Showing papers on "Ferroelectricity published in 1973"

Effects of Grain Size and Porosity on Electrical and Optical Properties of PLZT Ceramics

Abstract: A group of transparent ferroelectric hot-pressed (Pb0.92La0.08)-(Zr0.65Ti0.35)0.98O3 specimens with controlled grain size and constant porosity and a group of similar specimens with controlled porosity and constant grain size were prepared. The electrical and optical constants and polarization-reversal properties of these ceramics were determined as functions of grain size and porosity. When poled PLZT ceramics were aged, the polarization-reversal characteristic was quite asymmetric, apparently because a space-charge field, E8p, was generated during aging. From a detailed study of the behavior of the E8p, including its (1) generation with increasing aging time, (2) relaxation with repeated polarization reversals, (3) relaxation by heat depolarization, and (4) grain-size and porosity dependence, it is concluded that the space-charge layer is present inside every domain. This layer also explains the grain-size dependencies of the remanent polarization, piezoelectric constants, and Curie point.

Depolarization fields in thin ferroelectric films

Abstract: A mechanism is proposed to explain depolarization phenomena that have been observed in thin ferroelectric films and related multilayer devices. It is shown that, for a short‐circuited electrode‐ferroelectric structure, incomplete compensation of the ferroelectric polarization charge results when the center of gravity of this charge and the free compensation charge are not coincident. Depolarization fields in the ferroelectric arising from such incomplete compensations are estimated. A simple switching calculation shows such fields to be of sufficient strength to account for the initial polarization decay rate observed in Pb0.92Bi0.07La0.01 (Fe0.405Nb0.325Zr0.27)O3 films. The results of measurements involving changes in film thickness, electron concentration in the electrodes, and contact materials will be discussed and shown to be consistent with the mechanism proposed.

Lattice Modes in Ferroelectric Perovskites: PbTi O 3

Abstract: A complete study of the lattice-dynamical behavior of the ferroelectric tetragonal perovskite PbTi${\mathrm{O}}_{3}$ has been carried out using Raman spectroscopy. The temperature dependence of all the long-wavelength mode frequencies are determined. We show that a damped-harmonic-oscillator model with a frequency-independent damping coefficient is sufficient to explain the observed shape of the soft $E(1\mathrm{TO})$ mode in the ferroelectric phase at all temperatures below ${T}_{c}=493$ \ifmmode^\circ\else\textdegree\fi{}C. Moreover, by combining our experimental mode-frequency data with pyroelectric measurements of the change in spontaneous polarization ${P}_{s}$ with temperature, we obtain values of ${P}_{s}(25 ^{\ensuremath{\circ}}\mathrm{C})=81$ \ensuremath{\mu}C/${\mathrm{cm}}^{2}$ and ${P}_{s}({T}_{c})=42$ \ensuremath{\mu}C/${\mathrm{cm}}^{2}$. This is in excellent agreement with a recent direct experimental measurement. The temperature dependence of all the mode strengths has also been determined to ${T}_{c}$. These results are used to extract the temperature dependence of the clamped dielectric constants. In PbTi${\mathrm{O}}_{3}$ the dielectric constant along the ferroelectric axis ${\ensuremath{\epsilon}}_{c}$ is determined primarily by the lowest frequency ${A}_{1}(1\mathrm{TO})$ mode at all temperatures to ${T}_{c}$, in contrast to BaTi${\mathrm{O}}_{3}$ where in the ferroelectric phase the lowest mode determines only $\ensuremath{\approx}25%$ of ${\ensuremath{\epsilon}}_{c}$. In PbTi${\mathrm{O}}_{3}$ the dielectric constant perpendicular to the $c$ axis ${\ensuremath{\epsilon}}_{a}$ is also determined by the lowest $E(1\mathrm{TO})$ mode at all temperatures. The possibility of observing critical effects near ${T}_{c}$ in the soft-mode data of PbTi${\mathrm{O}}_{3}$ has been examined. These effects are not observed. Also, it is shown that very careful fitting of the soft-mode temperature dependence to a functional form containing a minimum number of separately determined parameters is required before critical effects can be invoked in first-order phase transitions of the displacive type.

Relaxation polarization of PbMg 1/3Nb2/3O3(PMN)-A ferroelectric with a diffused phase transition

Abstract: Peculiarities of the dielectric properties of the compound PbMg 1/3 Nb2/3 O3(PMN) such as the relaxation character of the dielectric polarization, deviation of permeability from the Curie-Weiss law above the Curie temperature etc. have been discussed on the basis of the idea of a diffused phase transition. 1-6 A model has been proposed, in accordance with which the features of the dielectric properties PMN are explained by the relaxation of the polar regions surrounded with a non polar phase, with the number of relaxing regions dependent on temperature.

