A. A. Esin

Time-dependent conduction current in lithium niobate crystals with charged domain walls

We present the experimental study of the increase and decrease of the abnormal conduction current appeared during polarization reversal at elevated temperatures (120–250 °C) in stoichiometric and MgO doped lithium niobate single crystals. It is shown that the conduction current is caused by existence of the through charged domain walls. The time dependence of the conduction current has been measured in low electric field immediately after partial switching. The maximal value of the conduction current in crystal with through charged domain walls is of 4–5 orders of magnitude higher than in initial single domain state. The activation energy is 1.1 eV.

Pyroelectric effect and polarization instability in self-assembled diphenylalanine microtubes

The natural ability of peptides and proteins to self-assemble into elongated fibrils is associated with several neurogenerative diseases. Diphenylalanine (FF) tubular structures that have the same structural motif as in Aβ-amyloid peptide (involved in Alzheimers disease) are shown to possess remarkable physical properties ranging from piezoelectricity to electrochemical activities. In this work, we also discover a significant pyroelectric activity and measure the temperature dependence of the pyroelectric coefficient in the temperature range of 20–100 °C. Pyroelectric activity decreases with temperature contrary to most ferroelectric materials and significant relaxation of pyrocurrent is observed on cooling after heating above 50 °C. This unusual behavior is assigned to the temperature-induced disorder of water molecules inside the nanochannels. Pyroelectric coefficient and current and voltage figures of merit are estimated and future applications of pyroelectric peptide nanostructures in biomedical appl...

Dielectric relaxation and charged domain walls in (K,Na)NbO3-based ferroelectric ceramics

The influence of domain walls on the macroscopic properties of ferroelectric materials is a well known phenomenon. Commonly, such “extrinsic” contributions to dielectric permittivity are discussed in terms of domain wall displacements under external electric field. In this work, we report on a possible contribution of charged domain walls to low frequency (10–106 Hz) dielectric permittivity in K1-xNaxNbO3 ferroelectric ceramics. It is shown that the effective dielectric response increases with increasing domain wall density. The effect has been attributed to the Maxwell-Wagner-Sillars relaxation. The obtained results may open up possibilities for domain wall engineering in various ferroelectric materials.

Electromechanical properties of electrostrictive CeO2:Gd membranes: Effects of frequency and temperature

Doped ceria is known for decades as an excellent ionic conductor used ubiquitously in fuel cells and other devices. Recent discovery of a giant electrostriction effect has brought world-wide interest to this class of materials for actuation applications in micromechanical systems. From this aspect, the electromechanical response has to be studied as a function of external parameters, such as frequency, temperature, and electrode material. In this work, we fabricated circular membranes based on Gd-doped ceria (CGO) with Ti electrodes and studied their electromechanical response using a sensitive interferometric technique. The self-supported membranes are flat at room temperature and reversibly buckle upon heating, indicating that the membranes are under in-plane tensile strain. We have found that the electromechanical response is strongly frequency dependent. Significant hysteresis is observed in the displacement-vs.-voltage curves, which is deleterious for micromechanical applications but can be eliminate...

Electronic structure, charge transfer, and intrinsic luminescence of gadolinium oxide nanoparticles: Experiment and theory

Abstract The cubic (c) and monoclinic (m) polymorphs of Gd2O3 were studied using the combined analysis of several materials science techniques – X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. Density functional theory (DFT) based calculations for the samples under study were performed as well. The cubic phase of gadolinium oxide (c-Gd2O3) synthesized using a precipitation method exhibits spheroidal-like nanoclusters with well-defined edges assembled from primary nanoparticles with an average size of 50 nm, whereas the monoclinic phase of gadolinium oxide (m-Gd2O3) deposited using explosive pyrolysis has a denser structure compared with natural gadolinia. This phase also has a structure composed of three-dimensional complex agglomerates without clear-edged boundaries that are ∼21 nm in size plus a cubic phase admixture of only 2 at.% composed of primary edge-boundary nanoparticles ∼15 nm in size. These atomic features appear in the electronic structure as different defects ([Gd…O OH] and [Gd…O O]) and have dissimilar contributions to the charge-transfer processes among the appropriate electronic states with ambiguous contributions in the Gd 5р – O 2s core-like levels in the valence band structures. The origin of [Gd…O OH] defects found by XPS was well-supported by PL analysis. The electronic and atomic structures of the synthesized gadolinias calculated using DFT were compared and discussed on the basis of the well-known joint OKT–van der Laan model, and good agreement was established.

