JP5548889B2 - Thermoelectric composition - Google Patents

Description

  The present invention relates to a thermoelectric power generation composition. Specifically, the present invention relates to a thermoelectric power generation composition having low thermal conductivity and excellent thermoelectric power generation performance.

  Thermoelectric power generation compositions have the property of converting thermal energy into electrical energy by the Seebeck effect. For this reason, electricity can be taken out, for example from exhaust heat of an engine, etc. using a thermoelectric-generation composition. Since the energy conversion by this thermoelectric power generation composition is direct conversion, it has attracted attention as a technology for efficiently using energy.

For example, in a half-Heusler type FeVSb-based material or FeNbSb-based material known as a thermoelectric power generation composition, Ti, Mo or the like is introduced into the atomic position of V or Nb, and at least a part of V or Nb is Ti, Mo A technique for substituting with is disclosed (see Non-Patent Document 1).
According to this technology, the electrical conductivity of the thermoelectric generator composition can be increased by replacing at least a part of V and Nb with Ti, Mo, etc. to adjust the carrier amount, and the excellent thermoelectric generator performance can be obtained. It is supposed that the thermoelectric power generation composition which has is obtained.

Journal of Applied Physics, vol. 87, P317-321.

However, in order to improve the thermoelectric power generation performance of the thermoelectric generator composition, it is not sufficient to increase the electric conductivity of the thermoelectric generator composition, and it is necessary to reduce the thermal conductivity of the thermoelectric generator composition. . This is because when the thermal conductivity is high, the temperature difference generated between the terminals when the element is formed cannot be maintained.
However, in the above Non-Patent Document 1, no consideration has been given to the reduction of the thermal conductivity of the thermoelectric power generation composition, and further improvement of the thermoelectric power generation performance is desired.

  The present invention has been made in view of the above, and an object of the present invention is to provide a thermoelectric power generation composition having a low thermal conductivity and excellent thermoelectric power generation performance as compared with the conventional art.

［一般式（１）中、Ａは、Ｎｂ、Ｔａ、及びＶからなる群より選択される２種以上の元素の組み合わせからなる。］

［一般式（２）中、ｘ及びｙは、０．２≦ｘ≦０．８、０．２≦ｙ≦０．８、及び０．５≦ｘ＋y≦１．０の関係を満たす。］ In order to achieve the above object, the thermoelectric power generation composition according to the present invention is represented by the following general formula (2) among those represented by the following general formula (1).

[In General Formula (1), A consists of a combination of two or more elements selected from the group consisting of Nb, Ta, and V. ]

[In General Formula (2), x and y satisfy the relationship of 0.2 ≦ x ≦ 0.8, 0.2 ≦ y ≦ 0.8, and 0.5 ≦ x + y ≦ 1.0. ]

In the present invention, among the compounds represented by the general formula (1), the thermoelectric power generation composition is composed of the compound represented by the general formula (2) .
Thereby, compared with the past, the thermal conductivity of a thermoelectric power generation composition can be reduced to 6.5 W / mK or less . For this reason, when the thermoelectric power generation composition according to the present invention is formed into an element, a large temperature difference can be ensured between the terminals of the element, and as a result, more excellent thermoelectric power generation performance can be obtained.

  In the thermoelectric power generation composition according to the present invention, in the general formula (2), x and y are 0.3 ≦ x ≦ 0.7, 0.3 ≦ y ≦ 0.7, and 0.7 ≦ More preferably, the relationship x + y ≦ 1.0 is satisfied.

  In a more preferred embodiment of the present invention, the compound represented by the general formula (2) is such that x and y are 0.3 ≦ x ≦ 0.7, 0.3 ≦ y ≦ 0.7, and 0. The thermoelectric power generation composition was composed of a compound satisfying the relationship of 7 ≦ x + y ≦ 1.0. Thereby, the thermal conductivity of the thermoelectric generator composition can be reduced to 6.0 W / mK or less. For this reason, as a result of securing a larger temperature difference between the terminals when it is made into an element, a further excellent thermoelectric power generation performance is obtained.

