From core–shell particles to dense Ba_0.8Sr_0.2Zr_0.1Ti_0.9O₃@Bi₂O₃–Fe₂O₃–SiO₂ ceramics with low sintering temperature and improved dielectric, energy storage properties

To achieve high energy storage in dielectric ceramics, a new designed material Ba_0.8Sr_0.2Zr_0.1Ti_0.9O₃@Bi₂O₃–Fe₂O₃–SiO₂ with core–shell structure was fabricated by the monodispersed submicron Ba_0.8Sr_0.2Zr_0.1Ti_0.9O₃ particles (diameter ~ 180 nm) coated with the 25-nm-thick shell of Bi₂O₃–Fe₂O₃–SiO₂. The influences of Bi₂O₃–Fe₂O₃–SiO₂ amount, Bi/Fe ratio, and sintering temperature on the phase composition, microstructure, and ceramic electrical properties were investigated. X-ray diffraction analysis of the ceramics revealed the formation of perovskite Ba_0.8Sr_0.2Zr_0.1Ti_0.9O₃ when the Bi₂O₃–Fe₂O₃–SiO₂ amount was below 6.0 wt%. The secondary phases Bi₂Fe₄O₉ and Bi₄Ti₃O₁₂ formed in ceramics when the Bi₂O₃–Fe₂O₃–SiO₂ amount exceeded 6.0 wt%, as the ceramic grain core–shell structure collapsed. Based on FESEM images, the densification of ceramics can be tenderly controlled at low sintering temperature, and the ceramic grains can maintain their core–shell structure. As the Bi₂O₃–Fe₂O₃–SiO₂ amount, the ratio of Bi to Fe, and the sintering temperature increase, the ceramic room temperature dielectric constant increases up to a maximum value then decreases. The energy storage density exhibits a similar tendency to increase first and then decrease. Fine-grained Ba_0.8Sr_0.2Zr_0.1Ti_0.9O₃@Bi₂O₃–Fe₂O₃–SiO₂ ceramics with Bi/Fe ratio of 1.04 and 6.0 wt% Bi₂O₃–Fe₂O₃–SiO₂ sintered at 1120 °C had a dielectric constant of 2599, the maximum energy storage density of 1.50 J/cm³ under 29.31 kV/mm. This work proposed a novel method to enhance electrical properties of functional materials, which could be potentially used in the fabrication of capacitors with high energy storage performance.