Properties Of Ferroelectric Materials Research Articles

Domain Wall Displacement is the Origin of Superior Permittivity and Piezoelectricity in BaTiO3 at Intermediate Grain Sizes

The dielectric and piezoelectric properties of ferroelectric polycrystalline materials have long been known to be strong functions of grain size and extrinsic effects such as domain wall motion. In BaTiO3, for example, it has been observed for several decades that the piezoelectric and dielectric properties are maximized at intermediate grain sizes (≈1 μm) and different theoretical models have been introduced to describe the physical origin of this effect. Here, using in situ, high‐energy X‐ray diffraction during application of electric fields, it is shown that 90° domain wall motion during both strong (above coercive) and weak (below coercive) electric fields is greatest at these intermediate grain sizes, correlating with the enhanced permittivity and piezoelectric properties observed in BaTiO3. This result validates the long‐standing theory in attributing the size effects in polycrystalline BaTiO3 to domain wall displacement. It is now empirically established that a doubling or more in the piezoelectric and dielectric properties of polycrystalline ferroelectric materials can be achieved through domain wall displacement effects; such mechanisms are suggested for use in the design of new ferroelectric materials with enhanced properties.

Strain effects on formation and migration energies of oxygen vacancy in perovskite ferroelectrics: A first-principles study

Oxygen vacancies (VO) and their migration and redistribution are believed to be the dominant factors resulting in the degradation of ferroelectrics. Thus, suppressing the formation and mobility of VO is quite crucial for the physical properties of ferroelectric materials. In this paper, the ab-biaxial strain effects on VO and their migration process in prototype perovskite ferroelectric BaTiO3 were studied by first principles total energy calculation. It is found that the formation energies for the two symmetrically inequivalent VO are enhanced under compressive strain. VO migration path between Vc (VO is located along the c-axis) and Vab (VO is located in the ab-plane) shows an “S” shape. The VO migration barrier between Vc and Vab is enhanced by the compressive strain while lowered by the tensile strain. These results suggest that the ferroelectricity degradation induced by VO and their migration can be effectively mitigated by applying compressive strain.

Polarization Dynamics in Ferroelectric Capacitors: Local Perspective on Emergent Collective Behavior and Memory Effects

AbstractFunctional properties of ferroelectric materials depend both on the residual domain states and on the mobility of domain walls in response to the applied electric and stress fields. This paper reviews the use of multidimensional scanning probe microscopy to assess these factors in the time‐ and voltage domains, with an emphasis on the manner in which domain walls respond collectively to stimuli. It is found that in many PbZr1‐xTixO3‐based capacitors, domain wall motion is correlated over length scales that exceed the domain and grain sizes by orders of magnitude, suggesting emergent collective electromechanical behavior. The role of mechanical boundary conditions and field history on the domain wall contributions and the stability of the ferroelectric domain state are discussed.

Light‐Induced Ferroelectricity in Bioinspired Self‐Assembled Diphenylalanine Nanotubes/Microtubes

The switchable SP together withthe unique properties of ferroelectric materials can lead toPNTs/PMTs that have a wide range of applications butexperimental verification of the predicted FE is imperative.In FF PNTs/PMTs, direct experimental demonstration ofthe hysteresis loop is rather difficult because of the highcoercive field of the PMTs. A change of the SP under anapplied external field is an important experimental indicatortoidentifythepossiblepresenceofFE.Inthiswork,theoriginof the SP based on the structure of the PNTs is studied. Byobserving the photoluminescence (PL) spectral shift and itssplitting with increasing intensity of the excitation light, wedisclose the photoinduced reduction of the PNT intrinsicpolarization field which implies that SP occurs at the nano-scale.Thesaturatedpolarization–electricfield(P-E)loopsareobtained by the action of light during the hysteresis loopmeasurements.Figure 1a depicts the optical microscopy image ofa cleaved PMT prepared by immersing the as-made FFPMTs in ethanol for several hours. The optical microscopicimage of some PNTs stripped from the PMTs is shown inFigure 1b. The remarkable stepwise surface of the cleavedPMT confirms that the PMTs are composed of multi-NTsproduced by a self-assembly process (inset),

