Poled Lead Zirconate Titanate Research Articles

압전 액추에이터를 이용한 저전압 구동 MEMS 가변 캐패시터

In this work, low voltage MEMS variable capacitor was presented. Compare with other RF MEMS technologies, piezoelectric MEMS devices offer certain benefits such as low actuation voltage and fast moving, etc. The proposed structure consists of dual piezoelectric actuation bridges of in-plane polarized lead zirconate titanate (PZT) film to improve actuation voltage and reliability of devices. The PZT thin film, deposited on Au structural layer using RF magnetron sputtering method, was poled and driven with interdigitated electrodes(IDEs) to exploit dSUB33/SUB mode actuation. The in-plane polarized PZT films make it possible to develope dSUB33/SUB mode bending devices which lead to about two times improvement in strain performance. The fabricated variable capacitor shows that the tuning range is varied 100.9 to 111.2 nF with control voltage ranging from 0 to 1 V.

Piezoelectricity in nominally centrosymmetric phases

Compound phases often display properties that are symmetry forbidden relative to their nominal, average crystallographic symmetry, even if extrinsic reasons (defects, strain, or imperfections) are not apparent. Specifically, breaking the macroscopic inversion symmetry of a centrosymmetric phase can dominate or significantly change its observed properties while the detailed mechanisms and magnitudes of the deviations of symmetry breaking are often obscure. Here, we choose piezoelectricity as a tool to investigate macroscopic inversion-symmetry breaking in nominally centrosymmetric materials as a prominent example and measure resonant piezoelectric spectroscopy (RPS) and Resonant Ultrasound Spectroscopy (RUS) in 15 compounds, 18 samples, and 21 different phases, including unpoled ferroelectrics, paraelectrics, relaxors, ferroelastics, incipient ferroelectrics, and isotropic materials with low defect concentrations, i.e., NaCl, fused silica, and ${\mathrm{CaF}}_{2}$. We exclude the flexoelectric effect as a source of the observed piezoelectricity yet observe piezoelectricity in all nominally cubic phases of these samples. By scaling the RPS intensities with those of RUS, we calibrate the effective piezoelectric coefficients using single-crystal quartz as standard. Using this scaling we determine the effective piezoelectric modulus in nominally nonpiezoelectric phases, finding that the ``symmetry-forbidden'' piezoelectric effect ranges from $\ensuremath{\sim}1$ to ${10}^{\ensuremath{-}5}$ pm/V ($\ensuremath{\sim}0.5%$ to $\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}%$ of the piezoelectric coefficient of poled ferroelectric lead zirconate titanate). The values for the unpoled ferroelectric phase are only slightly higher than those in the paraelectric phase. The extremely low coefficients are well below the detection limit of conventional piezoelectric measurements and demonstrate RPS as a convenient and ultrahighly sensitive method to measure piezoelectricity. We suggest that symmetry-breaking piezoelectricity in nominally centrosymmetric materials and disordered, unpoled ferroelectrics is a common phenomenon.

Quasi-static and dynamic fracture behavior of lead zirconate titanate: A study of poling and loading rate

In this study, coupon specimens of both poled and de-poled lead zirconate titanate (PZT) are examined under quasi-static and stress-wave loading conditions. Mode-I crack initiation and fracture behavior is examined using ultra high-speed imaging in conjunction with 2D digital image correlation on symmetrically impacted specimens. Measured displacement fields ahead of the dynamically loaded crack tip are used to extract the critical stress intensity factor (KICd) at initiation and are compared with quasi-static SENT fracture toughness tests. Results demonstrate that under static conditions, the difference between poled and de-poled specimens is not statistically significant, however under dynamic conditions, poled samples exhibited a 70% greater fracture toughness compared to the de-poled specimens. To verify the increase was not due to thermal degradation of material mechanical properties during the de-poling process, re-poled specimens were also prepared and examined under dynamic fracture loading conditions. In general, impulsively loaded samples exhibited greater fracture toughness compared to their quasi-statically loaded counterparts, regardless of the poling. Specifically, the critical stress intensity factor increased seven to tenfold compared to static fracture toughness values, with poled samples exhibiting the greatest toughness of all samples explored. In terms of rate, the increase in fracture toughness under dynamic conditions likely comes from microcracking and potentially phase transformations at the crack tip. In terms of poling, the increase in fracture toughness is likely due to a bulk manifestation of ferroelastic toughening, where dynamic domain reorientation provides crack tip shielding.

