Fujio Suda

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.

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.

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.

Spiral Patterns on Cleavage Surfaces of Ferroelectric Guanidinium Aluminum Sulfate Hexahydrate

Spiral patterns due to screw dislocation have been revealed by a charged-powder deposition technique on cleavage surfaces in {0001} growth region of ferroelectric guanidinium aluminum sulfate hexahydrate crystals grown from aqueous solution of high temperatures (60°C–95°C). The patterns are observed not as surface topography on the natural faces of crystal, but as charge distribution on the cleavage surfaces in the crystal. Dislocation etch pits found at the center of the spirals are direct evidence for the spiral growth of crystal along the trigonal axis. The rotational motion of the spiral patterns during crystal growth is discussed on the basis of the spiral growth theory.

Shapes of Moving Domain Boundary Affected by Edge Dislocation in Ferroelectric Crystal of Triglycine Sulfate

Shapes of moving 180°-wall affected by stresses due to a dislocation were obtained for TGS crystals from calculations based on Nakamuras theory of domain growth. Anisotropic sidewise velocity, v , of wall motion under the stress T was determined on the assumption that v depended on T through the wall energy density σ; the T dependence of σ was derived from the Zhirnov-type continuum theory. An edge component, rather than a screw component, of a dislocation which is parallel to the ferroelectric axis affects the value of σ. Under a low field the wall is caught in the dislocation, while under a high field it easily passes through the dislocation. The results are in qualitative agreement with experimental observations.

Temperature Effect on the Morphology and Fractal Dimensions of Zinc Metal Leaves

Zinc metal leaves grown two-dimensionally by electrodeposition were experimentally investigated with particular attention to the temperature dependence of their morphology. They changed form from a DLA-like to a disclike pattern with increasing temperature. The results of fractal analyses indicated that at temperatures lower than 20°C, their fractal dimension D is almost constant at 1.66, which is nearly equal to that of the two-dimensional DLA. At temperatures higher than 20°C, D increases almost linearly with temperature. From the analysis of scanning electron microscope images of various magnifications, it is shown that zinc metal leaves are fractals over a wide length range spanning five orders of magnitude with a single value of D. The relationship of the temperature-dependent change in the morphology of the metal leaves with variation of D has been successfully interpreted on the basis of Nittmann and Stanleys statistical mechanical model [J. Nittmann and H. E. Stanley: Nature 321 (1986) 663].

Present use and the future of the environmental energy

In the present paper, it was shown firstly that the world population, GDP, energy consumption and CO2 emission vary exponentially with time constants of several ten years. Secondly, present use of world photovoltaics, wind power and various renewable energies in Japan were briefly overviewed. Lastly, it was concluded that improvement of the utilization system of environmental energy is necessary to increase the installation capacity.

Indoor performance tests of a new type solar still

In our previous study, results of the indoor performance test of a tilted-tray, wick-type solar still with a condensing chamber have been reported. In the present study, dependence of total distillate on saline water flow rate has been experimentally investigated. Performance tests were done and their results were compared with those of the non-circulation type solar still. It was found that the effect of the distillate on saline water flow rate was smaller at higher solar insolation than at lower insolation.

Indoor performance tests of a new type solar still. (II). Effect of moist-air circulation on distillate output.

In our previous study [J. Adv. Sci. 8, 57 (1996)], results of the indoor performance test of a tilted-tray, wick type solar still with a condensing chamber have been reported. In the present study, this solar still has been improved so as to be a circulation type, where the moist air can circulate between the evaporator and the condenser. Performance tests were done and their results have been compared with those of the non-circulation type. The distillation efficiency was considerably improved, especially at lower solar insolation, and its performance characteristics became more stable to irradiation changes.In our previous study [J. Adv. Sci. 8, 57 (1996)], results of the indoor performance test of a tilted-tray, wick type solar still with a condensing chamber have been reported. In the present study, this solar still has been improved so as to be a circulation type, where the moist air can circulate between the evaporator and the condenser. Performance tests were done and their results have been compared with those of the non-circulation type. The distillation efficiency was considerably improved, especially at lower solar insolation, and its performance characteristics became more stable to irradiation changes.