Designing novel lead-free NaNbO3-based ceramic with superior comprehensive energy storage and discharge properties for dielectric capacitor applications via relaxor strategy

There are urgent demands for high performance capacitors with superior energy storage density and discharge performances. In this work, novel NaNbO₃-based lead-free ceramics (0.91NaNbO₃-0.09Bi(Zn_0.5Ti_0.5)O₃) with high energy storage capability, high power density and fast discharge speed were designed and prepared. Bi(Zn_0.5Ti_0.5)O₃ was chosen for the purpose to reduce the remnant polarization and improve the induced polarization. Consequently, a large stored energy storage density (W_s˜ 3.51 J/cm³) and high recoverable energy storage density (W_rec˜ 2.20 J/cm³) were obtained in 0.91NaNbO₃-0.09Bi(Zn_0.5Ti_0.5)O₃ ceramic under a high breakdown strength of 250 kV/cm, with excellent thermal stability in the range of 20–120 °C. More importantly, the investigated ceramics exhibited high power density (P_D˜ 20 MW/cm³) and ultrafast discharge rate (t_0.9˜ 0.25 μs), demonstrating potential application in pulse powehr systems. This work provides an effective means of achieving excellent energy storage and discharge performances in NaNbO₃-based ceramics for application in dielectric capacitors.     

High energy storage performance in BaTiO3-based lead-free relaxors via multi-dimensional collaborative design

The application of advanced pulse power capacitors strongly depends on the fabrication of high-performance energy storage ceramics. However, the low recoverable energy storage density (W_rec) and energy efficiency (η) become the key links limiting the development of energy storage capacitors. In this work, a high W_rec of ～5.57 J cm^?3 and a large η of ～85.6% are simultaneously realized in BaTiO₃-based relaxor ceramics via multi-dimensional collaborative design, which are mainly attributed to the ferroelectric-relaxor transition, enhanced polarization, improved breakdown electric field, and delayed polarization saturation. Furthermore, the excellent temperature stability (ΔW_rec < ± 5%, 25–140 °C), frequency stability (ΔW_rec < ± 5%, 1–200 Hz), and outstanding charge/discharge performance (current density ～1583.3 A cm^?2, power density ～190.0 MW cm^?3) with good thermal stability are also achieved. It is encouraging that this work demonstrates that multi-dimensional collaborative design is a good strategy to develop new high-performance lead-free materials used in advanced dielectric capacitors.     

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.     

Effective strategy to realise excellent energy storage performances in lead-free barium titanate-based relaxor ferroelectric

High-performance capacitors, which possess a high energy storage density, large power density and fast charge/discharge rate, are in high demand in pulsed power systems. Although several studies have been conducted to obtain excellent energy storage performances, the scientific and feasible guidance is lacking on how to quickly and efficiently find a material system with high recoverable energy storage density (W_rec), large energy storage efficiency (η), and excellent thermal stability. Herein, a strategy is proposed to concurrently regulate the temperature corresponding to the maximum dielectric constant (T_m) to around room temperature and enhance the relaxor characteristic. To our satisfaction, excellent energy storage performances with a high W_rec of 3.05 J/cm³, large η of 95%, and wide temperature stability (20–180 °C) were achieved in 0.85BaTiO₃-0.15Bi(Mg₀₅Sn_0.5)O₃ (0.15BMS) ceramics. In addition, these ceramics also exhibited a large discharge energy density (W_dis = 0.74 J/cm³) and fast discharge time (t_0.9 = 105 ns) over a broad temperature range (20–180 °C), which confirms their significant application potential in the high-temperature field. These results indicate that this work can provide an effective guideline approach to attain high-performance capacitors for application in pulsed power capacitors.     

Improvement of energy storage properties of NaNbO3-based ceramics through the cooperation of relaxation and oxygen vacancy defects

The development of materials with high energy storage plays a crucial role in solving energy consumption. Traditional dielectric ceramics have the disadvantages of low energy storage and low efficiency. The most effective solution is to reduce the dielectric loss and increase the breakdown strength. In this paper, (Na_0.73Bi_0.08Sm_0.01)(Nb_0.91Ta_0.09)O₃ relaxor ferroelectric ceramics were prepared, which achieved a high energy storage density of 1.66 J cm^?3, high efficiency (83.6%) at 214 kV/cm at room temperature. The addition of Bi₂O₃ makes the A site cations disordered, thereby generating random fields, breaking the long-range order, and forming polar nanodomains. That allows the ceramic to acquire relaxation properties, reducing the dielectric loss. The impedance analysis proves that the breakdown strength is related to the addition of Sm₂O₃. The addition of Sm reduces the oxygen vacancy defect concentration and inhibits the migration of carriers, thereby improving its breakdown strength. Through proper doping of Bi and Sm, the relaxation properties and breakdown field strength of the ceramics are enhanced to obtain excellent energy storage performance. This provides a new idea in terms of relaxation and oxygen vacancy defects for NaNbO₃-based energy storage ceramics.     

