JP5126723B2 - Thermoelectric conversion element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a thermoelectric conversion element made of 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 (A).
ZT = α ² σT / κ (A)
Here, α, σ, κ, and T represent the Seebeck coefficient, electrical conductivity, thermal conductivity, and measurement temperature, respectively.

  As apparent from the above formula (A), in order to improve the performance of the thermoelectric conversion element, it is necessary to increase the Seebeck coefficient and electrical conductivity of the material used for the element, and to decrease the thermal conductivity. is important.

On the other hand, Z in the figure of merit ZT has a proportional relationship represented by the formula (B) among effective mass (m ^* ), mobility (μ), and thermal conductivity (κ).
Z ∝m ^* 3/2 μ / κ (B)
From the above formula (B), it is understood that it is important to improve the effective mass and mobility in order to improve Z.

  Conventionally, 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. Furthermore, a thermoelectric conversion material formed by molding and baking zinc oxide powder doped with aluminum is known (for example, see Patent Document 1).

JP 2002-118296 A

  An object of this invention is to provide the thermoelectric conversion element which consists of a novel clathrate compound. Furthermore, an object of this invention is to provide the manufacturing method of a novel thermoelectric conversion element.

  That is, the present invention includes the following inventions.

The invention according to claim 1 of the present application is a thermoelectric conversion element made of a sintered body of a clathrate compound represented by the following composition formula (1).
A ₈ B _x C _46-X (where 0 <x ≦ 10) (1)
However, A is a 7B group element, B is a 5B group element, C is a 4B group element.

  The invention according to claim 2 is the thermoelectric conversion element according to claim 1, wherein B is antimony in the clathrate compound according to claim 1.

  Similarly, the invention according to claim 3 is the thermoelectric conversion element according to claim 1 or 2, wherein C is germanium or tin in the clathrate compound according to claim 1.

  The invention according to claim 4 is the thermoelectric conversion element according to any one of claims 1 to 3, wherein A is iodine in the clathrate compound according to claim 1.

  Further, the invention according to claim 5 is characterized in that the component elements of A, B and C constituting the clathrate compound are mixed in a mechanical alloying step and then sintered. It is a manufacturing method of the thermoelectric conversion element in any one.

  Furthermore, the invention according to claim 6 is characterized in that, in the mechanical alloying process according to claim 5, a raw material containing a compound composed of two or three elements among the respective components is used. This is a method for manufacturing a thermoelectric conversion element.

  ADVANTAGE OF THE INVENTION According to this invention, the thermoelectric conversion element with a high thermoelectric conversion efficiency using a novel clathrate compound and its manufacturing method can be provided.

It is a figure which shows the X-ray-diffraction pattern of the clathrate compound calculated | required in Examples 1-3. 6 is a diagram showing an X-ray diffraction pattern of a clathrate compound obtained in Example 4. FIG.

  The present invention is a thermoelectric conversion element comprising a clathrate compound having a novel composition and a novel method for producing the clathrate compound.

These will be described in detail below sequentially.
<Clathrate compound>
The clathrate compound used in the present invention is represented by the following composition formula (1).
A ₈ B _x C _46-X (where 0 <x ≦ 10) (1)
However, A is a 7B group element of a periodic table, B is a 5B group element, C is a 4B group element.

When x in the composition formula (1) is out of the above range, the clathrate compound exhibits metallic characteristics and may not be suitable as a thermoelectric conversion element. The atomic concentration of the clathrate compound is about 5 × 10 ²² cm ⁻³ . Since the unit cell of the clathrate compound (for example, I ₈ Sn _{46 and the} like) has 54 constituent atoms, if one of the 54 is an acceptor (donor) atom, the carrier concentration is about 1 × 10 ²¹ cm ⁻³ . Become. In the range of x <6 and x> 10, the carrier density is larger than 2 × 10 ²¹ cm ^−3, and exhibits metallic characteristics.

  In the clathrate compound 1, the preferred range of x is 7 ≦ x ≦ 9.

