Shin-ichiro Kondo

Skutterudite structure and thermoelectric property in CefFe8−xCoxSb24 (f = 0–2, x = 0–8)

The skutterudite structure and thermoelectric properties of CefFe8−xCoxSb24 were investigated by means of X-ray diffraction (XRD) experiments, energy-dispersive X-ray (EDX) measurements under a transmission electron microscope, and measurements of the thermoelectromotive force. The filling number of Ce into voids in the skutterudite (f) is variable at each substitution number of Fe by Co (x) and decreases with increasing x. The four-cornered ring of Sb tends to become square more rapidly with increasing f than with increasing x. The lattice parameter increases with increasing f, whereas it decreases with increasing x. The sign of the thermoelectromotive force depends on x for f 1. The type of semiconductor changes at a critical valence electron density of 194/nm3.

Mössbauer effect of Co- or Mn-doped β-FeSi2

Abstract The Mossbauer effect of 57Fe in transition metal (Co or Mn)-doped β-FeSi2 was measured at room temperature so as to examine the local atomic structure around iron atoms. From the analysis of Mossbauer spectra, it is disclosed that (1) many vacancies exist in site I in undoped β-FeSi2; and (2) Mn atoms occupy I sites in β-FeSi2 whereas Co atoms occupy II sites. Isomer shifts of I sites and II sites in Co- or Mn-doped β-FeSi2 are found to be greater than those in β-FeSi2.

Diffusion of copper, aluminum and boron in nickel

Secondary ion mass spectroscopy (SIMS) is a valuable technique for analyzing the distributions of solutes which diffused from the surface to the interior side of metals. The high resolution of SIMS can determine small diffusion coefficients below 10[sup [minus]12] cm[sup 2]/s observed at low temperature, and also measure the diffusion coefficients of various solutes including aluminum and boron isotopes which are not easily available. By means of a radioactive tracer technique, the diffusion coefficients of various solutes in nickel have been measured only at temperature higher than 0.7T[sub m], where T[sub m] is the melting temperature of nickel. With the benefit of SIMS, the present paper investigates the diffusion coefficients of copper, aluminum and boron in the blocks and the melt-spun ribbons of nickel from 0.7T[sub m] to 0.36T[sub m].

Mössbauer studies of Cr- or Ni-doped β-FeSi2

Abstract Iron disilicide β-FeSi2 has two iron siites (site I and site II) with an equivalent number of atoms in the unit cell. We estimated the occupation ratio of iron between the two sites when 2 at.% Cr or Ni is doped in β-FeSi2. It is found that the amplitude of site I is greater than that of site II in Ni doped β-FeSi2 whereas the amplitude of site I is smaller than that of site II in Cr-doped β-FeSi2. These results indicate that Ni atoms occupy site II while Cr atoms occupy site I preferentially. The increase in the isomer shift for each sites is observed in Ni-doped β-FeSi2, implying that Ni doping causes enhancement of 3d-screening of 57Fe nuclei.

Thermoelectric properties of Cu-Sn-S

X-ray diffraction patterns and thermoelectric properties were measured on Cu-Sn-S compacts with Cu:Sn:S = x:1:4 (x = 4 ∼ 12) compositions. The crystal structures of the compacts were Cu4SnS4 for x = 4, Cu2S + Cu1.81S for x = 6, Cu2S + Cu1.81S + Cu3Sn for x = 8, Cu2S + Cu41Sn11 + Cu3Sn for x = 10, Cu2S + Cu41Sn11 for x = 12. A compact having the largest power factor and figure of merit was the one of x = 8. The dimensionless figure of merit of this compact was evaluated to be 0.4 ∼ 0.6 at 300 ∼ 370 K and 0.6 at 370 ∼ 570 K. The Cu-Sn-S compact of x = 0.8 is prospective for thermoelectric energy conversion technology.

