WO2019168029A1

WO2019168029A1 - Thermoelectric conversion material, thermoelectric conversion element, thermoelectric conversion module and method for producing thermoelectric conversion material

Info

Publication number: WO2019168029A1
Application number: PCT/JP2019/007563
Authority: WO
Inventors: 中田　嘉信
Original assignee: 三菱マテリアル株式会社
Priority date: 2018-02-27
Filing date: 2019-02-27
Publication date: 2019-09-06

Abstract

This thermoelectric conversion material is characterized by being formed of a sintered body of an undoped magnesium compound and by having an electrical resistance of 1.0 × 10-4 Ω·m or less. It is preferable that the magnesium compound is composed of one or more compounds which are selected from among MgSi compounds, MgSn compounds, MgSiSn compounds and MgSiGe compounds.

Description

Thermoelectric conversion material, thermoelectric conversion element, thermoelectric conversion module, and method of manufacturing thermoelectric conversion material

The present invention relates to a thermoelectric conversion material composed of a sintered body of a magnesium-based compound, a thermoelectric conversion element including the thermoelectric conversion material, a thermoelectric conversion module, and a method for manufacturing the thermoelectric conversion material.
This application claims priority based on Japanese Patent Application No. 2018-033664 filed in Japan on February 27, 2018 and Japanese Patent Application No. 2019-022732 filed on February 12, 2019 in Japan. , The contents of which are incorporated herein.

A thermoelectric conversion element made of a thermoelectric conversion material is an electronic element capable of mutually converting heat and electricity, such as Seebeck effect and Peltier effect. The Seebeck effect is an effect of converting thermal energy into electric energy, and is a phenomenon in which an electromotive force is generated when a temperature difference is generated between both ends of the thermoelectric conversion material. Such electromotive force is determined by the characteristics of the thermoelectric conversion material. In recent years, thermoelectric power generation utilizing this effect has been actively developed.
The thermoelectric conversion element described above has a structure in which electrodes are formed on one end side and the other end side of a thermoelectric conversion material.

As an index representing the characteristics of such a thermoelectric conversion element (thermoelectric conversion material), for example, the power factor (PF) expressed by the following formula (1) or the dimensionless figure of merit expressed by the following formula (2) (ZT) is used. In addition, in a thermoelectric conversion material, since it is necessary to maintain a temperature difference by the one surface and the other surface side, it is preferable that thermal conductivity is low.
PF = S ² σ (1)
Where S: Seebeck coefficient (V / K), σ: electrical conductivity (S / m)
ZT = S ² σT / κ (2)
Where T = absolute temperature (K), κ = thermal conductivity (W / (m × K))

Here, as the above-mentioned thermoelectric conversion material, for example, as shown in Patent Documents 1 and 2, materials obtained by adding various dopants to magnesium silicide have been proposed. In addition, in the thermoelectric conversion material which consists of magnesium silicide shown in patent document 1, 2, it manufactures by sintering the raw material powder adjusted to the predetermined composition.

JP 2013-179322 A JP 2017-152691 A

Here, elements such as Sb and Bi used as dopants in the thermoelectric conversion material described above correspond to chemical substances specified by, for example, the chemical substance management promotion method (PRTR method), and therefore, it is necessary to strictly manage them. And handling was very complicated. In addition, since other dopant elements such as Al may be deteriorated by oxidation of the dopant element, the handling becomes complicated and there is a problem of oxidation during production.
However, without the addition of a dopant element, magnesium silicide does not have a stable and low resistance, and generally has a very high electrical resistance, a large variation in electrical resistance depending on manufacturing conditions, and is important for thermoelectric materials. Since the electric resistance greatly fluctuates from a low temperature to a middle temperature, it could not be used as a thermoelectric conversion material.

The present invention has been made in view of the above-described circumstances, and can reduce the electric resistance value without adding a dopant element that is complicated to handle, and uses a thermoelectric conversion material excellent in thermoelectric characteristics. It is an object of the present invention to provide a thermoelectric conversion element, a thermoelectric conversion module, and a method for manufacturing the thermoelectric conversion material.

