Details of a Researcher - Kamihara, Yoichi

Presentations -

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A Pressure-Temperature Phase diagram of BN

Y. Sakai,M. Matoba, I. Yamada, K. Funakoshi, T. Kunimoto, Y. Higo, T. Atou, Y. Kamihara

[International presentation] The Eighth International Conference on the Science and Technology for Advanced Ceramics (STAC8) (Mielparque-Yokohama, Yokohama, Japan) ,

2014.06

Oral presentation (general)

Wurtzite boron nitride (w-BN) and cubic boron nitride (c-BN) have interested researchers because of their high hardness and chemical inertia to ferrous materials. Moreover, recent theoretical calculations verify that w-BN is harder than diamond [1]. However, since w-BN phase exists in the low-temperature and high-pressure range between h-BN and c-BN phases [2,3], it was difficult to obtain pure w-BN excluding h-BN and c-BN as second phase. We demonstrate an optimal temperature to obtain single phase w-BN at relatively low pressure (around 10 GPa) by in situ Energy Dispersive X-ray diffraction (EDXRD) under HPHT at the synchrotron radiation facility, SPring-8.
w-BN appears under 10(1) GPa and an optimal temperature to obtain w-BN single-phase exists at 1000 C, and h-BN and c-BN are mixed under and over this temperature.

[1] Zicheng Pan, Hong Sun, Yi Zhang and Changfeng Chen, Phys. Rev. Lett. 102, 055503 (2009).
[2] F. P. Bundy and R. H. Wentorf, Jr., J. Chem. Phys. 38, 1144 (1963).
[3] T. Taniguchi, Special Issue of The Review of High Pressure Science and Technology. 18, 34 (2008). (In Japanese.)

アンモニア合成の新触媒設計のためのN2およびH2の解離現象の理論的評価

木下拓郎, 宮尾修平, 後藤陽介, 的場正憲, 神原陽一

[Domestic presentation] 日本材料科学会主催平成26年度学術講演大会 (工学院大学　高層棟3階　アーバンテックホール（新宿キャンパス）　(東京都新宿区西新宿1-24-2)) ,

2014.06

Oral presentation (general)

第一原理計算による三方晶型AAl2X2 (A = Mg,Ca,Sr, X = Si,Ge) 熱電変換機能予測

関根絵里菜,宮尾修平, 後藤陽介, 神原陽一, 的場正憲

2014.06

Oral presentation (general)

層状プニクタイドSrCr2(As, P)2の合成と電子磁気特性

小野仁, 岡野智宏, 酒井雄樹, 後藤陽介, 神原陽一, 的場正憲

2014.06

Oral presentation (general)

異価数イオンドープBNの高温高圧合成と電子物性

馬渕貴洋, 塩沢啓, 酒井雄樹, 的場正憲, 神原陽一

2014.06

Oral presentation (general)

鉄系超伝導体SmFeAsO1-xFxの臨界電流密度と磁場侵入長

飯原潤, 庄司浩一朗, 二瓶卓也, 的場正憲, 海住英生, 西井準治, 神原陽一

[Domestic presentation] 2014年春季低温工学・超電導学会 (タワーホール船堀) ,

2014.05

Oral presentation (general)

SmFeAsO1-xFx, SmFeAs1-x PxO1-yFy (Sm1111)の多結晶試料について, magnetic Jcを拡張Beanモデルを用いて求め, 4端子法により測定される電圧降下の閾値を定義して求まるtransport Jcと比較した同一試料の磁束密度分布をSQUID顕微鏡により直接観察し, 多結晶体における磁場侵入長の算出を試みた.
5 Kにおけるmagnetic JcはSmFeAsO1-xFx (x = 0.082) が〜13kA cm-2, SmFeAs1-xPxO1-yFy (x=0.02, y = 0.10)が〜12 kA cm-2であった.
多結晶試料の磁場侵入長をLondonの理論[1]を仮定し, 算出すると単結晶等で報告されるIntrinsicな値[2]に比べ数桁大きい値を示した.学会では, この値を多結晶の結晶粒界の影響を考慮し解釈する.

