Showing papers on "Ferroelectricity published in 1998"
TL;DR: Ferroelectric, dielectric, and piezoelectric properties of ferroelectric thin films and ceramics are reviewed with the aim of providing an insight into different processes which may affect the behaviour of Ferroelectric devices.
Abstract: Ferroelectric, dielectric and piezoelectric properties of ferroelectric thin films and ceramics are reviewed with the aim of providing an insight into different processes which may affect the behaviour of ferroelectric devices, such as ferroelectric memories and micro-electro-mechanical systems. Taking into consideration recent advances in this field, topics such as polarization switching, polarization fatigue, effects of defects, depletion layers, and depolarization fields on hysteresis loop behaviour, and contributions of domain-wall displacement to dielectric and piezoelectric properties are discussed. An introduction into dielectric, pyroelectric, piezoelectric and elastic properties of ferroelectric materials, symmetry considerations, coupling of electro-mechanical and thermal properties, and definitions of relevant ferroelectric phenomena are provided.
1,835 citations
TL;DR: An exceptionally high electrostrictive response was observed in electron-irradiated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer, suggesting that the electron irradiation breaks up the coherent polarization domain in normal ferroelectric P( VDF- TrFE)Copolymer into nanopolar regions that transform the material into a relaxor ferroElectric.
Abstract: An exceptionally high electrostrictive response ( approximately 4 percent) was observed in electron-irradiated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer. The material exhibits typical relaxor ferroelectric behavior, suggesting that the electron irradiation breaks up the coherent polarization domain (all-trans chains) in normal ferroelectric P(VDF-TrFE) copolymer into nanopolar regions (nanometer-size, all-trans chains interrupted by trans and gauche bonds) that transform the material into a relaxor ferroelectric. The expanding and contracting of these polar regions under external fields, coupled with a large difference in the lattice strain between the polar and nonpolar phases, generate an ultrahigh strain response.
1,451 citations
TL;DR: In this paper, a phenomenological thermodynamic theory of ferroelectric thin films epitaxially grow on cubic substrates is developed using a new form of the thermodynamic potential, which corresponds to the ac tual mechanical boundary conditions of the problem.
Abstract: A phenomenological thermodynamic theory of ferroelectric thin films epitaxially grow on cubic substrates is developed using a new form of the thermodynamic potential. which corresponds to the ac tual mechanical boundary conditions of the problem, For single-domain BaTiO3 and PbTiO3 films, the "misfit-temperature" phase diagrams are constructed. It is found that the 2D clamping of the films, apart from a shift of the temperature of the ferroelectric transition, results in a change of its order. A change of the sequence of the phases and the appearance of phases forbidden in the bulk crystals are predicted. [S0031-9007(98)05421-0].
1,434 citations
TL;DR: In this article, it was shown that a first-order ferromagnetic phase transition with a transition temperature nearly equal to the bulk value can be found in trifluoroethylene polymers with diameters as small as 10'A (two monolayers) even in these almost two-dimensional films.
Abstract: Ultrathin crystalline films offer the possibility of exploring phase transitions in the crossover region between two and three dimensions. Second-order ferromagnetic phase transitions have been observed in monolayer magnetic films1,2, where surface anisotropy energy stabilizes the two-dimensional ferromagnetic state at finite temperature3. Similarly, a number of magnetic materials have magnetic surface layers that show a second-order ferromagnetic–paramagnetic phase transition with an increased Curie temperature4. Ferroelectricity is in many ways analogous to ferromagnetism, and bulk-like ferroelectricity and finite-size modifications of it have been seen in nanocrystals as small as 250 A in diameter5, in perovskite films 100 A thick6 and in crystalline ferroelectric polymers as thin as 25 A (7-10). But these results can be interpreted as bulk ferroelectricity suppressed by surface depolarization energies, and imply that the bulk transition has a minimum critical size11,12,13. Here we report measurements of the ferroelectric transition in crystalline films of a random copolymer of vinylidene fluoride and trifluoroethylene just 10 A (two monolayers) thick. We see a first-order ferroelectric phase transition with a transition temperature nearly equal to the bulk value, even in these almost two-dimensional films. In addition, we see a second first-order transition at a lower temperature, which seems to be associated with the surface layers only. The near-absence of finite-size effects on the bulk transition implies that these films must be considered as two-dimensional ferroelectrics.
