KATO MASAKI
Faculty of Science and Engineering Department of Molecular Chemistry and Biochemistry
Professor
Last Updated :2020/08/09

Researcher Profile and Settings

Research Interests

  • Magnetism
  • Superconductivity
  • Solid State Physics

Research Areas

  • Natural sciences/Magnetism, superconductivity, and strongly correlated systems
  • Nanotechnology/Materials/Functional solid-state chemistry
  • Nanotechnology/Materials/Inorganic and coordination chemistry

Academic & Professional Experience

  • Faculty of Science, Kyoto University, 1994 - 2003
  • - Associate Professor, Faculty of Engineering, Doshisha University, 2004
  • Research associate, Faculty of Science, Kyoto University, 1994 - 2003

Education

  • Kyoto University, 1994
  • Kyoto University, Graduate School, Division of Natural Science, 1994
  • Kyoto University, 1992
  • Kyoto University, Graduate School, Division of Natural Science, 1992
  • Kyoto University, Faculty of Science, 1990
  • Kyoto University, Faculty of Science, 1990

Academic Degrees

  • Doctor of Science, Kyoto University
  • Master of Science, Kyoto University

Association Memberships

  • Physical Society of Japan
  • Chemical Society of Japan

Published Papers

  • Crossover from Metallic to Semiconducting in Pb2-xLnxRu(2)O(7-delta) (Ln = Eu, Sm) Compounds with Pyrochlore Structure
    Masaki Kato, Tetsuya Imamaura, Miho Fukatsu, Ken Hirota
    We study the synthesis and physical properties of Pb(2-x)Ln(x)Ru(2)O(7-delta) (Ln = Sm, Eu) compounds with pyrochlore structure. The lead-lanthanoid pyrochlores Pb(2-x)Ln(x)Ru(2)O(7-delta) (Ln = Sm, Eu) have been successfully synthesized by the solid-state reaction. All samples were characterized by X-ray diffraction, magnetic susceptibility, and electrical resistivity measurements. Magnetic susceptibility measurements showed that the spin-glass transition temperature, T-SG, decreases with Ln content x and goes to zero at x = 0.2 and 0.6 for Sm and Eu, respectively. From electric resistivity measurements, a crossover from metallic to semiconducting behavior was observed in the range of 0.2 <= x <= 0.4 and 0.4 <= x <= 0.8 in Pb2-xSmxRu2O7-delta and Pb2-xEuxRu2O7-delta, respectively. These boundaries between metallic and insulating phases mostly correspond to values of x with T-SG = 0. These metal-insulator transitions can be caused by the strongly correlated couplings between the itinerant 4d electrons which are possibly attributed to the magnetic frustration., MULTISCALE, MULTIFUNCTIONAL AND FUNCTIONALLY GRADED MATERIALS, TRANS TECH PUBLICATIONS LTD, 631-632483 - 488, 2010, English, Research paper (international conference proceedings)
  • Metal-insulator transition in Pb(2-x)Ln(x)Ru(2)O(7-delta) (Ln = sm, eu) compounds
    M. Kato, Y. Tani, T. Imamura, K. Hirota, K. Yoshimura
    We have investigated the physical properties of Pb(2-x)Ln(x)Ru(2)O(7-delta) (Ln = Sm, Eu) compounds with pyrochlore crystal structure. The solid-solution compounds of Pb(2-x)Ln(x)Ru(2)O(7-delta) show from metallic (x = 0) to insulating (x = 2) behaviors. These compounds with x > 1.0 also indicate the spin-glass like behaviors at low temperature (T < T-SG) which are attributed to the geometrical frustration on pyrochlore lattice. The transition temperature TSG decreases monotonously with decreasing x and goes to zero at x = 0.6. The sample with 0.4 <= x <= 0.8 shows the metal-insulator (MI) transition at 10-30K where the sign of temperature derivative of electric resistivity changes. (C) 2007 Elsevier B.V. All rights reserved., PHYSICA B-CONDENSED MATTER, ELSEVIER SCIENCE BV, 403(5-9)1315 - 1317, Apr. 2008, English, Research paper (scientific journal)
  • Methane oxidation on perovskite-type Ca(Mn1-xTix)O3-delta
    Hideki Taguchi, Katsuyuki Nakade, Masashi Yosinaga, Masaki Kato, Ken Hirota
    X-ray photoelectron spectroscopy was performed to elucidate the catalytic activity of CH4 oxidation on perovskite-type Ca(Mn1-xTix)O3-delta synthesized at 1173 K in a flow of oxygen from a gel with citric acid and ethylene glycol. The Mn ion content decreases and the ratio of the Mn3+ ion in the Mn ion increases with increases in x. Ca(Mn1-xTix)O3-delta has a high catalytic activity of CH4 oxidation at x=0.4. These results indicate that the catalytic activity strongly depends on the Mn3+ ion content of the surface., JOURNAL OF THE AMERICAN CERAMIC SOCIETY, BLACKWELL PUBLISHING, 91(1)308 - 310, Jan. 2008, English, Research paper (scientific journal)
  • Synthesis and magnetic properties of Cu oxides with low-dimensional structure
    M. Kato, Y. Nogi, S. Hongo, K. Hirota
    J. Phys., 344(012010)43471 , 2012
  • Effect of elemental substitutions on ruthenates with pyrochlore-type structure
    M. Kato, S. Harada, M. Fukatsu, K. Hirota
    J. Phys., 313(012010)43471 , 2011
  • Fabrication of full-density Mg-Ferrite/Fe-Ni permalloy nanocomposites with a high-saturation magnetization density of 1 T
    M. Kato, K. Hirota, M. Obata, H. Taguchi
    Int. J. Appl. Technol. Online, 643478 , 2011
  • Fabrication of Al2O3/TiN dense composites directly from Al2O3/Ti raw material powder compacts using N2 capsule-free HIPing and their evaluation
    M. Kato, K. Takaoka, H. Yagura, K. Hirota
    Adv. Tech. Mat. Mat. Proc. J., 13(2)93 - 98, 2011
  • HIP synthesis of -carbide-type nitrides Fe3W3N and Fe6W6N and their magnetic properties
    M. Kato, T. Waki, S. Terazawa, Y. Tabata, Y. Murase, K. Hirota, S. Ikeda, H. Kobayashi, K. Sato, K. Kindo, H. Nakamura
    J. Alloy. Compd., 5069451 - 9455, 2011
  • Crossover from Metallic to Semiconducting in Pb2-xLnxRu(2)O(7-delta) (Ln = Eu, Sm) Compounds with Pyrochlore Structure
    Masaki Kato, Tetsuya Imamaura, Miho Fukatsu, Ken Hirota
    We study the synthesis and physical properties of Pb(2-x)Ln(x)Ru(2)O(7-delta) (Ln = Sm, Eu) compounds with pyrochlore structure. The lead-lanthanoid pyrochlores Pb(2-x)Ln(x)Ru(2)O(7-delta) (Ln = Sm, Eu) have been successfully synthesized by the solid-state reaction. All samples were characterized by X-ray diffraction, magnetic susceptibility, and electrical resistivity measurements. Magnetic susceptibility measurements showed that the spin-glass transition temperature, T-SG, decreases with Ln content x and goes to zero at x = 0.2 and 0.6 for Sm and Eu, respectively. From electric resistivity measurements, a crossover from metallic to semiconducting behavior was observed in the range of 0.2 <= x <= 0.4 and 0.4 <= x <= 0.8 in Pb2-xSmxRu2O7-delta and Pb2-xEuxRu2O7-delta, respectively. These boundaries between metallic and insulating phases mostly correspond to values of x with T-SG = 0. These metal-insulator transitions can be caused by the strongly correlated couplings between the itinerant 4d electrons which are possibly attributed to the magnetic frustration., MULTISCALE, MULTIFUNCTIONAL AND FUNCTIONALLY GRADED MATERIALS, TRANS TECH PUBLICATIONS LTD, 631-632483 - 488, 2010, English, Research paper (international conference proceedings)
  • Preparation of zinc oxide ceramics with a sustainable antibacterial activity under dark conditions
    M. Kato, K. Hirota, M. Sugimoto, K. Tsukagoshi, T. Tanigawa, H. Sugimoto
    Ceramics Int., 36497–506 , 2010
  • Behavior of Mn 3+ ions in four-layered hexagonal (Sr1 -x -yLaxBay)MnO3
    M. Kato, H. Taguchi, K. Hirata, K. Hirota
    Solid State Sci., 11491–495 , 2009
  • Hopping conductivity of distorted K2NiF4-type (Ca1+xNd1- x)CrO4
    M. Kato, H. Taguchi, K. Hirata, H. Kido, Y. Takeda, Ken Hirota
    Solid State Sci., 111222–1225 , 2009
  • The Study on Carbon Nanofiber (CNF)-Dispersed B4C Composites
    Ken Hirota, Yoshihiro Nakayama, Masaki Kato, Shingo Nakane, Toshiyuki Nishimura
