Formation of Pyroelectricity in Unoriented Polytrifluoroethylene

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Abstract
Pyroelectricity in polytrifluoroethylene was studied in detail on unoriented samples. The pyroelectricity was found to be anomalous as regards the temperature dependence of the pyroelectric coefficient, since the latter changed signs twice over the temperature range 100 to 350 K. Also, the sample with the lowest initial crystallinity exhibited the greatest degree of pyroelectric activity. Crystallization coupled with poling was found to be responsible for the pyroelectricity, i.e., spontaneous polarization was induced in the new crystalline region developed during the poling process, and not in the existing crystalline region, because it is difficult for the main chain in the crystal to rotate. The spontaneous polarization was found to increase as the temperature was increased from 185 to 273 K, resulting in the anomalous pyroelectricity. A model analogous to ferrielectricity is proposed to explain this phenomenon.