Magnetic, half-metallicity, electronic, elastic, and thermodynamic studies of new lead-free halide double perovskites Cs2GdAuCl6: Ab-initio analysis

We explore the structural, electronic, magnetic, optical, elastic, and thermodynamic properties of lead-free double perovskite Cs₂GdAuCl₆ using density functional theory (DFT). The material crystallizes in a cubic phase (Fm-3m) with a formation energy of −1.82 eV/atom. It exhibits half-metallicity, with a 1.7 eV band gap in the spin-down channel and metallic behavior in the spin-up direction. A total magnetic moment of 7 μB per formula unit is obtained, mainly due to the Gd atom with a ferromagnetic order. The optical analysis yields a static dielectric constant of ε₁(0) = 3.32 and a refractive index of n(0) = 1.82, making the compound suitable for optoelectronic applications. Elastic constants C₁₁ = 52.10 GPa, C₁₂ = 27.46 GPa, and C₄₄ = 9.67 GPa confirm mechanical stability, with a B/G ratio of 2.43, indicating ductile behavior, and a Zener anisotropy factor of 0.79, highlighting moderate elastic anisotropy. Thermodynamic properties calculated using the quasi-harmonic Debye model shows that at 300 K, the specific heats are C_v = 244.2 J/mol·K and C_p = 258.1 J/mol·K, demonstrating good thermal stability.