Optical and electrical properties of Ba1−x Sr x TiO3 nanopowders at different Sr2+ ion content

Abstract

Barium strontium titanate (BST) Ba1−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.