JP2009188284A - Thermoelectric conversion material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Fe<SB>2</SB>VAl-based thermoelectric conversion material comprised of a combination of low cost and nonpoisonous elements that achieves not only more preferable power generation efficiency but also low cost as well as non-poisonous characteristic. <P>SOLUTION: In a basic Fe<SB>2</SB>VAl structure having a Heusler alloy crystal structure whose total number of valence electrons per chemical formula is 24, at least part of each of Fe and V is replaced with other elements. More specifically, the other element replaced with Fe is Ni, and the one replaced with V is Ti. The replacement amount by Ni and Ti is adjusted to the extent of 0<α<1 and 0<β<1 that satisfies a general expression of (Fe<SB>1-α</SB>Ni<SB>α</SB>)<SB>2</SB>(V<SB>1-β</SB>Ti<SB>β</SB>)Al. The thermoelectric conversion material is controlled to be p-type, so that the total number of valence electrons per chemical formula is <24 and ≥23.5. Further, the material is controlled to be n-type, so that the total number of the valence electrons is >24 and ≤24.5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermoelectric conversion material.

  Thermoelectric conversion materials are materials that convert thermal energy into electrical energy or convert electrical energy into thermal energy. This thermoelectric conversion material is roughly classified into two types, n-type and p-type. A thermoelectric conversion element can be obtained by alternately arranging and connecting n-type thermoelectric conversion materials and p-type thermoelectric conversion materials so as to be electrically in series and thermally parallel. If a temperature difference is given between both surfaces of the thermoelectric conversion element, power generation can be performed. Moreover, if a voltage is applied between the both terminals of a thermoelectric conversion element, a temperature difference will generate | occur | produce between both surfaces.

  There is a Bi-Te compound as a general thermoelectric conversion material, which is widely used because it has a high Seebeck coefficient, that is, relatively good power generation efficiency (Non-patent Document 1). However, a thermoelectric conversion material made of a Bi—Te compound is expensive because Bi and Te, which are constituent elements, are expensive metals. In addition, since these metals are toxic, this thermoelectric conversion material has a large environmental load.

In response to these drawbacks, the inventors have proposed a thermoelectric conversion material described in Patent Document 1. This thermoelectric conversion material has a Heusler alloy type crystal structure, and the composition ratio is adjusted with respect to the basic structure having a total number of valence electrons of 24 per chemical formula, or a part of the constituent elements is replaced with other elements. In other words, the total number of valence electrons per chemical formula is controlled. The basic structure is Fe ₂ VAl.

The inventors have also proposed a thermoelectric conversion material described in Patent Document 2. This thermoelectric conversion material is obtained by substituting a part of the constituent element with another element and controlling the atomic weight of the element to be substituted with respect to the basic structure of Fe ₂ VAl.

The Fe ₂ VAl thermoelectric conversion materials according to these proposals are made of relatively inexpensive elements, and each element has no toxicity. The thermoelectric conversion material has a total valence electron number of 24 or more and n-type, and 24 or less is p-type. For example, n-type Fe ₂ V (Al _1−α M _α ) (M = Si, Ge or Sn, 0 <α <1) having a total valence electron number of 24 or more has a Seebeck coefficient of about −120 μV / K. (Patent Documents 1 and 2, Non-Patent Document 2). On the other hand, p-type Fe ₂ (V _1−α M _α ) Al (M = Ti, 0 <α <1) having a total valence electron number of 24 or less has a Seebeck coefficient of about +80 μV / K (patent document) 1, Non-Patent Document 3).

WO03 / 019681 Japanese Patent Laid-Open No. 2004-253618 "New Textbook Series Thermoelectric Conversion-Fundamentals and Applications-" pp. 96-97, Hanafusa (2005) Ryo Sakata "Thermoelectric properties of pseudogap-type Heusler compounds" Materia 44, No. 8 (2005) pp. 648-653, Yoichi Nishino "Element substitution effect on thermoelectric properties of pseudogap Fe2VAl alloy" Journal of the Japan Institute of Metals, Vol. 66, No. 7 (2002), p. 767-771, Hitoshi Matsuura, Yoichi Nishino, Yuichiro Mizutani, Shigeru Asano

However, a thermoelectric conversion material with better power generation efficiency is desired. For this reason, the inventors proposed a thermoelectric conversion material in which at least a part of each of Fe and V is substituted with another element for the basic structure of Fe ₂ VAl in PCT / JP2006 / 323903.

