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Electronic states of superionic conductors such as alpha-AgI, Li₃N, and the lithium sulfate superionic conducting glasses, were calculated by the DV-Xalpha cluster method. The movements of the cations were simulated by several model clusters with different positions of the moving cation. The net charge of moving cations and the total bond overlap population between the moving cation and the other ions were used for discussion of chemical bonding of the moving cation. In alpha-AgI and Li₃N crystals, the total bond overlap population of the moving cation along the conduction path changed smaller than those of the other paths. On the other hand, the changes of the net charges of the moving cations were similar in any paths. Furthermore the relationship between ionic conductivity and the differential bond overlap population were discussed in the lithium sulfate superionic conducting glasses. In these glasses, the DBOP had good negative correlations with the ionic conductivities and positive correlations with the activation energies.

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The Structure and the location of deuterium atoms were investigated for the deuterated nano-graphite by neutron diffraction. The deuterated nano-graphite was prepared by mechanical milling under deuterium gas atmosphere. The structure of graphite was changed by a creation of dangling bonds and deuterium was absorbed by the solid-gas reaction when the milling proceeds. The RDF(r) observed by neutron diffraction indicates two kinds of locations of deuterium atoms, that is, some deuterium atoms bond with the carbon atoms and others exist between layers of the graphite.

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Silicon nitride (Si₃N₄) continues to attract many researchers because of interesting mechanical and dielectric properties. The purpose of this work is to study the electron-density distribution of alpha-Si3N4 using synchrotron powder diffraction data. The covalent bonding between Si and N atoms is observed in the electron-density distribution of alpha-Si₃N₄) for the first time in the present study.Commercial silicon nitride powders (SN-R10, Ube Industrial Co., Ube, Japan) were utilized for a synchrotron powder diffraction measurement. The synchrotron powder diffraction experiment was carried out at 26oC on the beamline BL-4B2 at the Photon Factory, Tsukuba, Japan.

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The effect of Fourier series truncation errors on the electron density distribution (EDD) of LiMn₂O₄ has been examined using the single-crystal synchrotron X-ray diffraction data and the molecular dynamics (MD) simulation. The MD crystal structure factors obtained from each MD snapshot taken at 2fs intervals in real space were time-averaged and then reversely Fourier transformed to calculate EDD in a similar way to the X-ray data. The EDD thus obtained in the range sin\q/\l < 3.33 Å-1 was scarcely affected by the series truncation errors, indicating unambiguously that a small portion of Li does exist close to interstitial positions near the 16c site of the space group Fd-3m. The residual EDD assuming a partial structure with eliminating Li atoms also reproduced a mostly correct picture about the distribution of interstitial Li atoms, even though the value of sin\q/\l of the MD data was reduced to 0.80 A^-1. The interpretation of EDD obtained from the single-crystal synchrotron X-ray diffraction data was thus verified and reinforced from the MD simulation, not only by looking at the real space distribution of atoms in the snapshots but also by a close examination of their Fourier transform.

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Crystal structure of a new ferroelectric barium titanate BaTi₂O₅ was investigated by the Rietveld analysis of neutron powder diffraction data measured at 706^oC. The crystal structure of BaTi2O5 at 706^oC was successfully refined assuming the centrosymmetric monoclinic A2/m space group. The crystal structures of the high-temperature A2/m and low-temperature A2 phases are similar. The displacement of atoms along the b axis is accompanied by the paraelectric A2/m to ferroelectric A2 phase transformation. The A2/m-A2 transition is not reconstructive but displacive.

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A novel porous carbon material called rice bran carbon (RBC) was mixed with a submicron SiC powder and consolidated by a pulse electric current sintering (PECS) method to prepare SiC/RBC composite ceramics. The mechanical and tribological properties of the SiC/RBC composites were evaluated and compared with those of a monolithic SiC, a monolithic RBC bulk material and a SiC/graphite composite. The SiC/RBC composites not only had superior fracture strength, but also showed low friction coefficients and high wear resistance in sliding tests under dry conditions. Compared with the conventional SiC/graphite composite, the SiC/RBC composites showed higher mechanical strength, lower friction coefficients and better wear resistance.

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Silicon nitride/tungsten compound composites were fabricated under hot press conditions. The composites had high wear resistance under unlubricated condition compared with a conventional silicon nitride, attributed to the formation of a protective layer during sliding. The tungsten compound addition did not affect the friction coefficient under hydrodynamic type lubrication, but the running in distance decreased under water lubrication.

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Nano-sized dense Si3N4 ceramics have been produced by high-energy mechanical milling followed by spark plasma sintering. The superplastic deformation of these ceramics is studied in compression over a wide range of strain rates and temperatures. Different deformation behaviors have been reported compared with that reported before for silicon nitride ceramics with sub-micron-sized grains.

