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 property and thermal stability of PLZT-based antiferroelectric ceramics

(Pb, La)(Zr, Ti)O₃ antiferroelectric (AFE) materials are promising materials due to their energy-storage density higher than 10 J cm⁻³, but their low energy-storage efficiency and poor temperature stability limit their application. In this paper, the (1 − x)(Pb_0.9175La_0.055)(Zr_0.975Ti_0.025)O₃–xPb(Yb_1/2Nb_1/2)O₃ (PLZTYN100x) AFE ceramics were prepared via two-step sintering method and investigated thoroughly. With the doping of Yb³⁺ and Nb⁵⁺, the phase structure transforms from the orthorhombic phase (AFE_O) to the coexistence of the orthorhombic-and-tetragonal phases. This structure reduces the free energy difference between the AFE and ferroelectric phases and reduces the fluctuation of energy with temperature, improving the energy storage efficiency and temperature stability. When the x = 0.05 (PLZTYN5), the AFE ceramic exhibits excellent temperature stability and ultrahigh energy storage performance, whose recoverable energy density (W_rec) is 6.8–8.2 J cm⁻³ at 30 kV mm⁻¹ in the temperature range from −55 to 75°C, and efficiency (ƞ) is 78%–86.7%. In addition, the change of W_rec is less than 15%, exceeding the performance of most AFE ceramics. The results demonstrate that the PLZTYN5 ceramic has great potential in pulse power capacitors.     

Hierarchical domain structures in (Pb,La)(Zr,Sn, Ti)O3 antiferroelectric ceramics

(Pb, La)(Zr, Sn, Ti)O₃ (PLZST) ceramic is one of the most prospective antiferroelectric (AFE) materials for variety of functional applications including energy storage and converter. Systematic structural investigation of domain structures should be of fundamental importance for understanding the structure-property relationship in AFE ceramics. In this study, the hierarchical domain structures and modulated structures correlated to the compositional variation in (Pb_0.97La_0.02) (Zr_0.50Sn_xTi_0.50-x)O₃ (x = 0.375, 0.45 and 0.50) were observed and investigated in details by transmission electron microscopy. The PLZST ceramics show exclusively incommensurate modulated structures (IMS) whose modulation period changed from 9.37 to 6.15 and to 4.04 with increasing of the x value. The hierarchical domain structures include, in decreasing scales, AFE domains, incommensurate domains and nanodomains. The elementary domains in PLZST ceramics are pinstriped nanodomains which were formed based on IMS configuration but by frequent modulation of IMS periodicity and formation of faults. Nanodomains accumulated and then dissociated into incommensurate domains and AFE domains successively. The presently revealed structural characteristics in antiferroelectric PLZST may stimulate future researches on the evolution of IMS-based hierarchical domains under external physical fields, e.g. thermal or electrical, and their correlation to the physical performance.     

Ultra-fast charge-discharge and high energy storage density realized in NaNbO3–La(Mn0.5Ni0.5)O3 ceramics

Lead-free antiferroelectric (AFE) NaNbO₃ (NN) is one of promising materials for dielectric capacitors, but the recoverable energy-storage density and efficiency get restrained owing to huge remanent polarization and limited dielectric breakdown field strength. In this work, a variety of NN based lead-free bulk (1-x)NaNbO₃-xLa(Mn_0.5Ni_0.5)O₃ (abbreviated as (1-x)NN-xLMN, x = 0, 0.05, 0.10, 0.15, 0.20) ceramics were designed using a solid-state synthesis method. Remarkably, an ultra-fast charge-discharge speed 47 ns and an acceptable recoverable energy-storage density W_rec ~1.77 J/cm³ with a high efficiency η = 77% were obtained under the E_b of 200 kV/cm at x = 0.05. The superior energy storage performance is attributed to the regulation of domain size and voltage resistance by special ions substitution of A and B sites. This work not only proposes an efficient strategy to realize high recoverable energy-storage density and efficiency, but also provide an candidate material for application of advanced pulsed power capacitors.     

