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  2. 中村 龍哉

中村 龍哉

ナカムラ タツヤ  (Tatsuya Nakamura)

基本情報

所属
兵庫県立大学 大学院 工学研究科 電気系工学専攻 物性・デバイス部門 教授 (博士（理学）)
学位
博士(理学)(広島大学)
J-GLOBAL ID
200901055102483640
researchmap会員ID
1000357821

研究キーワード

 6

研究分野

 3

経歴

 5

学歴

 5

委員歴

 1

論文

 71
  • Hirotoshi Yamada, Tomoko Ito, Tatsuya Nakamura, Raman Bekarevich, Kazutaka Mitsuishi, Sanoop Palakkathodi Kammampata, Venkataraman Thangadurai
    Small 2023年4月28日  
  • Takeshi KAKIBE, Toshiki OHATA, Takumi SAITO, Reona HONDA, Satoshi MATSUDA, Tatsuya NAKAMURA, Hajime KISHI
    Electrochemistry 90(3) 037006-037006 2022年3月16日  査読有り
  • T. Konya, Y. Kobayashi, T. Nakamura
    Solid State Ionics 374 115820-115820 2021年12月4日  査読有り
  • Takahiro Saito, Kei Nishikawa, Tatsuya Nakamura, Shiro Seki
    The Journal of Physical Chemistry C 124(31) 16758-16762 2020年8月6日  
    The research and development of secondary batteries, such as the lithium-ion batteries, have been widely conducted. Most electrodes are of composite type and comprise an active material, a conductive additive, and a binder. To achieve a precise analysis of electrochemical properties for only an active material, electrochemical measurement of a single particle of an active material was carried out using an ultramicroelectrode in an Ar-filled glovebox under an inert atmosphere. Although detection of cyclic voltammetry and resistance values of LiCoO2 (LCO) secondary particles has been reported using a single-particle electrode, we succeeded in achieving the first detailed analysis of capacity and resistance components of a single active material particle by charge-discharge and alternating current impedance measurements using LCO primary particles to elucidate the battery reaction process. The capacity values of LCO single particles were detected in units of mA h g-1, whose values were close to the theoretical capacity values of LCO single particles based on their mass and size. The resistance components of an LCO single particle were detected by alternating current impedance spectroscopy, which cannot be measured in conventional electrode systems, such as applied sheet materials. A resistance model for the active material is proposed.
  • Takayuki Konya, Yuji Shiramata, Tatsuya Nakamura
    BUNSEKI KAGAKU 68(10) 793-800 2019年10月  
    An electrochemical cell with a specifically designed X-ray window was fabricated in order to evaluate the structural evolution of the cathode material under the operating condition. It enabled us to obtain strong signals from a positive electrode material without a significant loss of the battery function. With use of this system, the structure evolution during the charge-discharge process of a layered cathode material Li[Ni1/3Co1/3Mn1/3]O-2 and a high voltage spinel cathode LiMn1.5Ni0.5O4 was studied. It was found from the experimental results that the Li [Ni1/3Co1/3Mn1/3]O-2 cathode exhibited a single-phase reaction, where the lattice parameters continuously changed. In the case of LiMn1.5Ni0.5O4 cathode, the charge-discharge reaction proceeded in two continuous two-phase reactions. Especially for the latter, the phase evolution was reversible in the low- current density reaction. On the other hand, in the high current density charge-discharge reaction, asymmetric behavior was observed. This means that the kinetic limitation of the battery reaction is observable even in this laboratory X-ray diffraction system.
  • T. Konya, Y. Shiramata, T. Nakamura
    Powder Diffraction 34(S1) S8-S13 2019年9月1日  
    Structural variation of LiMn1.5Ni0.5O4 spinel cathode during the Li+ extraction/insertion reaction was studied using operando X-ray diffraction. It was found that the reaction in the voltage range from 3.5 to 4.9 V consisted of two consecutive two-phase reactions, where three spinel phases of LiMn1.5Ni0.5O4, Li0.5Mn1.5Ni0.5O4 and Mn1.5Ni0.5O4 were identified and the lattice volume change in the whole reaction was evaluated as 6%. The reactions were symmetric and reversible under low-current conditions, but some asymmetries were detected during high current operation. Furthermore, a two-phase reaction between cubic and tetragonal phases was observed in the low-voltage reaction at 2.1-3.5 V, where the lattice volume change was approximately 4.9%. The rate-determining step was discussed based on these operando results.
  • T. Nakamura, M. Tabuchi, T. Konya, Y. Shiramata, Y. Kobayashi
    Solid State Ionics 319 105-109 2018年6月  
