The Study on Physical and Optical Properties of Ferroelectric Polymers Applying Crystal Technology

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Vinylidene fluoride and trifluoroethylene copolymers (P(VDF/TrFE)) are ferroelectric polymers. P(VDF/TrFE) crystals exhibit the point group C_<2v> symmetry, hence they have five Pockels coefficients (PCFs). Recently, Ohigashi et al. reported that P(VDF/TrFE) formed a highly double-oriented crystalline film (HDCF) with no noncrystalline areas or lamella crystals. The macroscopic axes of the HDCFs (drawing and poling axes) were observed for the first time, to directly correspond to each crystalline axis of the P(VDF/TrFE) crystals. Namely, further progress in the research on the optical behavior of ferroelectric polymers using crystal technology is expected. In this study, we propose for the first time a new experimental system for measuring the optical behavior of polymer thin films (PTFs). Furthermore, using the system, we investigate, mainly, the Pockels effects (PEFs) of HDCF.We developed the experimental system for measuring the indicatrix, double refraction and PEF of PTFs. The sig … More nificant characteristics of this system are as follows. The diameter of the laser beam is reduced while maintaining the degree of polarization so that the laser beam can be introduced in the direction perpendicular to the thickness direction of PTFs, to facilitate measurement of PEF in various directions of PTFs. Furthermore, using this system, we can obtain the change in film thickness simultaneously during measurements of the temperature dependence of double refraction for PTFs. Namely, we can estimate the intrinsic value by correcting the apparent results.Many results were obtained from measuring PEFs of HDCFs using the system, the most significant, of which, are as follows.1) The HDGF satisfies the phenomenological theory of single-crystalline ferroelectric substances.2) The maximum PCF obtained for the HDCF was 20 pm/V, which is significantly larger than that of conventional polymer ferroelectric films (lamella crystalline films).3) The HDCF exhibits structural and optical behaviors similar to those of single crystals. Less