Effective piezoelectric properties of ferroelectric 0-3 composites

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Effective piezoelectric properties of ferroelectric 0-3 composites

 

Author: Wong, Chung-kwan
Title: Effective piezoelectric properties of ferroelectric 0-3 composites
Degree: M.Phil.
Year: 2002
Subject: Hong Kong Polytechnic University -- Dissertations
Piezoelectric materials
Piezoelectricity
Ferroelectricity
Department: Dept. of Applied Physics
Pages: iii, 144 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1637847
URI: http://theses.lib.polyu.edu.hk/handle/200/4279
Abstract: Explicit formulas were found for the effective piezoelectric coefficients of a 0-3 composite of ferroelectric spherical particles in a ferroelectric matrix. Both tensile loading and hydrostatic loading conditions were studied. Assuming that both phases were dielectrically and elastically isotropic, explicit expressions in simple closed-form for the effective d33, d31*, and dh coefficients were derived in terms of the constituents' piezoelectric coefficients and the dielectric and elastic properties of the composite and constituents. Expressions for the effective g, e and h coefficients for both loading conditions were also found. Predictions of the piezoelectric coefficients for PZT/epoxy, PZT/PVDF, PZT/P(VDF-TrFE) and PbTiO3/P(VDF-TeFE) were compared with experimental values reported in the literature, and good agreement with data were obtained. As the method employed is suitable for the case of more concentrated suspension, goodness of fit is not limited to low volume fraction of inclusions. Temperature and frequency dependence of the complex effective piezoelectric coefficient d31* for a ferroelectric 0-3 composite of small ceramic volume fraction has been studied. Theoretical predictions are based on our explicit expression of d31 for a dilute dispersion of spherical particles in a continuous matrix. Comparison is made with the well-known Furukawa's model and his experimental measurements on a PZT/epoxy composite with 13 vol. % PZT. The real part and the imaginary part of the effective piezoelectric coefficient of the composite were investigated separately. Concerning the temperature dependence of effective d31*, predictions for the real part of d31* agree well with the observed values for temperatures larger than 60 C, but are larger than the observed values for lower temperatures. On the other hand, predictions for the imaginary part of d31* give fairly good agreement with the experimental data throughout the temperature range. Concerning the frequency dependence of effective d31*, comparison with experimental data shows good agreement. For higher inclusion volume fraction, apart from the method suggested previously, the predictions of piezoelectric properties given by an effective medium theory (EMT) were also investigated. Explicit formulas were derived for the effective piezoelectric e33, e31, and eh coefficients of a 0-3 composite of ferroelectric spherical particles in a ferroelectric matrix, which were then combined to obtain explicit formulas for d33, d31 and dh coefficients. For elastic stiffness constants of the inclusion phase sufficiently larger than those of the matrix phase, the previously derived explicit expressions for the case of low volume concentration of inclusion particles were transformed analytically by EMT to suit the case of more concentrated suspension. Predictions of the EMT expressions were compared with the experimental values of PZT/PVDF and PZT/P(VDF-TrFE), and fairly good agreement with data was obtained. Comparisons with the predictions given by solving the EMT scheme numerically were also made. It was found that the analytic and numeric EMT schemes gave excellent agreement with each other for inclusion volume fraction not exceeding 60%.

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