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Yukio Hinatsu - One of the best experts on this subject based on the ideXlab platform.

  • Magnetic ordering of divalent europium in double perovskites Eu2LnTaO6 (Ln = rare earths) Magnetic interactions of Eu2+ ions determined by magnetic susceptibility, specific heat, and 151Eu Mössbauer Spectrum measurements
    Journal of Solid State Chemistry, 2011
    Co-Authors: Yoshitaka Misawa, Yoshihiro Doi, Yukio Hinatsu
    Abstract:

    Structures and magnetic properties of double perovskite-type oxides Eu{sub 2}LnTaO{sub 6} (Ln=Eu, Dy-Lu) were investigated. These compounds adopt a distorted double perovskite structure with space group P2{sub 1}/n. Magnetic susceptibility, specific heat, and {sup 151}Eu Moessbauer Spectrum measurements show that the Eu{sup 2+} ions at the 12-coordinate sites of the perovskite structure are antiferromagnetically ordered at {approx}4 K, and that Ln{sup 3+} ions at the 6-coordinate site are in the paramagnetic state down to 1.8 K. - Graphical abstract: Magnetic properties of double perovskite-type oxides Eu{sub 2}LnTaO{sub 6} (Ln=Eu, Dy-Lu) were investigated. Magnetic susceptibility, specific heat, and {sup 151}Eu Moessbauer Spectrum measurements show that the Eu{sup 2+} ions at the 12-coordinate sites of the perovskite structure are antiferromagnetically ordered at {approx}4 K. Highlights: > Crystal structures of double perovskites Eu{sub 2}LnTaO{sub 6} (Ln=rare earth) were determined. > We found that these compounds show an antiferromagnetic ordering at {approx}4 K. > The magnetic ordering is due to the interactions of Eu{sup 2+} ions. > It was elucidated by specific heat and {sup 151}Eu Moessbauer Spectrum measurements.

  • A Study of the Magnetic and Thermal Properties of Ln
    Journal of Solid State Chemistry, 2001
    Co-Authors: Daijitsu Harada, Yukio Hinatsu
    Abstract:

    Crystal structures, and magnetic, electric, and thermal properties of fluorite related compounds Ln{sub 3}RuO{sub 7} (Ln=Sm, Eu) have been investigated. For Eu{sub 3}RuO{sub 7}, a magnetic transition due to Ru{sup 5+} ions is found at T{sub N}=22.5 K on the susceptibility-temperature curve. Specific heat measurements also exhibit a {lambda}-type anomaly at the same temperature. The Moessbauer Spectrum measured at 10 K shows broadening of the line corresponding to magnetic splitting. For Sm{sub 3}RuO{sub 7}, two magnetic anomalies have been observed at 10.5 and 22.5 K from its magnetic susceptibility measurements. Below 22.5 K Ru{sup 5+} ions are antiferromagnetically coupled, and when the temperature is decreased through 10.5 K the ordering of Sm{sup 3+} ions occurs rapidly. Specific heat measurements show first-order transition peaks at T=280 and 190 K for Eu{sub 3}RuO{sub 7} and Sm{sub 3}RuO{sub 7}, respectively. T he results of magnetic susceptibility and electric resistivity measurements indicate that these transitions are structural phase transitions.

  • Magnetic Properties of Layered Perovskites NaLnTiO4(Ln=Sm, Eu, and Gd)
    Journal of Solid State Chemistry, 1998
    Co-Authors: Keitaro Tezuka, Yukio Hinatsu, Nobuyuki M. Masaki, Masakatsu Saeki
    Abstract:

    The magnetic properties of the layered perovskite compounds NaLnTiO{sub 4} (Ln = Sm, Eu, and Gd) are reported. Their dc susceptibilities were measured from 4.5 to 320 K. The Moessbauer Spectrum of {sup 151}Eu and the electron paramagnetic resonance (EPR) Spectrum of Gd{sup 3+} were also measured at room temperature. NaEuTiO{sub 4} shows Van Vleck paramagnetism which corresponds to the singlet ground state {sup 7}F{sub 0} of Eu{sup 3+} ions, with a spin-orbit coupling constant {lambda} = 323 cm{sup {minus}1}. NaSmTiO{sub 4} also behaves as a Van Vleck paramagnet. The magnetic susceptibility of NaGdTiO{sub 4} follows the Curie law. The Moessbauer Spectrum of NaEuTiO{sub 4} clearly shows that Eu is in the trivalent state, and a quadrupole interaction is found to exist in this compound. From the EPR measurement the g value of Gd{sup 3+} in NaGdTiO{sub 4} is determined to be 1.99. Both the magnetic susceptibility results and the EPR measurements show that Gd{sup 3+} ion in this compound is scarcely affected by the crystal field.

