Simultaneously achieving high energy storage density and efficiency under low electric field in BiFeO3-based lead-free relaxor ferroelectric ceramics

BiFeO₃-BaTiO₃-based relaxor ferroelectric ceramic has attracted increasing attention for energy storage applications. However, simultaneously achieving high recoverable energy storage density (W_rec) and efficiency (η) under low electric field has been a longstanding drawback for their practical applications. Herein, a novel relaxor ferroelectric material was designed by introducing (Sr_0.7Bi_0.2)TiO₃ (SBT) into the composition 0.67BiFeO₃-0.33BaTiO₃ (BF-BT-xSBT). A large W_rec of ∼2.40 J/cm³ and a high η of ∼90.4 % were simultaneously realized under a low electric field of 180 kV/cm, which is superior to that of most previously reported lead-free ceramics. Moreover, moderate temperature endurance and excellent frequency stability were also obtained. More importantly, this ceramic has a large discharge current density (∼289.18 A/cm²), a discharge power density (∼14.46 MW/cm³) and short discharge time (<0.25 μs). These results not only demonstrate superior potential in BF-BT-SBT ceramics, but also offer a new design to tune the energy storage performance of lead-free relaxor ferroelectric ceramics.     

Large energy storage density in BiFeO3-BaTiO3-AgNbO3 lead-free relaxor ceramics

Lead-free (0.70-x)BiFeO₃-0.30BaTiO₃-xAgNbO₃+5‰mol CuO (abbreviated as BF-BT-xAN) ceramics were fabricated using a modified thermal quenching technique. BF-BT-xAN ceramics are of a perovskite structure with morphotropic phase boundary (MPB) and show strong relaxor properties. Remarkably, the high recoverable energy storage density of 2.11 J/cm³ is obtained for BF-BT-xAN with x = 0.14. For the x = 0.14 ceramics, its energy storage efficiency is as high as 84 % at relative low field of 195 kV/cm, together with an outstanding thermal stability in a broad temperature range from 25 °C to 150 °C. In addition, this ceramic maintains superior energy storage performance even after 8 × 10⁴ electrical cycles due to its high densification after doping Ag₂O and Nb₂O₅. The result suggests that lead-free BF-BT-xAN ceramics may be promising candidate for dielectric energy storage application.     

Enhanced electromechanical properties of SrTiO3-BiFeO3-BaTiO3 ceramics via relaxor behavior and phase boundary design

High temperature lead-free piezoceramics of 0.06SrTiO₃-0.94[(1-x)BaTiO₃- xBiFeO₃] were fabricated by the traditional solid state reaction method. The ceramics possess the pure perovskite structures, and a morphotropic phase boundary (MPB) with the pseudo-cubic and rhombohedral phases is observed at x = 0.55-0.71. The ceramics have the obvious relaxor behaviors as confirmed by the temperature and frequency dependent dielectric curves. The largest positive electrostrain (0.25%) under 65 kV/cm is achieved in the ceramics with x = 0.63. The ceramics with x = 0.63 also exhibit a large d₃₃* (425 pm/V) with a high curie temperature (T_C =282 °C) and a low hysteresis (43%). The improved electromechanical properties are attributed to the existence of relaxor behavior at BiFeO₃-BaTiO₃ phase boundary after doping SrTiO₃. These results demonstrate that the design of a ternary system like ST-BF-BT based ceramics with relaxor behavior and phase boundary composition provides an effective way to optimize the electrostrain behavior of high temperature lead-free ceramics.     

