JP2001085751A - Thermoelectric conversion material, element using the same, and method of manufacturing thermoelectric conversion material - Google Patents

Abstract

(57) [Problem] To provide a Bi ₂ Te ₃ type thermoelectric material conventionally used at around room temperature, the raw material of the constituent material is expensive, and highly toxic S
It is necessary to add an element such as e, which poses a practical problem. Further, the conventional thermoelectric material using an oxide has a problem that the electric resistance is too high to be used near room temperature and the performance is extremely poor. SOLUTION: In the present invention, a general formula: InGaO _y (Z
nO) _m (2 <y <3, 1 ≦ m ≦ 19)
Optimum carrier introduction is performed on the substance having the bFe ₂ O ₄ -related layered structure by appropriate reduction treatment or element substitution. According to the present invention, it is possible to provide an oxide thermoelectric material having no toxicity, low electric resistance from room temperature to about 300 ° C., and excellent thermoelectric properties.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric conversion material, an element using the same, and a method for producing the thermoelectric conversion material, and more particularly to an oxide thermoelectric conversion material suitable for a heat source from room temperature to about 300.degree.

[0002]

2. Description of the Related Art In recent years, the problem of alternative energy to fossil fuels has been increasing.
Alternatively, environmental protection issues are receiving worldwide attention.
Among them, the importance of thermoelectric energy conversion technology that emits no harmful gases such as carbon dioxide and nitrogen oxides, uses distributed waste heat, and thermoelectric cooling technology that does not use harmful cooling media such as chlorofluorocarbons. Sex is growing more and more.

[0003] The energy conversion efficiency of thermoelectric conversion is represented by a figure of merit (ZT).
Required from.

ZT = S ² / ρκ (1) where S is the Seebeck coefficient, ρ is the electrical resistivity, and κ is the thermal conductivity.

The figure of merit (Z) obtained from the equation (1)
The conversion efficiency increases as T) increases. Therefore, in general, a material having a large absolute value of the Seebeck coefficient (S) and a small electric resistivity (ρ) and a small thermal conductivity (κ) has been a target of the thermoelectric conversion material development.

In general, the figure of merit (ZT) has a temperature dependency inherent to a substance, and the temperature range in which the substance can be put into practical use differs depending on the substance.

Conventionally, as a non-oxide semiconductor, a bismuth-tellurium-based thermoelectric conversion material has been used as a non-oxide semiconductor.
Up to about 00 ° C., up to about 700 ° C. for lead-tellurium-based materials and up to about 1000 ° C. for silicon-germanium-based materials are known as materials exhibiting good performance. this house,
Bismuth-tellurium-based materials are used for thermoelectric cooling, and lead-tellurium-based materials and silicon-germanium-based materials are used for thermoelectric power generation.

Conventionally, as an oxide thermoelectric conversion material,
Is (Zn_0.98Al_0.02) O (M.Ohtaki, T.Tsubota, K.
Eguchi and H. Arai, J. Appl. Phys. 79 (1996) 181
6), AB _TwoO_Four (A and B are metal elements and B site
(Including In) is disclosed in Japanese Patent Application Laid-Open No. 7-231122.
Report) mainly assumes the use of a high-temperature heat source of about 700 ° C.
Has been proposed as a thermoelectric power generating element.

[0009]

The trend of thermoelectric conversion technology in the future is not limited to thermoelectric power generation using a high-temperature heat source of 700 ° C. or more, but relatively low temperature of about 300 ° C. in automobiles, factories, and homes. In addition, it is expected that demand for thermoelectric conversion technology using a distributed heat source will increase more and more. Therefore, it is non-toxic, relatively inexpensive, and 3
There is a strong demand for a thermoelectric conversion material that exhibits good performance at around 00 ° C.

Bismuth-tellurium-based thermoelectric materials exhibiting good performance from room temperature to about 300 ° C. are relatively expensive as constituent material elements. In the case of n-type devices, it is necessary to add highly toxic selenium. Yes, there is a problem when considering the impact on the environment and the spread to general households.

