JP2000261049A - P-type thermoelectric converting material and manufacture of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily and efficiently manufacture P-type thermoelectric converting materials in which CoSb3 is used as main components, a small amount of Fe is included as dopant for deciding a conductive type, and a stable P-type is indicated, and high performance can be obtained, electrical conductivity can be increased, chemical stability can be realized, and fluctuation due to the fluctuation of composition can be reduced by using a general baking process. SOLUTION: The chemical composition of the main components of P-type thermoelectric converting materials is represented by CoFexSby (0.001<x<0.6, 2.7<y<5.7), and the oxygen contents are set to 0.08 mol or less with respect to CoFexSby of 1 mol. Material powder, in which the chemical composition of main components is expressed by CoFexSby (0.001<x<0.6, 2.7<y<5.7) is baked in a reducing atmosphere such as hydrogen or material powder, in which the chemical composition of the main components is expressed by Co1-xFexSby (0.001<x<0.4, 2.7<y<3.4), and oxygen contents are 0.08 mol or less with respect to 1 mol is backed in a nonoxidizing atmosphere such as nitrogen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a thermoelectric conversion material used as a P-type semiconductor of a thermoelectric conversion module and a method for producing the same, in particular, a main component represented by a chemical composition CoSb ₃ ;
The present invention relates to a P-type thermoelectric conversion material containing a small amount of Fe for controlling the conductivity type to P-type and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as high performance thermoelectric conversion materials,
Tellurium compounds such as Bi ₂ Te ₃ , Bi ₂ Sb ₈ Te ₁₅ and BiTe ₂ Se are known. Among antimony compounds such as TSb ₃ (T: Co, Ir, Ru), for example, CoSb ₃ is also known as a thermoelectric conversion material. This CoSb ₃ thermoelectric conversion material is known as a thermoelectric conversion material usable in a temperature range up to about 600 ° C.

[0003]

A thermoelectric conversion material composed of a tellurium compound represented by a Bi-Te compound has a relatively high figure of merit Z (Z = 3 × 10 ⁻³ [1 / K]) at room temperature. Have, but 30
At a high temperature of 0 ° C. or higher, there is a problem that characteristics are deteriorated. Here, the figure of merit Z is such that α is a Seebeck coefficient, σ
Is electrical conductivity and κ is thermal conductivity, Z = α ² σ /
It is represented by κ. Further, the thermoelectric conversion material made of a tellurium-based compound has a problem that it has a low melting point, lacks chemical stability, and tends to cause variations in characteristics due to composition fluctuation.

_{Further, TSb 3 (T: Co,} Ir, Ru) of the thermoelectric conversion material composed of Sb-based compounds, such as, in particular CoSb ₃ is much usable temperature range is compared to the Bi-Te-based compound Although it has the advantage of being wide, there are the following problems in obtaining a P-type conductivity type material. That is, a stoichiometric composition without doping
In the case of CoSb ₃ , the conductivity type is originally P-type, but if active doping is not performed, it is easily affected by the purity of the raw material, and stable thermoelectric characteristics cannot be obtained. Or even more
In some cases, the controllability of the conductivity type may be lost.

[0005] In addition to the problem of raw material impurities, in the actual material manufacturing process, compositional fluctuations inevitably occur. Particularly, when a composition in which Sb is lost from the stoichiometric composition occurs,
The conductivity type is reversed and becomes N-type.

For the above reasons, in order to obtain P-conductivity type CoSb ₃ having high performance and stable thermoelectric characteristics, active doping is performed to eliminate the influence of the source impurities.
It is necessary to control the conductivity type, and at the same time, it is necessary to eliminate the influence of composition fluctuation in the material manufacturing process.

An object of the present invention is to at least reduce the above-mentioned problems of a thermoelectric conversion material containing CoSb ₃ as a main component, to have high performance over a wide temperature range and to have high electric conductivity.
An object of the present invention is to provide a P-type thermoelectric conversion material which is chemically stable and has small variation due to composition fluctuation.

Another object of the present invention is to provide a method capable of easily and efficiently producing a P-type thermoelectric conversion material having such excellent characteristics by using a general-purpose sintering process. .

[0009]

Means for Solving the Problems The present invention provides a thermoelectric conversion material that is used as P-type semiconductor thermoelectric conversion module, the chemical composition of the main _{component, CoFe x Sb y (0.001 <} x <
0.6, 2.7 <y <5.7), and the oxygen content z
Is characterized in that with respect to Fe _x Sb _y 1 mol 0.08 mol or less.

