Showing papers on "Ferroelectricity published in 1978"
TL;DR: In this paper, it was shown that changes induced in the orientation of the axes of crystallites in thin films of polyvinylidene fluoride by the application of 6×107 V/m at 100°C for 1/2h have been observed.
Abstract: Changes induced in the orientation of the axes of crystallites in thin films of polyvinylidene fluoride by the application of 6×107 V/m at 100 °C for 1/2 h have been observed. The changes were observed by measuring the intensity of x rays diffracted from the film as a function of the orientation of the film relative to the diffracting x‐ray beam. A simple model calculation shows that the results are consistent with the assumption that the changes are induced by the interaction of the applied electric field with the dipole moments of the polyvinylidene fluoride molecules. The model uses the fact that the orthorhombic symmetry of the unit cell results from a small distortion of a hexagonal primitive lattice, the distortion being a 1% decrease in the separation between molecules in the direction of the dipole moments. This model is consistent with the assumption that polyvinylidene fluoride is ferroelectric.
296 citations
TL;DR: The dispersion relations for molecular orientation fluctuations in a freely suspended ferroelectric smectic-C$ liquid-crystal film have been determined by inelastic light scattering.
Abstract: The dispersion relations for molecular-orientation fluctuations in a freely suspended ferroelectric smectic-$C$ liquid-crystal film have been determined by inelastic light scattering The smectic-$C$ film geometry appears to be ideal for the experimental study of the space-time behavior of a two-dimensional orientational field
241 citations
227 citations
TL;DR: In this paper, an analysis of the ac deconstriction of the hysteresis loop and microscopical observation of moving domain walls was performed, and it was concluded that the ferroelectric domain stabilization in Mn-doped BaTiO3 crystals is due to bulk effects.
Abstract: From an analysis of the ac deconstriction of the hysteresis loop and microscopical observation of moving domain walls, it is concluded, that the ferroelectric domain stabilization in Mn-doped BaTiO3 crystals is due to bulk effects. Esr measurements have revealed that in reduced crystals Mn2+-V0 associates exist, having an excess orientation parallel to Ps-. It is hypothesized that the domain stabilization processes involve a gradual orientation of polar defect associates of this type.
168 citations
TL;DR: In this article, the authors show that tetramethylammonium tetrachlorozincate exhibits ferroelectricity along a axis in the temperature range between 3.3 and 6.0°C.
Abstract: Tetramethylammonium tetrachlorozincate, {N(CH 3 ) 4 } 2 ZnCl 4 has been found to undergo successive phase transitions at about -112, -92, 3.3, 6.0 and 20°C and to show ferroelectricity along the a axis in the temperature range between 3.3 and 6.0°C.
141 citations
TL;DR: ABO 3-type oxides have a relatively simple structure of the mineral perovskite (CaTiO 3 ) and have a cubic unit cell as discussed by the authors, however, distortions are common and depend upon the value of the tolerance factor t given by γ A + γ O /√2( γ B + ε O ).
136 citations
TL;DR: The ferroelectric and dielectric properties of La, Sr, Zr, Fe and Mn doped BaTiO3 ceramic are measured within wide limits of the amplitude Eapproximately of the external electrical AC field.
Abstract: The ferroelectric and dielectric properties of La, Sr, Zr, Fe and Mn doped BaTiO3 ceramic are measured within wide limits of the amplitude Eapproximately of the external electrical AC field. At sufficiently low Eapproximately the losses are not ferroelectric in origin but are rather determined by the low frequency relaxational response of the material, which is influenced by doping. In the ferroelectric phases a well defined threshold Eapproximately 0 exists at any composition such that the permittivity and the loss factor are independent of Eapproximately for Eapproximately Eapproximately 0 due to domain wall motions and reversal of the spontaneous polarisation Ps.Eapproximately 0 is less than 20 V cm-1 in La doped BaTiO3 and is up to 5000 V cm-1 in Fe or Mn doped samples. Compositions with large Eapproximately 0 show constricted hysteresis loops which are described by an internal bias field Ei. In Mn doped BaTiO3 both Eapproximately 0 and Ei are increased by annealing at low partial pressures of oxygen, Ei and Eapproximately 0 are a measure of the stability of the domain configuration established during ageing below the temperature of the para-electric to ferro-electric phase transition.
132 citations
TL;DR: In this article, the symmetry properties of liquid crystals with respect to the orientation of the molecules, and the conditions for the appearance of a modulated orientational structure, are considered, and a general scheme of the phase transitions between liquid-crystalline phases is given.
