JP2013161948A - Thermoelectric conversion element, and method for manufacturing thermoelectric conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent breakage of an element itself in a temperature region between room temperature and 800°C and join a thermoelectric conversion section and an electrode, even when a Ba-Ga-Al-Si-based clathrate compound, which contains no harmful element and is an inexpensive material, is used.SOLUTION: A thermoelectric conversion element (1) includes: a thermoelectric conversion section (10) comprising a Ba-Ga-Al-Si-based clathrate compound; and Cu or Ni electrodes (20, 30).

Description

  The present invention relates to a thermoelectric conversion element using a clathrate compound, which is a thermoelectric conversion material, and a method for manufacturing the thermoelectric conversion element.

  A thermoelectric conversion module that uses the Seebeck effect makes it possible to convert thermal energy into electrical energy. Utilizing this property, it is possible to convert waste heat exhausted from industrial and consumer processes and mobile objects into effective power, so thermoelectric conversion is attracting attention as an energy-saving technology that takes environmental issues into consideration.

The dimensionless figure of merit ZT of the thermoelectric conversion element using the Seebeck effect can be expressed by the following formula [1].
ZT = S ² T / ρκ [1]
In the formula [1], S, ρ, κ, and T represent the Seebeck coefficient, electrical resistivity, thermal conductivity, and measurement temperature, respectively.

  As apparent from the equation [1], in order to improve the performance of the thermoelectric conversion element, it is important to increase the Seebeck coefficient of the element, to decrease the electrical resistivity, and to decrease the thermal conductivity. . Conventionally, thermoelectric conversion elements using bismuth / tellurium-based materials, silicon / germanium-based materials, lead / tellurium-based materials, and the like are known as thermoelectric conversion materials exhibiting a high performance index.

By the way, the conventional thermoelectric conversion element has the problem which should be solved, respectively.
For example, bismuth-tellurium-based materials have a large ZT value at room temperature, but when the temperature exceeds 100 ° C, the ZT value decreases rapidly. Disappear. Bismuth / tellurium and lead / tellurium contain lead and tellurium, which are environmentally hazardous substances.

  Therefore, there is a demand for new thermoelectric conversion materials that have good thermoelectric performance, low environmental impact, and light weight. A clathrate compound has attracted attention as one of such new thermoelectric conversion materials. Several types of clathrate compounds that are promising as thermoelectric conversion elements have been reported, but Ba, Ga, Al, and Si-based clathrate compounds have attracted attention because of cost and the like.

Several compositions and synthesis methods of clathrate compounds composed of Ba, Ga, Al, and Si have already been disclosed. For example, Patent Document 1 discloses Ba ₈ (Al, Ga) _x Si in which x (10.8 ≦ x ≦ 12.2) Si atoms per unit cell are replaced with either Al atoms or Ga atoms. _{A 46-x} single crystal and a method for producing the same are disclosed.

In addition, a technique for modularizing a clathrate compound as a thermoelectric conversion element has begun to be studied. In such modularization, damage to the element due to thermal stress and difficulty in joining the thermoelectric conversion part composed of the clathrate compound and the electrodes are one of the problems. In order to solve this problem, in Patent Document 2, a thermoelectric conversion part composed of a Ba, Ga, Ge-based clathrate compound and an electrode having a composition of Ti ₃ Cu ₄ (linear expansion coefficient = 12.8 × 10 ⁻⁶ [/ K]) is provided with a Ti layer.

JP 2004-67425 A JP 2006-352023 A

  As described above, clathrate compounds composed of Ba, Ga, Al, and Si are considered to be promising as thermoelectric conversion materials, including Patent Document 1, but research and publications that describe the mounting method in detail are still in progress. It is not disclosed. That is, Patent Document 2 only discloses disclosure of ternary clathrate compounds such as Ba—Ga—Ge system, and shows that the technology can be diverted to Ba—Ga—Al—Si systems having different compositions. I can't say. It can be easily imagined that various characteristics change if the alloy system is different, and research and development of a promising method for module mounting of Ba-Ga-Al-Si-based clathrate compounds. There is a need.

