Giant energy storage density, high efficiency and excellent stability achieved in lead-free KNN-based ceramic via a composition optimization strategy

The (1- x )K 0.5 Na 0.5 NbO 3- x Bi(Zn 2/3 Sb 1/3 )O 3 ceramics, abbreviated as (1-x)KNN-xBZS with x values of 0.05, 0.10, 0.15, and 0.20, were prepared via solid-state reaction technique. Their structural and electrical characteristics, including dielectric and ferroelectric characteristics, were systematically examined. The achievement of an optimized phase transition-field and the broadening of the bandgap in the 0.85KNN-0.15BZS ceramics contribute to the delay of polarization and improvement in the breakdown field strength. Dielectric measurements indicate that the introduction of BZS disrupts the original large domain structure of KNN ceramics, giving rise to small domains and polar nano regions (PNRs). Specifically, the 0.85KNN-0.15BZS ceramic exhibits exceptional energy storage density ( W rec = 5.90 J /cm 3 ) and an ultra-high energy efficiency (eta = 79.9 %) at an applied electric field of 570 kV/cm. Furthermore, this ceramic displays excellent frequency stability in the range of 1-100 Hz and temperature stability between 30 and 150 degrees C. The remarkable energy storage properties of (1-x)KNN-xBZS ceramics position them as highly promising materials for future pulse power capacitors and various energy storage applications.