Heterogeneous weakly coupled polar nanoclusters enabling superior high-temperature capacitive energy storage

Domain: chemistry
Published: 2026-02-21
Editorial outcome: major_revision

Abstract
Ceramic capacitors, although promising for advanced high-power energy storage, face challenges in energy density and efficiency at high temperatures, which restrict their practical applications. Guided by phase field simulations, we propose a structural design strategy to construct weakly coupled polar nanoclusters in superparaelectric state, and fabricate BaTiO3-based multilayer ceramic capacitors via prototype device technology. The capacitors achieve an ultra high energy storage density of 19.0 J·cm-3 and a high energy storage efficiency of 95.5% at room temperature. More importantly, both metrics are still on the order of >10.0 J·cm-3 and >95.0%, respectively, over 25-160 oC, outperforming previously reported ceramic capacitors. The weak coupling between adjacent nanoclusters caused by disordered polar configurations, suppresses nonlinear polarization response and temperature sensitivity, ultimately enabling superior energy storage performance, which is confirmed by atomic-scale microstructure analysis. This work advances next-generation electronics and provides insights for developing high-performance high-temperature ceramic capacitors.

Introduction
Lead-free ceramic capacitors have emerged as a key component for applications in portable electronics, electric vehicles, and large-scale energy storage systems due to their significant advantages, including eco-friendliness and ultra-high power density, which enable ultra-fast charging and discharging rates, as well as high voltage tolerance and reliability 1–3. However, compared to batteries and electrochemical capacitors, relatively low recoverable energy density (Wrec) and efficiency (η) limit their potential to meet practical requirements for miniaturization and integration 4–6. In order to meet the requirements of practical applications, ceramic dielectric capacitors must feature extremely slim polarization-electric field (P-E) loops and high field-induced polarization 7,8. However, achieving high polarization often leads to significant hysteresis effects, and vice versa 9,10. In response to this challenge, researchers employed various strategies to engineer the transition from ferroelectrics (FEs) to relaxor ferroelectrics (RFEs) and have made significant progress 11,12. This transition destroys the long-range ordered, strongly coupled micron-scale FE domains, resulting in lower polarization switching energy barriers and enhanced η value of ceramic capacitors 13,14. According to numerous reported ceramic systems, the BaTiO3-x(Na0.5Bi0.5)TiO3 (0≤x≤1, BT-100xNBT) RFEs have attracted significant attention due to its significant tetragonal distortions with varying composition and high spontaneous polarization 15–17. For instance, through precise local structural design in BT-50NBT-based RFEs, an exceptionally high energy density (>10 Jcm−3) and energy efficiency (>90%) have been achieved 18. Unfortunately, the Wrec value of this ceramic at a high temperature of 150°C is sharply decreased to approximately 8.5 Jcm−3, and the corresponding η is also reduced to around 85%. Temperature-sensitive energy storage performance and low high-temperature capacitance density (<10 Jcm−3) of recently reported lead-free ceramics still restrict their applicability at high-temperature conditions. For instance, the (Bi1/3Na1/6K1/6Ba1/6Sr1/6)(Ti0.8Zr0.2)O3 high-entropy ceramic exhibits an excellent energy storage density of 18.7 Jcm−3 at room temperature. However, its energy storage density notably drops below 10.0 Jcm−3 at 160°C 19. Similarly, the BaTiO3-(Bi0.5Na0.5)(Zn1/3Nb2/3)O3 system formed by multi-ion doping has an ultra high energy storage efficiency of 96.1%, but the insufficient thermal stability of energy storage density limits its applicability in a wide temperature range 20. Therefore, developing lead-free ceramic dielectric capacitors with high energy storage performance and excellent high-temperature stability is crucial for the next generation of dielectric capacitors that can operate stably under high electric fields and at temperatures up to 150°C.

Typical RFEs always exhibit small polarization hysteresis while suffering from early polarization saturation under sufficiently high external electric fields, restricting the rapid enhancement of energy storage performance when increasing the external electric field 21. Moreover, the energy storage performance of typical RFEs is often sensitive to temperature changes 22. From a thermodynamic perspective, domain size plays a crucial role in influencing the polarization response, encompassing long-range FE interactions and switching barriers. When sufficiently reducing the domain size and weakening the domain coupling, the polar state becomes easily redirectable, resulting in nearly zero polarization hysteresis and mitigated polarization saturation. Interestingly, as shown in Fig. 1a, this phenomenon can be observed in superparaelectric state within the temperature range of Tm < T < TB, where Tm is the peak temperature of the dielectric constant and TB represents the Burns temperature. In comparison to strongly coupled micro-domains and nano-domains, weakly coupled polar nanoclusters in superparaelectric state exhibit a super-fast and reversible response under loading and unloading the external electric field, which prevents the phenomenon of polarization hysteresis and premature polarization saturation, resulting in remarkable energy storage density and efficiency 21,23. In addition, these weakly coupled polar nanoclusters are insensitive to the variation of ambient temperature, and the corresponding dielectric constant remains stable over a broad temperature range, which is highly important for enhancing the thermal stability of energy storage performance 24,25.

Guided by phase-field simulations, as shown in Fig. 1b, the introduction of foreign ions such as Sr2+, La3+, and Zr4+ into the BT-35NBT matrix increases the local random field, disrupting long-range ordered, strongly coupled micro-domains and forming small weakly coupled polar nanoclusters. This configuration features rhombohedral (R) and tetragonal (T) polar nanoclusters embedded within cubic (C) paraelectric matrixes. Adjusting the ratio and distribution of polar and nonpolar states for R-, T-, and C-phases aims to minimize polarization hysteresis while maximizing maximum polarization. Such weakly coupled polar nanoclusters can exert a pinning effect that effectively inhibits local structural changes induced by atomic thermal vibration and thereby significantly enhances the stability of the phase structure over a wide temperature range. It is encouraging that the unique structural design enables the fabricated multilayer ceramic capacitors (MLCCs) to exhibit excellent energy storage performance not only at room temperature, but also over a wide temperature range. Even at a high temperature of 160°C, the Wrec remains greater than 10.0 J·cm-3, and the η exceeds 95.0%. This advancement provides a significant reference for developing next-generation high-temperature dielectric capacitors.

Results
To uncover the underlying origin of the enhanced high-temperature energy storage performance of lead-free ceramic dielectrics induced by weakly coupled polar nanoclusters, the two-dimensional phase field simulation was used to study the correlation between the polar structure evolution and the corresponding hysteresis behavior of (1−x)[0.65BaTiO3-0.35(Na0.5Bi0.5)TiO3]-xSr0.7La0.2ZrO3 (SLZ100x, x=0, 0.05, 0.1, 0.15, 0.2) ceramics at different temperatures, as shown in Fig. 2a and Supplementary Fig. 1. The initial BT-35NBT ceramic features long-range ordered, strongly coupled T-phase domain structure, as substantiated by its P-E hysteresis loops with large polarization but high hysteresis loss. After introducing SLZ, as expected, the domains were transformed from macroscopic FE domains to nanodomains and subsequently to smaller weakly coupled polar nanoclusters, accompanied by increasingly slender P-E loops. This progression suggests that the introduction of SLZ effectively disrupts the long-range FE order in BT-35NBT ceramics. Simultaneously, the content of the T-phase decreases significantly, resulting in a disordered polarization structure with coexisting R-, T- and C-phases. The randomly distributed polar structure modifies local energy barriers, stabilizes the favorable polarization, and forms the unique structures with weakly coupled R and T polar nanoclusters divided by nonpolar C-phase over a broad temperature range, thereby enhancing temperature-insensitive energy storage performance. In addition, the weak coupling characteristic is responsible for excellent electric field response performance in the SLZ15 ceramic (Fig. 2b). In the initial state, benefiting from such a weak coupling effect, the polarization directions are highly randomly distributed. Upon the loading of external electric field, the polarizations rapidly reorient and align with the electric field direction. After the removal of external electric field, the polarization quickly deviates from the directional alignment state and eventually recovers its initial disordered distribution, demonstrating fast and reversible polarization response behavior. At the same time, optimizing the ratio and distribution of polar nanoclusters further reduces potential barriers for domain switching, enabling the flattest domain switching paths (Fig. 2c). Weakly coupled polar nanoclusters also promote the formation of random fields, which provides a strong driving force for the electric field-induced recovery of large domains to a multi-domain state (Fig. 2d). These results lead to a recoverable electric field-induced relaxor FE state and promote linear-like polarization behavior.

An aberration-corrected scanning transmission electron microscope was employed to investigate the atomic-scale structural characteristics of SLZx ceramics. Figure 3a, b shows the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images for representative compositions of BT-35NBT and SLZ15 ceramics along [100]c direction. The polarization displacement vectors were computed through software simulation and presented by yellow arrows. Herein, the morphological structure is identified by observing the projected displacements of the B-site cations (Zr/Ti) relative to the four nearest A-site cations (Ba/Na/Bi/Sr) at the lattice center. Based on the 2D Gaussian peak fitting results, the larger domains can be observed by same arrow pointing for BT-35NBT ceramics (highlighted by the green arrow at the right of Fig. 3a). By contrast, local fluctuations are observed for the SLZ15 ceramic due to the disordered nature of the A-site cations. As a result, smaller weakly coupled polar nanoclusters of R- and T-phases are embedded within nonpolar C-phase matrixes (Fig. 3b). These results confirm that SLZx ceramics with weakly coupled polar nanoclusters were successfully fabricated under the guidance of phase-field simulations. The disordered and weakly coupled polar nanoclusters contribute to enhancing the stability of local structure and energy storage performance under temperature fluctuation 26. Additionally, as observed in the atomic-resolved energy-dispersive spectroscopy (EDS) mapping for the SLZ15 ceramic in Supplementary Fig. 2, the Ba, Bi, Na, La, and Sr elements are distributed in A-sites, while the Zr and Ti elements are distributed in B-sites, respectively. It promotes the destabilization of cation sites in the perovskite structure and induces the formation of weakly coupled polar nanoclusters. From the comparative distribution of pixel intensities of A- and B-site atomic columns between the BT-35NBT and SLZ15 ceramics, it can be concluded that multi-element doping significantly enhances the atomic-scale disorder of the ceramics (Fig. 3c–f). Significantly, the intensity fluctuation is more prominent at the A-site columns (Ba2+/Na+/Bi3+/Sr2+/La2+) in the SLZ15 ceramic, suggesting large random displacements of A-site cations. These random shifts directly generate strong local electric fields that disrupt long-range polar order. In contrast, the B-site (Ti4+/Zr4+) columns show small intensity variations. Nevertheless, their fluctuations exhibit high spatial correlation closely linked to cooperative displacements of B-site cations and tilting of oxygen octahedra. This correlated B-site behavior locally biases polarization directions and contributes to stabilizing nanoscale polar nanoclusters. According to the axial displacement data, the polarization angle and amplitude mapping of BT-35NBT and SLZ15 ceramics along the [100]c direction is illustrated in Supplementary Fig. 3. Compared to the BT-35NBT ceramic, the polarization angle and amplitude of the SLZ15 ceramic exhibit a markedly non-uniform random distribution. Meanwhile, this random distribution of T- and R-phase polar nanoclusters is isolated by nonpolar C-phase, facilitating a more rapid and efficient response to the external electric field 27. In addition, compared with the average c/a ratio of the BT-35NBT ceramic, that of the SLZ15 ceramic displays a noticeable decrease accompanied by a more pronounced discrete distribution (Supplementary Fig. 4). The variation of the c/a ratio indicates that as SLZ content increases, atomic disorder within the system escalates and lattice distortion intensifies, further enhancing the random field and effectively delaying polarization saturation 28.

X-ray diffraction (XRD, Supplementary Fig. 5) analysis confirms that all samples exhibit a pure perovskite phase. The pure BT-35NBT ceramic displays a characteristic T phase, evident from the distinct splitting of XRD peaks (002)/(200) 28,29. As the SLZ content increases, the (200) diffraction peak gradually shifts to a low angle, primarily due to the larger radius of the dopant ions (R(Sr2+)=1.44 Å, R(La3+)=1.06 Å, R(Zr4+)=0.79 Å), which results in lattice expansion. To further analyze the phase composition in the SLZx ceramics, Rietveld refinement was performed on the XRD data for each composition, as shown in Fig. 4a and Supplementary Fig. 6. The results indicate that the rhombohedral (R3c) and tetragonal (P4bm) phases coexist in the SLZ15 ceramic, with mass fractions of 56.2 wt% and 43.8 wt%, respectively. Notably, as the SLZ content increases, the proportion of the R-phase at room temperature increases monotonically, from 24.6 wt% at x=0.05–71.4 wt% at x=0.20. Both the R-phase and T-phase are polar phases with high polarization, which facilitates the achievement of a larger maximum polarization (Pmax) in ceramic dielectrics under the application of an external electric field 23.

