First-principles prediction of the ground-state crystal structure of double-perovskite halides Cs2AgCrX6 (X = Cl, Br, and I)

Cesium halide double-perovskites (Cs2AgCrX6; X = Cl, Br, and I) have been investigated for potential applications in optoelectronic devices. Density functional theory (DFT) has been utilized to study the structural, chemical bonding, electronic, mechanical, optical, and thermoelectric properties of these materials. Structural analysis has revealed that these compounds favor a face-centered cubic double-perovskite crystal structure with space group Fm-3m. The electronic properties show that Cs2AgCrX6 (X = Cl, Br) are indirect whereas Cs2AgCrI6 is a direct band-gap semiconductor, and their band-gap values are 2.81, 2.1, and 0.9 eV, respectively. The bonding nature between Ag-X and Cr-X atoms is covalent, while ionic bonds exist between Cs-X atoms. The systems are good dielectric materials and have the potential to be used in optoelectronic devices. Post-DFT calculations have been performed to calculate thermoelectric parameters. The increase of the Seebeck coefficient in these materials with temperature up to 400 K satisfies the Mott formula. Above this temperature, thermal excitations of extrinsic carriers decrease the Seebeck coefficient. The mechanical properties of these compounds indicate that they are ductile and anisotropic. •Double-perovskite halides Cs2AgCrX6 (X = Cl, Br, I) favor a face-centered cubic crystal structure with space group Fm-3m.•They are good dielectric materials and show interesting variations in their optical properties.•Spin-orbit coupling calculations predict a reduction in the band-gaps of these perovskites.•Mechanically, the crystals of these compounds are ductile and anisotropic.