First-principles study of martensitic transformation of IrTi alloy

Ab initio phonon calculations were performed to probe the martensitic transformation of IrTi. The details of the orthorhombic structure were obtained by the soft-phonon approach. We demonstrate that the tetragonal ( L 1 0 ) → orthorhombic (Cmmm) transition is driven by the softening of a phonon at the R point (0 1 / 2 1 / 2 ) of the Brillouin zone. The energy landscapes between the various phases of IrTi show that the structural behaviors of IrTi alloy are from cubic to tetragonal, then to orthorhombic and thus the original thought of cubic to monoclinic transition is modified.