Long-range Ferroelectric Order Research Articles

Ultrahigh Energy Storage Performance of BiFeO3-BaTiO3 Flexible Film Capacitor with High-Temperature Stability via Defect Design.

Nanoengineering polar oxide films have attracted great attention in energy storage due to their high energy density. However, most of them are deposited on thick and rigid substrates, which is not conducive to the integration of capacitors and applications in flexible electronics. Here, an alternative strategy using van der Waals epitaxial oxide dielectrics on ultra-thin flexible mica substrates is developed and increased the disorder within the system through high laser flux. The introduction of defects can efficiently weaken or destroy the long-range ferroelectric ordering, ultimately leading to the emergence of a large numbers of weak-coupling regions. Such polarization configuration ensures fast polarization response and significantly improves energy storage characteristics. A flexible BiFeO3-BaTiO3 (BF-BT) capacitor exhibits a total energy density of 43.5 J cm-3 and an efficiency of 66.7% and maintains good energy storage performance over a wide temperature range (20-200 °C) and under large bending deformation (bending radii ≈ 2mm). This study provides a feasible approach to improve the energy storage characteristics of dielectric oxide films and paves the way for their practical application in high-energy density capacitors.

Structurally Regulated Design Strategy of Bi0.5Na0.5TiO3-Based Ceramics for High Energy-Storage Performance at a Low Electric Field.

Dielectric ceramic capacitors are prospective energy-storage devices for pulsed-power systems owing to their ultrafast charge-discharge speed. However, low energy-storage density makes them difficult to commercialize for high-pulse-power technology applications. Herein, we presented a structurally regulated design strategy to disrupt a long-range ferroelectric order, refined grains, and eventually achieve excellent comprehensive energy-storage performance in (1 - x) (0.7Bi0.5Na0.5TiO3-0.3SrTiO3)-x Sm(Zn2/3Nb1/3)O3 eco-friendly ceramics. A large Wrec of ∼7.43 ± 0.05 J/cm3 and a high η of ∼85 ± 0.5% of 0.96 (0.7Bi0.5Na0.5TiO3-0.3SrTiO3)-0.04 Sm(Zn2/3Nb1/3)O3 were obtained at a low electric field of 290 kV cm-1 with good energy-storage temperature (25-120 °C), frequency (1-100 Hz) stability, and charge-discharge properties (PD ∼ 74 ± 1 MW/cm3 and τ0.9 ∼ 159 ± 2 ns). This strategy inspires rational structurally regulated designs and aims to promote the development of eco-friendly 0.7Bi0.5Na0.5TiO3-based ceramics with excellent energy-storage characteristics.

Intrinsic-strain-induced ferroelectric order and ultrafine nanodomains in SrTiO3

Nano ferroelectrics holds the potential application promise in information storage, electro-mechanical transformation, and novel catalysts but encounters a huge challenge of size limitation and manufacture complexity on the creation of long-range ferroelectric ordering. Herein, as an incipient ferroelectric, nanosized SrTiO3 was indued with polarized ordering at room temperature from the nonpolar cubic structure, driven by the intrinsic three-dimensional (3D) tensile strain. The ferroelectric behavior can be confirmed by piezoelectric force microscopy and the ferroelectric TO1 soft mode was verified with the temperature stability to 500 K. Its structural origin comes from the off-center shift of Ti atom to oxygen octahedron and forms the ultrafine head-to-tail connected 90° nanodomains about 2 to 3 nm, resulting in an overall spontaneous polarization toward the short edges of nanoparticles. According to the density functional theory calculations and phase-field simulations, the 3D strain-related dipole displacement transformed from [001] to [111] and segmentation effect on the ferroelectric domain were further proved. The topological ferroelectric order induced by intrinsic 3D tensile strain shows a unique approach to get over the nanosized limitation in nanodevices and construct the strong strain-polarization coupling, paving the way for the design of high-performance and free-assembled ferroelectric devices.

