Papers by Author: Y. Shinzato

Abstract: A new expression for the chemical bond in perovskite-type oxides is proposed based on the atomization energy concept. The atomization energies,
Eo for oxygen atom and
EM for metal atom in each oxide are evaluated theoretically using the energy density analysis of the total energy, and the 9EO vs. 9EM diagram called atomization energy diagram, is constructed. Every oxide can be located on the atomization energy diagram, although there are significant differences in the nature of the chemical bond among the oxides.

Abstract: Niobium metal is one of the promising material for hydrogen purification because of its high hydrogen permeability. In order to design and develop a new palladium-free hydrogen permeable membrane, it is important to understand the effects of alloying elements on the hydrogen permeability through metals. However, to the niobium metal, the alloying effects still remain unclear. In the present study, using a DC-polarization technique under the diffusion limiting condition, the hydrogen permeability of Nb-5mol%M alloys were investigated in high precision at 573K. Here, M’s were 4d transition metals, Zr, Mo, Ru and Pd. The permeability of niobium is found to be varied with the addition of a small amount of alloying element. For example, the hydrogen permeability of niobium increases by the addition of Zr but decreases by the addition of Ru.

Abstract: Formation energies of various defects in Al₂O₃ and SiO₂ are calculated by using the plane-wave pseudopotential method. Also, the formation energies of Schottky defects and Frenkel defects are evaluated on the basis of these calculations. It is shown that formation energies of these defects are higher in SiO₂ than in Al₂O₃. In other words, less defects are formed in SiO₂ than in Al₂O₃. It is also found that the principal defect is the cation Frenkel defect in Al₂O₃ but the anion Frenkel defect in SiO₂. These results agree with the experimental results that Al ions diffuse preferably in Al₂O₃ but oxygen ions diffuse in SiO₂ at high temperatures.