Exploring the mechanical, dynamical, and thermal stability of Cs₂AgBiX₆ (X = Br, Cl) for optoelectronic and...

This study investigates the mechanical, dynamical, and thermodynamic properties of Cs₂AgBiX₆(X = Br, Cl) using first-principles calculations. Structural analysis confirms the cubic double perovskite arrangement, with Cs₂AgBiCl₆ exhibiting a more compact lattice due to the smaller ionic radius of Cl⁻ compared to Br⁻. Mechanical stability is assessed through elastic constants and Born criteria, confirming the robustness of both compounds, with Cs₂AgBiCl₆ demonstrating higher stiffness and resistance to deformation. Phonon dispersion calculations reveal no imaginary frequencies, verifying their dynamical stability. Thermodynamic analysis explores heat capacity, entropy, Debye temperature, and thermal expansion behavior under varying temperatures and pressures. The results indicate that Cs₂AgBiCl₆ possesses superior mechanical and thermal stability.