First-principles insights into the optoelectronic and thermoelectric properties of X3NbY4(X= Cu, Ag, Au; Y=S, Se, Te) sulvanite compounds for energy applications

Abstract

The structural, electronic, optical and transport properties of X3NbY4(X= Cu, Ag, Au; Y=S, Se, Te) sulvanite chalcogenides materials have been investigated using the Full Potential Linear Augmented Plane wave (FP-LAPW) within the density functional theory (DFT). The calculated structural information of X3NbY4 compounds is consistent with reported results of the same family compounds. The electronic band diagram exhibit indirect type band structures with bandgap value in the range of Eg 1.65- 0.50 eV using PBE-GGA functional and 1.80 eV-1.18 eV using TB-mBJ functional which indicates that these are semiconductor materials. The density of states (DOS) shows that the amount of bandgap decreases owing to move of valence band maximum (VBM) to the high energy level whereas the conduction band minimum (CBM) to the low energy level owing to the replacement of S-S-Te and Cu-Ag-Au atoms. The hybridized orbital by X-d, Nb-d and Y-p atomic orbitals dominate the VBM while hybridized by Nb-d and Y-p atomic orbitals mainly contribute the CBM. The elastic calculations exhibit that Cu-based materials have brittleness nature whereas Ag- and Au-based compounds are ductile nature. Furthermore, the phonon dispersion curves probes that these X3NbY4 compounds are dynamically stable. However, the calculated optical properties: dielectric function, absorption coefficient, refractive index, and energy loss function; specifically, the higher value of absorption coefficient (105 cm-1) indicates that these materials are attractive candidates in optoelectronics applications. Finally, thermoelectric parameters such as Seebeck coefficient, thermal conductivity, electrical conductivity, power factor (P.F) and ZT value of these compounds have also been investigated. Overall, the finding explores that these materials are potential candidates for the applications in optoelectronic and thermoelectric devices.