Synthesis, characterization and dielectric properties of nanometer-sized barium strontium titanates prepared by the polymeric citrate precursor method

Abstract

Barium strontium titanate (BST) powders of the formula Ba_{1 − x}Sr_xTiO₃ (0 ≤ x ≤ 1) have been prepared for the first time by the polymeric precursor route using citric acid and ethylene glycol. Pure BSTs were obtained at 500 °C. These oxides were found to have the cubic structure, which is retained even after heating at 800 °C. Detailed X-ray studies on samples sintered at 1100 °C show weak tetragonal distortion for BaTiO₃, while the other BSTs retain their cubic structure. The particle size of the sintered oxides increases from 55 nm for BaTiO₃ to 88 nm for SrTiO₃, from X-ray line-broadening studies. The nano-sized grains are reasonably stable to sintering (the particle size for BaTiO₃ changes from 25 nm at 500 °C to 55 nm at 1100 °C). The dielectric constant of the sintered oxides decreases from 510 for BaTiO₃ (x = 0) to 190 for SrTiO₃ (x = 1) at 100 kHz. The dielectric loss decreases from 0.05 for BaTiO₃ to 0.001 for SrTiO₃ at 100 kHz. No ferroelectric transition was observed in either the dielectric studies or by differential scanning calorimetry.