TEMPERATURE-DEPENDENCE OF ELASTIC, DIELECTRIC, AND PIEZOELECTRIC PROPERTIES OF SINGLE-CRYSTALLINE FILMS OF VINYLIDENE FLUORIDE TRIFLUOROETHYLENE COPOLYMER

Elastic, dielectric, and piezoelectric constant matrix elements of a ' 'single crystalline'' (SC) film of vinylidene fluoride trifluoroethyle ne copolymer, P(VDF/TrFE), in which the orthorhombic [001] and [110] a xes of fully extended chain crystals are preferentially oriented paral lel to the stretching axis and normal to the surface, respectively, we re measured at temperatures ranging from 10 K to the Curie point (402- 404 K) by using a piezoelectric resonance method. All of the electrome chanical coupling factors (k(31), k(32), k(33), k(24), and k(15)) are larger than those of conventional lamellar crystalline films, Some of the matrix elements for a P(VDF/TrFE) single crystal are derived from the measured values of constant matrix elements for the SC film. Some features characteristic of the SC film are revealed: The SC him has a large Young's modulus for the stretching direction (1/s(11)) (121 GPa at 10 K). The properties related to the molecular motions along the ch ain axis, such as 1/s(11), shear stiffness constant c(55), shear piezo electric constant e(15), etc., exhibit strong relaxations around 250 K . The origin of these relaxations in the crystalline phase is discusse d. (C) 1997 American Institute of Physics.