Properties Of Ferroelectric Materials Research Articles

Differentiating Ferroelectric and Nonferroelectric Electromechanical Effects with Scanning Probe Microscopy.

Ferroelectricity in functional materials remains one of the most fascinating areas of modern science in the past several decades. In the last several years, the rapid development of piezoresponse force microscopy (PFM) and spectroscopy revealed the presence of electromechanical hysteresis loops and bias-induced remnant polar states in a broad variety of materials including many inorganic oxides, polymers, and biosystems. In many cases, this behavior was interpreted as the ample evidence for ferroelectric nature of the system. Here, we systematically analyze PFM responses on ferroelectric and nonferroelectric materials and demonstrate that mechanisms unrelated to ferroelectricity can induce ferroelectric-like characteristics through charge injection and electrostatic forces on the tip. We will focus on similarities and differences in various PFM measurement characteristics to provide an experimental guideline to differentiate between ferroelectric material properties and charge injection. In the end, we apply the developed measurement protocols to an unknown ferroelectric material.

Piezoelectric properties of rhombohedral ferroelectric materials with phase transition

The temporal evolution of domain structure and its piezoelectric behavior of ferroelectric material BaTiO 3 during the transition process from rhombohedral to tetragonal phase under an applied electric field have been studied by employing Landau–Ginzburg theory and the phase-field method. The results obtained show that, during the transformation process, the intermediate phase was monoclinic MA phase, and several peak values of piezoelectric coefficient appeared at the stage where obvious change of domain pattern occurred. In addition, by comparing the cases of applied electric field with different frequencies, it was found that the maximum piezoelectric coefficient obtained decreased with increasing frequency value. These results are of great significance in tuning the properties of engineering domains in ferroelectrics, and could provide more fundamentals to the design of ferroelectric devices.

Giant electrocaloric effect in ferroelectric nanotubes near room temperature.

Ferroelectric perovskite oxides possess large electrocaloric effect, but only at high temperature, which limits their potential as next generation solid state cooling devices. Here, we demonstrate from phase field simulations that a giant adiabatic temperature change exhibits near room temperature in the strained ferroelectric PbTiO3 nanotubes, which is several times in magnitude larger than that of PbTiO3 thin films. Such giant adiabatic temperature change is attributed to the extrinsic contribution of unusual domain transition, which involves a dedicated interplay among the electric field, strain, temperature and polarization. Careful selection of external strain allows one to harness the extrinsic contribution to obtain large adiabatic temperature change in ferroelectric nanotubes near room temperature. Our finding provides a novel insight into the electrocaloric response of ferroelectric nanostructures and leads to a new strategy to tailor and improve the electrocaloric properties of ferroelectric materials through domain engineering.

Electric field-induced phase transitions in Li-modified Na0.5K0.5NbO3 at the polymorphic phase boundary

The electric field-induced phase transitions in Li-modified Na0.5K0.5NbO3 at the polymorphic phase boundary (PPB) were observed using in situ X-ray diffraction. The ratio of monoclinic to tetragonal phase fraction was used as an indicator of the extent and reversibility of the phase transitions. The reversibility of the phase transition was greater in compositions further from the PPB. These results demonstrate that the field-induced phase transition is one of the origins of high piezoelectric properties in lead-free ferroelectric materials.

