Piezoelectricity of vinylidene fluoride-trifluoroethylene copolymers

Abstract

Abstract Piezoelectric properties have been measured for the copolymers of vinylidene fluoride (VDF) and trifluoro-ethylene (TrFE) with a wide range of monomer compositions. The piezoelectric constants of these copolymers have been found to give much larger values than those of PVDF films even for undrawn specimens under the same poling condition. In a series of the copolymers with different monomer compositions, the 55 mol% VDF copolymer has the largest piezoelectric constant as well as the largest dielectric constant. VDF-TrFE copolymers show a characteristic behavior that the piezoelectric constant increases as the temperature arises and decreases abruptly down to zero in the vicinity of a certain temperature, which depends only upon the monomer compositions. This temperature may be considered to be a phase transition temperature related to molecular motions based on X-ray diffraction and infrared spectroscopic studies.