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The action of NaF on rare earth oxides with the columbite or aeschynite structure leads to pyrochlore-type phases of formula NaTTiNbO 6 F (T = Y, Ce, …, Yb). On the other hand, the substitution of cadmium by a rare earth and of oxygen by fluorine in T 2 Ti 2 O 7 gives isostructural phases of formula CdTTI 2 O 6 F (T = Y, Nd … Yb). The dielectric properties of the solid solutions between both phases and Cd 2 Nb 2 O 7 characterize ferroelectric-paraelectric transitions. The substitution of oxygen by fluorine brings about a decrease in the Curie temperature, but a very small substitution rate increases the dielectric constant and the spontaneous polarization.

A functional form of the spontaneous polarization P0 of the eight-vertex model below the critical temperature is conjectured, and an exact expression then determined by considering three special cases. The result agrees to fourth order with the low-temperature series expansion. It implies that the critical exponent beta e varies linearly with pi /$Gm, as do the other exponents previously obtained.

The bond nonlinear polarizability is shown to increase with increasing bond length for covalent compounds but to decrease with bond length for sufficiently ionic compounds. This behavior is shown to explain, for example, the anomalously small value of the ${d}_{31}$ nonlinear coefficient in LiTa${\mathrm{O}}_{3}$ as compared with the isomorphic LiNb${\mathrm{O}}_{3}$, as well as the opposite signs of ${d}_{33}$ in the isomorphic BaTi${\mathrm{O}}_{3}$ and PbTi${\mathrm{O}}_{3}$. The unusually large deviation of ${\mathrm{Pb}}_{5}$${\mathrm{Ge}}_{3}$${\mathrm{O}}_{11}$ from the Jerphagnon relationship between the vector part of Miller's $\ensuremath{\Delta}$ and the spontaneous polarization is also discussed.

The half-wave voltages, the electro-optic (EO) and the polarization-optic (PO) coefficients of orthorhombic KNbO 3 have been evaluated. We used a method where the refractive index changes are induced by very small electric fields to prevent formation of domains. From the temperature dependence of the EO coefficients we can conclude that the PO coefficients are temperature independent and that the linear EO effect is a quadratic effect biased by the spontaneous polarization.

General problems arising from the use of a resistor-type commercial high-temperature X-ray camera are analysed. Solutions are suggested, and tested by measuring the thermal expansion in LiNbO3 between 25 and 1100°C. Results compare well with and complete some previous studies. In particular the competitive effects of lattice thermal expansion and electrostriction due to the spontaneous polarization are clearly established.

The microscopic parameters for the Kobayashi model and their pressure derivatives are evaluated from Raman scattering results on K${\mathrm{H}}_{2}$P${\mathrm{O}}_{4}$ and Rb${\mathrm{H}}_{2}$P${\mathrm{O}}_{4}$. The results are used within the framework of this model to calculate the temperature and pressure dependences of the dielectric properties, including the dielectric constant, Curie constant, spontaneous polarization, and the suppression of ferroelectricity at high pressure.

The spontaneous fluctuations of polarization in polar dielectrics are considered by using the Einstein thermodynamic method, a general dielectric theory method, and an equivalent circuit method. Mean‐square fluctuation of the polarization field is obtained by the first two methods and the frequency spectrum by use of the dispersion properties. The equivalent circuit method gives frequency spectra directly and the two lines of analysis are shown to give consistent results. Noise magnitudes are exhibited and noise is shown to be a consequence of dielectric dispersion in all matter.