Enhanced energy storage performance in bismuth layer-structured BaBi2Me2O9 (Me = Nb and Ta) relaxor ferroelectric ceramics

Bismuth layer-structured BaBi₂Nb₂O₉ (BBN) and BaBi₂Ta₂O₉ (BBT) relaxor ferroelectric ceramics were explored as potential energy storage materials. Remarkable energy storage performances were obtained in both BBN and BBT ceramics, featured by large recoverable energy storage density (~0.84 J/cm³ and ~0.68 J/cm³) and high energy storage efficiency (~90% and ~94%), respectively. Furthermore, both the two ceramics exhibit good thermal and frequency stabilities. Delightedly, both the BBN and BBT ceramics can complete the discharge process within 0.15 μs, resulting in ultrahigh current density of 195 A/cm² and 234 A/cm² and excellent power density of 10.74 MW/cm³ and 12.89 MW/cm³, respectively. The obtained results suggest that BaBi₂Nb₂O₉ and BaBi₂Ta₂O₉ ceramics could have a promising future in energy storage applications. This study also demonstrates that the bismuth layer-structured relaxor ferroelectric ceramic can be considered as a novel potential lead-free energy storage materials, in addition to the widely studied pervoskite-structured relaxor ferroelectric ceramics.     

Enhanced breakdown strength and energy storage density in a new BiFeO3-based ternary lead-free relaxor ferroelectric ceramic

A new ternary lead-free relaxor ferroelectric ceramic of (0.67-x)BiFeO₃-0.33(Ba_0.8Sr_0.2)TiO₃-xLa(Mg_2/3Nb_1/3)O₃+y wt.% MnO₂+z wt.% BaCu(B₂O₅) (BF-BST-xLMN+y wt.% MnO₂+z wt.% BCB) was prepared by a solid-state reaction method. The substitution of LMN for BF was believed to induce a typical dielectric relaxation behavior owing to the increased random fields. After co-doping MnO₂ and BCB, a significant decrease in the conductivity and grain size was simultaneously realized, resulting in obviously enhanced dielectric breakdown strength and energy-storage performances at room temperature. A high recoverable energy storage density W˜3.38 J/cm³ and an acceptable energy storage efficiency η˜59% were achieved in the composition with x = 0.06, y = 0.1 and z = 2 under a measuring electric field of 23 kV/mm. In addition, the energy-storage performance is quite stable against both frequency (0.1 Hz–100 Hz) and temperature (30–170 °C), suggesting that BF-BST-xLMN+y wt.% MnO₂+z wt.% BCB lead-free relaxor ferroelectric ceramics might be a promising dielectric material for high-power pulsed capacitors.     

Excellent energy storage properties over a wide temperature range under low driving electric fields in NBT-BSN lead-free relaxor ferroelectric ceramics

To develop environment-friendly dielectric capacitors with low working electric field and wide useable temperature, in this work, we fabricate (1-x)Na_0.46Bi_0.54TiO₃- xBaSnO₃((1-x)NBT-xBSN) lead-free relaxor ferroelectric ceramics by adding BaSnO₃ into Na_0.46Bi_0.54TiO₃ matrix. BSN exhibits slim polarization-electric field (P-E) loops, small remnant polarization (P_r) and good temperature stability because of its room-temperature paraelectric characteristics, and has different cation ionic radii with Na_0.46Bi_0.54TiO₃. Therefore, when BSN is introduced into NBT, the relaxor behavior of the (1-x)NBT-xBSN ceramics is more pronounced and the P-E loops are much slimmer. Besides, because the substitution of Ba²⁺ ions with higher valence for Na⁺ ions neutralizes the hole carriers, which are caused by the volatilization of Na₂O, the resistivity and breakdown strength are improved with increasing BSN content. As a consequence, at x = 0.30, the ceramic exhibits simultaneously a large recoverable energy density (W_rec) of 1.51 J/cm³ and high energy efficiency (η) of 81.2% at a low driving electric field of 145.3 kV/cm because of the collaborative enhancement effect of the high breakdown strength and low remnant polarization. More interestingly, variations of the W_rec and the η for this kind of ceramic are respectively as small as 10% and 0.8% over a wide temperature range of 20–140 °C, demonstrating superior temperature stability. In this report, we provide a new and efficient way for designing and fabricating environment-friendly dielectric capacitors with good reliability and superior high-temperature energy storage capacity.     

