Fabrication,structural and dielectric property of lead-free perovskite silver niobate ceramics

Dielectric capacitors with high recoverable energy density are in high demand for their application in electrical and electronic systems. Among lead-free dielectric materials, silver niobate (AgNbO₃) has attracted growing interest due to its superior energy storage density at room temperature. The field-induced phase transition from antiferroelectric (AFE) phase to ferroelectric (FE) phase contributes to its large energy density. In this work, pure perovskite silver niobate ceramics were fabricated in an oxygen atmosphere by the solid-state reaction technique. The Pbcm orthorhombic phase of AgNbO₃ was closely observed using the Rietveld refinement method to provide explanation for the origin of high spontaneous polarization within a unit cell. Local structural analysis via piezoelectric force microscopy revealed the existence of ferroelectric nano domains, which may contribute to the high energy storage efficiency (η = 99.9926%) in AgNbO₃ at low electric fields. The phase transitions of AgNbO₃ were also investigated via the dependence of the dielectric permittivity (ε′ and ε″) and loss angle tangent (tanδ) on temperatures, providing insights into the further modification of AgNbO₃.     

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.     

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.     

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.     

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.     

Grain size tailoring and enhanced energy storage properties of two-step sintered Nd3+-doped AgNbO3

AgNbO₃ as a lead-free antiferroelectric material, has received widespread attention in recent years due to its promising application in the aspects of energy storage devices. However, the high remnant polarization and low breakdown strength limits its energy storage properties. In this work, Nd³⁺-doped AgNbO₃ (Ag_1−3xNd_xNbO₃, x=0−0.015) ceramics were prepared and a two-step sintering method was employed. The introduction of Nd³⁺ leads to the enhanced stability of the antiferroelectric phase, refined grain size and increased resistivity. Furthermore, by adjusting the pre-heating temperature in the two-step sintering, the homogeneity of microstructure is improved and the resistance of pre-heated samples increases by one order of magnitude compared with normally sintered samples, leading to the enhanced breakdown strength. Ag_0.97Nd_0.01NbO₃ pre-heated at 1100 °C for 2 h exhibits promising energy storage properties, with a recoverable energy storage density of 3.2 J/cm³ and energy efficiency of 52 % under an applied electric field of 210 kV/cm.     

Novel NaNbO3–Sr0.7Bi0·2TiO3 lead-free dielectric ceramics with excellent energy storage properties

NaNbO₃ (NN) is considered to be one of the most prospective lead-free antiferroelectric energy storage materials due to the merits of low cost, nontoxicity, and low density. Nevertheless, the electric field-induced ferroelectric phase remains dominant after the removal of the electric field, resulting in large residual polarization, which prevents NN ceramics from obtaining superior energy storage performance. In this work, the relaxor ferroelectric Sr_0·7Bi_0·2TiO₃ (SBT) was chosen to partially replace the NN ceramics, and the introduction of the nanodomain of the relaxor ferroelectric hinders the generation of field-induced ferroelectric phases, allowing the material to combine the large polarization strength of the relaxor ferroelectric with the near-zero residual polarization of the antiferroelectric. Large recoverable energy storage density (4.5 J cm^?3) and ultra-high energy storage efficiency (90.3%) were gained in NN-20SBT under an electric field of 288 kV cm^?1. Furthermore, superior temperature (25–120 °C) and frequency (1–500 Hz) stabilities were acquired. These performances demonstrate that NN-20SBT ceramics are potential candidates as dielectric materials for high energy storage density pulsed power capacitors.     

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.     

B-site acceptor doped AgNbO3 lead-free antiferroelectric ceramics: The role of dopant on microstructure and breakdown strength

B-site aliovalent modification of AgNbO₃ with a nominal composition of Ag(Nb_1-xM_x)O_3-x/2 (x = 0.01, M = Ti, Zr and Hf) was prepared. The effects of dopants on microstructure, dielectric, ferroelectric and conduction properties were investigated. The results indicate that the introduction of acceptor dopant does not lead to grain coarsening. Zr⁴⁺ and Hf⁴⁺ doping are beneficial to stabilize the antiferroelectric phase of AgNbO₃. Among all the samples, Ti⁴⁺ doped AgNbO₃ has the minimum resistivity while Hf⁴⁺ doped AgNbO₃ has the maximum resistivity, therefore, Hf⁴⁺ doped AgNbO₃ has high BDS. The XPS results indicate that the conduction behaviour is associated with the concentration of oxygen vacancies. This work hints that acceptor dopant is also effective on the microstructure control and chemical modification of AgNbO₃-based ceramics.     

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.     

AgNbO3基反铁电陶瓷储能性能研究进展

反铁电材料在场致诱发相变过程可释放与储存大量能量，在储能领域极具应用价值。无铅铌酸银(AgNbO₃)反铁电陶瓷作为环境友好型储能材料深受关注。在大量已有研究的基础上，本文从结构特性和性能调控的角度出发，重点介绍了以AgNbO₃为代表的无铅反铁电陶瓷在介电储能领域的最新进展；从组分调控和工艺优化两个角度总结了现有的储能性能调控手段，归类了储能性能增强的起源机制，并对铌酸银反铁电体陶瓷储能性能的进一步发展进行了展望。相信本文能为未来AgNbO₃基反铁电材料储能性能的提高提供新的研究思路。     

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.     

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.     

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.     