X-ray dilatometric measurements have been made on lattice strains along the A- and B-axes of KH2PO4 as a function of temperature and biasing electric field near the Curie point. It has been clearly observed that the forced ferroelectric transitions take place in a very small but definite temperature range of 0.65 deg. A phenomenological treatment has been developed, and the coefficients of the elastic Gibbs function of KH2PO4 have been successfully determined to γ = −1.19 × 10−10 e.s.u. and Δ = 1.10 × 10−18 e.s.u., where γ stands for the coefficient of the P4 term and Δ for that the of P6 term. γ is negative. These values explain well the reported spontaneous polarization and dielectric stiffness when strong tendency to coexistence of two phases at the transition is duly allowed for. From the observations it is concluded that the ferroelectric phase transition of KH2PO4 is unequivocally of first order. Les mesurages dilatometriques par rayons-X ont ete effectues sur des deformations des A- et B-axes de KH2PO4 pres du point de Curie en fonction de temperature et champs electriques applique. Il a ete clairement observe que les transformations ferroelectriques forcees ont lieu dans une petite mais definite rangee de temperature de 0,65 deg. Un traitement phenomenologique a ete developpe et les coefficients du fonction elastique de Gibbs de KH2PO4 ont ete bien determines comme γ = −1,19 × 10−10 e.s.u., δ = 1,10 × 10−18 e.s.u., ou γ montre un coefficient du terme de P4 et δ celui du terme de P6. γ est negatif. Cettes valeurs expliquent bien la polarization spontanee et la radeur dielectrique raportees, quand la tendance forte d'une coexistence des deux phases a la transformation soit dǔment consideree. Des evidences observees, il est conclure que l'ordre de la transformation ferroelectrique de KH2PO4 est nettement premier.

A phenomenological theory has been developed for explaining the anomalous dielectric and electro-mechanical properties of some improper ferroelectrics. An ordering parameter 8, which plays the role of a trigger for the onset of the spontaneous polarization P is introduced into the thermodynamical potential function. The peculiar dielectric properties of (NH4)2SO4- and Gd2(MoO4)3-group crystals and the anomalous behaviour of the lattice strains of Fe-I-boracite can be well explained on the basis of this theory. A graphical investigation in a proper θ–P plane shows how the strength of the coupling between 8 and P characterizes the transition mechanisms of the improper ferroelectrics. As a result, it has become clear that the common origin of the peculiar physical properties of both crystal groups lies in the extreme weakness of the couplings. Experimental methods to disclose improper ferroelectric mechanisms are discussed. Eine phanomenologische Theorie wurde entwickelt, die die anomalen dielektrischen und elektromechanischen Eigenschaften einiger nichtidealer Ferroelektrika erklart. Ein Ordnungsparameter θ, der die Rolle eines Triggers fur den Einsatz der spontanen Polarisation P spielt, wird in die thermodynamische Potentialfunktion eingefuhrt. Die eigen-artigen dielektrischen Eigenschaften von (NH4)2SO4- und Gd2(MoO4)3-Kristallen und das anomale Verhalten der Gitterdeformation der Fe–I-Borazite lassen sich auf der Grundlage dieser Theorie gut erklaren. Eine graphische Untersuchung in einer geeigneten θ–P-Ebene zeigt, wie die Kopplungsstarke zwischen θ und P die Ubergangsmechanismen nichtidealer Ferroelektrika charakterisiert. Als Ergebnis wird klar, das der gemeinsame Ursprung der besonderen physikalischen Eigenschaften der beiden Kristallgruppen in der extrem geringen Kopplung liegt. Es werden experimentelle Methoden zur Aufdeckung der Mechanismen nichtidealer Ferroelektrika diskutiert.

This paper describes the measurement of the absolute signs of the nonlinear optical coefficients ${d}_{\mathrm{ij}}$ that give rise to second-harmonic generation in piezoelectric crystals. The measurements were made with a repetitively $Q$-switched Nd-yttrium aluminum garnet (Nd-YAG) laser (1.064 \ensuremath{\mu}) and involve relative sign determinations between two crystals followed by a comparison of at least one of them with ${d}_{14}$ of GaP, which has been shown previously to be positive with respect to the +[111]. To determine the unique directions in the crystals studied, several different methods were used, including: the piezoelectric effect, the pyroelectric effect, the etching behavior, and the electric field aligned spontaneous polarization. The crystals investigated included the following: zinc-blende crystals (ZnSe, ZnTe, and CdTe), wurtzite crystals (ZnO, BeO, CdS, and CdSe), ferroelectric crystals [LiTa${\mathrm{O}}_{3}$, LiNb${\mathrm{O}}_{3}$, BaTi${\mathrm{O}}_{3}$, ${\mathrm{Ba}}_{2}$Na${\mathrm{Nb}}_{5}$${\mathrm{O}}_{15}$, ${\mathrm{Gd}}_{2}$${(\mathrm{M}\mathrm{o}{\mathrm{O}}_{4})}_{3}$, and ${\mathrm{Tb}}_{2}$${(\mathrm{M}\mathrm{o}{\mathrm{O}}_{4})}_{3}$], and several other crystals (LiI${\mathrm{O}}_{3}$, LiGa${\mathrm{O}}_{2}$, LiCH${\mathrm{O}}_{2}$\ifmmode\cdot\else\textperiodcentered\fi{}${\mathrm{H}}_{2}$O, and quartz). Strong absorption of the second harmonic complicates the interpretation of the experimental results for ZnTe, CdTe, and CdSe. The present results and those of several recent theoretical predictions are in good agreement.

