DFT Insights Into K ₂ SnBr ₆ and Rb ₂ SnBr ₆ Double Perovskites: Unravelling Their Thermoelectric Potential

This work presents an investigation on the physical properties of the X 2 SnBr 6 (X = K and Rb) double perovskites, using WIEN2k computational code, density functional theory (DFT) approach, full potential linearized augmented plane wave method (FP‐LAPW) method. The total energy of K 2 SnBr 6 and Rb 2 SnBr 6 double perovskites compound was calculated as a function of volume, with the lattice constants being 10.83Å and 11.01 Å for K 2 SnBr 6 and Rb 2 SnBr 6 , respectively. The Goldschmidt's tolerance factor was 0.991 and 0.934 for K 2 SnBr 6 and Rb 2 SnBr 6 , indicating structural stability. The results show that the material has a direct band gap semiconductor at (Γ‐Γ) symmetry points. The energy band gaps were calculated 2.37 and 2.25 eV for K 2 SnBr 6 and Rb 2 SnBr 6 , respectively. The reduction in band gap indicates enhancement in electrical applications. Thermoelectric properties were also studied, with K 2 SnBr 6 having the largest thermal, electrical, and power factors values at room temperature 300 K. Rb 2 SnBr 6 and K 2 SnBr 6 compound had a negative Seebeck coefficient in the 200 to 600 K range. Overall, K 2 SnBr 6 has better bulk modulus, pressure derivative modulus, and Goldschmidt's tolerance factors, which align with trends in various applications of this it.