    Carbon nanofiber (CNF)-dispersed B4C composites have been synthesized and consolidated directly from mixtures of elemental raw powders by pulsed electric current pressure sintering (1800 degrees C/10 min/30 MPa). A 15 vol% CNF/B4C composite with similar to 99% of dense homogeneous microstructures (similar to 0.40 mu m grains) revealed excellent mechanical properties at room temperature and high temperatures: a high bending strength (Sigma(b)) of similar to 710 MPa, a Vickers hardness (H-v) of similar to 36 GPa, a fracture toughness (K-IC) of similar to 7.9 MPa m(1/2), and high-temperature Sigma(b) of 590 MPa at 1600 degrees C in N-2. Interfaces between the CNF and the B4C matrix were investigated using high-resolution transmission electron microscopy, EDS, and electron energy-loss spectroscopy., INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, WILEY-BLACKWELL, 6(5)607 - 616, 2009, English, Research paper (scientific journal)
  • Crystal structure and methane oxidation on perovskite-type (La1-2xNdx)CoO3 synthesized using citric acid
    M. Kato, H. Taguchi, S. Matsuoka, Ken Hirota
    J. Mater. Sci., 445732–5736 , 2009
  • The Study on Carbon Nanofiber (CNF)-Dispersed B4C Composites
    Ken Hirota, Yoshihiro Nakayama, Masaki Kato, Shingo Nakane, Toshiyuki Nishimura
    Carbon nanofiber (CNF)-dispersed B4C composites have been synthesized and consolidated directly from mixtures of elemental raw powders by pulsed electric current pressure sintering (1800 degrees C/10 min/30 MPa). A 15 vol% CNF/B4C composite with similar to 99% of dense homogeneous microstructures (similar to 0.40 mu m grains) revealed excellent mechanical properties at room temperature and high temperatures: a high bending strength (Sigma(b)) of similar to 710 MPa, a Vickers hardness (H-v) of similar to 36 GPa, a fracture toughness (K-IC) of similar to 7.9 MPa m(1/2), and high-temperature Sigma(b) of 590 MPa at 1600 degrees C in N-2. Interfaces between the CNF and the B4C matrix were investigated using high-resolution transmission electron microscopy, EDS, and electron energy-loss spectroscopy., INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, WILEY-BLACKWELL, 6(5)607 - 616, 2009, English, Research paper (scientific journal)
  • Metal-insulator transition in Pb(2-x)Ln(x)Ru(2)O(7-delta) (Ln = sm, eu) compounds
    M. Kato, Y. Tani, T. Imamura, K. Hirota, K. Yoshimura
    We have investigated the physical properties of Pb(2-x)Ln(x)Ru(2)O(7-delta) (Ln = Sm, Eu) compounds with pyrochlore crystal structure. The solid-solution compounds of Pb(2-x)Ln(x)Ru(2)O(7-delta) show from metallic (x = 0) to insulating (x = 2) behaviors. These compounds with x > 1.0 also indicate the spin-glass like behaviors at low temperature (T < T-SG) which are attributed to the geometrical frustration on pyrochlore lattice. The transition temperature TSG decreases monotonously with decreasing x and goes to zero at x = 0.6. The sample with 0.4 <= x <= 0.8 shows the metal-insulator (MI) transition at 10-30K where the sign of temperature derivative of electric resistivity changes. (C) 2007 Elsevier B.V. All rights reserved., PHYSICA B-CONDENSED MATTER, ELSEVIER SCIENCE BV, 403(5-9)1315 - 1317, Apr. 2008, English, Research paper (scientific journal)
  • 59Co, 23Na, and 1H NMR studies of double-layer hydrated superconductors NaxCoO2⋅yH2O
    M. Kato, Y. Itoh, H. Ohta, C. Michioka, K. Yoshimura
    Advances in Solid State Physics, Springer, 47329 - 341, 2008
  • Methane oxidation on perovskite-type Ca(Mn1-xTix)O3-delta
    Hideki Taguchi, Katsuyuki Nakade, Masashi Yosinaga, Masaki Kato, Ken Hirota
    X-ray photoelectron spectroscopy was performed to elucidate the catalytic activity of CH4 oxidation on perovskite-type Ca(Mn1-xTix)O3-delta synthesized at 1173 K in a flow of oxygen from a gel with citric acid and ethylene glycol. The Mn ion content decreases and the ratio of the Mn3+ ion in the Mn ion increases with increases in x. Ca(Mn1-xTix)O3-delta has a high catalytic activity of CH4 oxidation at x=0.4. These results indicate that the catalytic activity strongly depends on the Mn3+ ion content of the surface., JOURNAL OF THE AMERICAN CERAMIC SOCIETY, BLACKWELL PUBLISHING, 91(1)308 - 310, Jan. 2008, English, Research paper (scientific journal)
  • Fabrication of carbon nanofiber(CNF)-dispersed Al2O3 composites by pulsed electric-current pressure sintering and their mechanical and electrical properties
    Ken Hirota, Yuichi Takaura, Masaki Kato, Yoshinari Miyamoto
    Dense Al2O3-based composites (>= 99.0% of theoretical) dispersed with carbon nanofibers (CNFs) were fabricated using the pulsed electric-current pressure sintering (PECPS) for 5 min at 1300 degrees C and 30 MPa in a vacuum. The dispersion of CNFs into the matrix depended much on the particle size of the starting Al2O3 powders. Mechanical properties of the composites were evaluated in relation with their microstructures; high values of three-point bending strength sigma(b) (similar to 800 MPa) and fracture toughness K-IC (similar to 5 MPa.m(1/2)) were attained at the composition of CNF/Al2O3 = 5:95 vol%, which sigma(b) and KIC values were similar to 25% and similar to 5%, respectively, higher than those of monolithic Al2O3. This might be due to the small Al2O3 grains (1.6 mu m) of dense sintered compacts compared with that (4.4 mu m) for the pure Al2O3 ceramics, resulting from the suppression of grain growth during sintering induced by uniformly dispersed CNFs in the matrix. Electrical resistivity of CNF/Al2O3 composites decreased rapidly from >10(15) to similar to 2.1 x 10(-2) Omega m (5vol%CNF addition), suggesting the machinability of Al2O3-based composites by electrical discharge machining., JOURNAL OF MATERIALS SCIENCE, SPRINGER, 42(13)4792 - 4800, Jul. 2007, English, Research paper (scientific journal)
  • Fabrication of carbon nanofiber(CNF)-dispersed Al2O3 composites by pulsed electric-current pressure sintering and their mechanical and electrical properties
    Ken Hirota, Yuichi Takaura, Masaki Kato, Yoshinari Miyamoto
    Dense Al2O3-based composites (>= 99.0% of theoretical) dispersed with carbon nanofibers (CNFs) were fabricated using the pulsed electric-current pressure sintering (PECPS) for 5 min at 1300 degrees C and 30 MPa in a vacuum. The dispersion of CNFs into the matrix depended much on the particle size of the starting Al2O3 powders. Mechanical properties of the composites were evaluated in relation with their microstructures; high values of three-point bending strength sigma(b) (similar to 800 MPa) and fracture toughness K-IC (similar to 5 MPa.m(1/2)) were attained at the composition of CNF/Al2O3 = 5:95 vol%, which sigma(b) and KIC values were similar to 25% and similar to 5%, respectively, higher than those of monolithic Al2O3. This might be due to the small Al2O3 grains (1.6 mu m) of dense sintered compacts compared with that (4.4 mu m) for the pure Al2O3 ceramics, resulting from the suppression of grain growth during sintering induced by uniformly dispersed CNFs in the matrix. Electrical resistivity of CNF/Al2O3 composites decreased rapidly from >10(15) to similar to 2.1 x 10(-2) Omega m (5vol%CNF addition), suggesting the machinability of Al2O3-based composites by electrical discharge machining., JOURNAL OF MATERIALS SCIENCE, SPRINGER, 42(13)4792 - 4800, Jul. 2007, English, Research paper (scientific journal)
  • Mechanical properties of simultaneously synthesized and consolidated carbon nanofiber (CNF)-dispersed SiC composites by pulsed electric-current pressure sintering
    Ken Hirota, Hiroaki Hara, Masaki Kato
