Research Projects -
-
Successive charge order pahse transition in electronic ferroelectrics
Grant number：22H01942 2022.04 - 2025.03
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
池田 直, 藤井 達生, 沖本 洋一, 藤原 孝将
Grant amount：\17420000 （ Direct expense: \13400000 、 Indirect expense：\4020000 ）
-
Stabilization of Battery Cathode Ligand Charge Transfer Based on Non-Equilibrium Electronic Structure Analysis
Grant number：18H03929 2018.04 - 2022.03
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
Uchimoto Yoshiharu
Grant amount：\43030000 （ Direct expense: \33100000 、 Indirect expense：\9930000 ）
We focused on the charge compensation of anions, not transition metal cations, for lithium-rich oxide cathode materials in which charge compensation of oxide ions occurs during insertion and deinsertion of lithium ions. We established a guideline for the design of materials by controlling anions. We found that oxide ions can contribute reversibly to charge compensation when either the covalent or ionic bonding between transition metal cations and oxide ions is extremely strong. Based on these results, in the field of lithium-rich materials, which have been researched and developed mainly with oxides in the past, high capacity was achieved by replacing some of the oxide ions with nitride ions.
-
Fabrication of room-temperature multiferroic materials by rare-earth iron oxide system with triangular lattices
Grant number：18H02057 2018.04 - 2022.03
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
FUJII Tatsuo
Grant amount：\17550000 （ Direct expense: \13500000 、 Indirect expense：\4050000 ）
RFe2O4 is expected as a next-generation multiferroic material. We attempted to synthesize its single-crystalline film by the sputtering method. As a result, the in-plane orientation of the RFe2O4 layer on the sapphire substrate rotates 30 ° depending on the presence of the Fe3O4 buffer layer. When Fe3O4 and RFe2O4 are laminated to form a multilayer film, the in-plane orientation also depends on their stacking order. In addition, when using the YSZ single crystal substrate, we succeeded in obtaining an RFe2O4 thin film that does not have twin domains and is almost completely composed of single domains.
-
Induced magnetization on non-magnetic nanoparticles by surface structural relaxations
Grant number：26630319 2014.04 - 2017.03
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
FUJII Tatsuo, TAKEMURA Daiki, ANDOU Daiki
Grant amount：\3900000 （ Direct expense: \3000000 、 Indirect expense：\900000 ）
In recent years, applications of magnetic nanoparticles in various fields are expected. We found that LaFeO3 nanoparticles having almost no magnetization in bulk form showed large magnetization at low temperatures. Therefore, it should be worth to clarify the mechanism of the induced magnetization systematically to evaluate the relationship between the crystal structure and magnetic properties of LaFeO3 nanoparticles. As a first step, we tried to prepare LaFeO3 nanoparticles with a uniform particle size distribution by using salt-assisted spray pyrolysis. The salt-assisted spray pyrolysis has been expected to synthesize complex oxide nanoparticles with single nanometric sizes.
-
Formation of biogenic iron oxides in acid solutions, development of functions and mine-drainage treatment
Grant number：26289261 2014.04 - 2017.03
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
Takada Jun
Grant amount：\16250000 （ Direct expense: \12500000 、 Indirect expense：\3750000 ）
Treatment of acid mine drainage with acidophilic iron oxidizing bacterium and production of biogenic iron oxide minerals were investigated. The futures of iron oxides, Schwertmannite and goethite, formed under various pH and temperature conditions with an acidophilic iron oxidizing bacterium “E10” were studied. The oxides were found to exhibit high adsorption of heavy metals, As(Ⅴ), Se(Ⅵ), and Mo(Ⅵ)
-
Development of functional iron titanium complex oxide films by control of mixed-valence state
Grant number：23350092 2011.04 - 2015.03
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
FUJII Tatsuo, NAKANISHI Makoto, ICHIKAWA Kazunori, TAKADA Jun
Grant amount：\20150000 （ Direct expense: \15500000 、 Indirect expense：\4650000 ）
In this study, we synthesized a single-phase of various mixed valence oxides including a hematite - ilmenite solid solution system, and surveyed their magnetic and electronic properties. Epitaxial thin films of their oxides were fabricated successfully in order to reveal and control the effects of crystal orientation and a lattice distortion on their structural and charge transfer properties. The morphology, microstructure and electric transport properties of hematite - ilmenite solid solution films were strongly influenced by the crystalline orientation. Not only the structural anisotropy of crystalline solids but also the lattice mismatch between the substrates and films played the important roles in their properties.
