Antiferroelectric Research Articles

Successive phase transitions–induced multiple boundaries and unprecedented electrocaloric effect in Pb(Yb1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3 system

AbstractTemperature stability of electrocaloric effect (ECE) is a thorny problem in ferroelectrics (FE). A general method is to design ferroelectric‐to‐relaxor phase transition at a sacrifice of electrocaloric (EC) strength. The Pb(Yb1/2Nb1/2)O3 antiferroelectrics (AFE) + Pb(Mg1/3Nb2/3)O3 relaxors strategy designed in this work is effective to tackle this dilemma [(1 − x)PYN–xPMN, x = 0.08–0.36]. PMN addition induces a successive phase transition and dual phase boundaries of ferrielectric (FIE)‐nonergodic relaxor (NER) and NER‐ergodic relaxor (ER), where ferroelectric polarization/strain and ECE reach a local maximum. Thermally stable ΔT is unexpectedly achieved in FIE (x = 0.14) and NER (x = 0.24), except for a generality for ER state (x = 0.30). A dome‐like variation trend is observed in x = 0.14 and 0.24 with a wide temperature span of ∼60 and ∼55 K (±15%ΔTmax). Notably, x = 0.24 NER possesses a large directly measured ΔTmax ∼0.64 K simultaneously. Dielectric/ferroelectric properties clarify that two‐stage transition of AFE rigid‐order de‐texture and dissociation of de‐textured AFE domains into polar nano‐entities accounts for thermal stability of ΔT as the alternation of ordered antipolar domains to disorder relaxors serves as a buffer to compensate for the thermal‐shock enhanced random field. This work not only accounts for the underlying mechanism for thermal stability of ΔT at FIE and NER side for the first time in physics but also provides an exotic approach to seek for high‐performance EC materials in practical applications.

Optimized Electrocaloric Refrigeration in Lead-Free NaNbO3-Based Ceramics via AFE ↔ FE Phase Transition Modulation.

An outstanding challenge for eco-friendly ferroelectric (FE) refrigeration is to achieve a large adiabatic temperature change within a broad temperature range originating from the electrocaloric (EC) effect, which is expected to be realized in antiferroelectric (AFE) materials owing to the large entropy change during electric field and thermally induced phase transition. In this work, a large EC response over a wide response temperature range can be achieved slightly above room temperature via designing the phase transition of NaNbO3. An irreversible to reversible AFE-FE phase transition on heating induced by the introduction of CaZrO3 into NaNbO3 plays a key role in the optimized electrocaloric refrigeration. Accordingly, accompanying the local structure transformation corresponding to the B-site ions, the transition temperature between the square polarization-electric field (P-E) hysteresis loop (the irreversible AFE-FE phase transition induced by the electric field) and the repeatable double P-E hysteresis loop (the electric field induced reversible AFE-FE phase transition) was tailored to around room temperature, in favor of extending large entropy change to the wide temperature range. This work provides an efficient approach to designing lead-free EC materials with excellent EC performance, promoting the advancement of environmentally friendly solid-state cooling technology.

Switchable hidden spin polarization and negative Poisson's ratio in two-dimensional antiferroelectric wurtzite crystals

Two-dimensional (2D) antiferroelectric materials have raised great research interest over the last decade. Here, we reveal a type of 2D antiferroelectric (AFE) crystal where the AFE polarization direction can be switched by a certain degree in the 2D plane. Such 2D functional materials are realized by stacking the exfoliated wurtzite (wz) monolayers with “self-healable” nature, which host strongly coupled ferroelasticity/antiferroelectricity and benign stability. The AFE candidates, i.e., ZnX and CdX (X = S, Se, Te), are all semiconductors with direct bandgap at Γ point, which harbors switchable antiferroelectricity and ferroelasticity with low transition barriers, hidden spin polarization, as well as giant in-plane negative Poisson's ratio (NPR), enabling the co-tunability of hidden spin characteristics and auxetic magnitudes via AFE switching. The 2D AFE wz crystals provide a platform to probe the interplay of 2D antiferroelectricity, ferroelasticity, NPR, and spin effects, shedding new light on the rich physics and device design in wz semiconductors.