Excellent energy storage properties and multi-scale regulation mechanism of Sr(Zr0.5Ti0.5)O3-(Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics

With the rapid advancement of energy storage technologies, dielectric capacitor materials with the outstanding recoverable energy density and power density have garnered significant attention from researchers in the past decades. In this study, (1-x) (Na0.5Bi0.5)0.94Ba0.06TiO3-xSr(Zr0.5Ti0.5)O3 ceramics were prepared via a solid-state reaction method, and the impact of composition on their structure, energy storage performance and stability were investigated. The results revealed that the introduction of Sr(Zr0.5Ti0.5)O3 induced the ferroelectric-relaxor transformation of (Na0.5Bi0.5)0.94Ba0.06TiO3 ceramics, leading to the destruction of the long-range ferroelectric order and the formation of polar nanoregions. In addition, the 0.7(Na0.5Bi0.5)0.94Ba0.06TiO3–0.3Sr(Zr0.5Ti0.5)O3 ceramic exhibited the optimal comprehensive energy storage performance: its recoverable energy storage Wrec attained 8.19 J/cm3 at 650 kV/cm, while the energy storage efficiency η was 85.6 %. Meanwhile, it displayed exceptionally high power density (315.7 MW/cm3) and charge-discharge rate (t0.9 = 50.4 ns). Moreover, this ceramic demonstrated the impressive energy storage performance, in particular, good temperature stability across a wide range of temperatures (20–140 °C), frequency stability (1–200 Hz), and fatigue resistance (1–106 cycles). Finite element analysis showed an enhancement in the breakdown field strength of the ceramics was attributed to the reduction in grain size. First-principles calculations revealed that the band gap increased after adding Sr and Zr elements, and the interactions between the states of O 2p and Ti 3d, Zr 3d, Bi 6p may serve as the microscopic origin of electron energy level polarization and enhanced dielectric performance. Thus, the ceramics have great potential for the application in high-power pulsed electronic systems.

Innovative Design of BNKT-xSLZT Ceramics: Maximizing the Polarization Difference for Enhanced Energy Storage.

Lead-free relaxor ferroelectric ceramics with outstanding energy-storage (ES) density (Wrec) and high ES efficiency (η) are crucial for advanced pulse-power capacitors. This study introduces a strategic approach to maximizing the polarization difference (ΔP) by inducing a transition from the ferroelectric phase to the ergodic relaxor (ER) phase. By employing this strategy, a series of ceramics, (1 - x)(Bi0.5Na0.4K0.1)TiO3-x(Sr0.85La0.1)(Zr0.5Ti0.5)O3 (BNKT-xSLZT), with varying SLZT content (x = 0.05, 0.10, 0.15, and 0.20), were designed. The addition of SLZT enhances cationic disorder, induces vacancies at A sites, and disrupts long-range ferroelectric order, facilitating the formation of polar nanoregions and enhancing relaxor ferroelectric behavior. Furthermore, a viscous polymer process (VPP) technology is employed to optimize the ceramics' structure, aiming to increase the breakdown strength (Eb) and enhance ΔP. Ultimately, enhanced ES performance is demonstrated in BNKT-0.15SLZTVPP, achieving a remarkable Wrec of 6.85 J/cm3 and η of 84% under 470 kV/cm. This composition demonstrates excellent stability with minimal variations in Wrec (3.0%) and η (4.4%) over the temperature range of 20-110 °C. Additionally, BNKT-0.15SLZTVPP exhibits exceptional pulse charge-discharge properties, featuring a high discharge density of 3.72 J/cm3, a large power density of 164.2 MW/cm3, and a short discharge time (t0.9) of 193 ns under 300 kV/cm. The study validates the practicality of BNKT-0.15SLZTVPP for pulse capacitors and underscores the potential to enhance ES performance through A-site donor doping and VPP technology. This work provides a comprehensive understanding of the interplay among composition, structure, and ES properties in lead-free relaxor dielectric ceramics, laying the groundwork for innovative advancements in the field.

Achieving High Energy Storage Performance under a Low Electric Field in KNbO3-Doped BNT-Based Ceramics.

