Investigating the Structural, Electronic, Optical, and Thermoelectric Properties of TlXO₃ (X = Nb, Ta) for Low-Cost Energy Applications

This study explores the structural, electronic, elastic, optical, and thermoelectric properties of two novel oxide perovskites, TlNbO3 and TlTaO3, using density functional theory with the generalized gradient approximation and modified Becke–Johnson potential to accurately capture exchange–correlation effects. Our analysis confirms the thermodynamic stability of both compounds through assessments of cohesive energy, formation enthalpy, and phonon dispersion, indicating their cubic and dynamic stability. The band structure reveals that TlNbO3 has a direct band gap of 0.17 eV, while TlTaO3 exhibits a wider gap of 1.52 eV, confirming their semiconductor behavior. Elastic property calculations indicate that TlNbO3 is brittle and TlTaO3 is more ductile, with both materials demonstrating elastic anisotropy and a mix of metallic and covalent bonding. The density of states analysis highlights significant contributions from Tl, O, and Nb/Ta in the valence and conduction bands, emphasizing their potential in optoelectronic applications. Optical analyses further reveal high refractive indices and favorable dielectric properties, supporting their use in devices. Additionally, thermoelectric evaluations show a κ/σ ratio on the order of 10-5, indicating low thermal conductivity alongside significant electrical conductivity. Notably, TlTaO3 demonstrates substantial power factor values, positioning it as a promising candidate for thermal applications and energy conversion systems. Overall, this comprehensive investigation underscores the potential of TlNbO3 and TlTaO3 for advanced technological applications.