Simultaneously optimizing both energy storage density and efficiency in a novel lead-free relaxor antiferroelectrics

Dielectric capacitors with both high energy density and efficiency are highly demanded in pulsed power systems. Relaxor antiferroelectrics have attracted much attention due to their unique advantages in optimizing both properties of a dielectric capacitor. In this work, a novel relaxor antiferroelectric ceramic with composition of (1-x)Bi_0.5Na_0.5TiO₃-xAg_0.91Sm_0.03NbO₃ was developed, where the antiferroelectricity was stabilized with the increase of Ag_0.91Sm_0.03NbO₃ counterpart. Moreover, the relaxor feature was also obviously improved, as a result of chemical and structural disorder introduced by hetero cations with different radii and valence states. As expected, a high recoverable energy density of 2.1 J/cm³ accompanied with efficiency of 83 % was simultaneously achieved at x = 0.15. The as-prepared ceramics also exhibited good thermal stability in energy storage performance with small variations (energy storage density <10 % and efficiency <5 %) over 30−130 °C. All these merits demonstrate that the 0.85Bi_0.5Na_0.5TiO₃-0.15Ag_0.91Sm_0.03NbO₃ ceramic has great potential for high power energy storage applications.     

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.     

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

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

Ultrahigh energy storage density in Ba0.85Ca0.15Zr0.1Ti0.9O3-based lead-free ceramics by introducing a relaxor end-member

Dielectric ceramics with relaxor characteristics are promising candidates to meet the demand for capacitors in next-generation pulse devices. In this work, Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT)-based lead-free ceramics with an ultrahigh recoverable energy storage density (W_rec) were designed and fabricated by introducing the relaxor end-member of Bi(Zn_2/3Ta_1/3)O₃ (BZT). The addition of BZT disrupted the ferroelectric (FE) long-range order and triggered an FE-to-relaxor FE (RFE) phase, leading to the formation of locally polar nano-regions (PNRs) and significantly inhibiting grain growth. Meanwhile, the presence of PNRs with good thermal stability improved the temperature stability of both the dielectric constant (ε') and W_rec. More importantly, the breakdown electric field strength was significantly improved up to ∼640 kV/cm, resulting in an ultrahigh W_rec of ∼7.11 J/cm³ for the 8%BZT doped BCZT (BCZT-BZT8) ceramic. Furthermore, the BCZT-BZT8 ceramic exhibited excellent charge/discharge performances (C_D ∼ 458.4 A/cm², P_D ∼ 50.4 MW/cm³, W_D ∼ 1.354 J/cm³, t_0.9 ∼ 320 ns) with good thermal stability in the temperature range of 298–373 K. The defect chemistry of the BCZT-BZT8 was explored using electron paramagnetic resonance (EPR) spectroscopy which revealed an EPR signal (g ∼ 1.955), associated with oxygen vacancies. The above findings indicate that the novel composition of BCZT-BZT8 has great prospects in energy storage capacitor applications.     

NaNbO3-based antiferroelectric multilayer ceramic capacitors for energy storage applications

Antiferroelectric materials feature electric-field-induced phase transitions followed by a large polarization change characterized by double polarization hysteresis loops. Therefore, antiferroelectrics are engaging for high-energy density and high-power density applications, especially in the form of multilayer ceramic capacitors (MLCCs). However, the development of lead-free antiferroelectrics with stable double hysteresis loops is still challenging, especially for compositions based on NaNbO₃. To this end, we have prepared MLCCs with the newly developed antiferroelectric composition 0.90NaNbO₃-0.06SrSnO₃-0.04(Na_0.5Bi_0.5)TiO₃. The double hysteresis loops were determined at 24 kV/mm in the temperature range of 25–150 °C, with resulting recoverable energy storage ranging from 1.16 to 1.42 J/cm³, respectively. Moreover, the energy efficiency is rather constant at 0.4 in the same temperature range. Finally, the MLCCs exhibit resistance to electric field cycling and could withstand up to 1000 cycles. These results verify that NaNbO₃-based antiferroelectrics in the form of MLCCs are promising for use in applications.     