Modeling Dynamic Ferroelectric Behavior with the Analytical Landau Theory

The Landau theory of phase transitions has been widely used to study the static and dynamic properties of ferroelectric materials but mainly through numerical procedures. However the exact solution of the Landau-Khalatnikov equation produces several important consequences. Derivation of explicit expressions for the polarization switching time and the equilibrium polarization as functions of applied electric field and temperatures has enabled the unification of empirical phenomenological theories of dynamic ferroelectric behavior with the Landau theory of phase transitions for ferroelectrics under conditions of high electric fields and temperature. The role of the applied electric field in determining whether a ferroelectric material undergoes partial or complete polarization switching is established explicitly. Concurrently analytical tools for modeling dynamic properties of ferroelectrics have been developed as alternatives to empirical rules currently used in experimental work.

Ferroelectric properties of Pb(Zr,Ti)O3 films under ion-beam induced strain

The influence of an ion-beam induced biaxial stress on the ferroelectric and dielectric properties of Pb(Zr,Ti)O3 (PZT) films is investigated using the ion beam process as a novel approach to control external stress. Tensile stress is observed to decrease the polarization, permittivity, and ferroelectric fatigue resistance of the PZT films whose structure is monoclinic. However, a compressive stress increases all of them in monoclinic PZT films. The dependence of the permittivity on stress is found not to follow the phenomenological theory relating external forces to intrinsic properties of ferroelectric materials. Changes in the ferroelectric and dielectric properties indicate that the application of a biaxial stress modulates both extrinsic and intrinsic properties of PZT films. Different degrees of dielectric non-linearity suggests the density and mobility of non-180o domain walls, and the domain switching can be controlled by an applied biaxial stress and thereby influence the ferroelectric and dielectric properties.

Analytical Landau-type model of polarization switching in ferroelectrics

The polarization switching properties of ferroelectric materials have been extensively studied, both experimentally and theoretically owing to their wide applications in industry and hence generating a need to gain a deeper understanding of factors affecting their switching behaviour. In this paper, an analytical Landau theory incorporating the Landau–Khalatnikov equation has been developed to describe the switching properties of second order ferroelectrics. Analytical expressions derived from exact results of Landau theory are used in modelling work carried out in this study for comparison with trends predicted by empirical laws used to describe polarization switching behaviour at high electric fields. As such this work has established the theoretical basis for empirical laws of polarization switching and developed simple numerical tools which can be quickly used to model trends in polarization switching behaviour of ferroelectrics.

Effect of alkyl chains length on properties of ferroelectric liquid crystals with the keto group attached to the molecule core

In order to contribute to better understanding of the molecular structure–physical property relationship, properties of ferroelectric liquid crystalline materials derived from the lactic acid with the keto group in the molecular core have been studied. These compounds differing only by the length of the chiral and non-chiral alkyl chains exhibit the paraelectric SmA* and the ferroelectric SmC* phases over 150 K broad temperature range down to the room temperature. Temperature dependences of spontaneous polarization, tilt angle, layer spacing, helix pitch length and dielectric permittivity have been compared and discussed for all studied compounds. The effect of the alkyl chains length on mesomorphic properties has been established and discussed in comparison to that of similar materials.

Multiscale modeling for ferroelectric materials: identification of the phase-field model’s free energy for PZT from atomistic simulations

Within a knowledge-based multiscale simulation approach for ferroelectric materials, the atomic level can be linked to the mesoscale by transferring results from first-principles calculations into a phase-field model. A recently presented routine (Völker et al 2011 Contin. Mech. Thermodyn. 23 435–51) for adjusting the Helmholtz free energy coefficients to intrinsic and extrinsic ferroelectric material properties obtained by DFT calculations and atomistic simulations was subject to certain limitations: caused by too small available degrees of freedom, an independent adjustment of the spontaneous strains and piezoelectric coefficients was not possible, and the elastic properties could only be considered in cubic instead of tetragonal symmetry. In this work we overcome such restrictions by expanding the formulation of the free energy function, i.e. by motivating and introducing new higher-order terms that have not appeared in the literature before. Subsequently we present an improved version of the adjustment procedure for the free energy coefficients that is solely based on input parameters from first-principles calculations performed by Marton and Elsässer, as documented in Völker et al (2011 Contin. Mech.Thermodyn. 23 435–51). Full sets of adjusted free energy coefficients for PbTiO3 and tetragonal Pb(Zr,Ti)O3 are presented, and the benefits of the newly introduced higher-order free energy terms are discussed.

