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.     

Li+ and Sm3+ co-doped AgNbO3-based antiferroelectric ceramics for high-power energy storage

Ag_1-x-3yLi_xSm_yNbO₃ (x≤0.05, y≤0.05) (ALSN) antiferroelectric ceramics were successfully prepared via conventional solid-state reaction and sinter routes in oxygen atmosphere for improving the energy storage characteristic of pure AgNbO₃. The results indicate that all of the studied compositions display a pure orthorhombic antiferroelectric (AFE) perovskite structure, while their key parameters of electric-field-induced antiferroelectric-ferroelectric transition can be affected by Li⁺ or/and Sm³⁺ doping contents. The Sm³⁺ doping can enhance the stability of antiferroelectric state, giving rise to higher antiferroelectric-ferroelectric transition electric-field (E_F and E_B), while Li⁺ doping can reduce E_F and E_B for Sm³⁺ doped AgNbO₃ with low Sm³⁺ content (y≤0.03). When co-doping the same amounts of Li⁺ and Sm³⁺ at x=y≤0.03, both E_F and E_B almost remain unchanged. At x=y=0.05, the diffuse phase transition (DPT) behavior of antiferroelectric-paraelectric (AFE-PE) phase transition occurred, resulting in a “slim-like” double-polarization hysteresis with significantly enhanced E_F. Due to these features, both W_rec and η are improved compared with pure AgNbO₃. The W_rec and η with composition at x=y=0.05 is 2.33 J/cm³ and 58% under applying electric field of 240 kV/cm, respectively. The results suggest that building DPT behavior of AFE-PE phase transition could be an alternative strategy to improve the energy storage characteristic of AgNbO₃.     

Revealing the solid-state processing mechanisms of antiferroelectric AgNbO3 for energy storage

AgNbO₃ is one of the prominent lead-free antiferroelectric (AFE) oxides, which readily exhibits a field-induced AFE to ferroelectric phase transition and thus a high energy storage density. The solid-state synthesis of AgNbO₃ is considered difficult and an oxidizing atmosphere is typically employed during AgNbO₃ processing, on the premise that oxygen can prevent possible decomposition of the silver oxide at high temperatures. However, details about the influence of processing parameters on the functional properties of AFE AgNbO₃ are insufficiently understood. In this work, the solid-state reaction of a stoichiometric AgO and Nb₂O₅ mixture was investigated. We found that ball milling can convert AgO into metallic Ag, which is beneficial for lowering the reaction temperature for the formation of the perovskite phase to 500‒600℃. Moreover, the influence of the processing atmosphere (air, O₂, and N₂) was investigated by thermal analysis and in situ X-ray diffraction. Since the reaction between Ag and Nb₂O₅ to form AgNbO₃ requires oxygen uptake, AgNbO₃ was only found to form in air and O₂, whereby the kinetics were faster in the latter case. All the sintered AgNbO₃ samples exhibited a similar crystallographic structure, although the samples processed in O₂ had a lower oxygen vacancy concentration. Despite this, well-defined AFE double polarization loops were obtained in all cases. Our results indicate that decomposition of sliver oxide during ball milling is beneficial for the solid-state reaction, while a pure O₂ atmosphere is not essential for the synthesis of high-quality AgNbO₃. These findings may simplify the processing and facilitate further research of AgNbO₃-based antiferroelectrics.     

Electrostatic energy storage performances of La(Ni2/3Ta1/3)O3-modified Na0.5Bi0.5TiO3 lead-free ceramics

Ceramic capacitors with high electrostatic energy storage performances have captured much research interest in latest years. Sodium bismuth titanate (Na_0.5Bi_0.5TiO₃)-based ferroelectric ceramics show great potential due to their environment-friendly composition, high polarization, and excellent relaxor properties. However, the nonergodic relaxor state of Na_0.5Bi_0.5TiO₃-based ceramics hampers the decrement of remanent polarization, leading to poor energy storage performance. Herein, the (1 − x)Na_0.5Bi_0.5TiO₃–xLa(Ni_2/3Ta_1/3)O₃ ceramics were designed to generate the transformation between nonergodic and ergodic relaxor state. As a result, the ceramics exhibit improved dielectric relaxation, slim polarization–electric field loops, and flattened current–electric field curves due to highly dynamic polar nanoregions. Particularly, the 0.85Na_0.5Bi_0.5TiO₃–0.15La(Ni_2/3Ta_1/3)O₃ ceramics show large breakdown electric field E_b (345 kV/cm), high recoverable energy density W_rec (3.6 J/cm³), and efficiency η (80.6%), revealing potential applications in electrostatic energy storage.     

