JP4415640B2 - Thermoelectric conversion element - Google Patents

Description

  The present invention relates to a thermoelectric conversion element, and more particularly to a thermoelectric conversion element containing a clathrate compound.

  Thermoelectric conversion elements using the Seebeck effect can convert thermal energy into electrical energy. Utilizing this property, it is possible to convert exhaust heat exhausted from industrial / consumer processes and mobile objects into effective electric power, and thermoelectric conversion elements are attracting attention as energy-saving technologies in consideration of environmental problems.

  The figure of merit ZT of the thermoelectric conversion material used for the thermoelectric conversion element utilizing the Seebeck effect can be expressed by the following formula (1).

ZT = α ² σT / κ (1)

  Here, α, σ, κ, and T represent the Seebeck coefficient, electrical conductivity, thermal conductivity, and measurement temperature, respectively.

  As is clear from the equation (1), in order to improve the performance of the thermoelectric conversion element, it is important to increase the Seebeck coefficient and the electrical conductivity of the material used for the element, and to decrease the thermal conductivity. It is.

On the other hand, Z in the figure of merit ZT has a proportional relationship represented by the equation (2) among effective mass (m ^* ), mobility (μ), and thermal conductivity (κ).

Z ∝m ^* μ / κ (2)

  From the above formula (2), it is important to improve the effective mass and mobility in order to improve Z.

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 elements exhibiting a high figure of merit. Furthermore, a thermoelectric conversion element formed by molding and baking zinc oxide powder doped with aluminum is known (for example, see Patent Document 1).
JP 2002-118296 A

  In the conventionally known thermoelectric conversion element, the above-described materials are used alone. However, since carriers (electrons or holes) contained in the thermoelectric conversion material can transmit both heat and electricity, the electrical conductivity and the thermal conductivity are in a proportional relationship. Furthermore, it is known that electrical conductivity and Seebeck coefficient are inversely related. Therefore, even if the electrical conductivity is improved with a single material, the thermal conductivity increases and the Seebeck coefficient decreases accordingly. In addition, since the effective mass and the mobility are in an inversely proportional relationship, the effective mass is reduced when the mobility is improved. Therefore, there has been a limit to the improvement of the figure of merit by improving the single material.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a thermoelectric conversion element having an excellent figure of merit, which is difficult to realize with a single material, solving the above-described conventional problems.

That is, the present invention
< 1 > A thermoelectric conversion element composed of a base material and fine particles dispersed in the base material , containing at least two types of clathrate compounds, wherein one type of the clathrate compound is an electron transfer degrees is the first of clathrate compound of 100~5000cm ² / V · s, the other one, the second clathrates electron concentration ^{1.0 × 10 20 ~1.0 × 10 22} / cm 3 a compound, wherein the base material, the contained first clathrate compound, wherein the microparticles are thermoelectric conversion elements you characterized by containing the second clathrate compound.

< 2 > A thermoelectric conversion element composed of a porous body formed by sintering particles and a filler impregnated in the voids of the porous body , containing at least two types of clathrate compounds, One type of the clathrate compound is a first clathrate compound having an electron mobility of 100 to 5000 cm ² / V · s, and the other type has an electron concentration of 1.0 × 10 ^{20 to} 1.0 × 10. ²² / cm ³ of the second clathrate compound, wherein the particles contain the first clathrate compound , and the filler contains the second clathrate compound . a thermoelectric conversion element you.

< 3 > The thermoelectric conversion element according to < 2 >, wherein the sintering is performed by a discharge plasma sintering method.

< 4 > A thermoelectric conversion element having a structure in which two kinds of thin films are alternately laminated , and contains at least two kinds of clathrate compounds, and one kind of the clathrate compounds has an electron mobility of 100 to 5000 cm. ² / V · s is the first clathrate compound, and the other kind is the second clathrate compound having an electron concentration of 1.0 × 10 ^{20 to} 1.0 × 10 ²² / cm ³ , kind of thin film contains the first clathrate compound, other kind is a thermoelectric conversion element you characterized by containing the second clathrate compound.

< 5 > A thermoelectric conversion element composed of a base material and fine particles dispersed in the base material , containing at least two types of clathrate compounds, wherein one type of the clathrate compound is a hole transfer A third clathrate compound having a degree of 100 to 2000 cm ² / V · s, and the other kind is a fourth clathrate having a hole concentration of 1.0 × 10 ^{20 to} 1.0 × 10 ²² / cm ³ a compound, wherein the base material, the contained third clathrate compound, wherein the microparticles are thermoelectric conversion elements you characterized by containing the fourth clathrate compound.