    High-voltage cathode LiMn1.5Ni0.5O4 particles with average size of approximately 2 μm were prepared using a two-step process. Low-temperature magnetic measurements indicated them as ferrimagnetic materials with high Neel temperature (146.5 K) and high magnetization (107 emu/g at 4.5 K) that closely approximates the theoretical value of the stoichiometric LiMn1.5Ni0.5O4 compound. Because of their high-purity and high crystallinity, their redox signals were observed only around 4.7 V. Their low-rate capacity was sufficiently high (about 140 mAh/g at 0.1 C). Their capacity retention after the 100th cycle was higher than 95%. In spite of the low specific surface area of the LiMn1.5Ni0.5O4 particles, they exhibited high reversible capacity even at a high-current rate. Additionally, the in-situ X-ray diffraction was conducted to elucidate the reaction process, which indicated that the electrochemical reaction progresses reversibly with two consecutive two-phase reactions. The lattice parameters of three corresponding phases remained almost unchanged on the reactions (0.8165, 0.8087, and 0.8000 nm). The presence of the intermediate phase might give the relaxation of the structural variation during the electrochemical reaction.
  • Yo Kobayashi, Kumi Shono, Takeshi Kobayashi, Yasutaka Ohno, Masato Tabuchi, Yoshihiro Oka, Tatsuya Nakamura, Hajime Miyashiro
    Journal of Power Sources 341 257-263 2017年2月15日  査読有り
    © 2016 Elsevier B.V. Ether-based solid polymer electrolyte (SPE) is one of the most well-known lithium ion conductors. Unlike the other inorganic electrolytes, SPE exhibits advantages of flexibility and large-area production, enabling low cost production of large size batteries. However, because the ether group is oxidized at 4 V versus Li/Li+ cathode, and due to its high irreversibility with the carbon anode, ether-based SPE was believed to be inapplicable to 4 V class lithium-ion batteries with carbon anode. Here we report a remarkably stable SPE in combination with a 4 V class cathode and carbon anode achieved by the proper design at the interface. The introduced boron-based lithium salt prohibits further oxidation of SPE at the cathode interface. The surface modification of graphite by the annealing of polyvinyl chloride mostly prohibits the continuous consumption of lithium at the graphite anode. Using above interface design, we achieved 60% capacity retention after 5400 cycles. The proposed battery provides a possible approach for realizing flammable electrolyte-free lithium-ion batteries, which achieve innovative safety improvements of large format battery systems for stationary use.
  • Yoshihiro Oka, Keiichiro Ohnishi, Keiichi Asami, Mitsuhiro Suyama, Yoshimi Nishimura, Tomohiro Hashimoto, Katsuhiko Yonezawa, Tatsuya Nakamura, Mitsuyasu Yatsuzuka
    VACUUM 136 209-213 2017年2月  
    High-speed and homogeneous water-dispersion of carbon nano tubes (CNTs) with superior characteristics is a key technology for industrial applications. Liquid-phase plasma is one of good method to disperse CNTs in aqueous solution. However, the treatment speed of the liquid-phase plasma is not enough for industrial applications. In the present experiment, a novel high-speed dispersion device using cavitation bubble plasma (CBP) was developed. In this method the plasma was generated efficiently in bubbles in water. The cup-stacked CNTs were uniformly dispersed in ion-exchange water by the CBP treatment without dispersant. A liter of CNTs suspension with 9.2 wt% in concentration can be treated with the CBP processing of 135 min. (C) 2016 Elsevier Ltd. All rights reserved.
  • R. Hanafusa, K. Kotani, K. Ishidzu, Y. Oka, T. Nakamura
    Solid State Ionics 288 180-183 2016年5月  査読有り
    High-voltage cathode material, LiMn Ni O , was successfully prepared by two-step process: LiMn Ni O particles were obtained by the solid state reaction of oxalate precursors at high temperature such as 900 °C and then the LiMn Ni O particles with Li-acetate di-hydrate and Ni-acetate tetra-hydrate were annealed at low temperature. Both spinel phases are ferromagnetic compounds: LiMn Ni O has higher Neel temperature (127 K) and larger magnetization (97 emu/g at 4.2 K) than LiMn Ni O does (103 K and 79 emu/g). The obtained LiMn Ni O particles had low specific surface area, which may reduce the side reaction with the organic electrolyte, and exhibited electrochemical capacity only at high voltage 4.7 V region. In addition, high reversible capacity as well as good cycle performance was attained. 1.5 0.5 4 1.6 0.4 4 1.6 0.4 4 1.5 0.5 4 1.6 0.4 4 1.5 0.5 4
  • K. Ishidzu, Y. Oka, T. Nakamura
    Solid State Ionics 288 176-179 2016年5月  査読有り
