The dielectric properties and diffuse phase transition of non-stoichiometric barium strontium titanate based capacitor ceramics

The microstructure, dielectric properties and ferroelectric-paraelectric phase transition of non-stoichiometric (Ba0.75Sr0.25)Ti1-delta O3-2 delta (delta = 0 -0.03) ceramics prepared by conventional solid state method were studied with the non-stoichiometric level using XRD, SEM and LCR measuring system. It is found that the non-stoichiometric (Ba0.75Sr0.25)Ti1-delta O3-2 delta ceramics are single phase solid solutions with typical cubic perovskite structure. The average grain size of (Ba0.75Sr0.25)Ti1-delta O3-2 delta ceramics decreases with the increasing non-stoichiometric level when delta is less than 0.02. The phase transformation temperature decreases significantly with the increase of non-stoichiometric level due to the appearance of charged vacancies and the oxygen vacancies V-o also contribute to the fine performance in dielectric loss of (Ba0.75Sr0.25)Ti1-delta O3-2 delta ceramics. The diffuseness of ferroelectric-paraelectric phase transition resulting from the composition fluctuation is exacerbated significantly as the non-stoichiometric level increases. A normal ferroelectric behavior with relatively weak diffuse phase transition is observed for stoichiometric (Ba0.75Sr0.25)TiO3 ceramic while a relaxor behavior is obtained in the non-stoichiometric (Ba0.75Sr0.25)Ti1-delta O3-2 delta ceramics with high non-stoichiometric level.