Superior energy storage performance with a record high breakdown strength in bulk Ba0.85Ca0.15Zr0.1Ti0.9O3-based lead-free ceramics via multiple synergistic strategies

A high breakdown strength (Eb) together with a large maximum polarization (Pm) is essential for achieving a high recoverable energy density (Wrec) in energy storage dielectric ceramics. However, meeting the urgent need for practical applications remains a challenge due to the intrinsic properties of bulk dielectric ceramics. Herein, a composition and structure optimization strategy combined with a two-step sintering (TSS) process is proposed to design and fabricate (1-x)Ba0.85Ca0.15Zr0.1Ti0.9O3-xBi(Mg1/2Sn1/2)O3 (BCZT-BMSx-TSS) lead-free ceramics. Highly dynamic locally polar nano-regions (PNRs) are formed via composition optimization, exhibiting a very high Pm and energy storage efficiency (eta). Compared to the traditional one-step sintering (OSS) process, the TSS process results in a composition with finer grain size and higher density, dramatically increasing Eb. As a result, an ultrahigh energy storage performance with Wrec similar to 10.53 J cm-3 and eta similar to 85.71% is achieved for the BCZT-BMSx-TSS (x = 0.08) ceramic which is attributed to a record high Eb similar to 830 kV cm-1 and a large Pm similar to 44.66 mu C cm-2. Complex impedance spectroscopy revealed that the activation energies of the bulk and grain boundary counterparts significantly increased, suggesting an increase in insulation resistance and a decrease in oxygen vacancies, which is the main reason for the high Eb value. In addition, excellent thermal/frequency stability is achieved in both energy density and efficiency, along with good charge-discharge performance. These findings suggest that BCZT-based lead-free ceramics have the potential for practical use in the future.