< 6 > A thermoelectric conversion element composed of a porous body formed by sintering particles and a filler impregnated in the voids of the porous body , containing at least two types of clathrate compounds, One type of the clathrate compound is a third clathrate compound having a hole mobility of 100 to 2000 cm ² / V · s, and the other type has a hole concentration of 1.0 × 10 ^{20 to} 1.0 × 10 6. ²² / cm ³ of the fourth clathrate compound, wherein the particles contain the third clathrate compound , and the filler contains the fourth clathrate compound . a thermoelectric conversion element you.

< 7 > The thermoelectric conversion element according to < 6 >, wherein the sintering is performed by a discharge plasma sintering method.

< 8 > A thermoelectric conversion element having a structure in which two kinds of thin films are alternately laminated , and contains at least two kinds of clathrate compounds, and one kind of the clathrate compounds has a hole mobility of 100 to 2000 cm. ² / V · s is the third clathrate compound, and the other kind is the fourth clathrate compound having a hole concentration of 1.0 × 10 ^{20 to} 1.0 × 10 ²² / cm ³ , kind of thin film contains the third clathrate compound, other kind is a thermoelectric conversion element you characterized by containing the fourth clathrate compound.

  According to the present invention, a thermoelectric conversion element having an excellent figure of merit can be provided.

Hereinafter, the thermoelectric conversion element of the present invention will be described in detail.
The thermoelectric conversion element of the present invention is characterized by containing at least two types of clathrate compounds. The clathrate compound is characterized by low lattice thermal conductivity. Therefore, in order to improve the figure of merit of the thermoelectric conversion element, it is important to increase the electric conductivity of the clathrate compound. In the present invention, by using at least two types of clathrate compounds in combination, the electrical conductivity is improved and a thermoelectric conversion element having an excellent figure of merit is realized.
In the present invention, the clathrate compound A, the clathrate compound B, the clathrate compound C, and the clathrate compound D described later are respectively the first clathrate compound, the second clathrate compound, and the third clathrate compound. It means a clathrate compound and a fourth clathrate compound.

  The electrical conductivity σ can be expressed by the following formula (3) using the charge e, the carrier concentration n, and the mobility μ.

σ = enμ (3)

  However, a material with high mobility generally has a trade-off relationship that the carrier concentration is small. Therefore, in the present invention, the type of clathrate compound used in combination is not particularly limited, but one of them uses a clathrate compound with a high carrier concentration, and the other uses a clathrate compound with a high mobility. It is preferable. By using a clathrate compound having a high carrier concentration and a clathrate compound having a high mobility, an improvement in electrical conductivity can be realized.

The thermoelectric conversion element of the present invention may be an n-type thermoelectric conversion element or a p-type thermoelectric conversion element. In the case of an n-type thermoelectric conversion element, one type of clathrate compound used in combination is clathrate compound A having an electron mobility of 100 to 5000 cm ² / V · s, and the other type is a carrier concentration (p-type thermoelectric conversion). for distinction between elements, or less, the carrier concentration in the n-type thermoelectric conversion element may be referred to as electron concentration.) in that ^{1.0 × 10 20 ~1.0 × 10 22} / cm 3 of clathrate compound B Preferably there is.

When the electron mobility of the clathrate compound A is less than 100 cm ² / V · s, it is equivalent to a general clathrate compound, and it is difficult to achieve the effects of the present invention. In addition, it is difficult for the clathrate compound to have an electron mobility larger than 5000 cm ² / V · s. Electron mobility of the clathrate compound A, 500～4000Cm more preferably ² / V · s, in particular 1000~3000cm ² / V · s is preferred.

If the electron concentration of the clathrate compound B is less than 1.0 × 10 ²⁰ / cm ^{3, the} clathrate compound B is equivalent to a general clathrate compound, and it is difficult to achieve the effects of the present invention. On the other hand, if it is larger than 1.0 × 10 ²² / cm ³ , it becomes a metal rather than a semiconductor, so that the contribution of the conductivity by electrons to the thermal conductivity is increased, resulting in an increase in thermal conductivity, which is not preferable. . The electron concentration of the clathrate compound B is more preferably 1.0 × 10 ^{20 to} 1.0 × 10 ²¹ / cm ³ , and particularly preferably 1.0 × 10 ^{20 to} 5.0 × 10 ²⁰ / cm ³ .

