Showing papers on "Ferroelectric ceramics published in 1992"
TL;DR: In this paper, the authors study cracks either in piezoelectrics, or on interfaces between the materials such as metal electrodes or polymer matrices, and derive the macroscopic field regarding the crack tip as a physically structureless point.
Abstract: We Study cracks either in piezoelectrics, or on interfaces between piezoelectrics and other materials such as metal electrodes or polymer matrices. The projected applications include ferroelectric actuators operating statically or cyclically, over the major portion of the samples, in the linear regime of the constitutive curve, but the elevated field around defects causes the materials to undergo hysteresis locally. The fracture mechanics viewpoint is adopted—that is, except for a region localized at the crack tip, the materials are taken to be linearly piezoelectric. The problem thus breaks into two subproblems: (i) determining the macroscopic field regarding the crack tip as a physically structureless point, and (ii) considering the hysteresis and other irreversible processes near the crack tip at a relevant microscopic level. The first Subproblem, which prompts a phenomenological fracture theory, receives a thorough investigation in this paper. Griffith's energy accounting is extended to include energy change due to both deformation and polarization. Four modes of square root singularities are identified at the tip of a crack in a homogeneous piezoelectric. A new type of singularity is discovered around interface crack tips. Specifically, the singularities in general form two pairs: r1/2±ieand r1/2±ie, where e. and k are real numbers depending on the constitutive constants. Also solved is a class of boundary value problems involving many cracks on the interface between half-spaces. Fracture mechanics are established for ferroelectric ceramics under smallscale hysteresis conditions, which facilitates the experimental study of fracture resistance and fatigue crack growth under combined mechanical and electrical loading. Both poled and unpoled fcrroelectrie ceramics are discussed.
1,112 citations
TL;DR: In this article, the piezoelectric and electrostrictive effects in ferroelectric ceramics are reviewed with an emphasis on those properties that are relevant for applications in actua tors.
Abstract: The piezoelectric and electrostrictive effects in ferroelectric ceramics are reviewed with an emphasis on those properties that are relevant for applications in actua tors. Various contributions to...
159 citations
TL;DR: In this paper, an empirical impedance expression has been deduced: Z ∗ =R 0 /(1+iω/ω 1 +(iω /ω 2 ) n ) where ω 1 and ω 2 characterize respectively the lattice response and the "universal behavior" of the charge carriers.
98 citations
TL;DR: In this paper, the authors investigated fatigue of ferroelectric polarization and the electric field induced strain in lead lanthanum zirconate titanate ceramics and found that the fatigue rate increases as the coercive field or the hysteretic nature of the induced polarization increases.
Abstract: In this paper fatigue of ferroelectric polarization and the electric field induced strain is investigated in lead lanthanum zirconate titanate ceramics. Fatigue rate increases as the coercive field or the hysteretic nature of the electric field induced polarization of the ferroelectric ceramics increases. The ferroelectric polarization lost during fatigue can be partly restored by decreasing the frequency and increasing the amplitude of the applied ac electric field. The ferroelectric fatigue is modeled phenomenologically by an increase of the energy barrier for the ferroelectric switching and atomistically by a coupling of the spontaneous polarization with defects and/or space charge in the orientation of ferroelectric fatigue.
77 citations
Proceedings Article•
25 May 1992TL;DR: In this article, a new high current density electron source is investigated, which consists of a polarized ceramic disk with aluminium electrodes coated on both faces, and the front electrode is etched in a periodic grid to expose the ceramic beneath, resulting in the emission of a high density electron cloud into a 1 to 10mm diode gap.
Abstract: A new high current density electron source is investigated The source consists of a polarized ceramic disk with aluminium electrodes coated on both faces The front electrode is etched in a periodic grid to expose the ceramic beneath A rapid change in the polarization state of the ceramic results in the emission of a high density electron cloud into a 1 to 10mm diode gap The anode potential is maintained by a charged transmission line Some of the emitted electrons traverse the gap and an electron current flows The emitted electron current has been measured as a function of the gap spacing and the anode potential Current densities in excess of 70 A/cm2 have been measured The current is found to vary linearly with the anode voltage for gaps < 10 mm, and exceeds the Child-Langmuir current by at least two orders of magnitude The experimental data will be compared with predictions from a model based on the emission of a cloud of electrons from the ferroelectric which in turn reflex in the diode gap
66 citations
TL;DR: In this paper, the electron emission was observed by applying pulse voltage to a thin plate of PZT ferroelectric ceramic, and the lowest pulse voltage for this emission was 75 V and the largest emission current in a sample having a 7×0.3 mm2 electrode was 30 mA.
