Regional Groups of Mössbauer Researchers - Japan
Reprinted from the June 2006 edition of the Mössbauer Spectroscopy Newsletter, published as part of Volume 29, Issue 6 of the Mössbauer Effect Reference and Data Journal and a Supplement published in the September 2006 edition of the Newsletter, part of Volume 29, Issue 7 of the MERDJ
Mössbauer Spectroscopy in Japan

This issue of the Newsletter features reports from 24 active Mössbauer research laboratories in Japan. The reports appear in descending order of most active Japanese institutions based on the records of the Mössbauer Effect Data Center.

Mössbauer Research Group
Radioisotope Research Center

Clockwise from top left: Misayuki Kurokuzu, Yasuhiro Nomura, Dr. Shotaro Morimoto, and Professor Tadashi Saito

Names of Researchers

  • Professor Tadashi Saito – Head of Laboratory
  • Dr. Shotaro Morimoto – Research Associate
  • Misayuki Kurokuzu – Graduate Student
  • Yasuhiro Nomura – Graduate Student

Description and Areas of Research

Upon Professor Emeritus Saboru Nasu’s retirement, the Mössbauer facilities at Osaka University were taken over by the research group of Professor Tadashi Saito in the Radioisotope Research Center. The group originally employed time differential perturbed angular correlation (TDPAC), positron-electron annihilation spectroscopy (PAS), and various radiochemical methods. Mössbauer spectroscopy has added a new feature to the group’s research. 57Fe, 119Sn, and 151Eu Mössbauer studies have been performed in the temperature range from 4.2 K to 350 K on various materials: rust-related iron oxide-hydroxides, dinuclear iron complexes, and mineral-related compounds with low-dimensional structure. Measurement under external magnetic field up to 7 T (parallel to the direction of the gamma-rays) is also available using a cryostat with a superconducting magnet. The low temperature center provides liquid helium liquefied from recovery helium gas, which is transferred through a 300-meter metal pipeline from the laboratory.

The group’s current research topics include: (1) high pressure Mössbauer studies on magnetic properties of iron nitrides and iron-nickel Invar alloys using diamond anvil cells (DAC), in collaboration with Assistant Professor Kawakami of Nihon University, especially focused on the spectrum with higher quality in statistics; and (2) high magnetic field Mössbauer studies on the charge order system of iron borate.

Nomura Group
Applied Chemistry and Radiation Safety
School of Engineering

From left: Toru Ohkubo, Cesar Barrero, Kiyoshi Nomura, Satoshi Iio, Junko Sakuma, and Yosuki Suzuki

Names and Titles of Researchers

  • Associate Professor Kiyoshi Nomura – Radioanalytical Chemistry and Applied Chemistry for Material Science
  • Dr. Cesar Barrero – Guest Researcher (Universidad de Antioquia, Colombia)
  • Mr. Toru Ohkubo – Technician
  • Mr. Satoshi Iio – Technician
  • Junko Sakuma – Graduate Student
  • Yosuke Suzuki – Student

Description and Areas of Research

The Mössbauer Group at the School of Engineering, University of Tokyo, has been working in the following areas.

Development of conversion electron and resonant X-ray Mössbauer spectroscopy (CEMS and XMS): Dual counters for CEMS and XMS have been developed to study the characterization of corrosion and surface finishing of iron and steel. Measuring 57Fe CEMS and XMS simultaneously can easily perform the layer-by-layer analysis. CEMS and XMS provide Mössbauer information of about 200 nm and 10 µm thick layers, respectively. It is possible to measure a depth selective CEMS (DCEMS) of less than 100 nm thin layers by discriminating the energy of emitted electrons even with a He+10%CH4 gas counter.

Corrosion process and structure analysis of oxide layers on iron and weathering steel by CEMS: The rust layers produced on steel surface in various solutions have been characterized by CEMS. γ-FeOOH is initially formed as a corrosion product and later Fe3O4 is formed as an intermediate layer in oxidative NO3- solutions. In addition to γ-FeOOH, green rust of Fe(OH)2 and Fe(OH)3 are formed in SO42- solutions, and β-FeOOH is additionally formed in Cl- solutions. Low temperature CEMS can distinguish these compounds easily. The samples prepared by wet corrosion process should be freeze-dried for CEMS measurement in order to detect the unstable and initial corrosion products. Both CEMS and XMS are useful for direct observation of thick rust layers on weathering steel from the viewpoints of practical layer analysis.