  According to the present invention, it is possible to provide a thermoelectric power generation composition having a lower thermal conductivity than the conventional one and having excellent thermoelectric power generation performance.

It is a figure which shows the relationship between temperature and thermal conductivity when Nb of FeNbSb is substituted with V and / or Ta. It is a thermal conductivity calculation result in the room temperature of the thermoelectric power generation composition which concerns on an Example , a reference example, and a comparative example. It is a figure which shows the relationship between the element seed | species of the thermoelectric power generation composition which concerns on an Example , a reference example, and a comparative example, a structural ratio, and thermal conductivity.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The thermoelectric power generation composition according to an embodiment of the present invention is represented by the following general formula (1), and A in the following general formula (1) is selected from the group consisting of Nb, Ta, and V It consists of a combination of the above elements.

The thermal conductivity of the thermoelectric generator composition according to this embodiment will be described.
FIG. 1 is a graph showing the relationship between temperature (K) and thermal conductivity (W / mK) when the Nb atom position of FeNbSb is substituted with V and / or Ta which are 5A group elements belonging to Nb. It is. The substitution rate% is the mol% of the substitution element with respect to Nb at the Nb atom position.

  Moreover, the thermal conductivity of each thermoelectric power generation composition was measured in the temperature range from room temperature to about 973 K using “TC-7000” manufactured by ULVAC Riko.

As can be seen from FIG. 1, the thermal conductivity of Nb substituted with V and / or Ta is greatly reduced as compared with FeNbSb (unsubstituted). That is, a thermoelectric power generation composition composed of a combination of two or more elements selected from the group consisting of Nb, Ta, and V of 5A homologous elements having different atomic masses and atomic sizes, represented by the above general formula FeASb The product has a greatly reduced thermal conductivity as compared with the prior art. Therefore, according to the thermoelectric power generation composition according to the present embodiment, it can be understood that the temperature difference generated between the terminals when the element is formed can be maintained, and excellent thermoelectric power generation performance can be obtained.
Here, the thermal conductivity of the thermoelectric generator composition is represented by the sum of the lattice thermal conductivity and the carrier thermal conductivity. The reduction in thermal conductivity in the present embodiment is presumed to be due to the decrease in lattice thermal conductivity, as shown in the examples described later.

Further, as can be seen from comparison of the V10% substitution, the V20% substitution, and the V30% substitution, the thermal conductivity decreases as the substitution rate increases. The same tendency is observed for V5%, Ta5% substitution, V10%, Ta10% substitution, and V15%, Ta15% substitution. The higher the total substitution rate, the lower the thermal conductivity.
Furthermore, when the total substitution rate is the same, the thermal conductivity is reduced in the case of substitution with two elements of V and Ta than in the case of substitution with V alone.

Moreover, the thermoelectric power generation composition according to the present embodiment is represented by the following general formula (2) among the compounds represented by the general formula (1), and x and y in the following general formula (2) are: A compound satisfying the relationship of 0.2 ≦ x ≦ 0.8, 0.2 ≦ y ≦ 0.8, and 0.5 ≦ x + y ≦ 1.0 (hereinafter referred to as the relationship of I) is preferable.

  As shown in the examples described later, when the compound represented by the general formula (2) and x and y satisfy the relationship I, the thermal conductivity of the thermoelectric composition is 6.5 W. / MK or less. As a result, when a device is formed, a large temperature difference can be secured between the terminals, and as a result, more excellent thermoelectric generation performance can be obtained.

In the thermoelectric power generation composition according to the present invention, in the general formula (2), x and y are 0.3 ≦ x ≦ 0.7, 0.3 ≦ y ≦ 0.7, and 0.7 ≦ It is more preferable to satisfy the relationship x + y ≦ 1.0 (hereinafter referred to as II relationship).
As shown in the examples described later, when the compound represented by the general formula (2) and x and y satisfy the above relationship II, the thermal conductivity of the thermoelectric composition is 6.0 W. / MK or less. As a result, when an element is formed, a larger temperature difference can be secured between the terminals, and as a result, a further excellent thermoelectric generation performance can be obtained.

