Dielectric relaxation behavior and energy storage properties of Sn modified SrTiO3 based ceramics

SrSn_xTi_(1−x)O₃ (x=0, 0.01, 0.03, 0.05, 0.07) dielectric ceramics were fabricated by the solid state reaction method. Significant refinement of grain size and improved resistivity were observed with the addition of Sn, accounting for effectively enhanced dielectric breakdown strength, beneficial for the energy storage applications. Impedance analysis was employed to calculate the conductivities of grain and grain boundary and resistance ratios (R_gb/R_g) of grain boundary to grain. The grain boundary effect was believed to dominate the modified macroscopic performance, which was confirmed by the complex impedance analysis. The optimal properties were achieved for samples with x=0.05, exhibiting a charge energy density of 1.1 J/cm³ and an energy efficiency of 87%.     

Relaxor behavior of BaTiO3-BiYO3 perovskite materials for high energy density capacitors

Dielectric materials with high dielectric constant and breakdown voltage are very promising for pulsed energy storage applications. In this paper, (1-x) BaTiO₃-xBiYO₃ (x=0–0.5) ceramics were synthesized using conventional solid-state reaction method. The ceramic structure transformed from ferroelectric tetragonal phases (x≤0.5) to pseudo-cubic phases (x≥0.1). When x=0.2, beyond the solid solubility limit of BaTiO₃-BiYO₃, the second phase and glassy phases were formed, accompanying lattice parameter excursion. It revealed a gradual change from classic ferroelectric behavior in pure BaTiO₃ to highly diffusive and dispersive relaxor-like characteristics with BiYO₃ content increasing. It exhibited high polarization maximum and low remnant polarization, which was favorable for energy storage in (1-x)BaTiO₃-xBiYO₃ ceramics, due to the disrupted long polarization, the created weak coupling and the formed second phase. Furthermore, the nonlinearity of the (1-x)BaTiO₃-xBiYO₃ ceramics were weakened obviously. A maximum energy storage density of 0.316 J/cm³ at 66 kV/cm with relative high energy efficiency of 82.7% was achieved in 0.8BaTiO₃-0.2BiYO₃ ceramic, which indicated that (1-x)BaTiO₃-xBiYO₃ ceramics were promising lead-free relaxor materials for energy storage applications.     

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.     

Interfacial origin of enhanced energy density in SrTiO3-based nanocomposite films

SrTiO₃-based films doped with different Al-precursors were prepared by sol-gel methods and the dielectric strengths and leakage currents of the materials were investigated. The best performance was found in SrTiO₃ films doped with Al₂O₃ nanoparticles (nano-Al₂O₃). When 5 mol% of nano-Al₂O₃ was added to SrTiO₃ films with Al electrodes, the dielectric strength was enhanced to 506.9 MV/m compared with a value of 233.5 MV/m for SrTiO₃ films. The energy density of the 5 mol% nano-Al₂O₃ doped SrTiO₃ films was 19.3 J/cm³, which was also far higher than that of the SrTiO₃ films (3.2 J/cm³). These results were attributed to interfacial anodic oxidation reactions, which were experimentally confirmed by cross-sectional transmission electron microscope studies and theoretically modelled based on Faraday's laws. The films with added nano-Al₂O₃ featured many conducting paths at the interfaces between the host phase and the guest nano-Al₂O₃, which promoted ion transport and contributed to the strong anodic oxidation reaction capability of the 5 mol% nano-Al₂O₃ doped SrTiO₃ films.     

Significantly enhanced energy density of amorphous alumina thin films via silicon and magnesium co-doping

The different Si-Mg co-doping content was explored to improve the dielectric properties of amorphous Al₂O₃ thin film. According to the analysis of DSC, FT-IR, and XPS spectra, it can be confirmed that a novel structure of glass network is formed in the co-doped Al₂O₃ thin film. More importantly, compared to Al₂O₃ thin film, the leakage current of (Al_.97Si_.02Mg_.01)₂O_y thin film is reduced by 2 orders of magnitude and the breakdown strength is improved from 276?MV/m to 544?MV/m. The corresponding energy density of the modified sample is up to 9.2?J/cm³, which is an enhancement of 6.2?J/cm³ over that of the undoped Al₂O₃ thin film. Based on finite element analysis, the simulation results show that the applied electric field is mainly focused on the glass network, which could strengthen the stability of Al₂O₃ structure and decrease the breakdown probability of the films. From the viewpoint of defect chemistry, another reason for the enhancement of the dielectric properties is that Si-Mg co-doping results in the generation of cation vacancies and thus the formation of oxygen vacancies could be effectively prevented. This work could provide a new design strategy for high-performance dielectric capacitor devices.     

