Realizing high energy density in BiFeO3-based ceramics capacitors via bandgap engineering and polarization optimization

BiFeO3-based lead-free ferroelectrics possess high spontaneous polarization. Nevertheless, achieving ultrahigh recoverable energy density in BiFeO3-based ceramics is limited by large remanent polarization and insufficient breakdown strength. Herein, (0.7-x)BiFeO3-0.3Ba(Hf0.05Ti0.95)O3-xNaTaO3 ceramics were designed and prepared. It exhibited a high recoverable energy density of 6.3 J/cm3 and high efficiency of 86.6 % due to the contribution of large breakdown strength and optimized polarization (high maximum polarization and small remanent polarization). These contributions stem from NaTaO3 being introduced into the 0.7BiFeO3-0.3Ba(Hf0.05Ti0.95)O3 matrix, which successfully brought in widened bandgap Eg, increased resistivity, and enhanced relaxor behavior. Large breakdown strength is also promoted by dense microstructure and decreased average grain size. This work proves that the strategies of bandgap engineering and polarization optimization for improving energy storage performance in BiFeO3 are practicable.