Next, the thermoelectric power generation performance of the thermoelectric power generation composition according to this embodiment will be described.
Usually, in the evaluation of the thermoelectric generation performance of the thermoelectric generation composition, a figure of merit Z calculated by the following formula (1) is used.

  Here, in the above formula (1), S is the Seebeck coefficient, σ is the electrical conductivity, and k is the thermal conductivity. As can be seen from this mathematical formula (1), in the thermoelectric power generation composition, a decrease in thermal conductivity means an improvement in the figure of merit Z. As shown in the examples described later, according to the thermoelectric generator composition according to this embodiment, the thermal conductivity can be reduced by up to 70%, which means that the figure of merit Z is improved by about 3 times or more. To do.

The method for producing the thermoelectric generator composition according to this embodiment is not particularly limited, and is produced by a conventionally known method. As each metal material which is a starting material, a commercially available high purity metal material can be used. The shape of the metal material is not particularly limited, and for example, a metal material such as a chunk shape or a flake shape can be used.
A specific manufacturing procedure will be described with an example.
First, the above metal material is weighed in a stoichiometric ratio so that a desired elemental composition ratio is obtained. After weighing, for example, arc melting is performed in a dilute argon atmosphere to melt and react. The obtained ingot is subjected to homogenization heat treatment under predetermined conditions, and then pulverized to control the grain system. Next, the obtained powder is subjected to a sintering process using plasma or the like under predetermined conditions. By cutting, shaping, and polishing the obtained sintered body, a target thermoelectric power generation composition is obtained.

  The thermoelectric power generation composition according to the present embodiment as described above can be used as a thermoelectric power generation device by processing into a desired shape and then joining an external electrode to form an element. Further, a larger power can be obtained by modularizing a plurality of elements electrically connected in series.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.

  Next, examples of the present invention will be described, but the present invention is not limited to these examples.

<Example , Reference Example and Comparative Example 1>
[Manufacture of thermoelectric power generation composition]
The thermoelectric power generation compositions of Examples , Reference Examples, and Comparative Examples were obtained by the following production methods that can obtain arbitrary thermoelectric power generation compositions.
Specifically, first, the following metal materials were prepared as starting materials for the thermoelectric power generation compositions according to Examples , Reference Examples, and Comparative Examples. The material shape was either a chunk shape or a flake shape.
V: manufactured by Furuuchi Chemical Co., Ltd., purity 99.99%
Nb: manufactured by Furuuchi Chemical Co., Ltd., purity 99.99%
Ta: High purity chemical company, purity 99.95%
Fe: Furuuchi chemistry, purity 99.9%
Sb: Furuuchi chemistry, purity 99.9%

Among the compounds represented by FeASb of the above general formula (1), each of the above metal materials was weighed at a stoichiometric ratio so that A had the element species and the composition ratio shown in FIG. That is, a thermoelectric power generation composition comprising a combination of two or more elements selected from the group consisting of Nb, Ta, and V is used as an example or reference example, and a thermoelectric power generation composition in which A is Nb 100% is compared. Example 1 was adopted.
After weighing, it was melted and reacted by arc melting in a diluted argon atmosphere. The obtained ingot was vacuum-sealed in a quartz tube, and then subjected to homogenization heat treatment at 850 ° C. for 3 days. The ingot after the heat treatment was pulverized with a WC mortar, and passed through a sieve having an opening of 53 μm, so that the particle size of the powder was made uniform. Next, the obtained powder was sintered by discharge plasma to obtain a polycrystalline bulk body. The sintered density of the obtained sintered bodies was 97% or more. The sintering conditions were 1173K under a molding pressure of 50 MPa and an argon stream. The obtained sintered body was cut, shaped, and polished to obtain thermoelectric power generation compositions of Examples , Reference Examples, and Comparative Examples.

  Moreover, as a result of calculating carrier thermal conductivity using the electrical conductivity measurement result of each thermoelectric generation composition of the example, the carrier thermal conductivity was approximately 0.5 W / mK or less. From this result, it was inferred that the decrease in the thermal conductivity of each thermoelectric power generation composition of the example was mainly due to the decrease in the lattice thermal conductivity.

