Energetic Validation of Various Crystal Structures in Zr2CoZ (Z = Al, Ga, In) Heusler Alloys

We energetically validate new Zr(2)CoZ (Z = Al, Ga, In) systems in the most common cubic crystal structures of Heusler alloys, that is, regular and inverse full-Heusler structures. The regular Heusler structure, namely, the L2(1) (Cu2MnAl-type), is energetically more favorable in Zr(2)CoZ than the inverse Heusler (Hg2CuTi-type), as confirmed by the density functional theory calculations and a semiempirical Miedema's model. The values of the independent elastic constants (c(11), c(12), c(44)) obtained for the studied Zr(2)CoZ Heusler alloys in the L2(1) structure fulfill the conditions of Born stability for cubic crystals. Our results of electronic structure calculations show that Zr2CoZ in the L2(1) structure are metallic ferromagnets with a main contribution from the Co magnetic moment, whose value is within the range of 1.425-1.472 mu B. By adapting the simplest deformation from a cubic to tetragonal structure (Bain transformation) as well as the orthorhombic distortion of an energetically favorable regular Heusler structure, we discuss the stability of the L2(1) structure and the possibility of structural transformation in Zr(2)CoZ series. The energy of the L2(1) phase in the Zr2CoIn compound increases leading to relative stabilization of the tetragonal phase of this compound with c/a = 1.37 for the volume 7% lower than the equilibrium value.