P-type thermoelectric converting substance and method of...

Batteries: thermoelectric and photoelectric – Thermoelectric – Processes

Reexamination Certificate

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

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

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

P-type thermoelectric converting substance and method of... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with P-type thermoelectric converting substance and method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and P-type thermoelectric converting substance and method of... will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-2475231

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.