[Calculation of thermal conductivity]
M.M. Zhou et. al, J. et al. Appl. Phys. Specifically, the thermal conductivity κ was estimated by the methods described on pages 2 to 3 of 98, 013708 (2005) using the equations (8) and (9) in the document. The parameters γ1 and β required at that time were obtained by the equations (6) and (7) in the document, respectively. At that time, the Debye temperature and the lattice constant used were a Debye temperature of 394 K and a lattice constant of 0.595 nm obtained experimentally from unsubstituted FeNbSb. The molecular weight was 270.56. For ε, fitting was performed independently for all the components that were tested, and the average value εave = 53 was used for the estimation.

FIG. 2 is a diagram showing thermal conductivity calculation results at room temperature of the thermoelectric power generation compositions according to Examples , Reference Examples, and Comparative Examples. FIG. 3 is a graph showing the relationship between the thermal conductivity and the element type and composition ratio (mol%) of each thermoelectric composition according to Examples , Reference Examples and Comparative Examples.
Here, FIG. 3 is created based on the respective compositions and thermal conductivity calculation results of FIG. 2, and each vertex of the equilateral triangle corresponds to FeNbSb, FeVSb, and FeTaSb, respectively. It means that the mol% of V increases from the top of FeNbSb to the top of FeVSb. Similarly, it means that the mole percentage of Ta increases from the top of FeVSb to the top of FeTaSb, and the mole percentage of Nb increases from the top of FeTaSb to the top of FeNbSb. Moreover, the numerical value described in each point including the vertex represents the thermal conductivity of the thermoelectric power generation composition having a composition corresponding to each point.

As shown in FIGS. 2 and 3, it was found that the thermoelectric power generation compositions of Examples and Reference Examples had lower thermal conductivity than the thermoelectric power generation composition of Comparative Example 1. From this result, according to the thermoelectric power generation composition represented by a combination of two or more elements selected from the group consisting of Nb, Ta, and V, A in the above general formula (1) As a result, it was confirmed that a low thermal conductivity was obtained and an excellent thermoelectric power generation performance was obtained.

  Further, as in Examples 20 to 26, 38 to 42, 44 to 48, 50 to 53, 55 to 57, 59 to 60, and 62 (black circles in FIG. 3), V is 20% to 80%, Ta Was 20% to 80%, and the total of V and Ta was 50% to 100%, it was found that the thermal conductivity was 6.5 W / mK or less. From this result, x and y in the general formula (2) satisfy the relationship of 0.2 ≦ x ≦ 0.8, 0.2 ≦ y ≦ 0.8, and 0.5 ≦ x + y ≦ 1.0. It was confirmed that according to the thermoelectric power generation composition composed of the satisfying compound, the thermal conductivity is greatly reduced, and more excellent thermoelectric power generation performance can be obtained.

  Further, as in Examples 21 to 25, 45 to 48, 51 to 53, 56 to 57, and 60, V is 30% to 70%, Ta is 30% to 70%, and the total of V and Ta is 70. In the case of% to 100%, it was found that the thermal conductivity was 6.0 W / mK or less. From this result, x and y in the general formula (2) satisfy the relationship of 0.3 ≦ x ≦ 0.7, 0.3 ≦ y ≦ 0.7, and 0.7 ≦ x + y ≦ 1.0. It was confirmed that according to the thermoelectric power generation composition composed of the satisfying compound, the thermal conductivity is further greatly reduced and further excellent thermoelectric power generation performance can be obtained.

Claims (2)

Thermoelectric composition you characterized by being represented by the following general formula (2).

[In General Formula (2), x and y satisfy the relationship of 0.2 ≦ x ≦ 0.8, 0.2 ≦ y ≦ 0.8, and 0.5 ≦ x + y ≦ 1.0. ] In the general formula (2), x and y satisfy a relationship of 0.3 ≦ x ≦ 0.7, 0.3 ≦ y ≦ 0.7, and 0.7 ≦ x + y ≦ 1.0. The thermoelectric power generation composition according to claim 1 .

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