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Encyclopedia of Physical Science and Technology en012f-594 July 26, 2001 11:9

Polymers, Ferroelectric 669

FIGURE 7 Temperature dependence of dielectric constant in two terpolymers: (right) sample 10 (VDF/
TrFE/CTFE = 59.3/32.9/7.8) and (left) sample 11 (VDF/TrFE/CTFE = 57.3/31.2/11.5) during heating–cooling cycles.
The frequencies from top to bottom of the dielectric curve range from 1 to 300 kHz.

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very slim loop with very small coercive field and remanent duced temperature (<0 C), another feature common to
polarization, as well as an overall reduced polarization all relaxor ferroelectrics.
level. These results indicate that the VDF/TrFE crystalline The electric field-induced strain was measured at am-
defects introduced by the incorporated CTFE termonomer bient temperature in the field range of 0–150 MV/m
units cannot be recovered by the application of a high using a bimorph-based strain sensor. Figure 9 shows
electric field. It is interesting to note that the polarization three samples, 9–11, having VDF/TrFE/CTFE mole ra-
hysteresis loop of sample 8 gradually appears with re- tios of 60.0/35.1/6.9, 59.3/32.9/7.8, and 57.3/31.2/11.5,

FIGURE 8 The comparison of polarization hysteresis loops between two VDF/TrFE/CTFE terpolymers (samples 2
and 8) with 66/22.5/11.5 and 55.6/36.1/8.3 mole ratios, respectively, and a VDF/TrFE (55/45) copolymer.