    The structural change of Li[Ni Co Mn ]O cathode materials (x + y + z = 1) during the electrochemical delithiation/lithiation was studied with the in-situ X-ray diffraction. It was found that the cathode having the larger Ni fraction of Ni gave the larger unit cell volume change (ΔV) during the reaction. While the initial capacity increased with an increase in the Ni fraction, the capacity fading became much significant for the cathode with high Ni fraction. It was shown that the impedance originating from the cathode grew after the cycling and its degree increased with the Ni fraction. Additionally, micro-cracks were frequently observed for the cathode particles after the cycling evaluation, and the development feature of the micro-cracks was affected by the chemical composition of the cathode compounds. The capacity fading was discussed from the view-points of the lattice volume change, the impedance growth and the microstructure variation. x y z 2
  • Yoshihiro Oka, Tomoya Sasaki, Hideyoshi Matsumoto, Tatsuya Nakamura
    SOLID STATE IONICS 288 167-170 2016年5月  
    LiCo1/3Ni1/3Mn1/3O2 cathode electrodes were prepared using the doctor blade technique, where distilled water was used instead of ordinary NMP as the solvent. A serious problem is caused because the dispersion of hydrophobic carbon particles used as a conducting additive is difficult in water solvent. In this study, as a novel technique for the carbon particle dispersion, low-temperature liquid-phase plasma treatment was applied. The surface of carbon particle was converted from hydrophobic to hydrophilic via OH radical formation. The treatment enabled us to obtain stable colloidal dispersion of the carbon particles. The film electrode with smooth surface and no aggregates was easily attained. The electrode prepared using the water-based slurry has superior cycling performance and slightly-poorer rate capability compared to that of the electrodes prepared using the NMP-based slurry. (C) 2016 Elsevier B.V. All rights reserved.
  • Hikari Takahara, Ryoya Ishigami, Kenji Kodama, Atsushi Kojyo, Tatsuya Nakamura, Yoshihiro Oka
    JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 31(4) 940-947 2016年  
    Glow discharge-optical emission spectroscopy (GD-OES) was evaluated for hydrogen analysis in diamondlike carbon (DLC) films. DLC film samples were prepared using the plasma-based ion-implantation and deposition method (PBIID). Their hydrogen contents were determined using elastic recoil detection analysis (ERDA). The hydrogen intensity obtained by GD-OES increased gradually concomitantly with increasing hydrogen contents at the lower hydrogen content region. However, the intensity increased drastically at the higher hydrogen content region of more than about 30 at%. When the hydrogen contents increased, the correlation between GD-OES hydrogen intensity and ERDA hydrogen contents was deviated from the linear relation obtained for hydrogen-implanted silicon samples as reference materials. The sputtering rate of the DLC sample was found to vary at the high H content region. A linear relationship was obtained between the hydrogen contents and GD-OES intensities corrected with the sputtering rate of samples.
  • 山本真一郎, 中村龍哉, 畠山賢一, 廣瀬美佳, 葭内 暁
    電気学会論文誌A 135(1) 55-56 2015年  査読有り
  • Y. Oka, T. Obata, Y. Nishimura, T. Nakamura
    Journal of the Electrochemical Society 162(2) A3032-A3037 2015年  査読有り
    Diamond-like carbon film (DLC) is selected as a cathode-protective film because it has chemical inertness, mechanical hardness, and high electrical resistivity. For this study, a DLC protective film was deposited onto a cathode electrode rather than individual cathode particles. A hybrid process of plasma-based ion implantation and deposition was applied to a uniform deposition of the DLC protective film, even at low processing temperature on the cathode electrode having complex surface geometry and low melting point binder. The electrochemical performance of the DLC-coated LiNi Co Mn O cathode was studied using galvano-static charge- discharge cycling at high operating temperature, compared to those of the pristine LiNi Co Mn O cathode. The electrochemical stability of the DLC-coated electrode was discussed. The DLC film provides good protection against cathode/electrolyte interface degradation. 1/3 1/3 1/3 2 1/3 1/3 1/3 2
  • R. Hanafusa, Y. Oka, T. Nakamura
    Journal of the Electrochemical Society 162(2) A3045-A3051 2015年  査読有り
    Li-deficient olivine compounds, Li Co Fe PO (x < 0.15), were prepared by calcination of the sol-gel derived precursors in ambient atmosphere. They were almost single phase at x < 0.10 but some impurity phases were found at x > 0.10. The lattice parameters changed continuously with an increase in the Fe substitution. Their variation in the range of x < 0.10 roughly obeyed Vergard's law. From the 57Fe Mössbauer spectrum at room temperature, it was shown that the introduced Fe took a trivalent highspin state in the olivine lattice. The temperature-dependent magnetic susceptibility exhibited that the Fe incorporation enhanced the antiferromagnetic ordering: the Neel temperature shifted higher. Furthermore, the electrochemical performances, such as cycling stability and rate capability, were improved significantly with an appropriate substitution (about 10%) with Fe3+. Consequently, the Fe3+ incorporated compounds with Li deficiency as the charge compensation are thought to be good candidates as high-voltage cathode material, which may enhance the energy density of Li ion battery. 1-x 1-x x 4
