Introduction

Dielectric capacitors, renowned for their exceptional power density and ultra-fast charge-discharge rate, have garnered considerable attention within the realm of pulse power systems1,2. Notably, research into dielectric ceramic capacitors stands out prominently, primarily attributed to their unparalleled voltage endurance and reliability. Nevertheless, their relatively modest recoverable energy density (Wrec) and efficiency (η) pose limitations on their widespread applications, particularly in the context of the electronics industry’s constant pursuit of miniaturization and integration. The storage capacity hinges on Wrec, while η dictates the degree of energy loss. Hence, the simultaneous improvement of both Wrec and η is imperative to fulfill the practical demands and advance their applicability. Typically, the key parameters of energy storage performance are assessed through the analysis of polarization-electric field (P-E) loop (Fig. S1), which can be quantitatively described using the following formulas3,4: Wrec = ({\int }_{{P}_{\rm{r}}}^{{P}_{\rm{m}}}{E\rm{{d}}}P), η = Wrec/Wtot × 100%. Here, Pm, Pr, and Wtot are the maximum polarization, the remnant polarization, and the total energy density, respectively. Notably, a significant difference between Pm and Pr (denoted as ΔP = Pm – Pr) coupled with a high electric field (E) is advantageous for enhancing both Wrec and η.

Over the years, substantial endeavors have been undertaken to optimize energy storage performance at ambient temperature. A tape-casting technique coupled with a two-step sintering approach was implemented to fabricate BiFeO3-SrTiO3 ceramics5, aimed at refining grain size and subsequently enhancing the breakdown strength (Eb). While ferroelectric-active ions (Bi3+, Zn2+ and Nb5+) were introduced into the A/B sites of BaTiO3 ceramics, resulting in significant improvements in energy storage performance, including a Wrec of 11.6 J cm–3 and a high η of 96.1% owing to mitigated polarization anisotropy and disrupted long-range ferroelectric polarization order6. Additionally, a supercritical relaxor state was successfully established in (Na,K)(Sb,Nb)O3-SrZrO3-(Bi0.5Na0.5)ZrO3 ceramics with nanoscale grains, achieving a Wrec of 13.1 J cm–3 alongside a notable η of 90% by modulating the coexistence of multiple local symmetries in the ergodic relaxor zone7. Our previous research has demonstrated the achievement of a remarkable Wrec of 9.0 J cm–3 in tetragonal tungsten bronze structured relaxor ferroelectric ceramics, another important dielectric family in addition to perovskite structured materials, featuring weakly interacting polar nanoregions8. Nevertheless, practical application scenarios put forward more stringent requirements on the energy storage performance of dielectric materials in high temperature environment9,10. For example, pulsed power supply needs to operate stably across a wide temperature range of 125 – 180 °C, while oil and gas exploration operations face the challenge of high temperature up to 175 °C. However, the extant research on the energy storage properties of dielectric ceramics under high temperature remains inadequate, notably characterized by a constrained operational temperature range and suboptimal Eb at elevated temperatures, thereby necessitating further exploration and advancements.

High-entropy materials (HEMs) exhibit exceptional properties that often exceed those of their individual components or traditional analogs, thereby rendering them highly desirable across a broad spectrum of fields, such as catalysts11 and batteries12. HEMs can be distinguished by their compositional intricacy, encompassing a plurality of (typically five or more) principal constituent elements. The quantification of configurational entropy, denoted as ΔS, is typically formulated as follows3: (\Delta S=- R [(\mathop{\sum }\nolimits_{\rm{i}=1}^{{\rm{M}}{x}_{{\rm{i}}}\mathrm{ln}{x}_{\rm{i}})_{{\rm{cation}}-{\rm{site}}}+(\mathop{\sum }\nolimits_{\rm{j}=1}}{\rm{N}}{x}_{\rm{j}}\mathrm{ln}{x}_{\rm{j}})_{\rm{anion}-\rm{site}}]), where R represents the universal gas constant, N (M) corresponds to the number of atomic species, and xi (xj) signifies the fraction occupying cation (anion) sites, respectively. A system is classified as a high-entropy material when its ΔS surpasses 1.5R. HEMs exhibit four noteworthy characteristics: high entropy effect of thermodynamics; hysteretic diffusion effect of dynamics; lattice distortion effect of structure; synergistic effect of components13. Recently, remarkable advancements in ambient-temperature energy storage capabilities have been achieved14,15,16,17,18, attributed to entropy-induced large lattice distortions and refined grain size, thus substantially enhanced dielectric breakdown strength. Nevertheless, to date, the high-temperature energy storage of the dielectric ceramics is needed to be greatly improved.