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.     

Novel Ca doped Sr0.7Bi0.2TiO3 lead-free relaxor ferroelectrics with high energy density and efficiency

Sr_0.7Bi_0.2TiO₃ with high relaxor behavior and energy storage efficiency (η) is expected to be applied in power energy storage capacitors. However, its energy storage density is limited by the relatively low dielectric breakdown strength (DBS). Herein, Sr_0.7Bi_0.2Ca_xTiO₃ (SBT-xC, x = 0 ∼ 0.15) was prepared to decrease the average grain size of Sr_0.7Bi_0.2TiO₃. This can effectively eliminate the oxygen vacancy and decrease the electrical conductivity and leakage current, which result in the enhanced DBS. Meanwhile, Ca doping increases the relaxor behavior and dielectric constant. When x = 0.1, the composition exhibits high DBS of 480.2 kV/cm and excellent energy storage properties, such as high energy storage density of 2.1 J/cm³ with high η of 97.6 % at 290 kV/cm, considerable thermal stability and great frequency stability. Moreover, SBT-0.1C shows high power density of 50.1 MW/cm³. These results suggest that SBT-0.1C is a potential candidate for high performance dielectric energy storage applications.     

Enhanced energy storage properties of lead-free (Ca0.5Sr0.5)1-1.5xLaxTiO3 linear dielectric ceramics within a wide temperature range

(Ca_0.5Sr_0.5)_1-1.5xLa_xTiO₃ (x = 0.000, 0.050, 0.075, 0.100, 0.150) ceramics were successively fabricated by conventional solid state method. Structure characterization were detected by XRD and SEM, demonstrating the influence of La₂O₃ doping on the microstructure. In addition, this effect on relaxor behavior corresponding to resistivity of grain boundary was discussed by dielectric and impendance spectra. The determining band gap energy (E_g) was estimated by Ultraviolet–Visible Spectrophotometry in order to investigate the effect of band gap on the breakdown strength. The dielectric breakdown strength was found to significantly enhanced on the basis of Ca_0.5Sr_0.5TiO₃ ceramics with La₂O₃ doping, the (Ca_0.5Sr_0.5)_0.8875La_0.075TiO₃ samples possessed widest band gap (∼5.2 eV) and exhibited maximum breakdown strength of 370 kV/cm corresponding with a large recoverable energy storage density of 2.07 J/cm³. Furthermore, the excellent stability of energy storage properties and ultrahigh energy efficiency of above 93% at wide frequency (1–1000 Hz) as well as high temperature (20–180 °C) was obtained for (Ca_0.5Sr_0.5)_0.8875La_0.075TiO₃ ceramics, which reveal samples as good candidate for linear energy storage fileds.     

Realizing excellent energy storage properties in Na0.5Bi0.5TiO3-based lead-free relaxor ferroelectrics

Development of lead-free dielectric capacitors with high recoverable energy storage density (W_rec), large energy storage efficiency (η), and wide usage temperature range are in high demanded for pulse power systems. Herein, we realized the enhancement of energy storage properties [high W_rec = 3.76 J/cm³, large η = 78.80 %, and broad operating temperature range (20?180 °C)] in lead-free Na_0.5Bi_0.5TiO₃ (BNT)-based relaxor ferroelectrics via component regulation. Excellent energy storage properties mainly originate from suppressing early polarization saturation and improving dielectric breakdown strength (E_b). Domain evolution on the nanoscale offers robust support to suppression of early polarization saturation. The enhancement of E_b can be derived from the contribution of the Mg-rich phase, which is also corroborative via first-principles calculation on basis of density functional theory (DFT). We believe that these findings in this work may provide a practicable guideline to build new lead-free ceramics for electrical energy storage applications.     