Energy-storage properties of Bi0.5Na0.5TiO3-BaTiO3-KNbO3 ceramics fabricated by wet-chemical method

0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃ (BNTBT) and KNbO₃ (KN) powders with average particle size of ∼50 nm and ∼300 nm were synthesized by sol-gel method and hydrothermal method, respectively. Then, (1 − x)(BNTBT)-xKN (BNTBT-KN, x = 0, 0.01, 0.03, 0.05, 0.07) ceramic samples were prepared using these two powder precursors. The structure, dielectric and energy-storage properties of BNTBT-KN ceramics were comprehensively investigated. All the ceramic samples were in single perovskite structure, indicating that KN can completely dissolve into BNTBT within the studied composition range. BNTBT-KN ceramics exhibited a high dielectric constant at room temperature, being in the order of 1430–1550. Ferroelectric hysteresis loops at room temperature became more slim with the increase of KN content, which largely improved energy-storage density and efficiency. For the composition of x = 0.05, the maximum recoverable energy-storage density reached 1.72 J/cm³ under 16.8 kV/mm, which is superior to linear dielectrics and even some Pb-based systems. All these results demonstrate that 0.95BNTBT-0.05KN fabricated by wet-chemical method is a promising lead-free dielectric material for energy-storage capacitors.     

Excellent energy-storage performances in La2O3 doped (Na,K)NbO3-based lead-free relaxor ferroelectrics

Relaxor ferroelectric (FE) materials have received increasing attention owing to their great potentials for energy-storage applications, especially for the ones with high energy-storage density, efficiency and thermal stability simultaneously. A novel lead-free [(Na_0.5K_0.5)_0.97-xLi_0.03](Nb_0.94-xSb_0.06)O₃-xBi(Zn_1/2Zr_1/2)O₃ (NKLNS-xBZZ) ceramics was developed by a solid-state reaction method. The addition of BZZ has induced obvious dielectric relaxation behavior, as well as improved thermal stability of dielectric response. Furthermore, 0.4 wt.% La₂O₃ was added into the NKLNS-0.06BZZ ceramic, leading to an increased breakdown strength as a result of the reduction of grain size, improvement of bulk resistivity and decrease of dielectric loss. A large recoverable energy-storage density (∼4.85 J/cm³) and a high efficiency (∼88.2 %) as well as an excellent thermal stability (±12 %, 25–140 °C) were simultaneously obtained, together with a fast discharge rate (t_0.9∼112 ns). These results suggest that La₂O₃ doped NKLNS-0.06BZZ ceramic could become an attractive dielectric material for temperature-stable energy-storage capacitors.     

Electrical properties and energy-storage performance of (Pb0.92Ba0.05La0.02)(Zr0.68Sn0.27Ti0.05)O3 antiferroelectric thick films prepared by tape-casing method

The energy-storage performance and dielectric properties of tape-cast (Pb_0.92Ba_0.05La_0.02)(Zr_0.68Sn_0.27Ti_0.05)O₃ (PBLZST) antiferroelectric (AFE) thick films with different thicknesses were systematically studied. As the thickness of the thick films increased from 40 to 80 µm, the dielectric constant and saturation polarization (P_s) of the thick films were gradually increased, while their corresponding breakdown strength (BDS) was decreased. A maximum recoverable energy-storage density of 6.8 J/cm³, companied by an efficiency of 61.2%, was achieved in the PBLZST AFE thick film with a thickness of 40 µm at room temperature. Moreover, the energy density of the PBLZST AFE thick films also displayed good thermal stability over 25–200 °C. In addition, all the samples had a low leakage current density of ~10⁻⁶ A/cm² at room temperature. These findings demonstrated that the PBLZST thick films should be a promising candidate for applications in high energy-storage capacitors.     

