Chikashi Suzuki

Nonempirical prediction of impurity segregation in α-Fe from first principles

The segregation and clustering of impurities in α-Fe were investigated by first principle density functional theory calculations. The segregation tendencies of various elements observed in reactor pressure vessels were considered and the interaction characteristics between Fe and each impurity element were estimated by mean field approximation. Stable N-atom impurity clusters were subsequently chosen to evaluate the changes in free energy for clustering. These calculations show that Cu and Mn impurities embedded in α-Fe are more stable when they are in the segregated state. Conversely, Nb and Ta are stable in the separately solute state. The present estimates provide reliable suggestions for the segregation characteristics, and the tendencies are in good agreement with the recent atom probe observations. We suggest that the segregation tendency is derived from the d-orbital interaction and that the solubility limit is not necessarily correlated with the tendency of clustering formation.

Clarification of the Mechanism of Sulfur Trioxide Electrolysis : Evaluation of SO3 and O Atom Adsorbed on Pt Surface

We developed a hybrid thermo-chemical process, which included a SO3 electrolysisprocess utilizing the heat supplied by a fast breeder reactor (FBR), as a new hydrogen production process. To clarify the mechanism of SO3 electrolysis, we evaluated the electronic states of SO3 and O atom adsorbed on the Pt (111) surface using first-principles calculations with a slab model. Moreover, we evaluated the chemical bonding states of SO3 and adsorbed O using molecular orbital calculation on the basis of the calculations using a slab model. We found that there were two stable adsorbed SO3 configurations on the Pt surface. From the molecular orbital calculation, it was found that the S-O bond became weak by SO3 absorption, and it was conjectured that SO3 dissociation proceededthrough the intermediate state of adsorbed SO2 and adsorbed O on the Pt surface. Moreover, we derived the O coverage considering the adsorbed SO2 and evaluated the influence of SO3 adsorption energy on the O coverage.

Resonant Inelastic X-ray Scattering at Ba-L3 Edge in BaTiO3

Resonant inelastic X-ray scattering (RIXS) measurements have been carried out at the Ba-L3 absorption edge on ferroelectric BaTiO3 for the first time. The absorption spectrum was measured in the partial fluorescence yield mode, by monitoring the intensity of the maximum of the Ba-Lα1 line through the Ba-L3 edge. The main peak, which reflects the unoccupied density of Ba 5d states, is found to be narrow, although broad shoulderlike tails appear towards both low and high energies. Using band structure calculations, these tails are ascribed to the strong hybridization between unoccupied Ba 5d and O 2p bands. Hybridization notwithstanding, the Ba 5d band is shown to retain a localized character, on the basis of the incident energy dependence of the Ba-Lα1 RIXS spectra.

Microscopic Approach to Water by Using the DV-Xα Method, and Some Innovative Applications

The importance of water is generally recognized; the human body contains about 70 % water by mass and water is widely used as a solvent for chemical reactions, and plants use water in forming starch. Despite this, there remain a number of mysteries in the science of water. At the atomic level, water molecules are linked by hydrogen bonds to form large clusters. Here, we apply the DV-Xα method to calculate the electronic structures of two water molecules for the case when the hydrogen bond between them is broken. Because the bonding electrons exist in a plasma-like state in the water molecule after breaking of the hydrogen bond, electromagnetic waves in the near-infrared through terahertz region are emitted as a result of the free movement of electrons in water with broken hydrogen bonds, which is known as minimal catalyst water (MICA water). This energy can be transferred to other substances. As a result, MICA has a variety of applications, such as the reduction of exhaust gases from automobiles or keeping foods fresh; the mechanism of such applications can be explained in terms of the activation of dinitrogen by MICA energy. Another application of MICA is deodorization of rooms by MICA-treated fluorescent lamps or activated ceramic honeycombs.