Superfast domain walls in KTP single crystals

Potassium titanyl phosphate KTiOPO4 (KTP) crystals with periodical ferroelectric domain structures are one of the most promising materials for nonlinear optics, in which the main types of nonlinear optical interactions have been demonstrated. Despite the crucial importance of the in situ visualization of domain structure kinetics for creation of high quality periodical domain gratings, there are only a few works concerning KTP. We present the results of in situ visualization of domain kinetics in KTP with the time resolution down to 12.5 μs and simultaneous recording of the switching current data. The wide range of wall velocities with two orders of magnitude difference was observed for switching in a uniform electric field. The kinetic maps allowed analyzing the spatial distribution of wall motion velocities and classifying the walls by velocity ranges. The distinguished slow, fast, and superfast types of domain walls differed by their orientation. It was shown that the fast and slow domain walls provide...

Increase and Relaxation of Abnormal Conduction Current in Lithium Niobate Crystals with Charged Domain Walls

The increase and relaxation of the conduction current caused by formation of intergrown charged domain walls (CDW) during polarization reversal have been studied in stoichiometric lithium niobate. The 103-104 times increase of the conduction current was revealed in the temperature range 100-200°C. The current, measured during polarization reversal, consists of the conventional switching current and the conduction current along CDW dominating for T>200°C. The model based on the complex conductivity pathway along CDW was proposed. The current data were analyzed in terms of the Kolmogorov-Avrami model taking into account the input of the CDW conductivity.

The electronic conductivity in single crystals of lithium niobate and lithium tantalate family

ABSTRACT The electronic conductivity was measured in single crystals of lithium niobate and lithium tantalate family at elevated temperatures using direct electrometric method with original technique of compensation of pyroelectric current. Experimentally measured temperature dependences of the bulk electrical conductivity along the polar direction followed the Arrhenius law with activation energy ranging from 1.0 to 1.2 eV. It was shown that bulk intrinsic conductivity became the main mechanism of screening at the temperatures above 160°C. The conductivity anisotropy was studied in MgOLN single crystals.

Polarization reversal in lithium niobate using electrodes of dendrite shape created by drying drops of protein-NaCl solution

ABSTRACT We present a new technique of fabricating the extended-shape electrodes with dendrite channels for formation of the multi-domain state in lithium niobate (LN). The dendrite structure of NaCl created by drying drops of protein-NaCl solution was used for electrode patterning. The linear dependence of the dendrite sizes on drying time has been revealed. The high resolution visualization of the static domain structures created using dendrite electrodes allowed revealing formation of quasi-periodic domain arrays. The produced LN plates with multi-domain regions will be used for manufacturing of the pyroelectric field generators with focusing effect for bioprinting.

Investigation of domain structure evolution during zero-field temperature treatment in 0.67PMN-0.33PT single crystals

ABSTRACT The temperature depolarization process has been studied in [001]-cut lead magnesium niobate-lead titanate single crystals with 33% lead titanate content by in situ visualization of as-grown domain structure evolution during zero-field heating and subsequent cooling. The phase transitions have been revealed during heat treatment. It has been shown by piezoresponse force microscopy and scanning electron microscopy that heat treatment leads to decay of maze-type as-grown domain structure into array of irregular domains with average diameter about 300 nm. Shallow etching of the surface during mechanochemical polishing has allowed keeping the surface relief corresponding to as-grown domain pattern.