Single-source facile synthesis of phase pure Na⁺- and Sr²⁺-modified Bismuth titanate—structural, optical and electrical properties for energy storage application

In this study, sodium- and strontium-modified bismuth titanate—Bi_0.5Sr_0.5TiO₃ and Bi_0.5Na_0.5TiO₃ (BNT and BST)—have been prepared via the autocombustion technique. Fuels (C₆H₈O₇ and C₂H₅NO₂) were added in an optimized ratio of 1.5:1 during preparation. The samples were characterized using X-ray diffractometer (XRD), energy dispersive (EDX) spectroscopy, UV–visible absorbance and FT-IR spectroscopy. The electrical behaviour of the samples calcinated at 950℃ was studied using an LCR meter. The synthesized samples presented a perovskite structure with an average crystallite size in the range of 10–25 nm. This variation in crystallite size may be due to the difference in ionic radii of Na and Sr. The lattice constant and volume of the unit cell increased with an increase in crystallite size. Furthermore, the Williamson Hall graph was plotted by utilizing XRD data. The EDX studies revealed that pure Na⁺ and Sr²⁺ incorporated with bismuth titanate were prepared without any trace of impurities. The optical properties were subsequently determined, capturing a sharp absorbance peak at a wavelength of 339.5 nm for BNT and 345.9 nm for BST. Tauc’s relation was adopted to measure the energy bandgap (E_g): 2.5eV and 2.00eV for Na- and Sr-doped bismuth titanate. The absorption band observed at 420cm^-1 to 720cm^-1 in FT-IR studies represented the presence of the Ti-O bond and confirmed the structure. To perform electrical characterization, the powder samples were transformed into pellets by applying a pressure of 3 tonnes and sintering at 1000℃ for 3 hours. The dielectric constant (Ꜫ_r) and the tangent loss (δ) of the prepared pellet samples were found to increase at higher frequency. The ac conductivity (σ) of both the BNT and BST samples was also measured. Through the realization of structural, optical and electrical efficiency, the optimized samples demonstrate potential for application in energy storage devices.