The use of exploration geophysics in the discovery of oil is well known, but applications of these methods in exploration for subsurface water are less publicized and less well known, despite the fact that geophysics has been employed in this field for more than thirty years and has been developing continually. Consequently, this paper is oriented towards exploration geo‐geophysical methods for ground‐water supplies. After a summary of the history of the methods, the paper examines the geophysical methods employed with their respective advantages and drawbacks: electrical prospecting using “electrical soundings” and resistivity mapping, shallow refraction, spontaneous polarization, and induced polarization. The principal problems that may be resolved by geophysics are reviewed, as well as practical considerations concerning the composition of a crew, its production, and costs. Some examples of hydrology surveys are presented to illustrate different types of problems that may be encountered. In conclusion, a large expansion in geophysical exploration and particularly electrical methods is expected as the need for sub‐surface water supplies increases in various regions of the world and the existing deficient supplies become known in industrialized nations.

A thermodynamic theory of the elastic and dielectric properties of gadolinium molybdate is developed on the basis of a free energy expansion, which properly describes the space group symmetry change of gadolinium molybdate at 159 °C. The temperature dependence of the material constants is qualitatively explained and it is shown to be connected with the sixth order terms in the phase transition parameters. The magnitude of coupling of the polarization with the phase transition parameters and the origin of the spontaneous polarization are discussed. Eine thermodynamische Theorie der elastischen und dielektrischen Eigenschaften von Gadoliniummolybdat wird auf der Grundlage einer Entwicklung der Freien Energie angegeben, die die Anderung der Raumgruppensymmetrie von Gadoliummolybdat bei 159 °C richtig wiedergibt. Die Temperaturabhangigkeit der Materialkonstanten wird qualitativ erklart und es wird gezeigt, das sie mit Termen sechster Ordnung in den Parametern des Phasenubergangs verknupft ist. Die Grose der Kopplung der Polarisation mit den Phasen-ubergangsparametern und der Ursprung der spontanen Polarisation werden diskutiert.

Spontaneous polarization measurement of ferroelectric Rochelle salt near Curie point, using nuclear magnetic resonance for phase transitions

The theoretical case of a polarized hidden sphere is discussed briefly. To determine location, depth and dip of an orebody displaying natural currents a method of practical value is explained and a master diagram is given. A distinction is made between anomalies which can be treated assuming a polarized sphere and those which can not be interpreted this way. A generalized method of topographical and regional correction is given. The procedure of interpretation and topographical correction is shown with two field examples. The method is not empirical and the results are precise when applied to the cases in which the assumption of a sphere is justified. It is shown that topographical corrections can not be overlooked.

It was reasoned that in normal ferroelastic crystals, if their prototypic (or peraelastic) phase transitions are of the second kind, the dependence of the spontaneous strain on temperature T should be proportional to ( T c - T ) 1/2 right below the transition temperature T c and the T dependence of the elastic compliance should obey the so-called “Curie-Weiss law” above and below T c . However, it is also considered that possible are ferroelastic crystals in which, whereas their prototypic phase transitions are of the second kind, the T dependence of the spontaneous strain should be proportional to T c - T right below T c and the T dependence of the elastic compliance should disobey the Curie-Weiss law above and below T c . In this paper, two models of such ferroelastic crystals are presented and thermodynamically investigated. One of these models is not only ferroelastic but also feeroelectric; its spontaneous polarization and electric susceptibility should so peculiarly depend on T as its spontaneous st...

