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Ishida S.,Japan National Institute of Advanced Industrial Science and Technology | Yanagi Y.,Japan National Institute of Advanced Industrial Science and Technology | Yanagi Y.,IMRA Material R and D Co. | Oka K.,Japan National Institute of Advanced Industrial Science and Technology | And 8 more authors.
Journal of the American Chemical Society | Year: 2014

The Ba-Ir-Ge ternary compounds BaIr2Ge7 and Ba 3Ir4Ge16 exhibit superconductivity (SC) at 2.5 and 5.2 K, respectively. Detailed single-crystal structural analysis revealed that these compounds share unique quasi-two-dimensional networks composed of crown-shaped Ge rings that accommodate Ba atoms at the center, referred to as "edge-shared crown-shaped BaGe16 polyhedra". The layered Ba-Ge network yielded a modest anisotropy of 1.3-1.4 in the upper critical field, which is in good agreement with the band structure calculations. The Ba-Ge structural unit is similar to cage structures seen in various clathrates in which the anharmonic vibration of the central atoms, the so-called "rattling" behavior, brings about strong-coupling SC. However, each Ba-Ge unit is relatively small compared to these materials, which likely excludes the possibility of unconventional SC. © 2014 American Chemical Society. Source


Tsukahara M.,IMRA Material R and D Co. | Tsukahara M.,Aisin Seiki
Materials Transactions | Year: 2011

Hydrogenation properties of the vanadium-rich ternary V-Ti-Cr alloy was investigated, which is of interest as a hydrogen carrier for fuelcell vehicles. The dependence of hydrogen content of the hydrides with low plateau pressure (β phase) on the unit cell volume of the dehydrogenated alloys (α phase) is found to be different from that of the hydrides (γ phase) with high plateau pressure. By optimizing the alloy composition, a large effective hydrogen storage capacity of 2.62 mass% is obtained. ©2011 The Japan Institute of Metals. Source


Iyo A.,Japan National Institute of Advanced Industrial Science and Technology | Kawashima K.,Japan National Institute of Advanced Industrial Science and Technology | Kawashima K.,IMRA Material R and D Co. | Kinjo T.,Japan National Institute of Advanced Industrial Science and Technology | And 9 more authors.
Journal of the American Chemical Society | Year: 2016

Fe-based superconductors have attracted research interest because of their rich structural variety, which is due to their layered crystal structures. Here we report the new-structure-type Fe-based superconductors CaAFe4As4 (A = K, Rb, Cs) and SrAFe4As4 (A = Rb, Cs), which can be regarded as hybrid phases between AeFe2As2 (Ae = Ca, Sr) and AFe2As2. Unlike solid solutions such as (Ba1-xKx)Fe2As2 and (Sr1-xNax)Fe2As2, Ae and A do not occupy crystallographically equivalent sites because of the large differences between their ionic radii. Rather, the Ae and A layers are inserted alternately between the Fe2As2 layers in the c-axis direction in AeAFe4As4 (AeA1144). The ordering of the Ae and A layers causes a change in the space group from I4/mmm to P4/mmm, which is clearly apparent in powder X-ray diffraction patterns. AeA1144 is the first known structure of this type among not only Fe-based superconductors but also other materials. AeA1144 is formed as a line compound, and therefore, each AeA1144 has its own superconducting transition temperature of approximately 31-36 K. © 2016 American Chemical Society. Source


Tamada D.,University of Tsukuba | Tamada D.,RIKEN | Nakamura T.,University of Tsukuba | Nakamura T.,RIKEN | And 2 more authors.
Physica C: Superconductivity and its Applications | Year: 2013

We measured the magnetic field distribution of a high Tc bulk superconducting magnet (c-axis oriented EuBa2Cu3O y crystals) during the magnetization process using magnetic resonance imaging. Measurements were performed in the field cooling process from 100 to 50 K in a 4.74 T magnetic field and in the field reducing process from 4.74 to 0 T at 50 K. In field cooling; we observed a significant decrease in the gradient coil efficiencies caused by the Meissner effect. Analysis of the trapped field suggested the presence of temperature gradients; microcracks; and inhomogeneity in the bulk crystals. © 2013 Elsevier B.V. All rights reserved. Source


Fujishiro H.,Iwate University | Itoh Y.,IMRA Material R and D Co. | Yanagi Y.,IMRA Material R and D Co. | Nakamura T.,RIKEN
Superconductor Science and Technology | Year: 2015

Three-dimensional (3D) numerical simulation has been performed for the field-cooled magnetization (FCM) process of REBaCuO superconducting bulk cylinders applicable to the bulk magnet for a 200 MHz (4.7 T) nuclear magnetic resonance (NMR). The influence of the position and size of the defect in the bulk on the inhomogeneity of the trapped field in the hollow space has been investigated. The trapped field profile changes depending on the position and the size of the defect, and the inhomogeneity of the trapped field can be drastically improved by inserting a superconducting thin cylinder with a critical current density (Jc2) higher than that of the bulk cylinder (Jc1). The superconducting current flows mainly on the outermost surface of the inserted thin cylinder to compensate for the inhomogeneous trapped field caused by the defect. The insertion of the superconducting thin cylinder with a higher Jc2 is significantly effective for the practical realization of a compact NMR bulk magnet. © 2015 IOP Publishing Ltd. Source

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