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.     

Systematical investigation on energy-storage behavior of PLZST antiferroelectric ceramics by composition optimizing

Featured with high polarization and large electric field-induced phase transition, PbZrO₃-based antiferroelectric (AFE) materials are regarded as prospective candidates for energy-storage applications. However, systematical studies on PbZrO₃-based materials are insufficient because of their complex chemical compositions and various phase structures. In this work, (Pb_0.94La_0.04)(Zr_1-x-ySn_xTi_y)O₃ (abbreviated as PLZST, 0 ≤ x ≤ 0.5, 0.01 ≤ y ≤ 0.1) AFE system was selected and the energy-storage behavior was regulated. It is found that low Ti content benefits to obtain satisfactory electric breakdown strength, realizing high energy-storage density. With Sn content increasing, the electric hysteresis decreases gradually, which is beneficial to improve energy conversion efficiency. As a result, a large recoverable energy-storage density of 9.6 J/cm³ and a high energy conversion efficiency of 90.2% were achieved in (Pb_0.94La_0.04)(Zr_0.49Sn_0.5Ti_0.01)O₃ ceramic. This work reveals energy-storage behavior of PLZST AFE materials systematically, providing reference for performance tailoring and new material designing in energy-storage applications.     

Excellent energy-storage properties of NaNbO3-based lead-free antiferroelectric orthorhombic P-phase (Pbma) ceramics with repeatable double polarization-field loops

The energy-storage performance of stable NaNbO₃-based antiferroelectric (AFE) ceramics was for the first time reported in (0.94-x)NaNbO₃-0.06BaZrO₃-xCaZrO₃ lead-free ceramics. A gradual evolution from an instable AFE phase (x≤0.01) to an orthorhombic AFE P phase (Pbma) (0.01<x≤0.05) was found to accompany the appearance of repeatable double-like polarization versus electric field loops although poled samples (x<0.01) own an AFE monoclinic phase (P2₁). Interestingly, compared with x≤0.01 samples with instable antiferroelectricity, a relatively high recoverable energy storage density W_rec ? 1.59 J/cm³ (@ 0.1 Hz) and a storage efficiency η of ?30% were achieved in the x = 0.04 ceramic. Moreover, a high W_rec of > 1.16 J/cm³ and an outstanding charge-discharge performance with fast discharge rate (t_0.9 < 100 ns) were generated in the temperature range from room temperature to 180 °C in the x = 0.04 ceramic. These results suggest that NaNbO₃-based AFE P-phase ceramics could be new potential dielectric materials for high-energy storage capacitors.     

Flexible antiferroelectric thick film deposited on nickel foils for high energy-storage capacitor

Flexible antiferroelectric (AFE) Pb_0.94La_0.04Zr_0.97Ti_0.03O₃ (PLZT) thick-film capacitors were fabricated on nickel foil substrates using sol-gel method. The thick PLZT film shows pure perovskite phase with dense microstructure. The discharge energy-storage properties of the thick PLZT film are directly evaluated by the resistance-inductance-capacitance (RLC) circuit. The maximum value of the discharge energy-storage density (W_dis) is 15.8 J/cm³ at 1400 kV/cm and 90% of the corresponding energy is released in a short time of about 250 ns. In addition, the W_dis and discharge time could be adjusted by the bent radius of the film, which provides a simple and feasible solution for the regulation of the electrical performance. Furthermore, the flexible AFE film exhibits good mechanical properties under cycling tests with bending radii down to 2.5 mm and 1500 rounds. This work shows a critical significance in fabricating flexible AFE capacitors for application in modern electronics and electrical power systems.     

