Electric Field-induced Strain Research Articles

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.

Solid state crystal growth of single crystals of 0.75(Na1/2Bi1/2)TiO3-0.25SrTiO3 and their characteristic electrical properties

ABSTRACT Ceramics of composition 0.75(Na1/2Bi1/2)TiO3-0.25SrTiO3 (NBT-25ST) show a giant electric field-induced strain, making them attractive for actuator applications. Single crystals generally have improved piezoelectric properties over their ceramic counterparts, but the electrical properties of NBT-25ST single crystals have not yet been studied. In this work, NBT-25ST single crystals are grown by the solid state crystal growth technique and their electrical properties measured for the first time. The single crystals show relaxor ferroelectric behavior typical of an NBT-type material. The ferroelectric and inverse piezoelectric properties depend strongly on crystallographic orientation, with superior properties in the (001) orientation. The inverse piezoelectric properties of the (001)-oriented NBT-25ST single crystal are superior to those of an NBT-25ST ceramic (Smax/Emax = 1042 pm/V vs. 739 pm/V).

Energy storage density and piezoelectric performances of barium strontium titanate modified bimuth sodium lanthanum titanate lead-free ceramics

Lead-free (1-x)(Bi0.487Na0.487La0.017)TiO3-x(Ba0.7Sr0.3)TiO3 or (1-x)BNLT-xBSrT ceramics were fabricated by a solid state reaction and sintered at 1050–1200 °C for 2 h. All sintered samples had a relative density > 97% of their theoretical values. With increasing BSrT, the transition from BNLT rhombohedral to BSrT tetragonal was observed. The addition of BSrT inhibited grain growth which resulted in the improvement of the densification of the BNLT ceramic. The changes in the BSrT content also induced a phase transition from the ferroelectric (FE) phase to the ergodic relaxor (ER) phase. These changes significantly disrupted long-range ferroelectric order, thereby correspondingly reducing the Pr and Ec values and resulting in the enhancement of the electric field-induced strain and electrostrictive response. A large Smax = 0.41%, d*33 = 788 pm/V and electrostrictive coefficient (Q33 = 0.04119 m4/C2) were observed for the x = 0.08 sample. In addition, the x = 0.15 sample showed good energy storage density (W = 0.66 J/cm3) and energy storage efficiency (η = 82.7%) @ 150 °C. Overall, these results indicated that these ceramics had the potential of becoming one of the promising lead-free piezoelectric candidates for piezoelectric applications.

Gaint electric field-induced strain and ferroelectric behavior of Bi0.5Na0.4K0.1TiO3-Na1-xLixNbO3 lead-free ceramics

0.96 Bi0.5Na0.4K0.1TiO3-0.04Na1-xLixNbO3 (BNKT-100xLi, x = 0, 0.25, 0.5, 0.75, 1.0) lead-free ceramics were prepared using traditional solid-state reaction method. X-ray diffraction patterns confirmed the pure perovskite structure of sintered ceramics. Electric field and composition-dependent strain behavior was investigated. The highest bipolar strain of 0.45% and the unipolar strain 0.443% was achieved at x = 0.75 under the applied electric field of 70 kV/cm. Meanwhile, the corresponding normalized strain (d33*) reached to 633 pm/V. Moreover, the giant strain exhibited excellent thermal stability and fatigue-resistance (within 105 switching cycles) properties, and the large strain was attributed to the reversible electric field-induced transition between relaxor and ferroelectric phase.

Dielectric, Ferroelectric, and Strain Study of BNT-BT-BKT Ceramics for Actuator Applications

The 0.88Bi0.5Na0.5TiO3-0.04BaTiO3-0.08Bi0.5K0.5TiO3 (BNT-BT-BKT) ceramics were synthesized by a conventional solid-state reaction, and their structural, dielectric, polarization versus electric field (P–E), and induced strain versus electric field (S–E) properties were studied in detail. The structural study confirmed the morphotropic phase boundary nature of the ceramics. The depolarization temperature (Td) and Curie temperature (Tc) were found to be ∼ 70°C and 299°C, respectively, which correspond to ferroelectric to antiferroelectric and antiferroelectric to paraelectric phase transitions, respectively. Remnant polarization (Pr) of ∼ 22 μC/cm2, a coercive field (Ec) of ∼ 22 kV/cm, and an electric field-induced maximum strain% of ∼ 0.63 were observed in the ceramics. as well as good ferroelectric properties, the high induced strain% points to the usefulness of this system for actuator applications.