Depolarization-Field-Induced Instability in Thin Ferroelectric Films-Experiment and Theory

Abstract: The existence of depolarization fields in thin ferroelectric films is experimentally demonstrated by investigating an unconventional electrode-ferroelectric configuration consisting of a triglycine sulphate (TGS) film sandwiched between a gold and a doped-silicon electrode. Due to nonidentical electrodes, the compensating-charge distribution for opposite polarization directions is asymmetric and consequently depolarization fields cannot be sufficiently reduced by domain formation. These depolarization fields manifest themselves by reducing the intrinsic polarization in thin ferroelectric films with respect to the bulk value and this aspect is experimentally confirmed. For a sufficiently thin film, depolarization fields become too strong and a polarization instability is observed. These effects are simulated by altering the compensation-charge extension in the silicon electrode by photoillumination. Other causes, like impurities, and structural defects, which can lead to reduction of polarization, are ruled out. Theoretical model calculations including the depolarization field are reported. The calculation predicts an intrinsic polarization reduction in thin ferroelectric films and is in good agreement with experiments reported here.

Phase Transition, Stability, and Depolarization Field in Ferroelectric Thin Films

Abstract: It is shown that the polarization in a thin ferroelectric film, which is sandwiched between semiconducting electrodes, is compensated incompletely The associated depolarization fields are size dependent and change the magnitude of the polarization, transition temperature, coercive field, and the order of the phase transition Thermodynamic considerations give stability requirements for thin films, which are different from the bulk The properties of a thin ferroelectric film, which in bulk form exhibits a second-order phase transition, are investigated as a function of thickness, temperature, biasing potential, and electrode properties Numerical results are presented for triglycinesulfate

Ferroelectricity in lead monohydrogen phosphate, PbHPO4, and the deuterated form, PbDPO4

Abstract: PbHPO4 and the deuterated form PbDPO4 are found to be ferroelectric at room temperature with space group Pc. Pyroelectric, dielectric and ferroelectric measurements as a function of temperature show the room temperature values of the spontaneous polarization Ps are 0.72 and 2.1 μC/cm2, for PbHPO4 and PbDPO4 respectively, and second order ferroelectric-paraelectric phase transitions occur at 37°C and 179°C, respectively. The ferroelectric behavior is discussed in terms of the crystal structure.

Acoustic surface waveguides - Analysis and assessment

Abstract: The properties of acoustic surface waveguides are reviewed, with particular reference to topographic structures in which guiding is achieved by drastic deformation of the substrate surface. A numerical technique, capable of computing efficiently and with high accuracy the mode spectrum of an anisotropic piezoelectric heterogeneous waveguide of arbitrary cross section, is described. Characteristics of both the ridge guide and the recently discovered wedge waveguide are discussed in some detail. Techniques for the fabrication of and transduction onto acoustic surface waveguides are discussed, and a preliminary assessment is made of potential linear and nonlinear waveguide applications. A number of experimental devices are described.

The effects of deuteration on the static ferroelectric properties of KH2PO4 (KDP)

Abstract: A detailed study was made of the static ferroelectric properties of a group of (H1-xDx)2 crystals with nominal x values of 0, 0.35, 0.80 and 0.98. The properties investigated included the transition temperature Tc, the Curie constant C, the saturation polarization Ps, the coercive field Ec and the electric field strength Es required to achieve saturation of the polarization. As far as we know, this is the first systematic study of the effects of deuteration on these properties employing the same experimental apparatus and techniques. Relatively large isotope effects are found in all of these properties, and the results render comparisons among crystals with different x more meaningful and help to remove some of the ambiguities and discrepancies in the earlier literature. For KH2PO4, Tc = 122°K, C = 2925°K and Ps = 5.1 μC/cm2, and these quantities increase nearly linearly by 83, 40 and 22%, respectively, on complete deuteration. The coercive field and Es increase by ∼20-fold and ∼6-fold, respectively: thes...

Studies of phases, phase transitions and properties of some plzt ceramics

Abstract: Lanthanum-doped lead zirconate titanate (PLZT) ceramics of composition 8/65/35 and 9/65/35 have been studied by electrical, optical and thermal means. The results obtained have been used to elucidate the nature and extent of the phases occurring and the phase transitions between them. Phase α is obtained by thermally depoling a ceramic. It is converted into phase β by the application of electric fields or stress. On removal of the electric field, phase β is retained below a temperature TD while it reverts back to phase α if the temperature is above Tt. If phase β is heated, it transforms into α at Tt, but there is no reverse transformation on cooling. The transition at Tt can be sharp for chemically homogeneous material. Phase α is found to be non-birefringent, even in a single grain. It has linear dielectric and elastic properties. Phase β is birefringent, ferroelectric and ferroelastic. The properties of the two phases and the transitions between them can be used to explain the effects of electric field...

