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Volume 73, Issue 8
Displaying 1-18 of 18 articles from this issue
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Special Issue on Frontiers of Computational Materials Science and Engineering (1)
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Yoshiyuki Kawazoe, Masanori Kohyama2009 Volume 73 Issue 8 Pages 549
Published: 2009
Released on J-STAGE: August 01, 2009
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Satoru Masatsuji, Yuji Misumi, Soh Ishii, Kaoru Ohno2009 Volume 73 Issue 8 Pages 550-554
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSA realistic lattice gas model with a tetrahedral 4-body interaction is derived for a system composed of Fe and Pt atoms and vacancies on the basis of first-principles calculations. Using this model, we carry out lattice Monte Carlo simulations of order-disorder phase transition in a bulk FePt alloy, aggregation into FePt clusters in vapor, and L10 ordering in FePt clusters. The order-disorder phase transition temperature of a bulk FePt is estimated to be 1970 K, which is slightly higher than the experimental value of 1572 K because of the ignorance of the off-lattice effects. The present model shows inherent atomic cohesion that leads to aggregation into clusters in a simulation starting from a random configuration in vapor. Finally for FePt alloy clusters, we find that the L10 ordered structure is maintained only for those clusters with a size (diameter) greater than 2.5 nm, in accordance with the recent experimental evidence reported by Miyazaki et al.
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A. Suvitha, R. V. Belosludov, H. Mizuseki, Y. Kawazoe, M. Takeda, M. K ...2009 Volume 73 Issue 8 Pages 555-558
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSA theoretical study has been performed on a hematoporphyrin and its dimers which are components of Photofrin, a photosensitizer. Full geometry optimizations have been carried out using the PBEPBE functional and 6-31 G(d) basis set. This combination gives better agreement with X-ray crystal data of porphyrin. Among the dimers studied, the C-C linked structure is found to have the highest stability. The predicted change of free energy (ΔG=-13.9 kcal/mol) suggests that the interconversation of ester to ether would be thermodynamically favorable. The time-dependent density functional theory (TDDFT) studies show that Q-band absorption maxima undergo a less intense transition and low oscillator strength, indicating that dimers have activity when treated under higher dosage.
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Ru-Zhi Wang, Masanori Kohyama, Shingo Tanaka, Tomoyuki Tamura, Shoji I ...2009 Volume 73 Issue 8 Pages 559-565
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSThe stability and interfacial bonding of coincidence tilt and twist grain boundaries (GBs) in Al and Cu have been examined by using the projector-augmented wave method within the density-functional theory. For the {221} Σ=9 tilt GB, glide models are more stable than mirror models for Al and Cu, and the {001} Σ=5 twist GBs are more stable than the Σ=9 tilt GBs for Al and Cu, due to smaller structural distortions. There is a tendency that the boundary energies in Al are substantially smaller than those in Cu. This can be explained by the electronic and atomic behavior of bond reconstruction at the interfaces in Al, due to the covalent nature of Al as observed in the charge density distribution, in contrast to rather simple metallic bonding at Cu GBs. The nature of GBs is discussed with respect to the micro-structural evolution and mechanical properties of metallic micro-crystalline formed by severe plastic deformation.
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Shigeto R. Nishitani, Ryohei Takeda, Hideki Ishii, Yosuke Yamamoto, Ta ...2009 Volume 73 Issue 8 Pages 566-570
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSThe quasi-harmonic approximation is a powerful tool for predicting the vibrational free energy using the first principles calculations. This method with the phonon density of states shows reliable estimation of the thermal expansion and the relative stabilities of SiC polytypes. For the binary systems, we derived a cancelling condition of the vibrational free energy change due to the phase separations within the first order approximation in terms of the nearest bond pair interaction.