754 citations
TL;DR: In this article, the effect of the film thickness and crystallinity on the imaging resolution of scanning force microscopy has been discussed and the application of SFM to visualization of domain structures in ferroelectric thin films is described.
Abstract: ▪ Abstract Scanning force microscopy (SFM) is becoming a powerful technique with great potential both for imaging and for control of domain structures in ferroelectric materials at the nanometer scale. Application of SFM to visualization of domain structures in ferroelectric thin films is described. Imaging methods of ferroelectric domains are based on the detection of surface charges in the noncontact mode of SFM and on the measurement of the piezoelectric response of a ferroelectric film to an external field applied by the tip in the SFM contact mode. This latter mode can be used for nondestructive evaluation of local ferroelectric and piezoelectric properties and for manipulation of domains of less than 50 nm in diameter. The effect of the film thickness and crystallinity on the imaging resolution is discussed. Scanning force microscopy is shown to be a technique well suited for nanoscale investigation of switching processes and electrical degradation effects in ferroelectric thin films.
484 citations
TL;DR: In this paper, a review is presented of deposition, switching, and leakage current in these devices, which are small enough to permit 1 Gbit memories on a standard Si chip.
Abstract: Recent studies have produced 0.1 × 0.1 μm ferroelectric cells in both bismuth titanate and strontium bismuth tantalate, thus taking thin-film ferroelectric memories into the regime of nanoscale (100 nm or less) devices. A review is presented of deposition, switching, and leakage current in these devices, which are small enough to permit 1 Gbit memories on a standard Si chip.
389 citations
TL;DR: In this paper, Doped alkaline-bismuth-titanate perovskite single crystals have been grown in ferroelectric phases with high piezoelectric actuation.
Abstract: Doped alkaline–bismuth–titanate perovskite single crystals have been grown in ferroelectric phases with high piezoelectric actuation. Rhombohedral-phase Na1/2Bi1/2TiO3–BaTiO3 crystals exhibit up to 0.25% free strain with low hysteresis along the cubic 〈001〉 direction (d33∼450 pC/N). Tetragonal phase crystals exhibit free strains as high as 0.85% with greater hysteresis characteristic of domain switching; low field d33 exceeds 500 pC/N. Strain energy densities exceed those of optimized polycrystalline lead perovskites, and actuation capability is retained at compressive stresses >100 MPa.
371 citations
TL;DR: In this paper, the effect of interfaces on the value of dielectric constant (K′) calculated from capacitance and geometry data for sub-micron barium titanate (BaTiO3) ceramics prepared with decreasing grain size and grain volumes was investigated.
Abstract: We report the effect of interfaces (and thus internal surface area effects) on the value of dielectric constant (K′) calculated from capacitance and geometry data for sub-micron barium titanate (BaTiO3) ceramics prepared with decreasing grain size (and grain volumes). A series model is proposed to explain the decreasing values of apparent K′ obtained for grain sizes below 0.5 μm. A distinction is made between the true dielectric constant (K′) and the apparent dielectric constant (K′) calculated from experimental data. The progressive suppression in K′ is explained in terms of ferroelectric grains of constant dielectric constant (K′1) separated by a lower-K 2 boundary region (i.e., grain boundary) of constant thickness (d 2). The problem is one of an increasing interfacial surface area to grain volume ratio in fine-grain dielectrics. We begin by reporting original dielectric data for high pressure-densified ultrafine-grain BaTiO3 ceramics. Chemically prepared BaTiO3 powder was consolidated at high...
348 citations
TL;DR: In this article, crystal ion slicing was used to create a buried sacrificial layer in single-crystal c-cut poled wafers of LiNbO3, inducing a large etch selectivity between the sacrificial layers and the rest of the sample.
Abstract: We report on the implementation of crystal ion slicing in lithium niobate (LiNbO3). Deep-ion implantation is used to create a buried sacrificial layer in single-crystal c-cut poled wafers of LiNbO3, inducing a large etch selectivity between the sacrificial layer and the rest of the sample. 9-μm-thick films of excellent quality are separated from the bulk and bonded to silicon and gallium arsenide substrates. These single-crystal films have the same room-temperature dielectric and pyroelectric characteristics, and ferroelectric transition temperature as single-crystal bulk. A stronger high-temperature pyroelectric response is found in the films.
