担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1016/j.tsf.2021.138802

DOI： 10.1016/j.tsf.2021.138802

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1088/1361-6668/ac0953

DOI： 10.1088/1361-6668/ac0953

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/5.0048693

DOI： 10.1063/5.0048693

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.35848/1347-4065/abdc32

DOI： 10.35848/1347-4065/abdc32

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1088/1361-6668/abaebf

DOI： 10.1088/1361-6668/abaebf

担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1088/1361-6668/aba544

DOI： 10.1088/1361-6668/aba544

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1088/1361-6668/ab4ccd

DOI： 10.1088/1361-6668/ab4ccd

担当区分：筆頭著者   記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）

<p>初期の超伝導物質探索においてマティアス則が活躍した．マティアス則とは，遷移金属およびその合金の臨界温度<i>T</i>_cがある特定の物質パラメータの組み合わせにおいて極大になるという経験則で，多くの超伝導物質の発見につながった．ところが最近，計算機パワーの進展に伴い，全く新しい経験的な<i>T</i>_c予測法が生みだされる可能性がある．それは最新の超伝導データベースと人工知能技術の一種である機械学習を用いて，計算機に既知物質の<i>T</i>_c実験値とその元素の組み合わせを学習させ，得られた学習モデルを未知物質の元素の組み合わせに適用して<i>T</i>_cを予測する手法である．これは強いていえば，21世紀版のマティアス則と呼ばれるようなもので，本稿は，この新しい超伝導物質探索手法に関するものである．</p>

DOI： 10.11470/oubutsu.89.4_222

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007830127

記述言語：英語   掲載種別：研究論文（学術雑誌）

<p>Improvement of critical current density (<i>J</i>_c) in magnetic fields is required in YBa₂Cu₃O₇ films, and process parameters should be optimized for controlling pinning centers. In the present study, a deposition temperature was varied in pulsed laser deposition of YBa₂Cu₃O₇+BaHfO₃ films to control the nanorod structure, and its influence on <i>J</i>_c was analyzed. The YBa₂Cu₃O₇+BaHfO₃ film deposited at 850°C exhibited pinning force maximum (<i>F</i>_p,max) as high as 413 GN/m³ at 40 K, while the <i>F</i>_p,max for the deposition temperature of 850°C at 77 K was smaller than that in the YBa₂Cu₃O₇+BaHfO₃ film deposited at 900°C. A critical temperature decreased and matching field increased with decreasing the deposition temperature. Increase in deposition temperature is effective in improving the <i>F</i>_p,max in high temperatures, since the critical temperature and matching field dependences of <i>J</i>_c value dominate the <i>F</i>_p,max. On the other hand, low deposition temperature improves the <i>F</i>_p,max in low temperatures since the <i>F</i>_p shift in accordance with matching field is dominant to the <i>F</i>_p,max. Thus, the deposition temperature should be set in pulsed laser deposition of YBa₂Cu₃O₇ films containing nanorods considering the <i>J</i>_c variation with critical temperature and matching field.</p><p> </p><p>This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. <b>83</b> (2019) 320–326.</p>

DOI： 10.2320/matertrans.MT-M2019303

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その他リンク： https://ci.nii.ac.jp/naid/130007801653

記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 American Chemical Society. Single-crystal SnSe exhibits extremely high thermoelectric properties, and fabrication of SnSe films is promising for practical application and basic research on properties. However, the high thermoelectric properties have not yet been reported in SnSe films and their thermoelectric properties and nanostructure have not yet been analyzed in detail. In the present study, a-axis-oriented epitaxial SnSe films were prepared to discuss the thermoelectric properties of the SnSe films. While the electrical conductivity of the films was orders of magnitude smaller than that in the single crystals at room temperature, surprisingly, the thermoelectric property (power factor) of the films was slightly higher than that in the single crystals at high temperatures (∼300 °C). The SnSe films contained orthorhombic domain boundaries with a spacing of several hundred nanometers. The orthorhombic domain boundaries caused carrier scattering and degraded the mobility of the films at room temperature, but their effect decreased with increasing temperature. Thus, the carrier scattering at domain boundaries results in characteristic temperature dependence of thermoelectric properties in the SnSe films. High thermoelectric properties at high temperatures were successfully achieved in the SnSe films in spite of the existence of domain boundaries, demonstrating the possibility of high-performance of SnSe thermoelectric films.

DOI： 10.1021/acsami.9b04868

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 IOP Publishing Ltd. Composite multilayer films (CMLs) comprising YBa2Cu3O7 + BaHfO3 (4.7 vol%)/YBa2Cu3O7 + BaHfO3 (3.1 vol%) were fabricated, and vortex behavior in the CMLs was evaluated to discuss inhomogeneous depinning of vortices. Magnetic field and angular dependences of critical current density (J c) in the CMLs were similar to those in the YBa2Cu3O7 + BaHfO3 (4.7 vol%) single layer film (SL). Variation of the CML structure shifted the matching field effect in global pinning force and irreversibility temperature. The J c in the YBa2Cu3O7 + BaHfO3 (4.7 vol%) SL was smaller than that in the YBa2Cu3O7 + BaHfO3 (3.1 vol%) SL, suggesting that vortices preferentially moved along the low-J c layers in the CMLs. The high-J c layers pinned the vortices in the low-J c layers, resulting in a shift of the matching field effect. These observations are characteristic of inhomogeneous depinning of vortices in the CMLs. The inhomogeneous depinning as well as pinned configuration should be considered for understanding J c and for structural design of pinning centers in YBa2Cu3O7 films.

DOI： 10.1088/1361-6668/ab1d2c

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 American Physical Society. Elastic strain and defects are important key words for controlling structure and properties in films. While epitaxial strain and misfit dislocations have been discussed in conventional films, the evolution of strain and defect can be significantly varied by nanocomposite strain and complicated defects in oxides. In the present study, long stacking faults with a spacing of 5-30 nm and a length of >500nm were self-organized by ex situ annealing highly strained nanocomposite films of YBa2Cu3O7-δ(YBCO)+BaMO3(M=Hf,Sn). It is surprising that the nonlocal nature of stacking faults, namely, the structural correlation over >500nm, was observed in spite of the local configuration of the nanocomposite interface. This kind of structural variation was not observed in the pure YBCO film without nanorods, even when the same annealing was performed. A strain energy analysis showed that the stacking fault formation led to the strain energy minimum by reducing the nanocomposite strain. The layered structure of YBCO stacking faults and the large nanocomposite strain realized the present nonlocal self-organization, which is not observed in the conventional systems with epitaxial strain and misfit dislocations.

DOI： 10.1103/PhysRevMaterials.3.013403

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 The Japan Society of Applied Physics. We propose a method to efficiently search for superconductors with higher critical temperature T c by machine learning based on a superconductor database. The T c prediction and the search for new superconductors are still difficult problems. With the progress of computer power and calculation algorithms, the possibility of finding new materials with higher T c at high throughput is emerging. Using the obtained T c prediction model, the scope is expanded to the search space of multielement materials that have never been searched, and candidates for superconductors with higher T c that can be synthesized are proposed.

