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 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.     

Enhanced energy density and thermal stability in relaxor ferroelectric Bi0.5Na0.5TiO3-Sr0.7Bi0.2TiO3 ceramics

Sr_0.7Bi_0.2TiO₃ (SBT) was introduced into Bi_0.5Na_0.5TiO₃ (BNT) via a standard solid-state route to modulate its relaxation behaviour and energy storage performance. With increasing SBT content, the perovskite structure of BNT transforms from a rhombohedral phase to a weakly polarized pseudo-cubic phase, and the relaxation behaviour is enhanced. In particular, the E_DBS is improved from 120 kV/cm of BNT to 160 kV/cm of 0.6BNT-0.4SBT, which displays a large recoverable energy storage density (W_rec = 2.20 J/cm³), implying a large potential ability of energy storage for the 0.6BNT-0.4SBT ceramic. Moreover, both dielectric properties (28–326 °C) and energy storage properties (20–140 °C) exhibit a good thermal stability for the same 0.6BNT-0.4SBT composition. These characteristics suggest 0.6BNT-0.4SBT ceramic could be a promising candidate to be applied in a pulse power system over a broad temperature range.     

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.     

Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3:ZnO relaxor ferroelectric composites with high breakdown electric field and large energy storage properties

0.82[0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃]-0.18K_0.5Na_0.5NbO₃:xZnO (BNT-BT-KNN:xZnO, x?=?0-0.40) relaxor composites were prepared and their electrical properties were investigated. The breakdown electric field increases with increasing ZnO content. For x?=?0 and x?=?0.40 samples, the maximum recoverable energy storage density is 0.74?J/cm³ and 1.03?J/cm³ while the maximum energy storage efficiency is 86.7% and 72.7% under the electric field of 9.0?kV/mm and 14.0?kV/mm, respectively. The recoverable energy storage density and efficiency of the composite vary less than 2.5% from 25?°C to 125?°C, which indicates temperature-insensitive energy storage performance. These results are discussed based on the ZnO-enhanced bulk resistivity and the ZnO-induced local electric field which suppresses the evolution of polar nanoregions.     

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.     

Improved dielectric energy storage performance of Na0.5Bi0.5TiO3-based lead-free relaxation ferroelectric ceramics achieved by domain structural regulation and enhanced densification

There is still a problem of low energy storage density in dielectric capacitors which is a core component of power systems. For the improvement of the energy storage density, the linear dielectric material CaTiO₃ (CT) was introduced in Na_0.5Bi_0.5TiO₃ (NBT) ceramics in this paper. By modifying the A site, a new relaxor ferroelectric ceramic was successfully synthesized and attained a recoverable density (W_rec) of 2.34 J/cm³ at x = 0.18. Moreover, the preparation process was optimized in this paper. Through the viscous polymer process (VPP) route, the energy density (W_A) of 82NBT-18CT_VPP ceramic further reaches 6.45 J/cm³ at 340 kV/cm, with efficiency (η) up to 75% and a W_rec of 4.82 J/cm³. At the same time, the change of W_rec is small at temperature (30–150 °C) and frequency (1 Hz–300 Hz), which demonstrates its excellent stability. The discharge power density reaches about 180 MW/cm³ and the discharge time is 0.117 μs, which indicates its excellent pulse discharge performance. The results show that 82NBT-18CT lead-free relaxation ferroelectric material is expected to become ideal for high-energy storage applications.     

Enhanced energy storage properties of Bi0.5Na0.5TiO3-based ceramics via regulating the doping content and sintering temperature

