Enhanced energy storage density in Ca and Ta co-doped AgNbO3 antiferroelectric ceramics

Ca and Ta co-doped AgNbO₃ antiferroelectric lead-free ceramics were fabricated by rolling process technique, and improved energy storage properties were obtained. X-ray diffraction and Raman spectra indicate a single perovskite structure for (Ag_1-2xCa_x)(Nb_1-xTa_x)O₃ ceramics. The dielectric performances were also investigated, showing that increasing the content of Ca and Ta from 0.1 to 5 mol% gradually decreased the temperatures of the phase transition of monoclinic M₁-M₂ and M₂-M₃. This proved the enhanced antiferroelectricity stability associated with the enlarged low temperature phase transition region. The obtained (Ag_0.90Ca_0.05)(Nb_0.95Ta_0.05)O₃ ceramics exhibit an enhanced recoverable energy storage density (3.36 J/cm³) and efficiency (58.3%) with good temperature and frequency stability. The same composition shows excellent charge and discharge properties with a discharge current as high as 91.5 A and fast discharge speed (150 ns discharge period). All these merits demonstrate that AgNbO₃-based antiferroelectric ceramics are competitive with other lead-based and lead-free dielectric capacitors, which are promising candidates for dielectric energy storage applications.     

Significantly improved energy storage properties of sol-gel derived Mn-modified SrTiO3 thin films

In this paper, x mol% Mn-doped SrTiO₃ (STMx, x?=?0, 0.5, 1, 3 and 5) thin films were synthesized by a sol-gel method. The effect of Mn doping on the microstructure and electrical performance was investigated. STMx (x?≤?1) thin films shows a single cubic perovskite phase while impurity phase appears for STM3 and STM5 thin films confirmed by X-ray diffraction. X-ray photoelectron spectra reveals that STM1 thin film has the lowest concentration of oxygen vacancy. The dielectric constant and loss of STMx (x?≤?1) films display good frequency stability, while decrease with the frequency for STM3 and STM5 thin films. And all samples display excellent bias stability of dielectric constant; this is advantageous for applications in a high electric field. The ferroelectric test demonstrates that the electrical breakdown strength increases and leakage current decreases for Mn doped SrTiO₃ films. A great recoverable energy storage density of 23.8?J/cm³ with an efficiency of 69.8% at 2.286?MV/cm is obtained in STM1 thin film. Furthermore, STM1 thin film shows good frequency stability of energy storage properties. It indicates that Mn doping is a simple and effective method to improve the energy storage properties of dielectric capacitors.     

Large recoverable energy density with excellent thermal stability in Mn‐modified NaNbO3‐CaZrO3 lead‐free thin films

Effect of Mn dopant on energy storage properties in lead‐free NaNbO₃?0.04CaZrO₃ (NNCZ) thin films was investigated. The leakage current was largely suppressed, whereas dielectric constant, breakdown fields, and the difference between maximum polarization and remnant polarization were improved significantly by Mn doping, resulting in a large enhancement of energy storage performance. A large recoverable energy storage density of ~19.64 J/cm³ and an excellent thermal stability (from 30 to 160°C) were simultaneously achieved in the NNCZ thin film with 1 mol% Mn addition. Our results ascertain the great potential of NNCZ lead‐free thin films for the applications in energy storage devices over a wide temperature range.     

Energy storage performance of BiFeO3–SrTiO3–BaTiO3 relaxor ferroelectric ceramics

Dielectric capacitors reveal great potential in the application of high power and/or pulsed power electronic devices owing to their ultrafast charge–discharge rate and ultrahigh power density. Among various dielectric capacitors, the environment-friendly lead-free dielectric ceramics have drawn extensive investigations in recent years. Nevertheless, the relatively small recoverable energy storage density (W_rec) is still an obstacle for their application. Herein, the (0.55−x)BiFeO₃–0.45SrTiO₃–xBaTiO₃ ternary ceramics with 0.1 wt% MnO₂ were prepared by the solid-state reaction, and achieved enhanced relaxor behavior as well as breakdown strength E_b. As a result, the x = 0.12 ceramic exhibited superior comprehensive energy storage performance of large E_b (50.4 kV/mm), ultrahigh W_rec (7.3 J/cm³), high efficiency η (86.3%), relatively fast charge–discharge speed (t_0.9 = 6.1 μs) and outstanding reliability under different frequency, fatigue, and temperature, indicating that the BiFeO₃-based relaxor ferroelectric ceramics are prospective alternatives for electrostatic energy storage.     