306 citations
TL;DR: In this paper, the authors measured and analyzed the Extended X-ray Absorption Fine Structure (EXAFS) of BaTiO3 at the barium k edge and the X-rays absorption near edge Structure (XANES) at the titanium K edge.
Abstract: We have measured and analyzed the Extended X-ray Absorption Fine Structure (EXAFS) of BaTiO3 at the barium k edge and the X-ray Absorption Near Edge Structure (XANES) at the titanium K edge. Our structural data show that the sequence of phase transitions in this material as the temperature increases is explained by a disordering of domains wherein the local structural environment remains approximately rhombohedrally distorted at all temperatures around both metal sites. As the temperature is raised, the long range correlations between these local distortions change, resulting in the observed sequence of phase transitions. Our measurements confirm the model of eight-site disorder used to explain the phase diagram of BaTiO3. We show that EXAFS and XANES are sensitive probes of both the magnitude and direction of the local structural distortions which accompany ferroelectricity and therefore are sensitive probes of the microscopic mechanism of ferroelectricity.
TL;DR: In this article, the authors developed possible domain patterns for (001) oriented (pseudocubic indexing) epitaxial rhombohedral perovskite ferroelectric (FR) films.
Abstract: Possible domain patterns are developed for (001) oriented (pseudocubic indexing) epitaxial rhombohedral perovskite ferroelectric (FR) films. We assume that the films are grown above their Curie temperature (TC) in a cubic paraelectric (PC) state. The rhombohedral distortion consists of a “stretch” along one of the four 〈111〉 crystallographic directions of the cubic perovskite unit cell. Domain pattern formation is concurrent with the PC→FR transformation on cooling from the growth temperature. The domain patterns form to minimize elastic energy in the film, at the energetic expense of both forming domain boundaries and developing local stresses in the substrate. Eight possible domains may form, half of which are related by inversion, thus leading to four mechanically distinct variants. The possible domain walls are determined by mechanical and charge compatibility and follow closely from the analysis of Fousek and Janovec [J. Appl. Phys. 40, 135 (1969)]. Domain patterns may develop with either {100} or {1...
TL;DR: In this paper, the microwave dielectric properties of ferroelectric barium titanate were measured as a function of grain and particle size, and it was shown that the relaxation phenomenon appears to be intimately linked to the domain state of the Ferroelectric.
Abstract: The use of ferroelectric ceramics and thin films in microwave devices requires that they possess frequency-stable, low-loss dielectric properties. At microwave frequencies, ferroelectric polycrystalline ceramic materials typically exhibit a large dielectric relaxation, characterized by a decrease in the relative permittivity (er) and a peak in the dielectric loss (tan δ). Mechanisms attributed to the relaxation phenomenon include piezoelectric resonance of grains and domains, inertia to domain wall movement, and the emission of gigahertz shear waves from ferroelastic domain walls. As a result, the relaxation phenomenon appears to be intimately linked to the domain state of the ferroelectric. The domain state of a ferroelectric is, in part, dependent upon its microstructure. In this study, the microwave dielectric properties of ferroelectric barium titanate were measured as a function of grain and particle size. Polycrystalline ceramic ferroelectric BaTiO3 (having average grain sizes of 14.4, 2.14, and 0.2...
TL;DR: In this article, an augmented constitutive model that accounts for the temperature-dependent piezoelectric properties was proposed to extrapolate nonlinear effects measured at one temperature to other temperatures with good accuracy.
Abstract: This paper presents research results on the electro–thermomechanical behavior of piezoelectric ceramics for use in actuator applications with an emphasis on ferroelectric fatigue. The material being investigated is a lead zirconate titanate piezoelectric ceramic with the composition PbZr0.53Ti0.47O3 (PZT-5H). Results presented in this paper include an augmented constitutive model that accounts for the temperature-dependent piezoelectric properties. Using this model, nonlinear effects measured at one temperature can be extrapolated to other temperatures with good accuracy. Experimental studies into 180° and 90° polarization switching of PZT-5H indicate that the dielectric flux to dipole the material appears to be an adequate criterion for predicting this nonlinear switching behavior. Fatigue studies show that material degradation is strongly influenced by temperature and by the magnitude of the applied electric field. Above a critical temperature, PZT-5H no longer fatigues in the presence of large electric...
