Abstract:
In this study, the effects of sulfur substitution on the structural, mechanical, electronic, optical, and thermodynamic properties of ATaO3-xSx have been investigated using the WIEN2k code in the framework of Density Functional Theory (DFT). The cubic phase of ATaO3 (A= K, Rb and Cs) transforms to tetragonal for ATaO2S and ATaOS2, the latter transforms again to a cubic phase with added sulfur for ATaS3. The results indicated a notable reduction in the band gap upon substituting S for O anions in ATaO3. Specifically, KTaO3 exhibited a band gap of 3.57 eV, which subsequently decreased to 1.808 eV, 0.264 eV, and 0.078 eV for KTaO2S, KTaOS2, and KTaS3, respectively. Similarly, RbTaO3 exhabit a reduction in its band gap from 2.717 eV to 1.438 eV, 0.286 eV, and 0.103 eV for RbTaO2S, RbTaOS2, and RbTaS3 compounds. CsTaO3 had an initial band gap of 3.076 eV, which decreased to 0.909 eV, 0.376 eV, and 0.143 eV for CsTaO2S, CsTaOS2, and CsTaS3 compounds, respectively. Furthermore, these compounds have displayed promising optical characteristics characterized by high absorption coefficients (∼106 cm−1), minimal reflectivity (<30%), and robust optical conductivity within the visible spectrum, making them ideal candidates for a range of optoelectronic technologies. Our comprehensive investigation has reinforced the stability of all computed phases, showcasing exceptional electronic, mechanical, and optical properties, including semiconducting behavior, ductility, anisotropy, high absorptivity, and low reflectivity. The altered band gap and optical features observed in KTaO2S and RbTaO2S suggest significant potential for their utilization in solar cells, offering promising prospects for enhancing solar energy conversion efficiency. Additionally, the elevated lattice thermal conductivity observed in KTaO3, RbTaO3, and CsTaO3 indicates their potential as promising candidates for heat sink materials.