Larry O. Spreer - One of the best experts on this subject based on the ideXlab platform.

  • Characterization of a delocalized mixed-valence bis-macrocyclic diiron compound
    Inorganic Chemistry, 1994
    Co-Authors: Larry O. Spreer, D. B. Macqueen, Christian B. Allan, J. W. Otvos, Melvin Calvin, Richard B. Frankel, G. C. Papaefthymiou
    Abstract:

    A mixed-valence Fe[sup II]/Fe[sup III] compounds has been obtained by electrochemical oxidation of a bis-macrocyclic Fe[sup II]/Fe[sup III] complex. The binucleating ligand provides a delocalized [pi] system that facilitates electronic interaction between the metals. The Moessbauer Spectrum of the mixed-valence compound consists of a single quadrupole-split doublet down to 4 K which establishes the equivalency of the two iron atoms. The cyclic voltammogram of the Fe[sup II]/Fe[sup III] species in rigorously dried acetonitrile shows two reversible oxidations with [Delta]E[sub 1/2] = 500 mV. This corresponds to a comproportionation constant for the mixed-valence compound of 10[sup 11]. This large value also indicates the mixed-valence species is valence-averaged class III and is stabilized by delocalization. The mixed-valence compound has an intense near-infrared band ([lambda][sub max] = 940 nm, [epsilon] = 27 000 M[sup [minus]1] cm[sup [minus]1]). Analysis of this band using Hush's equations for an intervalence transition also indicates the system is delocalized.

  • Spectroscopic and Electrochemical Characterization of a Bis-Macrocyclic Diiron Compound
    Inorganic Chemistry, 1994
    Co-Authors: H. S. Mountford, D. B. Macqueen, J. W. Otvos, Melvin Calvin, Richard B. Frankel, Larry O. Spreer
    Abstract:

    The properties of the complex [Fe[sub 2](C[sub 20]H[sub 36]N[sub 8])(CH[sub 3]CN)[sub 4]](ClO[sub 4])[sub 4] have been extensively investigated by optical and Moessbauer spectroscopy as well as by electrochemistry. The binucleating ligand TIED (tetraiminoethylene dimacrocycle) is an exceptionally good [pi] acceptor as indicated by the Moessbauer Spectrum, which shows a low value for the center shift and a high value for the quadrupole splitting parameter. This behavior is consistent with the unusually high value for the first oxidation potential (1.18 V vs NHE) since Fe[sup 2+] is a much better [pi] donor than Fe[sup 3+]. Also, extensive back-bonding from iron to an unoccupied [pi]* orbital of the ligand may help produce the very short Fe-N(imine) distance of 1.89 [angstrom] that was found in the complex. Electrochemical oxidation apparently occurs at the metal centers, since the potential shows a large solvent dependence, which is attributed to axial ligand exchange by coordinating solvent molecules. Electrochemical reduction, while formally occurring at the ligand, shows indications of extensive mixing of ligand and metal orbitals. There is a change from two, well-separated one-electron reductions in CH[sub 3]CN to closely overlapping reductions in DMF and H[sub 2]O. Another indication of orbital mixing is the fact that substitutionmore » of Ni for Fe in the complex causes a large shift of 780 mV in the first ligand reduction potential.« less

G. C. Papaefthymiou - One of the best experts on this subject based on the ideXlab platform.

  • Characterization of a delocalized mixed-valence bis-macrocyclic diiron compound
    Inorganic Chemistry, 1994
    Co-Authors: Larry O. Spreer, D. B. Macqueen, Christian B. Allan, J. W. Otvos, Melvin Calvin, Richard B. Frankel, G. C. Papaefthymiou
    Abstract:

    A mixed-valence Fe[sup II]/Fe[sup III] compounds has been obtained by electrochemical oxidation of a bis-macrocyclic Fe[sup II]/Fe[sup III] complex. The binucleating ligand provides a delocalized [pi] system that facilitates electronic interaction between the metals. The Moessbauer Spectrum of the mixed-valence compound consists of a single quadrupole-split doublet down to 4 K which establishes the equivalency of the two iron atoms. The cyclic voltammogram of the Fe[sup II]/Fe[sup III] species in rigorously dried acetonitrile shows two reversible oxidations with [Delta]E[sub 1/2] = 500 mV. This corresponds to a comproportionation constant for the mixed-valence compound of 10[sup 11]. This large value also indicates the mixed-valence species is valence-averaged class III and is stabilized by delocalization. The mixed-valence compound has an intense near-infrared band ([lambda][sub max] = 940 nm, [epsilon] = 27 000 M[sup [minus]1] cm[sup [minus]1]). Analysis of this band using Hush's equations for an intervalence transition also indicates the system is delocalized.

