Hideo Futama

Domain Structure and Deflection of Light at Domain Walls in RbHSeO4

Domain structures of feroelectric RbHSeO 4 , which undergoes phase transitions at 102°C and 173°C, were observed and examined in the presence of either electric field or shear stresses, and the intensity of a laser beam deflected at domain walls was measured. In addition, dielectric and piezoelectric examinations were made above and below the 102°C transition. It was found that there are two types of domain structures observable at room temperature, i.e., the ferroelectric and simultaneously ferroelastic domain struc-structure with the (001) domain walls and the ferroelastic one with the (100) domain walls. The former is observable below 102°C, while the latter is observable even above 102°C. The intensity of the light beam deflected at the (001) domain walls is observed to be proportional to the square of the spontaneous polarization.

Refraction and Reflection of Light at Ferroelastic Domain Walls in Rochelle Salt Crystal

When a laser beam transmits through an a -cut plate of Rochelle salt in the ferroelectric (simultaneously ferroelastic) phase, two types of weak intensity beams deflected from the direct beam direction are observed. The relation between the angle of incidence and the angle of deflection, and polarizing directions of light are satisfactorily explained by refraction and reflection at a domain wall, on both sides of which refractive indicatrices are mutually inclined a few degrees. The refraction and reflection occur at equal angles, and the respective polarizing directions are symmetrical with respect to the wall. There exists a critical angle of incidence, above which one type of deflection beams appears. Diffraction effects due to multi-walls do not account for the experimental results.

Deflection of Light by Ferroelastic Domains in Gd2(MoO4)3 and Bi4Ti3O12 Crystals

The relation between angles of incidence and deflection caused by the refraction and reflection of light beam at the ferroelastic domain walls in Gd 2 (MoO 4 ) 3 , Bi 4 Ti 3 O 12 and Rochelle salt crystals has been treated on the basis of crystal optics. Numerical analysis of the relation has been carried out for incident angles from 0° to 90°. At the incident angle of 0°, the deflection angles obtained by the analysis are 2.25° for the c plate of Gd 2 (MoO 4 ) 3 , 14.6° for the b plate of Bi 4 Ti 3 O 12 and 4.43° for the a plate of Rochelle salt. The experimental results with a He-Ne laser for these crystals are in satisfactory agreement with the calculated ones. The intensity ratio of the deflected beam to the direct beam is in the order of 10 -2 for Gd 2 (MoO 4 ) 3 and 10 -3 for Rochelle salt.

Orientation of the Ferroelectric Domain Wall in Triglycine Sulfate Crystals

The domain wall energy as a function of wall orientation in triglycine sulfate (TGS) crystals has been calculated on the basis of the Zhirnov-type continuum theory. Contrary to the Fouseks misleading conclusion [Japan. J. appl. Phys. 6 (1967) 950.], the isotropic treatment of the correlation-energy coefficient κ gives an inadequate result to explain the observed wall orientation which is nearly perpendicular to the crystallographic c axis. An anisotropy of κ has been reasonably introduced; a wall orientation consistent with the observations has been successfully brought about. The. anisotropies of the dielectric, elastic and electrostrictive constants of TGS rather ineffectively contribute to the orientation of the domain walls.

Light deflection induced by ferroelastic layered domains

Abstract Specific light deflection phenomena are observed in ferroelastic crystals. Above a critical angle of incidence x c , four deflected beams, which are linearly polarized, are observed with a laser beam incidence. The polarizing directions of the deflected beams are directly related to the directions of axes of the optical indicatrix in the ferroelastic domains. The relation between the angle of incidence α and the angles of deflection χ, and the polarizing directions of the deflected beams are explained by the Huygens constructions to the ray-velocity cross sections at the crystal surfaces and the domain walls in the incident plane. This optical phenomenon is confirmed as a specific property of ferroelastic crystals with multidomains. The properties of the deflected beams are described in detail.

Domain-Wall Orientations and Wall Energies in Ferroelectric Triglycine Selenate Crystals

Detailed observations of domain structure in triglycine selenate crystals have been made in special respect to the orientations of the 180° domain-walls by an improved powder-deposition technique. Two kinds of flat wall can be seen; one is parallel to the crystallographic (001) planes and another is to the (\bar201) planes. The angular dependence of the wall-energy density has been numerically calculated on the basis of the Zhirnov-type continuum theory. Two minima in the energy are obtained, each of which corresponds to the wall orientations observed experimentally. The numerical values of elastic stiffness, electrostrictive, dielectric constants and correlation-energy coefficients required for the calculation have been also determined experimentally. The theoretical and experimental results of wall orientations are discussed in comparison with those of triglycine sulfate crystals.

Spiral patterns on GASH

Abstract On the center region of cleavage surface of GASH (guanidinium aluminum sulfate hexahydrate) crystals grown at high temperatures, peculiar spiral domains have been observed by a powder deposition technique. Triangular etch pits found at the center of the spirals are direct evidence for the screw dislocation mechanism of crystal growth. Dislocations of high density are associated with the defects at the sites of crystallization water introduced during crystal growth at high temperatures. The formation model of the spiral domains are discussed on the basis of the spiral growth theory of crystal.

Sonoluminescence in X-Rayed KCl Crystals

Luminescence induced by 100 kHz ultrasonic excitation in X-rayed KCl crystals which previously are heated in chlorine vapor is observed at room temperature. Under prolonged excitation by a constant ultrasonic stress amplitude, the luminescence continues during initial several tens seconds. Simultaneous measurements of internal friction are carried out by the Marxs method in order to reveal a role of dislocation motion in the luminescent processes. Existence of critical strain amplitudes was found above which the luminescence becomes notable and the internal friction indicates an abrupt increase. The results are discussed with the vibrating string model of dislocation motion, and it is concluded that excitation of color centers electrons is caused by unpinning of dislocation and that the unpinning process annihilates defects that have pinned the dislocation.

Domain Structures and Domain Wall Energies in Ferroelectric Guanidinium Aluminum Sulfate Hexahydrate

Fine details of ferroelectric domain structure in guanidinium aluminum sulfate hexahydrate have been revealed by an improved powder pattern technique. Within large positive or negative segments which correspond to growth pyramids, striation-type domains and small circular domains have been clearly resolved. Two types of the preferential wall orientation are characterized; one is parallel to the crystallographic symmetry planes, and the other is perpendicular to them. Spontaneous switching of many small domains has been found at low temperature (about 1.2×10 5 cm -2 at -100°C); they change in shape with lowering temperature from circle to hexagon with edges parallel to the symmetry planes. From an application of the Zhirnov-type continuum theory, the wall energy density is obtained as 0.3 erg/cm 2 , and is shown to be almost independent of wall orientation.

Effect of Annealing in Chlorine Gas on Photoluminescence of X-Rayed KCl and a Hole-Trapped Center

Luminescence was induced by F-light illumination on KCI crystals which were subjected annealing in chlorine gas at an elevated temperature and subsequent X-irradiation at room temperature. The emission was evident above 150 K, and its emission spectra exhibited peak around 2.7 eV. The luminescence was ascribed to recombination of photoelectrons from F centers with hole-trapped centers which were created in crystals by diffusion of chlorine molecules during the chlorine-treatment. The hole-trapped center has a character that it is destroyed by X-rays.