Excellent thermal stability and aging behaviors in BiFeO3-BaTiO3 piezoelectric ceramics with rhombohedral phase

BiFeO₃-BaTiO₃ (BF-BT) solid solutions are lead-free candidates for high-temperature piezoelectric applications. BF-BT ceramics with compositions near the morphotropic phase boundary (MPB) separating rhombohedral (R) and pseudo-cubic (PC) phases were fabricated by the conventional high temperature sintering method, and their thermal stability and aging properties were studied in detail. BF-BT ceramics with rhombohedral (R) phase show much better thermal stability and aging properties than those with pseudo-cubic (PC) or coexistence of PC and R phases. The thermal degradation and aging rates of BF-BT ceramics with R phase are on the order of 1% and 1.2% per decade, respectively. X-ray diffraction results reveal that the domain state of poled rhombohedral BF-BT ceramics is stable up to its Curie temperature, which is responsible for the high thermal stability. The Rayleigh analysis shows that the low aging rate is attributed to the low domain wall contribution to the overall piezoelectric response. The high thermal stability and low aging rates indicate that the lead-free BF-BT ceramics with R phase are potential candidates for sensor and transducer applications over a broad temperature range.     

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.     

Phase transition and thermal stability of ceramics from Na-based geopolymers

Geopolymer ceramics undergo a series of thermal phase transitions, progressing from an amorphous geopolymer gel to a crystalline phase, and eventually to an amorphous glass phase as the temperature increases. However, there is a lack of mechanism understanding regarding to the crystallization process and the subsequent thermal degradation. Here, we fundamentally investigated the kinetics of nepheline formation in Na-based geopolymer systems and its thermal stability up to 1400°C. Nepheline crystallization is controlled by bulk nucleation and three-dimensional crystal growth based on the Avrami factor of 4.64, where the activation energy of nepheline formation is 350.59 kJ/mol. High thermal stability of geopolymer ceramics is achieved due to the appearance of nepheline up to 1400°C with the Si/Al ratio ranging from 1.40 to 1.94, while melting and amorphous structure are formed above a higher Si/Al ratio of 2.22. The nature of sintering for geopolymer ceramics consists of shrinkage, expansion and shrinkage corresponding to dehydroxylation, crystallization, and densification, leading to a thermal shrinkage of 21% at 1400°C.     

Relaxor antiferroelectric ceramics with ultrahigh efficiency for energy storage applications

Enhancing the efficiency in energy storage capacitors minimizes energy dissipation and improves device durability. A new efficiency-enhancement strategy for antiferroelectric ceramics, imposing relaxor characteristics through forming solid solutions with relaxor compounds, is demonstrated in the present work. Using the classic antiferroelectric (Pb_0.97La_0.02)(Zr_1-x-_ySn_xTi_y)O₃ as model base compositions, Bi(Zn_2/3Nb_1/3)O₃ is found to be most effective in producing the “relaxor antiferroelectric” behavior and minimizing the electric hysteresis. Specifically, a remarkable energy storage efficiency of 95.6% (with an energy density of 2.19 J/cm³ at 115 kV/cm) is achieved in the solid solution 0.90(Pb_0.97La_0.02)(Zr_0.65Sn_0.30Ti_0.05)O₃–0.10Bi(Zn_2/3Nb_1/3)O₃. The validated new strategy, hence, can guide the design of future relaxor antiferroelectric dielectrics for next generation energy storage capacitors.     

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.     

Excellent energy storage performance in La and Ta co-doped AgNbO3 antiferroelectric ceramics

Lead-free dielectric materials with high breakdown electric field strength and energy density are required for pulsed power devices with high level of integration. This work describes: (Ag_0.94La_0.02)(Nb_1-xTa_x)O₃ lead-free antiferroelectric ceramics, which were prepared by rolling process. Following composition engineering, an outstanding energy density of 6.9 J cm^-3 at electric field of 490 kV cm^-1 was achieved, coupled with remarkable frequency stability (<1% over 1-100 Hz under E = 420 kV cm^-1) for (Ag_0.94La_0.02)(Nb_0.80Ta_0.20)O₃ ceramics. Moreover, it also shows excellent charge-discharge properties (discharge density = 1429 A cm^-2, power density = 144 MW cm^-3). The addition of La³⁺ and Ta⁵⁺ induced a disordered local structure, which gradually decreased the phase transition temperature of M₂-M₃ to room temperature, reflecting the enhanced antiferroelectricity. All advantageous properties observed for the La and Ta co-doped AgNbO₃ ceramics highlight their significant potential for energy storage applications.     

