Details of a Researcher - Kamihara, Yoichi

Presentations -

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Tc of a Copper-based high-Tc superconductor after heat treatments under hydrogen atmosphere

H. Namita, H. Sato, M. Matoba, S. Iwasaki, M. Fujioka, Y. Hara, T. Harada, M. Miura, and Y. Kamihara

International Conference of Asian Union of Magnetics Societies (IcAUMS) 2025,

2025.04

Oral presentation (general)

Synthesis of the iron-based superconductor Sr2Mg0.3Ti0.7FeAsO3-delta

Y. Ueno, N. Azuma, Y. Kamihara, and M. Matoba

International Conference of Asian Union of Magnetics Societies (IcAUMS) 2025,

2025.04

Oral presentation (general)

Thermoelectric properties of Rb(Cd, Zn)4As3

Keigo ONO, Yosuke GOTO, Yoichi KAMIHARA, Chul-ho LEE

Joint March Meeting and April Meeting: Global Physics Summit 2025 (Anaheim Convention Center, CA, USA) ,

2025.03

Oral presentation (general)

Zintl phase compound is one of the most promising thermoelectric materials. In particular,
various high-performance thermoelectric materials were found in 122-Zintl phase compounds AM2X2 (A: alkali metal, alkaline-earth metal, M: transition metal, X: pnictogen).
Recently, we found that 143-Zintl phase compounds of RbZn4As3, whose crystal structure is close to 122-Zintl phase compounds, exhibits relatively high thermoelectric performance with the value of the dimensionless figure-of-merit (ZT) to be 0.53 (T=797K) [1]. We proposed that 143-Zintl phase compound can be a new class of high-performance thermoelectric materials.
In this study, we extended the study to Rb(Cd,Zn)4As3, where Zn was replaced by Cd to reduce the lattice thermal conductivity.
We synthesized those samples by solid-state reactions. The total thermal conductivity of RbCd4As was extremely low to be 0.83 W/mK (T=470 K) that is advantageous for achieving high ZT value. Crystal structure analysis was conducted by powder neutron diffraction measurement. The results show that Rb atoms vibrate relatively large, which can be the origin of its low lattice thermal conductivity.

Microstructure Analysis of Nominal SmFeAsO0.77H0.12 using Magneto-optical Imaging Method

Hideo Namita, Tomoki Suemura, Ryosuke Sakagami, Tsuyoshi Tamegai, and Yoichi Kamihara

Iron-based Superconductors: Advances towards applications 2025 (IBS2app 2025),

2025.02

Poster presentation

Evaluation of the catalytic abilities of oxygen evolution reaction (OER) of Co doped YBa2Cu3O7-delta (YBCO)

Rei Kuramochi, Taisuke Kaizuka, Masanori Matoba, and Yoichi Kamihara

Iron-based Superconductors: Advances towards applications 2025 (IBS2app 2025),

2025.02

Poster presentation

Nominal SmFeAsO0.77H0.12の磁気光学イメージング

浪田秀郎, 末村智紀, 坂上良介, 為ケ井強, 神原陽一

第48回日本磁気学会学術講演会,

2024.09

Oral presentation (general)

鉄系高温超伝導体Sr2Mg0.3Ti0.7FeAsO3-δの多結晶合成

上野友貴，東　伸彦，神原陽一，的場正憲

第48回日本磁気学会学術講演会,

2024.09

Oral presentation (general)

Synthesis Co doped YBa2Cu3O7-delta (YBCO) and evaluation of catalytic ability in oxygen evolution reaction (OER) of YBCO

R. Kuramochi, T. Kaizuka, M. Matoba, and Y. Kamihara

The 5 th international symposium on advanced magnetic materials and applications (ISAMMA2024) (Quang Binh) ,

2024.08

Poster presentation

The Catalytic Activity of Co-doped YBa2Cu3O7-δ for Oxygen Evolution Reaction

H. Tahara, R. Kuramochi, M. Matoba, and Y. Kamihara

The 5 th international symposium on advanced magnetic materials and applications (ISAMMA2024) (Quang Binh) ,

2024.08

Poster presentation

Review on Functional Mixed Anion Layered Compounds (MALC) and Computational Chemical Analysis on a Representative MALC, Sr2VFeAsO3-δ