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Hajime Kimizuka, Hideki Mori, Hiroki Ushida, Shigenobu Ogata2009 Volume 73 Issue 8 Pages 571-576
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSWe have analyzed the diffusion behavior of interstitial hydrogen in bcc iron and niobium using path-integral centroid molecular dynamics (CMD) method, which can describe the real-time evolution of particles based on quantum statistical mechanics. In this study, the embedded-atom-method (EAM) potential model for the iron-hydrogen interaction is developed to reproduce the ab initio minimum energy path of hydrogen migration based on the density functional theory (DFT) data in the literature, while the description of niobium-hydrogen interaction is based on an empirical potential model. Time evolutions of mean-square displacements of hydrogen atoms in the two bulk metals are calculated at various temperatures, and then diffusion coefficients and activation energies of hydrogen migration are evaluated. Especially in the case of iron, the results are in good agreement with experimental measurements over a wide temperature range. In order to characterize the quantum effects on the hydrogen diffusion process, the CMD results are compared with those obtained from classical molecular dynamics method. The obtained results indicate that the quantum effects can play a significant role in hydrogen diffusivity over a wide temperature range in these bcc metals.
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S. Watanabe, T. K. Gu, Z. C. Wang, T. Tada2009 Volume 73 Issue 8 Pages 577-582
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSAs a first step to clarify the microscopic working mechanism of atomic switches using solid electrolytes, we have examined electronic states and electron transport properties of Ag-Ag2S-Ag and Cu-Ta2O5-Pt systems using standard density functional theory and novel non-equilibrium Green's function method. In both the systems, we found that the bridge structures consisting of excess Ag or Cu in the middle solid electrolyte layer work as electronic conduction paths. In Cu-Ta2O5-Pt, we also found that O vacancy is much less effective for the enhancement of electronic conduction than excess Cu.
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Takahiro Yamamoto, Junichiro Shiomi2009 Volume 73 Issue 8 Pages 583-588
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSCarbon nanotubes (CNTs) are potential candidates for heat removal materials that dissipate heat from devices because of their high thermal conductivity, mechanical stiffness and flexibility. The fact that the thermal management is one of the key issues for next generation electronics has attracted much attention to the thermal transport properties of CNT. Computational simulations have served as powerful tools not only to predict the CNT thermal transport properties but also to gain insight into detailed and unique characteristics that are not yet accessible in experiments. In this paper, we present an overview of recent progress on theoretical and computational research on thermal transport in CNTs and see how they compare with recent experimental results.
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Yoshinao Okajima, Yasushi Shibuta, Shu Yamaguchi, Toshio Suzuki2009 Volume 73 Issue 8 Pages 589-594
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSThe growth of silver pillars and switching behavior in Ag/Ag2S nanometer scale switch were numerically simulated. The mechanism of silver pillar growth, which is assumed to be the same one of the frost column growth, was modeled using a phase field method. Supply of the silver flux reduced by tunneling electron at the Ag/Ag2S interface into the upper part of the pillar led to the growth of silver pillar successfully. The growth velocity of the pillar increased with the increase of the applied voltage. However, it decreased by applying a potential necessary for the precipitation of silver from Ag2S phase. Moreover, the switching behavior was also well reproduced with the fact that switching time decreased with the increase of the switching voltage.
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Hideki Mori, Hajime Kimizuka, Shigenobu Ogata2009 Volume 73 Issue 8 Pages 595-600
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSWe calculate the generalized-stacking-fault (GSF) energy surface of BCC iron by using first principles density functional theory (DFT). We employ the semidiscrete variational Peierls-Nabarro (SVPN) model to investigate the edge dislocation properties of BCC iron. The dislocation core width and Peierls stress are estimated as 0.20 nm and 80 MPa, respectively. We also estimate the GSF energy surface and dislocation properties using two different embedded atom method (EAM) potentials and compare with the DFT results.
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Yoshinao Okajima, Yasushi Shibuta, Toshio Suzuki2009 Volume 73 Issue 8 Pages 601-607
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSEffect of the phase-boundary potential at the electrode-electrolyte interface and the anisotropy of interfacial energy on the morphology of the electrodeposits have been investigated by phase-field simulation. In equilibrium system, the change in the phase-boundary potential due to the interfacial curvature satisfies the Gibbs-Thomson effect. The stability analysis of the electrode-electrolyte interface reveals that the marginal wavelength is proportional to the inverse of the square root of the growth velocity of the interface. It is found that the linear relationship between the marginal wavelength and tip radius during electrodeposition satisfies the crystal growth theory confirmed by the dendrite growth in solidification process.