Structural analysis of phosphate coating on steel and black coating on steel by CEMS: Iron, zinc, and manganese phosphate coatings, among others, have been used in the automobile and other industries. The different formation processes and structures of each deposited coating have been characterized by CEMS. It was clarified that the interface between coatings and substrate can be estimated from the peak area ratio of a magnetic sextet of the substrate in addition to the analysis of iron states in many coatings. The black coating of steel, treated in hot alkaline solutions, consists of small particles of magnetite. Measuring CEMS spectra at a low temperature of 78K has done the detail analysis.

Analysis and chemical application of ultra thin layers on stainless steel and thin films of stainless steel by DCEMS: The group has studied thin oxide films on various stainless steels heated at high temperature or treated chemically. The thin layer structures have been clarified by CEMS with the help of other surface analysis tools, such as glow discharge optical spectroscopy and X-ray photoelectron spectroscopy. It is further found that oxide films on a certain stainless steel are useful as a solid-state pH sensor. It can provide the rapid response and good tolerance factor against the other cations in a solution between pH=1 and pH=13. Thin stainless steels have been prepared by DC and RF sputtering and pulsed laser ablation. It was found from the CEMS analysis that these films consist of martensite phase even if austenite steel is used as the target, and that the direction of magnetic moments on the film planes was different between films deposited by DC sputtering and by RF sputtering.

Surface analysis of soft magnetic materials and noise filters for high frequency bands: Soft magnetic material films, such as Sendust [Fe3(Si,Al)], have been analyzed by CEMS. The material is practically used as a surface cover film of magnetic memory cards. The composite polymer thick films using Sendust have been recently developed as noise filters for high frequency bands (NEC-Tokin).

Structural chemistry of perovskite for partial oxidation catalysis and for CO2 absorption: Perovskite of Co-Fe mixed oxides prepared by a sol-gel method is useful for the catalysis for oxidative coupling of methane. In this study, the group was aware of the properties for rapid absorption of CO2 at high temperature and developed CO2 absorption materials. Various A(Fe,Co)O3 perovskites with A=(Ba, Sr) or (Sr, Ca) have the possibility of controlling the absorption temperature ranges by varying the compositions. The group has also studied the mechano-chemical effect for activation of the CO2 absorbents, and it was found that the activation can be realized by pretreatment of ball milling for only five minutes. A(Fe, Mg) oxides with A=(Ba, Sr) or (Sr, Ca) also show the rapid CO2 absorptions at more than 400o C. It is considered that brownmillerite of ABO2.5 contributes a skeletal structure with lattice vibration induced by different ionic radius in site A, and the rapid absorption of CO2 is promoted due to the valence change at site B of perovskite.  

Structural chemistry of transparent semiconductors such as indium tin oxide (ITO) films by 119Sn CEMS: The electronic properties of ITO and SnO2 transparent films depend on the preparation conditions. The different properties have been clarified by characterization of tin chemical states in these films using 119Sn CEMS. The transparent semiconductors are used for solar cell electrodes. The iron oxide films formed on these semiconductors by spray pyrolysis have been clarified by 57Fe CEMS. It is found that iron oxide thin films with large grains are formed on SnO2 film, while iron oxide thin films with small grains are formed on ITO film due to chemical reaction at the interface with the solution.

Gas selectivity and sensitivity of a SnO2 based sensor: The gas sensitivity and selectivity of a SnO2 based sensor with some dopants have been studied, and the spillover effect of H2 gas has been clarified, using Pd doped SnO2 mixed with and without Ni or Mn oxides. The group has shown that gas selectivity could be directly observed by in situ CEMS using a gas flow proportional 2π counter loaded with a heater. 

Development and characterization of spintronics materials: The chemical pressure effect of double perovskite Sr1-xAx(Fe,Mo)O3 (x = 0.05, A = Ba, Ca), which shows colossal magneto-resistance, has been studied by temperature dependence Mössbauer spectrometry. The chemical pressure effect of Sr1-xAx(Ru0.5Fe0.5)O3 perovskites (x = 0.05, A = Ba, Ca) also are studied, and the spin glass behavior is directly shown by in field Mössbauer spectroscopy (in Czech). It is reported recently that the dilute magneto transparent semiconductor (DMS) of TiO2 doped with Co shows ferromagnetism at room temperature. The thin films of 57Fe doped TiO2 deposited by a pulsed laser ablation were analyzed by CEMS. CEMS is a very nice tool for characterization of micro-magnetism to consider the macro-magnetism of DMS. However, the preparation methods of spintronics materials are not well enough established at this point. The group is also developing various transparent oxide semiconductors doped with Fe using a sol-gel method.