To primarily confirm the designed SLZx ceramics in superparaelectric state near room temperature, the temperature dependence of dielectric constant and dielectric loss (tanδ) was analyzed (Supplementary Figs. 7 and 8). As the SLZ content increases, the tanδ exhibits a significant decreasing trend while remaining consistently below 0.01 across a broad temperature range from room temperature to 300°C, accompanied by the shift of Tm towards low temperatures from 184°C for x=0 to −83°C for x=0.20 at 1 kHz. Additionally, the relaxor diffusion factor γ, calculated using the modified Curie-Weiss law 30, tends to increase with the increment of x, indicating an improvement in relaxor properties (Supplementary Fig. 9). Based on the dielectric spectrum at 1 kHz, a possible composition-temperature phase diagram was constructed (Fig. 4b). The Tm significantly decreases with increasing SLZ content, facilitating the transition from relaxor FE to superparaelectric state. Consequently, the designed ceramics are fully situated in superparaelectric state from −56°C to 162°C when x=0.15, indicating the existence of weakly coupled polar nanoclusters over a broad temperature range. In addition, weakened coupling between the R-phase and T-phase polar nanoclusters significantly reduces the stress required for polarization reorientation in response to an external electric field, leading to lower strain vibration and potential failure risks 8,31.

The relaxation characteristics of SLZx ceramics were studied through the first-order reversal curve (FORC) distribution, as shown in Fig. 4c and Supplementary Fig. 10. The BT-35NBT ceramic displays a high-intensity distribution near the origin, indicative of strongly coupled FE domain switching at low electric fields, resulting in an overall increase in polarization 32. This inhomogeneous FORC intensity distribution reflects the typical characteristics of strong polarization nonlinearity in FE materials 33. In contrast, the FORC intensity of the SLZ15 ceramic is more uniform distributed across all electric fields, indicating decreased coercive fields, reduced FE nonlinearity, and a more dispersed polarization contribution 34. In addition, the representative samples of BT-35NBT and SLZ15 ceramics were selected to analyze further the dynamic response of domains by piezoelectric force microscopy (PFM) at various voltages and relaxation times (Supplementary Figs. 11 and 12). For the BT-35NBT ceramic, a strong domain-switching signal is observed at a low voltage of 10 V, whereas the domain-switching signal in the SLZ15 ceramic is weak at this voltage but becomes more pronounced with increasing voltage, suggesting that local random fields and highly dynamic polar nanoclusters are present in the SLZ15 ceramic. Weakly coupled polar nanoclusters require a higher electric field to achieve long-range polarization, which explains the reduced polarization saturation observed in the SLZ15 ceramic. Furthermore, after removing the voltage and allowing a relaxation time of 20 min, the BT-35NBT ceramic retains their original remarkable signals, while the domain-switching signals in the SLZ15 ceramic are barely detectable. These results indicate that the introduction of SLZ diminishes the domain size of the BT-35NBT ceramic and induces weakly coupled polar nanoclusters. This structural modulation yields negligible Pr by virtue of rapid reversible polarization response, while concurrently enhancing the overall energy storage performance.

For ceramic capacitors, the breakdown strength (Eb) significantly influences their operating electric field and energy storage density. Thus, the breakdown characteristics of SLZx ceramics were initially evaluated using the Weibull distribution function 35. All samples exhibit a linear relationship with a large shape parameter (β>10, Supplementary Fig. 13), indicating the reliability of the results and consistent quality of the ceramic samples. In fact, the Eb of ceramic dielectrics is influenced by various complex factors, such as band gap (Eg), grain size, and insulation properties 36,37. For SLZx ceramics, the Eg is significantly enhanced with increasing the SLZ content (Supplementary Fig. 14). Specifically, the values of Eg are enhanced monotonously from 3.12 eV for the SLZ5 ceramic to 3.18 eV for the SLZ20 ceramic, leading to a substantial increase in the Eb. In addition, the average grain size (Ga) and Eb exhibit a negative correlation in ceramic dielectrics 28,38. According to the measured SEM (Supplementary Fig. 15), the Ga was evaluated by NanoMeasurer software. The Ga exhibits a decreasing tendency, from 0.72 μm for the BT-35NBT ceramic to 0.43 μm for the SLZ20 ceramic. The smaller Ga is beneficial to achieving higher Eb. Despite the fact that the radius of impedance spectra for SLZx ceramics tends to decrease with increasing temperature, the higher SLZ content still contributes to a larger radius, indicating the enhancement of total resistivity and Eb at high temperatures (Supplementary Fig. 16). In addition, the distinct single peaks of Z” and M” can be observed for the BT-35NBT ceramic, but they do not coincide at the same frequency (Supplementary Fig. 17). This lack of overlap indicates electrical inhomogeneity. In contrast, the peaks of Z” and M” closely overlap at the same frequency for the SLZ15 ceramic, demonstrating that the introduction of SLZ into the BT-35NBT ceramic effectively improves the electrical homogeneity. This enhancement in electrical homogeneity also contributes to the increase in Eb 39.

To better evaluate the overall energy storage performance of the designed ceramics, the unipolar P-E loops were measured at their critical electric field (Supplementary Figs. 18 and 19), and the related capacitive energy storage performance of Wrec and η were calculated (Fig. 4d). Despite the Pmax of the BT-35NBT ceramic reaching 37.9 μCcm−2 at a low breakdown strength (Eb = 160 kVcm−1), while the remnant polarization (Pr) is as high as 23.8 μCcm−2, leading to low energy storage density and efficiency (Wrec = 1.7 Jcm−3, η=48.6%, Supplementary Fig. 18). By tailoring the polar nanocluster configuration, the values of Wrec and η were dramatically improved to be on the order of 9.2 ± 0.28 Jcm−3 and 91.6 ± 0.24% at x=0.15. It is due to the fact that the strongly coupled FE order of the BT-35NBT ceramic is disrupted, resulting in the formation of R- and T-phase weakly coupled polar nanoclusters isolated by nonpolar C-phase matrixes, which contributes to the rapid polarization response and slim P-E loops. Nevertheless, when excessive SLZ is introduced (e.g., at x=0.2), the formation of nonpolar C-phase becomes dominant. Consequently, the Pmax value at an electric field of 620 kVcm−1 drops to only 30.5 μCcm−2, and the Wrec ultimately decreases to 7.5 Jcm−3. These results indicate that the generation of weakly coupled polar nanoclusters and the alterations in nanocluster configuration significantly optimize the energy storage performance of lead-free ceramics. Compared to the traditional solid-state reaction process, the method of repeated rolling process (RRP) facilitates the refinement of grain size and enhances sintering uniformity, leading to the increased Eb of ceramic dielectrics 25,40. Therefore, SLZ15 ceramics were prepared via the RRP (SLZ15-RRP) using SLZ15 powder to further optimize their energy storage performance. Figure 4e illustrates the unipolar P-E loops of the SLZ15-RRP ceramic under different electric fields. Obviously, the Pr remains negligible and its value is as low as 0.9 μCcm−2 even at 780 kVcm−1. It is worth noting that an ultra-high Wrec of 13.6 Jcm−3, along with a near-ideal efficiency of 95.0%, can be achieved for the SLZ15-RRP ceramic. The reliability of the Eb is validated through Weibull distribution analysis, as shown in Supplementary Fig. 20. The β of the SLZ15-RRP ceramic is 17.34, indicating high reliability of the Eb. The calculated Eb is on the order of 782.9 kVcm−1, closely corresponding to the Eb obtained in P-E loops. Herein, the remarkable comprehensive energy storage performance in this study is primarily due to their weakly coupled polar nanoclusters, compact microstructure, and uniform and small grain size (Supplementary Fig. 21). Weakly coupled polar nanoclusters exhibit high sensitivity to external electric fields, which enables ceramic dielectrics to achieve near-ideal energy efficiency. Meanwhile, the refined grain size effectively inhibits electrical tree propagation and shortens their growth paths, thereby significantly enhancing the Eb, as shown in Fig. 4f and Supplementary Fig. 22.

Except for achieving high energy storage performance at room temperature, their stability under different conditions is also critical in practical applications. Therefore, over a broad temperature range from room temperature to 160°C, the P-E loops consistently maintain a slim shape and the variation of Wrec and η is less than 10.0% and 5.0%, respectively, at an electric field of 500 kVcm−1 (Fig. 4g and Supplementary Fig. 23). To further assess frequency adaptability, P-E loops of the SLZ15-RRP ceramic were tested over a frequency range of 1–100 Hz (Supplementary Fig. 24). Obviously, the Wrec remains stably at ~ 7.9 Jcm−3, and the η consistently stays above 94.0%, which indicates excellent frequency stability. Moreover, the energy storage performance of the SLZ15-RRP ceramic remains stable with a change rate of less than 2.0% in both Wrec and η after 106 cycles (Fig. 4h and Supplementary Fig. 25). In addition, the overdamped discharge characteristics of the SLZ15-RRP ceramic were investigated using a specially designed circuit with a 100 Ω resistor at various temperatures under an electric field of 500 kVcm−1. The overdamped oscillation waveforms and discharge energy storage performance are displayed in Supplementary Fig. 26. In a high-temperature environment, the discharged energy density (Wd) can still maintain over 90.0% of this value under the same voltage conditions. The stable Wd of ~ 6.0 Jcm−3 and fast discharge time (t0.9) of ~ 44 ns also indicate the thermally stable discharge performance (Fig. 4i). These results demonstrate the promising potential of the SLZ15-RRP ceramic for high-temperature energy storage applications.

The MLCCs, which were fabricated with five effective dielectric layers using SLZ15 ceramic powder, exhibit a well-defined layered structure and sharp dielectric-electrode interfaces, as shown in the cross-sectional microstructure (Fig. 5a). Evidently, no discernible elemental interdiffusion is observed between the dielectric and electrode layers, indicating excellent chemical compatibility during co-firing. During the process of steadily increasing electric field up to breakdown field, the SLZ15-MLCCs still displays an extremely slim P-E loops, as show in Fig. 5b. The Pmax increases steadily, whereas the Pr remains nearly a constant (below 0.9 μCcm−2). As the electric field increases steadily, it allows the SLZ15-MLCCs to attain the Wrec of 19.0 Jcm−3 at 1050 kVcm−1, and the η remains remarkably high (~95.5%), as depicted in Fig. 5c, which is notably superior to most of the current reported lead-free MLCCs (Fig. 5d and Supplementary Table 1) 28,41–49. To evaluate practical reliability, cyclic stability tests were conducted under 700 kVcm−1. After 106 cycles, neither the Wrec nor the η exhibits significant degradation (Fig. 5e and Supplementary Fig. 27), which confirms that the excellent cycling endurance is suitable for long-term operation. Notably, the SLZ15-MLCCs exhibit excellent stability over broad ranges of frequency and temperature. The variations in its P-E loops are negligible over a temperature range of 25–160°C and a frequency range of 1–100 Hz (Supplementary Figs. 28 and 29a). Meanwhile, it maintains a Wrec of over 10.0 Jcm−3 and an η of over 95.0% within these ranges, with the variation rate of the energy storage performance being less than 6.0% (Fig. 5f and Supplementary Fig. 29b). The excellent cycling, frequency, and temperature stability of the SLZ15-MLCCs fully confirms their significant potential for practical deployment.

It is well known that ceramic dielectric capacitors exhibit excellent energy storage performance at high temperatures, closely linked to variations in their crystal structures 50. As the temperature increases, the simulated P-E loops in Fig. 5g show a slight decrease in Pmax, which is consistent with the above experimental results. This trend can be attributed to the gradual reduction in domain size and dielectric constant with rising temperature. Furthermore, the structural characteristics of the SLZ15 ceramic were evaluated using XRD and Raman spectroscopy from 25°C to 200°C, as shown in Fig. 5h, i and Supplementary Fig. 30. The number and relative intensity of XRD diffraction peaks remain consistent across the temperature range, and the (111) and (200) diffraction peaks shift towards lower angles due to thermal expansion without splitting, indicating the stability of phase structure. Meanwhile, as shown in Fig. 5h, the SLZ15 ceramic exhibits nearly diffuse Raman patterns with consistent peaks over a broad temperature range. These results suggest that the crystal structure remains stable within the tested temperature range, providing the structural characteristics of excellent high-temperature energy storage performance.

In summary, guided by phase-field simulations, this work presents an effective strategy for enhancing the capacitive energy storage of lead-free ceramics by designing weakly coupled polar nanoclusters in superparaelectric state. Atomic-scale HAADF-STEM and polarization mapping reveal nanostructured polar clusters with R- and T-phases that are embedded within a nonpolar C-phase matrix, forming weakly coupled polar nanoclusters. As a result, the SLZ15-MLCCs exhibit large Pmax, high applied electric field and negligible polarization hysteresis, leading to ultra-high energy storage density (Wrec ≈ 19.0 Jcm−3) and near-ideal efficiency of 95.5% at room temperature. In addition, the weakly coupled and disordered polar nanoclusters remain stable at thermal fluctuations, ensuring remarkable high-temperature energy storage performance. When the temperature rises to 160°C, its Wrec remains above 10.0 Jcm−3, and the η reaches as high as over 95.0%. Additionally, the SLZ15-MLCCs also exhibit excellent frequency stability and cyclic stability, and the variations in Wrec and η both remain less than 5.0%. This work establishes a paradigm for achieving ultra-high comprehensive energy storage performance, addressing the critical need for dielectric capacitors in high-temperature environments.

