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Dielectric composites with a high dielectric constant and electric breakdown strength are highly desired for the excellent energy storage behavior of the microelectronic and electric power systems. Sandwich-structured composites with an insulating layer can provide a pathway to improve the dielectric and energy storage performance, and in general, the fillers design and volume control of the insulating layer are very important. Herein, we present a novel designed sandwich-structured aluminum nitride/potassium niobate/poly(vinylidene fluoride) (AlN/KNbO 3 /PVDF) nanocomposites by the solution-casting and hot-pressing process. The effect of the introduction of an insulating phase AlN in the two outer layers and a different KNbO 3 volume fraction in the middle layer on the dielectric properties and energy storage behavior of the sandwich-structured composites were investigated in detail. The results demonstrate that dielectric constant, electric breakdown strength, energy storage density and discharged efficiency of the AlN/KNbO 3 /PVDF sandwich-structured composites are significantly enhanced. Moreover, a high energy density of 10.54 J/cm3 and a superior discharged energy efficiency of 70% at the electric breakdown strength of 337 MV/m are achieved in the sandwich-structured nanocomposites with 1 vol% KNbO 3 in middle layer and with 1 vol% AlN in the outer layers, which are much higher than the conventional single-layered KNbO 3 /PVDF composites. It is indicated that the introduction of insulating layers in sandwich-structure composites can improve the electric breakdown strength and discharge efficiency, as confirmed by analyzing results of the finite element simulations. This work may provide an effective approach to develop excellent performance dielectric composites for electrical energy storage applications. [ABSTRACT FROM AUTHOR]

Polymer dielectric capacitor have attracted much attention in the field of electronic power systems recently due to high power density and high breakdown strength. However, with the development of miniaturization and integration, further demands have been set on the higher energy storage density as well as better temperature resistance for dielectric polymers. Up to now, hierarchical structure provides an effective way to meet these requirements. Herein, we report a sandwich-structured all-organic composite via inserting polymethyl methacrylate/poly(vinylidene fluoride) (PMMA/PVDF) blend layer into polyetherimide layers. Increasing temperature increases the permittivity of the middle layer and the addition of PMMA makes the permittivity increase faster with temperature than pure PVDF middle layer. The capacitor series model and finite element simulation confirmed that the change of the middle layer permittivity realized the electric field redistribution to self-adapt to the temperature, preventing premature breakdown at elevated temperature. At 100 °C, optimized composite exhibits a high breakdown strength of 486.05 MV/m along with high polarization. Eventually, a high discharge energy density of 8.65 J/cm3 is obtained, which is 229.44% of pure PEI. The high polarization at high temperature was realized by utilizing the permittivity of PMMA/PVDF rising with temperature, thereby increasing the energy density at elevated temperature. [Display omitted] • Self-adaptive temperature capability of electric field distribution was achieved. • High breakdown strength and high polarization were simultaneously obtained at 100 °C. • Efficiency of 72.12% and energy density of 8.65 J/cm3 were obtained at 100 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • Utilize the topological-structure engineering to obtain the multilayer-structured nanocomposite films. • The optimized multilayer-structured nanocomposite film shows a larger D max of 11.7 μC/cm2. • A high U e of 18.84 J/cm3 and an ultrahigh η of 79.81% under an intermediate electric field are achieved. • The introduction of PMMA polymer into outer layers is benefical to depress the energy loss. • The structure design is an effective approach to attain excellent overall energy storage properties for nanocomposite films. The development of excellent performances polymer-based nanocomposite films with high discharge energy density and high discharge efficiency are eagerly desirable for promoting their electric energy storage applications. However, the high discharge energy density and efficiency of polymer-based nanocomposite films are usually not compatible above intermediate electric fields. To address this issue, here we propose a newly designed multilayer-structured nanocomposite film with a combination of introducing the BaTiO 3 /CaCu 3 Ti 4 O 12 @SiO 2 (BT/CCTO@SO) hybrid nanoparticles with core–shell structure in middle layer and the poly(methyl methacrylate) (PMMA) linear polymer with low loss in outer layers. These motivations of introducing the core–shell structured hybrid nanoparticles with high dielectric constant and designing the multilayered structure give rise to an enhancement of maximum electric displacement while maintaining a relatively high breakdown strength. Also importantly, bring the PMMA polymer into top and bottom layers results in the low energy loss of whole nanocomposite film. Benefiting from these merits, a larger maximum electric displacement of 11.7 μC/cm2 and a higher discharge energy density of 18.84 J/cm3 accompanied with an ultrahigh discharge efficiency of 79.81% under an intermediate electric field of 418.13 MV/m are achieved in multilayer-structured nanocomposite film even at a very low filler loading of 2 wt% BT/CCTO@SO hybrid nanoparticles in middle layer, and these enhanced values are far higher than that of the monolayer nanocomposite films. This work validates the advantages of multilayered structure to integrate multiple components and presents outstanding overall performances of nanocomposite films in further applications of the dielectric capacitors with miniaturization and integration. [ABSTRACT FROM AUTHOR]

