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

Abstract

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.

Enhanced piezoelectric properties and electrocaloric effect in novel lead‐free (Bi0.5K0.5)TiO3‐La(Mg0.5Ti0.5)O3 ceramics

“…The 200‐400 cm −1 region characterized by the A, B, and C bands, is closely related to the B‐O vibrations in the perovskites. The D, E, and F bands in the range 400‐700 cm −1 correspond to the BO 6 octahedral vibrations . Variations in the band position and the FWHMs for B–O bond and BO 6 octahedral vibrations can provide useful information regarding the structural changes and their evolutions as a function of LMT content are plotted in Figure B‐D.…”

“…It can be seen that the C and F bands exhibit a redshift with increasing LMT content. The redshift of the B–O bonds can be ascribed to the enhanced structural disorder and the reduced polarity of the unit cell . In addition, the sudden increase in the FWHM for the B and F bands is believed to be an indication of the phase transition.…”

Recent progress of ecofriendly perovskite-type dielectric ceramics for energy storage applications

“…For example, in BNT-SrTiO 3 -NaNbO 3 ternary systems, an optimal W R of 0.73 J/cm 3 has been obtained as a result of the reversibility between the field-induced FE phase and ergodic phase transition. 35 It should be noted that: (1) the nonergodic relaxor state irreversibly transforms to FE order, thus weakening W R and η; and (2) the pure ergodic state might contribute to a large η. However, W R is probably low because the enhanced local random field retards the appearance of long-range order and then P max might be low.…”

“…3. 35,37,38,[42][43][44][45][46][47][48][49][50][51][52][53][54] Generally speaking, high W R is obtained under high external electric field, but η is closely related with the local structure in BNT-based materials and is relatively low for most systems.…”

“…Interestingly, BNT-based FE ceramics exhibit strong ferroelectricity and diffused dielectric properties, which have recently drawn much attention in the research field of electromechanical strain, charge-discharge and electrocaloric properties. 32,35,38,[121][122][123][124][125][126][127][128][129] However, domain switching will inevitably result in hysteresis loss and low BDS. Therefore, coupling the respective advantage of ST and BNT-based ceramics might be conducive for improving of energy storage performance.…”