Thermoelectric semiconductor compound and method of making...

Details Thermoelectric semiconductor compound and method of making... Thermoelectric semiconductor compound and method of making...

1999-11-29

2001-05-01

Gorgos, Kathryn (Department: 1741)

Batteries: thermoelectric and photoelectric

Thermoelectric

Processes

C136S236100, C136S238000, C136S240000, C136S241000

Reexamination Certificate

active

06225548

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a thermoelectric semiconductor compound and a method of making the thermoelectric semiconductor compound.
2. Description of Related Art
It is well known that thermoelectric semiconductor compounds exhibit the Seebeck effect, where heat is converted to electricity, and the Peltier effect, where application of an electric current causes cooling or heating.
The thermoelectric performance of a thermelectric semiconductor compound is indicated by a performance index Z (=&agr;
2
&sgr;/&kgr;, where &agr; is the Seebeck coefficient, &sgr; is the electrical conductivity, and &kgr; is the thermal conductivity). A higher performance index Z results in higher thermoelectric performance. For example, a higher performance index Z results in a higher voltage being developed if a temperature difference is provided across a thermoelectric semiconductor. A higher performance index Z also results in a larger temperature difference being developed across a thermoelectric semiconductor upon application of an electric current. Thus, much research and development effort has focused on increasing the performance index Z to as high a value as possible.
One improved thermoelectric semiconductor compound is disclosed in Japanese Laid-open Patent No. Hei. 10-242535, which was published, without examination, on Sep. 11, 1998. The performance index Z was increased by adding BN to a thermoelectric semiconductor with a molecular formula of (Bi
2
Te
3
)
70
(Sb
2
Se
3
)
5
or (Bi
2
Te
3
)
70
(Sb
2
Se
3
)
30
, even though the addition of BN led to a reduction in thermal conductivity.
Another improved thermoelectric semiconductor compound is disclosed in Proc. XII Int. Conf. On Thermoelectric, IEEJ, Tokyo, Yokohama (Japan), pp.121-125, 1994. The performance index Z was increased by a factor of 1.2 by the addition of 2 volume % MgO, in the form of powders having an average diameter of 0.01 &mgr;m, to a thermoelectric semiconductor having a molecular formula of (Bi
0.25
Sb
0.75
)
2
Te
3
.
In both cases, the performance index Z of a thermoelectric semiconductor compound was increased by the addition of a dielectric material that also decreased the electrical conductivity. Thus, the increases in the performance index Z resulted from an improvement in one or more of &agr; and 1/&kgr;, while &sgr; was sacrificed. As long as improvements in the performance index Z require a trade-off of one or more of the factors of Z, improvements in Z will be limited.
Accordingly, a need exists for a thermoelectric semiconductor compound with a remarkably improved performance index Z that is not the result of sacrificing one of the factors of Z.
SUMMARY OF THE INVENTION
The present invention has been developed to satisfy the need noted above and thus has as a primary object the provision of a thermoelectric semiconductor compound which comprises:
a first thermoelectric semiconductor which is in the form of a matrix; and
a second thermoelectric semiconductor which is in the form of particles dispersed in the matrix, the first thermoelectric semiconductor and the second thermoelectric semiconductor having a common element, an average diameter D of the dispersed particles complying with a formula of A<D<B where A is the mean free path of a carrier in a single crystal of the second thermoelectric semiconductor and B is the mean free path of a long wavelength phonon in the single crystal of the second thermoelectric semiconductor.


REFERENCES:
patent: 3095330 (1963-06-01), Epstein et al.
patent: 4489742 (1984-12-01), Moore et al.
patent: 4497973 (1985-02-01), Heath et al.
patent: 5763293 (1998-06-01), Yamashita et al.
patent: 10-242535 (1998-09-01), None
I. Ohnaka et al. “Thermoelectric Properties of (Bi0.25Sb0.75)2Te3with Ceramic Addition”, Proc. XII Int. Conf. On Thermoelectric, IEEJ, Tokyo, Yokohama, pp. 121-125, 1994.

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