Dielectric, mechanical and optical properties of orthorhombic KNbO-3

Abstract: Dielectric, piezoelectric and elastic constants have been measured in single domain KNbO3, and electrooptic r-coefficients are estimated. Results allow a thorough verification of Devonshire's theory for the orthorhornbic phase. Good agreement is found for the dielectric and piezoelectric properties whereas fitting the elastic behaviour requires inclusion of terms coupling stiffness to spontaneous strain. The temperature dependence of clamped dielectric constants and elastic stiffness points to the importance of piezoelectric coupling for the low temperature phase transitions. Absorption measurements reveal a nearly isotropic polarization-induced band edge shift of 200 meV. Large anisotropy is observed in the polarized UV reflectance spectra measured up to 10 eV. Comparison of reflectivity in ferroelectric KNbO3 with electroreflectance in cubic KTaO3 gives further evidence for the unified nature of electro-optic effects in oxygen-octahedra compounds. Differences in e''-spectra derived from Kramers-Kronig a...

Electron-phonon interaction, microscopic mechanism and properties of ferroelectric phase transitions

Abstract: The vibronic theory of ferroelectric phase transitions is reviewed and the essential contribution of electron-phonon interaction into the microscopic origin of the ferroelectricity is demonstrated. In the narrow-gap (semiconducting) systems the soft mode is caused by interband vibronic interaction and the temperature dependencies are essentially determined by band occupation numbers. In a general case the phonon anharmonicity must also be taken into account. In the large-gap dielectric systems (BaTiO3) this mechanism leads to a negative value of the square of an initial anomalously small frequency. The thermal jumps of electrons are now absent and the temperature dependencies (and the stabilization of the crystal) are essentially determined by the phonon anharmonicity. A theory for hydrogen-containing ferroelectrics with proton-proton, proton-phonon and phonon-phonon interactions taken into account is also developed. The main properties and characteristics of phase transitions in the mentioned scheme are ...

Soft modes and the structure, spontaneous polarization and Curie constants of perovskite ferroelectrics: tetragonal potassium niobate

Abstract: The structure of potassium niobate KNbO3 in the ferroelectric tetragonal phase has been determined at 270 degrees C by neutron diffraction. The atomic displacements along (001) from the cubic perovskite positions are Delta (K)=-0.030+or-0.035 AA, Delta (Nb)=0.064 AA, Delta (OI)=-0.095+or-0.012 AA and Delta (OII)= Delta (OIII)=-0.102+or-0.012 AA. The phase transition is seen as the condensation of a soft lattice vibrational mode in which comparatively rigid oxygen octahedra vibrate against the K and Nb atoms. The spontaneous polarization, Curie constant and entropy change for this and the other perovskite ferroelectrics BaTiO3, PbTiO3 and K(Ta, Nb)O3 have been calculated according to Cochran's soft mode theory. The agreement with experiment is satisfactory.

Pressure and Temperature Dependences of the Dielectric Properties and Raman Spectra of Rb H 2 P O 4

Abstract: The pressure (0-21 kbar) and temperature [(4-300)\ifmmode^\circ\else\textdegree\fi{}K] dependence of the static dielectric properties of rubidium dihydrogen phosphate were investigated. Among the important results of these measurements are the large decrease in the transition temperature with pressure leading to the eventual vanishing of the ferroelectric state at all temperatures for $P\ensuremath{\ge}15.2$ kbar and the decreases with pressure of the Curie constant and dielectric constant in the paraelectric phase. The pressure (0-4 kbar) and temperature [(140-300)\ifmmode^\circ\else\textdegree\fi{}K] dependences of the Raman-active phonons in the range 0-1000 ${\mathrm{cm}}^{\ensuremath{-}1}$ were also investigated. The mode Gr\"uneisen parameter $\ensuremath{\gamma}$ for each of these modes was determined and the pressure dependences of the mode frequencies permitted the modes to be separated into internal and external vibrations relative to the P${\mathrm{O}}_{4}^{\ensuremath{-}3}$ ions. From the coupled-mode spectra for the ${B}_{2}$ symmetry phonons, the pressure dependence for the "soft" mode as well as the interaction between this mode and another mode of the same symmetry were determined. These data, together with the dielectric results, were examined within both the coupled proton-tunneling-optic-mode model of Kobayashi and the coupled-mode description discussed by Scott and Wilson. Evaluation of the pressure dependences of the parameters of the Kobayashi model using normally accepted approximations leads to internal inconsistencies in this model. The approximations appropriate to the present measurements and the resulting indeterminancy of the model parameters are briefly discussed.

