Computational study of novel scandium and lithium perovskites based materials for sustainable energy devices

The current first-principles density functional theory (DFT) study explores how anionic affects substitution structural, electronic, thermodynamic, mechanical, and optical features of lead-free halide-based double perovskite K₂ScLiX₆ (X = F, Cl). Both materials are crystallized in a stable cubic structure that has lattice constants of 8.29 Å (X = F) (and 10.13 Å (X = Cl), both confirmed by tolerance factors of 0.97 and 0.93 and negative formation energies. Direct band gaps of 6.34 eV and 3.78 eV are reported as calculated by the electronic structure of K₂ScLiF₆ and K₂ScLiCl₆, respectively. Mechanically, fluoride material is stiffer and ductile (B = 41.41 GPa, E = 57.77 GPa, B/G = 1.82), while the chloride is softer and brittle (B = 21.28 GPa, E = 33.32 GPa, B/G = 1.58). Thermally, K₂ScLiF₆ displays superior stability (=389 K, Tm = 913 K), whereas K₂ScLiCl₆’s lower Debye temperature (θ_D = 270 K) suggests low thermal conductivity. The K₂ScLiX₆ (X = F, Cl) compounds are ideal for devices requiring high power and high voltage capabilities due to their ability to withstand higher energy levels without breaking down. The diverse optical responses, including high UV absorption and a strong plasmon peak at 16.40 eV for the chloride, designate K₂ScLiF₆ for deep-UV applications and K₂ScLiCl₆ for UV shielding and thermoelectric.