Influence of Sr²⁺ ion content on the structural and electrical properties of Ba_1-xSr_xTiO₃ nanopowders

Barium Strontium Titanate (Ba_1-xSr_xTiO₃, BST) nanopowders with different compositional ratios of Ba/Sr have been successfully synthesized using the sol–gel method. With an increase in Sr²⁺ ion concentration from x = 0.0 to x = 0.8, a reduction in crystallite size from 28 to 21 nm was observed. A phase transition of the sample from tetragonal to cubic structure occurred with an increase in the stoichiometric ratio from x = 0.2 to x = 0.5. The scanning electron micrographs of all the samples confirmed the formation of spherical nanoparticles. The room temperature dielectric constants at 1 kHz of the prepared BST samples with x = 0.0, 0.2, 0.5, and 0.8 were found to be 1080, 1275, 1038, and 740, respectively. The decrease in the dielectric constant with the increase in the Sr²⁺ ion concentration is attributed to the phase transition from tetragonal to cubic phase. The shift in the Curie temperature towards lower temperatures with the increase in Sr²⁺ ion concentration may be due to the substitution of A-site Ba²⁺ with Sr²⁺ ions. The calculated AC-conductivity of the prepared BST samples follows a decreasing trend as the temperature increases, depicting a positive temperature coefficient of resistivity (PTCR) nature. Additionally, impedance analysis of the sample confirms a non-Debye type ceramic with improved effective resistance as Sr²⁺ concentration increases.