Study on the effect of Bi dopant on the structural and optical properties of BaTiO₃ nanoceramics synthesized via sol-gel method

In this study the preparation of pure and Bismuth (Bi) doped barium titanate (BaTiO₃) nanoceramics by sol-gel process is reported. The structural and optical properties of the samples were investigated using X-ray diffraction (XRD) and UV-visible spectroscopy. XRD results show that the samples are crystallized in the pure perovskite structure when calcined at relatively low temperature (800 C) for 3 h, without the presence of secondary phases. Both Bi doping (1%, 2%) decrease the lattice parameters, tetragonality and the crystallite size. The decrease of their sizes can be explained by the replacement of large ionic radii of Ba²⁺ (1.35Å) ion by smaller ionic radii Bi³⁺ (1.03 Å) ion. A close investigation of the results shows that BT is a tetragonal-phase ferroelectric. The band gap of the Bi-doped BaTiO₃ nanopowders is lower compared to that of pure BaTiO₃, as determined from the analysis of UV absorbance spectra.