  Therefore, the main object of the present invention is to prevent damage to the element itself in a temperature range of room temperature to 800 ° C. even when a Ba—Ga—Al—Si-based clathrate compound that does not contain harmful elements and is an inexpensive material is used. It is providing the thermoelectric conversion element which can prevent and can join a thermoelectric conversion part and an electrode, and its manufacturing method.

  As a result of intensive studies to solve the above-described problems, the inventors have solved the above-described problems by bonding Cu and Ni electrodes to a Ba-Ga-Al-Si-based clathrate compound. It came.

That is, according to one aspect of the present invention,
There is provided a thermoelectric conversion element comprising a thermoelectric conversion part composed of a Ba-Ga-Al-Si-based clathrate compound and a Cu or Ni electrode.

According to another aspect of the invention,
There is provided a thermoelectric conversion element including a thermoelectric conversion portion made of a Ba-Ga-Al-Si-X (X = Pd, Sr) -based clathrate compound and a Cu or Ni electrode.

According to another aspect of the invention,
A method for producing the thermoelectric conversion element, comprising:
A preparation process for preparing a clathrate compound of a predetermined composition by mixing, melting and solidifying raw materials;
A crushing step of crushing the clathrate compound into fine particles;
A sintering step of sintering a mixture of the fine particles and Cu or Ni metal powder;
The manufacturing method of the thermoelectric conversion element which has this is provided.

  According to the present invention, even when a Ba-Ga-Al-Si-based clathrate compound that does not contain harmful elements and is an inexpensive material is used, the element itself is prevented from being damaged in a temperature range of room temperature to 800 ° C, and thermoelectric The conversion part and the electrode can be joined.

It is sectional drawing of the thermoelectric conversion element which concerns on one Embodiment of this invention. It is sectional drawing of the thermoelectric conversion element which concerns on other embodiment of this invention. It is an electron micrograph in the junction part of the thermoelectric conversion element which concerns on the Example sample of this invention.

  Hereinafter, preferred embodiments of the present invention will be described. Of course, the present invention is not limited to the embodiments described below.

(A) Thermoelectric conversion element and method for mounting module of thermoelectric conversion element In the present embodiment, the term “thermoelectric conversion element” means a form in which an electrode is bonded to a thermoelectric conversion unit. The thermoelectric conversion part is composed of a clathrate compound, and the electrode is composed of Cu or Ni. Therefore, a thermoelectric conversion element is obtained by bonding a Cu or Ni electrode to a thermoelectric conversion portion made of a clathrate compound.
In the present embodiment, a Ba-Ga-Al-Si-based clathrate compound is used as the thermoelectric conversion material of the thermoelectric conversion section, and this embodiment provides an n-type thermoelectric conversion element.
In addition, the n-type thermoelectric conversion element of this embodiment becomes a thermoelectric conversion module by connecting with a p-type thermoelectric conversion element.

An example of a cross-sectional view of a thermoelectric conversion element according to an embodiment of the present invention is shown in FIG.
The thermoelectric conversion element 1 according to this embodiment basically includes a thermoelectric conversion unit 10, a high-temperature side electrode 20 tightly bonded to the thermoelectric conversion unit 10, and a low-temperature side electrode 30 tightly bonded to the thermoelectric conversion unit 10. It is comprised by.