Reinvestigation on polarization and strain response of electrically poled lead titanate zirconate ceramics under low-to-medium electric field loading

The polarization and strain response of electrically poled lead zirconate titanate ceramics was reinvestigated under low-to-medium electric field loading. A phenomenon that is usually ignored was pointed out and discussed. That is, under low-to-medium cyclic electric field loading, remnant strains measured under a negative electric field loading are larger than those measured under a positive electric field loading. Here, ‘positive’ and ‘negative’ mean that the applied electric field is aligned or antiparallel to the pre-poling direction of the material, respectively. Moreover, a reverse trend was observed for remnant polarizations. Texture-dependent domain switching, defect dipole reorientation, and interactions between them were used to rationalize this phenomenon. In addition, the equation which is used to describe the strain response, was modified by taking the asymmetry of the electric field versus strain curve into consideration. The modified equation can better describe the strain response than the original equation.

Anomalous elastic moduli and internal frictions in unpoled and poled lead titanate zirconate ceramics near the Curie temperature

Phase transitions in ferroelectric materials are always accompanied by mechanical property variations; thus, besides the dielectric measurement, the measurement of mechanical properties can also be used to study the phase transition process in ferroelectrics. In this work, the temperature-dependent Young’s modulus, shear modulus, and the related internal frictions of unpoled and poled lead titanate zirconate (PZT) ceramics (including soft PZT-5H and hard PZT-4) were comparatively measured at tens of kilohertz by using a modified piezoelectric ultrasonic composite oscillator technique (M-PUCOT). It is found that for the unpoled and poled PZT ceramics at Curie temperature (190 °C for PZT-5H and 330 °C for PZT-4), both moduli reach their local minima and both internal frictions exhibit peaks. Below the Curie temperature, the Young’s modulus of the poled PZT is larger than that of the unpoled one, while the tendency of the shear modulus is just the opposite. Above the Curie temperature, both moduli increase quickly and both internal frictions drop quickly, and all the four mechanical parameters of poled PZT coincide with those of the unpoled PZT; they stabilize at about 400 °C for PZT-5H and at about 480 °C for PZT-4. In addition, it is found from the mechanical measurement that poled PZT-5H can be partially depolarized even at 180 °C, slightly below the Curie temperature of 190 °C. The results in this work are very helpful to deeply understand ferroelectric phase transitions, and the M-PUCOT is strongly suggested to measure the temperature-dependent mechanical properties of ferroelectrics.

In situ XRD analyses for asymmetric responses of poled PLZT ceramics during electric fatigue

Electric fatigue behaviors of the poled lanthanum-doped lead zirconate titanate (PLZT) ceramics were investigated using a home-made electric loading apparatus in conjunction with a conventional X-ray diffractometer. The XRD data were measured under actions of the applied direct current electric fields on the as-received poled PLZT specimens being experienced various cycles (10N) of alternating current (AC) electric fields. Experimental data showed that in addition to apparent degradation in remnant polarization, asymmetries in hysteresis loops and fraction of 90° domain switching curves were observed. It was found that an offset electrical field (\(\Delta {{\text{E}}_N}\)) was induced in the poled specimen by polarization with its direction against the direction of the polarization. Furthermore, the magnitude of \(\Delta {{\text{E}}_N}\) and the degree of asymmetry (δN) decreased as the number of AC electric fatigue cycles (10N) varied from 100 to 106. In situ XRD data suggested that the poled specimen exhibited different abilities to reorient a-domains into c-domains when the applied electric fields were opposite. The δN not only depended linearly on \(\Delta {{\text{E}}_N}\), but also on abilities of the poled specimen to reorient a-domains into c-domains.

