Lead‐Free Trirelaxor Ferroelectrics: High Energy Storage Capacity in the Paraelectric State and Broad Operating Temperature Range

Abstract The development of lead‐free dielectric capacitors capable of reliable operation across extreme temperatures is crucial for next‐generation energy storage technologies. While relaxor ferroelectrics below the Burns temperature ( T B ) have demonstrated promising energy storage characteristics via polar nanoregions (PNRs), their performance typically deteriorates above T B . Surprisingly, a trirelaxor—a state composed of PNRs is reported with three coexisting symmetries (tetragonal, orthorhombic, and rhombohedral)—that exhibits high energy storage performance in the paraelectric state above T B . In lead‐free Bi(Mg 2/3 Nb 1/3 )O 3 ‐doped Ba(Zr,Ti)O 3 ‐(Ba,Ca)TiO 3 perovskite ceramics, the trirelaxor above T B achieves a remarkable energy storage density of 9.3 J cm −3 and an efficiency of 93%, which is comparable to the performance of other lead‐free dielectrics measured below T B . More importantly, the high energy storage properties of trirelaxor above T B enable the material to exhibit excellent comprehensive energy storage performance over a broad operating temperature range of −90 to 200 °C, which outperforms existing lead‐free perovskite dielectric materials. This work provides new insights into developing desirable energy‐storage dielectrics with high energy storage performance over an extended operating temperature range.