Lead-free double perovskites are attracting attention as sustainable alternatives to toxic lead-based halides for next-generation optoelectronics. In this work, we employed density functional theory (DFT) with PBE-GGA using the CASTEP framework to investigate the structural, electronic, optical and mechanical properties of K 2 SbAuF 6 and K 2 SbAuCl 6 . Both compounds exhibit stable cubic structures with tolerance factors of 0.92 (F) and 0.878 (Cl). The calculated band gaps are 0.655Formula: see texteV for K 2 SbAuF 6 and 0.20Formula: see texteV for K 2 SbAuCl 6 , confirming semiconducting behavior with tunable electronic properties. Optical analyses reveal strong absorption across the ultraviolet–visible (UV–Vis) region; K 2 SbAuCl 6 displays superior optical conductivity (3.60Formula: see textFormula: see textcmFormula: see text at 7.45–10.65Formula: see texteV), while K 2 SbAuF 6 shows enhanced response in the high-energy UV range with conductivity up to 4.44Formula: see textFormula: see textcmFormula: see text at 19.09–24.45Formula: see texteV. Mechanical evaluations confirm elastic stability, with K 2 SbAuF 6 exhibiting greater ductility (Formula: see text) and anisotropy (Formula: see text), whereas K 2 SbAuCl 6 demonstrates higher stiffness (Formula: see textFormula: see textGPa) and shear resistance. These results highlight halide substitution as an effective strategy to tailor optoelectronic properties, positioning K 2 SbAuX 6 (XFormula: see textF, Cl) as promising lead-free candidates for photovoltaic, photonic and spintronic applications.
Rahman et al. (Mon,) studied this question.