Experimental investigation of electrostrictive polarization biased direct apparent piezoelectric properties in polyurethane elastomer under quasistatic conditions

Polyurethane elastomer was recently discovered to demonstrate a very high field induced electrostrictive response. In this work an experimental setup, consisting of an electric circuit and a mechanical system, was designed and constructed for the measurement of the electrostrictive polarization biased apparent piezoelectric response of polyurethane elastomers in a direct piezoelectric effect under quasistatic conditions. The electric circuit design allows the application of a direct current (dc) bias electric field to the sample and the possibility of picking up the generated quasistatic electrical signal separately. The mechanical system provides the function of a vibration source from which the stress and strain of the sample can be measured. Therefore, such effective piezoelectric properties as d₃₁ and k₃₁ can be measured. The electromechanical coupling coefficient was derived by two different methods. One was from the deduction based on the piezoelectric equations. The other was from the calculation based on the basic definition of the electromechanical coupling coefficient (i.e., through the exact measurement of input mechanical energy and output electric energy). In the latter case, the internal resistance of the sample and the dc bias blocking capacitor were found to be the critical factors for precision determination of the total electrical energy output. The different approaches led to close agreement. The effective d₃₁ can be 184 pC/N under a 25 MV/m bias electric field in a 30-µm thick sample, which is much higher than that of typical piezoelectric polymers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2603–2609, 1999     

Static fatigue behavior of cracked piezoelectric ceramics in three-point bending under electric fields

This paper describes an experimental and analytical study on the static fatigue behavior of piezoelectric ceramics under electromechanical loading. Static fatigue tests were carried out in three-point bending with the single-edge precracked-beam specimens. The crack was created perpendicular to the poling direction. Time-to-failure under different mechanical loads and dc electric fields were obtained from the experiment. Microscopic examination of the fracture surface of the piezoelectric ceramics was performed as well. A finite element analysis was also made, and the applied energy release rate for the permeable crack model was calculated. The effect of applied dc electric fields on the energy release rate versus lifetime curve is examined. The most important conclusion we reach is that the lifetimes for the piezoelectric specimens under a positive electric field are much shorter than the failure times of specimens under a negative electric field for the same mechanical load level.     

Effects of uniaxial prestress on the ferroelectric hysteretic response of soft PZT

This paper deals with the influence of preload stress on the ferroelectric hysteretic behavior of piezoelectric ceramics. The polarization and strain versus electric field hysteresis loops were measured for soft lead zirconate titanate (PZT) piezoceramic material under various uniaxial compressive stress preloads of up to −400 MPa. The investigation revealed that the superimposed compression load reduced the remnant polarization, decreased the coercive field, and also had a significant impact on the dielectric and piezoelectric properties. With increasing mechanical load, dielectric hysteresis and butterfly hysteresis became less and less pronounced, as the compressive stress prevented full alignment of the domains and induced mechanical depolarization. The slopes of the polarization and strain curves at zero electric field were measured to evaluate the dependence of permittivity and piezoelectric coefficients on the prestress. The experimental results were interpreted in terms of the non-180° domain switching process under combined electromechanical loading.     

Electromechanical Properties of PMN–PZT Piezoelectric Single Crystals Near Morphotropic Phase Boundary Compositions

Pb(Mg_1/3Nb_2/3)O₃–PbZrO₃–PbTiO₃ (PMN–PZT) ferroelectric single crystals near morphotropic phase boundary compositions were fabricated by solid-state crystal growth. The Curie temperatures ( T _C) of the grown PMN–PZT crystals were found to be on the order of 210°C, with ferroelectric phase transition temperatures ( T _{R – T} ) in the range of 96°–165°C. The electromechanical coupling factors k ₃₃ and k ₃₂ were found to be >90% and >−87%, respectively. The coercive field E _C for all the compositions was on the order of 5 kV/cm, double the value of pure Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMNT) crystals. The temperature dependence of the piezoelectric and electromechanical properties and dc bias effect on the dielectric behavior were investigated. The temperature usage range under dc bias was found to be improved when compared with pure PMNT crystals with similar piezoelectric properties.     

Cyclic Fatigue Crack Growth in Three-Point Bending PZT Ceramics under Electromechanical Loading

This paper investigates experimentally and analytically the cyclic fatigue crack growth in piezoelectric ceramics under electromechanical loading. Cyclic crack growth tests were conducted on lead zirconate titanate (PZT) ceramics subjected to dc electric fields, and a finite element analysis was used to calculate the maximum energy release rate for the permeable crack model. Based on bending experiments using single-edge precracked-beam specimens, cyclic fatigue crack growth rates are found to be sensitive to the maximum energy release rate and applied dc electric fields. Possible mechanisms for crack growth were discussed by scanning electron microscope examination of the fracture surface of the PZT ceramics.     

