Co和Ni过量影响Co_(2)NiGa合金晶体结构及相稳定性的第一性原理研究  

First-principles study of Co and Ni excess effects on crystal structure and phase stability of Co_(2)NiGa alloy

作　　者：周金萍 李春梅 姜博 黄仁忠[1] Zhou Jin-Ping;Li Chun-Mei;Jiang Bo;Huang Ren-Zhong(College of Physical Science and Technology,Shenyang Normal University,Shenyang 110034,China)

机构地区：[1]沈阳师范大学物理科学与技术学院,沈阳110034

出　　处：《物理学报》2023年第15期192-203,共12页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:12174269,11674233,51301176);辽宁省教育厅基金(批准号:LJKMZ20221472)资助的课题.

摘　　要：采用精确的Muffin-Tin轨道结合相干势近似方法,系统计算研究了0 K下Co和Ni过量对Co_(2+x)Ni1–xGa,Co_(2+x)NiGa_(1-x),Co_(2)-xNi_(1+x)Ga和Co_(2)Ni_(1+x)Ga_(1–x)(0≤x≤0.4)合金晶体结构及原子占位、马氏体相变、磁矩和弹性常数的影响规律及其物理机理.研究结果表明:绝大多数合金奥氏体相均具有XA稳定结构,且过量Co和Ni原子均占据在不足原子位置,仅当Ni取代Ga时其处于反常占位;随x的增加,仅有两组Ga不足合金的L10相对于XA的电子总能逐渐降低,前者四方剪切弹性常数逐渐增加,而后者其则逐渐减小,在能量和力学上Co和Ni取代Ga均促进了马氏体相变的发生,并有望提高马氏体相变温度;各合金XA和L10相总磁矩(μtot)主要源于Co原子的贡献,Ni原子仅贡献较小部分,且两相μtot在四组合金中随x变化关系相同,在同一组分下,它们相差不超过约0.32μB;电子结构计算分析表明,相对于XA相而言,L10-Co_(2)NiGa合金的稳定性主要源于Co和Ni原子在费米能级附近自旋向下的电子态密度分布,即归结于Jahn-Teller效应.上述结果有望为实验上Co_(2)NiGa基三元合金结构与性能的优化设计提供理论参考.Using the first-principles exact muffin-tin orbital method combined with the coherent potential approximation,the crystal structure and site occupation,martensitic transformation,magnetic moment and elastic constant for each of Co_(2+x)Ni_(1–x)Ga,Co_(2+x)NiGa_(1-x),Co_(2–x)Ni_(1+x)Ga and Co_(2)Ni_(1+x)Ga_(1–x)(0≤x≤0.4)alloys with Co and Ni excess at 0 K are systematically investigated.It is shown that most of the austenitic phases of the alloys have XA stable structure,and the excess Co and Ni atoms occupy the insufficient atomic positions,and it is inversely occupied only when Ni replaces Ga.With the increase of x,the total electron energy of L10 relative to XA of only two Ga-insufficient alloys gradually decreases,for the former,the tetragonal shear elastic constant gradually increases,but for the latter,it gradually decreases.It is indicated that the martensitic transformation is promoted by the substitution of both Co and Ni for Ga in the energy and mechanics,and the martensitic transformation temperature is expected to increase.The values of total magnetic moment(μtot)of the XA phase and L10 phase of each alloy are mainly contributed by Co atoms,but onlya relatively small portion by Ni atoms.And the values ofμtot of two phases in the four alloys have the same relationship with x,and the difference between them with the same compositions is not more than about 0.32μB.The analyses of electronic structure calculations show that the distributions of spin-down electronic density of states of Co and Ni atoms near the Fermi energy level have contributed significantly to the stability of L10 relative to the XA phase,which is attributed to the Jahn-Teller effect.The above results are expected to provide a theoretical reference for the optimal design of the structure and properties of Co_(2)NiGa-based ternary alloys.

关 键 词：第一性原理计算 原子占位 相稳定性 Co2NiGa 合金 

分 类 号：O469[理学—凝聚态物理] TG146.16[理学—电子物理学]