Measurement of the pyroelectric coefficient of poly(vinylidene fluoride) down to 3 K

Abstract

The temperature dependence of the pyroelectric coefficient pЈ of polyvinylidene fluoride (PVF 2) was measured from 307 K to the previously unexplored region of 3 K. The measurements were performed on a film of oriented (␤-phase͒ PVF 2 by monitoring its surface charge response to quasistatic heating and cooling transients. The data exhibit a pure cubic temperature dependence from 3 to 6 K with no evidence of a linear term. This is consistent with the prediction by Szigeti and the Debye limit, respectively, for the primary ͑i.e., strain-free͒ and secondary contributions to pyroelectricity. The data from ϳ20 to ϳ150 K, which include the region of largest change, are well fit by an exponential function ͑i.e., a 0 e Ϫ/T), corresponding to a thermal activation energy of ϭ(25.9Ϯ0.06) K. Our data for pЈ, from 100 to 250 K, are approximately proportional to the thermal expansion coefficient, recently published by Hartwig, which indicates that the observed pyroelectricity is dominated by piezoelectric ͑i.e., secondary͒ contributions in that temperature regime. ͓S0163-1829͑97͒08211-8͔ I. INTRODUCTION A. Overview

The Effect of Gases on Pyroelectric Properties of PVDF/TiO₂ Treated by Plasma Etcher

“…This suggests that the presence of TiO 2 contributes to the pyroelectric activity of the composites together with the PVDF polymer. Note that the applied electric field used in this work is below the standard coercive field of pure PVDF which is 80 MVm -1 as reported by several researchers [9]. The pyroelectric coefficient obtained can be higher than what is shown in Fig.…”

Progress in developing a thermal method for measuring the output power of medical ultrasound transducers that exploits the pyroelectric effect

“…This figure is considered to be comparable to the increase demonstrated in Fig. 4, in view of the uncertainties in interpolating data [9] and in the measurements shown in Fig. 4.…”

“…This most probably arises due to a change in the temperature dependent pyroelectric coefficient of pvdf, which has a direct, proportional influence on the Switch ON and Switch OFF voltages [4]. Values for the pyroelectric coefficient and the way this varies with temperature for pvdf may be found in the technical literature [9], and this indicates that there are notable changes above room temperature with an increase of approximately 20% between 20°C and 30°C. This figure is considered to be comparable to the increase demonstrated in Fig.…”

Low-temperature measurements of the specific heat capacity of a thick ferroelectric copolymer film of vinylidene fluoride and trifluoroethylene

“…Covalent bonding between carbon and fluorine atoms is the dominant source of electric dipole moments in both monomers. 1,4,6 Additional details about the structure of PVDF and PVDF/TrFE are provided by recent ab initio studies. [48][49][50] Note that PVDF requires mechanical stretching to create the polarized ␤ phase required for pyroelectric measurements.…”

“…Our measurements of the specific heat capacity c p of a 110 m thick sample of this copolymer extend from 2 to 20 K in intervals of 0.2 K and supplement the uneven coverage of prior measurements. 3,7,8 These data are used, in conjunction with prior measurements of the pyroelectric coefficient, 4,5 to infer the temperature dependence of the macroscopic Grüneisen parameter and to compare it with similar results deduced from available data for PVDF. 9 Our data also exhibit an excess value of c p that exceeds the predictions of the Debye approximation and a hump in the plot of c p / T 3 .…”