Batteries: thermoelectric and photoelectric – Thermoelectric – Processes
Reexamination Certificate
1999-03-16
2001-05-22
Gorgos, Kathryn (Department: 1741)
Batteries: thermoelectric and photoelectric
Thermoelectric
Processes
C136S236100, C136S239000, C136S240000
Reexamination Certificate
active
06235981
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a p-type semiconductor substance having a thermoelectric converting property for use in a thermoelectric converting module, and more particularly to a p-type thermoelectric converting substance mainly consisting of a substance represented by a chemical formula of CoSb
3
and a small amount of Sn or Ge serving as an additive for controlling the conductivity of the substance to p-type. The present invention also relates to a method of manufacturing such a thermoelectric converting substance.
2. Description of the Related Art
Heretofore, there have been proposed telluric compound such as Bi
2
Te
3
, Bi
2
Sb
8
Te
15
and BiTe
2
Se as a thermoelectric converting substance. Among antimony compounds generally expressed as TSb
3
(T: Co, Ir, Ru), CoSb
3
has been known as the thermoelectric converting substance. CoSb
3
thermoelectric converting substance can be used in a temperature range up to about 600° C.
The above mentioned telluric compounds generally expressed by Bi-Te have a relatively high performance index Z of about 3×10
−3
[l/k] at room temperature, but the performance index is decreased in a temperature range higher than 300° C. Furthermore, the thermoelectric converting substance mainly consisting of the above mentioned telluric compound has a low melting point and a poor chemical stability, and moreover its thermoelectric converting property might be largely varied depending upon a deviation in composition.
Among the Sb base compounds expressed by TSb
3
(T: Co, Ir, Ru), CoSb
3
can operate satisfactorily over a much wider temperature range than Bi—Ti series compounds. Such thermoelectric converting compound semiconductor CoSb
3
has been described in L. D. Dudkin and N. Kh. Abrikosov, Sov. Phys. Solid State, 1(1959), pp. 126-133. In such a compound semiconductor, however, there is a problem in obtaining a thermoelectric converting substance having a p-type conductivity. That is to say, stoichiometric CoSb
3
having no additive shows p-conductivity type, but when an additive is not added, the conductivity of the substance could not be controlled due to the influence of non-purity of raw materials and it is difficult to attain a stable thermoelectric converting property. Moreover, the control of the conductivity type could not be performed effectively.
In addition to the problem of the non-purity of raw materials, there is a problem in that the composition of the substance is inevitably changed during the manufacturing process. Particularly, when a lack of Sb occurs in the stoichiometric composition, the conductivity type might be inverted and the finally obtained thermoelectric converting substance becomes n-type.
Due to the above explained reasons, in order to obtain p-type CoSb
3
showing high and stable thermoelectric conversion properties, it is necessary to dope a raw material of CoSb
3
with impurities controlling the conductivity type to the p-type, and further it is also necessary to remove the variation in composition during the manufacturing process.
SUMMARY OF THE INVENTION
The present invention has for its object to provide a novel and useful p-type thermoelectric converting substance mainly consisting of CoSb
3
, which can remove or at least mitigate the above mentioned drawbacks of the known substance, has a higher performance over a wide temperature range, has a higher electric conductivity, has a chemical stability, and has a small variation in chemical composition.
According to a first aspect of the invention, a thermoelectric converting substance used as a p-type semiconductor in a thermoelectric converting module is mainly consisting of a substance expressed by a chemical formula of CoSb
x
Sn
y
(2.7<x<3.4, 0<y<0.4, x+y>3), and contains an oxygen by an amount z of 2(x+y−3)≧z.
According to a second aspect of the invention, a thermoelectric converting substance used as a p-type semiconductor in a thermoelectric converting module is mainly consisting of a substance expressed by a chemical formula of CoSb
x
Ge
y
(2.7<x<3.4, 0<y<0.4, x+y>3), and contains an oxygen by an amount z of 2(x+y−3)≧z.
In the above mentioned p-type thermoelectric converting substance according to the invention, it is preferable to limit said amount of oxygen z such that an amount of the oxygen is not higher than 0.1 molecules per 1 molecule of Co in order to improve the electrical conductivity. That is to say, a molecular ratio of O/Co is preferably set to be equal to or smaller than 0. 1.
Further, according to the invention, the p-type thermoelectric substance may be preferably formed by a sintered body which can be easily and efficiently manufactured by a typical sintering process.
In the p-type thermoelectric converting substance according to the invention, the substance is essentially consisting of CoSb
x
Sn
y
(2.7<x<3.4, 0<y<0.4, x+y>3) or CoSb
x
Ge
y
(2.7<x<3.4, 0<y<0.4, x+y>3) and an amount of oxygen z is limited to 2(x+y−3)≧z. If an amount of oxygen z is higher than 2(x+y−3), Sn or Ge serving as a dopant for controlling the conductivity type into p-type, i.e. acceptor is selectively oxidized and the substance could no more show the p-type conductivity stably. That is to say, although the compound semiconductor CoSb
3
deviating from stoichiometry shows the n-type conductivity due to a lack of antimony Sb, when impurities Sn or Ge serving as dopant are introduced into lattice defect sites, the substance shows the p-type conductivity. If an amount of oxygen z is higher that 2(x+y−3), the dopant is oxidized to produce SnO
2
or GeO
2
and such oxidized dopant could not enter into the defect sites, and thus the substance could no more reveal the p-type conductivity.
Furthermore, according to the invention, an amount of Sb is limited to 2.7<x<3.4, an amount of Sn or Ge is limited to 0<y<0.4, and a sum of these amounts is set to be larger than 3 (x+y>3). If amounts of Sb and Sn deviate from these ranges, the electrical conductivity and Seebeck coefficient might be lowered and the substance could not have a good performance as the p-type semiconductor for the thermoelectric conversion module.
The present invention also relates to a method of manufacturing the above mentioned p-type thermoelectric converting substance.
According to the invention, a method of manufacturing a p-type thermoelectric converting substance comprises the steps of:
preparing a raw material powder mainly consisting of a substance expressed by a chemical formula of CoSb
x
Sn
y
or CoSb
x
Ge
y
(2.7<x<3.4, 0<y<0.4, x+y>3), in which Sn or Ge serves as a dopant for controlling the p-type conductivity;
casting said raw material powder into a mold having a given shape; and
sintering said mold under a reducing atmosphere.
In the method according to the invention, said sintering may be preferably carried out under a hydrogen atmosphere.
According to further aspect of the invention, a method of manufacturing a p-type thermoelectric converting substance comprises the steps of:
preparing a raw material powder mainly consisting of a substance expressed by a chemical formula of CoSb
x
Sn
y
or CoSb
x
Ge
y
(2.7<x<3.4, 0<y<0.4, x+y>3) and containing an oxygen by an amount z of 2(x+y−3)≧z, Sn or Ge serving as a dopant for controlling the p-type conductivity;
casting said raw material powder into a mold having a given shape; and
sintering said mold under a non-oxidizing atmosphere.
In such a method according to the invention, said sintering may be carried out under an inert gas atmosphere such as nitrogen and argon atmosphere. Furthermore, said sintering may be carried out under a reducing atmosphere such as a hydrogen atmosphere. It is also possible to perform the sintering in high vacuum.
In the method of manufacturing the p-type thermoelectric converting substance according to the invention, in or
Furuya Kenji
Imanishi Yuichiro
Kobayashi Masakazu
Kushibiki Keiko
Miyoshi Makoto
Gorgos Kathryn
NGK Insulators Ltd.
Parkhurst & Wendel L.L.P.
Parsons Thomas H.
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