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 ($${\theta}_{D}$$=389 K, Tm = 913 K), whereas K2ScLiCl6’s lower Debye temperature (θD = 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.