(Bi_0.5Na_0.5)TiO₃-based relaxor ferroelectrics with medium permittivity featuring enhanced energy-storage density and excellent thermal stability

High energy density, efficiency and thermal stability of energy-storage properties are extremely pivotal for the application of dielectric ceramics in advanced pulsed power systems. In this work, we utilize a composition-driven strategy to induce polar nanoregions, refine grain size and adjust permittivity of (1-x)Bi_0.5(Na_0.9Li_0.1)_0.5TiO₃-xSr(Al_0.5Nb_0.25Ta_0.25)O₃ ceramics. As a result, an extraordinary W_rec of 6.43 J/cm³ and high η of 88% are simultaneously obtained in the x = 0.16 composition. Meanwhile, the x = 0.16 sample also shows good frequency stability (5–100 Hz), cycle stability (10⁵ cycles) and superior thermal stability (-55 ~ 225 ℃). The enhanced breakdown strength is analyzed by Weibull distribution and mainly attributed to the decreased average grain size. The typical relaxor behavior is reflected by the broadened and diffused Raman spectra as well as the dispersive and temperature-stable dielectric curves. The existence of dynamic polar nanoregions as confirmed by piezoresponse force microscopy measurements enables the nearly hysteresis-free polarization–electric field response and the related frequency and cycle stability. The mitigated polarization saturation is related to the field-insensitive moderate permittivity and will be conducive to the energy-storage properties at elevated electric field. In addition, the temperature-dependent Raman spectra and the slightly fluctuated ΔP (P_m - P_r) value over the whole temperature range reflect the temperature-stable energy-storage properties. Hence, the current work may provide some novel perspectives for designing dielectric ceramics with enhanced energy-storage properties.