BioFerroelectricity: Diphenylalanine Peptide Nanotubes Computational Modeling and Ferroelectric Properties at the Nanoscale

Ferroelectricity and piezoelectricity are two of the common ferroelectric material properties, which have widespread observations in many biological systems, and these are referred to as biopiezoelectricity and bioferroelectricity. This paper presents a short overview of the main issues of piezoelectricity and ferroelectricity, their manifestation in organic, biological, and molecular systems. As a showcase of novel biopiezomaterials, the investigation of diphenylalanine (FF) peptide nanotubes (PNTs) is described by computational molecular modeling, as well by experimental AFM/PFM measurements. FF PNTs present a unique class of self-assembled functional biomaterials, owing to their wide range of useful properties, including nanostructural piezoelectric and ferroelectric properties.

Electromechanical coupling and temperature-dependent polarization reversal in piezoelectric ceramics

Electrostriction plays a central role in describing the electromechanical properties of ferroelectric materials, including widely used piezoelectric ceramics. The piezoelectric properties are closely related to the underlying electrostriction. Small-field piezoelectric properties can be described as electrostriction offset by the remanent polarization which characterizes the ferroelectric state. Indeed, even large-field piezoelectric effects are accurately accounted for by quadratic electrostriction. However, the electromechanical properties deviate from this simple electrostrictive description at electric fields near the coercive field. This is particularly important for actuator applications, for which very high electromechanical coupling can be obtained in this region. This paper presents the results of an experimental study of electromechanical coupling in piezoelectric ceramics at electric field strengths close to the coercive field, and the effects of temperature on electromechanical processes during polarization reversal. The roles of intrinsic ferroelectric strain coupling and extrinsic domain processes and their temperature dependence in determining the electromechanical response are discussed.

Special Issue on Omnipresent Intelligent Computing – New Developments and Societal Impact

When the computer revolution began in the second half of the 20th century, few could have foreseen the pervasiveness that intelligent devices would have only half a century later. Today, consumers deal with numerous computing devices providing increasingly sophisticated services. Arguably, no other invention has so profoundly impacted on daily home and work lives as the computer. The downside, however, holds the worrying realization that many artifacts of modern technology now touch on the human sphere to the point of risking an individualfs privacy, security, and well-being. The new millennium carries the computer revolution to unprecedented levels where new computing paradigms excite researchers beyond the limits of science fiction. The burgeoning field of synthetic biology, for example, has given rise to novel computing approaches based on biomolecular materials. Indeed, silicon is no longer the only substrate for intelligent information processing. Other unconventional approaches such as computing with slime molds, for example, now embrace even living organisms. Information processing and problem solving strategies observed in nature have inspired the design of novelmachine learning algorithms. Seemingly unlimited computer power now enables the in silico simulation of living organisms and the study of evolutionary processes with enormous efficiency. Although many of these novel, nature-inspired approaches are still in their infancy, they might bring a paradigm shift in computational science. How such a technology-driven paradigm shift may affect the gsofth components of our modern complex society is a many-faceted issue that deserves our consideration and exploration. This special issue focuses on new developments in intelligent computing. A. Schuster and D. Berrar analyze the potentials and risks of current and emerging intelligent computing paradigms. Their article focuses on the interface between humans and intelligent systems and explores potentials and risks emerging for individuals and for the information society at large. L. Palafox and H. Hashimoto propose a new human activity recognition system that relies on the analysis of five key variables to categorize human activities. A prototypical implementation of the system demonstrates promising results for applications in intelligent room settings. M. Kimura and M. Sugiyama propose a novel approach to unsupervised clustering, which is based on least squares mutual information. The advantage of this approach is that hyperparameters of clustering algorithms such as kernel parameters no longer need to be manually calibrated, but they can be automatically optimized. D. Ricinschi and E. Tokumitsu explore new ways of exploiting physical properties of ferroelectric materials. They investigate how the amount of polarization generated by two electrical pulses can be modeled and explained in the framework of game theory. This special issue informs the research community about exciting new developments in intelligent computing, with an outlook on their societal impacts.