An example of a cross-sectional view of a thermoelectric conversion element according to another embodiment of the present invention is shown in FIG.
The thermoelectric conversion element 1 according to this embodiment includes a thermoelectric conversion unit 10, a high temperature side intermediate layer 40 and a low temperature side intermediate layer 50 that are tightly bonded to the thermoelectric conversion unit 10, and a high temperature side intermediate layer 40 and a low temperature side intermediate layer. The high-temperature side electrode 20 and the low-temperature side electrode 30 are tightly bonded to each other.
In the thermoelectric conversion element 1 according to the embodiment of FIG. 2, a high temperature side intermediate layer 40 is formed between the thermoelectric conversion unit 10 and the high temperature side electrode 20, and a low temperature side intermediate is formed between the thermoelectric conversion unit 10 and the low temperature side electrode 30. A layer 50 is formed, which is different from the thermoelectric conversion element 1 mainly according to the embodiment shown in FIG.

  Although the p-type thermoelectric conversion material used for a thermoelectric conversion module is not specifically limited, What has a thermal expansion coefficient similar to a Ba-Ga-Al-Si type clathrate compound is preferable. Moreover, as this p-type thermoelectric conversion material, the material which can be used in the temperature range of room temperature-800 degreeC is preferable.

(B) Clathrate Compound The thermoelectric conversion part is composed of a thermoelectric conversion material, and the thermoelectric conversion material is composed of a Ba—Ga—Al—Si based clathrate compound.
The clathrate compound according to the present embodiment is mainly composed of a clathrate lattice in which the basic lattice is Si, the Ba element is included therein, and some of the atoms constituting the clathrate lattice are Ga, Al. It has the structure substituted by. This clathrate compound is a compound containing Ba, Ga, Si, and Al simultaneously.

The chemical formula of such clathrate compound according to the present _{embodiment, Ba a Ga b Al c Si} d (7.77 ≦ a ≦ 8.16,7.47 ≦ b ≦ 15.21,0.28 ≦ c ≦ 6 as an example .92, 30.35 ≦ d ≦ 32.80, a + b + c + d = 54). This clathrate compound becomes an n-type thermoelectric conversion material.
In addition, the thermoelectric conversion material concerning this embodiment has the said clathrate compound as a main component, and may contain a small amount of other additives.

  The “clathrate compound” according to the present embodiment only needs to be mainly composed of a Si clathrate phase, and may include other phases not corresponding to the clathrate phase. The “clathrate compound” is preferably a single phase of Si clathrate.

In addition, among the composition ratios of the chemical formula Ba _a Ga _b Al _c Si _d of the clathrate compound, the composition ratios b, c, and d of Ga, Al, and Si generally have the following relationship [2]. If such a relationship is satisfied, the clathrate compound can be realized mainly with a Si clathrate phase and can have an ideal crystal structure.
b + c + d = 46 [2]

In addition, as a thermoelectric conversion material which comprises a thermoelectric conversion part, the clathrate compound in which the said Ba-Ga-Al-Si type clathrate compound contained a small amount of other additives may be used. That is, the thermoelectric conversion material may be a Ba-Ga-Al-Si-X (X = Sr, Pd) -based clathrate compound. Sr and Pd may be useful for increasing the Seebeck coefficient.
The chemical formula of such clathrate compounds, for example, _{Ba a Ga b Al c Si d} X e (7 ≦ a ≦ 8,9 ≦ b ≦ 12,0 ≦ c ≦ 2,33 ≦ d ≦ 35,0 ≦ e ≦ 2, a + b + c + d + e = 54). In this case, the relationship of the above equation [2] is preferably b + c + d + e = 46.
The Ba-Ga-Al-Si-based clathrate compound may also contain a small amount of other additives.

(C) Electrode The electrode applied to the thermoelectric conversion element is preferably a Cu (copper) electrode or a Ni (nickel) electrode. The Cu electrode has high conductivity and is suitable for use as an electrode. In addition, Cu electrodes are relatively inexpensive and easy to handle. The Ni electrode is suitable for use in a high temperature range.

  The composition (concentration / component) of Cu or Ni used for the electrode can be appropriately selected according to the application. In other words, pure Cu or pure Ni containing less impurities, alloyed ones, or ones prepared with components may be used. These can be appropriately selected according to a specific usage mode when the thermoelectric conversion element is mounted on the module.

