We have studied the effect of surface treatment on oxygen self-diffusion in Sm doped BaTiO3 ceramics. The sample prepared with the chemical mechanical polishing (CMP) showed the suitable diffusion profile and 18O image. In mechanical polished sample, the enhancement of oxygen diffusion due to the damage introduced by the polishing was observed. The CMP method is the suitable technique to prepare the surface for diffusion study.
The phase transition phenomena were investigated with respect to the local environments around the cations with EXAFS, where Ho was used as a probe. When Ho replaced the Ba site, Ho-O distance decreased with temperature. On the other hand, Ho-O in the Ti site showed opposite response against temperature.
ZnO thin film on glass substrates is a significant candidate as a transparent conductive electrode. It is known that its conductivity will be given from the zinc between lattices and an oxygen defect. We report here ZnO thin film fabrication on a glass substrate by molecular precursor method. ZnO precursor solution was prepared from a Zn complex of EDTA. Another type of precursor solution was newly prepared from the reaction of zinc formate with propylamine. By applying the solutions with spin-coating method, ZnO thin films were obtained by heat-treating of the precursor film on quartz glass substrate.
We synthesized Ce0.15Nd1.85CuO4-y by the polymerized complex method. For the generation of the oxygen defects, the synthesized samples were annealed at 900-950 ºC for 20h under Ar atmosphere and then quenched to room temperature under the same atmosphere. The oxygen content for these samples was measured by hydrogen reduction with thermogravimetric analyzer. The dc magnetic susceptibility for these samples was measured by SQUID magnetometer.From the result, we could get samples which have different oxygen content by control of annealing temperature and it suggests correlation between oxygen content and Tc.
A Li-Nb oxynitride was synthesized through ammonia nitridation of LiNb3O8. The structural analysis revealed that the crystal structure of this oxynitride consists of alternate stacking of octahedral and prismatic layers: Li and Nb ions coexist in the octahedral layer, while the prismatic site is preferentially occupied by Nb. This oxynitride shows a metallic behavior, accompanied by an abrupt drop of electrical resistivity at about 3 K. Furthermore, a large diamagnetism was observed below this temperature, suggesting the appearance of superconductivity.
A novel pnictide-oxide BaTi2Sb2O was synthesized by solid state reaction. XRD revealed that BaTi2Sb2O consists of alternate stacking Ba layers and Ti2Sb2O layers with lattice constants a = 4.111, c = 8.072. This compound shows metallic behavior and an anomaly was observed in electrical resistivity and magnetic susceptibility at around 50 K, as seen in the related compound Na2Ti2As2O, where a SDW/CDW transition was reported.
Hybrid films of brookite (TiO2) and 12 tungsto (VI) phosphoric acid (PW12) were prepared via layer-by-layer (LBL) processes on the quartz substrate. The photocatalytic activity and photo-induced hydrophilicity of heat-treated film of brookite two layers (H-TT) and brookite two layers covered with PW12 layer (H-TTP) were compared. The H-TTP film showed better photocatalytic decomposition activity against gaseous IPA, and faster hydrophilic conversion in the early stage. The mechanism on these results was discussed.
Technologies of hydrophobic coating on solid surface have been applied to various industrial items for droplet formation and removal from solid surfaces. However, for such surfaces, excellent water shedding properties and droplet control in a desired direction are not easily attainable unless detailed understandings on the relation between solid characteristics and static/dynamic hydrophobicity. Recent researches revealed that static and dynamic liquid droplet behaviors are affected by nano-scale surface characteristics on hydrophobic solids, and the importance of the viewpoint from materials science is gradually increasing in this topic. This paper presents a review of recent studies of the past decade of our group, investigating the relation between solid characteristics and static/dynamic hydrophobicity.