-
Study on nanometric amorphous iron oxide of bacterial origin as Li-ion battery cathode
Grant number：23360309 2011.04 - 2014.03
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
TAKADA Jun, FUJII Tatsuo, NAKANISHI Makoto, KUSANO Yoshihiro, KANNO Ryouji
Grant amount：\18980000 （ Direct expense: \14600000 、 Indirect expense：\4380000 ）
We studied the discharge-charge properties of Li+ ions of nanometric amorphous iron oxide of bacterial origin for use as Li-ion battery cathode. This material was found to have the unique nanostructure. The iron oxide showed excellent cycle characteristics in a voltage range of 1.5-4.0 V at high current rate. X-ray absorption fine structure measurement revealed that the Fe3+ Fe2+ reaction is predominant in these discharge-charge processes.
-
Characterization of biogenous iron oxide and its Li-ion charge/discharge behavior
Grant number：19360300 2007 - 2008
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
TAKADA Jun
Grant amount：\20670000 （ Direct expense: \15900000 、 Indirect expense：\4770000 ）
バクテリア(鉄細菌)が作るチューブ状酸化鉄の特徴を詳細に検討した結果、非常にユニークな酸化鉄材料であることを明らかにした。即ち、直径が約1μmの中空チューブ状の形状で、非晶質構造を有し、3nmの1次粒子から成り、化学組成も特徴ある。さらに、この微生物由来バイオ酸化鉄はLiイオンについて優れた充放電特性を示すことを見出した。
-
Development of hexagonal ferrite materials for electronic devices used at high frequency of GHz range on the basis of research on phase diagrams
Grant number：17360326 2005 - 2006
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
TAKADA Jun, FUJII Tatsuo, WADA Osami, NAKANISHI Makoto, KUSANO Yoshihiro
Grant amount：\15400000 （ Direct expense: \15400000 ）
Some of the intrinsic properties of ferroxplaner-type ferrites are still unknown. In this study, preparation conditions, compositional range and electromagnetic properties of ferroxplanar-type ferrite were investigated and the relationships between them were clarified. And the development of novel magnetic thin films and wide-band electromagnetic wave absorbing sintered composites used in GHz range was aimed on the basis of that invesitgations.
First, we have investigated preparation conditons for monophasic ferroxplaner-type ferrites and the phase diagrams of this system at 1000 and 1200 ℃ were constructed on the basis of the results. In this procedure, we have investigated the formation mechanisms of Y-type and Z-type ferrites by X-ray diffraction measurements and proposed the models of them. And we have clarified the relationships between the structures, electromagnetic properties like permeability and conpositions.
Then we have investigated the preparation conditions of highly orientated magnetic thin films of ferroxplaner-type ferrites by polymerized complex method, the effects of trace elements and formation mechanisms. We have also tried to prepare wide-band electromagnetic wave absorbing materials at GHz range by hybridizing with magnetic loss and dielectric loss materials, i.e. Y-type ferrite and silicon carbide. By optimizing the preparation conditions we succeeded to prepare the absorbing materials, which showed enough reflection, less than-20dB, at the frequency range from 3.5 to 6.5 GHz. The relationship between reflection loss and band-width were thought to be trade-off, but these materials satisfy the required performace in both abilities. -
微生物が常温で作るナノサイズ酸化鉄のキャラクタリゼーションとその応用の試み
Grant number：17651071 2005 - 2006
日本学術振興会 科学研究費助成事業 萌芽研究
高田 潤, 藤井 達生, 中西 真
Grant amount：\3400000 （ Direct expense: \3400000 ）
近年鉄細菌を用いた「バイオ浄水法」は、地下水の浄水法として実際に採用され、環境に優しい浄水法と注目されていて、今後急速に全国に広がると予想されている。このバイオ浄水法では、レプトシリックス鉄細菌が地下水中のFeイオンを体内に取込んで、細菌の体の周りにパイプ状酸化鉄鞘などの無機化合物を常温で生成し、濾過槽上部に褐色沈殿物を形成する。しかし、現在この酸化鉄鞘の詳細が全く不明かつ分離・回収が困難であるため、沈殿物を埋立廃棄しているのが現状であり、バイオ浄水法の利点が十分に活かされていない。