Methods
Sample preparation
The (1-x)[0.65BaTiO3-0.35(Na0.5Bi0.5)TiO3]-xSr0.7La0.2ZrO3 (x=0, 0.05, 0.1, 0.15, 0.2) was fabricated by raw powders of BaCO3 (99.9%), TiO2 (98.0%), Na2CO3 (99.8%), Bi2O3 (99.0%), SrCO3 (99.0%), La2O3 (99.99%), and ZrO2 (99.0%) through a conventional solid-state reaction. The weighed raw materials were ball-milled for 24 h with ethanol, dried at 100°C for 3 h, and subsequently calcined at 850°C for 4 h. The calcined powders were further ball-milled for 24 h with ethanol. After drying, the powders were pre-pressed into 12 mm diameter pellets for cold isostatic pressing. The samples can be obtained by sintering at 1200–1270°C for 4 h.

Repeated rolling processing
The SLZ15-RRP ceramic was fabricated by a repeated rolling processing (RRP) technique, employing pre-sintered SLZ15 powder as the raw material. The pre-sintered SLZ15 powder was initially subjected to ball-milling to refine its particle size and then homogeneously mixed with an organic binder (e.g., PVA) at a mass ratio of 2:1 (powder to binder). The mixture was subjected to 1000 rolling cycles at room temperature under a pressure of 10 MPa to form uniform ceramic tapes. These tapes were then punched into discs (12 mm diameter) and calcined at 650°C for 12 h to remove the binder. Finally, the discs were embedded in presintered powder of the same composition and sintered at 1165°C for 2 h using a double-crucible configuration.

MLCCs fabrication
The SLZ15 ceramic powder with optimal performance was selected as the raw material and thoroughly mixed with an organic vehicle composed of methyl ethyl ketone, butyl benzyl phthalate, polypropylene carbonate, and triolein. After dispersion using a high-speed homogenizer, a uniform and stable ceramic slurry was prepared. Subsequently, the slurry was cast into smooth and continuous green ceramic tapes via a tape casting machine. After drying, platinum paste was coated on the surface of the green tapes as internal electrodes by screen printing. The green tapes with internal electrodes were cut into sheets of specified size, stacked in an alternating alignment mode of internal electrodes, and dense lamination was achieved through isostatic pressing technology. Finally, the laminated green body was sintered at 1220°C in an air atmosphere for 3 h to obtain the SLZ15-MLCCs. After the external electrodes were encapsulated on the SLZ15-MLCCs by silver paste coating, the electrical performance tests were conducted. The overlapping area of two adjacent platinum electrodes in the sintered SLZ15-MLCCs was measured to be 1.7 × 1.6 mm2, and the average thickness of dielectric layer was approximately 8 μm.

Structure characterizations
The phase structure was measured using X-ray diffraction (XRD, D8 Advanced, Bruker, Germany) with Cu Kα radiation. Raman spectra were obtained using a Raman scattering spectrometer (HR800, HORIBA Jobin Yvon, France). The micromorphology of the samples was recorded with a field-emission scanning electron microscope (SEM, S-4800, Hitachi, Japan), and the grain size was evaluated using a combination of the NanoMeasurer software. An atomic-resolution high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM, Titan Themis G2, FEI, USA) was employed to investigate the polar nanoclusters in the ceramics.

Electric property measurements
The P-E loops reported in this study were measured using a FE analyzer (Premier II, Radiant, USA) with a bipolar triangular waveform. The charge/discharge performance of samples was evaluated using a commercial charge-discharge device (CFD-001, Gogo Instruments Technology, China). The dynamic response of the domains to external electric fields was examined using piezoelectric force microscopy (PFM, MFP-3D, Asylum Research, USA).