Improved energy storage density and energy efficiency of Samarium modified PMNT electroceramic

We report the improved energy storage density and efficiency after 2.5% of Samarium substitution in ferroelectric Pb[(Mg_1/3Nb_2/3)_0.80Ti_0.20]O₃ (PMNT) electroceramic. The microstructure and surface morphology were analyzed and correlated with various functional properties. The energy storage density, leakage current density, ferroelectric and dielectric properties were investigated thoroughly, indicating that Samarium's substitution significantly modified the microstructure, the dielectric strength, breakdown electric field, and turned ferroelectric PMNT to relaxor ferroelectrics. Due to the relaxor nature, the gap between remanent polarization and maximum polarization increases with the substitution of Samarium in PMNT matrix, which further increases the recoverable energy storage density and energy efficiency. A nearly 100% increase in recoverable energy density and efficiency was obtained at an electric field strength of 35 kV/cm at room temperature (～296 K). The electroceramic shows maximum energy density near the ferroelectric phase transition temperature (325 K–345 K) region and provides a moderate energy storage density for possible applications in power microelectronics.     

Realizing high-performance capacitive energy storage in lead-free relaxor ferroelectrics via synergistic effect design

Developing lead-free dielectric ceramics with outstanding energy storage properties has become urgent for dielectric capacitors. Herein, a synergistic effect design strategy has been proposed that combined the merits of relaxor ferroelectrics with high polarization/low remanent polarization and enhanced linear materials with relatively high polarization/ultrahigh dielectric breakdown strength. Hence, a novel lead-free 0.955Bi_0.5Na_0.5TiO₃-0.045Ba(Al_0.5Ta_0.5)O₃-based ceramics are engineered though introducing the enhanced linear dielectrics of 0.9CaTiO₃-0.1BiScO₃. A large recoverable energy density (W_rec～3.13 J/cm³) and high efficiency (η～88.4 %) as well as excellent power density (P_D～95.1 MW/cm³) and discharge speed (t_0.9～36 ns), along with superior stabilities, have been simultaneously realized. The piezoelectric force microscope measurements reveals that incorporating CT-BS generates more highly-dynamic polar nanoregions (PNRs), giving rise to rapid reversibility of PNRs with concurrently tailored energy storage performance. This study demonstrates synergistic effect design is a feasible and paradigmatic way to explore high-efficiency dielectrics for high-power energy storage applications.     

Crystallization behavior,ultrahigh power density and high actual discharge energy density of lead-free borate glass-ceramics containing TiO2

This work presents SrO-BaO-Nb₂O₅-B₂O₃-P₂O₅-K₂O-TiO₂ glass-ceramics prepared by controlled crystallization method. The uniformly dense microstructure with fine grains can be achieved by introducing TiO₂. The structural changes were confirmed by the results of SEM and TEM. The 0.5 mol% TiO₂ added glass heated at 750 °C for 2 h demonstrates excellent comprehensive properties of ε_r= 110, BDS = 1408 kV/cm, high energy storage efficiency (η) of 92% and energy storage density of 9.65 J/cm³. The as-prepared glass-ceramic exhibits ultrahigh power density (86.21 MW/cm³), actual discharge energy density (1.00 J/cm³) and excellent temperature stability. These findings qualify this environment-friendly glass-ceramics as one potential candidate for energy storage applications, especially in high power and pulsed power system field.     

