Showing papers on "Ferroelectricity published in 1988"
TL;DR: In this paper, a new switching process was observed in surface stabilized ferroelectric liquid crystals, associated with a third stable state in addition to the well-known bistable states.
Abstract: A new switching process was observed in surface stabilized ferroelectric liquid crystals. The switching is associated with a third stable state in addition to the well-known bistable states. The appearance of the third state is characteristic of materials with a large spontaneous polarization and is caused by minimizing induced polarization charges. The switching between each bistable state and the third state exhibits a sharp dc-threshold and hysteresis, suggesting a possible application for a switching device.
380 citations
TL;DR: In this paper, the internal bias field which is observed in many ferroelectric materials is explained semiquantita-tively by Dipolar defects in the Ferroelectric cause div P # O at the defect sites.
Abstract: The internal bias field which is observed in many ferroelectric materials is explained semiquantita-tively Dipolar defects in the ferroelectric cause div P # O at the defect sites The el
321 citations
TL;DR: In this article, the ac field dependence of the polarization and strain responses of three different compositions of doped lead zirconate titanate ceramics were measured for samples in both the poled and depoled states.
Abstract: The ac field dependence of the polarization and strain responses of three different compositions of doped lead zirconate titanate ceramics were measured for samples in both the poled and the depoled states. The results indicate that a reversible domain wall excitation exists which contributes to the weak‐signal response of these materials. Irreversible domain wall motion can be excited within the frequency range measured by applying a field above a threshold field, which is much smaller than the coercive field. Therefore, the weak‐signal linear dielectric, piezoelectric, and elastic coefficients of these materials may not provide a suitable description of their behavior when the external applied field exceeds this threshold field. All the observed phenomena can be explained by thermally activated domain wall fluctuations and nucleations.
227 citations
Patent•
28 Jul 1988
TL;DR: In this article, a liquid crystal device including a ferroelectric liquid crystal disposed between plates treated to enforce a particular magnetometer orientation to the plates is described. But the plates are spaced by a distance sufficiently small to ensure unwinding of the helix typical in a bulk of the material to form either monostable, bistable or multistable states which exhibit novel electrooptic properties.
Abstract: A liquid crystal device including a ferroelectric liquid crystal disposed between plates treated to enforce a particular ferroelectric molecular orientation to the plates. The devices employ alone or in combination non-planar boundary conditions, polar boundary conditions, boundaries with multiple physical states, intrinsic spontaneous splay distortion of the polarization orientation field, combined ferroelectric and dielectric torques, layers tilted with respect to the plates. The plates are spaced by a distance sufficiently small to ensure unwinding of the helix typical in a bulk of the material to form either monostable, bistable or multistable states which exhibit novel electro-optic properties. The liquid crystal is responsive to an externally applied electric field, temperature or the like to make a light valve or other electro-optical device.
174 citations
TL;DR: In this paper, a thermodynamic phenomenological formulation of a theory capable of displaying electromechanical hysteresis effects in continous media, which should apply to ferroelectric ceramics, is presented.
167 citations
TL;DR: In this article, a review of dielectric aging and a discussion of the possible mechanisms that may be responsible for the time dependent decrease in complex dielectrics constant is presented, divided into three material systems: barium titanate, PZT and relaxors.
Abstract: This paper is a review of dielectric aging and a discussion of the possible mechanisms that may be responsible for the time dependent decrease in complex dielectric constant. The discussion is divided into three material systems: barium titanate, PZT and relaxors. Aging is considered as it affects the real portion of the dielectric constant, tanδ and P-E hysteresis loops.
155 citations
TL;DR: The ferroelectric effect has been demonstrated for sol-gel derived lead zirconate titanate (PZT) thin films with simple and compatible with Si planar technology, and offers a wide variety of potential uses for counting, memory, and integrated optical circuit applications.
Abstract: The ferroelectric effect has been demonstrated for sol-gel derived lead zirconate titanate (PZT) (53/47) thin films The respective values of coercive field and remanent polarization were 4*10/sup 6/ V/m and 036 C/m/sup 2/ The thin-film fabrication process is simple and compatible with Si planar technology, and offers a wide variety of potential uses for counting, memory, and integrated optical circuit applications >
155 citations
TL;DR: Fast switching displays with memory properties are provided, which can display digits, symbols, and images, and which contain as chemically and thermally stable ferroelectric liquid crystalline substances.
