A comprehensive analysis of the structural, phonon, electronic, mechanical, optical, and thermophysical properties of cubic Ca3SbX3 (X = Cl, Br): DFT - GGA and mBJ studies

Abstract

The current investigation employed first-principles calculation to assess the structural, phonon, mechanical, electronic, optical, thermodynamic, and thermoelectric properties of lead-free cubic Ca₃SbX₃ (X = Cl, Br). The dynamic stability of both compounds is assessed by analyzing the phonon dispersion spectrum. The distance between atoms is significantly reduced, leading to a large drop in the bond length, cell volume, and lattice constant of Ca₃SbX₃ (X = Cl, Br) compounds upon applying pressure. Ca₃SbCl₃ and Ca₃SbBr₃ compounds have direct bandgaps (Γ-Γ) of 2.57 and 2.27 eV via mBJ functional and 1.82 and 1.34 eV via GGA functional at 0 GPa pressure. Additionally, the bandgaps of Ca₃SbCl₃ and Ca₃SbBr₃ decrease to 1.65 eV and 1.45 eV, respectively, when accounting for the quantum effects of spin-orbit coupling (SOC). As the level of pressure rises to 30 GPa, Ca₃SbCl₃ and Ca₃SbBr₃ compound's band gaps reduce to 0.89 and 0.65 eV via mBJ functional and 0.27 and 0.12 via GGA functional. Increasing pressure is shown to reduce the effective mass, thereby enhancing the conductivity of both types of charge carriers. The reduced recombination rate signifies both compounds' greater absorption capabilities, making them more suitable for solar absorbers. The analysis of the mechanical properties indicates that as pressure increases, the elastic moduli rise, and the material transitions from being brittle to becoming more ductile. Additionally, both materials show a redshift of absorption and optical conductivity with improved dielectric constants at high pressure owing to the alteration in the bandgap, which is more appropriate for surgical instruments and solar absorbers. Thermodynamic properties show their temperature tolerance and appropriateness for high temperatures. Lastly, their thermoelectric property evaluation indicates high PF and near unity ZT, suggesting their use in thermoelectric devices.