Nuclear resonant scattering using synchrotron radiation: Phonon densities of states (DOS) on perovskite and brownmillerite have been studied by measuring nuclear inelastic scattering spectra, using synchrotron radiation at Spring-8. The temperature dependency of Mössbauer-Lamb factors can be determined directly using the inelastic scattering spectra measured. For example, the Mössbauer-Lamb factors of perovskite related oxides become small after absorption of CO2. Together with Dr. A. Rykov, who was a visiting researcher in the group, they have studied many kinds of perovskite and related oxides, and found that the soft phonons are created with the increase of oxygen defects. They are now focusing on the study of DMS materials by nuclear inelastic scattering.

The group’s publication list is available from its Web site (see above for address).

Dr. Kiyoshi Nomura collaborates with the following researchers to accomplish Mössbauer studies for material science:

  • Professor Z. Hommonay, Professor E. Kuzmann, and Professor A. Vertes – Laboratory of Nuclear Chemistry, Eotvos Lorand University, Budapest, Hungary
  • Professor M. Mashlan and Professor R. Zboril – Department of Inorganic and Physical Chemistry and Department of Experimental Physics, Palacky University, Olomouc, Czech Republic
  • Professor I. Felner – The Racah Institute of Physics, The Hebrew University of Jerusalem, Israel
  • Professor M. Takeda and Professor M. Takahashi – Department of Inorganic Chemistry, Toho University, Chiba
  • Professor S. Hasegawa and Professor S. Ohgoshi – Department of Chemistry, School of Science, The University of Tokyo, Tokyo
  • Professor K. Hashimoto – Department of Applied Chemistry, School of Engineering, The University of Tokyo, Tokyo
  • Professor T. Terai – Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, Tokyo
  • Professor Y. Yamada – Department of Chemistry, Science University of Tokyo, Tokyo
  • Professor T. Yajima – Department of Applied Chemistry, Faculty of Engineering, Saitama Institute of Engineering, Saitama
  • Professor K. Takehira – Department of Chemistry and Chemical Engineering, Graduate School of Engineering, Hiroshima University, Hiroshima
  • Dr. A. Rykov – Siberian Synchrotron Radiation Center, Novosibirsk, Russia
  • Dr. T. Ohki – Kobelco Research Institute, Inc., Koube

Mössbauer Group

International Research Center for Nuclear Material Science
Institute for Materials Research
Tohoku University

Advanced Science Research Center
Japan Atomic Energy Agency
Tokai, Ibaraki

The Mössbauer Group is a joint venture between the International Research Center for Nuclear Material Science, Institute for Materials Research, Tohoku University at Oarai and the Advanced Science Research Center of the Japan Atomic Energy Agency (JAEA) at Tokai, Ibaraki.

The Group has three Mössbauer spectrometers at Oarai and has started to measure Fe-57 and Np-237 Mössbauer effects.

Dr. Homma (left) and Dr. Aoki (right) in front of the newly installed closed-cycle cryostat for actinide Mössbauer spectroscopy.

The research group at Tohoku University consists of Professor Dr. Y. Shiokawa, Dr. Y. Homma, and Dr. D. Aoki. Professor Shiokawa’s research concerns the radiochemistry of metals, especially chemical and physical properties of actinides, and he has succeeded in preparing high quality actinide metal by electrolysis of an aqueous solution. Using a high quality single crystal actinide compound, Dr. Aoki, et al. have observed the de Haas-van Alphen effect in NpNiGa5.  Dr. Homma has started to use Fe-57 and Np-237 Mössbauer spectroscopy to investigate the physical and chemical properties of NpFeGa5.

The research subject of the group from the Advanced Science Research Center of the Japan Atomic Energy Agency is “exotic magnetism and superconductivity in new actinide compounds” and the group consists of Dr. Y. Haga (leader), Dr. A. Nakamura, Dr. E. Yamamoto, Dr. T. D. Matsuda, Dr. N. Tateiwa, Dr. H. Sakai, Dr. S. Ikeda, Professor Y. Shiokawa (guest), Professor Y. Onuki (guest), and Professor S. Nasu (guest). This group is rather new in Japan and concentrates their research on actinide science. The group has close contact with the Mössbauer group at Tokai (Dr. Nakada and Dr. Masaki). They have also a good relationship with the Institute for Transuranium Elements in Karlsruhe.