  • Hikari Takahara, Atsushi Kojyo, Kenji Kodama, Tatsuya Nakamura, Kumi Shono, Yo Kobayashi, Masahiro Shikano, Hironori Kobayashi
    JOURNAL OF ANALYTICAL ATOMIC SPECTROMETRY 29(1) 95-104 2014年1月  
    Depth profiling and quantification using glow discharge optical emission spectroscopy (GD-OES) were applied to a graphite electrode in a lithium ion battery. To improve the measurement time and reliability beyond conventional argon discharge plasma, reactive sputtering with the respective addition of oxygen (0.50% v/v O-2 in Ar) and hydrogen (1.00% v/v H-2 in Ar) was investigated. Samples contained dispersed 0-5 wt% LiF or 0-0.5 wt% Li3PO4 in graphite electrodes. Adding oxygen to argon plasma increased the sputtering rate and the sensitivity in quantitative analysis of lithium drastically. That unexpected depth profile was obtained for graphite electrode samples possibly because chemical etching by oxygen was inhomogeneous. In contrast, adding hydrogen to argon plasma exhibited benefits both for depth profiling and for quantifying Li for graphite electrode samples with a shorter measurement time and higher sensitivity than that, of conventional pure argon discharge. Molecular spectra showed strong C-H and C-C bands, suggesting that formation of volatile material fragments of CH and CC increased with hydrogen addition during measurements. Surface analysis results with SEM and XPS showed that redeposition of sputtered materials and Ar+ ion implantation that occurred in pure argon plasma were also suppressed.
  • Hikari Takahara, Yo Kobayashi, Kumi Shono, Hironori Kobayashi, Masahiro Shikano, Tatsuya Nakamura
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 161(10) A1716-A1722 2014年  査読有り
    Solid electrolyte interphase (SEI) and Mn deposition formed on capacity-degraded graphite electrodes in commercially available Mn-based/Graphite lithium ion batteries were characterized using glow discharge-optical emission spectroscopy (GD-OES). The depth profile of the whole electrode showed a homogeneous distribution of Li and Mn except for the surface region at the initial state. With the progress of degradation, Li and Mn concentrations increased inhomogeneously in the depth-direction of the electrode; the Li and Mn concentrations were high in the outer layer and decreased with depth to the current collector in the degraded electrodes. The SEI layer deposited on the electrode surface was separately analyzed in detail. The GD-OES surface profile was explained by comparing to the XPS analysis results. The amount of Li deposited on the electrode surface was almost constant with the capacity degradation, though the Li concentration in the whole electrode increased along with the capacity degradation. In contrast, the amount of Mn deposition increased with the capacity degradation both in the surface deposition layer and in the whole electrode. (C) 2014 The Electrochemical Society. All rights reserved.
  • 友延 千裕, 岡 好浩, 中村 龍哉
    粉体および粉末冶金 61(8) 392-396 2014年  
    The composite cathodes were prepared using carbon wool as a current collector, where carbon-coated LiFePO4 fine particles and acetylene black particles were applied as active material and conducting additive, respectively. The composite electrodes were thick film with sufficiently high active material loading. From the electrochemical redox test, they had almost the same energy density at low current density as the ordinary electrode on Al current collector. Simultaneously, the composite electrodes exhibited larger current density as compared with that of the ordinary electrode. According to the results, it is possible to fabricate the composite electrodes suitable to the battery application combining high-energy and high-power performance.
  • 友延 千裕, 岡 好浩, 中村 龍哉
    粉体および粉末冶金 61(4) 158-162 2014年  
    LiFePO4 particles were prepared by the solid state reaction, and coated with conducting carbon layer through the hydrocarbon gas decomposition technique. The uniformity of the carbon layer was examined using the small angle X-ray diffraction with the core shell model. The half cell using these composite particles as cathode exhibited a peculiarity, that is, the capacity increment during the initial cycling process. In this study, the initial cycling process was studied with the AC impedance method. As a result, it was found that the interfacial impedance becomes small on the cycling sequence. It implies that the cathode/electrolyte interface is built on the initial cycling.