High energy storage density and efficiency in AgNbO3 based relaxor antiferroelectrics with reduced silver content

Silver niobate based lead-free antiferroelectric ceramics have demonstrated great advantages, but the high consumption of noble metal silver may restrict their commercial application. In this work, Na⁺ and Ta⁵⁺ co-modified (Ag_1-xNa_x)(Nb_1-yTa_y)O₃ (100xNa-100yTa) ceramics were investigated, aiming to reduce the silver consumption and achieve good energy storage properties. The Na⁺ tended to increase M2-M3 phase transition temperature (T_M2-M3), while Ta⁵⁺ was more likely to reduce T_M2-M3. A new current peak (E_R) was observed for the first time in all current-electric field curves. As expected, a room temperature M2-M3 phase boundary with relaxor AFE property was realized in 40Na-65Ta with obviously reduced silver content, in which high recoverable energy storage density (W_rec) of 6.5 J/cm³ and good energy storage efficiency (η) of 78% were achieved. This work demonstrates a strategy to realize relaxor antiferroelectrics in AgNbO₃ based ceramics for energy storage performance, and promotes the commercialization potential.     

Simultaneously enhanced energy storage density and efficiency in novel BiFeO3-based lead-free ceramic capacitors

In this work, a series of novel lead-free (1-x)Bi_0.83Sm_0.17Fe_0.95Sc_0.05O₃-x(0.85BaTiO₃-0.15Bi(Mg_0.5Zr_0.5)O₃) [(1-x)BSFS-x(BT-BMZ), x = 0.45?0.85] relaxor ceramics were prepared by solid phase sintering, and their dielectric properties and energy storage performances were explored. It was revealed that all the samples have a dense structure with pure pseudo-cubic phase. With the increase of x, the ferroelectric hysteresis loop is gradually slimmed accompanied by a decreasing polarization, indicating an enhanced relaxor behavior. Moreover, the electric breakdown strength increases linearly with x due to the fine grain size and enhanced relative density. Interestingly, a large recoverable energy density (～3.2 J/cm³) with an outstanding efficiency (～92 %) is achieved under an electric field ～206 kV/cm for the optimized component x = 0.75, which is superior to other reported lead-free ceramic systems. Moreover, the optimized ceramics of 0.25BSFS-0.75(BT-BMZ) show good thermal stability (25?100 °C) and excellent fatigue endurance (cycle number: > 10⁵) in energy storage performances. This work opens up a new route to tailor lead-free dielectric ceramics with high energy storage properties.     

Energy storage properties of NaNbO3-CaZrO3 ceramics with coexistence of ferroelectric and antiferroelectric phases

Anti-ferroelectric materials with large saturated polarization, small remnant polarization, and moderate breakdown strength are receiving increasing attention for modern high-power electrical systems. Here we demonstrated that by incorporating CaZrO₃ into NaNbO₃ ceramics, the antiferroelectricity in NaNbO₃-CaZrO₃ solid solutions could be stabilized at room temperature. The effects of phase constitution and microstructure on the dielectric properties, electrical breakdown strength, and energy storage properties of the NaNbO₃-CaZrO₃ ceramics were investigated. Ferroelectric and antiferroelectric phase coexistence in the NaNbO3-CaZrO₃ was confirmed by XRD and TEM analyses. With increasing CaZrO₃ content, the grain size was reduced, and the dielectric breakdown strength was improved. Therefore, a high energy density of 0.55?J/cm³ and efficiency of 63% was obtained in the NaNbO₃-0.04CaZrO₃ ceramics. These lead-free NaNbO₃-CaZrO₃ antiferroelectrics with good electrical energy storage can be exploited for high-power storage devices.     

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.     

Influence of BaSnO3 additive on the energy storage properties of Na0.5Bi0.5TiO3-based relaxor ferroelectrics

(1-x)NBT-xBSN (0.1?≤?x?≤?0.35) ceramics were prepared by solid state methods and their energy storage properties and high-temperature capacitor applications were systematically investigated. All samples showed a perovskite structure and the structure transformed to lower symmetry orthorhombic phase (x?≥?0.1) from rhombohedral phase (x?<?0.1) to with the addition of BSN. The more addition content of BSN significantly decreases phase transition temperature T_m of NBT ceramics. The x?=?0.25 sample exhibits a stable relative permittivity of 1605?±?15% in a broad temperature range of 38?°C to 319?°C. With increasing BSN concentration, the slope of the P-E loops and the energy loss gradually decreases. When x?=?0.25, a high breakdown strength of 190?kV/cm and the maximum discharge energy density of 1.91?J/cm³ were obtained, of which the energy efficiency was as high as 86.4%. Thus, it was believed that our work could provide a significant guidance for designing the new system for energy storage.     

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.