    Carbon nanofiber (CNF) dispersed beta-SiC composites with the addition of 0.2 mass% boron and 2.0 mass% carbon as sintering aids have been synthesized and consolidated simultaneously from mixtures of Si, amorphous C and B powders and CNF by pulsed electric-current pressure sintering (PECPS). Synthesis and consolidation process, which were observed from their expansion and shrinkage curves during PECPS, have been examined using X-ray diffraction and scanning electron microscopy for the powder compacts. CNF/SiC composites sintered at 1800 degrees C for 10 min under 40 MPa in a vacuum have similar to 96.0% of theoretical density and homogeneous structures consisting of similar to 4.0 mu m grains. A 10 vol% CNF/SiC composite exhibited excellent mechanical properties: a bending strength of similar to 720 MPa, a Vickers hardness of similar to 26.0 GPa, and a fracture toughness of similar to 5.5 MPa m(1/2). High-temperature bending strength of similar to 890 MPa at 1200 degrees C in air was attained with the same nanocomposites. (c) 2006 Elsevier B.V. All rights reserved., MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ELSEVIER SCIENCE SA, 458(1-2)216 - 225, Jun. 2007, English, Research paper (scientific journal)
  • Mechanical properties of simultaneously synthesized and consolidated carbon nanofiber (CNF)-dispersed SiC composites by pulsed electric-current pressure sintering
    Ken Hirota, Hiroaki Hara, Masaki Kato
    Carbon nanofiber (CNF) dispersed beta-SiC composites with the addition of 0.2 mass% boron and 2.0 mass% carbon as sintering aids have been synthesized and consolidated simultaneously from mixtures of Si, amorphous C and B powders and CNF by pulsed electric-current pressure sintering (PECPS). Synthesis and consolidation process, which were observed from their expansion and shrinkage curves during PECPS, have been examined using X-ray diffraction and scanning electron microscopy for the powder compacts. CNF/SiC composites sintered at 1800 degrees C for 10 min under 40 MPa in a vacuum have similar to 96.0% of theoretical density and homogeneous structures consisting of similar to 4.0 mu m grains. A 10 vol% CNF/SiC composite exhibited excellent mechanical properties: a bending strength of similar to 720 MPa, a Vickers hardness of similar to 26.0 GPa, and a fracture toughness of similar to 5.5 MPa m(1/2). High-temperature bending strength of similar to 890 MPa at 1200 degrees C in air was attained with the same nanocomposites. (c) 2006 Elsevier B.V. All rights reserved., MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, ELSEVIER SCIENCE SA, 458(1-2)216 - 225, Jun. 2007, English, Research paper (scientific journal)
  • Magnetic excitation and Na-deficient effects on spin-gapped compound Na2CU2TeO6
    K. Morimoto, Y. Itoh, C. Michloka, M. Kato, K. Yoshimura
    We studied magnetic excitations of a spin-gapped compound Na2Cu2TeO6, the hole doping effect on the Cu2TeO6 plane via topotactic Na deficiency introduced by soft-chemical treatment, the spin vacancy effect by Zn substitution and the magnetic impurity effect by Ni substitution for Cu by means of magnetic susceptibility measurements. It turned out that impaired moments of the doped holes by Na deficiency, Zn and Ni impurities induce Curie magnetism and lower the broad maximum temperature T-max in the uniform spin susceptibility. The decrease of T-max indicates the decrease of a predominant superexchange interaction. (c) 2006 Elsevier B.V. All rights reserved., JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 310(2)1254 - 1256, Mar. 2007, English, Research paper (scientific journal)
  • Magnetic excitation and Na-deficient effects on spin-gapped compound Na2CU2TeO6
    K. Morimoto, Y. Itoh, C. Michloka, M. Kato, K. Yoshimura
    We studied magnetic excitations of a spin-gapped compound Na2Cu2TeO6, the hole doping effect on the Cu2TeO6 plane via topotactic Na deficiency introduced by soft-chemical treatment, the spin vacancy effect by Zn substitution and the magnetic impurity effect by Ni substitution for Cu by means of magnetic susceptibility measurements. It turned out that impaired moments of the doped holes by Na deficiency, Zn and Ni impurities induce Curie magnetism and lower the broad maximum temperature T-max in the uniform spin susceptibility. The decrease of T-max indicates the decrease of a predominant superexchange interaction. (c) 2006 Elsevier B.V. All rights reserved., JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, ELSEVIER SCIENCE BV, 310(2)1254 - 1256, Mar. 2007, English, Research paper (scientific journal)
  • In-plane anisotropy of the magnetic fluctuations in NaxCoO2⋅yH2O
    M. Kato, C. Michioka, Y. Itoh, H. Ohta, K. Yoshimura
    J. Phys. Chem. Solids, 682115 - 2118, 2007
  • Effect of iodine intercalation on structural and physical properties of misfit cobaltates
    M. Kato, K. Umehara, Y. Goto, K. Hirota, K. Yoshimura
    J. Mag. Mag. Mater., 3101116 - 18, 2007
  • Simultaneous synthesis and consolidation of W-added ZrB2 by pulsed electric current pressure sintering and their mechanical properties
    M. Kato, K. Hirota, T. Endo, S. Nakane, T. Nishimura, Y. Morisada, K. Mizuuchi
    Mater. Sci. Forum, 561-565527 - 530, 2007
  • Possible spin triplet superconductivity in NaxCoO2・yH2O—59Co NMR studies
    M. Kato, C. Michioka, T. Waki, Y. Itoh, K. Yoshimura, K. Ishida, H. Sakurai, E. Takayama-Muromachi, K. Takada, T. Sasaki
    J. Phys.: Condens. Matter, 18669 - 682, 2007
  • Metal-insulator transition in NaxTiO2 (x=0.20-0.25)
    M. Kato, H. Sakurai, K. Yoshimura, N. Tsujii, K. Kosuge
    Phys. Rev. B, 75115128.1-115128.5 , 2007
  • Effect of the Mn3+ ion on electrical and magnetic properties of orthorhombic perovskite-type Ca(Mn1-xTix)O3-
    M. Kato, K. Nakade, K. Hirota, H. Taguchi
    Mater. Res. Bull., 421069 - 76, 2007
  • Fabrication of Al-added TiN materials by the combination of double self-propagating high-temperature synthesis and pulsed electric-current pressure sintering
    Shingo Nakane, Sho Hikawa, Takaya Endo, Masaki Kato, Ken Hirota, Hiroya Miyauchi, Tadashi Hioki
    Crystalline phases of Al-added TiN, denoted as (Ti1-xAlx)N-y (0 <= x <= 0.10, 0.8 < y < 1.0), prepared from a mixture of Ti and Al powders by self-propagating high-temperature synthesis (SHS) in a nitrogen atmosphere, have been investigated. By repeating SHS twice, in the region of 0.0 < x <= 0.02 cubic (Ti1-xAlx)N-y solid solutions, and in the region of 0.02 < x <= 0.10 composites consisting of (Ti1-xAlx)N-y and hexagonal Ti2AlN were formed. After powder characterization, they were consolidated to dense materials (> 97% of theoretical) by pulsed electric-current pressure sintering. With increasing Al addition, the optimum sintering temperatures were lowered, followed by reduction of grain size. Their mechanical properties, that is, three-point bending strength sigma(b), Vickers hardness H-v, and fracture toughness K-IC were evaluated as a function of Al content., INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, BLACKWELL PUBLISHING, 4(2)175 - 183, 2007, English, Research paper (scientific journal)
  • Fabrication of Al-added TiN materials by the combination of double self-propagating high-temperature synthesis and pulsed electric-current pressure sintering
    Shingo Nakane, Sho Hikawa, Takaya Endo, Masaki Kato, Ken Hirota, Hiroya Miyauchi, Tadashi Hioki
    Crystalline phases of Al-added TiN, denoted as (Ti1-xAlx)N-y (0 <= x <= 0.10, 0.8 < y < 1.0), prepared from a mixture of Ti and Al powders by self-propagating high-temperature synthesis (SHS) in a nitrogen atmosphere, have been investigated. By repeating SHS twice, in the region of 0.0 < x <= 0.02 cubic (Ti1-xAlx)N-y solid solutions, and in the region of 0.02 < x <= 0.10 composites consisting of (Ti1-xAlx)N-y and hexagonal Ti2AlN were formed. After powder characterization, they were consolidated to dense materials (> 97% of theoretical) by pulsed electric-current pressure sintering. With increasing Al addition, the optimum sintering temperatures were lowered, followed by reduction of grain size. Their mechanical properties, that is, three-point bending strength sigma(b), Vickers hardness H-v, and fracture toughness K-IC were evaluated as a function of Al content., INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, BLACKWELL PUBLISHING, 4(2)175 - 183, 2007, English, Research paper (scientific journal)
