MEASUREMENT OF THE PYROELECTRIC COEFFICIENT IN COMPOSITES USING A TEMPERATURE-MODULATED EXCITATION

Ferroelectric polymers such as PVDF and its copolymer P(VDF/TrFE) as well as ferroelectric ceramic-polymer composites have to be annealed at a high temperature for an extended period of time after poling, before the measurement of the pyroelectric coefficient by the direct method can be performed, in order to eliminate the high depolarization current which hinders the determination of the true pyroelectric current. Here it is suggested that a periodic temperature oscillation of a ceramic-polymer composite sample would permit measurement of its true pyroelectric coefficient without the need to anneal the sample. The temperature distribution inside the composite sample, the magnitude of the pyroelectric current and their variation with the frequency of temperature oscillation have been simulated with the present theory. Pyroelectric measurements using this technique have been made on a poled composite of calcium-modified lead titanate (PbTiO3) and a copolymer of vinylidene fluoride and trifluorethylene P(VDF/TrFE) and compared with the results of the direct measurements before and after annealing, in order to test the validity of the method.