Compositions – Barrier layer device compositions – Group iii element containing binary compound; e.g. – ga – as
Reexamination Certificate
2002-02-25
2004-12-21
Gupta, Yogendra N. (Department: 1751)
Compositions
Barrier layer device compositions
Group iii element containing binary compound; e.g., ga, as
C252S06230S, C252S518100, C423S511000, C423S561100, C136S203000, C136S236100, C136S239000, C136S292000, C136S240000
Reexamination Certificate
active
06833083
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a thermoelectric material and a thermoelectric element and, more particularly, to a thermoelectric material in chalcogen series containing transition metal such as titanium and a thermoelectric converting element using the same.
DESCRIPTION OF THE RELATED ART
Alternative energy from fossil fuel and environmental conservation are important in the world, and are discussed worldwide. Thermoelectric converting technologies are attractive alternative energy sources. Thermoelectric conversion does not produce any anti-environmental gas such as carbon dioxide gas and nitrooxides. Waste heat is reused as electric energy through the thermoelectric conversion, and refrigerants adverse to the environment such as freon are not required for refrigerators. Thus, thermoelectric conversion is free from environmental destruction, and thermoelectric conversion technologies are promising.
The efficiency of the thermoelectric conversion is defined by the “figure of merit” ZT, and the figure of merit is expressed as
ZT=S
2
T/&rgr;&kgr; (1)
where S is Seebeck coefficient, T is temperature, &rgr; is the electrical resistivity and &kgr; is the thermal conductivity. When the figure of merit increased in value, the thermoelectric converting efficiency is improved. From equation (1), it is understood that a large figure of merit is achieved by a substance which has a large Seebeck coefficient, small electrical resistivity and small thermal conductivity. The figure of merit has a certain temperature dependency unique to the thermoelectric material. For this reason, the thermoelectric materials have each temperature ranges available for applications.
Electric generators driven by steam turbines and compressor-type refrigerators are now the major thermoelectric converter. In order to achieve the thermoelectric efficiency larger than that of the electric generators/refrigerators by using the thermoelectric materials, the thermoelectric materials are to have the figure of merit ZT of the order of 3.
Even though such a large figure of merit ZT is difficult, certain thermoelectric materials are active in the relatively low temperature range, in which the steam turbines can not operate, and have a position superior to the conventional thermoelectric converters. Nevertheless, the thermoelectric materials are to exhibit the figure of merit greater than 1 for practical application.
Various non-oxide semiconductor thermoelectric materials have been proposed. Thermoelectric materials in the bismuth-tellurium series have the unique temperature range from room temperature to 400 degrees in centigrade, and exhibit good performance in the unique temperature range. Thermoelectric materials in the lead-tellurium series exhibit good performance until 700 degrees in centigrade, and silicon-germanium series exhibit good performance until 1000 degrees in centigrade. The thermoelectric materials in the bismuth-tellurium series are used for the thermoelectric refrigeration, and the thermoelectric materials in the lead-tellurium series and silicon-germanium series are used for the thermoelectric generation.
On the other hand, (Zn
0.98
Al
0.02
)O, AB
2
O
4
, which is disclosed in Japanese Patent Application laid-open No. 7-231122, and NaCo
2
O
4
are examples of the oxide thermoelectric material. A and B are metal elements, and In is contained in B site. (Zn
0.98
Al
0.02
)O, AB
2
O
4
and NaCo
2
O
4
are proposed as thermoelectric generators using a high temperature heat source of the order of 700 degrees in centigrade and thermoelectric generators active from room temperature to high temperature range. However, those thermoelectric materials exhibit the figure of merit of the order of 1.
A problem inherent in the conventional thermoelectric materials is the low conversion efficiency. The conventional energy converters are undesirable from the viewpoint of the environment and safety. The petroleum, coal, natural gas and electric power generated by the nuclear power plants will be superceded by clean energy obtained through the thermoelectric conversion. If so, there will be a great demand for thermoelectric material greater in converting efficiency than the conventional thermoelectric materials in the bismuth-tellurium series, lead-tellurium series and silicon-germanium series.
SUMMARY OF THE INVENTION
It is therefore an important object of the present invention to provide thermoelectric material, which exhibits the thermoelectric converting efficiency greater than the conventional thermoelectric materials.
It is also an important object of the present invention to provide a thermoelectric generator, which achieves a high energy converting efficiency.
It is also an important object of the present invention to provide a thermoelectric refrigerator, which achieves a high energy converting efficiency.
In accordance with one aspect of the present invention, there is provided a compound having a CdI
2
analogous layer structure and expressed by general formula of A
x
BC
2−y
where x is fallen within the range of 0≦x≦2 and y is fallen within the range of 0≦y<1, the A is at least one element selected from the group consisting of lithium, sodium, potassium, rubidium and cesium, the B is at least one element selected from the group consisting of titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten, iridium and tin, and the C is at least one element selected from the group consisting of sulfur, selenium and tellurium.
In accordance with another aspect of the present invention, there is provided a compound having a CdI
2
analogous layer structure and expressed by general formula of A
x
BC
2−y
where x is fallen within the range of 0≦x≦2 and y is fallen within the range of 0≦y <1, the A is vacant, the B is at least one element selected from the group consisting of titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten, iridium and tin, and the C is at least one element selected from the group consisting of sulfur, selenium and tellurium.
In accordance with yet another aspect of the present invention, there is provided a compound having a CdI
2
analogous layer structure and expressed by general formula of A
x
BC
2−y
where x is fallen within the range of 0≦x≦2 and y is fallen within the range of 0≦y<1, the A is at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc (Zn), zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, cadmium, hafnium, tantalum, tungsten, rhenium, iridium, platinum, gold, rare-earth elements containing scandium and yttrium, boron, aluminum, gallium, indium, thallium, tin, lead, antimony and bismuth, the B is at least one element selected from the group consisting of titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten, iridium and tin, and the C is at least one element selected from the group consisting of sulfur, selenium and tellurium.
In accordance with still another aspect of the present invention, there is provided a thermoelectric generator comprising a first piece of thermoelectric material and a second piece of thermoelectric material different from the second thermoelectric material, the thermoelectric material having a CdI
2
analogous layer structure and expressed by general formula of A
x
BC
2−y
where x is fallen within the range of 0≦x≦2 and y is fallen within the range of 0≦y<1, in which the A is at least one element selected from the group consisting of lithium, sodium, potassium, rubidium and cesium, and in which the B is at least one element selected from the group consisting of titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten, iridium and tin, and in which the C is at least one element selected from the group consisting of sulfur, selen
Imai Hideto
Kubo Yoshimi
Manako Takashi
Shimakawa Yuichi
Gupta Yogendra N.
NEC Corporation
Scully Scott Murphy & Presser
Vijayakumar Kallambella
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