Ceramic capacitors have great potential for application in power systems due to their fantastic energy storage performance (ESP) and wide operating temperature range. In this study, the (1 - x)Bi0.5Na0.47Li0.03Sn0.01Ti0.99O3-xKNbO3 (BNLST-xKN) energy storage ceramics were synthesized through the solid-phase reaction method. The addition of KN disrupts the long-range ferroelectric order of the BNLST ceramic, inducing the emergence of polar nanoregions (PNRs), which enhances the ESP of the ceramics. The BNLST-0.2KN ceramic demonstrates a high recovered energy density (Wrec ∼ 3.66 J/cm3) and efficiency (η ∼ 85.8%) under a low electric field of 210 kV/cm. Meantime, it exhibits a large current density (CD ∼ 831.74 A/cm2), high power density (PD ∼ 78.86 MW/cm3), and fast discharge rate (t0.9 ∼ 0.1 μs), along with good temperature stability and excellent fatigue stability. These properties make the BNLST-0.2KN ceramic a promising candidate for energy storage applications in low electric fields.

Structural phase coexistence enhances the energy storage density of (Bi0.5Na0.5)0.8Ba0.2Ti1-ySnyO3 lead-free ceramics

In the present study, BaSnO3 was introduced into polycrystalline NBT-BT ferroelectric ceramics and conducted a comprehensive investigation into the structural, dielectric, ferroelectric, and energy storage characteristics of the (Bi0.5Na0.5)0.8Ba0.2Ti1-ySnyO3 (BNBTS) ceramics. The coexistence of structural phases P4mm and Amm2 was observed through Rietveld refinement and also confirmed by Raman analysis. The formation energy decreases with an increase in substitution concentration favouring the formation of the orthorhombic phase. The SEM analysis revealed a denser microstructure characterised by smaller grain sizes, which favourably enhances energy storage density. Furthermore, Raman spectroscopic analysis unveiled a softening of Ti–O bonds, indicating the emergence of macroscopic relaxor behaviour. Dielectric studies provided evidence of a transition from ferroelectric to relaxor behaviour, an observation further confirmed by P-E loop measurements. This transition can be linked to the partial substitution of Sn4+ ions for Ti4+ ions, disrupting the ferroelectric long-range order within the matrix phase. Notably, the polarization-electric field (P-E) loop of BNBTS2 ceramics exhibited a substantial value of polarization (Ps) 30 μC/cm2 with a reduced value of remnant polarization (Pr) 2.29 μC/cm2. These characteristics contributed to the achievement of higher energy recovery (Wrec) and lower energy loss (Wloss) values, measuring 1.184 J/cm3 and 0.142 J/cm3, respectively, with a notable efficiency of 88.8%. Consequently, the system of ternary ceramics demonstrates promise as a potential option for energy storage ceramics among NBT-BT-based materials.

Enhanced temperature stability of piezoelectric properties and electrostrain via a diffused phase transition in LaMnO3-doped (K, Na)NbO3-based ceramics

Modern-generation electronic devices face a significant challenge in enhancing the temperature stability of their electrical properties, which are crucial for their practical applications. This study introduces an effective approach to diffused phase engineering, involving doping LaMnO3 to induce diffused phase transition. Consequently, the material achieves temperature-insensitive piezoelectric properties and electrostrain. We combine temperature-dependent X-ray diffraction, first-principle calculations, and other dielectric/piezoelectric properties to elucidate the relationship between dopants, structures, and properties in the (0.96-x)K0.48Na0.52NbO3-0.04Bi0.5Na0.5ZrO3-xLaMnO3 systems. Additionally, LaMnO3 doping in KNN-based ceramics maintains long-range ferroelectric order (LRFO) and enhance ferroelectric relaxor behavior, thereby optimizing the electrical properties (such as the d33*of ∼400 pm/V and the TC of ∼300 °C) of ternary co-doped systems. The normalized unipolar strain (Suni/SRT) exhibits a variation of less than 12.2% over the temperature range of 25–150 °C, while d33 at 200 °C retains 80% of its value at 25°C. Moreover, LaMnO3 doping leads to an increase in both depolarization temperature (Td) and d33. Overall, this study provides an effective paradigm for balancing Td and d33 and designing the composition of temperature-insensitive commercial piezoelectronic devices.

