Dielectric capacitors with ultrahigh power density have emerged as promising candidates for essential energy storage components in electronic and electrical systems. They enable enhanced integration, miniaturization, and lightweight design. However, the development of dielectric materials for cutting-edge energy storage applications has been significantly limited by their low recoverable energy storage density (Wrec) and energy efficiency (η), especially at moderate electric fields. In this study, we fabricated 0.85K0.5Na0.5NbO3-0.15Sr0.7Nd0.2ZrO3 ceramics with an outstanding energy storage performance (Wrec ~7 J cm− 3, η ~ 92% at 500 kV cm− 1; Wrec ~14 J cm− 3, η ~ 89% at 760 kV cm− 1). The exceptional energy storage performance can be primarily attributed to the heterogeneous structure, where orthorhombic and tetragonal polar nanoregions are embedded in a cubic matrix, accounting for the delayed polarization saturation. This work provides a good paradigm for designing dielectric materials with ultrahigh energy storage density and excellent energy efficiency at a moderate applied electric field, aligning with the stringent demands for advanced energy storage applications.
Article
Excellent energy storage properties in lead-free ferroelectric ceramics via heterogeneous structure design
https://doi.org/10.21203/rs.3.rs-4958862/v1
This work is licensed under a CC BY 4.0 License
Version 1
posted
You are reading this latest preprint version
Energy storage density
Energy efficiency
Polarization
Heterogeneous structure
Polar nanoregions
Lead-free dielectric ceramics are increasingly sought after for various electrical device components due to their environmentally friendly nature, ultrahigh power density (PD), ultrafast charge-discharge rate (t0.9), and good reliability. They are particularly appealing owing to the increasing demand for enhanced energy storage density, and the need for integration and miniaturization in electronic devices [1–4]. However, these ceramics have lower recoverable energy storage density and higher energy dissipation, i.e., lower energy efficiency, compared to their lead-based counterparts. This deficiency is primarily attributed to their unsatisfactory microstructure, rendering them unsuitable for advanced electronic applications [5–7]. Therefore, numerous efforts have been made to improve the performance of lead-free ceramics for energy storage dielectric capacitors, considering sustainable development [8]. Among various lead-free materials, including Bi0.5Na0.5TiO3 (BNT) [9], BiFeO3 (BF) [10] and BaTiO3 (BT) [11], K0.5Na0.5NbO3 (KNN)-based ceramics are one of the most extensively studied dielectric for advanced energy storage applications [1–4,12].
Many researchers have attempted to develop KNN-based ceramics with high Wrec and η. Various strategies, such as high-entropy design [13], domain engineering [14,15], defect engineering [16], superparaelectric state [17,18], grain size engineering [19], and enhanced local random field [20] have been proposed to achieve high Wrec. High Wrec values of ~ 10.06 J cm− 3 [13], ~ 8.09 J cm− 3 [21], and ~ 7.4 J cm− 3 [22] have been realized in KNN-based bulk ceramics prepared by conventional solid-state sintering. However, the corresponding electrical breakdown (Eb) values of 740 kV cm− 1, 870 kV cm− 1, and 800 kV cm− 1, respectively, are exceedingly high, while under a moderate electric field of 500 kV cm− 1, they possess Wrec below 5.7 J cm− 3, which hinder their integration into electronic devices and miniaturization [9]. Given the practical application of electronic devices within relatively low electric field environments, a more reasonable approach is to optimize Wrec by improving the maximum polarization (Pmax), reducing the remnant polarization (Pr), and mitigating polarization saturation [23,24].
High Wrec can be achieved by designing ceramics with fine grains, a dense microstructure, high polarization under external electric fields, a highly dynamic structure, an isotropic lattice structure, and minimal impurities [25–28]. Subsequently, significant challenges persist in realizing ceramics with both ultrahigh Wrec and outstanding η, particularly when employing a conventional solid-state method. Introducing paraelectric end members or linear compounds into a ferroelectric ceramic is a generally accepted approach for achieving relaxor ferroelectric (RFE) ceramics. This involves disrupting the long-range ferroelectric order and creating nanodomains [29–31]. Thus, high energy storage performance can be achieved by incorporating SrTiO3 or Sr2+ into BNT ceramics, due to the coexistence of multiphase nanoclusters [12,24,32]. The polymorphic nanodomain structure can effectively weaken the energy barrier and polarization anisotropy, resulting in a flattened energy profile compared to single-phase nanodomains, which is expected to significantly enhance both Wrec and η simultaneously [19,33].