Electron emission from Pb(Mg1/3Nb2/3)O3-PbTiO3 ferroelectric cathode

(1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 materials near the morphotropic phase boundary are selected for tentative electron emission experiments due to their excellent piezoelectric and ferroelectric properties and relatively high dielectric constants. The influences of ferroelectric and dielectric properties of ferroelectric cathode material on its threshold voltage are studied. The relationship between emission current and triggering voltage is investigated, and the relationship between emission current and extracting voltage is studied as well. The electron emission mechanism is also analyzed. The results show that emission threshold voltage of the relaxation ferroelectric 0.9Pb(Mg1/3Nb2/3) O3-0.1PbTiO3 is smaller due to its high dielectric constant at room temperature and large polarization variation. Low threshold voltage means low power consumption. This is an important factor to be considered in actual application for ferroelectric cathode and it has an important reference value. Electron emission is associated with fast polarization reversal and the formation of the plasma. The self-emission current starts on the falling edge of the triggering voltage pulse, which means that it is caused by polarization reversal. The amplitude of the self-emission current grows exponentially with the increase of triggering voltage. The amplitude of emission current shows a linear growth with the increase of extracting voltage when it is larger. It indicates that large current is determined mainly by extracting voltage. Larger current needs larger extracting voltage. The emission current starts on the rising edge of the triggering voltage pulse. It is associated with the field enhancement effect near “three interface points” and the formation of the plasma. An emission current of 210 A is obtained from the ferroelectric cathode under an extracting voltage of 2500 V, and the corresponding current density is 447 A/cm2.

G0100203 モルフォトロピック相境界における多結晶PZTのマルチスケール解析

PZT is widely used for actuators and sensors of electromechanical devices and it has multiple crystal systems. Although PZT outputs large piezoelectricity, it shows a complicated hysteresis behavior caused by domain switching and structural phase transition at morphotropic phase boundary (MPB). It is important for development and improvement of lead-free piezoelectric materials to understand the mechanism of huge piezoelectricity in PZT. In this study, a multiscale nonlinear finite element method was developed to estimate ferroelectric material properties. The homogenization theory was employed for scale-bridging between macrostructure and microstructure. We utilized an incremental form of fundamental constitutive law in consideration with physical property change caused by domain switching and structural phase transition. Crystal morphologies, which are characterized as an inhomogeneous structure composed of many grains and domains with individual orientations, are modeled at a micro scale. Then the homogenized physical properties of macrostructure can be estimated with perfect correlation to microstructural changes such as domain switching and structural phase transition. The proposed multiscale finite element method was applied to a polycrystalline PZT, and the relation between the macroscopic properties and microscopic domain switching and structural phase transition were investigated. Especially the difference among tetragonal single phase, rhombohedral single phase and their dual phases were discussed.

Thermoeconomic Optimization for a Ferroelectric Ericsson Refrigerator

Using the finite-time thermodynamics, based on the thermodynamics properties of ferroelectric materials and a linear heat-transfer law, the inherent regenerative losses in the cycle are calculated and the fundamental optimum relations and other relevant performance parameters are determined. The thermoeconomic optimization for ferroelectric Ericsson refrigeration-cycle is reported. The cooling load for the refrigerator per unit total cost is proposed as objective functions for the optimization. The optimum performance parameters which maximize the objective functions are investigated. Since the optimization technique consists of both investment and energy consumption costs, the obtained results are more general and realistic.

Effects of Oxygen Vacancy on Ferroelectric Hysteresis under External Electric and Stress Fields

Effects of oxygen vacancies on properties of ferroelectric materials were investigated through their hysteresis characteristics using Monte Carlo simulation. The purpose of this work is to study the roles of oxygen vacancy in ferroelectrics. The 2D four-state Potts model was considered for dipole switching. Under the application of external electric and stress fields, for both static and periodic field conditions, the electrical polarization and strain were numerically calculated with varying stress field and oxygen-vacancy probability (or concentration). It was found that, with or without an applied stress, the coercivity, remnant and saturation of the ferroelectric and elastic properties decrease with increasing oxygen vacancies. Moreover, under an applied periodic stress, the shapes of strain-electric-field butterfly loops were found similar to those obtained from applying the combination of two static stresses.

Domain configuration and piezoelectric properties of (K0.50Na0.50)1−Li (Nb0.80Ta0.20)O3 ceramics

Abstract Domain structure plays an important role in determining piezoelectric properties of ferroelectric materials. However, limited studies have been carried out on the domains of (K,Na)NbO 3 -based lead free ceramics. The domain configuration, domain reversal behavior and piezoelectric properties of (K 0.50 Na 0.50 ) 1− x Li x (Nb 0.80 Ta 0.20 )O 3 (KNN-Li x ) ceramics with x = 0.02, 0.035 and 0.05, were studied in this research. It was observed that ceramics with different phases show distinctly different domain configurations and domain reversal behaviors. When compared to other two compositions, x = 0.035 with coexistent orthorhombic-tetragonal phases at room temperature was found to possess curved domain stripes and larger average domain width, leading to optimal piezoelectric properties with d 33 * = 260 pm/V and k p = 48%. Based on the microstructures, polarization hysteresis loops and unipolar strain curves under high electric field, it was concluded that the larger domain size and easier domain switching are due to the coexistence of orthorhombic and tetragonal phases, account for the improved properties in KNNT-Li 0.035 ceramics.