Fulfilling X9R specification in CeO2 modified BNBST-based relaxor ferroelectric energy storage ceramic capacitors

Future low-voltage driven capacitor devices are appealed to employ the eco-friendly ceramics featured with high-stable dielectric energy storage capabilities. Herein, the dielectric energy storage properties of (Bi0·5Na0.5)0.65(Ba0·3Sr0.7)0.35(Ti0·98Ce0.02)O3+8 wt% K0·5Na0·5NbO3+x wt% CeO2 (BNBSTCK + Cx) lead-free relaxor ferroelectric ceramics were comprehensively investigated. By maintaining the relaxor ferroelectric phases near room temperature and disrupting the ferroelectric long-range order via CeO2 additive, the EIA X9R specification was fulfilled at the best composition of x = 8 over a wide range of −74∼208 °C with a relatively high dielectric constant εr = 904 and low loss tanδ = 10−3 (@25 °C & 1 kHz). Meanwhile, the good recoverable energy storage density Wrec = 0.77 J/cm3 and high efficiency η = 91.6% were achieved only at a low electric field of 95 kV/cm. Furthermore, these ceramics exhibited exceptional frequency and cycle dependent energy storage stability, which could guide the design ideas of long-life X9R ceramic capacitors suitable for high and low working temperature environments in low-voltage driven energy storage applications.

Effect of chemical intercalation on ferroelectricity in van der Waals layered CuInP2S6

Chemical intercalation brings about intriguing opportunities to tailor the properties of van der Waals (vdW) layered materials by crafting molecular composite at an atomic scale. Despite a plethora of reports on various materials, the chemical intercalation effect on long-range ferroelectric order remains scarcely explored. Herein, we report the construction of hybrid supercrystal based on a model vdW ferroelectric, CuInP2S6 by molecular intercalation. Although the out-of-plane lattice structure remains commensurate, its ferroelectric polarization is largely destroyed by the chemical intercalation, as confirmed by combined piezoresponse microscopy and Raman spectroscopy. Alternatively, we observed a dipole glass transition at about 280 K by dielectric spectroscopy and correlated it with the Raman analysis. This work highlights the impact of chemical intercalation on collective ferroic orders and paves the routes for creating artificial hybrid crystals by incorporating functional molecules.

Large electrostrictive response via tailoring ergodic relaxor state in Bi1/2Na1/2TiO3-based ceramics with Bi(Mn1/2Ce1/2)O3 end-member

Lead-free Bi1/2Na1/2TiO3 (BNT)-based relaxor ferroelectric ceramics with superior electrostrictive coefficient features have recently gained a lot of attention due to their application in high-precision displacement actuators. In this work, we propose an effective approach to enhance the electrostrictive effect via tuning the phase transition temperature around ambient temperature in BNT-based ceramics. Herein, a novel Bi(Mn1/2Ce1/2)O3 (BMnCe) modifier was adopted as an activator into 0.935Bi1/2Na1/2TiO3-0.065BaTiO3 (0.935BNT-0.065BT) for modifying the phase boundary (TF-R) around the ambient temperature. The compositional and temperature-dependent dielectric, ferroelectric, and electrostrain were systematically investigated. All samples exhibit a pure perovskite structure. Rietveld refinement revealed that the 0.935BNT-0.065BT ceramic presents a coexistence of rhombohedral (R3c) and tetragonal (P4bm) phases. As the BMnCe content increases, the tetragonal (P4bm) phase becomes more prevalent and eventually shifts into a pseudocubic phase. It was found that the addition of BMnCe can effectively tune the TF-R below ambient temperature and enhance the relaxor behavior. The polarization and electrostrain analysis revealed that the ferroelectric long-range order decreases with increasing BMnCe; specifically, a unique region emerges where remnant polarization, quasistatic d33, and negative strain abruptly drop. As a result, a high electrostrain (S) of 0.43 % with a normalized strain (Smax/Emax) of 716 pm/V was achieved at the critical composition (0.01 M concentration of BMnCe). More importantly, (0.935-x)BNT-0.065BT-xBMnCe (x = 0.01) shows a large electrostrictive coefficient (Q33) of 0.032 m4/C2 with a giant normalized electrostrictive coefficient (Q33/E) of 5.33ｘ10−9 m5/C2V at room temperature. Furthermore, the Q33 and Q33/E values show temperature insensitivity up to 120 °C, rendering the compound suitable for actuation-based devices. These results offer an effective avenue for designing high-performance BNT-based materials with giant electrostrictive coefficients.