Y. Kamihara

The 2024 TechConnect World Innovation (メリーランド州) ,

2024.06

Poster presentation

Mixed anion layered compounds (MALCs), which contain several different anions in crystallographic sites, are novel functional materials. Indeed, high-Tc superconductors [1], high-efficient thermoelectric conversion materials [2], transparent semiconductor [3], and electrical catalyst for oxygen evolution reaction [4] have been found in MALCs. In the conference, we demonstrate a review on the MALCs and magnetic properties of a representative MALC, Sr2VFeAsO3-δ. Sr2VFeAsO3-δ is a mixed anion layered compound with a thick-blocking layer composed by a perovskite-related vanadium oxide layer. In 2019, an electric and magnetic phase diagram as a function of oxygen deficiency (δ) on superconducting Sr2VFeAsO3-δ was experimentally demonstrated. In this study, the magnetic stability of V and Fe in Sr2VFeAsO3-δ (δ = 0, 0.25, 0.50) was theoretically verified based on the density functional theory. Stable magnetic phases of the V are antiferromagnetic ordered phase between two ferromagnetic V magnetic layers (so-called A-AFM) for δ = 0. And the stable magnetic phases of V are ferrimagnetic ordered phase (Ferri.) for δ = 0.25, 0.50. Magnetic phases of Fe are a stripe-type antiferromagnetic ordered phase (s-AFM) in δ = 0, 0.25, 0.50, although the magnetic phases of the Fe with δ = 0.25 shows almost the same formation energy between s-AFM and paramagnetic (PM) ordered phases. Theoretical magnetic ordered phases are qualitatively consistent with the experimental electronic and magnetic phase diagrams for Sr2VFeAsO3-δ, although quantitative differences appear between measured for amounts of element specific magnetic moments and theoretical ones. I wiil talk on "Mixed anion compound iron-based superconducting wire and its manufacturing method" in the conference.[5] [1] Y. Kamihara, et al, J. Am. Chem. Soc. 130, 3296-3297 (2008). Iron-based layered superconductor La[O1-xFx]FeAs (x = 0.05-0.12) with Tc = 26 K [2] M. Ishizawa, et al, J. Appl. Phys. 123, 245104 (2018). [3] K. Ueda, et al, Phys. Rev. B 69, 155305_1-4 (2004). Single-atomic-layered quantum wells built in wide-gap semiconductors LnCuOCh (Ln=lanthanide, Ch=chalcogen). [4] S. Hirai, et al, J. Mater. Chem. A 6, 15102-15109 (2018). Oxygen vacancy-originated highly active electrocatalysts for the oxygen evolution reaction [5] Y. Tojo, S. Iwasaki, M. Matoba, and Y. Kamihara, Japanese Patent No. 6814007 (2020). Mixed anion compound iron-based superconducting wire and its manufacturing method (in Japanese)

Thermoelectric properties of a mixed anion layered compound, LaCuChO (Ch = S, Se) with copper defects

Yoichi Kamihara, Nobuhiko Azuma, Tastuhide Fujioka, Yuya Tanaka, Masanori Matoba

The 9th Korea-Japan International Symposium on Materials Science & Technology (KJMST2024) in GCIM2024,

2024.06

Oral presentation (general)

Several mixed anion layered compounds (MALCs) exhibit relatively high figure of merit (ZT).[1,2] Experimental and theoretical researches expect a promising functionality for the MALCs as thermoelectric materials, [3,4] however detailed carrier-doping mechanism and relations between crystallographic defect and resistivity are still controversial for representative mixed anion layered compounds, polycrystalline LaCu(S, Se)O bulk.[5,6,7,8] In the symposia, we demonstrate thermoelectric properties of polycrystalline LaCu(S, Se)O with a little deficient in Cu site.
[1] L. D. Zhao et al., Appl. Phys. Lett. 97, 092118_1-3 (2010). Bi1−xSrxCuSeO oxyselenides as promising thermoelectric materials
[2] Y. Liu et al., J. Am. Chem. Soc. 133, 20112-20115 (2011). Remarkable enhancement in thermoelectric performance of BiCuSeO by Cu deficiencies
[3] For a review, W. Tang et al., Materials Today Physics 35, 101104_1-22 (2023). BiCuSeO based thermoelectric materials: Innovations and challenges
[4] For a review, A. R. Natarajan et al., Phys. Rev. Mater. 7, 025405 (2023). High thermoelectric performance of layered LaAgXO (X = Se, Te) from electrical and thermal transport calculations
[5] H. Hiramatsu et al., J. Am. Chem. Soc. 132, 15060-15067 (2010). Origins of hole doping and relevant optoelectronic properties of wide gap p-type semiconductor, LaCuOSe
[6] Y. Goto et al., Appl. Phys. Lett. 105, 022104-022107 (2014). Effects of the Cu off-stoichiometry on transport properties of wide gap ptype semiconductor, layered oxysulfide LaCuSO
[7] T. Kato et al., Mater. Sci. Tech. Jpn. 55, 67-71 (2018). Anisotropic thermoelectric exchange properties of high density polycrystalline layered oxychalcogenide, LaCuSeO obtained by uniaxial hot pressing (in Japanese)
[8] N. Azuma et al., Mater. Sci. Tech. Jpn. 58, 64-68 (2021). In-gap-states of a mixed anion layered compound, polycrystalline LaCu1-deltaS0.5Se0.5O (delta~ 0.01) as a degenerate semiconductor (in Japanese)