A novel process to synthesize high-k ‘Y5V’ nanopowder and ceramics

The present work proposes a simple one-step sol-gel process for the synthesis of high-k (Ba_0.87Sr_0.04Ca_0.09)(Ti_0.86Zr_0.08Sn_0.06)O₃ (BSCTZS) powders and ceramics. Characterization using TG-DTG, XRD, SEM and TEM methods reveals that the powders are of nanometer scale and exhibit a cubic perovskite structure. After sintering, cubic BaTiO₃ structure ceramics were obtained. Compared to the traditional method of preparation, the powders and ceramics prepared by the one-step sol-gel process exhibit a high dielectric constant due to narrow grain size distribution, controlled morphology, and high purity. Doped niobium decreases the grain size of BSCTZS ceramics and lowers the Curie temperature. At a Nb concentration of 0.38 mol%, BSCTZS ceramics meet the EIA Y5V specifications and the room temperature (25 °C) permittivity is greater than 16,000. The BSCTZS nanopowders prepared through the process with uniformity component will increase the volumetric efficiency of multi-layer ceramic capacitors by decreasing the dielectric layer thickness. Most importantly, this new approach greatly simplifies the preparation processes.     

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.     

Impact of synthesis route on the microstructure and energy-storage properties of (Bi1/2K1/2)TiO3–SrTiO3 relaxor ferroelectric ceramics: Solid-state and hydrothermal approaches

Bismuth potassium titanate (Bi_1/2K_1/2)TiO₃-based relaxor ferroelectrics are promising materials for high-energy-density ceramic capacitors. Herein, we compare the microstructure and energy-storage properties of (Bi_1/2K_1/2)_0.5Sr_0.5TiO₃ (BKST50) ceramics fabricated via two different routes: solid-state and hydrothermal reactions. A BKST50 fine powder composed of well-dispersed cubic nanoparticles was obtained via the hydrothermal reaction, whereas the conventional solid-state reaction resulted in the aggregation of primary particles. The grain size of the ceramics prepared from the hydrothermal powder could be controlled between 273 ± 24 and 936 ± 69 nm while maintaining a relative density of over 95% by simply varying the sintering temperature. On the other hand, ceramics prepared via the solid-state reaction could not be fully densified even at 1200 °C (the highest tested sintering temperature). The hydrothermally derived ceramics withstood higher electric field owing to dense and fine-grained microstructure, leading to a high recoverable energy-storage density of 2.25 J cm⁻³ at 240 kV cm⁻¹.     

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.     

High breakdown strength and energy density in antiferroelectric PLZST ceramics with Al2O3 buffer

In this work, a new core-shell structure of antiferroelectric ceramic powder (Pb_0.97La_0.02Zr_0.85Sn_0.12Ti_0.03O₃-PLZST) coated with linear dielectric (Al₂O₃) has been successfully prepared to realize high energy density through tape-casting process. According to the experimental results of electron microscope, the sol-gel derived Al₂O₃ layer was uniformly coated on the PLZST particles and the Al₂O₃ layer can be taken as the buffer layer to effectively refine the grain growth as well. Therefore, the modified PLZST particles were fine and uniform compared with the pure PLZST. It was found that the buffer layer could undertake higher electric field and the electric field applied to PLZST particles was weakened based on finite element analysis, which can avoid the premature breakdown of PLZST. And the actual measured breakdown strength was significantly enhanced from 22.2 kV/mm to 35.5 kV/mm. Correspondingly, an extremely high recoverable energy storage density of 5.3 J/cm³ was obtained for PLZST with 0.5%wt Al₂O₃, an 204% enhancement over the pure PLZST ceramics (2.6 J/cm³), and the corresponding efficiency was up to 88.3%. In addition, impedance spectroscopy measurement was carried out to further confirm the better insulation of the ceramic with Al₂O₃ buffer.     

Submicron-grained Yb:Lu2O3 transparent ceramics with lasing quality

We report on our recent progress of fabricating Yb³⁺-doped Lu₂O₃ transparent ceramics for 1 μm solid-state laser application. Well-dispersed 3.3 at.% Yb:Lu₂O₃ nanopowders were synthesized using a co-precipitation method. Without using any sintering aids, the Yb:Lu₂O₃ nanopowders could be densified by vacuum sintering at 1500°C/10 hours followed by HIPing at 1480°C/4 hours. Such obtained Yb:Lu₂O₃ ceramics had not only dense microstructure and submicron grain size of about 0.6 μm, but also in-line transmission of 80.0% at 600 nm. Preliminary continuous wave (CW) laser experiments with an uncoated Yb:Lu₂O₃ ceramic slab have demonstrated highly efficient CW laser oscillation at 1079.8 nm.     

