Effective regulation of breakdown strength through the synergistic effect of defect chemistry and energy band engineering in Ba0.85Ca0.15Zr0.1Ti0.9O3-based lead-free ceramics

Abstract

Based on the fundamentals of energy storage capacitors, recoverable energy storage density (W_rec) is greatly dependent on breakdown strength (E_b). In this work, the breakdown performance of 0.92Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃–0.08Bi_2/3(M_1/3Ta_2/3)O₃ (M = Mg and Zn) is significantly improved through the synergistic effect of defect chemistry and energy band engineering. The addition of A-site deficient Bi_2/3(M_1/3Ta_2/3)O₃ triggers a ferroelectric-to-relaxor ferroelectric phase transition, leading to the formation of local polar nano-regions (PNRs). More importantly, the introduction of Bi_2/3(M_1/3Ta_2/3)O₃ into Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ effectively increases the band gap of samples and reduces grain growth and leakage current density by inhibiting the formation of oxygen vacancies, thus enhancing E_b. As a result, an ultrahigh E_b of ∼681.7 kV cm⁻¹ for the 0.92Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃–0.08Bi_2/3(Zn_1/3Ta_2/3)O₃ ceramic accompanied by a large maximum polarization (∼31.6 μC cm⁻²) contributes to a high W_rec of ∼6.93 J cm⁻³ and efficiency of ∼82%. Furthermore, all these ceramics exhibited excellent thermal/frequency stability and charge–discharge performances. These findings suggest that defect chemistry and energy band engineering is an effective strategy for developing novel lead-free relaxor ferroelectric ceramics.