Properties Of Ferroelectric Materials Research Articles

Structure and Properties of Ferroelectric Materials after Mechanoactivation

The mechanoactivation of ferroelectric materials with perovskite structure is performed. Structural changes of the ferroelectric materials after mechanoactivation based on X-ray absorption spectra (XAFS) and X-ray diffraction data (XRD) are studied. The Fourier analysis of EXAFS spectra allows quantitative estimates to be obtained for the local atomic structure of the investigated materials after activation. The effect mechanoactivation has on permittivity in a wide range of frequencies and temperatures is considered.

Infrared and Structural Studies of Micro and Nano-crystalline Ta Doped Lead Zirconate Titanate Ceramics

<p> In this paper, influence of additives on structural properties of Tantalum (<em>Ta</em>) doped PZT ceramics, prepared by solid-state oxide and mechanical activation (MA) routes, has been studied. The Fourier transformation infrared spectroscopy (FTIR) studies, are done to understand the structural interactions, confirmed that the wave number and bond energy decreases with the increase in Ta content accompanied by decrease in grain size. FTIR spectrum becomes broader in nanocrystalline Ta-PZT. The fraction of tetragonal phase decrease along with reduction in grain size as the <em>Ta </em>content increase. The remnant polarisation and coercive field also follows the similar trend on <em>Ta </em>doping. It is seen that infrared spectroscopy results corroborate the structure and ferroelectric properties of PZT materials.</p>

Stabilization of Polar Nanoregions in Pb-free Ferroelectrics.

The formation of polar nanoregions through solid-solution additions is known to enhance significantly the functional properties of ferroelectric materials. Despite considerable progress in characterizing the microscopic behavior of polar nanoregions (PNR), understanding their real-space atomic structure and dynamics of their formation remains a considerable challenge. Here, using the method of dynamic pair distribution function, we provide direct insights into the role of solid-solution additions towards the stabilization of polar nanoregions in the Pb-free ferroelectric of Ba(Zr,Ti)O_{3}. It is shown that for an optimum level of substitution of Ti by larger Zr ions, the dynamics of atomic displacements for ferroelectric polarization are slowed sufficiently below THz frequencies, which leads to increased local correlation among dipoles within PNRs. The dynamic pair distribution function technique demonstrates a unique capability to obtain insights into locally correlated atomic dynamics in disordered materials, including new Pb-free ferroelectrics, which is necessary to understand and control their functional properties.

Understanding the effect of porosity on the polarisation-field response of ferroelectric materials

This paper combines experimental and modelling studies to provide a detailed examination of the influence of porosity volume fraction and morphology on the polarisation-electric field response of ferroelectric materials. The broadening of the electric field distribution and a decrease in the electric field experienced by the ferroelectric ceramic medium due to the presence of low-permittivity pores is examined and its implications on the shape of the hysteresis loop, remnant polarisation and coercive field is discussed. The variation of coercive field with porosity level is seen to be complex and is attributed to two competing mechanisms where at high porosity levels the influence of the broadening of the electric field distribution dominates, while at low porosity levels an increase in the compliance of the matrix is more important. This new approach to understanding these materials enables the seemingly conflicting observations in the existing literature to be clarified and provides an effective approach to interpret the influence of pore fraction and morphology on the polarisation behaviour of ferroelectrics. Such information provides new insights in the interpretation of the physical properties of porous ferroelectric materials to inform future effort in the design of ferroelectric materials for piezoelectric sensor, actuator, energy harvesting, and transducer applications.