Highly-reliable dielectric capacitors with excellent comprehensive energy-storage properties using Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramics

The development of capacitors with high reliability and good comprehensive performances is of great significance for practical applications. In this work, lead-free relaxor ferroelectric (FE) ceramics of (1-x)(0.5(Bi_0.5Na_0.5)TiO₃-0.5SrTiO₃)-xBi(Mg_2/3Nb_1/3)O₃ ((1-x)(BNT-ST)-xBMN) were prepared by a conventional solid-state reaction method. The introduction of BMN was found to enhance local structure disorder, leading to the significantly reduced size of FE nanodomains, which is responsible for the slim polarization-electric field hysteresis loops. A giant energy-storage density of 6.62 J/cm³ and a high efficiency of 82 % can be achieved simultaneously under a moderate electric field of 34 kV/mm at x = 0.08. It also exhibits high discharge density ～ 2.74 J/cm³, large power density ～ 248 MW/cm³ and ultrafast discharge rate ～ 28 ns at 20 kV/mm in addition to excellent temperature (10–130 °C) and frequency (1–100 Hz) stabilities. These results demonstrate that the (1-x)(BNT-ST)-xBMN ceramic system is a promising lead-free candidate for advanced pulsed power capacitor applications.     

High recoverable energy storage density in nominal (0.67-x)BiFeO3-0.33BaTiO3-xBaBi2Nb2O9 lead-free composite ceramics

A series of novel lead-free energy storage ceramics, (0.67-x)BiFeO₃-0.33BaTiO₃-xBaBi₂Nb₂O₉ (BF-BT-xBBN), were fabricated by traditional solid-state reaction, where bismuth layer-structured BaBiNb₂O₉ was incorporated into perovskite-structured BiFeO₃–BaTiO₃ ceramic as an additive. The addition of BaBi₂Nb₂O₉ increased the relaxor behavior and breakdown strength of BF-BT ceramics due to the formation of polar nanoregionals (PNRs), inducing enhanced energy storage performance. The composite ceramics, with x = 0.08, showed a large recoverable energy density (W_rec) of 3.08 J/cm³ and an outstanding energy storage efficiency (η) of 85.57% under an applied electric field of 230 kV/cm. Moreover, the composite ceramics exhibited excellent thermal stability and high stability toward different frequencies in a temperature range of 20–100 °C and a frequency range of 0.1–1500 Hz. These results demonstrate great potential of novel BF-BT-xBBN composite ceramics for next-generation energy storage applications.     

Enhanced piezoelectric and ferroelectric properties of BiFeO3-BaTiO3 lead-free ceramics by optimizing the sintering temperature and dwell time

0.7BiFeO₃-0.3BaTiO₃ (BFO-0.3BT) ceramics were prepared to uncover the impacts of sintering temperature (T_S) and dwell time (t_d) on the microstructure and electrical properties. With increasing the T_S or t_d, the grain sizes increase along with the porosity decreases, which is in favor of the alignment of dipole. However, excess T_S or t_d are inclined to cause the volatilization of Bi₂O₃, which deteriorates piezoelectric properties. Because of the R-T two-phase coexistence, low defect ions concentration and porosity, as well as appropriate grain size, the excellent d₃₃?=?208?pC/N and k_p?=?35.46% as well as P_r?=?28.52?μC/cm² were achieved in BFO-0.3BT ceramics at T_S?=?1000?°C and t_d?=?6?h. In addition,large unipolar strain 0.13% and d₃₃*?=?256.2?pm/V also were obtained in BFO-0.3BT ceramics at T_S?=?1000?°C and t_d?=?6?h. This research indicates that the porosity and defect ion concentration as well as grain size also play an important role in piezoelectric properties in BFO-BT ceramics.     

Enhanced energy storage performances of Bi(Ni1/2Sb2/3)O3 added NaNbO3 relaxor ferroelectric ceramics

In the development of dielectric ceramic materials, the requirements of miniaturization and integration are becoming increasingly prominent. How to obtain greater capacitance in a smaller volume is one of the important pursuits. In this paper, lead-free (1-x)NaNbO₃-xBi(Ni_1/2Sb_2/3)O₃(xBNS) with high recoverable energy storage density (W_rec) and relatively high energy storage efficiency(η) were prepared by a solid state sintering method. Bi(Ni_1/2Sb_2/3)O₃ was introduced into the Sodium niobate ceramics(NN)-based ceramics to reduce the sintering temperature and increase the maximum breakdown field strength (E_b). Finally, 0.15BNS achieved a high E_b of 460 kV/cm, W_rec of 3.7 J/cm³ and η of 77%. In addition, the sample maintained excellent stability in the frequency range of 1–120 Hz. And the 0.15BNS ceramics also exhibited high power density (P_D = 36.4 MW/cm³), large current density (C_D = 520.8 A/cm²) and relatively fast charge-discharge rate (t_0.9 = 1050 ns). These results demonstrate the potential application value of xBNS ceramics in 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.     

