Ming-Jen Pan

Electric field induced phase transition of antiferroelectric lead lanthanum zirconate titanate stannate ceramics

The electric field induced phase transition behavior of lead lanthanum zirconate titanate stannate (PLZTS) ceramics was investigated. PLZTS undergoes a tetragonal antiferroelectric (AFETet) to rhombohedral ferroelectric (FERh) phase transition with the application of an electric field. The volume increase associated with this antiferroelectric (AFE)–ferroelectric (FE) phase transition plays an important role with respect to actuator applications. This volume increase involves an increase in both transverse and longitudinal strains. The E field at which the transverse strain increases is accompanied by an abrupt jump in polarization. The longitudinal strain, however, lags behind this polarization jump exhibiting a slight decrease at the onset of phase switching. This decoupling was related to the preferentially oriented AFE domain configuration, with its tetragonal c-axis perpendicular to the applied electric field. It is suggested that phase switching involves multiple steps involving both structural tran...

Relaxor-based ferroelectric single crystals for electromechanical actuators

The piezoelectric properties of relaxor based ferroelectric single crystals, such as Pb(Zn1/3Nb2/3)O3 - PbTiO3 (PZN-PT) and Pb(Mg1/3Nb2/3)O3 - PbTiO3 (PMN- PT) were investigated for electromechanical actuators. In contrast to polycrystalline materials such as Pb(Zr,Ti)O3 (PZTs), morphotropic phase boundary compositions were not essential for high piezoelectric strain. Piezoelectric coefficients (d33s) > 2500 pC/N and subsequent strain levels up to > 0.6% with minimal hysteresis were observed. Crystallographically, high strains are achieved for <001> oriented rhombohedral crystals, though <111> is the polar direction. Ultrahigh strain levels up to 1.7%, an order of magnitude larger than those available from conventional piezoelectric and electrostrictive ceramics could be achieved, being related to an E-field induced phase transformation. Strain vs. E-field behavior under external stress was also much superior to that of conventional piezoelectric ceramics. High electromechanical coupling (k33) > 90% and low dielectric loss <1%, along with large strain make these crystals promising candidates for high performance solid state actuators.

Novel method for producing high frequency 2-2 composites from PZT ceramic

The fabrication of 2-2 PZT/epoxy composites by laminating ceramic tape printed with carbon black was investigated as a way to make very high frequency ultrasound transducers. When the laminates were fired, the tape layers densified to form the PZT beams and the carbon volatilized leaving behind kerf space. The kerf was then filled with epoxy, and resulting composites had properties equivalent to those routinely made by conventional dice and fill technology. Since tape casting and screen printing methods can provide feature sizes less than 5 /spl mu/m, the techniques investigated in this work could potentially be used to fabricate linear and perhaps even phased arrays in the 30 to >50 MHz range.

Electric field induced phase transition in lead lanthanum stannate zirconate titanate (PLSnZT) antiferroelectrics: tailoring properties through compositional modification

Abstract In this study, we investigated the effects of dopants on the antiferroelectric-to-ferroelectric (AFE-FE) phase transition behavior of lead lanthanum stannate zirconate titanate (PLSnZT) family of ceramics. In particular, the possibility to lower both the switching field and hysteresis by compositional modification was sought. Based on tolerance factor considerations, barium (Ba) and strontium (Sr) were chosen as modifiers to stabilize ferroelectric and antiferroelectric phases, respectively. With the right starting composition and proper amount of dopant, we demonstrated that the properties of PLSnZT can be tailored to fit the needs of specific applications. It was also observed that the temperature dependence of dielectric constants, such as the ferroelectric-to-antiferroelectric transition temperature (T FE-AFE) and the temperature of the maximum dielectric constant (T MAX), is strongly related to the phase switching behavior. The influence of dopants on the operating temperature range was also...

Effect of Grain Size on Actuator Properties of Piezoelectric Ceramics

Properties of piezoelectric ceramics important for actuator applications have been measured as a function of grain size. Fine grain piezoelectrics (≤1 μm) have been found to exhibit improved machinability and increased mechanical strength over conventional materials. Actuators made from fine grain ceramic are, therefore, expected to have improved reliability, higher driving fields, and lower driving voltages (from thinner layers in stacked or co-fired actuators) over devices fabricated from conventional materials. TRS Ceramics in collaboration with the Pennsylvania State Universitys Materials Research Laboratory, has developed fine grain piezoelectric ceramics with minimal or no reduction in piezoactivity. New chemical doping strategies designed to compensate ferroelectric domain clamping effects from grain boundaries have been successful in yielding submicron grain sized ceramics with both low and high field properties equivalent to conventional materials. In the case of Type II ceramics, reduced grain size results in a very stable domain state with respect to both electric field and compressive prestress. Work is in progress to develop both epoxy bonded stack and co-fired actuators from fine grain piezoelectrics.

