Effect In Ferroelectric Materials Research Articles

Substantial bulk photovoltaic effect enhancement via nanolayering.

Spontaneous polarization and inversion symmetry breaking in ferroelectric materials lead to their use as photovoltaic devices. However, further advancement of their applications are hindered by the paucity of ways of reducing bandgaps and enhancing photocurrent. By unravelling the correlation between ferroelectric materials' responses to solar irradiation and their local structure and electric polarization landscapes, here we show from first principles that substantial bulk photovoltaic effect enhancement can be achieved by nanolayering PbTiO3 with nickel ions and oxygen vacancies ((PbNiO2)x(PbTiO3)1−x). The enhancement of the total photocurrent for different spacings between the Ni-containing layers can be as high as 43 times due to a smaller bandgap and photocurrent direction alignment for all absorption energies. This is due to the electrostatic effect that arises from nanolayering. This opens up the possibility for control of the bulk photovoltaic effect in ferroelectric materials by nanoscale engineering of their structure and composition.

Simulation of Size Effects in Ferroelectric Materials using a Phase Field Model

AbstractAn electro‐mechanically coupled phase field model for domain evolution in ferroelectric materials is presented. The inner length scale introduced by the model gives rise to size effects, especially in the context of the poling behavior of polycrystals. Such size effects are investigated by 2D numerical simulations for barium titanate polycrystals. Ferroelectric hysteresis curves and coercive fields are calculated for two different transition conditions for the order parameter at the grain boundaries. The results show that there is a significant size effect for the investigated polycrystal systems. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Large Electrocaloric Effect in Ferroelectric Materials

The electrocaloric effect (ECE) in polar materials shows great potential in realizing high efficient solid-state cooling devices with a smaller size and high efficiency. The thermodynamic theory was introduced in order to achieve a large ECE in ferroelectrics. The previous experimental researches were reviewed and discussed. A novel method to directly measure the ECE entropy change and temperature change was developed. Results indi- cated that the relaxor ferroelectric polymers and first-order phase transition polymers demonstrated larger ECE. Recently published larger electrocaloric effect in BaTiO3 crystal and multilayer ceramic capacitors, and the proto- type ferroelectric cooling devices reveal attractive application prospects in the near future.

Polarization rotation theory for field-induced-phase transitions in BaTiO3 single crystal

We have proposed the polarization rotation theory to understand the underlying physics of the large piezoelectric effect in ferroelectric crystals by referring to the coherent rotation model in ferromagnetism. When both the electric field energy and crystalline anisotropy energy are taken into account, the polarization in BaTiO3 crystal can be rotated toward the field direction. The numerical results are in agreement with the experimental observations and have indicated the highly anisotropic polarization rotations and the field-induced-phases with different symmetries in the crystal. This theory is helpful for understanding the polarization reversal and the electromechanical effect in ferroelectric materials.

Review on Ferroelectrics in Developing Novel Solar Cells

The study in ferroelectric photovoltaic (PV) effect has become an important topic in fields of condensed matter physics and materials sciences in recent years. For the rapidly growing needs in solar energy, the interest in developing ferroelectric PV devices with specific properties has drastically increased. This paper firstly focuses on the fundamental aspects of PV effect in ferroelectric materials, and presents a review on the latest developments in ferroelectric PV cells. For the application of ferroelectrics on solar cells, relevant patents are also presented and discussed, to describe the main characteristics of ferroelectric PV cells and achieve the understanding on their future development.

Refractive Index memory effect of ferroelectric materials by domain control

ABSTRACTFerroelectric electro-optics materials are widely studied for optical applications, such as optical switches, optical scanners, and optical shutters. However, conventional operation of those devices requires a continuous external electrical field. On the other hand, our group proposes an optical property memory effect by controlling domain structure as either full-polarized or depolarized state using asymmetric voltage operation. The optical property memory effect can keep its optical value, such as refractive index and light transmittance without any external electrical field. In this study, it was confirmed that the refractive index state had two stable values depending on domain conditions. This memory effect should be useful for innovative optical switch or scanner in the future.