Stress Effects on Stabilizing Antiferroelectric Phase in Multilayer Ceramics

Controllable phase transformation between antiferroelectric (AFE) and ferroelectric (FE) states suggests multifunctional properties valuable for many device applications. Compared to AFE bulk ceramics with large voltage required for driving electric field‐induced phase transition, implementation of structures comprising multiple thin AFE ceramic layers can realize applications by reducing the switching operation voltage in the feasible range. Here, it is found that a compressive residual stress is developed in multilayer (Pb_0.97,La_0.02)(Zr_0.66,Sn_x,Ti_0.34?x)O₃ (PLZST) ceramic co‐fired with multiple Pd/Ag electrode layers, and the compressive residual stress can stabilize AFE phase. AFE phase forms in the PLZST multilayer ceramic with composition corresponding to FE in the bulk materials. Thermodynamic analysis based on free energy of FE and AFE phases well explains the FE to AFE phase transformation observed in the multilayer ceramic under the compressive stress. The findings exhibit a new strategy to tune structure and functional properties of multilayer ceramics through stress engineering for achieving device applications.     

Fine-grained BNT-based lead-free composite ceramics with high energy-storage density

The low breakdown strength of BNT-based dielectric ceramics limits the increase in energy-storage density. In this study, we successfully reduced the sintering temperature of BNT-ST-5AN relaxor ferroelectric ceramics from 1150 to 980 °C by two-phase compounding with nano-SiO₂. Meanwhile, the average grain size of the composite ceramics is also greatly reduced from 4.45 μm to 0.37 μm. Thus, a large recoverable energy-storage density (3.22 J/cm³) is achieved under the ultrahigh breakdown strength (316 kV/cm). Moreover, good temperature (25–150 °C) and frequency (10–200 Hz) stabilities are simultaneously achieved. The excellent energy-storage properties suggest that BNT-ST-based ceramics composited with SiO₂ form a promising low-temperature sintered dielectric material for pulsed power multilayer ceramic capacitors.     

Dielectric and ferroelectric properties of lanthanum‐modified lead zirconate stannate titanate (42/40/18) ceramics

The effect of lanthanum (La) content on the phase transformation of Pb_1?3x/2La_x(Zr_0.42Sn_0.40Ti_0.18)O₃ (PLZST 100x/42/40/18, 0 ≤ x ≤ 0.06) ceramics was investigated by the dielectric and ferroelectric properties. The base composition PLZST 0/42/40/18 located in the ferroelectric (FE) rhombohedral phase region. As x increased, the compositions showed successively FE and antiferroelectric (AFE) state at room temperature, and their peak temperatures (T_max) decreased gradually in line as T_max = 162.21‐1507x. Evidence was presented that there were two dielectric anomalies in PLZST 2/42/40/18, which were corresponding to the FE‐AFE and AFE‐paraelectric (PE) phase transformations, respectively. With increasing the dc bias fields, the two phases merged into one. PLZST 3/42/40/18 showed AFE characteristics with the first loop outside of the second loop and there was only one dielectric inflection. The critical lanthanum content occurred at x = 0.03 from the dielectric temperature spectra and hysteresis loops. Furthermore increase in La above 0.03, these compositions showed typical antiferroelectric behaviors with double hysteresis loops. The stored energy properties of the three compositions (PLZST 4/42/40/18, 5/42/40/18 and 6/42/40/18) displayed different temperature dependencies from room temperature to 140°C (over their respective T_max). Comparing the above results with previous investigations on PLZSTs, some questions were discussed.     

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.     

