Electrostriction and pyroelectricity of PZT/PU composites

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Electrostriction and pyroelectricity of PZT/PU composites


Author: Lam, Kai-siu
Title: Electrostriction and pyroelectricity of PZT/PU composites
Degree: M.Phil.
Year: 2004
Subject: Hong Kong Polytechnic University -- Dissertations
Ferroelectric thin films
Lead -- Electrometallurgy
Department: Dept. of Applied Physics
Pages: xv, 161 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1749084
URI: http://theses.lib.polyu.edu.hk/handle/200/3054
Abstract: A composite system, comprising an electrostrictive thermoplastic elastomer Polyurethane (PU) and a ferroelectric ceramic Lead Zirconate Titanate (PZT) has been investigated in this project. This material system exhibits various features that have attracted both scientific interest and attention for engineering applications. The present work aims at the study of the electrostrictive and the pyroelectric properties of these PZT/PU composites of various ceramic contents. The full understanding of their properties can help us design prototype devices based on these composites for sensor and actuator applications. 0-3 composites of PZT/PU with various ceramic volume fractions were prepared by extrusion. The samples for characterization were produced by hot pressing. The microstructures of the samples were studied by different techniques including scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. Other physical properties such as dielectric permittivities, resistivities and thermal conductivities of the samples which affect electromechanical and pyroelectric performance have been determined. It is interesting to point out that the measured pyroelectric coefficients of the composites increase almost linearly with the volume fraction of the PZT inclusions, which in general is not the case. A model is proposed to provide an explanation of such a relationship. Based on the measured physical properties of the composites, samples of 26% and 30% PZT were chosen as pyroelectric sensor elements. This responsivity and detectivity were measured with a chopped light source and a lock-in amplifier. The electrostriction of the composites was measured by a modified Michelson interferometer. Quasi-static fields were applied across the samples when strains and displacement currents were measured simultaneously. It was found that the electrostriction of the composites was dependent on the ceramic volume fraction. Switching in the electrostrictive strain of the samples was also observed. It occurs at a critical field which decreases with the PZT content. Electrode clamping can affect the electrostriction performance. By using compliant electrodes (a mixture of carbon black and silicone) instead of metallic electrodes, an enhancement in the electrostriction of PU was obtained. Electrostrictive bending is another interesting feature that was observed in pure PU and PZT/PU composites. Several types of bending actuators with a combination of PU and PZT/PU composite were fabricated and their bending performances were studied. Hysteretic bending response was observed. The bending mechanisms of these actuators are also discussed in this thesis.

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