In this thermoelectric conversion material, when the other element that replaces Fe is M ₁ , the element M ₁ is selected from the group consisting of groups 7 to 10 of the 4th to 6th periods in the periodic table, and V When the other element to be substituted in place of is M ₂ , the element M ₂ is selected from the group consisting of groups 4 to 6 of the 4th to 6th periods in the periodic table. Further, in this thermoelectric conversion material, the substitution amount of the element M ₁ and the element M ₂ is 0 <α <1 and 0 <where the general formula (Fe _1-α M _1α ) ₂ (V _1-β M _2β ) Al is satisfied. Adjustment is made within the range of β <1. Further, the thermoelectric conversion material is controlled to be p-type so that the total number of valence electrons per chemical formula is less than 24 and 23.5 or more, and is made n-type so that it exceeds 24 and is 24.5 or less. Be controlled. For example, a thermoelectric conversion material in which M ₁ is Ir and M ₂ is Ti has a Seebeck coefficient of about +90 μV / K, and the output factor and the figure of merit are improved as compared with a thermoelectric conversion material in which M ₂ is simply replaced with Ti. .

  However, the proposed thermoelectric conversion material inevitably increases the manufacturing cost due to the use of Ir, which is a noble metal.

The present invention has been made in view of the above-described conventional circumstances, and provides an Fe ₂ VAl-based thermoelectric conversion material that can exhibit better power generation efficiency and is composed of a combination of inexpensive and non-toxic elements. Is a problem to be solved.

At this time, the inventors replaced part of Fe with the element Co (cobalt) and part of V with the element Zr (zirconium) or Hf (haunium) with respect to the basic structure of Fe ₂ VAl, By controlling the total number of valence electrons per chemical formula, it has been demonstrated that thermoelectric conversion materials are regularly p-type with holes as majority carriers and n-type with electrons as majority carriers.

  However, although the thermoelectric conversion material obtained in this way is characterized by a low electrical resistivity as a metallic property, the electrical resistivity is not yet sufficiently low. In addition, these thermoelectric conversion materials still do not have a sufficiently large Seebeck coefficient. For this reason, the output factor of these thermoelectric conversion materials is not sufficiently large.

  For this reason, the inventors verified a thermoelectric conversion material in which a part of Fe was replaced with the element Ni (nickel) and a part of V was replaced with the element Ti (titanium). These thermoelectric conversion materials have a lower electrical resistivity and a higher Seebeck coefficient than thermoelectric conversion materials in which part of Fe is replaced with element Ni and part of V is replaced with element Zr or Hf. It was confirmed that the output factor was large. Thus, the practicality has been further improved and the following first and second inventions have been completed.

That is, the thermoelectric conversion material of the first invention has a Heusler alloy type crystal structure, and at least a part of each of Fe and V is different from the basic structure of Fe ₂ VAl having 24 total valence electrons per chemical formula. Is replaced with
The other element that substitutes for Fe is Ni,
The other element that substitutes for V is Ti,
The amount of substitution of element Ni and element Ti is adjusted within the range of 0 <α <1 and 0 <β <1 satisfying the general formula (Fe _1-α Ni _α ) ₂ (V _1-β Ti _β ) Al, and The total number of valence electrons per chemical formula is controlled to be p-type so as to be less than 24 and 23.5 or more.

The thermoelectric conversion material of the second invention has a Heusler alloy type crystal structure and Fe ₂ VAl having a total number of valence electrons of 24 per chemical formula, and at least a part of each of Fe and V is another element. Is replaced with
The other element that substitutes for Fe is Ni,
The other element that substitutes for V is Ti,
The amount of substitution of element Ni and element Ti is adjusted within the range of 0 <α <1 and 0 <β <1 satisfying the general formula (Fe _1-α Ni _α ) ₂ (V _1-β Ti _β ) Al, and The total number of valence electrons per chemical formula is more than 24 and 24.5 or less, and the n-type is controlled.

  The thermoelectric conversion material of the present invention is characterized by a lower electrical resistivity. Further, in this thermoelectric conversion material, if at least a part of each of Fe and V is substituted with another element, the scattering of lattice vibration increases, and the thermal conductivity decreases. For this reason, a thermoelectric conversion element with high thermoelectric conversion efficiency can be manufactured using this thermoelectric conversion material.