Ferroelectric Domain Continuity Over Grain Boundaries for Tetragonal, Orthorhombic, and Rhombohedral Crystal Symmetries

Domain mobility is understood to have a significant impact on ferroelectric material properties. Grain boundaries are known to inhibit ferroelectric domain wall mobility, thereby limiting the properties of polycrystalline ferroelectrics. Continuous domains across grain boundaries can change the grain boundary impact on domain wall mobility. Such microstructures have been observed since the 1950s, but their impact on properties is not well understood. This paper predicts the likelihood of domain wall continuity over grain boundaries for typical perovskite oxide ferroelectric symmetries of tetragonal, orthorhombic, and rhombohedral. Five two-grain systems are studied for domain continuity over all possible grain boundary space. Results show that rhombohedral and orthorhombic symmetries have a higher probability for domain continuity over grain boundaries as compared with tetragonal symmetry. This observation is due to the greater number of domain wall planes and polarization vectors in these symmetries. Grain boundaries probable for domain continuity can be identified in each misorientation for each symmetry. This knowledge, combined with developments in microstructural measurements and ceramic processing techniques, may be used to control domain continuity at grain boundaries, and hence, influence the final properties of the material.

Effect of geometric configuration on the electrocaloric properties of nanoscale ferroelectric materials

The electrocaloric properties of ferroelectrics are highly dependent on the domain structure in the materials. For nanoscale ferroelectric materials, the domain structure is greatly influenced by the geometric configuration of the system. Using a real-space phase field model based on the Ginzburg-Landau theory, we investigate the effect of geometric configurations on the electrocaloric properties of nanoscale ferroelectric materials. The ferroelectric hysteresis loops under different temperatures are simulated for the ferroelectric nano-metamaterials with square, honeycomb, and triangular Archimedean geometric configurations. The adiabatic temperature changes (ATCs) for three ferroelectric nano-metamaterials under different electric fields are calculated from the Maxwell relationship based on the hysteresis loops. It is found that the honeycomb specimen exhibits the largest ATC of ΔT=4.3 °C under a field of 391.8 kV/cm among three geometric configurations, whereas the square specimen has the smallest ATC of ΔT=2.7 °C under the same electric field. The different electrocaloric properties for three geometric configurations stem from the different domain structures. There are more free surfaces perpendicular to the electric field in the square specimen than the other two specimens, which restrict more polarizations perpendicular to the electric field, resulting in a small ATC. Due to the absence of free surfaces perpendicular to the electric field in the honeycomb specimen, the change of polarization with temperature in the direction of the electric field is more easy and thus leads to a large ATC. The present work suggests a novel approach to obtain the tunable electrocaloric properties in nanoscale ferroelectric materials by designing their geometric configurations.

Fabrication of barium titanate doped strontium using co-precipitation method

Fabrication of barium titanate (BaTiO3/BT) doped strontium (Sr) using co-precipitation method has been successfully conducted. The research aim is to get the best of mole variation of Sr doping to ferroelectric material properties. Doping Sr was varied at 1%, 2%, 3%, 4% and 5% in BaTiO3. Each sample was sintered at temperature of 1100°C with holding time for 6 h and temperature rate at 10°C/min. They were then characterized by XRD instrument to investigate the crystal structure, LCR meter to measure the dielectric constant, and Sawyer Tower circuit to reveal the hysteresis curve. The peaks of XRD shift towards larger angle when mole doping Sr increase. The crystallinity of all samples is above 90% and the crystallite size is in the range of 27 nm to 34 nm. Hysteresis curve from Sawyer Tower testing confirms that all samples are ferroelectric material. The RLC measurement results reveal that the less frequency leads to the higher dielectric constant while the highest dielectric constant belongs to the BT doped 3% of Sr. Therefore, it is the best variation obtained in this research.

Effect of the nanopore on ferroelectric domain structures and switching properties

Porous ferroelectrics have some special properties and features for specific promising applications. The nanopores structure have been observed in experiments may have great influence on the ferroelectric domain structures and the switching properties of ferroelectrics. In this study, we proposed a phase field model to predict the domain structures of porous ferroelectrics and their evolution under a switching electric field. The effects of the pores size/shape on domain structure, switching properties, and dielectric/piezoelectric properties are investigated and analyzed. The simulated hysteresis loop is in good agreement with experimental reports. It is shown that the porosity can strongly affect the ferroelectric domain size, and furthermore, will influence the hysteresis loop. Therefore controlling the porosity of ferroelectrics may provide a possible way to adjust the properties of porous ferroelectric materials.