  • 中村 龍哉
    244 532-537 2013年12月  査読有り
  • Tatsuya Nakamura, Shingo Okano, Noriko Yaguma, Yukari Morinaga, Hikari Takahara, Yoshihiro Yamada
    JOURNAL OF POWER SOURCES 244 532-537 2013年12月  
    LiCo1/3Ni1/3Mn1/3O2 cathode electrodes were prepared onto Al current collectors with different surface morphologies through usual doctor blade technique. Their electrochemical performances, especially at high current rate, were influenced by the surface morphology of the current collector:. These implied the less polarization for the electrode prepared on the surface roughened current collector. In addition, the AC complex impedance analysis exhibited that the interface resistance between the film electrode and the current collector as well as the interface resistance between the electrode and the electrolyte was reduced in the case of the surface-roughened current collector, but that the Ohmic resistance was enlarged. (C) 2013 Elsevier B.V. All rights reserved.
  • 小原 学, 高橋 潤, 中村 龍哉, 山田 義博
    電気学会論文誌. A, 基礎・材料・共通部門誌 = The transactions of the Institute of Electrical Engineers of Japan. A, A publication of Fundamentals and Materials Society 133(9) 484-488 2013年9月1日  
    Fe3O4 spinel ferrite nano-particles, promising electrode materials for redox capacitors, were prepared with chemical coprecipitation technique. In this research, the effects of electrical reduction on electrochemical properties of Fe3O4 spinel ferrite electrodes were studied. The results show that the pseudo-capacity of Fe3O4 electrodes was increased after the electrochemical reduction at -0.7V vs. Ag/AgCl reference electrode. Moreover, it was found that crystal structure of Fe3O4 electrodes remained almost unchanged even after the electrochemical reduction.
  • 中村 龍哉
    121(1412) S1-S5 2013年4月  査読有り
  • 中村 龍哉
    160(2) A272-A278 2013年  査読有り
  • Hikari Takahara, Hironari Miyauchi, Mitsuharu Tabuchi, Tatsuya Nakamura
    JOURNAL OF THE ELECTROCHEMICAL SOCIETY 160(2) A272-A278 2013年  
    LiFePO4/graphite cells with an aging state and several capacity fading levels were studied using glow discharge - optical emission spectroscopy (GD-OES). Depth profiles were obtained from the surface to the collector in positive and negative electrodes. Results show that Li is distributed homogeneously in terms of depth in LiFePO4 and graphite electrodes for cells with 85-100% capacity retention. For a cell that deteriorated to 44% capacity retention after only 50 cycles, the Li amount was apparently slightly lower toward the current collector in the positive electrode. Deposits formed on the graphite electrode surface (SEI) comprise Li, H, C, F, O, and P, with a large amount of Li for the cell with sudden deterioration. The deposition amount increases with progression of capacity fading, suggesting that deposits on the negative electrode are related to cell deterioration. The deposition surface shows Fe, implying that Fe dissolved and migrated from the positive electrode during charge-discharge cycles at 45 degrees C. The Li intensities obtained from GD-OES spectra of all cells were correlated with Li contents obtained using induced coupled plasma - optical emission spectroscopy (ICP-OES) and atomic absorption spectroscopy (AAS), which enable us to ascertain the Li contents of the electrodes quantitatively. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.061302jes] All rights reserved.
  • Takeyuki Kikuchi, Shinji Yoshida, Tatsuya Nakamura, Tohru Yamasaki, Makoto Nakanishi, Tatsuo Fujii, Jun Takada, Yasunori Ikeda
    ELECTROCERAMICS IN JAPAN XV 566 227-230 2013年  
    Synthesis of U-type hexaferrite was investigated in the various strontium-based systems (Sr-Me-Fe-O system, Me = Co, Zn, Cu, and Ni). Precursors of ferrites were prepared by polymerizable complex method. Sr4Me2Fe36O60 (Me = Co and Zn) U-type hexaferrites were synthesized at the temperature range between 1423 and 1483 K in air. Coercivity of obtained ferrite was decreased with increasing heat treatment temperatures. Cu substitution reduced formation temperature of U-type hexaferrite.
  • Takuya Tainaka, Takeyuki Kikuchi, Tatsuya Nakamura, Tohru Yamasaki, Makoto Nakanishi, Tatsuo Fujii, Jun Takada, Yasunori Ikeda
    ELECTROCERAMICS IN JAPAN XV 566 231-234 2013年  