High energy storage density under low electric fields in BiFeO3-based ceramics with max configurational entropy

Dielectric capacitors play an increasingly important role in power systems because of their fast charging and discharging speed. Applications are usually limited due to the low W_rec. We design materials with high values of ΔP(P_max-P_r) and recoverable energy storage density(W_rec) from the high entropy perspective. Two single phases with a large Curie temperature T_c difference have been selected, which leads to the enlarged entropy. The ceramics (Bi_0.85Nd_0.1Sm_0.05)_1-xBa_x)(Fe_1-xTi_x)O₃(BNSBFT_x) are prepared by the solid-state reaction. As x increases, the corresponding configuration entropy(S_config) goes from 1.4 R to 1.52 R. The increased entropy destroys the long-range order, accompanied by the reduced remanent polarization(P_r) and the improved W_rec. The W_rec of BNSBFT_0.5 ceramics reaches 4.9 J/cm³ at a low field of 250 kV/cm. Both temperature change(∼ 0.5% from 30 °C to 140 °C) and frequency variation(∼ 4.8% from 1 Hz∼50 Hz) in W_rec show excellent stability.     

High energy storage density achieved in Bi3+-Li+ co-doped SrTi0.99Mn0.01O3 thin film via ionic pair doping-engineering

The demand for lead-free dielectric capacitors with rapid charge-discharge ability and high energy storage density is increasing owing to the rapid development of electronic equipment. Lead-free Sr_1-x(Bi_0.5Li_0.5)_xTi_0.99Mn_0.01O₃ (x = 0.02, 0.025, 0.03, 0.035) thin films grown on Pt/Ti/SiO₂/Si substrates were prepared by sol-gel method. A huge enhancement in polarization was found in Bi³⁺-Li⁺ co-doped SrTiO₃ thin films. The large lattice distortion and local broken-symmetry due to formation of Bi³⁺-Li⁺ ionic pairs are responsible for ferroelectricity and high polarization. The maximum polarization (42.1 μC/cm²) and largest energy storage density of 47.7 J/cm³ at 3307 kV/cm were both achieved in Sr_0.975(Bi_0.5Li_0.5)_0.025Ti_0.99Mn_0.01O₃ thin film. Moreover, an excellent temperature-dependent stability was also obtained in Sr_0.975(Bi_0.5Li_0.5)_0.025Ti_0.99Mn_0.01O₃ thin film from 30 to 110 °C.     

Significantly improved energy storage properties of sol-gel derived Mn-modified SrTiO3 thin films

In this paper, x mol% Mn-doped SrTiO₃ (STMx, x?=?0, 0.5, 1, 3 and 5) thin films were synthesized by a sol-gel method. The effect of Mn doping on the microstructure and electrical performance was investigated. STMx (x?≤?1) thin films shows a single cubic perovskite phase while impurity phase appears for STM3 and STM5 thin films confirmed by X-ray diffraction. X-ray photoelectron spectra reveals that STM1 thin film has the lowest concentration of oxygen vacancy. The dielectric constant and loss of STMx (x?≤?1) films display good frequency stability, while decrease with the frequency for STM3 and STM5 thin films. And all samples display excellent bias stability of dielectric constant; this is advantageous for applications in a high electric field. The ferroelectric test demonstrates that the electrical breakdown strength increases and leakage current decreases for Mn doped SrTiO₃ films. A great recoverable energy storage density of 23.8?J/cm³ with an efficiency of 69.8% at 2.286?MV/cm is obtained in STM1 thin film. Furthermore, STM1 thin film shows good frequency stability of energy storage properties. It indicates that Mn doping is a simple and effective method to improve the energy storage properties of dielectric capacitors.     

Dielectric constant and energy density of poly(vinylidene fluoride) nanocomposites filled with core-shell structured BaTiO3@Al2O3 nanoparticles

Ceramics-polymer nanocomposites consisting of core-shell structured BaTiO₃@Al₂O₃ (BT@Al₂O₃) nanoparticles as the filler and poly(vinylidene fluoride) (PVDF) as the polymer matrix were fabricated by solution casting. At the same volume fraction, the BT@Al₂O₃/PVDF nanocomposites, with larger dielectric constant and higher energy density, outperformed the BT/PVDF nanocomposites. The 2.5 vol% BT@Al₂O₃/PVDF nanocomposites at 360 MV/m had a double more energy density than pure PVDF at 400 MV/m (6.19 vs. 2.30 J/cm³), and a remarkably 42% lower remnant polarization than the 2.5 vol% BT/PVDF nanocomposites (0.99 vs. 1.69 μC/cm² at 300 MV/m). Such significant enhancement was closely related to the surface modification by Al₂O₃, which improved the insulation of BT nanoparticles and reduced the contrast of dielectric constant between the filler and the PVDF matrix.     