In this paper, we propose a feasible strategy for constructing a heterogeneous nanodomain structure that encompasses an orthorhombic (O, Amm2) and tetragonal (T, P4mm) phases within a cubic (C, Pm-3m) paraelectric matrix. The objective of this strategy is to address the challenges associated with achieving ceramics that possess exceptional η and ultrahigh Wrec under a moderate electric field. We developed a binary system in which paraelectric end member, Sr0.7Nd0.2ZrO3, is incorporated into K0.5Na0.5NbO3 (KNN) matrix to investigate the advantages of the heterogeneous structure. Leveraging the maximum polarization potential [21], we selected KNN as the primary component. We also introduced Sr2+ and Zr4+ ions to modify the TO−T and TT−C, resulting in the formation of an orthorhombic-tetragonal-cubic heterogeneous nanodomain structure, in line with the multiphase regulation of KNN-based ceramics [34]. Meanwhile, the rare earth ion of Nd3+ contributes to enhancing energy storage performance by reducing grain size and improving the compactness of dielectric ceramics [35,36]. As expected, we achieved a remarkable Wrec of approximately 7 J cm− 3 with an outstanding η of approximately 92% at 500 kV cm− 1. This represents the highest level of performance achieved in KNN-based bulk ceramics at a moderate electric field, underscoring the effectiveness of the heterogeneous structure strategy in the development of advanced pulse power capacitors with exceptional Wrec and η.
Energy storage performance and charge-discharge properties for practical application
Unipolar P-E hysteresis loops were measured under 200 kV cm− 1 for (1-x)KNN-xSNZ ceramics. The corresponding Pmax and Pr values, as well as energy storage properties (Wrec, Wtotal, and η were calculated using 
respectively), are presented in Fig. S1a-c, (Supporting Information). Comprehensively, ceramics with x = 0.15 exhibit a relatively strong energy storage capacity, with Wrec reaching approximately 1.6 J cm− 3 and η approaching 91% (Fig. S1c, Supporting Information). Additionally, a high Wrec of ~ 1.6 J cm− 3 with a large η of ~ 86% and a large Wrec of ~ 1.5 J cm− 3 with a ultrahigh η ~ 93% can be obtained in samples with x = 0.14 and x = 0.16, respectively. This is attributed to their slender P-E shapes (Fig. S1a, Supporting Information) and significantly reduced Pr (Fig. S1b, Supporting Information). Furthermore, the unipolar P-E hysteresis loops with x ≥ 0.14 and x ≤ 0.12 were measured up to their breakdown electric fields. The results are illustrated in Figs. 1a-d and S2a-d (Supporting Information), respectively. The slender unipolar P-E loops of KNN-xSNZ (x = 0.14, 0.15, 0.16, and 0.18) ceramics under various electric fields showcase the canonical relaxor behaviors. To further explore the properties of the ceramics, the energy storage parameters (Wrec, Wtotal, and η) are depicted in Figs. 1e-h and S2e-h (Supporting Information). Ceramics with x ≥ 0.14 consistently maintain superior energy storage performance even under electric fields approaching their Eb values. Encouragingly, a record-high Wrec of 14 J cm− 3 with a high η of 89% is achieved for x = 0.15 ceramic under an electric field of 760 kV cm− 1. Meanwhile, a record-high η of 94% is achieved in x = 0.18 ceramic with a large Wrec of 10 J cm− 3 under an electric field of 695 kV cm− 1. Fig.S3 (Supporting Information) shows the corresponding Pmax, Pr and ΔP (Pmax - Pr) values of ceramics with x ≥ 0.14 obtained from the P-E loops (Fig. 1a-d), indicating the appropriate introduction of SNZ can maintain a large Pmax of 48.5 µC cm− 2 while reducing Pr to 1.4 µC cm− 2 prior to critical breakdown electric fields. It should be noted that the ceramics with x ≥ 0.14 in this study exhibit excellent overall energy storage properties and wide-composition stability characteristics. This can be attributed mainly to the high ΔP and the delayed polarization saturation (compare Fig. 1a-d to Fig.S2a-b, Supporting Information), demonstrating a promising candidate for practical application in the advanced energy storage capacitors.
Figure 1. Ambient-temperature P-E loops of (1-x)KNN-xSNZ ceramics measured under various electric fields of a) x = 0.14, b) x = 0.15, c) x = 0.16, d) x = 0.18. Composition-dependent energy storage parameters (Wrec, Wtotal, and η) of e) x = 0.14, f) x = 0.15, g) x = 0.16, h) x = 0.18.