  • Hole doping effects on spin-gapped Na2Cu2TeO6 via topochemical Na deficiency
    Kumiko Morimoto, Yutaka Itoh, Kazuyoshi Yoshimura, Masaki Kato, Ken Hirota
    We report the magnetic susceptibility and NMR studies of a spin-gapped layered compound Na2Cu2TeO6 (the spin gap Delta similar to 250 K), the hole doping effect on the Cu2TeO6 plane via a topochemical Na deficiency by soft chemical treatment, and the static spin vacancy effect by nonmagnetic impurity Zn substitution for Cu. A finite Knight shift at the Te-125 site was observed for pure Na2Cu2TeO6. The negative hyperfine coupling constant (125)A(tr) is an evidence for the existence of a superexchange pathway of the Cu-O-Te-O-Cu bond. It turned out that both the Na deficiency and Zn impurities induce a Curie-type magnetism in the uniform spin susceptibility in an external magnetic field of 1 T, but only the Zn impurities enhance the low-temperature Na-23 nuclear spin-lattice relaxation rate whereas the Na deficiency suppresses it. A spin glass behavior was observed for the Na-deficient samples but not for the Zn-substituted samples. The dynamics of the unpaired moments of the doped holes are different from that of the spin vacancy in the spin-gapped Cu2TeO6 planes., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 75(8), Aug. 2006, English, Research paper (scientific journal)
  • Synthesis and physical properties of Bi-Sr-Co-oxides with 2D-triangular Co layers intercalated by iodine
    M Kato, Y Goto, K Umehara, K Hirota, K Yoshimura
    We have investigated the synthesis and physical properties of BiCo221 and BiCo222 compounds intercalated by the iodine. The intercalation of the iodine was successfully performed by the heat treatment at a constant iodine partial pressure. The result of BiCo221 suggests possible substitution of oxygen in Bi-O layer by the iodine. In the case of BiCo222, it was found that the c-axis drastically increased by the intercalation. From thermogravimetric analysis, the iodine content x was determined to be 0.97. Results of magnetic and electric measurements for BiCo222 suggest that the interaction between CoO2 layers are probably reduced by the intercalation. (c) 2006 Elsevier B.V. All rights reserved., PHYSICA B-CONDENSED MATTER, ELSEVIER SCIENCE BV, 378-80(SPEC. ISS.)1062 - 1063, May 2006, English, Research paper (scientific journal)
  • Bi and Sr substitution effects on the spin-gap system Pb2V3O9
    T Waki, Y Itoh, C Michioka, K Yoshimura, M Kato
    We report the magnetic properties of Sr- and Bi-substituted samples of the one-dimensional alternating S=1/2 spin chain compound Pb2V3O9. In the Sr-substituted system, we obtained two series of samples synthesized by different heat treatments; one series shows the reduction of the spin gap without antiferromagnetic long-range order (AF-LRO) and the other shows AF-LRO at low temperatures. We also observed impurity-induced AF-LRO in the Bi-substituted system. The fitting results of magnetic susceptibilities imply the possible coexistence of a spin gap and AF-LRO in both AF-LRO systems. These observations of AF-LRO with a small amount of substitution indicate that the magnetic instability involving a quantum critical point is inherent in the spin-gap system Pb2V3O9., PHYSICAL REVIEW B, AMERICAN PHYSICAL SOC, 73(6), Feb. 2006, English, Research paper (scientific journal)
  • Triplon condensation of spin-gapped chain Pb2V3O9
    T Waki, M Kato, Y Itoh, C Michioka, K Yoshimura, T Goto
    We found the field-induced magnetic ordering for a quasi-one-dimensional alternating spin chain compound Pb2V3O9, which can be understood by Bose-Einstein condensation of triplons. In this paper, we present the temperature-field magnetic phase diagram, which is drawn from magnetic susceptibility, high field magnetization and V-51 NMR measurements. (c) 2005 Elsevier Ltd. All rights reserved., JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, PERGAMON-ELSEVIER SCIENCE LTD, 66(8-9)1432 - 1434, Aug. 2005, English, Research paper (scientific journal)
  • Observation of Bose-Einstein condensation of triplons in quasi 1D spin-gap system Pb2V3O9
    T Waki, Y Morimoto, C Michioka, M Kato, H Kageyama, K Yoshimura, S Nakatsuji, O Sakai, Y Maeno, H Mitamura, T Goto
    We observed a field-induced magnetic ordering in the quasi one-dimensional anti ferromagnetic alternating chain system Pb2V3O9 for the first time. The characteristic temperature dependence of the magnetic susceptibility below T-N and the power law behavior of phase boundary between paramagnetic and ordered phases in the Pb2V3O9 system can be comprehended in terms of Bose-Einstein condensation of triplons, as in the case of TlCuCl3 [Phys. Rev. Lett. 84 (2000) 58681. Our results indicate that BEC of triplons can be observed in the present strongly-coupled-dimer system, while TlCuCl3 is a weak inter dimer coupling system., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 73(12)3435 - 3438, Dec. 2004, English, Research paper (scientific journal)
  • Observation of Bose-Einstein condensation of triplons in quasi 1D spin-gap system Pb2V3O9
    T Waki, Y Morimoto, C Michioka, M Kato, H Kageyama, K Yoshimura, S Nakatsuji, O Sakai, Y Maeno, H Mitamura, T Goto
    We observed a field-induced magnetic ordering in the quasi one-dimensional anti ferromagnetic alternating chain system Pb2V3O9 for the first time. The characteristic temperature dependence of the magnetic susceptibility below T-N and the power law behavior of phase boundary between paramagnetic and ordered phases in the Pb2V3O9 system can be comprehended in terms of Bose-Einstein condensation of triplons, as in the case of TlCuCl3 [Phys. Rev. Lett. 84 (2000) 58681. Our results indicate that BEC of triplons can be observed in the present strongly-coupled-dimer system, while TlCuCl3 is a weak inter dimer coupling system., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 73(12)3435 - 3438, Dec. 2004, English, Research paper (scientific journal)
  • Magnetic fluctuations in the metallic state of Na0.7CoO2 revealed by Na-23 nuclear magnetic resonance
    Y Ihara, K Ishida, C Michioka, M Kato, K Yoshimura, H Sakurai, E Takayama-Muromachi
    Nuclear magnetic resonance (NMR) studies were performed on Na0.7CoO2 to investigate its magnetic proper-ties from the microscopic viewpoint. Na0.7CoO2 is a starting compound of the recently discovered superconductor Na(0.35)CoO(2)(.)1.3H(2)O, in which Co atoms form a triangular structure. Although Na-23 NMR results show no magnetic anomaly down to 1.5 K, Knight shift (K-23) and (23)(1/T1T) of 23Na continue to increase, suggestive of the vicinity of the magnetic phase. From the relation between K-23 and (23)(1/T1T), it is shown that ferromagnetic fluctuations are dominant below 100 K. In addition to ferromagnetic correlations, antiferromagnetic fluctuations are found develop to in a low-temperature region below 4 K. Magnetic fluctuations considered from our experiment are discussed., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 73(11)2963 - 2966, Nov. 2004, English, Research paper (scientific journal)
  • Magnetic fluctuations in the metallic state of Na0.7CoO2 revealed by Na-23 nuclear magnetic resonance
    Y Ihara, K Ishida, C Michioka, M Kato, K Yoshimura, H Sakurai, E Takayama-Muromachi