Achieving high-energy storage performance in 0.67Bi1-xSmxFeO3-0.33BaTiO3 lead-free relaxor ferroelectric ceramics

BiFeO₃–BaTiO₃ (BF-BT)-based lead-free ferroelectric ceramic has attracted immense interest in energy storage applications due to its great spontaneous polarization (P_max) strength. However, high remanent polarization (P_r) has become a serious obstruction for its practical application. In this work, Sm ions were doped into 0.67BiFeO₃-0.33BaTiO₃ (0.67Bi_1-xSm_xFeO₃-0.33BaTiO₃, BS_xF-BT) to tailor the structure and energy storage properties. It was found that the doping of Sm ions effectively reduced P_r by enhancing the relaxor behavior of BF-BT ceramic, which produce an enhancement in the energy storage performance. Large recoverable energy storage density W_rec of 2.8 J/cm³ with moderate energy storage efficiency η of 55.8% (200 kV/cm) were achieved in the ceramics with x = 0.1. Moreover, the energy storage capabilities exhibited good stability at temperature (20–95 °C) and frequency (0.1–50 Hz). Furthermore, the ceramic also possessed a predominant discharge speed with a discharge time less than 0.1 μs in a circuit with a load of 200 Ω. These results showed that the W_rec and η of BF-BT ceramic could be availably promoted by the doping of Sm ions, which may be helpful for the enhancement of energy storage performance of BF-BT-based ceramics.     

Enhanced energy storage performance in Na(1-3x)BixNb0.85Ta0.15O3 relaxor ferroelectric ceramics

High-performance lead-free dielectric containers have excellent energy storage performance such as higher power density and energy density. While being eco-friendly materials, lead-free dielectric materials are more suitable for pulse power systems than other dielectric materials. In this study, Ta⁵⁺and Bi³⁺ ions were introduced into the A site and B site of the NaNbO₃ matrix. The introduction of Bi³⁺ ions induced the formation of a vacancy in the A site, yielding Na_(1-3x)Bi_xNb_0.85Ta_0.15O₃ (NBNT, x = 0.05, 0.08, 0.11, 0.14) ceramics. The recoverable energy density (W_rec) and the energy storage efficiency (η) were highest for the Na_0.67Bi_0.11Nb_0.85Ta_0.15O₃ ceramic, with values of 3.37 J/cm³ and 89% respectively. Batteries employing the Na_0.67Bi_0.11Nb_0.85Ta_0.15O₃ ceramic achieved a current density of 830.4 A/cm², an energy density of 49.8 MW/cm³ and 60.2 ns discharge time. These results show that the Na_0.67Bi_0.11Nb_0.85Ta_0.15O₃ ceramic is an effective energy storage material with broad application prospects.     

High-energy storage performance in lead-free (1-x)BaTiO3-xBi(Zn0.5Ti0.5)O3 relaxor ceramics for temperature stability applications