    Synthesis of Sr3Zn2Fe24O41 Z-type ferrite was investigated. Precursors of ferrite were prepared by polymerizable complex method. Identification of formed phases in the obtained samples and determination of lattice parameters of Z-type ferrite were performed by powder X-ray diffraction (XRD). Single-phase of Sr3Zn2Fe24O41 Z-type ferrite was synthesized by heating at 1463 K for 5hours in air. M-H curve of prepared single-phase Sr3Zn2Fe24O41 Z-type ferrite was measured by using vibrating sample magnetometer (VSM). It was revealed that Sr3Zn2Fe24O41 Z-type ferrite has larger saturation magnetization (23.5 mu(B)/formula unit) than that of Sr3Co2Fe24O41 (22.7 mu B/formula unit) and shows characteristic two-step saturation of magnetization as well as Sr3Co2Fe24O41 Z-type ferrite.
  • 小原 学, 倉橋 峻, 清田 昌宏, 中村 龍哉, 山田 義博
    粉体および粉末冶金 59(3) 149-155 2012年3月15日  
    The MnxFe3-xO4 powders were prepared by a coprecipitation method or a solid state reaction. The effect of specific surface area on electrochemical properties and the relationship between the electrochemical properties and manganese substitution values were examined by BET method and chrono-potentiometry. The results indicate that capacitance per unit weight of MnFe2O4 is proportional to specific surface area. Furthermore, capacitance per specific surface of MnxFe3-xO4 is constant to about 65 μF/cm2 despite the increase of the manganese substitution values (x≥1.0).
  • 中村 龍哉
    196(16) 6969-6973 2011年8月  査読有り
  • Takeyuki Kikuchi, Tatsuya Nakamura, Tohru Yamasaki, Makoto Nakanishi, Tatsuo Fujii, Jun Takada, Yasunori Ikeda
    MATERIALS RESEARCH BULLETIN 46(7) 1085-1087 2011年7月  
    Synthesis of single-phase Sr3Co2Fe24O41 Z-type (Sr(3)CO(2)Z) ferrite was realized by adopting the polymerizable complex method. Crystal structure of samples has been investigated by powder X-ray diffraction (XRD). Single-phase Sr(3)Co(2)Z ferrite was obtained by heating at 1473 K for 5 h in air. Magnetic properties were discussed by measurements of M-H curves with vibrating sample magnetometer (VSM). Sr(3)CO(2)Z ferrite prepared by polymerizable complex method showed typical M-H curve of soft ferrite, with a saturation magnetization of 21.5 mu(B)/formula unit (50.5 emu/g) and a coercive force of 0.0141 at room temperature. (C) 2011 Elsevier Ltd. All rights reserved.
  • 山本真一郎, 中村龍哉, 畠山賢一, 廣瀬美佳, 葭内 暁
    J. Jpn. Soc. Powder Powder Metallurgy 58(3) 181-185 2011年3月  査読有り
  • 中村 龍哉
    18 122003-1-122003-4 2011年  査読有り
  • 中村 龍哉
    18 122006-1-122006-4 2011年  査読有り
  • 中村 龍哉
    電子情報通信学会技術研究報告. EMCJ, 環境電磁工学 EMCJ2011-2(18) 7-12 2011年  査読有り
    筆者らはこれまで,日本古来の伝統的な瓦製造法の一つである燻し技術を用いて,瓦粘土から成るピラミッド成形体表面に導電性のカーボン膜を形成させ,ピラミッド形電波吸収体を試作してきた.また,導電性カーボン膜の抵抗値を制御することにより,電波吸収特性を改善できることについて報告した.本研究では,マイクロ波帯に加え,ミリ波帯用の燻し瓦ピラミッド電波吸収体を作製し,その電波吸収特性について検討した.さらに,FDTD法による数値解析により,電波吸収特性を計算した.
  • 中村 龍哉
    57(11) 725-728 2010年11月  査読有り
  • Yuya Shima, Tatsuya Nakamura, Hiroki Matsui, Yoshihiro Yamada, Hironari Miyauchi, Satoshi Hashimoto, Kazuo Abe
    Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy 57(11) 729-733 2010年11月  査読有り
    LiFePO4/C composite particles were prepared by gas-solid phase reaction. The reaction temperature had a detrimental effect on the purity of the composite particles. The suitable temperature was around 650 °C, above and below which ferromagnetic impurities were found. The retention time influenced only the carbon deposition amount, but the excess amount of carbon caused the degradation of the electrochemical performance. The specimen prepared at the optimum conditions exhibited superior performances in both rate capability and cycle stability as well as less impedance growth during the cycling.
  • 中村 龍哉
    195(19) 6879-6883 2010年10月  査読有り
  • Takeyuki Kikuchi, Tatsuya Nakamura, Tohru Yamasaki, Makoto Nakanishi, Tatsuo Fujii, Jun Takada, Yasunori Ikeda
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322(16) 2381-2385 2010年8月  
    Magnetic properties of La-Co substituted M-type strontium hexaferrites were studied. The samples were prepared by polymerizable complex method. Crystal structure of samples has been investigated by powder X-ray diffraction (XRD). Single-phase M-type strontium hexaferrites with chemical composition of Sr(1.05-x)La(x)Fe(12-x)Co(x)O(19) (x = 0-0.4) were formed by heating at 1173 K for 24 h in air. Magnetic properties were discussed by measurements of M-H curves with vibrating sample magnetometer (VSM). La-Co substituted M-type strontium hexaferrites prepared by polymerizable complex method showed typical magnetic hysteresis of hard ferrite. The coercive force increased significantly by La-Co substitution with polymerizable complex method. Maximum coercive force achieved in this study is 8.0 kOe (640 kA/m). Scanning electron microscopy revealed that the prepared ferrite particles have plate-like shape of diameter range between 20 and 500 nm. (C) 2010 Elsevier B.V. All rights reserved.
  • 中村 龍哉
    322(13) 1816-1821 2010年7月  査読有り
  • 中村 龍哉
    157(4) A544-A549 2010年  査読有り
