Theoretical analysis of double perovskite Ca₂GdMO₆ (M = As, Te) for spintronics and optical applications using density functional theory

In this study, the density functional theory (DFT) analysis of Ca₂GdMO₆ (M = As, Te) double perovskites highlights their potential for next-generation multifunctional applications. Both compounds crystallize in a stable cubic phase. Ca₂GdTeO₆ is found to be paramagnetic, whereas Ca₂GdAsO₆ exhibits a ferromagnetic ground state, attributed to the electronic contribution of the As atom influencing spin alignment within the structure. Electronic structure calculations using the TB-mBJ potential reveal that Ca₂GdTeO₆ possesses a direct bandgap of 2.12 eV, while Ca₂GdAsO₆ exhibits a wider direct bandgap of 3.32 eV, indicating stronger ionic interactions in the latter. The optical absorption spectra show pronounced peaks in the ultraviolet region, around 3.75 eV for Ca₂GdTeO₆ and 4.15 eV for Ca₂GdAsO₆, suggesting their suitability for UV photonic and optoelectronic devices. Mechanical analysis confirms their structural robustness, with calculated bulk moduli of 112.18 GPa for Ca₂GdTeO₆ and 143.24 GPa for Ca₂GdAsO₆, indicating good mechanical stability under external stress. Magnetically, both compounds exhibit significant total magnetic moments of approximately 7.0 μB per Gd atom, stemming from the localized Gd-4f electrons. The application of a Hubbard U parameter of 6 eV ensures accurate treatment of strong electron correlations. Thermoelectric performance, evaluated via the Boltzmann transport theory, indicates a promising figure of merit (ZT) of 0.82 for Ca₂GdTeO₆ at 800 K. For Ca₂GdAsO₆, the calculated ZT reaches 0.67, demonstrating its potential as a viable thermoelectric material despite the wider bandgap.