Influence of the dynamic polarization of a ferroelectric material on the magnitude of its electrocaloric response

Investigations of the electrocaloric effect in ferroelectric materials are of interest for applications and of importance for an adequate description of the electrical properties of ferroelectric films, in particular, their switching dynamics. A theoretical approach is developed based on the Landau-Khalatnikov model, which can be used to describe the dynamic spontaneous polarization of a ferroelectric material and the influence of this polarization on the character of the temperature dependence of the electrocaloric effect.

Computational modelling of microcracking effects in polycrystalline piezoelectric ceramics

AbstractPiezoelectric ceramics nowadays are widely commercialised in various fields of engineering technology and related constitutive modelling approaches constitute an active field of research. The physical performance of these materials is often limited by fatigue effects, possibly in combination with micro‐cracking phenomena. In this contribution, such micro‐crackbased fatigue effects in ferroelectric materials are computationally investigated by applying a cohesive‐type approach embedded into a finite element context. The geometry or rather discretisation of a representative specimen elaborated in this work refers to a natural grain structure on the meso‐level. Accordingly, the overall response of the underlying grains is approximated by means of coupled continuum elements, while the grain boundaries are discretised with interface elements. Interfacial constitutive relations are chosen to reflect highcycle‐fatigue, which finally is demonstrated by a fatigue‐motivated benchmark‐type boundary value problem. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation on Aging Behavior in Ferroelectric Materials with Perovskite Structure

The aging effect in ferroelectric materials plays a central role in the reliability of the related devices. These materials exhibit various kinds of aging behavior. Potassium doped barium titanate was aged below its Curie temperature for different periods of time. The transformation temperature was measured precisely by differential scanning calorimetry. It was observed that the transformation temperature increased with the increase of aging time. The dielectric performance in lanthanum doped ferroelectric lead titanate ceramics after aging was measured. A change of the dielectric spectrum was revealed. Furthermore, the fourier transformation infrared spectroscopy (FTIR) in the (Ba,Mg)TiO 3 system during aging was used and it showed unstable FTIR spectra as well. These phenomena are discussed in terms of diffusion of point defects during aging.

On the simulation of cohesive fatigue effects in grain boundaries of a piezoelectric mesostructure

Ferroelectric materials offer a variety of new applications in the field of smart structures and intelligent systems. Accordingly, the modelling of these materials constitutes an active field of research. A critical limitation of the performance of such materials is given when electrical, mechanical, or mixed loading fatigue occurs, combined with, for instance, microcracking phenomena. In this contribution, fatigue effects in ferroelectric materials are numerically investigated by utilisation of a cohesive-type approach. In view of finite element-based simulations, the geometry of a natural grain structure, as observed on the so-called meso-level, is represented by an appropriate mesh. While the response of the grains themselves is approximated by coupled continuum elements, grain boundaries are numerically incorporated via so-called cohesive-type or interface elements. These offer a great potential for numerical simulations: as an advantage, they do not result in bad-conditioned systems of equations as compared with the application of standard continuum elements inhering a very high ratio of length and height. The grain boundary behaviour is modelled by cohesive-type constitutive laws, designed to capture fatigue phenomena. Being a first attempt, switching effects are planned to be added to the grain model in the future. Two differently motivated fatigue evolution techniques are applied, the first being appropriate for low-cycle-fatigue, and a second one adequate to simulate high-cycle-fatigue. Subsequent to a demonstration of the theoretical and numerical framework, studies of benchmark boundary value problems with fatigue-motivated boundary conditions are presented.