Specific examples of the clathrate compound A that can be used in the present invention include Ba ₈ Ga ₁₅ Si ₃₁ and Ba ₈ Ga ₁₆ Si ₃₀ . Specific examples of the clathrate compound B include Ba ₈ Ga ₁₅ Ge ₃₁ , Ba ₈ Ga ₁₄ Sn ₃₂ , Ba ₈ Ga ₁₆ Ge ₃₀ , Ba ₈ Ga ₁₅ Sn _{31 and the} like.

When the thermoelectric conversion element of the present invention is a p-type thermoelectric conversion element, one type of clathrate compound used in combination is a clathrate compound C having a hole mobility of 100 to 2000 cm ² / V · s, and the other type is (to distinguish the n-type thermoelectric conversion element, hereinafter, the carrier concentration in the p-type thermoelectric conversion element may be referred to as hole density.) carrier concentration of ^{1.0 × 10 20 ~1.0 × 10 22} / A clathrate compound D of cm ³ is preferred.

When the hole mobility of the clathrate compound C is less than 100 cm ² / V · s, it becomes equivalent to a general clathrate compound, and it is difficult to achieve the effects of the present invention. On the other hand, it is difficult to achieve a hole mobility larger than 2000 cm ² / V · s with a clathrate compound. The hole mobility of the clathrate compound C is more preferably 500 to 2000 cm ² / V · s, and particularly preferably 1000 to 2000 cm ² / V · s.

When the hole concentration of the clathrate compound D is less than 1.0 × 10 ²⁰ / cm ³ , the performance is equivalent to that of a general clathrate compound, and the effect of the present invention cannot be exhibited. On the other hand, if the hole concentration is higher than 1.0 × 10 ²² / cm ³ , the electrical conductivity is improved and the thermal conductivity is improved, and the thermoelectric characteristics of the thermoelectric conversion element are extremely lowered. The hole concentration of the clathrate compound D is more preferably 1.0 × 10 ^{21 to} 1.0 × 10 ²² / cm ³ , and particularly preferably 5.0 × 10 ^{21 to} 1.0 × 10 ²² / cm ³ .

Specific examples of the clathrate compound C that can be used in the present invention include Ba ₈ Ga ₁₈ Si ₂₈ and the like. Specific examples of the clathrate compound D include Ba ₈ Ga _18-X O _x Ge ₂₈ in which a part of Ga in Ba ₈ Ga ₁₈ Ge ₂₈ is substituted with an oxygen atom. Here, the X in the _{Ba 8 Ga 18-X O X} Ge 28, preferably from 0.001 to 0.1, more preferably 0.001 to 0.05.

  In the present invention, the mobility (electron mobility and hole mobility) and carrier concentration (electron concentration and hole concentration) of the clathrate compound are measured by the Van der Pauw method when the sample shape is 3 × 3 × 0.3 mm. Value. Specifically, the voltage was measured by changing the current passed through the sample to 3, 5, and 10 mA, the current-voltage characteristics were graphed, and only the voltage component proportional to the current was used as a true value in the calculation. The applied magnetic field was 5 T, and the temperature was 27 ± 5 ° C.

Hereinafter, the thermoelectric conversion element of the present invention will be described in more detail with reference to the drawings.
<First aspect>
FIG. 1 is a schematic configuration diagram showing a first aspect of an n-type thermoelectric conversion element according to the present invention. The n-type thermoelectric conversion element 10 according to the first aspect includes a base material 12 constituting a matrix and fine particles 14 dispersed in the base material 12. The base material 12 contains a clathrate compound A, and the fine particles 14 contain a clathrate compound B. The fine particles 14 containing the clathrate compound B having a high electron concentration are dispersed in the base material 12 containing the clathrate compound A having a high electron mobility, thereby optimizing the electron concentration of the n-type thermoelectric conversion element 10. The conductivity can be further improved. As a result, the figure of merit of the n-type thermoelectric conversion element 10 can be improved.

Further, the thermal conductivity κ is expressed by the following formula (4) using the conductivity κ _e by electrons and the lattice thermal conductivity κ _p .

κ = κ _e + κ _p (4)

In the n-type thermoelectric conversion element 10, lattice scattering occurs at the interface between the base material 12 and the fine particles 14 and κ _p decreases, so that the thermal conductivity κ can be decreased. As a result, the figure of merit of the n-type thermoelectric conversion element 10 can be improved.