そこで本研究では、先ず、鉄細菌が常温で作るパイプ状鉄細菌鞘酸化鉄やそれを構成する微細な酸化鉄微粒子を詳細に検討し、酸化鉄の種類、化学組成、微細構造を調査した。次に、浄水沈殿物からの分離・回収方法と鞘の増殖条件を検討した。更にパイプ状鉄細菌鞘酸化鉄の特性と再利用を検討した。その結果、欧文誌への論文1件と特許出願1件の成果を得た。
得られた結果を要約すると以下の通りである。
(1)パイプ状酸化鉄鞘は中空円柱状のマイクロチューブの形態を呈し、その内径と外径の平均値はそれぞれ1.1および1.4μm、長さは50〜200μmであることが明らかとなった。鞘の壁の厚さは平均0.15μmと非常に薄い。
(2)このパイプ状酸化鉄の結晶構造は、21-ferrihydriteの構造に似ているが、より結晶性が低いことが判明した。
(3)パイプ状酸化鉄鞘の壁は100nm以下の超微粒子から構成されており、それぞれの微粒子の組はほぼFe:Si:P=80:15:5であることを見出した。
(4)このパイプ状酸化鉄はspin-glass的な磁気特性を示すことが明らかになった。
(5)バイオ浄水沈殿物からの分離・回収方法を確立し、高純度サンプルを得ることに成功した。
(6)このパイプ状酸化鉄鞘を加熱することによって、ヘマタイトへの変化と赤色顔料としての利用の可能性を見出した。 -
Development of new recyclable materials based on iron oxides for nano-devices
Grant number：14350353 2002 - 2004
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
FUJII Tatsuo, TAKADA Jun, NAKANISHI Makoto
Grant amount：\14900000 （ Direct expense: \14900000 ）
To develop new spintronics materials with environment friendly, we prepared well-crystallized epitaxial Fe_<1.2>Ti_<0.8>O_3 films which had the largest magnetization within the hematite (α-Fe_2O_3)-ilmenite (FeTiO_3) solid solution system. The films were prepared by reactive sputtering technique with an FeTi alloy target. The precise control of substrate temperature and oxygen pressure during sputtering was necessary to obtain ferromagnetic films with R^^- symmetry, in which Fe-rich and Ti-rich layers alternately stacked along the c-axis.
By the way it is well known that the exchange coupling between two magnetic layers influence the magnetic properties of adjacent layers. We prepared Fe_<1.2>Ti_<0.8>O_3/Fe_2O_3 bilayered films and measured the magnetic Curie temperature (T_c) of them. In spite of the higher substrate temperature of 550℃, the films had a sharp interface between layers. The T_c of bilayered films was about 220 K, which was a little higher than that (210 K) of Fe_<1.2>Ti_<0.8>O_3 single layered films. The strong magnetic coupling to the antiferromagnetic α-Fe_2O_3 layer, which had the high Neel temperature of 960 K, could increase the T_c of the Fe_<1.2>Ti_<0.8>O_3 layer.
The electronic structures of α-Fe_2O_3-FeTiO_3 are generally considered as the mixed valence states between Fe^<2+> and Fe^<3+> due to the substitution of Fe^<3+> for Ti^<4+>. The nominal valence states of Ti are fixed to 4+. However high-resolution X-ray fluorescence spectra of various titanium oxides suggested that the Ti Kα and Kβ peak profiles of FeTiO_3 were slightly different form those of other Ti^<4+> compounds and were better to assign to have some Ti^<3+> characters. Moreover the valence band spectra of FeTiO_3 by X-ray photoelectron spectroscopy had a small density just below the Fermi edge, probably assigned to the localized Ti 3d electron. -
Studies on the magnetic anisotropy in single-layer films and magnetic interaction in bilayer films :
Grant number：13650761 2001 - 2002
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
KOHMOTO Osamu, FUJII Tasuo
Grant amount：\2400000 （ Direct expense: \2400000 ）
1. Theoretical investigation of ferromagnetic resonance (FMR) has been done. To analyze the magnetic anisotropy, exact solution proposed by Smit and beljers and approximate solution by Kittel is known. However, equation of effective demagnetizing factors (N_x^e, N_y^e) by Kittel is not correct. We derived a new equation of N_x^e and H_y^e and we obtained resonance equation for thin films. By this derivation method, the resonance equations of thin films having a uniaxial or a fourfold anisotropy are obtained when a static field is rotated in the film plane, six arrangements are calculated : (1) perpendicular anisotropy, (2) in-plane anisotropy, (3) cubic-crystal (001) face, (4) cubic-crystal (011) face, (5) cubic-crystal (111) face, and (6) oblique anisotropy films.