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Regular Article
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Seon-Woo Park, Byung-Koog Jang, Young-Jei Oh2009 Volume 73 Issue 8 Pages 608-612
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSThe effect of glycerol as a drying control chemical additive for ambient pressure drying of silica aerogel was investigated. Silica hydrosol was prepared by the addition of 0.5~2.0 mass% glycerol to the mixture of metal alkoxide (TEOS) precursor and isopropanol as a solvent. The glycerol additive in silica aerogel is located on the hydroxyls of silica surface and could suppress a formation of crack in silica aerogel during ambient drying. The addition of excess glycerol affected a gelation time and springback effect. Crack-free silica aerogels were obtained. Specific surface area, average pore size, total pore volume, porosity and transparency of the silica aerogel were decreased but bulk density and hydrophobicity were increased as increasing the glycerol contents. Silica aerogel with 1 mass% glycerol addition was showed 0.42 g/cm3 of bulk density, 888 m2/g of specific surface area, 4.6 nm of average pore diameter and 85% of porosity.
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Shigeo Sugawara, Naoharu Kamada2009 Volume 73 Issue 8 Pages 613-617
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSAnodic dissolution of n-GaP (111) surfaces at high voltages in aqueous KOH solutions is an effective method of electropolishing the surfaces to remove damage induced by mechanical polishing. However, anodic dissolution at certain high voltages causes the formation of whiskers at dislocation sites. As such a phenomenon is peculiar, it is necessary to systematically investigate the behavior of the dissolution under varying experimental conditions. Therefore, we carried out a series of anodic dissolutions of n-GaP (111) surfaces in aqueous NaOH solutions. The morphology of the anodically dissolved surfaces was observed by optical microscopy and scanning electron microscopy. When the surface is dissolved at 16 V for 1.8×103 s in a 0.2 kmol/m3 NaOH solution, there is marked whisker nucleation at dislocation sites on the surface. Dissolutions at 20-30 V in 0.2-0.5 kmol/m3 NaOH solutions produce smooth surfaces; however, microscopic pits are detected on the electropolished surfaces by atomic force microscopy.
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H. Onishi, S. Ueno, H. Nakajima2009 Volume 73 Issue 8 Pages 618-621
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSPorous nickel with cylindrical pores was fabricated by unidirectional solidification in a mixture gas of hydrogen and argon. The pore size is significantly affected by the addition of NiO powder. The diameter and length of the pores decrease by the addition of NiO. The number of pores increases with increasing amount of NiO powder. The pore diameter decreases with decreasing NiO particle size. It is concluded that NiO powder can serve as nucleation sites for the pore formation in the process of the solidification.
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Hiroaki Nakano, Satoshi Oue, Masaaki Uranaka, Masataka Masuda, Hisaaki ...2009 Volume 73 Issue 8 Pages 622-629
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSElectrodeposition behavior of Sn-Ag alloys was investigated at 1 to 1000 A/m2 in both sulfate and pyrophosphate-iodide baths of 298 K, and the contact resistance of Sn-Ag alloys deposited on Cu connector was evaluated. In both baths, Ag behaved as more noble metal than Sn, showing the typical feature of regular type codeposition. The difference of deposition potential between Ag and Sn was 0.4 V in pyrophosphate-iodide bath, while it was 0.2 V in sulfate bath containing thiourea as complexing agent for Ag+ ions. The deposits obtained from pyrophosphate-iodide bath consisted of blocks of a few micron in size, while those from sulfate bath showed grains smaller than 1 μm. The deposits containing Ag less than 45 mass% were composed of Ag3Sn metallic compound and Sn in accordance with the equilibrium phase diagram of binary Ag-Sn system. The contact resistance of deposited Sn-Ag alloys after heating at 433 K for 120 hours was somewhat smaller at Ag contents less than 45 mass% than that of reflow Sn plating. The connecting reliability of connector after abrasion was better in deposited films of Sn-Ag alloys than in reflow Sn plating.
