First principles calculations on martensitic transformation and phase instability of Ni–Mn–Ga high temperature shape memory alloys

Martensitic transformation and phase instability of Ni8+xMn4Ga4−x high-temperature shape memory alloys have been investigated by first principles calculations using the pseudopotentials plane wave method. The tetragonality (the ratio between the lattice parameter c and a) increases with the increasing of Ni content. The total energy difference between parent and martensite phases plays an important role on the martensitic transformation. The formation energy calculations indicate the instability of Ni–Mn–Ga alloy with extra high Ni content. The densities of states of the alloys are discussed.