Mesoporous silica MCM-41 with the hexagonally ordered mesoporous structure was sintered in air or N2 in order to obtain bulk sintered bodies with highly ordered mesopores. Although XRD patterns showed that the ordering of the mesoporous structure of MCM-41 disappeared during sintering at 700 ˚C in air, the sintered samples with the porosity of 10-50% showed significantly low thermal conductivities in comparison with conventional porous materials. Moreover the ordering of the mesoporous structure was maintained in N2 at higher temperature than in air, because MCM-41 shows higher thermal stability in the absence of oxygen.
We investigated the influence of doping on the (BiS)1.2(TiS2)2 misfit layer sulfides as a novel thermoelectric material. The substitutional doping was attempted to improve its thermoelectric performance through decreasing the carrier concentration. The alkaline earth doping successfully reduced the carrier concentration. However, ZT value could not be optimized due to a slight decrease in Seebeck coefficient and an increase in lattice thermal conductivity. We analyzed this strange result and discussed the effect of structural change by doping on the thermoelectric properties of (BiS)1.2(TiS2)2.
BaBi1-xSbxO3 (x = 0.0 - 0.5) ceramics were prepared and the electrical conductivity and Seebeck coefficient were measured at high temperatures to elucidate the substitution effect of Sb on the thermoelectric properties of BaBiO3. All the ceramics exhibited p-type semiconducting behavior and the electrical conduction for x = 0.0 - 0.4 was attributed to hopping of 6s holes between Bi5+(6s0) and Bi3+(6s2). Substitution of Bi with Sb led to the systematic decrease in cell volume, the decrease in electrical conductivity, and the increase in Seebeck coefficient, suggesting that the Sb atoms were doped as Sb5+ replacing Bi5+ and reducing 6s holes as carriers. The power factor was maximized for Sb-undoped BaBiO3 (3*10-5 Wm-1K-2 at 773 K).
The thermal conductivity, κ, of metal oxides ATaWO6 (A = K, Rb, Cs) with β-pyrochlore structure was investigated in terms of the "rattling" motion of the smaller A cations, which is expected to scatter phonons effectively. Interestingly, the κ values are lower for the oxides containing the lighter A cations, obviously contradicting the conventional prediction of the phonon thermal conductivity. Moreover, the κ values observed for KTaWO6 were virtually the same as the theoretically predicted minimum thermal conductivity, κmin. These results strongly suggest that the phonon scattering in the oxide would really be maximized by the rattling motion of K+ in the cage.
Na8B74.5Si17.5 was synthesized by heating a mixture of sodium, silicon and amorphous or crystalline boron at 1073−1273 K. The black hexagonal prismatic single crystals were obtained at 1273 K. Na8B74.5Si17.5 bulk ceramics was prepared by heating a compact of boron powder with Na and Si at 1173 K. The bulk ceramics had a density of 1.90 Mg/m3, which was about 77 % of the theoretical density (2.48 Mg/m3). The fracture bending stress of the Na8B74.5Si17.5 bulk was evaluated to be 104 MPa at room temperature.
The sintering of hBN-TiN-TiB2 composite was performed by spark plasma sintering (SPS) at 2173 K under the pressure of 100 MPa for 300 s. TiB2 formation was observed in hBN-TiN-TiB2 composite containing 50 vol%hBN. With increasing hBN content from 10 to 90 vol%, the apparent densities decrease from 4.8 to 2.6 Mg m-3. The sintering mechanism in this ternary system was mainly occurred by the densification of TiN and TiB2, while the in-situ TiB2 formation has been also beneficial to the densification.
Alumina and titania were used as sintering additives for silicon carbide, and sinterability of hot-pressed silicon carbide with alumina and titania was investigated. Bulk density of hot-pressed silicon carbide ceramics with 5 wt% and 10 wt% Al2O3-TiO2 additives at 1800oC was 2.62 g/cm3 and 2.73 g/cm3, respectively. In the case of silicon carbide ceramics hot-pressed at 1900oC, they were so dense and their bulk densities were 3.10 g/cm3 and 3.17 g/cm3, respectively. XRD pattern of silicon carbide ceramics hot-pressed at 1900oC indicated that they mainly consisted of β-silicon carbide and contained titanium carbide derived from sintering additives.
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