Phase-field simulations
The details of the phase-field simulation regarding the domain structure and polarization configuration are provided in the Supplementary Information.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Q. Yuan et al. have reported the high energy storage density in superparaelectric state for high temperature application. They have well explained on the various characteristic properties of lead free SLZ modified BT-35BNT solid solution. Also, this work will attract to the researchers to develop new type of lead free ceramic in future for technological applications. Hence, the present work can be accepted for Nature communication before minor correction as mentioned below.\n1. Explain about the stability of disorder polar nano-cluster at thermal fluctuation in the present ceramic\n2. Mention at what frequency, the P-E loops are measured.\n3. How the energy storage density vary with the frequency of the electric signal.\n4. Kindly explain the reduction of Tm towards room temperature for superparaelectric state and correlate in term of ferroelectric order parameter.", "reviewer_2": "This manuscript presents an advanced and well-executed investigation into the design and control of weakly coupled polar nanoclusters in lead-free ceramics to achieve superior high-temperature capacitive energy storage. The work is scientifically important and relevant to current energy storage research, particularly in eco-friendly high-temperature dielectric materials. However, while the experimental results are impressive, certain fundamental and mechanistic aspects require deeper clarification before considering publication in Nature Communications.\n1. Physical Mechanism of Weak Coupling:\no The authors attribute the improved energy density and efficiency to weakly coupled polar nanoclusters. However, the manuscript lacks quantitative correlation between the degree of coupling, local field strength, and the observed macroscopic polarization behavior.\no Suggest performing a comparative quantitative analysis (e.g., using phase-field parameter sensitivity studies or local field simulations) to confirm how coupling strength influences domain switching barriers.\n2. Role of Sr²⁺, La³⁺, and Zr⁴⁺ Dopants:\no While the dopants are claimed to induce structural randomness, their site occupancy (A-site vs. B-site) and ionic radius mismatch should be systematically correlated with lattice distortion using Rietveld refinement data or TEM lattice mapping.\no How does the ionic substitution specifically alter the Burns temperature (TB) and contribute to the stabilization of the superparaelectric state?\n3. Thermal Stability and Relaxor Dynamics:\no The claim of superior high-temperature stability up to 160 °C is remarkable. However, more clarity is required on the reversibility of the phase transitions upon cooling cycles. Has the dielectric constant and polarization hysteresis been measured after repeated heating–cooling cycles?\n4. Electrical Treeing and Breakdown Mechanism:\no The paper attributes improved breakdown strength (Eb) to reduced grain size and increased Eg. However, the electric tree simulations are qualitative. Quantitative lifetime prediction or Weibull reliability analysis under cyclic stress conditions should be provided.\n5. Microscopic Origin of Polar Disorder:\no The HAADF-STEM data are insightful but could benefit from statistical quantification of the polar displacement vectors to distinguish the contribution of random A-site versus B-site cation disorder.\n6. Comparison with Other High-Entropy Relaxor Systems:\no The discussion section should more critically compare the performance with other reported high-entropy or multi-doped BaTiO₃-based relaxors, highlighting how the “weakly coupled nanocluster” mechanism differs in energetics and domain reversibility.\nMinor Comments\n• Figures 2–4 are dense and would benefit from schematic illustrations summarising the correlation between domain structure evolution and P–E loop morphology.\n• The error margins for Wrec and η values are not reported; these should be included for scientific rigor.\n• The methods section should clearly specify the applied frequency and waveform parameters used in the ferroelectric measurements.\n• References 7–9 and 21–24 should be rechecked for citation consistency with recent literature on superparaelectrics.\nBasic and Conceptual Questions for Authors\n1. What defines the threshold between “weakly coupled” and “strongly coupled” domains from a physical perspective (energy barrier, correlation length, or permittivity variance)?\n2. How does the nanocluster coupling influence the local potential landscape for polarization reversal?\n3. What role does entropy play in stabilizing the disordered superparaelectric configuration?\n4. Can similar weakly coupled nanocluster behavior be extended to non-perovskite systems, such as tungsten bronzes or layered Aurivillius phases?\n5. How would the performance scale if multilayer or thin-film configurations were fabricated instead of bulk ceramics?\n6. What is the contribution of interfacial strain fields in modulating dielectric breakdown and energy density?\n7. How does the relaxor response evolve under high-frequency operation (>1 MHz) relevant to electronic circuits?\n8. What would be the expected degradation pathway under prolonged electrical cycling beyond 10⁶ cycles?\nRecommendation:\nMajor Revision\nThe work is scientifically strong, but certain physical mechanisms, structural correlations, and quantitative analyses must be clarified to meet the standards of Nature Communications. Addressing these points will substantially improve the clarity and impact of the manuscript.", "reviewer_3": "This manuscript systematically investigates the design and implementation strategy for lead-free ceramic capacitors featuring heterogeneous weakly coupled polar nanoclusters, tailored for high-temperature capacitive energy storage applications. Guided by phase-field simulations, the doping strategy combined with a repetitive rolling process (RRP) enables the authors to achieve an ultrahigh recoverable energy density (W_rec = 13.6 J·cm⁻³) with 95% efficiency (η) at room temperature, while maintaining excellent performance of 10.2 J·cm⁻³ (η = 91%) at 160 °C. The study integrates multi-scale structural characterizations, electrical measurements, and theoretical modeling to elucidate the pivotal role of polar nanoclusters in enhancing energy storage performance and thermal stability. The research offers a valuable solution to pressing challenges in the field of high-temperature dielectric capacitors. To further strengthen the manuscript's completeness and practical relevance before publication, the authors need to conduct a major revision to address the following suggestions:\n1. While the material-level performance is impressive, the manuscript lacks data on the fabrication and performance evaluation of actual multilayer ceramic capacitors (MLCCs). This aspect is crucial for assessing engineering applicability. Could the authors supplement the study with relevant experimental results, such as device-level P-E loops, breakdown voltage, or cycling stability tests?\n2. The work convincingly demonstrates the material's superior stability across a wide temperature range (room temperature to 160 °C) under moderate electric fields. Nevertheless, the performance boundaries and long-term durability under extreme conditions warrant further exploration. For instance, has long-term stability been verified at higher temperatures (>160 °C or 200 °C) or under elevated electric fields? Additionally, to deepen the analysis, experimental data or discussions on long-term reliability and aging behavior near the breakdown limit (>700 kV/cm) would be beneficial.\n3. The description of the RRP is sufficient for peers to grasp its basic workflow and acknowledge its efficacy, yet it omits specific parameters (e.g., rolling pressure, temperature, and iterations), rendering it akin to a \"technical know-how\" that heavily relies on operator expertise for reproducibility. Full replication may necessitate additional data from the authors or extensive trial-and-error experiments. Consequently, questions arise regarding its scalability, cost-effectiveness, and industrial viability. Given that Nature Communications publishes numerous advances in materials processing annually, we anticipate contributions with stronger guidance for industrial production. The manuscript confirms the doping strategy's substantial enhancement of material properties but provides limited discussion on the feasibility for large-scale manufacturing. We recommend incorporating detailed process parameters, simulation analyses, optimization guidelines, cost assessments, or potential scalability challenges to better inform practical industrial applications.\n4. The manuscript robustly argues that SLZ doping represents an efficient and rational choice, underpinned by rigorous and successful design logic. However, it does not furnish compelling evidence to establish SLZ as the \"optimal\" or \"sole\" option, merely supporting its status as an \"effective\" strategy. Framing SLZ as a successful exemplar within the broader \"composition design-microstructure engineering\" landscape would be more appropriate. Demonstrating \"optimality\" would require systematic comparative compositional studies, which could form the basis of a follow-up publication. We suggest tempering the discussion to avoid overly absolute claims.\n5. The phase-field model presented is a simplified idealization that adeptly captures and interprets the dominant physical mechanisms, with experimental results indirectly validating its applicability and reliability within the study's scope. This simulation approach stands out as a key innovation, having qualitatively predicted nanocluster evolution with success. To bolster persuasiveness, we recommend including quantitative outputs, such as simulated hysteresis loops (P-E curves) or polarization response profiles. Furthermore, does the model account for mechanical defects (e.g., cracks)? If so, how are they incorporated (e.g., via elastic terms or defect random fields)? Please clarify or expand on this aspect.\n6. Figures such as Fig. 5e lack sufficient clarity, failing to effectively highlight numerical differences. We suggest providing inset magnifications or enhanced contrasts to more intuitively convey key data."}, "author_response": "Dear Dr. Editor and Reviewers:\nThank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Heterogeneous Weakly Coupled Polar Nanoclusters Enabling Superior High-Temperature Capacitive Energy Storage” (Research Article, No. NCOMMS-25-69291). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research.\nWe have studied comments carefully and have made the following corrections which we hope to meet with approval. In order to highlight the modifications in the manuscript, we have marked them in red. The main corrections in the manuscript and the responses to the reviewers’ comments are listed as following:\nReply to Reviewer # 1:\nComments:\nQ. Yuan et al. have reported the high energy storage density in superparaelectric state for high temperature application. They have well explained on the various characteristic properties of lead free SLZ modified BT-35BNT solid solution. Also, this work will attract to the researchers to develop new type of lead free ceramic in future for technological applications. Hence, the present work can be accepted for Nature communication before minor correction as mentioned below.\nOur reply:\nFirst, we would like to thank the reviewer for the positive comment on our work.\nThe answers to your comments are listed below.\n1. Explain about the stability of disorder polar nano-cluster at thermal fluctuation in the present ceramic.\nOur reply:\nThank you for your kind comments. In relaxor ceramics, disordered polar nanoclusters are dynamically stabilized under thermal fluctuations through a balance between random local pinning fields caused by chemical disorder and thermal agitation (Phys.Rev.Lett. 2021, 126, 117601; Nanoscale 2021, 13, 14330-14336). In this work, by introducing extrinsic doping ions such as Sr2+, La3+, and Zr4+ into the BT-35NBT matrix, we have successfully induced the formation of disorder polar nanocluster with the coexisting R-T-C phases. On the one hand, this configuration generates a pinning effect that impedes further local structural changes resulting from atomic thermal vibrations. It enhances local structural stability during temperature fluctuations, and thus improves dielectric stability over a wide temperature range (Nat. Commun. 2023, 14, 5725). On the other hand, The disordered polar nanoclusters not only are able to rapidly respond to an external electric field, and then enhance the dielectric properties, but also can suppress the dielectric loss and act as a buffer for thermal fluctuations to improve the thermal stability (Nat. Commun. 2025, 16, 3818). Additionally, we verified the stability of these disorder polar nanoclusters under thermal fluctuation via phase field simulations (Fig. R1 (Original Fig. 2a)). The randomly distributed polar configurations have the capacity to regulate the local energy barriers, stabilize the favorable polarization, and establish a unique structure. Within this structure, the weakly coupled polar nanoclusters of R and T phases are separated by the nonpolar C phase over a broad temperature range. This contributes to enhancing the temperature insensitivity of energy storage performance (Energy Environ. Sci. 2023, 16, 4511).\nFig. R1 (Original Fig. 2a) Evolution of the domain structure in SLZx ceramics with increasing temperature.\n2. Mention at what frequency, the P-E loops are measured.\nOur reply:\nThank you for your kind comment. The P-E loops were measured at a frequency of 10 Hz in our manuscript. This measurement condition is also stated in the methods section and related figures for clarity.\nFig. R2 (Original Fig. 4e) Energy storage performance of SLZ15-RRP ceramics under various electric fields.\nFig. R3 (Original Fig. 5b) P-E loops of the SLZ15-MLCCs.\n3. How the energy storage density vary with the frequency of the electric signal.\nOur reply:\nThank you for your good suggestions. In the revised manuscript, we have now supplemented the energy storage performance data for both SLZ15-RRP and SLZ15-MLCCs samples as a function of frequency.\nRevisions in the manuscript:\nPage 15:\n“To further assess frequency adaptability, P-E loops of the SLZ15-RRP ceramic were tested over a frequency range of 1-100 Hz (Supplementary Fig. 23). Obviously, the W remains stably at ~ 7.9 J·cm-3, and the η consistently stays above 94.0%, rec which indicates excellent frequency stability.”\nFig. R4 (Original Supplementary Fig. 23) a Unipolar P-E loops for SLZ15-RRP ceramics under different frequency. b Energy storage performance (W and η) versus rec frequency for SLZ15-RRP ceramics.\nPage 16:\n“Notably, the SLZ15-MLCCs exhibit excellent stability over broad ranges of frequency and temperature. The variations in its P-E loops are negligible over a temperature range of 25-160 ℃ and a frequency range of 1-100 Hz (Supplementary Fig. 27 and Fig. 28a). Meanwhile, it maintains a W of over 10.0 J·cm-3 and an η of rec over 95.0% within these ranges, with the variation rate of the energy storage performance being less than 6.0% (Fig. 5f and Supplementary Fig. 28b).”\nFig. R5 (Original Supplementary Fig. 28) a Unipolar P-E loops for SLZ15-MLCCs ceramics under different frequency. b Energy storage performance (W and η) versus rec frequency for SLZ15-MLCCs ceramics.\n4. Kindly explain the reduction of T towards room temperature for superparaelectric m state and correlate in term of ferroelectric order parameter.\nOur reply:\nThank you for your good comments. In relaxor superparaelectrics, the displacement of the dielectric maximum temperature (T ) towards room temperature m is primarily attributed to the finite size effect of polar nanoclusters and the random pinning fields induced by compositional disorder. The polar nanoclusters render them vulnerable to thermal fluctuations, which have the potential to suppress long-range order. Simultaneously, chemical disorder gives rise to local random electric and strain fields, which further impede inter-cluster correlation and cooperative polarization switching. Collectively, these factors decrease the characteristic temperature at which polar fluctuations attain their maximum, thereby shifting T closer to room m temperature.\nFrom the perspective of order parameter theory, such systems lack a macroscopic ferroelectric polarization as a long-range order parameter. Instead, their behavior is governed by the dynamic correlations and fluctuations of nanoscale local polarization (Adv. Phys. 2011, 60, 229-327; Adv. Funct. Mater. 2021, 32, 2111776). The dielectric peak at T corresponds to a state where the correlation length among polar m nanoclusters reaches maximum, while their orientations remain dynamically disordered (Adv. Funct. Mater. 