Bi0.5Na0.5TiO3-based relaxor-ferroelectric ceramics for low-electric-field dielectric energy storage via bidirectional optimization strategy

Dielectric ceramics for electrostatic energy storage suffer from low recoverable-energy-density (Wrec) at a low-electric-field (LEF), constraining their use in downsizing integrated electronic devices and low operating voltage environments. Here, we report a 0.85Bi0.5Na0.5TiO3–0.15(Sr0.7Bi0.2)(Mg1/3Nb2/3)O3 (0.85BNT–0.15SBMN) relaxor ferroelectric ceramic that exhibits a high Wrec of 3.6 J/cm3 at a LEF of 200 kV/cm. This Wrec is among one of the highest under the equivalent applied electric field for relaxor ferroelectrics reported so far. It is revealed that the construction of Sr2+-Sr2+ ion pairs to replace the pristine Bi3+-Na+ ion pairs and the introduction of SBMN yield a high concentration of Bi3+ at the A-site, leading to high polarization (52.4 μC/cm2 at 200 kV/cm). Additionally, the newly introduced Mg2+ and Nb5+ at the B-site to replace the host Ti4+ causes local random fields (LRFs) that disrupt the long-range-ordered ferroelectric micro-domains, leading to the generation of the polar nanoregions with favorable relaxation properties. Above bidirectional optimization strategy leads to substantial Wrec improvements at a LEF. Furthermore, the variation of Wrec is less than 0.4 J/cm3 and 0.5 J/cm3 in a wide frequency (10 Hz–1000 Hz) and temperature (20 to 120 °C) range, indicating a good frequency and thermal stability. This finding provides a new guideline for fabricating LEF dielectric energy storage ceramics.