Co_(2)CrZ(Z=Al,Ga,Ge和Si)合金相稳定性和弹性常数的第一性原理分析

First-principles study on phase stability and elastic constant of Co_(2)CrZ(Z=Al,Ga,Ge and Si)alloys

采用精确Muffin-Tin轨道结合相干势近似方法,系统计算研究了0 K下Co_(2)CrZ(Z=Al,Ga,Ge和Si)合金立方奥氏体和四方马氏体相的晶格结构、电子总能和弹性常数。研究结果表明:4种合金在铁磁态下均具有L2_(1)立方稳定结构,而在顺磁态下均具有D0_(22)四方稳定结构;在铁磁态下,4种合金的弹性常数均满足立方晶格力学稳定性要求,且比顺磁状态下的值要更大些,证明它们在基态下具有更好的力学稳定性;在由铁磁到顺磁状态的转变过程中,各合金四方剪切弹性常数明显软化,表明磁无序均有利于它们发生四方晶格变形,因而在顺磁状态下,它们均具有D0_(22)结构。

In this paper,the lattice structure,magnetic moment,elastic constant and total electron energy of Co_(2)CrZ(Z=Al,Ga,Ge and Si)shape-memory alloys are investigated by using the first-principles exact muffin-tin-orbital method in combination with the coherent potential approximatin.According to the research,it can be proved that the four Co_(2)CrZ(Z=Al,Ga,Ge and Si)alloys all have the L2_(1) cubic stable structure under the ferromagnetic state.While in the paramagnetic state,they all the D0_(22) tetragonal structure.In the ferromagnetic state,the elastic constants of the four alloys all meet the requirements of cubic lattice mechanical stability,and the value is larger than that in the paramagnetic state,which proves that they include better mechanical stability in the ground state.After that,during the transition from ferromagnetic to paramagnetic state,the tetragonal shear elastic constant C′of each alloy is obviously softened.It indicates that the magnetic disorder is conducive to their tetragonal lattice deformation.Therefore,under the paramagnetic state,the four alloys all belongs to D0_(22) structure.