Fast discharge and high energy density of nanocomposite capacitors using Ba0.6Sr0.4TiO3 nanofibers

Nanocomposites combining high breakdown strength (BDS) polymer and high dielectric permittivity ceramic fillers have shown great potential for pulsed power application. Here a new composite material based on surface-functionalized Ba_0.6Sr_0.4TiO₃ nanofibers/poly(vinylidene fluoride) (BST NF/PVDF) has been prepared by solution casting. The nanocomposites containing 2.5 vol% isopropyl dioleic(dioctylphosphate) titanate (NDZ 101)-functionalized BST NF (N-h-BST NF) have large energy density of 6.95 J cm⁻³ at 380 MV m⁻¹, which is 1.85 times larger than that of the pure PVDF at the same electric field. Also, the discharge speed of the nanocomposites containing 7.5 vol% N-h-BST NF is approximately 0.11 μs. The good properties, together with the large energy density and fast discharge speed, make this material a promising candidate for pulsed power capacitor.     

Enhanced the energy storage performance in AgNbO3‑based antiferroelectric ceramics via manipulation of oxygen vacancy

The applications of silver niobate (AgNbO₃)-based antiferroelectric (AFE) ceramics for potential energy storage are limited by the introduction of oxygen vacancies (OVs). The inevitable OVs narrow the band gap and promote grain growth, resulting in poor breakdown strength and low recoverable energy density (W_rec). Here, we report a significant energy density performance of (Ag_1–2xSr_x)(Nb_0.78Ta_0.22)O₃ AFE ceramics designed by restraining OVs. Electron paramagnetic resonance (EPR) and UVvis absorption spectra experiments demonstrate that the OV content gradually decreases and the band gap increases with increasing Sr content. Donor doping of Sr leads to the generation of silver ion vacancies, thus, the OV concentration decreases to maintain the electrical neutrality of the system. As a result, a high W_rec of ∼5.6 J/cm³ together with an energy efficiency of 70.1% at 300 kV/cm is achieved in the (Ag_0.92Sr_0.04)(Nb_0.78Ta_0.22)O₃ ceramic. This work offers a novel strategy for improving the energy storage properties of AgNbO₃-based AFE ceramics.     

(Bi0.5Na0.5)TiO3-based relaxor ferroelectrics with simultaneous high energy storage properties and remarkable charge-discharge performances under low working electric fields for dielectric capacitor applications

High energy storage and charge-discharge performances under low electric field are desirable for lead-free dielectric materials because of environmental hazards, the risk of high voltage and the high cost of insulation technology. Herein, lead-free ceramics based on 0.6BNT-0.4Sr_0.775Bi_0.15TiO₃ (BNT-SBT) were designed, which simultaneously achieves a large energy storage density (W_rec~ 2.41 J/cm³) and a high efficiency (η~87.5%) under a low electric field of 190 kV/cm due to enhanced dielectric properties and the relaxation response. Moreover, the energy storage properties of the BNT-SBT ceramic exhibit moderate temperature stability, excellent frequency dependence, and cycling reliability. Furthermore, the charge-discharge performance simultaneously features a high power density (P_D~51.4 MW/cm³), an ultrafast discharge speed (t_0.9–77 ns), and remarkable stability against temperature and cycling. This study exploits a high-efficiency BNT-related ceramics with concurrently high energy storage and charge-discharge performances under low electric fields, which provides great potential in practical dielectric capacitor applications.     

High discharge energy density in novel K1/2Bi1/2TiO3-BiFeO3 based relaxor ferroelectrics

An increasing number of new dielectrics are being reported for the development of next-generation ceramic capacitors for power electronics used in clean energy technologies. Here, high discharge energy density (W_dis) ~6.1 J cm^?3 with efficiency (η)~72% under a pulsed field (E_max) of 410 kV cm^?1 is reported along with temperature stability up to 150 °C (E_max = 200 kV cm^?1) for 0.5 K_0.5Bi_0.5TiO₃-0.42BiFeO₃-0.08Sm(Mg_2/3Nb_1/3)O₃ (KBT-BF-SMN) bulk ceramics. The optimised composition is chemically heterogeneous but electrically homogenous, similar to several BiFeO₃-based dielectrics reported previously and adding to the growing body of evidence that electrical (measured at weak-field) not chemical homogeneity is the best guide to increased E_max and enhanced energy density. KBT-BF-SMN ceramics are therefore considered as promising candidates for pulsed power and power electronics applications.     