TL;DR: In this paper, the authors used a double crucible Czochralski method to grow LiTaO3 single crystals with a composition close to stoichiometry by using a double-crazed double-branched crystal Czarnecki method and compared the switching field required for 180° ferroelectric domain reversal and the internal fields originating from nonstoichiometric point defects for the stoichiometric and conventional commercially available crystals.
Abstract: We grew LiTaO3 single crystals with a composition close to stoichiometry by using a double crucible Czochralski method. The switching field required for 180° ferroelectric domain reversal and the internal fields originating from nonstoichiometric point defects were compared for the stoichiometric and conventional commercially available crystals. The switching fields for the domain reversal in the stoichiometric crystal with a Curie temperature of 685 °C was 1.7 kV/mm. This is about one thirteenth of the switching field required for the conventional LiTaO3 crystals with a Curie temperature near 600 °C. The internal field in the stoichiometric crystal drastically decreased to 0.1 kV/mm.
TL;DR: In this paper, the authors investigated the nature of atomic relaxations around oxygen-vacancy defects in the ferroelectric perovskite through first-principles pseudopotential total energy calculations.
Abstract: We investigate the nature of atomic relaxations around oxygen-vacancy defects in the ferroelectric perovskite ${\mathrm{PbTiO}}_{3}$ through first-principles pseudopotential total energy calculations. A tail-to-tail polarization is one of the patterns that emerges from atomic relaxations around oxygen vacancies and its stability is found to be enhanced by charge trapping. Oxygen vacancies in Ti-O-Ti chains along the polarization axis are more favorable than those in Ti-O-Ti planes normal to the axis. The possible role of oxygen vacancies in fatigue and aging is discussed.
TL;DR: The freezing process in lead magnesium niobate (PMN) has been investigated by measurements of the frequency-dependent complex dielectric constant and its third harmonic component as discussed by the authors.
Abstract: The freezing process in lead magnesium niobate (PMN) has been investigated by measurements of the frequency-dependent complex dielectric constant and its third harmonic component. The linear complex dielectric susceptibility was analyzed by a temperature-frequency plot in order to determine the temperature dependence of the dielectric relaxation spectrum and to identify the freezing temperature. It was found that both the shape of the relaxation spectrum and its temperature behavior in the PMN relaxor show remarkable similarities to dipolar glasses, i.e., the longest relaxation time diverges according to the Vogel-Fulcher law, while the bulk of the distribution of relaxation times remains finite even below the freezing temperature. The frequency and the temperature dependence of the third harmonic susceptibility, similar to the behavior observed in linear dielectric response, indicate that the same underlying relaxation spectrum and therefore the same slowing-down mechanism is controlling both linear and nonlinear dynamic response. The observed splitting between the field-cooled and zero-field-cooled dielectric constant---comparable to the one obtained in spin glasses---effectively demonstrates the occurrence of typical glassy nonergodic behavior in the vicinity of the transition temperature where the ferroelectric phase would appear above a threshold electric field.
TL;DR: In this paper, a comprehensive review of the work on ferroelectric materials is presented, including models of the Ferroelectric permittivity and loss tangent as well as methods of measurement of these properties.
Abstract: When an electric field is applied to a ferroelectric material, the microwave permittivity undergoes a substantial change. This change in permittivity can be utilized in microwave devices to produce frequency-agile functions. This paper is a comprehensive review of the work on ferroelectric materials; this includes models of the ferroelectric permittivity and loss tangent, as well as methods of measurement of these properties. New measurements are presented on thin-film strontium titanate and single-crystal strontium barium titanate substrates. These results are compared with the model. A brief discussion is given of the applications of ferroelectric material in microwave devices.
TL;DR: In this paper, the authors discuss high-dielectric films, in general, oxide ferroelectrics based on simple perovskite structures and related Aurivillius-phase layered structure perovsites employed as thin-film capacitors in dynamic random access memories (DRAMs).