On the other hand, a thermoelectric material using an oxide does not particularly cause the above-described problem, but since a carrier is added to a semiconductor close to an insulator from the beginning, the electric resistance exhibits semiconductor-like temperature dependence, Although suitable mainly for high temperatures exceeding 700 ° C., there is a problem that the electric resistance is too high and the performance is extremely low for use near room temperature. Therefore, development of an oxide thermoelectric material exhibiting good thermoelectric properties even at around room temperature is strongly desired.

Accordingly, an object of the present invention is to provide an oxide thermoelectric material which is non-toxic, has a lower electrical resistivity at around room temperature than conventional materials, and exhibits good thermoelectric properties, in order to solve such problems. An object is to provide an element using the same.

[0013]

Means for Solving the Problems The first invention is directed to YbFe
_{It has a 2} O ₄ -related layered structure and has the general formula ABO _y (CO) _m
(2 <y <3, 1 ≦ m ≦ 19), and in this general formula, the A site is at least one selected from the group IIIB elements, scandium (Sc), yttrium (Y), and lanthanoid elements. B site is made of at least one element selected from Group IIIB elements, and C site is made of zinc (Zn), 3d, 4d,
The present invention relates to a thermoelectric conversion material comprising at least one element selected from d transition metal elements and Group IIA elements, which is heat-treated in a reducing atmosphere to introduce oxygen defects.

The second invention has a YbFe ₂ O ₄ -related layered structure, and has the general formula ABO _y (CO) _m (2 <y <3, 1 ≦
m ≦ 19), and in this general formula, the A site is made of at least one element selected from group IIIB elements, scandium (Sc), yttrium (Y), and lanthanoid elements, and the B site is III At least one element selected from Group B elements, wherein the C site is zinc (Zn), 3d, 4d, 5d transition metal element, II
A thermoelectric element comprising at least one element selected from Group A elements, wherein at least one of the A site and the B site contains at least one element selected from Group IVB elements. Regarding conversion materials.

A third invention relates to the thermoelectric conversion material according to the second invention, wherein the thermoelectric conversion material is heat-treated in a reducing atmosphere to introduce oxygen defects.

A fourth aspect of the present invention relates to a thermoelectric power generation element using the thermoelectric conversion material according to the first, second or third aspect.

A fifth invention relates to a thermoelectric cooling element characterized by using the thermoelectric conversion material according to the first, second or third invention.

The sixth invention has a YbFe ₂ O ₄ -related layered structure, and has a general formula ABO _y (CO) _m (2 <y <3, 1 ≦
m ≦ 19), and in this general formula, the A site is made of at least one element selected from group IIIB elements, scandium (Sc), yttrium (Y), and lanthanoid elements, and the B site is III At least one element selected from Group B elements, wherein the C site is zinc (Zn), 3d, 4d, 5d transition metal element, II
The present invention relates to a method for producing a thermoelectric conversion material, comprising: forming an oxide material composed of at least one element selected from Group A elements, and then performing heat treatment in a reducing atmosphere to introduce oxygen defects.

The seventh invention has a YbFe ₂ O ₄ -related layered structure, and has a general formula ABO _y (CO) _m (2 <y <3, 1 ≦
m ≦ 19), and in this general formula, the A site is made of at least one element selected from group IIIB elements, scandium (Sc), yttrium (Y), and lanthanoid elements, and the B site is III At least one element selected from Group B elements, wherein the C site is zinc (Zn), 3d, 4d, 5d transition metal element, II
An oxide material comprising at least one element selected from Group A elements and further containing at least one element selected from Group IVB elements on at least one of the A site and the B site is formed. Thereafter, the present invention relates to a method for producing a thermoelectric conversion material, which comprises heat-treating in a reducing atmosphere to introduce oxygen defects.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

The present inventors have a YbFe ₂ O ₄ -related layered structure and have the general formula InGaO _y (ZnO) _m (2 <y <
3, 1 ≦ m ≦ 19), a series of compounds represented by the formula (1) can be subjected to optimal carrier introduction by substitution of a specific element or heat treatment in a reducing atmosphere. The oxide thermoelectric conversion material has an electric resistivity of about 1 mΩcm or less and an absolute value of the Seebeck coefficient of 1 even at around room temperature.
About 00 μV / K or more, and 3
It has been found that it can be used favorably at around 00 ° C. Further, they have found that the same performance can be obtained even in a structure in which In or A at the site and Ga at the B site are partially or entirely substituted by the elements described below.