In order to solve the above problems, the thermoelectric conversion material of the present invention is a thermoelectric conversion material made of a sintered body of a non-doped magnesium-based compound and has an electric resistance value of 1.0 × 10 ⁻⁴ Ω · m or less. It is characterized by being.

The thermoelectric conversion material comprising the sintered body of the non-doped magnesium compound of the present invention has an electrical resistance value of 1.0 × 10 ⁻⁴ without intentionally adding a dopant of a metal element such as Sb, Bi, or Al. It is a thermoelectric conversion material having a low power of Ω · m or less and a high power factor (PF) and dimensionless figure of merit (ZT). The thermoelectric conversion material of the present invention is particularly excellent in thermoelectric characteristics in a relatively low temperature region from room temperature to about 300 ° C.

Here, in the thermoelectric conversion material of the present invention, the magnesium compound is preferably one or more selected from MgSi compounds, MgSn compounds, MgSiSn compounds, and MgSiGe compounds.
In this case, since the magnesium compound is one or more selected from MgSi compounds, MgSn compounds, MgSiSn compounds, and MgSiGe compounds, it is possible to obtain a thermoelectric conversion material having further excellent thermoelectric characteristics. it can.

Further, the thermoelectric conversion material of the present invention is characterized by being n-type. In this case, n-type thermoelectric power can be used without intentionally adding a dopant of a metal element such as Sb, Bi, or Al, which is difficult to handle. It can be a conversion material.

A thermoelectric conversion element of the present invention is characterized by including the above-described thermoelectric conversion material and electrodes bonded to one surface of the thermoelectric conversion material and the other surface facing each other.
According to the thermoelectric conversion element of this structure, since it consists of the thermoelectric conversion material mentioned above, the thermoelectric conversion element excellent in the thermoelectric characteristic can be obtained.

The thermoelectric conversion module of the present invention is characterized by including the above-described thermoelectric conversion element and terminals respectively joined to the electrodes of the thermoelectric conversion element.
According to the thermoelectric conversion module having this configuration, since the thermoelectric conversion element made of the thermoelectric conversion material described above is provided, a thermoelectric conversion module having excellent thermoelectric characteristics can be obtained.

The manufacturing method of the thermoelectric conversion material of the present invention is a manufacturing method of the thermoelectric conversion material for manufacturing the above-described thermoelectric conversion material, in which silicon oxide powder is mixed with non-doped magnesium-based compound powder and sintered raw material powder is mixed. It is characterized by comprising a sintered raw material powder forming step to be obtained and a sintering step in which the sintered raw material powder is heated while being pressed to form a sintered body.

According to the method for producing a thermoelectric conversion material having this configuration, non-doped magnesium compound powder, that is, magnesium compound powder to which no dopant is intentionally added, is mixed with silicon oxide powder to obtain sintered raw material powder. Since it has a sintering raw material powder forming step to be obtained, it becomes possible to keep the electrical resistance value of the sintered body of the magnesium-based compound low by adding silicon oxide without adding a dopant element. . Therefore, the thermoelectric conversion material mentioned above can be manufactured.
Further, since silicon oxide is a chemically stable substance, it is easy to handle silicon oxide at the time of manufacture, and it becomes possible to efficiently manufacture a thermoelectric conversion material.

Here, in the manufacturing method of the thermoelectric conversion material of the present invention, the amount of the silicon oxide powder added in the sintering raw material powder forming step is in the range of 0.1 mass% to 10.0 mass%. Is preferred.
In this case, since the addition amount of the silicon oxide powder is in the range of 0.1 mass% or more and 10.0 mass% or less, the electrical resistance value of the magnesium compound sintered body can be reliably reduced. .

According to the present invention, without adding a dopant element that is complicated to handle, the electric resistance value can be kept low, and a thermoelectric conversion material excellent in thermoelectric characteristics, a thermoelectric conversion element using the thermoelectric conversion element, a thermoelectric conversion module, and It is possible to provide a method for producing the thermoelectric conversion material.