Large Electric Field-Induced Strain Response Under a Low Electric Field in Lead-Free Bi1/2Na1/2TiO3-SrTiO3-BiAlO3 Ternary Piezoelectric Ceramics

Bismuth-based lead-free ceramics are some of the most promising candidates for actuator applications due to their large strain response. Despite the large strains in bismuth-based piezoelectric ceramics, there still remain challenges regarding their utilization in practical applications. For instance, a relatively high operating field is required to obtain the large strain properties. In this work, lead-free Bi1/2Na1/2TiO3-SrTiO3-BiAlO3 (BNT-ST-BA) ternary piezoelectric ceramics are proposed as materials that could enhance the electromechanical strain performance under low driving field. We found that the highest normalized strain d33* value of 707 pm/V was achieved at a relatively low electric field of 3 kV/mm from 2 mol.% BA-modified BNT-ST ceramics. We suggest that the naturally induced nonergodicities in the ergodic relaxor generate internal stress. This induced internal stress is responsible for the excellent strain properties of this material. We believe that the materials synthesized in this study are promising candidates for actuator applications.

0.4% Electrostrain at Low Field in Lead-Free Bi-Based Relaxor Piezoceramics by La Doping

This work investigates the effects of lanthanum doping on the crystal structure, surface morphology, dielectric properties, ferroelectric properties, piezoelectric properties, and electromechanical strain properties of lead-free (Bi0.47Na0.47Ba0.06)1−xLaxTiO3 piezoelectric ceramics. All specimens were fabricated by a traditional solid-state reaction method. The results of crystal structure and dielectric properties categorize all specimens as relaxor materials. The results of dielectric properties and ferroelectric properties confirm the nonergodic-to-ergodic transformation as a function of La content. At the phase transition point, the material shows a high electric field-induced strain of 0.4% under an applied electric field of 5 kV/mm. The large electromechanical strain response at low applied field in the 0.02 mol La specimen may contribute to the two synergistic effects. First, the electric field induced the reversible ergodic-ferroelectric phase transition, which can generate the large strain. Second, the nonergodic and ergodic phases coexist at the phase transformation point, which can reduce the driving field by facilitating the growth of ferroelectric domains.

Phase evolution and origin of the high piezoelectric properties in lead-free BiFeO3–BaTiO3 ceramics

La-substitution effects for Bi3+-site in 0.7Bi1.03(1-x)LaxFeO3-0.3BaTiO3 (abbreviated as BF30BT-100xLF with x = 0.00, 0.01, 0.035, 0.06, 0.07 and 0.10) ceramics were investigated systematically. All ceramics were synthesized by a conventional solid-state reaction method and quenched in water from its sintering temperature. The crystal structure Rietveld refinement shows that undoped BF30BT ceramic exhibited dominant rhombohedral (R) symmetry and gradually changed to the tetragonal (T) phase with La-doping. However, for x ≥ 0.07 compositions the lattice distortions (cT/aT and 90°−αR) significantly decrease as a result crystal structures become close to the cubic-like (CL) phase. Hence, two different morphotropic phase boundaries (MPBs) were reported for BF30BT-100xLa ceramic system; one MPB-I between the R and T phases and the other MPB-II between T and CL phases. The largest direct piezoelectric coefficient (d33 = 274 pC/N) with a high Curie temperature (TC = 532 °C) for BF30BT-1LF composition was obtained due to the typical MPB-I between R and T phases. However, a maximum electric field-induced strain (Smax = 0.27%) with a high converse piezoelectric coefficient (d33* = 500 pm/V) for BF30BT-7LF ceramic was mainly attributed to the MPB-II of T + CL phases and soft ferroelectric switching properties.

Synergetic effect of BiYb0.9Sc0.1O3 substitution on the energy storage performance of Ba0.90Sr0.10Ti0.90Zr0.10O3 ferroelectric ceramic

Novel lead-free (1−x)Ba0.90Sr0.10Ti0.90Zr0.10O3–(x)BiYb0.9Sc0.1O3 (0 ≤ x ≤ 0.10) relaxor ceramic solid solutions were prepared by modified mechano-chemical activation technique with the aim of improving the energy storage properties. The Rietveld analysis of the materials indicated that all the samples show a tetragonal crystal structure with a perovskite phase. The grain morphology and density of the materials have significantly improved with BiYb0.9Sc0.1O3 (BYS) substitution. The dielectric study indicates a gradual transformation from classical to relaxor dielectric with increasing BYS substitution. The ferroelectric to paraelectric transition temperature increases with increasing BYS concentration and has shown a rise of approximately 24 °C for the sample with x = 0.10 compared to the bare sample (x = 0.0). Further, the ferroelectric hysteresis loops have become significantly slimmer with a slight increase in saturation polarization, which indicates an improvement in energy storage performance of the material with BYS substitution. The optimum energy storage properties have been obtained at x = 0.06, and the sample showed a high recoverable energy density of 1.24 J cm−3 under the applied electric field of ±100 kV cm−1. The electric field-induced bipolar strain is improved by 12% for the sample with concentration x = 0.06 compared to the bare sample. This study provides a basis for preparing BaTiO3 based high performance ferroelectric ceramics with their potential application in pulse capacitors.

