Relaxor Ferroelectric System Research Articles

The phase composition, dielectric, and energy storage performance of A-site vacancy modulated BaTiO3 ceramics with Bi(In1/2(Li0.5Ta0.5)1/2)O3 modification

The (1-x)Ba0.94Ce0.04TiO3-xBi(In1/2(Li0.5Ta0.5)1/2)O3 (BCT-BILT) relaxor ferroelectric ceramic system was explored based on the A-site vacancy design and defect dipole engineering. The impacts of different doping concentrations on the phase composition, dielectric and energy storage performance of the BCT-BILT ceramics were studied and discussed in detail. The pure BCT and 0.95BCT-0.05BILT samples exhibited a mixed crystal structure of tetragonal (T) and pseudo-cubic (PC) phase, while the BCT-BILT samples with x > 0.05 possessed a cubic (C) phase, accompanied by the secondary phases of BaBi2Ta2O9 and BaTa2O6. With an increase in the BILT doping concentration, the surface morphologies of the ceramics were continuously modulated, and the dielectric loss had been reduced to 0.001 at 1 kHz, which was beneficial to improve the energy storage properties. Compared to the pure BCT, the breakdown field strength was significantly enhanced owing to the formation of Aurivillius phase BaBi2Ta2O9 and the increased dielectric relaxation. Ultimately, the highest energy storage density of Wrec = 0.7 J/cm3 and high energy conversion efficiency of η = 95 % was realized at the composition of x = 0.05 under a small electric field of 130 kV/cm. Furthermore, the good temperature stability with the ΔWrec/Wrec30°C < 9 % and Δη/η30°C < 6.5 % was acquired for the samples with x = 0.20–0.30 in the temperature range of 30–120 °C, owing to the synergistic roles of the defect dipoles, impurities BaBi2Ta2O9, and polar nanoregions (PNRs). The 0.95BCT-0.05BILT ceramic obtains discharge energy density Wdis of 0.35 J/cm3 and fast discharge speed t0.9 of 312 ns at 60 kV/cm, current density CD of 255.4 A/cm2 and power density PD of 10.2 MW/cm3 at 80 kV/cm. This work is of guiding significance for designing and optimizing energy storage performance of lead-free relaxors from the perspective of defect building and engineering.

Synergistic optimization of delayed polarization saturation and enhanced breakdown strength in lead-free capacitors for superior energy storage characteristics

High-performance dielectric energy-storage ceramics are indispensable core components in pulsed power systems. Despite progress in enhancing energy storage performance, there are still significant constraints among various macroscopic performance parameters, hindering their miniaturization and integration into devices. Herein, we propose a novel weakly coupled relaxor ferroelectric ceramic system that delays premature polarization saturation of BaTiO3-based ceramics to achieve the desirable energy storage characteristics. The ceramic exhibits a high energy storage density (Wrec) of ∼4.58 J cm−3 and high energy efficiency (η) of ∼95.2 % under an electric field of 540 kV cm−1, along with good performance stability in the range of 40–160 °C and 1–120 Hz. Furthermore, the enhanced insulation properties and refined average grain size contribute to the high breakdown field strength (Eb) of the system. These findings provide a viable framework for the design of dielectric ceramic capacitors with high energy-storage characteristics.

Outstanding energy density and charge-discharge performances in Sr2KNb5O15-based tungsten bronze ceramics for dielectric capacitor applications

Relaxor ferroelectric ceramics are extremely encouraging materials for energy storage capacitor applications in pulse equipment. As the second largest ferroelectric ceramic system, tungsten bronze structure relaxor ferroelectric ceramics have emerged as a significant contender and garnered significant attention in the pulse capacitor research field. In this work, an Sb-modified Sr2KNb5O15-based tungsten bronze relaxor ferroelectric ceramic system is designed to explore its energy storage potential. XRD refinement reveals the declines in the oxygen octahedra tilting and distortion after the introduction of Sb, which significantly augments the relaxation behavior. Additionally, refined grain size and reduced oxygen vacancy concentration are observed, greatly improving the breakdown strength. Consequently, a superior energy storage density (∼4.57 J/cm3) accompanied by wonderful energy storage efficiency (∼89.3 %) is received at 540 kV/cm, with wide frequency stability and great thermal stability. Moreover, amazing discharging performances are also achieved with rapid discharge speed (τ0.9 < 70 ns), towering discharge current density (815.2 A/cm2) and surprising power density (130.4 MW/cm3). All these performances indicate that the designed Sr2KNb5O15-based tungsten bronze relaxor ferroelectric ceramic can be one encouraging option in the dielectric energy storage field.

