Papers by Keyword: Polarization Reversal

Abstract: Utilizing the Landau-Khalatnikov equation of motion, the polarization reversal characteristics of a ferroelectric thin film with surface transition layers have been first investigated. We have discussed the effects of the thickness, the surface transition layer parameters and the temperature on the switching properties of a ferroelectric thin film. The results show that the stronger the surface transition layer effects are, the smaller the coercive field and switching time are.

Abstract: Vinylidene fluoride and trifluoroethylene [P(VDF-TrFE)] ferroelectric thin film was spin-coated on Au-coated polyimide substrate and its polarization reversal was investigated by analyzing the evolution of activation field (α) with temperature. Although α is nearly a constant between 300 and 330 K, it increases linearly when temperature rates between 200 and 230 K, and between 230 and 300 K. On the other hand, the intensity of X-ray diffraction for P(VDF-TrFE) films from 200 to 330 K indicates that glass-transition process plays a significant role in both the microstructure and the polarization reversal of P(VDF-TrFE) copolymer.

Abstract: Thin films of polyvinylidene (PVDF) and its copolymers containing 50 to 30 mole % of trifluoroethylene (TrFE) demonstrate rapid reversal of polarization under applied electric field, and can be used as ferroelectric materials in non-volatile memory devices. In this study, Fourier-transform infrared transmission (FTIR-TS) and grazing incident reflection absorption (FTIR-GIRAS) spectroscopy techniques were used to examine the changes in Curie transition temperature (T_c), chain and dipole orientation in selected VDF copolymer spun-cast films as a subjected to a reversible thermal-cycling treatment. A reversible solid-to-solid β-crystalline phase transition with thermal hysteresis and a favorable C-F dipole orientation along the electric field direction were observed for the sample subjected to thermal-cycling below its melting point (T_m). An irreversible β-crystalline phase transition with unfavorable C-F dipole orientation was observed for the sample treated to heating-cooling cycle above T_m. The results are reported in detail here.

Abstract: In this study, the relationships between the electrical properties and polarization switching of lead-free (Li_0.06Na_0.94)NbO₃ (LNN6) ceramics were investigated. The electrical properties of stoichiometric LNN6 did not change with polarization switching. On the other hand, the frequency dependence of the impedance of Na-deficient LNN decreased with polarization switching, and the coupling factor k_p, the piezoelecric constant d₃₃ and the dielectric constant ε33T/ε0 decreased with polarization switching. Moreover, the dielectric curve of Na-deficient LNN6 after 10 switchings showed peaks at approximately 330, 400 and 500 °C