Eco-friendly lead-free energy-storage ceramics featuring high energy storage properties and ultra-high stability have been regarded to be one of the most potential materials in the field of energy storage. In this work, a new element system, (1-x)(0.6Bi_0.5Na_0.5TiO₃-0.4SrTiO₃)-xBi[Zn_2/3(Nb_0.5Ta_0.5)_1/3]O₃ ((1-x)BNST-xBZNT) lead-free ceramics, were synthesized via a conventional solid-state sintering technology. And the phase structure, microstructure and energy storage properties of the (1-x)BNST-xBZNT ceramics were comprehensively studied. After the introduction of BZNT, the average grain size of the materials is greatly decreased, thereby enhancing the dielectric breakdown strength (DBS). Additionally, the thermal stability of the ceramics is significantly improved via regulating the doping content and sintering temperature. Furthermore, the ferroelectric long-range order of the ceramics is decomposed into randomly-oriented polar nano-domains (PNRs) after introducing BZNT, leading to strong relaxor behavior and significantly reducing remanent polarization (P_r). As a result, even under a relatively low electric field of 139 kV/cm, the 0.98BNST-0.02BZNT ceramic sintered at 1150 °C possesses high values of energy storage efficiency (η) value of 92.78% and total energy storage density (W_tot) of 1.67 J/cm³ as well as remarkable thermal stability (25–175 °C), frequency stability (20–70 Hz) and fatigue resistant stability (10⁰-10⁵ cycles). This investigation provides a useful reference for developing advanced energy storage ceramics by regulating the doping content and sintering temperature.     

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.     

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.     

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.     

Electrical properties and relaxor phase evolution of Nb-Modified Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-SrTiO3 lead-free ceramics

In this work, the crystalline phase, domain structure, and electrical properties of [Bi_0.5(Na_0.84K_0.16)_0.5]_0.96Sr_0.04Ti_1-xNb_xO₃ (x = 0.010–0.030) ceramics are investigated. Increasing the Nb content induces the phase transition from coexistent rhombohedral and tetragonal phases to a single pseudo-cubic phase, and the lamellar ferroelectric domains evolve into polar nanoregions. Decreased ferroelectric-to-relaxor transition temperature and enhanced frequency dispersion are found in the temperature-dependent dielectric constant and loss, implying a transition from the non-ergodic to ergodic relaxor state. The Nb substitution significantly degrades the long-range ferroelectric order with sharply decreased piezoelectric coefficients from ? 140 to ? 1 pC/N. However, a large strain of 0.32% at 5 kV/mm (normalized strain of 640 pm/V) is obtained around the critical composition of x = 0.0225. The composition of x = 0.030 shows good temperature insensitivity of the strain response, characterized by 308 pm/V with less than 15% reduction from 25 °C to 125 °C.     

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.     

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.     

Enhanced energy storage in temperature stable Bi0.5Na0.5TiO3-modified BaTiO3-Bi(Zn2/3Nb1/3)O3 ceramics

Recently, BaTiO₃-BiMeO₃ ceramics have garnered focused research attention due to their outstanding performance, such as thermal stability, energy efficiency and rapid charge-discharge behavior, however, a lower recoverable energy storage density (W_rec) caused by a relatively low P_max (<30 μC/cm²) mainly hinders practical applications. Herein, the energy density and thermal stability are improved by adding a tertiary component, i.e., Bi_0.5Na_0.5TiO₃, into BaTiO₃-BiMeO₃, resulting in xBi_0.5Na_0.5TiO₃-modified 0.88BaTiO₃-0.12Bi(Zn_2/3Nb_1/3)O₃ ceramics, with x = 0, 0.1, 0.2, 0.3 and 0.4, with superior dielectric properties and eco-friendly impact. Incorporating Bi_0.5Na_0.5TiO₃ with a high saturation polarization and Curie temperature not only significantly enhances P_max of BaTiO₃-Bi(Zn_2/3Nb_1/3)O₃ but also improves Curie temperature of (1-x)[0.88BaTiO₃-0.12Bi(Zn_2/3Nb_1/3)O₃]-xBi_0.5Na_0.5TiO₃ system. Combined with complementary advantages, modified ceramics render a superior energy storage performance (ESP) with a high W_rec of 3.82 J/cm³, efficiency η of 94.4% and prominent temperature tolerance of 25–200 °C at x = 0.3. Moreover, this ceramic exhibit excellent pulse performance, realizing discharge energy storage density W_dis of 2.31 J/cm³ and t_0.9 of 244 ns. Overall, the proposed strategy effectively improved comprehensive properties of BaTiO₃-based ceramics, showing promise in next-generation pulse applications.     