Piezoelectric and Electrostatic Properties of Electrospun PVDF‐TrFE Nanofibers and their Role in Electromechanical Transduction in Nanogenerators and Strain Sensors

Piezo‐ and ferroelectric nanofibers of the polymer poly(vinylidenefluoride) (PVDF) have been widely employed in strain and pressure sensors as well as nanogenerators for energy harvesting. Despite this interest, the mechanism of electromechanical transduction is under debate and a deeper knowledge about relevant piezoelectric or electrostatic properties of nanofibers is crucial to optimize transduction efficiency. Here poly(vinylidenefluoride‐trifluoroethylene) nanofibers at different electrospinning conditions are prepared. Macroscopic electromechanical response of fiber mats with microscopic analysis of single nanofibers performed by piezoelectric and electrostatic force microscopy are compared. The results show that electrospinning favors the formation of the piezoelectric β‐phase in the polymer and leads directly to piezoelectric properties that are comparable to annealed thin films. However, during electrospinning the electric field is not strong enough to induce direct ferroelectric domain polarization. Instead accumulation of triboelectric surface charges and trapped space charge is observed in the polymer that explain the electret like macroscopic electromechanical response.     

Enhanced piezoelectric properties of Sm3+-modified PMN-PT ceramics and their application in energy harvesting

Piezoelectric materials are widely used in electromechanical energy conversion, such as in sensors, transducers, and self-powered materials. In this paper, the influence of the Sm doping content on the microstructure and ferroelectric, piezoelectric, dielectric, and field-induced strain properties of 0.70Pb(Mg_1/3Nb_2/3)O₃-0.30PbTiO₃ (PMN-PT) ceramics was investigated. Sm-doped PMN-PT ceramics with both high piezoelectric properties (d₃₃～1406 pC/N) and a large electromechanical coupling coefficient (k_p～0.69) were synthesized. Based on their piezoelectric effect, a maximum output voltage of 31 V was achieved under external forces. The output voltages showed satisfactory stability, repeatability, and sensitivity under periodic external forces; hence, Sm-doped PMN-PT piezoelectric ceramics are potential candidates for energy conversion and signal monitoring.     

Phase‐Composition‐Dependent Piezoelectric and Electromechanical Strain Properties in (Bi1/2Na1/2)TiO3–Ba(Ni1/2Nb1/2)O3 Lead‐Free Ceramics

New lead‐free perovskite solid solution ceramics of (1 ? x)(Bi_1/2Na_1/2)TiO₃–xBa(Ni_1/2Nb_1/2)O₃[(1?x)BNT–xBNN,x = 0.02–0.06) were prepared and their dielectric, ferroelectric, piezoelectric, and electromechanical properties were investigated as a function of the BNN content. The X‐ray diffraction results indicated that the addition of BNN has induced a morphotropic phase transformation from rhombohedral to pseudocubic symmetry approximately at x = 0.045, accompanying an evolution of dielectric relaxor behavior as characterized by enhanced dielectric diffuseness and frequency dispersion. In the proximity of the ferroelectric rhombohedral and pseudocubic phase coexistence zone, the x = 0.045 ceramics exhibited optimal piezoelectric and electromechanical coupling properties of d₃₃~121 pC/N and k_p~0.27 owing to decreased energy barriers for polarization switching. However, further addition of BNN could cause a decrease in freezing temperatures of polar nanoregions till the coexistence of nonergodic and ergodic relaxor phases occurred near room temperature, especially for the x = 0.05 sample which has negligible negative strains and thus show the maximum electrostrain of 0.3% under an external electric field of 7 kV/mm, but almost vanished piezoelectric properties. This was attributed to the fact that the induced long‐range ferroelectric order could reversibly switch back to its original ergodic state upon removal of external electric fields.     

PLZT驰豫铁电陶瓷偏压压电效应的研究

本文研究了铌掺杂的ＰＬＺＴ驰豫铁电陶瓷在不同直流偏压及温度下的介电常数ε３３,平面机电耦合系数ｋ和等效横向压电常数ｄ３１。实验表明,铌掺杂的ＰＬＺＴ驰豫铁电陶瓷ｄ３１值可由直流偏压控制及ｄ３１值的温度系数远小于ＰＭＮ－ＰＴ系陶瓷。室温上２ｍｏｌ％和３ｍｏｌ％的铌掺杂的ＰＬＺＴ１０／６５／３５驰豫铁电陶瓷在１０ＫＶ／ｃｍ的偏压下│ｄ３１│分别为２０５ｐＣ／Ｎ和１６０Ｃ／Ｎ。     

Fatigue of Ferroelectric Polarization and the Electric Field Induced Strain in Lead Lanthanum Zirconate Titanate Ceramics

Fatigue of ferroelectric polarization and the electric field induced strain is investigated in lead lanthanum zirconate titanate ceramics. Fatigue rate increases as the coercive field or the hysteretic nature of the electric field induced polarization of the ferroelectric ceramics increases. The ferroelectric polarization lost during fatigue can be partly restored by decreasing the frequency and increasing the amplitude of the applied ac electric field. The ferroelectric fatigue is modeled phenomenologically by an increase of the energy barrier for the ferroelectric switching and atomistically by a coupling of the spontaneous polarization with defects and/or space charge in the orientation of ferroelectric fatigue.     