Here, A is a halogen element, and chlorine, bromine and iodine are particularly preferably used. Of these, iodine is particularly preferable.
B is a Group 5 element, and arsenic or antimony is particularly preferable. Furthermore, C is a 4B group element, and silicon, germanium, and tin are preferable. Among these, tin is particularly preferably used.

That is, a composition that can be suitably produced can be represented by the following composition formulas (2) and (3).
A ₈ B _x Si _46-x or A ₈ B _x Ge _46-x (0 <x ≦ 10) (2)
A ₈ As _x Sn _46-x or A ₈ Sb _x Sn _46-x (0 <x ≦ 10) (3)
In the production of the clathrate compound used in the present invention, it is essential to have at least a mechanical alloying step. In that case, each raw material may be mixed as a single substance, or a compound corresponding to each component may be used.
The operation time of mechanical alloying is preferably 1h to 200h, and more preferably 20 to 100h. The gas atmosphere in the pulverization vessel is preferably a gas atmosphere when the component raw material is a gaseous element, or a mixed gas atmosphere of an inert gas and hydrogen when the component raw material is a solid. By using a mixed gas of an inert gas and hydrogen, an effect of preventing oxidation of the raw material or the synthesized product and an effect of reducing and removing the oxide can be obtained.

As the inert gas, He, Ne, Ar or the like can be used, and among these, Ar is preferable. The hydrogen content in the inert gas is preferably 5 to 10%.
<Thermoelectric conversion element>
The thermoelectric conversion element of the present invention can be obtained by sintering the clathrate compound of the present invention.

  In the sintering step, sintering can be performed using a discharge plasma sintering method, a hot press sintering method, a hot isostatic pressing sintering method, or the like.

  As sintering conditions when using the discharge plasma sintering method, the temperature is preferably 300 to 950 ° C, more preferably 300 to 700 ° C. The sintering time is preferably 20 to 120 minutes, more preferably 30 to 90 minutes. The pressure is preferably 25 to 40 MPa, more preferably 30 to 40 MPa.

The present invention can be confirmed by X-ray diffraction. Specifically, if the sample after firing shows only the clathrate phase by X-ray diffraction, it can be confirmed that the clathrate compound has been synthesized.
(Example)
EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited by the following Example.

<Manufacture of thermoelectric conversion element 1 (I ₈ Ge ₃₈ Sb ₈ )>
8.28 grams of Ge, 4.02 grams of antimony iodide SbI ₃ and 1.95 grams of Sb were weighed to achieve a composition ratio of I ₈ Ge ₃₈ Sb ₈ . Each is pulverized to 500 μm or less. It was placed in a 45 cc stainless steel container for mechanical alloying. At the same time, 11 silicon nitride balls having a diameter of 10 mm were placed. The lid was closed with a glove box in an argon atmosphere diluted with 10% hydrogen. It was taken out of the glove box and set on a planetary ball mill P-7 manufactured by Fritsch. It drove for 100 hours at a speed of 10. Thereafter, the pulverized powder was taken out and sintered using a discharge plasma sintering apparatus. The sintering conditions were a sintering temperature of 600 ° C., an argon atmosphere of 0.6 atm, and a sintering holding time of 30 minutes. The thermoelectric conversion element 1 was manufactured by the above process. As a result of performing X-ray diffraction measurement and comparing the theoretical values obtained by simulating the diffraction patterns, it was confirmed that the thermoelectric conversion element 1 had I ₈ Ge ₃₈ Sb ₈ having a clathrate structure. The diffraction pattern together with the simulation result is shown in FIG.

<Manufacture of thermoelectric conversion element 2 (I ₈ Ge ₃₈ Sb ₈ )>
8.28 grams of Ge, 3.05 grams of I, and 2.92 grams of Sb were weighed to achieve a composition ratio of I ₈ Ge ₃₈ Sb ₈ . Each is pulverized to 500 μm or less. It was placed in a 45 cc stainless steel container for mechanical alloying. At the same time, 11 silicon nitride balls having a diameter of 10 mm were placed. The lid was closed with a glove box in an argon atmosphere diluted with 10% hydrogen. It was taken out of the glove box and set on a planetary ball mill P-7 manufactured by Fritsch. It drove for 100 hours at a speed of 10. Thereafter, the pulverized powder was taken out and sintered using a discharge plasma sintering apparatus. The sintering conditions were a sintering temperature of 600 ° C., an argon atmosphere of 0.6 atm, and a sintering holding time of 30 minutes. The thermoelectric conversion element 2 was manufactured by the above process. As a result of performing X-ray diffraction measurement and comparing the theoretical values obtained by simulating the diffraction patterns, it was confirmed that the thermoelectric conversion element 2 has I ₈ Ge ₃₈ Sb ₈ having a clathrate structure. The diffraction pattern together with the simulation result is shown in FIG.

