A first-principles study of electronic, optical and thermoelectric properties of TlXF₃ (X: Zn, Sr) perovskite crystal structure

Abstract

Abstract This study communicates the structural, electronic, optical, and thermoelectric properties of a perovskite TlXF 3 (X: Zn, Sr) crystal structure using first-principles calculations. Both compounds were found structurally as well as thermodynamically stable in cubic phase. To check the kinetic stability, the phonon frequancy band structure is calculated which indicates that there is no negative frequency in the phonon spectrum, which confirms the dynamic stability of TlXF 3 . The bandgaps of both compounds belong to insulating region. The TlSrF 3 exhibits direct bandgap of 4.37 eV at X symmetry point while TlZnF 3 possess indirect bandgap of 3.95 eV (M-X). Using HSE functional, the calculated electronic bandgaps of TlSrF 3 and TlZnF 3 are 5.74 eV(X-X) and 5.36 eV (M-X), respectively. The analysis of electronic states in band structure shows that for TlSrF 3 , the top of valence band is composed of the F- p states whereas the states in lower potion of conduction band are impacted by the significant contribution of Tl- p orbital states. In case of TlZnF 3 , the states near the valence band maxima and conduction band minima are coming mainly form Tl atom. The effect of spin–orbit coupling (SOC) on the electronic band structure is also considered. The SOC in the valance band is negligible, while in the conduction band it shows a dominant effect at Γ-point in both TlSrF 3 and TlZnF 3 compounds. The dependence of thermoelectric properties such as electrical conductivity σ , Seebeck coefficient (S), Power factor (PF), electronic thermal conductivity ( κ ) and figure-of-merit (ZT) as a function of carrier concentration and temperature are investigated. The optical properties were also studied to understand the response of TlXF 3 to incident photons of energies upto 14 eV. We conclude that the TlXF 3 are promising candidates for electronic, thermoelectric and optoelectronic devices.