ABSTRACT:The hydrogen desorption reaction of magnesium hydride (MgH 2 ), MgH 2 3 MgϩH 2 , is accelerated by mixing catalytic metal oxides (e.g., Nb 2 O 5 ). This catalytic effect of metal oxides, MxOy, is theoretically estimated in a quantitative way using atomization energy concept. The atomization energies, ⌬E M for metal ion and ⌬E O for oxide ion in various metal oxides are evaluated using the energy density analysis of the total energy. It is shown that the hydrogen desorption rate increases monotonously with increasing y ϫ ⌬E O values of metal oxides. This indicates that the oxide ion in MxOy interacts mainly with hydrogen atoms in MgH 2 . The y ϫ ⌬E O value is a measure of the magnitude of the OOH interaction operating between MxOy and MgH 2 , and hence, it is indeed a good parameter to show the catalytic activities of metal oxides. This approach is useful for the analysis of other catalyst and catalytic reactions.

ABSTRACT:The hydrogen desorption reaction of MgH 2 , MgH 2 ! Mg þ H 2 , is accelerated by the addition of metal oxide catalysts (e.g., Nb 2 O 5 ). From our theoretical calculation of electronic structure, it was predicted that the catalytic activities of metal oxides are related closely to the OAH interaction operating at the interface between oxide catalyst and MgH 2 . In this study, the OAH vibration on the Nb 2 O 5 -catalyzed MgH 2 was investigated experimentally using FTIR spectroscopy. The broad absorption band due to the OAH stretching mode was observed in the region of 2,800-3,600 cm À1 in the FTIR spectra of the specimens when hydrogen desorption reaction was in progress. The absorbance of the band decreased monotonously with decreasing hydrogen content in the specimen during the course of dehydrogenation of MgH 2 . This experimental result was in agreement with our prediction for the existence of OAH interaction in the hydrogen desorption process.

To understand the phase transition from perovskite to postperovskite MgSiO3, total energy is partitioned into atomic energy densities of constituent elements in the oxide, using the energy density analysis. The atomization energies, ΔEMg for Mg atom, ΔESi for Si atom, and ΔEO for O atom, are then evaluated by subtracting the atomic energy density from the energy of the isolated neutral atom, Mg, Si, and O, respectively. It is found that ΔESi and ΔEMg are much larger than ΔEO in the perovskite phase, but ΔEO is much larger than ΔESi and ΔEMg in the postperovskite phase. This means that most of the energies partitioned into Mg and Si atoms in the perovskite phase transfer to the O atoms in the postperovskite phase during the transition. Such an extremely stable O‐atom state is formed by the introduction of edge‐shared SiO6 octahedra into the postperovskite structure. This is because the edge‐sharing makes the Si–O interatomic distances longer even in very high pressure conditions. The unusual energy balance between atoms is also seen in the other postperovskite, MgGeO3 and NaMgF3.

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Various metalˆlms were deposited by magnetron sputtering, and their thickness distributions were measured. The distributions are considered to depend on the angular distribution of the atoms ejected from a target. Some metals showed a thickness distribution with its maximum at the anode center while the others showed a thickness distribution with its maximum at a position slightly inside the target erosion. According to a theory and computer simulation, as the binding energy (i.e. cohesive energy) of a target decreases and the mass of the target atoms increases, the atoms tend to be ejected normally with their angular distribution being apt to be over-cosine. Thus, the thickness distributions were discussed in relation to the binding energy of the metals and the mass of the target atoms. The thickness distributions were also investigated for diŠerent discharge voltages.