First-principles study of structural, electronic, optical, and thermoelectric properties of BaXSe2 (X = Fe, Co, and Ni) for optoelectronic devices

This study investigates the structural, electrical, optical, and thermoelectric properties of BaXSe2 (X = Fe, Co, Ni) using DFT within the WIEN2K software package. The results reveal that these compounds exhibit semiconductor behavior, significantly contributing to the density of states near the Fermi level primarily from Fe, Co, and Ni atoms, which strongly hybridize with Se and Ba atoms. The compounds display distinct spin-dependent electronic properties, highlighting their potential for spintronic applications. Among the alloys, BaFeSe2 exhibits the most prominent optical response, with a sharp peak in the refractive index and extinction coefficient within the visible energy range, indicating its suitability for optoelectronic devices. For electronic band structure and thermal characteristics, the mBJ potential is employed, while the density of state analysis is used to determine the contributions and polarization of electronic states. The compounds exhibit unsymmetrical behavior of majority charge carriers in spin up and down, and Fe, Co, and Ni atoms contribute most in the vicinity of the Fermi level having strong hybridization with Se and Ba atoms. These alloys show semiconductor characteristics, with BaFeSe2 having the largest peak on the optical properties graph. The optical properties graph shows that BaFeSe2 has the highest peak at 1 eV and that all compounds exhibit a comparable pattern as they move towards greater energies. The negative value in the real part indicates that electromagnetic radiation is partially reflected from the surface of the material. The extinction coefficient of BaFeSe2 and BaCoSe2 have sharp peaks in the visible energy range. The refractive index of BaXSe2 (X = Fe, Co, Ni) is higher than 1 due to the interplay of electrons within the substance slowing down photons. The refractive indices show distinct peaks at 0.1 eV, 0.2 eV, and 0.3 eV for BaFeSe2, BaCoSe2, and BaNiSe2, respectively, followed by a gradual decline at higher energies. In terms of thermoelectric properties, BaXSe2 alloys demonstrate excellent potential with significant Seebeck coefficients, low thermal conductivity, and high figures of merit (ZT), suggesting their suitability for efficient thermoelectric applications. The rapid response to charge mobility, combined with favorable magnetic and thermal properties, further underscores the versatility of these materials for advanced energy conversion and spintronic technologies.