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High field ferroelectric behavior and temperature dependence of the dielectric and piezoelectric properties are examined for hard lead-free ceramics. The studies have shown that when compared to conventional hard PZT ceramics, the lead-free contains lower dielectric and piezoelectric properties, and comparable values of mechanical Q, dielectric loss and coercive fields are obtained, thus making acceptor modified [K.sub.0.45][Na.sub.0.55]Nb[O.sub.3] (KNN) based lead-free piezoelectric material good for high-power applications.

The electrical properties of large-size and high-quality Y[Ca.sub.4]O[(B[O.sub.3]).sub.3] (YCOB) single crystals grown by the Czochralski pulling method is characterized at room temperature and elevated temperature. The results for the temperature-independent electrical resistivity of YCOB crystals showed them to be promising candidates for sensing applications at elevated temperatures.

The electric and the electromechanical properties measured are studied as a function of temperature for lead-free piezoelectric ceramics with compositions around the morphotropic phase boundary (MPB). The properties are found to be optimum for the MPB composition but their temperature dependence reveals evidence of a curved rhombohedral to tetragonal phase boundary and a phase transformation to ferroelectric occurs.

A study on the influence of domain switching on the evolution of macroscopic polarization in the ferroelectric [Pb(Mg1/3Nb2/3).sub.1-x][Ti.sub.x]O3 material is conducted. Results reveal that stress depolarization is controlled by 90 degree domain reorientation.

The design and fabrication of a high-frequency annular array as well its performance is reported. The resulting array attained an average impulse response that exhibited a 43 MHz center frequency, 30 percent relative bandwidth, and an average insertion loss of 31 dB at 45 MHz.

Manganese modified (1-x)BiScO3-(x)PbTiO3 (BSPT) compositions near the morphotrophic phase boundary are investigated and the electrical behavior is characterized at high temperatures, and a full set of material constants is determined using the resonance method. Studies revealed that these data should provide a basis to perform future theoretical analysis as well as device design, the temperature of the properties and very high RC modifying BSPT as a new material for high temperature actuation and sensing applications.

The temperature behavior of various relaxor-PT piezoelectric single crystals is investigated. Due to a strongly curved morphotrophic phase boundary, the usage temperature of these perovskite single crystals is limited by T (sub R-T), the rhombohedral totetragonal phase transformation temperature, which occurs at significantly lower temperatures than the Curic temperature T (sub c).

A fine grain, relaxor-based piezoelectric ceramic has been investigated, which was fabricated using the columbite precursor method. The measurement results show that this fine-grain investigated ceramic is a very good material for making ultrasonic array transducers.

Results of an attempt to develop a 30MHz linear array are reported. design goals are achieved, and coupling with an appropriate beamformer should improve performance and make clinical applications possible.

The fabrication and properties of BZN thin films prepared by a metalorganic deposition (MOD) process is reported. The structures, morphologies, and dielectric properties of films with two compositions such as(Bi1.5Zn0.5) (Zn0.5 Nb1.5)O7 and Bi2(Zn1/3 Nb2/3)(sub 2)O7, are investigated.

A new method is presented for determining the electromechanical properties of high frequency thin strip piezoelectric vibrators.

Research was conducted to examine the dielectric and piezoelectric properties of BaTiO3 single crystals polarized along the (001) crystallographic axes as a function of temperature and dc bias. The low-temperature phases of BaTiO3 single crystals were poled along (001) to induce an engineered domain state. The derived piezoelectric properties were compared with values predicted by axis transformation for single-domain BaTiO3 crystals using the Devonshire theory.

Templated grain growth produced single crystals of Ba(ZrxTi1-x) by heating a BaTiO3 crystal in contact with a sintered polycrystalline matrix at 4.5, 5.0 or 8.5 mol% Zr-doped barium titanate for 30 h at 1350 degrees Celsius. The ceramic compact was made 3 mol% TiO2 excess to stimulate boundary migration. At room temperature, the 4.5 and 5.0 mol% Zr-doped crystals were orthorhombic and showed polarizations of 13 uC/sqcm and a high field of d33 of 340-355 pC/N.

The piezoelectric behavior as a function of electric field direction was examined for rhombohedral Pb(Zn1/3Nb2/3)O3:PbTiO3 crystals as a function of crystallographic direction and subsequent domain configuration. Inconsistency among low field piezoelectric properties was believed to be a result of domain instability and subsequent partial depolarization for crystals oriented along the polar direction. High field strain versus electric field behavior was characterized by an induced phase transition rhombo-tetragonal, resulting in volume strain as high as 0.35%.

A study is conducted on the E-field induced phase transitions and other changes in the dielectric/piezoelectric properties of (001)-oriented rhombohedral 0.92Pb(Zn1.3Nb2/3)O3-0.08PbTiO3 crystals. It is shown that induced phases were nucleated and grown with increasing E-field beginning at E > 20kV.cm. Increased crystal anisotropy of the induced phase led to a lower dielectric constant and lateral mode piezoelectric properties and increased the thickness coupling.

The electromechanical properties of [111]-oriented tetragonal Pb(In1/2Nb1/2O3)-Pb(Mg1/3Nb2/3O3)- PbTiO3 (PIN-PMN-PT) crystals were investigated for potential high frequency ultrasonic transducers. The domain-engineered tetragonal crystals exhibit an ultrahigh free dielectric permittivity ε33T > 10 000 with a moderate electromechanical coupling factor k33 ~ 0.79, leading to a high clamped dielectric permittivity ε33 S of 2800, significantly higher than those of the rhombohedral relaxor-PT crystals and high-K (dielectric permittivity) piezoelectric ceramics. Of particular significance is that the [111]-oriented tetragonal crystals were found to possess high elastic stiffness, with frequency constant N33 of ~2400 Hz m, allowing relatively easy fabrication of high-frequency transducers. In addition, no scaling effect of piezoelectric and dielectric properties was observed down to thickness of 0.1mm, corresponding to an operational frequency of ~24 MHz. These advantages of [111]-oriented tetragonal PIN-PMN-PT crystals will benefit high-frequency ultrasonic array transducers, allowing for high sensitivity, broad bandwidth, and reduced noise/crosstalk. [ABSTRACT FROM AUTHOR]

Researchers have considered whether relaxor-based materials offer superior dielectric and piezoelectric performance to that of Pb(Zr1-chi,Ti-chi)O3 (PZT) materials when used in ultrasonic transducers. It was established that Relaxor-PT materials can give significant improvements in transducer performance. However, there will be considerable challenges to be addressed before single crystal piezoelectrics can become piezoelectric materials for the new generation of ultrasound transducers.

Research has been undertaken into the impact of the properties of the piezoelectric materials used in the production of transducers operating at high frequencies on the performance of these transducers. It was possible to establish measured properties for a range of commercially available piezoelectric materials. It was found that conventional lead zirconate titanate materials (PZT) have greatly reduced Kt and higher losses at high frequencies. There are less frequency-dependent properties with new fine grain PZT materials.

Piezoelectric behavior and ultrahigh strain in relaxor-based ferroelectric single crystals are discussed. The crystals studied are pseudocubic (001)-oriented and rhombohedral. They are promising candidates for high-performance solid state electromechanical actuators in that they have high electromechanical coupling and low dielectric loss with large strain. Ultrahigh piezoelectric coefficients and strain levels up to 0.6% with low hysteresis were found. Morphotropic phase boundary compositions were not required for high piezoelectric strain.