Abstract: Fast-switching displays with memory properties are provided, which can display digits, symbols, and images, and which contain as chemically and thermally stable ferroelectric liquid crystalline substances, according to the invention, liquid crystalline derivatives which contain a chiral alkyl halide residue corresponding to the general formula ##STR1## are used in mixtures of one another as well as in conjunction with other liquid crystalline or non-crystalline liquid substances.
151 citations
TL;DR: In this article, surface acoustic wave delay lines on polycrystalline lead zirconate titanate [Pb(Zr,Ti)O3 or PZT] thin films were fabricated on glass substrates.
Abstract: Piezoelectric activity in reactively sputtered lead zirconate titanate [Pb(Zr,Ti)O3 or PZT] thin films has been confirmed through the fabrication of surface acoustic wave delay lines on poled polycrystalline films of PZT deposited on glass substrates. Films of varying thickness ranging from 3.4 to 6 μm show a dispersion in resonant frequency for interdigital transducers designed to resonate at 44 MHz on bulk PZT material. The electromechanical coupling coefficient k2 was in the range 0.57–0.79% for hk=0.21–0.37.
131 citations
TL;DR: In this paper, the authors measured electrical and spectroscopic properties of thin films of ferroelectric ceramic potassium nitrate and developed a mean field theory which explicitly incorporates film thickness effects.
Abstract: We have measured electrical and spectroscopic properties of thin films (d = 75–500 nm) of ferroelectric ceramic potassium nitrate and developed a mean field theory which explicitly incorporates film thickness effects. Variations of Tc(d) are observed as are changes in the shape of Ps(T) with thickness. Comparisons with earlier work on TGS are made.
129 citations
TL;DR: Clark and Lagerwall as discussed by the authors showed a fast electro-optic effect in a surface-stabilized ferroelectric liquid crystal (SSFLC) structure, which was later used in the development and characterization of a number of compounds and mixtures.
Abstract: The last decade has seen a tremendous growth in the research and development activities in the area of ferroelectric liquid crystals. The field was opened up by the work of Meyer in 1974, and has now grown rapidly into one of the major research areas in liquid crystal science. The emphasis of the earlier work was on basic material characterization and phenomenology. Only very few liquid crystalline compounds exhibiting a ferroelectric phase were known at that time, and furthermore these Schiff-base organic compounds were chemically and thermally unstable and presented their ferroelectricity only at elevated temperatures. After the work by Clark and Lagerwall in 1980 on a fast electro-optic effect in a surface-stabilized ferroelectric liquid crystal (SSFLC) structure, both basic and applied research have accelerated, and today a great number of papers deal with development and characterization of ferroelectric compounds and mixtures and various aspects of device physics and manufacturing. It is of...
TL;DR: In this article, the soft mode (SMFLC) was introduced, where instead of using the phase variable Φ, it uses the tilt angle θ, which in principle is a hard variable, but is expected to soften on approaching the transition to a lower-lying adjacent tilted smectic phase.
Abstract: In this paper a presentation is given of some of the basic physics of the soft-mode ferroelectric effect, along with its experimental background. Further, possible applications in electrooptic devices are elucidated. A fast (sub-microsecond) electrooptic switching can be achieved in the A* phase, and in similar orthogonal smectic phases made up of chiral molecules. Instead of using the phase variable Φ, it uses the tilt angle θ, which in principle is a “hard” variable, but is expected to soften on approaching the transition to a lower-lying adjacent tilted smectic phase. However, the switching is efficient in the whole range of the orthogonal phase (in fact, less efficient near the tilting transition) and is observed whether an adjacent tilted phase is present or not. As compared to the surface-stabilized (SSFLC) electrooptic mode, this soft mode (SMFLC) is based on the electro clinic, effect of essentially ferroelectric nature very closely related to the presently more investigated ferroelectric...
TL;DR: In this paper, the crystals of (CH3NH3)3Bi2Br9 have been grown which at room temperature are isomorphous with Cs3Bi 2Br9 and CH3NH 3 Sb 2Br 9 and showed three phase transitions at 188 ± 0.5, 140 ± 1, and 101.5 K.
Abstract: The crystals of (CH3NH3)3Bi2Br9 have been grown which at room temperature are isomorphous with Cs3Bi2Br9 and (CH3NH3)3Sb2Br9. The space group is P3m1, a = 0.807, c = 1.008 nm, V = 0.5685 nm3, Z = 1. The crystals reveal, when cooling, three phase transitions at 188 ± 0.5, 140 ± 1, and 101.5 ± 0.5 K. The high temperature phase (I) behaves as a plastic one with respect to a freedom of rotation of methylammonium cations. The two high temperature transitions I II and II III can be related, similarly to (CH3NH3)3Sb2Br9, to a freezing of reorientation of those cations. At 101.5 K a transition to the improper ferroelectric phase IV was discovered. The features of this phase are non-typical and the nature of the transition is unknown.