2. Magnetic anisotropy of Co and Ni films and magnetoresistance of bilayer films of Ni/NiO and NiFe/NiO has been experimentally studied. (1) In single layer Ni films, a large perpendicular anisotropy field was observed by FMR.
(2) In Co films, Perpendicular anisotropy field increases with decreasing the thickness.
(3) In bilayer Ni/NiO and NiFe/NiO films, magetoresistance was studied. -
インテグレーション超高周波デバイス用新規プラナ型フェライト薄膜の開発
Grant number：13025231 2001
日本学術振興会 科学研究費助成事業 特定領域研究(A)
藤井 達生, 中西 真, 高田 潤
Grant amount：\2100000 （ Direct expense: \2100000 ）
電子通信機器の小型化・高性能化にともない、高い周波数帯域で優れた高周波磁気特性を有する磁性薄膜の開発が切望されている。しかし、スピネル型フェライトに代表される従来の磁性材料は、高周波で透磁率が急激に低下し使用できない。我々の研究グループでは、理論的に優れた高周波磁気特性を持つことが期待されるプラナ型フェライトに注目し、その薄膜の作製に世界ではじめて成功した。その特徴は、金属イオンが均一に分散固定される錯体重合法を用いて原料溶液を調製し、コーティング法により薄膜を作製した点である。そこで本研究では、プラナ型フェライト薄膜のグローバルインテグレーションを目標に、1.薄膜の膜質向上(平滑性・クラック等)を目的として、原料溶液組成の検討2.薄膜の焼成温度の低温化を目的として、基板材料の検討を行った。
その結果、平滑かつクラックの無いプラナ型フェライト薄膜の作製のためには、原料溶液の混合比を、金属:クエン酸:エチレングリコール=1:4:12とすること、溶液のpHはpH<1とすること、そして粘度については10mPa・s以下とすることを明らかにした。また、種々の貴金属基板上に成膜した結果、プラナ型フェライト(Y型六方晶フェライト)の結晶化には、一般的に1000℃以上の高温焼成が必要とされるが、Ag基板を用いたときのみ特異的に結晶化温度が低下し、800℃の低温においてプラナ型フェライト薄膜が成長することを見出した。
得られたプラナ型フェライト薄膜の高周波磁気特性を評価し、改善することが今後の課題である。 -
Preparation of Electromagnetic wave absorber Barium Ferrites for Electromagnetic Environment by liquid State Reaction
Grant number：12450269 2000 - 2002
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
YOSHIO Tetsuo, FUJII Tatsuo, TAKADA Jun, NAGAE Masahiro
Grant amount：\14900000 （ Direct expense: \14900000 ）
In the present study, we tried the synthesis of Y-type Ba-hexaferrite expected as an electromagnetic wave absorber by the glass ceramic method. The results are summarized as follows.
The glasses with composition of 0.1MO[xB_2O_3・yBaO・(1-x-y)Fe_2O_3] were prepared and the precipitation process of Y-type Ba-hexaferrite from the glass matrix was investigated. Y-type Ba-hexaferrite particles were precipitated by heating the glass at temperatures between 820℃ and 1100℃. Based on these results, hexagonal platelets of Y-type Ba-hexaferrite with fairly uniform dimension were obtained as precipitates from the glass matrix by leaching with a dilute HCl solution. The low-temperature formation of Y-type Ba-hexafcrrite was due to a reaction between M-type Ba-ferrite and liquid phase. Substitutional solid solutions of Y-type Ba-hexaferrite (Ba_2Zn_<2-x>Co_xFe_<12>O_<22>) were obtained in all composition range. These Y-type Ba-hexaferrite solid solutions showed electromagnetic absorption spectra at frequency range of 8 to 9 GHz. -
Controlled spin-polarized electron transport of oxide magnetic semiconductor films of hematite-ilumenite solid solutions by the exchange coupling
Grant number：11650697 1999 - 2001
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
FUJII Tatsuo, NAKANISHI Makoto, TAKADA Jun
Grant amount：\3500000 （ Direct expense: \3500000 ）
Magnetic semiconductors are one of die promising electronics materials for the next generation, so-called spintronics materials. In this research we proposed a novel technique to control the spin-polarized transport of magnetic semiconductors and tried to realize it. The first subject was to develop thin films of new oxide magnetic semiconductors focused on a hematite-ilumenite solid solution system having a high spin polarization at room temperature. There had been many difficulties to prepare well-defined hematite ilumenite solid solution films having good magnetic semiconductive properties, because they had many controllable factors such as an order-disorder transition and Fe^<2+>/Fe^<3+> mixed valence states, etc. We found optimized preparation conditions for the solid solution films by helicon sputtering to control remanent oxygen pressure and substrate temperature precisely. The films showed magnetic semiconductive properties such as magnetoresistance at room temperature. The second subject was to control magnetic structures of ferromagnetic layers by means of a spin-flip transition of antiferromagnetic layers. Only epitaxial hematite films showed a unique spin-flip transition. We prepared hematite/spinel ferrite bilayered films by helicon sputtering and surveyed magnetic properties around the spin-flip transition. The spin-flip transition in a hematite layer disappeared because of a large in-plane magnetic anisotropy of a spinel ferrite layer. We first found the 90° exchange coupling between oxide magnetic layers. Unfortunately we could not realize the proposing spin control technique, but we could obtain huge results concerning preparation techniques for well-defined iron oxide films and their structural, magnetic and electronic properties.