Results and discussion

Design of strain-modulated dielectric ceramics via entropy enhancement

It is interesting to note that high-entropy structural ceramics exhibit exceptional thermal stability, effectively resisting the phase evolution and microstructural variation even at elevated temperatures, thereby positioning them as excellent contenders for high-temperature applications19. It is thus anticipated that the structural stability induced by high-entropy strategy in functional ceramics, such as dielectric ceramics, will also yield unparalleled high-temperature energy storage performance. Relaxor ferroelectrics, characterized by their flattened local free energy potentials stemming from the presence of nanodomains reinforced by random fields (electric and strain fields), exhibit good electric properties against temperature20. The enhancement of configurational entropy in relaxor ferroelectrics, through the introduction of local structural disorder and compositional inhomogeneity to further disturb nano polar regions to polar clusters, is expected to minimize the Pr and augment the η. In addition, it is widely acknowledged that the lattice strain field will provoke modifications in the lattice vibration mode, which in turn leads to a higher generation of acoustic phonons. The interaction between these phonons and electrons causes electron scattering, forcing the electrons to continuously shift their direction and energy as they move. This occurrence subsequently boosts the resistance to electron flow and decreases the electrons mobility. From the perspective of energy storage, the hindered electron migration enhances insulation properties, thereby resulting in a high Eb, as shown in Fig. 1a.

Fig. 1: Schematic illustration of the strain modulation strategy enabling ultra-high energy storage in ceramic capacitors.

a A schematic diagram showing the correlation among the atomic configurations, local lattice strain field, and P–E loop within BNT-based relaxor ferroelectric ceramics. b Comparisons of Wrec and η between the studied 1.5R single-layer ceramic and other state-of-the-art ceramics and polymers at 200 °C. c Comparisons of Wrec across a wide operating temperature range between the studied 1.5R MLCCs and other state-of-the-art counterparts.

In light of the above analyses, we employ a strain modulation strategy by increasing configuration entropy within bismuth sodium titanate-based relaxor ferroelectrics. This approach impedes electron migration and consequently elevates the Eb at elevated temperatures. The underlying mechanism involves strain heterogeneity driven by structural heterogeneity. Herein, relaxor ferroelectrics 0.6Bi0.5Na0.5TiO3-0.4Sr0.7Bi0.2TiO3 (BNSBT) ceramics were chosen as the base composition, given their widespread utilization in energy storage systems and remarkable temperature stability21,22. To promote ionic disorder and enhance the structural heterogeneity, several cations with different ionic radii and valence states, including Sc3+, Nb5+, and Ta5+, were incorporated into the A and B sites of the BNSBT matrix, denoted as (1–x)(0.6Bi0.5Na0.5TiO3-0.4Sr0.7Bi0.2TiO3)–xSr(Sc0.5Nb0.425Ta0.075)O3 (BNSBT-xSSNT, where x = 0.03, 0.06, 0.09 and 0.12). The designed compositions are defined as 1.3R, 1.4R, 1.5R, and 1.6R ceramics according to their respective entropy values (Table S1 and Fig. S2). Impressively, 1.5R single-layer ceramics achieve an outstanding Wrec of 8.0 J cm–3 and an impressive η of approximately 87% at 200 °C compared with other leading-edge ceramics and polymers, as shown in Fig. 1b6,23,24,25,26,27,28,29. Figure 1c presents a comparative analysis of the temperature-dependent Wrec between the 1.5R multilayer ceramic capacitors (MLCCs) and state-of-the-art counterparts reported in recent studies15,30,31,32. Notably, the 1.5R MLCCs demonstrate exceptional temperature stability across an ultra-wide temperature range (−75 to 200 °C).

