Takao Morimura

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].

Partially filled skutterudite structure in CefFe8-xNixSb24

Abstract Observation of a Ce–Fe–Ni–Sb system with a partially filled skutterudite structure was performed using high-resolution transmission electron microscope imaging. Multislice high-resolution transmission electron microscopy image simulation was satisfactorily performed using the number of Ce atoms filling in voids and the lattice coordinates of Sb atoms as determined from X-ray measurements. The simulated images depend on these structural parameters.

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.

Magnetic properties and microstructure of Sm-Co/α-Fe nanocomposite thick film-magnets composed of multi-layers over 700 layers

We synthesized Sm-Co/α-Fe nanocomposite film-magnets, approximately 10 μm in thickness, composed of 780 layers by the pulse laser deposition method. Transmission electron microscopic observations revealed that the synthesized film is composed of Sm-Co and α-Fe layers with the well-controlled α-Fe thickness of approximately 10–20 nm, which is suitable one predicted by the micromagnetic simulation. In spite of the enhanced interlayer diffusion of Fe and Co by annealing for crystallization, the (BH)max value of 100 kJ/m3 was obtained at the averaged compositions of Sm/(Sm + Co) = 0.16 and Fe/(Sm + Co + Fe) = 0.47. The α-Fe fraction for obtaining the highest (BH)max value was smaller than that expected from the micromagnetic simulation. Although the annealing for crystallization lay the easy direction of magnetization in the plane, the film is not expected to have strong crystallographic texture.

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.

Phase equilibria of L10-type order in Cu-Au-Pd and Cu-Au-Ni ternary systems

Abstract The IKL-ALCHEMI (intersecting Kikuchi-line-atom-location by electron channeling-enhanced X-ray microanalysis) method of electron diffraction was employed to study the atomic configuration in L10-type ordered phases in Cu-Au-Pd and Cu-Au-Ni ternary alloys annealed at 573 K. In the L10 phase of Cu-Au-Pd, Au and Pd atoms tend to share the same sublattice, while Cu atoms prefer the other sublattice. If the sum of Au and Pd contents exceeds 50 at.%, most Pd atoms still remain on the favourite sites, while excess Au atoms are driven to the opposite sublattice. In the ordered Cu-Au-Ni alloys, Ni atoms weakly prefer the Cu sublattice rather than the other for Au, but the distribution of Ni atoms depends on the alloy composition. Most Ni atoms reside on the Cu sublattice when the Au content is 50 at.%, while about two thirds of Ni atoms are found on the Au sublattice in the alloy with 50 at.% Cu. The cluster variation method (CVM) in the tetrahedral approximation explains well not only the experimental re...

Phase transformation in a dental PdCuGa alloy

Abstract Phase transformation behavior in a dental PdCuGa alloy was studied by means of hardness tests, electrical resistivity measurements, X-ray diffraction and transmission electron microscopy. Annealing at 673 K produces two hardness peaks which correspond to the formation of a metastable phase with ordered fet structure and the precipitation of the equilibrium phases, α1(fcc) + α2(fcc) + Pd2Ga (orthorhombic), respectively. On the other hand, annealing at 873 K exhibits only one peak due to the precipitation of the equilibrium phases. The difference of the phase transformation between both annealings is interpreted in terms of the free energy.

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.