Phase stability and energy storage properties of polycrystalline antiferroelectric BaTiO3-substituted NaNbO3 thin films

Lead-free sodium niobate (NN) thin films with varying barium titanate (BT) content and 1 mol% manganese were deposited on platinized silicon substrates by chemical solution deposition. Microstructural analysis reveals a change in nucleation mechanism, and X-ray diffraction and Raman spectroscopy confirmed a composition-driven antiferroelectric (AFE) to ferroelectric (FE) phase transition at 0.01 < x < 0.03, providing a stability interval for the AFE phase despite increasing the tolerance factor. The thin films show well-shaped ferroelectric response under applied electric field, indicating an irreversible field-induced phase transition. The composition with 7 mol% BaTiO3 showed the most promising energy storage properties (Wrec ∼5.7 J/cm3 and 68% efficiency (η)), along with excellent thermal stability up to 120 °C and largely improved cyclic stability up to 5 * 106 bipolar cycles. These findings highlight the potential of NN-based thin films as lead-free candidates for energy storage, emphasizing the importance of stabilizing the AFE phase under electric fields for practical applications.

High energy storage density in NaNbO3 antiferroelectrics with double hysteresis loop

Antiferroelectrics (AFEs) possess great potential for high performance dielectric capacitors, due to their distinct double hysteresis loop with high maximum polarization and low remnant polarization. However, the well-known NaNbO3 lead-free antiferroelectric (AFE) ceramic usually exhibits square-like P–E loop related to the irreversible AFE P phase to ferroelectric (FE) Q phase transition, yielding low recoverable energy storage density (Wrec). Herein, significantly improved Wrec up to 3.3 J/cm3 with good energy storage efficiency (η) of 42.4% was achieved in Na0.7Ag0.3Nb0.7Ta0.3O3 (30Ag30Ta) ceramic with well-defined double P–E loop, by tailoring the A-site electronegativity with Ag+ and B-site polarizability with Ta5+. The Transmission Electron Microscope, Piezoresponse Force Microscope and in-situ Raman spectra results verified a good reversibility between AFE P phase and high-field-induced FE Q phase. The improved stability of AFE P phase, being responsible for the double P–E loop and improved Wrec, was attributed to the decreased octahedral tilting angles and cation displacements. This mechanism was revealed by synchrotron X-ray diffraction and Scanning Transmission Electron microscope. This work provides a good paradigm for achieving double P–E loop and high energy storage density in NaNbO3-based ceramics.

Phase structure and piezoelectric properties in K/Bi co-doped AgNbO3 lead-free ceramics

The ferroelectric (FE) and anti-ferroelectric (AFE) properties of AgNbO3, an AFE material, can be altered by ion doping. K-doping is an effective strategy to enhance the FE properties by inducing an AFE-FE phase transition in the AgNbO3 ceramics, which boosts the FE and piezoelectric properties of (Ag,K)NbO3 ceramics. In this study, the phase structure and piezoelectric properties of the (Ag,K)NbO3 ceramics were further optimized via Bi doping. Doping with a small amount of Bi shifted the orthogonal-tetragonal (O-T) phase boundary to a lower temperature, leading to enhanced piezoelectric properties at room temperature in the (Ag0.9-3xK0.1Bix)NbO3 (x = 0.01–0.04) ceramics. The room-temperature phase structure of the ceramics changed from the FE phase to the AFE phase as x was increased from 0.01 to 0.04. A d33 of 83 pC/N was obtained for the (Ag0.84K0.1Bi0.02)NbO3 ceramics at room temperature, which increased to 140 pC/N at the O-T phase boundary. This study further reveals the controllable phase structure of AgNbO3-based ceramics for their potential applications as piezoelectric ceramics.

Superior comprehensive energy storage performances in Eu-doped AgNbO3 antiferroelectric ceramics

Antiferroelectric (AFE) dielectrics are considered promising materials for pulse power applications due to their high energy density. However, the energy storage performance of AgNbO3 lead-free AFE ceramics suffers from low breakdown strength (Eb) and weak AFE stability at room temperature. Along these lines, in this work, the tape-casting process together with Eu-doping was used to improve Eb and enhance AFE stability of the AgNbO3 ceramics. As a result, an ultrahigh recoverable energy storage density of 10.0 J/cm3 was obtained in the (Ag0.91Eu0.03)NbO3 ceramic, which surpasses all the reported values of AgNbO3-based ceramics in the literatures. Meanwhile, the recoverable energy storage density of (Ag0.91Eu0.03)NbO3 ceramic showed excellent temperature- and frequency-stability. Interestingly, a remarkable discharge energy density of 8.0 J/cm3 was obtained in the pulsed charge/discharge test. These results clearly indicate that the (Ag0.91Eu0.03)NbO3 ceramics prepared via the tape-casting process exhibit great potential for energy storage applications and shed light on the design of energy storage ceramics in other materials.

