Investigation of Pressure-Dependent Electronic and Optical Properties of Double Perovskites Cs2AgXY6 (X = Bi, In; Y = Cl, Br).

The electronic, optical and structural properties of Cs2AgXY6 (X = Bi, In; Y = Cl, Br), were investigated under external pressure (0–50 GPa) using the full potential density functional theory. In this study, the Tran–Blaha modified Becke–Johnson (TB-mBJ) functional was used to evaluate the electronic and optical properties of the double perovskites, and the GGA-PBEsol functional was used to examine the structural properties. The formation energy and tolerance factor predict the stability of these compounds. With increasing pressure, the lattice parameters and unit cell volume of these compounds decreased, resulting in a reduction in the bond length between the cations and anions. Comparatively Cs2AgInCl6 has shown a low compressibility. At zero pressure, Cs2AgInBr6 and Cs2AgInCl6 exhibit direct band gap while Cs2AgBiBr6 and Cs2AgBiCl6 has indirect band gap. Band gaps decrease with pressure. High pressure decreases peak height, shifts energy lower, and widens bandwidth in density of states. The density of states plots at zero pressure showed mixed ionic and covalent bonds, and with increasing pressure, a strengthening of covalent bonds is observed. Reflectivity/optical conductivity spectra show redshifts (Cs2AgBiBr6, Cs2AgBiCl6) and blueshifts (Cs2AgInBr6, Cs2AgInCl6). This study provides insights into double perovskite behavior under pressure, aiding material design. Additionally, our work highlights the variations in energy band gap and band structure is dependent on the choice of functional utilized. [ABSTRACT FROM AUTHOR]