Showing papers in "Ferroelectrics in 1978"
TL;DR: In this paper, a non-linear theory of self-diffraction on the light induced grating of refractive index in electrooptic crystals is developed and the intensities of the diffracted beams, the diffraction efficiency, and the shape of the surfaces of equal index change are calculated analytically for saturation holograms.
Abstract: The non-linear theory of the self-diffraction on the light induced grating of refractive index in electrooptic crystals is developed. The intensities of the diffracted beams, the diffraction efficiency, and the shape of the surfaces of equal index change are calculated analytically for saturation holograms.Holographic storage in nominally pure reduced crystals of LiNbO3 is studied experimentally. It is shown that the developed theory in diffusion approximation satisfactorily describes the experimental data.
1,537 citations
TL;DR: In this paper, the theory of energy transfer between two coupled beams writing holograms in electrooptic crystals is developed and the gain is calculated for different processes causing holographic recording in the crystal.
Abstract: The theory of energy transfer between two coupled beams writing holograms in electrooptic crystals is developed. The gain is calculated for different processes causing holographic recording in the crystal.The amplifications of the light beam in the course of recording holograms in nominally pure reduced LiNbO3 crystals is investigated. The amplification of about 10 cm''-1 is obtained for small signals. The gain is found to be independent of the total light intensity and intensity ratio of the writing beams and decreases linearly with the grating spacing.
357 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, a theory for the air flow generation caused by centrifugal forces acting in a vibrating PVF2 multimorph fan in the resonant condition is presented, and the relevant parameters of this system are then determinable, particularly the vibration amplitude and the wing tip velocity.
Abstract: A theory is presented for the air flow generation caused by centrifugal forces acting in a vibrating PVF2 multimorph fan in the resonant condition. The vibration system is approximated by a mass acting at the center of inertial force against an elastic plate (the cantilever wing arm). The effect of air was represented by a non-linear dissipative load in the oscillating system. The relevant parameters of this system are then determinable, particularly the vibration amplitude and the wing tip velocity. These parameters determine the generated air flow velocity and volume flow rate. Air flow velocity is predicted to vary inversely as wing length, and the air volume flow rate to remain constant. These predictions agree well with experiment, particularly for larger wing lengths of the fan. Useful design information was obtained.
143 citations
TL;DR: In this paper, the behavior of the diffuse phase transition in a Pb(Zn1/3Nb2/3)O3 crystal of the disordered perovskite type was investigated.
Abstract: The behavior of the diffuse phase transition in a Pb(Zn1/3Nb2/3)O3 crystal of the disordered perovskite type was investigated. The electrooptic effect, spontaneous polarization, dielectric constant and thermal expansion were measured carefully as a function of temperature in the region of the phase transition. Using the technique suggested by Rolov, statistical treatments based on a Gaussian distribution function for the local Curie temperature were applied in interpreting the temperature dependence of various physical properties of Pb(Zn1/3Nb2/3)O3. Good agreement was obtained between the calculated and experimental results.
141 citations
TL;DR: In this paper, the light damage of Fe doped KNbO3 is interpreted in terms of photoconductivity results, and the spatial frequency dependence of the light-induced index changes indicates, that diffusion processes of charge carriers are important for light damage if the fringe spacing α of the recorded hologram is smaller than 2 μm.
Abstract: Holographic measurements of optically induced refractive index changes (light damage) of Fe doped KNbO3 are interpreted in terms of photoconductivity results. In “undoped” KNbO3 the light damage is one order of magnitude smaller than in LiNbO3-The light induced index changes can be drastically reduced or enhanced by applying a relatively small de-field along the polar ±c axis. The space-charge field due to the “photovoltaic effect” is then increased or decreased by photoconductivity.The spatial frequency dependence of the light-induced index changes indicates, that diffusion processes of charge carriers are important for the light damage in KNbO3 if the fringe spacing α of the recorded hologram is smaller than 2 μm. For α = 0.35 μm this term is two orders of magnitude larger than the “photovoltaic effect” and the photoconductivity term.The dispersion of the absorption-and photoinduced current-density measurements yield basic information on the energy levels of the photorefractive centers controlling the i...
125 citations
TL;DR: In this paper, the E, T phase diagram of lead zirconate in electric fields up to 1,400 kV/cm was described, and the E-T phase diagram was shown to be stable in the presence of lead-zirconite.