  The electrodes are used on the high temperature side and the low temperature side. These electrodes may use the same material as a material constituting them, or may use different materials. For example, it is possible to appropriately select the high temperature side electrode as a Ni electrode and the low temperature side electrode as Cu.

  The thickness of the electrode is not particularly specified. The electrode itself is effective even if it is thin, but bonding with a thermoelectric conversion material (or intermediate layer) is important. If the adhesion of the joint is poor, the power generation efficiency decreases.

(D) Intermediate layer In the thermoelectric conversion element, adhesion between the thermoelectric conversion part (thermoelectric conversion material) and the electrode is required from the viewpoint of power generation efficiency. In addition, it is necessary that the thermoelectric conversion portion, the electrode, or the interface thereof is not damaged by thermal stress or the like.
Therefore, in the thermoelectric conversion element according to the present embodiment, an intermediate layer may be provided between the thermoelectric conversion part and the electrode. This intermediate layer is a layer constituted by a multiphase having at least a clathrate compound constituting the thermoelectric conversion part and a Cu or Ni phase which is the same element as the electrode.

  The thermoelectric conversion part and the intermediate layer are joined substantially continuously due to the presence of the clathrate compound in the intermediate layer. The composition of the clathrate compound of the thermoelectric conversion part and the clathrate compound of the intermediate layer may be the same or different, but in order to achieve continuous bonding, the composition is approximated. Preferably it is.

  The Cu or Ni electrode and the intermediate layer are joined substantially continuously due to the presence of the Cu or Ni phase in the intermediate layer. Needless to say, if the electrode is a Cu electrode, the intermediate layer includes a Cu phase, and if the electrode is a Ni electrode, the intermediate layer includes a Ni phase. The composition (concentration) of the Cu or Ni electrode and the Cu or Ni phase of the intermediate layer may be the same or different.

  In the intermediate layer, the ratio of the clathrate compound phase and the Cu or Ni phase is not particularly limited as long as both phases are present. Since the clathrate phase is more brittle than the Cu or Ni phase, if the proportion of the clathrate compound phase is too large, the function of the intermediate layer as the buffer layer may be lowered. If the ratio of the clathrate compound phase is too small, the bonding ability between the thermoelectric conversion element and the intermediate layer may be lowered, which is not preferable.

  The thickness (width) of the intermediate layer is preferably 0.1 to 10% with respect to the thickness (full width) of the thermoelectric conversion part (clathrate compound). If the thickness of the intermediate layer is too thin, the effect as a buffer layer may be lowered, which is not preferable. If the thickness of the intermediate layer is too large, the package may become coarse, which is also not preferable.

  An intermediate | middle layer may be provided in both the high temperature side and low temperature side of a thermoelectric conversion part, and the aspect provided only in one side may be sufficient. When provided on both the high temperature side and the low temperature side, the composition and configuration of the intermediate layer may both be the same or different. This is because the state (for example, thermal stress state) of the thermoelectric conversion portion is different between the high temperature side and the low temperature side.

By providing the intermediate layer, the thermoelectric conversion part (clathrate compound) and the electrode (Cu or Ni electrode) are more firmly bonded.
This is because continuous bonding with “clathrate compound in thermoelectric conversion part—clathrate phase in the intermediate layer—Cu or Ni phase in the intermediate layer—Cu or Ni electrode” becomes possible, and cracking at the interface occurs. Relying on low frequency. In other words, the presence of the intermediate layer results in a so-called functionally gradient material. By providing the intermediate layer, the thermoelectric conversion element is resistant to thermal stress and the like, and the reliability with respect to the thermal cycle is improved.

