Structural and elastic properties of Ni2+xMn1-xGa alloys

The structural parameters and the energetics of the Ni2+xMn1-xGa alloys have been investigated by the first-principles Exact Muffin Tin Orbital-Coherent Potential Approximation (EMTO-CPA) for 0.10 < x < 0.30. The difference in total energies (delta E) between the low-temperature tetragonal phase and the high-temperature cubic phase has been considered as a qualitative indicator of the martensitic transformation temperature T-m. The qualitative behavior of delta E with variation of x has been found to be in agreement with the experimentally observed variation of T-m with x. The elastic constants for the entire range of x have also been calculated and the determination of a relationship between delta E and the elastic shear modulus has been attempted. It is seen that delta E varies linearly with elastic shear modulus C', qualitatively similar to the relation between T-m and C'. The energetics calculated with the EMTO method agrees quite well with the all-electron full-potential results ensuring the accuracy of the method. These results show that the EMTO-CPA method is one of the most reliable and accurate first-principles methods, in the context of off-stoichiometric alloys which undergo martensitic phase transformations. (C) 2011 Elsevier B.V. All rights reserved.