In the P-type thermoelectric conversion material according to the present invention, it is particularly preferable that the P-type semiconductor is constituted by a sintered body. Such a P-type semiconductor can be easily and efficiently manufactured by a general-purpose baking process.

A method for producing a P-type thermoelectric conversion material according to the present invention comprises a P-type thermoelectric conversion material containing a main component represented by a chemical composition CoSb ₃ and a small amount of Fe for controlling the conductivity type to P-type. in producing the firing method, and characterized in that the chemical composition of the main component is CoFe _x Sb _y raw material powder represented by (0.001 <x <0.6, 2.7 <y <5.7), firing in a reducing atmosphere Is what you do.

Further, the method for producing a P-type thermoelectric conversion material according to the present invention provides a P-type thermoelectric conversion material containing a main component represented by the chemical composition CoSb ₃ and a small amount of Fe for controlling the conductivity type to P-type. in producing the material by firing method, CoFe chemical composition of the main component _{x Sb y (0.001 <x <} 0.6, 2.7 <y <5.7)
In _{expressed, CoFe x Sb y (0.001 <} x <0.6, 2.7 <y <5.7)
It is characterized in that a raw material powder having an oxygen content of 0.08 mol or less per mol is fired in a non-oxidizing atmosphere.

Here, the non-oxidizing atmosphere includes not only an inert atmosphere such as nitrogen or argon, but also a reducing atmosphere such as hydrogen gas.

[0014] In the P-type thermoelectric conversion material according to the present invention described _{above, CoFe x Sb y (0.001 <} x <0.6, 2.7 <y <5.
Has a main component represented by 7), the oxygen content, CoFe _x Sb _y
0.08 mol or less per 1 mol.
The reason for limiting below 0.08 mol per CoFe _x Sb _y 1 mole, to contain oxygen more is because Fe acts as a dopant is not a P-type stable so would be selectively oxidized.

Further, the main component represented by CoFe _x Sb _y, Co
The content of Fe per mole is set to 0.001 <x <0.6 and the content of Sb is set to 2.7 <y <5.7. The reason for this is that when the content is out of such a range, the electric conductivity σ or Seebeck This is because the coefficient α becomes low and the P-type semiconductor material of the thermoelectric conversion module does not exhibit good characteristics.

In the method for producing a P-type thermoelectric conversion material according to the present invention, as described above, in order to limit the oxygen content, the raw material powder before firing is reduced in oxygen content to be fired in a non-oxidizing atmosphere. Or baking in a reducing atmosphere to remove oxygen. According to such a method, it was confirmed that Fe as a dopant was not oxidized, so that the controllability of doping was improved, and a P-type thermoelectric conversion material having desired characteristics was obtained.

An attempt to produce a thermoelectric conversion material by adding Fe to CoSb ₃ described above is described in, for example, “LDDudkin and N.Kh.
rikosov; Sov. Phys. Solid State, 1 (1959)
It is described on pages 6-133. However, this document does not specify the amount of Fe added or the oxygen content for making the thermoelectric conversion material P-type, and the P-type-N-type inversion occurs depending on the composition. Was not possible.

On the other hand, in the present invention, as described above,
By defining the Fe content and the oxygen content, a P-type thermoelectric conversion material can be obtained stably, and the electric conductivity can be controlled by controlling the Fe content within the above range. The rate can be adjusted arbitrarily.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Some examples of the P-type thermoelectric conversion material according to the present invention are shown below together with comparative examples. Both of these examples and comparative examples were produced by the following processes.

Using granular Co, Sb, Fe as a starting material,
After weighing a predetermined amount, compacting it in a non-oxidizing atmosphere
The heat treatment was performed for 96 hours. After coarsely pulverized in a mortar, dry pulverization was performed using a planetary rotary ball mill, and finely pulverized until the average particle diameter became 100 μm or less. After the alloy powder thus produced is compacted at a compaction pressure of 7 Ton / cm ^2, it is placed in a non-oxidizing atmosphere of nitrogen or a reducing atmosphere of hydrogen at 600 to 750 ° C. for 3 to 6 hours. Was performed to obtain a sintered body.

Here, the raw material powder before firing is not limited to the raw material powder composed of a single element which is weighed in a predetermined amount and then mixed, as described above. It is also possible to use, for example, a mixture of a powder obtained by melting and pulverization and a powder of a single element so that the element content ratio becomes a target ratio.