As summarized in Fig. 2a, this study signifies a significant breakthrough in KNN-based ceramics, surpassing previously documented results [2,13,21–23,33,37–39]. Furthermore, comparisons of Wrec values under different electric fields between the x = 0.15 ceramics and other actively studied KNN-based dielectric ceramics are recorded in Fig. 2b. As seen, a large Wrec of 7 J cm− 3 with high η of 92% is obtained at an electric field of 500 kV cm− 1 for x = 0.15 ceramics, demonstrating superior comprehensive energy storage performance under moderate electric fields. This further indicates that the high ΔP plays a more crucial role in the overall energy storage properties. Another critical aspect for evaluating advanced dielectric capacitors for real applications is their charge-discharge performance. The underdamped discharge behaviors of the x = 0.15 ceramic under various electric fields are illustrated in Figs. 2c and 2d. These behaviors are followed by a linear increase in positive current peak (Imax), current density (CD, calculated as CD = Imax/S), and power density (PD, calculated as PD = EImax/2S) up to 32 A, 4120 A cm− 2, and 930 MW cm− 3, respectively, under 450 kV cm− 1. Additionally, overdamped discharge properties are presented in Fig. 2e-g, showing a high discharge energy density (Wd, calculated as 
) of ~ 5.3 J cm− 3 and an ultrafast discharge rate (t0.9) of ~ 39 ns at 450 kV cm− 1 (Fig. 2f). Figure 2h shows that the Wd of most lead-free systems is below 4 J cm− 3 [1,4,9–13,15,19,22,24,30,32,37,39,40,41], while the studied 0.85KNN-0.15SNZ ceramic exhibits a higher test electric field and the maximum Wd value. All these findings suggest that the 0.85KNN-0.15SNZ ceramics hold significant promise for using in advanced capacitors.
Elucidation of O-T-C multiphase nanoregion coexistence by a multi-scale process
To explore the underlying mechanism of the improved energy storage properties, we investigated the phase structure of the current system (Figs. 3 and S4,S5, Supporting Information). Figure 3a presents the Rietveld refinement result of the 0.85KNN-0.15SNZ ceramic over a range of 20° to 80°. It reveals the coexistence of the orthorhombic (O, Amm2) and tetragonal (T, P4mm) phases, with weight fractions of 26.14% and 73.86%, respectively. Notably, no secondary phase is observed, indicating the complete incorporation of the SNZ into the KNN lattice (Fig. S4a, Supporting Information). In addition, the enlarged view depicted in Fig. S4b, (Supporting Information) confirms that as x increases, the phase gradually transitions into a low-polar pseudo-cubic phase structure, which is conducive to achieving low Pr and high ΔP. Additional insights into the structural characteristics of 0.85KNN-0.15SNZ ceramics across the temperature range of 25–600°C were obtained through temperature-dependent powder XRD techniques, as depicted in Figs. 3b and S4d (Supporting Information). These images (Fig. 3b) display amplified diffraction peaks of (110), (200), and (210) corresponding to the pseudo-cubic phase structures. The relative intensity and the number of characteristic peaks remain constant over the studied temperature range, except for a shift towards lower angles associated with lattice expansion, indicating the absence of any phase structure changes [8]. On the other hand, as shown in Fig. S4c,d (Supporting Information), the phase structure gradually changes from O (25°C) phase to T (~ 200°C) phase and then to C (~ 350°C) phase for x = 0.03 ceramic, in contrast to x = 0.15 ceramic. The crystal phase feature of the x = 0.15 ceramic is primarily attributed to the coexistence of O-T phases, in other words, the pseudo-cubic phase structure. The temperature-dependent dielectric constant of all components aligns with the aforementioned analysis. The presence of an exceedingly broad and flat dielectric peak ( x ≥ 0.06, see Fig. 3c) strongly indicates the coexistence of multiple phases. The inset in Fig. 3c clearly illustrates the frequency dispersion of the x = 0.15 sample, a canonical relaxor behavior attributed to the presence of PNRs. Moreover, the superior Pmax in the current systems is closely related to the large dielectric constant. Figure 3d gives TT − C and TO − T values of (1-x)KNN-xSNZ ceramics at a frequency of 1 kHz to construct a phase diagram for identifying the composition dependence of phase structures. From Fig. 3d, it can be observed that both TT − C and TO − T decrease with the increase of x, leading to the formation of a coexisted O-T phases in the composition of x ≥ 0.12. In addition, the phase diagram strongly supports the results of temperature-dependent XRD analysis. Additionally, the Raman spectra presented in Fig. S5 (Supporting Information) not only confirm the enhanced relaxor behavior but also support the conclusion that the phase structure of (1-x)KNN-xSNZ samples transforms from the O phase to pseudo-cubic phase as x increases [34]. Furthermore, the selected area electron diffraction patterns taken along [001]c and [110]c directions are illustrated in Fig. 3e and Fig. 3f, respectively. The diffused and weak spots as indicated by white arrows confirm the existence of orthorhombic structure“\(\:\sqrt{2}\) unit cell”which is orientated along the cubic [110]c in the x-direction, the [1–10]c in the y-direction and the [001]c in the z-direction [13].
