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Journal Articles

Behavior of Nb$$_{3}$$Sn cable assembled with conduit for ITER central solenoid

Nabara, Yoshihiro; Suwa, Tomone; Takahashi, Yoshikazu; Hemmi, Tsutomu; Kajitani, Hideki; Ozeki, Hidemasa; Sakurai, Takeru; Iguchi, Masahide; Nunoya, Yoshihiko; Isono, Takaaki; et al.

IEEE Transactions on Applied Superconductivity, 25(3), p.4200305_1 - 4200305_5, 2015/06

https://doi.org/10.1109/TASC.2014.2360562
 Times Cited Count：0 Percentile：0(Engineering, Electrical & Electronic)

Journal Articles

Effects of high-pressure annealing on critical current density in 122 type iron pnictide wires

Pyon, S.*; Tsuchiya, Yuji*; Inoue, Hiroshi*; Koizumi, Norikiyo; Kajitani, Hideki; Tamegai, Tsuyoshi*

Physica C, 504, p.69 - 72, 2014/09

https://doi.org/10.1016/j.physc.2014.03.008
 Times Cited Count：5 Percentile：23.98(Physics, Applied)

no abstracts in English

Journal Articles

Comparison of $$J$$c characteristics in PIT wires based on BaFe$$_{2}$$As$$_{2}$$ with different substitutions

Tamegai, Tsuyoshi*; Pyon, S.*; Ding, Q. P.*; Inoue, Hiroshi*; Kobayashi, Hiroki*; Tsuchiya, Yuji*; Sun, Y.*; Kajitani, Hideki; Koizumi, Norikiyo

Journal of Physics; Conference Series, 507(2), p.022041_1 - 022041_4, 2014/05

https://doi.org/10.1088/1742-6596/507/2/022041
 Times Cited Count：3 Percentile：76.6(Engineering, Electrical & Electronic)

The author studied the effect of chemical compound for superconducting performance ($$J$$c) of iron-based superconductors. As a result, it was revealed that BaFe$$_{2}$$As$$_{2}$$ showed high Jc. And more, BaFe$$_{2}$$As$$_{2}$$ showed higer $$J$$c such as 32,000A/cm$$^{2}$$ (4.2K) by being applied of 120 MPa of hot isostatic pressure (HIP). Thus, higher $$J$$c performance could be achieved.

Journal Articles

Enhancement of critical current densities in (Ba,K)Fe$$_{2}$$As$$_{2}$$ by 320 MeV Au irradiation in single crystals and by high-pressure sintering in powder-in-tube wires

Pyon, S.*; Taen, Toshihiro*; Otake, Fumiaki*; Tsuchiya, Yuji*; Inoue, Hiroshi*; Akiyama, Hiroki*; Kajitani, Hideki; Koizumi, Norikiyo; Okayasu, Satoru; Tamegai, Tsuyoshi*

Applied Physics Express, 6(12), p.123101_1 - 123101_4, 2013/12

https://doi.org/10.7567/APEX.6.123101
 Times Cited Count：21 Percentile：63.34(Physics, Applied)

We demonstrate a large enhancement of critical current density ($$J$$$$_{rm c}$$) up to 1.0 $$times$$ 10$$^{7}$$ A/cm$$^{2}$$ at 5 K under self-field in (Ba,K)Fe$$_{2}$$As$$_{2}$$ single crystals by irradiating 320 MeV Au ions. With the very promising potential of this material in mind, we have fabricated a (Ba,K)Fe$$_{2}$$As$$_{2}$$ superconducting wire through a powder-in-tube method combined with the hot isostatic pressing technique, whose effectiveness has been proven in industrial Bi2223 tapes. The Jc in the wire at 4.2 K has reached 37 kA/cm$$^{2}$$ under self-field and 3.0 kA/cm$$^{2}$$ at 90 kOe. Magneto-optical imaging of the wire confirmed the large intergranular Jc in the wire core.

Journal Articles

Two-dimensional sodium fluctuation at high temperatures in high-temperature thermoelectric material $$gamma$$-Na$$_{0.7}$$CoO$$_{2}$$

Shamoto, Shinichi; Hasegawa, Yuki*; Kajitani, Tsuyoshi*

Japanese Journal of Applied Physics, Part 1, 45(8A), p.6395 - 6397, 2006/08

https://doi.org/10.1143/JJAP.45.6395
 Times Cited Count：4 Percentile：17.08(Physics, Applied)

A thermoelectric material, $$gamma$$-Na$$_{0.7}$$CoO$$_{2}$$, with a high figure of merit, ZT$$>$$1, at high temperatures has been studied using the atomic pair distribution function (PDF) analysis of pulsed neutron powder diffraction data. We have found significant PDF peak broadening in the correlation between sodium and oxygen atoms at high temperatures. The broad peak indicates that a sodium atom frequently leaves a NaO$$_{6}$$ prism. In other words, sodium atoms hop in a two-dimensional layer at high temperatures. The PDF intensity of the Na-O correlation below a critical length, where a sodium atom is leaving a prism, is inversely proportional to thermal conductivity. This suggests that the short phonon lifetime originates from the frequent sodium hopping in the two-dimensional layer, leading to high-performance thermoelectric generation.

