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

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_2/3Nb_1/3)O₃-doped Ba(Zr,Ti)O₃-(Ba,Ca)TiO₃ 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.