PHOTO INDUCED CURRENT IN (Pb0.97La0.03) (Zr0.52Ti0.48)O3 THIN FILMS OF DIFFERENT THICKNESSES

ABSTRACT Photovoltaic effect in ferroelectric materials exhibits potential for applications of sensors and remote controls in micro-electro-mechanical systems, and a systematic evaluation on the photovoltaic behavior in ferroelectric materials becomes important. However, as a critical parameter that determines the photovoltaic output in ferroelectric thin films, the film thickness effect on photocurrent output has not been investigated for thin film samples. In this work, a theoretical model has been developed to describe the thickness-dependent photocurrent in (Pb0.97La0.03)(Zr0.52Ti0.48)O3(PLZT) thin films with a sandwich electrode structure. This model indicates that photocurrent increases exponentially with the decrease in film thickness. Therefore, a significantly enhanced photocurrent can be expected in thinner PLZT films. The predicted thickness dependence of the short circuit photocurrent was also supported by our experimental results.

Aging Effect on Lanthanum Doped Ferroelectric Lead Titanate Ceramics

Ferroelectric devices are widely applied in many fields, such as energy conversion and communication. The aging effect in ferroelectric materials plays a central role in the reliability of the related equipments. But it is very difficult to understand the origin of aging effect in ferroelectrics because these materials possess different defects and exhibit various aging behavior. The reverse transition temperature in lead titanate doped with lanthanum increases during aging at ferroelectric phase was reported. It is well known that lattice defects, such as vacancies and solute atoms, are ubiquitous in crystalline solids. These point defects affect physical properties in ferroelectrics significantly. The abnormal increase of the reverse transition temperature was discussed in terms of diffusion of point defects during aging. Dielectric performance in the material after aging was measured and discussed as well.

Stabilization effect in ferroelectric materials during aging in ferroelectric state

We report that aging in ferroelectric state results in an increase of reverse transition temperature Tf in both BaTiO3 single crystal and Pb0.84La0.16Ti0.96O3 polycrystal. This indicates that the ferroelectric phase is gradually stabilized during aging below Curie temperature. The evolution of the stabilization with aging time in these two different systems obeys the same kinetic function, but with different relaxation time. This indicates that the stabilization effect of the two systems stems from a common origin. We suggest that the stabilization is due to a short-range ordering of point defects, driven by a symmetry-conforming tendency of point defects.

Quasi‐localized low‐frequency vibrational modes of disordered solids: Study by single‐molecule spectroscopy

AbstractEditor's Choice of this issue of physica status solidi (b) is the article [1] by Andrei V. Naumov et al. This paper is Part II (Part I see [2]) of a study on elementary excitations in glasses, presented at the 11th International Conference on Phonon Scattering in Condensed Matter, St. Petersburg, 25–30 July 2004. For his outstanding talk, Naumov received the new physica status solidi Young Researcher Award which was bestowed for the first time at this conference.The cover picture is a sketch of a glass with a single impurity molecule and one hypothetical quasi‐localized vibrational mode. The broadening and shift of the chromophore spectral line are caused by the interaction with this mode.Andrei V. Naumov is senior scientific researcher and deputy head of the Molecular Spectroscopy Department of the Institute of Spectroscopy, Troitsk. His main research interests are experimental and theoretical studies of low‐temperature dynamics of amorphous solids (glasses, polymers etc.) via high resolution laser selective spectroscopy techniques.The second Editor's Choice is an article by E. A. Eliseev and M. D. Glinchuk [3]. Eugene A. Eliseev is scientific researcher at the Frantsevich Institute for Problems of Materials Science of the Ukrainian National Academy of Sciences, Kiev. His research areas are the theory of size and correlation effects in ferroelectric materials as well as modelling of disordered ferroelectrics properties. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Design and Simulation of a Tunable Multilayer Lange Coupler

Full-wave electromagnetic simulators based in the method of moments (HP-EEsof Momentum) and in the finite difference time domain technique (Remcom's XFDTD) are ideal to analyze and study the effect of ferroelectric materials on the output response of microwave passive structures. The nonlinear electric field dependence of ferroelectric thin films has been used by the microwave research community to design tunable components. The fabrication of these structures is expensive and time consuming, hence, estimated results of the S-parameters using electromagnetic simulators are desirable previous to the fabrication process. In this work, BSTO ferroelectric thin film is used on MgO to simulate the output response of a K band multilayer Lange coupler. The S-parameters of the couplers are estimated for different bias conditions for the BSTO. Isolation, insertion loss, coupling, and return loss are computed for different bias conditions.