Observation methods, localization sites, configuration of reciprocal domains and their formation in PbTiO3 crystals are described. These domains appear at the ferroelectric phase transition. The reciprocal domain concentration in a crystal depends on the velocity of the phase front travel and becomes minimum at velocities of the order of 0.1 mm/ min. A suggestion is advanced about the role of such domains in the spontaneous polarization screening mechanism.

Spontaneous polarization of Triglycine Selenate and Triglycine Fluoberyllate was investigated with crystals produced under various growing conditions. Spontaneous polarization of TGSe crystals grown at the Curie temperature is of the greatest value. The higher the supersaturation of the solution from which TGSe crystals were grown, the greater the spontaneous polarization. TGFB crystals grown at high temperatures are of greater value of spontaneous polarization than those grown at low temperatures. Die spontane Polarisation von Triglycinselenat- und Triglycinfluoberyllat-Kristallen wurde in Abhangigkeit von verschiedenen Zuchtungsbedingungen untersucht. Je hoher die Ubersattigung der Losung, desto hoher war die spontane Polarisation der TGSe-Kristalle. TGFB-Kristalle hatten den hoheren Wert der spontanen Polarisation bei hoheren Zuchtungstemperaturen.

The mossbauer effect for Fe 57m in the BaTiO 3 lattice has been studied from 300 to 1200°K with particular emphasis on the region near the Curie temperature. The mossbauer probe seems to serve as a useful tool for the study of ferroelectrics. The electric-field gradient as seen by the probe at room temperature is -0.52×10 14 esu cm -3 and is closely proportional to P s 2 as the spontaneous polarization P s varies with temperature. The strength of the resonant absorption was also determined as a function of temperature in the region above T c . Much above T c these measurements are compatible with a Debye temperature of 450°K. However, as the Curie temperature is approached, the lamb-mossbauer factor decreases appreciably. These results are discussed in the light of Cochran's theory of ferroelectricity. From the isomer shift at room temperature (0.50±0.02 mm/sec with respect to 310 stainless steel) the over-all degree of ionicity is estimated to be 60±20%. The temperature shift shows a discontinuity at T c and is attributed to the change in covalent binding.

Results of measurements of the dielectric constant, dielectric nonlinearity and spontaneous polarization of tri-glycine sulfate are given. These data demonstrate clearly that this material exhibits a second-order ferroelectric transition. The properties discussed are described in terms of the usual expansion of the free energy in even powers of the polarization F(P,T)=F(O,T)+A(T-T 0 )P 2 +BP 4 +CP 6 , where A,T 0 ,B and C are constants and T and P are the temperature and polarization, respectively. From the various data taken it is found that A=1.96×10 −3 (°C) −1 , T 0 =49.8°C,B=2.0×10 −10 (esu/cm 2 ) -2 and C=8.4×10 −19 (esu/cm 2 ) −4 . From these results the nonlinearity of the dielectric constant above the Curie point is calculated at various temperatures.

Curie temperature (T C ) and spontaneous polarization (P S ), dielectric constant (e), and voltage for half-wave retardation (V π ) of 0.6328μ radiation, all at room temperature, are given for single crystals of a Ba, Sr, Na niobate series which have tetragonal tungsten bronze-like structures. P s is a relatively constant 0.38 ± 0.02 C/m 2 for most of the series while T c varies between 560°C and 200°C. V π declines approximately linearly with increasing Sr-content and the product eV π tends to remain constant for poled crystals. Resistivity data are also given.

We show, using the concept of the polarization potential tensor β which relates energy band shifts to the crystal polarization, that the nonlinear optical (NLO) tensor coefficients δ in oxygen‐octahedra ferroelectrics are proportional to the quantity βPs where Ps is the crystal spontaneous polarization. Because β is found to be nearly the same in all oxygen‐octahedra ferroelectrics, we are able to calculate the δ coefficients from a knowledge of Ps. The polarization‐induced energy band shifts are shown to be nearly the same for static polarizations (giving rise to the clamped electro‐optic effect) and for optical‐frequency electronic polarizations (giving rise to nonlinear optical effects).