Achieving ultrahigh energy storage density under low electric field in (Na0.5Bi0.5)TiO3-based relaxor ferroelectric ceramics via a synergistic optimization strategy

Lead-free dielectric ceramic capacitors are attracting much interest in pulse power systems owing to their fast charge/discharge rate and high power density. However, their development towards integration and miniaturization in electronic devices has been severely impeded by low energy storage performance (ESP) under low electric field (E). Herein, a synergistic optimization strategy of composition design and domain engineering was proposed in the Bi(Mg0.5Hf0.5)O3-modified Na0.5Bi0.5TiO3-Sr0.7Bi0.2Ca0.1TiO3 ceramics [(1-x)(NBT-SBCT)-xBMH], aiming to improve ESP at low E. As a result, an ultrahigh recoverable energy density (Wrec) of ∼5.9 J/cm3 and a high efficiency (η) of ∼85 % can be obtained in x = 0.20 ceramics under a low E of 260 kV/cm, which is superior to previously reported lead-free materials under the equivalent E. The outstanding Wrec is mainly ascribed to the ultrahigh polarization discrepancy (ΔP) of ∼50.8 μC/cm2 since the rich hybridization of Bi 6 s and O 2p orbitals maintains a maximum polarization and the addition of Mg2+ and Hf4+ transforms the long-range ferroelectric order into polar nanoregions (PNRs) with good relaxation characteristics. Moreover, a fast discharge time (∼62 ns), good temperature (20–120 °C) and frequency (1–103 Hz) stabilities, and excellent fatigue resistance (×105 cycles) can be concurrently realized in x = 0.20 ceramics. These results demonstrate the promising strategy of developing low E lead-free ceramics for dielectric energy storage.

Achieving improved electrocaloric effect and broad operation temperature by tailoring phase fraction in BaTiO3-based ceramics

Ferroelectric electrocaloric (EC) materials are a pivotal part of sustainable micro-cooling, which complements conventional cooling methods in miniaturized devices. However, the application of EC materials is largely limited by the unsatisfactory room-temperature EC response and narrow operation temperature window. In this work, with careful tuning the composition of BaTiO3 (BT)-based ceramics through the conventional doping method, enhanced EC properties were achieved in Ba0.8Sr0.2Zrx(Ti0.999Mn0.001)1-xO3 (BSZMT) (x = 0.05, 0.10, 0.15, and 0.20). We especially found that the electrocaloric temperature change (ΔT) of > 0.50 K was achieved in a broaden temperature ranging from 20 °C to 95 °C and a peak ΔT value of 1.08 K was achieved at temperature of 70 °C in our BSZMT with x = 0.15. To ascertain the physical mechanism, we employed hybrid characterization methods including XRD, Raman, and dielectric analysis together with Density Functional Theory (DFT) calculation. Our results clearly show that the doped Zr and Mn at B site of BSZMT effectively modulate the microstructure leading to coexistence of different ferroelectric phases and broken long-range ferroelectric order, which subsequently results in the enhanced EC performance and broad operating temperature window.

Boosting energy storage performance in Na0.5Bi0.5TiO3-based lead-free ceramics modified by a synergistic design

Na0.5Bi0.5TiO3-based relaxor ferroelectric ceramics have attracted widespread attention due to their potential applications in energy storage capacitors for pulse power system. We herein propose a synergistic strategy of introduction of 6s2 lone pair electrons, breaking the long-range ferroelectric order, and band structure engineering for high performance energy storage by introducing Bi(Mg0.5Sn0.5)O3 (BMS) with weak ferroelectric active cations into 0.7Na0.5Bi0.5TiO3-0.3SrTiO3 (BNT-ST) to form BNT-ST-BMS ceramics. The doped ceramics display the excellent dielectric stability versus temperature and frequency. The suitable BMS doping can increase the band gap of the BNT-ST ceramic and effectively avoids early dielectric breakdown and polarization saturation. The BNT-ST-BMS ceramic in the composition of x = 0.08 exhibits an outstanding recoverable energy storage density (Wrec) of 5.99 J/cm3, together with a good efficiency (ƞ) of 76% as well as an excellent dielectric stability versus temperature (Δεr/εr(150°C) ≤ ±15%) and frequency. The findings in this work demonstrate that the BNT-ST-BMS ceramics have exceptional potential as candidate materials for pulse power and high voltage capacitors applications, and provide a path for the development of the other lead-free energy storage materials.

