In recent years, relaxor ferroelectrics (RFE) ceramics are recognized as materials with a tremendous potential for energy storage applications. Their relaxor characteristics significantly contribute to enhancing the energy storage performance of ceramics. BaTiO₃ (BT) as a typical lead-free ferroelectric ceramic is popular due to its immense dielectric constant and long-range ordered spontaneous polarization. This ceramic is extensively investigated and applied in dielectric capacitor materials. However, pure BT materials often exhibit a large residual polarization and a considerable energy loss due to polarization reversal upon the application of an electric field, affecting the further development of BT materials in energy storage. To optimize the energy storage performance of the original BT ceramics, effective methods such as compositional modulation and ionic doping are proposed. The objective of this paper was to disrupt an original long-range ordered ferroelectric domain structure, creating nano-sized polar nanodomains. This could accelerate the polarization response speed and enhance the relaxor behavior of ferroelectrics.

(1-x)BT-x(BNT-SLT) ceramics were synthesized by a solid-state reaction method. Na₂CO₃ (purity: 99.500%, in mass fraction, the same below), BaCO₃ (purity: 99.000%), Bi₂O₃ (purity: 99.975%), SrCO₃ (purity: 99.000%), TiO₂ (purity: 99.000%) and La₂O₃ (purity: 99.000%) were used as raw materials. These materials were dried and mixed in stoichiometric proportions. The mixture was then ground with anhydrous ethanol in a grinding mill with zirconium dioxide balls in a mass ratio of 1.0∶2.5∶4.0 for 12 h. After grinding, the slurry was dried at 100 ℃ for 12 h. The dried materials were subsequently ground using an agate mortar for over half an hour. The ground materials were firstly transferred and compacted in an alumina crucible, pre-sintered in a box furnace at 850 ℃ for 2 h, and then cooled naturally to room temperature. The powder obtained from the second pre-sintering was further ground and mixed with a polyvinyl alcohol (PVA) as a binder at a mass fraction of 8%. The mixture was manually pressed into small discs with 10 mm in diameter and 0.5 mm in thickness under 10 MPa for 5 min. These discs were sintered at 1 130-1 220 ℃ for 2 h to produce BT-BNT-SLT ceramic samples. After post-sintering, the ceramic samples were polished and coated with 2 mm diameter gold electrodes for ferroelectric testing.

The phase composition of the ceramics was analyzed by a model PANalytical Empyrean X-ray diffractometer (XRD), while the surface morphology was characterized by a model Regulus 8230 scanning electron microscope (SEM). The dielectric properties, such as dielectric constant and loss, were assessed by a model TH2838A dielectric performance analysis system. The ferroelectric properties were evaluated by a model Polyk TF Analyzer 2000, and the temperature in testing was controlled by a model TLRS-003 high-low temperature thermal system.

The energy storage ceramics of (1-x)BaTiO₃-x(0.6Bi_0.5Na_0.5TiO₃-0.4Sr_0.7La_0.2TiO₃)(x=0.20, 0.30, 0.40, 0.45, 0.50) ((1-x)BT-x(BNT-SLT)) with different compositions (i.e., x of 0.20, 0.30, 0.40, 0.45, and 0.50) were prepared to enhance the energy storage performance of BT ferroelectric ceramics. The incorporation of BNT material can strengthen the system saturation polarization through an enhanced orbital hybridization. Also, the inclusion of SLT can further increase an ionic size disparity, thereby enhancing a relaxor behavior. The system integrates a partial vacancy design, typically resulting in the formation of defect dipoles within the ceramics. These defect dipoles in an external electric field are less likely to alter their polarization direction, preserving the initial state of polarization. This mechanism inhibits a polarization reversal and increases the coercive field (E_c). Furthermore, in the absence of the external field, a generated reaction force can revert the polarization direction back to its initial state, leading to a reduction or even a nullification of the residual polarization, consequently enhancing the energy storage density.

(1-x)BT-x(BNT-SLT) ceramics were fabricated by a solid-state reaction method. The SEM images revealed that the ceramics had clear grains and great density. The dielectric spectroscopy indicated that ion doping regulated the relaxor behavior of BT-based ceramics. The results by ferroelectric tests demonstrated substantial improvements in energy storage performance of the relaxor-modulated BaTiO₃-based ceramics, particularly for the 0.55BT-0.45(BNT-SLT) ceramic, obtaining an optimal energy storage performance at 280 kV/cm with a recoverable energy density (W_rec) of approximately 3.12 J/cm³ and an efficiency (η) of 93.3%. In addition, these ceramics also exhibited superior frequency stability, temperature stability, and fatigue properties. The amalgamation of these data and stability tests indicated that the relaxor-modulated BT-based ferroelectric ceramics could have a promising potential for energy storage applications.