GdFeAsO1-xFxの電子磁気状態相図

塩沢啓, 櫻井信, 的場正憲, 安井伸太郎, 伊藤満,神原陽一

[Domestic presentation] 日本物理学会第69回年次大会 (東海大学湘南キャンパス(神奈川県平塚市北金目4-1-1)) ,

2014.03

Oral presentation (general)

層状遷移金属オキシニクタイトSr2ScMPO3の物性

岡田悟志, 神原陽一, 大久保尚紀, 伴周一, 的場正憲

[Domestic presentation] 日本物理学会第69回年次大会 (東海大学湘南キャンパス(神奈川県平塚市北金目4-1-1)) ,

2014.03

Oral presentation (general)

鉄系混合アニオン化合物超伝導体の基礎と応用への課題

KAMIHARA Yoichi

[Domestic presentation] 首都大学東京新超伝導体研究会(TMUNSC 2014) (首都大学東京) ,

2014.03

Oral presentation (invited, special)

これまでに報告された鉄系高温超伝導体の内,は最も高い超伝導転移温度、上部臨界磁場、及び不可逆磁場を示すのはいずれも混合アニオン化合物である。しかしながら、これらの混合アニオン化合物を利用した超伝導線材の臨界電流密度は、ThCr2Si2構造を示すBa1-xKxFe2As2を初めとするいわゆる122系に比べて, 数桁低い値にとどまる。鉄系超伝導体の歴史と現状を紹介し、混合アニオン化合物の電子磁気相図の重要性と、今後の展望を概説する。

Modulation of Critical Current Density in Superconducting Diamond by Surface Modification

K. Natsui, T. Yamamoto, T. Watanabe, Y. Kamihara, and Y. Einaga

[International presentation] International Symposium on Diamond Electrochemistry (Keio University, Hiyoshi, Yokohama, Japan) ,

2014.03

Poster presentation

Introduction
In 2004, the boron-doped diamond (BDD) was found to be a superconductor [1]. On the other hand, it is known that diamond surface is easily modified by chemical treatment [2], and physical properties, such as surface conductivity, could be modulated by the surface modification [3]. Along these lines, it is expected that superconducting properties of BDD could be modulated by surface modification.
Experimental Section
The as-deposited BDD was hydrogenated, and then oxidized electrochemically to obtain the oxygen-terminated BDD. Thus obtained oxidized BDD was re-hydrogenated to obtain the hydrogen-terminated BDD. For each termination, superconducting properties were examined with transport and magnetic measurements.
Results and Discussion
In the transport measurements, although the critical temperature unchanged, critical current density (JC) decreased after oxidation and recovered after hydrogenation. In the magnetic measurements, the JC were determined from M-H curves using the extended Bean model. As is the case with the transport measurements, the JC could be modulated in a reversible manner between the hydrogen- and oxygen-terminated BDD (Fig.). This is because the volume fractions of the superconducting phases changed by surface modification.
References
[1] Ekimov, E. A. et al. Nature 2004, 428, 542.
[2] Szunerits, S. et al. J. Solid State Electrochem. 2008, 12, 1205.
[3] Maier, F. et al. Phys. Rev. Lett. 2000, 85, 3472.

Crystal structure and thermoelectric properties of kuramite Cu3Sn(Se,S)4 with cation disorder

Y. Goto, Y. Kamihara, and M. Matoba

[International presentation] APS March Meeting 2014 (Denver, USA) ,

2014.03

Oral presentation (general)

Ternary or quaternary compounds Cu2–TM–A–Ch4 (TM; transition metal, A; group 14 or 15 elements, Ch; chalcogen) are promising p-type thermoelectric materials because of their heavy but still conducting valence band, which is composed of Cu 3d and Ch 3p orbitals. Lattice thermal conductivity should be suppressed by cation disorder, however, coexistence of transition metals such as Cu and Zn on quaternary compounds complicate the understanding of the details of cation disorder by means of conventional X-ray diffraction.
In this work, We demonstrate the crystal structure and thermoelectric properties of kuramite Cu3Sn(Se,S)4. Structural analysis revealed that polycrystalline samples crystallize in tetragonal I–42m space group. The 2a site was occupied by Cu only, while 2b and 4d sites were occupied by Cu and Sn partial disorder. A decrease of electrical conductivity (rho) with temperature indicates that kuramite is metal or degenerate semiconductor, which is in contrast to most of other stannite–type compounds with band gap of 0.96–3.25 eV. At the conference, we will also report the alloy effect on thermal conductivity of Cu3Sn(Se,S)4 solid solution.