DOI： 10.7567/1882-0786/ab2922

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担当区分：筆頭著者   記述言語：日本語   掲載種別：記事・総説・解説・論説等（その他）

<p>超伝導材料は低温，強磁場中で電気抵抗ゼロという重要な性質を持つため，医療用MRIや素粒子加速器，あるいは磁気浮上列車，等々において広く応用されている．超伝導材料開発の歴史は長く，その応用範囲を広げるため，物理的・化学的・工学的な試みが世界各国で継続的に続けられてきた．現在では，実用材料である金属系超伝導体（NbTi合金，Nb₃Sn化合物）に加えて，Bi系銅酸化物（1988年発見）や希土類系銅酸化物REBCO（1987年発見）の高温超伝導体，MgB₂超伝導体（2001年発見），および鉄系超伝導体（2008年発見）が実用化競争に参列してきている．特に，高温超伝導体は発見後すでに30年以上が経過し，冷凍機技術の進歩も相まって，強磁場発生コイルからモーター，ケーブル等の幅広い応用展開が進んでいる．一方，MgB₂は組成がシンプル，鉄系超伝導体は異方性が小さい，という長所があり，それぞれの特徴を活かした実用化研究も並行して行われている．最近では，超伝導永久電流モードに不可欠な超伝導体同士の接続や従来のNb₃Snの特性向上においてもスポットが当てられ，新たな展開も起こりつつある．超伝導状態の上限を定める臨界温度と臨界磁場は物質固有の性質であるため結晶構造や原子の配列状態に起因するが，実用上最も重要なパラメータである臨界電流は材料組織に強く依存している．そのため，超伝導体の種類を問わず，臨界電流の向上においては金属学分野における組織制御技術の知見が大変重要である．これまで日本金属学会誌では，2000年代に入ってすでに4回の超伝導材料に関する特集が組まれ，着実な超伝導材料研究の進歩が報告されてきた．本特集においても材料組織制御の観点から「超伝導材料の最前線」にせまり，実用化を加速するための一助としたい．</p>

DOI： 10.2320/jinstmet.JPR2019901

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007695364

記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019, Japan Society of High Pressure Science and Technology. All rights reserved. In this article, uniaxial compression effects on cuprate superconductors such as YBa2Cu4O8 [Y-124], Y0.98Ca0.02Ba2Cu4O8 [Y0.98Ca0.02-124], and Hg0.83Re0.18Ba2Ca2.4Cu3.6O14 [Hg0.83(Re0.18)-1223] were reviewed. The uniaxial compression effects were compared with the hydrostatic compression effects via measuring the Meissner signal of their single crystals in the setup of using a diamond anvil cell. In Y-124 and Y0.98Ca0.02-124, the disappearance of the Meissner signal depended on the style of compression, and the difference in the change in the superconducting transition temperature Tc against initial compression are discussed with the structural symmetry of the CuO5 pyramid. In Hg0.83(Re0.18)-1223, the mechanism of increasing Tc is discussed on the basis of the first principle calculation.

DOI： 10.4131/jshpreview.29.262

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 The Japan Institute of Metals and Materials. Improvement of critical current density (Jc) in magnetic fields is required in YBa2Cu3O7 films, and process parameters should be optimized for controlling pinning centers. In the present study, a deposition temperature was varied in pulsed laser deposition of YBa2Cu3O7+BaHfO3 films to control the nanorod structure, and its influence on Jc was analyzed. The YBa2Cu3O7+BaHfO3 film deposited at 850°C exhibited pinning force maximum(Fp,max) as high as 413 GN/m3 at 40 K, while the Fp,max for the deposition temperature of 850°C at 77 K was smaller than that in the YBa2Cu3O7+BaHfO3 film deposited at 900°C. A critical temperature decreased and matching field increased with decreasing the deposition temperature. Increase in deposition temperature is effective in improving the Fp,max in high temperatures, since the critical temperature and matching field dependences of Jc value dominate the Fp,max. On the other hand, low deposition temperature improves the Fp,max in low temperatures since the Fp shift in accordance with matching field is dominant to the Fp,max. Thus, the deposition temperature should be set in pulsed laser deposition of YBa2Cu3O7 films containing nanorods considering the Jc variation with critical temperature and matching field.

DOI： 10.2320/jinstmet.JA201902

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記述言語：英語   掲載種別：記事・総説・解説・論説等（学術雑誌）

© 2019 Jha and Matsumoto. The lossless transmission of direct electrical currents in superconductors is very often regarded as an "energy superhighway" with greatly enhanced efficiency. With the discovery of high temperature superconductors (HTS) in the late eighties, the prospect of using these materials in efficient and advanced technological applications became very prominent. The elevated operating temperatures as compared to low temperature superconductors (LTS), relaxing cooling requirements, and the gradual development of facile synthesis processes raised hopes for a broad breakthrough of superconductor technology. The impact of superconductor technology on the economy and energy sectors is predicted to be huge if these are utilized on a large scale. The development of superconducting tapes with high critical current density (Jc) is crucial for their use in transmission cables. Many countries these days are running projects to develop wires from these HTS materials and simultaneously field trials are being conducted to assess the feasibility of this technology. These HTS wires can carry electrical currents more than 100 times larger than their conventional counterparts with minimal loss of energy. The increased efficiency of HTS electric power products may result in greatly reduced carbon emissions compared to those resulting from using the conventional alternatives. In order to use the thin films of YBa2Cu3O7-δ (YBCO) and REBCO [RE (rare-earth) = Sm, Gd, Eu etc.], members of the HTS family, for future technological applications, the enhancement of Jc over wide range of temperatures and applied magnetic fields is highly desired. The enhancement of Jc of YBCO and REBCO films has been successfully demonstrated by employing different techniques which include doping by rare-earth atoms, incorporating nanoscale secondary phase inclusions into the REBCO film matrix, decoration of the substrate surface etc. which generate artificial pinning centers (APCs). In this review, the development of the materials engineering aspect that has been conducted over the last two decades to improve the current carrying capability of HTS thin films is presented. The effect of controlled incorporation of APCs through various methods and techniques on the superconducting properties of YBCO and REBCO thin films is presented, heading toward superior performance of such superconducting thin films.

DOI： 10.3389/fphy.2019.00082

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

© Published under licence by IOP Publishing Ltd. The magnetic properties of YBa2Cu3O7-x (YBCO) multilayered film containing BaHfO3 (BHO) nanorods at zero and small fields have been investigated. The dc magnetization and the ac susceptibility were measured with a SQUID magnetometer. The paramagnetic magnetization is shown after the field-cool-warming below the transition temperature T c = 87 K. The nonlinear susceptibility had a large peak around T c, which reflects a glass-transition. An aging effect occured in the relaxation of zero-field-cooled magnetization below the T c. Paramagnetic behavior and magnetic-glass properties were observed in the YBCO multilayered film containing BHO nanorods. The results suggest that the YBCO multilayered film is a novel magnetic-glass system at low fields.

DOI： 10.1088/1742-6596/1054/1/012026

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2002-2011 IEEE. The critical current performance of REBa 2 Cu 3 O y -coated conductors must be isotropically improved for use in high-field coil-based applications operated at low temperatures less than 50 K. The high and isotropic critical current densities (J c ) with respect to the directions of the magnetic field under these operating conditions were achieved by a 3.8 vol.% BaHfO 3 (BHO)-doped SmBa 2 Cu 3 O y (SmBCO) film on a metallic substrate deposited with low-temperature growth (L-BHO film). In particular, the L-BHO film attained a high flux pinning force density over 1.5 TN/m 3 at a temperature of 4.2 K. From the anisotropic scaling approach based on the effective mass model, a high density of random pinning centers in the L-BHO film plays an important role in achieving the high J c performance at 4.2 K. In order to reveal the reason why the L-BHO film includes high density of random pinning centers, we compared the flux pinning properties and the dominant flux pinning centers between the L-BHO film and the other two samples: A 3.8 vol.% BHO-doped SmBCO film fabricated with relatively high-temperature growth, and a nondoped SmBCO film fabricated with low-temperature growth. From the comparison, it is revealed that the random pinning centers are induced by BHO nanorods.