YbFe ₂ contained in the thermoelectric conversion material of the present invention
The O ₄ -related layered structure has a structure in which layers having a relatively high electrical conductivity and layers having a relatively high insulating property are alternately stacked. While introducing a high concentration to lower the electrical resistivity,
The Seebeck coefficient can maintain a relatively large absolute value due to low dimensional conductivity. The feature of the present invention resides in utilizing the characteristics of such a YbFe ₂ O ₄ -related layered structure.

YbFe_TwoO_FourHas an analogous layered structure,
Formula ABO_y(CO)_m (2 <y <3, 1 ≦ m ≦ 19)
The thermoelectric conversion material of the present invention is represented by A_TwoO_ThreeLayer consisting of
And B _TwoC_TwoO_FiveHas a structure in which layers consisting of
In addition, a structure in which a layer made of CO is added as m increases
have.

For example, InGaO _y (ZnO) _m (2 <
In the case of y <3, 1 ≦ m ≦ 19), the In ₂ O ₃ layer can introduce carriers by forming oxygen vacancies or replacing part of In with an element having a valence different from that of In. The mobility of the introduced carriers is also high, and it is easy to lower the electric resistance. Further, the Ga ₂ C ₂ O ₅ layer has a role of introducing carriers by adding elements into the In ₂ O ₃ layer, and also has a role of reducing the dimension of the electric conduction layer and increasing the absolute value of the Seebeck coefficient.

The constituent elements of the thermoelectric conversion material of the present invention are not limited to indium, gallium and zinc at the A site, the B site and the C site, respectively. Indium at the A site has a valence of three. Elements can replace some or all of them. Specifically, group IIIB elements (boron (B), aluminum (Al), gallium (Ga), thallium (T
l)), scandium (Sc), yttrium (Y),
It is at least one element selected from lanthanoid elements.

For gallium (Ga) at the B site, the same group IIIB elements (boron (B), aluminum (A
l), indium (In), and thallium (Tl)) can be partially or entirely substituted with at least one element selected from the group consisting of:

As for zinc (Zn) at the C site, 3d, 4d, 5d transition metals (iron (Fe),
Manganese (Mn), cobalt (Co), nickel (N
i), copper (Cu), etc.) and Group IIA elements (magnesium (Mg), calcium (Ca), strontium (S
r), barium (Ba), etc.).

By these element substitutions, it is possible to control the temperature at which the figure of merit takes the maximum value,
In making a system using actual thermoelectric conversion, it becomes possible to select a material according to the generated temperature difference and the operating temperature.

An oxide material obtained by introducing a carrier at a high concentration into the oxide having the basic structure described above is the thermoelectric conversion material of the present invention.

For the production of the thermoelectric conversion material of the present invention, a general method of synthesizing a ceramic, which is obtained by mixing the raw material powder and then firing the mixture in accordance with the known conditions for forming a YbFe ₂ O ₄ analogous layer structure, can be applied. Further, it can be synthesized as a single crystal using a precipitation from a high-temperature liquefied state, a zone melting method, a chemical transport method, or the like. In addition, sputtering, laser deposition,
It is also possible to form a film using a vacuum deposition method.

As a method for introducing the carrier, hydrogen gas,
A method of introducing oxygen deficiency by heat treatment in a reducing atmosphere such as nitrogen gas or argon gas (hereinafter referred to as “oxygen deficiency introducing method”), or an element having a valence different from that of the element constituting the basic structure. There is a method of introducing a carrier by substituting part or all of a specific constituent element (hereinafter referred to as an “element substitution method”), or a method of performing both of them.