Tailoring high energy density with superior stability under low electric field in novel (Bi0.5Na0.5)TiO3-based relaxor ferroelectric ceramics

Large energy storage density in relaxor ferroelectrics is commonly accompanied with high breakdown strength, which is adverse to the actual dielectric capacitor applications. We demonstrate that such drawback can be effectively resolved by using Sr_0.7Bi_0.2TiO₃ (SBT) to partially replace relaxor ferroelectric 0.76(Bi_0.5Na_0.5)TiO₃-0.24NaNbO₃ (BNT-NN-xSBT). In this study, a high recoverable energy storage density (W_rec∼3.12 J/cm³) and favorable efficiency (η∼75.3 %) are achieved in the BNT-NN-0.1SBT ceramic under a low electric field of 200 kV/cm, which is superior to that of most previously reported dielectric ceramics under the same electric field level. Good temperature stability (25−120 °C), moderate frequency dependence (1−500 Hz), and excellent fatigue resistance (up to 10⁵ cycles) are also realized. More interestingly, the indicated ceramics perform high power density (P_D∼36.40 MW/cm³) and fast discharge time (t_0.9∼0.149 μs) with remarkable temperature endurance. Moreover, of particular significance is that this study offers a feasible guideline to design comprehensive energy storage performance dielectric ceramics for practical applications.     

Optimized energy storage performances in morphotropic phase boundary (Na0.8K0.2)0.5Bi0.5TiO3-based lead-free ferroelectric thin films

As microelectronic devices move toward integration and miniaturization, the thin film capacitors with high energy density and charge/discharge efficiency have attracted immense interests in modern electrical energy storage systems. Despite morphotropic phase boundary (Na_0.8K_0.2)_0.5Bi_0.5TiO₃-based lead-free materials with outstanding ferroelectric and piezoelectric properties, while large ferroelectric hysteresis with high remanent polarization (P_r) hinder to improve energy storage capability. Here, novel lead-free relaxor-ferroelectric (RFE) thin film capacitors with high energy density are successfully prepared in (1-x) (Na_0.8K_0.2)_0.5Bi_0.5TiO₃-xBa_0.3Sr_0.7TiO₃ [(1-x)NKBT-xBST] systems. Introducing BST into the NKBT systems is expected to reduce remanent polarization (P_r) on account of coupling reestablishment of the polar nano-regions (PNRs) and improving the relaxation behavior. As a result, 0.6NKBT-0.4BST thin film exhibits high energy density (W_rec ～ 54.79 J/cm³) together with satisfactory efficiency (η ～ 76.42%) at 3846 kV/cm. The stable energy storage performances are achieved within the scope of operating temperatures (20–200 °C) and fatigue cycles (1-10⁷ cycles). This work furnishes a new technological way for the design of high energy-density thin film capacitors.     

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.     

Influence of secondary phases on ferroelectric properties of Bi0.5Na0.5TiO3 ceramics

The effects of secondary phases on ferroelectric properties of Bi_0.5Na_0.5TiO₃ (BNT) have been studied. Ceramic powders were prepared by solid state reaction employing different sintering temperatures and characterized by X-ray diffraction (XRD), Scanning Electron Microscopy and impedance spectroscopy. The perovskite structure was detected by XRD; together with small peaks corresponding to a secondary phase assigned to the Na₂Ti₆O₁₃-based phase in calcined powders. In addition, morphology and the content of the secondary phase were modified by the sintering temperatures, affecting the ferroelectric properties, and ac and dc conductivities. We believe that our results can benefit not only the understanding of BNT ceramics, but also expand the range of applications.     

Antiferroelectric-like properties in MgO-modified 0.775Na0.5Bi0.5TiO3-0.225BaSnO3 ceramics for high power energy storage

Antiferroelectric-like 0.775NBT-0.225BSN-x wt%MgO ceramics have been prepared by solid state methods. The second phase of MgO was found in grain boundary surroundings with fine grains, which has been confirmed by EDS mapping and XRD results. Frequency dispersion of x?=?0 sample was replaced by diffuse phase transition of MgO-doped samples. Antiferroelectric-like properties were firstly observed in MgO modified ceramics. The evolution of antiferroelectric-like /ferroelectric transitions was demonstrated by I-E curves. With increasing MgO concentration, the BDS and E_F-E_B gradually increase. The leakage current can be reduced by suitable amount of MgO addition. When the doping content is 5?wt.%, the maximum discharge energy density of 2.13?J/cm³ at an electric field of 215?kV/cm was achieved. Detailed analysis can be found in the study.