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 energy storage performance in Sn doped Sr0.6(Na0.5Bi0.5)0.4TiO3 lead-free relaxor ferroelectric ceramics

SnO₂ doped Sr_0.6(Na_0.5Bi_0.5)_0.4TiO₃ (NBT-ST) ceramics were prepared by a conventional solid-state reaction method. Their phase structures, microstructures and electrical properties were characterized in details. It is found that SnO₂ doping could increase the lattice parameters, density and average grain size. A suitable amount of SnO₂ can improve dielectric properties, and affect the relaxor behavior of the NBT-ST matrix, thereby it can effectively reduce the energy loss and optimize the energy storage performance. Furthermore, the energy storage properties are improved with SnO₂ doping. Especially, the 1 at. % SnO₂ doped NBT-ST achieves a high recoverable energy density of 2.35 J/cm³, which is mainly attributed to large maximum polarization of 43.2 μC/cm², small remnant polarization of 5.83 μC/cm² and high breakdown strength of 180 kV/cm. Also, relatively good temperature stability for dielectric performance and excellent fatigue resistance are observed in this composition. These properties are attractive for lead-free energy storage applications.     

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.     

Effect of Sr(Zn1/3Nb2/3)O3 modification on the energy storage performance of BaTiO3 ceramics

Lead-free (1-x)BaTiO₃-xSr(Zn_1/3Nb_2/3)O₃ (abbreviated as BT-xSZN, x = 0–0.08) relaxor ferroelectric ceramics were prepared using the traditional solid phase technology, and the effects of SZN modification on their phase structures, microstructures, dielectric performance, ferroelectricity and energy storage performance were studied in detail. A pure perovskite phase was observed in the BT-xSZN ceramics. The BT-based ceramics modified by SZN exhibited refined grain size. As the SZN content was increased, the breakdown strength initially increased and then decreased, and the ferroelectric loops gradually became ‘slim’. The BT-xSZN (x = 0.07) ceramics demonstrated a favourable energy storage performance with high recoverable energy density (W_rec = ~1.45 J/cm³) and energy storage efficiency (η = ~83.12%) at 260 kV/cm. Results indicate that the energy storage performance of BaTiO₃ ceramics modified by SZN can be remarkably improved, widening their applications in energy storage at low temperatures.     

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.     

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.     

Influence of K0.5Bi0.5TiO3 on the structure,dielectric and ferroelectric properties of (Ba,Ca)(Zr,Ti)O3 ceramics

A new lead-free ferroelectric solid solution between (Ba,Ca)(Zr,Ti)O₃ (BCZT) and K_0.5Bi_0.5TiO₃ (KBT) has been systematically investigated in terms of its phase transformations, microstructure, dielectric and ferroelectric properties. The incorporation of KBT into BCZT was found to enhance the sintering behavior, although secondary phases of K₄Ti₃O₈ and BaBi₄Ti₄O₁₅ were detected at high KBT contents. Chemical heterogeneity was also observed in the form of core-shell grain structures comprising tetragonal ferroelectric BCZT-rich cores with pseudo-cubic relaxor ferroelectric KBT-rich shell regions. Temperature-dependent dielectric property measurements revealed that the BCZT-KBT ceramics exhibited both normal and relaxor ferroelectric behaviour simultaneously, associated directly with the core-shell structure. Ferroelectric hysteresis measurements indicated that the remanent polarisation and coercive field were strongly dependent on KBT content. In common with other lead-free relaxor ferroelectrics, increasing temperature led to the formation of constricted polarisation-electric field hysteresis loops, indicating the occurrence of a reversible electric field-induced nanopolar to long-range ordered ferroelectric state.     

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.     

Achieving outstanding temperature stability in KNN-based lead-free ceramics for energy storage behavior

Lead-free ceramics with prominent energy storage properties are identified as the most potential materials accessed in the dielectric capacitors. Nevertheless, high recoverable energy storage density (W_rec), large energy storage efficiency (η) and preferable temperature stability can hardly be met simultaneously. The Bi(Zn_2/3Ta_1/3)O₃ and NaNbO₃ components are doped in KNN ceramics to substantiate the reliability of this tactic. A high recoverable energy density (W_rec) of ～ 4.55 J/cm³ and a large energy storage efficiency (η) of ～ 87.8% are acquired under the dielectric breakdown strength (DBS) of ～ 375 kV/cm, along with a splendid thermal stability (W_rec variation: ～ 2.3%, η variation: ～ 4.9%) within the temperature range of 20 ℃? 120 ℃. This article demonstrates that the KNN-based ceramics integrate high energy storage properties and outstanding temperature stability at the same time, which broadens the application fields of pulse power systems.     