Effect of BiFeO3 on the ferroelectric and energy storage properties of (Bi1/2Na1/2)0.94Ba0.06TiO3 based compositions

The compound of (1 − x)[(Bi1/2Na1/2)0.94Ba0.06TiO3)]–xBiFeO3 (BNBT–BF), (0 ≤ x ≤ 0.15) sintered ceramic was processed by chemical route. The XRD patterns revealed the formation of single structured perovskite of Bi1/2Na1/2TiO3 (BNT) ceramics. The temperature-dependent dielectric characteristics indicated different dielectric phase changes in the fabricated compounds. Ferroelectric P–E hysteresis loop showed temperature sweep variations in saturation (P) and residual polarizations (Pr). Storage density (w) increases with temperature. This is due to the presence of AFE (Antiferroelectric) phase at temperatures >120 °C. The energy storage efficiency (η) and the dielectric break down strength (DBS) of the samples were observed to decrease with BF doping. The maximum energy storage density (w) of 0.29 J/cm3 was observed for × = 0.15 at 60 kv/cm.

Modulating polarization and carrier migration characteristics via constructing sandwich-structured heterojunction interfaces for achieving excellent high-temperature energy storage properties in polymer nanocomposites

Dielectric polymer nanocomposites are ideal choices for electrostatic energy storage due to their high power density and reliability, but they cannot operate efficiently at high temperature. To solve this issue, herein, we designed and developed sandwich-structured montmorillonite (MMT)/polyetherimide (PEI)-(Pb,La)(Zr,Sn,Ti)O3 (PLZST) antiferroelectrics (AFEs)@dopamine (DA)-MMT/PEI nanocomposites. On one hand, compared to current wide-band gap fillers, i.e., TiO2, Al2O3, ZrO2, and MgO, two-dimensional MMT nanosheets possess unique electrically insulating performances along the thickness direction, and thus can effectively stop charges injecting and migrating, causing low conduction loss, and large breakdown strength (Eb). On the other hand, PLZST AFEs with orthorhombic structure can exhibit high maximum electric displacement (Dmax) and small remnant electric displacement (Dr) at high temperature, which is beneficial for achieving large Dmax-Dr in the nanocomposites. In addition, large dielectric constant differences between MMT/PEI and PLZST@DA/PEI layers can inhibit electrical tree growth, resulting in further raised Eb. Finite element simulations on electrical tree evolving confirm experimental breakdown results. The sandwich-structured nanocomposite displays impressive high-temperature (150 °C) capacitive performances possessing meanwhile a high Eb of 5265.9 kV/cm, large discharged energy density (Ue) of 7.1 J/cm3, being about 6 times that of the commercial biaxially oriented polypropylene, and large charge-discharge efficiency (η) of 81.6 %, which exceeds obviously latest polymer and polymer composites in terms of overall energy storage performances. More encouragingly, it displays an ultrahigh power density of 15.63 MW/cm3 and ultrafast discharge rate of 19.2 ns at 150 °C, indicate its excellent application potential in high-temperature pulse power systems.

Superior energy-storage performances achieved in NaNbO3-based antiferroelectric ceramics by phase-structure and relaxation regulation

Lead-free NaNbO3-based antiferroelectric (AFE) ceramics are highly considered as promising substitutes of lead-based ones in dielectric energy-storage field. However, their low breakdown strength and large electric hysteresis loss originating from the field-induced metastable ferroelectric (FE) Q phase and/or AFE P phase still remains challenging, which severely impedes the further improvement of energy-storage performances. Herein, an effective phase-structure and relaxation regulation via A-site cation substitution strategy has been proposed to solve this issue. The phase-structures of the designed NN-based AFE ceramics evolve from orthorhombic P phase to R phase accompanying with the enhancement of relaxation behavior. Accordingly, an effective transformation from a plump and pinched polarization–electric field (P–E) hysteresis loop to a slim and slanted one has undergone, contributing to superior energy-storage performances. Noticeably, an expected large recoverable energy density (Wrec) of 4.0 J/cm3 with a high energy conversion efficiency (η) of 80.0 % was realized in 0.94(Na0.88Sm0.04NbO3)-0.06(BiFeO3) relaxor AFE ceramics at 460 kV/cm. Meanwhile, a great discharge energy density (Wdis) of 1.2 J/cm3 and a large power density (PD) of 92.4 MW/cm3 were achieved at 200 kV/cm. Furthermore, the favorable functional reliabilities in frequency, temperature, and fatigue cycle were also confirmed. These results not only demonstrate the great potential of NaNbO3-based relaxor AFE ceramics for dielectric energy-storage applications, but also confirm the validity of the strategy proposed in this work to obtain superior energy-storage performances.

