Electric-field-induced phase changes in poly(vinylidene fluoride)

Abstract

The antipolar crystal form of poly(vinylidene fluoride) can be made piezoelectric and pyroelecric by the temporary application of electric fields in excess of 1 MV/cm at room temperature. Infrared and x-ray diffraction data reveal that the polarization occurs in two stages. At fields near 1 MV/cm, a phase transition to a polar form II occurs with presumably no change in chain conformation. Fields near 5 MV/cm cause a change in conformation to produce form I. Our results indicate that at least a portion of the residual polarization occurs within the crystal phase of the polymer.

Effects of an external electric field on the ferroelectric-paraelectric phase transition in polyvinylidene fluoride-trifluoroethylene copolymer Langmuir–Blodgett films

“…At intermediate fields, Davis et al were able to convert the nonpolar trans-gauche phase ͑they assumed this was the bond-ordered orthorhombic ␣ phase, which could be considered antiferroelectric because the individual chains are polar but packed into opposing sublattices͒ to a polar ͑i.e., orthorhombic ␣ p ͒ structure. 30 Upon application of even higher electric fields, they were able to further convert some of the sample to the all-trans ␤ phase, thus implying that the proper sequence of phases was ␣-␣ p -␤, which made sense considering the structures of these phases. 30 However, …”

“…30 Upon application of even higher electric fields, they were able to further convert some of the sample to the all-trans ␤ phase, thus implying that the proper sequence of phases was ␣-␣ p -␤, which made sense considering the structures of these phases. 30 However, …”

“…This is in contrast to poling studies of PVDF, which did not exhibit a return of the paraelectric phase upon removal of the applied electric field. 30 Because the cross-sectional area of the x-ray beam was larger than that of the top electrode, not all of the sample was subjected to the applied electric field. We determined the appropriate proportion of this field-free by noting that the phase conversion appeared saturated by 22.5 V. We assumed that the remaining intensity in the paraelectric peak at 22.5 V came from the part of the film not covered by the top electrode and subtracted this value from intensities at all other voltages to determine the contribution from the portion of the film subjected to the applied electric field.…”

“…17,19,28,30 To demonstrate this effect in the LB copolymer films, temperature-dependent capacitance measurements were made at a series of applied voltages. Figure 4͑a͒ shows the results of such measurements made on a 30-monolayer film of P͑VDF-TrFE͒ 70/ 30.…”

Measurement of the flexoelectric response in ferroelectric and relaxor polymer thin films

“…[15][16][17] It is difficult, however, to rule out piezoelectric contributions from residual ferroelectric beta and delta phases, because PVDF is, in general, a polymorphous material, 14,18,19 containing a substantial amorphous component 20 and various crystalline phases that depend strongly on synthesis and sample preparation procedures. [21][22][23] Therefore, we have made a study of thin films of VDF copolymer and a VDF terpolymer, which allow us to compare the flexoelectric response in three distinct states-ferroelectric, paraelectric, and relaxor.…”