    Nuclear magnetic resonance (NMR) studies were performed on Na0.7CoO2 to investigate its magnetic proper-ties from the microscopic viewpoint. Na0.7CoO2 is a starting compound of the recently discovered superconductor Na(0.35)CoO(2)(.)1.3H(2)O, in which Co atoms form a triangular structure. Although Na-23 NMR results show no magnetic anomaly down to 1.5 K, Knight shift (K-23) and (23)(1/T1T) of 23Na continue to increase, suggestive of the vicinity of the magnetic phase. From the relation between K-23 and (23)(1/T1T), it is shown that ferromagnetic fluctuations are dominant below 100 K. In addition to ferromagnetic correlations, antiferromagnetic fluctuations are found develop to in a low-temperature region below 4 K. Magnetic fluctuations considered from our experiment are discussed., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 73(11)2963 - 2966, Nov. 2004, English, Research paper (scientific journal)
  • Correlation between superconducting transition temperature T-c and increase of nuclear spin-lattice relaxation rate devided by temperature 1/T1T at T-c in the hydrate cobaltate NaxCoO2 center dot yH(2)O
    Y Ihara, K Ishida, C Michioka, M Kato, K Yoshimura, K Takada, T Sasaki, H Sakura, E Takayama-Muromachi
    We have performed Co-nuclear quadrupole resonance (NQR) studies on NaxCoO2.yH(2)O compounds with different Na (x) and hydrate (y) contents. Two samples with different Na contents but nearly the same T-c values (x = 0.348, T-c = 4.7 K; x = 0.339, T-c = 4.6 K) were investigated. The spin-lattice relaxation rate 1/T-1 in the superconducting (SC) and normal states is almost the same for the two samples except just above T-c. NQR measurements were also performed on different-hydrate-content samples with different T-c values, which were prepared from the same Na-content (x = 0.348) sample. From measurements of 1/T-1 using the different-hydrate-content samples, it was found that a low-T-c sample with T-c = 3.9 K has a larger residual density of states (DOS) in the SC state and a smaller increase of 1/T1T just above T-c than a high-T-c sample with T-c = 4.7 K. The former behavior is consistent with that observed in unconventional superconductors, and the latter suggests the relationship between T-c and the increase in DOS just above T-c. This increase, which is seemingly associated with the two-dimensionality of the CoO2 plane, is considered to be one of the most important factors for the occurrence of superconductivity., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 73(8)2069 - 2072, Aug. 2004, English, Research paper (scientific journal)
  • Correlation between superconducting transition temperature T-c and increase of nuclear spin-lattice relaxation rate devided by temperature 1/T1T at T-c in the hydrate cobaltate NaxCoO2 center dot yH(2)O
    Y Ihara, K Ishida, C Michioka, M Kato, K Yoshimura, K Takada, T Sasaki, H Sakura, E Takayama-Muromachi
    We have performed Co-nuclear quadrupole resonance (NQR) studies on NaxCoO2.yH(2)O compounds with different Na (x) and hydrate (y) contents. Two samples with different Na contents but nearly the same T-c values (x = 0.348, T-c = 4.7 K; x = 0.339, T-c = 4.6 K) were investigated. The spin-lattice relaxation rate 1/T-1 in the superconducting (SC) and normal states is almost the same for the two samples except just above T-c. NQR measurements were also performed on different-hydrate-content samples with different T-c values, which were prepared from the same Na-content (x = 0.348) sample. From measurements of 1/T-1 using the different-hydrate-content samples, it was found that a low-T-c sample with T-c = 3.9 K has a larger residual density of states (DOS) in the SC state and a smaller increase of 1/T1T just above T-c than a high-T-c sample with T-c = 4.7 K. The former behavior is consistent with that observed in unconventional superconductors, and the latter suggests the relationship between T-c and the increase in DOS just above T-c. This increase, which is seemingly associated with the two-dimensionality of the CoO2 plane, is considered to be one of the most important factors for the occurrence of superconductivity., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 73(8)2069 - 2072, Aug. 2004, English, Research paper (scientific journal)
  • Unconventional superconductivity and nearly ferromagnetic spin fluctuations in NaxCoO2 center dot gamma H2O
    K Ishida, Y Ihara, Y Maeno, C Michioka, M Kato, K Yoshimura, K Takada, T Sasaki, H Sakurai, E Takayama-Muromachi
    Co nuclear-quadrupole-resonance (NQR) studies were performed in the recently discovered superconductor NaxCoO2-yH(2)O to investigate physical properties in the superconducting (SC) and normal states. Two samples from the same NaxCoO2 were examined, a SC bilayer-hydrate sample with T-c similar to 4.7 K and a non-SC monolayer-hydrate sample. From the measurement of nuclear-spin lattice relaxation rate 1/T-1 in the SC sample, it was found that the coherence peak is absent just below T-c and that 1/T-1 is proportional to temperature far below T-c. These results, which are in qualitative agreement with the previous result by Fujimoto et al., suggest strongly that unconventional superconductivity is realized in this compound. In the normal state, 1/T1T of the SC sample shows a gradual increase below 100 K down to T-c, whereas 1/T1T of the non-SC sample shows the Korringa behavior in this temperature range. From the comparison between 1/T1T and chi(bulk) in the SC sample, the increase in 1/T1T is attributed to nearly ferromagnetic fluctuations. These remarkable findings suggest that the SC sample possesses nearly ferromagnetic fluctuations, which are possibly related to the unconventional superconductivity in this compound. The implication of this finding is discussed., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 72(12)3041 - 3044, Dec. 2003, English, Research paper (scientific journal)
  • Unconventional superconductivity and nearly ferromagnetic spin fluctuations in NaxCoO2 center dot gamma H2O
    K Ishida, Y Ihara, Y Maeno, C Michioka, M Kato, K Yoshimura, K Takada, T Sasaki, H Sakurai, E Takayama-Muromachi
    Co nuclear-quadrupole-resonance (NQR) studies were performed in the recently discovered superconductor NaxCoO2-yH(2)O to investigate physical properties in the superconducting (SC) and normal states. Two samples from the same NaxCoO2 were examined, a SC bilayer-hydrate sample with T-c similar to 4.7 K and a non-SC monolayer-hydrate sample. From the measurement of nuclear-spin lattice relaxation rate 1/T-1 in the SC sample, it was found that the coherence peak is absent just below T-c and that 1/T-1 is proportional to temperature far below T-c. These results, which are in qualitative agreement with the previous result by Fujimoto et al., suggest strongly that unconventional superconductivity is realized in this compound. In the normal state, 1/T1T of the SC sample shows a gradual increase below 100 K down to T-c, whereas 1/T1T of the non-SC sample shows the Korringa behavior in this temperature range. From the comparison between 1/T1T and chi(bulk) in the SC sample, the increase in 1/T1T is attributed to nearly ferromagnetic fluctuations. These remarkable findings suggest that the SC sample possesses nearly ferromagnetic fluctuations, which are possibly related to the unconventional superconductivity in this compound. The implication of this finding is discussed., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 72(12)3041 - 3044, Dec. 2003, English, Research paper (scientific journal)
  • Superconductivity and high-field magnetization in EuSr2RuCu2O8
    MH Fang, ZA Xu, YF Lin, GF Zhang, K Yoshimura, M Kato, K Kosuge, T Goto
    The magnetic and transport properties have been investigated by means of magnetization and resistivity measurements for EuSr2RuCu2O8 compound. It is shown that EuSr2RuCu2O8 compound exhibits ferromagnetic order of Ru moments below T-c = 130.2 K and becomes superconducting at T-c = 10 K. The fact that the magnetization increases with increasing external magnetic field and does not show the saturation even at the highest applied field 42 T indicates that the magnetic order in this compound is an itinerant-electron ferromagnetic. It is estimated that Ru exists in a mixed valance state (near Ru4.8+) between Ru4+ and Ru5+ in this compound from the estimated saturation moment value. We have discussed the ferromagnetic order by the viewpoint of a band model. (C) 2002 Elsevier Science B.V. All rights reserved., PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 386667 - 670, Apr. 2003, English, Research paper (scientific journal)