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

The applications of silver niobate (AgNbO3)-based antiferroelectric (AFE) ceramics for potential energy storage are limited by the introduction of oxygen vacancies (OVs). The inevitable OVs narrow the band gap and promote grain growth, resulting in poor breakdown strength and low recoverable energy density (Wrec). Here, we report a significant energy density performance of (Ag1-2xSrx)(Nb0.78Ta0.22)O3 AFE ceramics designed by restraining OVs. Electron paramagnetic resonance (EPR) and UVvis absorption spectra experiments demonstrate that the OV content gradually decreases and the band gap increases with increasing Sr content. Donor doping of Sr leads to the generation of silver ion vacancies, thus, the OV concentration decreases to maintain the electrical neutrality of the system. As a result, a high Wrec of ~5.6 J/cm3 together with an energy efficiency of 70.1% at 300 kV/cm is achieved in the (Ag0.92Sr0.04)(Nb0.78Ta0.22)O3 ceramic. This work offers a novel strategy for improving the energy storage properties of AgNbO3-based AFE ceramics.

Local structural mechanism for enhanced energy storage properties in heterovalent doped NaNbO3 ceramics

In recent years, there is a growing interest for new lead-free oxides with reversible antiferroelectric (AFE)-ferroelectric (FE) phase transition for high-power energy-storage applications. NaNbO3-based ceramics are particularly attractive due to their easy synthesis and cost-effectiveness. In order to stabilize reversible AFE-FE phase transition, NaNbO3 is doped with a combination of heterovalent substitutions, although the underlying structural mechanism for the same is poorly understood. Here, we investigated local and average structures of Ca/Zr doped NaNbO3 using neutron total scattering. We show that Ca/Zr doping increases the average AFE phase (Pbma) fraction, however, the material remains as a composite of both FE (P21ma) and AFE regions. Analysis of local structure suggests that increase in the long-range AFE phase results from more extensive twinning of local FE regions, due to introduced charge disorder. We propose that enhanced energy-storage properties of Ca/Zr-doped NaNbO3 arises from localized twin boundary motion between the defect-induced pinning centers.

Antiferroelectric ceramic capacitors with high energy-storage densities and reduced sintering temperature

Field-driven transition from antiferroelectric (AFE) to ferroelectric (FE) states has gained extensive attention for microelectronics and energy storage applications. High dielectric-breakdown-strength (DBDS) for a given material is a necessity to attain full capacity of electrical energy storage. An approach to increasing energy performances is to modulate the related materials to own a higher phase transition electric field (EFE-AFE) using elemental dopants. In this case, Cd2+ was selected as the dopant at A-site in the Pb0.97La0.02Zr0.50Sn0.45Ti0.05O3 ceramics to tailor this EFE-AFE value due to the ionic difference enhanced antiferroelectricity. Surprisingly, the doped ceramics increased EFE-AFE by half, DBDS by 16 %, and maintained energy storage efficiency η of over 85 %, providing a way to improve energy storage density. It is worth mentioning that while the performance has been improved, the sintering temperature has been reduced by 170 °C. At the same time, the ceramics maintain good temperature stability, extremely fast discharging speed and discharging energy storage density, indicative of a promising choice in pulse power devices.

Achieving low field-induced large strain by La-Nb co-doping in PZST-based anti-ferroelectric ceramics for high-performance actuators

Anti-ferroelectric (AFE) dielectrics are promising for actuators due to their large strain resulting from the phase transition from AFE phase to ferroelectric (FE) phase. However, their high phase transition electric field and strain hysteresis (Hs) limit their application in actuators. In this work, La-Nb co-doping in Pb(Zr0.85Sn0.08Ti0.07)O3 AFE ceramics realizes collaborative optimization of AFE-FE phase transition electric field (EAFE-FE), Hs and strain. La3+ ions replace Pb2+ ions to weaken long-range FE coupling and refine hysteresis loops. Nb5+ ions replacing B-site ions enhance the stability of FE phase in PZST ceramics, hence further reducing EAFE-FE. Furthermore, doping Nb5+ decreases grain size, which is conducive to producing higher field-induced strains. As a result, EAFE-FE decreases from 119 kV cm−1 to 47 kV cm−1 and Hs decreases from 75 % to 44 %, while strain remains at 0.47 %. The results demonstrate that La-Nb co-doping strategy promotes the application of large-strain AFE materials in actuators.