Electrical properties of BNT-based energy storage ceramics

To delve into the origins of ultra-high energy storage, an investigation into the electrical properties of BNT-based energy storage ceramics is conducted. The calculated Eb values for all the samples fitted by the Weibull distribution are shown in Fig. 2a, enhancing remarkably from 320 to 620 kV cm–1 as the entropy increases. All the Weibull parameters (β) exceed 20, suggesting good reliability and good ceramic sintering quality. Figure 2b showcases the corresponding P-E hysteresis loops for varying compositions at their respective Eb. Notably, a phenomenon of delayed polarization saturation is observed, where the rate of polarization increases with the applied electric field progressively decelerates, being conducive to the energy storage performance33. Specifically, nanodomains or polar nanoregions in relaxor ferroelectrics tend to evolve into microdomains to facilitate polarization alignment. On one hand, the reorientation of nanodomains needs a higher external electric field, leading to the observed delayed polarization saturation and an elevated Eb. On the other hand, the reduction in domain switching energy barriers of nanodomains favors the mitigation of hysteresis loss. The combination of high Eb and minimal energy loss contributes favorably to the enhancement of Wrec and η. As depicted in Fig. 2c, both Eb and η demonstrate a consistent increasing trend with configurational entropy. Specifically, Eb rises progressively from 320 kV cm–1 for 1.3R ceramics to 620 kV cm–1 for 1.6R ceramics, while η improves from 91% to 97% over the same composition range. In contrast, Wrec exhibits a non-monotonic composition dependence. It undergoes an increase from 4.3 J cm–3 (1.3R) to 5.5 J cm–3 (1.4R), peaking at 10.0 J cm–3 (1.5R), followed by a modest reduction to 9.1 J cm–3 (1.6R). This reduction in Wrec reduction at 1.6R is attributed to increased dipole disorder and the corresponding weakening of macroscopic polarization. Consequently, the 1.5R ceramics represent the optimal balance, offering the best compromise between high Wrec (10.0 J cm–3) and η (94%). Figure S3 illustrates the energy storage performance of the ceramics with 1.5R under different electric fields. It can be seen in Fig. S3a that P–E loops keep slender even at elevated electric fields, demonstrating an electric field-insensitive characteristic. The current-electric field (I–E) curves show a diffused behavior with the increase of electric field, indicative of relaxor ferroelectric, as shown in Fig. S3b. The Pm reaches up to 41.9 µC cm–2 with near-zero Pr of 0.9 µC cm–2 at a high electric field of 590 kV cm–1. The large Pm and negligible Pr lead to a large value of ΔP (~41.0 µC cm–2), as shown in Fig. S3c. The values of Wtot, Wrec, and η at various electric fields are calculated and displayed in Fig. S3d. To visually illustrate the entropy effect on energy storage performance enhancement, radar diagrams for ceramics with 1.3R and 1.5R are presented in Fig. S4. It is evident that the 1.5R ceramics exhibit comprehensive and substantial improvements across various energy storage parameters, encompassing Pm, Pr, Eb, Wrec, Wtot, and η. Furthermore, Fig. S5 compares the Wrec and η values of the 1.5R ceramics against recently reported bulk ceramics (listed in Supplementary Table S2)8,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57, showcasing an impressive balance between Wrec and η.

