The Effect of Electric Aging on Vinylidene Fluoride Copolymers for Ferroelectric Memory.

Copolymers based on vinylidene fluoride are potential materials for ferroelectric memory elements. The trend in studies showing that a decrease in the degree of crystallinity can lead to an unexpected increase in the electric breakdown field is noted. An analysis of the literature data reveals that in fluorine-containing ferroelectric polymers, when using a bipolar triangular field, the hysteresis loop has an unclosed shape, with each subsequent loop being accompanied by a decrease in the dielectric response.

The Domain and Structural Characteristics of Ferroelectric Copolymers Based on Vinylidene Fluoride Copolymer with Tetrafluoroethylene Composition (94/6).

This paper presents data on the macroscopic polarization of copolymer films of vinylidene fluoride with tetrafluoroethylene obtained with a modified apparatus assembled according to the Sawyer-Tower Circuit. The kinetics of the polarization process were analyzed taking into consideration the contributions of both bound and quasi-free (impurity) charges. It was shown that an "abnormal" decrease in conductivity was observed in fields near the coercive fields.

Effect of Composition and Surface Microstructure in Self-Polarized Ferroelectric Polymer Films on the Magnitude of the Surface Potential.

The values of the surface potentials of two sides of films of polyvinylidene fluoride, and its copolymers with tetrafluoroethylene and hexafluoropropylene, were measured by the Kelvin probe method. The microstructures of the chains in the surfaces on these sides were evaluated by ATR IR spectroscopy. It was found that the observed surface potentials differed in the studied films.

Optical and Electrophysical Properties of Vinylidene Fluoride/Hexafluoropropylene Ferroelectric Copolymer Films: Effect of Doping with Porphyrin Derivatives.

Polymer films doped by different porphyrins, obtained by crystallization from the acetone solutions, differ in absorption and fluorescence spectra, which we attribute to the differences in the structuring and composition of the rotational isomers in the polymer chains. According to the infrared spectroscopy data, the crystallization of the films doped with tetraphenylporphyrin (TPP) proceeds in a mixture of α- and γ-phases with TGTG and TGTG conformations, respectively. Three bonds in the planar zigzag conformation ensures the contact of such segments with the active groups of the porphyrin macrocycle, significantly changing its electronic state.

Boosting Magnetoelectric Effect in Polymer-Based Nanocomposites.

Polymer-based magnetoelectric composite materials have attracted a lot of attention due to their high potential in various types of applications as magnetic field sensors, energy harvesting, and biomedical devices. Current researches are focused on the increase in the efficiency of magnetoelectric transformation. In this work, a new strategy of arrangement of clusters of magnetic nanoparticles by an external magnetic field in PVDF and PFVD-TrFE matrixes is proposed to increase the voltage coefficient (α) of the magnetoelectric effect.

Dual Vibration and Magnetic Energy Harvesting With Bidomain LiNbO-Based Composite.

With the recent thriving of low-power electronic microdevices and sensors, the development of components capable of scavenging environmental energy has become imperative. In this article, we studied bidomain congruent LiNbO (LN) single crystals combined with magnetic materials for dual, mechanical, and magnetic energy harvesting applications. A simple magneto-mechano-electric composite cantilever, with a trilayered long-bar bidomain LN/spring-steel/metglas structure and a large tip proof permanent magnet, was fabricated.

Low-Frequency Vibration Sensor with a Sub-nm Sensitivity Using a Bidomain Lithium Niobate Crystal.

We present a low-frequency sensor for the detection of vibrations, with a sub-nm amplitude, based on a cantilever made of a single-crystalline lithium niobate (LiNbO₃) plate, with a bidomain ferroelectric structure. The sensitivity of the sensor-to-sinusoidal vibrational excitations was measured in terms of displacement as well as of acceleration amplitude. We show a linear behavior of the response, with the vibrational displacement amplitude in the entire studied frequency range up to 150 Hz.

Mapping Disorder in Polycrystalline Relaxors: A Piezoresponse Force Microscopy Approach.

Relaxors constitute a large class of ferroelectrics where disorder is introduced by doping with ions of different size and valence, in order to maximize their useful properties in a broad temperature range. Polarization disorder in relaxors is typically studied by dielectric and scattering techniques that do not allow direct mapping of relaxor parameters, such as correlation length or width of the relaxation time spectrum. In this paper, we introduce a novel method based on measurements of local vibrations by Piezoresponse Force Microscopy (PFM) that detects nanoscale polarization on the relaxor surface.