High nonlinearities in Langevin transducer: A comprehensive model

The design and simulation of power transducers are difficult since piezoelectric, dielectric and elastic properties of ferroelectric materials differ from linear behavior when driven at large levels. This paper is devoted to modeling of a resonant power transducer at a high level of dynamic mechanical stress. The power transducer is subjected to a sine electrical field E of varying frequency which was considered as the excitation of the transducer. The mechanical equation of the piezoelectric element is written using electrostriction. The dielectric part is written as a nonlinear function of an equivalent electric field including stress influence (scaling relationship between electric field and mechanical stress). Using various simulations, we show then that typical resonance nonlinearities are obtained, such as jump phenomenon of transducer speed amplitude and phase, resonance peak that become asymmetric, and diminution of mechanical quality factor. As a consequence, we state that those typical nonlinearities are only due to dielectric nonlinearities, in good correlation with typical ferroelectric behavior. Moreover, this demonstrates the usefulness of scaling relationships in ferroelectrics, which explain static depoling under stress and butterfly strain hysteresis loop. The same scaling law gives here several nonlinearities for resonant transducers as well.

Description of the low field nonlinear dielectric properties of ferroelectric and multiferroic materials

Ferroelectric and multiferroic materials present a nonlinear variation in their permittivity due to domain wall motion. Currently, this variation is described either by the Rayleigh law for fields above a threshold or by a power law for soft ferroelectrics. We propose a hyperbolic law based on the contributions of domain walls and intrinsic lattice which includes the two classic approaches. The threshold field is clearly defined by considering reversible and irreversible components of the permittivity. A good agreement between the hyperbolic law and experimental data is obtained. Moreover, we show that the threshold field obeys to the Volgel–Fulcher law.

Size-dependent growth of polymorphs in nanopores and Ostwald's step rule of stages

More than 100 years after Ostwald postulated his step rule of stages, predictive understanding as to early crystallization stages of polymorphic materials is still premature. We studied crystallization of the polymorphic pharmaceutical acetaminophen in nanoporous glasses as a model for early stages of bulk crystallization since the surface energy significantly contributes to the total Gibbs free energy of nanosized crystals in both cases. Systematic studies of transitions between different polymorphs inside nanoporous glasses show that the thermodynamic stability of the polymorphs depends on the crystal size. Accordingly, the transient occurrence of different polymorphs during crystal growth in bulk systems can be related to surface energy contributions to the total Gibbs free energy of the developing crystals. In nanosized early-stage crystals with high surface-to-volume ratios other polymorphs may be stable than in large crystals with low surface-to-volume ratios. Improved control of the crystallization of polymorphic materials by imposing well-defined confinement is a promising strategy to tailor release of polymorphic drugs and to optimize optical, electronic, magnetic and ferroelectric properties of polymorphic materials.

Characterization of ferroelectric material properties of multifunctional lead zirconate titanate for energy harvesting sensor nodes

We propose a microsystem integration technique that is ideal for low-cost fabrication of vibration energy harvesting sensor nodes. Our approach exploits diverse uses of sol-gel deposited lead zirconate titanate, effectively combining fabrication of several microsystem components into a single process and significantly reducing manufacturing cost and time. Here, we measure and characterize thin film parameters—such as the piezoelectric coefficient e31 (−4.0 C/m2), the dielectric constant εr-eff (219 at 3.3 V), and the total switching polarization (2Pr;52 μC/cm2)—in order to verify this material’s potential for energy harvesting, energy storage, and nonvolatile memory applications simultaneously on the same device.