Synthesis and thermoelectric performance of a layered oxychalcogenide compound LaCuS0.25Se0.75O

Tatsuhide Fujioka, Nobuhiko Azuma, Ryoma Takeuchi, Yoichi Kamihara, Masanori Matoba

The 9th Korea-Japan International Symposium on Materials Science & Technology (KJMST2024) in GCIM2024 (済州) ,

2024.06

Poster presentation

Layered oxychalcogenide RETMChO (RE: rare-earth, TM: transition metal, Ch: chalcogen) is known as a compound that exhibits various electronic properties such as transparent p-type conductivity and high thermoelectric efficiency. The crystallographic structure of RETMChO can be composed by variety of elements, which are replacd by several RE and TM as cations and Ch as anions. Furthermore, the carrier transport is seemed as two-dimensional because the carrier-conducting TMCh layer and the carrier-blocking REO layer are sandwiched in an unit cell. In the unit cell, a square lattice is formed by TM of the constituent elements. LaCuChO is a a representative RETMChO. In 2000-2010, several reserchers had tryed to generate p-type carrier in LaCuChO using aliovalent ion doping in the insulating TMCh layer. Hiramatsu et al. and Goto et al. reports that Cu deficient is a dominant factor to generate p-type carriers in LaCuChO. [H. Hiramatsu, T. Kamiya, T. Tohei, E. Ikenaga, T. Mizoguchi, Y. Ikuhara, K. Kobayashi, and H. Hosono, J. Am. Chem. Soc. 132, 15060 (2010). Y. Goto, M. Tanaki, Y. Okusa, T. Shibuya, K. Yasuoka, M. Matoba, and Y. Kamihara, Appl. Phys. Lett. 105, 022104 (2014).]
In this study, polycrystalline LaCuS0.25Se0.75O samples were synthesized via solid state reaction. Purity of the obtained bulk samples was examined by X-ray diffraction (XRD) using CuK radiation (Rigaku Rint 2500). Total diffuse reflectance spectra were measured using a spectrometer equipped with integrating sphere (Hitachi High-Tech, U-4100). Electrical resistivity (r) was measured by the four-probe method. Thermal conductivity (k) and seebeck coefficient (S) were measured by the steady state method to evaluate dimensionless figure of merit (ZT) of the samples. The samples exhibit optical band gap ~ 2.83 eV. Broad optical absorption around 2.3 eV was also observed indicateing in-gap states due to Cu deficiency. r = 55 Ωcm, k = 5.2 Wm-1K-1, S = 339 micro VK-1, giving ZT ~ 2•10-5 at 673 K.

Magneto-optical imaging measurement of nominal SmFeAsO0.77H0.12

Tomoki Suemura, Hideo Namita, Ryosuke Sakagami, Tsuyoshi Tamegai, Masanori Matoba, Yoichi Kamihara

The 9th Korea-Japan International Symposium on Materials Science & Technology (KJMST2024) in GCIM2024 (済州) ,

2024.06

Poster presentation

Synthesis of mixed anion layered compound, polycrystalline LaNiPO samples

Haruyoshi Suzuki, Ryoma Takeuchi, Yuki Ueno, Yoichi Kamihara, Masanori Matoba

The 9th Korea-Japan International Symposium on Materials Science & Technology (KJMST2024) in GCIM2024 (済州) ,

2024.06

Poster presentation

Evaluation of OER catalystic activity of Bi2Sr2CaCu2O8+x

Masahiro Takeuchi, Hayata Miyamoto, Takahiro Matsumura, Masanori MATOBA, Yoichi KAMIHARA