TL;DR: In this article, thin films of ferroelectric Pb1−xCaxTiO3 (x=0.0-0.4) were formed on MgO, Pt/MgO and SrTiO 3 substrates by rf magnetron sputtering.
Abstract: Thin films of ferroelectric Pb1−xCaxTiO3 (x=0.0–0.4) were formed on MgO, Pt/MgO, SrTiO3, and Pt/SrTiO3 substrates by rf magnetron sputtering. Characterization of the films by x‐ray diffraction, x‐ray precession, scanning electron microscopy, and electron probe microanalysis showed them to be epitaxially grown with their c‐axis oriented perpendicular to the substrate. The decrease in the Curie temperature Tc and the increase in the pyroelectric coefficient dPs/dT with an increase in Ca doping were successfully explained by assuming that the Ca ions occupied Pb ion sites. Pyroelectric infrared detectors using Pb0.7Ca0.3TiO3 thin‐film elements gave better performance than the detectors using PbTiO3 ceramic elements. The internal bias field EB and fixed polarization PB were observed to be a function of both the Ca content and temperature in ferroelectric hysteresis curves as well as in hysteresis curves of the dielectric constant as a function of the applied electric field. These phenomena were explained by t...
TL;DR: Several addition compounds of the amino acid betaine and inorganic acids were found in the last years to possess structural, ferroelastic and antiferroelectric phase transitions as discussed by the authors.
Abstract: Several addition compounds of the amino acid betaine and inorganic acids were found in the last years to possess structural, ferroelastic, ferroelectric or antiferroelectric phase transitions. As well commensurate as incommensurate phases are observed. The materials are betaine phosphate (antiferroelectric), betaine arsenate (ferroelectric, but antiferroelectric if deuterated), betaine borate (ferroelastic), betaine phosphite (ferroelectric), and betaine calcium chloride dihydrate (several commensurate and incommensurate phases with soft mode behavior, ferroelectric in its lowest phase).
Patent•
13 Jun 1988TL;DR: In this paper, the authors provided a ferroelectric liquid crystal device where the yellowing due to a cell thickness increase or occurrence of voids is suppressed, and the device consisted of a pair of substrates each having thereon a group of electrodes for liquid crystal drive, and a layer of liquid crystal disposed between the substrates, wherein thermosetting adhesive particles and thermoplastic polymer particles having a diameter which is 1.5-5 times the liquid crystal layer thickness are dispersed and pressed between the substrate.
Abstract: There is provided a ferroelectric liquid crystal device wherein the yellowing due to a cell thickness increase or occurrence of voids is suppressed. The ferroelectric liquid crystal device includes a pair of substrates each having thereon a group of electrodes for liquid crystal drive, and a layer of ferroelectric liquid crystal disposed between the substrates, wherein thermosetting adhesive particles and thermoplastic polymer particles having a diameter which is 1.5-5 times the liquid crystal layer thickness are dispersed and pressed between the substrates. The polymer particles preferably have a glass transition temperature of at most -20° C.
TL;DR: In this paper, the spontaneous polarization is used as the true order parameter for liquid ferroelectric phases (proper ferroelectrics) in the presence of spontaneous polarization, which has not yet been discovered.
Abstract: The idea either to reveal or to construct a liquid ferroelectric was never abandoned by researchers since the discovery of ferroelectricity in solid crystals at the beginning of this century. In principle, nature does not forbid the existence of ferroelectric liquids. For instance, a centro-symmetric liquid can change its point symmetry from the K h , to C∝v , group with the formation of a uniform ferroelectric phase. A liquid without the inversion center can have a phase transition K → C∝, into the inhomogeneous, helical structure. In both these hypothetical cases the spontaneous polarization, P s , would play the role of the true order parameter. However, such liquid ferroelectric phases (proper ferroelectrics) have not been discovered as yet.
TL;DR: Ferroelectric smectic liquid crystalline polymers were synthesized in this article, which are acrylate polymers whose side chains contain a flexible spacer unit, a mesogen unit and an optically active substrate.
Abstract: Ferroelectric smectic liquid crystalline polymers were synthesized. They are acrylate polymers whose side chains contain a flexible spacer unit, a mesogen unit and an optically active substratate. Their liquid crystalline properties were determined by DSC analysis, optical microscopy, X-ray diffraction and the observation of spontaneous polarization. The response time was as small as milliseconds.