The effect of multidirectional bias magnetic fields on the converse magnetoelectric response of multiferroic concentric composite ring

A composite multiferroic ring was characterized under two orthogonal bias magnetic fields while electrically loaded near resonance to measure the circumferential converse magnetoelectric (CME) response. The composite multiferroic structure consisted of an inner magnetostrictive Terfenol-D ring with an axially aligned preferred magnetocrystalline axis bonded to a radially polarized outer piezoelectric poled lead zirconate titanate ring to form a concentric ring structure. A single uniform bias magnetic field was varied from zero to beyond magnetic saturation while the composite ring's axial alignment was changed from perpendicular to parallel with respect to the bias magnetic field direction. The change in the ring orientation thus subjected the ring to two orthogonal bias magnetic fields, whose strengths were calculated based on the orientation angle. The overall CME behavior was found to be largely correlated with the perpendicular magnetic field strength assisted with the shape anisotropy of the ring structure favoring magnetization along the longest axis. Nonetheless, the parallel magnetic field had a notable contribution to the CME response by enhancing the magnetization in the preferred axial direction and activating other unique magnetocrystalline axes. In all, the CME behavior with respect to two orthogonal bias magnetic fields is characterized by an interplay of magnetocrystalline and shape anisotropies bolstered by the parallel and perpendicular magnetic fields.

Giant actuation strain nearly 0.6% in a periodically orthogonal poled lead titanate zirconate ceramic via reversible domain switching

The widely used ferroelectric ceramics based actuators always suffer from small output strains (typically ∼0.1%–0.15%). Non-180° domain switching can generate a large strain in ferroelectrics but it is usually irreversible. In this work, we tailored the domain structures in a soft lead titanate zirconate (PZT) ceramic by periodical orthogonal poling. The non-180° switching in this domain-engineered PZT ceramics turns to be reversible, resulting in a local giant actuation strain of nearly 0.6% under a field of 2 kV/mm at 0.1 Hz. The large interfacial stresses between regions with different poling directions during electric loading/unloading were thought to be responsible for the reversible non-180° domain switching. The switching strain drops quickly with the increasing frequency, and stabilized at about 0.2% at or above 1.0 Hz. The large actuation strain remains quite stable after 104 cycles of loading, which is very promising for low-frequency, large-strain actuators.

Experiment and Prediction of Nonlinear Behavior at High Temperatures of Ferroelectric Ceramics Switched by Electric Field at Room Temperature

Changes in polarization and thermal expansion coefficients during temperature increase of a poled lead zirconate titanate (PZT) cube specimen switched by an electric field at room temperature are measured. The measured data are analyzed to construct governing differential equations for polarization and strain changes. By solving the differential equations, an experimental formula for the high temperature behavior of ferroelectric materials is obtained. It is found that the predictions by the formula are in good agreement with measures. From the viewpoint of macroscopic remnant state variables, it appears that the processes of electric field-induced switching at different temperatures are identical and independent of temperature between 20°C and 110°C. Key words: Ferroelectric, Temperature, Switching, Remnant, Empirical formula

Development and application of an empirical formula for the high temperature behavior of ferroelectric ceramics switched by electric field at room temperature

The strain changes during temperature rise of a poled lead titanate zirconate rectangular parallelepiped switched by electric field at room temperature are obtained by integrating thermal expansion coefficients that are measured using an invar-specimen. By estimating and analyzing pyroelectric and thermal expansion coefficients, first-order differential equations are constructed for polarization and strain changes during temperature increase. The solutions to the differential equations are found and used to calculate the high temperature behavior of the materials. It is shown that the predictions are well compared with measured responses. Finally, the developed formulae are applied to calculate strain butterfly loops from a polarization hysteresis loop at a high temperature.

