論文 - 的場　正憲

Electronic Structure and Transport Properties of Cu-deficient Kuramite Cu_3-xSnS₄

Yosuke Goto, Yuki Sakai, Yoichi Kamihara, and Masanori Matoba

Japanese Journal of Applied Physics 54 （ 2 ） 021801 (5 pages) 2015年01月

研究論文（学術雑誌）, 共著, 最終著者, 査読有り

　概要を見る

銅欠陥のあるクラマイト型Cu3-xSnS4 (CTS)の電気/熱輸送特性を明らかにした。CTSの結晶学的な特徴はCuとSnのサイト間の構成イオンの部分的な交換(アンチサイト)である。CTSはバンド絶縁体的な挙動を示すCu2ZnS4とCu3SbS4と異なり, キャリアドープにより 10の21乗程度のキャリア密度を示す金属であり, 格子熱伝導率は 2 Wm-1K-1であった.この輸送現象はCu 3d と S 3p 軌道に由来する.

Transport Properties of the layered transition Metal Oxypnictide Sr₂ScMPO₃ with MP layers (M = Mn, Ni and Co_0.5Fe_0.5)

Satoshi Okada, Yoichi Kamihara, Naoki Ohkubo, Shuichi Ban, and Masanori Matoba

Journal of Physics: Conference Series 568   022034 (5 pages) 2014年12月

研究論文（学術雑誌）, 共著, 最終著者, 査読有り

Enhancement of thermoelectric properties by Se substitution in layered bismuth-chalcogenide LaOBiS_2-xSe_x

Yoshikazu Mizuguchi, Atsushi Omachi, Yosuke Goto, Yoichi Kamihara, Masanori Matoba, Takafumi Hiroi, Joe Kajitani, Osuke Miura

Journal of Applied Physics 116   163915 (4 pages) 2014年10月

研究論文（学術雑誌）, 共著, 査読有り

The effect of simultaneous substitution on the electronic band structure and thermoelectric properties of Se-doped Co₃SnInS₂ with the Kagome lattice

Masaya Fujioka, Taizo Sibuya, Junya Nakai, Keigo Yoshiyasu, Yuki Sakai, Yoshihiko Takano, Yoichi Kamihara, and Masanori Matoba

Solid State Communications 199   56 - 60 2014年09月

研究論文（学術雑誌）, 共著, 最終著者, 査読有り

New phases of binary compounds: CsCl-type RuGe and RuSn

Yuki Sakai, Masanori Matoba, Ikuya Yamada, Kenichi Funakoshi, Takehiro Kunimoto, Yuji Higo, and Yoichi Kamihara

Euro physics letters 107   56003 (6 pages) 2014年09月

研究論文（学術雑誌）, 共著, 査読有り

Effects of the Cu off-stoichiometry on transport properties of wide gap p-type semiconductor, layered oxysulfide LaCuSO

Yosuke Goto, Mai Tanaki, Yuki Okusa, Taizo Shibuya, Kenji Yasuoka, Masanori Matoba, and Yoichi Kamihara

Applied Physics Letters 105   022104 (4 pages) 2014年07月

研究論文（学術雑誌）, 共著, 査読有り

From kesterite to stannite photovoltaics: stability and band gaps of the Cu₂(Zn,Fe)SnS₄ alloy

Taizo Shibuya, Yosuke Goto, Yoichi Kamihara, Masanori Matoba, Kenji Yasuoka, Lee A. Burton and Aron Walsh

Applied Physics Letters 104 （ 2 ） 021912 2014年01月

研究論文（学術雑誌）, 共著, 査読有り

Relations between Superconducting Critical Temperatures and Crystallographic Local Structures in Iron-based Mixed Anion Compounds

Hiromu Shiozawa, Seiya Inagi, Masanori Matoba, Toshiyuki Atou, Mitsuru Itoh, and Yoichi Kamihara

JPS Conference Proceedings: Proceedings of the 12th Asia Pacific Physics Conference (APPC12, Makuhari, Chiba, Japan) 1   012026 (4 pages) 2014年01月

研究論文（国際会議プロシーディングス）, 共著, 査読有り

Enhanced Thermoelectric Figure of Merit in Stannite–Kuramite Solid Solutions Cu_2+xFe_1-xSnS_4-y (x=0-1) with Anisotropy Lowering

Yosuke Goto, Fumihiko Naito, Rina Sato, Keigo Yoshiyasu, Takanori Itoh, Yoichi Kamihara, and Masanori Matoba

Inorganic Chemistry 52 （ 17 ） 9861-9866 2013年08月

研究論文（学術雑誌）, 共著, 最終著者, 査読有り

Ferromagnetic Quantum Critical Point Induced by Tuning the Magnetic Dimensionality of the Heavy-Fermion Iron Oxypnictide Ce(Ru_1-xFe_x)PO

Shunsaku Kitagawa, Kenji Ishida, Tetsuro Nakamura, Masanori Matoba, and Yoichi Kamihara