High polarization and low remnant polarization for high energy storage performance in PLZST/P(VDF-CTFE) composites

Energy storage materials have received increasing attention for sustainable energy production and use. Despite the excellent properties of ferroelectric/antiferroelectric ceramics, PVDF-based co/terpolymer films, and related composites, few materials meet the high-performance energy storage requirements. Here, we design antiferroelectric composites by combining anti-ferroelectric fillers with a high dielectric permittivity and ferroelectric copolymers with high breakdown fields. As a result, a high discharge energy density of 2.9?J/cm³ under much lower fields, i.e., 175?MV/m is realized. Such high-performance antiferroelectric composites could aid in the further development of promising new energy storage materials.     

Modulating the energy storage performance of NaNbO3-based lead-free ceramics for pulsed power capacitors

Nb-containing antiferroelectric materials have recently attracted great research interest as energy storage materials for pulsed power capacitors due to their extraordinary energy storage performances. In this case, the optimization of the energy storage performance is obtained by a compositional modulation of NaNbO₃-Bi(Zn_2/3Nb_1/3)O₃ bulk ceramics. An optimal energy performance can be obtained with a composition of 0.85NaNbO₃-0.15Bi(Zn_2/3Nb_1/3)O₃, which is accompanied by a stable charge energy density in temperatures up to 150 °C owing to its relaxor characteristics and excellent cycling stability after 10⁵ cycles. This work further broadens the scope of NaNbO₃-based ceramic applications in the area of pulsed power sources.     

Softening of antiferroelectric order in a novel PbZrO3-based solid solution for energy storage

PbZrO₃-based antiferroelectric (AFE) materials have received growing attention for their attractive energy storage performance. However, a major drawback of PZ is its high critical electric field (E_cr) which makes it difficult to switch the antiparallel dipoles therein so as to be useful. Therefore, softening of AFE order in PbZrO₃ is thought to be a promising approach for its practical applications. In this work, a new binary AFE solid solution of (1-x)PbZrO₃-xPb(Mg_1/2Mo_1/2)O₃ (PZ-PMM), with x = 0.00–0.10, was successfully synthesized in form of ceramics via the solid-state reaction method. The effect of chemical modification by introducing Pb(Mg_1/2Mo_1/2)O₃ on the crystal structure, phase transition behavior and electrical properties of the PbZrO₃ ceramics are investigated systemically. It is found that a perovskite phase with orthorhombic Pbam symmetry is preserved at room temperature for all the compositions studied, and a broadened ferroelectric intermediate phase exists between the paraelectric (PE) and the antiferroelectric phases of the PZ-PMM solid solution. At 160 °C, typical double hysteresis loop can be displayed for all the compositions. Most importantly, the maximum electric field-induced polarization is significantly increased, whereas the critical field is decreased with increasing PMM content, suggesting a remarkable softening effect of the antiferroelectric order in PZ due to some degree of dipole frustration. This work could bring about the development of a new series of PZ-based solid solutions for energy storage applications in the future.     

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.     

Tunable antiferroelectric ceramic polarization via regulating incommensurate phase and domain features

Due to the high demand for dielectric materials with high energy density, the energy storage performance of antiferroelectric ceramic capacitors has always gained much attention. Polarization intensity is a key factor that is closely related to the energy storage density. However, thus far, there has been a lack of research studies or successful methods to effectively modulate polarization intensity. The behavior of the polarization process is complex and contains domain nucleation, growth, and flip-flapping. Based on this finding, the introduction of Nb⁵⁺ at the B-site was designed to influence the three stages of antiferroelectric polarization by regulating the balance between the ferroelectric and antiferroelectric phases, and eventually realized regulation of the saturation polarization intensity in the (Pb_1-1.5xLa_x)(Zr_0.5Sn_0.43Ti_0.07)O₃ antiferroelectric ceramics. The saturation polarization intensity has increased from 25.56 to 42 μC/cm² with Nb⁵⁺ content increases from 0 to 4 mol% and the hysteresis was kept low, Pb_0.94La_0.04(Zr_0.65Sn_0.35)_0.975Nb_0.02O₃ is the optimal component with a high releasable energy density of 8.26 J/cm³ and an energy storage efficiency of 90.31%. This work provides an in-depth explanation of the microscopic mechanism of antiferroelectric ceramic polarization and presents a novel approach for the composition design of high-energy storage density antiferroelectric ceramics.     

Hydrothermal synthesized AgNbO3 powders: Leading to greatly improved electric breakdown strength in ceramics

Silver niobate AgNbO₃ ceramics have been regarded as a promising lead-free material for energy storage applications. In present work, pure and fine AgNbO₃ powders were successfully fabricated via the hydrothermal method using AgNO₃ as the raw material. It is found that the reaction products show strong dependence on the molar ratio of NH₄HF₂:AgNO₃:Nb₂O₅, pH value and reaction time. Pure AgNbO₃ powders were obtained when the process conditions are 3NH₄HF₂:2AgNO₃:xNb₂O₅ with x≤0.85 or yNH₄HF₂:2AgNO₃:1Nb₂O₅ with y = 4–5, pH = 5 and reaction time t ≥ 10 h. Benefitting from the hydrothermal synthesised AgNbO₃ powders, AgNbO₃ ceramics with fine-grain of ∼3.4 μm were obtained. The fine-grain leads to increased electric breakdown strength E_b up to 250 kV/cm, which is the highest among the pure AgNbO₃ ceramics to our best knowledge. The further enhancement in E_b and recoverable energy density could be highly anticipated if the antiferroelectric phase could be stabilized.