Structure and energy storage performance of lanthanide elements doped AgNbO3 lead-free antiferroelectric ceramics

The aliovalent A-site modification in Silver niobate (AgNbO₃, AN) antiferroelectrics has exhibited its advances in improving energy storage performance, but lack of a comprehensive understanding. In this work, 3 mol% lanthanide elements (Re: Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm) modified AgNbO₃ (ReAN) ceramics were investigated. Compared with pristine AN, the ReAN ceramics exhibited decreased M1-M2 phase transition temperature and typical double-like P-E loops. The antiferroelectricity improved firstly from SmAN to TbAN because of reduction of tolerance factor, then it decayed with increasing atomic number due to partial Re³⁺ ions entering into B-site. Consequently, high recoverable energy density (W_rec ≈ 4.5 J/cm³) and efficiency (η ≈ 65 %) were achieved for the compositions from SmAN to TbAN under 250 kV/cm. While a general decrease in W_rec and η was observed by further increasing atomic number. This study provides a comprehensive knowledge of lanthanide element dopants in AgNbO₃ system.     

High energy storage performance in Ca-doped PbZrO3 antiferroelectric films

In this work, antiferroelectric Pb_1-xCa_xZrO₃ (PCZ) thin films with different concentrations of Ca²⁺ were prepared by chemical solution deposition, and the effects of Ca²⁺ concentration on the antiferroelectric properties and energy storage performance were investigated. The results show that the optimal Ca²⁺ concentration in the PCZ thin films is x = 0.12 for electric properties and energy storage performance. The recoverable energy storage density and energy storage efficiency is 50.2 J/cm³ and 83.1 % at 2800 kV/cm, which is 261 % and 44.8 % higher than those of the PbZrO₃ (PZ) films. These effects are attributed to the enhancement of stability of antiferroelectric phase, diffuseness in the field-induced phase transition and electric breakdown strength by Ca²⁺-doping in the PZ films. Our results demonstrate that doping an appropriate amount of Ca²⁺ ions in antiferroelectric thin films is an effective way to improve their energy storage performance.     

Excellent energy storage performance of NaNbO3-based antiferroelectric ceramics with ultrafast charge/discharge rate

Dielectric capacitors have drawn increasing attention due to their fast charge/discharge rates and high power density. Among all known ceramic dielectric materials, antiferroelectrics are more attractive for their unique double ferroelectric hysteresis loops and higher energy densities. Here, a series of antiferroelectric ceramics x(0.95Bi_0.5Na_0.5TiO₃-0.05SrZrO₃)-(1-x)NaNbO₃ (xBNTSZ-(1-x)NN, x = 0.23, 0.30, 0.35, 0.50) have been prepared. By stabilizing the antiferroelectric phase and postponing the critical electric field of the antiferroelectric-ferroelectric phase transition, an impressive discharge energy storage density of 4.08 J/cm³ at a breakdown strength of 370 kV/cm was achieved for the 0.35BNTSZ-0.65 N N. A superior comprehensive performance for the 0.50BNTSZ-0.50 N N ceramic with a discharge energy storage density (W_dis) of 3.78 J/cm³ and an efficiency of 86 % at an electric field strength of 320 kV/cm along with excellent frequency, temperature, and fatigue stabilities (fluctuations of W_dis≤±5% within 0.01∼100 Hz, W_dis≤10 % over 20∼140 °C, and W_dis≤1% over 10⁶ cycle numbers) is realized. Furthermore, 0.50BNTSZ-0.50 N N ceramics simultaneously exhibit a high current density (622.5 A/cm²), high power density (112 MW/cm³), and fast discharge rate (t = 47 ns), all of which make it an excellent candidate for the pulsed power devices.     

