Poled Crystals Research Articles

Unusual ferroelastic behavior in ferroelectric lead bismuth niobate (PbBi2Nb2O9)

Abstract X-ray and optical measurements are used to show that the spontaneous strain (b/a-1) and optical birefringence Anab in single crystals of ferroelectric PbBi2Nb2O9 are a function of the state of electrical poling, going to a zero in the unpoled state. In poled crystals all spontaneous strain is lost at a temperature ∼220°C below the dielectric Curie temperature in a manner reminiscent of the behavior of the perovskite relaxer ferroelectrics which have diffuse phase transitions

IR-absorption study of H and D-impurities in BaTiO3crystals

Abstract The temperature dependence and polarization of five bands due to OH-vibrations in poled BaTiO3 single crystals yield information leading to a microscopic model for the position of the hydrogen in the host lattice. Values for the anharmonic contribution to the localized oscillation are deduced from the overtone frequency of OH and the isotrope shift of the OH/OD stretching vibration.

Dielectric and pyroelectric properties of LiTaO3single crystals

Abstract Ferroelectric hysteresis loops of LiTaO3 single crystals have been observed by Sawyer and Tower hysteresis bridge at room temperature. Hysteresis loops of as-growth crystals are double loops and ones of poled crystals are biased single loops. Spontaneous polarization Ps=50±2/C/cm2 and coercive field Ec=1.8 × 104V/cm at 50Hz are obtained. Pyroelectric coefficient is obtained by the charge integration method. Dielectric constant is measured as a function of temperature near Curie point. The results have been compared with the predictions of Devonshire's theory. The internal bias field is introduced probably by defects in the crystals.

Origin of theT32specific-heat term in triglycine sulfate at low temperatures

Two sets of specific-heat experiments on single crystals of ferroelectric triglycine sulfate (TGS) at low temperatures are reported aimed at discriminating between bulk and surface contributions to the unusual ${T}^{\frac{3}{2}}$ specific-heat term. In the first set, two large crystals with small surface-to-volume ratios ($\frac{S}{V}$) were measured, where one (poled) crystal was single domain and the other crystal multidomain. In the second set, two assemblies of small TGS crystals with large $\frac{S}{V}$ values were measured. The data demonstrate that a surface excitation is responsible for the ${T}^{\frac{3}{2}}$ term in TGS, and an unusually thick ($\ensuremath{\simeq}0.02$ cm) surface layer is indicated.

Czochralski single crystal growth of Sr .61Ba .39Nb 2O 6 for surface acoustic wave applications

Ferroelectric Sr .61Ba .39Nb 2O 6 (SBN) single crystals approximately 2 cm. in diameter and 5–6 cm. long have successfully been grown by the Czochralski technique. All the crystals were grown in the [001] direction in argon or oxygen, and it was found that the degree of difficulty of growth increased as the diameter of the crystals increased. Temperature dependence measurements on the poled Z-cut SBN crystals showed that this composition has temperature compensated orientations which make this material useful for surface acoustic wave devices.

Elastooptic Effect in BaTiO3

The temperature dependence of the elastooptic coefficient in BaTiO3 is theoretically and experimentally investigated in the vicinity of the cubic-tetragonal phase transition point (∼113°C). A theory of the elastooptic effect in BaTiO3 is developed through the anharmonic potential method. It is shown that nonlinear coupling among the electronic polarization, strain and soft phonon causes the temperature dependence of the elastooptic coefficient. The elastooptic coefficient p11 of a poled BaTiO3 single crystal is measured by the Dixon-Cohen method as a function of temperature near the phase transition point. In the tetragonal phase, p11 is almost temperature-independent, whereas in the cubic phase, p11 is strongly dependent on temperature. The above theory accounts for these experimental results.

Preparation of KNbO3 Single Crystal for Optical Applications

A modified Kyropoulos technique is applied to obtain large single domain KNbO3 crystals suitable for optical applications. Colorless and high resistivity crystals up to 30×30×15 mm3 in size are grown with 52∼55 mole% K2CO3 content under the condition of shallow temperature gradient. Single domain crystals up to 8 mm cube are obtained through poling procedure with a d-c field of approximately 1 kV/cm at about 190°C under slight stress along an a axis. The poled crystals are found to be of good optical quality by microscopic examination with polarized light and experiments on second harmonic generation using 1.06 µCW Nd:YAG laser. The second harmonic efficiency for up-conversion of KNbO3 is found to be as high as that of Ba2NaNb5O15. KNbO3 is revealed to be a potentially useful non-linear material for optical device application.

Ferroelectrics in the k2O-SrO-Nb2O5 system

Research into the tungesten bronze phase field of the K2O-SrO-Nb2O5 system (KSN) has shown that ferroelectricity occurs over a wide range of compositions close to the KNbO3-SrNb2O6 binary line. The approximate location of the congruently melting composition was found by chemical and X-ray analyses of crystals produced from vertical float zoning and Czochralski pulling experiments and was centred on k2Sr9Nb20O60. This composition gave crystals of much improved optical quality-free from striae but containing vertical structure.K2Sr9Nb20O60 crystals have distinctive dielectric properties, the dielectric constant of poled crystals being half that of the as-grown ones. The true lattice spacing in the 'c' direction is double that of the basic tetragonal unit cell and may be explained in terms of tilted NbO6 octahedra.The low half-wave voltage and dielectric properties of K2Sr9Nb20O60 make it potentially useful for electro-optic and pyroelectric applications. However, the reproducibility of striae free crystals ...

Optically Induced Change of Refractive Indices in LiNbO3 and LiTaO3

Local changes of indices of refraction observed in poled single crystals of ferroelectric LiNbO3 and LiTaO3 when illuminated by focused light have been studied. The extraordinary index of refraction was observed to decrease as much as 10−3 with a focused Ar laser light of 20 mW intensity as λ=0.488 μ, while the change of ordinary index was much smaller. The effect is attributed to the drifting of photoexcited electrons out of the illuminated region followed by their retrapping near the beam periphery. The space-charge field between these retrapped electrons and the positive ionized centers in the illuminated region causes the observed change of refractive indices via the electro-optic effect of the samples.

Some characteristics of Ba, Sr, Na niobates

Curie temperature (T C) and spontaneous polarization (P S), dielectric constant (ε), 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 εV π tends to remain constant for poled crystals. Resistivity data are also given.

Optical memory planes using LiNbO3and LiTaO3

Optical memory planes are proposed in which writing and nondestructive reading would be performed optically using a laser-induced inhomogeneity of refractive indices which has been observed in poled single crystals of LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> and LiTaO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> . Writing times of the order of 0.5 millisecond using a 0.4-watt Ar laser with a bit density in excess of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> per square inch appear feasible.