JP2003273411A - Thermoelectric conversion material and thermoelectric conversion device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric conversion material having excellent electric conductivity and a high thermoelectromotive force, and also to provide a thermoelectric conversion device using the same. <P>SOLUTION: The thermoelectric conversion material is formed of a composite oxide, main component of which is In and Zn, with a composition ratio of In and Zn being 0.2<In/(In+Zn)<1. The thermoelectric conversion material can raise both the absolute value of a thermoelectromotive force and electric conductivity, or can suppress a decline in the absolute value of the thermoelectromotive force. The thermoelectric conversion material is used as an n-type thermoelectric conversion material 2 to manufacture the thermoelectric conversion device 1. <P>COPYRIGHT: (C)2003,JPO

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 having good electric conductivity and high thermoelectromotive force, and a thermoelectric conversion element using the same.

[0002]

2. Description of the Related Art Thermoelectric power generation is a technology for directly converting thermal energy into electric power by utilizing the thermoelectric effect. Since this technology has no moving parts and is excellent in stability, this technology uses wristwatches and remote power sources that operate at body temperature, It has been put to practical use as a power source for space and a military power source.

However, PbT that has been used so far
Since the e-type and Bi ₂ Te ₃ -type thermoelectric conversion materials use expensive elements such as Te and toxic elements such as Pb, there is a problem in terms of price and toxicity as a material for power generation. .

Therefore, as thermoelectric conversion materials which have improved the above problems, Japanese Patent Laid-Open No. 9-321346 and Japanese Patent Laid-Open No. 1-321346 have been proposed.
JP-A 0-256612 discloses a layered perovskite oxide containing Na, which is an element having low toxicity and low cost, and having high thermoelectric performance.

However, since the Na-based composite oxides disclosed in the above publications are p-type thermoelectric conversion materials,
In order to realize a thermoelectric conversion element using a safe and chemically stable oxide, it was necessary to use it in combination with an n-type thermoelectric conversion material. As the n-type thermoelectric conversion material,
For example, a composite oxide in which Nd ₂ CuO ₄ is doped with Zr (Japanese Patent Laid-Open No. 2000-012914) and a composite oxide in which indium oxide contains manganese (Japanese Patent Laid-Open No. 7-23).
No. 1122) and a complex oxide in which ZnO is doped with indium (Japanese Patent Laid-Open No. 2000-012915) and the like are disclosed.

[Problems to be Solved by the Invention]

However, all of the composite oxides disclosed in the above publications have a problem in thermoelectric power generation performance at a relatively low temperature (room temperature to 200 ° C.), so that they are not suitable for use as a thermoelectric conversion material. There was a problem of being insufficient. Therefore, there has been a demand for the development of a higher performance n-type thermoelectric conversion material that can be used in combination with the p-type thermoelectric conversion material.

An object of the present invention is to provide a thermoelectric conversion material having good electric conductivity and high thermoelectromotive force, and a thermoelectric conversion element using the same.

As a result of intensive studies to solve the above problems, the present inventors have found that a composite oxide mainly composed of In and Zn has high electric conductivity and negative conductivity even at a relatively low temperature (room temperature to 200 ° C.). It was found that they also have high thermoelectromotive force and have excellent properties as a thermoelectric conversion material.

[0009]

According to the first aspect of the present invention, a composite oxide mainly composed of In and Zn and having a composition ratio of In and Zn of 0.2 <In / (In + Zn) <1. A thermoelectric conversion material is provided.

According to a second aspect of the present invention, there is provided a thermoelectric conversion element using the above thermoelectric conversion material.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The thermoelectric conversion material of the present invention is mainly composed of In and Zn and has a composition ratio of 0.2 <In / (I
n + Zn) <1 (0 <Zn / (In + Zn) <0.8)
It consists of a complex oxide of. In this composite oxide, Zn
Is a solid solution in indium oxide or the general formula In ₂ O ₃ (Zn
O) A hexagonal layered compound represented by _m (m = 2 to 20) is formed to exert the effect of improving the electrical conductivity of the composite oxide. If Zn is not contained, the electric conductivity will be low, and as a result, the output factor will be low. On the other hand, if the amount of Zn is too large, ZnO is generated, and this ZnO becomes a cause of electron scattering, so that the electrical conductivity becomes low and, as a result, the output factor decreases. The composition ratio is preferably 0.3 <In /
(In + Zn) <1 (0 <Zn / (In + Zn) <0.
7), more preferably 0.5 <In / (In + Zn) <
1 (0 <Zn / (In + Zn) <0.5).