DOI： 10.1109/TASC.2018.2804667

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2018 IOP Publishing Ltd. Critical current density (J c ) was investigated in YBa 2 Cu 3 O 7-δ films containing nanorods prepared with various nanorod materials, with variation of nanorod content, substrate temperature, and oxidization condition. Three types of compositional situation were realized: films containing strain induced oxygen vacancies; fully oxidized films containing cation compositional deviation; and oxygen deficient films. Normalized J c -B behavior was determined via the matching field, which is a geometric factor, regardless of the compositional details. A J c -critical temperature (T c ) relation depending on distribution and fraction of compositional deviation (cation compositional deviation and strain induced oxygen vacancies) was found: the J c values decreased with decreasing T c due to the effect of T c on nanorod pinning strength in the fully oxidized films; J c decreased with decreasing oxygen pressure in the film cooling process after film deposition in spite of T c remaining almost the same, due to reduction of the effective area for current flow in the oxygen deficient films. Thus, a J c landscape based on geometric and compositional factors was obtained. The study highlights the importance of the J c -T c analysis in the understanding of J c in YBa 2 Cu 3 O 7-δ films containing nanorods.

DOI： 10.1088/1361-6668/aabe68

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 IOP Publishing Ltd. Nanorods, which are nano-scaled columnar-shape precipitates, have recently been used to improve critical current density Jcin magnetic fields for REBa2Cu3Oy(RE123, RE: rare earth element) high temperature superconducting tapes/films. However, the flux pinning mechanism of the nanorod is not clear yet. We investigated the Jcand resistivity ρ properties in detail and discussed the flux pinning properties on the basis of the flux pinning state diagram for high-quality Sm123 films with well-aligned 5.6 vol% BaHfO3nanorods. Plateaus were observed in the field dependence of Jcand ρ at high temperatures above the delocalization temperature. This suggests that nanorod pinning becomes effective in the vortex liquid phase and it grows up when the temperature decreases toward the delocalization temperature. In the 'many-nanorod' state in the high temperature region above the delocalization temperature, double peaks in the Fpcurves appear due to the coexistence of nanorod pinning and random pinning. At low temperatures below 70 K, however, the well-scaled Fpcurves at low fields and temperature dependent (non-scaled) normalized Fpcurves are observed. From detailed analysis using the cooperation model of the random and the correlated pinning centers, we found that nanorod pinning is dominant below the matching field and the cooperation between nanorod pinning and random pinning determines the high field Jcproperties above the matching field.

DOI： 10.1088/1361-6668/aa8d10

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 The Japan Society of Applied Physics. A high flux pinning performance was obtained for a 3.8 vol% BaHfO3-doped SmBa2Cu3Oysuperconducting film on a metallic substrate. At a temperature of 77.3 K, an irreversibility field of 16.8 T and the maximum flux pinning force density of 32.5GN/m3in fields applied parallel to the c-axis of the film were achieved, which are the highest values reported thus far for REBa2Cu3Oyfilms, to our knowledge. The introduction of wellaligned BaHfO3nanorods with a high number density into REBa2Cu3Oyfilms with little or no degradation of the critical temperature is an effective method for improving the flux pinning performance.

DOI： 10.7567/APEX.10.103101

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 IOP Publishing Ltd. Conventionally, δTctype (order parameter modulation) and δl type (mean free path modulation) pinning mechanisms have been proposed to explain the temperature dependence of the flux pinning of superconducting materials. According to previous studies, it is assumed that the temperature dependence of Jcof REBa2Cu3O7(REBCO, RE =Y, Gd, Sm, etc) films without artificial pinning centers (APCs) is δl type, but it is unidentified when APCs are introduced into the films. In this paper, GdBCO thin films doped with BaHfO3(BHO) deposited on LaAlO3substrates by pulsed laser deposition were studied. A target exchange method was used to alternately ablate two targets of pure GdBCO and BHO for introducing nanorods as APCs into GdBCO films. Since the insulative BHO acts as a strong pinning center, the δTcpinning mechanism is expected for the temperature dependence of Jcof these thin films. However, the experimental results showed that the Jcof the films with BHO nanorods was determined by the δl pinning mechanism over a wide temperature range. In order to explain these unexpected results, we examined the pinning mechanism by nanorods based on a resultant pinning force model.

DOI： 10.1088/1361-6668/aa835b

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 Author(s). The effect of incorporation of nanoscale Y2BaCuO5(Y211) inclusions on the vortex pinning properties of YBa2Cu3O7-δ(YBCO or Y123) superconducting thin films is investigated in detail on the basis of variation of critical current density (JC) with applied magnetic field and also with the orientation of the applied magnetic field at two different temperatures: 77 K and 65 K. Surface modified target approach is employed to incorporate nanoscale Y211 inclusions into the superconducting YBCO matrix. The efficiency of Y211 nanoinclusions in reducing the angular anisotropy of critical current density is found to be significant. The observed angular dependence of the critical current density is discussed on the basis of mutually occupied volume by a vortex and spherical and/or planar defect. A dip in JCnear the ab-plane is also observed which has been analyzed on the basis of variation of pinning potential corresponding to a spherical (3-D) or planar (2-D) pinning center and has been attributed to a reduced interaction volume of the vortices with a pinning center and competing nature of the potentials due to spherical and planar defects.

DOI： 10.1063/1.5001273

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 IOP Publishing Ltd. REBa2Cu3Oysuperconducting tapes are appropriate for high field magnet applications at low temperatures (i.e. below liquid nitrogen temperature). To clarify the morphology and the volume of the effective pinning center at low temperatures, we used a low-temperature growth technique to fabricate SmBa2Cu3Oy(SmBCO) films with various amounts of BaHfO3(BHO) nanorods onto MgO-buffered metal substrates produced by ion-beam-assisted deposition; we investigated their flux pinning properties using a 25 T cryogen-free superconducting magnet that was recently developed at Tohoku University. According to the microstructural analysis using transmission electron microscopy, the BHO nanorods have a content-dependent morphology and are aligned for the higher content. The inclined and discontinuous BHO nanorods were observed in SmBCO films with BHO contents up to 3.8 vol%; they show an excellent flux pinning force density (1.5 TN m-3at 21 T and 4.2 K) even when the magnetic field is perpendicular to the films. Based on the effective mass model for the flux pinning, the random pinning centers are dominant at low temperatures. The correlated flux pinning is stronger for aligned nanorods; however, the random pinning center becomes weaker in the 4.5 vol% BHO-doped films. Therefore, the optimal BHO doping level is approximately 3.8 vol% in terms of the amplitude of the critical current density and the anisotropy from 4.2 K to 20 K because this provides the best mixture of correlated and random flux pinning centers.

DOI： 10.1088/1361-6668/aa7ef0

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 IOP Publishing Ltd. This paper reviews the progress of studies to determine optimum shapes of the artificial pinning center (APC) of REBa2Cu3Oythin films and coated conductors towards superconducting magnets operating at temperatures of 77 K or less. Superconducting properties vary depending on the kind and quantity of BaMO3materials. Therefore, we study changes in the shapes of nanorods that are due to the difference in the quality of additives and growth temperature. In addition, we aim to control the APC using an optimum shape that matches the operating temperature. In particular, we describe the shape control of nanorods in SmBCO thin films and coated conductors by employing lower temperature growth (LTG) technology using seed layers. From the cross-sectional transmission electron microscopy observations, we confirmed that using the LTG method, the BaHfO3(BHO) nanorods, which were comparatively thin and short in length, formed a firework structure in the case of SmBCO films with coated conductors. The superconducting properties in the magnetic field of the SmBCO-coated conductor with the optimum amount of BHO showed that Fmax= 1.6 TN m-3on a single crystalline substrate and 1.5 TN m-3on metallic substrate with a biaxially textured MgO layer fabricated by ion-beam assisted deposition method tape 4.2 K.