TL;DR: In this paper, the complex admittance was measured for CsH2PO4 in the frequency range from 30 Hz to 60 MHz and in the temperature range 90-550 K. The domain wall relaxation time was found to decrease anomalously when approaching to Tc.
Abstract: The complex admittance was measured for CsH2PO4 in the frequency range from 30 Hz to 60 MHz and in the temperature range 90-550 K. The domain wall relaxation time was found to decrease anomalously when approaching to Tc. From the investigations of the conductivity of CDP the structural phase transition at Tsi.=503K was shown to be superionic.
TL;DR: In this paper, the authors measured the frequency and temperature dependence of the complex dielectric constant near the Smectic-A liquid-crystal phase (Sm-${C^{\mathrm{*}}$--Sm-A) transition for two ferroelectric liquid crystals with a very large spontaneous polarization.
Abstract: The frequency and temperature dependence of the complex dielectric constant was measured near the smectic-${C}^{\mathrm{*}}$--smectic-A liquid-crystal phase (Sm-${C}^{\mathrm{*}}$--Sm-A) transition for two ferroelectric liquid crystals with a very large spontaneous polarization. The dielectric strengths as well as the corresponding relaxation frequencies of the dielectric modes were determined. Due to the large polarization we were able to resolve the contributions from the soft mode and the Goldstone mode in a comparatively large temperature interval in the Sm-${C}^{\mathrm{*}}$ phase close to the transition to the Sm-A phase. In the Sm-A phase, the relaxation frequency and the inverse dielectric strength of the soft mode decrease linearly when approaching ${T}_{c}$. Comparing the experimental data with a recent theoretical calculation of the complex dielectric constant, we conclude that we have a fairly good understanding of the behavior of the complex dielectric constant in the whole Sm-${C}^{\mathrm{*}}$--Sm-A transition range.
TL;DR: In this article, a ferroelectric liquid crystal electrooptic device was demonstrated using polyimide Langmuir-Blodgett films for the orientation of the liquid crystals without performing rubbing.
Abstract: Excellent bistability was demonstrated in a ferroelectric liquid crystal electrooptic device prepared using polyimide Langmuir-Blodgett films for the orientation of the liquid crystals without performing rubbing.
TL;DR: Betaine phosphite, an addition compound of the amino acid betaine and phosphorous acid, can be grown in single crystal form from aqueous solutions Structural, optical, dielectric, and caloric data of this new material are reported at least two phase transitions are observed in (CH3)3NCH2COO˙H3PO3.
Abstract: Betaine phosphite, an addition compound of the amino acid betaine and phosphorous acid, can be grown in single crystal form from aqueous solutions Structural, optical, dielectric, and caloric data of this new material are reported At least two phase transitions are observed in (CH3)3NCH2COO˙H3PO3 The lower one, around 216 K, leads to a ferroelectric phase with a spontaneous polarization of about 17 μC/cm2
TL;DR: In this article, the temperature dependence of dielectric polarization, permittivity, and the E −field dependence of the permittivities of tetragonal tungsten bronze ferroelectrics in the strontium barium niobate system has been investigated.
Abstract: The tetragonal tungsten bronze ferroelectrics in the strontium barium niobate system have been extensively studied over many years. As for many of the bronzes, a crude interpretation of the experimental data has been attempted in the past using the simple Landau‐Ginsburg‐Devonshire expansion of the Gibbs free energy as a Taylor series in powers of the polarization, lumping all the temperature dependence into the lowest order term. In this paper new measurements are presented for the temperature dependence of dielectric polarization, permittivity, and the E‐field dependence of the permittivity. It is shown that for a realistic fitting of the data, the Taylor expansion must be taken to at least the eighth power term, and that the coefficients of terms up to the sixth power must be taken as functions of temperature. Since the phenomenology describes equilibrium behavior, it is the total static polarizability that is being explored in this treatment. The nature of this temperature dependence strongly suggests that the phase transition from a macropolar to a macrononpolar state is tetracritical.
TL;DR: It is shown that reasonable electric dipole interactions between diskshaped molecules may lead to a ferroelectric nematic phase, and the phase diagram is calculated using mean-field theory.
Abstract: There is no fundamental reason that fluids should not be ferroelectric. However, the only knownferroelectric fluids are chiral smectic-$C$ liquid crystals and related structures. We examine the possibility that molecules with permanent dipole moments can form a ferroelectric nematic phase, the least ordered conceivable ferroelectric phase. We show that reasonable electric dipole interactions between diskshaped molecules may lead to such a phase, and calculate the phase diagram using mean-field theory. Some constraints on the constituent molecules are discussed.