High‐throughput combinatorial approach expedites the synthesis of a lead‐free relaxor ferroelectric system

AbstractDeveloping novel lead‐free ferroelectric materials is crucial for next‐generation microelectronic technologies that are energy efficient and environment friendly. However, materials discovery and property optimization are typically time‐consuming due to the limited throughput of traditional synthesis methods. In this work, we use a high‐throughput combinatorial synthesis approach to fabricate lead‐free ferroelectric superlattices and solid solutions of (Ba0.7Ca0.3)TiO3 (BCT) and Ba(Zr0.2Ti0.8)O3 (BZT) phases with continuous variation of composition and layer thickness. High‐resolution x‐ray diffraction (XRD) and analytical scanning transmission electron microscopy (STEM) demonstrate high film quality and well‐controlled compositional gradients. Ferroelectric and dielectric property measurements identify the “optimal property point” achieved at the composition of 48BZT–52BCT. Displacement vector maps reveal that ferroelectric domain sizes are tunable by varying {BCT–BZT}N superlattice geometry. This high‐throughput synthesis approach can be applied to many other material systems to expedite new materials discovery and properties optimization, allowing for the exploration of a large area of phase space within a single growth.image

A novel lead‐free relaxor with endotaxial nanostructures for capacitive energy storage

AbstractDielectric capacitors with a fast charging/discharging rate, high power density, and long‐term stability are essential components in modern electrical devices. However, miniaturizing and integrating capacitors face a persistent challenge in improving their energy density (Wrec) to satisfy the specifications of advanced electronic systems and applications. In this work, leveraging phase‐field simulations, we judiciously designed a novel lead‐free relaxor ferroelectric material for enhanced energy storage performance, featuring flexible distributed weakly polar endotaxial nanostructures (ENs) embedded within a strongly polar fluctuation matrix. The matrix contributes to substantially enhanced polarization under an external electric field, and the randomly dispersed ENs effectively optimize breakdown phase proportion and provide a strong restoring force, which are advantageous in bolstering breakdown strength and minimizing hysteresis. Remarkably, this relaxor ferroelectric system incorporating ENs achieves an exceptionally high Wrec value of 10.3 J/cm3, accompanied by a large energy storage efficiency (η) of 85.4%. This work introduces a promising avenue for designing new relaxor materials capable of capacitive energy storage with exceptional performance characteristics.

Structural quantification of polar/nonpolar phases of relaxor clusters in transparent ferroelectric ceramics

A dual-phase refinement protocol considering distinct amounts of polar/nonpolar phases reflecting the polar nano phases formation in two relaxor ferroelectric systems was performed. The samples of PLZT and PLMN-PT have shown a typical relaxor behavior with different freezing temperatures, and the amounts of the polar phase of the lack of ergodicity were obtained using structure parameters.

Anisotropy free energy contribution of the ferroelectric domain dynamics in PMN‐PT and PIN‐PMN‐PT relaxor ferroelectrics

AbstractA direct correlation between the materials property behavior with its associated ferroelectric domain mechanisms and the anisotropic component of the Landau free energy is established for binary PMN‐PT (generation I) and ternary PIN‐PMN‐PT (generation II) relaxor ferroelectric single crystal material systems. In addition to their trade‐off in material properties, the observed ferroelectric domain dynamic and the determined free energy anisotropies, especially as approaching phase transition, provide direct insights into the materials field‐dependent behavior between the binary and ternary ferroelectric systems. Domain configuration features such as lamellar structures in binary PMN‐PT and concentric oval‐like structures in ternary PIN‐PMN‐PT result in different material responses to external stimuli. Compared to binary PMN‐PT, the concentric oval‐like domain structures of ternary PIN‐PMN‐PT result in a 20°C higher temperature range of field‐dependent linear behavior, 40% increase in coercive electric field higher elastic stiffness during ferroelectric domain switching, and lower electromechanical energy losses. Separation of the isotropic and anisotropic components in the Landau free energy reveals a higher anisotropic free energy contribution from the ternary system, especially at temperature for practical applications. The high anisotropic free energy found in the ternary PIN‐PMN‐PT system implies that the concentric oval‐like domain structure contributes to reduced electromechanical energy losses and enhanced stability under external applied fields.