It is sectional drawing which shows the thermoelectric conversion material which is one Embodiment of this invention, a thermoelectric conversion element using the same, and a thermoelectric conversion module. It is a flowchart which shows an example of the manufacturing method of the thermoelectric conversion material which is one Embodiment of this invention. It is sectional drawing which shows an example of the sintering apparatus used with the manufacturing method of the thermoelectric conversion material shown in FIG.

Hereinafter, a thermoelectric conversion material, a thermoelectric conversion element, a thermoelectric conversion module, and a method of manufacturing a thermoelectric conversion material according to an embodiment of the present invention will be described with reference to the accompanying drawings.
Each embodiment described below is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. In addition, in the drawings used in the following description, in order to make the features of the present invention easier to understand, there is a case where a main part is shown in an enlarged manner for the sake of convenience. Not necessarily.

In FIG. 1, the thermoelectric conversion material 11 which is embodiment of this invention, the thermoelectric conversion element 10 using this thermoelectric conversion material 11, and the thermoelectric conversion module 1 are shown.
A thermoelectric conversion module 1 shown in FIG. 1 includes a thermoelectric conversion material 11 according to the present embodiment,

electrodes

12a and 12b formed on one surface 11a of the thermoelectric conversion material 11 and the other surface 11b opposite to the surface 11a. And

terminals

13a and 13b connected to the

electrodes

12a and 12b.
A thermoelectric conversion element 10 includes the thermoelectric conversion material 11 and the

electrodes

12a and 12b.

The

electrodes

12a and 12b are made of nickel, silver, cobalt, tungsten, molybdenum or the like. The

electrodes

12a and 12b can be formed by current sintering, plating, electrodeposition, or the like.
The

terminals

13a and 13b are formed of a metal material having excellent conductivity, for example, a plate material such as copper or aluminum. In this embodiment, an aluminum rolled plate is used. The

electrodes

12a and 12b of the thermoelectric conversion element 10 and the

terminals

13a and 13b can be joined by Ag brazing, Ag plating, or the like.

The thermoelectric conversion material 11 in the present embodiment is composed of a magnesium compound sintered body.
Here, the magnesium compound constituting the sintered body is preferably one or more selected from MgSi compounds, MgSn compounds, MgSiSn compounds, and MgSiGe compounds.
In the present embodiment, the compound constituting the sintered body is magnesium silicide (Mg ₂ Si).

The thermoelectric conversion material 11 according to the present embodiment is a non-doped thermoelectric conversion material and has an electric resistance value of 1.0 × 10 ⁻⁴ Ω · m or less in a temperature range of 100 ° C. to 550 ° C. The electric resistance value of the thermoelectric conversion material 11 in the temperature range of 100 ° C. or more and 550 ° C. or less is preferably 6.0 × 10 ⁻⁵ Ω · m or less.
The lower limit value of the electric resistance value of the thermoelectric conversion material 11 in the temperature range of 100 ° C. or higher and 550 ° C. or lower is preferably 1.0 × 10 ⁻⁵ Ω · m.
Further, the thermoelectric conversion material 11 according to the present embodiment is an n-type thermoelectric conversion material in which electrons are carriers.

Here, the term “non-doped” means that a metal element dopant is not added intentionally.
However, as an unavoidable impurity, for example, a dopant element such as Sb, Bi, or Al may be included. In this case, it is preferable that the Sb content is less than 0.001 mass%, the Bi content is less than 0.001 mass%, and the Al content is 0.25 mass% or less. In addition to Sb, Bi, and Al, elements such as Na, K, B, Ga, In, P, As, Cu, and Y may be included as inevitable impurities, but even in that case, the content of each element Is preferably 0.01 mass% or less.