Structure variation and energy storage properties of acceptor-modified PBLZST antiferroelectric ceramics

Energy storage capacitors with high recoverable energy density and efficiency are greatly desired in pulse power system. In this study, the energy density and efficiency were enhanced in Mn-modified (Pb_0.93Ba_0.04La_0.02)(Zr_0.65Sn_0.3Ti_0.05)O₃ antiferroelectric ceramics via a conventional solid-state reaction process. The improvement was attributed to the change in the antiferroelectric-to-ferroelectric phase transition electric field (E_F) and the ferroelectric-to-antiferroelectric phase transition electric field (E_A) with a small Mn addition. Mn ions as acceptors, which gave rise to the structure variation, significantly influenced the microstructures, dielectric properties and energy storage performance of the antiferroelectric ceramics. A maximum recoverable energy density of 2.64 J/cm³ with an efficiency of 73% was achieved when x = 0.005, which was 40% higher than that (1.84 J/cm³, 68%) of the pure ceramic counterparts. The results demonstrate that the acceptor modification is an effective way to improve the energy storage density and efficiency of antiferroelectric ceramics by inducing a structure variation and the (Pb_0.93Ba_0.04La_0.02)(Zr_0.65Sn_0.3Ti_0.05)O₃-xMn₂O₃ antiferroelectric ceramics are a promising energy storage material with high-power density.     

PLZST antiferroelectric ceramics with promising energy storage and discharge performance for high power applications

Capacitors are widely used as energy storage elements in electric vehicles (EVs) and pulsed power. At present, it is still challenging to develop capacitor dielectrics with good energy storage and discharge performance. In this work, antiferroelectric (AFE) ceramics (Pb_0.94La_0.04)[(Zr_0.6Sn_0.4)_0.92Ti_0.08]O₃ with enhanced antiferroelectricity were fabricated by a rolling process. The obtained ceramics have a high recoverable energy density of 5.2 J/cm³ and an extremely high efficiency of 91.2% at 327 kV/cm. The ceramics have good energy storage and discharge performance in the temperature range from −40°C to 100°C due to the existence of AFE phase. An energy density of 3.7 J/cm³ can be released at 200 kV/cm in less than 500 ns and the discharge current keeps stable after 1000 charge-discharge cycles. By direct short experiment, a current density of 1657 A/cm², which is the highest result in recently developed AFE ceramics, and a power density of 228 MW/cm³ were achieved. The possibility of using AFEs at low temperature was confirmed. The excellent energy storage and discharge performance prove the great potential of the obtained ceramics in high energy and power density applications.     

Enhanced energy storage performance in samarium and hafnium co-doped silver niobate ceramics

Improving energy storage density and efficiency of antiferroelectric materials could promote their use within energy storage field, particularly in the context of pulsed power sources. In this study, Sm and Hf co-doped silver niobate (AgNbO₃; AN) ceramics were prepared using traditional solid-state method. Comprehensive analysis of crystal structure, microstructure, defects, absorbance, and energy storage performance of the material was conducted. Results reveal that co-doping increased the concentration of cation vacancies and band gap, decreased the M₁–M₂ and M₂–M₃ phase transition temperatures, and enhanced the antiferroelectric phase stability and energy storage performance. The (Ag_0.955Sm_0.015)(Nb_0.95Hf_0.05)O₃ ceramic exhibited energy storage density of 5.35 J/cm³ and energy storage efficiency of 73% at electric field (E) of 295 kV/cm, demonstrating significant improvement. The (Ag_0.955Sm_0.015)(Nb_0.95Hf_0.05)O₃ ceramic exhibited excellent thermal stability (<5% in the range of 25 °C-125 °C) and frequency stability (<3% in the range of 1–100 Hz under E = 290 kV/cm). Additionally, the (Ag_0.955Sm_0.015)(Nb_0.95Hf_0.05)O₃ ceramic exhibited ultrahigh discharge speed (∼18 μs) and high discharge energy density (4.9 J/cm³). These advantages make these ceramics promising materials for energy storage applications.     