Fig. 2: Electrical properties of BNT-based ceramics.

a Weibull distributions of the Eb with the increase of entropy. b P–E loops for different compositions at their respective Eb. c Comparisons of the Wrec, η, and Eb of different BNT-based ceramics at their respective Eb. d Electron localization functions obtained from DFT calculations for 1.3R and 1.5R ceramics. e Electric field distributions and electrical tree evolutions of the 1.3R and 1.5R ceramics. f Temperature-dependent εr and tanδ of the 1.5R ceramic with varying frequencies. g Calculated Wrec and η for 1.5R ceramic from –50 to 200 °C at 500 kV cm–1. h Comparisons of Wrec across a wide operating temperature range against other recently reported lead-free ceramics.

As mentioned above, lattice strain fields have an influence on the electron migration path. Atomic configurations, corresponding local lattice distortion field, band structure and electron localization function (ELF) and band structure based on density-functional theory (DFT) calculations for 1.3R and 1.5R ceramics are illustrated in Fig. S6 and Fig. 2d, respectively. The modulation of the lattice strain field is achieved by altering the entropy. An analysis of the ELF reveals that a greater degree of strain field corresponds to a higher level of electronic localization. This implies that electrons experience greater scattering and obstruction during migration, leading to a higher resistance. Consequently, the calculated band gaps for 1.3R and 1.5R ceramics are 1.9 eV and 2.4 eV, respectively, reflecting an enhancement in their insulation properties. These findings suggest that lattice strain field modulated by entropy enhancement indeed enhances Eb of relaxor ferroelectrics.

Energy storage performance of dielectric ceramics is closely related to breakdown strength, while the breakdown strength presents an exponential decay relationship with the grain size2. The grain size gradually reduces from 2.1 μm to 1.7 μm with the increasing entropy, as shown in Fig. S7. The multicomponent nature of these ceramics hinders cooperative diffusion processes, leading to a sluggish diffusion rate. This combination of lattice distortion and sluggish diffusion dynamics acts as a barrier for grain growth, thereby preventing the expansion of grain sizes15. From Fig. S8, one can see that the ceramics with 1.5R display a uniform element distribution without any obvious segregation, demonstrating that Sc3+, Nb5+, and Ta5+ have been successfully incorporated into the matrix lattice. For dielectric capacitors, disparities in electrical characteristics between grains and grain boundaries lead to significant local electric field intensification, creating vulnerable sites susceptible to electromechanical breakdown58. It’s crucial to elucidate the breakdown path and the intricate evolution of electrical trees within dielectric ceramics under an applied electric field. The finite element simulation method provides valuable insights into this phenomenon, in which BNT-based ceramics with 1.3R and 1.5R serve as representative cases. The simulation framework is based on the experimental SEM images and measured dielectric constants. The dielectric constant distributions, electric potential distribution, and electrical tree evolutions are depicted in Fig S9. An electric field intensity of 540 kV cm–1 was imposed to the simulation samples. Figure 2e illustrates the dynamic evolution process of the electric field and the electrical tree propagation. Within grains, atomic order facilitates free electron mobility, yielding higher dielectric constants compared to grain boundaries. This disparity in dielectric constants distorts equipotential contours, leading to non-uniform electric potential distributions, with localized electric field hotspots at grain boundaries. Typically, grain boundaries act as current barriers, such that under identical electric field conditions, grain boundaries experience higher electric field intensities than grains. This phenomenon impedes the expansion of electrical branches and effectively lengthens the breakdown pathway. Consequently, 1.5R ceramics with higher grain boundary density, characterized by smaller grain sizes, exhibit enhanced resistance to dielectric breakdown.

To analyze the influence of lattice strain modulation on insulation properties, the impedance spectra for all ceramic components obtained at 610 °C, are depicted in Fig. S10. These spectra exhibit a distinctive semicircular pattern, which implies that the resistance of all the ceramic components under investigation is predominantly governed by grain boundary effects across the measured frequency range. As the entropy increases, a notable rightward shift is observed at the X-axis intercept of the semicircle. This shift underscores a significant enhancement in resistance, ultimately contributing to the improvement of insulation characteristics, thereby demonstrating the beneficial effects of increased entropy on the electrical properties of dielectric ceramics. Consequently, the superior energy storage performance of 1.5R ceramics is inextricably linked with their enhanced Eb, which results from the combined effects of composition homogenization, strengthened lattice strain field, grain refinement, and improved electrical resistivity.