The complex oxides having various compositions are obtained by uniformly mixing raw materials containing a necessary element source in the form of powder or the like and firing. As a raw material used for producing the composite oxide, each component element, an oxide of each component element, or a raw material that becomes an oxide when firing the component element can be used.
Examples of the In source include metal (In) and oxide (In
₂ O ₃ ), hydroxide [In (OH) ₃ ], nitrate [In (NO
₃ ) ₃ ] etc. are used, and examples of the Zn source include metal (Zn), oxide (ZnO), and hydroxide [(Zn (OH)
₂ )], nitrate [Zn (NO ₃ ) ₂ ] and the like are used.

Since the thermoelectric conversion material of the present invention has a high electric conductivity and a large negative thermoelectromotive force, the output factor (electric conductivity × square of Seebeck coefficient) which is an index of the performance of thermoelectric generation. ) Is high and about 1 μW / K ² c even at room temperature
The value of m is shown. In general, the magnitude of the absolute value of the thermoelectromotive force and the electric conductivity have a negative correlation, and the absolute value of the thermoelectromotive force decreases as the electric conductivity increases, but the thermoelectric conversion material of the present invention. Since it is composed of a composite oxide mainly composed of In and Zn, both the absolute value of thermoelectromotive force and the electric conductivity are increased or the absolute value of thermoelectromotive force is decreased as compared with the conventional composite oxide. Can be suppressed.

The thermoelectric conversion element of the present invention is a thermoelectric conversion element using the above-mentioned thermoelectric conversion material, and the thermoelectric conversion material is used as an n-type thermoelectric conversion material. Other components can be made of known materials. For example, as the p-type thermoelectric conversion material used together with the n-type thermoelectric conversion material, the materials disclosed in the above publications can be used.

FIG. 1 is a schematic view showing an embodiment of the thermoelectric conversion element of the present invention. In the thermoelectric conversion element 1, the n-type thermoelectric conversion material 2 and the p-type thermoelectric conversion material 3 are bonded to the common high temperature side electrode 4 and the two low temperature side electrodes 5 and 6. Here, when the high temperature side electrode 4 is heated, the temperature of the high temperature side joint portion 7 rises to Th, and the temperature T of the low temperature side joint portion 8 is increased.
A temperature difference ΔT (ΔT = Th−Tc) is generated between the high temperature side electrode 4 and the low temperature side electrode 5, and a voltage is generated between the high temperature side electrode 4 and the low temperature side electrodes 5 and 6. The load resistance (R) is applied between the low temperature side electrodes 5 and 6.
Current (I) flows when this is connected, and this current is converted to power (W)
Can be taken out as. The thermoelectric conversion element configured in this way can not only extract electromotive force from the temperature difference, but can also be used as a heat pump for cooling or heating by applying electric power in the opposite direction.

[0016]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to these examples.

Example 1 9.78 g of indium oxide (In ₂ O ₃ ) powder (purity 4N, average particle size about 2 μm) and 2.2 g of zinc oxide (ZnO) powder (purity 3N, average particle size about 2 μm) Weighed, mixed in an automatic mortar for 2 hours and crushed. Next, this mixed powder is
It was baked at 200 ° C. for 8 hours. At this time, the heating rate is 10
C./min., And the cooling after firing was spontaneous cooling in the firing furnace. The obtained fired product was pulverized again in an automatic mortar for 2 hours and then put into a mold to have a width of 5 mm, a thickness of 2 mm and a length of 20.
It was pressure molded into a rod shape of mm. The obtained molded body is 1,3
It was fired at 80 ° C. for 5 hours to obtain a sintered body (composite oxide).
At this time, the rate of temperature increase was 4 ° C./minute, and the rate of temperature decrease was 10 ° C./minute. As a result of analyzing the composition of this sintered body, the ratio (mol%) of indium and zinc was 96.3: 3.7. The density of this sintered body was 6.7 g / cm ³ .

The electrical conductivity and Seebeck coefficient at 60 ° C. and 200 ° C. of the obtained sintered body were measured by the following methods, and the output factor was determined from these values. The results are shown in Table 1. (1) Electric conductivity Measured using a direct current 4-terminal method. (2) Seebeck coefficient A thermocouple was adhered to both ends of the sintered body, and the temperature of the sintered body was directly measured. The sintered body was passed between two copper blocks, a temperature difference was made between the copper blocks, the thermoelectromotive force was measured, and the Seebeck coefficient was obtained from the slope of the temperature difference and the straight line of the thermoelectromotive force.

This sintered body has a large negative Seebeck coefficient at both temperatures of 60 ° C. and 200 ° C. even though it has a high electric conductivity.
It has been found to be useful as a thermoelectric conversion material for molds.

