In this report, piezoelectric Pb(Zr<sub>x</sub>Ti<sub>1-x</sub>)O<sub>3</sub> (PZT) thin films have been prepared onto platinized silicon and stainless steel substrates (SS) respectively, by using the sol-gel spin-on techniques and rapid thermal annealing (RTA) process. (i) Near 4 μm (100) oriented PZT thin films were prepared onto (111)Pt/Ti/SiO<sub>2</sub>/Si. The dielectric constant and remnant polarization achieved 1658 and 35 μC/cm<sup>2</sup> respectively. Zr-rich PZT thin films had higher dielectric constant. The as-prepared PZT thin films were observed to have spontaneous piezoelectric responses, which was prominent in the relatively thinner films. (ii) PZT thin films were successfully deposited onto SS substrates by using a thin template of PbTiO<sub>3</sub> layer. The annealing temperature of PZT was decreased to 550°C. No second phase was detected to the limit of X-ray diffractmeter. The remnant polarization and piezoelectric d<sub>31</sub> constant were determined to be 35 μC/cm<sup>2</sup> and -76 pC/N, respectively. (iii) The origin of the self-poling effect was conjectured to the formation of an internal bias field in PZT thin films. The shift of Curie temperature Tc of PZT thin films was discussed on the base of two-dimensional compressive and tensile stresses introduced by different substrates.
The clamant need for field controlled high strain actuator materials in a multitude of emerging smart materials applications has lead to extensive studies over a very wide range of materials systems from ultra soft elastomers to exceedingly stiff martensitic metals. The capabilities which have been achieved and the basic strain mechanisms exploited to achieve high controlled deformation will be briefly reviewed. The focus of the talk will be upon the importance of ferroic systems, where incipient or full spontaneous ordering permits the achievement of strain levels which would otherwise be impossible in such stiff matrices. The struggle to discipline and control spontaneous ordering so as to achieve well controlled anhysteretic response will be discussed, drawing on the examples of the electron irradiation modified polyvinylidene fluoride:trifluoroethylene copolymer and the high strain high coupling response in the single crystal lead zinc niobate: lead titanate (PZN:PT) perovskites. It is interesting to note the common theme of engineering instability in domain and/or sub domain structures important in these two grossly dissimilar material systems and the manner in which this is carried forward in other ferroics. The final important question to be discussed is where these considerations lead for the design of the next generation of improved high strain actuator materials.
Crystallographic engineering, a concept to utilize crystal anisotropy as well as an engineered domain configuration, resulted in significant enhancement in piezoelectric activity for normal ferroelectric BaTiO<SUB>3</SUB> crystals. Electromechanical couplings (k<SUB>33</SUB>) approximately 85 percent and piezoelectric coefficients (d<SUB>33</SUB>) as high as 500 pC/N, higher or comparable to those of lead based ceramics such as PZT and significantly larger than those of tetragonal BaTiO<SUB>3</SUB> crystals, were detected from crystallographically engineered orthorhombic BaTiO<SUB>3</SUB> crystals. Orthorhombic BaTiO<SUB>3</SUB> phase could be stabilized by Zr-doping at room temperature and enhanced electromechanical coupling (k<SUB>33</SUB>) approximately 75 percent was detected also by using crystallographic engineering. Macroscopic symmetry was suggested for <001> poled rhombohedral (3m) and orthorhombic (2mm) crystals, based on the engineered domain configuration.
Acoustic source used for Active Noise Control at low frequency (80 - 250 Hz) is designed and developed by using a piezoelectric ceramic actuator and a flextensional panel diaphragm. In order to reach the vibration magnitude and radiation area needed for high and flat sound pressure level in the low frequency range. Pseudo-Shear Universal (PSU) actuator has been used as the driving part which is a new type of multilayer piezoelectric actuator originated from MRL offering the advantages of large displacement and high blocking force; on the other hand, Carbon Fiber Reinforced Composite has been used as the diaphragm material which provides a more rigid structure than conventional loudspeaker paper. A prototype device was fabricated which has the following characterizations: 40 layers PSU actuator with a compact dimension: 38 mm X 50 mm X 23.6 mm. Two of them are needed for a device. Diaphragm area is 126 mm X 152 mm. At quasistatic condition (5 Hz) and at the 0.84 kV/cm electric field, 344 micrometers displacement could be achieved at the apex of the diaphragm resulted from the flextensional amplifying mechanism with an amplification factor more than 11. The sound passive level in the frequency range 100 - 250 Hz shows better flat behavior than the acoustic sources studied earlier such as Double Amplifier and PANEL air transducers which exhibit a significant reduction of sound pressure level in the low frequency range. By a slight modification, it is likely to make this device in a total thickness of 10 - 15 mm range. High and stable sound pressure level as well as thin flat structure make it much more competitive in the whole area of applications for low frequency active noise control.
A new technique is presented for active distributed fiber sensing for interrogating structural integrity and environmental monitoring using an innovation in low power integrated compact tunable fiber optic laser capability.
Piezoelectric actuators have significant potential for use in smart systems like vibration suppression and acoustic noise canceling devices. In this work, a novel piezoelectric bending actuator CRESCENT was developed. CRESCENT is a stress-biased ceramic-metal composite actuator. The technology involves the use of the difference in thermal contraction between the ceramic and the metal plates bonded together at a high temperature by a polymeric agent to produce a stress-biased curved structure. An extensive experimental investigation of this device in the cantilever configuration was carried out. The tip displacement, blocking force and electrical admittance and were chosen to characterize the performance of the actuator under quasistatic conditions. The device fabricated at optimum temperature exhibits large tip displacement and blocking force and possesses superior electromechanical characteristics to conventional unimorph actuators.
