Large Piezoelectricity Research Articles

Ferroelectric domains and phase transition of sol-gel processed epitaxial Sm-doped BiFeO3 (001) thin films

BiFeO3, a room-temperature multiferroic material, has recently been increasingly applied as a potential lead-free piezoelectric material due to its large piezoelectricity achieved by doping. In this work, 12% Sm-doped BiFeO3 epitaxial thin films were fabricated on Nb-doped SrTiO3 (001) single crystal substrates via sol-gel method. The epitaxy was verified by reciprocal space mapping (RSM) and transmission electron microscope (TEM). The TEM results indicated the coexistence of R3c and Pbam phases in the film. The domains and piezoelectric properties from room temperature to 200 °C were characterized by piezoresponse force microscopy (PFM). Domains became active from 110 °C to 170 °C, and domain configurations changed obviously. A partially fading piezoresponse indicated the emergence of antiferroelectric Pbam. The in-situ domain analysis suggested that the phase transition was accompanied by domain wall motion. Switching spectroscopy PFM (SS-PFM) was further conducted to investigate the piezoresponse during the phase transition. Anomalous responses were found in both ON and OFF states at 170 °C, and the film exhibits typical antiferroelectric behavior at 200 °C, implying that the completion of phase transition and structure turned to the Pbam phase. This work revealed the origin of the high piezoresponse of Sm-doped BiFeO3 thin films at the morphotropic phase boundary (MPB).

Piezoelectric nanofibrous scaffolds as in vivo energy harvesters for modifying fibroblast alignment and proliferation in wound healing

Since the last decade, piezoelectric polymer nanofibers have been of great interest in the stimulation of cell growth and proliferation for tissue engineering and wound healing applications. To date, there is no clear understanding of how the piezoelectric properties of piezoelectric materials can be affected by electrospinning parameters and how the piezoelectricity from the electrospun polymer nanofibers produced under optimized electrospinning conditions in vivo would affect cell growth, proliferation and elongation. In this paper, it is shown for the first time how electrospinning parameters, such as solution concentration and collecting distance (from the needle to the rotating mandrel), can affect the piezoelectricity of the poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) nanofibers. Here, the optimized electrospinning conditions for P(VDF-TrFE) nanofibers were achieved and these nanofiber scaffolds (NFSs) were used for implanted energy harvester in SD rats, cell proliferation and cell alignment growth applications. During the process of slightly pulling implanted site of SD rats, the implanted PVDF-TrFE NFSs generated a maximum voltage and current of 6mV and ~6nA, respectively. With great cytocompatibility and relatively large piezoelectric effect, fibroblast cells grew and aligned perfectly along the electrospinning direction of P(VDF-TrFE) nanofiber direction and cell proliferation rate was enhanced by 1.6 fold. Thus, electrospun P(VDF-TrFE) NFSs show great promise in tissue engineering and wound healing applications.

Kinetic features of the new phase nucleation in the electric field in some lead-containing relaxors

The kinetics and dynamics of the new phase nucleation in an external electric field E in ferroelectric relaxors Pb1/2Nb1/2O3–PbMg1/3Nb2/3O3–x (x = 25 and 32%) and PbMg1/3Nb2/3O3–29PbTiO3 have been investigated. The joint measurements of optical transmittance at different wavelengths as well as the sound speed and attenuation at different frequencies have been carried out at room temperature. The analysis of the character of the changes of the optical and acoustic properties in different electric fields has been performed with the aim of identifying the mechanisms of such changes under phase transition conditions. The reduction of optical transmission with time is associated only with the size change of nanoregions in the process of phase transition. The observed acoustic anomalies are the consequence of phase transition and conditioned by the lattice increased rigidity, caused by a large piezoelectric effect in the ferroelectric phase.

Effect of shear stress in ferroelectric solid solutions with coexisting phases

One common feature of ferroelectric solid solutions with large piezoelectricity is the coexistence of two or more phases. Due to the strain mismatch among coexisting phases, adaptive structures near the interfaces or domain walls develop to maintain the atomic coherency. Shear stresses commonly exist, especially when the domain size is small. The effect of shear stresses on phase morphology in Pb(Zr1-xTix)O3 solid solutions with compositions within the morphotropic phase boundary region was studied within the framework of Landau phenomenological theory. Our results show that the coexisting rhombohedral (R) and tetragonal (T) phases can be modified to form stable or metastable R-like and/or T-like monoclinic phases under shear stresses. Large stresses may also induce first order or second order phase transitions.