Achieving Ultrahigh Energy Storage Performance for NaNbO3-Based Lead-Free Antiferroelectric Ceramics via the Coupling of the Stable Antiferroelectric R Phase and Nanodomain Engineering.

NaNbO3(NN)-based lead-free eco-friendly antiferroelectric (AFE) ceramics with an extremely high maximum polarization (Pm) are believed to be a promising alternative to traditional lead-based ceramics. Nevertheless, the high energy dissipation resulting from the large polarization hysteresis, which arises from the AFE-ferroelectric (FE) phase transition, poses a great challenge to the application of this promising ceramic. Herein, an excellent recoverable energy storage density (Wrec) was attained by intentionally designing a (0.86 - x) NaNbO3-0.14CaTiO3-xBiMg2/3Nb1/3O3 (NN-CT-xBMN) relaxor antiferroelectric ceramic, attributed to the synergistic effect of the stable AFE R phase and nanodomain engineering to overcome the bottleneck. The obtained results illustrate that the inclusion of BMN causes the transition from AFE microdomains to nanodomains and stabilizes the relaxor AFE orthorhombic R phase, which generates a highly stable polarization field response with low hysteresis and delays the AFE-FE phase transition, thus improving energy storage density. As a consequence, a high Wrec of 5.41 J cm-3 with an excellent conversion efficiency η of 86.7% was obtained in the NN-CT-0.08BMN ceramic. Moreover, the NN-CT-0.08BMN ceramic exhibits superior stability in temperature (25-150 °C), frequency (1-600 Hz), and fatigue behavior (10°-104 cycles) together with a large current density (CD = 810 A cm-2), ultrahigh power density (PD = 118 MW cm-3), and ultrafast discharge rate (t0.9 < 0.7 μs). This superior energy storage density, coupled with outstanding stability, suggests that the NN-CT-0.08BMN ceramic has the potential to be a promising candidate for pulsed power applications and power electronics.

Dielectric and Improved Energy-Storage Properties in A-Site Nd3+ Doped Lead-Free 0.88NaNbO3-0.12Sr0.7Bi0.2TiO3 Ceramics

Sodium niobate (NaNbO3)-based antiferroelectric (AFE) ceramics have received significant attention for energy storage applications because of their good performance, low cost, and nontoxicity. However, the existence of the antiferroelectric P phase at room temperature causes large hysteresis, resulting in reduced energy storage efficiency. In this study, 0.88NaNbO3–0.12Sr0.7Bi0.2TiO3 ceramics doped with Nd3+ (i.e., 0.88Na1-3 x Nd x NbO3-0.12Sr0.7Bi0.2TiO3) at x = 0.0 − 0.025 were prepared via conventional solid-state mixed oxide route. The XRD data showed that all samples exhibited an orthorhombic structure. With increasing Nd3+ doping content, the antiferroelectric P (Pbma) phase to R (Pnma) phase transition temperature (T P-R) shifted to lower temperatures. Consistent with the dielectric properties, a transition to a relaxor-like slim P-E loop indicative of an AFE R phase was observed at the composition x ≥ 0.01. This led to an increase in both the recoverable energy-storage density (W rec) and efficiency (η) with an increasing amount of Nd3+ doping level. The maximum recoverable energy storage density (W rec = 0.54 J/cm3) and high energy storage efficiency (η = 93%) were observed at x = 0.025 under an applied electric field of 100 kV/cm. In addition, the optimum composition at x = 0.025 also exhibited excellent temperature stability from 25 °C to 150 °C. This research demonstrates that the NN–SBT–xNd system has the potential for use for high-energy-density pulsed power capacitor applications.

AgNbO3-Based Multilayer Capacitors: Heterovalent-Ion-Substitution Engineering Achieves High Energy Storage Performances.