From a practical application standpoint, the acquisition of energy storage materials capable of functioning across a broad temperature spectrum is paramount. Inevitably, operational heat generation stemming from energy dissipation necessitates the tolerance of these devices to temperature fluctuations. Furthermore, in some industries, devices must endure extremely high-temperature environments. To this end, we take an assessment of the temperature-dependent electrical properties of the 1.5R ceramics. The temperature-dependent dielectric constant (εr) and loss tangent (tanδ) with vary frequencies for the BNT-based ceramics are illustrated in Figs. S11 and 2f. All the compositions show typical frequency dispersion and broad dielectric peaks, characteristic of relaxor ferroelectric behavior. The observed decrease in εr is attributed to the reduction in increased atomic disorder as entropy increases.

We also measured the leakage current as a function of the electric field of the prepared BNT-based ceramics, as given in Figs. S12 and S13. As expected, leakage current increases with rising temperature due to enhanced carrier mobility in high-temperature environments. However, a clear trend of decreasing leakage current with increase of entropy is observed, suggesting that entropy modulation effectively suppresses leakage current pathways. These findings align with the enhanced Eb trend observed in Fig. 2a, suggesting higher entropy compositions maintain excellent high-temperature Wrec due to the decreased high-temperature leakage current. Furthermore, the Ohmic conduction mechanism (Fig. S14) for the BNT-based ceramics with different configuration entropy indicates that the leakage current arises from the directional movement of free carriers under an electric field. This supports our proposed entropy-modulated strain heterogeneity strategy, which enhances insulation by increasing carrier scattering and elongating migration paths, thereby reducing leakage current and enhancing energy storage performance.

Consequently, as illustrated in Fig. S15, a series of slender P–E loops for 1.5R bulk ceramic are recorded from −50 °C to 200 °C under an applied field of 500 kV cm–1. Notably, the Pm remains relatively invariant with temperature escalation, whereas the Pr exhibits a modest increase of up to 2.0 µC cm–2 above 100 °C, contributing to a slight degradation in Wrec and η upon heating, as depicted in Fig. 2g. The 1.5R bulk ceramic demonstrates a remarkable thermal stability, maintaining a Wrec of approximately 8.5 J cm–3 across an extensive temperature range from –50 °C to 200 °C. Fig. 2h provides a comparative analysis of the temperature-dependent Wrec between the 1.5R bulk ceramic and other state-of-the-art ceramic systems reported in recent literature, highlighting the superior temperature resilience of our studied system6,16,24,59,60,61. Our research showcases an exceptionally wide temperature operation window coupled with remarkable energy storage performance.

Microstructure of BNT-based energy storage ceramics

The microstructure of dielectric ceramics is fundamental to their energy storage performance. All the prepared BNT-based ceramics show typical pseudo-cubic perovskite structure, as illustrated in Fig. S16. In addition, the peaks of (111) and (200) gradually shift to lower angles with the increase of entropy, indicating the existence of lattice expansion. It can be explained by the fact that the ionic radii of Sc3+ (0.745 Å, CN = 6), Nb5+ (0.64 Å, CN = 6) and Ta5+ (0.64 Å, CN = 6) are larger than that of Ti4+ (0.605 Å, CN = 6) at B-site. Moreover, all Raman modes exhibit a diffused and broadened feature in Fig. S17a, implying a relaxor nature. The corresponding peak positions as a function of entropy based on Gaussian–Lorentzian function are illustrated in Fig. S17b. The multiple peaks within 200–600 cm–1 show softening behavior, which can be reflected by the fact that Raman modes shift to lower wavenumbers. This is related to the bond weakening between the A/B-site cations and oxygen induced by the multi-element introduction, indicating a higher distortion degree in the BO6 octahedron and the enhanced disorder in the short-range structure.

