Papers by Author: M. Yoshino

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.

Abstract: The electron density distributions in a series of metal oxides are calculated using the DV-Xα molecular orbital method. It is found that the logarithm of the electron density, logρ(r), decreases with the distance, r, from the oxygen nucleus, while keeping a constant slope relevant to oxygen atom. The magnitude of the slope is about 15.75 for O-1s electrons, and about 6.61 for O-2s, 2p electrons, being nearly close to the respective values of 16 and 8, expected from the radial distribution functions of hydrogen-like atom containing only one electron. The extent of the region for the O-2s, 2p electrons changes with metal species in the oxides, but the slope remains unchanged. Furthermore, it is shown that the nature of the chemical bonding is well represented in log (ρ _minZ-3) vs. 2(Z/n) r_{minb plots, where ρmin is the minimum electron density, rmin is the distance r at ρmin, Z is the atomic number, and n is the principal quantum number.}