In the thermoelectric conversion material 11 in this embodiment, since the electric resistance value is 1.0 × 10 ⁻⁴ Ω · m or less, the dopant element mixed as an unavoidable impurity is very small. Therefore, the electrical resistance value is suppressed to be sufficiently low.
Here, in this embodiment, the electrical resistance value is suppressed low by adding silicon oxide. Oxygen constituting the added silicon oxide reacts with the magnesium compound Mg during sintering to form magnesium oxide, while Si constituting the silicon oxide segregates to the magnesium compound grain boundary. It is considered that dangling bonds at the interface are formed to reduce the resistance, or diffuse into the Mg compound and enter the Mg lattice sites to emit electrons and lower the electrical resistance. Of the added silicon oxide, unreacted silicon oxide may be contained in the thermoelectric conversion material 11.

Hereinafter, an example of a method for manufacturing the thermoelectric conversion material 11 according to the present embodiment described above will be described with reference to FIGS. 2 and 3.

(Magnesium compound powder preparation step S01)
First, powder of a non-doped magnesium-based compound (magnesium silicide) serving as a parent phase of a sintered body that is the thermoelectric conversion material 11 is manufactured.
In this embodiment, the magnesium-based compound powder preparation step S01 includes a magnesium-based compound ingot forming step S11 for obtaining an ingot of a non-doped magnesium-based compound (magnesium silicide), and pulverizing the magnesium-based compound ingot (magnesium silicide) to form magnesium. And a pulverizing step S12 to make a system compound powder.

In the magnesium-based compound ingot forming step S11, the dissolved raw material powder is weighed and mixed. In this embodiment, since the magnesium-based compound is magnesium silicide, the melting raw material is silicon grains and magnesium grains.
In the present embodiment, in the silicon grains and magnesium grains, the Sb content is less than 0.001 mass%, the Bi content is less than 0.001 mass%, and the Al content is 0.25 mass% or less. It is preferable that the content of each element of Na, K, B, Ga, In, P, As, Cu, and Y be 0.01 mass% or less.

Then, this mixture is charged into a crucible in an atmosphere melting furnace and melted, and then cooled and solidified. Thereby, the ingot of a magnesium type compound (magnesium silicide) is manufactured.
In addition, since a small amount of magnesium is sublimated during heating, it is preferable to add a large amount of magnesium, for example, about 5 at% with respect to the stoichiometric composition of Mg: Si = 2: 1 when the raw materials are weighed.

In the pulverization step S12, the obtained magnesium-based compound (magnesium silicide) ingot is pulverized by a pulverizer to form magnesium-based compound powder (magnesium silicide powder) (pulverization step S12).
The average particle size of the magnesium-based compound powder (magnesium silicide powder) is preferably in the range of 0.5 μm to 100 μm, and more preferably in the range of 1 μm to 75 μm.

In addition, when using a commercially available non-doped magnesium compound powder (magnesium silicide powder), the magnesium compound ingot forming step S11 and the pulverizing step S12 can be omitted.

(Sintering raw material powder forming step S02)
Next, silicon oxide powder is mixed with the obtained magnesium-based compound powder (magnesium silicide powder) to obtain sintered raw material powder.
Here, the amount of silicon oxide powder added is preferably in the range of 0.1 mass% to 10.0 mass%, and more preferably in the range of 0.3 mass% to 5.0 mass%. .
The average particle diameter of the silicon oxide powder is preferably in the range of 0.1 μm to 100 μm, and more preferably in the range of 0.5 μm to 50 μm.
Further, the silicon oxide to be added is preferably SiOx (X = 1 to 2). Furthermore, the silicon oxide to be added may be either amorphous or crystalline.

(Sintering step S03)
Next, the sintered raw material powder obtained as described above is heated while being pressed to obtain a sintered body.
In the present embodiment, the sintering apparatus (electric current sintering apparatus 100) shown in FIG. 3 is used in the sintering step S03.

The sintering apparatus (electric current sintering apparatus 100) shown in FIG. 3 includes, for example, a pressure-resistant housing 101, a vacuum pump 102 that depressurizes the inside of the pressure-resistant housing 101, and a hollow cylinder disposed in the pressure-resistant housing 101. The carbon mold 103 having a shape, a pair of

electrode portions

105a and 105b for applying a current while pressurizing the sintering raw material powder Q filled in the carbon mold 103, and a voltage is applied between the pair of

electrode portions

105a and 105b. And a power supply device 106. Further, a carbon plate 107 and a carbon sheet 108 are disposed between the

electrode portions

105a and 105b and the sintering raw material powder Q, respectively. In addition to this, a thermometer, a displacement meter, etc. (not shown) are provided.