The 0.63(1-x)Bi 1.02 FeO 3 -0.37BaTiO 3 -xBi(Zn 2/3 (Nb 0.85 Ta 0.15) 1/3)O 3 (abbreviated BF-BT-xBZNT) high temperature dielectric ceramics were prepared via a two-step sintering (TTS) method. The appropriate medium permittivity achieved in the BF-BT-0.13BZNT ceramic is conducive to mitigating the polarization saturation and improving the breakdown field strength. The domain evolution behavior from piezoresponse force microscopy (PFM) reveals that the introduction of BZNT promotes the formation and switching of more nanodomains of BF-BT ceramics, facilitating the enhancement of energy storage efficiency. The excellent energy storage performance of total energy storage density (W tot) of 6.06 J/cm3, recoverable energy storage density (W rec) of 4.85 J/cm3 and a high energy storage efficiency (η) of 80% are simultaneously obtained under 410 kV/cm in the BF-BT-0.13BZNT ceramic. Meanwhile, the ceramic exhibits excellent thermal endurance (10–130 ℃), frequency (1–100 Hz) and fatigue (105 cycles) stability. The current work provides a promising strategy for designing high-performance dielectric energy storage materials which operate in harsh environments. • Utilize a composition design strategy to simultaneously obtained optimized polarization and large electric field strength. • The excellent W rec (~ 4.85 J/cm3) and η (~ 80%) at a large field of 410 kV/cm were achieved in BiFeO 3 -based ceramics. • The domain dynamic evolution behavior is confirmed by PFM measurements. • The energy storage performance has a good frequency, temperature, and cycling stability. [ABSTRACT FROM AUTHOR]

• Modulate polar nanoregions in the local structure to decrease the remnant polarization. • Maintain a high maximum polarization by introducing Bi-containing dopants. • Obtain a high W rec of 3.03 J/cm3 together with a moderate η of 79.5 % under a low electric field of 200 kV/cm. • Achieve high W rec (2.41–2.52 J/cm3) and excellent thermal stability (W rec varying less than 4.3 % and η > 90 %) from 50 °C to 200 °C under 150 kV/cm. High energy density and high thermal stability of energy-storage properties (ESP) under low electric fields are extremely crucial for the application of dielectric ceramics in miniaturized equipment. In present work, we use a composition-optimization approach to break the long-range ferroelectric order and modulate polar nanoregions (PNRs) in the local structure of (1-x)[0.7(Na 0.5 Bi 0.5)TiO 3 -0.3(Sr 0.7 Bi 0.2)TiO 3 ]-xBi(Mg 0.5 Ti 0.5)O 3 system. The large P max value is maintained due to the existence of Bi ions in both the matrix and dopants. As a result, a high W rec of 3.03 J/cm3 together with a moderate η of 79.5 % was obtained in x = 0.05 sample at a low electric field of 200 kV/cm. Meanwhile, the high W rec (2.41–2.52 J/cm3) and excellent thermal stability of ESP (W rec varying less than 4.3 % and η > 90 %) from 50 °C to 200 °C at 150 kV/cm were also observed. The current system will be a promising candidate in energy-storage capacitor applications under low-fields and high-temperature. [ABSTRACT FROM AUTHOR]

Piezoelectric actuators play an important role in modern electronic devices. In this work, 0.7Bi(1−x)SmxFeO3–0.3BaTiO3 lead-free piezo-ceramics are fabricated through the rapid thermal quenching technique for enhancing the electric-field-induced strain response. All the ceramic samples own a typical perovskite structure, and the morphotropic phase boundary can be achieved after Sm substitution. Additionally, a high TC of 403 °C and excellent ferroelectricity can be obtained at room temperature for the x = 0.03 composition, together with a large peak-to-peak strain value (∆S = 0.5%). Furthermore, a larger strain value ∆S of 0.45% at 150 °C can also be realized in 0.7Bi0.95Sm0.05FeO3–0.3BaTiO3 ceramic. Our results could further stimulate the investigations on lead-free ceramics for piezoelectric actuator applications. [ABSTRACT FROM AUTHOR]