Ultra-large electric field-induced strain in potassium sodium niobate crystals.

Electromechanical coupling in piezoelectric materials allows direct conversion of electrical energy into mechanical energy and vice versa. Here, we demonstrate lead-free (K x Na1-x )NbO3 single crystals with an ultrahigh large-signal piezoelectric coefficient d 33* of 9000 pm V-1, which is superior to the highest value reported in state-of-the-art lead-based single crystals (~2500 pm V-1). The enhanced electromechanical properties in our crystals are realized by an engineered compositional gradient in the as-grown crystal, allowing notable reversible non-180° domain wall motion. Moreover, our crystals exhibit temperature-insensitive strain performance within the temperature range of 25°C to 125°C. The enhanced temperature stability of the response also allows the materials to be used in a wider range of applications that exceed the temperature limits of current lead-based piezoelectric crystals.

Dielectric, ferroelectric, and strain properties of lead-free (1−y)BNT–yST ceramics

Lead-free ceramics (1−y) (Bi1/2Na1/2)TiO3–ySrTiO3 (1−y)BNT–yST with y = 0, 0.1, 0.20, 0.25, 0.28, 0.30, and 0.32 were synthesized via a solid-state reaction process. A uniform grain morphology was obtained, and the mean grain size was around 2.0 μm for y = 0, which decreased slightly for y > 0. The undoped compound displayed a crystal structure with rhombohedral symmetry, and increasing amounts of ST gradually transformed the material to cubic phase. The maximum dielectric constant temperature (Tm) was observed to decrease from 305 °C for sample y = 0 to 135 °C for sample y = 0.30. Remnant polarization (Pr) decreased with increasing ST, and the ferroelectric loops narrowed. The coercive field (Ec) was also observed to decrease with enhanced ST content; however, Ec and Pr increased for y = 0.30. The electric field-induced strain gradually increased up to y = 0.28 but decreased for y > 0.28. The loops of strain became slimmer and saturated with increasing ST ratio to attain the maximum dynamic strain of 624 pm/V.

Electric field-induced strain in Sr(Hf0.5Zr0.5)O3-modified Bi0.5(Na0.8K0.2)0.5TiO3 piezoelectric ceramics

Lead-free Sr(Hf0.5Zr0.5)O3-modified Bi0.5(Na0.8K0.2)0.5TiO3 (SHZ-BNKT) ceramics were synthesized using a conventional solid-state, mixed-oxide method. In complex solid solutions such as BNKT, the role of a ternary additive is important because it can break up the long-range dipole order, which destabilizes the ferroelectric phase leading to relaxor behavior. In this system, as verified by x-ray diffraction, SHZ was incorporated into the BNKT perovskite lattice throughout the studied compositional range. The coexistence of tetragonal and rhombohedral phase was observed for x = 0.00 and with the addition of SHZ, a transition to pseudocubic symmetry was observed, which is indicative of the onset of relaxor behavior. To characterize the relaxor properties of the material, the polarization–electric field hysteresis, dielectric, and electric-field-induced strain behaviors were studied as a function of composition. The temperature-dependent dielectric spectra showed frequency dependence for all the SHZ-modified BNKT ceramics, which is a typical characteristic of relaxor ferroelectrics. Furthermore, constriction in polarization loops and an absence of negative strain in the bipolar strain measurement for SHZ-modified BNKT compositions confirms that the addition of SHZ significantly disrupts the ferroelectric order. The addition of 2 mol. % SHZ in BNKT markedly enhanced the electric field-induced strain from 0.10% (for pure BNKT) to 0.33% (for 2% SHZ-BNKT). The corresponding normalized strain coefficient (d33∗=Smax/Emax) increased from 196 pm/V to 663 pm/V at a moderate electric field of 50 kV/cm. These results indicate that BNKT–SHZ ceramics can be designed for an improved strain response via a cation substitution-induced relaxor state for electromechanical actuator applications.