In this embodiment, the heater 109 is disposed on the outer peripheral side of the carbon mold 103. The heater 109 is disposed on four side surfaces so as to cover the entire outer peripheral side of the carbon mold 103. As the heater 109, a carbon heater, a nichrome wire heater, a molybdenum heater, a Kanthal wire heater, a high frequency heater, or the like can be used.

In the sintering step S03, first, the raw material powder Q is filled into the carbon mold 103 of the electric current sintering apparatus 100 shown in FIG. For example, the carbon mold 103 is covered with a graphite sheet or a carbon sheet. Then, using the power source device 106, a direct current is passed between the pair of

electrode portions

105a and 105b, and the current is passed through the sintered raw material powder Q to raise the temperature by self-heating (energization heating). Further, of the pair of

electrode portions

105a and 105b, the movable electrode portion 105a is moved toward the sintering raw material powder Q, and the sintering raw material powder Q is moved to a predetermined pressure with the fixed electrode portion 105b. Pressurize. Further, the heater 109 is heated.
As a result, the sintered raw material powder Q is sintered by self-heating of the sintered raw material powder Q, heat from the heater 109, and pressurization.

In the present embodiment, the sintering condition in the sintering step S03 is that the heating temperature of the sintering raw material powder Q is in the range of 850 ° C. or more and 1030 ° C. or less, and the holding time at this heating temperature is 0 minute or more and 3 minutes or less. It is within the range. Further, the pressurizing load is in the range of 15 MPa or more and 60 MPa or less.
The atmosphere in the pressure-resistant casing 101 is preferably an inert atmosphere such as an argon atmosphere or a vacuum atmosphere. In a vacuum atmosphere, the pressure is preferably 5 Pa or less.

In addition, it is preferable that the minimum of the heating temperature of sintering raw material powder is 850 degreeC or more. On the other hand, the upper limit of the heating temperature of the sintered raw material powder is preferably 1030 ° C. or less.
Further, the lower limit of the holding time at the heating temperature is preferably 0 minutes or more. On the other hand, the upper limit of the holding time at the heating temperature is preferably 3 minutes or less.
Furthermore, the lower limit of the pressure load is preferably 15 MPa or more. On the other hand, the upper limit of the pressure load is preferably 60 MPa or less.

In the sintering step S03, when a direct current is passed through the sintering raw material powder Q, the polarities of the one electrode portion 105a and the other electrode portion 105b may be changed at predetermined time intervals. That is, the state in which one electrode part 105a is energized with the anode and the other electrode part 105b as the cathode and the state in which one electrode part 105a is energized with the cathode and the other electrode part 105b as the anode are alternately performed. It is. In this embodiment, the predetermined time interval is set within a range of 10 seconds to 300 seconds. The predetermined time interval is preferably in the range of 30 seconds to 120 seconds.

The thermoelectric conversion material 11 which is this embodiment is manufactured according to the above process. As described above, in the silicon grains and magnesium grains, the Sb content is less than 0.001 mass%, the Bi content is less than 0.001 mass%, the Al content is 0.25 mass% or less, and Na , K, B, Ga, In, P, As, Cu, and Y, the content of each element is 0.01 mass% or less, and since no dopant is added, thermoelectric conversion comprising a sintered body of a magnesium-based compound Also in the material, the Sb content is less than 0.001 mass%, the Bi content is less than 0.001 mass%, the Al content is 0.25 mass% or less, and Na, K, B, Ga, In, P, Content of each element of As, Cu, and Y will be 0.01 mass% or less.

