Insight into the structural, optoelectronic, elastic and thermodynamic properties of new lead free double halides perovskites Cs2XCuF6 (X = Sc, Y): a first principle study

We conducted a thorough investigation of Cs2XCuF6 (X = Sc, Y) using a first-principles approach, exploring a wide range of material properties. We began by confirming the structural and thermodynamic stability of these compounds, employing analyses such as formation energy calculations, examination of the phonon band structure, and the utilization of the Birch-Murnaghan equation of state (EOS) curve. A noteworthy finding was the tunability of the band gaps in these double perovskite materials, achieved by substituting Sc with Y, resulting in a band gap range from 2.67 to 2.62 eV. Our analysis extended to the mechanical stability of these compounds, characterized by elastic constants and revealing mechanical anisotropy and ductility. Additionally, we explored the optical properties, highlighting their broad absorption band from the infrared (IR) to visible regions, which holds significant promise for diverse optoelectronic applications. To provide a comprehensive understanding of these materials, we delved into their thermodynamic properties, encompassing thermal expansion coefficients (kappa), heat capacities, entropy (S), volume, and Debye Temperature (theta(D)). This investigation spanned a wide pressure range from 0 to 30 GPa and a temperature range from 0 to 1400 K, contributing to a holistic grasp of the fundamental characteristics of Cs2XCuF6 (X = Sc, Y).