Abstract: The paper describes the E, T phase diagram of lead zirconate in electric fields up to 1,400 kV/cm.
82 citations
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...
80 citations
TL;DR: The results of measurements of spontaneous birefringence versus temperature for the fully ferroelectric/fully ferroelastic phases of Mg-Cl, Cr-Cl and Mn-Cl are discussed in this paper.
Abstract: The techniques and results of measurements of the spontaneous birefringence versus temperature are discussed for the fully ferroelectric/fully ferroelastic phases of Mg-Cl, Cr-Cl, Mn-Cl, Mn-Br, Mn-I, Fe-Cl, Fe-Br, Fe-I, Co-Cl, Co-Br. Co-I, Ni-Cl, Ni-Br, Cu-Cl, Cu-Br, Zn-Cl, Zn-Br, Zn-I, Cd-Cl, Cd-Br and Cd-I boracites. Three types of phase sequence occur: 43m↔mm2↔m↔3m (Fe-Cl, Fe-I, Co-Cl, Zn-Cl), 43m↔mm2↔3m (Fe-Br) and 43m↔mm2 (all other compositions). All transitions are of first order. The magnetic ones are excluded from discussion.Crystallophysical and potential technological applications of the spontaneous birefringence are commented:-Light gates (display, page composers, holographic storage): the favorable symmetry species 43mFmmm2, 43mFm, 43mF3m and the high spontaneous birefringence of boracites allow light gate devices with longitudinal electrode configuration. Feasibility studies on single crystalline Fe-I and of epitaxial growth of Ni-Cl boracite show that the development of zero shear compositi...
77 citations
TL;DR: In this article, the photoconductivity of LiNbO3 was studied in the visible and near uv region, where Fe-crystals were oxidized and partially reduced by annealing treatments.
Abstract: The photoconductivity of LiNbO3: Fe-crystals oxidized and partially reduced by annealing treatments is studied in the visible and the near uv-region. The measurements yield information on the influence of Fe2 +- and Fe3 +-ions.
67 citations
TL;DR: In this article, a high-resolution structural study of strain-free SrTiO3 in its cubic phase at room temperature was performed and it was shown that the oxygen thermal motion is not very significantly anharmonic.
Abstract: A high-resolution structural study of strain-free SrTiO3 in its cubic phase at room temperature shows that the oxygen thermal motion is not very significantly anharmonic.
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 paper, the authors compared the charge transport giving rise to the photovoltaic effect with the photoconductivity in the photon energy range from 2.5 eV to 5 eV.
Abstract: The charge transport giving rise to the photovoltaic effect is compared with the photoconductivity in the photon energy range from 2.5 eV to 5 eV. The photoconductivity at 2.5 eV is activated with about the same activation energy as the Hall mobility, which was measured for reduced samples between room temperature, where it is 1.1×10−3 cm2/Vs, and 200°C. The dependence on temperature, intensity, and time demonstrates different charge transport mechanisms for the short-circuit photocurrent and for the photoconductivity.
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 article, photo assisted domain switching (PDS) is used to store high resolution, high contrast, nonvolatile optical information, including gray scale images in PLZT ceramics.
Abstract: A photoferroelectric effect described as photoassisted domain switching (PDS) is used to store high resolution, high contrast, nonvolatile optical information, including gray scale images in PLZT ceramics Image storage is achieved by switching the ferroelectric remanent polarization while exposing the image on one of the indium tin oxide electroded surfaces of a PLZT plate, using near-UV light at the PLZT band gap energy (335 eV) PDS eliminates the photoconductive films required in previous PLZT image storage devices Some characteristics of the PDS effect which apply to image storage and selective erasure are described Image processing to achieve contrast enhancement is also discussed
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.
TL;DR: In this article, the existence of three phase transitions at 106°C, 184°C and 282°C for the pyrochlore structure of Cd2NB2O6S.
Abstract: Several compounds with the pyrochlore structure have been investigated. Dielectric and structural studies of the compound Cd2NB2O6S show the existence of three phase transitions at 106°C, 184°C and 282°C. The ferroelectric properties have been studied by several methods (x-Ray, DTA, dielectric and dilatometric methods, second harmonic generation). We also discuss some structural hypotheses. Bi2MIIIMvO7, oxides (MIII=Cr, Fe, In, Sc; Mv=Nb, Ta, Sb) with the cubic pyrochlore structure have been prepared. Some compounds exhibit broad maxima in the temperature dependence of the dielectric constant and the tangent of dielectric loss angle.