The demand for miniaturization and integration in next-generation advanced high-/pulsed-power devices has resulted in a strong desire for dielectric capacitors with high energy storage capabilities. However, practical applications of dielectric capacitors have been hindered by the challenge of poor energy-storage density (Urec) and efficiency (η) caused by large remanent polarization (Pr) and low breakdown strength (BDS). Herein, we take a method of heterovalent ion substitution engineering in combination with the multilayer capacitor (MLCC) technology and thus achieve a large maximum polarization (Pmax), zero Pr, and high BDS in the AgNbO3 (AN) system simultaneously and obtain excellent Urec and η. The substitution of Sm3+ for Ag+ in SmxAN+Mn MLCCs at x ≥ 0.01 decreases the M1-M2 phase transition temperature, and the antiferroelectric (AFE) M2 phase appears at room temperature, which is beneficial to achieving a low Pr value. Due to the low Pr value and high BDS ∼ 1300 kV·cm-1, an excellent Urec ∼9.8 J·cm-3 and PD,max ∼ 34.8 MW·cm-3 were achieved in SmxAN+Mn MLCCs at x = 0.03. The work suggests a paradigm that can enhance the energy storage capabilities of AFE MLCCs to meet the demanding requirements of advanced energy storage applications.

Stable relaxor ferroelectric phase of NaNbO3-based ceramic with superb energy storage performances

NaNbO3-based ceramics (NN) as a lead-free antiferroelectric (AFE) material has received widespread attention in electrostatic capacitors. Nevertheless, complex structural phase transformation with low threshold switching electric fields hinders the enhancement of energy storage capability. Herein, a feasible avenue for attaining a stable relaxor ferroelectric (FE) phase in NN-based ceramic is designed by introducing Ca0.7Sm0.2TiO3 (CST) to improve the capacitive performance. The experimental results demonstrate that (1-x)NN-xCST ceramics transform from the AFE P to the FE Q phase and domain size evolves from sub-micro to nano-scale as the CST content increases. Meanwhile, the filling behavior of non-isovalent ions induces local random fields caused by the disruption of the long-range polar structure. Ultimately, an ultra-high Wrec ∼9.10 J/cm3 and a desirable η ∼80.1% are attained simultaneously in 0.85NN-0.15CST relaxor FE ceramic, surpassing most NN-based and other lead-free ceramics. Moreover, Wrec and η exhibit excellent stability under the test conditions of frequency, temperature, and cycling. This work demonstrates that the stabilized FE Q phase is an effective approach to accelerate the development of NN-based dielectric materials in advanced energy-storage devices.

Highly compatible and reliable ZrN interfacial layer between TiN top electrode and antiferroelectric ZrO2 thin film to boost the electrocaloric behavior

A highly compatible and reliable ZrN interfacial layer with different cycles of atomic layer deposition was inserted between the TiN top electrode and antiferroelectric (AFE) ZrO2 thin film to achieve low oxygen vacancies and high crystallinity of the ZrO2 thin film, boosting the AFE and electrocaloric (EC) characteristics of TiN/ZrO2/TiN metal–insulator–metal (MIM) capacitors. An outstanding adiabatic temperature change (ΔT) of − 21 K was realized for devices with a ZrN interfacial layer of nine cycles, which can be ascribed to the reduction in redox between the TiN and ZrO2 for the suppression of interfacial dead layer during annealing as confirmed via high-angle annular dark field images and interfacial capacitance measurement. Hence, the reliability of ZrO2 MIM capacitors with a nine-cycle ZrN interfacial layer was examined with a negligible change in AFE and EC behaviors after a cycling endurance test of 106 cycles, exhibiting great potential for future applications in solid-state cooling.

Relaxor antiferroelectric-relaxor ferroelectric crossover in NaNbO3-based lead-free ceramics for high-efficiency large-capacitive energy storage

Relaxor ferroic dielectrics have garnered increasing attention in the past decade as promising materials for energy storage. Among them, relaxor antiferroelectrics (AFEs) and relaxor ferroelectrics (FEs) have shown great promise in term of high energy storage density and efficiency, respectively. In this study, a unique phase transition from relaxor AFE to relaxor FE was achieved for the first time by introducing strong-ferroelectricity BaTiO3 into NaNbO3-BiFeO3 system, leading to an evolution from AFE R hierarchical nanodomains to FE polar nanoregions. A novel medium state, consisting of relaxor AFE and relaxor FE, was identified in the crossover of 0.88NaNbO3–0.07BiFeO3–0.05BaTiO3 ceramic, exhibiting a distinctive core-shell grain structure due to the composition segregation. By harnessing the advantages of high energy storage density from relaxor AFE and large efficiency from relaxor FE, the ceramic showcased excellent overall energy storage properties. It achieved a substantial recoverable energy storage density Wrec ∼ 13.1 J/cm3 and an ultrahigh efficiency η ∼ 88.9%. These remarkable values shattered the trade-off relationship typically observed in most dielectric capacitors between Wrec and η. The findings of this study provide valuable insights for the design of ceramic capacitors with enhanced performance, specifically targeting the development of next generation pulse power devices.