First-principles investigation of the composition dependent properties of Ni2+xMn1-xGa shape-memory alloys
First-principles investigation of the composition dependent properties of Ni2+xMn1-xGa shape-memory alloys
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DOI：
10.1103/physrevb.82.024201
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发表时间：
2010-07-07
影响因子：
3.7
通讯作者：
Vitos, Levente
中科院分区：
文献类型：
--
作者：
Li, Chun-Mei;Luo, Hu-Bin;Vitos, Levente
采用第一性原理精确Muffin-tin轨道方法结合相干势近似，研究了Ni 2 + xMn 1-xGa形状记忆合金的成分依赖的晶格常数、相稳定性、弹性模量和磁转变温度.立方L-21奥氏体相的晶格参数和四方剪切模量随着过量Ni原子浓度x的增加而线性减小。立方L-21和四方β“”相的生成热及其差值随x的增加而增加，表明立方和四方相的稳定性降低，而L-21向β“”马氏体转变的驱动力增加。通过对电子态密度的研究，我们发现Ni引起的相稳定性的降低主要是由于Ni和Ga的少数自旋态之间的共价键的减弱。利用计算的参数，马氏体相变温度的成分依赖性进行了讨论。从海森堡模型结合平均场近似估计的理论居里温度，β相比L-21相大。对于这两个阶段，居里温度随x的增加几乎线性下降。
The composition dependent lattice parameter, phase stability, elastic moduli, and magnetic transition temperature of the Ni2+xMn1-xGa shape-memory alloys are studied by using the first-principles exact muffin-tin orbital method in combination with the coherent potential approximation. The lattice parameter and tetragonal shear modulus of the cubic L-21 austenite phase decreases linearly with increasing concentration x of excess Ni atoms. The heats of formation of both cubic L-21 and tetragonal beta''' phases and their difference increase with x, indicating decreasing stability of the cubic and tetragonal phases and increasing driving force for the L-21 to beta''' martensitic transition. Investigating the electronic density of states, we find that the Ni-induced decreasing phase stability can mainly be ascribed to the weakening of the covalent bonding between minority spin states of Ni and Ga. Using the computed parameters, the composition dependence of the martensitic transition temperature is discussed. The theoretical Curie temperature, estimated from the Heisenberg model in combination with the mean-field approximation, is larger for the beta''' phase than for the L-21 phase. For both phases, the Curie temperature decreases nearly linearly with increasing x.