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.     

Excellent temperature stability of strain in PZ-PT-BNT ternary ceramics

Lead-based Pb(Zr, Ti)O₃ ceramics have been widely applied in piezoelectric actuators, and yet high temperature stability and large strain have been pursued for further application. In this work, a novel PbZrO₃–PbTiO₃-(Bi_0.5Na_0.5)TiO₃ (PZ-PT-BNT) piezoelectric ceramic is designed and prepared by solid-state route. It is found that the introduction of BNT constituent enhances the relaxation behavior of PZ-PT ceramic, inhibits the abrupt change in dielectric properties near Curie temperature, and increases the proportion of tetragonal phase with high temperature stability. Meanwhile, the patterns of electric domains are intentionally modified by adjusting composition of PZ-PT-BNT. Short and broad electric domains in PZ-PT-0.03BNT ceramic are observed by piezoresponse force microscopy, which are insensitive to temperature and have faster response under electric field, contributing to strain characteristics. As a result, through integrating phase structure and electric domain configuration, a strain of 0.21% and excellent temperature stability where the variation of strain is less than 8% in the temperature range of 25–250 °C are achieved in PZ-PT-0.03BNT ceramic. The findings provide an effective strategy for improving the strain stability of PZ-PT-based piezoelectric ceramics, and demonstrate that PZ-PT-BNT ceramics have potential application prospects in high-temperature piezoelectric actuators.     

Excellent thermal stability and energy storage properties of lead-free Bi0.5Na0.5TiO3-based ceramic

The ceramic capacitors with excellent energy storage properties and wide operating temperature are the main challenges in power system applications. Here, the lead-free (1-x)Bi_0.5Na_0.5TiO₃-xCaTiO₃ (abbreviated as BNT-xCT) ceramics were synthesized through solid-state reaction method. The introduction of CT reduced the temperature of permittivity peak of BNT ceramic, guaranteeing excellent thermal stability over a wide temperature range of −100 ∼ 136°C. Meanwhile, the long-range order structure of BNT was destructed by structural distortion, and the relaxor behavior was enhanced after doping CT. Moreover, the direct current breakdown strength was improved from 203 to 455 kV/cm, and the high recoverable energy density (W_rec ∼ 2.74 J/cm³) with high efficiency (η ∼ 91%) was achieved for BNT-0.25CT ceramic, along with a fast discharge speed (t_0.9 ∼ 110 ns) superior cycle stability and thermal stability. Those properties enabled a promising practical prospect of BNT-CT ceramics.     

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.     

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.     

Pulse energy-storage performance and temperature stability of Bi2O3-added BaTiO3 based ceramics

The temperature stability and temperature stability range of barium titanate-based pulse energy-storage ceramics were modified by Bi₂O₃ tailoring in (Ba_0.98-xLi_0.02Bi_x) (Mg_0·04Ti_0.96)O₃ (x = 0, 0.025, 0.05, 0.075, 0.1) and (Ba_1.03-1.5xLi_0.02Bi_x) (Mg_0·04Ti_0.96)O₃ (x = 0.125, 0.15, 0.2, 0.25) ceramics. Excellent pulse energy-storage performances of ceramic films are achieved via the new dual priority strategy of establishing cationic vacancies and forming a liquid phase. The dielectric constant plateau appears due to the cubic phase and space charges. Outstanding temperature stability, frequency stability and antifatigue performance are obtained in the ceramics, and their variations are all less than 15%. The comprehensive energy-storage properties with dual priority parameters of energy-storage density and efficiency of 3.13 J/cm³ and 91.71%, accompanied by an excellent pulse discharge energy density of 2.48 J/cm³, current density of 1313.23 A/cm² and power density of 195.26 MW/cm³ are gained at x = 0.1. The perfect pulse energy-storage performances as well as ultrahigh stability are correlated with synergistic effects of multiphase coexistence, cubic phase, liquid-phase sintering, grain size, ceramic resistance, space charges and polar nanoregions. The comprehensive parameters indicate that the (Ba_0·88Li_0·02Bi_0.1) (Mg_0·04Ti_0.96)O₃ ceramics have potential application in high precision fields.     