Figure 3. a) Rietveld refinement XRD pattern of x = 0.15 ceramic. b) Temperature -dependent XRD patterns of x = 0.15 ceramic collected in the temperature range of 25 ℃ to 600 ℃. c) Temperature-dependent dielectric constant of (1-x)KNN-xSNZ ceramics at various frequencies. Inset presents the dielectric constant and dielectric loss of x = 0.15 ceramic as a function of temperature, measured at various frequencies ranging from 1 kHz to 200 kHz. d) Phase diagram of (1-x)KNN-xSNZ ceramic. e) Selected area electron diffraction patterns along the [001]c, and f) along [110]c of x = 0.15 ceramic.
In addition, Fig. S6 (Supporting Information) shows a significant refinement in the average grain size (AGS) calculated by Nano Measurer for the ceramics, particularly for x ≥ 0.06, with the smallest grain size observed for x = 0.12–0.15, with values being on the order of 150 nm. The findings from FE-SEM analysis support a uniform and compact microstructure with low apparent porosity and refined grains for the x = 0.15 ceramic, as further illustrated in Fig. S7a (Supporting Information). These characteristics have a favorable impact on Eb. Meanwhile, the refined grain boundaries can effectively impede domain growth, which is an important factor for achieving PNRs.
We then applied the vertical piezoresponse force microscopy (VPFM) technique to uncover the domain morphology under various DC tip bias voltages. Figure 4 a1-h1 and Fig. 4 a2-h2 respectively illustrate the effects of applied voltages on the dynamic behavior of domain switching in the pure KNN and x = 0.15 ceramics at ambient temperature. The amplitude diagrams record the piezoresponse strength, while the phase diagrams represent the polarization orientation [15,42–44]. Applying a driving voltage of merely 3 V (Fig. 4a & 4e) leads to the emergence of striped ferroelectric domains in pure KNN ceramic, while nanoscale domains are observed in the x = 0.15 ceramic. Fig. S7b (Supporting Information) further shows the striped ferroelectric domains in pure KNN ceramic. As the DC tip bias voltage increases to 3 V, partial reversal of the domains is observed (Fig. 4b & 4f). For x = 0.15 ceramic, a voltage of 12 V is adequate to induce complete reversal, with the polarized domains easily reverting when a -12 V tip bias is applied (Fig. 4c2,d2,g2,h2). In stark contrast to the x = 0.15 ceramic, the striped ferroelectric domains remain clearly distinguishable for the pure KNN ceramic (Fig. 4c1,d1,g1,h1), suggesting that the x = 0.15 ceramic gives rise to the emergence of highly dynamic polar nanoregions (PNRs). PNRs, characterized by local structural heterogeneity, confirm enhanced relaxor behavior and contribute to slimmer P-E loops due to their high sensitivity to external electric fields [37,44]. The topography of PFM image presented in Fig. 4i underscores the homogeneous and dense microstructure, as well as small AGS on the order of 150 nm. Figure 4j displays the switching spectral piezoelectric response force microscopy (SSPFM) loops at ambient temperature for detecting the local piezoresponse of the 0.85KNN-0.15SNZ ceramic. The amplitude and phase hysteresis loops are recorded by applying ± 12 V DC voltage on the selected domain region. Compared to previous studies [45,46], the 0.85KNN-0.15SNZ ceramic exhibits a high phase angle and a well-defined saturated square phase loop with a phase angle close to 180º, indicating the appearance of two reverse-parallel reversible polarization states under an applied electric field. The nearly perfect rectangular phase hysteresis loop provides direct evidence for a well-defined polarization along the direction of the applied electric field [47]. The amplitude hysteresis loop of the same domain region, as illustrated by Fig. 4j, exhibits a typical, asymmetric, and saturated butterfly loop. The asymmetry can be explained by the presence of a built-in internal field and domain movement under the tip region [48]. The origin is inferred to be the substitution of Nd3+ at the A-site, leading to the generation of vacancies and expansion of the oxygen octahedron. This results in a more facile displacement of ions at the B-site and enhanced polarization. Furthermore, the formation of dipoles between Nd3+ and vacancies at non-equilibrium positions creates a built-in internal field, which enhances the relaxation behavior of ceramics.