Imprint in ferroelectric Pb(Zr,Ti)O3 thin films with thin SrRuO3 layers at the electrodes

The imprint behavior of ferroelectric Pb(Zr,Ti)O3 (PZT) films with thin SrRuO3 (SRO) layers at the platinum electrodes was investigated. Different models (defect dipole alignment, bulk screening and interface screening) are discussed which are usually applied to explain the imprint effect in ferroelectric materials. Based on our experimental results for the material under investigation, we suggest that the interface screening mechanism is the dominant mechanism which is responsible for the imprint scenario in ferroelectric thin films.

The Properties of Ferroelectric Films at Small Dimensions

▪ Abstract This paper reviews the literature on size effects in ferroelectric materials, with an emphasis on thin film perovskite ferroelectrics. The roles of boundary conditions, defect chemistry, electrode interfaces, surface layers, and microstructure in controlling the measured properties of ferroelectric films, as well as the observed deviation from bulk properties are discussed. Examples of the manifestation of size effects in terms of the low and high field dielectric properties, the piezoelectric effect, and the leakage behavior of films are given.

Theory of far infrared optics of ferroelectrics

We review a general fomalism for the calculation of both linear and nonlinear optical effects in ferroelectric materials from the Landau free energy combined with a Landau-Khalatnikov equation of motion. The first application is to the calculation of conventional nonlinear-optical tensors in the far infrared spectral region. We then show how the formalism can be extended to give a general framework for the calculation of linear and nonlinear optical effects at surfaces and in thin films. It is shown that measurements of linear reflectivity of a ferroelectric film should serve as a sensitive probe of the behaviour of the order parameter near the surfaces of the film.

Magnetooptical effects in ferroelectric materials

An expression for high-frequency susceptibility of a ferroelectric material in a constant magnetic field H0 parallel to the direction of spontaneous polarization P0 has been derived. The reflection and transmission of light through the ferroelectric is considered for the normal incidence at the surface (along the normal ν⃗ to the surface). It is shown that the polarization plane in reflected light should be rotated through an angle proportional to the product P0H0. For H0⊥ν⃗, the angle of rotation of the polarization plane of transmitted light is a periodic function of the optical path, its amplitude being proportional to P0H0. In the H0‖ν⃗ geometry, a weak gyration effect proportional to P0H0 is observed in transmitted light, in addition to the Faraday effect. This effect does not depend on the optical path, and is canceled during backward transmission, in contrast with the Faraday effect. The effect is apparently similar to “magnetopolarization gyration,” but the estimates give a much smaller magnitude of the effect. The above magnetooptical effects can be observed not only in ferroelectric crystals of any symmetry, but also in insulators in constant electric and magnetic fields.

The Application of Optical Interferometry to the Study of Field-Induced Effects in Bulk and thin Film Ferroelectrics

AbstractA study is reported of field-induced effects in ferroelectric materials using optical interferometry. One of the techniques used is based on the use of a WYKO TOPO3 system and provides a three dimensional representation of field-induced displacement. The information provided is supplemented by optical transmission measurements on thin sections of material fabricated to allow interference fringing to be seen. Initial work has centred on the characterisation of ceramic PLZT material. Both transverse and longitudinal electrode configurations have been studied and have highlighted the magnitude of the effects possible and the importance of electrostrictive processes in determining the direction of deformation. These can result in anomalously high strain gradients over distances of the order of 50-100µm. This behaviour is compared with that found for preliminary samples of thin film ferroelectric materials.