Abstract: All the diverse types of liquid-crystalline states can be described in a unified manner by analogy with the group-theoretical description of the symmetry and properties of crystals. The symmetry properties of liquid crystals with respect to the orientation of the molecules, and the conditions for the appearance of a modulated orientational structure, are considered. The phase diagrams in liquid crystals are described, and a general scheme of the phase transitions between liquid-crystalline phases is given. The problem of the ferroelectric state in liquids is considered, and the classes of anisotropic liquids that possess ferroelectric and piezoelectric properties are demonstrated. A thermodynamic description is given of the ferroelectric phenomena observed experimentally in smectic liquid crystals. The question of the physical nature of the low-symmetry smectic phases is discussed and the character of the phase transitions in liquid crystals is considered.
119 citations
TL;DR: In this article, the successive phase transitions from a prototype to an incommensurate phase and then to a commenurate phase are studied on the basis of a model thermodynamic potential where the instability of a one-dimensional representation is assumed.
Abstract: The successive phase transitions from a prototype to an incommensurate phase and then to a commensurate phase are studied on the basis of a model thermodynamic potential where the instability of a one-dimensional representation is assumed. The model is suitable to a unified description of the phase transitions in SC(NH 2 ) 2 and NaNO 2 which show ferroelectricity in their commensurate phases. The incommensurate states of the model and its dielectric properties are analysed by taking harmonics into account. It has turned out that the present model can satisfactorily reproduce the transitions actually observed in SC(NH 2 ) 2 and NaNO 2 .
114 citations
TL;DR: In this article, the dielectric properties of chiral liquid crystal DOBAMBC are compared with those of crystalline ferroelectrics, and temperature-variations of spontaneous polarization and relaxation time are studied.
Abstract: Measurements of electric permittivity, and polarization are reported for chiral liquid crystal DOBAMBC. Dielectric hysteresis was found. Temperature-variations of spontaneous polarization and relaxation time are studied. The dielectric properties of chiral smectic C and those of crystalline ferroelectrics are compared.
91 citations
TL;DR: In this article, the phase diagrams of four ferroelectric ceramics based on lead zirconate (PbZrO 3 ) were determined using dielectric constant and loss measurements.
TL;DR: A review of the foundation, developments and latest results of the so-called vibronic theory of ferroelectricity, a new approach to the microtheory of spontaneous polarization and phase transitions in crystals incorporating the interactions of electrons with nuclear displacements (vibronic interactions), is presented in this article.
Abstract: A review of the foundation, developments and latest results of the so-called vibronic theory of ferroelectricity—a new approach to the microtheory of spontaneous polarization and ferroelectric phase transitions in crystals incorporating the interactions of electrons with nuclear displacements (vibronic interactions), is presented.The origin of dipolar instability as due to the pseudo Jahn-Teller effect is demonstrated for a two level system and octahedral [TiO6]8- cluster and generalized for perovskite (BaTiO3) and rock salt (GeTe) type crystals; simple criterion of spontaneous polarization occurrence being derived.The ferroelectric phase transitions are considered in two approaches depending on whether the lattice stabilization at high temperatures is due to the vibronic anharmonicity or to the electron population of the conductivity band (for ferro-electrics-semiconductors). The recent more rigorous treatments, by means of diagram and Green function methods allowing for a better account of the optical m...
TL;DR: Tetramethylammonium tetrachlorocobaltate, {N(CH3)4}2 CoCl4, has been found to undergo successive phase transitions at about −151, −81, 3.0, 4.6, 7.1 and 20°C as discussed by the authors.
TL;DR: In this article, perovskite and pyrochlore structures were successfully fabricated on several kinds of substrates by rf diode sputtering, and a semiquantitative analysis of the deposited thin films were made with Auger electron spectroscopy (AES).
Abstract: Lead‐zirconate–lead‐titanate (PZT) thin films with perovskite and pyrochlore structures were successfully fabricated on several kinds of substrates by rf diode sputtering. Semiquantitative compositional analysis of the deposited thin films were made with Auger electron spectroscopy (AES). The films were deposited from targets consisting of mixed powder oxides. One target had a composition corresponding to 10 mol% PbO‐modified PZT 52/48 (Zr to Ti ratio in the PZT, target A), while the other had the composition corresponding to 10 mol% PbO‐modified PZT 42/58 (target B). The films in the perovskite structure had ferroelectricity, while the films in pyrochlore had none. The perovskite films deposited from target A had a dielectric constant of 751, a remanent polarization of 20.4 μC/cm2, and a coercive field of 23.3 kV/cm. The films deposited from target B had a dielectric constant of 654, a remanent polarization of 6.37 μC/cm2, and a coercive field of 12.2 kV/cm. The composition of the former film was PZT 60/...