Example 2 8.9 g of indium oxide (In ₂ O ₃ ) powder (purity 4N, average particle size of about 2 μm), zinc oxide (ZnO) powder (purity 3
1.1 g of N, average particle size of about 2 μm) were weighed, mixed in an automatic mortar for 2 hours and pulverized. Next, the mixed powder
It was baked at 00 ° C. for 8 hours. At this time, the heating rate is 10 ° C
/ Min, and the cooling after firing was spontaneous cooling in the firing furnace. The obtained fired product was crushed again in an automatic mortar for 2 hours, and then put in a mold to have a width of 5 mm, a thickness of 2 mm and a length of 20 m.
m was pressed into a rod shape. The obtained molded product was 1,38
It was fired at 0 ° C. for 5 hours to obtain a sintered body (composite oxide). At this time, the rate of temperature increase was 4 ° C./minute, and the rate of temperature decrease was 10 ° C./minute. As a result of analyzing the composition of this sintered body, the ratio (mol%) of indium and zinc was 83:17. Also,
The density of this sintered body was 6.9 g / cm ³ . The electrical conductivity and Seebeck coefficient of this sintered body were measured in the same manner as in Example 1, and the output factor was determined from these values. The results are shown in Table 1.

This sintered body has a large negative Seebeck coefficient at both temperatures of 60 ° C. and 200 ° C. even though it has a high electric conductivity.
It has been found to be useful as a thermoelectric conversion material for molds.

Example 3 12.6 g of indium oxide (In ₂ O ₃ ) powder (purity 4N, average particle size of about 2 μm) and zinc oxide (ZnO) powder (purity 3
7.4 g of N, average particle size of about 2 μm) was weighed, mixed and pulverized in an automatic mortar for 2 hours. Next, the mixed powder
It was baked at 00 ° C. for 8 hours. At this time, the heating rate is 10 ° C
/ Min, and the cooling after firing was spontaneous cooling in the firing furnace. The obtained fired product was crushed again in an automatic mortar for 2 hours, and then put in a mold to have a width of 5 mm, a thickness of 2 mm and a length of 20 m.
m was pressed into a rod shape. The obtained molded product was 1,38
It was fired at 0 ° C. for 5 hours to obtain a sintered body (composite oxide). At this time, the rate of temperature increase was 4 ° C./minute, and the rate of temperature decrease was 10 ° C./minute. As a result of analyzing the composition of this sintered body, the ratio (mol%) of indium and zinc was 50:50. Also,
The density of this sintered body was 6.9 g / cm ³ . The electrical conductivity and Seebeck coefficient of this sintered body were measured in the same manner as in Example 1, and the output factor was determined from these values. The results are shown in Table 1.

This sintered body has a large negative Seebeck coefficient at both temperatures of 60 ° C. and 200 ° C. even though it has a high electric conductivity.
It has been found to be useful as a thermoelectric conversion material for molds.

Comparative Example 1 10 g of indium oxide (In ₂ O ₃ ) powder (purity 4N, average particle size of about 10 μm) was weighed and pulverized in an automatic mortar for 2 hours. Next, put this powder in a mold, width 5 mm, thickness 2
mm was pressed into a rod shape having a length of 20 mm. The obtained molded body was fired at 1,100 ° C. for 5 hours to obtain a sintered body.
At this time, the rate of temperature increase was 4 ° C./minute, and the rate of temperature decrease was 10 ° C./minute. The density of this sintered body was 4.0 g / cm ³ . The electrical conductivity and Seebeck coefficient of this sintered body were measured in the same manner as in Example 1, and the output factor was determined from these values. The results are shown in Table 1.

This sintered body has a very large negative Seebeck coefficient at both temperatures of 60.degree. C. and 200.degree. C., but its electric conductivity is small, so that the output factor is 6
0.053 μW / K ² cm at 0 ° C., and 0.2 at 200 ° C.
The value was as low as 14 μW / K ² cm.

[0026]

[Table 1]

[0027]

According to the present invention, a thermoelectric conversion material having good electric conductivity and high thermoelectromotive force and a thermoelectric conversion element using the same can be provided.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a thermoelectric conversion element of the present invention.

[Explanation of symbols] 1 Thermoelectric conversion element 2 n-type thermoelectric conversion material (composite oxide) 3 p-type thermoelectric conversion material 4 High temperature side electrode 5, 6 Low temperature side electrode 7 High temperature side joint 8 Low temperature side joint

Claims (2)

[Claims] 1. A thermoelectric conversion material comprising a composite oxide mainly composed of In and Zn and having a composition ratio of In and Zn of 0.2 <In / (In + Zn) <1. 2. A thermoelectric conversion element comprising the thermoelectric conversion material according to claim 1.