Achieving high-energy storage performance of PbZro3-based thin films utilizing insulation interlayer and low-temperature annealing

PbZrO₃ (PZO)-based antiferroelectric thin films are of great interest due to their high-power density and fast charging and discharging capability. However, the problems of low breakdown strength and inferior energy storage density of PZO films have not been well solved. In this work, the insulating MgO as the blocking interlayer is inserted into PbZrO₃ films (abbreviated as P/M/P), which can inhibit the electric charge transfer and enhance the breakdown strength, as well as regulation of the polarization behavior. The results show that the maximal endurable electric field is significantly improved, and the double-hysteresis characteristic disappeared after introducing MgO blocking interlayer. The energy storage density of P/M/P films reaches 21.97 J/cm³ under 1700 kV/cm, accompanying an ultralow efficiency of 44.01% due to the severe polarization loss. Furthermore, low-temperature annealing is performed to suppress the polarization loss, and an energy storage density of 17.27 J/cm³ accompanying a high efficiency of 75.53% is obtained at 3100 kV/cm, still exhibiting good stability after 1 × 10⁷ fatigue cycles. This study demonstrates that combining the insulating interlayer and the low-temperature annealing endow the PZO-based films significantly improved energy storage properties, having great potential to be used in the dielectric capacitors.     

High energy storage performance in BaTiO3-based lead-free relaxors via multi-dimensional collaborative design

The application of advanced pulse power capacitors strongly depends on the fabrication of high-performance energy storage ceramics. However, the low recoverable energy storage density (W_rec) and energy efficiency (η) become the key links limiting the development of energy storage capacitors. In this work, a high W_rec of ～5.57 J cm^?3 and a large η of ～85.6% are simultaneously realized in BaTiO₃-based relaxor ceramics via multi-dimensional collaborative design, which are mainly attributed to the ferroelectric-relaxor transition, enhanced polarization, improved breakdown electric field, and delayed polarization saturation. Furthermore, the excellent temperature stability (ΔW_rec < ± 5%, 25–140 °C), frequency stability (ΔW_rec < ± 5%, 1–200 Hz), and outstanding charge/discharge performance (current density ～1583.3 A cm^?2, power density ～190.0 MW cm^?3) with good thermal stability are also achieved. It is encouraging that this work demonstrates that multi-dimensional collaborative design is a good strategy to develop new high-performance lead-free materials used in advanced dielectric capacitors.     

Influences of crystallization temperature on the structure,dielectric, and energy storage characteristics of KBaSrNb5O15-based glass–ceramics

Glass–ceramics capacitors have great application potential in pulsed power systems, due to ultrafast discharge speed and high dielectric breakdown strength (BDS). Here, lead-free niobate glass–ceramic dielectric materials were synthesized, and the effects of heat treatment temperature on the dielectric, ferroelectric, and energy storage properties of glass–ceramics were investigated comprehensively. The results exhibit that the dielectric permittivity first increases and then decreases as the crystallinity increases; however, the dielectric BDS diminishes. At the optimum crystallization temperature of 740°C, the maximum value of discharge energy density is 2.2 J/cm³ at 600 kV/cm, which is about 7.6 times that of mother glass. Furthermore, an ultrahigh power density of about 380.9 MW/cm³ and ultrafast discharge speed of about 11.2 ns were achieved simultaneously. Meanwhile, great thermal stability of charge–discharge property was verified in this glass–ceramics. According to P–E loops and dielectric test result, a high dielectric constant (∼207) and low dielectric loss (<0.005) as well as high energy storage efficiency of about 94.9% were achieved for G740 sample. The previous results make the obtained glass–ceramic as potential candidates in dielectric capacitors.     