TL;DR: It has been found that K 2 ZnCl 4 shows ferroelectric activity below the Curie point of 123°C (on cooling process) and spontaneous polarization is about 0.15 µCcm -2 at room temperature as discussed by the authors.
Abstract: It has been found that K 2 ZnCl 4 shows ferroelectric activity below the Curie point of 123°C (on cooling process). The spontaneous polarization is about 0.15 µCcm -2 at room temperature.
TL;DR: In this paper, the effect of aging on the temperature dependence of permittivity and tan δ as a function of frequency was examined for both ferroelectric and antiferroelectric PLZT compositions.
Abstract: The effect of aging on the temperature dependence of permittivity (K) and tan δ as a function of frequency was examined for both ferroelectric and antiferroelectric PLZT compositions. All compositions aged near their transition temperatures exhibited a marked decrease in dispersion between the aging temperature and the temperature of the high frequency (100 kHz) permittivity peak. These results are discussed in terms of the Smolenskii model for dielectric relaxation.
TL;DR: Ferroelectric hysteresis of a copolymer with tetrafluoroethylene and of uniaxially stretched polyvinylidene fluoride has been observed at 60 Hz at room temperature as mentioned in this paper.
Abstract: Ferroelectric hysteresis of a copolymer of vinylidene fluoride with tetrafluoroethylene and of uniaxially stretched polyvinylidene fluoride has been observed at 60 Hz at room temperature. The measured remanent polarization of the copolymer was in good agreement with a calculated value using a frozen dipole model and measured piezoelectric coefficients. The dielectric constant for the copolymer has been measured at 1000 Hz as a function of temperature. Also, a set of copolymer films of varying thickness were poled above the melt temperature and their piezoelectric stress coefficients g31 were measured as a function of the poling field. These measurements indicate that the copolymer, when poled above the melt temperature, exhibits bulk polarization. These results suggest that this copolymer is ferroelectric and that poling aligns the dipoles in the β crystal phase of the material.
TL;DR: Chynoweth experiments conducted at low temperatures reveal a weak pyroelectric effect which disappears above 28 K, but no anomalies in the electric permittivity or electric conductivity occur at the Neel point as mentioned in this paper.
Abstract: Chromium chrysoberyl undergoes a phase transformation from a paramagnetic state to a complex antiferromagnetic state at 28 K. The spiral spin structure of the antiferromagnetic state violates all the crystallographic symmetry elements, making Cr2BeO4 potentially ferroelectric. Chynoweth experiments conducted at low temperatures reveal a weak pyroelectric effect which disappears above 28 K. Cr2BeO4 ceramics can be poled electrically between 24 and 28 K, giving rise to remnant polarizations four to six orders of magnitude smaller than normal ferroelectrics. The pyroelectric coefficient and the remnant polarization reverse in sign with the poling field, but no anomalies in the electric permittivity or electric conductivity occur at the Neel point.
Patent•
13 Feb 1978
TL;DR: In this paper, a monolithic semiconductor integrated circuit -ferroelectric device is disclosed together with the method of manufacturing the same, which is particularly adapted for fabricating a potassium nitrate ferroelectric memory.
Abstract: A monolithic semiconductor integrated circuit - ferroelectric device is disclosed together with the method of manufacturing same. The ferroelectric device preferably consists of a layer of stable ferroelectric potassium nitrate disposed between electrical contacts positioned on opposite surfaces of the ferroelectric layer. The ferroelectric layer has a thickness of less than 110 microns, and preferably falling within a range of from 100 Angstrom units to 5,000 Angstrom units. The process of manufacturing the monolithic structure is multi-stepped and is particularly adapted for fabricating a potassium nitrate ferroelectric memory on a semiconductor integrated circuit.
TL;DR: In this paper, the properties of chiral smectic liquid crystal DOBAMBC were studied and the phenomenological description of static and dynamic phenomena connected with helix unwinding in the electric field was performed.
Abstract: Thermodynamical, optical and dielectric properties of chiral smectic liquid crystal DOBAMBC were studied. It was found that the ferroelectric phase transition in DOBAMBC is of the second order, and critical exponents for 6 (order parameter), Ps (spontaneous polarization), Cp. (specific heat) were estimated. The phenomenological description of static and dynamic phenomena, connected with helix unwinding in the electric field is performed.
TL;DR: In this paper, the dependence of the amplitude and pitch of the ferroelectric helix on the material parameters is calculated in the framework of the phenomenological theory of phase transitions, and experiments which can help to estimate the independent material constants determining the physical properties of such pseudo-proper liquid ferroelectrics are discussed.
