Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Teaching & Learning Packages Pyroelectric Materials Polyvinylidene fluoride
Pyroelectric Materials AimsBefore you startIntroductionPolarisationVariation of Polarisation with TemperatureBehaviour around the Curie pointThe Direct and Indirect EffectExample Pyroelectric MaterialsTriglycine sulphatePolyvinylidene fluorideApplication of a Pyroelectric-Infrared detectionPollutant ControlSummaryQuestionsGoing further
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Polyvinylidene fluoride

This is a carbon backbone polymer, with repeat unit (-CH2-CF2-). It takes up several different conformations, which possess different varying properties. The trans-gauche configuration results in molecules stacked so as to produce a non-polar unit cell, whereas the all-trans configuration results in a polar unit cell.

Possible configurations:

The arranged crystal structure of PVDf

Unit cells:

The arranged crystal structure of PVDf

PVDF does not possess a particularly impressive pyroelectric coefficient, (−0.27 × 10−4 C m−2 K−1) but it is highly useful in that large area thin films can very easily be made. These structures are important, as they generate a large charge which can be easily detected. This overcomes most of the other failings of PVDF.

The large area thin film is most often used for measuring the energy of laser beams in laboratories, as a large area is required to detect the entire beam. Since it is also possible to very cheaply make small area thin films, PVDF is easily made use of in burglar alarms.

(This information sourced from; Pyroelectric devices and materials (review article), R W Whatmore, Rep. Prog. Phys. 49 (1986) 1335-1386, which provides plenty of good information on pyroelectrics.)

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