Electronic, structure, mechanical, optical and thermodynamic properties of double perovskite oxides X2ZrTeO6 (X =Cs, Rb, K): A first-principles study

Double perovskite compounds remain a central focus in materials research. We investigate the physical properties of X₂ZrTeO₆ (X = Cs, Rb, K) using first-principles calculations. Our results demonstrate the absence of imaginary frequencies in their phonon spectra, which satisfies the Born-Huang stability criteria and confirms their robust thermodynamic and kinetic stability. Mechanical stability is further verified through elastic constant analysis, with all compounds meeting the criteria: C₁₁ > 0, C₄₄ > 0, C₁₁-C₁₂ > 0, and C₁₁ + 2C₁₂ > 0. Electronic structure calculations reveal indirect bandgap semiconducting behavior, with HSE06-corrected band gaps of 3.002 eV (Cs), 3.550 eV (Rb), and 3.877 eV (K). Density of states analysis identifies O-p and Zr-d orbitals dominating the valence band maximum and O-p and Te-s states constituting the conduction band minimum, highlighting their role in charge transport. To assess the potential for optoelectronic applications, we calculate key optical properties, including dielectric functions, optical conductivity exceeding 8000 S cm⁻¹ in the UV range. Thermodynamic studies indicate that the heat capacity approaches the Dulong-Petit limit near 800 K, consistent with high-temperature stability. The combination of stability, tunable bandgap, and strong UV absorption (peak at 5–15 eV) suggests promise for ultraviolet optoelectronic applications.