We now shift our focus to the intrinsic origins of the enhanced energy storage properties. Atomic resolution high-angle annular dark-field (HAADF) scanning transmission electron microscopy was performed to further analyze the local polarization configuration of PNRs. Figure 5a shows the atomic resolution HAADF STEM image taken along [001]c direction, where the integrated intensity is a function of average atomic number Z of atomic columns scanned by the electron probe, [49] B sites atoms are the brighter and larger while A sites atoms are darker and smaller. Figure 5b presents the corresponding local polarization configuration of Fig. 5a derived from the 2D Gaussian peak fitting and quantification. [50] The T phase can be obviously determined by the arrows along the horizontal and vertical directions. The nearly C phase can be confirmed by the arrows with near-zero polarization magnitude whereas the O phase can be determined by the arrows oriented close to the diagonal direction (ie. <110 > c) of Fig. 5b. The alternating polar and nonpolar regions can be clearly distinguished, and the size of nano polar region is determined to be around 3 nm. Figure 5c presents the statistic histogram of polarization magnitude of Fig. 5b. The polarization magnitudes are in the range of 0 and 9 pm, and the averaged polarization magnitude is only ≈ 3.42 pm, which is consistent with X-ray diffraction refinement data indicating the averaged phase is pseudo-cubic, as illustrated in Figs. 3a and S4b (Supporting Information). The atomic resolution HAADF-STEM image taken along [110]c is given in Fig. S7c (Supporting Information). The coexistence of O, T, and C multiphase PNRs exhibits a rapid response to applied electric fields, which is of great significance for the reduction of Pr. Moreover, for the x = 0.15 sample, the TEM micrograph and corresponding elemental distribution are presented in Fig. 5d. Evidently, the 0.85KNN-0.15SNZ ceramic exhibits refined grain size and highly uniform distributions of K, Na, Nb, Sr, Nd, Zr, and O, all of which contribute to achieving high Eb.
Phase-field simulations of domain structures
Theoretical phase-field simulations were performed to simulate the binary (1-x)KNN-xSNZ (x = 0.12, 0.15, and 0.18) solid solutions [8,14]. We found that the studied compositions with x = 0.12, x = 0.15, and x = 0.18 indeed possess a disordered structure, where O and T nanodomains are embedded in a cubic matrix (Fig. 6 and Fig. S8, Supporting Information). The randomly distributed nanodomains with different symmetries and polarization magnitudes make a significant contribution to a reduced energy loss and the delayed saturation. Moreover, we found the fraction of the O nanodomains decreases evidently with x increase, being responsible for the relatively low Pr. Apart from multiphase nanodomains, a significant refinement of the domain size can be observed by increasing x, facilitating polarization rotation and enhancing the relaxation behavior, subsequently contributing to the reduced hysteresis and enhanced η. However, the local polarization is weakened due to a decrease in the polar phase ratio, which ultimately compromises Pmax and hence Wrec for larger x contents. These simulation results are consistent with our experiment findings, highlighting the benefits of the heterogeneous structure design in hysteresis and polarization, signifying an impressive advancement in energystorage performance.
Optical Transparency of the relaxor ceramics
In addition to the excellent energy storage performance, (1-x)KNN-xSNZ samples exhibit a satisfactory transparency which may find application in some specific scenarios, such as energy storage components in solid-state lighting, electro-optical devices, and even biomedical materials. Fig. S9 (Supporting Information) gives the optical transmittance (T%) and physical picture. It can be found that as the SNZ content (x) increased from 0.03 to 0.20, the T% values in the visible regions exhibited an initial increase followed by a decrease. The highest value of 64% was observed at x = 0.09, as evidenced by the physical sample. Notably, the ceramics with x = 0.06, x = 0.12, and x = 0.15 demonstrate exceptional T% values up to 78% at wavelength of 2000 nm, indicating outstanding transparency at near-infrared region.
