Synchronous realization of remarkable energy-storage density and efficiency in (Na0.5Bi0.5)0.75Sr0.25TiO3-based lead-free ceramics at moderate electric fields

Lead-free dielectric ceramics, as vital components of eco-friendly advanced pulse power systems, have encountered challenges for simultaneously achieving excellent energy-storage density (Wrec) and efficiency (eta) at moderate electric fields. To address this issue, a novel class of (1-x)(Na0.5Bi0.5)0.75Sr0.25TiO3-x (K0.5Ag0.5)0.97Bi0.01NbO3 (NBST-xKABN, x = 0, 0.05, 0.10 and 0.15) relaxor ferroelectric ceramics are designed and synthesized in this work. K+-Bi3+ ion pairs are introduced into NBST-xKABN ceramics to alter charge distribution and destroy local structural symmetry of A-site. Thereby, large saturation polarization is maintained, which assists in energy storage at lower electric fields and minimizing the likelihood of aging failure in energystorage devices that operate at high electric fields. Moreover, the incorporation of KABN strengthens breakdown strength of ceramics via reducing grain size and improving density and electrical uniformity (simulated by COMSOL). Along with the enhanced relaxor behavior induced by compositional inhomogeneity and ionic disorder, NBST-0.10KABN ceramics synchronously obtain Wrec of 5.3 J/cm3 and high eta of 90.0 % at a moderate electric field of 330 kV/cm. The optimum composition also exhibits satisfactory temperature (30-130 degrees C) and frequency (1-100 Hz) stability, accompanied by large power density (PD) of 38.2 MW/cm3 and rapid discharge rate t0.9 of 34.8 ns. This work offers an achievable tactic to develop dielectric ceramics with remarkable comprehensive energy-storage properties at moderate electric fields, so as to satisfy requirements of energystorage capacitors in harsh circumstances.