  Unlike the conventional thermoelectric conversion material, the thermoelectric conversion material of the present invention can be hot-worked at a temperature of 750 ° C. or higher and a melting point or lower as a metallic property. For this reason, the yield in the case of manufacturing a thermoelectric conversion element can be increased, the number of manufacturing steps can be reduced, and the manufacturing cost of the thermoelectric conversion element can be reduced.

As the inventors have confirmed in a previous application (Patent Document 1), the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure has 24 total valence electrons per chemical formula. That is, when the average electron concentration per atom is 24/4 = 6, the thermoelectric conversion material has a sharp pseudogap at the Fermi level. In the thermoelectric conversion material according to the first and second inventions, the chemical structure can be obtained by substituting a part of the basic structure Fe with the element Ni and a part of the basic structure V with the element Ti. By controlling the total number of valence electrons, the Fermi level can be shifted from the center of the pseudogap, and the sign and magnitude of the Seebeck coefficient can be changed.

  According to the test results of the inventors, the thermoelectric conversion materials of the first and second inventions exhibit better power generation efficiency. Further, these thermoelectric conversion materials do not use Ir, which is a noble metal, and are composed of a combination of inexpensive and nontoxic elements.

The thermoelectric conversion materials of the first and second inventions can control the total number of valence electrons per chemical formula by adjusting the chemical composition ratio with respect to this basic structure. As a result, the Fermi level can be shifted from the center of the pseudogap, and the sign and magnitude of the Seebeck coefficient can be changed. In this case, if the chemical composition ratio is adjusted with the adjustment amounts x, y, and z, a part of the basic structure Fe is replaced with the element Ni, and a part of the basic structure V is replaced with the element Ti. The formula is (Fe _1-α Ni _α ) _{2 + x} (V _1-β Ti _β ) _{1 + y} Al _{1 + z} .

  The thermoelectric conversion material of the present invention can be produced by the following production method. This manufacturing method includes a first step of preparing a raw material mixture having an element capable of manufacturing the thermoelectric conversion material and a constituent ratio, and melting or vaporizing and solidifying the raw material mixture in a vacuum or an inert gas, And a second step of obtaining a conversion material.

  If the thermoelectric conversion material is manufactured by this manufacturing method, a thermoelectric conversion material having high thermoelectric conversion efficiency and less risk of environmental pollution can be manufactured at low cost.

  As a 2nd process, the method of cooling, after melt | dissolving a raw material mixture in a vacuum or an inert gas is employable, for example. In order to make an n-type thermoelectric conversion material or a p-type thermoelectric conversion material as an aggregate of powders having as small a particle size as possible, first, the raw material mixture is melted by arc melting or the like and then solidified. A method for obtaining a substantially uniform powder by mechanically pulverizing it in an inert gas or nitrogen gas atmosphere, and a method for obtaining a substantially uniform powder by molten metal atomization or gas atomization. Further, a method of obtaining a substantially uniform powder by repeatedly pressing and breaking the raw material mixture in an inert gas or nitrogen gas atmosphere by a mechanical alloying method can be employed. The powder thus obtained can be sintered by a hot press method in a vacuum, a HIP (hot isostatic pressing) method, a discharge plasma sintering method, a pulse current method or the like. When the powder is sintered by the HIP method, for example, compression molding and sintering can be performed simultaneously with high-pressure (150 MPa) argon gas at 800 ° C. to solidify at a true density. Further, according to the pseudo-HIP method, the true density can be solidified at low cost by using a molding press. In addition, in order to make an n-type thermoelectric conversion material or a p-type thermoelectric conversion material as an aggregate of crystal grains having a particle size as small as possible, strain processing such as hot rolling is performed, or a molten raw material is used. A method of reducing the crystal grains by rapid cooling or the like can be employed.

  It is possible to manufacture a thermoelectric conversion element with the thermoelectric conversion material of the present invention. In the thermoelectric conversion element thus obtained, the thermoelectric conversion material having a positive sign of the Seebeck coefficient exhibits a behavior as a p-type, and the thermoelectric conversion material having a negative sign of the Seebeck coefficient is an n-type. Shows behavior. These thermoelectric conversion elements have high thermoelectric conversion efficiency, can be manufactured at low cost, and are less likely to cause environmental pollution.

[Test Example 1]
The thermoelectric conversion material of Test Example 1 is obtained by substituting a part of Fe with Co and a part of V with Zr with respect to Fe ₂ VAl having a basic structure. The substitution amount α of Co is selected to be 0.015, and the substitution amount β of Zr is selected to be 0.1.

