Influence of structural evolution on energy storage properties in Bi0.5Na0.5TiO3-SrTiO3-NaNbO3 lead-free ferroelectric ceramics

Lead-free (1−x)(0.8Bi0.5Na0.5TiO3-0.2SrTiO3)-xNaNbO3 (x = 0–0.1, abbreviated as BNT-ST-xNN) ceramics were fabricated by a conventional sintering route with pure perovskite phase via XRD analysis. Raman spectrum was exploited in order to give an insight into the variation of local structural evolution. All compositions exhibited an obvious evolution of dielectric relaxation behaviors. Dielectric and ferroelectric properties clarified that a crossover from nonergodic to ergodic relaxor properties was obtained with the addition of NN content. A relatively large energy storage density was obtained WRec ∼ 0.74 J/cm3 at 7 kV/mm for x = 0.05 at room temperature. Particularly, the energy storage properties exhibited temperature (25–160 °C) and frequency stability (0.1–20 Hz) with WRec around 0.6 J/cm3 at 6 kV/mm for x = 0.05 within the ergodic region. Pulsed discharging current waveforms were measured under different electric fields to detect the energy storage density and discharging speed behavior. An illustration of the charge-discharge process for the nonergodic and ergodic relaxor was depicted in order to disclose the difference of energy storage properties in BNT-ST-xNN system, and it is believed that this concept can be a guideline for fixing a position when designing a new energy-storage system for BNT-based relaxor ferroelectric ceramics.