  • 中村 龍哉
    157(4) A544-A549 2010年  査読有り
  • Yuki Horie, Shun-ichi Kawashima, Yoshihiro Yamada, Gaku Obara, Tatsuya Nakamura
    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 2010年  
    The C14 Laves phase TaFe(2) is a paramagnet. The magnetic properties and phase diagrams of V, Cr, Mn, Co and Ni substituted systems for Fe in TaFe(2) have been investigated using magnetization and NMR measurements. Antiferro- or/and ferromagnetic states appeared by the V, Cr and Mn substitutions. In the Cr and Mn cases ferromagnetic states appeared first (very weak in Cr case) and then the both change to be antiferromagnetic. In the V case only antiferromagnetic state appeared from the beginning of substitution. The susceptibilities of the slightly V-substituted compounds were, however, exchange-enhanced at low temperatures. The above mentioned magnetic changes are qualitatively the same to the previously reported Nb(Fe(1-x)T(x))(2) systems. The electronic condition of the appearance of ferro- and antiferromagnetism can systematically be interpreted in both systems.
  • 中村 龍哉
    56(7) 461-464 2009年7月  査読有り
  • Hiroyuki Demidzu, Tatsuya Nakamura, Yoshihiro Yamada
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 42(12) 2009年6月  査読有り
    LiMn2-XCuXO4 (X &lt; 0.5) compounds were synthesized by the citrate gel method. It was found that the specimens with X &lt; 0.3 had a cubic symmetry of Fd3m, while further substitution (X &gt; 0.4) lowered the symmetry from Fd3m to P4(3)32. The Cu2+-substitution led to the enhancement of low-temperature magnetic susceptibility M/H. Simultaneously, the Weiss constant changed its sign from negative to positive. This implied that the dominant exchange interaction varies from antiferromagnetic to ferromagnetic couplings. For the compounds with X = 0.5, the magnetic moment per chemical formula at 4.2K was 3.99 mu B and Curie temperature was approximately 39 K. The value of the magnetic moment was close to the theoretical value, in which a ferrimagnetic collinear spin structure was attained: the spins of the Cu2+ ion were antiferromagnetically coupled with those of the Mn4+ ion. Additionally, the magnetic properties of Li-Mn-Cu spinel oxides were briefly discussed, comparing them with those of Li-Mn-M (M = Ni, Mg) spinel oxides.
  • 中村 龍哉
    Journal of the Magnetics Society of Japan 33(6) 441-446 2009年  査読有り
    Li1+x(Ni1/2Mn1/2)1-xO2 was prepared by co-precipitation and calcination technique. The compounds had a layered rock-salt structure with R<font style="text-decoration: overline;">3</font>m symmetry, and the degree of non-stoichiometry x was an important factor for the structural and magnetic properties. The degree of cationic ordering was improved with an increase in x and simultaneously, the ferrimagnetic characters were reduced. That is, the magnetic interaction network is converted from three-dimensional to two-dimensional ones, and is restricted within each c-plane. Hence, the long range magnetic correlation as well as the local magnetic interaction is weakened. The spontaneous magnetization was evaluated using a ferrimagnetic cluster model. As the degree of non-stoichiometry was increased, the cluster density was reduced, and it resulted in the lowering in the spontaneous magnetization at low temperature.
  • 中村 龍哉
    69(10) 2349-2355 2008年10月  査読有り
  • 中村 龍哉
    電磁環境工学情報EMC 243 47-55 2008年  査読有り
  • 中村 龍哉
    EMCJ2008-81 39-44 2008年  査読有り
  • 中村 龍哉
    Journal of the Magnetics Society of Japan 32(5) 504-508 2008年  査読有り
    The structure and magnetic properties of LiMn2-XMgXO4 (X < 0.5) compounds prepared by the sol-gel technique were studied by means of powder X-ray diffraction and magnetic measurement. Specimens with X < 0.2 had a cubic symmetry of Fd3m, while those with X > 0.3 exhibited extra reflections attributable to the P4332 space group, where Mg2+ and Mn4+ have 1:3 cation ordering on a 16d octahedral sublattice. Mg2+-substitution led to the enhancement of low-temperature magnetic susceptibility, indicating magnetic phase conversion from antiferromagnetic to ferromagnetic characters. This was attributed to variation of the average Mn valence state. The Mn valence state was sensitive not only to the substitution but also the preparation conditions. Ideally, ferromagnetic ordering was expected in specimens of the compound with X = 0.5. However, both the magnetization and the Curie temperature depended on the preparation temperature (Tprep): they took maximum values (Ms = 4.68μB, Tc = 23K) at Tprep = 700°C, where the chemical composition of the specimen was the closest to the stoichiometric composition. The magnetic properties of Li-Mn-Mg spinel oxides were briefly discussed in comparison with those of Li-Mn-Ni spinel oxides.