Abstract: ▪ Abstract We discuss high-dielectric films, in general, oxide ferroelectrics based on simple perovskite structures and related Aurivillius-phase layered structure perovskites employed as thin-film capacitors in dynamic random access memories (DRAMs). Emphasis is on breakdown mechanisms and limits, leakage currents, electrodes and electrode interfaces, scaling to submicron geometries, and deposition techniques.
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27 Feb 1998
TL;DR: In this paper, the authors present a model for the second-order phase transition in a single-Ion model of a Diatomic crystal and apply the Landau theory to phase transitions in Uniaxial Ferroelectrics and demonstrate the applicability of Landau Theory to Phase Transitions of Displacive and Order-Disorder types.
Abstract: 1. General Characteristics of Structural Phase Transitions in Crystals.- 1.1 First- and Second-Order Structural Phase Transitions.- 1.2 Structural Phase Transitions of Displacive and Order-Disorder Types.- 1.3 The Domain Structure.- 1.4 Ferroelectric Phase Transitions.- 1.5 Basic Types of Ferroelectric Crystals.- 2. Phenomenological Theory of Second-Order Structural Transitions in Crystals.- 2.1 The Incomplete Thermodynamic Potential.- 2.2 Structural Phase Transitions Described by a One-Component Order Parameter.- 2.3 Structural Phase Transitions Described by Two- and Three-Component Order Parameters.- 3. Proper Ferroelectrics: Anomalies of Physical Properties in Phase Transitions.- 3.1 Anomalies of Thermal and Electrical Properties (One-Component Order Parameter).- 3.2 Anomalies of Electrical Properties (Multicomponent Order Parameter).- 3.3 First-Order Phase Transitions Close to Second-Order Transitions.- 3.4 The Tricritical Point.- 4. Dielectric Anomalies in Structural Nonferroelectric and Improper Ferroelectric Phase Transitions.- 4.1 Nonferroelectric Phase Transitions: Dielectric Anomalies.- 4.2 Improper Ferroelectric Phase Transitions: Dielectric Anomalies.- 5. Anomalies of Elastic and Electromechanical Characteristics of Crystals in Second-Order Phase Transitions.- 5.1 One-Component Order Parameter: Elastic Properties of an Isotropic Liquid.- 5.2 One-Component Order Parameter: Elastic Properties of an Anisotropic Crystal.- 5.3 Ferroelectric-Ferroelastics: One-Component Order Parameter with Transformation Properties of the Component of a Second-Rank Tensor and the Polar Vector.- 5.4 Temperature Dependences of "Morphic" Moduli of Elasticity.- 5.5 Two-Component Order Parameter: Elastic Properties of Crystals.- 5.6 Piezoelectric Effect and Electrostriction in the Case of One-Component Order Parameter and Centrosymmetric Paraelectric Phase.- 5.7 Piezoelectric Effect in the Case of One-Component Order Parameter and Noncentrosymmetric Paraelectric Phase.- 6. Fluctuations of the Order Parameter in Phenomenological Theory.- 6.1 Spatially Inhomogeneous Fluctuations of the Order Parameter in the Incomplete Thermodynamic Potential.- 6.2 Applicability of Landau Theory to Nonferroelectric Structural Phase Transitions.- 6.3 Applicability of Landau Theory to Phase Transitions in Uniaxial Ferroelectrics.- 6.4 Fluctuational Phenomena in Ferroelectric-Ferroelastics and in Phase Transitions in Multiaxial Ferroelectrics.- 7. Structural Phase Transitions in the Single-Ion Model.- 7.1 Problems of the Microscopic Theory.- 7.2 The Single-Ion Model of a Diatomic Crystal.- 7.3 Phase Transitions of Displacive and Order-Disorder Types in the Single-Ion Model.- 7.4 Applicability of the Landau Theory to Phase Transitions of Displacive and Order-Disorder Types.- 8. Statistical Theory of Ferroelectric Phase Transitions of the Order-Disorder Type.- 8.1 The Hamiltonian of a Uniaxial Ferroelectric with an Order-Disorder Phase Transition.- 8.2 The Free Energy of an Order-Disorder Crystal in the Self-Consistent Molecular Field Approximation.- 8.3 Tunneling Effects in Hydrogen-Containing Ferroelectrics.- 8.4 The Cluster Approximation: Crystals of the KH2P04 Group.