Enhanced the energy storage performance in AgNbO3‑based antiferroelectric ceramics via manipulation of oxygen vacancy

The applications of silver niobate (AgNbO₃)-based antiferroelectric (AFE) ceramics for potential energy storage are limited by the introduction of oxygen vacancies (OVs). The inevitable OVs narrow the band gap and promote grain growth, resulting in poor breakdown strength and low recoverable energy density (W_rec). Here, we report a significant energy density performance of (Ag_1–2xSr_x)(Nb_0.78Ta_0.22)O₃ AFE ceramics designed by restraining OVs. Electron paramagnetic resonance (EPR) and UVvis absorption spectra experiments demonstrate that the OV content gradually decreases and the band gap increases with increasing Sr content. Donor doping of Sr leads to the generation of silver ion vacancies, thus, the OV concentration decreases to maintain the electrical neutrality of the system. As a result, a high W_rec of ∼5.6 J/cm³ together with an energy efficiency of 70.1% at 300 kV/cm is achieved in the (Ag_0.92Sr_0.04)(Nb_0.78Ta_0.22)O₃ ceramic. This work offers a novel strategy for improving the energy storage properties of AgNbO₃-based AFE ceramics.     

Electric field tunable thermal stability of energy storage properties of PLZST antiferroelectric ceramics

The electrical hysteresis behaviors and energy storage performance of Pb_0.97La_0.02(Zr_0.58Sn_0.335Ti_0.085)O₃ antiferroelectric (AFE) ceramics were studied under the combined effects of electric field and temperature. It was observed that the temperature dependence of recoverable energy density (W_re) of AFE ceramics depends critically on the applied electric field. While W_re at lower electric fields (<8 kV/mm) shows increasing tendency with increasing temperature from 20°C to 100°C, W_re at higher electric fields (>8 kV/mm) demonstrates decreasing dependence. There exists an appropriate electric field (8 kV/mm) under which the AFE ceramics exhibit nearly temperature‐independent W_re (the variation is less than 0.5% per 10°C). The underlying physical principles were also discussed in this study. These results indicate that the temperature dependence of W_re of AFE materials can be tuned through selecting appropriate electric fields and provide an avenue to obtain thermal stable energy storage capacitors, which should be of great interest to modern energy storage community.     

High energy storage properties of lead-free Mn-doped (1-x)AgNbO3-xBi0.5Na0.5TiO3 antiferroelectric ceramics

In this work, 0.2 wt.% Mn-doped (1-x)AgNbO₃-xBi_0.5Na_0.5TiO₃ (x = 0.00–0.04) ceramics were synthesized via solid state reaction method in flowing oxygen. The evolution of microstructure, phase transition and energy storage properties were investigated to evaluate the potential as high energy storage capacitors. Relaxor ferroelectric Bi_0.5Na_0.5TiO₃ was introduced to stabilize the antiferroelectric state through modulating the M₁-M₂ phase transition. Enhanced energy storage performance was achieved for the 3 mol% Bi_0.5Na_0.5TiO₃ doped AgNbO₃ ceramic with high recoverable energy density of 3.4 J/cm³ and energy efficiency of 62% under an applied field of 220 kV/cm. The improved energy storage performance can be attributed to the stabilized antiferroelectricity and decreased electrical hysteresis ΔE. In addition, the ceramics also displayed excellent thermal stability with low energy density variation (<6%) over a wide temperature range of 20−80 °C. These results indicate that Mn-doped (1-x)AgNbO₃-xBi_0.5Na_0.5TiO₃ ceramics are highly efficient lead-free antiferroelectric materials for potential application in high energy storage capacitors.     

