Piezo- and Pyroelectricity in Polymer Electrets.
NATIONAL BUREAU OF STANDARDS WASHINGTON D C INST FOR MATERIALS RESEARCH
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A model for a polymer electret, based on an elastically isotropic solid with orientationally frozen molecular dipoles, was developed and tested experimentally. This electret is shown to be both piezoelectric and pyroelectric. The polarization is shown to change with mechanically and thermally induced strains in the polarization direction. The currents generated by the electret will be proportional to the strain rate and, for thin contact electrodes and uniform strains, unaffected by the presence of real charges. Polyvinyl chloride films were poled at 80C, just above their glass transition temperature. The pressure- and temperature-induced short-circuit currents in the polarization direction equalled 0.15pAsq cmbarmin and 2.2pAsq cmKmin respectively for a specimen poled at 320 kVcm. These currents were reversible and proportional to the rate of temperature or pressure change, proportional to poling voltage up to 320 kVcm, in the direction corresponding to increasing polarization with increasing pressure and decreasing temperature, about 1.6 times as great for temperature induced strains as for equivalent pressure induced strains, and about 2-4 times as great in magnitude as expected from dielectric constant measurements. Author Modified Abstract
- Electricity and Magnetism
- Solid State Physics