Electronic Structure and Structural Transformation of Co1−xNi1+xAl (x=0, ±1⁄2)

To expand our knowledge of the martensitic transformation from a B1 to an L1 0 structure for ferromagnetic shape memory Co-Ni-Al alloys, we have performed first-principles hand calculations for the supercell structures corresponding to Co 1 - x Ni 1 + x Al (x = 0, ′½) in a nonmagnetic state. From the investigation of total energy vs c/a, we have found that the total-energy gain for x = 0 due to the distortion is 3∼4 times as large as those for x = ′½. This result indicates that the stabilization of an L1 0 structure becomes weak in a rich Co or Ni region compared with the composition ofCo:Ni:Al = 1:1:1. We have discussed the result in terms of band energy and such components as CoAl, NiAl, CoNi and etc., which compose Co 1 - x Ni 1 + x Al.