Antiferroelectric‐ferroelectric phase transition in lead‐free AgNbO3 ceramics for energy storage applications

The high‐energy storage density reported in lead‐free AgNbO₃ ceramics makes it a fascinating material for energy storage applications. The phase transition process of AgNbO₃ ceramics plays an important role in its properties and dominates the temperature and electric field dependent behavior. In this work, the phase transition behavior of AgNbO₃ ceramics was investigated by polarization hysteresis and dielectric tunability measurements. It is revealed that the ferrielectric (FIE) phase at room temperature possesses both ferroelectric (FE)‐like and antiferroelectric (AFE)‐like dielectric responses prior to the critical AFE‐FE transition point. A recoverable energy storage density of 2 J/cm³ was achieved at 150 kV/cm due to the AFE‐FE transition. Based on a modified Laudau phenomenological theory, the stabilities among the AFE, FE and FIE phases are discussed, laying a foundation for further optimization of the dielectric properties of AgNbO₃.     

NaNbO3-based short-range antiferroelectric ceramics with ultrahigh energy storage performance

Lead-free NaNbO₃ (NN) antiferroelectric ceramics provide superior energy storage performance and good temperature/frequency stability, which are solid candidates for dielectric capacitors in high power/pulse electronic power systems. However, their conversion of the antiferroelectric P phase to the ferroelectric Q phase at room temperature is always accompanied with large remnant polarization (P_r), which significantly reduces their effective energy storage density and efficiency. In this study, to optimize the energy storage properties, short-range antiferroelectric (0.95-x)NaNbO₃-xBi(Mg_2/3Nb_1/3)O₃-0.05CaZrO₃ (xBMN) ceramics were designed to stabilize the antiferroelectric phase, in which the local random fields were simultaneously constructed. The results showed that the antiferroelectric orthorhombic P phase was transformed into the R phase, and the local short-range random fields were generated, which effectively inhibited the hysteresis loss and P_r. Of great interest is that the 0.12BMN ceramics displayed a large recoverable energy storage density (W_rec) of 5.9 J/cm³ and high efficiency (η) of 85% at the breakdown strength (E_b) of 640 kV/cm. The material also showed good frequency stability in the frequency range of 2–300 Hz, excellent temperature stability in the temperature range of 20–110 ℃, and a very short discharge time (t_0.9∼4.92 μs). These results indicate that xBMN ceramics have great potential for advanced energy storage capacitor applications.     

Thermally stable energy storage properties in relaxor BNT-6BT-modified antiferroelectric PNZST ceramics

Relaxor ferroelectric 0.94Na_0.5Bi_0.5TiO₃-0.06BaTiO₃-modified antiferroelectric Pb_0.99Nb_0.02[(Zr_0.57Sn_0.43)_0.94Ti_0.06]_0.98O₃ ceramics, (1−x)PNZST-x(BNT-6BT), were prepared to acquire high energy storage and thermal stability properties. X-ray diffraction and element mapping revealed that a solid solution between PNZST and BNT-6BT occurs, and Ti cations enter the PNZST lattice, partly extruding Sn cations and leading to the formation of isolated SnO₂ particles at the grain boundaries and a 0-3 type composite structure. Such a composite structure helps to create deviatoric stress in the solid solution component. The BNT-6BT content significantly influences the energy storage capacity, and the x = 0.2 composition renders optimal performance. The room-temperature-recoverable energy density and energy efficiency are 2.23 J/cm³ and 78%, respectively, at 260 kV/cm. Both parameters vary less than 6% within a temperature range of 25°C and 125°C. The improved energy storage and temperature stability indicate that the ceramics can potentially be applied in pulse power capacitors and that this relaxor-modified antiferroelectric ceramic preparation method is a valuable reference for further optimizing the functional properties.     