The millimeter wave absorption of ferroelectric NaNO2 changes during the reversal of the spontaneous polarization Ps. If Ps is periodically switched by an external electric square-wave, a modulation S of the crystal transmission is observed. This paper deals with the temperature and electric field dependence of S. We attribute S to the interaction of the millimeter wave radiation with configuration defects appearing in the crystal during the polarization reversal. Experimental results obtained give some information about the concentration of these defects and hence about the switching mechanism. Die Millimeterwellen-Absorption des Ferroelektrikums NaNO2 andert sich wahrend der Umkehr der spontanen Polarisation Ps. Wenn Ps mit Hilfe von elektrischen Rechteck-impulsen periodisch hin und her geklappt wird, last sich eine Modulation S der Transmission des Kristalls beobachten. Diese Arbeit berichtet, wie S von der Temperatur und von der Hohe der Rechteckimpulse abhangt. Wir fuhren S zuruck auf die Wechselwirkung der Millimeterwellen mit Struktur-Defekten, die im Kristall wahrend der Polarisationsumkehr entstehen. Aus unseren experimentellen Ergebnissen folgen Aussagen uber die Konzentration dieser Defekte und damit auch uber den Umklapp-Vorgang.

The effect of hydrostatic pressure up to 103 atm has been measured on the ferroelectric phase transition temperature of Co3B7O13l. It was found that δTtr/δp = -11.1 × 10-3 deg/atm on cooling while δTtr/δp = -8.1 × 10-3 deg/atm on heating so that thermal hysteresis which reflects the 1st order nature of the transition increases with increasing pressure. Experimental data have been related to the thermodynamic theory developed by Dvorˆak which accounts for the fact that polarization is not the parameter of the transition in boracites. It is shown that the pressure dependence of the ideal transition temperature Ttr is governed by the interaction of stress with nonhomogeneous lattice modes and co-governed by the electrostrictive interaction. On the other hand, maximum thermal hysteresis. permittivity above Ttr and spontaneous polarization depend on pressure due to electrostriction only.

Geatzte (001)-Flachen von GMO zeigen eine neue Art vonDomanen. Sie entstehen durch eine Translation, welche die spontane Polarisation und den Umwandlungsparameter invariant last. Der Translationsvektor ist ein Teil von einem Gittervektor, ahnlich wie bei Stapelfehlern. Etching (001)-faces of GMO reveals a new kind of domains. Theyare created by a translation, that leaves the spontaneous polarization and the transition parameter invariant. The translation vector is a part of a lattice vector, similar to stacking faults.

Polarized infrared reflectivity measurements have been made on single-crystal LiTa${\mathrm{O}}_{3}$ in the frequency range 20 - 10 000 ${\mathrm{cm}}^{\ensuremath{-}1}$ at 300 \ifmmode^\circ\else\textdegree\fi{}K. Kramers-Kronig and classical-oscillator dispersion-theory analyses of these data have yielded values for the frequency, strength, and linewidth of the infrared-active transverse optic modes and longitudinal optic modes. Analysis of the far-infrared interference spectrum yields values of 41 and 40 for the ordinary and extra-ordinary clamped dielectric constants, as well as values for their temperature dependence and dispersion. A calculation is made of the spontaneous polarization in LiTa${\mathrm{O}}_{3}$ and LiNb${\mathrm{O}}_{3}$ using the x-ray ion displacements.

An experiment suitable for a junior or senior physics laboratory is described, in which the spontaneous polarization and coercive field for Rochelle salt are measured from the ferroelectric hysteresis loops, over the temperature range −18° to +24°C in which this crystal is ferroelectric. The suitability of triglycine sulfate for this experiment is discussed. The apparatus is also useful in demonstrating the relation of capacitance to electrode geometry, and in determining dielectric constants.

