Strong Local Polarization\nFluctuations Enabled High\nElectrostatic Energy Storage in Pb-Free Relaxors

Abstract

Electrostatic energy-storage ceramic capacitors are essential\ncomponents\nof modern electrified power systems. However, improving their energy-storage\ndensity while maintaining high efficiency to facilitate cutting-edge\nminiaturized and integrated applications remains an ongoing challenge.\nHerein, we report a record-high energy-storage density of 20.3 J cm^–3 together with a high efficiency of 89.3% achieved\nby constructing a relaxor ferroelectric state with strongly enhanced\nlocal polarization fluctuations. This is realized by incorporating\nhighly polarizable, heterovalent, and large-sized Zn and Nb ions into\na Bi_0.5Na_0.5TiO₃–BaTiO₃ ferroelectric matrix with very strong tetragonal distortion.\nElement-specific local structure analysis revealed that the foreign\nions strengthen the magnitude of the unit-cell polarization vectors\nwhile simultaneously reducing their orientation anisotropy and forming\nstrong fluctuations in both magnitude and orientation within 1–3\nnm polar clusters. This leads to a particularly high polarization\nvariation (Δ<i>P</i>) of 72 μC cm^–2, low hysteresis, and a high effective polarization coefficient at\na high breakdown strength of 80 kV mm^–1. This work\nhas surpassed the current energy density limit of 20 J cm^–3 in bulk Pb-free ceramics and has demonstrated that controlling the\nlocal structure via the chemical composition design can open up new\npossibilities for exploring relaxors with high energy-storage performance.