Amelioration on energy storage performance of KNN-based transparent ceramics by optimizing the polarization and breakdown strength

Transparent ceramic capacitors have broad application prospects in electronic devices due to their excellent optical transparency and energy storage properties. However, the low polarizability and high remnant polarization of the existing transparent dielectric ceramics limit the promotion of energy storage performance. Here, Bi(Li_0.5Nb_0.5)O₃ (BLN) was chosen to modify the (K_0.5Na_0.5)NbO₃ (KNN)-based ceramics to optimize the optical transmittance and energy storage characteristics simultaneously. On the one hand, the grain growth is inhibited, contributing to the improved breakdown strength and transmittance. On the other hand, the doping BLN could reduce the polar nanoregions size, which makes them respond more quickly to the external electric field and, thus, improves the energy storage efficiency. As a consequence, 0.95KNN–0.05BLN ceramic possesses the excellent W_rec of 4.39 J/cm³, η of 81.4%, and transparency of 77.9% with an average grain size of ∼109 nm. This work opens up a paradigm to develop a transparent pulse capacitor.     

Excellent Polyimide Dielectrics Containing Conjugated ACAT for High-Temperature Polymer Film Capacitor

In order to meet the requirements of polymer dielectric materials for high thermal stability and excellent dielectric properties in the application of high-temperature film capacitors, a series of polyimide (PI) films are fabricated by introducing a self-synthesized aniline trimer (ACAT) with a conjugated structure in this work. Since the conjugated ACAT in the main chains of PI improves the electron polarization and carrier mobility of the PI molecular chains, the dielectric constant of the ACAT-PI films is greatly enhanced (4.4–7.4). Meanwhile, the dissipation factor does not increase apparently (0.002–0.013). The dielectric properties are stable even when the temperature is up to 200 °C, the thermal degradation temperature is as high as 450 °C, and the mechanical properties are also excellent (70–105 MPa). Among all the films, the PI film with 5 mol% ACAT exhibits the maximal energy density of 3.6 J cm⁻³ under the field of 426 kV mm⁻¹, the high tensile strength (90 MPa) and the excellent thermal stability (T_d5 = 515 °C). The work paves the way to prepare high-temperature polymer dielectric film materials with high energy storage density.     

Lead-free BaTiO3-Bi0.5Na0.5TiO3-Na0.73Bi0.09NbO3 relaxor ferroelectric ceramics for high energy storage

A series of (1-x)(0.65BaTiO₃-0.35Bi_0.5Na_0.5TiO₃)-xNa_0.73Bi_0.09NbO₃ ((1-x)BBNT-xNBN) (x = 0–0.14) ceramics were designed and fabricated using the conventional solid-state sintering method. The microstructure, dielectric property, relaxor behavior and energy storage property were systematically investigated. X-ray diffraction results reveal a pure perovskite structure and dielectric measurements exhibit a relaxor behavior for the (1-x)BBNT-xNBN ceramics. The slim polarization electric field (P-E) loops were observed in the samples with x ≥ 0.02 and the addition of Na_0.73Bi_0.09NbO₃ (NBN) could decrease the remnant polarization (P_r) of the (1-x)BBNT-xNBN ceramics obviously. The sample with x = 0.08 exhibits the highest energy storage density of 1.70 J/cm³ and the energy storage efficiency of 82% at 172 kV/cm owing to its submicron grain size and high relative density. These results show that the (1-x)BBNT-xNBN ceramics may be promising lead-free materials for high energy storage density capacitors.     