The temperature dependences of single-domain permittivity, spontaneous polarization, and spontaneous birefringence of CAS have been measured. The decrease of ϵ at Ttr and the temperature independence of Ps show that an interaction P2q2 of polarization with the transition parameters q must be considered in the thermodynamic potential of this material. The birefringence of CAS cannot be explained by electrooptical effects and is mostly due to the improper nature of the ferroelectric transition. The optical distinguishability of domains is discussed and results of a detailed twinning study are presented. Antiparallel domains differ in extinction angles by 18°; they are separated by {100} walls. Boundaries between domains with mutually perpendicular Ps-vectors have the orientations {570}. They are shown to be stressed, not fulfilling the mechanical compatibility requirements. Finally, results of coercive field measurements and of switching mechanism observations are described. Die Temperaturabhangigkeiten der spontanen Polarisation. der Doppelbrechung und der Dielektrizitatskonstanten eines CAS-Eindomanenkristalls wurden gemessen. Der Abfall von ϵ bei Ttr (Ubergangstemperatur) zeigt zusammen mit der Temperaturunabhangigkeit von Ps, das eine Wechselwirkung P2q2 der Polarisation mit dem Ubergangsparameter q im thermodynamischen Potential des Stoffes in Betracht gezogen werden mus. Die Doppelbrechung von CAS kann nicht durch elektrooptische Effekte allein erklart werden, sondern ist uberwiegend auf die Unvollkommenheit des ferroelektrischen Uberganges zuruckzufuhren. Die optische Unterscheidbarkeit der Domanen wird diskutiert und die Ergebnisse einer ausfuhrlichen Untersuchung der Zwillingsbildung werden vorgeleget. Die antiparallelen Domanen unterscheiden sich in den Extinktionswinkeln um 18°; sie sind durch {100}-Wande voneinander getrennt. Die Grenzen zwischen den Domanen mit aufeinander senkrechten Vektoren Ps sind nach {570} orientiert. Es wird gezeigt, das diese Grenzen unter einer Spannung stehen, indem in ihnen die Bedingungen der mechanischen Kompatibilitat nicht erfullt sind. Zum Schlus werden die Resultate der Messung der Koerzitivfeldstarke und die Beobachtungen des Umpolarisierungsprozesses beschrieben.

Studies of the temperature dependence of Bragg reflections and critical scatterings of X-rays have been carried out for the ferroelectric NaNO 2 in a manner analogous to those made by Shibuya and Mitsui for (glycine) 3 ·H 2 SO 4 . Experimental observations agree with theoretical predictions which are based on an assumption that the phase transition in NaNO 2 is of the order-disorder type. A long-range order parameter and the spontaneous polarization are estimated as functions of temperature by using the temperature variation of Bragg reflections. The observed intensity of the critical scattering drops rather abruptly just above the Curie point in a manner similar to the case of (glycine) 3 ·H 2 SO 4 .

The temperature characteristics of dielectric constants, spontaneous polarization, thermal‐expansion coefficients, indices of refraction, and optical rotatory power of Pb5Ge3O11 single crystals have been investigated in detail from room temperature up to above the Curie temperature, 177°C. From the results of these measurements, the following constants were obtained: linear thermal‐expansion coefficients (αa)F=7.75×10−6/deg°C and (αc)F=7.79×10−6/deg°C (ferroelectric phase), (αa)P=13.8×10−6/deg°C and (αc)P=13.4×10−6/deg°C (paraelectric phase); quadratic electro‐optic constants g33T=0.47×108 cm4 /C2, g13T=0.37×108 cm4 /C2; and electrogyration coefficient γ33 =8.7 cm2/C. An isomorphous compound Pb5(Ge2O7)(SiO4) was synthesized and was found to be ferroelectric with T c=60°C and Ps=1.7 μC/cm2 at room temperature. Ferroelectric properties and electrogyration coefficient were studied in the solid‐solution system Pb5(Ge2O7)(GeO4)1−x (SiO4)x.

An anomalous decrease of the spontaneous polarization P s of ammonium sulfate single crystals with decreasing temperature is reported. Cooling to below −190°C even reverses the sign of P S . A maximum value, P S max = 0.62 μ Ccm −2 , was measured at −51.5°C. In the paraelectric state no deviation from a linear dielectric behaviour could be detected up to fields E = 10 5 Vcm −1 .

Il est possible d'etablir entre le champ electrique E et la polarisation P parallele a l'axe binaire une relation du type E = a P + b P3 + c P5 + d P7 qui rend compte a la fois des valeurs de la constante dielectrique et de la polarisation spontanee. Les coefficients a, b, c, d varient generalement en fonction de la temperature et a n'est pas une fonction lineaire de la temperature au-dessous du point de transition. A relation of the type E = a P + b P3 + c P5 + d P7 is established between the electric field E and the polarization P along the binary axis. This relation accounts for both the dielectric constant and spontaneous polarization. Coefficients a, b, c, d are in general functions of temperature, and a is non-linear function of temperature below the transition point.

