Strong Local Polarization Fluctuations Enabled High Electrostatic Energy Storage in Pb-Free Relaxors
Zheng Sun, Hui Liu, Ji Zhang, Huajie Luo, Yonghao Yao, Yuanpeng Zhang, Laijun Liu, Jöerg C. Neuefeind, Jun Chen
Abstract
Electrostatic energy-storage ceramic capacitors are essential components of modern electrified power systems. However, improving their energy-storage density while maintaining high efficiency to facilitate cutting-edge miniaturized and integrated applications remains an ongoing challenge. Herein, we report a record-high energy-storage density of 20.3 J cm –3 together with a high efficiency of 89.3% achieved by constructing a relaxor ferroelectric state with strongly enhanced local polarization fluctuations. This is realized by incorporating highly polarizable, heterovalent, and large-sized Zn and Nb ions into a Bi 0.5 Na 0.5 TiO 3 –BaTiO 3 ferroelectric matrix with very strong tetragonal distortion. Element-specific local structure analysis revealed that the foreign ions strengthen the magnitude of the unit-cell polarization vectors while simultaneously reducing their orientation anisotropy and forming strong fluctuations in both magnitude and orientation within 1–3 nm polar clusters. This leads to a particularly high polarization variation (Δ P ) of 72 μC cm –2, low hysteresis, and a high effective polarization coefficient at a high breakdown strength of 80 kV mm –1 . This work has surpassed the current energy density limit of 20 J cm –3 in bulk Pb-free ceramics and has demonstrated that controlling the local structure via the chemical composition design can open up new possibilities for exploring relaxors with high energy-storage performance.