Reaction Sintering of Polycarbosilane-Impregnated Compact of Silicon Carbide Hollow Particles and the Resultant Thermoelectric Properties

Porous SiC ceramics fabricated from hollow particles and polycarbosilane (PSC) are promising materials for high-temperature thermoelectric energy conversion. Reaction sintering of PCS-impregnated compacts of SiC hollow particles gave rise to porous microstructures with the hollow shape remaining. The repetition of the PCS-impregnation and sintering process resulted in only a slight increase in density but in a great improvement in thermoelectric properties.     

Analogy Between Mechanical and Dielectric Strength Distributions for BaTiO3 Ceramics

Mechanical and dielectric strengths were measured for BaTiO₃, ceramics at room temperature. The results were evaluated in terms of Weibull statistics, and a clear analogy between the mechanical and dielectric strength distributions was found.     

High-Resolution Electron Microscopy Observations of Stacking Faults in β-SiC

Structural images of the stacking faults in β-SiC were obtained with a high-resolution electron microscope. Stacking faults initially present in β-SiC powder particles were eliminated as grain growth proceeded at elevated temperatures.     

Exfoliation of layers in NaxCoO2

We proposed and developed an exfoliation process for layer-structured NaxCoO2 to prepare CoO nanosheets. Na+ ion exchange by acid treatment was utilized to expand the spacing between the two CoO2 layers in NaxCoO2. Ethylamine was then effectively utilized for the exfoliation of cobalt oxide sheets having nanometer-order thickness and high aspect ratio. CoO nanosheets were observed by TEM micrographs and electron diffraction patterns after drying. Further efforts are needed for the application of exfoliated sheets to an integration process to fabricate self-assembled nanomaterials such as desired layer structures composed of two (or more) kinds of nanosheets.     

Nano/micro-patterning of anatase TiO2 thin film from an aqueous solution by site-selective elimination method

We proposed a novel method to fabricate nano/micro-scaled patterns of thin films and successfully fabricated patterns of anatase TiO₂ thin films in an aqueous solution at 50 8C. The patterned self-assembled monolayer (SAM) having octadecyltrichlorosilane (OTS) regions and silanol regions was immersed in a solution containing a Ti precursor and subjected to ultrasonication for several hours. The difference in adhesion of thin films on substrates was employed for the site-selective elimination method. Heterogeneously nucleated TiO₂ and homogeneously nucleated TiO₂ particles adhering to the OTS–SAM could be easily eliminated from the substrate by ultrasonication, whereas those on silanol groups maintained their adhesion during the immersion period. TiO₂ can form chemical bonds such as Ti–O–Si with silanol groups, but cannot form them with octadecyl groups, resulting in the difference in adhesion, which is the essence of the site-selectivity of this method. The site-selective elimination method can be applied to fabricate nano/micro-scaled patterns in the solution by the immersion of the substrate that has regions on which depositions adhere strongly and regions on which depositions adhere weakly, enabling elimination by treatment such as ultrasonication. © 2003 Elsevier Ltd. All rights reserved.     

Polymer/polymer blend solar cells with 2.0% efficiency developed by thermal purification of nanoscale-phase-separated morphology

We have fabricated polymer/polymer blend solar cells consisting of poly(3-hexylthiophene) as the electron donor and poly{2,7-(9,9-didodecylfluorene)-alt-5,5-[4',7'-bis(2-thienyl)-2',1',3'-benzothiadiazole]} as the acceptor. The power conversion efficiency (PCE) was strongly dependent on solvents employed for spin coating. The best PCE of 2.0% was obtained for thermally annealed devices prepared from a chloroform solution, in contrast to devices fabricated from chlorobenzene and o-dichlorobenzene solutions. On the basis of the morphology-performance relationship in the polymer blends examined by atomic force microscopy and the photoluminescence quenching measurements, we conclude that the highly efficient performance is achieved by thermal purification of nanoscale-phase-separated domains formed by spin coating from chloroform.     

Effect of mixing procedures and compaction pressures on the powder reaction of CuO-η-Al2O3 and ZnO-η-Al2O3 systems

The rate of reaction of the compacted powders of CuO-η-Al₂O₃ and ZnO-η-Al₂O₃ systems was measured in air at 800 to 900° C and the effect of the mixing procedure (dry and wet mixing) and compaction pressure (0 to 8.3×10⁸ Pa) of reactant oxides on the fraction of reaction completed (α) was investigated. In the reaction of the CuO-η-Al₂O₃ system, the α-values obtained for the sample prepared by wet mixing in ethanol were higher than those for the sample prepared by dry mixing in air and were not influenced by the compaction pressure, whereas in the case of dry mixing they varied with the compaction pressure and had a maximum value at 2.1×10⁸ Pa. On the other hand, in the reaction of the ZnO-η-Al₂O₃ system the α-values for the sample obtained by wet mixing were lower than the values obtained by dry mixing, in contrast to the results in CuO-η-Al₂O₃ system, and the α-values for the samples prepared by both dry and wet mixing were not influenced by the compaction pressure. The effect of mixing procedure and compaction pressure of reactant powders on the α-values was found to be explained on the basis of the aggregate size of CuO and ZnO dispersed in the matrix of η-Al₂O₃ fine powder.     

Barium Titanate Ceramics with High Piezoelectricity Fabricated from Fibrous Particles

Barium titanate ceramics with high degrees of c-axis orientation were fabricated from fibrous particles. The maximum piezoelectric constant, d₃₃, obtained was ≅270 pC/N, which is much higher than values reported previously.     

Curie point of perovskite-type oxides containing bivalent ions of the 4th period in the B-site

The effects of different B-site elements on the Curie points of the PbTiO₃-Pb(M₁/3Nb_2/3)O₃ and 0.99BaTi0₃-0.01Ba(M_1/3Nb_2/3)O₃ series (M = Ca, Mn, Fe, Co, Ni, Cu, Zn), were examined. The Curie point was high when M was copper, while it was low when M was nickel. This was caused by the Jahn-Teller effect in the CuO₆ octahedron keeping the Curie point high. For the 0.99BaTiO₃-0.01 Ba(M_1/3Nb_2/3)O₃ systems, the Curie points were correlated with axial ratioc/a.     

Stochastic analysis of OneMax problem using Markov chain

Experimental and analytical investigations are performed for OneMax problem using Wright–Fisher model. This study investigates the distribution of the first order schema frequency in the evolution process of Genetic Algorithm (GA). Effects of mutation in GA are analyzed for the standard mutation and asymmetric mutation models. If a population is in linkage equilibrium, it can be shown that OneMax problem is equivalent to the asymmetric mutation model. Thus, we can apply theoretical results obtained in the asymmetric mutation model to OneMax problem and investigate the convergence time of GA calculation within the framework of Wright–Fisher model.