Energy Storage Behavior in ErBiO₃-Doped (K,Na)NbO₃ Lead-Free Piezoelectric Ceramics

In this study, good energy storage properties are obtained via enhancing dielectric breakdown strength (DBS) in transparent ErBiO3 (EB)-doped (K0.5Na0.5)NbO3 (KNN-xEB) ceramics. The doping of EB makes a strong impact on the grain size and densities of KNN-based ceramics, which decreases the average grain size and enhances the densities significantly. A gradual transformation of crystal structures from orthorhombic to pseudocubic occurs via EB modification. Rietveld refinement is carried out to further investigate the influence of doped EB on the crystal structure, especially on the distortion degree of the pseudocubic phase. The domain structures change from irregular macroscopic and lamellar domains to nanodomains because of the donor doping of EB. The contribution of the second phase to DBS is also confirmed through first-principles calculation on the basis of density functional theory (DFT). The energy storage properties are also investigated with an energy storage density of W ∼ 2.68 J/cm3 and a recoverable energy storage density of Wrec ∼ 1.85 J/cm3 for the KNN-0.015EB ceramic, which also present a good thermal stability. The results imply that the KNN-xEB ceramics have huge potential for optical and energy storage applications as multifunctional materials.