Gradient dielectric constant sandwich-structured BaTiO3/PMMA nanocomposites with strengthened energy density and ultralow-energy loss

High energy storage density with low-energy loss polymer films are essential for high-performance electric devices. To avoid the high-energy loss of utilizing nonlinear polymer materials, a sandwich nanostructure comprising a linear polymer poly(methyl methacrylate) (PMMA) matrix embedded with a high dielectric constant BaTiO₃ (BT) interlayer and poly(vinylidene fluoride) (PVDF) binder was constructed using a solution casting strategy. This structural design takes advantage of each component in the composite. The good dispersion of BT particles in the binder, which was incorporated between PMMA, enabled a high dielectric constant and fewer defects. Additionally, the excellent film formation ability of the PVDF binder guarantees the uniform thickness and stable structure of the BT mid-layer, and good miscibility between PVDF and PMMA enhanced the interaction between each layer. Interestingly, since the dielectric constant of PVDF was between BT fillers and PMMA, a dielectric gradient distribution mitigated the local electric field concentration, as proven by the simulation results. Consequently, a low-loss linear PMMA composite film exhibited satisfying breakdown strength and excellent discharged energy density, which were 25% and 460% higher than those of pristine PMMA, respectively.     

Tunable BaxSr1-xTiO3 nanoparticles induced high energy storage density in layer-structured asymmetric polymer-based nanocomposites

In order to solve the problem of low charging and discharging energy density of dielectric capacitors, the structure design of layered polymer matrix composites is carried out in this paper. Ba_0.7Sr_0.3TiO₃, Ba_0.8Sr_0.2TiO₃ and Ba_0.9Sr_0.1TiO₃ nanoparticles were successfully prepared by the oxalate coprecipitation method. The surface of Ba_xSr_1-xTiO₃ was successfully coated with dopamine, which promoted the dispersion of the polymer matrix of the ceramic powder. Monolayer Ba_xSr_1-xTiO₃/PVDF composites containing Ba_xSr_1-xTiO₃ with different Ba/Sr ratios were successfully prepared by the casting method. Three-layer asymmetric composites with different fillers were successfully prepared by layer-by-layer casting. The phase and microstructure of the as-prepared materials were analyzed by XRD and SEM. The dielectric, electrical conductivity, ferroelectric and energy storage properties of the composites were tested. The effects and laws of the design of the three-layer asymmetric structure on the dielectric properties and energy storage properties of the layered composites are mainly studied. When the structure of the three-layer asymmetric composite is 1-2-3, the breakdown field strength reaches 330 kV/mm, the discharge energy density reaches 8.51 J/cm³, and the charge-discharge efficiency is 67%. This work demonstrates that layered composites with asymmetric properties can facilitate the development of electrical energy storage.     

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.     

Thermal-stability of electric field-induced strain and energy storage density in Nb-doped BNKT-ST piezoceramics

In this work, the relationship between the structural mechanisms and macroscopic electrical properties of the Nb-modified 0.96(Bi_0.5Na_0.84K_0.16TiO₃)–0.04SrTiO₃ (BNKT–ST) system were elucidated by using temperature dependent and in situ synchrotron X-ray diffraction (XRD) techniques. For the composition x?=?0.0175, a large-signal piezoelectric coefficient (S_max/E_max?=?d₃₃*) of 735 pm?V^?1 at 6?kV mm^?1 was observed at room temperature. Interestingly, at a higher temperature of 110?°C, the sample still showed a large d₃₃* of 570 pm V^?1. Furthermore, the temperature-invariant electrostrictive coefficient for this sample was found to be 0.0285?m⁴?C^?2 over the temperature range of 25–170?°C. Moreover, the energy density for x?=?0.030 sample was ～1.0?J?cm^?3 with an energy storage efficiency of ?70% in the temperature range of 25–135?°C. These results suggest that the synthesized Nb-modified BNKT–ST system is promising for the design of ceramic actuators as well as capacitor applications.