Table 1 shows the composition ratio, sintering temperature and atmosphere of the sintered body obtained when the composition ratio of the raw material powder in the above-mentioned process was variously changed with Co being 1 mol. In Table 1, some of the conditions deviate from the conditions of the present invention, which are shown as comparative examples. That is, sample 1
Samples 18 to 2 are examples according to the present invention.
4 is a comparative example.

[0023]

[Table 1]

As can be seen from Table 1, not only in a reducing atmosphere but also in a non-oxidizing nitrogen atmosphere, the oxygen content in the sintered body is smaller than the oxygen content in the raw material powder before firing. Is low. This is because, when firing in a non-oxidizing atmosphere, no new oxygen is mixed into the powder component, and oxygen adsorbed on the surface of the compact is removed to some extent during firing. It is believed that there is. The amount of oxygen adsorbed on the surface of the compact depends on the particle size and surface area of the powder, but as long as the calcination is performed in a non-oxidizing atmosphere, the oxygen content in the sintered compact is It does not exceed the oxygen content. Therefore, in carrying out the method for producing a P-type thermoelectric conversion material according to the present invention, a powder having a chemical composition equivalent to a target chemical composition is prepared, molded, and then fired in a non-oxidizing atmosphere. It turns out that it is good. Examples of such a non-oxidizing atmosphere include an inert gas atmosphere such as argon and an ultra-high vacuum atmosphere in addition to the nitrogen used in this embodiment. Of course, a reducing atmosphere can be employed as the non-oxidizing atmosphere.

Samples 13 to 17 in Table 1 described above show the relationship between the chemical composition of various powder samples and the chemical composition of a sintered body obtained by firing the powder samples in a hydrogen atmosphere as a reducing atmosphere. It is shown. Accordingly, in producing a P-type thermoelectric conversion material having a limited oxygen content by sintering as defined in the present invention, sintering in a reducing atmosphere such as hydrogen is a more reliable method. I understood that. That is, as the sample 17, the oxygen content of the starting raw material powder is, if the relative CoFe _x Sb _y 1 mole deviate from the condition that 0.08 mol or less, by performing firing in a reducing atmosphere The oxygen content of the resulting sintered body falls within the scope of the present invention.

As described in the above-mentioned document, Co
That the sb ₃ by the addition of Fe to produce a thermoelectric conversion material has already been tried. However, the addition amount of Fe and the oxygen amount for making the thermoelectric conversion material P-type are not specified, and PN inversion occurs depending on the composition, and the conductivity type is not controlled.

In the present invention, by defining the amount of Fe added and the amount of oxygen in the sample, a thermoelectric conversion material having a P-type can be produced consistently within the measurement temperature range, and it can be used as a dopant. The electric conductivity can be arbitrarily adjusted by changing the amount of Fe added.

FIG. 1 is a graph showing the temperature dependence of the Seebeck coefficient α representing the thermoelectric efficiency of some of the sintered bodies which are comparative examples shown in Table 1, and FIG. 2 is an example of the present invention. 4 is a graph showing the temperature dependence of the Seebeck coefficient α of some sintered bodies. In these graphs, when the Seebeck coefficient α is positive, it indicates that the sintered body is of P conductivity type, and when it is negative, it indicates that it is of N conductivity type.

As is clear from FIGS. 1 and 2, in the case of the sintered body of the comparative example, the phenomenon that the conductivity type is reversed depending on the temperature range occurs, whereas in the case of the sintered body according to the present invention. Is a stable P-type in all measured temperature ranges, and a large Seebeck coefficient α is obtained.

[0030] In the present invention, in the main component represented by CoFe _x Sb _y, the amount of Sb and 2.7 <y <5.7, for an amount of 0.001 <x <0.6 of Fe is such range If it deviates, the electrical conductivity σ or the Seebeck coefficient α will be low, and the P-type semiconductor material of the thermoelectric conversion module will not exhibit good characteristics.

[0031] In addition, the chemical _{composition, CoFe x Sb y (0.001 <} x
<0.6, 2.7 <thermoelectric conversion material according to the present invention represented by y <5.7), the the oxygen content was 0.08 moles or less with respect CoFe _x Sb _y 1 mole, contains more oxygen than it Then, Fe acting as a dopant is selectively oxidized, and a thermoelectric conversion material exhibiting a P-type cannot be stably obtained.

FIG. 3 shows the electrical conductivity at room temperature of some of the sintered bodies of the above-mentioned examples and comparative examples of the present invention,
Is a graph showing the relationship between oxygen content relative to Fe _x Sb _y 1 mol. As is apparent from this graph, CoFe _x Sb _y
The electrical conductivity sharply decreases as the oxygen content per mole increases.