Probing the Giant Piezoelectric response of ferroelectric perovskites

By analogy with ferromagnetism and the hysteresis of the magnetic moment with a magnetic field, materials that exhibit a macroscopic spontaneous polarization Ps, which can be reversed under electric field E were defined as ferroelectrics. Ps, the directional order parameter can give rise to different polar structural phase transitions and finally disappear as a function of temperature T and/or hydrostatic pressure P in a transformation from a non-centrosymmetric to a centrosymmetric space group. The physical properties of ferroelectric materials are the basis of many technological applications based on their hysteretic properties (Ps / E in ferroelectric random access memories) or based on their coupled properties (η (mechanical strain)/ E in piezoelectric applications). In order to understand the origin and the mechanisms associated with the ferroelectric properties, "in-situ" structural studies as a function of E, T and P have to be performed. In addition ferroelectric materials exhibit based on their directional properties (Ps) a particular domain configuration which makes the structural understanding of these compounds much more complex. Different scales should be taken into account: from the atomic scale (individual polar displacements) to the macroscopic scale (macroscopic piezoelectric effect) and finally the mesoscopic scale in between, which is governed by the domain wall motion. High piezoelectric/ferroelectric properties in lead perovskite materials (PZT, PMN, PZN) are structurally linked to strong disorder which can be characterized by the presence of diffuse scattering in diffraction experiments and by nanosized domains. Here we will present "in-situ" characterization in lead perovskite materials as a function of the applied electric field based on X-ray and neutron diffraction and EXAFS techniques. A brief overview of the challenges to solve in future studies as a function of pressure and temperature will also be discussed.

Mechanical and Electrical Control of Charged Domain Walls in Ferroelectric Materials

Charged domain walls (CDWs) in ferroelectrics, as a result of “head-to-head” or “tail-to-tail” polarization configurations, are of significant scientific and technological importance, as they have been shown to play a critical role in affecting the atomic structures and controlling the electric, photoelectric and piezoelectric properties of ferroelectric materials. An understanding of the local response and underlying dynamic mechanism of CDWs under external excitations is necessary to engineer reliable ferroelectric devices. In this work, we present the nanoscale behavior of individual CDWs under applied mechanical stress and electric fields in a BiFeO3 thin film using in situ transmission electron microscopy (TEM).

The Influence of Thermal Resistances and Nonperfect Regenerative Losses on the Performance of a Ferroelectric Ericsson Refrigerator

Using the finite-time thermodynamics, the influence of thermal resistances and nonperfect regenerative losses on the optimal performance of a ferroelectric Ericsson refrigeration-cycle is analyzed. Based on the thermodynamics properties of ferroelectric materials and a linear heat-transfer law, the inherent regenerative losses in the cycle are calculated and the fundamental optimum relations and other relevant performance parameters are determined. The ecological optimization criterion of the refrigerator is derived. The results obtained here may reveal the general characteristics of the ferroelectric Ericsson refrigeration cycle.