Creep in 0.91(Na1/2Bi1/2)TiO3-0.06BaTiO3-0.03K0.5Na0.5NbO3 lead-free piezoceramic under constant electric field loads

This work explores the creep behavior of polycrystalline 0.91(Na1/2Bi1/2)TiO3-0.06BaTiO3-0.03K0.5Na0.5NbO3 under constant electric fields. It reveals intriguing time-dependent variations in both polarization and strain response, which can be attributed to a transformation from the relaxor state to a long-range ferroelectric order. Meanwhile, bulk volume resistivity values are obtained to eliminate the influence of leakage current on the polarization assessment. The findings provide valuable insights into the creep behavior of lead-free relaxor ferroelectrics, laying a solid foundation for enhancing the performance and reliability of piezoactuators.

Structure and dielectric properties in Mg/Nb co-substituted bismuth sodium titanate

A systematic study of pseudo-isovalent B site co-substitution of Ti4+ by Mg2+ and Nb5+ in bismuth sodium titanate is presented. A complete solid solution in the Bi0.5Na0.5Ti1−x(Mg1/3Nb2/3)xO3 system is formed. With increasing level of substitution, dielectric anomalies associated with depoling and maximum permittivity temperatures (Td and Tm, respectively) are suppressed and shift to lower temperatures. Variable temperature X-ray powder diffraction on the x = 0.2 composition reveals a non-linear thermal expansion at temperatures below Tm. B-site co-substitution by Mg and Nb has the effect of interrupting the long-range ferroelectric ordering in the system, resulting in lower saturation and remnant polarizations. A maximum energy storage density of 4.14 J cm−3 with a recoverable energy density of 2.35 J cm−3 was obtained for the x = 0.1 composition, while the x = 0.5 composition appears to have the best balance between energy storage and energy efficiency.

Quantum fluctuation of ferroelectric order in polar metals

The polar metallic phase is an unusual metallic phase of matter containing long-range ferroelectric (FE) order in the electronic and atomic structure. Distinct from the typical FE insulating phase, this phase spontaneously breaks the inversion symmetry without global polarization. Unexpectedly, the FE order is found to be dramatically suppressed and destroyed at moderate ~ 10% carrier density. Here, we propose a general mechanism based on carrier-induced quantum fluctuations to explain this puzzling phenomenon. The quantum kinetic effect would drive the formation of polaronic quasi-particles made of the carriers and their surrounding dipoles. The disruption in dipolar directions can therefore weaken or even destroy the FE order. We demonstrate such polaron formation and the associated FE suppression via a concise model using exact diagonalization, perturbation, and quantum Monte Carlo approaches. This quantum mechanism also provides an intuitive picture for many puzzling experimental findings, thereby facilitating new designs of multifunctional FE electronic devices augmented with quantum effects.

Enhanced energy storage properties of Bi0.5Na0.5TiO3-based ceramics via regulating the doping content and sintering temperature

Eco-friendly lead-free energy-storage ceramics featuring high energy storage properties and ultra-high stability have been regarded to be one of the most potential materials in the field of energy storage. In this work, a new element system, (1-x)(0.6Bi0.5Na0.5TiO3-0.4SrTiO3)-xBi[Zn2/3(Nb0.5Ta0.5)1/3]O3 ((1-x)BNST-xBZNT) lead-free ceramics, were synthesized via a conventional solid-state sintering technology. And the phase structure, microstructure and energy storage properties of the (1-x)BNST-xBZNT ceramics were comprehensively studied. After the introduction of BZNT, the average grain size of the materials is greatly decreased, thereby enhancing the dielectric breakdown strength (DBS). Additionally, the thermal stability of the ceramics is significantly improved via regulating the doping content and sintering temperature. Furthermore, the ferroelectric long-range order of the ceramics is decomposed into randomly-oriented polar nano-domains (PNRs) after introducing BZNT, leading to strong relaxor behavior and significantly reducing remanent polarization (Pr). As a result, even under a relatively low electric field of 139 kV/cm, the 0.98BNST-0.02BZNT ceramic sintered at 1150 °C possesses high values of energy storage efficiency (η) value of 92.78% and total energy storage density (Wtot) of 1.67 J/cm3 as well as remarkable thermal stability (25–175 °C), frequency stability (20–70 Hz) and fatigue resistant stability (100-105 cycles). This investigation provides a useful reference for developing advanced energy storage ceramics by regulating the doping content and sintering temperature.