An optical method for characterizing domain wall motions and ferroelectric hysteresis in tetragonal Mn:Fe:KTN co-doped crystals

An optical method is proposed to extract the displacement vector of domain wall (DW) sidewise motion from ferroelectric domain configuration pattern on a tetragonal Mn:Fe:KTN crystal. The ferroelectric domain configuration evolution under an external electric field is observed in situ using optical microscope imaging system, and the relative displacement of DW sideways motion between two adjacent electric fields is extracted. By the combination of the new domain length vector extracted, the ferroelectric domain displacement vector as a function of field strength can be obtained; what is more, the hysteresis loop can be achieved during field cycling. The method provides an access to directly manipulating DW motion and exploring the properties of ferroelectric materials from ferroelectric domain configuration pattern.

Adjusting the Operating Voltage of an Nanoelectromechanical Relay Using Negative Capacitance

The operating voltage of a nanoelectromechanical (NEM) relay can be scaled down significantly using negative capacitance (NC), which is a unique property of ferroelectric materials. It has been observed that a ferroelectric capacitor can amplify the internal voltage of a device (higher than the externally applied voltage) by means of the NC effect. In this simulation work, depending on the structural parameters of a ferroelectric capacitor and an NEM relay, an NC + NEM relay (in which the gate electrode of the NEM relay is connected in series to the ferroelectric capacitor) was investigated. As a result, a sub-0.5-V operating voltage is theoretically estimated.

Analytic model for the electrical properties of negative capacitance metal-ferroelectric insulator silicon (MFIS) capacitor

ABSTRACTIn this paper, we present an analytical model for the voltages across the Metal-Ferroelectric-Insulator-Silicon(MFIS) capacitor and show how the surface potential is amplified due to the negative capacitance property of ferroelectric materials. Our model is based on the Landau-Khalatnikov equation coupled with the charge based MOS capacitor model. It is also used to analyse the effect on the total capacitance of the MFIS capacitor. Furthermore, we analyse the impact of ferroelectric and gate oxide thicknesses on the amplified surface potential and also on the threshold voltage of the capacitor.

Temperature-Dependent Coercive Field Measured by a Quantum Dot Strain Gauge.

Coercive fields of piezoelectric materials can be strongly influenced by environmental temperature. We investigate this influence using a heterostructure consisting of a single crystal piezoelectric film and a quantum dots containing membrane. Applying electric field leads to a physical deformation of the piezoelectric film, thereby inducing strain in the quantum dots and thus modifying their optical properties. The wavelength of the quantum dot emission shows butterfly-like loops, from which the coercive fields are directly derived. The results suggest that coercive fields at cryogenic temperatures are strongly increased, yielding values several tens of times larger than those at room temperature. We adapt a theoretical model to fit the measured data with very high agreement. Our work provides an efficient framework for predicting the properties of ferroelectric materials and advocating their practical applications, especially at low temperatures.

In-situ observation of ultrafast 90\xb0 domain switching under application of an electric field in (100)/(001)-oriented tetragonal epitaxial Pb(Zr0.4Ti0.6)O3 thin films

Ferroelastic domain switching significantly affects piezoelectric properties in ferroelectric materials. The ferroelastic domain switching and the lattice deformation of both a-domains and c-domains under an applied electric field were investigated using in-situ synchrotron X-ray diffraction in conjunction with a high-speed pulse generator set up for epitaxial (100)/(001)-oriented tetragonal Pb(Zr0.4Ti0.6)O3 (PZT) films grown on (100)cSrRuO3//(100)KTaO3 substrates. The 004 peak (c-domain) position shifts to a lower 2θ angle, which demonstrates the elongation of the c-axis lattice parameter of the c-domain under an applied electric field. In contrast, the 400 peak (a-domain) shifts in the opposite direction (higher angle), thus indicating a decrease in the a-axis lattice parameter of the a-domain. 90° domain switching from (100) to (001) orientations (from a-domain to c-domain) was observed by a change in the intensities of the 400 and 004 diffraction peaks by applying a high-speed pulsed electric field 200 ns in width. This change also accompanied a tilt in the angles of each domain from the substrate surface normal direction. This behaviour proved that the 90° domain switched within 40 ns under a high-speed pulsed electric field. Direct observation of such high-speed switching opens the way to design piezo-MEMS devices for high-frequency operation.