DOI： 10.1088/1361-6668/aa8236

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 IOP Publishing Ltd. In order to apply REBa2Cu3Oy(REBCO, RE = rare earth elements or Y) coated conductors in high magnetic field, coil-based applications, the isotropic improvement of their critical current performance with respect to the directions of the magnetic field under these operating conditions is required. Most applications operate at temperatures lower than 50 K and magnetic fields over 2 T. In this study, the improvement of critical current density (Jc) performance for various applied magnetic field directions was achieved by controlling the nanostructure of the BaHfO3(BHO)-doped SmBa2Cu3Oy(SmBCO) films on metallic substrates. The corresponding minimum Jcvalue of the films at 40 K under an applied 3 T field was 5.2 MA cm-2, which is over ten times higher than that of a fully optimized Nb-Ti wire at 4.2 K. At 4.2 K, under a 17.5 T field, a flux pinning force density of 1.4 TN m-3for B//c was realized; this value is among the highest values reported for REBCO films to date. More importantly, the Fpfor B//c corresponds to the minimum value for various applied magnetic field directions. We investigated the dominant flux pinning centers of films at 4.2 K using the anisotropic scaling approach based on the effective mass model. The dominant flux pinning centers are random pinning centers at 4.2 K, i.e., a high pinning performance was achieved by the high number density of random pins in the matrix of the BHO-doped SmBCO films.

DOI： 10.1088/1361-6668/aa76a1

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 IOP Publishing Ltd. High critical current density (Jc) was achieved in low temperatures of 40 and 20 K in YBa2Cu3O7-δ films containing elongated BaHfO3 nanorods and stacking faults, which were prepared using pulsed laser deposition and post-oxygen-annealing. The YBa2Cu3O7-δ + BaHfO3 film exhibited global pinning force maximum (Fp,max) of 312 GNm-3 at 40 K and 619 GNm-3 at 20 K due to strong pinning by nanorods. These Fp,max values are comparable to those in the previously-reported high-Jc films with almost the same matching field. Thus, the present study demonstrated that YBa2Cu3O7-δ superconducting matrix realized high Jc in low temperatures like other REBa2Cu3O7-δ (RE = Gd, Sm, (Gd, Y)). Furthermore, high Jc was obtained also for magnetic field parallel to the ab-plane, indicating hybrid pinning of nanorods and stacking faults. Thus, the stacking faults significantly affected the Jc properties in the YBa2Cu3O7-δ films containing nanorods.The present film structure with strong c-axis correlated pinning and hybrid pinning is effective in simultaneous control of Jc values and Jc anisotropy in YBa2Cu3O7-δ films.

DOI： 10.1088/1361-6668/aa70d3

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 American Chemical Society. Intriguing properties of self-organized nanocomposites of perovskite oxides are usually derived from the complex interface of constituent material phases. A sophisticated control of such a system is required for a broad range of energy and device applications, which demand a comprehensive understanding of the interface at the atomic scale. Here, we visualized and theoretically modeled the highly elastically strained nanorod, the interface region with misfit dislocations and heterointerface distortion, and the matrix with strain-induced oxygen vacancies in the self-organized YBa2Cu3O7-δnanocomposite films with Ba perovskite nanorods. Large misfit strain was elastically accommodated in the nanocomposites, but since the elastic strain was mainly accommodated by the nanorods, the concentration of strain-induced oxygen vacancies was small enough for the matrix to keep high critical temperature (>85 K). The interfacial bonding distorted the atomic structure of YBa2Cu3O7-δ, but the thickness of distortion was limited to a few unit cells (less than the coherence length) due to the electron screening. The effect of volume fraction on elastic strain and the electron screening are crucial for strong vortex pinning without significant degradation of both the elementary pinning force and critical temperature in the nanocomposites. Thus, we comprehensively clarified the self-organized nanocomposite structure for on-demand control of superconductivity and oxide functionality in the nanocomposite engineering of perovskite oxides.

DOI： 10.1021/acsnano.6b07716

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 American Physical Society. The effects of uniaxial strain and hydrostatic pressure on Hg0.83Re0.18Ba2Ca2.4Cu3.6O14[Hg0.83(Re0.18)-1223] were investigated by ac magnetic measurements under stress corresponding to a pressure of 20 GPa at maximum. According to a previous thermal study based on the Ehrenfest relation, in-plane contraction should increase the superconducting transition temperature Tc, whereas out-of-plane contraction should decrease Tc. This suggests that the increase in Tc under hydrostatic-pressure contraction must be smaller than that under in-plane contraction. However, the present uniaxial-strain experiments revealed enhancement of Tc under both in-plane and out-of-plane contraction, and the largest enhancement was observed under hydrostatic-pressure contraction. According to a band calculation, all contraction styles induce hole doping from the HgO blocks to the CuO2 blocks, and hydrostatic-pressure contraction yields the largest hole doping among three contractions. This behavior explains well a series of changes in Tc in the stress region of below 8 GPa. More specifically, under hydrostatic-pressure contraction, Tc exhibited an increase, a decrease, and another increase with increasing pressure, and this multistep change is similar to that observed in Bi-2223-type cuprate superconductors, suggesting that it is necessary to distinguish the effect of strain on the middle CuO2 plane in the three-CuO2-plane package from that on the outer planes.

DOI： 10.1103/PhysRevB.95.064503

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 Author(s). The pin size effect and mixed pinning of nanorods and matrix defects are discussed for YBa2Cu3O7-δfilms containing nanorods. BaSnO3nanorods with a diameter of 11 nm and BaHfO3nanorods with a diameter of 7 nm were prepared, and critical current density (Jc) and resistivity were measured in the films. When the coherence length was larger than the nanorod size at high temperatures near the critical temperature, the trapping angle and activation energy of the vortex flow depended on the nanorod diameter. At a moderate temperature of 65−77 K, the pin size effect on Jcdisappeared since the coherence length became smaller than the nanorod size. At a low temperature of 20 K, the contribution from matrix pinning became comparable to that of nanorods in a high magnetic field due to the small coherence length. Thus, the temperature-dependent coherence length caused the pin potential situation to vary significantly, namely, the pin size effect and mixed pinning, which strongly affected vortex pinning in YBa2Cu3O7-δcontaining nanorods.

DOI： 10.1063/1.4975300

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2017 by American Scientific Publishers. The nanoengineering approach by PLD method can produce a variety of complex nanocomposite oxide thin films with unique properties for sustainable applications. We report on the epitaxial growth and superconducting properties of YBa2Cu3O7-x(YBCO) multilayers incorporating BaSnO3(BSO) nanorods and Y2O3nanoparticles at the same time in order to combine the advantages of both columnar (1D, BSO) and isotropic (3D, Y2O3) pinning with the purpose of enhance the pinning force of the films for a wide range of applications in large external magnetic fields. Multilayered films, alternating YBCO+Y2O3and YBCO+BSO layers were grown in pulsed laser deposition chamber by switching a surface-modified YBCO+~2A% Y2O3target and a mixed YBCO+4 wt% BSO target. Different combinations for films' growth have been tried via varying the thickness of the alternating layers. The best result was obtained with the combination [(90 nm YBCO +BSO)/(30 nm YBCO+Y2O3)]×3 presenting a maximum global pinning force Fmaxp= 17.6 GN/m3(77 K, 2.2 T, B//c), more than 3 times larger than for typical pure YBCO films. These results demonstrate that the nanoengineering approach is at very advanced level: satisfactory control of nanodefects size and distribution was achieved. At the end, a renewed approach based on the Ginzburg-Landau single vortex theory is used to discuss the contributions of 1D, 3D and 1D+3D APCs to the global pinning force of the hybrid multilayers.