According to the thermoelectric conversion material 11 of the present embodiment configured as described above, a dopant element, in particular, Sb, Bi, Al, which is difficult to handle, is not used as a dopant element, and it is relatively easy to manufacture. can do.
In addition, since the electrical resistance value is kept low at 1.0 × 10 ⁻⁴ Ω · m or less, the power factor (PF) and the dimensionless figure of merit (ZT) are high, and the thermoelectric characteristics are excellent.

Furthermore, according to the present embodiment, the magnesium compound constituting the thermoelectric conversion material 11 is one or more selected from MgSi compounds, MgSn compounds, MgSiSn compounds, and MgSiGe compounds. Therefore, the thermoelectric conversion material 11 having further excellent thermoelectric characteristics can be obtained.

Further, according to the thermoelectric conversion material 11 of the present embodiment, an n-type thermoelectric conversion material can be obtained without intentionally adding a dopant of a metal element such as Sb, Bi, or Al that is difficult to handle.

Moreover, according to the method for manufacturing a thermoelectric conversion material according to the present embodiment, a sintering raw material powder forming step of obtaining a sintering raw material powder by mixing silicon oxide powder with non-doped magnesium-based compound powder (magnesium silicide powder). Since S02 and the sintering step S03 in which the sintered raw material powder Q is heated while being pressed to form a sintered body, the thermoelectric conversion material 11 according to the present embodiment described above can be manufactured. it can.

Furthermore, in this embodiment, by adding silicon oxide, it is possible to keep the electrical resistance value of the sintered body of the magnesium compound (magnesium silicide) low without adding a dopant element.
Further, since silicon oxide is a relatively stable substance, it can be easily handled during production, and the thermoelectric conversion material 11 can be produced efficiently.

Since the thermoelectric conversion element 10 and the thermoelectric conversion module 1 according to the present embodiment include the thermoelectric conversion material 11 described above, the thermoelectric characteristics are excellent. Therefore, it is possible to configure a thermoelectric conversion device having excellent thermoelectric conversion efficiency.

As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.
For example, in this embodiment, although it demonstrated as what comprises the thermoelectric conversion element and thermoelectric conversion module of a structure as shown in FIG. 1, it is not limited to this, The thermoelectric conversion material of this invention may be used. For example, the structure and arrangement of the electrodes and terminals are not particularly limited.

In the present embodiment, the magnesium-based compound constituting the sintered body has been described as magnesium silicide (Mg ₂ Si). However, the present invention is not limited to this, and any other composition may be used as long as it has thermoelectric properties. The magnesium-based compound may be used.
For example, a magnesium compound that forms a non-doped sintered body by adding a predetermined silicon oxide to one or more selected from MgSi compounds, MgSn compounds, MgSiSn compounds, and MgSiGe compounds You may get

Hereinafter, the results of experiments conducted to confirm the effects of the present invention will be described.

Mg having a purity of 99.9 mass% (manufactured by Kojundo Chemical Laboratory Co., Ltd., granular φ6 mm × about 6 mmL) and Si having a purity of 99.999 mass% (manufactured by Kojundo Chemical Laboratory Co., Ltd., granular 2 to 5 mm) were weighed. In consideration of the deviation from the stoichiometric composition of Mg: Si = 2: 1 due to Mg sublimation, 5 at% of Mg was mixed.

The above-mentioned raw material particles weighed were charged into a crucible in an atmosphere melting furnace and melted, and then cooled and solidified. This produced the magnesium compound (magnesium silicide) ingot.
Next, the ingot was crushed and classified to obtain a non-doped magnesium-based compound powder (magnesium silicide powder) having an average particle size of 30 μm.

Moreover, silicon oxide powder (SiO ₂ powder) having an average particle size of 15 μm was prepared, and magnesium silicide powder and silicon oxide powder were mixed to obtain sintered raw material powder. At this time, as shown in Table 1, the content of silicon oxide powder was adjusted. In the comparative example, no silicon oxide was added.

The obtained sintered raw material powder was filled into a carbon mold whose inside was covered with a carbon sheet. Then, current sintering was performed by a sintering apparatus (electric current sintering apparatus 100) shown in FIG. The current sintering conditions were as follows: atmosphere: vacuum (5 Pa or less), sintering temperature: 940 ° C., holding time at sintering temperature: 30 seconds, and pressure load: 40 MPa.
Thus, the thermoelectric conversion material of this invention example and the comparative example was obtained.