• SrTiO 3 doped xBiFeO 3 -(1-x)BaTiO 3 ternary ceramics are successfully fabricated. • The phase diagram of the ceramics is confirmed by XRD and dielectric analyses. • The largest electromechanical properties are obtained in the ceramics with x = 0.63. • The enhanced property is due to relaxor behavior and morphotropic phase boundary. High temperature lead-free piezoceramics of 0.06SrTiO 3 -0.94[(1-x)BaTiO 3 - xBiFeO 3 were fabricated by the traditional solid state reaction method. The ceramics possess the pure perovskite structures, and a morphotropic phase boundary (MPB) with the pseudo-cubic and rhombohedral phases is observed at x = 0.55-0.71. The ceramics have the obvious relaxor behaviors as confirmed by the temperature and frequency dependent dielectric curves. The largest positive electrostrain (0.25%) under 65 kV/cm is achieved in the ceramics with x = 0.63. The ceramics with x = 0.63 also exhibit a large d 33 * (425 pm/V) with a high curie temperature (T C =282 °C) and a low hysteresis (43%). The improved electromechanical properties are attributed to the existence of relaxor behavior at BiFeO 3 -BaTiO 3 phase boundary after doping SrTiO 3. These results demonstrate that the design of a ternary system like ST-BF-BT based ceramics with relaxor behavior and phase boundary composition provides an effective way to optimize the electrostrain behavior of high temperature lead-free ceramics. [ABSTRACT FROM AUTHOR]

• The simple A-site single K+ ion doped 0.63Bi1-xKxFeO3-0.37BaTiO3 ceramics are successfully fabricated. • The optimal d 33 * (861pm/V) under low electric field at 105 ℃ is obtained in 0.63Bi 0.9975 K 0.0025 FeO 3 -0.37BaTiO 3 ceramic. • The relaxor and domain evolution behavior which are related to the electromechanical properties are investigated by PFM. Designing high temperature piezoelectric ceramics with large electromechanical properties is key to the actuators application in harsh environment. BiFeO 3 -BaTiO 3 based piezoelectric ceramics are the promising candidates due to their high electromechanical properties and high Curie temperature. Here, the simple A-site single K+ doped 0.63Bi 1−x K x FeO 3 -0.37BaTiO 3 (abbreviated as 0.63B 1−x K x F-0.37BT) ceramics with positive temperature dependent electromechanical properties were fabricated via conventional solid phase method. The electromechanical properties in the 0.63B 1−x K x F-0.37BT ceramics are closely related to the content of K+ doping. The excellent electromechanical properties of S= 0.26% and d 33 *=861 pm/V under low electric field of 30 kV/cm at 105 ℃ are achieved in the 0.63B 0.9975 K 0.0025 F-0.37BT ceramic, which is conducive to their application at high temperature. Combined with the microstructure and PFM, the optimized electromechanical properties in 0.63B 0.9975 K 0.0025 F-0.37BT ceramic are mainly due to more nanodomains switching facilitated by the large grain size and local structural heterogeneity. The site engineering of A-site single ion doping is an efficient and simple strategy for BF-BT based piezoelectric ceramics to achieving excellent electromechanical properties under low electric field at high temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • Utilize a composition-driven strategy to induce PNRs, refine grain size and adjust permittivity. • Obtain an extraordinary W rec of 6.43 J/cm3 and high η of 88% at 505 kV/cm. • The existence of dynamic PNRs is confirmed by PFM measurements. • The field-insensitive medium permittivity can mitigate polarization saturation and boost W rec. • The temperature-dependent Raman spectra reveal the variation of local structure. High energy density, efficiency and thermal stability of energy-storage properties are extremely pivotal for the application of dielectric ceramics in advanced pulsed power systems. In this work, we utilize a composition-driven strategy to induce polar nanoregions, refine grain size and adjust permittivity of (1- x)Bi 0.5 (Na 0.9 Li 0.1) 0.5 TiO 3 - x Sr(Al 0.5 Nb 0.25 Ta 0.25)O 3 ceramics. As a result, an extraordinary W rec of 6.43 J/cm3 and high η of 88% are simultaneously obtained in the x = 0.16 composition. Meanwhile, the x = 0.16 sample also shows good frequency stability (5–100 Hz), cycle stability (105 cycles) and superior thermal stability (-55 ~ 225 ℃). The enhanced breakdown strength is analyzed by Weibull distribution and mainly attributed to the decreased average grain size. The typical relaxor behavior is reflected by the broadened and diffused Raman spectra as well as the dispersive and temperature-stable dielectric curves. The existence of dynamic polar nanoregions as confirmed by piezoresponse force microscopy measurements enables the nearly hysteresis-free polarization–electric field response and the related frequency and cycle stability. The mitigated polarization saturation is related to the field-insensitive moderate permittivity and will be conducive to the energy-storage properties at elevated electric field. In addition, the temperature-dependent Raman spectra and the slightly fluctuated Δ P (P m - P r) value over the whole temperature range reflect the temperature-stable energy-storage properties. Hence, the current work may provide some novel perspectives for designing dielectric ceramics with enhanced energy-storage properties. [ABSTRACT FROM AUTHOR]