  • Superconductivity and high-field magnetization in EuSr2RuCu2O8
    MH Fang, ZA Xu, YF Lin, GF Zhang, K Yoshimura, M Kato, K Kosuge, T Goto
    The magnetic and transport properties have been investigated by means of magnetization and resistivity measurements for EuSr2RuCu2O8 compound. It is shown that EuSr2RuCu2O8 compound exhibits ferromagnetic order of Ru moments below T-c = 130.2 K and becomes superconducting at T-c = 10 K. The fact that the magnetization increases with increasing external magnetic field and does not show the saturation even at the highest applied field 42 T indicates that the magnetic order in this compound is an itinerant-electron ferromagnetic. It is estimated that Ru exists in a mixed valance state (near Ru4.8+) between Ru4+ and Ru5+ in this compound from the estimated saturation moment value. We have discussed the ferromagnetic order by the viewpoint of a band model. (C) 2002 Elsevier Science B.V. All rights reserved., PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, ELSEVIER SCIENCE BV, 386667 - 670, Apr. 2003, English, Research paper (scientific journal)
  • Magnetic properties of V-jarosite AV3(SO4)2(OH)6 (A=Na, K) with kagome lattice
    Physica B, 3293331042 - 1043, 2003
  • CuNQR study of hole doped 1D Cu chain oxide Ca0.85CuO2
    T Yokoyama, T Mitsui, M Kato, K Yoshimura
    The magnetic susceptibility and the Cu-63.65 nuclear quadrupole resonance have been measured in the quasi-one-dimensional cuprate Ca0.85CuO2 which contains edge-sharing CuO2 chains separated by Ca layers. The behaviors of the magnetic susceptibility and the Cu-63 nuclear spin-lattice relaxation rate are well explained by assuming the coexistence of an antiferromagnetic ordering and spin gap states which can be realized in the hole doped ID Cu-O chain. (C) 2002 Elsevier Science Ltd. All rights reserved., JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, PERGAMON-ELSEVIER SCIENCE LTD, 63(6-8)1111 - 1114, Jun. 2002, English, Research paper (scientific journal)
  • NMR study of Na3-xRu4O9
    H Ohno, H Sakai, M Kato, K Yoshimura
    Low-dimensional conductor Na3-xRu4O9 has been studied by means of Na-23 nuclear magnetic resonance measurement in order to clarify the electronic state of this compound. The magnetic susceptibility chi is almost constant from 100 to 300 K, then increases with temperature, and shows a kink at 584 K. The temperature dependence of the Knight shift K is almost in proportion to chi. From the result of the temperature dependence of spin-lattice relaxation time, it has been found that this compound has an energy gap, Delta, which is closely correlated with the gap-like behavior of chi. Consequently, we consider that there exists a spin-singlet state in all or a part of RuO6 chains in Na3-xRu4O9. (C) 2002 Elsevier Science Ltd. All rights reserved., JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, PERGAMON-ELSEVIER SCIENCE LTD, 63(6-8)1017 - 1019, Jun. 2002, English, Research paper (scientific journal)
  • CuNQR study of hole doped 1D Cu chain oxide Ca0.85CuO2
    T Yokoyama, T Mitsui, M Kato, K Yoshimura
    The magnetic susceptibility and the Cu-63.65 nuclear quadrupole resonance have been measured in the quasi-one-dimensional cuprate Ca0.85CuO2 which contains edge-sharing CuO2 chains separated by Ca layers. The behaviors of the magnetic susceptibility and the Cu-63 nuclear spin-lattice relaxation rate are well explained by assuming the coexistence of an antiferromagnetic ordering and spin gap states which can be realized in the hole doped ID Cu-O chain. (C) 2002 Elsevier Science Ltd. All rights reserved., JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, PERGAMON-ELSEVIER SCIENCE LTD, 63(6-8)1111 - 1114, Jun. 2002, English, Research paper (scientific journal)
  • Low-temperature structural change and magnetic anomaly in superconducting Cd2Re2O7
    Physical Review B, 661005091 - 6, 2002
  • Antiferromagnetic order in 2D-spin system Cu3B2O6
    Physical Review B, 660244281-6 , 2002
  • Magnetic properties of CuSb2-xTaxO6 with tri-rutile structure
    Jounal of Physics: Condensed Matters, 631129 - 1131, 2002
  • Thermoelectric power of the superconducting pyrochlore Cd2Re2O7
    Jounal of Physics: Condensed Matters, 14257 - 260, 2002
  • Collapse of superconductivity in the Y123/Y124 superlattice system Y2Ba4Cu7O15-d
    Journal of Physical Society of Japan, 71574 - 581, 2002
  • 23Na NMR study of Na3-xRu4O9: observation of spin-singlet formation
    Journal of Physical Society of Japan, 71350 - 352, 2002
  • Magnetic Structure of CuSb2O6
    Masaki Kato, Koji Kajimoto, Kazuyoshi Yosihmura, Koji Kosuge, Masakazu Nishi, Kazuhisa Kakurai
    We study on the magnetic structure of CuSb2O6 by means of NMR and neutron diffraction experiments. This compound has a tri-rutile type structure in which CU atoms form a square lattice. The CuSb2O6 compound was found to undergo a magnetic phase transition to a collinear order, which can be attributed to the magnetic frustration between J(1), along the edges of the square, and J(2), along the diagonal. The one-dimensional behavior above 20 K shows that the ratio of J(2)/J(1) is fairly larger than 0.5., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 71187 - 189, Jan. 2002, English, Research paper (scientific journal)
  • V-51 NMR study of the V Hollandite system, BixV8O16: spin-singlet formation below M-I transition
    Takeshi Waki, Harukazu Kato, Masaki Kato, Kazuyoshi Yoshimura
    V-51 nuclear magnetic resonance and relaxation (NMR) are reported for the Hollandite compound Bi1.77V8O16. The Hollandite system Bi1.77V8O16 exhibits metal-insulator transition (MIT) in the range of 1.72 < x <1.8. The charge and orbital orderings have been suggested to be the origin of the MIT in this system. To investigate the magnetic and electronic properties of Bi1.77V8O16 we have measured the Knight shift K and the spin-lattice relaxation rate 1/171 of V-51 NMR, which provide microscopic information below and above MIT in this system. These experiments revealed that the ground state of Bi1.77V8O16 is of spin singlet, which would be originated from the orbital ordering of the charge disproportionated vanadium cations below MIT, and that the antiferromagnetic interactions are dominant in the itinerant electronic state ahove.MIT, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 71160 - 162, Jan. 2002, English, Research paper (scientific journal)
  • Magnetic Structure of CuSb2O6
    Masaki Kato, Koji Kajimoto, Kazuyoshi Yosihmura, Koji Kosuge, Masakazu Nishi, Kazuhisa Kakurai
    We study on the magnetic structure of CuSb2O6 by means of NMR and neutron diffraction experiments. This compound has a tri-rutile type structure in which CU atoms form a square lattice. The CuSb2O6 compound was found to undergo a magnetic phase transition to a collinear order, which can be attributed to the magnetic frustration between J(1), along the edges of the square, and J(2), along the diagonal. The one-dimensional behavior above 20 K shows that the ratio of J(2)/J(1) is fairly larger than 0.5., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 71187 - 189, Jan. 2002, English, Research paper (scientific journal)
  • V-51 NMR study of the V Hollandite system, BixV8O16: spin-singlet formation below M-I transition
    Takeshi Waki, Harukazu Kato, Masaki Kato, Kazuyoshi Yoshimura