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Yasuhiro Aruga, Koichi Makii, Seiji Nishi2009 Volume 73 Issue 8 Pages 630-635
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSAl-Zn-Mg foams manufactured by a batch casting process were subjected to aging treatments with and without solution treatment. The effect of the heat treatments on matrix strength (micro-hardness) and precipitation behavior in the foams was investigated by means of transmission electron microscopy (TEM) and X-ray absorption fine structure (XAFS) analysis at a synchrotron radiation facility.
Foam aged at 398 K for 8 h after the solution treatment showed the greatest increase in strength. Fine precipitates were dispersed homogeneously and densely, which were speculated to be metastable η′ and equilibrium η phases transformed from GP zones. It is estimated that the GP zones were formed during water-quenching after the solution treatment. Overaging treatment at 423 K for 48 h after solution treatment softened the foam past its peak strength by approximately 10 in Vickers hardness. During this treatment, η′ and η phases coarsened significantly and the number density of these precipitates decreased. It is concluded that a significant drop in the strength was suppressed during overaging by the presence of a high density of the GP zones, defined as Zn-Mg ordered phases by the XAFS analysis.
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Ayako Miura, Wei Dong, Masahiro Fukue, Noriharu Yodoshi, Takamichi Miy ...2009 Volume 73 Issue 8 Pages 636-642
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSMono-sized [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 alloy particles with desired particle size and high sphericity have been prepared by Pulsated Orifice Ejection Method (POEM). Each particle has uniform compositional distribution along with the same composition during processing. Phase transition of a particle from fully amorphous to amorphous/crystalline and then fully crystalline shows that the diameter of a single fully amorphous particle is less than 300 μm in Ar atmosphere and 700 μm in He atmosphere. The critical diameter of a fully amorphous phase particle shifts toward larger diameter with an increase in the initial melt temperature. The critical cooling rate to realize fully amorphous phase is estimated to be in the range of (700-900 K×s-1), which only depends on the initial melt temperature, irrespective of the atmospheres gases.
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Noriharu Yodoshi, Naohito Morita, Rui Yamada, Akira Kawasaki, Ryuzo Wa ...2009 Volume 73 Issue 8 Pages 643-650
Published: 2009
Released on J-STAGE: August 01, 2009
JOURNAL FREE ACCESSTo consolidate [(Fe0.5Co0.5)0.75Si0.05B0.2]96Nb4 metallic glass powder to full density, a pressurized liquid phase sintering was employed, which was intended to promote densification by an enhanced wetting of a liquid phase with solid particles. Pd42.5Ni7.5P20Cu30 metallic glass powder, which has been reported to have a high glass forming ability and the lowest critical cooling rate of glass formation of 0.067 K/s, was chosen a liquid phase component. The melting point of the Pd42.5Ni7.5P20Cu30 metallic glass alloy of 763 K is lower than the glass transition temperature of the [(Fe0.5Co0.5)0.75Si0.05B0.2]96Nb4 metallic glass alloy of 808 K. However, the wettability of this alloy with the Pd42.5Ni7.5P20Cu30 alloy was revealed to be poor. Therefore, sintering pressure was applied to the compacts to promote a viscous flow deformation of solid particles and also to enhance the intergranular permeation of the liquid phase. A specially designed micro-hot press was devised for the pressure-sintering experiment. A pseudo wettability was observed during pressure-sintering, and the liquid phase was found to fill completely the intergranular space of the powder compact. The relative density of 64-95%, as well as the sintering structure, could be controlled by the punch displacement to squeeze out a part of the liquid phase from the compact. The compressive fracture strength of the obtained metallic glass composite was found to be as high as 2051 MPa, and the fracture was observed to be intragranular type, suggesting a good bonding in the particle-binding phase interface.
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