Effect of Composition on the Electromechanical Properties of (1-x)Pb(Mg1/3Nb2/3)O3−XPbTiO3 Ceramics

Ceramic lead magnesium niobate–lead titanate ((1-x)PMN_-xPT) of different compositions has been prepared by the columbite precursor method. This study discusses compositions ranging from 0.94PMN–0.06PT to 0.60PM–N0.40PT, focusing on two areas of the (1-x)PMN_xPT system: compositions that exhibit electrostrictive behavior, and those that show piezoelectric behavior. In electrostrictive compositions where x is in the range of 0.06–0.20, the dielectric constant and electromechanical coupling factor dependencies on the bias field are evaluated. The optimal electromechanical properties are obtained with the composition 0.82PMN–0.18PT, measured at temperature T = T_m (the temperature of maximum dielectric constant) = 80°C and with a dc bias of 5 kV/cm. X–ray diffractometry is used to show that the (1-x)PMN_-xPT system has a compositionally wide two–phase region and that 0.655PMN–0.345PT is the morphotropic phase boundary (MPB) composition. Electromechanical property evaluation shows that the optimal piezoelectric properties (piezoelectric charge coefficient ( d₃₃ ) value of 720 pC/N, dielectric constant ( K ) value of 5400, and electromechanical planar and thickness coupling coefficient ( k_p and k_t , respectively) values of 62% and 46%, respectively) are obtained at the MPB composition.     

Piezoelectricity in the Field-Induced Ferroelectric Phase of Lead Zirconate-Based Antiferroelectrics

The piezoelectric characteristics were investigated in the field-induced ferroelectric phase of the antiferroelectric Pb_0.99 Nb_0.02[(Zr_0.6Sn_0.4) _{1 − y} Ti _y ]_0.98O₃ family. The electromechanical coupling factors k _p and k _t were measured, and the piezoelectric anisotropy was calculated. The piezoelectricity was controlled easily by the applied electric field pulse. The large piezoelectric anisotropy of these materials in comparison to that of conventional PZT piezoelectric materials makes them very applicable for ultrasonic probes and surface acoustic wave filters.     

Design,fabrication and properties of 1–3 piezoelectric ceramic composites with varied piezoelectric phase distribution

Here the 1–3 connectivity cement/polymer based piezoelectric composites with varied piezoelectric phase distribution were designed. The dielectric, piezoelectric and electromechanical properties of the composites were studied. The results indicate that the composite with varied distribution of piezoelectric ceramic has large relative permittivity, piezoelectric strain constant and electromechanical coupling coefficient at the thickness vibration mode. The composites with varied distribution of matrix phase have larger piezoelectric voltage constant, smaller mechanical quality factor and acoustic impedance value than those with varied distribution of piezoelectric ceramic phase. The electromechanical coupling property of the composites at the planar vibration mode shows obvious dependence on matrix phase distribution. The novel piezoelectric composites show potential applications in fabricating ultrasonic transducers with specific surface vibration amplitude.     

Effect of grain size on piezoelectric,ferroelectric and dielectric properties of PMN-PT ceramics

Grain size has significant effects on the electromechanical response of piezoceramics. Since the sintering temperature and holding duration affect the grain size and correspondingly their effective piezoelectric response, these issues should be appropriately addressed in order to properly design smart and intelligent systems. In this paper, PMN-PT piezoceramics with different grain sizes are synthesized by using conventional solid state processing and two-stage sintering method. Grain size effects on the hysteresis, fatigue and creep response are analyzed. Dielectric, ferroelectric and piezoelectric material properties of PMN-PT ceramics are investigated. The piezoelectric coefficient and remnant polarization exhibit diverse grain size effects depending on the sintering temperature and holding duration. The relative dielectric permittivity, piezoelectric coupling constant and dielectric constant show maximum values of 4104.2, 559 pC/N 562.291 pC/N and 0.705 for the microstructure with average grain size of 3.8?μm. The myriad effects of grain size on piezoelectric response are reported in details.     