The room‐temperature spontaneous polarizations in LiNbO3, LiTaO3, Ba2NaNb5O15, Sr0.5Ba0.5Nb2O6, Ba1.1Sr0.9NaNb5O15, and Sr2KNb5O15 have been measured directly by a pulsed field method using an aqueous solution of LiCl as the electrode material. The experimental results are: P8 (LiNbO3) = 0.71±0.02 C/m2, P8 (LiTaO3) = 0.50±0.01 C/m2, P8 (Ba2NaNb5O15) = 0.40±0.01 C/m2, P8 (Ba1.1Sr0.9NaNb5O15) = 0.36±0.01 C/m2, P8 (Sr2KNb5O15) = 0.25±0.01 C/m2, and P8 (Sr0.5Ba0.5Nb2O6) = 0.25±0.01 C/m2. Experimental techniques are presented, and the advantages of the pulsed‐field method over hysteresis‐loop methods are discussed.

The dielectric permittivity, spontaneous polarization and coercive field at 60 Hz have been measured for fields applied along the ‘c’ axis of unpoled bismuth titanate crystals over the temperature range from 350°K to 5°K. In contrast to the behavior of normal ferroelectrics, P s decreases with temperature; E c at first decreases slowly to a minimum at about 100°K, then increases rapidly on further cooling. The permittivity e c only decreases slightly over the whole measured range.

Spontaneous polarization of NaNO 2 was determined by reversing P s with a relatively low d c field of from 60 V/cm to 12 kV/cm and measuring the polarization reversal charge with an electrometer and a recorder. A clear jump in P s of 5.8 µC/cm 2 was observed at the Curie point T c . The dielectric constant e 22 in the ferroelectric phase obeys the Curie-Weiss law very well over a wide temperature range and P s is proportional to (1- T / T 0 ) 0.20±0.02 over 25°C below T c , where T 0 is the ferroelectric Curie-Weiss temperature. Below room temperature P s does not vary appreciably. The saturation polarization is estimated to be 11.9 µC/cm 2 . The electronic contribution to P s is discussed on the basis of a point-dipole approximation. It is probable that about one third of the total spontaneous polarization is contributed from the electronic polarization. The experimental technique is described in detail.

An investigation is made of the EPR spectrum of Cu2+ ions in ferroelectric triglycine fluoroberyllate. The values g∥ = 2.24 g∥ = 2.06, and A = 132 cm−1 are similar to those obtained for copper ions in triglycine sulphate and diglycine nitrate. The new lines are typical of S = 1 and the spectrum is found to have an anomaly at the Curie point. The D parameter of the spectrum is linearly dependent on the spontaneous polarization changes. Es wird das EPR-Spektrum von Cu2+-Ionen in ferroelektrischem Triglyzinfluoroberyllat untersucht. Die Werte fur g∥ = 2,24, g⊥ = 2,06 und A = 132 cm−1 sind denen ahnlich, die ohne Anomalie am Curiepunkt fur Kupferionen in Triglyzinsulfat und Diglyzinnitrat erhalten wurden. Es werden neue Linien typisch fur S=1 gefunden und eine Anomalie des Spektrums am Curiepunkt beobachtet. Der Parameter D des Spektrums hangt linear von den spontanen Polarisationsanderungen ab.

The maximum current i m and the switching time t s have been measured as functions of pressure p (\({\lesssim}2\) k bar) at room temperature in the field range: \(E{\lesssim}2\) k V/cm. The quantities i m and 1/ t s increase with hydrostatic pressure and decrease with two-dimensional pressure perpendicular to c -axis. The exponential laws: i m = i ∞ e -α/ E and t s = t ∞ e α/ E hold under every fixed pressure. The activation field α decreases linearly at the rate: (∂α/∂ p )/α=-5.0×10 -11 cgs with hydrostatic pressure, and increases linearly at the rate: (∂α/∂ p )/α=4.3×10 -11 cgs with two-dimensional pressure. These results agree qualitatively and quantitatively in the order of magnitude with the prediction of the Miller-Weinreich model. The pressure dependences of the 180° wall energy and the spontaneous polarization, which quantities have close relations with α, have been calculated by the molecular theory of Kinase and Takahasi, and fair agreement has been found between the theory and the experiment.