High energy storage density realized in Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramics at ultralow sintering temperature

The miniaturization and integration trend of electronic applications requires high energy storage performance, and the development of multilayer ceramic capacitors (MLCC) demands the compatibility between ceramic sintering temperature and co-firing temperature of metal electrodes. Herein, we obtained a high recoverable energy storage density and a low sintering temperature simultaneously in 0.5(Bi_0.5Na_0.5)TiO₃-0.5SrTiO₃-x mol% CuO (0.5BNT-0.5ST-x mol% CuO) via the combination of adding CuO sintering aid and citrate sol-gel synthesis method. The optimum sintering temperature decreases significantly from 1130 °C for x = 0 to 820 °C for x = 2.0. The ceramic of 0.5BNT-0.5ST-1.5 mol% CuO exhibits a large W_rec of 2.20 J/cm³ and η of 72.39% under 230 kV/cm. Furthermore, the same sample also possesses a large C_D of 1740.97 A/cm², an extremely high P_D of 139.28 MW/cm³ and an ultrafast discharge speed of 82 ns. These merits reveal that the ceramic of 0.5BNT-0.5ST-1.5 mol% CuO has great potential in practical MLCC production.     

Improved energy storage performance of Bi(Mg0.5Ti0.5)O3 modified Ba0.55Sr0.45TiO3 lead-free ceramics for pulsed power capacitors

(1–x)Ba_0.55Sr_0.45TiO₃–xBi(Mg_0.5Ti_0.5)O₃ (x = 0, 0.08, 0.1, 0.12, 0.15, 0.2) ceramics were fabricated via a solid-state reaction route. The ultrahigh recoverable energy density (W_rec = 4.05 J cm^?3), efficiency (η = 78%), maximum polarization (P_max = 51.40 μC cm^?2), and high dielectric breakdown strength (BDS = 230 kV cm^?1) were achieved for the 0.9BST?0.1BMT ceramic. The fast discharge rate (t_0.9～0.14 μs), current density (C_D～637.02 A cm^?2), high power density (P_D～38.70 MW cm^?3), good temperature stability (20?180 °C), frequency stability (10?500 Hz), and fatigue endurance for cycling (10⁵) of 0.9BST?0.1BMT ceramic make it suitable for the development of energy-storage devices. The relaxor behavior with a high W_rec (3.06 J cm^?3) and η (93%) at BDS (220 kV cm^?1) was also achieved for the 0.8BST?0.2BMT ceramic. This study systematically investigates the correlation among the structural, dielectric, impedance, and energy storage properties of BMT-doped BST ceramics.     

Ultrahigh and field-independent energy storage efficiency of (1-x)(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3-xBi(Mg0.5Ti0.5)O3 ceramics

Relaxor ferroelectrics are attracting an increasing interest in the application of pulse power systems due to their excellent energy storage performance. In this paper, the (1-x)(Ba_0·85Ca_0.15)(Zr_0·1Ti_0.9)O₃-xBi(Mg_0·5Ti_0.5)O₃ ((1-x)BCZT-xBMT, x ≤ 0.2) relaxor ceramics are prepared by the solid state method. The influence of BMT on the microstructure, dielectric and energy storage properties of the prepared ceramics is investigated. The XRD results show that the peak intensity of impurities (Bi₂O₃, TiO₂ and Ba₂Bi₄Ti₅O₁₈) is gradually stronger than that of BCZT phase with x increasing. Meanwhile, the grain size of (1-x)BCZT-xBMT ceramics gradually increases on account of the appearance of impurities Bi₂O₃. Influenced by the impurities and BMT, the dielectric constant of prepared ceramics gradually decreases with x increasing. A large W_rec value of 0.65 J/cm³ with an ultrahigh η value of 97.89% is achieved at x = 0.15 due to the high breakdown strength and slim P-E hysteresis loop. Meanwhile, the η is insensitive to the electric field. The ultrahigh η leads to lesser energy loss during the charge and discharge process. It makes the 0.85BCZT-0.15BMT ceramic more attractive in the application of pulse power systems.     