Domain morphologies and phase structure play an important role in optimizing the electrical properties of relaxor ferroelectric materials. Previous work demonstrates that relaxor ferroelectrics display macroscopic cubic structure, while the local symmetry can be modulated by chemical modification to optimize the energy storage performances15,62. The coexistence of multiple symmetries is beneficial to weaken the polarization anisotropy and domain-switching barriers. The high-resolution transmission electron microscope and selected area electron diffraction (SAED) analyses were performed on the 1.5R ceramics to explore their local structure. As shown in Fig. S18a, b, no obvious long-range ordered ferroelectric domain structure can be identified within the grain, indicating the nature of relaxor ferroelectrics. The SAED patterns reveal the ½(ooe) and ½(ooo) superlattices along [100]c and [110]c, respectively. These features suggest a mixed-phase system with R3c symmetry and P4bm symmetry, confirming structural heterogeneity, as shown in Fig. S18c, d. The XRD refinement results provide additional evidence for this interpretation, as shown in Fig. S19.

To elucidate the influence of entropy modulation on polar cluster size and lattice distortion, aberration-corrected scanning transmission electron microscopy in high-angle angular dark-field (STEM-HAADF) mode was employed to analyze BNT-based ceramics with different configurational entropy. The corresponding polarization vector is determined by the B-site cations with respect to the displacement of its adjacent four nearest A-site cation, which was computed through 2D Gauss function, represented by arrows in Figs. 3a and S20. Among them, the T phase exhibits polarization vectors along the [001]c direction, while R phase shows polarization vectors along the [110]c direction when viewed along the [100]c zone axis. According to the direction of polarization vectors, it can be determined that R and T polar clusters with diffuse boundaries are dispersed in the non-polar C matrix, indicating a strong local polymorphic distortion. The formation of localized polymorphic polar clusters reduces the polarization anisotropy, resulting in similar free energy profiles for both R and T polar clusters15. Thus, polarization switching is facilitated, which is advantageous for achieving a lower Pr. Moreover, the polar clusters with higher dynamics necessitate a greater external electric field to stabilize the long-range ordered ferroelectric state, leading to a delayed polarization saturation, and corresponding to an increase in Pm at elevated electric fields. Figure S21 displays the calculated polarization magnitude distributions for BNT-based ceramics with varying configurational entropies. A distinct inverse correlation emerges between polarization magnitude and configuration entropy, exhibiting a systematic reduction from 28.02 pm (1.3R) to 21.78 pm (1.4R), 17.25 pm (1.5R), and ultimately 13.42 pm (1.6R). This monotonic decrease provides compelling evidence for entropy-stabilized short-range ordering, which concurrently weakens interdomain correlations and reduces the energy threshold for domain switching processes15. Consequently, these entropy-stabilized structural modifications lead to significantly reduced polarization hysteresis and markedly improved energy storage characteristics.

Fig. 3: Domain structures, lattice distortion and In-situ phase structures of BNT-based ceramics.

a Atomic polarization configurations of 1.3R and 1.5R ceramics. b The c/a ratio within the 1.5R ceramic along the [001]c zone axis. c Atomic Energy-Dispersive Spectroscopy (EDS) mapping of the 1.5R ceramic, including the corresponding HAADF image along [001]c, along with EDS mappings of Bi, Na, Sr, Ti, Nb, Ta, Sc, and O elements. d In situ X-ray diffraction peaks of (111) and (200) and e Raman spectra of the 1.5R ceramic as a function of temperature. f In-situ domain morphologies and SAED patterns along [1-12]c for 1.5R ceramic at RT (g) and 250 °C (h).

