Structural, elastic, electronic, optical and thermoelectric response of lead-free double perovskite Rb2TlInX6 (X=Cl, I) for energy storage devices: DFT+SOC investigations

Abstract

Double perovskites Rb2TlInX6 (X = Cl, I) have been simulated with the help of density functional theory to determine their structural, elastic, electronic, optical and thermal properties. The full-potential linearized augmented plane wave (FP-LAPW) method is used through the WIEN2K code. Exchange-correlation potential is described by using the well-organized modified Becke-Johnson (mBJ) with the combination of spin-orbit coupling (SOC). Structural optimization and formation energy calculations justify the stability of both compounds. The elastic parameters are calculated to measure the mechanical stuff, such as shear modulus (G), Poisson ratio (ν) and anisotropic factor (A). The studied compounds showing semiconductor nature with a bandgap of 3.51eV and 3.47eV for Rb2TlInCl6 and 1.43eV and 1.40eV for Rb2TlInI6 with mBJ and mBJ+SOC potentials, respectively. The density of states also exposes the bandgap and semiconductor nature of the materials. The optical properties of the compounds have been examined in terms of the dielectric function, refractive index, absorption, reflection, and energy loss. We also investigated the temperature-dependent transport parameters for both compounds. High electrical and low thermal conductivity with good ZT values for both materials make them potential candidates for thermoelectric applications.