Abstract: Electron emission into vacuum has been observed by applying pulse voltage to a thin plate of PZT ferroelectric ceramic. This electron emission has been obtained even in low vacuum of less than 10-1 Torr. The lowest pulse voltage for this emission is 75 V, and the largest emission current in a sample having a 7×0.3 mm2 electrode is 30 mA. The electrons are considered to be emitted from the surface of the ferroelectric plate near the electrode by very high field induced by polarization reversal. This electron emission can be applied as the electron emitter in vacuum electronic devices such as micro-triodes and flat panel displays.
50 citations
TL;DR: In this paper, complex impedance measurements were performed on Pb 2 KNb 5 O 15 ferroelectric ceramics (T c = 733 K) in a frequency range of 20-3 × 10 5 Hz between room temperature and 820 K.
42 citations
TL;DR: The anomalous dielectric absorption current of BaTiO3 ceramics when an electric field is applied at above the Curie point was measured as discussed by the authors, and the total charge of the charging and discharging absorption current was more than 1000 µC/cm2.
Abstract: The anomalous dielectric absorption current of BaTiO3 ceramics when an electric field is applied at above the Curie point was measured. The results cannot be explained by the famous Maxwell-Wagner double layer theory. The total charge of the charging and discharging absorption current was more than 1000 µC/cm2. The giant space charge produces "internal bias field" in the opposite direction to the first applied field. Another space charge is generated during the aging process after poling at below the Curie point. In this report, two types of space charge effects are described and discussed respect to "space charge stabilized effects" for electromechanical strength and the difficulties of polarization reversal applications due to "space charge asymmetric effects".
40 citations
TL;DR: A theory of the banded domain a-structures in tetragonal ferroelectric ceramics is presented in this article, where the mechanical sources of internal stresses appearing on the grain and band boundaries at a phase transition are modelled by arrays of wedge disclinations and continuously distributed fictitious dislocations.
Abstract: A theory of the banded domain a-structures in tetragonal ferroelectric ceramics is presented. The mechanical sources of internal stresses appearing on the grain and band boundaries at a phase transition are modelled by arrays of wedge disclinations and continuously distributed fictitious dislocations. With the aid of the disclination and dislocation models the ceramic elastic energy due to the internal stress field is evaluated. This result is used to calculate the equilibrium geometric parameters of the banded domain structure which minimize the internal energy of a coarse-grained ceramic. The dependencies of the equilibrium parameters on the grain size are discussed. The influence of external static and low-frequency electric fields on the banded domain structure is also considered on the basis of an energetic approach. The amplitudes of reversible displacements are calculated for the 90° domain walls inside bands and for the band boundaries consisting of alternating stripes of 90° and 180° wal...
37 citations
TL;DR: In this article, experimental and theoretical studies on the room temperature capacitance-voltage (CV) and (tan delta )-V response of a highvoltage barium titanate ceramic disc capacitor with prescribed nonlinear CV response, as fabricated for an intended power electronics application, are reported.
Abstract: Experimental and theoretical studies are reported on the room temperature capacitance-voltage (CV) and (tan delta )-V response of a high-voltage barium titanate ceramic disc capacitor with prescribed nonlinear CV response, as fabricated for an intended power electronics application. The CV response was modeled in terms of a voltage-dependent series equivalent circuit incorporating grain-boundary junction capacitances and grain ferroelectric capacitances. A modified Langevin function was used to relate intergrain ferroelectric polarization, which yielded good agreement between theory and experiment for a 3-to-1 capacitance variation over the DC bias range up to 1000 V. >
33 citations
TL;DR: In this paper, thermal and pressure pulse measurements are reported of the polarization distribution in poled, ferroelectric ceramic samples and the results obtained from both methods are complementary so that there is a benefit to using both.
Abstract: This paper is the first of a series with the common theme of comparing thermal and acoustic pulse methods of measuring charge or polarization profiles across the thickness of slab‐shaped samples that are representative of different types of materials. In this paper, thermal and pressure pulse measurements are reported of the polarization distribution in poled, ferroelectric ceramic samples. The results obtained from both methods are complementary so that there is a benefit to using both. The results also demonstrate that large deviations from uniform polarization can be induced by processing differences.
TL;DR: In this paper, the authors report on the sintering and dielectric properties of new ceramics based on the niobate K0·2Sr0·4NbO3 (KSN) which exhibits the TTB structure.