Excellent mechanical property of fast hot pressure sintering CaZr4(PO4)6 low thermal expansion ceramics

The low mechanical property of the CaZr₄(PO₄)₆ (CZP) ceramics restrict its application prospects in area of high anti-thermal shock applications. Herein, the fast hot pressure sintering (FHP) was adopted to modify the microstructure and optimize the mechanical property of CZP ceramics for the first time. The as-fabricated CZP ceramics exhibited smaller grain size and lower stomatal rates than that of the normal-pressure sintering ceramics owing to the lower processing temperature and shorter insulation time. Consequently, the CZP ceramics prepared with FHP method demonstrated an unprecedented bending strength of 94.5 MPa, with the thermal expansion coefficient of the CZP ceramics remaining at a low level. This study is important for promoting the application of CZP ceramics in flood anti-thermal shock applications, the fast hot pressure sintering would trigger a new direction of improvement methods of sodium zirconium phosphate ceramics.     

Giant strains of 0.70% achieved via a field-induced multiple phase transition in BNT-based relaxor antiferroelectric ceramics

Bismuth sodium titanate (BNT)-based lead-free ceramics have attracted a great deal of attention due to their large electrostrains. In this work, a remarkably symmetric strain of 0.7% together with excellent temperature (0.5–0.7% from 25 to 100 °C)/frequency (ΔS<4% from 1 to 20 Hz) stability was observed in the 0.91(Bi_0.5Na_0.5)TiO₃-0.06BaTiO₃-0.03NaNbO₃ (BNT-6BT-3NN) AFE P4bm ceramic through constructing R3c/P4mm/P4bm triple-phase coexistence phase boundary. Compared with other two compositions near double-phase coexistence ferroelectric (FE)-antiferroelectric (AFE) phase boundaries, the BNT-6BT-3NN ceramic exhibits a unique field-induced multiple phase transition from the initial AFE P4bm phase to the metastable FE P4mm phase and finally into the FE R3c phase. In-situ structural analysis evidenced a significantly enhanced lattice strain but a comparable strain value from domain switching in BNT-6BT-3NN compared with other compositions. The present study provides a novel strategy for designing high-performance large-strain ceramics in BNT-based relaxor AFE systems.     

Effect of lanthanum content on the conduction behaviors and relaxation processes of lead lanthanum zirconate titanate antiferroelectric ceramics

(Pb_1-xLa_x) (Zr_0.92Ti_0.08)_1-x/4O₃ (PLZT x/92/8, x = 3, 5 and 7 at%) ceramics with compositions near the antiferroelectric (AFE)-ferroelectric (FE) phase boundary were fabricated by a solid-state reaction method. The effect of lanthanum content on the conduction behaviors and relaxation processes has been investigated. It was verified that the main phase with orthorhombic structure was formed in all compositions. The increase of lanthanum substitution resulted in an enhancement of diffuse phase transition. Impedance analysis suggested that the ac conductivity decreased with increasing lanthanum content. Moreover, thermally stimulated depolarization current study was utilized to establish the correlation between defect structures and relaxation processes. It showed three peaks with distinct characteristics, which originated from dipole orientation, oxygen vacancy migration and phase transition respectively. The oxygen vacancy-related defects induced by lanthanum doping were mainly responsible for the variation of conduction behaviors and relaxation processes.