TAILORED MICROSTRUCTURE OF CERAMICS BY USING ELECTRIC AND MAGNETIC FIELDS

The mechanical and functional properties of ceramics can be improved by designing their microstructures, such as grain size, grain geometry, crystallographic orientation, second phase and so on. Tailoring the crystallographic orientation in ceramics is one of effective ways for improving their properties. Layered structure with different crystalline orientation layer by layer has been proposed as an alternative for the design of structural ceramics. Grain sliding during the high temperature deformation depends on the grain boundary structure and misorientation angle between grains. The energy release mechanisms during the crack propagation such as crack deflection and crack bifurcation can improve the crack growth resistance in the laminar ceramics. The residual stress generated in each layer during cooling down from the sintering temperature has an influence on the crack deflection and crack bifurcation, hence the control of the residual stress is important for the crack growth resistance in order to improve the mechanical properties. There are some reports about the laminate composite materials with different components for controlling the thermal expansion coefficients in order to generate the residual stress. Our concept is that the crystalline axis depending on the thermal expansion coefficients aligns for controlling the residual stress in the monolithic ceramics. We controlled the layered structure in the monolithic ceramics, such as alumina and silicon carbide for control the crack deflection. The starting materials were spherical a-Al2O3 powder and a-SiC powder with trigonal and hexagonal crystal structure, respectively. These powders were dispersed in ethanol using an ultrasonic homogenizer and a magnetic stirrer. The suspension was placed in a superconducting magnet with a room temperature bore of 100mm, and then a strong magnetic field of 12T was applied to the suspension to rotate each particle due to the magnetic torque. The magnetic field was maintained in the suspension during the electrophoretic deposition (EPD) at room temperature. The crystalline-oriented laminate ceramics were produced by alternately changing the angle between the vectors E and B, jB-E, layer by layer during EPD in the 12 T magnetic field. Please click Additional Files below to see the full abstract

Spin Drift in Highly Doped n-type Si

A quantitative estimation of spin drift velocity in highly doped n-type silicon (Si) at 8 K is presented in this letter. A local two-terminal Hanle measurement enables the detection of a modulation of spin signals from the Si as a function of an external electric field, and this modulation is analyzed by using a spin drift-diffusion equation and an analytical solution of the Hanle-type spin precession. The analyses reveal that the spin drift velocity is linearly proportional to the electric field. The contribution of the spin drift effect to the spin signals is crosschecked by introducing a modified nonlocal four-terminal method.Comment: 16 pages, 3 figure

FABRICATION OF POROUS, CRYSTALLINE-ORIENTED TITANIA LAYER ON TRANSPARENT ELECTRODE BY MAGNETIC FIELD-ASSISTED EPD

Dye-sensitized solar cells (DSSCs) are the most extensively investigated systems for the conversion of solar energy into electricity, since it can convert light at longer wavelengths into electricity and can be manufactured using less energy compared to the bulk semiconductor-type cells with a p-n junction. Despite these advantages, DSSC commercialization is still limited because of its low conversion efficiency and low reliability of the liquid electrolyte. The low conversion efficiency is due to the non-uniformity of the electrode components with respect to the packing density of TiO2 particles and film thickness of the electrode. Therefore the research on DSSC in general has been directed toward improving the photo-current and photo-potential. In order to significantly enhance the cell performance, it is important to optimize the photo-anode structure of the DSSC on the basis of its fundamental properties. In this study, crystalline-oriented porous TiO2 thin films were fabricated on indium-tin oxide (ITO) or fluorine-doped tin oxide (FTO) glass substrates by electrophoretic deposition (EPD) in a superconducting magnet. Please click Additional Files below to see the full abstract

Bending strength of multi‐layered alumina with controlled residual stress

Please click Additional Files below to see the full abstract