DFT study of the half-metallic variant perovskites A₂OsX₆ (A = Rb/Cs; X = Cl/Br) for spintronic and thermoelectric applications

We present our results of the spin-polarized calculations on the structural, magneto-electronic, thermodynamic, and thermoelectric properties of vacancy-ordered double perovskites A(2)OsX(6) (A = Rb/Cs; X = Cl/Br). We utilized the Wu-Cohen generalized gradient approximation (Wu-GGA) and the mBJ scheme to determine a more reliable electronic structure. The compounds exhibit negative formation energy, suitable tolerance factor, and a stable phonon spectrum, indicating their stability. The compounds show half-metallicity, acting as semiconductors with direct band gaps between 2 and 3 eV in the spin-up orientation while metallic in the spin-down. Each compound shows a total spin magnetic moment of 2.00 mu B per formula unit, with Os-t(2)g states contributing the most (similar to 1.5 mu B). The computed thermoelectric coefficient indicates the usability of these compounds across a wide temperature range (200-800 K) with high electrical conductivity and low electronic thermal conductivity. The compounds exhibit high Seebeck coefficient and figure of merit (ZT), making them suitable for thermoelectric applications. With ferromagnetic and half-metallic characteristics, these compounds could be promising candidates for spintronics, thermoelectronic, and data storage applications.