Electric Field-induced Transformation Research Articles

Analyses of Electric Field-Induced Phase Transformation by Luminescence Study in Eu3+-doped (Na, K)0.5Bi0.5TiO3 Ceramics.

Most analyses of phase transformations detected by rare earth ions are based on the luminescence spectrum, while in this study we focus on the luminescence decay processes. We prepared Eu3+-doped (Na, K)0.5Bi0.5TiO3 ceramics and studied their phase structure before and after poling by luminescence spectra, decay curves, and X-ray diffraction (XRD). Luminescence spectra indicated that electric fields induced a transformation in (Na0.8, K0.2)0.5Bi0.497Eu0.003TiO3 (NKBET20) ceramic from tetragonal to rhombohedral phase (R phase). Based on the decay kinetics and the Judd–Ofelt theory, decay curves were shown to identify the fraction of the transformation quantitatively. The data from decay curves suggest that with electric fields increasing from 0 to 50 kV/cm, the R phase fraction increases from about 23 to 89% and the tetragonal phase (T phase) fraction decreases from about 77 to 11%. XRD Rietveld analyses further confirmed the results. In this work, the analyses of the phase fractions are simplified by the monoexponential decay of the pure phases and the biexponential decay of the mixed phase, showing an easy and inexpensive way of studying the phase structures of the materials.

Electric field-controlled transformation of the eigenmodes in a twisted-nematic Fabry\u2013P\xe9rot cavity

The polarized optical states in the transmission spectrum of a twisted-nematic Fabry–Pérot cavity with the distinctly broken Mauguin’s waveguide regime have been theoretically and experimentally investigated. Specific features of the electric field-induced transformation of the polarization and spectral characteristics of eigenmodes of the neighboring series at the overlap resonant frequencies have been examined. It is demonstrated that the linear polarizations of eigenmodes at the cavity boundaries remain nearly orthogonal and their frequency trajectories reproduce the avoided crossing phenomenon. The experimental data are confirmed analytically and by the numerical simulation of light transmission through the investigated anisotropic multilayer with the use of a Berreman matrix method. The results obtained can be generalized to any materials with the helix response.

Structural characterization of the electric field-induced ferroelectric phase in Na0.5Bi0.5TiO3-KNbO3 ceramics

(1−x)Na0.5Bi0.5TiO3-xKNbO3 (NBT-xKN) ceramics, with x in the range 0.01–0.09, were prepared by solid state reaction and conventional sintering. A progressive transformation from a nano-polar to a long-range ordered ferroelectric phase was observed after the application of a cyclic electric field with an amplitude of 5kVmm−1. It is shown by analysis of the crushed ceramic pellets, using high resolution synchrotron x-ray diffraction, that the application the cyclic electric field induced an irreversible transformation from a pseudo-cubic nano-polar phase to a rhombohedral ordered ferroelectric phase having R3c symmetry. Furthermore, a systematic variation, from 89.6° to 90°, was observed in the rhombohedral interaxial angle as the KN content increased from 1 to 9%. By comparing the structural evidence with the ferroelectric polarization-electric field hysteresis loops, it is shown that the electric field-induced transformation is partially reversible for NBT-5KN and completely reversible or nonexistent for NBT-9KN.

Frustration of ferroelectricity in epitaxial film of relaxor ferroelectric PbSc1/2Nb1/2O3

Relaxor-to-ferroelectric transformations induced by varying electric fields and temperatures are studied experimentally in acube-on-cubetype epitaxial PbSc1/2Nb1/2O3 film grown on La1/2Sr1/2CoO3/MgO(001). Dielectric response, quasi-static and dynamic polarization, and dynamic current–voltage characteristics evidence the absence of spontaneous relaxor-to-ferroelectric transition. The electricfield-induced transformation from a glass-like relaxor state to a new dynamic polar state is detected at low temperatures below 100 K only. The frustration of ferroelectricity is discussed in relation to orientational anisotropy of the dipolar system in the epitaxial (001) film.

The electric field-induced transformation of the melting state of langasite from incongruent into congruent

The electric field required for the transformation of the melting state of langasite from incongruent into congruent was semi-quantitatively and quantitatively evaluated. Both evaluation methods demonstrated that the required electric field was on the order of 10 4–10 5 V/cm. This was significantly higher than the external electric field of 600 V/cm, which was experimentally observed. This large difference was attributed to the possibility that nucleation occurred in the electric double layer, which could sustain a very large electric field.

In situ transmission electron microscopy study of the electric field-induced transformation of incommensurate modulations in a Sn-modified lead zirconate titanate ceramic

Electric field-induced transformation of incommensurate modulations in a Sn-modified lead zirconate titanate ceramic was investigated with an electric field in situ transmission electron microscopy technique. It is found that the spacing between the (1∕x){110} satellite spots and the fundamental reflections do not change with external electric field, indicating that the modulation wavelength stays constant under applied field. The intensity of these satellites starts to decrease when the field level reaches a critical value. Further increase in the field strength eventually leads to the complete disappearance of the satellite reflections. In addition, the 12{111}-type superlattice reflections showed no response to electrical stimuli.

Forming process and stability of bubble domains in dielectrically positive cholesteric liquid crystals

Abstract The nucleation of bubble domains in homeotropic samples of a dielectrically positive cholesteric liquid crystal is described. These domains are found to be more stable in an electric field than the rectilinear double-twisted fingers. The electric field-induced transformation of a looped finger into a bubble domain is described in detail: it is discontinuous and irreversible, and operates only at a large enough confinement ratio C = d/p, where d is the sample thickness and p the quiescent cholesteric pitch. Finally, in contrast with Stieb's model [4], we propose that there are two point defects along the bubble axis and not a disclination line.