R-phase and electronic structures of TiNi and TiNi8/9Fe1/9 : Special issue on smart materials-fundamentals and applications

Titanium nickel (TiNi) and the pseudo binary containing a small amount of iron has the R phase as an intermediate phase. To examine theoretically the stability of the R phase, the electronic structures of TiNi and TiN1 8/9 Fe 1/9 were calculated for four structures of B2, P3, P31m and P31m. The total energies predict that the P3 structure is most stable among the four structures and in the P3 structure the added iron atoms prefer the 1c site. It is also revealed that the approach between a nickel (or iron) atom at the 1c site and a titanium atom at the 1c site in the P3 structure plays an important role in stabilizing the P3 structure. These features are clearly reflected on the band energies and the local density-of-states of the constituent atoms.