T. Morimura

Thermoelectric properties of Fe1−yCrySi2 ribbons

This paper describes the thermoelectric properties of Fe1−yCrySr2 ribbons and bulks fabricated by spin‐casting and usual casting. The thermoelectric powers, the electrical resistivities, the power factors of the ribbons and the bulks were measured, and the X‐ray diffraction patterns, the scanning electron microscopic images were observed. The thermoelectric powers, the electrical resistivities and the power factors of the ribbons and the bulks for y=0∼0.7 become large after annealing. The thermoelectric power, the power factor of the annealed ribbon are larger than those values of the annealed bulk for y=0∼0.7. The annealed ribbons consist of the β phase for y≤0.07, and of the β phase and the CrSi2 phase for 0.07<y≤0.7. With increasing y below y=0.07, the thermoelectric power and the electrical resistivity become small because of increase in hole density in the β phase. With increasing y from 0.07 to 0.1, the thermoelectric power and the electrical resistivity become large because hole density decreases w...

Electron channeling X-ray microanalysis for site occupation of the additional element in half-Heusler

The site occupancy of Sb atoms in a thermoelectric material TiNiSn/sub 0.9/Sb/sub 0.1/ with the half-Heusler structure was analyzed by measuring characteristic X-ray intensities at various electron incident directions in a transmission electron microscope (TEM). This technique is called the method for determining atomic locations by channeling enhanced microanalysis (ALCHEMI). The incident electron intensities in half-Heusler structure calculated by dynamical electron diffraction theory were compared with the measured characteristic X-ray intensities. The measured characteristic X-ray intensity for each element changed together with the change of incident electron intensities, depending on the electron incident directions. From the dependence of the X-ray intensities, the distribution fractions of Sb atoms on each site were quantitatively clarified. As a result, the distribution fractions of Sb atoms on Ti, Ni and Sn sites were shown to be -0.07, 0.12 and 0.95, respectively.

Thermoelectric property and microstructure of iron-silicide doped with Co and Ag

/spl beta/-FeSi/sub 2/ is enumerated as a prospective material for thermoelectric conversion as well as photoelectric conversion and light emitting. In this paper, thermoelectric property and microstructure of /spl beta/-FeSi/sub 2/ sintered with Ag were investigated by the measurements of Seebeck coefficient, electrical resistivity, X-ray diffraction and transmission electron microscopic observation. /spl alpha/-FeSi and /spl epsiv/-FeSi/sub 2/ were observed in an as-cast sample. /spl beta/-FeSi/sub 2/ was produced by transformation from /spl alpha/-FeSi and /spl epsiv/-FeSi/sub 2/ after annealing at 1073K. /spl beta/-FeSi/sub 2/ hardly contained Ag but contained Co as a dopant. Ag precipitated in the boundaries of /spl beta/-FeSi/sub 2/ grains and between particles. Power factor was enhanced by Ag addition because of the large decrease in electrical resistivity and the slight decrease in Seebeck coefficient. The distribution of Ag was important factor for the power factor. The relation between microstructures and thermoelectric properties was revealed.

Temperature analysis of thermoelectric device of Cu 4 SnS 4 with two dimension by boundary element method

Temperature distribution of a thermoelectric device composed of Cu/sub 4/SnS/sub 4/ compound in two-dimension is evaluated by the boundary element method (BEM). It is found that temperature distribution is strongly dependent on the length of the thermoelectric device. Temperature distribution shows very strong dependence of the direction of length of device when the length of device is very thin. In the case of small electric current density such as -1 A/cm/sup 2/, temperature distribution can be approximately expressed as the solution of Laplace equation.

Quantitative TEM analysis on atomic configuration of half-Heusler compound

The site occupancies of Zr and Hf atoms in a high performance thermoelectric material Ti0.5(Zr0.5Hf0.5)0.5NiSn 0.998Sb0.00 2 with the half-Heusler structure were clarified by a quantitative TEM analysis. This TEM technique is called the method for determining atomic locations by channeling enhanced microanalysis (ALCHEMI). In this technique, the dependence of the characteristic X-ray intensities on the electron diffraction conditions was measured in TEM. As a result, the distribution fractions of Zr atoms on Ti, Ni and Sn sites were shown to be 0.72, 0.17 and 0.11, respectively. Those of Hf atoms were shown to be 0.73, 0.12 and 0.15, respectively

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.