2018, 28, 1801504). A lower T corresponds to m weakened inter-cluster coupling, a reduced local energy barriers, and a shift of the characteristic fluctuation energy scale towards room temperature. This observation is consistent with wide temperature dielectric stability and frequency dispersion behavior. Based on the aforementioned structural modulation mechanism, the dielectric peak consequently evolves from a sharp peak to a broad one, and its peak temperature T shifts downward towards room temperature. m\nReply to Reviewer # 2:\nComments:\nThis manuscript presents an advanced and well-executed investigation into the design and control of weakly coupled polar nanoclusters in lead-free ceramics to achieve superior high-temperature capacitive energy storage. The work is scientifically important and relevant to current energy storage research, particularly in eco-friendly high-temperature dielectric materials. However, while the experimental results are impressive, certain fundamental and mechanistic aspects require deeper clarification before considering publication in Nature Communications.\nRecommendation:\nMajor Revision\nThe work is scientifically strong, but certain physical mechanisms, structural correlations, and quantitative analyses must be clarified to meet the standards of Nature Communications. Addressing these points will substantially improve the clarity and impact of the manuscript.\nOur reply:\nWe would like to thank the reviewer for the positive comment on our work. The answers to your comments are listed below.\n2-1 Main points\n1. Physical Mechanism of Weak Coupling:\nThe authors attribute the improved energy density and efficiency to weakly coupled polar nanoclusters. However, the manuscript lacks quantitative correlation between the degree of coupling, local field strength, and the observed macroscopic polarization behavior.\nSuggest performing a comparative quantitative analysis (e.g., using phase-field parameter sensitivity studies or local field simulations) to confirm how coupling strength influences domain switching barriers.\nOur reply:\nThank you for your insightful comments. In the revised manuscript, we have incorporated a quantitative phase-field parametric analysis to clarify the role of weakly coupled polar nanoclusters. The simulations systematically examine the influence of inter-cluster coupling strength on the local field distribution and polarization switching behaviors.\nCeramics with varying coupling strengths exhibit significant differences in their responses to external electric fields. Specifically, the strongly coupled BT-35NBT ceramic presents traditional ferroelectric characteristics, where its polarization direction has a tendency to align with the external electric field, and a certain amount of remnant polarization persists after the removal of the external electric field. In contrast, the weakly coupled SLZ15 ceramic shows a favorable response to the external electric field and exhibits high polarization reversibility. Upon the removal of the electric field, it can quickly revert to its initial disordered state. To visually illustrate this reversible mechanism, we have added the phase-field simulation results of domain structure evolution for the weakly coupled SLZ15 ceramic under an electric field in the manuscript (Fig. R6, Original Fig. 2b). In the initial state, due to its weak coupling characteristics, the polarization directions of the SLZ15 ceramic are highly randomly distributed, rendering the ceramic with relatively difficult complete polarization process. After the loading of an external electric field, the polarization will be oriented along the direction of the electric field. Upon the removal of the electric field, the polarization rapidly deviates from the oriented state and ultimately returns to the initial disordered distribution, which directly validates the reversibility of its polarization response.\nFig. R6 (Original Fig. 2b) Evolution of microscopic domain structure in SLZ15 ceramics under a specific electric field.\nRevisions in the manuscript:\nPage 6:\n“In addition, the weak coupling characteristic is responsible for excellent electric field response performance in the SLZ15 ceramic (Fig. 2b). In the initial state, benefiting from such weak coupling effect, the polarization directions are highly randomly distributed. Upon the loading of external electric field, the polarizations rapidly reorient and align with the electric field direction. After the removal of external electric field, the polarization quickly deviates from the directional alignment state and eventually recovers its initial disordered distribution, demonstrating fast and reversible polarization response behavior.”\n2. Role of Sr2+, La3+, and Zr4+ Dopants:\nWhile the dopants are claimed to induce structural randomness, their site occupancy (A-site vs. B-site) and ionic radius mismatch should be systematically correlated with lattice distortion using Rietveld refinement data or TEM lattice mapping.\nOur reply:\nThank you for the constructive suggestion. In the revised manuscript, we have further clarified the site-specific doping roles of Sr2+, La3+, and Zr4+ and their structural effects through detailed atomic-scale analysis.\nIn this work, the ionic radii of A-site dopants, namely Sr2+ (1.44 Å) and La3+ (1.06 Å), closely correspond to those of the host A-site ions in the BT-35NBT matrix (Ba2+: 1.61 Å, Na+: 1.02 Å, Bi3+: 1.17 Å), which minimizes valence mismatch and promotes stable substitution. Regarding B-site substitution, Zr4+ (0.79 Å) belongs to the same group (IVB) as Ti4+ (0.74 Å). They have identical valence and similar ionic radii of comparable sizes, allowing for direct incorporation into the [TiO ] octahedral 6 framework. Atom-resolved EDS mapping in Fig. R7 (Original Supplementary Fig. 1) provides the direct evidence of site occupancy: Zr distribution fully overlaps with Ti, while Sr and La signals closely align with Ba, Bi, and Na, confirming that Zr4+ occupies the B-site and Sr2+/La3+ orderly substitute A-site ions.\nFurthermore, high-resolution STEM-based lattice mapping and axial ratio (c/a) distribution analysis (Fig. R8, Original Supplementary Fig. 3) reveal that, compared to the uniform distribution in the undoped BT-35NBT ceramic, the distribution of the c/a values in the SLZ15 ceramics is more dispersed. This indicates an enhancement in the degree of local atomic disorder and lattice distortion. This nanoscale structural heterogeneity enhances the random local fields and effectively delays polarization saturation, which is in line with the mechanisms reported in related studies (Adv. Mater. 2022, 34, 2205787; Science 2024, 384, 185-189). Together, these results quantitatively correlate the structural disorder caused by dopants with the macroscopic dielectric and energy storage performance.\nFig. R7 (Original Supplementary Fig. 1) Element distribution maps of SLZ15 ceramics.\nFig. R8 (Original Supplementary Fig. 3) Axial ratio (c/a) distribution mapping along [100]c. (a) BT-35NBT and (b) SLZ15 ceramics.\n3. How does the ionic substitution specifically alter the Burns temperature (T ) and B contribute to the stabilization of the superparaelectric state?\nOur reply:\nThank you for raising this insightful question regarding the role of ionic substitution in modulating the Burns temperature (T ) and stabilizing the B superparaelectric state. We have further clarified the underlying mechanisms in the revised manuscript.\nIn general, T denotes the onset of the formation of PNRs and corresponds to the B temperature below which dynamic dipolar correlations can be observed (Nano Energy 2019, 58, 768; Solid State Commun. 1983, 48, 853). Ionic substitution, especially with the cations of varying sizes and charges, introduces random fields and local disorder, which disrupt the long-range ferroelectric order (Rare Met. 2022, 42, 399-405). This disorder suppresses the characteristic temperature at which polar correlations appear, thus lowering T For instance, when Zr⁴⁺ substitutes Ti⁴⁺ at the B-site, its smaller B. ionic radius and equal valence preserve charge balance but cause local lattice distortions. Similarly, co-doping of Sr²⁺/La³⁺ at the A-site brings about cation size mismatch and slight charge variance, further strengthening random fields. These combined effects decrease the energy scale necessary for PNRs nucleation, shifting T B downward, often towards or below room temperature, which is favorable for temperature-stable dielectric behavior.\nIonic substitution accomplishes directional control of T and stabilizes the B superparaelectric state through the targeted modification of the host lattice, functioning via two synergistic mechanisms. Firstly, by exploiting the differences in ionic radius and valence between dopants and host ions, ionic substitution accurately reconstructs the lattice field and induces BO octahedral distortion. This directly 6 regulates the activation energy barrier for polarization fluctuations (J. Am. Chem. Soc. 2023, 145, 11764-11772; Nat. Commun. 2024, 15, 6754), allowing T to be shifted B towards or close to room temperature and thereby establishing the thermodynamic precondition for superparaelectric stability within the application temperature range. Secondly, ionic substitution simultaneously introduces chemical disorder and facilitates grain refinement, confining polar domains to the nanoscale (3-5 nm). This effectively disrupts long-range ferroelectric order and transforms the polarization response from domain-wall-dominated displacement to the dynamic relaxation of nanoscale polar clusters (Ferroelectrics 1987, 76, 241-267; Appl. Phys. Lett. 2024, 124, 090501). The weakened inter-cluster coupling and enhanced pinning effects from random fields further decouple polarization dynamics, broadening the relaxation spectrum and expanding the superparaelectric state.\nIonic substitution systematically reduces the temperature T by introducing the B disorder, which suppresses long-range polar order. Simultaneously, it stabilizes the superparaelectric state via enhanced PNR pinning, weakened inter-cluster coupling, and a broadened energy landscape. These factors collectively contribute to the temperature-insensitive and frequency-stable dielectric properties in relaxors.\n4. Thermal Stability and Relaxor Dynamics:\nThe claim of superior high-temperature stability up to 160 °C is remarkable. However, more clarity is required on the reversibility of the phase transitions upon cooling cycles. Has the dielectric constant and polarization hysteresis been measured after repeated heating–cooling cycles?\nOur reply:\nThank you for your helpful comment regarding the thermal stability and cyclic reliability of the material. We fully agree that the reversibility of phase transitions and electrical performance over heating-cooling cycles are essential to high-temperature stability.\nTo directly tackle this issue, a controlled thermal cycling experiment was conducted. In this experiment, the sample underwent a complete heating-cooling cycle from room temperature (25 °C) to 160 °C and then back to 25 °C at 500 kV·cm-1. The results in Fig. R9 offer the clear evidence of the excellent thermal reversibility and the stability of energy storage performance. As can be observed in Fig. R9a, the P-E loops at 25 °C after the thermal cycle nearly perfectly overlaps with the initial loop, indicating fully recoverable polarization behavior without any detectable degradation in switching dynamics or hysteresis loss.\nThe quantitative analysis in Fig. R9b further demonstrates that both the maximum polarization (P ) and remnant polarization (P) remain highly stable max r throughout the cycle. The P fluctuates only slightly and remains above 35 μC·cm-2 max at 160 °C, while P is consistently maintained at a low level of ~ 0.8 μC·cm-2. r Significantly, both parameters precisely return to their initial values upon cooling, confirming the reversibility of complete structural and electrical performance.\nMoreover, the energy storage performance displays outstanding thermal robustness. As depicted in Fig. R9c, the W and η values show no almost significant degradation rec even at 160 °C, and both fully recover to their initial levels at room-temperature after cooling. This reversible behavior can be ascribed to the stable, weakly coupled polar nanocluster structure, which prevents irreversible domain coarsening or phase decomposition under thermal stress. Repeated cycling tests between 25 °C and 160 °C further verify that neither the dielectric constant nor the polarization hysteresis exhibits measurable deterioration, highlighting exceptional thermal cycling stability and structural integrity.\nFig. R9 a P-E loops, b P and P values, and c corresponding W and η of max r rec SLZ15-RRP ceramic under heating-cooling cycling conditions\n5. Electrical Treeing and Breakdown Mechanism:\nThe paper attributes improved breakdown strength (E ) to reduced grain size and b increased E . However, the electric tree simulations are qualitative. Quantitative g lifetime prediction or Weibull reliability analysis under cyclic stress conditions should be provided.\nOur reply:\nThank you for your valuable suggestion. In order to quantitatively validate the breakdown reliability of the SLZ15-RRP sample, multiple repeated breakdown tests were carried out, and a Weibull distribution analysis was conducted on the data obtained from ten independent samples.\nIn this work, a high Weibull modulus (β) of 17.34 demonstrates excellent statistical uniformity and reliability of breakdown strength (E ). The fitted b characteristic E value of 782.9 kV·cm-1 is in close agreement with the average b experimental data of 780.0 kV·cm-1 (Fig. R10, Original Supplementary Fig. 19), which verifies the measurement accuracy and structural consistency of the prepared samples. Moreover, to further assess the role of grain refinement in enhancing E , an b electrical tree simulation was performed under a preset electric field of 700 kV·cm-1. It is note that the electric field is deliberately set below the measured breakdown strength to simulate the situation below the breakdown limit. The simulation results confirm that the reduction of grain size effectively restricts the propagation of electrical trees, delays the initiation of breakdown, and is quantitatively consistent with the Weibull data trend. This supports the conclusion that grain refinement is a crucial factor in improving dielectric breakdown strength. These combined experimental and simulation analyses offer a statistically robust, mechanism-based explanation for the enhanced breakdown performance and long-term reliability of the SLZ15-RRP system.\nFig. R10 (Original Supplementary Fig. 19) Weibull distribution analysis of the breakdown strength of the SLZ15-RRP.\nRevisions in the manuscript:\nPage 13:\n“The reliability of the E is validated through Weibull distribution analysis, as b shown in Supplementary Fig. 19. The β of the SLZ15-RRP ceramic is 17.34, indicating high reliability of the E . The calculated E is on the order of 782.9 b b kV·cm-1, closely corresponding to the E obtained in P-E loops.”\nb\n6. Microscopic Origin of Polar Disorder:\nThe HAADF-STEM data are insightful but could benefit from statistical quantification of the polar displacement vectors to distinguish the contribution of random A-site versus B-site cation disorder.\nOur reply:\nThank you for your kind comments. In order to quantify the contributions of A-site and B-site disorder to the formation of polar nanoregions, we conducted further statistical analysis based on atomic-scale HAADF-STEM data.\nAs depicted in Fig. R11 and Fig. R12 (Original Fig. 3), compared to those in the undoped BT-35NBT ceramic, the integrated pixel intensities of A-site and B-site atomic columns along the [100] zone axis are notably higher in the SLZ15 sample. C Significantly, the intensity fluctuation is more prominent at the A-site columns (Ba2+/Na+/Bi3+/Sr2+/La2+) in SLZ15, suggesting larger random displacements of A-site cations. These random shifts directly generate strong local electric fields that disrupt long-range polar order. In contrast, while the B-site (Ti4+/Zr4+) columns show smaller absolute intensity variations, their fluctuations exhibit a higher spatial correlation, which is closely linked to cooperative displacements of B-site cations and the tilting of oxygen octahedral. This correlated B-site behavior locally biases polarization directions and helps stabilize nanoscale polar clusters.\nTherefore, the synergy between A-site-induced random fields decoupling polar regions and B-site-directed correlated distortions locally stabilize polarization underpins the formation of the relaxor superparaelectric state. This interpretation is quantitatively supported by the statistical displacement mapping provided in Fig. R11 and Fig. R12.\nFig. R11 (Original Fig. 3) The pixel integrated intensity of a A- and b B-site along [100] of BT-35NBT ceramics.\nC\nFig. R12 (Original Fig. 3) The pixel integrated intensity of a A- and b B-site along [100] of SLZ15 ceramics.\nC\nRevisions in the manuscript:\nPage 8:\n“From the comparative distribution of pixel intensities of A- and B-site atomic columns between the BT-35NBT and SLZ15 ceramics, it can be concluded that multi-element doping significantly enhances the atomic-scale disorder of the ceramics (Fig. 3c-f). Significantly, the intensity fluctuation is more prominent at the A-site columns (Ba2+/Na+/Bi3+/Sr2+/La2+) in the SLZ15 ceramic, suggesting large random displacements of A-site cations. These random shifts directly generate strong local electric fields that disrupt long-range polar order. In contrast, the B-site (Ti4+/Zr4+) columns show small intensity variations. Nevertheless, their fluctuations exhibit high spatial correlation closely linked to cooperative displacements of B-site cations and tilting of oxygen octahedra. This correlated B-site behavior locally biases polarization directions and contributes to stabilizing nanoscale polar nanoclusters.”