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 thermal stability of energy storage density and large strain improvement of lead-free Bi0.5(Na0.40K0.10)TiO3 piezoelectric ceramics doped with La and Zr

Properties of lead-free Bi_0.5-xLa_xNa_0.40K_0.10Ti_0.98Zr_0.02O₃ (x?=?0.000–0.040) ceramics were investigated. All ceramics have a pure perovskite structure. A high energy storage density (～1.00?J/cm³) at room temperature (RT) is noted for the x?=?0.030 sample, while x?=?0.020 and 0.040 samples have very high thermal stability of energy storage density of ～3% (at 75–150?°C). Furthermore, the x?=?0.030 and 0.040 samples have the highest energy storage efficiency (η) value of 94% at 125?°C with high thermal stability (η?=?84–95% at 25–150?°C). The x?=?0.005 sample has high electric field-induced strain (S_max?=?0.42%) and high normalized strain coefficient (d^*₃₃?=?S_max/E_max?=?700?pm/V) with large improvements (～200% and 163% for S_max and d^*₃₃, respectively), as compared to the based composition. This ceramic system has potentials for piezoelectric and/or energy storage density applications.     

High energy storage and ultrafast discharge in NaNbO3-based lead-free dielectric capacitors via a relaxor strategy

Dielectric capacitors with decent energy storage and fast charge-discharge performances are essential in advanced pulsed power systems. In this study, novel ceramics (1-x)NaNbO₃-xBi(Ni_2/3Nb_1/3)O₃(xBNN, x = 0.05, 0.1, 0.15 and 0.20) with high energy storage capability, large power density and ultrafast discharge speed were designed and prepared. The impedance analysis proves that the introducing an appropriate amount of Bi(Ni_0·5Nb_0.5)O₃ boosts the insulation ability, thus obtaining a high breakdown strength (E_b) of 440 kV/cm in xBNN ceramics. A high energy storage density (W_total) of 4.09 J/cm³, recoverable energy storage density (W_rec) of 3.31 J/cm³, and efficiency (η) of 80.9% were attained in the 0.15BNN ceramics. Furthermore, frequency and temperature stability (fluctuations of W_rec ≤ 0.4% over 5–100 Hz and W_rec ≤ 12.3% over 20–120 °C) were also observed. The 0.15BNN ceramics exhibited a large power density (19 MW/cm³) and ultrafast discharge time (~37 ns) over the range of ambient temperature to 120 °C. These enhanced performances may be attributed to the improved breakdown strength and relaxor behavior through the incorporation of BNN. In conclusion, these findings indicate that 0.15BNN ceramics may serve as promising materials for pulsed power systems.     

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.     

Lead-free high performance Bi(Zn0.5Ti0.5)O3-modified BiFeO3-BaTiO3 piezoceramics

In this article, structure, dielectric, ferroelectric and piezoelectric properties of Bi rich Bi_1.05(Zn_0.5Ti_0.5)O₃-modified BiFeO₃-BaTiO₃ (BF-BT-xBZT) ceramics were investigated experimentally. Crystal structure, phase purity and microstructure were examined through X-ray diffractometry and scanning electron microscopy, respectively. The crystallographic results show the formation of single-phase solid solutions for all compositions except x?=?10?mol%. The BF-BT modification through BZT instigates variation in grain size, enhancement in Curie temperature (T_C) and field induced polarization and strain response. Large field induced strain of ～0.24% at low driving field along with a small hysteresis of ～38% was observed for 2?mol% BZT modified BF-BT ceramics. These investigated results signpost the potentiality of BF-BT-xBZT ceramics in high temperature piezoelectric device applications.     