Nonlocal large-amplitude vibration of embedded higher-order shear deformable multiferroic composite rectangular nanoplates with different edge conditions

Based on the nonlocal elasticity theory, a unified nonlocal, nonlinear, higher-order shear deformable nanoplate model is developed to investigate the size-dependent, large-amplitude, nonlinear vibration of multiferroic composite rectangular nanoplates with different boundary conditions resting on an elastic foundation. By considering a unified displacement vector and using von Kármán’s strain tensor, the strain–displacement components are obtained. Using coupled nonlocal constitutive relations, the coupled ferroelastic, ferroelectric, ferromagnetic, and thermal properties of multiferroic composite materials and small-scale effect are taken into account. The electric and magnetic potential distributions in the nanoplate are calculated via Maxwell’s electromagnetic equations. Furthermore, Hamilton’s principle is utilized to obtain the mathematical formulation associated with the coupled governing equations of motions and boundary conditions. The developed model enables us to consider the effects of rotary inertia and transverse shear deformation without using any shear correction factor. Also, it can be degenerated to the models based on the Kirchhoff and existing shear deformation plate theories. To solve the large-amplitude vibration problem, an efficient multistep numerical solution approach is utilized. Effects of various important parameters such as the type of the plate theory, and parameters of nonlocality and coupled fields on the nonlinear frequency response are investigated.

Stress-Induced Cubic-to-Hexagonal Phase Transformation in Perovskite Nanothin Films.

The strong coupling between crystal structure and mechanical deformation can stabilize low-symmetry phases from high-symmetry phases or induce novel phase transformation in oxide thin films. Stress-induced structural phase transformation in oxide thin films has drawn more and more attention due to its significant influence on the functionalities of the materials. Here, we discovered experimentally a novel stress-induced cubic-to-hexagonal phase transformation in the perovskite nanothin films of barium titanate (BaTiO3) with a special thermomechanical treatment (TMT), where BaTiO3 nanothin films under various stresses are annealed at temperature of 575 °C. Both high-resolution transmission electron microscopy and Raman spectroscopy show a higher density of hexagonal phase in the perovskite thin film under higher tensile stress. Both X-ray photoelectron spectroscopy and electron energy loss spectroscopy does not detect any change in the valence state of Ti atoms, thereby excluding the mechanism of oxygen vacancy induced cubic-to-hexagonal (c-to-h) phase transformation. First-principles calculations show that the c-to-h phase transformation can be completed by lattice shear at elevated temperature, which is consistent with the experimental observation. The applied bending plus the residual tensile stress produces shear stress in the nanothin film. The thermal energy at the elevated temperature assists the shear stress to overcome the energy barriers during the c-to-h phase transformation. The stress-induced phase transformation in perovskite nanothin films with TMT provides materials scientists and engineers a novel approach to tailor nano/microstructures and properties of ferroelectric materials.

Comparative first-principles studies of prototypical ferroelectric materials by LDA, GGA, and SCAN meta-GGA

Originating from a broken spatial inversion symmetry, ferroelectricity is a functionality of materials with an electric dipole that can be switched by external electric fields. Spontaneous polarization is a crucial ferroelectric property, and its amplitude is determined by the strength of polar structural distortions. Density functional theory (DFT) is one of the most widely used theoretical methods to study ferroelectric properties, yet it is limited by the levels of approximations in electron exchange-correlation. On the one hand, the local density approximation (LDA) is considered to be more accurate for the conventional perovskite ferroelectrics such as BaTiO3 and PbTiO3 than the generalized gradient approximation (GGA), which suffers from the so-called super-tetragonality error. On the other hand, GGA is more suitable for hydrogen-bonded ferroelectrics than LDA, which largely overestimates the strength of hydrogen bonding in general. We show here that the recently developed general-purpose strongly constrained and appropriately normed (SCAN) meta-GGA functional significantly improves over the traditional LDA/GGA for structural, electric, and energetic properties of diversely-bonded ferroelectric materials with a comparable computational effort, and thus enhances largely the predictive power of DFT in studies of ferroelectric materials. We also address the observed system-dependent performances of LDA and GGA for ferroelectrics from a chemical bonding point of view.