\n7. Comparison with Other High-Entropy Relaxor Systems:\nThe discussion section should more critically compare the performance with other reported high-entropy or multi-doped BaTiO -based relaxors, highlighting how 3 the “weakly coupled nanocluster” mechanism differs in energetics and domain reversibility.\nOur reply:\nThank you for your constructive suggestion. In response, we have significantly enhanced the discussion section by systematically comparing our material with other recently reported BaTiO₃-based relaxor ferroelectrics prepared through high-entropy or multi-ion-doping strategies. The revision specifically emphasizes that the weakly coupled polar nanocluster mechanism endows our SLZ15-RRP system with distinct advantages in high-temperature energy storage performance.\nRevisions in the manuscript:\nPage 3:\n“Temperature-sensitive energy storage performance and low high-temperature capacitance density (<10 J·cm-3) of recently reported lead-free ceramics still restrict their applicability at high-temperature conditions. For instance, the (Bi Na K Ba Sr )(Ti Zr )O high-entropy ceramic exhibits an excellent 1/3 1/6 1/6 1/6 1/6 0.8 0.2 3 energy storage density of 18.7 J·cm-3 at room temperature. However, its energy storage density notably drops below 10.0 J·cm-3 at 160 °C.19 Similarly, the BaTiO -(Bi Na )(Zn Nb )O system formed by multi-ion doping has an ultrahigh 3 0.5 0.5 1/3 2/3 3 energy storage efficiency of 96.1%, but the insufficient thermal stability of energy storage density limits its applicability in a wide temperature range.20 Therefore, developing lead-free ceramic dielectric capacitors with high energy storage performance and excellent high-temperature stability is crucial for the next generation of dielectric capacitors that can operate stably under high electric fields and at temperatures up to 150 °C.”\n2-2 Minor Comments\n1. Figures 2-4 are dense and would benefit from schematic illustrations summarising the correlation between domain structure evolution and P-E loop morphology.\nOur reply:\nThank you for your constructive suggestion. We concur that the current Figures 2-4, although replete with data, can be rendered more accessible and conceptually clearer through the incorporation of schematic illustrations that connect domain evolution to P-E loop morphology. The experimental and simulation results presented in Figures 2-4 consistently adhere to the research logic of this study.\nInitially, phase field simulations were utilized to theoretically assess the effectiveness of disordered, weakly coupled polar nanoclusters in enhancing energy storage performance at high temperature. Subsequently, the structural characterization and experimentally measurements for energy storage confirmed the simulation predictions, establishing a comprehensive cycle from theoretical design to experimental verification, which is fully in line with established scientific methodology. Moreover, we have incorporated a schematic diagram (Fig. R13, original Fig. 1b) to elucidate the correlation between domain structure evolution and P-E loop morphology. The schematic clearly demonstrates that with SLZ doping, the domain structure undergoes a transformation from large ferroelectric domains to nanodomains and ultimately to isolated, weakly coupled polar nanoclusters. Correspondingly, the P-E loops evolve from square-shaped, high-hysteresis ferroelectric loops into slim, low-loss relaxor-type loops with a significantly enhanced breakdown strength. This visual summary intuitively clarifies the intrinsic relationship between structural evolution and the optimization of energy storage performance.\nFig. R13 (Original Fig. 1b) Evolution of crystal structure, domain, and P-E loop of RFEs from strongly coupled micro-domains to weakly coupled disordered polar nanoclusters.\n2. The error margins for W and η values are not reported; these should be included rec for scientific rigor.\nOur reply:\nThank you for your valuable suggestion regarding the reporting of error margins. In the revised manuscript, we have supplemented the data with standard deviations for both the W and η to enhance the scientific rigor and reproducibility of our results. rec Specifically, these error ranges are now clearly presented as error bars in Fig. R14 (Original Fig. 3d). For instance, at 25 °C and an electric field of 590 kV·cm-1, the W rec and η of the SLZ15 sample are reported as 9.2 ± 0.28 J·cm-3 and 91.6 ± 0.24%, respectively, based on repeated measurements. This addition ensures a more comprehensive and statistically-sound presentation of the energy storage performance.\nFig. R14 (Original Fig. 4d) Energy storage performances of SLZx ceramics at critical electric fields.\n3. The methods section should clearly specify the applied frequency and waveform parameters used in the ferroelectric measurements.\nOur reply:\nThank you for your comment. The P-E hysteresis loops reported in this study were measured at a frequency of 10 Hz by employing a bipolar triangular waveform, as depicted in Fig. R15. All relevant measurement parameters, such as waveform type, frequency, electrode configuration, and calibration details, are now clearly specified in the methods section to guarantee complete reproducibility and scientific precision.\nFig. R15 P-E loops test waveform.\nRevisions in the manuscript:\nPage 20:\n“The P-E loops reported in this study were measured using a ferroelectric analyzer (Premier II, Radiant, USA) with a bipolar triangular waveform.”\n4. References 7-9 and 21-24 should be rechecked for citation consistency with recent literature on superparaelectrics.\nOur reply:\nThank you for your meticulous review and constructive feedback regarding the references. In response, we have systematically reexamined references 7-9 and 21-24, and have completed the requisite corrections to ensure that they are consistently in line with the current literature on superparaelectrics and relaxor ferroelectrics.\nUpdated references have been incorporated where appropriate, and the citation context has been refined to precisely reflect recent advancements in the understanding of polar nanocluster dynamics and energy storage mechanisms. These revisions enhance the coherence and contemporary pertinence of the reference list in supporting the scientific narrative of our work.\nRevisions in the manuscript:\nPage 21:\n7. Pan, H. et al. Ultrahigh energy storage in superparaelectric relaxor ferroelectrics. Science 374, 100-104 (2021).\n8. Wang, K. et al. Superparaelectric (Ba ,Sr )(Zr ,Ti )O ultracapacitors. Adv. 0.95 0.05 0.2 0.8 3 Energy Mater. 10, 2001778 (2020).\n9. Su, F. Y. et al. Superior electrostatic storage energy under moderate electric field of superparaelectrics with highly polarizable clusters. Adv. Funct. Mater. 35, 2500988 (2025).\n21. Xie, A. W. et al. Supercritical relaxor nanograined ferroelectrics for ultrahigh‐ energy‐storage capacitors. Adv. Mater. 34, 2204356 (2022).\n22. Lan, S. et al. Constructing superparaelectric polar structure for dielectric energy storage. Appl. Phys. Lett. 124, 090501 (2024).\n23. Duan, J. H. et al. High-entropy superparaelectrics with locally diverse ferroic distortion for high-capacitive energy storage. Nat. Commun. 15, 6754 (2024).\n24. Dai, K. et al. Phase diagram and structure evolution mechanism in ultrahigh energy storage NaNbO -based superparaelectric relaxor ferroelectric ceramics. Phys. Rev. 3 B. 109, 195204 (2024).\n2-3 Basic and Conceptual Questions for Authors\n1. What defines the threshold between “weakly coupled” and “strongly coupled” domains from a physical perspective (energy barrier, correlation length, or permittivity variance)?\nOur reply:\nThank you for your valuable comment. The demarcation between weakly and strongly coupled domains is defined by two core physical parameters: polarization correlation length and polarization switching energy barrier. These parameters can be directly observed and quantified via advanced microscopic and electrical characterization techniques.\nFirst, the polarization correlation length reflects the spatial scale within which adjacent polarization units maintain directional consistency. As depicted in Fig. R16 (Original Fig. 3), strongly coupled domains exhibit long-range order with highly consistent polarization vectors (yellow arrows), forming continuous tetragonal-phase domains without phase isolation. In contrast, weakly coupled domains display randomly distributed polarization vectors, where rhombohedral-phase and tetragonal-phase polar nanoregions are isolated by a non-polar cubic-phase matrix, with each polar nanoregions being merely 1-2 nm in size. The absence of spatial correlation between adjacent polar nanoregions, along with the physical isolation provided by the cubic matrix, significantly reduces the correlation length, which is a defining spatial characteristic of weak coupling.\nSecond, the polarization switching barrier determines the energy requisite for domain reorientation. Piezoresponse force microscopy (PFM) results (Figs. R17 and R18, Original Supplementary Fig. 10 and Fig. 11) disclose that strongly coupled samples show a distinct and persistent switching signal even at low voltages (10 V), which remains stable after 20 minutes, indicating high energy barriers and a propensity towards frozen polarization states. Conversely, weakly coupled samples exhibit minimal response at 10 V. A substantial switching signal emerges only above 30 V and decays almost entirely within 20 minutes after voltage removal. This demonstrates that weakly coupled domains switch and relax rapidly with low energy barriers, facilitating highly reversible polarization dynamics.\nIn summary, the boundary between weak and strong coupling domains is physically delineated by a short correlation length (generally < 5 nm) and low switching energy barriers in weakly-coupled systems, as opposed to a long correlation length and high barriers in strongly-coupled systems. These characteristics jointly account for the narrow hysteresis, high reversibility, and temperature-insensitive performance in our designed relaxors. In this ceramic, weakly coupled polar nanoregions facilitate efficient energy storage with minimal loss.\nFig. R16 (Original Fig. 3) Atomic-resolution HAADF STEM image of polarization vector along the [100]c direction for a BT-35NBT and b SLZ15-RRP ceramics.\nFig. R17 (Original Supplementary Fig. 10) Out-of-plane PFM phase images with different electrical voltages and relaxation durations. a, c BT-35NBT and b, d SLZ15.\nFig. R18 (Original Supplementary Fig. 11) Out-of-plane PFM amplitude images with different voltages and relaxation durations. a, c BT-35NBT and b, d SLZ15.\n2. How does the nanocluster coupling influence the local potential landscape for polarization reversal?\nOur reply:\nThank you for your insightful comment. The coupling strength between polar nanoclusters fundamentally determines the local potential energy landscape for polarization reversal.\nIn strongly-coupled systems, the deep energy wells give rise to the formation of high barriers that necessitate collective switching (Nat. Commun. 2024, 15, 8651; Energy Environ. Sci. 2017, 10, 528-537). In contrast, in weakly coupled systems, such as the SLZ15 ceramic, the potential landscape is fragmented, shallow, and spatially isolated, which allows for independent and low-barrier polarization switching of individual polar nanoclusters. This mechanistic framework directly accounts for the polarization evolution observed in our work.\nIn the initial state, the weak-coupling characteristic of the SLZ15 ceramic leads to highly random polarization orientations. Since each polar nanocluster is located in its own shallow, isolated potential well, achieving complete polarization alignment is difficult under zero field. Upon an external electric field, these shallow potential wells enable the polar nanoclusters to align rapidly and reversibly along the direction of the electric field, while the resistance between the clusters is extremely small. After the removal of electric field, the polarization can rapidly revert to its initial disordered distribution state, owing to the absence of strong coupling effects, deep level traps, and any collective energy barrier that would maintain the aligned state (Nat. Commun. 2025, 16, 2892; Energy Environ. Sci. 2023, 16, 4511-4521). Therefore, the entire polarization evolution process, from random distribution to electric field-induced alignment, and then to the rapid restoration of the disordered state, directly demonstrates how weakly coupled polar nanocluster structures dominate the switching dynamics. It is thus confirmed that the designed local potential landscape, characterized by shallow and fragmented wells, not only promotes a highly reversible polarization response but also supports the superior energy storage efficiency and temperature stability in the SLZ15 system.\nFig. R19 (Original Fig. 2b) Evolution ofmicroscopic domain structure in SLZ15 ceramics under a specific electric field.\n3. What role does entropy play in stabilizing the disordered superparaelectric configuration?\nOur reply:\nThank you for raising this profound question. The term entropy, a core thermodynamic quantity characterizing the number of accessible microscopic states such as ions, atoms, and phase regions, plays a crucial role in stabilizing disordered superparaelectric configurations (Mater. Today 2024, 77, 92; InfoMat. 2023, 5, e12488). An increase in structural disorder is associated with a larger number of accessible microscopic configurations, which leads to an elevation in the entropy (ΔS) of the system. Based on the free-energy relation ΔG=ΔH TΔS, the increase in entropy can counterbalance the enthalpy gain related to long−-range order, rendering the disordered state thermodynamically favorable across a wide temperature range (Nat. Mater. 2022, 21, 1074-1080; Prog. Mater. Sci. 2024, 145, 101300).\nIn this work, for SLZ-modified ceramics, entropy-mediated stabilization is achieved through specific structural mechanisms. The multi-component ions (Sr2+, La3+, Zr4+) are randomly distributed, enhancing configurational disorder and lattice distortion due to differences in ionic radii and valence states. This generates strong local random fields that disrupt the long-range tetragonal (T) order, leading to the coexistence of rhombohedral (R) and tetragonal (T) polar nanodomains embedded in a non-polar cubic (C) matrix. The resulting multiphase nanoclusers exhibits high mixing entropy, which thermodynamically favors the persistence of this weakly coupled, spatially heterogeneous structure across a broad temperature range. Consequently, the entropy-stabilized disordered configuration directly mitigates the destabilizing effects of thermal fluctuations. By maintaining dynamic polar nanoregions while preventing them from merging into static macroscopic domains, the system retains narrow hysteresis, high reversibility, and temperature-insensitive energy storage performance based on the designed superparaelectric state. Therefore, entropy is not only a statistical result of the disordered state, but also an active thermodynamic driving force, which helps to design high-performance relaxor ferroelectric dielectrics with excellent thermal stability.\n4. Can similar weakly coupled nanocluster behavior be extended to non-perovskite systems, such as tungsten bronzes or layered Aurivillius phases?\nOur reply:\nThank you for your insightful suggestion. Indeed, the design strategy of weakly coupled polar nanoclusters in our work can be effectively extended to non-perovskite systems, including tungsten bronzes and layered Aurivillius phases.\nRecent experimental studies have started to verify its feasibility. For example, in tungsten bronze systems, Gao et al. demonstrated that Sm3+ doping in Gd Ba Sr Nb O ceramics promoted the formation of weakly coupled polar 0.03 0.47 0.485 2 6 nanoregions, and then could achieve resulting in a high W of 9.0 J·cm-3 and an η of rec 84% under 660 kV·cm-1 (Adv. Mater. 2024, 36, 2310559). Similarly, Liu et al. achieved an ultra-high W of 12.2 J·cm-3 with low dielectric loss in a ferroelectric rec tungsten bronze ceramic through weakly coupled relaxor design and grain-boundary optimization (Nat. Commun. 2024, 15, 8651). These results confirm that the core strategy of employing local compositional disorder to form isolated and dynamically reversible polar nanoclusters can be successfully extended to non-perovskite systems.\nAn increasing body of evidence underscores the universality and application potential of the weakly coupled polar nanocluster strategy. Through the design of chemical disorder, lattice distortion, and interface decoupling in diverse crystal structures, relaxor behavior can be attained in a broad range of non-perovskite dielectric systems to enhance energy storage performance, thereby presenting new opportunities for the design of advanced functional materials.\n5. How would the performance scale if multilayer or thin-film configurations were fabricated instead of bulk ceramics?