(E) Manufacturing method The manufacturing method of the thermoelectric conversion element concerning preferable embodiment of this invention is the following.
(A) a preparation step of preparing a clathrate compound having a predetermined composition by mixing, melting and solidifying raw materials;
(B) pulverizing the clathrate compound into fine particles;
(C) a sintering step of sintering a mixture of the fine particles and Cu or Ni metal powder (or the fine particles and powder constituting the intermediate layer and Cu or Ni metal powder);
Have
By passing through these steps, there is an advantage that a material having a predetermined composition, a small number of pores (voids), and a uniform composition can be obtained. Hereinafter, the process will be described in detail.

(A) Preparation Step In the preparation step, an ingot of a clathrate compound having a predetermined composition and a uniform composition is produced. First, a predetermined amount of raw materials (Ba, Ga, Al, Si, X) are weighed and mixed so as to obtain a desired clathrate compound composition. The raw material may be a simple substance, an alloy or a compound, and the shape thereof may be powder, flakes or lumps. In addition, it is more preferable to use an Al—Si master alloy as the Si raw material instead of a single Si because the melting point is lowered.

  As the melting time, a time required for all raw materials to be homogeneously mixed in a liquid state is required, but considering the energy required for production, it is desirable that the melting time be as short as possible. Therefore, the melting time is preferably 1 to 100 minutes, more preferably 1 to 10 minutes, and particularly preferably 1 to 5 minutes.

  The method for melting the powder composed of the raw material mixture is not particularly limited, and various methods can be used. Examples of the melting method include heating with a resistance heating element, high frequency induction melting, arc melting, plasma melting, and electron beam melting. As the crucible, graphite, alumina, cold crucible or the like is appropriately used according to the heating method. When melting, it is preferably performed in an inert gas atmosphere or a vacuum atmosphere in order to prevent oxidation of the material.

  In order to obtain a homogeneously mixed state in a short time, it is preferable that fine powdery raw materials are mixed. However, Ba is preferably used in the form of a lump in order to prevent oxidation. It is also preferable to add mechanical stirring or electromagnetic stirring at the time of melting.

  After melting, ingots may be cast using a mold or solidified in a crucible. In order to homogenize the completed ingot, an annealing treatment may be performed after melting.

  The annealing treatment time is preferably as short as possible in consideration of energy saving during manufacturing, but a long time is required in consideration of the annealing effect. The treatment time for the annealing treatment is preferably 1 hour or more, more preferably 1 to 10 hours.

  The treatment temperature for the annealing treatment is preferably 700 to 950 ° C, more preferably 850 to 930 ° C. When the processing temperature is less than 700 ° C., there is a problem that homogenization becomes insufficient. When the processing temperature exceeds 950 ° C., concentration segregation due to remelting occurs.

(B) Pulverization step In the pulverization step, the ingot obtained in the preparation step can be pulverized using a ball mill or the like to obtain a fine-particle clathrate compound. The fine particles obtained are desired to have a fine particle size in order to improve the sinterability. In the present embodiment, the particle diameter of the fine particles is preferably 150 μm or less, more preferably 1 μm or more and 75 μm or less.

  In order to obtain fine particles having a desired particle size, the particle size is prepared after the ingot is pulverized by a ball mill or the like. The particle size may be adjusted by sieving using a ISO 3310-1 standard Lecce test sieve and a Lecce sieve shaker AS200 digit. In addition, it can replace with this grinding | pulverization process, and can also manufacture fine powder using various atomizing methods, such as a gas atomizing method, and a flowing gas evaporation method.

(C) Sintering Step In the sintering step, the finely divided clathrate compound obtained in the pulverization step can be sintered to obtain a solid having a uniform shape with few voids.
Moreover, in the manufacture of the thermoelectric conversion element according to the present embodiment, the electrode is formed simultaneously with the thermoelectric conversion portion in this step. Specifically, when realizing the embodiment of FIG. 1, a predetermined amount of clathrate compound powder as a thermoelectric conversion material and copper powder or nickel powder as an electrode material is prepared, and these are fired. Fill the mold and sinter.

