Ferroelectric and Relaxor-Ferroelectric Phases Coexisting Boosts Energy Storage Performance in (Bi0.5Na0.5)TiO3-Based Ceramics.

With the intensification of the energy crisis, it is urgent to vigorously develop new environment-friendly energy storage materials. In this work, coexisting ferroelectric and relaxor-ferroelectric phases at a nanoscale were constructed in Sr(Zn1/3Nb2/3)O3 (SZN)-modified (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT) ceramics, simultaneously contributing to large polarization and breakdown electric field and giving rise to a superior energy storage performance. Herein, a high recoverable energy density (Wrec) of 5.0 J/cm3 with a conversion efficiency of 82% at 370 kV/cm, a practical discharged energy density (Wd) of 1.74 J/cm3 at 230 kV/cm, a large power density (PD) of 157.84 MW/cm3, and an ultrafast discharge speed (t0.9) of 40 ns were achieved in the 0.85BNBT-0.15SZN ceramics characterized by the coexistence of a rhombohedral-tetragonal phase (ferroelectric state) and a pseudo-cubic phase (relaxor-ferroelectric state). Furthermore, the 0.85BNBT-0.15SZN ceramics also exhibited excellent temperature stability (25-120 °C) and cycling stability (104 cycles) of their energy storage properties. These results demonstrate the great application potential of 0.85BNBT-0.15SZN ceramics in capacitive pulse energy storage devices.

Achieving High Energy Storage Performance under a Low Electric Field in KNbO3-Doped BNT-Based Ceramics.

Ceramic capacitors have great potential for application in power systems due to their fantastic energy storage performance (ESP) and wide operating temperature range. In this study, the (1 - x)Bi0.5Na0.47Li0.03Sn0.01Ti0.99O3-xKNbO3 (BNLST-xKN) energy storage ceramics were synthesized through the solid-phase reaction method. The addition of KN disrupts the long-range ferroelectric order of the BNLST ceramic, inducing the emergence of polar nanoregions (PNRs), which enhances the ESP of the ceramics. The BNLST-0.2KN ceramic demonstrates a high recovered energy density (Wrec ∼ 3.66 J/cm3) and efficiency (η ∼ 85.8%) under a low electric field of 210 kV/cm. Meantime, it exhibits a large current density (CD ∼ 831.74 A/cm2), high power density (PD ∼ 78.86 MW/cm3), and fast discharge rate (t0.9 ∼ 0.1 µs), along with good temperature stability and excellent fatigue stability. These properties make the BNLST-0.2KN ceramic a promising candidate for energy storage applications in low electric fields.

Enhanced Electromechanical Performance in Lead-free (Na,K)NbO3-Based Piezoceramics via the Synergistic Design of Texture Engineering and Sm-Modification.

Next-generation electromechanical conversion devices have a significant demand for high-performance lead-free piezoelectric materials to meet environmentally friendly requirements. However, the low electromechanical properties of lead-free piezoceramics limit their application in high-end transducer applications. In this work, a 0.96K0.48Na0.52Nb0.96Sb0.04O3-0.04(Bi0.5-xSmx)Na0.5ZrO3 (abbreviated as T-NKN-xSm) ceramic was designed through phase regulation and texture engineering, which is expected to solve this difficulty. Through our research, we successfully demonstrated the enhanced electromechanical performance of lead-free textured ceramics with a highly oriented [001]c orientation. Notably, the T-NKN-xSm textured ceramics doped with 0.05 mol % Sm exhibited the optimal electromechanical performance: piezoelectric coefficient d33 ≈ 710 pC N-1, longitudinal electromechanical coupling k33 ≈ 0.88, planar electromechanical coupling kp ≈ 0.80, and Curie temperature Tc ≈ 244 °C. Finally, we conducted a detailed investigation into the phase and domain structures of the T-NKN-Sm ceramics, providing valuable insights for achieving high electromechanical properties in NKN-based ceramics. This research serves as a crucial reference for the development of advanced electromechanical devices by facilitating the utilization of lead-free piezoelectric materials with superior performance and environmental benefits.