DOI： 10.1166/sam.2017.2848

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2016 Author(s). Transport measurements revealed flux pinning properties and vortex phases in SmBa2Cu3O7-δ(Sm123) superconducting films with BaHfO3nano-rods on LaAlO3substrates. The films have large matching fields BΦup to 9.9 T, nano-rod diameters of ∼6 nm, and a slight Tcdegradation with Tc∼ 91.8 K by using the low temperature growth technique. According to the transport results, a small critical exponent ∼4 indicates the presence of a Bose-glass phase in the films. Double peaks of the flux pinning force density are unexpectedly observed at high temperatures over 80 K, which is accompanied by steep drops of the crossover magnetic fields between the single vortex pinning and the collective pinning states. The drops are explained by the delocalization of the vortex where the vortex is pinned by many nano-rods in the single vortex pinning state. From the viewpoint of the vortex delocalization, we conclude that BΦshould be less than 11 T for applications at liquid nitrogen temperature.

DOI： 10.1063/1.4962398

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2016 IOP Publishing Ltd. To control the anisotropy of critical current density (Jc), hybrid artificial pinning centers (APCs) of elongated-nanorods and segmented-nanorods were incorporated into YBa2Cu3O7films. The elongated-nanorods and segmented-nanorods were formed by fabricating multilayer films using YBa2Cu3O7+BaSnO3targets with a different BaSnO3content. According to the elastic calculation, the BaSnO3-free YBa2Cu3O7regions between BaSnO3segmented-nanorods were highly strained, resulting in their alignment along the c-axis. Pinning of the vortex kinks and straight vortices by the nanorod ends improved Jcin a wide range around B//ab. The angular dependence of Jcsystematically varied with the multilayer structure of layer thickness and BSO content. Jcdepended on the layer thickness even with keeping the constant average BSO content, showing that the BaSnO3distribution, as well as the average BaSnO3content, affected the Jc. The hybrid pinning effect of elongated-nanorods and nanorod ends improved the Jcanisotropy although the effect was not so large in the present films. The control of strain and interface is expected to lead to further improvement of Jc.

DOI： 10.1088/0953-2048/29/10/105010

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2015 Elsevier B.V. All rights reserved. The influence of self-grown seed has been studied on thermoelectric performance of 2% Al-doped ZnO(AZO) thin films. The thickness and orientation of c-axis domains in seed layer change on different substrates while other deposition conditions were kept unchanged for a comparable study. The changes occur because of the different nucleation process of thin film growth on substrate interface and the different lattice mismatch between AZO and substrate. Thin films are grown by pulsed laser deposition on single crystals (SrTiO3(STO) and Al2O3) and cheap amorphous fused silica (FS) substrates at 400 °C. All thin films are c axis oriented. The grains are highly connected and elongated in shapewhich leads to high thermoelectric properties. The thicker self-grown seed layer is found in thin film deposited on FS substrates which shows best performance: electrical conductivity s=93 S/cm and Seebeck coefficient S=-203 μV/K, which estimate power factor (S2.σ) about 0.37 × 10-3Wm-1K-2 at 600 K.The value of thermal conductivity (k) was found lowest (4.89Wm-1K-1) for thin film deposited on FS than the other thin films (6.9Wm-1K-1on Al2O3and 6.55Wm-1K-1on STO) at 300 K. The figure ofmerit, ZT=S2.σ.T/κ, is calculated 0.046 at 600 K, 5 times larger than the ZT of our previous reported bulk AZO,which is promising for practical applications of thermoelectric oxide thin films.

DOI： 10.1016/j.tsf.2015.09.060

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2016 IEEE. YbBa2Cu4O8(Yb124) films were fabricated using metal-organic deposition method, and crystal growth of c-axis oriented films was discussed based on transmission electron microscopy (TEM) and X-ray diffraction. The c-axis oriented YbBa2Cu3O7-x(Yb123) and Yb124 films were formed depending on annealing time and temperature. Yb123 grew in high temperature (800 °C-840 °C) even at short annealing time, but Yb124 was formed in lower temperature (760 °C-800 °C) at long annealing time. It is expected that the growth rate of Yb123 is larger than that of Yb124 due to the simple structure of Yb123. The phase diagram of Y-Ba-Cu-O indicates that Y123 is unstable in temperature lower than 750 °C, and Y124 and Y123 coexist in higher temperature. Assuming that the phase diagram is similar in Y-Ba-Cu-O and Yb-Ba-Cu-O, the present results are consistent with the phase diagram. Annealing time dependence of microstructure was evaluated for annealing temperature of 760 °C using TEM. The thickness of Yb124 increased with the increase in annealing time, and Yb124, which was transformed from Yb123, contained planar defects parallel to the c-axis. Yb124 grows without transforming to other phases, and metastable Yb123 transforms to Yb124 by forming the planar defects at the temperature where Yb124 is stable and Yb123 is unstable.

DOI： 10.1109/TASC.2016.2542272

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記述言語：英語   掲載種別：研究論文（学術雑誌）

CiNii Article

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

The critical current density (Jc) properties of the Artificial Pinning Center (APC) introduced YBa2Cu3O7 (YBCO) films in the longitudinal magnetic field were measured. Y2O3 or Y2BaCuO5 (Y211) was introduced as APCs to YBCO, and YBCO films with APC were fabricated on SrTiO3 single crystal substrate. The sizes of Y2O3 and Y211 were 5 - 10 nm and 10 - 20 nm, respectively. As a result, Jc enhancement in the longitudinal magnetic field was observed in Y2O3 introduced YBCO films. However, it was not observed in Y211 introduced YBCO films. Therefore, it was considered that Jc properties in the longitudinal magnetic field were affected by introducing of small size APC, and it was necessary that APC does not disturb the current pathway in the superconductor.

DOI： 10.1016/j.phpro.2016.04.012

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記述言語：日本語   掲載種別：記事・総説・解説・論説等（その他）

DOI： 10.2320/jinstmet.JPR2016901

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2016 The Japan Institute of Metals and Materials. BaMO3 (M = Hf, Sn)-doped Sm1+xBa2-xCu3Oy (x= 0, 0.04) superconducting films were fabricated by pulsed-laser deposition (PLD). It is known that BaMO3 nanorods are formed in superconducting films and that the morphology of nanorods affects the superconducting properties, particularly the critical current density ( JC) properties. In this study, superconducting films were fabricated by conventional PLD and by PLD using a low-temperature growth technique to control the morphology of the nanorods. The relationship between the nanorod morphology and JC properties is discussed.

DOI： 10.2320/jinstmet.JC201604

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2014, The Minerals, Metals & Materials Society. We have investigated the thermoelectric properties of 2% Al-doped ZnO (AZO) thin films depending on the postdeposition cooling atmosphere [in oxygen pressure (AZO-O) or vacuum (AZO-V)]. Thin films were grown by pulsed laser deposition on sapphire (Al2O3) substrates at various deposition temperatures (400∘C to 600∘C). All films were c-axis oriented. The electrical conductivity of AZO-V thin films was higher than that of AZO-O thin films across the whole temperature range from 300 K to 600 K, due to the optimal carrier concentration (1020cm-3) of AZO-V samples. Furthermore, the thermoelectric performance of AZO-V films increased with the deposition temperature; for instance, the highest power factor of 0.87 ×10-3Wm-1K-2and dimensionless figure of merit of 0.07 at 600 K were found for AZO-V thin film deposited at 600∘C.

