Superior Energy Storage Performance up to 200°C in a Self-organized Trirelaxor-antiferroelectric Nanocomposite

Despite extensive efforts over the past decade in enhancing the energy storage properties of dielectric materials, a challenging issue has remained unsolved that a material with good room-temperature-performance usually degrades significantly at higher temperatures. This issue renders many otherwise promising dielectric energy storage materials unusable because significant temperature rise of the energy storage devices is inevitable during their service and some applications are in high temperature environment. The challenge at high temperatures arises from the physical inevitability of vanishing ferroelectric domains that lead to drop in polarization, and exponentially increased charge transport activity which leads to charge leakage and electrical breakdown. Here we report a material strategy to meet this challenge by designing a self-organized nanocomposite (1-x)(Ba,Sr)(Ti,Sn)O 3 -xBi 1.5 ZnNb 1.5 O 7 composed of nano-sized antiferroelectric particles embedded into a trirelaxor matrix through a nanoscale phase separation process. At the optimal composition of x=0.11, the antiferroelectric-trirelaxor nanocomposite ceramic exhibits an outstanding energy storage performance from room temperature (energy density=8.5 J/cm 3 , efficiency=94.8% and a high figure of merit of 167 J/cm 3 ) up to a high temperature of 200°C (energy density ~4.85 J/cm 3 , efficiency>90% and figure of merit of 49 J/cm 3 ), which outperforms existing Pb-free dielectric materials. High-resolution transmission electron microscopy (TEM) and synchrotron x-ray diffractometry reveal that the coherent nanometric antiferroelectric particles and the trirelaxor nanodomains sustain over a wide temperature range. In-situ piezoresponse force microscopy (PFM) observation and phase-field simulations show that the nearly hysteresis-free switching of trirelaxor nanodomains is responsible for enhanced polarization (and hence energy density) and low hysteretic loss. Resistivity shows a 2~3 order of magnitude increase in electrical resistivity accompanying significant increase in breakdown strength up to high temperatures. Thermally stimulated depolarization current (TSDC) measurements suggest that the suppression of charge transport or leakage up to high temperature stems from charge trapping effect at high-density nanointerfaces between antiferroelectric and trirelaxor phases. These favorable effects in the nano-composite are responsible for its high energy storage performance up to high temperatures. Our research may provide a generic approach to achieving advanced dielectrics with outstanding performance at high temperatures.