  On the other hand, when an intermediate layer is provided to realize the configuration shown in FIG. 2, the powder of the thermoelectric conversion material (clathrate compound) and electrode material (Cu or Ni) prepared at a predetermined ratio as the intermediate layer material The intermediate layer material is filled into a sintering mold together with the thermoelectric conversion material and the electrode material and sintered.

  As the sintering method, a discharge plasma sintering method, a hot press sintering method, a hot isostatic pressing method, or the like can be used. When using the discharge plasma sintering method, the sintering temperature, which is one condition for the sintering, is preferably 600 to 900 ° C, more preferably 800 to 900 ° C. The sintering time is preferably 1 to 10 minutes, more preferably 3 to 7 minutes. The pressure is preferably 40 to 80 MPa, more preferably 50 to 70 MPa.

  When the sintering temperature is 600 ° C. or lower, the sintering is not performed, and when the sintering temperature is 1000 ° C. or higher, it is dissolved. When the sintering time is less than 1 minute, the density is low, and when the sintering time exceeds 10 minutes, the sintering is completed and saturated, and it is considered that there is no significance in taking more time.

  In particular, in the sintering process, a mixture of a finely powdered thermoelectric conversion material and electrode material (or thermoelectric conversion material, electrode material and intermediate layer material) is heated to the sintering temperature and the above-mentioned sintering is performed at that temperature. Hold for the settling time and then cool the mixture to the temperature before heating. In this case, in the step of heating the fine powder mixture to the sintering temperature and the step of maintaining the mixture at the temperature, the pressurized state is set, and in the subsequent step of cooling the mixture, the pressurized state is released. According to such pressure operation, it is possible to suppress cracking in the sintering process of the particles by the mixture.

(F) Confirmation of production of clathrate compound phase Whether or not a clathrate compound is produced by the above production method can be confirmed by powder X-ray diffraction (XRD). Specifically, if the sintered sample is pulverized again and subjected to powder X-ray diffraction measurement, if the obtained peak shows only the type 1 clathrate phase (Pm-3n, No. 223), type 1 It can be confirmed that the clathrate compound was synthesized.

  However, since there are actually a type 1 clathrate phase alone and an impurity phase, an impurity peak is also observed. The strongest peak ratio of the Si clathrate compound phase in the clathrate compound according to this embodiment is 85% or more, preferably 90% or more, and more preferably 95% or more.

The strongest peak ratio is, for example, a Ba—Ga—Al—Si clathrate compound, the strongest peak (IHS) of the Si clathrate compound phase measured in powder X-ray diffraction measurement, and the impurity phase A (BaGa). _4-Y (Al, Si) _Y (0 ≦ Y ≦ 4)) strongest peak intensity (IA), impurity phase B (BaAl) ₂ (Si) ₂ etc.) strongest peak intensity (IB) Defined in [3].
“Strongest peak ratio” = IHS / (IHS + IA + IB) × 100 (%) (3)

(G) Confirmation of joining In order to confirm the joining of the thermoelectric conversion part and the electrode of the thermoelectric conversion element, composition analysis and microstructure observation are performed by an electron beam microanalyzer (EPMA-1610 manufactured by Shimadzu Corporation).

(H) Characteristic evaluation test When the characteristic of a thermoelectric conversion element is evaluated, the following test method is used. The characteristic evaluation items for calculating the dimensionless figure of merit ZT of the thermoelectric conversion element are Seebeck coefficient S, electric resistivity ρ, and thermal conductivity κ.

  In the characteristic evaluation test, composition analysis, microstructure observation, and sintering density measurement are performed using an electron beam microanalyzer (EPMA-1610 manufactured by Shimadzu Corporation). Various characteristic evaluation samples are cut out and shaped from a cylindrical sintered body of 20 mmφ (diameter 20 mm) × 5 to 20 mm (height 5 to 20 mm).