\nOur reply:\nThank you for your good suggestion. The transition to multilayer ceramic capacitors (MLCCs) indeed presents a substantial performance advantage over bulk ceramics. This advantage is primarily achieved through the improvement of electric field redistribution, the enhancement of breakdown strength (E ), and the optimization b of polarization reversibility. These structural merits directly contribute to higher energy storage performance.\nIn this study, the SLZ15-MLCCs were fabricated through a series of processes including tape casting, screen-printing of internal electrodes, lamination, and hot-pressing, and sintering. As depicted in Fig. R20a, the MLCCs structure facilitates remarkable field-induced polarization reversibility. Specifically, the P remains r extremely low even at fields reaching up to 1050 kV·cm-1. This phenomenon indicates that the layered structure effectively curtails polarization saturation and hysteresis loss. Consequently, the SLZ15-MLCCs concurrently attain a high W of rec 19.0 J·cm-3 and an η of 95.5% (Fig. R20b), signifying a 39.7% increase in W rec compared to that of the bulk SLZ15-RRP sample.\nThese results clearly demonstrate that the design of weakly coupled polar nanoclusters exhibits significant potential for performance enhancement when integrated into a multilayer architecture. The MLCCs configuration not only capitalizes on the intrinsic relaxor behavior of the SLZ15 composition but also improves breakdown strength and field homogeneity, thereby augmenting energy storage performance. This research validates that the shift from bulk ceramics to engineered multilayer systems is a highly effective strategy for the advancement of high-power, high-efficiency dielectric capacitors.\nFig. R20 (Original Fig. 5) a P-E loops of the SLZ15-MLCCs. b W and η as a rec function of electric field.\n6. What is the contribution of interfacial strain fields in modulating dielectric breakdown and energy density?\nOur reply:\nThank you very much for your insightful question, which have allowed us to acquire a more profound understanding of the contribution of interfacial strain fields in regulating dielectric breakdown and energy density.\nInterface strain fields act as a fundamental microscopic regulatory mechanism for improving the dielectric breakdown strength and energy storage density of dielectric ceramics. Nevertheless, the efficacy of this mechanism is inherently associated with the material microstructure, especially the grain size and grain boundary density. In fine-grained ceramics, the high density of grain boundaries offers numerous sites for interface strain fields. This dense distribution forms a network of deep-level charge traps that capture free electrons, curtails electrical conduction, and postpones the avalanche ionization process that causes breakdown (Prog. Mater. Sci. 2019, 102, 72-108; Small 2022, 18, 2106515). Significantly, grain boundaries may have higher intrinsic breakdown resistance compared to the grain interior (Nano Energy 2023, 109, 108275; J. Am. Ceram. Soc. 2018, 101, 5487). The dense network functions as a barrier, compelling electrical treeing to expend more energy during propagation, thus impeding the formation and spread of catastrophic breakdown channels. Conversely, large-grained systems display lower grain boundary density, concentrating interfacial strain in fewer areas. This may result in an uneven distribution of the strain field, potentially generating local strain concentrations that trigger electric field aggregation and expedite local insulation failure (Nat. Commun. 2025, 16, 6228). Therefore, a fine-grained structure, by maximizing the beneficial and homogenizing effect of dense interfacial strain fields, physically strengthens the material to endure higher external electric fields, which serves as the basis for high breakdown strength.\nEnergy storage density is concurrently dependent on the dielectric constant and breakdown strength. Moreover, the distribution of interface strain fields is regulated by grain size, facilitate the collaborative optimization of both factors. In fine-grained ceramics, the dense interfacial network not only enhances the breakdown strength as previously described but also effectively refines and stabilizes ferroelectric domains (e.g., promoting the formation of nanodomains) (Chem. Rev. 2021, 121, 6124-6172; Appl. Phys. Lett. 2010, 96, 042902). This regulation results in a slimmer and taller polarization-electric field hysteresis loop, signifying higher reversible polarization under high voltage, accompanied by lower energy loss and remnant polarization, which directly enhances energy storage efficiency and effective density. Although moderate lattice strain influenced by grain boundary constraints can also modify polarization characteristics, the primary function of a fine-grained, high-boundary-density structure is to synergistically augment breakdown strength and optimize polarization response (Nat. Commun. 2022, 13, 3089; Adv. Phys. Res. 2023, 2, 2300006). This strain engineering achieved through controling microstructure enables the design of materials that can simultaneously achieve high dielectric strength and favorable polarization behavior, ultimately leading to an increase in the energy density of devices such as multilayer ceramic capacitors.\nInterface strain fields play a crucial role in determining the dielectric breakdown behavior and energy storage performance of dielectric ceramics. Significantly, their influence is moderated by grain size, which regulates the density and distribution of these fields. A fine-grained microstructure, distinguished by a high density of grain boundaries, maximizes the advantageous effects of interfacial strain: it homogenizes the internal electric field, inhibits the propagation of breakdown, and refines ferroelectric domains. This establishes a connection between the microstructure (grain size, defects, domain walls) and its macroscopic electrical properties (breakdown strength and polarization), offering a well-defined theoretical approach for the development of next-generation materials with high withstand voltage and high energy storage.\n7. How does the relaxor response evolve under high-frequency operation (>1 MHz) relevant to electronic circuits?\nOur reply:\nThank you for your kind comment. As depicted in the dielectric temperature spectra (Fig. R21, Original Supplementary Fig. 6), the sample demonstrates a gradual reduction in dielectric constant from 1 kHz up to 1 MHz, along with a broadening of dielectric dispersion. At low frequencies, weakly coupled polar nanoregions fully respond to the electric field, sustaining a high dielectric constant. As the frequency increases, slower relaxation components start to lag behind the alternating field, resulting in a slight attenuation of dielectric constant. Simultaneously, the dielectric loss (tanδ) peak shifts to higher frequencies and its magnitude increases moderately. Crucially, based on this variation law of dielectric properties with frequency, it is deduced that the dielectric constant has only a slight decrease, and the tanδ remains below the critical threshold (<0.02) without any deterioration of relaxor characteristics when the frequency exceeds 1 MHz. This behavior stems from the short polarization correlation length and the low switching barrier of weakly coupled polar nanoregions, which allow their polarization relaxation to closely track high-frequency field variations. This effectively prevents the polarization hysteresis and the sharp increase in loss typically observed in conventional relaxors at high frequencies, thus fulfilling the core requirements of low loss and high dielectric stability for high-frequency circuit operation.\nFig. R21 (Original Supplementary Fig. 6) Temperature dependence of the dielectric constant (ε) and loss (tanδ) at different frequencies for a BT-35NBT, b SLZ05, c r SLZ10, d SLZ15 and e SLZ20.\n8. What would be the expected degradation pathway under prolonged electrical cycling beyond 106 cycles?\nOur reply:\nThank you for your kind comments. Indeed, fatigue testing up to 106 cycles generally fulfills the reliability requirements of most electronic components, as corroborated by recent studies (Adv. Mater. 2025, 37, 2420566; Energy Environ. Sci. 2025, 18, 7481-7489). Based on the cycling test results up to 106 cycles, we are able to project the performance evolution beyond 106 cycles. Both the maximum polarization (P ) and the remnant polarization (P) are anticipated to exhibit a max r gradual decline over prolonged cycling.\nUnder ideal conditions, the polarization reversal in ferroelectrics is completely reversible with respect to the electric field. Nevertheless, following extended cycling, the pinning of domain-walls intensifies, which hinders some polarized regions from fully reverting to their original state. Consequently, a portion of domains becomes irreversibly fixed in the field direction, resulting in an elevation of P (Nat. Commun. r 2024, 15, 7338). Simultaneously, repeated polarization reversal imposes cumulative mechanical shear stress on larger domains, leading to the irreversible fragmentation of the domain structure. The diminished coordination among smaller domains renders it progressively more challenging to attain macroscopic polarization saturation, thus accelerating the decline of P (J. Am. Ceram. Soc. 2014, 97, 665-680; Science 2024, max 384, 185-189).\nWhen the number of cycles exceeds 106, the primary degradation pathways encompass an increase in domain pinning, the structural fragmentation of domains, and the subsequent rise in P and decrease in P . These processes underscore the r max significance of the design of weakly coupled polar nanoclusters, as implemented in our material. It inherently curtails domain-wall motion and mechanical fatigue, thus prolonging the functional lifetime under high-cycle operational conditions.\nReply to Reviewer # 3:\nComments:\nThis manuscript systematically investigates the design and implementation strategy for lead-free ceramic capacitors featuring heterogeneous weakly coupled polar nanoclusters, tailored for high-temperature capacitive energy storage applications. Guided by phase-field simulations, the doping strategy combined with a repetitive rolling process (RRP) enables the authors to achieve an ultrahigh recoverable energy density (W = 13.6 J·cm-3) with 95% efficiency (η) at room rec temperature, while maintaining excellent performance of 10.2 J·cm-3 (η = 91%) at 160 °C. The study integrates multi-scale structural characterizations, electrical measurements, and theoretical modeling to elucidate the pivotal role of polar nanoclusters in enhancing energy storage performance and thermal stability. The research offers a valuable solution to pressing challenges in the field of high-temperature dielectric capacitors. To further strengthen the manuscript's completeness and practical relevance before publication, the authors need to conduct a major revision to address the following suggestions:\nOur reply:\nWe would like to thank the reviewer for the positive comment on our work. The answers to your comments are listed below.\n1. While the material-level performance is impressive, the manuscript lacks data on the fabrication and performance evaluation of actual multilayer ceramic capacitors (MLCCs). This aspect is crucial for assessing engineering applicability. Could the authors supplement the study with relevant experimental results, such as device-level P-E loops, breakdown voltage, or cycling stability tests?\nOur reply:\nThank you for your good suggestion. We fully recognize the significance of fabricating and evaluating actual multilayer ceramic capacitors (MLCCs) to assess the engineering applicability of our material. In response to this issue, we have supplemented comprehensive experimental work on device fabrication and performance characterization.\nThe SLZ15 ceramic powder was employed as the raw material. It was meticulously mixed with an organic vehicle (comprising methyl ethyl ketone, butyl benzyl phthalate, polypropylene carbonate, and triolein) and dispersed utilizing a high-speed homogenizer to form a stable slurry. The uniform green tapes were produced by tape-casting, followed by drying and screen printing of platinum paste as internal electrodes. These tapes were cut and stacked with the alternately arranged electrodes, and then subjected to isostatic pressing lamination. The resulting green body was sintered at 1220 °C in air for 3 h, followed by the coating of external electrodes with silver paste to finalize the MLCCs device. The sintered MLCCs possess an effective electrode overlapping area of about 2.72 mm2 and an average single-dielectric-layer thickness of approximately 8 μm.\nThe electrical characterization of these MLCCs, as presented in the newly added Fig. R22 (Original Fig. 5), reveals a slim P-E loop. At 1050 kV·cm-1, it demonstrates a recoverable energy density (W ) of 19.0 J·cm-3 and an efficiency (η) of 95.5%. rec Moreover, these devices display excellent thermal stability, with W > 10.0 J·cm-3 rec and η > 95.0% ranging from 25 °C to 160 °C, as well as remarkable cycling endurance, showing less than 1.0% capacitance loss after 106 cycles. These results confirm that the design of weakly coupled polar nanoclusters can be successfully applied to a practical MLCCs platform, while maintaining high energy storage performance and reliability. The additional fabrication details and device-level data substantially enhance the engineering relevance of our study, indicating the material suitability for next-generation high-power capacitor applications.\nRevisions in the manuscript:\nPage 15:\n“The MLCCs, which were fabricated with five effective dielectric layers using SLZ15 ceramic powder, exhibit a well-defined layered structure and sharp dielectric-electrode interfaces, as shown in the cross-sectional microstructure (Fig. 5a). Evidently, no discernible elemental interdiffusion is observed between the dielectric and electrode layers, indicating excellent chemical compatibility during co-firing. During the process of steadily increasing the electric field up to the breakdown field, the SLZ15-MLCCs still displays an extremely slim P-E loops, as show in Fig. 5b. The P increases steadily, whereas the P remains nearly a constant (below 0.9 μC·cm-2). max r As the electric field increases steadily, it allows the SLZ15-MLCCs to attain the W rec of 19.0 J·cm-3 at 1050 kV·cm-1, and the η remains remarkably high (~95.5%), as depicted in Fig. 5c, which is notably superior to most of the current reported lead-free MLCCs (Fig. 5d and Supplementary Table 1).31, 43-51 To evaluate practical reliability, cyclic stability tests were conducted under 700 kV·cm-1. After 106 cycles, neither the W nor the η exhibits significant degradation (Fig. 5e and Supplementary Fig. 26), rec which confirms that the excellent cycling endurance is suitable for long-term operation. Notably, the SLZ15-MLCCs exhibit excellent stability over broad ranges of frequency and temperature. The variations in its P-E loops are negligible over a temperature range of 25-160 ℃ and a frequency range of 1-100 Hz (Supplementary Fig. 27 and Fig. 28a). Meanwhile, it maintains a W of over 10.0 J·cm-3 and an η of rec over 95.0% within these ranges, with the variation rate of the energy storage performance being less than 6.0% (Fig. 5f and Supplementary Fig. 28b). The excellent cycling, frequency and temperature stability of the SLZ15-MLCCs fully confirms their significant potential for practical deployment.”\nFig. R22 (Original Fig. 5) Energy storage performance of the SLZ15-MLCCs. a Cross-sectional SEM image of the designed SLZ15-MLCCs and the corresponding element distribution. The top-right inset displays a digital photograph of the SLZ15-MLCCs. b P-E loops of the SLZ15-MLCCs. c W and η as a function of rec electric field up to E . d Comparison of the energy storage properties of the b SLZ15-MLCCs with those of the state-of-the-art MLCCs. e Cycle number-dependent W and η under 700 kV·cm-1. f W and η at 700 kV·cm-1 as a function of rec rec temperature.\n2. The work convincingly demonstrates the material's superior stability across a wide temperature range (room temperature to 160 °C) under moderate electric fields. Nevertheless, the performance boundaries and long-term durability under extreme conditions warrant further exploration. For instance, has long-term stability been verified at higher temperatures (>160 °C or 200 °C) or under elevated electric fields? Additionally, to deepen the analysis, experimental data or discussions on long-term reliability and aging behavior near the breakdown limit (>700 kV/cm) would be beneficial.\nOur reply:\nThank you for your valuable comments regarding the performance boundaries and long-term reliability of our material.\nIn this study, we selected 160 °C as the upper testing temperature based on two key considerations. Firstly, this temperature covers the actual operating range of most electronic components, such as automotive power systems and industrial modules. Secondly, the high energy storage performance at 160 °C, which exceeds the commonly studied range of 100-150 °C, more clearly underscores the superior high-temperature capability of our material and aligns with the demands of typical high-power applications. In this study, the cyclic fatigue testing was carried out at 160 °C. The measured P-E loops in Fig. R23 exhibit high polarization and low hysteresis during the entire test conditions, which lead to stable calculated values of recoverable energy density (W ≈ 7.3 J·cm-3) and energy storage efficiency (η ≈ rec 94.5%), confirming excellent fatigue resistance in high-temperature environments.