DOI： 10.1007/s11664-014-3471-0

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記述言語：英語   掲載種別：研究論文（学術雑誌）

� 2015 IOP Publishing Ltd. We report the epitaxial growth and superconducting properties of Y2O3-added YBa2Cu3Ox (YBCO) films grown on SrTiO3-buffered MgO substrates by pulsed-laser deposition using surface-modified YBCO targets. Areas of Y2O3sectors on the YBCO target were increased to 5.44% and 9.22% of the total YBCO pellet in order to find a correlation between the Y2O3content, morphology, and the pinning properties of YBCO+Y2O3mixed films. The maximum global pinning forces, FP, at 77 K were 14.3 GN m-3and 1.15 GN m-3for the Y2O35.44A% and 9.22A%, respectively. The 5.44A% Y2O3-added sample presents a very high value of pinning force at 77 K, approaching the value obtained in YBCO films with added BaZrO3nanorods, but with less depression in the superconducting critical temperature, Tc. In accordance with scanning transmission electron microscopy (STEM) observations, both films present nanoparticulate Y2O3dispersed in a YBCO matrix where Y2Ba4Cu8O16 (Y248) intergrowths were also observed. Consistent with the strong pinning theory, the size and distribution of randomly dispersed Y2O3particles are optimal for the flux pinning of a 5.44A% Y2O3-YBCO film, while in the case of a 9.22A% film, the YBCO matrix is degraded by jam-packed Y248 intergrowth, which leads to a comparatively poor pinning performance. We further used the single-vortex dynamics model to account for vortex pinning in the samples. The 5.44A% Y2O3-YBCO film result shows good agreement with the model fit up to 4 T of the applied magnetic field.

DOI： 10.1088/0953-2048/28/2/024002

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記述言語：英語   掲載種別：研究論文（学術雑誌）

High <i>T</i><i>_c</i> cuprate superconducting films, such as REBa₂Cu₃O_7-<i>_x</i> (RE=Y, Sm, Gd), REBa₂Cu₄O₈ (RE=Y, Yb),(Hg, Re)Ba₂CaCu₂O₆₊<i>_x</i>, (Hg, Re)Ba₂Ca₂Cu₃O₈₊<i>_x</i>, Bi₂Sr₂CaCu₂O₈ and Bi₂Sr₂Ca₂Cu₃O₁₀, have been studied based on "atomic level control" including lattice strain control, carrier control, and nanostructure control, in order to simultaneously improve critical temperature <i>T</i><i>_c</i>, irreversibility field<i> B</i><i>_irr</i>, and critical current density <i>J</i><i>_c</i> of the films. We successfully fabricated high-performance cuprate superconducting films with higher <i>T</i><i>_c</i>, <i>B</i><i>_irr</i>, and<i> J</i><i>_c</i> on IBAD-MgO substrates.

DOI： 10.2221/jcsj.50.510

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.4878536

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記述言語：英語   掲載種別：研究論文（学術雑誌）

CiNii Article

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

We studied growth substrate temperature dependent morphologies of BaHfO3(BHO) nano-rods for SmBa2Cu3Oy, (SmBCO) films with BHO fabricated by pulsed laser deposition (PLD) method. The morphology of BHO nano-rods within the SmBCO matrix could be controlled by changing substrate temperatures adoping a Low Temperature Growth (LTG) technique. Using the LTG technique, we could fabricate SmBCO films showed c-axis orientation even at low substrate temperature during deposition without a degradation of superconducting properties, which is one of the most advantages of the LTG technique. In this study, we found an optimal morphology of the BHO nano-rods and the morphology was fine, straight and various growth directions. The BHO nano-rods were more effective to improve the Jcin a magnetic field than other morphologies of the BHO nano-rods.

DOI： 10.1088/1742-6596/507/2/022021

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

© 2014 The Authors. In order to clarify the influence of RE/Ba substitution on superconducting properties on REBCO films in magnetic fields, we fabricated BHO-doped Nd1+xBa2-xCu3Oy films in which Nd composition were controlled by PLD method using alternating-targets technique. The Tc of NdBCO(x = 0.01, 0.08) films were about 92 K. For the field applied parallel to the c-axis, a Jc and a characteristic magnetic field of the maximum pinning force of the NdBCO(x = 0.08) film increased compared with those of the NdBCO(x = 0.01) film. Additionally, a Jc of a BHO-doped NdBCO(x = 0.08) film improved for all applied angles of magnetic field in 1 T. The forms of Jc-θ curves for the BHO-NdBCO films with x = 0.01 and 0.08 were similar form. Therefore, it is considered that the reason of Jc increase in the BHO-doped NdBCO(x = 0.08) film is introduction of three-dimensional pinning centers of fine Nd/Ba solid solutions and the solid solution do not influence on the BHO growth.

DOI： 10.1016/j.phpro.2014.09.031

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

For the improvement of superconducting properties of BaMO3(M=Zr, Sn, HQ-doped REBa2Cu3Oyfilms, we focused on the Tcreduction caused by lattice misfit between BaMO3and REBa2Cu3Oy. We compared the influence on the Tc reduction of BaZrO3, BaSnO3and BaHfO3-doped SmBa2Cu3Or (SmBCO) films with various BMO contents. From the correlation between configuration of nanorods and c-axis expansion, it was suggested that the lattice strain working on the SmBCO matrix became stronger in the order of BaHfO3, BaZrO3and BaSnO3. Therefore, the combination of SmBCO and BaHfO3is better regarding the suppression of the Tc reduction compared with other combinations of SmBCO and BaMO3.

DOI： 10.1088/1742-6596/507/2/022043

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2014, Springer Science+Business Media New York. Flux pinning properties of a BaHfO3(BHO)-doped SmBa2Cu3Oy(SmBCO) film, which was fabricated by pulsed laser deposition method adopting a seed layer technique, have been investigated. Nano-rods of the film were small in a diameter of 5.4 nm and had high number density (high-n) of 4,775/μm2. The flux pinning properties of the film were compared with a SmBCO film including BHO nano-rods with a larger diameter and a lower number density (low-n). At 65 K, the flux pinning force density of the high-n sample (105.0 GN/m3) showed much higher than that of the low-n sample (70.6 GN/m3).

DOI： 10.1007/s10948-014-2754-2

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記述言語：日本語   掲載種別：研究論文（学術雑誌）

For the improvement and stable use of various superconducting applications using REBa₂Cu₃O<i>_y</i> (REBCO) coated conductors, the enhancement of the critical current density (<i>J</i>_c) in high magnetic fields is essential. It is known that BaMO₃ (BMO; M = Zr, Sn, Hf) nanorods can improve the in-field <i>J</i>_c of REBCO films. Furthermore, the density and formation can be controlled by the deposition conditions such as deposition temperature and BMO content. In this study, our aim was to improve the <i>J</i>_c of SmBa₂Cu₃O<i>_y</i> (SmBCO) films in high magnetic fields. We tried to introduce high-density BaHfO₃ (BHO) nanorods into SmBCO films by increasing the BHO content. We fabricated 2.3, 4.9 and 7.2 vol.% BHO-doped SmBCO films at the same deposition temperature, and compared the geometric formation of nanorods and flux pinning properties. From TEM observation, the densities of BHO nanorods increased with increases in BHO content, and the diameters of all nanorods were almost the same (i.e., approximately 12 nm). The highest density and matching field were 1711 /μm² and 3.54 T in a 7.2 vol.% sample. The flux pinning force of the sample with a higher matching field was effective in higher fields in the magnetic field dependence of <i>J</i>_c. This was in good agreement with theories and many reports. In irreversibility field lines, a unique behavior, which probably originated in the thick diameters, was observed around the low magnetic field.