-
A Study of Magnetic Interaction Between Magnetic Layers in Laminated Films
Grant number：10650691 1998 - 1999
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
KOHMOTO Osamu, FUJII Tatsuo
Grant amount：\1100000 （ Direct expense: \1100000 ）
Four types of the magnetic films has been studied.
(1) Single-layer Ni Films : Dependencies of the saturation magnetization, coercive force remanence ratio and perpendicular magnetic anisotropy in sputtered Ni films on the film thickness (100 and 300 nm) and Ar pressure (3-50 mTorr) have been studied.
(2) Single-layer Ni-O films prepared by sputtering in Ar+OィイD22ィエD2 atmosphere : Single phase NiO films are obtained below the oxygen partial pressure (OィイD22ィエD2/(Ar+OィイD22ィエD2)) of 9%. Lattice constant (a) and axis angle (α) of the Ni-O films have been studied. With increase in OィイD22ィエD2 pressure, the two values of a and α become close to those of the bulk. Saturation magnetization, coercive force, remanence ratio and electrical resistivity (ρ) has been studied. The NiO films are not stoichiometric composition. Oxygen deficient value (γ) in NiィイD21-γィエD2O decrease rapidly with annealing temperature. With decreasing γ, the electrical resistivity increases rapidly from 6x10ィイD1-1ィエD1 to 10ィイD14ィエD1 μΩcm.
(3) Layered Ni/NiO films : Sifted MH loops are observed in bilayered films. With increase in NiO layer thickness, exchange field(HィイD2exィエD2) coercive force (HィイD2cィエD2) and magetoresistance (Δρ/ρ) increases. HィイD2exィエD2 increase with decrease in the Ni layer thickness. With increase in the NiO layer thickness, the Ni layer thickness at which the field of appearing HィイD2exィエD2 increases.
(4) Layered Ni/Cu/Ni/NiO films : Shifted and asymmetrical MH loops have been observed. The latter indicated two ferromagnetic Ni layers have been surely separated by the Cu layer. HィイD2exィエD2 and HィイD2cィエD2 tend to increase with Cu layer thickness. -
Development of Novel Electromagnetic-Wave-Absorber of SiC-Ferrite Hybrid Materials
Grant number：10450250 1998 - 1999
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
TAKADA Jun, TOMII Yoichi, NAKANISHI Makoto, FUJII Tatsuo, YAMAMOTO Shigehisa
Grant amount：\13700000 （ Direct expense: \13700000 ）
First, We firmed the experimental technique and evaluation of the electromagnetic properties concerning with wave-absorption by using an network analyzer for frequency range from 100MHz to 10GHz. Next two different types of novel sintered composites of Ni-Zn ferrite SiC were first succeeded to prepare as an electromagnetic-wave-absorber through a soft chemical technique and subsequent tow different manners of sintering : a two-step sintering and an one-step sintering. Amorphous SiC particles with an average diameter of approximately 30 μm dispersed uniformly in Ni-Zn spinel ferrite matrix. In the two-step-sintering method, the density of the composite decreased continuously as the amount of SiC increased. The absorption characteristics of the sintered composite were found to depend upon the amount of SiC particles. The center frequency of the absorption shifted toward higher frequency around 2GHz. Furthermore in the one-step-sintering method, we first succeeded another new electromagnetic-wave-absorber having interesting wave-absorption properties with the two different center frequencies of about 800MGz and 8.6GHz.