Crystallization kinetics and enhanced dielectric properties of free standing lead-free PVDF based composite films

Ferroelectric composites, integrating dielectric ceramic fillers with mechanically flexible polymers, are promising materials for flexible electronic applications. Plenty of research has demonstrated the enhanced dielectric and ferroelectric properties of composite materials. However, the mechanisms responsible for these enhancements are not completely understood. Herein, we used typical dielectric materials, poly(vinylidene fluoride) (PVDF) and BaTiO3 (BTO), to study the effect of a dielectric filler on the crystallization, phase transformation and dielectric properties of PVDF. The crystallization of β-PVDF was not affected by the presence of BTO particles, but small amounts of BTO (< 3 vol %) made PVDF crystallize into larger spherulites. This is linked to crystallization kinetic studies, which showed that BTO acted as a nucleation agent for large full ring banded spherulites when its content was less than 1 vol %. Furthermore, solid state drawing in the presence of BTO particles promoted the formation of β-PVDF with more pronounced preferred crystalline orientation at high drawing temperatures (120 °C). The dielectric and ferroelectric properties were enhanced with BTO filling. The 100 °C oriented drawn PVDF tape exhibited a dielectric permittivity of 14 (100 Hz) and remnant polarization of 0.080 C/m2 (10 Hz), which increased to 23 and 0.095 C/m2, respectively, after filling with 5 vol % BTO; neither resulting in high dielectric loss tangent (∼ 0.02) nor obvious current leakage. Moreover, the coercive field decreased from 80 to 50 kV/mm with increasing BTO content from 0 to 5 vol %.

Effect of Ca, Sr and Ba distribution on the relaxor properties of CSBN single crystals

ABSTRACTIn the present work, we aimed to find the correlation between the distribution of Ca, Ba and Sr over the volume and ferroelectric properties of CSBN materials. As a result, it is shown that in the CSBN25 which is characterized by relaxor properties there exists smaller excess oxygen compared with CSBN50 and CSBN75 crystals. CSBN25 also have more nonuniform distribution of elements, which occupy the same position (A1) in tetragonal tungsten bronze structure.

A new method to determine the un-poled elastic properties of ferroelectric materials

Piezoelectric devices with complex electrode geometries often contain ferroelectric regions that experience little or no electric field and remain unpolarised. Since the un-poled and poled material properties differ it is desirable to account for these regions in a device when developing predictive models or to design piezoelectric transducers. The lack of published data on the elastic properties for un-poled ferroelectrics, specifically the numerous commercial compositions such as lead zirconate titanate, reflects the difficulty of experimental measurement. In this work, a method for predicting un-poled properties from more commonly available poled data has been developed. A new method of calculating these properties is presented which provides a rapid and practical solution to the problem of evaluating the isotropic stiffness and Poisson’s ratio for an un-poled ferroelectric material. The way in which this calculation has been derived and validated is presented and detailed comparisons are made with alternative methods and experimental data.

Origin of stationary domain wall enhanced ferroelectric susceptibility

Ferroelectrics usually adopt a multi-domain state with domain walls separating domains with polarization axes oriented differently. It has long been recognized that domain walls can dramatically impact the properties of ferroelectric materials. The enhancement of low-field susceptibility/permittivity under subswitching conditions is usually attributed to the reversible domain wall vibration. Recent experiments highlight the stationary domain wall contribution to the dielectric susceptibility irrespective of any lateral displacements or deformations of the wall. We study the effects of domain walls on low-field permittivity of PbTiO$_3$ with density functional theory and molecular dynamics simulations. The static dielectric constant is calculated as a function of increasing domain wall density and temperature. We find an increase of dielectric permittivity with increasing domain wall density, which is expected to occur at low driving field where the lateral motion of domain walls is forbidden. Real-space decomposition of dielectric response reveals that frustrated dipoles within the finite width of the domain walls are responsible for the enhanced low-field permittivity.