DOI： 10.2221/jcsj.49.117

CiNii Article

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記述言語：日本語   掲載種別：研究論文（学術雑誌）

YBa₂Cu₃O₇(YBCO) films containing hybrid artificial pinning centers(APCs) of BaSnO₃(BSO) nanorods and Y₂O₃ nanoparticles were fabricated on ion beam assisted deposition(IBAD)-MgO substrates. By changing contents of BSO and Y₂O₃, critical current density (<i>J</i>_c) properties were controlled. The YBCO film containing high density of BSO and Y₂O₃ exhibited high <i>J</i>_c in high magnetic fields, and an isotropic angular dependence of <i>J</i>_c was obtained in a low magnetic field in a film containing moderate density of nanorods and nanoparticles, showing that hybrid APCs have the potential to improve <i>J</i>_c performance. BSO content is the most crucial factor for <i>F</i>_p,max in a magnetic field parallel to the <i>c</i>-axis, and Y₂O₃ nanoparticles can significantly improve <i>F</i>_p,max in a magnetic field tilted from the <i>c</i>-axis. Advanced control of nanorods and nanoparticles is needed for realization of higher <i>J</i>_c performance.

DOI： 10.2221/jcsj.49.105

CiNii Article

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記述言語：日本語   掲載種別：研究論文（学術雑誌）

We have proposed a low-temperature growth (LTG) technique which makes it possible to fabricate SmBa₂Cu₃O<i>_y</i> (SmBCO) films with <i>c</i>-axis orientation in a wide range of growth temperatures without the degradation of superconducting properties. In this study, using the LTG technique, we fabricated SmBa₂Cu₃O<i>_y</i> (SmBCO) films with BaHfO₃ (BHO) nano-rods at low substrate temperatures using the pulsed laser deposition (PLD) method. The effect of low substrate temperatures on BHO nano-rods in SmBCO films are discussed in terms of their microstructures and superconducting properties. The nano-rods were observed clearly in transmission electron microscopic (TEM) images of the films. We found that the morphologies of the nanorods were small in diameter, had high densities and inclined along the <i>c</i>-axis of SmBCO. In the case of the substrate temperature of 750^°C, the diameter and density of nano-rods with 2.7 vol.% BHO-doping were 5.7 nm and 2300 /μm², respectively. The film showed high flux pinning force, <i>F</i>_p, of 25 GN/m³ (77 K, <i>B</i>//<i>c</i>) in a high field, 4 T. Furthermore, in the film, the angular dependence of <i>J</i>_c showed a broad peak at <i>B</i>//<i>c</i>, due to the flux pinning by nano-rods growing in various directions.

DOI： 10.2221/jcsj.49.123

CiNii Article

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

We have prepared 2% Al doped ZnO (AZO) thin films on SrTiO3and Al2O3substrates by Pulsed Laser Deposition (PLD) technique at various deposition temperatures (Tdep= 300 °C - 600 °C). Transport and thermoelectric properties of AZO thin films were studied in low temperature range (300 K - 600 K). AZO/STO films present superior performance respect to AZO/Al2O3films deposited at the same temperature, except for films deposited at 400 °C. Best film is the fully c-axis oriented AZO/STO deposited at 300 °C, with electrical conductivity 310 S/cm, Seebeck coefficient -65 uV/K and power factor 0.13 × 10-3Wm-1K-2at 300 K. Its performance increases with temperature. For instance, power factor is enhanced up to × 10-3Wm-1K-2at 600 K, surpassing the best AZO film previously reported in literature. © 2013 Materials Research Society.

DOI： 10.1557/opl.2013.989

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

© 2012 Materials Research Society. Changes in critical current properties depending on growth temperature (T<inf>s</inf>) were clarified for Ba-Nb-O-doped YBa<inf>2</inf>Cu<inf>3</inf>O<inf>y</inf> (Y123) films deposited by YAG- and excimer-PLD. Due to the introduction of Ba-Nb-O-nanorods, a vortex-Bose-glass-like behavior emerged as irreversibility lines and in-field critical current densities (J<inf>c</inf>s) were improved. Crossover magnetic fields (B<inf>cr</inf>) and in-field J<inf>c</inf>s increased with the increase in T<inf>s</inf> for the Y123 films with nanorods. These T<inf>s</inf>-dependent critical current properties were attributable to the changes in morphology of the nanorods with T<inf>s</inf> and were independent of laser source in PLD apparatuses. For the fabrication of RE123 coated conductors containing nanorods, optimization of T<inf>s</inf> with taking both materials of RE123 matrix and nanorod into account is necessary to achieve higher in-field J<inf>c</inf>.

DOI： 10.1557/opl.2012.1588

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

© 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. Growth of artificial pinning centers (APCs) in YBa2Cu3O7-δ(YBCO) films are discussed. The APCs used in this research are BaZrO3 and BaSnO3 nanorods which are reported by Mele et al. TEM images show these nanorods gradually bend accordingly with approaching to a surface of films. This feature showed a growth pattern like a firework. We explain the feature of the nanorods as follows; At an early growth stage, films grow in a layer by layer growth mode. The surface of the films is flat and very smooth. After the early growth stage, the film surface gradually becomes rough, indicating the film grows in a Stranski-Krastanov growth mode. This roughness was caused by a spiral growth of films with many steps. At the step of YBCO films, nanorod materials such as BaZrO3 are supplied from one direction. Then, the center of nanorods sifts to the same direction of the step flow. Then, the nanorods bend to the edge of the grains in the films. As a grain in spiral growth had a convex surface, nanorods bent to the direction perpendicular to the grain surface. Finally, nanorods in rough grains form firework structures.

DOI： 10.1016/j.phpro.2012.06.320

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

© 2012 Materials Research Society. Epitaxial Fe-Te-Se thin films were deposited by pulsed laser deposition at 250-600 °C on SrTiO<inf>3</inf> (100, STO), MgO (100), LaAlO<inf>3</inf> (100, LAO) and CaF<inf>2</inf> (100) single crystal substrates. Best superconducting film was grown on CaF<inf>2</inf>: T<inf>c</inf>^onset = 20.0 K and T<inf>c</inf>⁰ = 16.18 K with T<inf>dep</inf> = 300 °C, 45000 pulses, 3 Hz. The critical current density J<inf>c</inf> at 4.2 K was 0.41 × 10⁶A/cm² at 0 T and 0.23×10⁶ A/cm² at 9 T. Angular dependence of J<inf>c</inf> showed broad c-axis correlated peak when B ≥ 3 T.

DOI： 10.1557/opl.2012.1419

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Oxygen K-edge and Fe L2,3-edge electron energy-loss near-edge structures (ELNES) were measured for FeO6octahedra and FeO4tetrahedra in the brownmillerite Ca(Sr)FeO2.5by focusing an electron probe at individual Fe sites using scanning transmission electron microscopy combined with electron energy-loss spectroscopy. The observed site-resolved oxygen K-ELNES showed different features reflecting the local chemical bonding around the FeO6octahedra and FeO4tetrahedra. A pre-peak in the O K-edge spectra, which is attributed to a transition to an unoccupied O 2p band hybridized with the Fe-3d band, shows splitting in the spectrum of the FeO6octahedral site. Additionally, for the oxygen linking the octahedral and tetrahedral Fe sites in CaFeO2.5, charge transfer was found to preferentially occur toward the tetrahedral Fe ions. In the case of SrFeO2.5, charge transfer from the oxygen located in the ac plane was biased toward the tetrahedral Fe atoms. Based upon an analysis of the pre-peak intensity of the O K-ELNES, it was concluded that bonding between the oxygen and iron atoms at the tetrahedral site was more covalent in character than at the octahedral site. The strong covalent character of the tetrahedral sites would be one of the reasons for distortion in the FeO6octahedra in Ca(Sr)FeO2.5, as exhibited by an extension along the b-axis. © 2011 American Institute of Physics.