About the obtained thermoelectric conversion material, Sb, Bi, Al, Na, K, B, Ga, In, P, As, Cu, Y content, electric resistance (R), Seebeck coefficient (S), power factor (PF), thermal conductivity (κ), dimensionless figure of merit (ZT) were evaluated.

The content of each element was measured by high frequency inductively coupled plasma emission spectrometry using an SPS3500 manufactured by Seiko Instruments. The evaluation results are shown in Table 1.

The electrical resistance value R and the Seebeck coefficient S were measured with ZEM-3 manufactured by Advance Riko. The measurement was performed at 100 ° C, 200 ° C, 300 ° C, 400 ° C, 500 ° C, and 550 ° C.
The power factor (PF) was obtained from the following equation (1).
PF = S ² / R (1)
Where S: Seebeck coefficient (V / K), R: electrical resistance (Ω · m)

The thermal conductivity κ was determined from thermal diffusivity × density × specific heat capacity. The thermal diffusivity was measured using a thermal constant measuring device (TC-7000 model manufactured by Vacuum Riko), the density was measured using Archimedes method, and the specific heat was measured using a differential scanning calorimeter (DSC-7 model manufactured by PerkinElmer). The measurement was performed at 100 ° C, 200 ° C, 300 ° C, 400 ° C, 500 ° C, and 550 ° C.
The dimensionless figure of merit (ZT) was obtained from the following equation (2).
ZT = S ² σT / κ (2)
Where T = absolute temperature (K), κ = thermal conductivity (W / (m × K))
The evaluation results are shown in Tables 2-6.

In the comparative example in which no silicon oxide was added, the dopant element was not contained, and the electric resistance value R was very high. Further, the value of the Seebeck coefficient S is relatively unstable, the power factor (PF) is low, the dimensionless figure of merit ZT is also low, and it is confirmed that the thermoelectric characteristics are inferior.
In the example of the present invention to which silicon oxide was added, the electric resistance value R was sufficiently low even without containing a dopant element. It is also confirmed that the Seebeck coefficient S is stable, the power factor (PF) is sufficiently high, the dimensionless figure of merit ZT is sufficiently high, and the thermoelectric characteristics are excellent.

From the above, according to the examples of the present invention, it was confirmed that the electrical resistance value can be kept low without adding a dopant element that is complicated to handle, and it is possible to provide a thermoelectric conversion material having excellent thermoelectric properties. It was.

Claims

A thermoelectric conversion material comprising a sintered body of a non-doped magnesium-based compound,
A thermoelectric conversion material having an electric resistance value of 1.0 × 10 −4 Ω · m or less.
The thermoelectric conversion material according to claim 1, wherein the magnesium compound is one or more selected from MgSi compounds, MgSn compounds, MgSiSn compounds, and MgSiGe compounds.
The thermoelectric conversion material according to claim 1 or 2, wherein the thermoelectric conversion material is n-type.
A thermoelectric conversion material according to any one of claims 1 to 3, and an electrode bonded to one surface of the thermoelectric conversion material and the other surface facing each other. Thermoelectric conversion element.
A thermoelectric conversion module comprising: the thermoelectric conversion element according to claim 4; and a terminal joined to each of the electrodes of the thermoelectric conversion element.
A method for producing a thermoelectric conversion material for producing the thermoelectric conversion material according to any one of claims 1 to 3,
A sintering raw material powder forming step for obtaining a sintering raw material powder by mixing silicon oxide powder with non-doped magnesium-based compound powder,
A sintering process in which the sintered raw material powder is heated while being pressed to form a sintered body;
A method for producing a thermoelectric conversion material, comprising:
The thermoelectric conversion material according to claim 6, wherein the amount of the silicon oxide powder added in the sintering raw material powder forming step is in a range of 0.1 mass% to 10.0 mass%. Method.