Dielectric and optical properties of a quasi-ferroelectric PLZT ceramic

Abstract: Certain compositions within the quaternary lead-lanthanum-titanate-zirconate (PLZT) system exhibit neither a "true" ferroelectric nor a "true" paraelectric behavior and are therefore best characterized as quasi-ferroelectric. The dielectric, hysteresis, and optical properties of quasi-ferroelectric PLZT ceramics have been investigated for the representative 9/65/35 composition which was prepared as a transparent ceramic by means of a two-stage sintering-densification process. The results of these studies suggest that the quasi-ferroelectric behavior of PLZT compositions between their Curie temperature and a transition temperature T p is brought about by the existence of polar distorted microregions (polar short-range order). By applying an electric field a transition to a macroscopic ferroelectric (FE) state (polar long-range order) is enforced which is, however, not stable at zero field at T > T p . This concept, which explains the experimental observations, is compared with the possibility of a FE to anti-FE phase transition at T p . Attention is drawn to the quasi-static memory behavior of this type of material that can be realized by disconnecting the sample in its ON state from the voltage source and which might enlarge the scope of applications of quasi-ferroelectric PLZT ceramics.

Domain structures in orthorhombic KNbO3 and characterisation of single domain crystals

Abstract: Domain configurations in large KNbO3 single crystals grown by a top seeded flux growth technique are studied by optical methods and etching techniques. The orientation of observed domain walls is consistent with the principles of mechanical compatibility and electrical neutrality. Experimental evidence for the existence of a new type of ferroelectric domain wall (S-wall) is presented. Miller indices of such walls are irrational and depend on spontaneous strain tensor coefficients. The preparation of large single domain crystals (up to 1/3 cm3) is described. Assessment of crystal perfection by x-ray topographic and interference methods reveals a very small mosaic spread (one minute of arc) and a good optical homogeneity.

Studies of the crystal structure of triglycine sulfate in connection with its ferroelectric phase transition

Abstract: The crystal structure of triglycine sulfate has been refined at 19°C and 37°C in the ferroelectric phase and at 57°C in the paraelectric phase, by using the data collected by a four-circle automatic diffractometer. Positions of 14 hydrogen atoms out of the 17 have been determined and those of the non-hydrogen atoms refined at 19°C, with the discrepancy factor R of 0.046. Refinement of the structures at 37°C and 57°C was made for non-hydrogen atoms, resulting in the R factor of 0.074 in both cases. The split atom method was used for the determination of the 57°C structure. Obtained results have established that the ferroelectric phase transition of TGS is of the order-disorder type.

New liquid‐crystal method for revealing ferroelectric domains

Abstract: It was found that a layer of the nematic liquid crystal p‐N‐(p‐Methoxybenzylidene) amino n‐butylbenzen, extended on a triglycine sulfate crystal, takes on an orientational pattern which delineates the polarized domain structures. This technique quickly delineates domain structures in great detail and can be used on a wide variety of ferroelectric crystals. It is even applicable to a uniaxial regular type in which a domain structure cannot be detected by ordinary optical methods. The new method and the ordinary carbon powder pattern technique were compared on a triglycine sulfate crystal.

Polarization Instability in Thin Ferroelectric Films

Abstract: An experimental study of critical phenomena in thin ferroelectric films is presented which, for the first time, conclusively demonstrates that the polarization in thin films is drastically reduced as a result of depolarization effects Other causes, like impurities, structural defects, and domain formation, which can lead to reduction of polarization, are ruled out

Ferroelectric and antiferroelectric materials

Abstract: A concise compilation of ferroelectric and antiferroelectric materials, known up to 1971, is presented together with the Curie and other transition temperatures. Spontaneous polarization values are given in the case of ferroelectrics.