Microscopic origins of the large piezoelectricity of leadfree (Ba,Ca)(Zr,Ti)O3

In light of directives around the world to eliminate toxic materials in various technologies, finding lead-free materials with high piezoelectric responses constitutes an important current scientific goal. As such, the recent discovery of a large electromechanical conversion near room temperature in (1−x)Ba(Zr0.2Ti0.8)O3−x(Ba0.7Ca0.3)TiO3 compounds has directed attention to understanding its origin. Here, we report the development of a large-scale atomistic scheme providing a microscopic insight into this technologically promising material. We find that its high piezoelectricity originates from the existence of large fluctuations of polarization in the orthorhombic state arising from the combination of a flat free-energy landscape, a fragmented local structure, and the narrow temperature window around room temperature at which this orthorhombic phase is the equilibrium state. In addition to deepening the current knowledge on piezoelectricity, these findings have the potential to guide the design of other lead-free materials with large electromechanical responses.

Crucial role of octahedral untilting R3m/P4mm morphotropic phase boundary in highly piezoelectric perovskite oxide

Large piezoelectricity is usually found at morphotropic phase boundary (MPB), a composition-induced phase boundary between two ferroelectric phases. However, only a small fraction of MPBs (e.g., in PZT and PMN-PT) show large piezoelectricity. It remains a long-standing puzzle why not all MPBs yield large piezoelectricity. Here, by a comparative study of two MPB systems of BaZr0.2Ti0.8O3-PbTiO3 (BZT-PT) and Bi0.5Na0.5TiO3-PbTiO3 (BNT-PT), we find that the symmetry relation between the two ferroelectric phases at MPB plays a crucial role in piezoelectric activity. BZT-PT ceramic, having an R3m/P4mm MPB, exhibits strong piezoelectricity of d33 = 500 pC/N, whereas BNT-PT ceramic, having an R3c/P4mm MPB, exhibits much weaker piezoelectricity of d33 = 150 pC/N. The sharp difference between the two types of R/T MPBs is shown to arise from a significant difference in free energy barrier associated with oxygen octahedral tilting at MPB. An oxygen octahedral tilting/untilting transition at R3c/P4mm MPB leads to a high free energy barrier and results in low piezoelectric activity, whereas R3m/P4mm MPB with octahedral untilting produces large piezoelectricity due to low free energy barrier at such MPB. This feature show quite general in most of present MPBs systems and may become a dependable guideline for designing highly piezoelectric Pb-free materials.

Optimum Conditions for Preparation of High-Performance (Ba0.97Ca0.03)(Ti0.94Sn0.06)O3 Ceramics by Solid-State Combustion

The effects of calcination conditions (950°C to 1200°C for 2 h to 6 h) and sintering temperature (1300°C to 1500°C for 2 h) on phase formation, microstructure, and electrical behavior of lead-free piezoelectric (Ba0.97Ca0.03)(Ti0.94Sn0.06)O3 (BCTS) ceramics produced by solid-state combustion using glycine as fuel have been investigated. BCTS powder with pure perovskite structure was obtained by calcination at 1100°C for 4 h. The microstructure of the BCTS powders showed almost spherical shape with average particle size increasing from 184 nm to 320 nm as the calcination temperature and soaking time were increased. The XRD patterns of all ceramics exhibited single perovskite structure. Rietveld refinement analysis indicated that the BCTS ceramics exhibited coexistence of orthorhombic and tetragonal phase in all samples with increased tetragonal phase content with increasing sintering temperature. The average grain size, density, dielectric constants at room (e r) and Curie temperature (e C), remanent polarization (P r), and piezoelectric constant (d 33) increased as the sintering temperature was increased up to 1400°C, then decreased. BCTS ceramic sintered at 1400°C exhibited the highest relative density (98%), highest dielectric response (e r = 4951, e C = 19,185), good ferroelectric behavior (P r = 12.74 μC/cm2 and coercive field E c = 1.60 kV/cm), and highest d 33 value (528 pC/N). The large piezoelectricity of BCTS ceramics makes them good candidates for use in lead-free applications to replace Pb-based ceramics.