Further, by using clathrate compound A and clathrate compound B as material compositions containing the same components, the bondability at the interface between base material 12 and fine particles 14 is improved, and scattering of electrons at the interface is suppressed. This is preferable because the electrical conductivity can be further improved. Here, that the clathrate compound has a material composition containing the same components as each other means that a part of the composition of each clathrate compound overlaps. Specifically, for example, when Ba ₈ Ga ₁₅ Si ₃₁ is used as the clathrate compound A and Ba ₈ Ga ₁₅ Ge ₃₁ is used as the clathrate compound B, Ba and Ga which are part of the composition overlap. These clathrate compounds are included in the category of material compositions containing the same components.

The n-type thermoelectric conversion element of the first aspect is manufactured by, for example, the following method.
The clathrate compound A pulverized into fine particles and the clathrate compound B pulverized into fine particles are added to an organic solvent such as ethanol and stirred with an ultrasonic stirrer or the like. The n of the first aspect is prepared through a step of preparing a dispersion containing clathrate compound B fine particles, a step of drying the dispersion to form a clathrate compound, and a step of sintering the clathrate compound. Type thermoelectric conversion elements are manufactured. In this case, the average particle size of the clathrate compound A is preferably 10 to 100 μm, and more preferably 10 to 70 μm. The average particle size of the clathrate compound B is preferably 100 to 1000 nm, and more preferably 100 to 500 nm. The mixing ratio of clathrate compound A and clathrate compound B is preferably 95: 5 to 30:70, and more preferably 90:10 to 50:50, by volume.

  In the step of molding the clathrate compound and the step of sintering, pressure molding and sintering may be performed separately, but sintering is preferably performed while pressure molding. As a method of sintering while pressure forming, any method such as a hot press sintering method, a hot isostatic pressure sintering method, a discharge plasma sintering method, or the like can be used. Among these, the discharge plasma sintering method is preferable. The sintering temperature in the discharge plasma sintering method is preferably 600 to 900 ° C, more preferably 650 to 850 ° C. The sintering time is preferably 30 to 90 minutes, and more preferably 40 to 60 minutes. The pressure at the time of pressurization is preferably 20 to 50 MPa, and more preferably 25 to 45 MPa.

<Second aspect>
FIG. 2 is a schematic configuration diagram showing a second aspect of the n-type thermoelectric conversion element according to the present invention. The n-type thermoelectric conversion element 20 according to the second embodiment includes a porous body 22 formed by sintering particles and a filler 24 impregnated in the voids of the porous body 22. The particles forming the porous body 22 contain the clathrate compound A, and the filler 24 contains the clathrate compound B. By filling the voids of the porous body 22 formed of particles containing the clathrate compound A having a high electron mobility with the filler 24 containing the clathrate compound B having a high electron concentration, the Seebeck coefficient is improved. This is presumably because the clathrate compound B impregnated in the voids of the porous body 22 has a structure close to nanowires, and thus the n-type thermoelectric conversion element 20 exhibits superlattice characteristics.

The n-type thermoelectric conversion element of the second aspect is manufactured by the following method, for example.
The n-type thermoelectric conversion element of the second embodiment is manufactured through a step of sintering the particulate clathrate compound A to form the porous body 22 and a step of impregnating the clathrate compound B into the voids of the porous body 22. Is done. In this case, the melting point of clathrate compound A is preferably higher than the melting point of clathrate compound B. Examples of the method of impregnating the clathrate compound B in the voids of the porous body 22 include a method of immersing the porous body 22 in the molten clathrate compound B. 10-100 micrometers is preferable and, as for the average particle diameter of the particle | grains which form the porous body 22, 20-75 micrometers is more preferable.

  As the particle sintering method, any method such as a hot press sintering method, a hot isostatic pressing method, a discharge plasma sintering method, or the like can be used. Among these, the discharge plasma sintering method is preferable. By making the porous body 22 by the discharge plasma sintering method, it is possible to further improve the electrical conductivity. This is presumed to be because the particles are sintered by a solid-phase reaction, and scattering of electron grain boundaries can be suppressed.

