Search

The dielectric spectra of poly(vinylidene fluoride-trifluoroethylene) copolymers and poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) terpolymers are studied in a wide temperature and frequency range with electric field. It is found that the dominant relaxation process displays a peculiar characteristic—a “dielectric relaxor” behavior, rather than a “ferroelectric relaxor” behavior reported in the current literature; furthermore, we show the experimental observation that the existence of nanometer scale crystals embedded in an amorphous matrix is the base of the dielectric relaxor behavior and high electroactive performance in these polymers. [ABSTRACT FROM AUTHOR]

The electrostrictive property and dielectric behavior of the stretched poly (vinylidene fluoride–trifluoroethylene) copolymers, denoted as P(VDF–TrFE), have been studied at cryogenic temperatures. Polarization hysteresis loops and high electrostrictive performance (strain ∼1%) are obtained at room temperature. An obvious dielectric relaxation process is observed and the relaxation rate follows the Vogel–Fulcher relation with T[sub VF]=160 K, U=0.18 eV, ν[sub 0]=5.7×10[sup 12] Hz. The dielectric relaxation behavior and high strain level decrease quickly with decreasing temperature, and below 160 K only a small strain level (∼0.1%) and an “intrinsic” dielectric constant sustains. The correlation of dielectric behavior and strain activity and the physical mechanism of the quick suppression of the strain with decreasing temperature are briefly discussed. The results indicate that a high dielectric constant is critical for obtaining high electrostrictive strains in the polymers at a reasonable electric field. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the influence of post-sintering annealing on the dielectric relaxation behavior in La-doped perovskite oxide. Peaking of dielectric permittivity with frequency dispersion; Dielectric polarization behavior; Similarity between La and Bi-doped perovskite oxide.