Journal of the Physical Society of Japan 82 （ 3 ） 033704 (4 pages) 2013年02月

研究論文（学術雑誌）, 共著, 査読有り

　概要を見る

擬二次元格子系であるCeRu1-xFexPOの組成制御を厳密に行い、微視的な磁性と量子臨界点付近の磁気ゆらぎの次元性を31P-NMRより明らかにした。母相 (x = 0)中のCeイオンは、正方格子をとるにも関わらず、状態密度とナイトシフトの相関にょり定義されたスケーリング指数から判断すると、三次元的な強磁性を示す。RuとFeの固溶体では量子臨界点(QCP)付近で三次元的な強磁性秩序から二次元的な強磁性秩序に変化する。

Pressure-induced tetragonal-orthorhombic phase transitions in CeRuPO

Shigeto Hirai, Yoichi. Kamihara, Atsushi Wakatsuki, Masanori Matoba, and Wendy L. Mao

Applied Physics Letters 102 （ 5 ） 051917 (5 pages) 2013年02月

研究論文（学術雑誌）, 共著, 査読有り

Ferromagnetic quantum critical point in heavy-fermion iron oxypnictide Ce(Ru_1-xFe_x)PO

Shunsaku Kitagawa, Kenji Ishida, Tetsuro Nakamura, Masanori Matoba, and Yoichi Kamihara

Physical Review Letters 109 （ 22 ） 227004 2012年11月

研究論文（学術雑誌）, 共著, 査読有り

　概要を見る

新規な擬二次元格子系であるCeRu1-xFexPOを合成し、微視的な磁性を31P-NMRにより明らかにした。磁化率、磁気ゆらぎのx依存性よりRu/Feの濃度が0.13-0.14 atom%程度の場合, RuとFeの固溶による強磁性状態, 及び重い電子状態の消失、すなわち量子臨界状態となる。

Paramagnetic phase of heavy-fermion compound, CeFePO, probed by ⁵⁷Fe Mossbauer spectroscopy

Tetsuro Nakamura, Takashi Yamamoto, Masanori Matoba, Yasuaki Einaga, Yoichi Kamihara

Journal of Physical Society of Japan 81 （ 5 ） 064714 (4 pages) 2012年05月

研究論文（学術雑誌）, 共著, 査読有り

　概要を見る

鉄系層状化合物CeFePOの磁性, 電子状態を57Feメスバウワ分光を用いて測定した。磁気分裂が存在しないことから、9.4 Kから293 Kの温度範囲でCeFePOは常磁性を示すことが示された。57Feメスバウワスペクトルの四極子分裂は小さく、デバイ温度は448 K程度であると示された。57Feの異性体シフトは0.32 mm/sと求まり、Feは金属的、または共有結合的な化学結合を示す。

Analysis of interdiffusion between SmFeAsO_0.92F_0.08 and metals for ex situ fabrication of superconducting wire

Masaya Fujioka, Masanori Matoba, Toshinori Ozaki, Yoshihiko Takano, Hiroaki Kumakura, and Yoichi Kamihara

Superconductor Science and Technology 24 （ 7 ） 075024- 075029 2011年06月

研究論文（学術雑誌）, 共著, 査読有り

　概要を見る

To find good sheath materials that react minimally with the superconducting core of iron-based superconducting wires, we investigated the reaction between polycrystalline SmFeAsO_0.92_F_0.08_ and the following seven metals: Cu, Fe, Ni, Ta, Nb, Cr and Ti. Each of the seven metals was prepared as a sheath-material candidate. The interfacial microstructures of SmFeAsO_0.92_F_0.08_ and these metal-sheath samples were analysed by an electron probe microanalyzer after annealing at 1000◦C for 20 h. Amongst the seven metal-sheath samples, we found that Cu was the best, because it reacted only very weakly with polycrystalline SmFeAsO_0.92_F_0.08_. Moreover, Cu is essential for superconducting wires as a stabilizing material. Metal sheaths made of Fe and Ni do not give rise to reaction layers, but large interdiffusion between these metals and polycrystalline SmFeAsO0.92F0.08 occurs. In contrast, metal sheaths made of Ta, Nb, Cr and Ti do form reaction layers. Their reaction layers apparently prevent electric current from flowing from the sheath material to the superconducting core. In general, through this research, Cu will be expected to be suitable not only as a stabilizing material but also as a sheath material for superconducting Sm-1111 wire fabricated by the ex situ PIT method.

Effective Ex-situ Fabrication of F-Doped SmFeAsO Wire for High Transport Critical Current Density

Masaya Fujioka, Tomohiro Kota, Masanori Matoba, Toshinori Ozaki, Yoshihiko Takano, Hiroaki Kumakura, and Yoichi Kamihara

Applied Physics Express 4   063102 (4 pages) 2011年05月

研究論文（学術雑誌）, 共著, 査読有り

　概要を見る

We demonstrate the fabrication of superconducting SmFeAsO_1-x_F_x_ (Sm-1111) wires by using the ex-situ powder-in-tube technique. Sm-1111 powder and a binder composed of SmF3, samarium arsenide, and iron arsenide were used to synthesize the superconducting core. Although the
F content of Sm-1111 is reduced in the process of ex-situ fabrication, the binder compensates by sufficiently supplementing the F content, thereby preventing a decrease in the superconducting transition temperature and a shrinkage of the superconducting volume fraction. Thus, in the superconducting Sm-1111 wire with the binder, the transport critical current density reaches the highest value of 4 kA/cm^2^ at 4.2 K.