Strong electromechanical coupling in paraelectric KTa1‐xNbxO3 crystals

A rare electromechanical resonance excited by a weak (<10 V/mm) alternating‐current electric field alone is observed in paraelectric KTa_1‐xNb_xO₃ crystals near the Curie temperature. We show that the transformation from a disordered to an ordered polar‐nanoregion arrangement under the electric field enhances the electrostrictive effect near the phase transition, leading to strong electromechanical coupling. This result establishes the fundamental correlations between the polar nanoregions and the macroscopic physical properties in relaxor ferroelectrics.     

Clamping of ferroelectric PVDF to enhance the electromechanical performance of a 1–3 PMN-PT/PVDF piezoelectric composite

A group of 1–3 type piezoelectric Pb (Mg_1/3Nb_2/3)O₃-PbTiO₃/polyvinylidene fluoride (PMN-PT/PVDF) composite sheets are prepared using a complex two-step hot-pressing method. Then the molecular structure model of piezoelectric materials and an inverse piezoelectric simulation of the composites are performed to express the horizontal compression, indicating the clamping activity of ferroelectric PVDF on PMN-PT. As such, this composite sheet possesses a high dielectric permittivity (ε_r) of 560 at 100 Hz for its compacted connecting of two phases. After polarization, a very large piezoelectric coefficient (d₃₃) of 1125 pC/N and a considerable electromechanical coupling factor (k_t) of 0.43 is obtained in PMN-PT/PVDF sheet with a proper aspect ratio of 1.4 and a thickness of 2.1 mm, further indicating that promoting effect of PVDF matrix on the strain in Z-direction of PMN-PT. The result shows that ferroelectric PVDF serving as polymer matrix favors the electromechanical coupling effect, and may provide a prospect of the potential application of PMN-PT/PVDF composite in sensor or transistor for matrix ultrasonic probes.     

Electric field-induced irreversible relaxor to ferroelectric phase transformations in Na0.5Bi0.5TiO3-NaNbO3 ceramics

(1-x)Na_0.5Bi_0.5TiO₃-xNaNbO₃ (x = 0.02, 0.04, 0.06, and 0.08) ceramics were fabricated by solid-state reaction. High-resolution synchrotron x-ray powder diffraction (SXPD) data, coupled with macroscopic electromechanical measurements, reveal the occurrence of an electric field-induced irreversible crystallographic transformation for x = 0.02 and 0.04, from a pseudo-cubic non-ergodic relaxor to a rhombohedral or coexisting rhombohedral-tetragonal long range-ordered ferroelectric phase, respectively. The highest unipolar electrostrain, corresponding to an effective longitudinal piezoelectric strain coefficient of approximately 340 pm V⁻¹, was obtained for x = 0.04; this effect is attributed to enhanced domain switching as a result of the co-existing rhombohedral and tetragonal phases for this composition, which is critical for piezoelectric actuator applications.     

Lead-free Na0.4K0.1Bi0.5TiO3 ceramic: Poling effect and enhancement in electromechanical and piezoelectric voltage coefficient

The effect of electric poling on the piezoelectric properties of the sintered Na_0.4K_0.1Bi_0.5TiO₃ is studied with varying poling field and temperature. An optimized poling condition (E_P =50 kVcm, T_P =110 °C) exhibited a high piezoelectric voltage (g₃₃∼ 85 mV m/N) and charge coefficients (d₃₃∼193pC/N). A combination of electric field induced irreversible transformation from polar nano regions embedded in a non-polar relaxor state to a long-range ordered ferroelectric state and increase in the structural ordering are responsible for the observed high piezoelectric properties. A mechanism is discussed to reveal the origin of high voltage coefficient due to poling, where the decrease of dielectric permittivity can facilitate high g₃₃. This investigation provides an approach for designing the high performance Na_0.4K_0.1Bi_0.5TiO₃based materials suitable for sensors and energy harvesting applications.     

Effect of crystal structure on polarization reversal and energy storage of ferroelectric poly(vinylidene fluoride-co-chlorotrifluoroethylene) thin films

A series of ferroelectric poly(vinylidene fluoride-co-chlorotrifluoroethylene) films with different crystallite sizes have been obtained by varying the film processing conditions. The impact of the crystallite size on the dipole switching and the electric energy density has been systematically studied by the electric displacement–electric field hysteresis loop measurements. The films with smaller crystallite sizes display larger polarizability, as evidenced by higher maximum polarization and lower dipole switching field in the charging process. Small crystals also facilitate fast dipole depolarization during the discharging process. Consequently, superior released energy densities have been achieved in the films containing small sizes of the ferroelectric crystallite domains. On the other hand, large crystallite sizes are beneficial for the dielectric breakdown strength and the Weibull distribution of the breakdown field of the films. This study sheds new fundamental light on the optimization of the crystal structures of the ferroelectric polymers for high electric energy storage applications.     

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 0.85Na_1/2Bi_1/2TiO₃–0.15BaZr_0.2Ti_0.8O₃, 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.