In summary, we propose an innovative design strategy for lead-free relaxors, characterized by a heterogeneous structure that is constructed through a multi-scale process from refining grain boundaries to domains, and then to O-T-C multiphase nanoclusters. Notably, the 0.85KNN-0.15SNZ bulk ceramics achieve exceptional energy storage capabilities (Wrec ~14 J cm− 3, η ~ 89%). This is further realized by 0.82KNN-0.18SNZ bulk ceramics possessing an ultrahigh η of 94% with a remarkable Wrec of 10 J cm− 3. Based on such excellent energy storage properties and wide-composition stability characteristics, the findings in this study not only introduce highly competitive candidates for advanced pulsed power applications but also open new avenues for designing high-performance materials in diverse areas.
Ceramics preparation
The (1-x)K0.5Na0.5NbO3-xSr0.7Nd0.2ZrO3 ((1-x)KNN-xSNZ) ceramics were fabricated through a conventional high temperature solid-state sintering method [12,15,23,27]. Raw powders, including K2CO3 (≥ 99.99%), Na2CO3 (≥ 99.999%), Nb2O5 (≥ 99.99%), SrCO3 (≥ 99.99%), Nd2O3 (≥ 99.99%), and ZrO2 (≥ 99.99%) from Aladdin, were utilized. Stoichiometric quantities of these raw materials were weighed and subjected to 24 h of ball milling in ethanol using yttrium stabilized zirconia grinding media. Subsequently, the mixture underwent calcination at 850 ℃ for 5 h before a second 24 h ball milling. Following this, the dried powders were cold isostatically pressed into pellets with a diameter of 11.5 mm and sintered at temperatures ranging from 1200 to 1300 ℃ for 5 h. All the samples were polished down to a thickness of 0.1 mm and electroded with fired-on silver paste with a diameter of 1 mm, for the energy storage properties evaluation.
Electrical property measurements
Ferroelectric measurements: The polarization-electric field (P-E) hysteresis loops were recorded with a ferroelectric test system (Premier II, Radiant, USA). Charge-discharge measurements: Charge-discharge capabilities were evaluated with a charge-discharge instrument (CFD001, Gogo Instruments Technology, China). Dielectric measurements: Dielectric properties were characterized at different temperatures and frequencies using an LCR meter (Agilent E4980A).
Optical performance measurements
Optical transparency: Transmittance was estimated using UV-vis-NIR spectroscopy (PerkinElmer Lambda 1050).
Structure characterizations
Phase structure measurements: The phase structures were examined using a high-resolution X-ray diffractometer (XRD, SmartLab-9, Rigaku, Japan) (Rietveld structure refinement was performed using the GSAS program) and a Raman spectrometer (inVia Reflex, Renishaw, UK). Scanning electron microscopy: Microstructural morphology was recorded utilizing a field emission scanning electron microscope (FE-SEM, SU8020, Japan). Domain structure: The observation of domain morphology was conducted through piezoresponse force microscopy (PFM, Dimension ICON, US Bruker Nano Inc, USA) and field emission transmission electron microscope (FE-TEM, Talos F200i, ThermoFisher Scientific Inc, USA). Transmission electron microscopy: Atomic resolution high-angle annular dark field (HAADF) scanning transmission electron microscopy investigations and selected area electron diffraction (SAED) analysis were performed on a ThermoFisher Scientific transmission electron microscope Titan Cubed Themis G2 300 microscope with a probe aberration corrector operated at 300 kV. Specimens for TEM observations were prepared by the conventional method including cutting, mechanical polishing, and finalized by Ar+ ion beam thinning and polishing with Gatan Precision Ion Polishing System (PIPS) 695.
Phase-field simulations
The method of phase field simulation is elaborated in detail in the ESI.†
Data availability
All relevant data are available in the main text or the supplementary materials. The data that support the findings of this study are available on request from the corresponding authors.
- Yang, L. et al. Perovskite lead-free dielectrics for energy storage applications. Prog. Mater Sci. 102,72-108 (2019).
- Dai, Z. et al. A strategy for high performance of energy storage and transparency in KNN-based ferroelectric ceramics. Chem. Eng. J. 427, 131959 (2022).
- Qu, B. et al. Lead-free relaxor ferroelectric ceramics with high optical transparency and energy storage ability. J. Mater. Chem. C 4, 2016, 1795-1803.
- Li, C. et al. Amelioration on energy storage performance of KNN-based transparent ceramics by optimizing the polarization and breakdown strength. J. Am. Ceram. Soc. 105, 6158-6167 (2022).