-
Bi系高温超伝導酸化物のLiのインターカレーションと二次電池正極材への応用の試み
Grant number：09875172 1997 - 1998
日本学術振興会 科学研究費助成事業 萌芽的研究
高田 潤, 武田 保雄, 中西 真, 藤井 達生
Grant amount：\1900000 （ Direct expense: \1900000 ）
Bi系高温超伝導酸化物(Bi-2212相など)は層状構造を有する化合物であり、これまで電極反応によるLiのインターカレーションの可能性が期待されていたが、現在まで殆ど報告例がない。
本研究は、Bi-2212相へ電気化学的にLiを導入することを試み、得られたBi-2212相の超伝導特性、構造及び酸素量と構成イオンの価数変化を明らかにするとともに、固相反応法によるLi導入の結果と比較検討することにより、Liのインタカレーションの特徴を明らかにし、更にLiディインターカレーションを試みることによって、Bi-2212相がLi二次電池の正極材として応用できる可能性を検討することを目的とした。得られた結果を要約すると以下の通りである。
1. 電気化学的手法を用いれば、LiをBi-2212相に常温・常圧でインターカレートすることが可能であり、Li量の制御は極めて容易であることを明らかにした。
2. Liを電気化学的に導入したBi-2212相の超伝導特性Toは、Li量によって大巾に変化することを初めて見い出した。すなわち、少量のLi導入でTcは85Kから93Kまで上昇した後、急激に低下し、X≧0.3(Li_X Bi_2Sr_<1.6> Ca_<1.5> Cu_2O_zの表記に対して)のLi量で非超伝導体となる。
3. 電気化学的Li導入では固相反応の場合とは全く異なり、酸素量は全く変化せず、Biの平均価数が減少する結果、Cuの平均価数がX≧0.3.で+2.0まで減少し、これがTcの著しい変化の原因であることを明らかにした。
4.予め導入したLiは電気化学的な逆反応(放電反応)によって、Bi-2212相より放出できる、すなわちディインターカレーションが可能であることを初めて見い出した。このディインターカレーションによって、Bi-2212相の構造、超伝導特性、酸素量とBiとCuの平均価数は可逆的に変化することを明らかにした。
5. 以上の結果より、Bi-2212相へのLi二次電池の正極材への応用の可能性は極めて高いことを示した。 -
In situ Raman分光法による酸化鉄薄膜の構造解析とスピン構造
Grant number：09740524 1997 - 1998
日本学術振興会 科学研究費助成事業 奨励研究(A)
藤井 達生
Grant amount：\2100000 （ Direct expense: \2100000 ）
本研究者は、数年前、α-Al_2O_3単結晶基板上に成長したエピタキシャルα-Fe_2O_3薄膜のスピン構造が、バルク結晶のものと大きく異なっており、温度により膜面内から垂直方向へと興味あるスピンフリップ転移を示すことを見出し、注目された。この原因として、α-Fe_2O_3薄膜の成長過程に由来する格子歪みの発生が考えられる。本研究では成摸時にin situ Raman分光測定を行い、エピタキシャルα-Fe_2O_3薄膜の薄膜成長過程における構造変化を、連続的にとらえることを試みた。しかし、昨年度に引き続きRaman分光装置の光学系の改善を試みたが、膜厚が数原子層程度しかない超薄膜のRamanスペクトルを測定することはできず、薄膜成長初期の構造変化をとらえることには残念ながら成功しなかった。
またその研究と並行して、活性化反応性蒸着法によりα-Al_2O_3(001)単結晶基板上にFeTiO_3-α-Fe_2O_3固溶体のエピタキシャル薄膜を作製した。基板温度500℃の低温で成膜した薄膜は、FeイオンとTiイオンが陽イオンサイトをランダムに占有したコランダム構造であった。一方、基板温度700℃で成膜したFe_<2-x>Ti_xO_3膜は、x≧0.4の組成範囲でFeイオンとTiイオンが規則的に配列したイルメナイト構造をとった。FeイオンとTiイオンか規則配列した薄膜のみかフェリ磁性を示した、しかしその自発磁化はイオンが完全に規則配列した場合に期待される値の半分以下であった。さらに、固溶体薄膜の比抵抗は、Fe^<2+>-Fe^<3+>イオンの混合原子価状態をとることにより10^<-1>Ωcmまで低下した。よって本系固溶体薄膜は、新しい酸化物磁性半導体薄膜の有力な候補となることを明らかにした。 -
Preparation and Properties of New Mo-based Alloys Strengthened by Dispersion of Nano-scale Nitride Superfine Particles
Grant number：08455311 1996 - 1997
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
TAKADA Jun, NAKANISHI Makoto, FUJII Tatsuo, HIRAOKA Yutaka
Grant amount：\7400000 （ Direct expense: \7400000 ）
Mo alloys, which are known to be one of high melgin-temperature metals, are used as high-temperature materials such as heaters, trays for heat-treatments and a X-ray target. Further wide use requires high strengthening of the alloys.
