A DFT study of physical properties of double perovskites Cs2XSnCl6 (X = Ca or Mg)

Abstract

This work investigates the physical properties of double perovskite systems Cs₂XSnCl₆ (X = Ca or Mg) using density functional theory (DFT), focusing on their structural, mechanical, optoelectronic, and thermoelectric characteristics. These materials crystallize in cubic structures, with lattice constants of 10.71 Å and 10.42 Å for Cs₂CaSnCl₆ and Cs₂MgSnCl₆, respectively. Mechanical stability assessments confirm that both materials are stable in the cubic phase. Furthermore, mechanical stress analysis clearly demonstrates that both compounds are mechanically stable and exhibit anisotropy. However, Cs₂CaSnCl₆ exhibits ductile behavior, whereas Cs₂MgSnCl₆ is brittle. The computed band gaps are 4.23 eV for Cs₂CaSnCl₆ and 3.40 eV for Cs₂MgSnCl₆, indicating their potential as wide-bandgap materials. Optical analysis reveals strong ultraviolet absorption, positioning these materials as promising candidates for UV-sensitive optoelectronic applications. Additionally, thermoelectric evaluations at room temperature show high Seebeck coefficients, enhanced electrical conductivity, and reduced electronic thermal conductivity. The dimensionless figures of merit (ZT) are 0.77 and 0.72 for Cs₂CaSnCl₆ and Cs₂MgSnCl₆, respectively, highlighting their suitability for thermoelectric device applications.