Substitution effect of Ba on magnetic properties of layered oxysulfide (Sr,Ba)₂Cu₂CoO₂S₂ with CoO₂ square planes

Satoshi Okada and Masanori Matoba

Journal of Physics: Conf. Ser. （the 25th International Conference on Low Temperature Physics (LT25)）  150   042154-042157 2009年04月

研究論文（学術雑誌）, 共著, 査読有り

　概要を見る

We have studied the magnetic properties of Ba-doped layered cobalt oxysulfide (Sr,Ba)_2_Cu_2_CoO_2_S_2_ with CoO_2_ squre-planes. The antiferromagnetic nature was considered to originate from the CoO_2_ layer dominantly. However, the effect of the inter-layer of CoO_2_ planes has not been clear. We therefore synthesized polycrystalline (Sr,Ba)_2_Cu_2_CoO_2_S_2_, and investigated the effect of inter-layer distance on the magnetic properties in detail. When Sr was substituted by Ba, the difference between zero-field-cooled and field-cooled magnetization was found to decrease clearly, and such difference was ascribed to reflect the increase of the distance between CoO_2_ layers owing to the difference of the ionic radii between smaller Sr and lager Ba. There is a possibility that two dimensional magnetic order has strengthened.

Thermoelectric Figure of Merit of Anisotropic Bulk Materials in the Presence of Polar Optical Phonon Scattering

Kazuma Ikeda and Masanori Matoba

Japanese Journal of Applied Physics 47   2189-2191 2008年04月

研究論文（学術雑誌）, 共著, 査読有り

　概要を見る

The effect of mass anisotropy on the thermoelectric figure of merit in the presence of polar optical phonon (POP) scattering is numerically studied. Electron transport is considered using the linear Boltzmann transport equation. The mass anisotropy is advantageous for the figure of merit along the principal directions of a small effective mass if phonon thermal conductivity is large. Inelasticity plays an essential role in the obtained result. The result is qualitatively different from that for an ionised impurity model.

Electronic and magnetic nature of shandite-type A₂Co₃S₂ (A=Sn,In)

Atsushi Umetani, Eiji Nagoshia, Takashi Kuboderaa, and Masanori Matoba

Physica B 403   1356-1358 2007年10月

研究論文（学術雑誌）, 共著, 査読有り

　概要を見る

We investigated electronic and magnetic nature of A_2_Co_3_S_2_ (A=Sn,In) to reveal two different characteristics of metallic Co–Sn and strongly correlated electronic Co–S bondings. Co 2p X-ray photoelectron spectroscopy (XPS) shows a complicated and mixed-valence like feature with strong satellite. This origin can be explained by two different characteristics of Co–Sn/Co–S bonding nature. This feature is consistent with characteristic electron-density distributions obtained by the maximum-entropy method (MEM)-based pattern fitting analysis and the LSDA+U band calculation.

Scattering Anisotropy Effect on Layered Thermoelectric Materials

Kazuma Ikeda, Toshihisa Yago, and Masanori Matoba

Japanese Journal of Applied Physics 46   4184-4188 2007年07月

研究論文（学術雑誌）, 共著, 査読有り

　概要を見る

The effect of scattering anisotropy caused by mass anisotropy on the thermoelectric figure of merit is investigated. The simplest electron transport model is considered assuming a single-band, parabolic energy dispersion relation and ionized impurity scattering, which is assumed to be elastic. The wave-vector dependence of the relaxation time is fully considered within the relaxation-time approximation. Transport coefficients are calculated using the anisotropic relaxation time at finite temperatures. The figure of merit perpendicular to the axis with the largest effective mass is shown to decrease as the effective mass ratio increases. This result indicates that the weak confinement of electrons into layers of bulk materials cannot be the direct cause of the enhancement of the figure of merit along the layers.

Mass anisotropic effects on the thermoelectric figure of merit

Kazuma Ikeda, Toshihisa Yago and Masanori Matoba

Proceedings of 25th-International Conference on Thermoelectrics (Vienna, 2006) （25th-International Conference on Thermoelectrics）     293-295 2006年09月

研究論文（研究会，シンポジウム資料等）, 共著, 査読有り

　概要を見る

The effect of scattering anisotropy caused by mass anisotropy on the thermoelectric figure of merit is investigated. The simplest electron transport model is considered assuming a single-band, parabolic energy dispersion relation and ionized impurity scattering, which is assumed to be elastic. The wave-vector dependence of the relaxation time is fully considered within the relaxation-time approximation. Transport coefficients are calculated using the anisotropic relaxation time at finite temperatures. The figure of merit perpendicular to the axis with the largest effective mass is shown to decrease as the effective mass ratio increases. This result indicates that the weak confinement of electrons into layers of bulk materials cannot be the direct cause of the enhancement of the figure of merit along the layers.