DOI： 10.1063/1.3610526

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

We investigated the effects of indium doping on the superconducting properties of YBCO sintered samples and thin films. In2O3-doped YBCO and YBa2Cu3 xInxOysintered samples showed a gradual decrease in the critical temperature (Tc) with increasing indium content; however, a Tcvalue above 80 K was maintained even up to 30 vol.% addition and x = 0.4, respectively. Ba3Cu3In4O12was detected by X-ray diffractometry and energy-dispersive X-ray spectroscopy as a reaction product for both sintered samples. The normalized Jcunder a magnetic field of 0.1 T showed a maximum at x = 0.3. Indium-doped YBCO films prepared by pulsed laser deposition showed a similar dependence of Tcon indium content as the sintered samples. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2010.05.073

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1002/9783527631049.ch1

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記述言語：英語   掲載種別：研究論文（学術雑誌）

We measured the critical current density Jcof optimally doped YBa2Cu3O7-δthin films obtained by dc sputtering on (100) oriented SrTiO3substrates and by pulsed laser deposition (PLD) on (100) oriented MgO substrates with SrTiO3buffers. Jc at various temperatures T was determined from the magnetization curves registered with a vibrating sample magnetometer for an external magnetic field H (oriented along the c axis) up to 90 kOe. It was found that Jcof the films obtained by PLD usually overcomes the Jcvalues of the sputtered films in the whole investigated (H, T) domain.

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記述言語：英語   掲載種別：研究論文（学術雑誌）

In order to improve a critical current density under applied magnetic fields, an addition of BaMO3(BMO; M=Zr, Sn) nanorods into REBa2Cu3Oy(REBCO) films is actively discussed. Although superconducting properties of the REBCO films are dramatically enhanced by self-assembled BMO nanorods, the growth mechanisms of the BMO nanorods have not been clarified yet. In this study, in order to clarify the growth mechanisms of the BZrO3(BZO) nanorods and to further improve the superconducting properties, we fabricated a BZO-doped Sm1+xBa2-xCu3Oy(Sm + BZO) film by using modified Vapor-Liquid- Solid (VLS) technique (VLS-Sm + BZO/i). From the surface morphologies, there are BZO particles grown at step in the spiral growth measured by Br-etched VLS films doped with BZO. In general the impurity-related phase was pinning of growth fronts on REBCO films on substrate. Thus, we can conclude the variation of the surface morphology in VLS films is explained, not by the difference the step energy, but impurity phase could be responsible for the pinning and bending of different growth fronts, resulting in the formation of screw dislocations. From the plan-view TEM images, VLS-SmBCO + BZO film is approximately 9 nm in diameter of BZO nanorods, whereas VLS-SmBCO + BZO/i film is 7-8 nm. To create the BZO nano island/dots on the seed layer introduced the increase of the density of BZO nanorods. From the cross-sectional TEM images, columns of BZO nanorods aligned along [001] or the c-axis of SmBCO are clearly seen in the VLS films. Columnar BZO structures growing from the substrate to the surface have been observed. Nano BZO particles grown on the seed layer remained after the VLS growth. Nano BZO rods separated by 5 nm SmBCO spacer layers are shown to exhibit self-organized growth along c-axis of SmBCO. © 2010 The Japan Institute of Metals.

DOI： 10.2320/jinstmet.74.416

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Effects of vicinal growth in ErBa2Cu307-δ(ErBCO) with one-dimensional nanorods are discussed from their microstructures. BaNb2O6doped ErBCO films were grown on vicinal substrates with tilted angles of 0°, 4° and 8° by a pulsed laser technique. Surface step structure appeared distinctly with increasing vicinal angles to 8° in images of scanning electron microscopy and atomic force microscopy. Then, Ba(Er0.5Nb0.5)O3nanorods continuously grew from the step on vicinal substrate to film surface steps in transmission electron microscopy images of the film. The alignment of one-dimensional nanorods relate closely to film growth morphology. © 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/234/1/012022

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

We fabricated Fe(Se1-xTex) thin films on LSAT(100), MgO(001), R-Al2O3substrates by ArF excimer pulsed laser deposition (ArF-PLD) and investigated pulse repetition rate dependence on film growth of Fe(Se1-xTex) thin films in ArF-PLD. Through x-ray diffraction measurements of Fe(Se1-xTex) thin films grown by ArF-PLD, 00l peaks of Fe(Se1-xTex) were confirmed in Fe(Se1-xTex) thin films grown by pulse repetition rate of 10 Hz but the 00l peaks were not confirmed in Fe(Se1-xTex) thin films grown at 5 Hz. Atomic force microscopy (AFM) revealed that 100 ∼ 250 nm sized grains were formed on surface of the thin films grown at 10 Hz. It was found that the thin films grown at 5 Hz were formed thinner than those grown at 10 Hz, in spite of the same pulses. Energy dispersive x-ray spectroscopy (EDX) analysis revealed that composition elements of the thin films grown at 5 Hz were re-evaporated from them more than those grown at 10Hz. In ρ-T measurements of the thin films grown at 10 Hz, it was confirmed that the thin films has TConset= 6.5 ∼ 10.5 K and TC0of the Fe(Se1-xTex) thin film on an MgO substrate is 3.9 K. © 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/234/1/012051

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Artificial superconductor/ normal conductor/ superconductor (SNS) junctions are fabricated using a-axis oriented films. The films are three axes orientation-controlled a-axis oriented YBa2Cu3O7-y/PrBa2Cu3O7-yalternately-layered thin films (Y123/Pr123 multilayer films). The multilayer films were grown by a pulsed laser deposition method using a sintered Y123 target with a Pr123 section. The dark contrast parallel to the substrate surface (bc-plane), which corresponds to the elemental distribution of Pr, are observed periodically in the transmission electron microscopic cross-sectional image. SNS junctions along a-axis were fabricated using the multilayer films by focused-ion-beam techniques. Nonlinear current-voltage curves with the critical current of ∼5×10-7A were obtained at 30 K for a fabricated junction with the area of ∼0.2×0.2 μm2. © 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/234/1/012044

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

The relaxation of the irreversible magnetization in optimally doped YBCO films with natural and artificial pinning centres was measured in zero-field cooling conditions using SQUID magnetometry. The external magnetic field H was oriented along the c axis. An appropriate method for the determination of the characteristic vortex pinning energy from the normalized vortex-creep activation energy is discussed. This is based on the existence of a crossover elastic (collective) vortex creep at low temperatures T - plastic vortex creep at high T, caused by the T dependent macroscopic currents induced in the sample during magnetization measurements. © 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/234/1/012026

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2011 Elsevier B.V. All rights reserved. The new routes toward preparation of nanostructured YBa2Cu3O7superconducting thin films and coated conductors, based mainly on pulsed laser and chemical solution deposition methodologies, are being reviewed in this chapter. Particular emphasis is given to clarify the relationship between the artificial nanostructure and the vortex-pinning enhancement. The success achieved in the different approaches indicates that a new frontier of superconducting applications has been opened based on the nanostructured superconductors with high critical currents at high temperatures and magnetic fields much higher than previously devised with any superconductor.

DOI： 10.1016/B978-0-12-374396-1.00112-4

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