Magnetic analysis of rapidly quenched LaFe alloys : a ferromagnetically coupled ferromagnetic cluster system. I: Experimental results

LaFe alloys of 1-25 at.% Fe were rapidly quenched from the melt and investigated magnetically. alpha -Fe was not detected in the alloys with less than 12% Fe. It was concluded that the alloys are composed of small ferromagnetic clusters dispersed in a non-magnetic matrix of beta -La and coupled with each other to form a ferromagnet as a whole below about 250 K. Ferromagnetism in a cluster disappeared at around 400 K, suggesting the formation of a metastable intermetallic compound unknown so far. The existence of non-magnetic Fe atoms dissolved in beta -La was detected in the 1% Fe alloy. Annealing at 400 degrees C for 30 min changed the cluster to antiferromagnetic at room temperature, indicating the existence of another intermetallic compound. Except for the absolute magnitude of the magnetization, the magnetic properties of the alloys did not depend on the Fe concentration. The quenching process of the alloys is discussed based on this fact.

Effect of Cr addition on magnetization of Cu‐Co alloy

The magnetic behavior of Cu97.7Co2Cr0.3 and Cu97Co2Cr1 alloys was examined in order to investigate the effect of Cr addition to the magnetization of the alloy and prove the presence of Cr atoms in the magnetic clusters. The magnetization of the Cu‐Co‐Cr alloys is strongly influenced by the amount of Cr added to Cu‐Co‐Cr alloys. Further, the results indicate there are Cr atoms in the magnetic clusters. The magnetic moment of the cluster was calculated from the experimental data. The results illustrate that the value of the magnetic moment is dependent on the Cr concentration in the noted alloys and this supports the presence of Cr atoms in the magnetic cluster.

Configurations of Pt and Mn in iron disilicides

Abstract The configurations of Pt and Mn atoms in the semiconductors Fe0.97Pt0.03Si2 and Fe0.97Mn0.03 Si2 with the β-FeSi2 structure were determined by using the method of atom location by channeling enhanced microanalysis. Both Pt and Mn atoms in the semiconductors were confirmed to occupy preferably Fe sites, since the intensities of characteristic X-rays emitted from the Fe, Pt, and Mn atoms were notably stronger in a dynamical condition than in a quasikinematical condition. The occupation probabilities of Pt atoms were 0.030 ± 0.002 on Fe sites and 0.000 ± 0.001 on Si sites, the occupation probabilities of Mn atoms being 0.028 ± 0.004 on Fe sites and 0.001 ± 0.002 on Si sites.

Influence of Band Width on the Scattered Ion Yield Spectra of a He+ Ion by Resonant or Quasi-Resonant Charge Exchange Neutralization

The influence of the band structure, especially the bandwidth, on the scattered ion yield spectra of a He + ion by the resonant or quasi-resonant neutralization was theoretically examined using quantum rate equations. When calculating the scattered ion yield spectra of He + to simulate the experimental data, we observed that the band structure, especially the bandwidth, had a strong influence on the spectra at relatively low incident He + ion energies of less than several hundred eV. Through many simulations, it was determined that theoretical calculations that include bandwidth calculation can simulate or reproduce the experimentally observed spectra of He + –In, He + –Ga, and He + –Sn systems. In contrast, simulations not including bandwidth simulation could neither reproduce nor account for such spectra. Furthermore, the calculated ion survival probability (ISP) at low incident ion energies tended to decrease with increasing bandwidth. This decrease in ISP probably corresponds to the relatively small s...

Molecular orbital calculations on iron disilicide β-FeSi2

Ab initio molecular orbital calculations were performed on two types of FeSi8 clusters forming crystalline β-FeSi2 to examine electronic states. Mulliken population analysis on both clusters shows that d-s hybridized orbitals are predominant at a low energy level and d-p hybridized orbitals gradually become predominant with increase in energy. Since d-p hybridized states close to the highest occupied MO (HOMO) level are found to be π-type antibonding for both clusters, d-p antibonding states between Fe and Si atoms are assumed to be formed near the Fermi level in actual crystalline β-FeSi2.