Hiromichi Nakashima

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.

Effect of boron addition on thermoelectric properties in iron silicides ribbons

This paper describes the thermoelectric properties and the microstructures of ribbons with various boron contents of (FeSi2)1−xBx(x=0∼0.5) fabricated by a spin‐casting technology. The mixture of the α and e phases with metallic properties appears in the as‐fabricated ribbons. When the ribbons were annealed, the β phase was observed below x=0.2, and the β and Si phases were observed above x=0.3. A long period superlattice of the β phase was observed at x=0.5. The annealed ribbons have the negative sign of thermoelectric power below x=0.2. As x increases, the thermoelectric power of the annealed ribbon increases to a maximum at x=0.03, while that of the annealed bulk decreases to a minimum at x=0.03. The power factor of the annealed ribbon increases to a maximum at x=0.03, above which it decreases. The energy of Eh+Ed calculated from the slope of plot of ρ/T versus 1/T between 300 and 400 K decreases with increasing x, where Eh is the activation energy of the hopping process, Ed is the activation energy of ...

Rod-like precipitates formed in vapor-deposited Fe-Si film

Semiconducting β-FeSi2 is a potential candidate material for solar cells. Various fabrication methods have therefore been proposed for smart films of this material. However, the dynamics of β-FeSi2 formation are not fully understood and require investigation. Our experimental results based on TEM and SEM observations imply that the mechanism for forming iron silicide is very complex, and exhibits strong dependence on the fabrication method. Rod-like precipitates form in a sample fabricated with double iron deposition and no precipitates form in a sample fabricated with single iron deposition on a silicon substrate.

Thermoelectric properties of the filled skutterudite in the Ce-Fe-Co-Sb-Sn system

Ribbons with Ce(6-x)/3Fe6Co2Sb 24-xSnx compositions were fabricated by spin-casting, and discs were prepared by sintering the powders. The samples were investigated by X-ray diffraction, transmission electron microscopic observation, energy dispersive X-ray (EDX) analysis and measurements of the Seebeck coefficient, electrical conductivity, Hall coefficient, and thermal conductivity at room temperature. Tin addition is effective to form the skutterudite rapidly without annealing. The skutterudite exists as a single phase for x les 0.25, while it coexists with the FeSb2 phase and Sb or beta-SbSn phase for x ges 0.5. The electrical conductivity, carrier mobility, and thermal conductivity increase with increasing x. The Seebeck coefficient, power factor, and dimensionless figure of merit increase, reach maxima and then decrease as x increases. The phases coexisted with the skutterudite phase are effective to improve the thermoelectric properties

Thermoelectric properties and microstructure of Co-doped iron-silicides mixed with Ag or Cu

Spin-cast ribbons and sintered discs of the Co-doped iron disilicides mixed with Ag or Cu were prepared and investigated by measuring the Seebeck coefficient, electrical conductivity, power factor, dimensionless figure of merit, and thermal conductivity at 300 K. The microstructure was characterized by powder X-ray diffraction analysis and transmission electron microscopic analysis. The ribbons and bulks possess an n-type of polarity. The Seebeck coefficient, electrical conductivity, power factor, dimensionless figure of merit, and thermal conductivity depend on the Si, Ag, or Cu content. The thermoelectric properties differ from the ribbons to the discs. The Ag or Cu phase disperses at grain boundaries and matrix of the /spl beta/ phase, and contributes to form the /spl beta/ phase, and is effective to improve the thermoelectric properties.