性性能和本征硬度.计算结果表明,M原子能自发固溶于Mg_(2)Sn相,且所得Mg_(8)Sn_(4-x)M_(x)(x=1或2)晶体结构均可稳定存在;当2个M原子固溶于Mg_(2)Sn时,使其晶体结构由立方晶系转变为四方晶系.态密度分析表明,M原子固溶后体系原子存在明显轨道杂化现象,表现出较强的共价键,增加M原子固溶量不会改变各原子对态密度的贡献规律,但会提高该原子对电子对态密度的贡献度.弹性性能和本征硬度分析表明:Mg_(2)Sn中固溶M原子后,体系力学性能仍稳定,增加M原子固溶量,体系硬度逐渐降低,韧塑性不断提高,即M原子固溶量增加能提升体系的韧塑性.

Using the CASTEP software based on density functional theory,the crystal structure model of Mg_(8)Sn_(4-x)M_(x)(M=Al,Cu;x=0,1 or 2)was constructed,and its lattice constant,structural stability and elastic constant were calculated by first-principles,as well as the electronic properties,elastic properties and intrinsic hardness of the crystal structure model with different amounts M atoms solid solution in Mg_(2)Sn phase were ana⁃lyzed.The calculation results show that the solid solution of the M atoms in Mg_(2)Sn can generate spontaneously,and the obtained Mg_(8)Sn_(4-x)M_(x)(x=1 or 2)crystal structure can exist stably;the crystal structure converts from cubic system to tetragonal system when two M atoms dissolve in Mg_(2)Sn.The analysis results of density of states indicate that the atoms in the system exist obvious orbital hybridization by M atoms solid solution,then show strong covalent bonds,and increasing the number of M atoms will not affect the contribution of each atom to the density of states,but will increase the contribution of electrons in the atom to the density of states.The analysis results of elastic properties and intrinsic hardness indicate that the mechanical properties of the system are still stable after dissolving M atoms in Mg_(2)Sn,and the hardness of the system decreases gradually and the plasticity increases continuously with the increase of M atoms solid solubility,i.e.,the toughness and plasticity of the sys⁃tem can be improved by increasing M atoms solid solubility.