- Gao, J. et al. High temperature-stability of (Pb0.9La0.1)(Zr0.65Ti0.35)O3 ceramic for energy-storage applications at finite electric field strength. Scr. Mater. 137, 114-118 (2017).
- Qiu, C. et al. Transparent ferroelectric crystals with ultrahigh piezoelectricity. Nature 577, 350-354 (2020).
- Xiao, Z. et al. Materials development and potential applications of transparent ceramics: A review. Mat. Sci. Eng. R 139, 100518 (2020).
- Li, D. et al. A high-temperature performing and near-zero energy loss lead-free ceramic capacitor. Energy Environ. Sci. 16, 4511-4521 (2023).
- Qiao, X. et al. Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramic with large energy density and high efficiency under a moderate electric field. J. Mater. Chem. C 7, 10514-10520(2019).
- Yan, F. et al. Composition and structure optimized BiFeO3-SrTiO3 lead-free ceramics with ultrahigh energy storage performance. Small 18, 2106515 (2022).
- Li, Y. et al. Energy storage performance of BaTiO3-based relaxor ferroelectric ceramics prepared through a two-step process. Chem. Eng. J. 419, 129673 (2021).
- Chai, Q. et al. Superior energy storage properties and optical transparency in K0.5Na0.5NbO3-based dielectric ceramics via multiple synergistic strategies. Small 19, 2207464 (2023).
- Chen, L. et al. Giant energy-storage density with ultrahigh efficiency in lead-free relaxors via high-entropy design. Nat. Commun.13, 3089 (2022).
- Pan, H. et al. Ultrahigh-energy density lead-free dielectric films via polymorphic nanodomain design. Science 365,578-582 (2019).
- Qi, H. et al. Superior energy-storage capacitors with simultaneously giant energy density and efficiency using nanodomain engineered BiFeO3-BaTiO3-NaNbO3 lead-free bulk ferroelectrics. Adv. Energy Mater. 10, 1903338 (2019).
- Zhang, T. et al. High energy storage density at low electric field of ABO3 antiferroelectric films with ionic pair doping. Energy Storage Mater. 18, 238-245 (2019).
- Pan, H. et al. Ultrahigh energy storage in superparaelectric relaxor ferroelectrics. Science 374, 100-104 (2021).
- Wang, K. et al. Superparaelectric (Ba0.95,Sr0.05)(Zr0.2,Ti0.8)O3 ultracapacitors. Adv. Energy Mater. 10, 2001778 (2020).
- Ren, X. et al. Regulation of energy density and efficiency in transparent ceramics by grain refinement. Chem. Eng. J. 390, 124566 (2020).
- Qi, H. et al. Local structure engineered lead-free ferroic dielectrics for superior energy-storage capacitors: A review. Energy Storage Mater. 45, 541-567 (2022).
- Zhang, M. et al. Significant increase in comprehensive energy storage performance of potassium sodium niobate-based ceramics via synergistic optimization strategy. Energy Storage Mater. 45,861-868 (2022).
- Zhang, M. et al. Energy storage performance of K0.5Na0.5NbO3-based ceramics modified by Bi(Zn2/3(Nb0.85Ta0.15)1/3)O3. Chem. Eng. J. 425, 131465 (2021).
- Xie, A. et al. Supercritical relaxor nanograined ferroelectrics for ultrahigh-energy-storage capacitors. Adv. Mater. 34, 2204356 (2022).
- Wang, W. et al. Enhanced energy storage properties in lead-free (Na0.5Bi0.5)0.7Sr0.3TiO3-based relaxor ferroelectric ceramics through a cooperative optimization strategy. ACS Appl. Mater. Interfaces 15, 6990-7001 (2023).
- Xu, M. et al. Optimizing the energy storage performance of NaNbO3 ceramics by rare-earth-based composite perovskite Sm(Mg0.5Zr0.5)O3 modification. Microstructures 3, 2023034 (2023).
- Krell, A. et al. Transmission physics and consequences for materials selection, manufacturing, and applications. J. Eur. Ceram. Soc. 29, 207-221 (2009).
- Wu, J. et al. Perovskite Srx(Bi1−xNa0.97-xLi0.03)0.5TiO3 ceramics with polar nano regions for high power energy storage. Nano Energy 50, 723-732 (2018).
- Tian, X. et al. Continuous control of polarization state and tunable dual-channel optical communication based on highly transparent PMN-PT electro-optic ceramics. Ceram. Int. 49, 23967-23974 (2023).