Large electro-strain with excellent fatigue resistance of lead-free (Bi0.5Na0.5)0.94Ba0.06Ti1-x(Y0.5Nb0.5)xO3 perovskite ceramics

A series of lead-free (Bi_0.5Na_0.5)_0.94Ba_0.06Ti_1-x(Y_0.5Nb_0.5)_xO₃ (for 0 ≤ x ≤ 0.03) perovskite ceramics were fabricated using a solid-state reaction technique. The effects of (Y_0.5Nb_0.5)⁴⁺ ions doping on phase structure, piezoelectric properties, AC impedance, and fatigue resistance were systematically studied. Crystal structure as a function of the composition revealed a single perovskite lattice structure with dense micromorphology. The transition temperature of the non-ergodic and ergodic relaxor ferroelectric phase shifted to near ambient temperature with increasing composition, which was related to the destruction of the long-range ordered ferroelectric domains. Hence, the transformation of ferroelectric-to-relaxor phase was easier under applied electric field at room temperature. The ceramic for x = 0.01 composition attained a large unipolar strain of ~ 0.452% with a corresponding normalized strain (d₃₃*) of ~ 603 pm/V under applied 75 kV/cm field. Besides, the excellent fatigue resistance of the sample was obtained after 10⁵ switching cycles under 70 kV/cm. These phenomena demonstrated that (Bi_0.5Na_0.5)_0.94Ba_0.06Ti_1-x(Y_0.5Nb_0.5)_xO₃ ceramics might be suitable for a wide range of electronic equipment applications such as actuators and sensors.     

Enhanced piezoelectric,electrocaloric and energy storage properties at high temperature in lead-free Bi0.5(Na1-xKx)0.5TiO3 ceramics

The piezoelectric, electrocaloric and energy storage properties were systemically investigated in lead-free Bi_0.5(Na_1-xK_x)_0.5TiO₃ ceramics from room temperature to high temperature region. These ceramics can be poled completely to obtain large piezoelectric coefficient (104–153 pC/N) at low electric field of ~30?kV/cm. The piezoelectric property shows good thermal stability due to high depolarization temperature (T_d). For BNKT₂₀, a large low electric field-induced strain of 0.36% is obtained at 120?°C under 50?kV/cm, the corresponding normalized strain coefficient is up to 720?pm/V, which is larger than other BNT-based ceramics at high temperature region. The electrocaloric properties of these ceramics are studied via indirect and direct methods. Large EC value (~1.08?K) in BNKT₂₀ ceramic is obtained at 50?kV/cm using indirect calculation. Above 100?°C, the dielectric energy storage density and efficiency of BNKT₂₀ is still up to ~0.85?J/cm³ and 0.75, respectively. The BNKT_x ceramics may become promising candidates in the fields of actuators, electrocaloric cooling and energy storage at high temperature region.     

Enhanced energy storage properties and large electrostrictive effect of Bi0.35Na0.35Ba0.09Sr0.21Ti(1-x)(Al0.5Nb0.5)xO3 relaxor ceramics

Ferroelectric ceramics have good piezoelectric and ferroelectric properties and can be used for energy storage equipment and actuators. Nevertheless, current research on dielectric capacitors has only focused on the energy storage density, but ignored efficiency. Moreover, conventional piezoelectric materials have a large strain hysteresis. In this work, (Al_0.5Nb_0.5)⁴⁺ (AN) complex ions doped 0.7Bi_0.5Na_0.5TiO₃-0.3Ba_0.3Sr_0.7TiO₃ (BNBST) ceramics were prepared. Doping AN destroyed the long-range ordered ferroelectric domains and generated polar nano regions, resulting in a gradual thinning and inclination of polarization hysteresis loops and an increase in relaxor degree. For BNBST-3AN ceramics, a W_rec of 1.52 J/cm³ and a η of 92.1% were achieved at 150 kV/cm. Meanwhile, BNBST-3AN ceramics had good energy storage temperature stability and cycling performance. The AN doping reduced the strain hysteresis in BNBST ceramics. BNBST-2AN ceramics exhibited a longitudinal electrostrictive coefficient Q₃₃ ～ 0.0292 m⁴/C² and a field-induced strain of 0.25% with low strain hysteresis (6.67%). Furthermore, BNBST-4AN ceramics had superior dielectric temperature stability from 24 to 270 °C. All results show that BNBST-100xAN ceramics have great promise for energy storage devices and actuators.