- 9. Dynamics of Displacive and Order-Disorder Phase Transitions.- 9.1 The Equation of Motion of the Order Parameter.- 9.2 Dynamic Dielectric Constant: Order-Disorder Phase Transitions.- 9.3 Dynamic Dielectric Constant: Displacive Phase Transitions.- 9.4 Microscopic Theory of Dynamic Processes in Displacive Phase Transitions.- 9.5 Microscopic Theory of Dynamic Processes in Order-Disorder Phase Transitions.- 9.6 Dielectric Constant and Soft Mode: The Lyddane-Sachs-Teller Relation.- 10. Domain Structure and Defects.- 10.1 Nucleation of Domains in a Structural Phase Transition.- 10.2 Domain Wall Structure: One-Component Order Parameter.- 10.3 Domain Wall Structure: Two-Component Order Parameter.- 10.4 Motion of the Domain Wall in an Ideal and a Real Crystal.- 10.5 Motion of the Domain Wall: Account of the Discreteness of the Crystal.- 10.6 Domain Walls and Defects.- 10.7 Defects in the Symmetrical Phase.- 10.8 Domains in Proper Ferroelectrics.- 10.9 Domains in Ferroelastics.- 10.10 Domains in Polyaxial Ferroelectrics.- 11. Ferroelectrics with an Incommensurate Phase.- 11.1 Phase Transitions into an Incommensurate Phase.- 11.2 Phenomenological Theory of Phase Transitions into an Incommensurate Phase.- 11.3 Specific Features of Crystal Lattice Vibrations in an Incommensurate Phase.- 11.4 The Incommensurate Phase in a Real Crystal.- 11.5 The Commensurate-Incommensurate Phase Transition: A Special Type of Phase Transition.- 11.6 Evolution of the Structure of the Incommensurate Phase (General Picture).- 11.7 Evolution of the Structure of the Incommensurate Phase (the Continuum Approximation).- 12. Ferroelectric Liquid Crystals.- 12.1 Basic Types of Orientational Ordering in Liquid Crystals.- 12.2 Conditions for Existence of Dipolar Ordering in Liquid Crystals.- 12.3 Phenomenological Theory of Phase Transition SmA* -? SmC*.- 12.4 The Behavior of a Ferroelectric Smectic Liquid Crystal in an External Electric Field.- 13. Crystallochemical Aspects of the Theory of Ferroelectric Phenomena.- 13.1 Calculation of the Constants of the Hamiltonians of Some Crystals.- 13.2 An Approach Based on the Classical Theory of Ionic Crystals.- 14. Recommended Literature.- References.
TL;DR: In this article, a simple and reliable method which allows one to distinguish between the two major microscopic scenarios for the suppression of the switching polarization (P-r(s)), i.e., pinning of ferroelectric domain walls (DWs) through the Pb(Zr,Ti)O-3 film (PZT) and inhibition of the growth of opposite domains due to the nucleus suppression at the electrode interfaces (interface scenario), is proposed.
Abstract: A simple and reliable method which allows one to distinguish between the two major microscopic scenarios for the suppression of the switching polarization (P-r(s)), i.e., pinning of ferroelectric domain walls (DWs) through the Pb(Zr,Ti)O-3 film (PZT) (bulk scenario) and inhibition of the growth of opposite domains due to the nucleus suppression at the electrode interfaces (interface scenario), is proposed. In addition, a new electric treatment able to significantly suppress P-r(s) in Pt-PZT-Pt ferroelectric capacitors (FECAPs) of thicknesses above 1.4 mu m, was discovered and studied. It consists of the application of an external alternating electric field (E-e) which cycles the polarization at very low frequency (1.7 mHz). After only 10-20 cycles, P-r(s) can be suppressed by a factor of 10. The same FECAP, when subjected to E-e at higher frequency (30 kHz), endures at least 10(8) switches, before attaining an equivalent P-r(s), suppression (hereafter called fatigue). The fatigued states obtained with the two different procedures appear to be different. In the first case (slow cycling) it is suggested that the suppression of P-r(s) is related to the DW pinning scenario, whereas in the second case-which corresponds to the normal fatiguing procedure-it is related to the interface scenario. (C) 1998 American Institute of Physics. [S0003-6951(98)01619-2].