Single-crystal piezoelectrics for advanced transducer and smart structures applications

Single crystal piezoelectrics based on xPb(Zn1/3Nb2/3)O3-(1-x)- PbTiO3 and xPb(Mg1/3Nb2/3)O3-(1- x)PbTiO3 show great promise for dramatically improving the performance of medical ultrasound transducers, sonar transducers, active flow control actuators, high strain energy density stack actuators, and microactuators. Improvements in crystal growth and manufacturing are yielding large numbers of crystals for device performance evaluations. Property variations have been minimized by identifying the sources of variations and designing manufacturing processes to eliminate property-degrading defects from the final components. Crystal size increases and cost reductions have resulted from replacing flux grown PZN-PT with PMN-PT crystals produced by the Bridgman method. Finally, low crystal stiffness has been shown to not be a hindrance in maintaining high properties under compressive prestress or in packaged devices such as epoxy bonded stack actuators.

Comparison of actuator properties for piezoelectric and electrostrictive materials

The field induced strain has been measured for a broad variety of piezoelectric and electrostrictive actuator materials. These measurements have been made under AC drive conditions with variations in DC bias, peak to peak voltage, and prestress. Data for three types of PMN-PT electrostrictors, hard and soft piezoelectric ceramics, and PZN-PT single crystal have been collected. For smart structures applications fine grain Type II ceramic and PZN- PT single crystals were found to have the best combination of moderate to high strain, low to moderate hysteresis, and resistance to stress depoling. Electrostrictive ceramics used for high frequency transducers were found to exhibit some stress induced domain reorientation effects that depended on drive conditions and operating temperature. These effects became more pronounced for electrostrictors with high lead titanate content. Epoxy bonded stacks have been constructed form some of the materials to determine the merits of materials properties for actuator performance. This work has shown that fine grain Type II ceramics have many advantages for high authority stack actuators including high strain energy density and lifetimes > 109 cycles at 100 percent rated peak-to-peak voltage.

Electroactive actuator materials: investigations on stress and temperature characteristics

The quasistatic electromechanical and dielectric behaviors of different electroactive actuator materials are investigated under the simultaneous influence of uniaxial stress and temperature at high driving field. An experimental setup capable of applying 9000 newtons of uniaxial force was carefully designed, based on a precisely guided steel frame. Extra caution was taken to minimize the effects of mis-alignment and contact surface clamping. The materials examined in this study include a prospective PLSnZT anitferroelectric ceramics which is currently under development, as well as electrostrictive ceramics, namely PMN-PT 90/10 and PMN-PT 76/24. To assess the applicability of these materials in real systems, multilayer stacks were assembled and their response to stress and temperature was examined. The overall strain of the PLSnZT composition showed increases with increasing uniaxial stress. This might be the result of re-orientation of antiferroelectric domains under pre-stress. It also showed excellent stability in strain over the temperature range 20 to 75°C under stress as high as 100 MPa. In contrast, the electrostrictive ceramics are less dependent on stress than antiferroelectrics but more susceptible to temperature changes.

Antiferroelectric-to-ferroelectric phase switching PLSnZT ceramics. I. Structure, compositional modification and electrical properties

Electric field induced antiferroelectric-to-ferroelectric (AFE-FE) phase transformation is usually accompanied by large strain, which is attractive for actuator applications. In this study, the AFE-FE switching of lead lanthanum stannate zirconate titanate (PLSnZT) was investigated and efforts were made to find high strain compositions with low switching field and hysteresis. Compositional modifications on both the A- and B- site were attempted in order to modify material properties. The B-site modifications were completed through manipulation of the Ti:Sn and Zr:Sn ratios. On the other hand, the A-site modifications were accomplished by the addition of Ba and Sr. It was demonstrated that one can tailor material properties to fit specific application requirements through compositional modifications.

Antiferroelectric-to-ferroelectric phase-switching lead lanthanum zirconite stannate titanate (PLZST) ceramics

Electric field induced antiferroelectric (AFE) to ferroelectric (FE) phase transformations are accompanied by large strain and significant hysteresis. The properties of these materials can be tailored to fit specific applications such as high strain actuators and charge capacitors. As an attempt to reduced hysteresis, Barium and Strontium A-site substitution of the phase transformation behavior of (Pb0.98-(delta )La0.02A(delta )) (ZrxSnyTiz)O3 (A equals Ba, Sr) ceramics have been investigated. The ceramic samples in this study produced 0.2% to 0.3% strain level. Barium proved to be a strong FE stabilizer with decreasing both switching field and hysteresis, while Strontium proved to be a strong AFE stabilizer. Some practical data, including temperature stability and current requirements, are also to be discussed.