Electronic, Optical and Thermoelectric Properties of Stable A₂LiIO₆ (A = Sr, Ba) Lead-Free Double Perovskites for Low-Cost Energy Applications

The new halogen-based non-toxic oxide double perovskites A₂BIO₆ compounds have attracted considerable research due to their excellent electronic, optical, and thermoelectric properties. To be part of this research interest, we have investigated A₂LiIO₆ (A = Sr, Ba) double perovskites for their structural, electronic, optical, and thermoelectric properties on the basis of first-principles calculations. Both compounds were found thermodynamically and dynamically stable from the values of Gibbs free energies and positive phonon frequencies. The structural stability of both the A₂LiIO₆ compounds was confirmed by optimum of tolerance factors. The Canband structure show direct band gaps with a value of 2.65 eV for Sr₂LiIO₆ and 2.08 eV for Ba₂LiIO₆ with modified Becke and Johnson potential. The absorption spectra for both double perovskites was found in the visible part of the electromagnetic spectrum. The reflectivity was predicted below 30%, and optical conductivity values were found high in the considered range. The observed figure of merit was 0.60 for Sr₂LiIO₆ and 0.61 for Ba₂LiIO₆ at 1000 K. Overall, the direct band gap nature, as well as excellent optical and thermoelectric properties, suggest the potential of A₂LiIO₆ double perovskites for low-cost energy technologies.