TL;DR: In this paper, the size, shape, and polarization orientation of fatigued areas formed during the suppression of the switchable polarization (P-r(s)) (fatigue) in Ft-FZT-Pt ferroelectric capacitors (FECAPs), were observed by means of atomic force microscopy and by imaging the phase of the piezoelectric vibration induced by a low ac field applied between the top and bottom electrodes.
Abstract: The size, shape, and polarization orientation of fatigued areas formed during the suppression of the switchable polarization (P-r(s)) (fatigue) in Ft-FZT-Pt ferroelectric capacitors (FECAPs), were observed by means of atomic force microscopy and by imaging the phase of the piezoelectric vibration induced by a low ac field applied between the top and bottom electrodes. In the virgin state (FECAP as prepared), the pattern of the polarization domains with opposite orientation was randomly distributed with typical sizes of 1-3 mu m. The application of a de field larger than the coercive field (E-c) enabled to fully orient the polarization of the regions in either directions. During the initial fatigue ( 65% of suppressed P-r(s)), two main configurations of the frozen polarization domains were distinguished. One was characterized by a strong preferential direction (top to bottom electrode) and the other by randomly distributed regions of opposite oriented frozen polarization. The degrees of fatigue obtained by analyzing the vibration phase images are in good agreement with those obtained by standard polarization measurements. It is concluded that the Ps. suppression (fatigue) is due to "region by region" or "grain by grain" freezing of P-r(s) and that the frozen P-r(s) can have a preferential orientation. (C) 1998 American Institute of Physics.
TL;DR: In this paper, a polarization switching model for polycrystalline ferroelectric ceramics was developed, in which a single ferro-electric crystallite in a ceramic, which is subjected to an electric field and/or a stress, undergoes a complete polarization change and a corresponding strain change if the resulting reduction in potential energy exceeds a critical value per unit volume of switching material.
Abstract: A polarization switching model for polycrystalline ferroelectric ceramics has been developed. It is assumed that a single ferroelectric crystallite in a ceramic, which is subjected to an electric field and/or a stress, undergoes a complete polarization change and a corresponding strain change if the resulting reduction in potential energy exceeds a critical value per unit volume of switching material. The crystallite’s switch causes a change in the interaction of its field and stress with the surrounding crystallites, which is modeled by the Eshelby inclusion method to provide a mean field estimate of the effect. Thus the model accounts for the effects of the mean electric and stress fields arising from the constraints presented by surrounding crystallites as well as the externally applied mechanical and electrical loads. The switching response of the ceramic polycrystal is obtained by averaging over the behavior of a large number of randomly oriented crystallites. The model, along with the linear dielect...
TL;DR: In this paper, a computational micromechanics model for polycrystalline ferroelectric ceramics is developed based on consideration of the constitutive behavior of single crystals.
TL;DR: In this article, it was shown that hydrogen incorporation is the primary mechanism for the degradation of ferroelectric properties and the most probable site for hydrogen ions is discussed based on ionic radii, crystal structure, electrical properties, and Raman spectra.
Abstract: The properties of ferroelectric films are known to degrade when subjected to hydrogen in forming gas anneals. Earlier studies have attributed this degradation to the loss of oxygen from these films during these anneals. In this study, we show that though oxygen is lost during forming gas annealing, hydrogen incorporation is the primary mechanism for the degradation of ferroelectric properties. Raman spectra obtained from the forming gas-annealed films show evidence of polar hydroxil [OH−] bonds in the films. The most probable site for hydrogen ions is discussed based on ionic radii, crystal structure, electrical properties, and Raman spectra. We propose that the hydrogen ion is bonded with one of the apical oxygen ions and prevents the Ti ion from switching. Pyroelectric measurements on forming gas-annealed capacitors confirm that the capacitors no longer possess spontaneous polarization.
TL;DR: In this paper, a complete interpretation for the pre-edge fine structure (PEFS) of the x-ray Ti K-absorption spectra for perovskite structure crystals is proposed based on the results of numerous calculations performed by a modified full multiple scattering method.