<Third aspect>
FIG. 3 is a schematic configuration diagram showing a third aspect of the n-type thermoelectric conversion element according to the present invention. The n-type thermoelectric conversion element 30 of the third embodiment has a structure in which thin films 32 containing the clathrate compound A and thin films 34 containing the clathrate compound B are alternately stacked. By alternately laminating thin films, the electron mobility can be improved while the electron concentration is improved. In addition, the Seebeck coefficient can be improved. This is presumably because a superlattice structure is formed by alternately laminating thin films 32 and thin films 34.

As a method for forming the thin film, a method such as a vacuum evaporation method or a sputtering method can be used. However, by using the sputtering method, a thin film having the same composition ratio as the target can be easily formed. preferable. The thickness of the thin film is preferably 10 nm to 100 nm, and more preferably 10 nm to 50 nm. By making the film thickness 10 nm to 100 nm, the Seebeck coefficient can be improved. Number of stacked films is preferably 10 ² to 10 ⁶ layers, more preferably 10 ³ to 10 ⁶ layers.

  As described above, the specific embodiment of the thermoelectric conversion element of the present invention has been described using the n-type thermoelectric conversion element as an example, but the clathrate compound A is the clathrate compound C and the clathrate compound B is the class. By replacing with the rate compound D, a p-type thermoelectric conversion element can be obtained.

  Moreover, the thermoelectric conversion element of this invention has high heat resistance, and can be used as a high-temperature thermoelectric conversion element.

  Hereafter, the thermoelectric conversion element of this invention is demonstrated concretely using an Example. However, the present invention is not limited to the following examples.

[Example 1]
Ba (99.99%), Ga (99.999%), Ge (99.9999%), Si (99.9999%) are used as raw materials and weighed to a desired molar ratio in a glove box under an argon atmosphere. Then, Ba ₈ Ga ₁₅ Ge ₃₁ as the clathrate compound B and Ba ₈ Ga ₁₅ Si ₃₁ as the clathrate compound A were synthesized by arc melting. The _{3 × 3 × Ba 8 Ga 15} Ge 31 and Ba ₈ Ga ₁₅ Si ₃₁ in the shape of 0.3mm was prepared, it was subject to electron density and electron mobility with Van der Pauw method at room temperature, Ba ₈ Ga The electron concentration of ₁₅ Ge ₃₁ is 1.0 × 10 ²² / cm ³ , the electron mobility is 1.1 cm ² / V · s, and the electron concentration of Ba ₈ Ga ₁₅ Si ₃₁ is 1.0 × 10 ¹⁹ / cm. ^3. Electron mobility was 250 cm ² / V · s.

Ba ₈ Ga ₁₅ Ge ₃₁ was pulverized to an average particle diameter of 50 nm and Ba ₈ Ga ₁₅ Si ₃₁ was pulverized to an average particle diameter of 50 μm, and these two kinds of particles were ultrasonically stirred in ethanol. The preparation ratio of Ba ₈ Ga ₁₅ Ge ₃₁ and Ba ₈ Ga ₁₅ Si ₃₁ was 1: 1 by volume.

After drying, discharge plasma sintering is performed, and the present invention is composed of a base material containing Ba ₈ Ga ₁₅ Si ₃₁ and fine particles containing Ba ₈ Ga ₁₅ Ge ₃₁ dispersed in the base material. An n-type thermoelectric conversion element A of the first aspect was obtained. The conditions of the discharge plasma sintering were a pressure of 50 MPa, a temperature of 800 ° C., and a time of 60 minutes. The electric conductivity value of the obtained n-type thermoelectric conversion element A is shown in FIG. 4 (Δ), and the figure of merit (ZT) is shown in FIG. 5 (Δ).

In addition, an n-type thermoelectric conversion element B was obtained in the same manner as the n-type thermoelectric conversion element A by using both Ba ₈ Ga ₁₅ Ge ₃₁ and Ba ₈ Ga ₁₅ Si ₃₁ ground to an average particle size of 50 μm. Formulation ratio of Ba ₈ Ga ₁₅ Ge ₃₁ and Ba ₈ Ga ₁₅ Si ₃₁ in the n-type thermoelectric conversion elements B is 1 volume ratio: 1. The electric conductivity value of the obtained n-type thermoelectric conversion element B is shown in FIG. 4 (●), and the figure of merit (ZT) is shown in FIG. 5 (●).

As a comparative example, the value of an n-type thermoelectric conversion element C made only of Ba ₈ Ga ₁₅ Si ₃₁ is shown in FIG. The figure of merit (ZT) of the n-type thermoelectric conversion element C was 1.0 (T = 500 ° C.).

