Papers by Author: Takashi Kamiyama

Abstract: The crystal structure and oxide ion conduction properties of La0.9Sr0.1Ga0.9Mg0.1O2.9 were compared with those of LaGa0.8Mg0.2O2.9 with the same oxygen vacancy concentration. Although La0.9Sr0.1Ga0.9Mg0.1O2.9 had a smaller free space through which oxide ions pass compared to LaGa0.8Mg0.2O2.9, the activation energy of oxide ion conduction in the former was lower. This was attributed to the large displacement of La and Ga in La0.9Sr0.1Ga0.9Mg0.1O2.9. The GaO6 octahedral tilts in the LaGaO3 perovskite structure were reduced by double doping with Sr and Mg. Reduction of the GaO6 octahedral tilt proved effective for oxide ion conduction.

Abstract: The microstructural change with drawing and subsequent annealing for a patented pearlite steel was investigated by means of neutron diffraction. The dissolution of cementite plates with drawing and re-precipitation of spherical cementite particles with annealing after sever drawing were observed. In situ neutron diffraction during tensile loading was performed and it is revealed that the strengthening mechanism of the specimen without cementite differs from that for a ferrite-cementite steel where the load transfer is a main mechanism. The possible strengthening mechanism for the heavily drawn specimen is proposed.

Abstract: Neutron imaging using a pulsed neutron time-of-flight method can give an energy dependent transmission image, namely, spectroscopic image. This image includes the structure information if the sample is coherent scatterer. Here, two examples are introduced. First, we obtained the transmission image of a welded sample of SS304 and 308. Change of the crystal structure depending on the position was observed. Furthermore, we measured spatial dependent transmission of SS samples treated in different ways, surface treatment and whole body treatment. There were almost no spatial dependent change, but the cross section change was found between surface and whole body treatment samples. It was suggested that this might be due to the difference of a grain size. These results demonstrated that the spectroscopic imaging using a pulsed neutron source is a useful tool for material characterization.

Abstract: Doping effects of Sr and/or Mg on the crystal structures of LaGaO3 perovskites were investigated. The doping with Mg into Ga-site in LaGaO3 led to structural change from the orthorhombic primitive lattice (Pbnm) to the orthorhombic body-centered lattice (Ibmm) at room temperature. The orthorhombic cell (Ibmm) of LaGa0.9Mg0.1O2.95 changed to the monoclinic (I2/a) by doping with Sr into La site. Neutron powder diffraction analyses revealed that these compounds had GaO6 octahedral tilt. The GaO6 octahedral tilt angles were reduced with doping with Sr and/or Mg.

Abstract: The structure of a high ionic conductor Rb₄Cu₁₆I_7.2Cl_12.8 at low temperature has been reinvestigated by use of angle-dispersive neutron powder diffraction. All the diffraction data have been analyzed with integrated software REMEDY consisting of RIETAN-2000 for whole-pattern fitting and MEED for calculating densities of electrons or atomic nuclei by the maximum-entropy method. The resulting nuclear-density maps have reconfirmed that Cu1-Cu2 chains are the main conduction pathways in this material, as previously suggested from the Rietveld analysis of neutron powder diffraction data.