Electric field-induced two-step phase transformation and its contribution to the electromechanical strain in lead-free relaxor-based ceramics

Sodium bismuth titanate-based solid solutions are important lead-free piezoelectrics with potential applications. Large electromechanical strain is of particular interest, which can be realized via the structural change in the relaxor states under an electric field. In this work, a polycrystalline ceramic 0.85Na1/2Bi1/2TiO3–0.15BaZr0.2Ti0.8O3, in which a long-range ordered ferroelectric phase and a relaxor state coexist, has been investigated to unveil the origin of its electromechanical strain using various experimental techniques. An ergodic-relaxor to nonergodic-relaxor transition is first observed under a relatively weak electric field, and a more stable long-range ferroelectric phase is induced under a larger electric field. This two-step phase transformation is accompanied with the process of local polarization freezing as well as ferroelectric domain growth. The domain formation during the reversible phase transition is found to be the main contribution to the macroscopic strain. Our investigation provides an in-depth understanding of the origin of reversible electromechanical strain in the NBT-based relaxor-ferroelectric system.

A combination of large unipolar electrostrain and d33 in a non-ergodic relaxor ferroelectric

One of the important requirements for piezoelectric materials for use as high strain actuators is that they exhibit large unipolar electrostrain with minimum hysteresis. While large unipolar electrostrain &amp;gt;1% is generally achievable in good quality single crystals, most polycrystalline piezoelectric show low values &amp;lt; 0.4%. Unipolar electrostrain 0.5%–0.7% in polycrystalline piezoelectrics has often been reported in Na0.5Bi0.5TiO3-based compositions at the non-ergodic ergodic boundary. Not amenable to poling, such materials exhibit almost nearly zero direct piezoelectric coefficient (d33 ∼ 0 pC/N) and cannot be simultaneously used as a sensor. In this paper, we report a combination of large unipolar electrostrain of ∼0.6% with small strain hysteresis of 25% in a Sn-modified relaxor ferroelectric system PbTiO3–Bi(Ni1/2Zr1/2)O3. It exhibits d33 ∼ 340 pC/N, which is stable up to 130 °C, and large signal converse piezoelectric coefficient d33* ∼ 1200 pm/V. A combination of large d33 and d33* in the same material makes it an important candidate for simultaneous use as a sensor and high strain actuators. X-ray diffraction study in situ with the electric field suggests that large electrostrain with low strain hysteresis in this system is because of the increased reversible switching of the field stabilized tetragonal ferroelastic domains.

Deciphering the atomic-scale structural origin for large dynamic electromechanical response in lead-free Bi0.5Na0.5TiO3-based relaxor ferroelectrics

Despite the extraordinary electromechanical properties of relaxor ferroelectrics, correlating their properties to underlying atomic-scale structures remains a decisive challenge for these “mess” systems. Here, taking the lead-free relaxor ferroelectric Bi0.5Na0.5TiO3-based system as an example, we decipher the atomic-scale structure and its relationship to the polar structure evolution and large dynamic electromechanical response, using the direct atomic-scale point-by-point correlation analysis. With judicious chemical modification, we demonstrate the increased defect concentration is the main driving force for deviating polarizations with high-angle walls, leading to the increased random field. Meanwhile, the main driving force for deviating polarizations with low-angle walls changes from the anti-phase oxygen octahedral tilting to the multidirectional A-O displacement, leading to the decreased anisotropy field. Benefiting from the competitive and synergetic equilibrium of anisotropic field versus random field, the facilitated polarization rotation and extension versus facilitated domain switching are identified to be responsible for the giant electromechanical response. These observations lay a foundation for understanding the “composition-structure-property” relationships in relaxor ferroelectric systems, guiding the design of functional materials for electromechanical applications.

