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Dielectric capacitors are very attractive for high power energy storage. However, the low energy density of these capacitors, which is mainly limited by the dielectric materials, is still the bottleneck for their applications. In this work, lead-free single-phase perovskite Sr x (Bi 1−x Na 0.97−x Li 0.03 ) 0.5 TiO 3 (x = 0.30 and 0.38) bulk ceramics, prepared using solid-state reaction method, were carefully studied for the dielectric capacitor application. Polar nano regions (PNRs) were created in this material using co-substitution at A-site to enable relaxor behaviour with low remnant polarization ( P r ) and high maximum polarization ( P max ). Moreover, P max was further increased due to the electric field induced reversible phase transitions in nano regions. Comprehensive structural and electrical studies were performed to confirm the PNRs and reversible phase transitions. And finally a high energy density (1.70 J/cm 3 ) with an excellent efficiency (87.2%) was achieved using the contribution of field-induced rotations of PNRs and PNR-related reversible transitions in this material, making it among the best performing lead-free dielectric ceramic bulk material for high energy storage. [ABSTRACT FROM AUTHOR]

High power dielectric capacitors with high energy density are needed in order to develop modern electronic and electrical systems, including hybrid vehicles, telecommunication infrastructures and portable electronic devices. Relaxor ferroelectric polymers (RFP) are considered to be the most promising candidates for the next generation of capacitors owing to their relatively high energy storage density. However, the commercialization of RFP capacitors in power systems is hindered by their high cost and low dielectric breakdown strength. In this study, inexpensive, free-standing nano-crystalline (~3.3 nm) poly (vinylidene fluoride) (PVDF) films with high β phase content (~98%), "relaxor-like" ferroelectric behaviour and high breakdown strength (880 kV/mm) were fabricated using the facile Press & Folding (P&F) technique. An internal stress dominated polarization switching model is proposed to explain the origin of the relaxor-like ferroelectric behaviour. The internal stress generated during pressing alters the intermolecular chain distance of the (200) plane of β -PVDF from 4.24 Å in internal stress free films to 4.54 Å in P&F films, corresponding to a tensile strain and residual stress of 7.11% and 142 MPa, respectively. The internal stress acts to partially reverse the polarization on reversal of the applied electric field. This, combined with preferred in-plane orientation of the crystallites, results in a polar nanostructure with high polarization reversibility at high electric fields. A giant discharged energy storage density of 39.8 J/cm3 at 880 kV/mm was achieved for P&F films, which surpasses all previously reported polymer-based materials. Image 1 • Low-cost, free-standing, relaxor-like ferroelectric PVDF films prepared using a facile press-fold approach. • >98% fraction of polar β -phase with nano-crystallite size of ~3 nm. • An internal stress dominated polarization switching model is proposed to explain the relaxor-like ferroelectric behaviour. • Highest polarization reversibility is observed in the PVDF film with highest internal stress (~142 MPa). • A giant discharged energy density of 39.8 J/cm3 at 880 kV/mm. [ABSTRACT FROM AUTHOR]

Poly(vinylidene fluoride)-based dielectric materials are prospective candidates for high power density electric storage applications because of their ferroelectric nature, high dielectric breakdown strength and superior processability. However, obtaining a polar phase with relaxor-like behavior in poly(vinylidene fluoride), as required for high energy storage density, is a major challenge. To date, this has been achieved using complex and expensive synthesis of copolymers and terpolymers or via irradiation with high-energy electron-beam or γ-ray radiations. Herein, a facile process of pressing-and-folding is proposed to produce β-poly(vinylidene fluoride) (β-phase content: ~98%) with relaxor-like behavior observed in poly(vinylidene fluoride) with high molecular weight > 534 kg mol−1, without the need of any hazardous gases, solvents, electrical or chemical treatments. An ultra-high energy density (35 J cm−3) with a high efficiency (74%) is achieved in a pressed-and-folded poly(vinylidene fluoride) (670-700 kg mol−1), which is higher than that of other reported polymer-based dielectric capacitors to the best of our knowledge. Dielectric materials are candidates for electric high power density energy storage applications, but fabrication is challenging. Here the authors report a pressing-and-folding processing of a dielectric with relaxor-like behavior, leading to high energy density in a polymer-based dielectric capacitor. [ABSTRACT FROM AUTHOR]

• Achieving ultrahigh W rec of 10.0 J/cm3 and η of 91 % in BST-based ceramics. • The variation of relaxor feature is analyzed by multi-polarization mechanism model. • Simultaneously toughening and enhanced energy storage performance are realized. Lead-free ceramic capacitors offer ultrahigh power density and ultrafast discharging rates, making them critical energy storage components for advanced pulsed power systems. However, the greatest obstacle to broader applications remains the relatively low energy storage density. In this study, a relaxor ferroelectric ceramic based on (0.6-x)Ba 0.55 Sr 0.45 TiO 3 -0.4Bi 0.5 Na 0.5 TiO 3 -xSrZrO 3 ((0.6-x)BST-0.4BNT-xSZ) is prepared using the tape casting method, resulting in an excellent energy density (W rec ≈ 10.0 J cm−3) and high energy storage efficiency (η ≈ 91 %). The solid solution of linear dielectrics SrZrO 3 synergistically regulates both relaxor properties and breakdown strength. The variation of relaxor property was explored utilizing New Glass model and the multi-polarization model, with confirmation provided by piezoresponse force microscopy. Furthermore, the breakdown strength could be attributed to improvements in electric insulation and the widening of the bandgap. As SrZrO 3 content increases, the in-situ emergence of the second phase ZrO 2 , accompanied by a martensitic transformation, not only improves the fracture toughness of ceramics but also serves to elongate the breakdown path. Encouragingly, x = 0.20 ceramics also achieve excellent temperature stability (−95–125 ℃), frequency stability (1–1000 Hz), cycling reliability (1–106 cycles), and great charging-discharging properties. This multiscale synergic regulation strategy plays a guiding role in the screening of high-performance energy storage dielectric materials. [ABSTRACT FROM AUTHOR]

Abstract Highly textured Ba 2 Bi 4 Ti 5 O 18 ceramic was prepared by spark plasma sintering (SPS). X-ray diffraction of the ceramics revealed the coexistence of a major ferroelectric phase (Space group, SG: B 2 cb) and a minor paraelectric phase (SG: I4/mmm) at room temperature. A diffused phase transition was observed at around 240 °C. The evolution of the switching current peaks in the electric current vs. electric field (I-E) loops with increasing temperature was interpreted by the structural changes and temperature dependent polarisation reversal processes. The slim polarisation vs. electric field (P-E) loops, the extra switching current peaks in the I-E loops and the non-zero piezoelectric d 33 coefficient indicate that Ba 2 Bi 4 Ti 5 O 18 is a relaxor ferroelectric material. The recoverable energy density (0.41 ± 0.01 J/cm3) of Ba 2 Bi 4 Ti 5 O 18 ceramics in the perpendicular direction to the SPS pressing direction is close to that of Pb(Mg 1/3 Nb 2/3)O 3 -based ceramics. The obtained results suggest Ba 2 Bi 4 Ti 5 O 18 ceramics might be promising for energy storage applications. [ABSTRACT FROM AUTHOR]