Jin-ho Choy - One of the best experts on this subject based on the ideXlab platform.

  • A Study of the Nonstoichiometry and Physical Properties of the Perovskite Nd1-xCaxFeO3-y System
    Journal of Solid State Chemistry, 1995
    Co-Authors: Ile Young Jung, Kwang Hyun Ryu, Kwang-sun Ryu, Jin-ho Choy
    Abstract:

    A series of samples of the perovskite Nd{sub 1-x}Ca{sub x}FeO{sub 3-6} system with the compositions x = 0.00, 0.25, 0.50, 0.75, and 1.00 has been prepared at 1150{degrees}C under atmospheric air pressure. In the perovskite system, the X-ray powder diffraction patterns assign the compositions x = 0.00 and 0.25 to the orthoferrite-type orthorhombic system, the composition x = 0.50 to the cubic system, and the compositions x = 0.75 and 1.00 to the brownmillerite-type orthorhombic system. The mole ratio of Fe{sup 4+} ions to total Fe ions, or {tau} value, has been determined and identified by Mohr salt titration and Moessbauer spectroscopic analysis. Except for the compositions x = 0.00 and 1.00, the samples contained the mixed valence state between Fe{sup 3+} and Fe{sup 4+}, and the composition x = 0.50 had the maximum {tau} value. Nonstoichiometric chemical formulas of the system are formulated from the x, {tau}, y values. The Moessbauer Spectrum of x = 0.50 exhibits a sharp peak due to rapid electron transfer between the Fe{sub 3+} and Fe{sub 4+}. The electrical conductivity increases with the number of Fe{sup 4+} ions because the e{sub g}-electron hole of the Fe{sup 4+} ion acts as a positive hole. Sincemore » the Fe{sup 4+} ions decrease the magnitude of the antiferromagnetic interaction of Fe{sup 3+} -O{sup 2-}-Fe{sup 3+}, the Neel temperature of the system decreases with increasing values of {tau}.« less

J. R. Dahn - One of the best experts on this subject based on the ideXlab platform.

  • In Situ Mössbauer Effect Studies of the Electrochemical Reaction of Lithium with Mechanically Alloyed Sn2Fe
    Journal of The Electrochemical Society, 1998
    Co-Authors: Ou Mao, R. A. Dunlap, Ian A. Courtney, J. R. Dahn
    Abstract:

    A convenient cell design for in situ {sup 57}Fe Moessbauer spectroscopy studies of electrodes for Li batteries is described. The reaction of lithium with Sn{sub 2}Fe is studied using this cell. During the first discharge of Li/Sn{sub 2}Fe cells, the cell reaction is 8.8 Li + Sn{sub 2}Fe {r_arrow} 2Li{sub 4.4}Sn + Fe, where the Fe regions which are formed are located at the interfaces between Li-Sn alloy grains, and give a Moessbauer Spectrum characterized by a doublet. If the cell is held in the discharged state (0 V vs Li) for 2 weeks, the Fe regions grow in size and a singlet (superparamagnetic) Spectrum results. This Spectrum splits into the six-line Spectrum characteristic of ferromagnetic iron if the sample is cooled below its blocking temperature (less than 30 K) to 4.2 K, indicating Fe grains of at most 3 nm in size. During the first charge (removing Li from the Li-Sn alloys) there is little change in the {sup 57}Fe Moessbauer Spectrum until almost all of the Li is removed, at which point the liberated Sn atoms begin to back react with Fe to form Sn{sub 2}Fe again. This back reaction begins at about 0.63 V vs. Li, atmore » which potential there is a two-phase region wherein Li{sub 2}Sn{sub 5} and Sn are present. Not all of the Fe can react with Sn, because the original Spectrum of the Sn{sub 2}Fe starting material is not recovered. Instead some Fe atoms, presumably at the centers of larger grains, remain as Fe. As the cell is cycled consecutively, the size of the Fe grains grows and grows, until by cycle five, the six-line Moessbauer Spectrum of ferromagnetic iron is observed even at room temperature in both the charged and discharged states, indicating Fe grains of at least 10 nm. Concurrently, the differential capacity and voltage profile of the electrode resemble those of a Li/Sn cell, indicating that the majority of the Fe atoms are not involved in the back reaction during charge after several cycles.« less