Medium electric field-induced ultrahigh polarization response and boosted energy-storage characteristics in BNT-based relaxor ferroelectric polycrystalline ceramics

Lead-free dielectric ceramics with a high recoverable energy-storage density (Wrec) and improved efficiency (η) are crucial for the development of pulse power capacitor devices. Although Wrec has been constantly improving, mainly via an increased breakdown electric field strength (Eb), a large driving electric field (>500 kV/cm) increases security risks and consequently increases insulating technology costs. In this work, we present a new (Bi0.5Na0.5)TiO3 (BNT)-based relaxor ferroelectric system, (1−x)(0.75Bi0.5Na0.4K0.1TiO3-0.25SrTiO3)-xBi(Mg0.5Ti0.5)O3 (BS-xBMT), with x ranging from 0.05 to 0.20. BMT disrupts both the A- and B-site long-range ferroelectric order of the ABO3 perovskite-structured BS matrix, induces polar nanoregions, and simultaneously increases Wrec and η. Aided by the viscous polymer process, the Eb with x = 0.15 increased to 270 kV/cm, and a maximum polarization (Pm) of 62 μC/cm2 was attained. A boosted Wrec of 4.82 J/cm3 and a high η of 84.9% were simultaneously obtained, together with good temperature stability from 30 to 140 °C. These results show that BNT-based dielectric ceramics with superior energy-storage properties can be obtained under a medium electric field.

Quantitative investigation of polar nanoregion size effects in relaxor ferroelectrics

Understanding the size effects of polar nanoregion (PNR) in relaxor ferroelectrics is vital for a deep understanding mechanism to improve piezoelectric/dielectric constants. In this work, we theoretically predict that, below a critical size, the polar nanoregions possess the collinear state with matrix phase, which leads to the enhancement of the piezoelectric effect. More significantly, the critical size quantitatively tends to increase with a reduced free energy barrier between the matrix and PNR phases. In contrast, it tends to decrease with gradient energy coefficient. This work promotes an understanding of the mechanism of the relaxor ferroelectric system and guides the design of high piezoelectric materials with a wide temperature range.

Nanomechanical measurements of PLZT ceramic during switching events

In this work, we track changes in the elastic modulus during switching-piezoresponse microscopy (SPRM) measurements on relaxor ceramic Pb0.88La0.08Zr0.6Ti0.4O3 (∼100 μm thick). SPRM measures the local strain in a nanometric volume of the material surface caused by an electric field sent through the tip probe. By tracking the contact resonance, it is possible to determine the contact normal stiffness and hence the elastic modulus. The results show that the applied field induces, in addition to the ferroelectric switching, a change in elastic properties that is reflected as a defined hysteretic elastic loop, indicating a softening and hardening of the material. Variations in the elastic modulus of about 5–10 GPa during ferroelectric switching are possibly induced by a rhombohedral to tetragonal phase transformation, and vice versa, during polarization switching. To reduce the contributions of charge injection through the probe, electrostriction, and electrostatic charges in the evaluated nanometric volume, our results are reported in the off-field condition. Our results broaden the understanding of the elastic behavior of relaxor ferroelectric systems.

Enhanced energy storage performance of eco-friendly BNT-based relaxor ferroelectric ceramics via polarization mismatch-reestablishment and viscous polymer process

In this work, we synthesized a novel and eco-friendly relaxor ferroelectric system, i.e., (1−x)(0.8Bi0.5Na0.4K0.1TiO3-0.2SrTiO3)-xNaNbO3 (BS-xNN) ceramics with x = 0.1–0.4 based on a solid state reaction technique. The structural, microstructural, dielectric as well as ferroelectric characteristics of BS-xNN ceramics were comprehensively examined. According to our findings, the Ti–O coupling reduces as the NN content increases, while the Nb–O coupling strengthens, leading in a nano-scale polarization mismatch-reestablishment process that enhances energy storage performance. Because of the reduction in thickness and porosity, the viscous polymer process significantly increases the breakdown strength of ceramic samples. More crucially, at 260 kV/cm, 0.6BS-0.4NN ceramics have an ultrahigh recoverable energy storage density Wrec of 4.44 J/cm3 and a high energy storage efficiency η of 81.8%. Furthermore, thermal stability of energy storage performance is also identified across a wide temperature range of 30 °C from 140 °C at 215 kV/cm. The higher performance of energy storage not only indicates the feasibility of our technique, but also serves as a model for the manufacturing of high-quality dielectric ceramics with a wide range of industrial applications.