    V-51 nuclear magnetic resonance and relaxation (NMR) are reported for the Hollandite compound Bi1.77V8O16. The Hollandite system Bi1.77V8O16 exhibits metal-insulator transition (MIT) in the range of 1.72 < x <1.8. The charge and orbital orderings have been suggested to be the origin of the MIT in this system. To investigate the magnetic and electronic properties of Bi1.77V8O16 we have measured the Knight shift K and the spin-lattice relaxation rate 1/171 of V-51 NMR, which provide microscopic information below and above MIT in this system. These experiments revealed that the ground state of Bi1.77V8O16 is of spin singlet, which would be originated from the orbital ordering of the charge disproportionated vanadium cations below MIT, and that the antiferromagnetic interactions are dominant in the itinerant electronic state ahove.MIT, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 71160 - 162, Jan. 2002, English, Research paper (scientific journal)
  • Structural and magnetic phase transitions of AV(6)O(11) (A = Na, Sr, and Pb)
    H Kato, M Kato, K Yoshimura, K Kosuge
    X-ray powder diffraction experiments have been made for mixed-valence vanadium compounds of AV(6)O(11) (A = Na, Sr, and Pb) between 12 and 700 K and their magnetic susceptibility has been measured between 5 and 700 K. It was revealed that each compound of AV(6)O(11) indicates a structural phase transition at T-t = 245 K for A = Na, 320 K for A = Sr and 560 K for A = Pb. This transition is accompanied by atomic displacement, leading to the formation of triangular trimers of the V(1) atoms, which construct a two-dimensional kagome lattice in AV(6)O(11). The Curie constant C, the Weiss temperature Theta (p) and the temperature-independent susceptibility chi (0) have been obtained in two temperature regions, T < T-t and T > T-t. The abrupt reduction of C below T-t may indicate that the d-electrons of V(1) show a transition to a spin-singlet ground state at T-t., JOURNAL OF PHYSICS-CONDENSED MATTER, IOP PUBLISHING LTD, 13(41)9311 - 9333, Oct. 2001, English, Research paper (scientific journal)
  • Structural and magnetic phase transitions of AV(6)O(11) (A = Na, Sr, and Pb)
    H Kato, M Kato, K Yoshimura, K Kosuge
    X-ray powder diffraction experiments have been made for mixed-valence vanadium compounds of AV(6)O(11) (A = Na, Sr, and Pb) between 12 and 700 K and their magnetic susceptibility has been measured between 5 and 700 K. It was revealed that each compound of AV(6)O(11) indicates a structural phase transition at T-t = 245 K for A = Na, 320 K for A = Sr and 560 K for A = Pb. This transition is accompanied by atomic displacement, leading to the formation of triangular trimers of the V(1) atoms, which construct a two-dimensional kagome lattice in AV(6)O(11). The Curie constant C, the Weiss temperature Theta (p) and the temperature-independent susceptibility chi (0) have been obtained in two temperature regions, T < T-t and T > T-t. The abrupt reduction of C below T-t may indicate that the d-electrons of V(1) show a transition to a spin-singlet ground state at T-t., JOURNAL OF PHYSICS-CONDENSED MATTER, IOP PUBLISHING LTD, 13(41)9311 - 9333, Oct. 2001, English, Research paper (scientific journal)
  • (23)NA-NMR study in NAV(6)O(11)
    H Kato, M Kato, K Yoshimura, K Kosuge
    A mixed valent vanadium compound NaV6O11 shows a magnetic phase transition at T-t = 245 K. For the microscopic investigation of the transition at T-t, Na-23-NMR measurements from 70 K to 300 K were carried out on NaV6O11. The Knight shift, K, and the nuclear spin-lattice relaxation rate, 1/T-1, were measured. While 1/T-1 above T-t has an almost constant value, 1/T-1 below T-t shows a gap-type temperature dependence. This is the first direct evidence that the d-electrons at V(1) ions, which form a kagome lattice in NaV6O11, exhibit a spin-singlet ground state below T-t. The formation of the spin-singlet ground state of V(1) seems to be closely related to the frustration effect., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 70(5)1404 - 1410, May 2001, English, Research paper (scientific journal)
  • (23)NA-NMR study in NAV(6)O(11)
    H Kato, M Kato, K Yoshimura, K Kosuge
    A mixed valent vanadium compound NaV6O11 shows a magnetic phase transition at T-t = 245 K. For the microscopic investigation of the transition at T-t, Na-23-NMR measurements from 70 K to 300 K were carried out on NaV6O11. The Knight shift, K, and the nuclear spin-lattice relaxation rate, 1/T-1, were measured. While 1/T-1 above T-t has an almost constant value, 1/T-1 below T-t shows a gap-type temperature dependence. This is the first direct evidence that the d-electrons at V(1) ions, which form a kagome lattice in NaV6O11, exhibit a spin-singlet ground state below T-t. The formation of the spin-singlet ground state of V(1) seems to be closely related to the frustration effect., JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, PHYSICAL SOC JAPAN, 70(5)1404 - 1410, May 2001, English, Research paper (scientific journal)
  • Temperature induced metal-insulator transition in BixV8O16
    Journal of Physical Society of Japan, 70(2)325 - 328, 2001
  • One-dimensional magnetic behavior of CuSb2O6
    Physica B, 281282663 - 664, 2000
  • Evidence for antiferromagnetic order in Bi2Sr2CuO6 phase with stoichiometric cation composition
    M Kato, K Yoshimura, K Kosuge
    We have succeeded in synthesizing the insulating phase of Bi2Sr2CuO6+delta (Bi2201) with the stoichiometric cation composition by use of a heat treatment technique in an evacuated tube with titanium powders. The excess oxygen content delta and the average valence of Bi were determined electrochemically by the coulometric titration method, The value of delta in the insulating phase was found to be 0.02, The hole concentration h was also estimated with values of delta and the average valence of Bi in Bi2201, As a result, temperature dependence of resistivity and It dependence of Tc and Meissner volume fraction indicated behaviors similar to those of other high-Tc systems, The antiferromagnetic order of Cu2+ spins in the insulating Bi2201 phase has been confirmed by nuclear magnetic resonance, Thus, we can obtain the three distinct electronic states observed in high-Tc oxides, i.e., over-doped metallic, superconducting, and antiferromagnetic phases in Bi2201 compounds by changing only the oxygen content, The static parameters of the hyperfine field and the electric field gradient at Cu sites in Bi2Sr2CuO6.02 were found to be almost comparable to those of other antiferromagnetic phases of high-Tc oxides. (C) 1997 Academic Press., JOURNAL OF SOLID STATE CHEMISTRY, ACADEMIC PRESS INC, 133(2)372 - 378, Nov. 1997, English, Research paper (scientific journal)
  • Effect of elemental substitutions on layered oxides Ba2CuGe2O7 with spin-spiral magnetism
    M. Kato, Y. Ueda, H. Ogawa, K. Hirota
    to be published in J. Phys.: Condens. Matter
  • Magnetic susceptibility of -carbide-type molybdenum and tungsten carbides and nitrides
    M. Kato, T. Waki, S. Terazawa, Y. Umemoto, Y. Tabata, Y. Murase, K. Hirota H Nakamura
    to be published in J. Mater. Sci.
  • Thermochemical characterization of layered cobaltate superconductors NaxCoO2•yH2O
    M. Kato, T. Ozono, K. Hirota, H. Sakurai, E. Takayama-Muromachi, H. Ohta, K. Yoshimura
    to be published in J. Mater. Sci
  • Synthesis and physical properties of pyrochlore-type oxides Bi2-xNdxRu2O7 and Pb2-xYxRu2O7 with metal-insulator crossover
    M. Kato, M. Ito, T. Aiba, K. Hirota
    to be published in J. Phys. Chem. Solids
  • Metal-insulator transition in BixV8O16: 51V NMR study
    Journal of Physical Society of Japan, 73275 - 279
  • Tl-NMR study of pyrochlore oxide Tl2Ru2O7: observation of spin-singlet formation
    Journal of Physical Society of Japan, 71422 - 424
  • Magnetic and transport properties of the solid solution system La2-xSrxMnRuO6 with double perovskite structure
    Journal of Alloys and Compounds, 317(318)136 - 140