Abstract: Type II ferroelectric ceramics with high dielectric constants and flat curves e = f(T) have, until now, only been obtained with oxides which exhibit the perovskite structure. Another family of oxides, the tetragonal tungsten bronze (TTB)-type niobates, should be of great interest for such applications because of their structure, which is, indeed, very closely related to that of perovskite. The authors report here on the sintering and dielectric properties of new ceramics based on the niobate K0·2Sr0·4NbO3 (KSN) which exhibits the TTB structure, and show how the addition of a perovskite such as a relaxor or BaTiO3 or a mixture of these perovskites can lead to a dielectric material compatible with the Y7 R or X7R Electronic Industries Association specifications with a dielectric constant e as high as 6000. Moreover, the use of a lithium salt as sintering agent has been shown to be important for the elaboration of those ceramics, and particularly allows the synthesis of type I materials with a dielectric constant e as high as 3000.
TL;DR: A brief overview of the materials and processes for making ceramic capacitors based on BaTiO3 and relaxor ferroelectric compositions is presented with special emphasis on more recent developments as mentioned in this paper.
Abstract: A brief overview of the materials and processes for making ceramic capacitors based on BaTiO3 and relaxor ferroelectric compositions is presented with special emphasis on more recent developments.
TL;DR: In this article, the static mechanical compressive strength and repeated fatigue test were carried out for ferroelectric ceramics such as Pb(Zr, Ti)O3, BaTiO3 and others.
Abstract: As is well known, ferroelectric ceramics are widely used for electro-mechanical transducers because of their strong piezoelectric effects. For practical applications, the electrical fatigue and aging are very important and have been investigated since 1957. On the other hand, the mechanical strength and fatigue should also be important; however, very few paper have been reported till now. In this report, static mechanical compressive strength and repeated fatigue test were carried out for ferroelectric ceramics such as Pb(Zr, Ti)O3, BaTiO3 ceramics and others. It is revealed that the mechanical strength of ferroelectric ceramics are greatly affected by the electrical conditions such as poling conditions, aging conditions and electrical conditions during compressive tests. Fracture patterns, intergranular and/or transgranular, are also systematically changed by the residual internal stress induced above conditions. In order to estimate the internal stress, microindentation technology was applied t...
TL;DR: In this article, the distribution of polarization in ferroelectric ceramic samples of Ca-modified lead titanate, for different Ca contents, has been determined from the measurement, as a function of frequency and for different poling fields, of pyroelectric currents, generated by sinusoidal thermal waves of low frequency.
Abstract: The distribution of polarization in ferroelectric ceramic samples of Ca-modified lead titanate, for different Ca contents, has been determined from the measurement, as a function of frequency and for different poling fields, of pyroelectric currents, generated by sinusoidal thermal waves of low frequency. Inferred from the results are the state of ferroelectric domains and their contribution to polarization, and the relation between the distribution of polarization and crystalline anisotropy.
TL;DR: In this article, the authors investigated the acoustic emission associated with the polarization switching in ferroelectric ceramics and attributed the AE signal to the elastic energy release associated with domain switching and the transmission of the elastic waves via a electromechanical coupling.
Abstract: Acoustic emission associated with the polarization switching in ferroelectric ceramics is investigated. Under bipolar ac electric field driving, whereby ferroelectric ceramics undergo a transition between the macroscopically poled and depoled states, the acoustic emission signal is large in the poled state and small in the depoled state. Under unipolar electric field driving, whereby a prepoled ferroelectric ceramic sample does not experience a macroscopic polarization reversal, the acoustic emission signal obtains the maximum amplitude at an intermediate polarization level. Furthermore, the acoustic emission signal decreases as the induced ferroelectric polarization decreases after ferroelectric fatigue. These phenomena have been interpreted by attributing the AE signal to the elastic energy release associated with the domain switching and the transmission of the elastic waves via a electromechanical coupling.
TL;DR: In this paper, the Raman spectra temperature dependence is discussed in relation with the dielectric and electric results in order to understand the occurrence of antiferroelectric, ferroelectric and paraelectric phase transitions and with the relaxor behaviour appearing in such materials.
Abstract: Raman scattering, dielectric and electrical properties have been studied systematically in Nb modified PZT 97/3, 94/6 and 95/5 ceramics. The Raman spectra temperature dependence is discussed in relation with the dielectric and electric results in order to understand the occurrence of the antiferroelectric, ferroelectric and paraelectric phase transitions and with the relaxor behaviour appearing in such materials.
TL;DR: In this paper, composites of piezoelectric ceramic powders, such as PZT and Calcium modified Lead Titanate (PT) in a matrix of P(VDF/TrFE) have been fabricated in order to investigate whether these materials could have the low acoustic, broad band properties of the polymers whilst retaining the high piezolectric coefficients of the ceramics.