Dielectric and Ferroelectric Properties of BST and Ni-Zn Ferrite Composites

Ferroelectric—ferrite composites are very important materials as they show both electric and magnetic properties and are drawing attention of researchers over the last few years due to their immense contribution to the improvement of science and technology. Electrical and ferroelectric properties of such ceramic materials are strongly dependent on composition and ratio of two constituents. In the present paper we are reporting the dielectric and ferroelectric properties of (1-x)Ba0.90Sr0.10TiO3- xNi0.80Zn0.20Fe2O4, (0 ≤ x ≤ 0.02 steps of 0.01) (BST-NZF) mixed phase materials. Both the constituent materials were prepared separately by conventional solid state method and then finally mixed by weight to form the mixture. The dielectric properties were measured as a function of temperature at 100 Hz, 1 kHz, 10 kHz and 100 kHz frequencies. P-E hysteresis loops were recorded at 20 Hz for all the mixture samples. Remanent polarization was found to decrease with increase in ferrite content. Magnetization measurements show the samples to be in ferromagnetic state. Structural analysis was done by X-ray diffraction analysis.

Density functional study ofPbTiO3nanocapacitors with Pt and Au electrodes

We present an ab initio density functional study of ferroelectricity in single-domain ${\text{PbTiO}}_{3}$-based nanocapacitors. We used density functional theory with the recently introduced PBEsol generalized-gradient exchange-correlation functional, which we found to give accurate properties of bulk ferroelectric (FE) materials. Pt and Au electrodes are used in our study to gain a thorough understanding of the electrode-oxide interfaces, and the role of the interfacial chemical bonding and charge transfer in stabilizing the FE polar phase. We found that the FE properties of the thin films depend not only on the electrode and the FE material but also on the electrode-perovskite termination (${\text{TiO}}_{2}$ vs PbO), exemplifying the key role of the interface in these systems. The critical thickness was found to be $24--28\text{ }\text{\AA{}}$. In addition, a L\"owdin orbital analysis gives a detailed description of the distribution of charges in the system, and shows the importance of charge passivation by the electrodes in stabilizing the FE polar phase.

A Simulation of Dielectric Spectroscopy of Some Ferroelectric Materials

Temperature dependent dielectric permittivity is a crucial parameter in determining the physical property of ferroelectric materials. A method of using temperature to predict the dielectric permittivity of some ferroelectric materials is studied. The object of this work is to search for the applicable method of using temperature to predict the dielectric permittivity and control the transition of some ferroelectric materials from ferroelectric phase to paraelectric phase. A typical numerical method is highlighted and discussed in light of the potential applications to the various experimental results. The simulations agree very well with the observed spectroscopy of twelve curves for dielectric permittivity versus temperature. The minimum value of correlation coefficients between actual and calculated data is 0.98. The maximum data of mean relative errors is 6.98%. This study may make a contribution to the theoretical and the practical aspects of the ferroelectric materials.

The effect of B-site cations on the properties of KTa xNb 1−xO 3 [1 0 0] surface: A study of density functional theory

Ferroelectric material and piezoelectric properties are different in potassium tantalite niobate (KTa x Nb 1− x O 3) crystal according to differences in x. Here, we show the results of KTa x Nb 1− x O 3 ( x = 0.25, 0.5, 0.75) crystal [1 0 0] surface properties calculated by density functional theory (DFT). Using local density approximation (LDA) and generalized gradient approximation (GGA), DFT has been employed to determine the structural, electronic, and optical properties of chemically ordered ferroelectric KTa x Nb 1− x O 3 crystal [1 0 0] surfaces. Based on the research, comparison and analysis of the results show that all kinds of properties of KTa x Nb 1− x O 3 [1 0 0] surfaces are vary with respect to x. It is found, for instance, that the ordering of B-site cations obviously influences the properties of the KTa x Nb 1− x O 3 surface. At the same time, this allows the experimental studies to be supervised effectively.