“Seebeck coefficient S” and “electric resistivity ρ” are measured by a four-terminal method using a thermoelectric property evaluation apparatus ZEM-3 manufactured by ULVAC-RIKO.
“Thermal conductivity κ” is calculated from the measurement results of specific heat c, density δ, and thermal diffusivity α according to the following equation [4].
κ = cδα (4)
The “specific heat c” is measured by a DSC (Differential Scanning Calorimetry) method. As a measuring device, a differential scanning calorimeter EXSTAR6000DSC manufactured by SII Nano Technology Co., Ltd. is used.
“Density δ” is measured by the Archimedes method. As a measuring apparatus, a precision electronic balance LIBBROR AEG-320 manufactured by Shimadzu Corporation is used.
“Thermal diffusivity α” is measured by a laser flash method. As a measuring device, a thermal constant measuring device TC-7000 manufactured by ULVAC-RIKO Inc. is used.

  From the above measurement results, the dimensionless figure of merit ZT, which is an index for evaluating the performance of the thermoelectric conversion element, can be calculated using the above-described equation [1]. The characteristic of the thermoelectric conversion element can be evaluated from the calculated dimensionless figure of merit.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited by the following Example.

(1) Preparation of sample (thermoelectric conversion element) High-purity Ba having a purity of 2N or more and high-purity Al, Ga, Si, Pd having a purity of 3N or more are weighed at the blending ratio shown in Table 1, and the raw material mixture is obtained. Prepared.

  The arc mixture is melted in an Ar (argon) atmosphere on a water-cooled copper hearth at a current of 300 A for 1 minute, and then the ingot is inverted in order to eliminate the unevenness of the raw material, and arc melting is performed again. Was repeated 5 times and cooled to room temperature on a water-cooled copper hearth to obtain an ingot having a clathrate compound. Thereafter, in order to improve the uniformity of the ingot, an annealing treatment was performed at 900 ° C. for 6 hours in an argon atmosphere.

  The obtained ingot was pulverized using an agate planetary ball mill to obtain fine particles. At this time, the particle size was adjusted using the ISO 3310-1 standard Lecce test sieve and the Lecce sieve shaker AS200 digit so that the average particle size of the obtained particles was 75 μm or less.

As particles (powder) for constituting the electrode, Cu powder having a purity of 3N and a particle size of 75 μm or less was used. Further, as particles (powder) for constituting the intermediate layer, particles in which the above-described clathrate compound particles having a particle diameter of 75 μm or less were mixed at a ratio of 50% and Cu particles at a ratio of 50% were prepared.
In the present embodiment, both the high temperature side and low temperature side electrodes and both intermediate layers are made of the same material.

  The obtained two kinds of sintering particles (mixture of thermoelectric conversion material / interlayer material / electrode material) were placed in a sintering mold so as to have the structure shown in FIG. The sintering was performed by using a discharge plasma sintering method (SPS method), pressurizing to a pressure of 60 MPa, heating to 900 ° C., and then sintering at 900 ° C. for 5 minutes. After the sintering was completed, the pressurized state was released, and cooling was performed from 900 ° C. to room temperature.

  In addition, after the sintering of the particles for sintering was finished, when the pressure state was kept and cooling was performed, cracking occurred, but the pressure state was released after sintering as described above. When cooling from 900 ° C. to room temperature, such cracks could be suppressed. Considering the deterioration of the sample and the die obtained, it is preferable to hold in a vacuum atmosphere at a cooling temperature of 500 ° C. or higher, but it may be held in an air atmosphere at less than 500 ° C.

  The sintered body of the sample thus obtained was subjected to composition analysis, X-ray diffraction of “(F) Confirmation of formation of clathrate compound” and “(H) characteristic evaluation test” It was used for.