Critical state to achieve a giant electric field-induced strain with a low hysteresis in relaxor piezoelectric ceramics

Due to the extrinsic contribution of domain wall motions to electro-strains, the incompatibility of the large electro-strain with a low hysteresis in piezoelectric ceramics is a stumbling block for designing high-performance piezoelectrical actuators. Herein, we report a critical state in relaxor ferroelectric systems enables to enhance the electro-strain and to reduce the hysteresis simultaneously. A room temperature ergodic relaxor state dominated by nanodomains with different local symmetries can be obtained by introducing Bi(Zn1/2Ti1/2)TiO3 into 0.73 Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 matrix. Like the morphotropic phase boundary (MPB) in ferroelectrics, the coexistence of different local symmetries is capable of facilitating the transition from the ergodic relaxor state to the ferroelectric under the applied field due to the ease of polarization rotation, thereby leading to a giant electro-stain (0.24%) under an electric field of 50 kV/cm. Furthermore, the field-induced ferroelectric state with the long-range ferroelectric order can spontaneously reverse back to the initial ergodic relaxor state during unloading the electric field, which contributes to a low hysteresis (15.4%). The present work not only introduces a solid solution system with excellent electro-strain properties but also affords a guidance for manipulating the electro-strain behavior by modulating phase structures and domain configurations of piezoelectric ceramics.

Re‐entrant ferroelectric relaxor phenomena in the (1 − x)[Bi1/2(Na1/2K1/2)1/2TiO3]‐xPbZrO3 system

AbstractThe solid solution (1 − x)[Bi1/2(Na1/2K1/2)1/2TiO3]‐xPbZrO3, (0.00 ≤ x ≤ 0.12) was investigated to examine the phase equilibria, dielectric and electromechanical properties. The composition corresponding to x = 0.00 exhibits tetragonal symmetry with the expected classical ferroelectric (FE) behavior. The system exhibited FE to relaxor crossover with the addition of lead zirconate at the composition x = 0.05. This is indicated by typical relaxor characteristics such as a transition to the global pseudocubic phase, a constriction in the FE hysteresis loop, and a sudden decrease in the negative strain accompanied by an increase in maximum strain. Most notably, with a further increase in x (&gt;0.05), there is evidence for a return to a FE phase that exhibits classical FE characteristics. The combined results demonstrate that there exists a narrow FE‐relaxor boundary near x = 0.05, where FE and relaxor phases coexist. At the critical composition, enhancement in the piezoelectric properties, including an increase in the effective (350 pm/V) was observed. This transition in the electromechanical properties is consistent with changes observed in the phase equilibria for this solid solution. The crystal structure transitions from tetragonal symmetry for x = 0.00, to pseudocubic symmetry for the relaxor compositions (x = 0.05), and finally to a lower symmetry perovskite phase for the re‐entrant FE phase (x&gt; 0.05). This composition‐induced transition from FE to relaxor to a re‐entrant FE state in the (1 − x)[Bi1/2(Na1/2K1/2)1/2TiO3]‐xPbZrO3 system is unusual among relaxor FE systems and thus is of great scientific and technological interest.

Multifunctional response of lanthanum-modified PZT relaxor ferroelectric system with improved electrocaloric effect and energy storage performance

A systematic investigation of both electrocaloric effect (ECE) and energy storage properties is presented in the Pb0.88La0.08(Zr0.60Ti0.40)O3 relaxor system. The ECE, studied from direct and indirect methods, revealed an electrocaloric temperature change (ΔT) around 1.6 K, under an applied electric field of 60 kV/cm at room temperature, with a corresponding electrocaloric strength (ΔT/ΔE) around 0.03 K cm/kV. The temperature dependence of ΔT displayed its maximum value (∼2.32 K) around the freezing temperature (Tf), which is known as a critical temperature for relaxor ferroelectrics, thus suggesting an important contribution of the polar nanoregions to the electrocaloric properties. This result, together with the observed recoverable energy density (Jr) value around 0.43 J/cm3 and a relatively high discharge energy efficiency, reveals the studied system as a promising material for application in multifunctional devices based on high ECE materials combined with excellent energy storage performance.