Additionally, the c/a ratios for the ceramics are depicted in Figs. S22 and 3b, highlighting a broad spread along the [001]c zone axis, further supporting the presence of strain heterogeneity associated with increasing entropy. This pattern suggests the existence of large local lattice strain fields within these ceramics. A heightened degree of lattice strain fields correlates with a more pronounced level of electronic localization, implying that the electrons experience greater scattering and obstruction during their migration, enhancing the insulation properties and elevating the Eb. Additionally, Fig. 3c presents the atomic energy-dispersive spectroscopy mappings of the 1.5R ceramic, accompanied by the corresponding HAADF image along the [001]c axis. These mappings reveal the spatial arrangement of elements including Bi, Na, Sr, Ti, Nb, Ta, Sc, and O. It is worth noting that Bi, Na, and Sr are predominantly concentrated in the A-sites, whereas Ti, Nb, Ta, and Sc display a random dispersion across the B-sites, suggesting a disordered lattice configuration that contributes to the formation of heightened strain fields. This phenomenon is beneficial for energy storage density. Combining the improved polarization switching in entropy-modulated relaxor ferroelectrics, the 1.5R ceramics achieve superior energy storage performance.

To investigate the microstructural origin for the exceptional high-temperature energy storage properties for 1.5R ceramics, in situ microstructural characterizations were performed. Two characteristic diffraction peaks (111) and (200) from the XRD patterns of the 1.5R ceramic over the temperature range of −50 to 250 °C are given in Fig. 3d. No peak splitting was observed, indicating the absence of any structural change across the whole temperature range. The shift of the peaks towards lower angles with increasing temperature can be attributed to thermal expansion of the material. Figure 3e depicts In-situ Raman spectra, spanning temperatures from −50 to 250 °C. A distinct softening behavior is observed with rising temperature, associated with the weakening of bonds between A/B-site cations and oxygen, suggesting a decrease in unit cell polarity, which aligns with the slight decline in Pm values shown in Fig. S15. Nevertheless, the number of Raman peaks across the measured temperature zone remains unchanged, indicative of stable local structural symmetry despite temperature fluctuations. Moreover, the In-situ domain morphologies and SAED patterns along [1–12]c zone of the 1.5R ceramic at RT and 250 °C are shown in Fig. 3f–h. Interestingly, the polar clusters remain largely unchanged, and the ½ (ooe) and ½ (ooo) superlattices persist even as the temperature rises from RT to 250 °C, indicating that the phase structure remains stable despite temperature variation. These findings underscore the robust structural stability of the 1.5R ceramics. As previously demonstrated, the 1.5R ceramics are resilient against the adverse impacts of electron migration, attributed to their large strain heterogeneity, and they maintain a relatively low leakage current at high temperatures (Figs. S12 and S13). Consequently, these ceramics exhibit exceptional energy storage performance under high-temperature conditions.

Energy storage performance of MLCCs

Given the exceptional energy storage performance exhibited by the 1.5R ceramic, we fabricated this composition into MLCCs via the tape-casting technique, anticipating robust energy storage characteristics. The resultant MLCCs comprise a total of five dielectric layers, each with a thickness of approximately 20 μm. The cross-section SEM image of the MLCCs after sintering is presented in Fig. 4a, where the inset shows the actual prepared MLCCs. The electrodes as well as elemental distributions mapping within the prepared MLCCs is displayed in Fig. 4b and Fig. S23, confirming the high-quality MLCCs without notable infiltration between the dielectric layer and the electrode. The P–E loop of the prepared MLCCs under the electric field of 1320 kV cm−‍1, prior to its breakdown strength, is depicted in Fig. 4c. Figure 4d illustrates the Wrec and η as a function of the electric field at room temperature, achieving approximately 19.0 J cm−3 and 90% at 1320 kV cm–1, respectively. Subsequently, the pulse current curves of the prepared MLCCs are shown in Fig. S24. Discharge energy density (Wdis) was evaluated using a resistor-capacitor circuit with a load resistance of 1 kΩ and given in Fig. 4e, yielding an energy density of 16.7 J cm–3. Thi