Large-Area Piezoelectric PVDF Fibers Fabricated by Near-Field Electrospinning with Multi-Spinneret Structures

In the study, we improved the near-field electrospinning (NFES) by multi-spinnerets with a cylindrical collector to fabricate a large area permanent piezoelectric of polyvinylidene fluoride (PVDF) fibers array. We designed multi-spinnerets by using printed circuit board (PCB) and drilled spinnerets on the solder balls. With different process parameters, we can obtain different diameters of PVDF fibers. By using the Taguchi method analysis, we found that the optimum sample of PVDF fiber arrays were manufactured by an electrical field of 1.6 × 107 V/m. The cylindrical collector with high tangential velocity of 1779.9 mm/s and the heat treatment temperature of 65 °C for one hour. In addition, we used X-ray diffraction (XRD) and scanning electron microscopy (SEM) to analyze β-phase crystal quality and the surface character of PVDF fibers, respectively. From the observation of XRD, it revealed a high diffraction peak at 2θ = 20.6° of piezoelectric crystal β-phase structure. As PVDF solution with concentration of 18 wt % and the conductivity of 44.2 μS/cm was electrospun via NFES with multi-spinneret structure, we obtained a smooth manufacturing process. When the periodical tapping frequency was applied with 9 Hz, the maximum peak voltage of 86.9 mV was generated. In a cicada’s wing test, when the tapping frequency input was applied during 10–50 Hz, the maximum output voltage signals of 6.2 mV were generated.

Efficient Raman scattering response and large piezoelectricity in noncentrosymmetric MnHg(SCN)4 crystals

Noncentrosymmetric MnHg(SCN)4 crystals show an efficient Raman scattering response and large piezoelectricity.

Large piezoelectricity in electric-field modified single crystals of SrTiO3

Defect engineering is an effective and powerful tool to control the existing material properties and produce completely new ones, which are symmetry-forbidden in a defect-free crystal. For example, the application of a static electric field to a single crystal of SrTiO3 forms a strained near-surface layer through the migration of oxygen vacancies out of the area beneath the positively charged electrode. While it was previously shown that this near-surface phase holds pyroelectric properties, which are symmetry-forbidden in centrosymmetric bulk SrTiO3, this paper reports that the same phase is strongly piezoelectric. We demonstrate the piezoelectricity of this phase through stroboscopic time-resolved X-ray diffraction under alternating electric field and show that the effective piezoelectric coefficient d33 ranges between 60 and 100 pC/N. The possible atomistic origins of the piezoelectric activity are discussed as a coupling between the electrostrictive effect and spontaneous polarization of this near-surface phase.

Temperature stable liquid gigahertz viscosity sensors by combining shear mode piezoelectric ScAlN thin film and AT-cut quartz crystal plate

We here propose the temperature stable liquid GHz viscosity sensors by combining shear mode piezoelectric thin film and AT-cut quartz crystal plate. In the ultrasonic viscosity sensors, longitudinal wave cannot be used because the longitudinal wave energy leaked into the liquid. Therefore, shear wave is required for the viscosity measurement. We recently reported new large shear wave piezoelectricity in the c-axis tilted ScAlN films. In this study, the resonator type viscosity sensor consisting of c-axis tilted ScAlN films (approximately 7 μm) grown on an AT-cut quartz crystal plate were fabricated. Because the thickness of AT-cut quartz crystal is large enough compared to that of ScAlN film, temperature coefficient of resonant frequency is approximately determined by the extremely temperature stable quartz crystal. This enable robust measurement for the external temperature change. Increase of the viscous penetration depth between the liquid and the resonator interface induces the decrease of resonant frequency. The change of liquid viscosity can be then determined by this frequency shift. We observed strong shear wave excitation at the 403 MHz by using a network analyzer in the air. When the sensor was immersed in the pure water, 50 kHz decrease of shear wave resonant frequency was clearly observed.

Structure-property in KNNS-BNT-BNH ternary system with rhombohedral-tetragonal phase boundary

We have attained a large piezoelectricity in (1−x−z)(K0.48Na0.52)(Nb1−ySby)O3−zBi0.5Na0.5TiO3−xBi0.5Na0.5HfO3 ternary lead free ceramics prepared by the conventional solid-state sintering method, where the rhombohedral-tetragonal (r−T) phase boundary was formed in the composition range 0.015≤x≤0.04 (y=0.05, z=0.01), 0.06≤y≤0.08 (x=0.015, z=0.01) as well as 0.0075≤z≤0.02 (x=0.015, y=0.07). A large piezoelectric constant (d33) i.e. 415 pC/N was observed in the ceramics with x=0.015, y=0.07 and z=0.0075 by forming an R-T phase boundary. As a result, the addition of BNT, BNH and Sb can significantly affect the phase structure and electrical properties of the ceramics.