High-temperature resistant polyimide-based sandwich-structured dielectric nanocomposite films with enhanced energy density and efficiency

Development of advanced dielectric materials with both high-electric energy density and high-temperature resistant attributes is highly desirable in modern electronics and electrical systems. Herein, a series of polyimide (PI)-based sandwich-structured dielectric nanocomposite films have been attempted to develop the advanced high-temperature resistant capacitor films, wherein the boron nitride nanosheets/PI nanocomposite acts as the outer layers and the zinc oxide (ZnO)/PI as the middle layer. Benefitting from the merits of both fillers and the unique structure, the resulting nanocomposite films can simultaneously achieve both high-dielectric constant and high-breakdown strength, as well as low-electrical conduction loss, thus leading to improved discharged energy densities (U_e) and charge/discharge efficiency (η) at elevated temperatures. It is found that the sandwich-structured nanocomposite film with 0.4 vol% ZnO (0.4ZnO/PI-S) can deliver a maximum U_e of 5.29 J cm⁻³ at 400 MV m⁻¹ and 150°C, which is about 1.9 times that of the pristine PI film. Moreover, outstanding dielectric stability over 10,000 charge/discharge cycles has been demonstrated in such PI-based sandwich-structured nanocomposite films at 150°C and 200 MV m⁻¹. This research may provide a new paradigm to explore polymer nanocomposites having excellent energy storage and efficiency at elevated temperatures.     

KNN based high dielectric constant X9R ceramics with fine grain structure and energy storage ability

In this study, SrZrO₃ doped K_0.5Na_0.5NbO₃ ceramics with Cu, Sn, and Mn as sintering aid are prepared to modulate the temperature stability by conventional solid-state sintering, and samples are denoted as KNNC-100xSZ, KNNS-100xSZ, and KNNM-100xSZ, respectively, where x is the doping amount. The average grain size of the KNNC-12.75SZ sample was ~150 nm. The dielectric constant of KNNC-13.00SZ was 2072 and its dielectric loss was 1.8% at room temperature, with a wide temperature stability range from −55°C to 220°C satisfying the X9R criteria. The discharge energy density of KNNC-12.75SZ reached 1.47 J/cm³ at room temperature; therefore, the modified KNN is a promising candidate for X9R dielectrics with a fine grain structure and potential anti-reduction capability due to the absence of variable valence elements. The modified KNN can also be applied to energy storage capacitors subjected to high working temperatures.     

Ba-based complex perovskite ceramics with superior energy storage characteristics

Linear dielectrics are widely used to create high power capacitors, where it is a big challenge to achieve high energy storage density in such dielectrics. Here, Ba-based complex perovskite ceramics with high dielectric strength, medium dielectric constant, and ultra-low dielectric loss are proposed as the candidates for high energy storage density dielectric materials, and the significant effects of 1:2 B-site ordering and ordering domain structure are systematically investigated. In Ba(Mg_1/3Nb_2/3)O₃ ceramics, high dielectric strength of 1452 kV cm⁻¹ combined with high energy storage density of 3.31 J cm⁻³ are achieved in the samples after post-densification annealing, and they are 28% and 57%, respectively, higher than those in the as-sintered samples. The significant enhancement of energy storage performance could be attributed to the increased B-site ordering degree, and the uniform ordering domain structure. Furthermore, amorphous alumina thin films are introduced as the charge blocking layers, which significantly enhance the energy storage density to 5.09 J cm⁻³. The present work provides a new approach to develop the dielectric ceramics with high energy storage density.     

Enhanced energy storage density and discharge efficiency in potassium sodium niobite-based ceramics prepared using a new scheme