Abstract: Ferroelectric phenomena in chiral smectic liquid crystals appearing as a result of the piezo- and flexoelectric effects in these substances are considered theoretically. The dependence of the amplitude and the pitch of ferroelectric helix on the material parameters is calculated in the framework of the phenomenological theory of phase transitions. The experiments which can help to estimate the independent material constants determining the physical properties of such pseudo-proper liquid ferroelectrics are discussed.
TL;DR: In this article, room temperature measurements of phonon dispersion relations in ferroelectric lithium niobate have been carried out by inelastic neutron scattering, and most of the measurements were made along the c* direction with two acoustic branches measured along an a* direction.
Abstract: Room temperature measurements of the phonon dispersion relations in ferroelectric lithium niobate have been carried out by inelastic neutron scattering. Most of the measurements were made along the c* direction with two acoustic branches measured along an a* direction. The q to 0 slopes of the acoustic branches are found to be in good agreement with the ultrasonic sound velocity measurements. Results on the phonon frequencies are compared with the optical data. Measurements carried out at elevated temperatures up to 900K failed to detect any softening of the 'ferroelectric mode' (the lowest-frequency optic Gamma 1 mode), thereby suggesting that the ferroelectric phase transition in lithium niobate is not associated with a soft phonon-mode instability. The possibility that the phase transition is of the order-disorder type, rather than the displacive type, is discussed, and, in this respect, similarities with the isomorphous lithium tantalate are pointed out.
TL;DR: In this paper, the Curie temperatures of these Rb compounds are near −80°C and N(CH3)4}2CoCl4 is ferroelectric in a narrow temperature range of 4.6-7.1°C.
Abstract: The compositions Rb2ZnCl4, Rb2ZnBr4, Rb2CoCl4, Rb2CoBr4 and {N(CH3)4}2CoCl4 have been found to be ferroelectric. The Curie temperatures of these Rb compounds are near −80°C. (N(CH3)4}2CoCl4 is ferroelectric in a narrow temperature range of 4.6–7.1°C.
TL;DR: In this paper, the mean-field approach to the dynamics of impurities in ferroelectric hosts has been used to support the mean field approach to determine the presence of a peak in the susceptibility near the paraelectric anomaly at 0 K. This effect is attributed to Li impurities which are frozen in an off-center position at the potassium site.
Abstract: Dielectric-constant measurements on KTaO/sub 3/:Li as a function of Li concentration, temperature, and frequency reveal the presence of a peak in the susceptibility near the paraelectric anomaly at 0 K. This effect is attributed to Li impurities which are ''frozen'' in an off-center position at the potassium site. For samples with a Li concentration of less than 24%, continuity of the elastic compliance ensures that a lattice polarization does not occur as for a true ferroelectric. Our results support the mean-field approach to the dynamics of impurities in ferroelectric hosts.
TL;DR: In this article, the response of a lead zirconate titanate ceramic to statically applied uniaxial stresses in the range 0.4 GPa has been investigated.
Abstract: The response of a lead zirconate titanate ceramic to statically applied uniaxial stresses in the range 0–0.4 GPa has been investigated. The material studied was a niobium‐doped composition with the chemical formula Pb0.99Nb0.02(Zr0.95Ti0.05)0.98O3. Properties measured as a function of stress include electrical charge release from poled specimens, ferroelectric hysteresis‐loop behavior, macroscopic strains, and ultrasonic velocities. Data from the experiments exhibit anomalous behavior at low‐stress levels (0.05–0.2 GPa). Comparison with similar data obtained under conditions of hydrostatic pressure indicate that the anomalies observed in the uniaxial‐stress experiments are caused by domain‐reorientation processes rather than by the ferroelectric to antiferroelectric phase transition. This transition occurs at 0.32 GPa under hydrostatic‐pressure conditions, but no evidence for it is seen in the uniaxial‐stress measurements to 0.4 GPa. The relationship of the present results to other uniaxial‐stress studies...
TL;DR: In this paper, the presintered layer structure bismuth compounds of PbBi2Nb2O9, Na0.5Bi4.5Ti4O15 and Pb2Bi4Ti5O18 are hot-worked by press forging under the maximum load of 200 kg/cm2 at a temperature of 1000°C to 1200°C.
Abstract: The presintered layer structure bismuth compounds of PbBi2Nb2O9, Na0.5Bi4.5Ti4O15, PbBi4Ti4O15 and Pb2Bi4Ti5O18 are hot-worked by press forging under the maximum load of 200 kg/cm2 at a temperature of 1000°C to 1200°C. The reduction ratio of height is more than 70%. The well-oriented polycrystalline samples with an orientation degree of more than 0.8 can be obtained. The measured results of dielectric and ferroelectric properties are correlated with SEM observations and x-ray diffractions.