Conference Activities & Talks

  • Synthesis and physical properties of Cu oxides with low-dimensional tri-rutile and α-PbO2 type structure
    KATO Masaki
    International and Interdisciplinary Workshop on Novel Phenomena in Integrated Complex Sciences: from Non-living to Living Systems, 2010
  • Crossover from metallic to semiconducting behaviors in Pb2-xLnxRu2O7- (Ln = Eu, Lu, Y) compounds with pyrochlore structure
    KATO Masaki
    7th Joint Symposium between Doshisha University and Chonnam National University, 2010
  • Synthesis and magnetic properties of Cu oxides with low-dimensional structure
    KATO Masaki
    7th Joint Symposium between Doshisha University and Chonnam National University, 2010
  • Physical Properties of Elementally Substituted Ruthenates with Pyrochlore-type Structure
    KATO Masaki
    International Conference on Strongly Correlated Electron Systems (SCES2010), 2010
  • Simultaneous Synthesis and Sintering of Al2O3/Mo2N Composites Using Capsule-free Nitrogen Hot Isostatic Pressing and their Characterization
    KATO Masaki
    CIMTEC2010, 2010
  • Unconventional Superconductivity and Strongly Correlated Electron Behaviors in Layered Transition Metal Oxides
    KATO Masaki
    6th Joint Symposium between Chonnam National University and Doshisha University, 2008
  • Crossover from Metallic to Semiconducting in Pb2-xLnxRu2O7- (Ln = Sm, Eu) Compounds with Pyrochlore Structure
    KATO Masaki
    The 10th International Symposium on Multiscale, Multifunctional and Functionally Graded Materials, 2008
  • Mechanical Properties of Simultaneously Synthesized and Consolidated Carbon Nanofiber (CNF)-Dispersed B4C Composites by Pulsed Electric-Current Pressure Sintering
    KATO Masaki
    6th International Conference on Inorganic Materials, 2008
  • Fabrication of carbon nanofiber (CNF)/SiAlON composites by pulsed electric-current pressure sintering and their mechanical and electrical properties
    KATO Masaki
    MS&T '07 (Materials Science and Technology '07), 2008, Detroit
  • Simultaneous synthesis and consolidation of carbon nanofiber (CNF)-dispersed composites by spark plasma sintering (SPS)
    KATO Masaki
    7th Pacific Rim Conference on Ceramic and Glass Technology, Shanghai International Convention Center, 2007, Shanghai, China
  • Metal-Insulator transition in Pb2-xLnxRu2O7- (Ln = Sm, Eu) compounds
    KATO Masaki
    The International Conference on Strongly Correlated Electron Systems, 2007, Houston, USA
  • Simultaneous Synthesis and Consolidation of W-Added ZrB2by Pulsed Electric Current Pressure Sintering and Their Mechanical Properties
    KATO Masaki
    The Sixth Pacific Rim International Conference on Advanced Materials and Processing, ICC Jeju Island, Korea

Research Grants & Projects

  • Synthesis and Physical Properties of Low-dimensional Transition-metal compounds
    Basic Science Research Program, 2004 -2009

Research Seeds

  • Synthesis of transition-metal compounds with novel physical properties based on strongly-correlated electrons
    Research Fields: Chemicals, Nanotechnology and Materials, Environment and Energy, Electric and Electronics, Machinery and Measuring Equipment
    Affiliation/Name: Masaki Kato