Journal Articles

Search for orbital excitation in YTiO$$_3$$ by neutron scattering

Shamoto, Shinichi; Tsubota, Masami*; Iga, Fumitoshi*; F${aa}$k, B.*; Kajitani, Tsuyoshi*

Journal of Neutron Research, 13(1-3), p.175 - 178, 2005/03

https://doi.org/10.1080/10238160412331299951

YTiO$$_3$$ with T$$_c$$~30 K has been studied by the MARI spectrometer with E$$_i$$=130 meV and 500 meV at T=5 K, 40K, and 200 K. We have not found any clear orbital excitation in a wide Q-E range (0.5$$<$$Q$$<$$25$AA $^{-1}$$, 6$$<$$E$$<$$350 meV). The intensity of orbital excitation would be significantly weak in comparison with the phonon.

Journal Articles

Phonon anomaly on Na$$_x$$HfNCl superconductors with ${it T}$$$_c$$=22 K

Shamoto, Shinichi; Hirai, Atsuo*; Yamanaka, Shoji*; Aso, Naofumi*; Kajitani, Tsuyoshi*

Journal of Neutron Research, 12(4), p.295 - 300, 2004/12

https://doi.org/10.1080/10238160412331299474

Inelastic neutron scattering measurements have been performed on superconducting Na$$_x$$HfNCl powder samples with x=0.27 and 0.38 (T$$_c$$ =22 K). We have observed several temperature dependent phonon anomalies, e.g., at E=15, 29, 76, and 81 meV for the former sample. A phonon peak with E=14.5 meV at Q=6 $AA $^{-1}$$ increases for both samples with decreasing temperature below T=40 K, which is much higher than T$$_c$$. The phonon peak is assigned to an ab-plane vibrational mode, E$$_u$$, of chlorine and hafnium atoms, which strongly modifies the electronic band structure. The phonon anomaly is discussed in terms of carrier inhomogeneity.

Oral presentation

Modulated structure of $$alpha$$'-Na$$_{x}$$CoO$$_{2}$$

Miyazaki, Yuzuru*; Igawa, Naoki; Yubuta, Kunio*; Kajitani, Tsuyoshi*

no journal, , 

The crystal structure of polycrystalline $$alpha$$'-Na$$_{x}$$CoO$$_{2}$$ has been determined by means of the (3+1)-dimensional superspace group approach using the neutron powder diffraction and Rietveld analysis method. Na site in the$$alpha$$'-Na$$_{x}$$CoO$$_{2}$$ is modulated along ${it a}$- and ${it c}$-axes and periodic vacancy sites are existed. It was founded that the octahedrons and prisms of NaO are combined along ${it a}$-axis and that the CoO$$_{2}$$ layers are modulated along ${it c}$-axis.

Oral presentation

Crystal structure and thermoelectric properties of Ba$$_{x}$$CoO$$_{2}$$ synthesized by means of ion-exchange method

Igarashi, Dai*; Miyazaki, Yuzuru*; Yubuta, Kunio*; Igawa, Naoki; Kajitani, Tsuyoshi*

no journal, , 

The crystal structures of polycrystalline ${it A}$ $$_{x}$$CoO$$_{2}$$ (${it A}$=Ca, Sr, Ba) have been determined by the neutron powder diffraction and the electron diffraction studies. In the profile of the Ba$$_{0.35}$$CoO$$_{2}$$, the 002 peak was shifted to lower diffraction angle compared with those of other samples, and the diffraction peak attributed to the superlattice structure was appeared between 002 and 004 peaks. The relationship between the crystal structures and thermoelectrical properties will be discussed in the presentation.

Oral presentation

Effect of cation-ordering on thermoelectric properties in layered cobaltates

Igarashi, Dai*; Miyazaki, Yuzuru*; Yubuta, Kunio*; Igawa, Naoki; Kajitani, Tsuyoshi*

no journal, , 

Layered cobaltates ${it A$_{x}$}$CoO$$_{2}$$ (A = Na, Ca, Sr, Ba) were prepared, and those cation orderings on thermoelectric properties were investigated. It was appeared that those samples had a (3+1) dimensional complexed crystal structure with the cation-disordering on the A layer to the Co$$_{2}$$ layer.

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