The reducing atmosphere in the oxygen defect introduction method is as follows:
It is more preferable to use argon gas. This is because the safety is relatively high, the reduction rate is moderate, and the process is simplified. Further, the heat treatment temperature is from 600 ° C to 90 ° C.
0 ° C. is preferred. If the temperature is too low, it is difficult to sufficiently perform deoxygenation, and if the temperature is too high, a decomposition reaction occurs and the metal element is easily deposited.

In the element replacement method, the element constituting the A site is replaced with a tetravalent valence IVB group element (silicon (S
i), germanium (Ge), tin (Sn), etc.), the carrier can be introduced by partially substituting at least one element. Similarly, the B site is partly composed of at least one element selected from the group IVB elements (silicon (Si), germanium (Ge), tin (Sn), etc.) having a tetravalent valence. Is replaced, the introduction of carriers becomes possible. Further, a part of the elements at both the A site and the B site may be respectively replaced with an IVB group element.

After the conductivity is imparted by introducing a carrier by such an element substitution method, the carrier is further introduced by an oxygen defect introduction method in which heat treatment is performed in a reducing atmosphere to lower the electric resistivity, thereby optimizing the conductivity. Can also be performed.

Using the thermoelectric conversion material synthesized as described above, a thermoelectric power generation element and a thermoelectric cooling element having a known element structure can be manufactured by a known method.

[0036]

The present invention will be described more specifically with reference to the following examples.

Indium oxide (In ₂ O ₃ ), gallium oxide (Ga ₂ O ₃ ), zinc oxide (ZnO), scandium oxide (Sc ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), cerium oxide (CeO ₂₎ ), Neodymium oxide (Nd ₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ), terbium oxide (Tb ₄
O ₇ ), dysprosium oxide (Dy ₂ O ₃ ), erbium oxide (Er ₂ O ₃ ), thulium oxide (Tm ₂ O ₃ ), ytterbium oxide (Yb ₂ O ₃ ), silicon oxide (SiO ₂ ),
Germanium oxide (GeO ₂ ), tin oxide (SnO ₂ ), aluminum oxide (Al ₂ O ₃ ), iron oxide (FeO), manganese oxide (MnO), nickel oxide (NiO), cobalt oxide (CoO), copper oxide ( CuO), magnesium carbonate (MgCO ₃ ), calcium carbonate (CaCO ₃ ), strontium carbonate (SrCO ₃ ), barium carbonate (BaC)
The O ₃ ) powder material was weighed to a predetermined molar ratio shown in Table 1, mixed well, and calcined in air at 1000 ° C. for 5 hours. Then, it was press-formed into a disk having a diameter of 15 mm at 1 GPa and sintered in air at 1400 ° C. for 12 hours.

At this point, there is a case in which sufficient conductivity has already been obtained, but in order to further introduce a carrier, a heat reduction treatment was performed at 800 ° C. for 24 hours in an argon atmosphere.

As a result of the crystal structure analysis by X-ray diffraction, the sample No. 1 to No. For 28, the general formula:
nGaO _y (ZnO) _m (2 <y <3, 1 ≦ m ≦ 19)
In m = 1, sample No. 29-No. 32, m = 2, sample no. 33-No. M for 36
= 3, Sample No. 37-No. M = 4 for 40,
Sample No. 41-No. M = 10 for Sample No. 44; 45-No. M = 15 for 48, sample N
o. 49-No. It was clear that the sample No. 52 had the above-mentioned YbFe ₂ O ₄ -related layered structure corresponding to m = 19.

The evaluation as a thermoelectric material was performed by measuring the Seebeck coefficient and the electric resistivity. The Seebeck coefficient was measured by a stationary method in which a temperature difference was applied to both ends of the sample, and the temperature difference and the generated thermoelectromotive force were measured. The electrical resistivity is
The test was performed by a DC four-terminal method. The measurement is performed at room temperature (28 ° C)
Performed in The thermoelectric properties were evaluated using a power factor represented by S ² / ρ.

Table 1 shows the results. A in the table
The site has the general formula InGaO _y (ZnO) _m (2 <y <
3, 1 ≦ m ≦ 19), the In site, the B site represent a gallium site, and the C site represents a zinc site.
In addition, No. in the table. Reference numeral 53 indicates the same measurement performed on a sample not subjected to the heat reduction treatment for comparison.