  The electrical conductivity was measured by the four probe method. The figure of merit (ZT) was calculated using the Seebeck coefficient, electrical conductivity, and thermal conductivity. The Seebeck coefficient is obtained by attaching a thermocouple wire to a sample piece from which a part of the thermoelectric conversion element is cut out, providing a temperature difference in the sample piece in a heating furnace, and measuring the thermoelectromotive force generated at this time. It was. The thermal conductivity was calculated by multiplying the density measured by the volume method, the specific heat measured by the DSC method, and the thermal diffusivity measured by the laser flash method.

[Example 2]
Ba (99.99%), Ga (99.999%), Ge (99.9999%), Si (99.9999%) are used as raw materials and weighed to a desired molar ratio in a glove box under an argon atmosphere. Then, Ba ₈ Ga _18-x O _x Ge ₂₈ (0.03 ≦ x ≦ 0.05) was synthesized as clathrate compound D and Ba ₈ Ga ₁₈ Si ₂₈ was synthesized as clathrate compound C by arc melting. When the hole concentration and hole mobility were measured by the same method as the method for measuring electron mobility and electron concentration in Example 1, Ba ₈ Ga _18-x O _x Ge ₂₈ (0.03 ≦ x ≦ 0.05) was measured. Has a hole concentration of 5.0 × 10 ²¹ / cm ³ and a hole mobility of 13 cm ² / V · s. Ba ₈ Ga ₁₈ Si _{28 has} a hole concentration of 3.2 × 10 ¹⁷ / cm ³ and a hole mobility. Was 1300 cm ² / V · s.

Ba ₈ Ga _18-x O _x Ge ₂₈ (0.03 ≦ x ≦ 0.05) was pulverized to an average particle size of 50 nm and Ba ₈ Ga ₁₈ Si ₂₈ was pulverized to an average particle size of 70 μm. Ultrasonic stirring in. The mixing ratio of Ba ₈ Ga _18-x O _x Ge ₂₈ (0.03 ≦ x ≦ 0.05) and Ba ₈ Ga ₁₈ Si ₂₈ was 1: 1 by volume ratio.

After drying, spark plasma sintering is performed, and a base material containing Ba ₈ Ga ₁₈ Si ₂₈ and Ba ₈ Ga _18-x O _x Ge ₂₈ (0.03 ≦ x ≦ 0. The p-type thermoelectric conversion element D according to the first aspect of the present invention, which is composed of fine particles containing (05), was obtained. The conditions of the discharge plasma sintering were a pressure of 50 MPa, a temperature of 800 ° C., and a time of 60 minutes. The electric conductivity value of the obtained p-type thermoelectric conversion element D is shown in FIG.

In addition, Ba ₈ Ga _18-x O _x Ge ₂₈ (0.03 ≦ x ≦ 0.05) and Ba ₈ Ga ₁₈ Si ₂₈ are both pulverized to an average particle size of 50 μm, and a p-type thermoelectric conversion element D is used. Similarly, a p-type thermoelectric conversion element E was obtained. The mixing ratio of Ba ₈ Ga _18-x O _x Ge ₂₈ (0.03 ≦ x ≦ 0.05) and Ba ₈ Ga ₁₈ Si _{28 in the} p-type thermoelectric conversion element E was 1: 1 by volume. . The electric conductivity value of the obtained p-type thermoelectric conversion element E is shown in FIG.
The electrical conductivity was measured in the same manner as in Example 1.

[Example 3]
Ba (99.99%), Ga (99.999%), Sn (99.9999%), Si (99.9999%) are used as raw materials and weighed to a desired molar ratio in a glove box under an argon atmosphere. Then, Ba ₈ Ga ₁₄ Sn ₃₂ was synthesized as clathrate compound B, and Ba ₈ Ga ₁₅ Si ₃₁ was synthesized as clathrate compound A by arc melting. When the electron concentration and the electron mobility were measured in the same manner as in Example 1, the electron concentration of Ba ₈ Ga ₁₄ Sn ₃₂ was 1.0 × 10 ²¹ / cm ³ and the electron mobility was 16 cm ² / V · s. , Ba ₈ Ga ₁₅ Si _{31 had} an electron concentration of 1.0 × 10 ¹⁹ / cm ³ and an electron mobility of 250 cm ² / V · s.