The development of lead-free ceramics with high recoverable energy density (W_rec) and high energy storage efficiency (η) is of great significance to the current energy situation. In this work, a new scheme was proposed to improve the W_rec and η of potassium sodium niobate ((K, Na)NbO₃, abbreviated as KNN) lead-free ceramics. Doping Bi elements in KNN ceramics to form a second phase (K₂BiNb₅O₁₅) can reduce the grain size and form Schottky-like contact. Meanwhile, the hybridization between the Bi 6p and O 2p orbitals can enhance the maximum polarization (P_max). So the K_1-3xBi_xNa_0.5NbO₃-1 mol%CuO ceramics was proposed to improve the W_rec of lead-free ceramics. A large W_rec (2.89 J/cm³) and dielectric breakdown strength (DBS) (300 kV/cm with a thickness of 0.2 mm) were achieved for K_0.14Bi_0.12Na_0.5NbO₃-1 mol%CuO ceramics. The high W_rec was supposed to benefit from low remnant polarization (P_r), high Ps and DBS of ceramics. In addition, a large η (80%) was simultaneously achieved for K_1-3xBi_xNa_0.5NbO₃-1 mol%CuO ceramics, which is superior to mostly reported lead-free bulk ceramics. The results show that K_1-3xBi_xNa_0.5NbO₃-1 mol%CuO ceramics have a good application prospect in the field of energy storage, and provide a new scheme for the preparation of lead-free ceramics with high energy storage density and high conversion efficiency.     

Synergic modulation of over-stoichiometrical MnO2 and SiO2-coated particles on the energy storage properties of silver niobate-based ceramics

AgNbO₃-based ceramics have been the spotlight for the lead-free dielectric capacitors due to its unique antiferroelectric feature and the ever-increasing environmental concerns. Herein, synergic modulation on the energy storage properties of AgNbO₃-based ceramics was reported, in which the over-stoichiometrical introduction of only 0.10 wt% MnO₂ at the atomic-scale leads to reduced leakage current, P_r and enhanced antiferroelectric stability while the SiO₂ coating on the AgNbO₃ particles at the micro-scale greatly inhibits the grain growth, increases the breakdown strength and the electric filed inducing the AFE-FE transitions. As a result, a large recoverable energy density up to 3.34 J/cm³ with efficiency of 60.0% was obtained in 0.10 wt% MnO₂-doped AgNbO₃@SiO₂ ceramic, which is 2.3 times larger than that of the pristine AgNbO₃. This work provides a rational approach to synergically modulate the energy storage properties.     

Lead-free Ag1−3xLaxNbO3 antiferroelectric ceramics with high-energy storage density and efficiency

Environmentally benign lead-free bulk ceramics with high recoverable energy density (W_rec) are very attractive in advanced pulsed power capacitors. In this work, composition engineering was adopted by La³⁺ modification to improve the energy storage performance of Ag_1−3xLa_xNbO₃ ceramics. It was found that the antiferroelectric (AFE) phase was stabilized after La³⁺ substitution, as a result of the reduced tolerance factor t. Significant improvement of W_rec and energy storage efficiency (η) were achieved with value of 3.12 J/cm³ and 0.63 for x = 0.02 at an electric field of 230 kV/cm, more than 1.5 times the value of pure AgNbO₃ (W_rec = 1.9 J/cm³, η = 0.40). The excellent energy storage properties are resulted from the increased antiferroelectric-ferroelectric phase transition electric field (E_F), ferroelectric-antiferroelectric phase transition electric field (E_A), and breakdown electric field (E_b). The enhanced E_b was ascribed to the decreased grain size and increased electrical resistivity upon La³⁺ modification. The feature makes Ag_1−3xLa_xNbO₃ a potential candidate for energy storage applications.     

Bi-modified SrTiO3-based ceramics for high-temperature energy storage applications

Dielectric capacitors with high energy storage performance are in great demand for emerging advanced energy storage applications. Relaxor ferroelectrics are one type dielectric materials possessing high energy storage density and energy efficiency simultaneously. In this study, 0.9(Sr_0.7Bi_0.2)TiO₃–0.1Bi(Mg_0.5Me_0.5)O₃ (Me = Ti, Zr, and Hf) dielectric relaxors are designed and the corresponding energy storage properties are investigated. The excellent recoverable energy density of 3.1 J/cm³ with a high energy efficiency of 93% is achieved at applied electric field of 360 kV/cm for 0.9(Sr_0.7Bi_0.2)TiO₃–0.1Bi(Mg_0.5Hf_0.5)O₃ (0.9SBT–0.1BMH) ceramic. High breakdown strength of 460 kV/cm in 0.9SBT–0.1BMH ceramic is obtained by Weibull distribution with satisfied reliability. In addition, 0.9SBT–0.1BMH shows outstanding thermal stability of energy storage performance up to 200°C, with the variation being less than 5%, together with satisfying cycling stability and high charge-discharge rate, making the 0.9SBT–0.1BMH ceramic a potential lead-free candidate for high power energy storage applications at elevated temperature.     