MISC

 39
  • 高原晃里, 石神龍哉, 児玉憲治, 古城篤志, 安田啓介, 中村龍哉, 岡好浩
    応用物理学会春季学術講演会講演予稿集(CD-ROM) 61st ROMBUNNO.17A-D6-4 2014年3月3日  
  • 中島 大輔, 中村 龍哉, 山田 義博
    兵庫県立大学大学院工学研究科研究報告 57 22-27 2005年2月28日  
    Lithium-nickel layered oxides were prepared by the solid-state reaction at temperature range of 700-850℃ in O_2 atmosphere. The structural refinement with the help of Rietveld analysis showed that the crystal structure of these compounds were identified as α-NaFeO_2 type layered rock-salt, where some extra Ni ions were present in Li-layers. As the Ni content in the Li-layer increased, the lattice parameter a increased and the ratio of C/a decreased. From the magnetic susceptibility measurement, it was found that both the asymptotic Curie temperature and the spontaneous magnetization at low temperature are sensitive to the presence of extra Ni ions in Li-layers. The asymptotic Curie temperature, which was always positive, shifted toward higher temperature with an increase in the non-stoichiometry degree. It was seen that the spontaneous magnetization 4.2K is also enhanced with the non-stoichiometry. Considering these magnetic variation with the non-stoichiometry enabled us to propose the following model; Ni-Ni magnetic coupling within the transition metal layer was weak and ferromagnetic, whereas the inter-layer Ni-Ni coupling is relatively strong and antiferromagnetic. The increase in the asymptotic Curie temperature may be attributed to the development of magnetic correlation from two to three dimension, and the enhancement of the spontaneous magnetization is described by ferromagnetic cluster formation.
  • Transaction of the Material Research Society of Japan 29 1683-1686 2004年  
  • Transaction of the Material Research Society of Japan 29 1663-1666 2004年  
  • 日本応用磁気学会誌 28 757-765 2004年  
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