Influence of Al2O3nanoparticle doping on depolarization temperature, and electrical and energy harvesting properties of lead-free 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3ceramics

In this research article, the effects of Al2O3 nanoparticles (0–1.0 mol%) on the phase formation, microstructure, dielectric, ferroelectric, piezoelectric, electric field-induced strain and energy harvesting properties of the 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 (BNT–6BT) ceramic were investigated. All ceramics have been synthesized by a conventional mixed oxide method. The XRD and Raman spectra showed coexisting rhombohedral and tetragonal phases throughout the entire compositional range. An increase of the grain size, TF–R, Tm, εmax and δA values was noticeable when Al2O3 was added. Depolarization temperature (Td), which was determined by the thermally stimulated depolarization current (TSDC), tended to increase with Al2O3 content. The good ferroelectric properties (Pr = 32.64 μC cm−2, Ec = 30.59 kV cm−1) and large low-field d33 (205 pC N−1) values were observed for the 0.1 mol% Al2O3 ceramic. The small Al2O3 additive improved the electric field-induced strain (Smax and ). The 1.0 mol% Al2O3 ceramic had a large piezoelectric voltage coefficient (g33 = 32.6 × 10−3 Vm N−1) and good dielectric properties (εr,max = 6542, Td = 93 °C, TF–R = 108 °C, Tm = 324 °C and δA = 164 K). The highest off-resonance figure of merit (FoM) for energy harvesting of 6.36 pm2 N−1 was also observed for the 1.0 mol% Al2O3 ceramic, which is suggesting that this ceramic has potential to be one of the promising lead-free piezoelectric candidates for further use in energy harvesting applications.

Structural and large electric field-induced bipolar strain study of lead free Bi0.5Na0.5TiO3: Gd piezoceramics

In the present work, crystal structure and field-induced bipolar strain response of Pb-free (Bi1−xGdx)0.5Na0.5TiO3 (BNT:Gd) ceramics with x ≤ 0.04 were investigated systematically. Pure perovskite phase exhibited without any notable change in the crystal structure within the range of specimen studied. Structural analysis of BNT: Gd ceramics was performed through Rietveld refinement by Fullprof software. Rhombohedral structure with space group R3c had been confirmed for x ≤ 0.04. Electric field-induced strain showed a butterfly characteristic of bipolar strain hysteresis curve for the composition x ≤ 0.04 in BNT: Gd ceramics at RT. The maximum normalized piezoelectric strain coefficient d*33 of 148 pm/V was obtained in BNT: Gd systems which is approximately 4.9 times greater than static piezoelectric constant d33 (30pC/N) for the specimen x = 0.04.

Antiferroelectric behavior and giant strain in BNKT ceramics complex Cs2Nb4O11 tungsten bronze phase

BNT-based ceramics are very attractive for the electrical energy storage and electric field-induced strain. However, the reported BNT-based ceramics are usually the perovskite solid solution. In this work, the super adjustability of Cs2Nb4O11 antiferroelectric phase for lead-free (1-x)Bi0.5(Na0.82K0.18)0.5TiO3-xCs2Nb4O11 ceramics with complex-phase are carefully studied. The Bi0.5(Na0.82K0.18)0.5TiO3 ceramics modified by a trace of Cs2Nb4O11 component suddenly transform to antiferroelectric phase from typical ferroelectric. A giant strain of 0.48% and a d33* of 600 pm/V are obtained originating from a reversible transition between antiferroelectric and ferroelectric states. And a high energy density of 1.0 J/cm3 is also achieved by reversible phase transitions. Therefore, the composite ceramics by designing tungsten bronze and perovskite complex phase illustrate great potential for actuator or energy storage applications.

Large electric field-induced strain in the novel BNKTAN-BNBLTZ lead-free ceramics

(1-x)Bi0.5(Na0.82K0.18)0.5Ti0.96(Al0.5Nb0.5)0.04O3-xBi0.46Na0.46Ba0.5La0.02Ti0.97Zr0.03O3 lead-free ceramics (abbreviated as BNKTAN-100xBNBLTZ) was prepared by the conventional solid reaction. XRD patterns and EDS spectrums revealed that a stable solid solution had been formed between BNBLTZ and BNKTAN. With the introduction of BNBLTZ anti-ferroelectric content, BNKTAN relaxor ferroelectrics exhibited the excellent field-induced-strain for x = 0.04 corresponding to electric field-induced strain S ∼ 0.505 % and normal strain d33* ∼777 pm/V at 65 kV/cm. The large strain response was attributed to the emergence of PNRs in the relaxation process. Additionally, an excellent fatigue resistance performance was obtained within 105 cycles (S = 0.505 %–0.495 % and d33* = 777–758 pm/V, 65 kV/cm). It suggested that prepared ceramics had the great potential to strain sensor and actuators.