TL;DR: In this article, the soft mode in PbHPO4 is of a relaxational type with the relaxation time τ ≃ 5.3 · 10−11 (T-Tc )-1s for T>Tc =310 K and τ = 1.3 −1 −1 s for T
Abstract: Polarized far-infrared reflectivity and submillimetre transmittance measurements revealed that the soft mode in PbHPO4 is of a relaxational type with the relaxation time τ ≃ 5.3 · 10−11 (T-Tc )-1s for T>Tc =310 K and τ ≃ 1.3 · 10−11 (Tc-T)−1 s for T
TL;DR: In this article, the symmetry aspects of probable distortions in perovskite-like crystals are discussed and four soft modes of the lattice which are condensed at different conditions lead to the distortions.
Abstract: The symmetry aspects of probable distortions in perovskite-like crystals are discussed. Four soft modes of the lattice which are condensed at different conditions lead to the distortions. The superpositions of the independent distortions (tilts and polar displacements) are considered and the symmetry of the phases is derived. The sequences of phase transitions in the ABX3-crystals are analysed.
TL;DR: In this paper, the permittivity and spontaneous polarization of LHP(PbHPO4) single crystals prepared by a gel method were measured in a wide range of temperatures and the effect of dc bias on permittivities above the transition was also studied.
Abstract: The permittivity and spontaneous polarization of LHP(PbHPO4) single crystals prepared by a gel method were measured in a wide range of temperatures. The effect of dc bias on permittivity above the transition was also studied.
TL;DR: In this article, the effects of hydrostatic pressure on the static dielectric constant, ec, Curie-Weiss constant, C, saturation polarization, Ps, and transition temperature, Ts, of the ferroelectrics K(H 1-xDx)2PO4, and RbH 2PO4 were investigated.
Abstract: The effects of hydrostatic pressure on the static dielectric constant, ec, Curie-Weiss constant, C, saturation polarization, Ps, and transition temperature, Ts, of the ferroelectrics K(H1-xDx)2PO4, and RbH2PO4 were investigated. The pressure dependence of Tc is known from earlier work and the present work extends the results to other deuterium concentrations, x; however, the results on C and Ps are largely new. An important feature of the results is the strong dependence of the pressure derivatives of these quantities on deuteration. The results are analyzed in terms of the order-disorder and the coupled proton-phonon models. The order-disorder model provides a good account of the results for the heavily deuterated (x ≃ 1) crystals but not for the lightly deuterated ones. For the latter crystals the coupled proton-phonon model appears satisfactory. In fact the use of known microscopic parameters and their pressure derivatives in this model provides an essentially quantitative account of the pressure depen...
TL;DR: In this article, the charge transport parameters describing the anomalous bulk photovoltages and photocurrents in KNbO3 with different Fe concentrations have been evaluated and the photosensitivity, i.e., the refractive index changes per absorbed energy density, has been derived.
Abstract: The charge transport parameters describing the anomalous bulk photovoltages and photocurrents in KNbO3 with different Fe concentrations have been evaluated. From these parameters the photosensitivity, i.e. the refractive index changes per absorbed energy density, has been derived. The samples used in this study have been prepared by reduction or oxidation treatment in order to obtain dark conductivities varying between 10-6 and 10-13 (ω · cm)-1. Photovoltages between 2 V/cm and 800 V/cm have been measured depending on dopant concentration and chemical treatment.
TL;DR: The domain structure of a TGS crystal can be seen under a polarizing microscope on a cleaved crystal surface covered with the nematic MBBA crystal in this paper, where the electric field can be applied on the TGS sample and slow domain switching directly observed.
Abstract: The domain structure of a TGS crystal can be seen under a polarizing microscope on a cleaved crystal surface covered with the nematic MBBA crystal. The domains with the minus end of Ps at the surface appear as dark areas at the extinction of the TGS sample (which corresponds to homeotropic alignment of liquid crystal molecules), in contrast with the antiparallel ones, which are bright (due to the parallel orientation of molecules). For observation of the domain structure close to the phase transition, MBBA + EBBA mixture is to be used. The electric field can be applied on the TGS sample and slow domain switching directly observed.