Systematic study of structure and piezoelectric properties of Pb(Ni1/3Nb2/3)O3‐PbTiO3 by in situ synchrotron diffraction

AbstractLead‐based ferroelectric materials are extensively employed in industrial applications and everyday life due to their excellent ferroelectric and piezoelectric performance. Pb(Ni1/3Nb2/3)O3‐PbTiO3 (PNN‐PT) is a typical binary relaxor ferroelectric system, whose refined structure and piezoelectric properties have not been systematically investigated. In this study, evolution of electric field‐based crystal structure and variation of ferroelectric, piezoelectric, as well as dielectric properties with composition and temperature of (1 − x)PNN‐xPT (0.32 ≤ x ≤ 0.36) ceramics were studied in full detail. The optimal performance is obtained at 0.66PNN‐0.34PT with maximum piezoelectric coefficient d33 of 560 pC/N and large dielectric constant of 28 684. In situ high‐energy synchrotron diffraction was employed to determine structural origins of enhanced properties of 0.66PNN‐0.34PT. Interestingly, crystal structure of poled 0.66PNN‐0.34PT ceramic is determined to be single monoclinic phase. Furthermore, both its lattice parameters and volume variation present butterfly shape under electric field. It is demonstrated that macroscopic strain of 0.66PNN‐0.34PT stems mainly from intrinsic structure. The present study provides evidence for the relationship between microstructure and macroscopic properties, which is beneficial to the design of new materials with piezoelectric properties.

Atomic-resolution electron microscopy of nanoscale local structure in lead-based relaxor ferroelectrics

Relaxor ferroelectrics, which can exhibit exceptional electromechanical coupling, are some of the most important functional materials, with applications ranging from ultrasound imaging to actuators. Since their discovery, their complex nanoscale chemical and structural heterogeneity has made the origins of their electromechanical properties extremely difficult to understand. Here, we employ aberration-corrected scanning transmission electron microscopy to quantify various types of nanoscale heterogeneities and their connection to local polarization in the prototypical relaxor ferroelectric system Pb(Mg1/3Nb2/3)O3-PbTiO3. We identify three main contributions that each depend on Ti content: chemical order, oxygen octahedral tilt and oxygen octahedral distortion. These heterogeneities are found to be spatially correlated with low-angle polar domain walls, indicating their role in disrupting long-range polarization and leading to nanoscale domain formation and the relaxor response. We further locate nanoscale regions of monoclinic-like distortion that correlate directly with Ti content and electromechanical performance. Through this approach, the connections between chemical heterogeneity, structural heterogeneity and local polarization are revealed, validating models that are needed to develop the next generation of relaxor ferroelectrics.

Factors contributing to the local polar-structural heterogeneity and ultrahigh piezoelectricity in Sm-modified Pb(Mg1/3Nb2/3)O3–PbTiO3

Recently, an ultrahigh piezoelectricity (longitudinal piezoelectric coefficient d33 ~ 1500 pC/N) was reported in polycrystalline specimens of Sm-modified relaxor ferroelectric system Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) (Li et al 2018 Nat. Mater. 17 349). Here, we examine the factors associated with this anomalous phenomenon by carrying out a comparative structural, dielectric, ferroelectric and impedance spectroscopy on Sm-free 0.71PMN-0.29PT (piezoelectric coefficient d33 ~ 380 pC/N) and its Sm modified counterpart (d33 ~ 1160 pC/N). We found that, apart from inducing a Cm → P4mm inter-ferroelectric instability, Sm modification stabilizes a considerable degree of oxygen vacancies, with Sm exhibiting valence fluctuation. Based on our results, we argue that these defect types are the important source for creating structural-polar heterogeneity on the local scale, the interaction of which with the long-range ferroelectric order makes the system exhibit an ultrahigh piezoelectric response.