Enhanced energy-storage performance and thermally stable permittivity for K_0.5Na_0.5NbO₃ modified [(Na_0.5Bi_0.5)_0.84Sr_0.16]_0.98La_0.01TiO₃ lead-free perovskite ceramics

(1-x)[(Na_0.5Bi_0.5)_0.84Sr_0.16]_0.98La_0.01TiO₃-xK_0.5Na_0.5NbO₃ (abbreviated as NBSLT-100xKNN) lead-free perovskite relaxor ferroelectric ceramics are synthesized through the conventional solid-state reaction. The effects of KNN on the ceramic polycrystalline structure, dielectric temperature stability, and energy-storage characteristics are studied systematically. All samples exhibit a single perovskite structure and compact surface morphology. Thermally stable dielectric permittivity (ε′) is obtained from 62 to 331 °C range for NBSLT-5KNN ceramic with ε′ ~ 2286 at 150 °C less than ± 10% fluctuation rate. The addition of KNN refines the hysteresis loops and gradually increases the dielectric breakdown strength, which endows NBSLT-5KNN ceramic with the best energy-storage performance compared to other compositions. A high effective energy-storage density (W_rec) ~ 1.234 J/cm³ with efficiency (η) ~ 74.7% are acquired at 90 kV/cm. The energy-storage performance is revealed an excellent fatigue resistant stability. Hence, the introduction of KNN makes NBSLT-5KNN ceramic an outstanding competitor for energy-storage equipment applications.