Exploring the Optoelectronic and Thermoelectric Potential of Tl ₂ LiScX ₆ (X = Cl, Br, I) Double Perovskites Using First‐Principles Methods

This study presents a comprehensive first‐principles investigation of the structural, electronic, elastic, mechanical, optical, and thermoelectric properties of Tl 2 LiScX 6 (X = Cl, Br, I) double perovskites using density functional theory. The compounds crystallize in a stable cubic Fm3m phase, with Goldschmidt tolerance factors ranging from 0.93 to 0.97, and negative formation energies confirming their structural and thermodynamic stability. Halogen substitution (Cl → I) induces a systematic increase in lattice parameters (19.17–22.00 a.u.) and a reduction in direct bandgaps (3.85 eV → 1.99 eV), positioning Tl 2 LiScX 6 (X = Cl, Br, I) as promising candidates for ultraviolet‐to‐visible optoelectronic applications. Mechanical property analysis reveals ductile behavior and anisotropic elasticity, while optical properties demonstrate strong ultraviolet absorption and tunable dielectric responses, with Tl 2 LiScI 6 exhibiting the highest refractive index (2.18). Thermoelectric calculations predict high figures of merit (ZT > 0.8) across 100–1000 K, driven by favorable Seebeck coefficients and electrical conductivities (10 15 –10 18 (Ωm) −1 ). The synergistic optoelectronic performance of Tl 2 LiScX 6 (X = Cl, Br, I) underscores their potential for sustainable technologies, including ultraviolet optoelectronics and waste heat recovery systems. This work advances the design of perovskite materials by elucidating the structure–property relationships in this novel class of materials.