In this paper, we prepared lead-free (1-x)BaTiO₃-xBi(Zn_0.5Ti_0.5)O₃ (x=0.04, 0.08, 0.10, and 0.14) ceramics by a conventional solid-state reaction technique. Pure perovskite structures and dense microstructures were demonstrated for all the compositions. Interestingly, it was found that the sintering temperature tended to decrease with increasing the Bi(Zn_0.5Ti_0.5)O₃ content. It should be stressed that a low sintering temperature of 1050 °C was utilized for the composition of x=0.14. Moreover, the dielectric permittivity-temperature curve became more flat and the relaxor degree became stronger with the augment in Bi(Zn_0.5Ti_0.5)O₃ content. We also conducted a detailed study on the energy storage performance for all the compositions from 25 °C to 180 °C.We found that relatively temperature-stable energy storage performance could be obtained in the compositions with x=0.08, 0.10 and 0.14 regardless of the evolution of dielectric constant during the test temperature range. In particular, due to a higher field of 12 MV m⁻¹, the discharge energy storage densities of x=0.14 could reach 0.81 J cm⁻³, 0.80 J cm⁻³, 0.78 J cm⁻³, 0.72 J cm⁻³, and 0.67 J cm⁻³ with high efficiencies of 94%, 92%, 94%, 88% and 77% at 25 °C, 50 °C, 100 °C, 150 °C, and 180 °C, respectively. All these results demonstrate the (1-x)BaTiO₃-xBi(Zn_0.5Ti_0.5)O₃ ceramics are quite promising for temperature-stable energy storage applications.     

An effective strategy to realize superior high-temperature energy storage properties in Na0.5Bi0.5TiO3 based lead-free ceramics

To develop and fabricate environmentally friendly dielectric capacitors used in high-temperature environment, in this work, we prepare La³⁺ doped 0.94Na_0.5Bi_0.5TiO₃-0.06BaTiO₃ lead-free relaxor ferroelectric ceramics with high and wide phase transition temperature. With the introduction of La³⁺, due to the enhancement of the A- and B- site cation ion disorder, the dielectric relaxation characteristics of the ceramics are more obvious. Therefore, the polarization-electric field loops become slimmer and the remnant polarization (P_r) reduces. In addition, because La³⁺ as a donor dopant has lower mobility than A-site cation ions in the ceramic matrix, the grain sizes decrease with increasing La³⁺ content, which significantly leads to an increase in the breakdown strength (E_b). As a result, both a large recoverable energy density (W_rec) of 1.92 J/cm³ and a high energy efficiency (η) of 85.7% are obtained in the ceramic with 12 mol% La³⁺ content. More importantly, even at 200 °C and a low driving electric field of 155 kV/cm, the W_rec and η of this kind of ceramic are still as high as 1.2 J/cm³ and 89.4%, indicating good temperature stability. This work provides an effective and simple way to prepare environmentally friendly dielectric capacitors that are applicable in high-temperature environment.     

(1-x)Bi0.5Na0.47Li0.03TiO3-xNaNbO3 lead-free ceramics with superior energy storage performances and good temperature stability

Dielectric capacitors show great potential in superior energy storage devices. However, the energy density of these capacitors is still inadequate to meet the requirement of energy storage applications. In this study, the Bi_0.5Na_0.47Li_0.03TiO₃-xNaNbO₃ (BNLT-xNN) ceramics were prepared via conventional solid-phase reaction. Results showed that NN can efficaciously enhance the breakdown strength (E_b) and the relaxation behavior of the BNLT ceramic because of the broken ferroelectric long-range order. When x = 0.3, the maximum E_b reached 350 kV/cm, at which the 0.7BNLT-0.3NN ceramic exhibited the high recoverable energy storage density (W_rec) of 4.83 J/cm³ and great efficiency (η) of 78.9%. The ceramic demonstrated good temperature stability at 20 °C-160 °C and excellent fatigue resistance. Additionally, the 0.7BNLT-0.3NN ceramic presented high power density (P_D; ～77.58 MW/cm³), large current density (C_D; ～861.99 A/cm²), and quite short discharge time (t_0.9; ～0.090 μs). These results indicated that the 0.7BNLT-0.3NN material has excellent energy storage properties and various application prospects.     