Smart piezoelectric fabric and its application to control of humanoid robot

ABSTRACTWe have developed a piezoelectric fabric for sensing applied stress and strain using piezoelectric poly-l-lactic acid (PLLA) fibers, and tailored smart clothing having the function of sensing complex human motion using the piezoelectric PLLA fabric. To provide a high-quality PLLA fabric with large piezoelectricity, simultaneously satisfying the characteristics of softness, stretchability, and wearability, we first attempted the to improve the balance of the physical properties of PLLA fibers. We investigated the use of an acrylic copolymer as a plastic additive for improving the piezoelectric and mechanical properties of PLLA fibers, since the acrylic copolymer has extremely high dispersibility and compatibility, and the optimized furthermore the PLLA fiber fabrication conditions to improve the physical properties. To realize a piezoelectric fabric with the ability of sensing complex human motion, plain, twill, and satin weaves with improved the piezoelectricity, softness, stretchability, and wearability were produced using the PLLA fibers by Teijin Limited, Japan, a joint research company. Moreover, we developed a prototype system that allows human movement, detected through the motion sensing of smart clothing obtained by sewing together pieces of piezoelectric fabric, to be linked with that of a humanoid robot. At present, simple procedures such as bending of the arms and twisting of the wrists can be replicated by the humanoid robot but not complex movements of the arms.

Contribution of Bi0.5Na0.5ZrO3 on phase boundary and piezoelectricity in K0.48Na0.52Nb0.96Sb0.04O3-Bi0.5Na0.5SnO3-xBi0.5Na0.5ZrO3 ternary ceramics

In this work, we have attained a large piezoelectricity (d33 ∼468 pC N−1) in (0.9925-x)K0.48Na0.52Nb0.96Sb0.04O3-0.0075Bi0.5Na0.5SnO3-xBi0.5Na0.5ZrO3 (abbreviation: KNNS-BNS-xBNZ) ternary ceramics, prepared by a conventional solid-state reaction method. We illuminated the role of BNZ on the phase boundary and piezoelectric properties of the ceramics. Rhombohedra-orthorhombic-tetragonal (R-O-T) phase coexistence can be developed by controlling BNZ content, and then a high d33 value of ∼468 pC N−1 can be attained in the ceramics with x = 0.03. This result indicates that a higher d33 value can be attained by forming a new phase boundary using the addition of BNZ with respect to those of 0.9925K0.48Na0.52Nb0.96Sb0.04O3-0.0075Bi0.5Na0.5SnO3 ceramics with an orthorhombic phase. In addition, the maximum value both strain and d33∗ are all obtained at x = 0.04 (strain ∼0.18% and d33∗ ∼440 pm/V), which means that optimum BNZ content can enhance the strain and d33∗ of the ceramics. As a result, the ternary ceramic system may become one of the most promising candidates for the practical applications of KNN-based materials.

Generalized Solutions of Piezoelectric Vibration-Based Energy Harvesting Structures Using an Electromechanical Transfer Matrix Method

Piezoelectric vibration-based energy harvesting (pVEH) offers much potential as renewable energy structures. Within the literature, often geometry-specific models are developed, making designs of new structures difficult. In this work, a generalized linear algebraic method is developed. The method incorporates the transfer matrix method (TMM) into the well-accepted distributed parameter electromechanical model for a composite-piezoelectric, Euler–Bernoulli beam. The result is an electromechanical TMM which is highly accurate at predicting both structural and energy harvesting performances for a wide variety of designs which have chainlike topologies. A simplification is made within the method to model structures which operate solely within bending modes, reducing the computation to analyses of only four-by-four state transition matrices, regardless of structural complexity. As many applications aim to optimize the large bending mode piezoelectric effect, this simplification does not limit the versatility of the method. To demonstrate the validity of this statement, comparisons were performed to evaluate the accuracy of the method's predictions for six piezoelectric topologies, including a unimorph without a tip mass, a bimorph with a tip mass, several partial-length bimorphs without a tip mass, and three different multibeam bimorph structures with inline and folded-back designs. The results show differences no greater than 2.24% for the first and second natural frequencies of the structures. Likewise, the method yields excellent predictions for the mode shapes, their slopes, and the voltage frequency responses, especially within the ±10% bounds of the natural frequencies. Thus, the future design of new structures is shown to be simplified using this generalizable method.

Fano resonance of Li-doped KTa(1-x)NbxO3 single crystals studied by Raman scattering.

