(Ba,Sr)TiO₃–Bi(Mg,Hf)O₃ Lead-Free Ceramic Capacitors with High Energy Density and Energy Efficiency

Dielectric capacitors with high energy storage performance have been actively studied for emerging applications. In this work, a series of environmental friendly lead-free relaxor ferroelectric ceramics, (1 – x)(Ba0.75Sr0.25)TiO3–xBi(Mg0.5Hf0.5)O3 with 0 ≤ x ≤ 0.5 [abbreviated as (1 – x)BST–xBMH], were synthesized by a high-temperature solid-state reaction method. The perovskite structure without any secondary phase can be obtained in samples with x ≤ 0.4. As the BMH content increases, the polarization–electric field (P–E) loop becomes slim and slanted. A large recoverable energy storage density of 4.3 J/cm3 and high energy efficiency of 92% were achieved simultaneously in 0.6BST–0.4BMH at 390 kV/cm. The fine grain morphology with minimal porosity and the high conductivity activation energy were responsible for the enhanced breakdown strength. Of particular importance is that the 0.6BST–0.4BMH ceramic shows excellent temperature stability and cycling reliability with energy density variations below 3 and 4%, respectively. In addition, the 0.6BST–0.4BMH ceramic possesses fast discharge time (∼0.59 μs) with a high power density of 3.5 MW/cm3. All these merits reveal that the lead-free 0.6BST–0.4BMH relaxor ceramic is a promising candidate for high-temperature and high-power energy storage capacitor applications.