Magnetic and Electronic Phase Diagram of Sr2VFeAsO3-d

Y. Tojo, T. Shibuya, T. Nakamura, K. Shoji, M. Matoba, S. Yasui, M. Itoh, S. Kitao, M. Seto, and Y. Kamihara

[International presentation] APS March Meeting 2014 (Denver, USA, 3/3-7 (2013)) ,

2014.03

Oral presentation (general)

Ae2MFePnO3 (so-called 21113 systems) with perovskite-type layers such as Ae2MO3, where Ae denotes alkaline earth metals, M does Sc, Ti, Cr, V and other transition metal atoms and Pn does As and P shows superconductivity at T < 46 K. Sr2VFeAsO3-d is a representative compound in 21113 systems. [Zhu et al, Phys. Rev. B (2009); Ogino et al, Supercond. Sci. Technol. (2009); Ogino et al, Supercond. Sci. Technol. (2009)] Although the oxygen deficiency (d) as a function of Tc is still controversial in Sr2VFeAsO3-d, many samples have been reported as superconductors with Tc = 24-37 K. In this study, a polycrystalline Sr2VFeAsO3-d (d = ~0.1- 0.6) were prepared by a solid state reaction using an alumina tube in a sealed silica tube. DC electrical resistivity was measured by a four-probe technique. Magnetization measurements were performed on a superconducting quantum interference device. 57Fe Mossbauer spectra were obtained using conventional equipment. The electronic and magnetic phase diagram of Sr2VFeAsO3-d is elucidated.

Magnetic phase transition of LnCr2Si2C (Ln = La, Sm)

T. Yuki, K. Takeuchi, M. Matoba, Y. Kamihara

[International presentation] International Workshop on Novel Superconductors and Super Materials 2013 (NS22013) (Tokyo, Japan) ,

2013.11

Poster presentation

Electronic phase diagram of superconductors, GdFeAsO1-xFx

H. Shiozawa, M. Matoba, S. Yasui, M. Itoh, Y. Kamihara

[International presentation] International Workshop on Novel Superconductors and Super Materials 2013 (NS22013) (Tokyo, Japan) ,

2013.11

Poster presentation

Quantum Critical Point in Heavy-Fermion Iron Oxypnictide Ce(Fe1-xRux)PO and Ce(Fe1-xCrx)PO

A. Wakatsuki, T. Okano, T. Nakamura, M. Matoba, Y. Kamihara

[International presentation] International Workshop on Novel Superconductors and Super Materials 2013 (NS22013) (Tokyo, Japan) ,

2013.11

Poster presentation

Magnetic and Electronic Phase Diagram of Sr2VFeAsO3-x

Y. Tojo, T. Shibuya, T. Nakamura, K. Shoji, M. Matoba, Y. Kamihara, S. Yasui, M. Itoh, S. Kitao, M. Seto

[International presentation] International Workshop on Novel Superconductors and Super Materials 2013 (NS22013) (Tokyo, Japan) ,

2013.11

Poster presentation

SmCr2(Si1-xBx)2Cの電気的・磁気的性質

竹内勝彦, 結城達也, 的場正憲, 神原陽一

[Domestic presentation] 日本物理学会2013年秋季大会 (徳島大学（常三島キャンパス）) ,

2013.09

Oral presentation (general)

ぺロブスカイト関連鉄系混合アニオン化合物Sr2CrFeAsO3-dの合成

藤岡弘考, 藤乘優治郎, 中村哲朗, 北尾真司, 瀬戸誠, 的場正憲, 神原陽一

[Domestic presentation] 日本物理学会2013年秋季大会 (徳島大学（常三島キャンパス）) ,

2013.09

Oral presentation (general)

層状コバルトオキシニクタイトの熱電特性

岡田悟志, 神原陽一, 大久保尚紀, ,伴周一, 的場正憲

[Domestic presentation] 第十回日本熱電学会学術講演会（TSJ2013) (名古屋大学豊田講堂（東山キャンパス）) ,

2013.09

Poster presentation

CoPn (Pn =P,As,Sb)の電子構造と輸送特性

MIYAO Shuhei, KAMIHARA Yoichi, MATOBA Masanori

[Domestic presentation] 第十回日本熱電学会学術講演会（TSJ2013) (名古屋大学豊田講堂（東山キャンパス）) ,

2013.09

Oral presentation (general)

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