Bandgap engineering of BaTi(O$$_{1-\text{x}}$$S$$_\text{x}$$)$$₃$$ as a function of sulfur concentration

In the present work the synthesis and characterization of BaTi(O $$_{1- ext{x}}$$ S $$_ ext{x}$$ ) $$₃$$ chalcogenide system is presented. The sample was synthesized by annealing in a tubular quartz furnace through high-temperature sulfurization processes, using powdered barium titanate as the precursor and under a reactive atmosphere $$hbox {CS}_{{2}}$$ . After the synthesis process, the elemental composition of the obtained samples was determined by energy-dispersed X-ray fluorescence, finding a maximum concentration of 23.9% sulfur. XRD obtained the crystalline characteristics of the samples. The samples are crystalline with a hexagonal perovskite structure. Finally, using diffuse reflectance UV–Vis spectroscopy in the range of 200–800 nm, samples exhibiting more than 20% of sulfur showed a very low reflectance (<0.04), which leads to a high absorption coefficient that exceeds 10 $$⁵$$ $$hbox {cm}^-1$$ in the ultraviolet region. And it is greater than 10 $$⁴$$ $$hbox {cm}^-1$$ , for the rest of the measured spectral range. Furthermore, using the Tauc procedure, it was possible to determine the bandgap for the samples. BaTi( $$hbox {O}_{1- ext{x}}$$ $$hbox {S}_{ ext{x}}$$ ) $$₃$$ has a direct bandgap and the value is gradually reduced to lower energies as a function of sulfur concentration.