TL;DR: In this article, the temperature dependence of dc steady state conductivity was measured in the three crystallographic directions for pure and y-irradiated TGS single crystals, and an exponential law was obeyed from 20 to 80°C, with a change in activation energy at Tc.
Abstract: The temperature dependence of dc steady state conductivity was measured in the three crystallographic directions for pure and y-irradiated TGS single crystals. An exponential law is obeyed from 20 to 80°C, with a change in activation energy at Tc. The electric conductivity is the highest along the c-axis. The three activation energies increase slowly with increasing defect concentration in the paraelectric state. In the ferroelectric phase, they increase initially up to about 0.5 MR and then decrease. Various radiation-induced changes in the three axes may suggest that the electric conductivity in TGS can vary in type from different crystallographic directions.
TL;DR: In this paper, it has been demonstrated that high pressure is an extremely useful (sometimes essential) variable in elucidating the properties of a variety of classes of ferroelectrics.
Abstract: The hydrogen bond plays an all important role in determining the physical properties of a variety of classes of ferroelectrics and antiferroelectrics of which potassium dihydrogen phosphate (KDP), lithium trihydrogen selenite and Rochelle salt are examples. This role is evidenced by the usually large isotope effects on the static and dynamic properties of these materials observed on deuteration. It has been demonstrated that high pressure is an extremely useful (sometimes essential) variable in elucidating these properties. Results on both deuterated and nondeuterated crystals will be summarized and discussed illustrating the usefulness and/or uniqueness of pressure as a variable in such studies. Emphasis will be on the KDP-class of crystals as this is the class which has been most widely studied and understood.
TL;DR: In this article, the fundamental features of successive transitions from the prototype to the incommensurate phase and then to the commensurate phases, induced by the instability of an irreducible representation from which the Lifshitz invariant can be constructed, are clarified, and discussed in the relationship with the phase transitions actually observed in ammonium fluoroberyllate and potassium selenate.
Abstract: The fundamental features of successive transitions from the prototype to the incommensurate phase and then to the commensurate phase, induced by the instability of an irreducible representation from which the Lifshitz invariant can be constructed, are clarified, and discussed in the relationship with the incommensurate phase transitions actually observed in ammonium fluoroberyllate and potassium selenate. Detection of two soft modes in potassium selenate in the incommensurate and the commensurate phases, by means of the Raman scattering experiments, will be mentioned.
TL;DR: In this article, the photo effect of an incident photon flux is primarily a change in a vibronic quantum number of the absorbing species, and several localized or delocalized couplings could be modified in ferroelectrics: e.g., electron-phonon interaction, the deformation-potential modulation, the electron-order parameter fluctuation coupling, electronion interaction.
Abstract: Photoferroelectricity is a new field which combines the photoelectric and ferroelectric phenomena.Different photoferroelectric processes can occur in pure, doped (compensated or uncompensated), semiconducting, partially ordered, polarized states. The relevant models are deduced and their application to photonic systems is discussed.The photoeffect of an incident photon flux is primarily a change in a vibronic quantum number of the absorbing species. Following this change several localized or delocalized couplings could be modified in ferroelectrics: e.g. the electron-phonon interaction, the deformation-potential modulation, the electron-order parameter fluctuation coupling, the electronion interaction.A set of “photoferroelectric” models is derived from these photoinduced couplings: the photoexcited ion model (Frank-Condon coupling), the photo-ferropolaron, the pseudo-Jahn-Teller optical centre (local vibrational hybridization), the Jahn-Teller optical centre, the Glass model (a polar character for the el...
TL;DR: In this paper, a simple model was developed to explain charge transfer effects in E.O. crystals by assuming pair formation of defects having dipole character, and orientation of these dipoles parallel to the internal polarization.
Abstract: A simple model is developed to explain charge transfer effects in E.O. crystals by assuming pair formation of defects having dipole character, and orientation of these dipoles parallel to the internal polarization.
TL;DR: In this paper, a neutron-diffraction structural study of the ferroelectric phase at room temperature (about Tc −20 K) shows partial onset of order in agreement with the observed half-saturation of Ps, at this temperature.
Abstract: PbHPO4 is believed to have a ferroelectric transition of the KDP-type. A neutron-diffraction structural study of the ferroelectric phase at room temperature (about Tc −20 K) shows partial onset of order in agreement with the observed half-saturation of Ps , at this temperature.