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Reaction bonded MgSiN2 (RBMSN) was prepared by direct nitridation of Si/Mg2Si/Mg/Si3N4 powder compact in a temperature range 1350-1550 C. It was shown that the starting powders should be in a ratio Mg2Si/Mg > 3 and Si3N4/Si < 0.5 respectively, to obtain single-phase MgSiN2. The oxygen content of MgSiN2 was in the range of 0.4 - 0.5 wt%. The thermal stability examination showed that MgSiN2 is stable up to 1420C at 0.1 MPa N2 pressure. The activation energy of decomposition was determined from the temperature dependence of weight loss. The nitrogen pressure dependence of decomposition showed that MgSiN2 is stable at 1560 C in 0.6 MPa N2 atmosphere. Using these experimental data together with the heat capacity published in a literaturte the thermodynamic properties (entropy, enthalpy and Gibbs free energy of formation) were calculated in a temperature range 300-2500 K.Pure MgSiN2 powder or MgSiN2/Si3N4 mixture with fluorine-based additives were densified by hot pressing. The composite materials had a 4-point bending strength and Vickers hardness (HV1) 427 MPa and 20.8 GPa, respectively. The indentation fracture toughness was 5.3 MPa.m^1/2, due to the presence of elongated b-Si3N4 grains. The dielectric constant of dense reaction bonded MgSiN2 was 9.5-10, while that of MgSiN2/Si3N4 composite was higher by orders of magnitude in the measured frequency range.

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Spark Plasma Sintering (SPS) and Plasma Activated Sintering (PAS) technique has been developed for more than one decade and a variety of materails, such as structural ceramics, ceramic composite, polymers and functionally graded materials have been rapidly prepared by SPS and PAS. However, the sintering process is not fully understood. It is suggested that metallic and non-metallic materials should be considered individually when attempting to clarify the SPS and PAS process. In this paper, sintering of non-metallic powder, i.e. Al2O3 powder by SPS and PAS was reported, focusing on the effects of SPS parameters, such as heating rate, holding time, mechanical pressure, and particle size of the starting powder, on the densification and microstructure development of Al2O3 powder compacts. Based on these research, understanding of the sintering process was proposed.

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We demonstrate a unique processing technique which we term the nano-explosion synthesis of multi-metal oxide nanopowders. This technique is based on engineering multi-component ceramic nanopowder with precise morphology by nano-blast deagglomeration/calcination. Multiple nano-explosions of impregnated cyclotrimethylene trinitramine deagglomerate the nanopowder due to the highly energetic impacts of the blast waves, while the solid-solubility of one component into the other is enhanced by the extremely high local temperature generated during the nano-explosions. We successfully applied this technique to produce nanosize agglomerate-free ceria-gadolinia solid solution powder with excellent morphology and an average aggregate size of 42 nm. In addition we synthesized lanthanum strontium gallium magnezium oxide nanopowder.

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We found that PCS fiber as a SiC precursor could be cured by EB oxidation only surface part of the fiber, and developed the hollowing process after curing of the PCS fiber by extracting of the un-crosslinked core. The diameter and wall thickness of the SiC micro tube could be controlled by the temperature, oxygen pressure and irradiation dose rate during EB curing. This presentation describe about these synthesis mechanisms and suitable conditions.

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We have found that nanocrystallites are formed in the TiO₂-Al₂O₃ gels by mechanical milling. In this work, homogeneous TiO₂-Al₂O₃ gels and mixtures of TiO₂ gel and Al₂O₃ gel were mechanically milled under various conditions. Crystallites formed in the gels were characterized using XRD, EDX and TEM and compared with those generated in the gels by heat treatment. It was found that novel Al-Ti (1:1) oxide crystallites with a high photocatalytic activity were obtainable.

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TiO₂ (anatase) coating was prepared on stainless mesh by electrophoretic (EPD) process utilizing an isopropanol (IPA)-based suspension with submicron TiO₂ powder. When the deposition thickness was 25 micrometer, a smooth thin coating was obtained. It remained crack-free even after sintering. Coating surface morphology was roughened by UV pre-illumination of the suspension. Photocatalytic decomposition of IPA to acetone and resultant electrochemical reaction at cathode during EPD gives heterogeneous deposition.

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Crystalline mesoporous TiO₂ thin films with a vertical porosity were synthesized through an inorganic/organic cooperative assembly. Cubic mesostructured TiO2 thin films (Im-3m) as its [111]-zone axis normal to the substrate were first prepared by employing titanium isopropoxide (TTIP) as inorganic titania source and a triblock copolymer called P123 as organic template. Calcination was carried out at 400 degree C in order to remove the organic template and to crystallize the amorphous titania pore wall. After calcination, the crystalline mesoporous TiO₂ thin film consisted of crystalline TiO₂ (anatase phase) nanopillar arrays were formed with an open and perpendicular porosity throughout the film.

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