Inorganic and Radiochemistry Laboratory and Coordination Chemistry Laboratory
Department of Chemistry, Faculty of Science

Names of Researchers

  • Professor Masuo Takeda – Inorganic and Radiochemistry Laboratory
  • Professor Masashi Takahashi – Inorganic and Radiochemistry Laboratory
  • Professor Takafumi Kitazawa – Coordination Chemistry Laboratory

From left: Professor Takafumi Kitazawa, Professor Masuo Takeda, and Professor Masashi Takahashi

Description and Areas of Research

The Mössbauer activities of the group at Toho University started in 1979 with studies on the stereochemical activity of the lone pair in the Sb(III) compounds by Professor Takeda; in 1984 Dr. Takahashi joined Professor Takeda with his research. Since then, many Mössbauer spectroscopic studies using 57Fe, 119Sn, 121Sb, 127I, 155Gd, 161Dy, 166Er, 197Au, and 237Np have been carried out. The research interests are widely spread from organoheteroatom compounds to inorganic solids including organometallic complexes. The research interests have been shifting to spin-crossover compounds and f-block elements compounds.

p-Block Compounds. The research group prepared and measured 121Sb Mössbauer spectra for more than 50 Sb(III) compounds having different coordinating spheres and showed a linear relationship between isomer shifts and quadrupole coupling constants. The p character of the lone pair was found to correlate strongly with the coordination configuration. They then began investigation on the hypervalent compounds using 121Sb and 127I Mössbauer spectroscopy. They have worked on a large number of hypervalent organoantimony(V) and organoiodine(III) compounds having one and two hypervalent bonds (3c-4e bond).

Spin-Crossover Iron(II) Cyanides. In 1992 Dr. Kitazawa, who has now moved to the Coordination Chemistry Laboratory, joined the research group and soon after two-dimensional cyano coordination polymer FeNi(CN)4(py)2 was found to show spin-crossover behavior. Although to date numerous spin-crossover materials have been developed, FeNi(CN)4(py)2 is the first example of the cyano-bridged two-dimensional materials. Since then, a considerable number of two-dimensional cyano-bridged iron(II) polymer complexes have been investigated, and recently the FeL2Ni(CN)4 and FeL2Ag(CN)2 systems have been the focus.

Actinide Compounds. 237Np Mössbauer spectroscopy is a powerful tool to investigate the physicochemical properties of neptunium compounds, through which we can extract the indispensable chemical information on actinide compounds. The wide range spread in 237Np isomer shifts (more than 80 mm s–1) is well recognized and clearly correlated with the oxidation state and coordination number. Recently, the research group has collaborated with Dr. Saeki’s group at the Japan Atomic Energy Research Institute (presently the Japan Atomic Energy Agency) to find that the isomer shift for neptunyl(VI) complexes reflects the covalency; there are some contribution of 5f electrons in the NpO22+–L bond.

Lanthanide Compounds. The research group is interested in the structure and bonding of the lanthanide compounds, including Gd, Dy, and Er. A number of coordination compounds with organic chelate have been synthesized and their crystal structures have been determined. They have shown some 6s character in the Gd(III)–L bond by the 155Gd spectra on more than 30 compounds. They also have applied 155Gd spectroscopy to structural studies on Gd2O3–ZrO2 solid solutions and related system in connection with an ionic conductor and back-end process of nuclear fuel as a joint research program with Dr. Akio Nakamura of the Japan Atomic Energy Agency. They have also worked on the magnetic interactions in Er(III) complexes by 166Er spectroscopy and lattice dynamics of the Dy-Fe cyano complex using 161Dy spectroscopy.

The research group has active collaborations with several research institutions:

  • Department of Chemistry, Toho University (Professor Tomoyuki Mochida): Solid-state chemistry of biferrocene charge-transfer complexes
  • School of Medicine, Toho University, Tokyo (Professor Mikio Nakamura and Dr. Yoshiki Ohgo): Spin states in iron(III) non-planar porphyrin complexes
  • Department of Applied Science, RMIT University, Melbourne (Professor S. K. Bhargava) and School of Chemistry, Australian National University, Canberra (Emeritus Professor M. A. Bennett): Coordination chemistry of the cycloaurated complexes
  • Division of Materials Chemistry, Ruder Boskovic Institute, Zagreb, Croatia (Dr. B. Grzeta): Structural studies of nanocrystalline Sb(III)-doped SnO2 using XRD and Mössbauer spectroscopy.

Nuclear Radiation Physics Laboratory