TL;DR: In this paper, a model for the electric response of a ferroelectric liquid crystal cell on application of an electric field was proposed. And the relation between the rotational viscosity and spontaneous polarization was derived for the application of a triangular wave voltage.
Abstract: Rotational viscosity and spontaneous polarization are the most important properties of a ferroelectric liquid crystal with regard to its switching time in surface stabilized or a.c. field stabilized displays. Whereas there is an abundant literature about spontaneous polarization, only a few attempts have been made to determine the rotational viscosity. We set up a model for the electric response of a ferroelectric liquid crystal cell on application of an electric field. For the application of a triangular wave voltage we derive a relation between the rotational viscosity, the spontaneous polarization, the tilt angle, the maximum induced polarization current and the electric field strength. Experiments are carried out on several ferroelectric liquid crystals and the derived relation was used to determine the rotational viscosity. The relation between the rotational viscosity and the polarization on the one hand and the optical switching time on the other hand is discussed in some detail.
TL;DR: In this paper, the requirements for ferroelectric liquid crystals (FLC) for an application in fast-switching electro-optic devices are summarized and typical molecular structures for FLC-mixtures are discussed.
Abstract: The requirements for ferroelectric liquid crystals (FLC) for an application in fast-switching electro-optic devices are summarized. Typical molecular structures for FLC-mixtures are discussed. New non-chiral SmC-substances as well as some chiral dopants are shown. Important material parameters which are presented include spontaneous polarization, tilt angle, helical pitch in the smectic and cholesteric phase, rotational viscosity, response time, optical anisotropy and dielectric anisotropy. New developed broad range FLC-mixtures with SmC*-phases, SmI*-phases or SmA*-phases at room temperature are introduced.
TL;DR: In this paper, a ferroelectric phase can be induced in PMN crystals by an electric field parallel to [110], [111], and [001], but only for optical investigations and X-ray analysis.
Abstract: Hysteresis loops and remanent polarization below Tt -70 °C suggest that a ferroelectric phase can be induced in PMN crystals by an electric field parallel to [110], [111], and [001]. This could be corroborated, however, only for the two former cases by optical investigations and X-ray analysis.
TL;DR: A thermodynamic model of the ferroelectric SmC* phase, based on an extended Landau expansion of the free energy density, is presented in this article, where the signs of the parameters entering the model are depending on whether the pitch of the helix is right-handed or left-handed and whether the compound is of the (+) or (-) type in regard to the sign of the polarization.
Abstract: A thermodynamic model of the ferroelectric SmC* phase, based on an extended Landau expansion of the free-energy density, is presented We discuss how the signs of the parameters entering the model are depending on whether the pitch of the helix is right-handed or left-handed and whether the compound is of the (+) or (-) type in regard to the sign of the polarization With the introduced Landau expansion as a basis, we derive the equations governing the behaviour of the tilt, polarization, pitch, dielectric susceptibility and heat capacity of the system We show that by rewriting the equations into dimensionless form, we can transform the original set of eleven parameters in the Landau expansion into a new set, consisting of six dimensionless parameters and five scaling factors The six dimensionless parameters are the only ones which enter the calculations of the quantities mentioned above, ie we need six dimensionless parameters to describe the temperature dependence of the five basic quantiti
TL;DR: In this article, the implications of a free energy expression for two media in contact are discussed, and exact implicit equations for the critical temperatures of two semi-infinite media are derived for the film of one medium embedded in another, and of a superlattice structure.
TL;DR: In this article, a transmission electron microscopy study of the order-disorder perovskite Pb(In 1/2Nb1/2)O3 (PIN) has shown that its microstructures are dependent on the In: Nb B-site cation distribution.
Abstract: A transmission electron microscopy study of the order-disorder perovskite Pb(In1/2Nb1/2)O3 (PIN) has shown that its microstructures are dependent on the In: Nb B-site cation distribution. In disordered PIN the dielectric properties are those of a relaxor ferroelectric. Lowering the temperature of disordered PIN by means of a liquid nitrogen-cooled stage has been found to stabilize polar ferroelectric micro-domains, ∼ 20 to 30 nm in size. On increasing the long range order of the B-site cations to give ordered domains > 80 nm in size, an antiferroelectric phase is shown to develop that is isostructural with the antiferroelectric perovskite, PbZrO3. Coexisting antiferroelectric and non-antiferroelectric regions have been observed in partially ordered PIN.