Tuning Susceptibility via Misfit Strain in Relaxed Morphotropic Phase Boundary PbZr1‐xTixO3 Epitaxial Thin Films

Epitaxial strain is a powerful tool to manipulate the properties of ferroelectric materials. But despite extensive work in this regard, few studies have explored the effect of epitaxial strain on PbZr0.52Ti0.48O3. Here we explore how epitaxial strain impacts the structure and properties of 75 nm thick films of the morphotropic phase boundary composition. Single‐phase, fully epitaxial films are found to possess “relaxed” or nearly “relaxed” structures despite growth on a range of substrates. Subsequent studies of the dielectric and ferroelectric properties reveal films with low leakage currents facilitating the measurement of low‐loss hysteresis loops down to measurement frequencies of 30 mHz and dielectric response at background dc bias fields as large as 850 kV/cm. Despite a seeming insensitivity of the crystal structure to the epitaxial strain, the polarization and switching characteristics are found to vary with substrate. The elastic constraint from the substrate produces residual strains that dramatically alter the electric‐field response including quenching domain wall contributions to the dielectric permittivity and suppressing field‐induced structural reorientation. These results demonstrate that substrate mediated epitaxial strain of PbZr0.52Ti0.48O3 is more complex than in conventional ferroelectrics with discretely defined phases, yet can have a marked effect on the material and its responses.

Local 90° switching in Pb(Zr0.2Ti0.8)O3 thin film: Phase-field modeling

Polarization switching under an applied electrical field is a fundamental property of ferroelectric materials and has been explored for ferroelectric memory and electromechanical sensor applications. Ferroelectric/ferroelastic Pb(Zr0.2Ti0.8)O3 (PZT) epitaxial thin films have been extensively studied due to their high electromechanical responses. Herein, we study the switching kinetics of PZT thin films under a local applied bias simulating a piezoresponse force microscopy tip via the phase-field approach. Local 90° switching was observed along with 180° switching, in good agreement with previous experimental observations. Different switching patterns are observed at different applied bias for films under different substrate strains. Generally, under low to medium bias, 90° switching is favored due to the huge release of elastic energy. While under a high applied bias, 180° switching dominates with large electrostatic energy decrease. It is worthwhile noting that the less mobile 90° domain wall cannot be fully switched back by a reverse electric field, which could lead to the “fatigue behavior”.

Large electrocaloric effect induced by the multi-domain to mono-domain transition in ferroelectrics

The electrocaloric properties of multi-domain ferroelectrics are investigated using a phase field model. The simulation results show that the extrinsic contribution from the multi-domain to mono-domain transition driven by temperature significantly enhances the electrocaloric response. Due to the abrupt decrease of polarization in the direction of electric field during the domain transition, a large adiabatic temperature change is achieved for the ferroelectrics subjected to a tensile strain. Furthermore, the domain transition temperature can be tuned by external strains as the phase transition temperature. A compressive strain decreases the domain transition temperature while a tensile strain increases it. The large temperature change associated with the domain transition provides guidance to engineer domain structures by strain to optimize the electrocaloric properties of ferroelectric materials below the Curie temperature.

Extensive domain wall motion and deaging resistance in morphotropic 0.55Bi(Ni1/2Ti1/2)O3–0.45PbTiO3 polycrystalline ferroelectrics

Domain wall motion is known as a major source of extrinsic contributions to the dielectric and piezoelectric properties of ferroelectric materials. In the present work, we report the extent of non-180° domain wall motion during strong and weak electric field amplitudes in situ using time-resolved, high-energy X-ray diffraction in the ferroelectric morphotropic phase boundary composition 0.55Bi(Ni1/2Ti1/2)O3–0.45PbTiO3 (BNT-45PT). After application of strong electric fields, two phases are shown to coexist. In the tetragonal phase of this material, the extent of 90° domain wall motion is significant and the domain alignment is nearly saturated. Weak (subswitching) cyclic electric fields are then also shown to induce domain wall motion. Deaging, or the progressive loss of preferred domain orientation during sequentially increasing field amplitudes, is notably low in these materials, showing that the initial domain alignment is strongly stabilized. Overall, the in situ measurements reveal that domain wall motion significantly impacts the structure and properties of BNT-45PT and reinforces the importance of understanding domain wall motion contributions to the physical properties of ferroelectrics.