Rate independence of material properties and remnant state variables during domain switching by electric field or stress in ferroelectric ceramics at room and high temperatures

Various numbers of electric field or compressive stress pulses with increasing magnitude are applied to a poled lead titanate zirconate rectangular parallelepiped specimen. Changes in linear material properties are estimated from measured responses and plotted versus remnant polarization. The dependence of linear material properties on remnant polarization is shown to be the same independent of the overall rate of domain switching by electric field or stress at room and high temperatures. The evolution path of remnant polarization and strains in the plane of remnant state variables is also found to be equal independent of switching rate at room and high temperatures. Finally, when the values of remnant state variables at high temperature are transformed to those of reference remnant state variables, the evolution path of the reference remnant state variables is compared to be coincident with that of remnant state variables at room temperature, implying the same switching process at different temperatures.

Micro-Positioning Stages for Adaptive Optics Based on Piezoelectric Thick Film Actuators

Piezoceramic actuators based on thick film technology offer the opportunity of integrated solutions for smart microsystems. Especially in adaptive micro-optics, where the height of devices is limited, outgassing has to be inhibited and complex actuator structures are required, screen printed actuators are of great interest. The paper highlights our recent research on micro-positioning stages for integration into a plenoptic camera. The first concept is based on through-thickness polarized lead zirconate titanate (PZT) thick films printed on a 45 mm × 44 mm × 0.17 mm LTCC (Low Temperature Cofired Ceramics) frame with 4 mm wide legs. Driving with an electrical field of 2 kV/mm resulted in an upright stroke of 115 μm. The second concept combines through-thickness and in-plane polarized thick films on four cantilever beams of an Al2O3 based micro-positioning stage. Because of the combination of d31- and d33-mode of excitation, each cantilever beam will provide an s-shaped bending profile allowing for a planar and tilt free lift of 130 μm at 1.66 kV/mm. Both actuator concepts were exploited to adjust position of a micro-lens array between main lens and image sensor in a plenoptic camera setup. With that, working range of the plenoptic camera could be extended.

Prediction of high temperature behavior of ferroelectric ceramics with state dependent thermal moduli

A poled lead titanate zirconate rectangular parallelepiped is subjected to an electric field at a room temperature called reference temperature to reach a specific value of polarization. Then the temperature of specimen is raised at the specific value of polarization under no electric field, measuring polarization and strain changes in the specimen. Pyroelectric and thermal expansion coefficients are estimated from measured responses. A set of modeling equations is proposed to predict the dependence of the thermal moduli on remnant state variables and the relations between remnant state variables at high temperatures.

Evolution of linear moduli and remnant state variables during polarization reversal in a lead zirconate rectangular parallelpiped at room and high temperatures

A poled lead titanate zirconate rectangular parallelepiped is subjected to electric field pulses with gradually increasing magnitude at room and high temperatures. From measured electric displacement and strain responses, permittivity and piezoelectric coefficients are estimated and plotted with respect to remnant polarization. Equations for piezoelectric coefficients are proposed as functions of relative remnant polarization and temperature. The so-called reference remnant polarization and strains are calculated from measured remnant polarization and strains. Reference remnant strains are plotted with respect to reference remnant polarization, and their evolutions during polarization reversal are analyzed and compared.

다양한 전계인가율과 온도에서 강유전 세라믹의 이력선도 계측과 기준 잔류 분극 및 변형률 거동 예측

A poled lead zirconate titanate (PZT) rectangular parallelepiped specimen was subjected to through-thickness electric fields at five loading rates and four temperatures. The rates of the electric field were 0.01, 0.10, 0.25, 0.50, and 1.00 MVm -1 s -1 ; the temperatures were 20, 50, 80, and 110 ℃. From the measured polarization hysteresis responses, the so-called reference remnant polarization and strains were calculated. Using the calculated reference remnant polarization hysteresis loops, the effects of loading rates and temperature were discussed; using the calculated reference remnant strains, strain butterfly loops were calculated and compared with observations.