Induced slim ferroelectric hysteresis loops and enhanced energy-storage properties of Mn-doped (Pb0·93La0.07)(Zr0·82Ti0.18)O3 anti-ferroelectric thick films by aerosol deposition

In this study, the high ferroelectric hysteresis loss of (Pb_0·93La_0.07)(Zr_0·82Ti_0.18)O₃ (PLZT 7/82/18) antiferroelectric (AFE) ceramics was reduced by employing a combinatorial approach of Mn acceptor doping followed by thick film fabrication via an aerosol deposition (AD) process. The grains of the as-deposited PLZT 7/82/18 AFE AD thick films were grown by thermal annealing at 550 °C to enhance their electrical properties. Investigation of the electrical properties revealed that Mn-doping results in improved dielectric and ferroelectric properties, increased dielectric breakdown strength (DBS), and energy-storage properties. The Mn-doped PLZT AFE AD films possess a frequency-independent high dielectric constant (ε_r ≈ 660) with low dielectric loss (tan δ ≈ 0.0146), making them suitable candidates for storage capacitor applications. The bipolar and unipolar polarization vs. electric field (P-E) hysteresis loops of PLZT 7/82/18 AFE AD thick films were found to be slimmer than those of their bulk form (double hysteresis) with significantly reduced ferroelectric hysteresis loss, which is attributed to the AD-induced mixed grain structure. The Mn-doped PLZT 7/82/18 AFE AD thick films exhibited a low remnant polarization (P_r ≈ 9.22 μC/cm²) at a high applied electric field (~2750 kV/cm). The energy-storage density and energy efficiency of the Mn-doped PLZT AFE AD thick films were calculated from unipolar P-E hysteresis loops and found to be ~38.33 J/cm³ and ~74%, respectively.     

High thermal stability in PLZST anti-ferroelectric energy storage ceramics with the coexistence of tetragonal and orthorhombic phase

The orthorhombic phase Pb_0.97La_0.02(Zr_0.93Sn_0.05Ti_0.02)O₃ (PLZST) and the tetragonal phase (Pb_0.93Ba_0.04La_0.02)(Zr_0.65Sn_0.3Ti_0.05)O₃ (PBLZST) were composited by the conventional solid state method to acquire high energy storage density and high thermal stability. X-ray diffraction spectra revealed the coexistence of orthorhombic and tetragonal structure, indicating that the ceramics were successfully composited. The component ratio of PLZST/PBLZST significantly influenced the thermal stability as well as the energy storage density due to the opposite energy storage performance-temperature trend of PLZST and PBLZST. The phase composition, microstructure and electric properties were discussed to explain the performance in the ceramic composites. High energy storage density of 3.20?±?0.02?J/cm³ at 20?°C with a variation <15% over a temperature range from 20?°C to 150?°C were found in the ceramic composite with a PLZST/PBLZST ratio of 55:45. This work provide an effective method to broaden applications of energy storage ceramics in high temperature.     

Synthesis,structure, and dielectric properties of a new binary antiferroelectric solid solution: (1−x)Pb(Mg1/2W1/2)O3–xPbHfO3

Dielectric ceramics are one of the most important electrical insulators because of their excellent electrical stability and nonconducting properties. In this work, new complex perovskite solid solutions, (1−x)Pb(Mg_1/2W_1/2)O₃–xPbHfO₃ [(1−x) PMW–xPHf] (0.00 ≤ x ≤ 0.04), were successfully synthesized in the form of ceramics by the solid-state reaction method and sintering process. The X-ray diffraction results indicate that a single perovskite phase with antiferroelectric (AFE) orthorhombic Pmcn symmetry is formed for x < 0.04 which corresponds to the PMW-type solid solution (SS-PMW). For the composition x = 0.04, however, a small amount (about 1%) of ferroelectric orthorhombic C2mm phase that arises from the PHf-type solid solution (SS-PHf) was found to coexist with the Pmcn phase (99%). The dielectric measurements show that the AFE-paraelectric phase transition temperature T_C of the (1−x)PMW–xPHf ceramics increases from 38.2°C (x = 0) to 40.1°C (x = 0.03) with the increasing PHf content, indicating a slightly enhanced AFE ordering degree. The studied materials show a relatively low dielectric constant (~10²), a low dielectric loss (~10⁻²), a high breakdown field strength (~140 kV/cm), and a linear electric field dependence of polarization at room temperature, which make them a new candidate for potential applications as ceramic insulators.