High energy storage performance of KNN-based relaxor ferroelectrics in multiphase-coexisted superparaelectric state

Although K 0.5 Na 0.5 NbO 3 (KNN) possesses large maximum polarization and relatively high breakdown strength, the large remnant polarization constrains their practical applications as energy storage materials. In this work, through multi-element doping, (K 0.5−0.5 x Na 0.5−0.5 x Bi x )(Nb 1− x Sn 0.2 x Zn 0.6 x Ta 0.2 x )O 3 relaxor ferroelectrics were prepared. As the superparaelectric states (SPE) were adjusted to room temperature, orthorhombic, tetragonal, and cubic phases coexisted, accompanied by the highly dynamic polar nanoregions (PNRs). In particular, a high recoverable energy storage density of 4.5 J/cm 3 and an energy storage efficiency of 83% were achieved for the x  = 0.125 ceramic, with the variations less than 11% and 4%, respectively, in the wide temperature range of 20–180 °C. These results demonstrate that the multiphase PNRs in the SPE state is an effective strategy for improving the energy storage performance of KNN-based ceramics.