Enhanced Energy Storage Performance and Efficiency in Bi0.5(Na0.8K0.2)0.5TiO3-Bi0.2Sr0.7TiO3 Relaxor Ferroelectric Ceramics via Domain Engineering.

Dielectric materials are highly desired for pulsed power capacitors due to their ultra-fast charge-discharge rate and excellent fatigue behavior. Nevertheless, the low energy storage density caused by the low breakdown strength has been the main challenge for practical applications. Herein, we report the electric energy storage properties of (1 - x) Bi0.5(Na0.8K0.2)0.5TiO3-xBi0.2Sr0.7TiO3 (BNKT-BST; x = 0.15-0.50) relaxor ferroelectric ceramics that are enhanced via a domain engineering method. A rhombohedral-tetragonal phase, the formation of highly dynamic PNRs, and a dense microstructure are confirmed from XRD, Raman vibrational spectra, and microscopic investigations. The relative dielectric permittivity (2664 at 1 kHz) and loss factor (0.058) were gradually improved with BST (x = 0.45). The incorporation of BST into BNKT can disturb the long-range ferroelectric order, lowering the dielectric maximum temperature Tm and inducing the formation of highly dynamic polar nano-regions. In addition, the Tm shifts toward a high temperature with frequency and a diffuse phase transition, indicating relaxor ferroelectric characteristics of BNKT-BST ceramics, which is confirmed by the modified Curie-Weiss law. The rhombohedral-tetragonal phase, fine grain size, and lowered Tm with relaxor properties synergistically contribute to a high Pmax and low Pr, improving the breakdown strength with BST and resulting in a high recoverable energy density Wrec of 0.81 J/cm3 and a high energy efficiency η of 86.95% at 90 kV/cm for x = 0.45.

Structural, dielectric, and morphological properties of (1-x)Ba0.65Sr0.35TiO3-xBi(Mg2/3Nb1/3)O3

Compared to other electrical energy storage devices, dielectric capacitors provide advantages like high power density, fast charge and discharge times, thermal stability, excellent mechanical strength, and a long cycling lifetime. Amongst the various dielectric materials, relaxor ferroelectric materials offer low remanent polarization and high energy efficiency. Previous research has shown that (i) doping Bi3+ ions into perovskite material can achieve improved results because its valence electronic configuration is close to that of Pb2+ and its ionic radius is also comparable to that of Ba2+, and (ii) introducing complex ions at the B-site can reduce the long-range ferroelectric order and result in the occurrence of polar nano regions.The present work aims at (i) incorporating both these strategies for the synthesis of the dielectric ceramic material and (ii) studying the structural, morphological, and dielectric properties of the prepared material. We have successfully synthesized (1-x) Ba0.65Sr0.35TiO3 – x BiMg2/3Nb1/3O3 with the help of a conventional solid-state reaction technique. The XRD analysis demonstrates the formation of cubic perovskite structure with space group Pm3m. The diffraction peaks shift towards lower 2θ angles with an increasing concentration of BMN, indicating a regular increase in unit cell volumes owing to the substitution of the smaller Ti4+ ions with bigger Mg2+ and Nb5+ ions. FESEM images illustrate the development of a homogeneous and dense microstructure. Element mapping analysis confirms the uniform distribution of all the elements within the prepared sample. From the dielectric measurements, we found that with the increase in doping, the dielectric peak broadens, and the frequency dispersion increases, indicating a rise in the relaxor behavior, which may be attributed to the increase in cation disorder due to the substitution of Bi3+ and [Mg2/3Nb1/3]4+ at the A- and B-site, respectively. The excellent dielectric properties indicate that (1-x)BST-xBMN is a promising ceramic material for use as a dielectric in capacitors for advanced pulsed power applications and consumer electronic devices.