First-principles investigations of the mechanically and thermodynamically stable potassium-based double perovskites K2TlAsX6 (X = Cl, Br) for optoelectronic and renewable applications

Abstract

Double perovskites with their significance properties are considered to be promising candidates for an extensive range of applications. Current research work includes the theoretical analysis of the physical characteristics of K2TlAsX6 (X = Cl, Br) double perovskites under the framework of DFT. The precise band structure calculations have been done using modified Becke-Johnson (mBJ) with the inclusion of spin–orbit coupling (SOC) effect. Negative formation energies, structural optimization, positive phonon frequencies and tolerance and octahedral factors support the stability of the perovskites. Elastic parameters, including anisotropic factor, Pugh's and Poisson's ratios, and Cauchy pressure, are calculated to quantify mechanical characteristics. A direct band gap is obtained in both perovskites possessing the values of 2.22 eV and 1.59 eV for K2TlAsCl6 and 1.97 eV and 1.51 eV for K2TlAsBr6 with mBJ and mBJ + SOC, respectively. The compound's optical response is scrutinized, showing the absorption in visible and UV regions. The transport characteristics are also evaluated, showing their high electrical conductivity and ZT values and simultaneously small thermal conductivity values for both perovskites. The optical and transport properties reveal the capacity of K2TlAsCl6 and K2TlAsBr6 to be used in optoelectronic and green energy applications.