Magnetism, Half-Metallicity, Structural Stability, and Thermoelectric Properties of Ba2MTaO6 (M = V, Ni): A Computational Perspective

The double perovskite oxides Ba₂MTaO₆ (M = V, Ni) are investigated for the first time due to their promising properties in materials science and spintronics. Using the FP-LAPW method within the framework of density functional theory (DFT), we examine the effects of magnetic transition metal cations (M) on the structural and electronic behavior of these compounds. The calculations are carried out using the generalized gradient approximation (GGA), GGA with Hubbard U correction (GGA + U), and the exact exchange for correlated electrons (EECE) approach for the exchange correlation functional. Both compounds crystallize in a cubic structure (space group: Fm-3m, No. 225) under ambient conditions, with optimized lattice parameters of 8.13 Å for Ba₂VTaO₆ and 8.08 Å for Ba₂Ni TaO₆. Moreover, the bulk modulus and its pressure derivative have been calculated. The elastic constants satisfy Born’s mechanical stability criteria, indicating that both compounds exhibit ductile behavior and elastic anisotropy. Notably, these oxides demonstrate half-metallic behavior, with a narrow band gap in the spin-down channel, as confirmed by band structure and density of states analyses. The calculated total magnetic moments are nearly integer values, around 2.00 and 1.00 µ_B per formula unit for Ba₂VTaO₆ and Ba₂Ni TaO₆, respectively. For Ba₂VTaO₆, the band gap values obtained using GGA, GGA + U, and EECE are 2.58 eV, 3.18 eV, and 3.29 eV, respectively. In the case of Ba₂Ni TaO₆, the corresponding values are 0.88 eV (GGA), 2.74 eV (GGA + U), and 2.95 eV (EECE). These results highlight the significant influence of the magnetic M³⁺ cation on both the magnetic moment and electronic transport, in contrast to the non-magnetic Ta⁵⁺ cation. Thermodynamic properties were also investigated over the temperature range of 0–1000 K using the quasi-harmonic Debye model, which remains valid across this range. Furthermore, thermoelectric properties such as the Seebeck coefficient, electrical conductivity, and thermal conductivity were evaluated using the BoltzTraP code between 200 and 800 K.