Tailoring optoelectronic and mechanical properties in Sr₂XNaY₆ perovskites: A first-principles roadmap for energy technologies

Double perovskites, with their structural flexibility and tunable properties, hold transformative potential for opto-electronics and energy technologies. Here, we computationally explore Sr 2 XNaY 6 (X [Formula: see text] Ag, Cu and Y [Formula: see text] Br, Cl) perovskites, combining density functional theory (DFT) and ab initio molecular dynamics (AIMDs) to unravel their stability, opto-electronic behavior, and functional performance. These compounds crystallize in a cubic Fm3[Formula: see text] lattice stabilized by rock-salt cation ordering, exhibiting negative formation energies ([Formula: see text] to [Formula: see text] [Formula: see text]eV/atom) and robust thermal stability at 300[Formula: see text]K. Composition-driven lattice contraction (Ag[Formula: see text]Cu, Br[Formula: see text]Cl) enables precise modulation of direct bandgaps (0.33–2.24[Formula: see text]eV), governed by transition metal-halide orbital hybridization. Optical spectra reveal strong UV absorption ([Formula: see text]4[Formula: see text]eV) and composition-dependent refractive index (0.17–0.20), while mechanical analyses highlight high bulk moduli (27–38[Formula: see text]GPa) and anisotropic elasticity. The interplay of ionic-covalent bonding and brittle fracture mechanics underscores their adaptability for high-stress environments. This work establishes Sr 2 XNaY 6 as a versatile platform for next-generation photo-voltaic, quantum devices, and resilient functional materials, bridging computational design with actionable material innovation.