During the last several years novel piezoelectric bending actuators have been developed: RAINBOW, CERAMBOW, CRESCENT, d<SUB>33</SUB> bimorph and THUNDER. A comparative experimental investigation of electromechanical characteristics of these devices along with conventional d<SUB>31</SUB> bimorph and unimorph actuators was conducted in this work. All transducers were fabricated from soft piezoelectric ceramics. The experimental results show the d<SUB>33</SUB> bimorph and unimorph elements have superior quasistatic characteristics as compared to other type of bending-mode actuators. All these piezoelectric devices demonstrate a significant dependence of electromechanical performance on the magnitude of the driving electric field. It was found that the decrease in the mechanical quality factor and resonant frequency of bending vibrations in d<SUB>31</SUB> unimorph, RAINBOW, CRESCENT (CERAMBOW) and THUNDER with increasing electric field is much smaller than that in bimorph and d<SUB>33</SUB> unimorph actuators. The dependence of the behavior of these devices on the operating conditions governs the selection of a particular device for a specific application.
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 (Pb<SUB>0.98-(delta</SUB> )La<SUB>0.02</SUB>A<SUB>(delta</SUB> )) (Zr<SUB>x</SUB>Sn<SUB>y</SUB>Ti<SUB>z</SUB>)O<SUB>3</SUB> (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.
Ce doped and undoped Sr<SUB>x</SUB>Ba<SUB>1-x</SUB>Nb<SUB>2</SUB>O<SUB>6</SUB> (SBN) fibers grown by the laser heated pedestal growth (LHPG) technique in Stanford University were investigated by 2D scanning electron microprobe analysis. The SBN fibers grown along c  or a  axes often show radially distributed optical inhomogeneities (core effects) of varying magnitude. Ba enrichment and Sr reduction were primarily detected in the core which can be qualitatively described by a complex-segregation effect. This defect structure as a complex-congruency related phenomenon modified by the composition-control mechanism of LHPG system. Its radial dependence of effective segregation coefficient is described by the modified Burton-Prim- Slichter equation.
A new type of piezoelectric air transducer has been developed for active noise control and other air acoustics applications. The transducer is based on the composite panel structure of a bimorph-based double amplifier, that is, two parallel bimorphs or bimorph arrays with a curved cover plate as an active face attached to the top of the bimorphs. The electro- mechanical and electro-acoustic properties of the double amplifier structure and the transducer are investigated in this paper. The displacement of the cover plate of the double amplifier structure can reach millimeter scale with a relatively low driving voltage, which is more than ten times larger than the tip displacement of bimorphs. The sound pressure level (SPL) of the transducer can be larger than 90 dB (near field) in the frequency range from 50 to 1000 Hz and be larger than 80 dB (far field) from 200 Hz to 1000 Hz, with the largest value more than 130 dB (near field). Because of its light weight and panel structure, it has the potential to be used in active noise control.
The electric field induced antiferroelectric-to-ferroelectric phase transition of lead zirconate titanate stannate ceramics was investigated by means of dielectric, polarization, and strain hysteresis measurements. Compositions of varying titanium and tin within the general formula (Pb<SUB>0.98</SUB>La<SUB>0.02</SUB>) (Zr<SUB>0.66</SUB>Ti<SUB>0.11-x</SUB>Sn<SUB>0.23+x</SUB>)O<SUB>3</SUB>, located in the tetragonal antiferroelectric phase field and near the ferroelectric rhombohedral boundary were prepared. As the applied electric field increased, a sudden increase in both longitudinal and transverse strain was observed with a corresponding change in dielectric constant, loss, and polarization, indicating the transition from antiferroelectric to ferroelectric phase. The longitudinal strain increased continuously into the ferroelectric phase, whereas the transverse strain became negative after the phase change. By defining the phase change field from polarization and high field dielectric constant and loss measurements, the longitudinal strains associated with the phase change for all of the compositions were less than 0.2%. For some compositions, however, the longitudinal strain increased to levels greater than 0.5% with increasing applied field. Owing to the relatively small decrease in transverse strain in the ferroelectric region, the volume strain continued to increase even after antiferroelectric to ferroelectric phase change.
Transverse piezoelectric mode ceramic-polymer composites provide several advantages over conventional longitudinal mode composites. It has been shown, from both analytical and experimental results, the hydrostatic performance of 1 - 3 tubular and 2 - 2 plate piezocomposites can be significantly improved by utilizing the transverse piezoelectric effect. By varying the geometry of the piezoelectric ceramics and the configuration of constituent phases, the undesirable components of piezoelectric response of the composites can be eliminated. Moreover, the effective uniaxial and hydrostatic responses can be greatly enhanced by optimizing the physical properties of the constituent phases and the structures of the composites.
Piezoelectric actuators and sensors made of tubular structure can provide a great agility of the effective response in the radial direction. For a radially poled piezoelectric tube, the effective piezoelectric constant in that direction can be tuned to be positive, zero, and negative by varying the ratio of the outer radius (R<SUB>0</SUB>) to the inner radius (r<SUB>0</SUB>) of the tube. For a suitable ratio of R<SUB>0</SUB>/r<SUB>0</SUB>, this effective constant can also be changed in sign or set to zero by adjusting the dc bias field level for tubes made of electrostrictive materials. Therefore, one can make a piezoelectric transducer with all the effective piezoelectric tensile constants having the same sign. The end capped thin wall tubes also exhibit exceptionally high hydrostatic response and the small size of the tubular structure makes it very suitable for integration into 1 - 3 composite which possesses low acoustic impedance and high hydrostatic response.