The total number of valence electrons per chemical formula of the basic structure of Fe ₂ VAl is 24 by the following calculation. That is, the number of valence electrons of Fe is 16, which is obtained by multiplying a total of 8 of 2 of the 4s orbit and 6 of the 3d orbit by the coefficient 2. Further, the number of valence electrons of V is a total of 5, 2 of 4s orbitals and 3 of 3d orbitals. Further, the number of valence electrons of Al is 3 in total, 2 of 3s orbitals and 1 of 3p orbitals. The total number of valence electrons 24 of Fe, V and Al is the total number of valence electrons per chemical formula of the basic structure.

In contrast to this basic structure, a thermoelectric conversion material in which part of Fe is replaced by Co and part of V is replaced by Zr is represented by the general formula (Fe _1-α Co _α ) ₂ (V _1-β Zr _β ) Al It is a compound represented by these. Here, by setting 2α <β, the total number of valence electrons is less than 24, and a p-type thermoelectric conversion material is obtained. Further, by setting 2α> β, the total number of valence electrons exceeds 24, and an n-type thermoelectric conversion material is obtained.

  This thermoelectric conversion material is manufactured as follows. First, five kinds of elements of Fe, V, Al, Co, and Zr were weighed so as to satisfy the above conditions. These elements were melted using an argon arc to produce a button-like ingot. In order to obtain a homogeneous ingot, the obtained ingot was redissolved. This re-dissolution was performed twice or more to obtain a homogeneous ingot. Since the change in weight before and after dissolution is within 0.1%, it was assumed that the change in composition due to dissolution was negligible.

An ingot produced with a total valence electron number of 23.93 is homogenized at 1273 K x 48 hr in a high vacuum of 5 x 10 ^-3 Pa or less and molded into strips, powders, and blocks. did. Thereafter, a distortion removing process of 1273 K × 1 hr and a regularizing process of 673 K × 4 hr were performed in a vacuum. Thus, the thermoelectric conversion material of Test Example 1 was obtained.

[Test Example 2]
The thermoelectric conversion material of Test Example 2 is obtained by substituting a part of Fe with Co and a part of V with Hf with respect to Fe ₂ VAl having a basic structure. The other conditions were the same as in Test Example 1, and the thermoelectric conversion material of Test Example 2 was obtained.

[Evaluation methods]
The thermoelectric conversion materials of Test Examples 1 and 2 were evaluated as follows.

(X-ray diffraction)
In order to determine the structure of each material, X-ray diffraction was performed using the powder produced by the above method. CuKα rays were used for the evaluation. Since these are alloy systems containing Fe, a monochromator was used for the purpose of removing the background. As a result, it was found that most of the produced material had a Heusler structure. In addition, the presence of a slight second phase was confirmed.

(Measurement of electrical resistivity)
The electrical resistivity ρ (μΩm) was measured by a DC four-terminal method using a 1 × 1.2 × 15 mm ³ strip sample. The measurement temperature range is from the liquid N ₂ temperature (77K) to 1273K. From 77 K to room temperature, the temperature was naturally raised and the measurement was performed. From room temperature to 1273 K, an electric furnace was used, and measurement was performed at a heating rate of 0.05 K / sec in a vacuum atmosphere of 5 × 10 ⁻³ Pa or less.

(Measurement of Seebeck coefficient)
Using a test piece of 0.5 × 0.5 × 5.0 mm ³ , the Seebeck coefficient S (μV / K) was measured in a temperature range of 90K to 400K with “SB-100” manufactured by MMR-Technologies.

About the thermoelectric conversion material ((Fe _0.985 Co _0.015 ) ₂ (V _0.9 Zr _0.1 ) Al) of Test Example 1 and the thermoelectric conversion material ((Fe _0.985 Co _0.015 ) ₂ (V _0.9 Hf _0.1 ) Al) of Test Example 2 1 and the Seebeck coefficient are shown in FIG. 1, and the relationship between temperature and electrical resistivity is shown in FIG.

FIG. 1 shows that these thermoelectric conversion materials are not yet sufficiently low in electrical resistivity. In addition, it can be seen from FIG. 2 that these thermoelectric conversion materials still do not have a sufficiently large Seebeck coefficient. For this reason, the output factor of these thermoelectric conversion materials is not sufficiently large. Specifically, at 300K, the thermoelectric conversion material of Test Example 1 is only 0.06 × 10 ⁻³ W / mK ² , and the thermoelectric conversion material of Test Example 2 is only 0.86 × 10 ⁻³ W / mK ^2. It was.