Depolarization and Electrical Response of Porous PZT 95/5 Ferroelectric Ceramics under Shock Wave Compression

The release of bound charges by shock wave loading of poled lead zirconate titanate (PZT 95/5) ferroelectric ceramics can result in a high-power electrical energy output. In this study, a theoretical formulation describing the depolarization and electrical response of porous PZT 95/5 ceramics in the normal mode to shock wave compression loading perpendicular to the polarization direction is developed. The depoling process in porous poled PZT 95/5 ceramics is analyzed by using a parallel circuit consisting of a current source, capacitance, conductance and a circuit load. This modeling takes the effects of porosity on wave velocity and remanent polarization and dielectric constant into account, and the effects of variations in dielectric constant and conductivity in the shocked region are assessed. The output current characteristics of porous PZT 95/5 ceramics under short-circuit and resistive load conditions are analyzed and compared with the experiment, with the results showing that theoretical predictions taking into consideration the porosity of ferroelectric ceramics are in close agreement with the experimentally measured electrical response of porous PZT 95/5 under shock wave compression loading.

Ferroelectric dipole electrets for output power enhancement in electrostatic vibration energy harvesters

We propose a ferroelectric dipole electret composed of polarized lead zirconate titanate. Deep insight into the physics behind the parallel plate capacitor theoretically predicts that we can extract large electric field near the surface of the ferroelectric dipole electret by increasing its surface charge density and thickness. Experiment for ferroelectric dipole electret shows good agreement with the theory. The maximum output power density of electrostatic vibration energy harvesters using the ferroelectric dipole electret was 78 μW/cm3, a three-fold increase over a conventional polymer electret. Our results will pave the way for use of ferroelectrics as electrets.

State-dependent pyroelectric and thermal expansion coefficients in a PZT rectangular parallelepiped after compressive loading and unloading

A poled lead titanate zirconate rectangular parallelepiped was subject to compressive stress loading and unloading. After reaching a specific polarization, stress is removed and temperature is increased. Longitudinal polarization and longitudinal and transverse strains are measured during the temperature rise. A false contribution of leakage current to measured polarization is removed. From measured polarization and strains, pyroelectric and thermal expansion coefficients are evaluated. Dependence of the two thermal properties on remnant state variables is investigated. The evolution of remnant strains with relative remnant polarization is also discussed and compared with a previous work.

The charge-free zone model for electrically conductive cracks in dielectric and piezoelectric ceramics

The charge-free zone model for electrically conductive cracks in dielectric and piezoelectric ceramics is reviewed with the simplified constitutive equations and the regular constitutive equations and then applied to interpret the experimental results on window ceramic glass and poled lead zirconate titanate PIC 151 ceramics. A good agreement is found between the experimental results and the theoretical predictions from the charge-free zone model, which indicates that the concepts of fracture mechanics can be applied to the failure of conductive cracks in dielectric and piezoelectric ceramics.

상온과 고온에서 압축하중을 받는 PZT에서의 잔류상태변수와 선형재료상수의 변화

A poled lead zirconate titanate (PZT) cube specimen is subjected to impulse-type compressive stress with increasing magnitude in parallel to the poling direction at four room and high temperatures. During the ferroelastic domain switching induced by the compressive stress, electric displacement in the poling direction and longitudinal and transverse strains are measured. Using the measured responses, linear material properties, namely, the piezoelectric and elastic compliance coefficients, are evaluated by a graphical method, and the effects of stress and temperature are analyzed. Finally, the dependency of the evaluated linear material properties on relative remnant polarization is analyzed and discussed.