Electronic Structure and Structural Transformation of Co_1−xNi_1+xAl (x=0, ±1⁄2)

Abstract

To expand our knowledge of the martensitic transformation from a B2 to an L1₀ structure for ferromagnetic shape memory Co-Ni-Al alloys, we have performed first-principles band calculations for the supercell structures corresponding to Co_1−xNi_1+xAl (x=0, ±1⁄2) 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=±1⁄2. This result indicates that the stabilization of an L1₀ structure becomes weak in a rich Co or Ni region compared with the composition of Co: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−xNi_1+xAl.