FIG. 4 shows the results of analyzing the chemical bonding state of Fe in the various sintered compact samples shown in Table 1 by X-ray photoelectron spectroscopy (XPS).
In FIG. 4, curve A shows the 2p spectrum of Fe for sample 14, and curve B shows the 2p spectrum of Fe for sample 20. From these curves, it was clarified that when oxygen was present in the sintered body, Fe in the sintered body was present in an oxide state.
Here, in the case of Sample 20 which is a comparative example,
It is clear that Fe has almost disappeared.

From these facts, it has been clarified that when oxygen is present in the sintered body, oxidation of Fe as a dopant occurs. Therefore, in the case of a sintered body having an oxygen concentration outside the chemical composition range according to the present invention, oxidation of Fe, which is a dopant, occurs, so that N-type is caused, and a desired P-type thermoelectric conversion material is used. You will not be able to get it. In this case, it is known that Fe becomes a trioxide.

[0035]

As a result of the above considerations, in the chemical composition according to the present invention, when the oxygen concentration is limited as described above, since the dopant element Fe for controlling the conductivity type exists in a metal state, a wide temperature range is obtained. It was found that a thermoelectric conversion material having excellent characteristics in the range and stably exhibiting P-type was obtained.

In the manufacturing method according to the present invention, a stable P-type semiconductor having high thermoelectric characteristics can be manufactured by using a general-purpose sintering method. It can be produced efficiently at low cost, and its industrial value is very large.

Further, this type of material is a cubic type of CoSb.
_Since the crystal structure of ₃ is used as the basic skeleton, each material containing P-type and N-type impurities has the same crystal structure. Therefore, it can be considered that the material has the same thermal stability and coefficient of thermal expansion, so that the PN junction can be easily formed by powder molding, and furthermore, it can be chemically formed in a wide temperature range from room temperature to 300 ° C. or more. Is also stable, does not deteriorate in thermal characteristics, is excellent in heat resistance and moldability, and is economically excellent.

[Brief description of the drawings]

FIG. 1 is a graph showing the temperature dependence of a Seebeck coefficient of a P-type thermoelectric conversion material of a comparative example.

FIG. 2 is a graph showing the temperature dependence of the Seebeck coefficient of a P-type thermoelectric conversion material according to the present invention.

FIG. 3 is a graph showing the relationship between the oxygen content and the electrical conductivity of the P-type thermoelectric conversion material of the present invention.

FIG. 4 is a graph showing an X-ray photoelectron spectroscopy spectrum showing the form of Fe in Examples and Comparative Examples of the P-type thermoelectric conversion material according to the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Miyoshi Minato 2-56, Suda-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Inside Nihon Insulators Co., Ltd. (72) Inventor Keiko Kushibiki Nissan Motor Co., Ltd. (72) Inventor Masakazu Kobayashi Nissan Motor Co., Ltd. F-term (reference: 2) Takaracho, Kanagawa-ku, Yokohama, Kanagawa 4K018 AC01 AD20 BA04 BC10 BC20 DA31 KA32

Claims (4)

[Claims] 1. A thermoelectric conversion material used as a P-type semiconductor thermoelectric conversion module, the chemical composition of the main component, CoFe _x Sb _y is represented by (0.001 <x <0.6, 2.7 <y <5.7), the oxygen content, 0 for CoFe _x Sb _y 1 mol.
A P-type thermoelectric conversion material characterized in that the amount is 08 mol or less. 2. The P-type thermoelectric conversion material according to claim 1, wherein the P-type semiconductor is made of a sintered body. 3. Manufacturing a P-type thermoelectric conversion material containing a main component represented by a chemical composition CoSb ₃ and a small amount of Fe for controlling the conductivity type to P-type by a firing method. chemical composition _{CoFe x Sb y (0.001 <x} <0.6, 2.7 <y <
5.7) A method for producing a P-type thermoelectric conversion material, wherein the raw material powder represented by 5.7) is fired in a reducing atmosphere. 4. When a P-type thermoelectric conversion material containing a main component represented by the chemical composition CoSb ₃ and a small amount of Fe for controlling the conductivity type to P-type is produced by a firing method, chemical composition _{CoFe x Sb y (0.001 <x} <0.6, 2.7 <y <
5.7) A method for producing a P-type thermoelectric conversion material, characterized by firing a raw material powder having an oxygen content of 0.08 mol or less per 1 mol in a non-oxidizing atmosphere.