Abstract: A complete interpretation is proposed for the pre-edge fine structure (PEFS) of the x-ray Ti K-absorption spectra for perovskite structure crystals. The interpretation is based on the results of numerous calculations performed by a modified full multiple scattering method which provides the theoretical spectra for the 3d transition metal oxides in fair agreement with experiment. It is shown that the three main peaks in the PEFS have quite different origin. The first long-wave side peak A is caused mainly by quadrupole transitions. The middle peak B is caused by the p-d mixture effect and the high intensity of it is considered to be a qualitative spectroscopic indication of ferroelectricity in the perovskite structure crystal. A simple formula is obtained which expresses the area under peak B through the lattice constants and mean-square displacement of the absorbing Ti atom from the instantaneous centre of the coordination polyhedron. The peak B area averaged over thermal atomic vibrations is determined by the three-particle atomic distribution function. The short-wave side peak C is caused by the Ti 1s electron transition to the unoccupied 3d states of the neighbouring transition metal atoms. We show that an additional peak on the short-wave side of peak C occurs if there are 4d atoms (for instance Zr atoms in the vicinity of the absorbing Ti atom in the (PZT) solid solution) within the oxygen atom octahedrons surrounding the absorbing 3d atom. The area under peak is directly determined by the average number of 4d atoms in the vicinity of the absorbing Ti one.
01 Sep 1998
TL;DR: The properties of three PZT-based piezoelectric ceramics and one PLZT electrostrictive ceramic were measured as a function of temperature.
Abstract: The properties of three PZT-based piezoelectric ceramics and one PLZT electrostrictive ceramic were measured as a function of temperature. In this work, the dielectric, ferroelectric polarization versus electric field, and piezoelectric properties of PZT-4, PZT-5A, PZT-5H, and PLZT-9/65/35 were measured over a temperature range of -150 to 250 C. In addition to these measurements, the relative thermal expansion of each composition was measured from 25 to 600 C and the modulus of rupture of each material was measured at room temperature. This report describes the experimental results and compares and contrasts the properties of these materials with respect to their applicability to intelligent aerospace systems.
TL;DR: In this article, a modified Schottky equation is applied to describe the conduction mechanism in perovskite-type titanate thin films, and the electronic mobility in thin films of barium strontium titanate is reported.
Abstract: In the literature, the Schottky emission equation is widely used to describe the conduction mechanism in perovskite-type titanate thin films. Though the equation provides a good fit to the leakage current data, the extracted values of the Richardson and dielectric constants are inconsistent with their experimental values. In this work, a modified Schottky equation is applied. This equation resolves the difficulties associated with the standard Schottky equation. Also, the electronic mobility in thin films of barium strontium titanate is reported.
TL;DR: In this article, high-resolution x-ray photoelectron spectra of the atomic constituents of Bi4Ti3O12 were recorded and the obtained results indicate that oxygen vacancies are preferentially sited in the vicinity of Bi ions, in the Bi2O2 layers.
Abstract: Ferroelectric Bi4Ti3O12 ceramics have been prepared by the method of reactive sintering. The ceramics exhibit good ferroelectric properties with a remanent polarization Pr=5.5×10−2 C/m2 and a coercive field Ec=3MV/m. High resolution x-ray photoelectron spectra of the atomic constituents of Bi4Ti3O12 were recorded. The obtained results indicate that oxygen vacancies are preferentially sited in the vicinity of Bi ions, in the Bi2O2 layers.
TL;DR: In this article, the authors measured the current density as a function of time for thin (⩽1000 A) barium strontium titanate (BST) capacitors with platinum electrodes.
Abstract: The current density is measured as a function of time for thin (⩽1000 A) barium strontium titanate (BST) capacitors with platinum electrodes. The current density curve shows a peak prior to the onset of resistance degradation. The peak position on the time axis varies with applied voltage and temperature. The data are explained by the theory for space-charge-limited (SCL) current transients, and the measured current is identified as ionic current associated with oxygen vacancies. Using the SCL analysis, the mobility of the oxygen vacancies is measured as a function of temperature. The mobility obtained from current measurements is shown to be compatible with the Einstein relation for mobility and diffusivity. In summary, the ionic current associated with oxygen vacancies is shown to be an important component of the measured current in thin BST films.