• The B-site single Sb ion doping 0.67BiFeO 3 -0.33BaTiO 3 ceramics are successfully fabricated. • The 0.67BiFe 99.75% Sb 0.25% O 3 -0.33BaTiO 3 ceramic owns large electromechanical properties at relative low electric field. • The possible mechanism of the large strain for 0.67BiFe 1-x Sb x O 3 -0.33BaTiO 3 ceramics is elucidated. Antimony modified 0.67BiFeO 3 -0.33BaTiO 3 based ceramics with pure perovskite structure have been fabricated by conventional solid-state reaction method. The effects of single Sb ion doping on the microstructure, permittivity, electric field induced strain (S) and ferroelectric performance are investigated systematically. The XRD and permittivity analysis results indicate a mixed phase of pseudo-cubic and rhombohedral at morphotropic phase boundary (MPB). Compared with other single ion doped BF-BT systems, Sb doped samples show a large strain under relatively small electric field. The highest unipolar strain (0.168%) and converse piezoelectric coefficient d 33 * (336 pm/V) at 50 kV/cm are obtained in 0.67BiFe 99.75% Sb 0.25% O 3 -0.33BaTiO 3 ceramic, Which may be attributed to the domains wall movement facilitated by the soft effect of donor doping Sb. This work suggests simple single B - site ion doping can also effectively improve the electromechanical performance of BiFeO 3 -BaTiO 3 based ceramics under low electric field. [ABSTRACT FROM AUTHOR]

• A comprehensive strategy of hybridizations of Bi3+ orbitals and relaxor was adopted. • Relaxor behavior was analyzed via Raman spectroscopy and the Curie-Weiss law. • BNT-0.40ST-0.02FN composition exhibits high W (3.36 J/cm3) and η (81%) under a low electric field of 170 kV/cm. • BNT-0.40ST-0.02FN ceramic shows superior thermal stability (25–200 °C). • The BNT-0.40ST-0.02FN ceramic possesses potential to be employed in pulsed power devices under extreme conditions. Dielectric ceramics are highly favorable for pulsed power applications owing to their ultra-fast charge-discharge speed and excellent reliability. However, their low energy density under low electric fields remains as a bottleneck for them to be employed in integrated electronic devices with shrinking dimensions. In this work, we have designed a comprehensive strategy to synthesize lead-free (Bi 1/2 Na 1/2) 1−x Sr x Ti 0.98 (Fe 1/2 Nb 1/2) 0.02 O 3 (BNT-xST-2FN, x = 0.30, 0.35, 0.40 and 0.45) ceramics via traditional solid-state method. On one hand, the hybridizations of Bi3+ orbitals and the displacement of B-site cations under the applied electric field lead to a high polarization. On the other hand, the (Fe 1/2 Nb 1/2)4+ complex-ion and SrTiO 3 were introduced to improve the relaxor behavior of the system, resulting in a high energy-storage efficiency. In this way, an excellent energy density of 3.36 J/cm3 and a high energy efficiency of 81% are simultaneously achieved in the BNT-0.40ST-0.02FN composition under a low electric field of 170 kV/cm, which is superior to other BNT-based materials under similar electric fields. Moreover, the ceramic exhibits a superior thermal stability (25–200 °C). This work provides a promising approach for designing high-performance lead-free energy storage ceramics under low electric fields. [ABSTRACT FROM AUTHOR]

High permittivity and low dielectric loss are important for the application of high-temperature dielectrics. In present study, high temperature dielectrics based on (1-x) [(Na 0.5 Bi 0.5) 0.92 Ba 0.08 0.955 La 0.03 TiO 3 -xNaNbO 3 compositions were synthesized by a conventional solid-state reaction method. The microstructure, dielectric, ferroelectric and electrical properties were systematically investigated. All the samples show relatively high permittivity and excellent low dielectric loss range from ∼ 90 °C up to 400 °C. Impressively, the composition x = 0.06 shows a high permittivity of 2436 at 150 °C (1 kHz), (ε r − ε r 150 ° C )/ ε r 150 ° C varying no more than 15% in the temperature range of 54 °C–344 °C together with a low loss (tan δ ≤ 0.02) range between 92 °C and 400 °C. By developing highly-localized complex defect-dipoles with La and NaNbO 3 dopants to restrain the mobility of oxygen vacancy, as verified by XPS and resistivity-temperature results, the dielectric loss is limited to rather low values. Hence, the current system will be a promising candidate in high temperature ceramic capacitors. • All the samples show relatively high permittivity and excellent low dielectric loss range from ∼ 90 °C up to 400 °C. • Fine-tune the dielectric loss through defect chemistry. • Developing highly-localized defect dipoles to restrain the mobility of oxygen vacancy. [ABSTRACT FROM AUTHOR]