Shotaro Morimoto

Stabilization of tetra- and pentavalent Fe ions in Fe-substituted Li2MnO3 with layered rock-salt structure

Origins of various valence states of various Fe ions above the 3+ state for 30% Fe-substituted Li2MnO3 [Li1+x(Fe0.3Mn0.7)1−xO2] with a layered rock-salt structure (R3¯m) have been investigated using magnetization measurement and Fe57 Mossbauer spectroscopy at less than 300K. The temperature dependence of magnetization data revealed that small spontaneous magnetization [1.26(9)Gcm3∕g at 5K] appeared at less than 81K and cusps were observed at 24K under both zero field and field cooling runs. Analyses of Fe57 Mossbauer spectra showed that all samples contained tetravalent (Fe4+) and pentavalent (Fe(5−δ)+) iron ions (20%–40%) along with trivalent ones. High-valence (Fe(5−δ)+) iron might be the result of Fe(3+δ)+∕Fe(5−δ)+ charge disproportionation from tetravalent iron, as in SrMn0.5Fe0.5O3. Small paramagnetic iron doublets (2%–5%) with highly negative isomer shift values (−0.5to−0.6mm∕s) were detected at less than 10K. They might be pentavalent Fe(5+δ)+ ion. The Fe(5+δ)+ ion can be stabilized under high exce...

Structure and electron density distribution of CaFeO3 in the “charge disproportionate” state

Mossbauer spectroscopy on CaFeO3 suggests a “charge disproportion” reaction of Fe4+ into Fe3+ and Fe5+ below 290 K. Crystal structure was investigated at 298 and 113 K (in “charge disproportionate” state) by using a monochromated synchrotron radiation at KEK-PF in Tsukuba. n nThe crystal structure is similar to GdFeO3 with Pbnm at 293 K. At 113 K, two kinds of nonequivalent Fe cation (which should be assigned to Fe3+ and Fe5+) form NaCl-type arrangment on Fe sub-lattice; the space group is monoclinic P21/n which is on of the sub-groups of Pbnm. On the difference Fourier map, a residual peak is observed at the center of Feue5f8O bond; this suggests the strong covalent mixing between eg(Fe) levels and 2p(O) ones. n nThe Feue5f8Oue5f8Fe bond angle in CaFeO3 is determined to be about 160°, which significantly differes from the 180° angle bonding SrFeO3. It indicates that the eg bandwidth in CaFeO3 is narrowed and that eventually the itinerant nature is suppressed. Therefore, the charge disproportion tends to occur in CaFeO3 with the decrease in temperature.

Mössbauer study of mechanically alloyed powders

Using the57Fe Mössbauer spectroscopy, the microscopic behavior of Fe powders has been investigated during and after the mechanical alloying (MA) process for Al−Fe and Ag−Fe systems. A repeated rolling method as well as a conventional ball-milling method are employed in order to understand the microscopic process of the kneading of Al and Fe powders during their MA and the resultant powders show quite similar Mössbauer spectra suggesting that the kneading by an impact between colliding balls is the same process as that of the thickness reduction by cold rolling. Mössbauer spectra show clearly the occurrence of the mutual atomic dispersion for the thermodynamically immiscible Ag−Fe system.

Charge disproportionation and magnetic properties in perovskite iron oxides

Abstract The physical properties of perovskite iron oxides are closely related to the network of FeO 6 octahedra. The charge disproportionation (2Fe 4+ →Fe 3+ +Fe 5+ ), not observed in SrFeO 3 , occurs in the oxides being cut the network of Fe 4+ O 6 octahedra, for example, by introduction of Fe 3+ by substitution La for Sr and change in the dimension by insertion of SrO layer. When Co is substituted 40% of Fe in Sr 3 Fe 2 O 7 , the magnetic order changes to ferromagnetic from antiferromagnetic and charge disproportionation is suppressed.

57Fe Mössbauer spectroscopic study of PrFe4P12

Abstract We have investigated the local electronic state of PrFe 4 P 12 at an Fe site using 57 Fe Mossbauer spectroscopy. All the 57 Fe Mossbauer spectra of PrFe 4 P 12 are a pure quadrupole pattern. The magnitude of the nuclear quadrupole splitting does not, however, show any temperature dependence at the phase transition reported by the X-ray diffraction experiment at low temperature. The present result suggests that the local symmetry around Fe atoms in PrFe 4 P 12 does not change beyond the experimental error of the 57 Fe Mossbauer spectroscopy.

Mössbauer spectroscopic study of Al deformed at high-speed

Abstract High-speed deformation of Al–0.01at.% 57 Fe at room temperature was investigated using 57 Fe Mossbauer spectroscopy. High-speed deformation performed by impact of steel block on the specimen plate, inducing rapid reduction in thickness. High-speed deformation introduces numerous defects in Al–0.01at.% 57 Fe, and mutual interactions between point defects and 57 Fe probe atoms produce a satellite component in Mossbauer spectra. Intensity of the satellite components of Mossbauer spectra arising from 57 Fe in the defect-associated state and in the precipitated second phase depends on heat-treatment performed after high-speed deformation.

57Fe Mössbauer Spectroscopic Study of Fe—B Compounds

57Fe Mossbauer measurements of Fe doped β-rhombohedral boron (β-B) were performed in the temperature range between 300 K and 4.5 K. The spectra of Fe doped β-B consist of three paramagnetic doublets at room temperature and show a magnetic ordered state below 11.8 K, the temperature of which was determined by the 57Fe Mossbauer thermal scanning method at zero Doppler-velocity. The magnitude of the hyperfine magnetic field of Fe atoms in β-B at 4.5 K is about 30 T or more according to hyperfine distribution analysis.