Comprehensive exploration of rare-earth chalcogenides: A DFT-based investigation into their optoelectronic, elastic, thermomechanical and magnetic properties for advanced functional and high-temperature applications

Abstract

Gd₂MgSe₄ and Tb₂MgSe₄, characterized by their stable cubic structures, mechanical stiffness reflecting their strong interatomic bonding and favorable formation energies, emerge as promising materials for applications in energy storage and optoelectronic devices such as light-emitting diodes (LEDs) and laser diodes. First-principles DFT calculations were employed within GGA and GGA + U approximations to investigate their structural, electronic, mechanical, elastic, thermodynamic, and optical properties. It was found that the FM state is energetically more stable than the NM state for both materials. Both compounds demonstrated direct bandgaps at the Γ point, with values of 1.05 eV (spin-up) and 1.37 eV (spin-down) for Gd₂MgSe₄, and 1.15 eV (spin-up) and 1.37 eV (spin-down) for Tb₂MgSe₄, respectively, suggesting their potential for infrared optoelectronic devices. Mechanical analysis revealed their mechanical stability, with moderate stiffness and brittle behavior. Thermodynamic calculations yielded Debye temperatures of 257.03 and 268.88 K for Tb₂MgSe₄ and Gd₂MgSe_4, respectively, indicative of relatively low thermal conductivity, a desirable property for thermoelectric applications. Optical properties analysis, encompassing absorption coefficient, refractive index, and dielectric function, revealed strong absorption in the visible to near-infrared region. The observed spectral peaks attributed to interband transitions further solidify these compounds as promising candidates for optoelectronic applications, including photovoltaic cells, photodetectors, and light-emitting diodes.