Abstract: Ferroelectric ceramics such as PZT, while exhibiting strong piezoelectric effect, have the disadvantages of a high acoustic impedance, difficulty to miniaturize and not being suitable to broad band ultrasonic applications. Polar ferroelectric polymer such as PVDF and its copolymers which can be obtained in thin film form, have low mechanical Q and low acoustical impedance although their piezoelectric coefficients are significantly lower than those of the piezoelectric ceramics. Composites of piezoelectric ceramic powders, such as PZT and Calcium modified Lead Titanate (PT) in a matrix of P(VDF/TrFE) have been fabricated in our laboratory, in order to Investigate whether these materials could have the low acoustic, broad band properties of the polymers whilst retaining the high piezoelectric coefficients of the ceramics. In the present paper the results of a study of the electromechanical coupling factor (kt), the quality factor (Qm) as well as the gh and dh piezoelectric coefficients of these 0-3 composites poled both by corona and by the conventional method are given.
TL;DR: Pb2KNb5O15 ferroelectric ceramics have been elaborated in this article to obtain the exact stoichiometric composition two processes were used: sintering either in open air with an excess of PbO or in a closed alumina vessel in a pbO-rich atmosphere.
Abstract: Pb2KNb5O15 ferroelectric ceramics have been elaborated. In order to obtain the exact stoichiometric composition two processes were used: sintering either in open air with an excess of PbO or in a closed alumina vessel in a PbO-rich atmosphere. The two types of obtained ceramics show dielectric properties close to those of single crystals. Furthermore, the crystallographic and dielectric data indicate that the best chemical homogeneity has been obtained using the closed system. The high dielectric constant results from two contributions: a MHz-GHz relaxation of the intrinsic polarization and a low-frequency dispersion of the space charge polarization.
TL;DR: In this article, the dielectric and charge storage properties of polypropylene-ceramic composite films were studied and it was shown that fine powder of appropriately modified ferroelectric ceramics in a polymer-ceramics composite enhances its charge storage property.
Abstract: Five different composite films of Polypropylene-Ceramic (both ferro- and antiferroelectric) materials were prepared by introducing fine grain ceramic powder in the matrix of polypropylene. The dielectric and charge storage properties of these composites were studied. The results show that an introduction of fine powder of appropriately modified ferroelectric ceramics in a polymer-ceramic composite enhances its charge storage properties.
TL;DR: In this paper, the authors reviewed the technology, composition, studies of physical properties and possible application of transparent ferroelectric ceramics and made an attempt to classify specific and common features of the TFC.
Abstract: Technology, composition, studies of physical properties and possible application of transparent ferroelectric ceramics are reviewed in terms of modern trends in advanced ceramics technology, and the physics of ferroelectricity and optoelectronics. An attempt is made to classify specific and common features of the TFC.
TL;DR: In this paper, computer simulation is applied to fracture toughness research of the transparent, cubic, non-cubic and ferroelectric ceramics and the processes occurring in the materials under sintering, cooling and further fracture by a macrocrack propagation are investigated.
Abstract: Computer simulation is applied to fracture toughness research of the transparent, cubic, noncubic and ferroelectric ceramics. The processes occurring in the materials under sintering, cooling and further fracture by a macrocrack propagation are investigated. Influence of the grain size on the ceramic fracture toughness is evaluated.
TL;DR: In this article, the constitutive properties of ferroelectric ceramics for large strain operation applications were investigated. But the constitutive laws applicable to this non-linear deformation were not considered.
Abstract: Experiments have been conducted to study the nonlinear constitutive properties of ferroelectric ceramics for large strain operation applications, where the mechanical behavior of the material dictates the overall electromechanical response of the devices. For this purpose, polarization and strain are measured continuously on a compression cuboid. Severe non-linear and hysteretic behavior is observed in these materials. An empirical formulation has been proposed to model the constitutive laws applicable to this non-linear deformation. Physical mechanism is provided, that is attributed to this constitutive law.
Journal Article•
TL;DR: In this article, different aspects of failure (breakdown and fracture) of ferroelectric ceramics in electric and mechanical fields were investigated, and it was concluded that local sites of failure in electric or mechanical fields are identical and are governed by the structure of the material.