- Lu, Z. et al. Superior energy density through tailored dopant strategies in multilayer ceramic capacitors. Energy Environ. Sci. 13,2938-2948 (2020).
- Ye, W. et al. Remarkable energy-storage performances and excellent stability in CaTiO3-doped BiFeO3-BaTiO3 relaxor ferroelectric ceramics. J. Eur. Ceram. Soc. 43, 900-908 (2023).
- Sun, Z. et al. Ultrahigh energy storage performance of lead-free oxide multilayer film capacitors via interface engineering. Adv. Mater. 29, 1604427 (2017).
- Wang, W. et al. Enhancing energy storage performance in Na0.5Bi0.5TiO3-based lead-free relaxor ferroelectric ceramics along a stepwise optimization route. J. Mater. Chem. A 11, 2641-2651 (2023).
- Yang, Z. et al. Grain size engineered lead-free ceramics with both large energy storage density and ultrahigh mechanical properties. Nano Energy 58, 768-777 (2019).
- Wu, J. et al. Potassium-sodium niobate lead-free piezoelectric materials: past, present, and future of phase boundaries. Chem. Rev. 115, 2559-2595 (2015).
- Wang, G. et al. Ultrahigh energy storage density lead-free multilayers by controlled electrical homogeneity. Energy Environ. Sci. 12, 582-588 (2019).
- Wang, H. et al. Reversible multi-mode modulations of optical behavior in photochromic-translucent Nd-doped K0.5Na0.5NbO3 ceramics. J. Mater. Chem. C 8, 2343-2352 (2020).
- Li, D. et al. Improved energy storage properties achieved in (K, Na)NbO3-based relaxor ferroelectric ceramics via a combinatorial optimization strategy. Adv. Funct. Mater. 32, 2111776 (2021).
- Shao, T. et al. Potassium-sodium niobate based lead-free ceramics: novel electrical energy storage materials. J. Mater. Chem. A 5, 554-563(2017).
- Xing, J. et al. Realizing high comprehensive energy storage and ultrahigh hardness in lead-free ceramics. ACS Appl. Mater. Interfaces 13, 28472-28483 (2021).
- Xie, A. et al. NaNbO3-(Bi0.5Li0.5)TiO3 lead-free relaxor ferroelectric capacitors with superior energy-storage performances via multiple synergistic design. Adv. Energy Mater. 11, 2101378 (2021).
- Guo, H. et al. Realizing high energy density in BiFeO3-based ceramics capacitors via bandgap engineering and polarization optimization. Chem. Eng. J. 461, 142071 (2023).
- Hu, Q. et al. Achieve ultrahigh energy storage performance in BaTiO3-Bi(Mg1/2Ti1/2)O3 relaxor ferroelectric ceramics via nano-scale polarization mismatch and reconstruction. Nano Energy 67, 104264 (2020).
- Xing, J. et al. High performance BiFe0.9Co0.1O3 doped KNN-based lead-free ceramics for acoustic energy harvesting. Nano Energy 84, 105900 (2021).
- Lin, J. et al. Ultrahigh energy harvesting properties in temperature-insensitive eco-friendly highperformance KNN-based textured ceramics. J. Mater. Chem. A 10, 7978-7988 (2022).
- Chen, X. et al. Enhanced energy storage performance of BNT-ST based ceramics under low electric field via domain engineering. Ceram. Int. 48,31381-31388 (2022).
- Li, B. et al. Decoding thermal depolarization temperature in bismuth ferrite-barium titanate relaxor ferroelectrics with large strain response. ACS Appl. Mater. Interfaces 13, 37422-37432 (2021).
- Zhang, J. et al. Significantly enhanced energy storage density in sodium bismuth titanatebased ferroelectrics under low electric fields. J. Eur. Ceram. Soc. 40, 5458-5465 (2020).
- Anthoniappen, J. et al. Electric field induced nanoscale polarization switching and piezoresponse in Sm and Mn co-doped BiFeO3 multiferroic ceramics by using piezoresponse force microscopy. Acta Mater. 132, 174-181 (2017).
- Pennycook, J. et al. Chemically sensitive structure-imaging with a scanning transmission electron microscope. Nature, 336, 565-567 (1988).
- Zhu, R. et al. Dynamics of polar skyrmion bubbles under electric fields. Phys. Rev. Lett. 129, 107601 (2022).
There is NO Competing Interest.