Electronic structure of NiTi and NiMn "shape memory" alloys

A self-consistent electronic structure calculations of austenitic and martensitic phases of NiTi and NiMn were performed using full-potential linearized augmented plane wave (FLAPW) method. The evolution of the electronic structure of alloys with the composition and alloying by the third element was also studied by means KKR-CPA and the average T-matrix (ATM) method. The alteration of electron characteristics for NiTi and NiMn at the martensitic transformations has been analyzed. It was shown that the electron states are changed qualitatively by Ti irrespective of the partial replacement of Mn or Ni. The potential scattering on the component of NiMn alloy and the damping of bands is analysed in the both cases. The change in the nesting range with alloying and the correlation between the peculiarities of the electronic structure and the change of the martensitic transformation (MT) temperature is discussed. The rather sharp decrease of MT temperature may be connected not only to the scattering of electrons by defects on Ni-sites, but more to imperfect nesting.