Abstract: Different aspects of failure (breakdown and fracture) of ferroelectric ceramics in electric and mechanical fields are investigated. Distributions of the electrical and mechanical strengths are found to be similar. Weak electric fields strengthen slightly these ceramics, whereas strong fields weaken them. A similar effect is observed also in a study of the influence of mechanical loads on the electrical strength (breakdown voltage). The results are explained by the dual role of local deformation processes in the course of fracture: relaxation occurs in the presence of weak fields, but there is a tendency for a sample to fracture or become damaged under strong loads. It is concluded that local sites of failure in electric and mechanical fields are identical and are governed by the structure of the material
TL;DR: In this paper, the authors demonstrate how these instabilities vary with the type of the ferroelectric ceramics and the manner in which the ceramic actuators are electrically driven.
Abstract: Several types of electromechanical and dielectric instabilities occur during continuous electric field cycling in ferroelectric ceramic actuators. The major instabilities include (i) the gradual drifting of the static actuator dimension, (ii) increase in electric field induced polarization and strain during initial cycling and (iii) substantial fatigue in electric field induced polarization and strain after a number of electric field cycles. The authors demonstrate how these instabilities vary with the type of the ferroelectric ceramics and the manner in which the ceramic actuators are electrically driven. The causes for these instabilities are explained in terms of development and stabilization of domain configuration in response to external stimuli.
30 Aug 1992
TL;DR: In this article, the ferroelectric polarization fatigue of donor-and acceptor-doped BaTiO/sub 3/ ceramics and PZT (lead zirconate titanate) thin films were investigated.
Abstract: The ferroelectric polarization fatigue (loss of polarization with cycling) of donor- and acceptor-doped BaTiO/sub 3/ ceramics and PZT (lead zirconate titanate) thin films have been investigated. Donor-doped BaTiO/sub 3/ ceramics showed significantly improved fatigue characteristics compared with acceptor-doped materials. Enhanced fatigue properties were also observed in donor-doped PZT thin films. The electric-field-assisted migration of charged species within ferroelectric materials may be responsible for the degradation/fatigue behavior. The results obtained confirm the expectation that oxygen vacancies play an important role in degradation/fatigue under electric switching. >
07 Sep 1992
TL;DR: In this paper, the pyroelectric and dielectric properties of composites made with a polymer, P(VDF/TrFE) and various ferroelectric ceramics such as PZT, PLZT and Ca modified PT were investigated.
Abstract: Discusses a polymer/ceramic composite, in which a fine ceramic powder is dispersed in a polymer matrix. This paper focuses on the relevant properties of composites that make them suitable for their use in pyroelectric detectors, using the pyroelectric figure of merit defined as p/ epsilon ( mu C/m/sup 2/K). The authors report the results for the pyroelectric and dielectric properties of composites made with a polymer, P(VDF/TrFE) and various ferroelectric ceramics such as PZT, PLZT, and Ca modified PT. PLZT ceramic was chosen as a ceramic dispersoid because of its high resistivity when compared to other ferroelectric ceramics.
TL;DR: In this article, field-induced lattice rearrangement and phase transition (PT), laser beam effects in transparent ferroelectric ceramics, dopant and radiation effects in PLZT, Kerr effect demonstration and application of an intracavity matrix-addressed spatial-time modulator are discussed.
Abstract: The studies of field-induced lattice rearrangement and field-induced phase transition (PT), laser beam effects in transparent ferroelectric ceramics (TFC), dopant and radiation effects in PLZT, Kerr effect demonstration and application of an intracavity matrix-addressed spatial-time modulator are discussed.
TL;DR: In this article, electron emission from a thin plate of PTI ferroelectric ceramic has been observed by applyrng comparatively low pulse voltage, and the largest emission current in a sample having 2.L mm2electrode is 30 mA.
Abstract: Electron emission into vacuum from a thin plate of PTI ferroelectric ceramic has been observed by applyrng comparatively low pulse voltage. This electnon emission has been obtained even in poor vacuum of less than 10-1 Torr. The lowest applied pulse voltage is 75 V, and the largest emission current in a sample having 2.L mm2electrode is 30 mA. These electrons are considered to be emitted out from the surface of the ferroelectric material near the electrode by very high field induced by polarization reversal. This electron emission can be applied for elertron emitter in vacuum electronic devices such as micro triode and flat panel display.
TL;DR: In this article, the effects of high temperature annealing on dielectric properties of PbSc1/2Nb 1/2O3 and PbIn 1/ 2Nb1/ 2O3 ceramics have been examined.
Abstract: The effects of high temperature annealing on dielectric properties of PbSc1/2Nb1/2O3 and PbIn1/2Nb1/2O3 ceramics has been examined. Dispersion of dielectric permeability ϵ and dielectric loss tan δ in the region of phase transition and 20 Hz-10 kHz frequency range for different exposure (0-80 h) to high temperature is reported.