  From the above test results, the following thermoelectric conversion materials in which part of Fe was replaced with element Ni and part of V was replaced with element Ti were verified.

[Example]
The thermoelectric conversion material of the example is obtained by substituting a part of Fe with Ni and a part of V with Ti with respect to Fe ₂ VAl having a basic structure. The substitution amount α of Ni is selected within the range of 0.005 ≦ α ≦ 0.125, and the substitution amount β of Ti is selected within the range of 0.01 ≦ β ≦ 0.23. Other conditions were the same as in Test Example 1, and the thermoelectric conversion material of the example was obtained.

[Comparative example]
A comparative example is Fe ₂ VAl. Other conditions were the same as in Test Example 1, and a basic structure of a comparative example was obtained.

[Evaluation methods]
About the thermoelectric conversion material of an Example and the basic structure of a comparative example, while performing X-ray diffraction, measurement of electrical resistivity, and measurement of Seebeck coefficient as described above, measurement of the following thermal conductivity, output factor and figure of merit Measurements were made.

(Measurement of thermal conductivity)
The thermal conductivity κ (W / mK) at room temperature was measured by a comparative stationary method. The size of the test piece was 3 × 3 × 3.5 mm ³ , and alumina having the same size as the test piece was used as the standard sample.

(Output factor and figure of merit)
As an index for evaluating the thermoelectric conversion material, there are an output factor: P = S ² / ρ and a performance index: Z = S ² / (ρκ). Here, S is the Seebeck coefficient, ρ is the electrical resistivity, and κ is the thermal conductivity. These values were taken as the above measured values, and the output factor P (10 ⁻³ W / mK ² ) and the figure of merit Z (10 ⁻³ / K) were determined.

Regarding the thermoelectric conversion material of the example ((Fe _0.985 Ni _0.015 ) ₂ (V ₁ -β Ti _β ) Al (β = 0.03, 0.06, 0.10, 0.15, 0.20)), the temperature 3 shows the relationship between the temperature and the electrical resistivity, and FIG. 4 shows the relationship between the temperature and the Seebeck coefficient.

From FIG. 3, it can be seen that the electrical resistivity of the thermoelectric conversion material of the example decreases to 800K or less as the addition amount of Ti increases. In particular, the thermoelectric conversion material in which α = 0.015 and β = 0.20 showed a low electric resistivity of about 0.7 μΩm at 77K. In addition, the thermoelectric conversion material having this composition increased in electrical resistivity with increasing temperature from 77K to 700K, and showed a semiconductor-like to metallic behavior. Further, as shown in FIG. 4, the thermoelectric conversion material of the example has an addition amount of Ti of 0.1 and a Seebeck coefficient of about 100 μV / K, which is the maximum. This value exceeds 90 μV / K which is the maximum Seebeck coefficient of (Fe _1−α Ir _α ) ₂ (V _1−β Ti _β ) Al exhibiting p-type characteristics.

Regarding the thermoelectric conversion material of the example ((Fe _0.975 Ni _0.025 ) ₂ (V _{1 -β} Ti _β ) Al (β = 0.10, 0.14, 0.19)), the relationship between temperature and electrical resistivity is FIG. 6 shows the relationship between temperature and Seebeck coefficient.

  FIG. 5 shows that the thermoelectric conversion material of the example also has an electrical resistivity of 800 K or less that decreases as the amount of Ti increases. Further, as shown in FIG. 6, the thermoelectric conversion material of the example has an addition amount of Ti of 0.1 and a Seebeck coefficient of about 100 μV / K which is the maximum.

Regarding the thermoelectric conversion material of the example ((Fe _0.965 Ni _0.035 ) ₂ (V ₁ -β Ti _β ) Al (β = 0.14, 0.18, 0.23)), the relationship between temperature and electrical resistivity is FIG. 8 shows the relationship between the temperature and the Seebeck coefficient.

  As can be seen from FIG. 7, the thermoelectric conversion material of the example also has an electrical resistivity of 800K or lower as the amount of Ti increases. Moreover, as shown in FIG. 8, the thermoelectric conversion material of the Example has the maximum Seebeck coefficient when the addition amount of Ti is 0.18. However, the absolute value is smaller than the above-described thermoelectric conversion materials of α = 0.015 and 0.025.