(2) Sample evaluation (2.1) Composition analysis Table 1 shows the results of composition analysis.
Table 1, in the samples of Examples 1 and 2, a desired composition _{Ba a Ga b Al c Si d} (7.77 ≦ a ≦ 8.16,7.47 ≦ b ≦ 15.21,0.28 ≦ c ≦ 6.92,30.35 ≦ d ≦ 32.80, a + b + c + d = 54 with a compound _{of), Ba a Ga b Al c} Si d Pd e (7 ≦ a ≦ 8,9 ≦ b ≦ 12,0 ≦ c ≦ 2, 33 ≦ d ≦ 35, 0 ≦ e ≦ 2, a + b + c + d + e = 54).

(2.2) X-ray diffraction analysis In order to confirm that the thermoelectric conversion material portion of the obtained sample was a clathrate compound, the central portion of the sample was cut out and analyzed by powder X-ray diffraction. As a result, it was confirmed that a type 1 clathrate phase was generated. From the obtained results, the strongest peak ratio was calculated based on the formula [3], and it was confirmed that the strongest peak ratio was 95% or more.

(2.3) Confirmation of joining The result of confirming the joining of the thermoelectric conversion part, the intermediate layer, and the electrode of the sample of Example 1 is shown in FIG. It was confirmed that the Cu electrode 30 (20) was joined to the thermoelectric conversion part 10 of the present example via the intermediate layer 50 (40). In the sample of Example 2, bonding was confirmed in the same manner. Moreover, after heating these thermoelectric conversion elements to 800 degrees and returning them to room temperature again, it was confirmed that there was no problem in bonding and that the elements themselves were not damaged.

  From the above, using a combination of a Ba-Ga-Al-Si clathrate compound having a constant composition ratio and a Cu electrode in a thermoelectric conversion element prevents damage to the element itself in the temperature range from room temperature to 800 ° C. And it turns out that it is useful in joining a thermoelectric conversion part and an electrode.

1 Thermoelectric conversion element 10 Thermoelectric conversion part (clathrate compound)
20 Cu or Ni electrode (high temperature side)
30 Cu or Ni electrode (low temperature side)
40 Intermediate layer (high temperature side)
50 Intermediate layer (low temperature side)

Claims (6)

  A thermoelectric conversion element comprising a thermoelectric conversion part composed of a Ba-Ga-Al-Si-based clathrate compound and a Cu or Ni electrode.   A thermoelectric conversion element comprising: a thermoelectric conversion portion composed of a Ba-Ga-Al-Si-X (X = Pd, Sr) -based clathrate compound; and a Cu or Ni electrode. The thermoelectric conversion element according to claim 1 or 2,
Between the thermoelectric converter and the electrode,
A thermoelectric conversion element in which an intermediate layer having at least a clathrate compound phase and a Cu or Ni phase is formed. A method for producing the thermoelectric conversion element according to claim 1, comprising:
A preparation process for preparing a clathrate compound of a predetermined composition by mixing, melting and solidifying raw materials;
A crushing step of crushing the clathrate compound into fine particles;
A sintering step of sintering a mixture of the fine particles and Cu or Ni metal powder;
The manufacturing method of the thermoelectric conversion element which has this. A method for producing the thermoelectric conversion element according to claim 3,
A preparation process for preparing a clathrate compound of a predetermined composition by mixing, melting and solidifying raw materials;
A crushing step of crushing the clathrate compound into fine particles;
A sintering step of sintering a mixture of the fine particles and the powder constituting the intermediate layer and a metal powder of Cu or Ni;
The manufacturing method of the thermoelectric conversion element which has this. In the manufacturing method of the thermoelectric conversion element according to claim 4 or 5,
The sintering step includes
A heating step of heating the mixture to a constant sintering temperature;
A temperature holding step of holding the mixture at the sintering temperature for a certain period of time;
Cooling the mixture to a temperature before heating,
In the heating step and the temperature holding step, a pressurized atmosphere is used,
A method of manufacturing a thermoelectric conversion element that releases a pressurized atmosphere in the cooling step.