Kakuei Matsubara

Effects of doping on the transport properties of CoSb3

Effects of doping on the transport properties of CoSb3 have been systematically investigated using Ni, Pd, and Pt as donor impurities. It is shown that the Hall mobility, the Seebeck coefficient, and the electrical conductivity depend strongly not only on the carrier concentration but also on these donor impurities. Our theoretical analysis suggests that the electron effective mass and the conduction band deformation potential are significantly affected by both the doping levels and the donor impurities. These doping effects in CoSb3 can be attributed to (1) the changes in the electronic structure with doping and (2) the specific nature of the conduction band structure, in particular, the nonparabolicity of the band which can be explained in terms of a two-band Kane model. The observed changes in the electronic properties with doping are also consistent with the predictions of a recent band structure calculation of CoSb3. On the other hand, the lattice thermal conductivity decreases markedly with increasi...

Structural and electronic transport properties of polycrystalline p-type CoSb3

The structural and electronic transport properties of polycrystalline p-type CoSb3 with different grain sizes (about 3 and 3×102u2009μm) were investigated. The magnetic susceptibility was also measured. Samples were characterized by x-ray diffractometry, electron-probe microanalysis, and optical microscope observation. Samples were found to be stoichiometric and homogeneous. The Hall carrier concentration of the samples is of the order of 1018u2009cm−3 and weakly dependent on the temperature. The temperature dependence of the Hall mobility suggests that the predominant scattering mechanism drastically changes depending on grain size: for large grain size a combination of the neutral impurity scattering and the acoustic phonon scattering, and for small grain size the ionized impurity scattering. The magnetic susceptibility was found to be essentially diamagnetic independently of grain size, and to vary slightly with temperature. The weak temperature dependence of the susceptibility can be explained by taking into ...

Development of a high efficient thermoelectric stack for a waste exhaust heat recovery of vehicles

The development of a high efficiency thermoelectric (TE) stack, which is a united system of thermoelectric modules and a heat exchanger, has been made to advance the applications of electrical power generation to vehicles. The thermoelectric materials under investigation are mostly heavily doped CoSb/sub 3/ and filled skutterudites RM/sub 4/Sb/sub 12/ (R= Ce, Yb,; M=Co, Fe, Ni, Pt, Pd). In order to maximize the conversion efficiency of the devices operating in the 350-750/spl deg/C temperature range, the p-, n-legs segmented with the skutterudites and state-of-the-art Bi/sub 2/Te/sub 3/ have been used to build the devices. We could obtain valuable data showing a validity of installing the thermoelectric stack in vehicles, but a few of problems to be solved in a practical level still remain.

Electronic transport properties of the Skutterudite CoSb 3 and mixed alloys

We present some results on physical and electrical properties of the Skutterudites CoSb/sub 3/ and mixed alloys. Most of samples measured were polycrystalline, which have been prepared by hot-pressing of powders under 10/sup 7/ Pa at /spl sim/650/spl deg/C and /spl sim/750/spl deg/C, and a few measurements on CoSb/sub 3/ single crystals were performed. We report some results of the Hall mobility, Seebeck coefficient and electrical conductivity measurements on CoSb/sub 3/ and mixed alloys. Based on the experimental results, we make clear important factors which have influence on the electronic transport properties, in particular, on the Hall mobility of the materials.

Preparation of Cu–O Films by Sputtering Using He Gas

Cu-O films have been deposited by rf sputtering using a mixture of Ar, He and O 2 as a sputtering gas. When He was mixed with the sputtering gas, highly oxidized Cu-0 films were obtained with low O 2 content of the sputtering gas, compared with those deposited without He. Activated particles in the plasma were investigated by optical emission spectroscopy analysis. This enhancement of oxidation of Cu-O films is related to an increase in O 2 + and O * generated through the Penning ionization process by He m in neutral excited metastable states

Electron tunneling experiments on skutterudite Co1−xFexSb3 semiconductors

Electron tunneling experiments were performed on p-Co1−xFexSb3–Al-oxide–Al junctions for x=0 and x=0.1 at 4.2 K. A U-shaped tunneling conductance curve obtained for polycrystalline p-CoSb3 clearly shows an energy-band gap of ∼50 meV. For p-Co0.9Fe0.1Sb3 skutterudites, a strong zero-bias conductance anomaly is observed. This anomaly may be due to a structural disorder arising from defects such as vacancies and interstitial Fe atoms.

The Performance of a Segmented Thermoelectric Convertor Using Yb-Based Filled Skutterudites and Bi 2 Te 3 -Based Materials

This paper reports an overview of the current state in our research program started in 1995 in collaboration with industries. This program has been aimed at making sure of the feasibility of a thermoelectric convertor for waste heat recovery of gasoline engine vehicle. Major results obtained include: (1) updated ZT -values for Pd,Pt-doped CoSb 3 and partially Yb-filled skutterudite antimonides Yb y M 4 Sb 12 (M=Co, Fe, Ni; 0 2 Te 3 -based alloys, (3) a preliminary test of a thermoelectric stack which is the united device of thermoelectric modules and heat exchanger, when properly installed in a 2000cc class automobile.

Phonon behaviors and electronic structures of the filled skutterudite YbyCo4Sb12 compounds: An electron tunneling study

Electron tunneling experiments were performed on YbyCo4Sb12–Al oxide–Al junctions for y=0–0.25 at 4.2 K. In the second derivative tunneling spectrum of CoSb3 compound (y=0), three peaks were observed at around 5, 20, and 33 mV, which are closely related to an optical phonon mode with a rigid rectangle, Sb–Sb bond bending and bond stretching, and a large Co atomic motion, respectively. Appearance of the strong peak at 7 mV observed in Yb-filled samples corresponds to a rattled phonon mode of Yb ions. The peak energy due to the Sb–Sb bonds is unchanged, whereas the one due to Co motions shifts to lower with increasing Yb concentration. This fact indicates that the filled Yb ions strongly interact to the host framework Co atoms, which were clearly observed in the change of tunneling conductance.

Preparation of Cu-O Films by Electron Cyclotron Resonance Plasma-Assisted Sputtering

Preparation of Cu-O films has been performed by using electron cyclotron resonance (ECR) plasma-assisted sputtering, and the effects of activated species in the ECR plasma on the properties of Cu-O films have been investigated from measurements of the optical emission spectroscopy. The emission intensities from O2+ molecular ions and O* atomic radicals in the ECR oxygen plasma increase monotonously with increasing microwave power of the ECR plasma source. The oxygen content of Cu-O films can be successfully controlled by changing the microwave power of the ECR plasma source. These results suggest that the role of the activated species of oxygen is important in oxidization of Cu atoms.

Magneto-Circular Dichroism Spectra of Cd1-xMnxTe-MnTe Multiple Quantum Well Prepared by Ionized-Cluster Beam Technique

Cd1-xMnxTe-MnTe multiple quantum wells were successfully grown on a sapphire (0001) substrate by the ionized-cluster beam deposition technique. In the magneto-circular dichroism spectra, peaks are observed at the energies where shoulders appear in the optical absorption spectra. The peaks shift toward higher energies as the Cd1-xMnxTe well width decreases. The magneto-optical effect is attributed to the Zeeman splitting of mini-band levels due to the spin exchange interaction between Mn2+ magnetic ions and electrons strongly confined in quantum wells.