A porous body formed by pulverizing Ba ₈ Ga ₁₅ Si ₃₁ to an average particle size of 0.1 μm, sintering it with a hot press (1000 ° C., 50 MPa), and sintering particles containing Ba ₈ Ga ₁₅ Si _31. Produced. Since the melting point of Ba ₈ Ga ₁₄ Sn ₃₂ (about 400 ° C.) is lower than the melting point of Ba ₈ Ga ₁₅ Si ₃₁ (about 900 ° C.), the Ba ₈ Ga ₁₄ Sn ₃₂ was melted at 550 ° C. soaking the body to give the n-type thermoelectric conversion elements F of the second aspect of the present invention by impregnating the Ba ₈ Ga ₁₄ Sn ₃₂ in the voids of the porous body. The value (Δ) of the Seebeck coefficient of the obtained n-type thermoelectric conversion element F is shown in FIG. Note that the Seebeck coefficient was determined by the method described above.

In addition, an n-type thermoelectric conversion element G was obtained in the same manner as the n-type thermoelectric conversion element A by using both Ba ₈ Ga ₁₅ Si ₃₁ and Ba ₈ Ga ₁₄ Sn ₃₂ ground to an average particle size of 50 μm. Formulation ratio of Ba ₈ Ga ₁₅ Si ₃₁ and Ba ₈ Ga ₁₄ Sn ₃₂ in the n-type thermoelectric conversion element G is 1 volume ratio: 1. The value (●) of the Seebeck coefficient of the obtained n-type thermoelectric conversion element G is shown in FIG.

As is clear from FIG. 7, the n-type thermoelectric conversion element F according to the second aspect of the present invention has a higher Seebeck coefficient than the n-type thermoelectric conversion element G. This is presumably because Ba ₈ Ga ₁₄ Sn ₃₂ impregnated in the voids of the porous body is in a state close to nanowires and the band structure has changed due to the quantum effect.

[Example 4]

sintering method Ba ₈ Ga ₁₅ Si ₃₁ in the n-type thermoelectric conversion elements F, spark plasma sintering (700 ° C., 40 MPa, 30 minutes) was changed to the same manner, a second embodiment according to the present invention N-type thermoelectric conversion element H was prepared. FIG. 8 shows the electric conductivity value (Δ) of the obtained n-type thermoelectric conversion element H together with the electric conductivity value (●) of the n-type thermoelectric conversion element F.

  As is apparent from FIG. 8, the electrical conductivity was improved by producing the porous body using the discharge plasma sintering method. This is presumed that the electric conductivity was improved because the particles forming the porous body were sintered by the solid-phase reaction by the discharge plasma sintering, and the electron grain boundary scattering was suppressed.

[Example 5]
The Ba ₈ Ga ₁₅ Ge ₃₁ as clathrate compound B in the same manner as n-type thermoelectric conversion elements A, was synthesized Ba ₈ Ga ₁₅ Si ₃₁ as clathrate compound A. Ba ₈ Ga ₁₅ Ge ₃₁ and Ba ₈ Ga ₁₅ Si ₃₁ were each pulverized to an average particle size of 50 μm and sintered by discharge plasma. The spark plasma sintering was performed at a pressure of 50 MPa, a temperature of 800 ° C., and a time of 60 minutes. Using the Ba ₈ Ga ₁₅ Si ₃₁ and Ba ₈ Ga ₁₅ Ge ₃₁ as targets, the layers were alternately stacked using a sputtering apparatus, and the n-type thermoelectric conversion element I according to the third aspect of the present invention was fabricated. In this case, the film thickness of Ba ₈ Ga ₁₅ Si ₃₁ was 30 nm and the film thickness of Ba ₈ Ga ₁₅ Ge ₃₁ was 50 nm, and 100 layers each were laminated. The Seebeck coefficient of the n-type thermoelectric conversion element I was 350 V / mK (T = 600 ° C.). The Seebeck coefficient of each of Ba ₈ Ga ₁₅ Si ₃₁ and Ba ₈ Ga ₁₅ Ge ₃₁ is 250 V / mK (T = 600 ° C.), and it was revealed that the Seebeck coefficient is improved by stacking. This is considered to be because a superlattice structure is formed by laminating Ba ₈ Ga ₁₅ Si ₃₁ and Ba ₈ Ga ₁₅ Ge ₃₁ and a quantum effect is generated.