Dielectric temperature stability and energy storage performance of NBT-based ceramics by introducing high-entropy oxide

In this study, a high-entropy perovskite oxide Sr(Zr_0.2Sn_0.2Hf_0.2Ti_0.2Nb_0.2)O₃ (SZSHTN) was first introduced to Na_0.5Bi_0.5TiO₃ (NBT) lead-free ferroelectric ceramics to boost both the high-temperature dielectric stability and energy storage performance. Excellent comprehensive performance was simultaneously obtained in the 0.8NBT–0.2SZSHTN ceramic with high ε′ value (> 2000), wide ε′-temperature stable range (TCC < 5%, 52.4–362°C), low tanδ value in a wide range (<0.01, 90–341°C) and high energy storage performance (W_rec = 3.52 J/cm³, W_rec and η varies ±6.08% and ±7.4% from 20 to 150°C), which endows it the promising potential to be used in high-temperature environments.     

High-performance antiferroelectric ceramics via multistage phase transition

Lead-based antiferroelectric (AFE) ceramics have attracted increasing interest in pulse power systems owing to their high-energy storage and power densities. However, the single AFE–ferroelectric (FE) phase transition in conventional AFE materials usually leads to premature polarization saturation and low breakdown strength, which are disadvantageous to energy storage performance. In this study, high energy storage performance was achieved in Pb_0.94−xLa_0.04Ca_x[Nb_0.02(Zr_0.99Ti_0.01)_0.975]O₃ (PLCNZT) AFE ceramics by constructing electric-field-induced multiple phase transitions. A maximum recoverable energy storage density of 12.15 J/cm³ and a high energy efficiency of 85.4% were obtained for the PLCNZT ceramic with x = 0.03 at 420 kV/cm. These excellent properties are attributed to the AFE–FE Ⅰ-FE Ⅱ multiple phase transitions induced by Ca²⁺ doping, which effectively enhances the breakdown strength. This result indicates that field-induced multiple phase transitions significantly improve the energy storage of AFE materials.     

High energy-storage performance of lead-free AgNbO3 antiferroelectric ceramics fabricated via a facile approach

AgNbO₃ lead free AFE ceramics are considered as one of the promising alternatives to energy storage applications. In the majority of studies concerning the preparation of AgNbO₃ AFE ceramics, an oxygen atmosphere is required to achieve high performance, increasing the complexity of the fabrication process. Herein, a facile approach to preparing AgNbO₃ ceramics in the ambient air was reported, in which the AgNbO₃ ultrafine powder with stable perovskite structure was synthesized by hydrothermal method instead of the conventional ball milling process, leading to a lower temperature of phase formation and thus smaller grain size. The resulting ceramics sintered at 940 °C displayed high breakdown strength (216 kV/cm) and a recoverable energy density of 3.26 J/cm³ with efficiency of 53.5 %. Also, the high thermal stability of recoverable energy density (with minimal variation of ≤20 %) and efficiency (≤ 10 %) over 30–150℃, enables AgNbO₃ ceramics achieved to be a promising candidate for energy storage applications.     

Structure and energy storage performance of Ba-modified AgNbO3 lead-free antiferroelectric ceramics

The AgNbO₃ antiferroelectric (AFE) ceramics have attracted increasing attention for their high energy storage performance and environmentally friendly characters. In this work, Ag_1–2xBa_xNbO₃ ceramics were successfully prepared by the conventional solid-state reaction method. The effect of Ba-modification on phase structure, microstructure, and electric properties was systematically investigated. The introduction of Ba²⁺ ion led to complex cell parameter evolution and significant refinement of grain size. Room temperature dielectric permittivity increased obviously from ~260 for the pure AgNbO₃ counterpart to ~350 for those after adding a small amount of Ba element. Slim P-E hysteresis loops with improved AFE phase were achieved after Ba modification, due to the decrease of tolerance factor. A high recoverable energy density up to 2.3?J/cm³ with energy efficiency of 46% can be obtained for the composition of Ag_0.96Ba_0.02NbO₃, in correlation with the enhanced AFE stability, reduced P_r, increased P_m and decreased ΔE. Moreover, the Ag_0.96Ba_0.02NbO₃ ceramics also exhibited excellent temperature stability in both energy density and efficiency with small variation of <?5% over 20–120?℃. The results suggest that the electric properties of AgNbO₃ system can be largely tuned after Ba modification, making it a promising candidate for energy storage applications.