First-principles investigation of non-toxic Sr2MAlO6 (M = Ta, Nb) perovskites: Electronic, optical, and magnetic characteristics

Abstract

Non-toxic double perovskites Sr₂MAlO₆ (M = Ta, Nb) are computationally investigated though density functional theory implemented using Wien2k package. Structural optimization was carried out employing the generalized gradient approximation (GGA) of Perdew- Burke- Ernzerhof (PBE) while the investigation of electronic properties was carried out with the modified Becke-Johnson mBJ potential for enhanced accuracy. Their elastic stability was validated by the evaluation of the calculated elastic constants, formation energy, and tolerance factor. Both materials are promising for ultraviolet UV optoelectronic devices, as the electronic band structure investigation revealed that Sr₂TaAlO₆ is a wide-bandgap insulator (4.82 eV) while Sr₂NbAlO₆ displays semiconducting behavior (3.65 eV). Optical studies reveal strong photon absorption and pronounced optical conductivity in the UV region with tailored energy thresholds and dielectric constants suitable for advanced optoelectronic devices. Using Monte Carlo simulations, we examined the critical responses of Sr₂NbAlO₆ and Sr₂TaAlO₆ under various magnetic fields in order to study their magnetic characteristics. The critical temperatures for Sr₂NbAlO₆ and Sr₂TaAlO₆ were determined to be 410 K and 330 K, respectively. Because of the heightened paramagnetic interactions from Nb 4d orbitals, Sr₂NbAlO₆ showed greater sensitivity to applied magnetic fields. Sharp thermodynamic changes were seen near Tc, where the application of magnetic fields greatly increased entropy variations and system responsiveness, according to specific heat capacity and susceptibility tests. Our findings highlight the viability of Sr₂MAlO₆ compounds in applications like UV detectors, anti-reflective coatings, and transparent optoelectronic technologies, paving the way for sustainable and eco-friendly materials in next-generation devices. These compounds' broad bandgaps, optical transparency, and stability in the presence of magnetic and thermal forces make them viable. They are also advantageous for green technology due to their non-toxic nature. Their phase stability at high temperatures and calculated optical absorption in the UV spectrum support their usefulness in UV optoelectronics, sensors, and spintronic devices.