The present research aims to harden a Mo-nitride surface layr formed by nitriding and also to strengthen the alloy by precipitation of very fine TiN particles dispersed in Mo matrix through preferred nitriding of dilute Mo-Ti alloys. Especially on the basis of basic and systematic investigations we tried to develop a new Mo-based composities in which a great number of nano-scale TiN superfine particles disperse through nitriding at much lower temperatures thatn those so far. As a result, it is quite lucky for us to succeed the development of a new Mo-based composite material having remarkably higher strength in comparison with any materials used at present.
For Mo-0.5 and 1.0wt% alloys and pure Mo nitrided in a NH_3 gas at 1100ﾟC which is much lower than 1300-1500ﾟC in previous works, nitriding behavior, hardness profiles on cross sections of nitrided specimens, and microstructure and crystallographic relationship of fine Ti-nitride particles in the Mo matrix were discussed. Main results are summarized below.
(1) The growth mechanism of the Mo-nitride surface layr was made clear. A maximum hardness was found to reach Hv=1800. Furthermore, the surface layr was found to consist of two different sublayrs : a gamma-Mo_2N sublayr near the specimen surface and a beta-Mo_2N sublayr beneath the gamma-Mo_2N layr. Each sublayr has a different twin. In particular, the formation of a new type of microtwin was found in the beta-Mo_2N sublayr.
(2) In nitrided Mo-Ti alloys an internal nitriding layr having high strength was formed beneath the Mo_2 surface layr. The formation of the internal nitriding layr was not observed in pure Mo. We attained markedly high hardness of Hv=1000, which is twice a maximum hardness of Hv=500 reported in Mo alloys so far. Moreover, we found first in the world that the nitriding at the very low temperature of 1100ﾟC brought the precipitation of nano-scale TiN superfine particles with a thickness of about 0.45nm (=1 unit length of TiN) and a diameter of 2-4nm. The superfine particles formed were found to have a special crystallographic-relationship and to give the great increase in strength. -
Magnetic and Optical properties of artifical superlattice
Grant number：05453079 1993 - 1994
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for General Scientific Research (B)
MIURA Yoshinari, FUJII Tatsuo, OSAKA Akiyoshi
Grant amount：\7100000 （ Direct expense: \7100000 ）
Magnetic superlattices including ferromagnetic and diamagnetic layrs bring interesting properties such as the giant magnetoresistance and the mangneto-optical effects. On the other hand, it is well known that titanium oxides change their properties sensitively with their metal to oxygen ratios.
Fe_3O_4/Mo (M=Mg, Co) superlattice films having various thickness combinations of the individual Fe_3O_4 and Mo were prepared by an activated reactive evaporation (ARE) method. Stoichiometric and monstoichiometric titanium oxide films were also epitaxially formed on alpha-Al_2O_3 (0001) substrates by ARE method. The summarized results are as follows :
1. Epitaxial growths and artificial modulations of (111) -and (100) -orientated Fe_3O_4/Mgo films deposited on (0001) -faced alpha-Al_2O_3 and (100) -faced Mgo single crystaline substrates, respectively, were confirmed. The saturation magnetization of each film at 5K was about 85-100 emu/g, being nealy consistent with that of the Fe_3O_4 bulk. However, with increasing temperature the magnetizations decreased linearly in proportion to 1/T below 40K.
2. For Fe_3O_4/CoO film the lattice spacing along the growth direction was contracted for the CoO layr but expanded for the Fe_3O_4 layr probably due to the lattice mismatch between these layrs. The magnetostriction of CoO layrs induced in-plane and perpendicular magnetic anisotropy in (100) -and (111) -oriented superlattices, respectively. Strong magnetic coupling between Fe_3O_4 and CoO layrs made the Neel temperature of the CoO layr higher and showed the ferrimagnetic/antiferromagnetic exchange anisotropy.
