Exploring the electronic structure, mechanical, optical, and thermoelectric performance of A₂LaAuCl₆ (A = K, Rb, Cs) via FP-LAPW + lo calculations

Utilizing the full potential linearized augmented plane wave and local orbitals (FP-LAPW + lo), the structure, electronics, optical, elastic as well as transport characteristics of A₂LaAuCl₆ (A = K, Rb or Cs) were computed by using density functional theory (DFT). The electronic band structure of the Halide double perovskites (HDPs) A₂LaAuCl₆ (A = K, Rb, or Cs) suggested the presence of indirect and wide band gaps in these compounds. The energy band gaps of such material decreased by replacing the cations from K to Rb to Cs (3.046 eV, 3.019 eV, and 2.912 eV). Strong p-d hybridization is observed in the compounds. Due to its wide bandgap nature, the compounds reveal prominent optical structures in the UV energy range. A₂LaAuCl₆ (A = K/Rb/Cs) compounds have an elastically anisotropic nature, as indicated by their estimated shear anisotropy values of 0.26, 0.61, and 0.31, correspondingly. The compounds appear to be inherently ductile based on their estimated Poisson ratios of 0.37, 0.32, and 0.37. P-type conduction is shown by the Seebeck coefficient values for A₂LaAuCl₆ (A = K/Rb/Cs), the estimated Seebeck coefficient at 800 K, which are 148 µV/K, 152 µV/K, and 141 µV/K, correspondingly. ZT values for such A₂LaAuCl₆ (A = K/Rb/Cs) compounds are (0.53, 0.54, and 0.47) at the 800 K temperature. The results of the computations serve as the basis for providing new data on A₂LaAuCl₆ (A = K/Rb/Cs) and have practical relevance for high-frequency devices.