Microstructures and thermoelectric properties of (FeSb/sub 3/)/sub 1-x/La/sub x/ ribbons

The microstructures and thermoelectric properties of the spin-cast (FeSb/sub 3/)/sub 1-x/La/sub x/ (x=0-0.4) ribbons were investigated by means of X-ray diffraction measurements, transmission electron microscopic observations, EDX analyses, measurements of the electrical resistivity and thermoelectromotive force. The ribbons consist of various structures : FeSb/sub 2/+Sb for x=0, LaFe/sub 4/Sb/sub 12/+FeSb/sub 2/+Sb for x=0.1, LaFe/sub 4/Sb/sub 12/ for x=0.2, LaFe/sub 4/Sb/sub 12/+La/sub 2/Sb+LaSb+LaSb/sub 2/+FeSb for x=0.3 and 0.4, where LaFe/sub 4/Sb/sub 12/ is the filled skutterudite structure. A precipitation zone appeared along the grain boundaries of LaFe/sub 4/Sb/sub 12/ for x>0.2, while it was not seen for x<0.2. As the amount of LaFe/sub 4/Sb/sub 12/ decreases with deviation from x=0.2, the electrical resistivity decreases more rapidly for x>0.2 than for x<0.2. The Seebeck coefficient is large between x=0.2 and 0.3. The large power factor is obtained between x=0.2 and 0.3, being the high value of 20 /spl mu/W/cmK/sup 2/ at 350 K and 50 /spl mu/W/cmK/sup 2/ at 550 K.

Mossbauer effect studies of filled skutterudite compounds

Mossbauer spectra of filled skutterudite compound of LaFe/sub 4/Sb/sub 12/, La/sub 1.71/Fe/sub 4/Sb/sub 12/, CeFe/sub 4/Sb/sub 12/ and Ce/sub 1.71/Fe/sub 4/Sb/sub 12/ are measured in order to investigate the hyperfine state of iron atoms. Iron atoms in these compounds are in para-magnetic states and quadrupole splitting (Q.S) differs between LaFe/sub 4/Sb/sub 12/ and CeFe/sub 4/Sb/sub 12/ specimens whereas, no difference was observed in isomer shifts (I.S). Due to calculations, it is proposed that the difference in Q.S is attributed to the difference in the density of state at Fermi surface.

Thermoelectric properties of Fe/sub 1-x/Ni/sub x/Sb/sub 3/ ribbons

This paper deals with the microstructures and thermoelectric properties of Fe/sub 1-x/Ni/sub x/Sb/sub 3/ ribbons between x=0 and 1.0. The ribbons were fabricated by casting on a rotating copper roll with the surface velocity of 10 m/s, and then annealed for 3.6 ks at 873 K. The microstructures were investigated by means of X-ray diffraction measurements and transmission electron microscopic observations. The CoAs/sub 3/ type of structure, namely skutterudite structure, appeared as well as the other structures of FeSb/sub 2/, NiSb/sub 2/ and Sb below x=0.45 and above 0.55. Only the skutterudite appeared and the other structures disappeared between x=0.45 and 0.55. The thermoelectromotive force and electrical resistivity were measured under a vacuum from 300 K to 670 K. The thermoelectromotive force was of p-type of semiconductor for x<0.5 and of n-type for x>0.5. The electrical resistivity recorded a maximum at x=0.5. The curve of electrical resistivity versus x was asymmetric at x=0.5. The electrical resistivity was larger for x<0.5 than for x>0.5 at the same deviation from x=0.5. The power factor, which was estimated from the thermoelectromotive force and electrical resistivity, reached to maximums at x=0.4 and x=0.6, and was small at x=0.5 at 300 K.