Thermoelectric Conversion Material of Example ((Fe _1-α Ni _α ) ₂ (V _0.97 Ti _0.03 ) Al (α = 0.015, 0.025, 0.050, 0.075, 0.100, 0.125) 9), the relationship between temperature and electrical resistivity is shown in FIG. 9, and the relationship between temperature and Seebeck coefficient is shown in FIG.

  FIG. 10 shows that the sign of the Seebeck coefficient in the thermoelectric conversion material of the example is reversed between α = 0.025 and 0.050.

Based on the above results, the thermoelectric conversion material of the example ((Fe _1-α Ni _α ) ₂ (V _1-β Ti _β ) Al) (α = 0.005, 0.015, 0.025, 0.035) , Β = 0.01, 0.03)), the dependence of the thermal conductivity at 300 K on the total valence number was determined. The result is shown in FIG.

  From FIG. 11, it can be seen that the thermal conductivity of the thermoelectric conversion material of the example decreases as the addition amount of the elements Ni and Ti increases. Further, the element Ni is more effective in reducing the thermal conductivity than the element Ti.

Moreover, the thermoelectric conversion material ((Fe _1-α Ni _α ) ₂ (V _1-β Ti _β ) Al) (α = 0.015, 0.025, 0.035, β = 0.01, 0 0.03)), the dependence of the Seebeck coefficient at 300K on the total valence number was determined. The result is shown in FIG.

  From FIG. 12, the thermoelectric conversion material of an Example shows the maximum value as Seebeck coefficient p-type at n = 24.00 vicinity. In addition, the characteristics of p-type and n-type are reversed at n = 24.007 to 24.15. In the n-type thermoelectric conversion material, the maximum value is not reached even when the total number of valence electrons is increased to n = 24.86.

Thermoelectric conversion material ((Fe _1-α Ni _α ) ₂ (V _1-β Ti _β ) Al (α = 0.015, 0.025, 0.035, β = 0.03)) and comparative example For the basic structure (Fe ₂ VAl), the dependence of the electrical resistivity at 300 K on the total valence number was determined. The result is shown in FIG.

  From FIG. 13, the thermoelectric conversion material of an Example shows the maximum electrical resistivity in the vicinity of n = 24.17. With this point at the center, the electrical resistivity decreases as the total number of valence electrons changes.

Example Thermoelectric Conversion Material ((Fe _1-α Ni _α ) ₂ (V _1-β Ti _β ) Al) (α = 0.015, 0.035, β = 0.03)) and Basic Structure of Comparative Example For (Fe ₂ VAl), the dependence of the output factor at 300 K on the total valence number was determined. The result is shown in FIG.

From FIG. 14, the thermoelectric conversion material of an Example shows about 2.2 * 10 < ^-3 > W / mK < ² > where the output factor as a p-type is the maximum at n = 23.96 vicinity. This output factor is a value comparable to a Bi-Te p-type thermoelectric conversion material used in practice. Moreover, the output factor as an n-type is low compared with a p-type thermoelectric conversion material.

Example thermoelectric conversion material ((Fe _1-α Ni _α ) ₂ (V _1-β Ti _β ) Al (α = 0.015, 0.035, β = 0.03)) and basic structure of comparative example ( For Fe ₂ VAl), the dependence of the figure of merit at 300 K on the total valence number was determined. The result is shown in FIG.

  From FIG. 15, the thermoelectric conversion material of an Example shows the maximum figure of merit as p-type around n = 23.96. Moreover, the figure of merit as n-type is lower than that of p-type thermoelectric conversion material.

  And the thermoelectric conversion material of an Example does not use Ir which is a noble metal, but consists of a combination of an inexpensive and nontoxic element.

  Therefore, according to the thermoelectric conversion material of an Example, while being able to exhibit more favorable power generation efficiency, compared with the conventional thermoelectric conversion material, drastic cost reduction is attained.

  The present invention can be used for a power generation device or the like using waste heat at a relatively low temperature such as a CPU of a personal computer or an automobile engine.