The enhancement of functionality of perovskite ferroelectrics by local structure is one of current interests. By the Li-doping to KTa1−xNbxO3 (KTN), the large piezoelectric and electro-optic effects were reported. In order to give new insights into the mechanism of doping, the microscopic origin of the Fano resonance induced by the local structure was investigated in 5%Li-doped KTN single crystals by Raman scattering. The coupling between the continuum states and the transverse optical phonon near 196 cm−1 (Slater mode) caused a Fano resonance. In the vicinity of the cubic-tetragonal phase transition temperature, TC-T = 31 °C, the almost disappearance of the Fano resonance and the remarkable change of the central peak (CP) intensity were observed upon heating. The local symmetry of the polar nanoregions (PNRs), which was responsible for the symmetry breaking in the cubic phase, was determined to E(x, y) symmetry by the angular dependence of Raman scattering. The electric field induced the significant change in the intensity of both CP and Fano resonance. From these experimental results, it is concluded that the origin of the Fano resonance in Li-doped KTN crystals is the coupling between polarization fluctuations of PNRs and the Slater mode, both belong to the E(x, y) symmetry.

Relationship between Poling Characteristics and Phase Boundaries of Potassium-Sodium Niobate Ceramics.

The controversy about the optimum poling conditions of (K,Na)NbO3 (KNN)-based lead-free ceramics was still unresolved and the relationships between poling characteristics and phase boundary types were rarely mentioned. Here, we tried to unveil the relationships between poling characteristics and phase boundary types of these ceramics. The optimum poling temperatures should be chosen near their corresponding phase transition temperatures. In addition, a large piezoelectricity can be attained in the ceramics with a multiphase coexistence under a lower poling electric field (<E(C)), while a higher poling electric field (≥E(C)) is required to achieve the sufficient polarization in the ones with single O or T phase. More interestingly, it is the first time to report that the ceramics with different phase boundaries can be fully poled after the measurement of P-E loops, where the d33 values match those of the corresponding ones poled by the DC electric field. We believe that this modified poling process can benefit the improved piezoelectricity of KNN-based ceramics.

Quenched bismuth ferrite-barium titanate lead-free piezoelectric ceramics

In this work, the quenched method can effectively promote the electrical properties of bismuth ferrite-barium titanate (BiFeO3BaTiO3, BFO-BTO) ceramics. Here we mainly focused on the modification of the quenched methods in the 0.67Bi1.05FeO3–0.33BaTiO3 ceramics with rhombohedral-cubic phase boundary. By optimizing the preparation conditions, the ceramics possess high Curie temperature (TC∼457 °C), large piezoelectricity (d33∼170 pC/N), and good ferroelectricity (Pr∼22 μC/cm2). The enhanced electrical properties are mainly assigned to the quenching technique with optimized conditions. We believe that such a systematic research can point out a way for further fabricating high-performance ceramics.

Phase Transition and Large Electrostrain in Lead‐Free Li‐Doped (Ba, Ca)(Ti, Zr)O3 Ceramics

Large piezoelectric effect is achieved in Li‐doped Ba0.85Ca0.15Ti0.90Zr0.10O3(BCTZ) ceramics by use of tuning the phase boundaries. Rhombohedral–orthorhombic (R–O) and orthorhombic–tetragonal (O–T) multiphase coexistence is constructed in the ceramics by changing Li contents. The high piezoelectric constant d33 (493 pC/N) and large electrostrain (dSmax/dEmax = 931 pm/V) have been observed in the Li‐doped (Ba, Ca)(Ti, Zr)O3 ceramics at low sintering temperature (1350°C/2 h). The significant enhancement in materials properties is ascribed to the multiphase region around room temperature induced by Li‐doped effect.

Hetero-epitaxial growth and large piezoelectric effects in (0 0 1) and (1 1 1) oriented PbTiO3–LaNiO3 multilayers

Hetero-epitaxial thin films were obtained in PbTiO3/LaNiO3 thin films by using laser ablation for sequential deposition of each thin film. Structural variations were built to characterize the differences in local ferroelectric properties. For this study, 50 nm-thick-PTO thin films with (0 0 1) and (1 1 1) orientations were investigated. Piezoresponse force microscopy (PFM) was used to investigate the local ferroelectricity in the thin films. High piezoelectric responses were obtained in the thin films, with values of approximately 75 and 83 pm V−1 in the (0 0 1) and (1 1 1)-oriented thin films, respectively. It is notable that remarkable piezoelectric properties were obtained in the (1 1 1)-oriented thin films. The (1 1 1)-oriented thin films have the potential to be used as multi-bit memory because of the reduction of degradation in ferroelectricity and various directional piezoelectricity. We compared the functionalities of the (0 0 1)- and (1 1 1)-oriented thin films and obtained different performances in the thin films.