Giant energy- storage density and high efficiency achieved in ( Bi0.5Na0.5) TiO3-Bi( Ni0.5Zr0.5) O3 thick films with polar nanoregions

The development of electronic devices towards integration, miniaturization and environmental friendliness has propelled much recent research on lead-free dielectric capacitors for energy storage, however, high energy-storage density is still an extremely challenging objective for lead-free dielectric materials. Here, a novel lead-free relaxor ferroelectric (1 - x)(Bi-0.5 Na-0.5)TiO3-xBi(Ni0.5Zr0.5)O-3 (BNT-xBNZ, x = 0-0.5) thick film (1 m) was fabricated by a water-based sol-gel method. Doping of BNZ into the BNT host promoted the formation of polar nanoregions (PNRs), whose domain switching became easier, leading to an improved energy-storage performance. Surprisingly, an ultrahigh recoverable energy density of 50.1 J cm(-3) and a high energy-storage efficiency of 63.9% under 2200 kV cm(-1) were achieved simultaneously with x = 0.4, which are both more than 100% higher than those of the pure BNT sample. This excellent energy-storage performance can be perfectly comparable with that of lead-based films. Furthermore, the BNT-0.4BNZ thick film showed strong fatigue endurance after 6 x 10(7) cycles, and it possessed good thermal and frequency stability. The pulsed discharge current waveform demonstrated that the BNT-0.4BNZ thick film showed a very fast discharge speed (210 ns). This study shows that BNT-based materials have an unexpected role as a lead-free family in the field of energy storage and could stimulate the design and fabrication of BNT-based dielectrics with ultrahigh energy-storage performance.