Ho3+-doped (K,Na)NbO3-based multifunctional transparent ceramics with superior optical temperature sensing performance

Ho³⁺-doped (K_0.5Na_0.5)NbO₃-based transparent ceramics have been prepared via pressureless solid-state method. The ceramics possess moderate optical transparency with the energy band gap of ~2.9 eV and submicron-sized grains (<500 nm). The temperature-dependent dielectric properties and ferroelectric polarization-electric field hysteresis loops demonstrate that the ceramics own relaxor-like characteristics. The up-conversion photoluminescence and optical temperature sensing properties of the ceramics have been investigated. The temperature dependence of photoluminescence provides a fluorescent method to detect phase transitions, which can be expanded to other ferroelectric systems. The outstanding optical temperature sensitivity (~0.0075/K at 430 K) of the ceramic is higher than many other rare-earth-doped ceramics or glasses. These results suggest that the Ho³⁺-doped (K_0.5Na_0.5)NbO₃-based transparent ceramics are promising lead-free transparent materials for multifunctional applications, especially in temperature sensing devices.     

Breakdown field enhancement and energy storage performance in four-layered Aurivillius films

In dielectric capacitors, ferroelectric thin films with slim polarisation electric (P-E) hysteresis loops, which are mainly characterised by small residual polarisation (P_r) and large saturation polarisation (P_s) are expected to obtain high recoverable energy density (U_r) and efficiency (η). However, a lower breakdown in ferroelectric thin films usually impedes this result. Here, through the co-doping of La³⁺ and Pr³⁺ ions, a larger U_r of 54.27 J/cm³ and high η of 85.6% were obtained in four-layered Aurivillius phase ferroelectric thin films capacitors due to the enhanced breakdown electric field. The doped films annealed at relatively low temperatures showed similar energy storage properties compared with those of the prototype and higher energy storage efficiency compared with that of higher annealing films. In addition, the obtained thin film shows excellent energy storage properties in a wide frequency range, fatigue durability and good thermal stability. These results indicated that four-layered Aurivillius films are promising candidate materials for dielectric energy storage capacitors. The co-doping of double ions was an effective way to improve energy storage performance.     

Investigation of the Structure and Electrical Properties of (KxNa0.96−xLi0.04)(Nb0.96−yTaySb0.04)O3 Piezoelectric Ceramics Modified with Manganese

The effect of high doping levels of manganese (Mn) on the structure and electrical properties of (K_xNa_1?x)NbO₃ (KNN) ceramics containing Li, Ta, and Sb has been investigated. The samples were measured using synchrotron X‐ray diffraction whereas Rietveld refinement with Fullprof was used to determine the structural information as a function of temperature. Temperature‐dependent dielectric measurement was used to compare the phase transition temperatures. The results show that Mn decreases the temperature range of phase coexistence between the orthorhombic and tetragonal phase from ~180°C to ~120°C. The Curie temperature remained unchanged with Mn addition while the dielectric constant and dielectric loss increased with Mn addition. High amounts of Mn led to a reduction in both piezoelectric and ferroelectric properties. The remnant polarization, remnant strain, and piezoelectric coefficient values decreased from 24 μC/cm², 0.000824, 338 ± 37 pm/V to 13 μC/cm², 0,00014 and 208 ± 27 pm/V, respectively for the undoped and 5 mol% Mn‐doped sample.