Enhanced energy storage efficiency by modulating field-induced strain in BaTiO3-Bi(Ni2/3Ta1/3)O3 lead-free ceramics

Nowadays, more attention has been paid to nontoxic lead-free ferroelectric (FE) materials as the substitution of lead-based energy storage materials, due to the increasing environmental awareness. BaTiO₃ (BT) has good comprehensive properties, however, its low breakdown electric field leads to the low energy storage density, which is the main challenge in BT-based ceramics. In this work, BT was modified by introducing the Bi(Ni_2/3Ta_1/3)O₃ (BNT) component in order to reduce the field-induced strain and further enhance the breakdown strength. Effects of BNT component on the microstructures, relaxor characteristics, energy storage efficiency and field-induced strain were investigated systematically. The results indicate that the long-range ordered ferroelectric domains of BT ceramics are destroyed by the incorporation of the BNT component, resulting in the distortion of the polar regions. As a result, the BT-BNT ceramics possess slim P-E hysteresis and extremely low remnant polarization, owing to the phase transition from the normal ferroelectrics to relaxor ferroelectrics. The reduced strain promotes to the increase of the breakdown field strength. Ultimately, the energy storage efficiency of BT-BNT ceramics can reach 87.15%, revealing a promising application in energy storage device.     

Role of sodium deficiency on the relaxor properties of Bi1/2Na1/2TiO3-BaTiO3

The influence of A-site deficiency on the relaxor properties in the lead-free (1-x)(Bi_1/2Na_1/2)TiO₃-xBaTiO₃ solid solution system was studied by intentionally reducing Na content in reference to the stoichiometric compositions. We observed that for all compositions, the higher the level of Na deficiency was, the lower the transition temperature from a ferroelectric to relaxor state became. The compositions with intermediate BaTiO₃ contents (x?=?0.06, 0.09, 0.13, and 0.40) showed sprout-shaped strains and pinched polarization curves at room temperature, indicating a crossover from a non-ergodic relaxor to ergodic relaxor state above a certain level of Na deficiency. We demonstrate that the presence of recently proposed oxygen octahedral tilt disorder as a prerequisite for the relaxor features in this system is not necessarily true, but the presence of stress-field-induced defect dipoles matters. A transmission electron microscopy confirmed that micro domains break down into nano domains with increasing Na deficiency level.     

Study of relaxor behavior in a lead-free (Na0.5Bi0.5)TiO3-SrTiO3-BaTiO3 ternary solid solution system

In this work, single phase lead-free (0.8-x)(Na_0.5Bi_0.5)TiO₃−0.2SrTiO₃-xBaTiO₃ (NBT-ST-BT) ceramics were prepared by conventional solid state reaction method. The effect of BT on the structure and on the dielectric and ferroelectric properties of NBT-ST-BT were investigated. A structural transformation from pseudo-cubic to tetragonal along with possible phase coexistence was witnessed as the BT content was increased. A diffuse phase transition with considerable frequency dispersion in the dielectric response and slim P-E loops evidenced strong relaxor behavior for the ternary system at higher compositions of BT. An analysis of the frequency dependent T_m according to V-F and Power law indicated substantial interaction between the polar nano-regions and relatively broad distribution of freezing temperatures. The study of the dielectric constant at much higher and lower temperatures than T_m in the range of Burn's temperature (T_B) to freezing temperature (T_f) to provide useful information about the growth rate of polar nano-regions and their interactions for a better understanding of the relaxor behavior exhibited by the present ternary system.     

High energy storage density and stable fatigue resistance of Na0.46Bi0.46Ba0.05La0.02Zr0.03Ti0.97-xSnxO3 ceramics

Energy density and fatigue resistance properties were investigated for lead-free Na_0.46Bi_0.46Ba_0.05La_0.02Zr_0.03Ti_0.97-xSn_xO₃ (for 0 ≤ x ≤ 0.15) ceramics, synthesized via solid-state reaction technique. Perovskite pseudo-cubic crystal structure was revealed for all ceramics using X-ray diffraction. Polarization and current density versus electric field were perceived and suggested the relaxor behavior with increasing composition. A high storage energy density ~1.58 J/cm³, and conversion efficiency ~71.7% at ~110 kV/cm applied field was obtained for x = 0.03 composition at room temperature. Energy storage density was revealed ~1.53 J/cm³, and efficiency ~88.6% at 110 °C with a 100 kV/cm applied field. In addition, ceramic x = 0.03 was fatigue-free from 1 to 10⁵ cycles. Hence, the composition x = 0.03 might be applicable for high energy storage devices.