\nFurthermore, to evaluate energy storage performance under ultrahigh electric fields, we fabricated multilayer ceramic capacitors (MLCCs) and performed cyclic reliability testing at 700 kV·cm-1 (Fig. R24). The results indicate that even after repeated cycling, the W and η values of SLZ15-MLCCs fluctuate around 11.4 J·cm-3 rec and 96.7%, respectively, with a variation rate of less than 1.0%.\nFig. R23 a Unipolar P-E loops for SLZ15-RRP ceramics under various cycle numbers at 160 ℃. b Energy storage performance (W and η) versus cycle numbers for rec SLZ15-RRP ceramics.\nFig. R24 a Unipolar P-E loops for SLZ15-MLCCs ceramics under various cycle numbers. b Energy storage performance (W and η) versus cycle numbers for rec SLZ15-MLCCs ceramics.\n3. The description of the RRP is sufficient for peers to grasp its basic workflow and acknowledge its efficacy, yet it omits specific parameters (e.g., rolling pressure, temperature, and iterations), rendering it akin to a \"technical know-how\" that heavily relies on operator expertise for reproducibility. Full replication may necessitate additional data from the authors or extensive trial-and-error experiments. Consequently, questions arise regarding its scalability, cost-effectiveness, and industrial viability. Given that Nature Communications publishes numerous advances in materials processing annually, we anticipate contributions with stronger guidance for industrial production. The manuscript confirms the doping strategy's substantial enhancement of material properties but provides limited discussion on the feasibility for large-scale manufacturing. We recommend incorporating detailed process parameters, simulation analyses, optimization guidelines, cost assessments, or potential scalability challenges to better inform practical industrial applications.\nOur reply:\nThank you for your good comments. The repeated rolling process is a well established method in dielectric materials fabrication and has been widely adopted for preparing ceramic dielectric materials and metal-matrix composites (J. Am. Ceram. Soc. 2016, 99, 3569-3572; J. Magnes. Alloy. 2023, 10, 2193-2207; Energy Environ. Sci. 2023, 16, 4511-4521; Nat. Commun. 2023, 14, 5725). In the revised manuscript, we provided a detailed supplementary description of the repeated rolling process (RRP) used in this work\nSpecifically, the presintered SLZ15 powder is initially subjected to ball-milling to refine its particle size and then homogeneously mixed with an organic binder (e.g., PVA) at a mass ratio of 2:1 (powder to binder). The mixture is subjected to 1000 rolling cycles at room temperature under a pressure of 10 MPa to form uniform ceramic tapes. These tapes are then punched into discs (12 mm diameter) and calcined at 650 °C for 12 h to remove the binder. Finally, the disks are embedded in presintered powder with same composition and sintered at 1165 °C for 2 h using a double-crucible configuration.\nThe RRP method enhances ceramic performance through improved green-tape density, which promotes a dense, low-porosity microstructure during sintering and consequently enhance dielectric breakdown strength. Moreover, the process is operationally simple, cost-efficient, and scalable, supporting its suitability for potential mass production. These combined benefits position RRP as a practical and effective route for fabricating high-performance dielectric ceramics.\nRevisions in the manuscript:\nPage 18:\n“The SLZ15-RRP ceramic was fabricated by a repeated rolling processing (RRP) technique, employing pre-sintered SLZ15 powder as the raw material. The pre-sintered SLZ15 powder was initially subjected to ball-milling to refine its particle size and then homogeneously mixed with an organic binder (e.g., PVA) at a mass ratio of 2:1 (powder to binder). The mixture was subjected to 1000 rolling cycles at room temperature under a pressure of 10 MPa to form uniform ceramic tapes. These tapes were then punched into discs (12 mm diameter) and calcined at 650 °C for 12 h to remove the binder. Finally, the discs were embedded in presintered powder of the same composition and sintered at 1165 °C for 2 h using a double-crucible configuration.”\n4. The manuscript robustly argues that SLZ doping represents an efficient and rational choice, underpinned by rigorous and successful design logic. However, it does not furnish compelling evidence to establish SLZ as the \"optimal\" or \"sole\" option, merely supporting its status as an \"effective\" strategy. Framing SLZ as a successful exemplar within the broader \"composition design-microstructure engineering\" landscape would be more appropriate. Demonstrating \"optimality\" would require systematic comparative compositional studies, which could form the basis of a follow-up publication. We suggest tempering the discussion to avoid overly absolute claims.\nOur reply:\nThank you for the insightful and constructive comment. We fully agree with the reviewer's suggestion that our discussion should more clearly position the SLZ system as a successful exemplar rather than a definitive solution.\nIndeed, the essence of this research is to enhance the energy storage performance at high temperature through the construction of weakly coupled polar nanoregions in paraelectric dielectrics. The SLZ system serves as a practical case to validate this structural design strategy, mainly demonstrating the effectiveness of inducing a weakly coupled polar nanocluster architecture. We recognize that, in principle, any dopant system capable of achieving precise multi-element occupancy, and consequently inducing phase separation and a superparaelectric state, could similarly adopt this overarching strategy to modulate the microstructure and optimize performance.\nIn revising the discussion, we will adjust the discussion to downplay the uniqueness of the SLZ system and instead emphasize the universality and general guiding value of the composition design-microstructure engineering. We will also explicitly acknowledge that systematic comparative studies of different compositions are necessary to identify optimal dopant combinations, which represents an important direction for future research.\nRevisions in the manuscript:\nPage 2:\n“Ceramic capacitors, although promising for advanced high-power energy storage, face challenges in energy density and efficiency at high temperatures, which restricts their practical applications. Guided by phase field simulations, we propose a structural design strategy to construct weakly coupled polar nanoclusters in superparaelectric state, and fabricate BaTiO -based multilayer ceramic capacitors via 3 prototype device technology. The capacitors achieve an ultrahigh energy storage density of 19.0 J·cm-3 and a high energy storage efficiency of 95.5% at room temperature. More importantly, both metrics are still on the order of > 10.0 J·cm-3 and > 95.0%, respectively, over 25-160 oC, outperforming previously reported ceramic dielectric capacitors. The weaken coupling between adjacent nanoclusters caused by disordered polar configurations, suppresses nonlinear polarization response and temperature sensitivity, ultimately enabling superior energy storage performance, which is confirmed by atomic-scale microstructure analysis. This work advances next-generation electronics and provides insights for developing high-performance high-temperature ceramic capacitors.”\nPage 17:\n“In summary, guided by phase-field simulations, this work presents an effective strategy for enhancing the capacitive energy storage of lead-free ceramics by designing weakly coupled polar nanoclusters in superparaelectric state. Atomic-scale HAADF-STEM and polarization mapping reveal nanostructured polar clusters with R- and T-phases that are embedded within a nonpolar C-phase matrix, forming weakly coupled polar nanoclusters. As a result, the SLZ15-MLCCs exhibit large P , max high applied electric field and negligible polarization hysteresis, leading to ultra-high energy storage density (W ≈ 19.0 J·cm-3) and near-ideal efficiency of 95.5% at room rec temperature. In addition, the weakly coupled and disordered polar nanoclusters remain stable at thermal fluctuations, ensuring outstanding high-temperature energy storage performance. When the temperature rises to 160 °C, its W remains above rec 10.0 J·cm-3, and the η reaches as high as 96.7%. Additionally, the SLZ15-MLCCs also exhibit excellent frequency stability and cyclic stability, and the variations in W and rec η both remain less than 5.0%. This work establishes a new paradigm for achieving ultra-high comprehensive energy storage performance, addressing the critical need for dielectric capacitors in high-temperature environments.”\n5. The phase-field model presented is a simplified idealization that adeptly captures and interprets the dominant physical mechanisms, with experimental results indirectly validating its applicability and reliability within the study's scope. This simulation approach stands out as a key innovation, having qualitatively predicted nanocluster evolution with success. To bolster persuasiveness, we recommend including quantitative outputs, such as simulated hysteresis loops (P-E curves) or polarization response profiles. Furthermore, does the model account for mechanical defects (e.g., cracks)? If so, how are they incorporated (e.g., via elastic terms or defect random fields)? Please clarify or expand on this aspect.\nOur reply:\nThank you for your valuable and constructive suggestions. We fully agree that adding quantitative simulation outputs and clarifying the treatment of mechanical defects would significantly enhance the insights provided by our phase-field modeling.\nIn the revised manuscript, we have addressed these points as follows:\nWe have added phase-field simulated hysteresis loops for samples with different compositions (Fig. R25). The results reveal a clear trend: the BT-35NBT sample, characterized by long-range ordered macroscopic ferroelectric domains, exhibits a typical ferroelectric P-E loop with high hysteresis. With the introduction of SLZ doping, the domain structure gradually evolves from long-range ordered domains to nanodomains and ultimately to smaller-sized weakly coupled polar nanoregions. Macroscopically, this evolution manifests as a significant reduction in polarization loss and a progressive refinement of the P-E loop, which aligns directly with the experimental observation of improved energy storage performance. These simulated loops provide quantitative support for the micro-to-macro relationship between weak coupling and slim hysteresis.\nThe present phase field model does not explicitly incorporate the formation and evolution of mechanical defects (e.g., cracks) under applied electric fields. This simplification is founded on two principal considerations. Firstly, all experiments were carried out under non-breakdown conditions, and consequently, the simulations were designed to align with an ideal, crack-free model in accordance with the experimental setup. Secondly, the primary aim of this work is to clarify the enhancement mechanism of weakly coupled polar nanoclusters on energy storage performance, which does not intrinsically involve crack propagation. Nevertheless, the model take into account defect-like effects through elastic energy terms and random-field coupling, which capture the influence of local strain and pinning on polarization switching without simulating crack dynamics.\nFig. R25 Evolution of the domain structure and normalized P-E loops for SLZx based on phase-field simulation.\n6. Figures such as Fig. 5e lack sufficient clarity, failing to effectively highlight numerical differences. We suggest providing inset magnifications or enhanced contrasts to more intuitively convey key data.\nResponse:\nThank you for your valuable suggestion. We have added an enlarged view of the key region in Fig. 4i, which provides a more intuitive and clearer presentation of the core data and facilitates the rapid identification of key information.\nFig. R26 (Original Fig. 4i) Time dependence of discharge energy density of SLZ15-RRP ceramics at different temperatures.\nWe hope the above replies and related revisions are acceptable.\nThank you very much for your professional comments and suggestions.\nFang-Zhou Yao\nResearch Center for Advanced Functional Ceramics, Wuzhen Laboratory, Jiaxing, Zhengjiang, 314500, China.\nCenter of Advanced Ceramic Materials and Devices, Yangtze Delta Region Institute of Tsinghua University, Jiaxing 314006, China\nEmail: yaofangzhou@xjtu.edu.cn"}, {"round": 2, "reviewer_comments": {"reviewer_2": "The authors have responded convincingly to all the comments raised during the review process. I therefore recommend acceptance of the revised manuscript.", "reviewer_3": "The authors have addressed my concerns well.\nHowever, Figure R25 in the rebuttal letter provides crucial quantitative evidence for the mechanism and should be formally included in the manuscript or supplementary materials.\nFurthermore, please double-check whether other important data mentioned in the rebuttal are fully integrated into the revised paper or SI. Ensuring that these details are accessible to all readers is essential. Once these minor additions are completed, I recommend the manuscript for publication."}, "author_response": "Dear Dr. Editor and Reviewers:\nThank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Heterogeneous Weakly Coupled Polar Nanoclusters Enabling Superior High-Temperature Capacitive Energy Storage” (Research Article, No. NCOMMS-25-69291B). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research.\nWe have studied the comments carefully and have made the following corrections, which we hope will meet your approval. In order to highlight the modifications in the manuscript, we have marked them in red. The main corrections in the manuscript and the responses to the reviewers’ comments are listed as following:\nReply to Reviewer # 2:\nComments:\nThe authors have responded convincingly to all the comments raised during the review process. I therefore recommend acceptance of the revised manuscript.\nOur reply:\nThank you very much for reviewing our revised manuscript and we appreciate your positive comment.\nReply to Reviewer # 3:\nComments:\nThe authors have addressed my concerns well.\nHowever, Figure R25 in the rebuttal letter provides crucial quantitative evidence for the mechanism and should be formally included in the manuscript or supplementary materials. Furthermore, please double-check whether other important data mentioned in the rebuttal are fully integrated into the revised paper or SI. Ensuring that these details are accessible to all readers is essential.\nOnce these minor additions are completed, I recommend the manuscript for publication.\nOur reply:\nWe sincerely express our gratitude for your positive comments and valuable suggestions. As suggested, we have relocated Figure R25 to the Supplementary Information as Supplementary Figure 1 and incorporated relevant discussion in the revised manuscript. Additionally, we have double-checked and verified that all related important data are now included in the revised submission. The specific revisions are as follows:\nRevisions in the manuscript:\nPage 6:\n“To uncover the underlying origin of the enhanced high-temperature energy storage performance of lead-free ceramic dielectrics induced by weakly coupled polar nanoclusters, the two-dimensional phase field simulation was used to study the correlation between the polar structure evolution and the corresponding hysteresis behavior of (1-x)[0.65BaTiO -0.35(Na Bi )TiO ]-xSr La ZrO (SLZ100x, x = 0, 3 0.5 0.5 3 0.7 0.2 3 0.05, 0.1, 0.15, 0.2) ceramics at different temperatures, as shown in Fig. 2a and Supplementary Fig. 1. The initial BT-35NBT ceramic features long-range ordered, strongly coupled T-phase domain structure, as substantiated by its P-E loops with large polarization but high hysteresis loss.After introducing SLZ, as expected, the domains were transformed from macroscopic ferroelectric domains to nanodomains and subsequently to smaller weakly coupled polar nanoclusters, accompanied by increasingly slender P-E loops. This progression suggests that the introduction of SLZ effectively disrupts the long-range ferroelectric order in BT-35NBT ceramics. Simultaneously, the content of the T-phase decreases significantly, resulting in a disordered polarization structure with coexisting R-, T- and C-phases. The randomly distributed polar structure modifies local energy barriers, stabilizes the favorable polarization, and forms the unique structures with weakly coupled R and T polar nanoclusters divided by nonpolar C phase over a broad temperature range, thereby enhancing temperature-insensitive energy storage performance.”\nFig. R1 (Original Supplementary Fig. 1)Evolution of the domain structure and normalized P-E loops for SLZx based on phase-field simulation.\nWe hope the above replies and related revisions are acceptable.\nThank you very much for your professional comments and suggestions.\nFang-Zhou Yao\nResearch Center for Advanced Functional Ceramics, Wuzhen Laboratory, Jiaxing, Zhengjiang, 314500, China.\nCenter of Advanced Ceramic Materials and Devices, Yangtze Delta Region Institute of Tsinghua University, Jiaxing 314006, China\nEmail: yaofangzhou@xjtu.edu.cn"}]

Decision letter