It is a schematic block diagram which shows the 1st aspect of the n-type thermoelectric conversion element which concerns on this invention. It is a schematic block diagram which shows the 2nd aspect of the n-type thermoelectric conversion element which concerns on this invention. It is a schematic block diagram which shows the 3rd aspect of the n-type thermoelectric conversion element which concerns on this invention. It is the figure which showed the value of the electrical conductivity of the n-type thermoelectric conversion elements A, B, and C. It is the figure which showed the value of the figure of merit (ZT) of the n-type thermoelectric conversion elements A and B. It is the figure which showed the value of the electrical conductivity of the p-type thermoelectric conversion elements D and E. It is the figure which showed the value of the Seebeck coefficient of the n-type thermoelectric conversion elements F and G. It is the figure which showed the value of the electrical conductivity of the n-type thermoelectric conversion elements F and H.

Explanation of symbols

10. Thermoelectric conversion element (first aspect)
12 Base material 14 Fine particle 20 Thermoelectric conversion element (second embodiment)
22 Porous body 24 Filler 30 Thermoelectric conversion element (third aspect)
32 Thin Film Containing Clathrate Compound A 34 Thin Film Containing Clathrate Compound B

Claims (8)

A thermoelectric conversion element composed of a base material and fine particles dispersed in the base material,
At least, contain two types of clathrate compounds, one of the clathrate compound is a first clathrate compound in an electron mobility 100~5000cm ² / V · s, the other kind, the electron concentration A second clathrate compound of 1.0 × 10 ^{20 to} 1.0 × 10 ²² / cm ³ ,
The base material, the second contains an clathrate compound, the fine particles, the second clathrate compound thermoelectric conversion elements you characterized by containing. A thermoelectric conversion element composed of a porous body formed by sintering particles and a filler impregnated in the voids of the porous body,
At least two kinds of clathrate compounds are contained, and one kind of the clathrate compounds is a first clathrate compound having an electron mobility of 100 to 5000 cm ² / V · s, and the other kind has an electron concentration. A second clathrate compound of 1.0 × 10 ^{20 to} 1.0 × 10 ²² / cm ³ ,
The particles, the first containing one clathrate compound, the filler, the second thermoelectric conversion element you characterized by containing a clathrate compound. The thermoelectric conversion element according to claim 2 , wherein the sintering is performed by a discharge plasma sintering method. A thermoelectric conversion element having a structure in which two types of thin films are alternately laminated,
At least two kinds of clathrate compounds are contained, and one kind of the clathrate compounds is a first clathrate compound having an electron mobility of 100 to 5000 cm ² / V · s, and the other kind has an electron concentration. A second clathrate compound of 1.0 × 10 ^{20 to} 1.0 × 10 ²² / cm ³ ,
One of the thin film, the second contains an clathrate compound, other kind, said second clathrate compound thermoelectric conversion elements you characterized by containing. A thermoelectric conversion element composed of a base material and fine particles dispersed in the base material,
At least two kinds of clathrate compounds are contained, and one of the clathrate compounds is a third clathrate compound having a hole mobility of 100 to 2000 cm ² / V · s, and the other kind has a hole concentration of A fourth clathrate compound of 1.0 × 10 ^{20 to} 1.0 × 10 ²² / cm ³ ,
The base material, the contained third clathrate compound, the fine particles, the fourth clathrate compound thermoelectric conversion elements you characterized by containing. A thermoelectric conversion element composed of a porous body formed by sintering particles and a filler impregnated in the voids of the porous body,
At least two kinds of clathrate compounds are contained, and one of the clathrate compounds is a third clathrate compound having a hole mobility of 100 to 2000 cm ² / V · s, and the other kind has a hole concentration of A fourth clathrate compound of 1.0 × 10 ^{20 to} 1.0 × 10 ²² / cm ³ ,
The particles, the contained third clathrate compound, the filler, the fourth thermoelectric conversion element you characterized by containing a clathrate compound. The thermoelectric conversion element according to claim 6 , wherein the sintering is performed by a discharge plasma sintering method. A thermoelectric conversion element having a structure in which two types of thin films are alternately laminated,
At least two kinds of clathrate compounds are contained, and one of the clathrate compounds is a third clathrate compound having a hole mobility of 100 to 2000 cm ² / V · s, and the other kind has a hole concentration of a fourth clathrate compound of ^{1.0 × 10 20 ~1.0 × 10 22} / cm 3,
One of said thin film, said containing third clathrate compound, other kind, the fourth clathrate compound thermoelectric conversion elements you characterized by containing.

Images