The thermoelectric conversion material ((Fe _0.985 Co _0.015 ) ₂ (V _1-β Zr _β ) Al of Test Example 1 and the thermoelectric conversion material ((Fe _0.985 Co _0.015 ) ₂ (V _1-β Hf _β ) Al of Test Example 2) It is a graph showing the relationship between temperature and electrical resistivity. The thermoelectric conversion material ((Fe _0.985 Co _0.015 ) ₂ (V _1-β Zr _β ) Al of Test Example 1 and the thermoelectric conversion material ((Fe _0.985 Co _0.015 ) ₂ (V _1-β Hf _β ) Al of Test Example 2) It is a graph showing the relationship between the temperature and the Seebeck coefficient. Thermoelectric conversion materials of Examples ((Fe _0.985 Ni _0.015) relates to _{2 (V 1-β Ti β} ) Al, it is a graph showing the relationship between temperature and electrical resistivity. It is a graph which shows the relationship between temperature and a Seebeck coefficient concerning the thermoelectric conversion material ((Fe _0.985 Ni _0.015 ) ₂ (V _1-β Ti _β ) Al) of an example. The thermoelectric conversion material of Example ((Fe _0.975 Ni _0.025) relates to _{2 (V 1-β Ti β} ) Al, it is a graph showing the relationship between temperature and electrical resistivity. Thermoelectric conversion materials of Examples ((Fe _0.975 Ni _0.025) relates to _{2 (V 1-β Ti β} ) Al, it is a graph showing the relationship between the temperature and the Seebeck coefficient. Thermoelectric conversion materials of Examples ((Fe _0.965 Ni _0.035) relates to _{2 (V 1-β Ti β} ) Al, it is a graph showing the relationship between temperature and electrical resistivity. It is a graph which shows the relationship between temperature and a Seebeck coefficient in connection with the thermoelectric conversion material ((Fe _0.965 Ni _0.035 ) ₂ (V _1-β Ti _β ) Al) of an example. Thermoelectric conversion material of Example (relates to _{(Fe 1-α Ni α)} 2 (V 0.97 Ti 0.03) Al, is a graph showing the relationship between temperature and electrical resistivity. Thermoelectric conversion material of Example (relates to _{(Fe 1-α Ni α)} 2 (V 0.07 Ti 0.03) Al, is a graph showing the relationship between the temperature and the Seebeck coefficient. Relates to a thermoelectric conversion material of Example _{((Fe 1-α Ni α} ) 2 (V 1-β Ti β) Al, is a graph showing the total number of valence electrons dependence of the thermal conductivity at 300K. Relates to a thermoelectric conversion material of Example _{((Fe 1-α Ni α} ) 2 (V 1-β Ti β) Al, is a graph showing the total number of valence electrons dependence of the Seebeck coefficient at 300K. It shows the thermoelectric conversion material ((Fe _1-α Ni _α ) ₂ (V _1-β Ti _β ) Al) of the example and the basic structure of the comparative example, and shows the total valence electron dependence of the electrical resistivity at 300K. It is a graph. A graph showing the dependence of the output factor at 300 K on the total valence electrons in relation to the thermoelectric conversion material of the example ((Fe _1-α Ni _α ) ₂ (V _1-β Ti _β ) Al) and the basic structure of the comparative example. It is. It is a graph showing the dependence of the figure of merit at 300 K on the basic structure of the thermoelectric conversion material ((Fe _1-α Ni _α ) ₂ (V _1-β Ti _β ) Al and the comparative example of the example. is there.

Claims (2)

With respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total number of valence electrons of 24 per chemical formula, at least a part of each of Fe and V is substituted with other elements,
The other element that substitutes for Fe is Ni,
The other element that substitutes for V is Ti,
The amount of substitution of element Ni and element Ti is adjusted within the range of 0 <α <1 and 0 <β <1 satisfying the general formula (Fe _1-α Ni _α ) ₂ (V _1-β Ti _β ) Al, and A thermoelectric conversion material characterized in that the total number of valence electrons per chemical formula is less than 24 and is controlled to be p-type so as to be 23.5 or more. With respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total number of valence electrons of 24 per chemical formula, at least a part of each of Fe and V is substituted with other elements,
The other element that substitutes for Fe is Ni,
The other element that substitutes for V is Ti,
The amount of substitution of element Ni and element Ti is adjusted within the range of 0 <α <1 and 0 <β <1 satisfying the general formula (Fe _1-α Ni _α ) ₂ (V _1-β Ti _β ) Al, and A thermoelectric conversion material characterized in that the total number of valence electrons per chemical formula exceeds 24 and is controlled to be n-type so as to be 24.5 or less.

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