Influence of Nanoparticles in PZT Ferroelectric Material Properties and Their Applications to Memory Devices

Ferroelctrics are technologically important materials, particularly for their applications in ferroelectric random access memory, based on semiconductor integrated technology have been a great success. Furthermore, these RAMS are very sensitive to radiation and this is detrimental for military and space applications. The properties of the layered perovskite ferroelectrics can be enhanced by addition or substitution of alternative cations. Among the important ferroelectric materials lead zirconate titanate (PZT), which is part of the solid solution formed between ferroelectric lead titanate and anti-ferroelectric lead zirconate with different compositions are used for different applications. Recent works indicate the influence of nanoparticles in PZT properties like decrease of synthesizing temperature, electrical conductivity and low dielectric loss. These materials will be the future ferroelectric materials for noval applications. The present paper Include a thorough study of these materials to finding out reasons for the improvement ferroelectric material properties in the nano scale and their optimization techniques for better applications.

Defect ordering and defect–domain-wall interactions in PbTiO3: A first-principles study

The properties of ferroelectric materials, such as lead zirconate titanate (PZT), are heavily influenced by the interaction of defects with domain walls. These defects are either intrinsic or are induced by the addition of dopants. We study here PbTiO3 (the end member of a key family of solid solutions) in the presence of acceptor (Fe) and donor (Nb) dopants, and the interactions of the different defects and defect associates with the domain walls. For the case of iron acceptors, the calculations point to the formation of defect associates involving an iron substitutional defect and a charged oxygen vacancy (Fe-Ti'-V-O ''). This associate exhibits a strong tendency to align in the direction of the bulk polarization; in fact, ordering of defects is also observed in pure PbTiO3 in the form of lead-oxygen divacancies. Conversely, calculations on donor-doped PbTiO3 do not indicate the formation of polar defect complexes involving donor substitutions. Last, it is observed that both isolated defects in donor-doped materials and defect associates in acceptor-doped materials are more stable at 180 degrees. domain walls. However, polar defect complexes lead to asymmetric potentials at domain walls due to the interaction of the defect polarization with the bulk polarization. The relative pinning characteristics of different defects are then compared, to develop an understanding of defect-domain-wall interactions in both doped and pure PbTiO3. These results may also help in understanding hardening and softening mechanisms in PZT.

Modeling the paraelectric aging effect in the acceptor doped perovskite ferroelectrics: role of oxygen vacancy

The time dependence of physical properties in the paraelectric phase was probed recently in a Mn3+ doped (Ba0.8Sr0.2)TiO3 ceramic, providing a simple situation (without spontaneous polarization or domain walls) to quantify the role of the oxygen vacancy during aging. In the present study, we propose a quantitative model for paraelectric aging to understand how the distribution of the oxygen vacancy evolves with time and consequently influences the dielectric response of the paraelectric phase. First, by comparing dielectric behavior of paraelectric aging in a Mn3+ doped (Ba0.75Sr0.25)TiO3 ceramic and the dielectric tunable effect, an internal bias field Ein related to the oxygen vacancy is shown to exist in the paraelectric phase. Second, by introducing such a time dependent Ein in a Landau-type model, we reproduce the dielectric response of Mn3+ doped (Ba0.8Sr0.2)TiO3 ceramic during paraelectric aging. It is suggested that the increase of dielectric permittivity can be ascribed to the decrease of Ein with time. The investigation of paraelectric aging is helpful for understanding the role of the oxygen vacancy in influencing the physical properties of ferroelectric materials.

Atomic Scale Structure Changes Induced by Charged Domain Walls in Ferroelectric Materials

Charged domain walls (CDWs) are of significant scientific and technological importance as they have been shown to play a critical role in controlling the switching mechanism and electric, photoelectric, and piezoelectric properties of ferroelectric materials. The atomic scale structure and properties of CDWs, which are critical for understanding the emergent properties, have, however, been rarely explored. In this work, using a spherical-aberration-corrected transmission electron microscope with subangstrom resolution, we have found that the polarization bound charge of the CDW in rhombohedral-like BiFeO3 thin films not only induces the formation of a tetragonal-like crystal structure at the CDW but also stabilizes unexpected nanosized domains with new polarization states and unconventional domain walls. These findings provide new insights on the effects of bound charge on ferroelectric domain structures and are critical for understanding the electrical switching in ferroelectric thin films as well as in memory devices.