3. Titanium di-and sesquioxide films were epitaxially grown on (0001) alpha-Al_2O_3. Films prepared at Po_2*2.0*10^<-4> Torr were stoichiometric (100) -oriented rutile of TiO_2. AtP_<02>=0.6*10^<-4> Torr, on the other hand, (001) -oriented Ti_2O_3 was formed and an electrical transition was clearly detected at about 400K. -
スパッタ法による歪み酸化鉄薄膜の磁気光学特性
Grant number：05855130 1993
日本学術振興会 科学研究費助成事業 奨励研究(A)
藤井 達生
Grant amount：\1200000 （ Direct expense: \1200000 ）
rfマグネトロンスパッタ法を用い、サファイア(alpha-Al_2O_3)単結晶基板上に酸化鉄(alpha-Fe_2O_3)薄膜を作製した。酸化鉄(alpha-Fe_2O_3)は約250Kにモ-リン転移と呼ばれるスピン相転移を持ち、その前後でスピン軸がc面内からc軸方向へと90°変化することが知られている。しかし、単結晶基板上に成長した酸化鉄薄膜の場合は、基板界面におけるミスフィットが結晶格子に歪みを与える結果、スピン相転移はそのスピン軸、転移温度ともバルクに比べ、異なった振舞を示すことが期待される。
alpha-Al_2O_3(102)単結晶基板上にエピタキシャル成長したalpha-Fe_2O_3(102)について、メスバウアー分光測定を行なった結果、スピン転移温度は400Kへと大きく上昇しており、しかもスピン軸はc軸から<102>方向へと変化していた。そこで4軸回折計による薄膜のX線構造解析を試みた結果、a軸長は約0.5%減少し、一方、c軸長は約0.2%増加していた。一方、alpha-Al_2O_3(001)単結晶基板上にエピタキシャル成長したalpha-Fe_2O_3(001)について、メスバウアー分光測定及びX線構造解析を行なった結果、スピン相転移は極低温(2K)に至まで観測されず、逆にa軸長が約0.3%増加し、c軸長が約0.5%減少していた。従って、得られた酸化鉄薄膜のスピン相転移の変化は、異方的な歪みが原因で生じたものと推論できる。得られた薄膜の磁気光学特性については、現在まだ検討中である。 -
Preparation of Fact-Ion Conductive Thin Films as nano-sized Battery Electrolytes
Grant number：04650705 1992 - 1993
Japan Society for the Promotion of Science Grants-in-Aid for Scientific Research Grant-in-Aid for General Scientific Research (C)
OSAKA Akiyoshi, FUJII Tatsuo, NANBA Tokurou
Grant amount：\1870000 （ Direct expense: \1870000 ）
The present research was exploited based on a demand for developing optical memory materials and electrolytes for fine scale solid batteries. Thin films of the systems F-O-Si-Pb and CuI-MoO_4-P_2O_5 were prepared with an rf-sputtering technique and their microstructure, electrical conductivity and phase change due to laser irradiation.
1. Amorphous thin films of the system F-O-Si-Pb
Amorphous thin films of the system F-O-Si-Pb were rf-sputtered under the conditions : the Ar chamber pressure : 0.06-0.07 Torr, rf-power : 100W, sputtering time : 45min. X-ray photoelectron spectra showed that the fluorine atoms were homogeneously distributed in the films but the ratio F-Si/F-Pb decreased in the direction from the surface to the film-substrate interface. The results were accounted for by an increase in non-bridging oxygen due to a reaction Si-O-Si->Si-F+Si-O^-. Irradiation of 3mW He-Ne laser beam (lambda=632.8nm) for 1/500s induced crystallization of a quartz in the area of 11mum radium, independent of the fluorine content, but not induced an expected PbF2 phase of high conductivity. Fluorine ionic conductivity obeyed an Arrhenius type temperature dependence with sigma=1.1x10-5 S/cm at 500K, two orders of magnitude larger than the corresponding bulk glass, and activation energy of 106.5kJ/mol.
2. Amorphous thin films of the system CuI-MoO_4-P_2O_5
A target of a composition 25CuI・25Cu_2O・25MoO_4・25Cu_3(PO_4)_3 was rf-sputtered with the same conditions above to prepare amorphous films. They had a particular microstructure and were insulators below 550K with conductivity as small as 10^<-8> S/cm. The increase in the rf-power grew cubic particles of gamma-CuI while a large fraction of Cu atoms were divalent. The laser irradiation dug holes of 8mum in diameter even at 1/500 s and the holes grew to 12 at 1s irradiation, whereas no crystallization was observed.