<Manufacture of thermoelectric conversion element 3 (I ₈ Ge ₃₈ Sb ₈ )>
7.84 grams of Ge, 2.92 grams of Sb, and 3.48 grams of germanium iodide GeI ₄ were weighed to achieve a composition ratio of I ₈ Ge ₃₈ Sb ₈ . Each is pulverized to 500 μm or less. It was placed in a 45 cc stainless steel container for mechanical alloying. At the same time, 11 silicon nitride balls having a diameter of 10 mm were placed. The lid was closed with a glove box in an argon atmosphere diluted with 10% hydrogen. It was taken out of the glove box and set on a planetary ball mill P-7 manufactured by Fritsch. It drove for 100 hours at a speed of 10. Thereafter, the pulverized powder was taken out and sintered using a discharge plasma sintering apparatus. The sintering conditions were a sintering temperature of 600 ° C., an argon atmosphere of 0.6 atm, and a sintering holding time of 30 minutes. The thermoelectric conversion element 3 was manufactured by the above process. As a result of performing X-ray diffraction measurement and comparing the theoretical values obtained by simulating the diffraction patterns, it was confirmed that the thermoelectric conversion element 3 has I ₈ Ge ₃₈ Sb ₈ having a clathrate structure. The diffraction pattern together with the simulation result is shown in FIG.

<Manufacture of thermoelectric conversion element 4 (I ₈ Sn ₃₈ Sb ₈ )>
11.11 grams of Sn, 2.40 grams of Sb, and 2.50 grams of I were weighed to achieve a composition ratio of I ₈ Sn ₃₈ Sb ₈ . Each is pulverized to 500 μm or less. It was placed in a 45 cc stainless steel container for mechanical alloying. At the same time, 11 silicon nitride balls having a diameter of 10 mm were placed. The lid was closed with a glove box in an argon atmosphere diluted with 10% hydrogen. It was taken out of the glove box and set on a planetary ball mill P-7 manufactured by Fritsch. I drove at speed 10 for 50h. Thereafter, the pulverized powder was taken out and sintered using a discharge plasma sintering apparatus. The sintering conditions were a sintering temperature of 340 ° C., an argon atmosphere of 0.6 atm, and a sintering holding time of 30 minutes. The thermoelectric conversion element 4 was manufactured by the above process. As a result of performing X-ray diffraction measurement and comparing the theoretical values obtained by simulating the diffraction patterns, it was confirmed that the thermoelectric conversion element 4 had I ₈ Sn ₃₈ Sb ₈ having a clathrate structure. FIG. 2 shows the diffraction pattern together with the simulation result.

Claims (6)

A thermoelectric conversion element comprising a sintered body of a clathrate compound represented by the following composition formula (1).
A ₈ B _x C _46-X (where 0 <x ≦ 10) (1)
However, A is a 7B group element, B is a 5B group element, C is a 4B group element.   The thermoelectric conversion element according to claim 1, wherein B is antimony in the clathrate compound according to claim 1.   The thermoelectric conversion element according to claim 1 or 2, wherein C is germanium or tin in the clathrate compound according to claim 1.   The thermoelectric conversion element according to any one of claims 1 to 3, wherein A is iodine in the clathrate compound according to claim 1.   5. The method for producing a thermoelectric conversion element according to claim 1, wherein the component elements A, B and C constituting the clathrate compound are mixed in a mechanical alloying step and then sintered.   6. The method of manufacturing a thermoelectric conversion element according to claim 5, wherein in the mechanical alloying step according to claim 5, a raw material containing a compound comprising two or three elements among the components is used.

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