A DFT investigation of the basic properties for Cr2XAl (X=V, Nb, Ta) full Heusler alloys

The generalized gradient approximation (GGA) is utilized to investigate the structural, mechanical, electronic, magnetic and thermodynamical properties of Cr₂XAl (X = V, Nb, Ta) full Heusler alloy. The L2₁ phase is more energetically favourable for each compound than their XA phase counterpart. To ensure structural stability, the phonon dispersion curves were computed using a first-principles linear response technique with the GGA approximation. The computed electronic and magnetic properties based on the GGA and GGA + U formalism revealed a metallic behaviour in both spin states, exhibiting high total magnetic moments and high Curie temperature for each material. The computed total magnetic moments are closer to the theoretical estimation from Slater Pauling (SP) rule (i.e., 4μ_B), when employing GGA + U assumption. From the elastic properties calculation, only Cr₂VAl was shown to be mechanically unstable, while Cr₂NbAl and Cr₂TaAl could achieve mechanical stability by satisfying the Born criteria. Further, the quasi-harmonic Debye approximation is used to describe a variety of thermodynamic features such as Debye temperature (ϴ_D), internal energy (E_V), vibrational entropy (S_V), Helmholtz free energy (A_V) and specific heat (C_V).