Katsuro Oda

Local interactions in carbon-carbon and carbon-M (M: Al, Mn, Ni) atomic pairs in FCC gamma -iron

Mossbauer spectra of Fe-8.0 at.%C, Fe-10.9 at.%Al-8.2 at.%C, Fe-1.4 at.%Mn-7.9 at.%C, Fe-2.4 at.%Mn-7.8 at%C and Fe-14.6 at.%Ni-6.2 at.%C FCC gamma -irons have been measured in order to investigate the distribution and the local interactions of C in the lattice. The local interaction energies in nearest and second-nearest C-C and M-C (M: Al, Mn, Ni) atomic pairs have been determined by a Monte Carlo method simulating the distribution obtained. The interaction energies in nearest and second-nearest C-C pairs are strongly repulsive, in contrast to the weak interaction in second-nearest N-N pairs. The results are compared with the interaction energies derived from activity data. The interaction in nearest Al-C pairs is repulsive but that in second-nearest pairs is strongly attractive, which can lead to the formation of the perovskite Fe3AlC-type ordering. The interaction between nearest Mn and C atoms is strongly attractive, while between Ni and C the interaction is very weak.

Interaction and arrangement of nitrogen atoms in FCC γ-iron

A Mossbauer effect measurement of 57Fe has been performed for the Fe-N austenite in order to study the interaction between nitrogen atoms and the distribution among the octahedral sites of the FCC lattice. The spectrum for Fe-N austenite is decomposed into one singlet gamma 0 and two sets of doublets gamma 1 and gamma 2 which are identified as being caused by iron atoms with different configurations of nitrogen atoms at the nearest-neighbour sites. The fractional intensities for the three components are precisely determined by taking into account the effect of the absorber thickness. It is concluded from the analysis that the interaction between the first-nearest-neighbour nitrogen atoms is strongly repulsive and that between the second nearest nitrogen is weakly attractive.

Appearance of ferromagnetism in f.c.c. solid solutions of binary and ternary Fe–Cu-based systems prepared by mechanical alloying technique

Abstract The ferromagnetic f.c.c. solid solutions are formed by mechanical alloying in the Fe–Cu binary systems containing less than 60% of iron. The Curie temperature of the alloy decreases with decreasing iron concentration. The expansion of average atomic volume of the alloys is about 1.6% of pure copper and 5.3% of f.c.c. γ-iron regardless of copper content except for dilute iron alloys. It is suggested from the present work that the ferromagnetism in the Fe–Cu alloys originates when the atomic volume is expanded by a certain value (5.3% of γ-iron is enough), and when a certain number of neighboring iron atoms exist to percolate the ferromagnetic interaction and possibly to generate the magnetic moment of iron. In the studies of ternary systems silver atoms hardly dissolved in Fe–Cu solution, whereas gold atoms formed solid solution.

Photorefractive effect and photochromism in the Fe-doped relaxor ferroelectric crystal Pb(Zn1∕3Nb2∕3)O3-PbTiO3

The photorefractive properties of the iron-doped Pb(Zn1∕3Nb2∕3)O3-PbTiO3 (PZN-PT) relaxor ferroelectric single crystals were investigated by two-beam coupling experiments. The Fe:0.01wt%- and the Fe:0.1wt%-doped 0.91PZN-0.09PT single crystals were grown with the flux solution method. The Extinction spectrum, the electro-opric coefficient, the light-induced absorption change, and the photoconductivity were measured in these samples. The maximum gain coefficient reached to 21cm−1, which is about twice as large as that of undoped PZN-PT. The grating formation rate decreases with the Fe concentration.

Crystallographic texture of melt-spun AlMn based and AlLiCu icosahedral quasicrystals

The atomic structure of the icosahedral phase is characterized both by long-range icosahedral orientational order and by a quasiperiodic translational one. Because the long-range orientational order generates anisotropy, it is natural that the icosahedral phase forms a crystallographic texture during solidification through preferred growth and/or nucleation. No texture was, however, observed in melt-spun quasicrystalline Al{sub 74}Si{sub 6}Mn{sub 20} by x-ray photography and diffractometry. The present work reports the observation of textures by pole figure measurements for Al-Mn based and Al-Li-Cu quasicrystals produced by melt-spinning.