Polymorphism and penferroelectricity in PLZT ceramics

Abstract: The interaction of structure with optical and electrical properties in lanthanum-doped lead zirconate-titanate (PLZT) ceramics is complex. An interpretation is presented which shows the critical dependence of structure and, hence, properties on the state of polarization, the temperature, and the La content. To explain the behavior of PLZT ceramics two new concepts are presented: polymorphism and penferroelectricity. Polymorphism occurs when either electrical or mechanical ordering fields generate a hybrid crystal structure in which an individual grain attains a crystal structure dependent on its orientation with respect to the field. Penferro-electricity refers to the condition in which material is noncubic and polar but with such a low spontaneous polarization that no domains exist. The justification for applying these concepts to PLZT rests on the existing structural, optical, and dielectric data supplemented by new X-ray evidence and new data on the temperature dependence of optical and electrical properties. Emphasis is placed on materials with 65/35 Zr/Ti ratio and 6 < X ≤ 8 where X is the atom % La substituted for Pb. Analysis of existing data disclosed 1) a lack of X-ray evidence for the morphotropic boundary predicted by average remanent birefrigence and planar coupling and 2) a discrepancy in the position of the phase transition located by the Curie point and by planar coupling coefficient. The new X-ray, optical insertion loss, dielectric and piezo-electric data show conclusively that the phase equilibria in 65/35 PLZT depend strongly on the state of polarization. In thermally annealed ceramics a state of penferroelectricity exists between the cubic paraelectric state and the rhombohedral ferroelectric state. Rhombohedral ferroelectric material with 6 < X < 8 transforms to polymorphic material with very strong ferroelectric properties during poling. Because of the large crystal distortions which accompany poling, the optical transmission in the poled state is much reduced. This behavior is the basis for many of the useful device applications of PLZT in this compositional range.

Ferroelectric memory device

Abstract: A ferroelectric memory device utilizing the remanent polarization of a thin, ferroelectric film to control the surface conductivity of a bulk semiconductor and perform the memory function. The structure of the device is similar to a conventional MIS field effect transistor with the exception that the gate insulating layer is replaced by a thin film of active ferroelectric material comprising a reversably polarizable dielectric exhibiting hysteresis.

Structure of rhombohedral ferroelectric barium titanate

Abstract: The Profile Analysis technique for neutron powder diffraction patterns has been used to show that the lowest temperature phase of barium titanate is rhombohedral R3m with cell angle α = 89.868 ± 0.004°at 77.4 K. The atomic displacements from the cubic perovskite positions are along [111], and have magnitudes of δ (Ba) = 0.001 ± 21 A, δ(Ti) = 0.091 A and δ(OI) = δ (OII) = δ(OIII) = -0.091 ± 14 A. The oxygen octahedron is slightly distorted by an additional oxygen displacement of δ⊥(O) = 0.023 ± 13 A perpendicular to this ferroelectric axis. These values yield 34 ± 7 μC. cm-1 for the spontaneous polarization in this phase, in good agreement with the measured value of 33.5 μC.cm-1.

Far infrared properties of the pseudoproper ferroelectric ammonium sulfate

Abstract: Far infrared reflectivity and transmission measurements of para-and ferroelectric ammonium sulfate (NH4)2SO4 in the spectral region 30-400 cm-1 and the temperature region 100-300°K were performed in the polarized light. The reflectivity spectra were subject to the Garners-Gonig analysis and the results were discussed with the help of the group analysis and structural considerations. The dynamic nature of the phase transition is discussed in terms of a coupled oscillator-relaxator model and the order-disorder mechanism is confirmed. The concept of a pseudo-proper ferroelectric is discussed and it is shown that the ammonium sulfate is a typical representant of this class of ferroelectrics.

New Ferroelastic-Ferroelectric Compound: Tanane

Abstract: We report here evidence for the first paraferroelectric transition observed in a pure molecular solid (without H bonds); we present results from x-ray diffraction, calorimetric and dielectric measurements, and direct optical observation of domain-wall displacement under an applied electric field.

Electronic Band Structures of SbSI in the Para- and Ferroelectric Phases

Abstract: The electronic band structures of the ferroelectric semiconductor SbSI, whose crystal structure is very complex compared with the crystals for which the band calculations have been made up to the present, have been calculated by the pseudopotential method in the para- and ferroelectric phases. It is shown that this material has an indirect gap (about 1.4 eV) in both phases and that the smallest direct gap exists at the $U$ point on the surface of the Brillouin zone. It is also found that the optical absorption edge shows the dichroism and electro-optic effect as observed in the experiments. As for the correlation of the band structures with the ferroelectric phase transition (the transition temperature is about 22 \ifmmode^\circ\else\textdegree\fi{}C) it is shown that some bands greatly change their energy values at the phase transition, in particular, the bands at the $U$ point. Further, the dielectric constants have been calculated and compared with the experimental result.

Pb5(Ge,Si)3O11 Ferroelectrics

Abstract: The compound Pb5Ge3O11 is an optically active ferroelectric with a transition temperature near 177°C. Solid solutions containing up to 62% Si replacing Ge were prepared from the melt. Increasing the Si content lowers the melting point, Curie point, and coercive field. Permittivity measurements on single crystals indicate a simple second-order phase change.