Energy Transfer from Pr3+ to Gd3+ and Upconversion Photoluminescence Properties of Y7O6F9:Pr3+, Gd3.

Upconversion materials have numerous potential applications in light energy utilization due to their unique optical properties. The use of visible light excitation to obtain ultraviolet emission is a promising technology with broad application prospects, while relevant research is absent. A series of Pr3+, Gd3+ doped Y7O6F9 phosphors were synthesized by traditional solid-state reaction. X-ray diffraction, scanning electronic microscopy, steady-state photoluminescence spectra, a decay dynamic, and upconversion emission spectra of the samples were studied. Under the excitation of 238 nm, the energy transfer from Pr3+ to Gd3+ was realized and a strong ultraviolet B emission due to the 6P7/2→8S7/2 transition of the Gd3+ ions was achieved. Under the excitation of a 450 nm blue laser, Pr3+ absorbed two blue photons to realize the upconversion process and then transferred the energy to Gd3+ to obtain the ultraviolet B emission.

High-Energy Storage Properties over a Broad Temperature Range in La-Modified BNT-Based Lead-Free Ceramics.

The development of high-performance energy storage materials is decisive for meeting the miniaturization and integration requirements in advanced pulse power capacitors. In this study, we designed high-performance [(Bi0.5Na0.5)0.94Ba0.06](1-1.5x)LaxTiO3 (BNT-BT-xLa) lead-free energy storage ceramics based on their phase diagram. A strategy combining phase adjustment and domain control via doping was proposed to enhance the energy storage performance. The obtained results showed that La3+ ions doped into BNT-BT improved the crystal structure symmetry and induced a strong dielectric relaxation behavior, which destroyed the long-term ferroelectric order and effectively promoted the formation of polar nanoregions. At x = 0.12, a high recoverable energy density (Wrec) of ∼5.93 J/cm3 and a relatively large energy storage efficiency (η) of 77.6% were obtained under a high breakdown electric field of 440 kV/cm. By using a two-step sintering approach for the microstructural optimization, the energy storage performance was further improved, yielding much higher Wrec (6.69 J/cm3) and η (87.0%). Additionally, both conventionally sintered and two-step-sintered samples showed excellent frequency stability (0.5-500 Hz), thermal endurance (25-180 °C), and fatigue resistance (105 cycles). Regarding the pulse charge-discharge performance, the samples exhibited ultrashort discharge time (t0.9 ∼ 89 ns for the conventionally sintered sample and ∼75 ns for the two-step-sintered sample) under an electric field of 240 kV/cm. Furthermore, the breakdown process of the material was simulated based on the finite element analysis, and it was shown that high breakdown strength of the material could be ascribed to fine grains, which significantly hindered the crack propagation during the application of the electric field. These results show that the presented materials have great potential as high-energy storage capacitors.

Effect of Bi2O3 content on the microstructure and electrical properties of SrBi2Nb2O9 piezoelectric ceramics.

Lead-free ceramics, SrBi2Nb2O9-xBi2O3 (SBN-xBi), with different Bi contents of which the molar ratio, n(Sr) : n(Bi) : n(Nb), is 1 : 2(1 + x/2) : 2 (x = -0.05, 0.0, 0.05, 0.10), were prepared by conventional solid-state reaction method. The effect of excess bismuth on the crystal structure, microstructure and electrical properties of the ceramics were investigated. A layered perovskite structure without any detectable secondary phase and plate-like morphologies of the grains were clearly observed in all samples. The value of the activation energy suggested that the defects in samples could be related to oxygen vacancies. Excellent electrical properties (e.g., d 33 = 18 pC N-1, 2P r = 17.8 µC cm-2, ρ rd = 96.4% and T c = 420 °C) were simultaneously obtained in the ceramic where x = 0.05. Thermal annealing studies indicated the SBN-xBi ceramics system possessed stable piezoelectric properties, demonstrating that the samples could be promising candidates for high-temperature applications.