Volume 88, Issue 1, 01 July 2000
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
88(2000); http://dx.doi.org/10.1063/1.373708View Description Hide Description
A method was developed and used to determine the electromechanical properties of high frequency (>20 MHz) piezoelectric strip vibrators. A nonlinear regression technique was employed to fit the impedance magnitude and phase as predicted by Mason’s model to measured values. Results from experimental measurements on 30 MHz array elements supported by an attenuative backing indicated degraded performance when compared to values predicted from the electromechanical properties measured at low frequency. This degradation may be attributed to damage incurred during fabrication and grain size effects, with a fine grain sized material providing superior relative performance. This technique may be used in the evaluation and comparison of different fabrication processes and materials for high frequency medical imaging arrays.
88(2000); http://dx.doi.org/10.1063/1.373672View Description Hide Description
For polymer composites to be used in electronic packaging, they must have a good combination of thermal and dielectric properties. A composite of aluminum-nitride (AlN) particles dispersed around polystyrene matrix particles has been synthesized in this study. The purpose of using this microstructure is to improve the thermal properties of the polymer at the low-filler content with a minimal increase in the dielectric constant of the polymer composite. The dielectric relaxation behavior of polystyrene–AlN composites has been investigated with broadband dielectric relaxation spectroscopy. The experimental results indicate that the dielectric property of polystyrene–AlN composites is a function of polystyrene particle size, AlN filler concentration, temperature, and frequency under this dispersion state. The dependence of Maxwell–Wagner–Sillars or interfacial polarization of polystyrene–AlN composites on AlN volume fraction has also been studied. The Davidson–Cole equation is used to fit the experimental Cole–Cole plot.
Fabrication and characterization of three-dimensional periodic ferroelectric polymer-silica opal composites and inverse opals88(2000); http://dx.doi.org/10.1063/1.373673View Description Hide Description
Using a high temperature solutioninfiltration process, ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymer is infiltrated into three-dimensional (3D) periodic opal lattices with the silicaopal diameters of 180, 225, and 300 nm to form periodic composite structures. By etching out the silicaopal, inverse copolymeropals can be fabricated, which retains the 3D periodic structure of the original silicaopal lattice. In addition to the optical observation, x-ray diffraction and dielectric study were carried out to characterize the change in the ferroelectric behavior of the composites and inverse opals. Although the copolymer in the composites and inverse opals remains ferroelectric, the ferroelectric transition in the composites and inverse opal becomes diffused and moves to a lower temperature, which is due to the random stress introduced by the irregular voids and interfaces and may be made use of to facilitate the transformation of the copolymer into a relaxor. These results suggest the feasibility of using ferroelectriccopolymer to form 3D photonic crystals.
88(2000); http://dx.doi.org/10.1063/1.373674View Description Hide Description
In this article, we report the successful growth of single-crystal fibers by the laser-heated pedestal growth technique. A single-phase perovskitestructure of the materials has been identified by the x-ray diffraction technique. The phase diagram for single crystals is established for Dielectric properties as function of temperature and frequency and room-temperature hysteresis loops are measured. The remnant polarization and coercive fields are obtained and compared for both single crystals and ceramics. The small dielectric relaxation has been observed for the lower-temperature phase transition (around 40 °C at 1 kHz) of the sample with The relaxation times follow the Arrhenius law with and A common feature of the low-temperature relaxation mode in the sample is also observed, which follows the Arrhenius law with the and
88(2000); http://dx.doi.org/10.1063/1.373675View Description Hide Description
The effective properties of 0–3- and 1–3-type piezoelectric composites of lead zirconate titanate and vinylidene fluoride–trifluoroethylene with different polarization status in both phases are calculated using an effective-medium theory. The effects of volume fraction and polarization orientation on the effective behavior are presented in detail. The theory gives results in reasonable agreement with recent experimental ones. The theoretical predictions demonstrate the interesting behavior of the composites and provide a general guideline for optimizing the microstructural scale of the composites for piezoelectric transducers and pyroelectric sensors.