Enhancing the tunability properties of pure (Ba,Sr)TiO3 lead-free ferroelectric by polar nanoregion contributions

In the present work, series compositions of (Ba1-xSrx)TiO3 (0 <= x <= 0.4) lead-free ferroelectric (BST) were successfully prepared by sol-gel method. The effects of Sr2+ on the optical properties, crystal structure and morphology of BaTiO3 were systematically investigated. Compositions with x < 0.4 exhibit single-phase tetragonal perovskite at room temperature, while a cubic structure of BST has been detected in the ceramic with x = 0.4. Phase transition temperature was shifted toward lower temperature by increasing Sr doping. Moreover, a detailed tunability analysis for the present ceramics confirmed an enhancement upon Sr addition and the maximum values were observed at Sr = 0.2. The enhancement back to present multiple components contribute to the DC field-induced dielectric constant, where at low electric fields the Langevin theory indicates present polar nanoregion (PNR) contributions to tunability data; however, domain switching contributions at high electric field was described by Johnson equation. Ferroelectric properties appraised by P-E loop and positive-up negative-down (PUND) methods have been introduced. The results showed that the remnant polarization appraised by PUND method is much lower than polarization estimated by P-E loop indicating that the different values of P-r are mostly owing to leakage current contribution in P-E method.