Yoshiyuki Kawaharada

Thermoelectric properties of CoSb3

Abstract The typical skutterudite structure compound CoSb 3 was prepared by arc melting followed by sintering. The samples were characterized by powder X-ray diffraction method, electron probe microanalysis (EPMA), and the thermoelectric properties such as the thermal diffusivity, electrical resistivity, and Seebeck coefficient were measured in the temperature range from room temperature to about 750 K. The thermal conductivity of CoSb 3 was estimated from the heat capacity, the experimental density, and the thermal diffusivity measured by the laser flash method. The calculated dimensionless figure of merit, ZT of CoSb 3 was lower than that of state of the art thermoelectric materials. In order to enhance the ZT , it was attempted to reduce the lattice thermal conductivity of CoSb 3 . The electronic contribution to the thermal conductivity was estimated by Wiedemann–Franz law, and the lattice thermal conductivity was determined. It was found that the lattice thermal conductivity of CoSb 3 can be decreased, and ZT of CoSb 3 can potentially be enhanced.

High temperature thermoelectric properties of NiZrSn half-Heusler compounds

Half-Heusler compounds of the type NiZrSn1−xSbx were prepared by arc melting in the concentration range 0<x<0.3. Their high-temperature electric and thermal properties were measured. The thermoelectric power (TEP) and electrical resistivity showed a strong antimony concentration dependence. The temperature and concentration dependences of the thermoelectric properties of NiZrSn1−xSbx were studied.

Thermophysical properties of Fe2VAl

Abstract The heat capacity at constant pressure of Heusler-type Fe 2 VAl was measured by using a differential scanning calorimeter in the temperature range from 300 to 1200 K under argon atmosphere. The heat capacity of Fe 2 VAl is expressed by the general equation as C P =2.29×10 2 −3.28×10 −1 T +2.50×10 −3 T 2 −5.63×10 6 / T 2 (J/mol/K). The measured heat capacity of Fe 2 VAl deviated from the values calculated by Neumann–Kopp’s law. The harmonic and dilatational terms of the heat capacity were estimated from the measured thermophysical properties such as the Debye temperature, thermal expansion coefficient, and compressibility.

High temperature thermoelectric properties of (Fe1−xVx)3Al Heusler type compounds

Heusler type compounds (Fe1−xVx)3Al were made by arc melting in the concentration range 0<x<1. Their mechanical properties, high temperature electric properties, and thermal properties were measured. The thermoelectric power (TEP) showed a strong concentration dependence. The temperature and concentration dependences of the thermoelectric properties of (Fe1−xVx)3Al were studied.

Thermoelectric properties of Fe-V-Si Heusler type compounds

Abstract The Heusler type compounds Fe 3− x V x Si were prepared by arc melting in the concentration range between x =0 and x =1. The samples were characterized by a powder X-ray diffraction method and EDXA. The thermoelectric properties such as the thermal diffusivity, electrical resistivity, and Seebeck coefficient were measured in the temperature range from 300 to 1073 K. The thermal conductivities of Fe 3− x V x Si were evaluated from the heat capacity, experimental density, and thermal diffusivity measured by a laser flash method. A strong vanadium concentration dependence is shown in the thermoelectric power (TEP) of Fe 3− x V x Si. The temperature and vanadium concentration dependences of the thermoelectric properties of Fe 3− x V x Si were studied.

Electronic states of BaUO3

The electronic states of BaUO3 were evaluated by a molecular orbital (MO) calculation. A relativistic MO calculation was performed by using a discrete variational Dirac-Fock-Slater (DV-DFS) method. A [U106Ba8U6024]-16 cluster with Oh symmetry was adopted for the present calculation. The energy level scheme, density of states (DOS), and net charge were obtained from the calculation. The measured electrical resistivity of the perovskite type compound was discussed from the calculated DOS. The calculated net charge was compared with the mechanical properties of BaUO3.