As is clear from Table 1, the general formula InGaO _y (ZnO) _m (2 <y <3, 1 ≦ m ≦ 1)
When a carrier is introduced into the material of the YbFe ₂ O ₄ analogous layer structure represented by 9) by performing an appropriate heat reduction treatment or element substitution, the electric resistivity is remarkably reduced to about 1 mΩcm or less, In addition, the absolute value of the Seebeck coefficient is maintained as large as about 100 μV / K or more. The power factor also shows a large value.

[0043]

[Table 1]

[0044]

According to the present invention, the general formula ABO _y (C
O) Yb represented by _m (2 <y <3, 1 ≦ m ≦ 19)
By introducing a carrier by performing an appropriate heat reduction treatment or element substitution on a substance having an Fe ₂ O ₄ analogous layered structure, the production process is relatively inexpensive, and the production process is easy.
A thermoelectric conversion material having low toxicity of the material, lower electric resistance than conventional materials and excellent thermoelectric conversion characteristics even when used near room temperature can be obtained.

Claims (7)

[Claims] 1. An ABO _y (CO) _m (2 <y <3, 1 ≦ m ≦ 19) having a YbFe ₂ O ₄ analogous layer structure.
In this general formula, A site is represented by IIIB
Group elements, scandium (Sc), yttrium (Y),
The B site is made of at least one element selected from the group IIIB elements, and the C site is made of zinc (Z
n) a thermoelectric conversion material comprising at least one element selected from the group consisting of a 3d, 4d, 5d transition metal element and a Group IIA element, wherein heat treatment is performed in a reducing atmosphere to introduce oxygen defects. . 2. A compound having a YbFe ₂ O ₄ analogous layer structure and having the general formula ABO _y (CO) _m (2 <y <3, 1 ≦ m ≦ 19)
In this general formula, A site is represented by IIIB
Group elements, scandium (Sc), yttrium (Y),
The B site is made of at least one element selected from the group IIIB elements, and the C site is made of zinc (Z
n) at least one element selected from the group consisting of 3d, 4d, 5d transition metal elements and Group IIA elements, and at least one of the A site and the B site has an IV
A thermoelectric conversion material comprising at least one element selected from Group B elements. 3. The thermoelectric conversion material according to claim 2, wherein the thermoelectric conversion material is heat-treated in a reducing atmosphere to introduce oxygen defects. 4. A thermoelectric power generation element using the thermoelectric conversion material according to claim 1, 2, or 3. 5. A thermoelectric cooling element using the thermoelectric conversion material according to claim 1, 2, or 3. 6. It has a YbFe ₂ O ₄ analogous layered structure and is represented by the general formula ABO _y (CO) _m (2 <y <3, 1 ≦ m ≦ 19). Is composed of at least one element selected from Group IIIB elements, scandium (Sc), yttrium (Y), and lanthanoid elements, and the B site is composed of at least one element selected from Group IIIB elements; C site is zinc (Z
n) forming an oxide material composed of at least one element selected from the group consisting of 3d, 4d, 5d transition metal elements and Group IIA elements, followed by heat treatment in a reducing atmosphere to introduce oxygen defects. A method for producing a thermoelectric conversion material. 7. It has a YbFe ₂ O ₄ analogous layered structure and is represented by the general formula ABO _y (CO) _m (2 <y <3, 1 ≦ m ≦ 19). Is composed of at least one element selected from Group IIIB elements, scandium (Sc), yttrium (Y), and lanthanoid elements, and the B site is composed of at least one element selected from Group IIIB elements; C site is zinc (Z
n) at least one element selected from the group consisting of 3d, 4d, 5d transition metal elements and Group IIA elements, and at least one of the A site and the B site includes at least one element selected from the group IVB elements. A method for producing a thermoelectric conversion material, comprising forming an oxide material containing a kind of element and then heat-treating it in a reducing atmosphere to introduce oxygen defects.