Optical and electrical properties of Ba_1−x Sr _x TiO₃ nanopowders at different Sr²⁺ ion content

Barium strontium titanate (BST) Ba_1−x Sr _x TiO₃ nanopowders have been successfully synthesized using oxalate precursor route. The effect of Sr²⁺ ion content from 0.3 to 0.7 on the crystal structure, crystallite size, microstructure, electrical and optical properties was systematically studied. The results revealed that well crystalline single BST phase was formed by annealing the oxalate precursor at 1,000 °C for 2 h. The crystallite size of the BST powders was decreased with increasing the Sr²⁺ ion molar ratios. The crystallite size was decreased from 56.0 to 33.1 nm when the Sr²⁺ ion content increased from 0.3 to 0.7. Additionally, the lattice parameter (a), unit cell volume and X-ray density of BST ware decreased whereas the porosity, % were increased with Sr²⁺ ion concentration. The BST phase appeared as cubic-like structure. The spectrophotometer measurement results demonstrated that the room temperature band gap energy varied with the Sr²⁺ ion composition x. The band gap energy was shifted to low energy and it was decreased from 3.6 to 3.2 eV with increasing the Sr²⁺ ion content from 0.3 to 0.7. Moreover, the DC resistivity was enhanced with increasing the Sr²⁺ ion ratio. The dielectric response obtained for the stressed samples corresponds to a true resonance rather than a dispersion process with a characteristic frequency around 1 GHz at room temperature. However, the peaks commonly observed at GHz frequency were changed with varying the Sr²⁺ ion composition. The high imaginary components of dielectric permittivity for x = 0.3 was found at higher frequency region around 1.6 GHz compared with the samples with x values of 0.5 and 0.7 in which the frequency regions were around 1.25 and 1.15 GHz, respectively.