Faculty Profiles - ASAHI Ryoji

Papers - ASAHI Ryoji

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Thermoelectric Properties of Si2Ti-Type Al-(Mn,Cr,Fe)-Si Alloys Reviewed

Toyama Yasuhiro, Hazama Hirofumi, Asahi Ryoji, Takeuchi Tsunehiro

JOURNAL OF ELECTRONIC MATERIALS Vol. 40 ( 5 ) page： 1052 - 1056 2011.5

A Hybrid Quantum-Classical Simulation Study on Stress-Dependence of Li Diffusivity in Graphite Reviewed

Ohba N., Ogata S., Tamura T., Yamakawa S., Asahi R.

CMES-COMPUTER MODELING IN ENGINEERING & SCIENCES Vol. 75 ( 3-4 ) page： 247 - 265 2011.5

1506 Hybrid quantum-classical simulation : development of O(N)-real-space DFT method and application to the Li-graphite intercalation compound

Ohba Nobuko, Ogata Shuji, Kobayashi Ryo, Tamura Tomoyuki, Asahi Ryoji

The Proceedings of The Computational Mechanics Conference Vol. 2011 ( 0 ) page： 481 - 482 2011

906 Phase-field Modeling of Lithium Intercalation in Polycrystalline Oxide

Yamakawa Shunsuke, Yamasaki Hisatsugu, Koyama Toshiyuki, Asahi Ryoji

The Proceedings of The Computational Mechanics Conference Vol. 2011 ( 0 ) page： 296 - 297 2011

Selected contributions from the 3rd Theory Meets Industry International Workshop, TMI2009 (Nagoya, Japan, 11-13 November 2009) PREFACE Reviewed

Tanaka Isao, Hafner Juergen, Wimmer Erich, Asahi Ryoji

JOURNAL OF PHYSICS-CONDENSED MATTER Vol. 22 ( 38 ) page： 380301 2010.9

Electronic Structure and Thermoelectric Properties of Al-Mn-Fe-Si Alloys Reviewed

Takeuchi T., Toyama Y., Hazama H., Asahi R.

JOURNAL OF ELECTRONIC MATERIALS Vol. 39 ( 9 ) page： 1433 - 1438 2010.9

Electronic Structure and Thermoelectric Properties of Si_2Ti-Type Al-(Mn, X)-Si (X=Cr, Fe) Alloys Reviewed

TOYAMA Yasuhiro, HAZAMA Hirofumi, ASAHI Ryoji, TAKEUCHI Tsunehiro

Journal of the Japan Institute of Metals and Materials Vol. 74 ( 9 ) page： 605 - 609 2010.9

Language：English Publishing type：Research paper (other academic) Publisher：The Japan Institute of Metals and Materials

In order to make variation in thermoelectric properties of Si2Ti-type Al32Mn34Si34, which possesses a large magnitude of Seebeck coefficient exceeding 300 μV/K, we partially substituted Fe and Cr for Mn, and succeeded in decreasing the number of valence electrons by the latter. The large, positive Seebeck coefficient up to 330 μV/K was observed for Al32CrxMn34−xSi34 (1≤x≤2.5), which consists almost solely of the phase of Si2Ti-type structure. The increase of hole concentration with increasing Cr concentration was confirmed by the fact that the electrical resistivity was decreased with Cr concentration. The positive sign and the decrease of Seebeck coefficient with increasing Cr concentration also lend a support on this scenario. The largest ZT-value with the positive sign of Seebeck coefficient (p-type behavior) was obtained at Al32Cr2.5Mn31.5Si34, and the resulting ZT-value was twice as large as the largest ZT-value of the ternary compound Al33Mn34Si33 that possesses a p-type behavior.

DOI： 10.2320/jinstmet.74.605

Scopus

Electronic Structure and Thermoelectric Properties of Si2Ti-Type Al-(Mn, X)-Si (X = Cr, Fe) Alloys Reviewed

Toyama Yasuhiro, Hazama Hirofumi, Asahi Ryoji, Takeuchi Tsunehiro

JOURNAL OF THE JAPAN INSTITUTE OF METALS Vol. 74 ( 9 ) page： 605 - 609 2010.9

Study of Electronic Structure and Defect Formation in Ti1-x Ni1+x Sn Half-Heusler Alloys Reviewed

Hazama Hirofumi, Asahi Ryoji, Matsubara Masato, Takeuchi Tsunehiro

JOURNAL OF ELECTRONIC MATERIALS Vol. 39 ( 9 ) page： 1549 - 1553 2010.9

Thermoelectric Properties of Si2Ti-Type Al-Mn-Si Alloys Reviewed

Takeuchi Tsunehiro, Toyama Yasuhiro, Yamamoto Akio, Hazama Hirofumi, Asahi Ryoji

MATERIALS TRANSACTIONS Vol. 51 ( 6 ) page： 1127 - 1135 2010.6

Language：English Publishing type：Research paper (other academic) Publisher：Materials Transactions

By using the first principle band calculations, we identified that Si2Ti-type Al-Mn-Si C54-phase possesses an electronic structure suitable for the thermoelectric materials. The formation range of the Al-Mn-Si C54-phase was determined by preparing samples at a number of different compositions, and the samples solely consisting of the C54-phase were successfully obtained around Al:Mn:Si=1:1:1. The carrier concentration of the Al-Mn-Si C54-phase was controlled by the partial substitution of the constituent elements, and behaviors in electrical properties characteristic to n-type and p-type thermoelectric materials were alternatively observed for the samples of a larger electron concentration and a smaller electron concentration, respectively. The absolute value of the Seebeck coefficient |S| was found to exceed 300 μV/K for both n-type and p-type samples.

DOI： 10.2320/matertrans.M2010022

Web of Science

Scopus

Anomalies in the response of V, Nb, and Ta to tensile and shear loading: Ab initio density functional theory calculations Reviewed

Nagasako Naoyuki, Jahnatek Michal, Asahi Ryoji, Hafner Juergen

PHYSICAL REVIEW B Vol. 81 ( 9 ) 2010.3