Tailoring electromechanical performance in BiScO3-modified Bi0.5Na0.5TiO3-based lead-free piezoceramics

The strain response of lead-free ternary solid solution (1 − x) (0.94 Bi0.5Na0.5TiO3–0.06BaTiO3)–xBiScO3 (BNT–BT–BS) have been tailored by controlling the phase transition temperature. The effects of BiScO3 on the phase structure, dielectric, ferroelectric, piezoelectric properties, and electric field-induced strain are systematically investigated. A schematic phase diagram has also been established to clarify the relationship between strain behavior and structure evolution. The field-induced strain increases progressively, and a large strain of 0.35% with Smax/Emax = 471 pm/V is achieved at the critical composition x = 0.03, owing to the shift of the ferroelectric-to-relaxor transition temperature TF–R to ambient temperature. Intriguingly, the established correlation between strain response and TF–R demonstrates that the optimization of strain behavior of BNT-based ceramics can be realized though the regulation of TF–R to room temperature. Furthermore, a high and thermally stable electrostrictive coefficient Q33 of 0.018 m4/C2 can also be attained at the composition x = 0.06. In this study, it is believed that the modulation of phase transition temperature is feasible to achieve the large strain response in BNT-based ceramics.

Phase Transition, Large Strain and Energy Storage in Ferroelectric (Bi0.5Na0.5)TiO3-BaTiO3 Ceramics Tailored by (Mg1/3Nb2/3)4+ Complex Ions

Lead-free relaxor-ferroelectric (Mg1/3Nb2/3)4+ complex ions modified (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT-xMN) ceramics were fabricated by traditional solid-phase reaction sintering, and the effects of (Mg1/3Nb2/3)4+ complex ions on the structural, ferroelectric, dielectric, energy storage, and strain properties of these ceramics were studied. All of the samples illustrated a single perovskite phase with a pseudo-cubic structure. Electric field-induced polarization and strain hysteresis loops indicated the occurrence of reversible ferroelectric-to-relaxor phase transition, which gave rise to a large strain of 0.49%. (Mg1/3Nb2/3)4+ complex ions greatly influenced the coercive field and remanent polarization of the ceramics; these properties also affected energy storage density of the materials. The optimal energy storage density and efficiency of the ceramics were 0.54 J/cm3 and 38.4%, respectively, when x = 0.04. These results may stem from the electric field-induced transition between the ferroelectric and relaxor-ferroelectric phase of the proposed ceramics.

Finsler geometry modeling of reverse piezoelectric effect in PVDF

We apply the Finsler geometry (FG) modeling technique to study the electric field-induced strain in ferroelectric polymers. Polyvinylidene difluoride (PVDF) has a negative longitudinal piezoelectric coefficient, which is unusual in ferroelectrics, and therefore the shape changes in this material are hard to predict. We find that the results of Monte Carlo simulations for the FG model are in good agreement with experimental strain-electric field curves of PVDF-based polymers in both longitudinal and transverse directions. This implies that FG modeling is suitable for reproducing the reverse piezoelectric effect in PVDF.

Effects of B-Site Donor Modification on the Crystal Structure and the Electrical Properties of Lead-Free 0.65BiFeO3-0.35BaTiO3 Ceramics

In the present work, lead-free piezoelectric ceramics 0.65Bi1.05Fe1−xTixO3-0.35BaTi1−yNbyO3, where x = y = 0, 0.01, 0.015, 0.02, and 0.025, abbreviated as BFT-BTNb, were successfully synthesized by a solid-state reaction method and an air quenching method. The effects of B-Site donor modifications (Nb5+ and Ti4+) on the crystal structure, the morphology and the electrical properties of the 0.65BF-0.35BT ceramics were studied. X-ray diffraction patterns showed the formation of a pure perovskite structure, without any secondary phases. Scanning electron microscope (SEM) micrographs revealed that the average grain size of the BF-BT ceramics decreased with the addition of B-Site donors. Improvements in the ferroelectric properties (P-E loops) and the electric field-induced strain properties (S-E loops) were obtained at the optimum composition of the BFT-BTN ceramics. In addition, the dynamic piezoelectric coefficient (d33*) was enhanced from 265 pm/V for (BFT-BTNb-0) to 360 pm/V for (BFT-BTNb-1) with high working temperature, Tm = 320 °C.