Interface and defect modulation via a core–shell design in (Na0.5Bi0.5TiO3@La2O3)-(SrSn0.2Ti0.8O3@La2O3)-Bi2O3-B2O3-SiO2 composite ceramics for wide-temperature energy storage capacitors

Abstract

Dielectric capacitors with high energy storage performance have attracted much attention in power electronics systems. However, the limited energy storage and unsatisfactory temperature stability are the main obstacles in practical applications. Herein, the joint control of interface and internal defects in core–shell structure is proposed to achieve capacitors with superior wide-temperature energy storage properties. Firstly, relaxor ceramics were prepared, in which multiphase ceramic phases including ferroelectric Na0.5Bi0.5TiO3 (NBT) and paraelectric SrSn0.2Ti0.8O3 (SST) were used to ensure relaxation, and Bi2O3-B2O3-SiO2 (BBS) glass was added to accelerate the ceramic densification. Secondly, notably, a buffer layer of La2O3 with wide band gap was introduced in a core–shell way at the interface between ceramic powders and glass to form composite ceramics. The experimental results show that the La2O3 coating can induce uniform and dense ceramic microstructure with a composition gradient, alleviating the local electric field distortion at the interface of ceramic/glass. Therefore, the capacitive wide-temperature energy storage properties are ultimately improved. Confirmed by XPS and EPR, partial La2O3 as a donor in grains generates LaA·-VTi‴ defect complex and optimizes the η and BDS of the ceramics. NBT@La2O3-SST@La2O3-BBS composites with 1.0 mol% La2O3 exhibit high η ∼ 82.1%, high BDS ∼ 275 kV/cm, medium Wrec ∼ 2.25 J/cm3, superior dielectric temperature stability (Δε/ε150 °C≤±15%) at 20–500 °C and thermal stability of energy storage. This work is expected to pave a new way to optimize the wide-temperature energy storage of composite ceramics via the core–shell design process.