Interaction and arrangement of nitrogen and carbon atoms in fcc γ-iron

A Mössbauer effect measurement has been done for Fe−N, Fe−Al−C and Fe−Ni−C austenite in order to study the interaction between the interstitial atoms and their distribution among the octahedral sites of the fcc lattice, together with the influence of Al and Ni atoms. The spectra for Fe−N and Fe−Al−C austenite are decomposed into three components; one singlet γ0, and two sets of doublet γ1 and γ2, with different quadrupole splittings, while no γ2 component is found in the spectrum for Fe−Ni−C. By analyzing the component ratio in each spectrum, it is concluded that, in Fe−N and Fe−Al−C, the interaction between 2nd nearest neighboring nitrogen or carbon atoms is attractive, and is repulsive between 1st nearest for Fe−N, and that the interaction between 2nd nearest atoms is repulsive for Fe−Ni−C. By measuring the spectra of Fe−Ni−C in magnetic field, the sign of EFG for most of the γ1 component is determined to be negative.

Local interaction energy of carbon and nitrogen atoms in FFC γ-iron

A Mossbauer effect study has been done for Fe−C and Fe−M−C (M: Al, Mn) γ-iron. From the obtained fractional intensity of each component of spectra, the local interaction energies between carbon atoms were determined by means of Monte-Carlo simulation. The interaction energiees between carbon atoms and M atoms are also derived.

The electromagnetic effect of the Mn4+ content in LaMn1-xNixO3 (0⩽x⩽0.1)

We report on magnetic and electronic properties of ceramic LaMn1-xNixO3+α (0≤x≤0.1). The purpose of the study is to control the Mn4+ concentration by doping Ni into Mn sites and to clarify the influence on the properties of the colossal-magnetoresistance (CMR) effect. All of the samples show the CMR effect. While the x = 0 sample exhibits a metal-insulator transition, the others do not. To analyse the dependence of the Curie temperature, TC, on x, we apply a model concerning polarons associated with electronic localization. And to determine the relation between the Mn4+ concentration and the content of Ni ( = x) doped into Mn sites, we apply Varmas model. We suggest a relation between the Mn4+ concentration and x for this series in order to explain the positive dependence of the concentration on x.

A Mössbauer study of Bi2Sr2Ca n-1 (Cu, Fe) n O y (n=1,2,3) oxide superconductors

Mossbauer spectra of57Fe have been measured for Bi2Sr2Can-1(Cu, Fe)nOy (n=1,2,3) oxide superconductors. Each spectrum was decomposed to a single set or two sets of double peaks. The assignment of these peaks to the specific sites for the iron atoms are discussed. The 4 fold planar sites of Cu2O plane are preferentially substituted by Fe atoms.

Stability of ferromagnetism in FCC Fe–Cu–Au alloys prepared by mechanical alloying

Abstract We have studied the relation between the stability of ferromagnetism and the atomic volume of FCC Fe–Cu–Au alloys prepared by mechanical alloying by means of X-ray diffraction, magnetization measurement and Mossbauer effect. The atomic volume of the FCC Fe 0.5 Cu 0.5 alloy increased almost linearly with the substitution of Au atoms for Cu from original 12.09×10 −3 to 13.31×10 −3 nm 3 for 40% replacement. The Curie temperature of the alloy also increased in the same manner from 489 to 582 K. It is found that the increase in atomic volume stabilizes the ferromagnetic state of the FCC alloys. The values of magnetic moment of iron in Fe 0.5 Cu 0.4 Au 0.1 and Fe 0.5 Cu 0.3 Au 0.2 were estimated to be 2.34 and 2.44 μB, respectively, which are larger than that of α-iron (2.22 μB). The magnetic hyperfine field of iron in Fe 0.5 Cu 0.4 Au 0.1 showed wide distribution from 22 to 38 T at 82 K, which is probably caused by the variation of species of surrounding atoms of iron.