JP2008047754A - n-TYPE Yb-Co-Sb-BASED THERMOELECTRIC TRANSDUCTION MATERIAL, YbxCoySbz-BASED THERMOELECTRIC TRANSDUCTION MATERIAL AND METHOD FOR PRODUCING n-TYPE SKUTTERUDITE-BASED Yb-Co-Sb THERMOELECTRIC TRANSDUCTION MATERIAL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an n-type Yb-Co-Sb-based thermoelectric transduction material, a Yb<SB>x</SB>Co<SB>y</SB>Sb<SB>z</SB>-based thermoelectric transduction material, and a method for producing an n-type skutterudite-based Yb-Co-Sb thermoelectric transduction material, which are precise and have a high thermoelectric transduction performance at an inexpensive production cost. <P>SOLUTION: A solidification characteristic of the n-type skutterudite-based Yb-Co-Sb thermoelectric transduction material is analyzed, and a kind and temperature of a peritectic reaction are specified in which a volume is reduced. Also, it has been ascertained that a framework in which a crystal phase formed from a liquid phase is linked prevents a supply of a melted liquid and is a cause for a porous state occurrence, and a kind of a crude material and an appropriate temperature during melting have been discussed in detail. As a result, a melting method of not generating the peritectic reaction in which a volume is reduced and a melting method of not forming the framework in which the crystal phase is linked, have been found out. Thus, for example, a dense Yb<SB>0.15</SB>Co<SB>4</SB>Sb<SB>12</SB>thermoelectric transduction material which does not have the porous state is produced, and the n-type skutterudite-based Yb-Co-Sb thermoelectric transduction material having the high thermoelectric performance is provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a thermoelectric conversion material used for a thermoelectric conversion element capable of directly converting heat energy into electricity or electricity directly into heat energy, and a method for producing the same, and in particular, an n-type having a skutterudite structure produced by a melting method. Yb-Co-Sb thermoelectric conversion material, Yb content x, Co content y, Sb content z in this n-type Yb-Co-Sb thermoelectric conversion material are appropriately determined and manufactured by a melting method The present invention relates to a Yb _x Co _y Sb _z- based thermoelectric conversion material, and a method for producing an n-type skutterudite-based Yb—Co—Sb thermoelectric conversion material for producing these thermoelectric conversion materials.

  In recent years, there has been a tendency to reduce the environmental burden on a global scale, and as a part of promoting efficient use of energy, technologies for recovering low-grade waste heat generated from heat engines, etc., and converting them to electricity have become popular. Has been researched and developed. The thermoelectric conversion material is a material that can directly convert heat into electricity or can be heated and cooled by applying electricity, and a p-type thermoelectric conversion material and an n-type thermoelectric conversion material are combined to form one thermoelectric conversion element. . If a thermoelectric conversion element is used, it can be easily heated and cooled, and low-grade waste heat, which is difficult to use conventionally, can be converted into electricity to effectively use energy.

The property of the thermoelectric conversion material is evaluated by the figure of merit Z. The figure of merit Z is expressed by the following equation (1) using the Seebeck coefficient S, the thermal conductivity κ, and the electrical resistivity ρ.
Z = S ² / (κρ) (1)
Moreover, the property of the thermoelectric conversion material may be evaluated by the product of the figure of merit Z and the temperature T. In this case, the following equation (2) is obtained by multiplying both sides of the above equation (1) by the temperature T.

ZT = S ² T / (κρ) (2)
ZT shown in the above formula (2) is called a dimensionless figure of merit, and is a good index indicating the performance of the thermoelectric conversion material. The thermoelectric conversion material has higher thermoelectric performance at the temperature T as the value of ZT is larger. From the above formulas (1) and (2), an excellent thermoelectric conversion material is a material that can increase the value of the dimensionless figure of merit ZT, that is, a material that has a large Seebeck coefficient S and a small thermal conductivity κ and electrical resistivity ρ. It is.

Further, the maximum conversion efficiency ηmax of the thermoelectric conversion material is expressed by the following formula (3).
ηmax = {(T _h −T _c ) / T _h } {(M−1) / (M + (T _c / T _h ))} (3)
M in the above equation (3) is represented by the following equation (4). Further, _Th is the temperature at the high temperature end of the thermoelectric conversion material, and T _c is the temperature at the low temperature end.
M = {1 + Z (T _h + T _c ) / 2} ^−0.5 (4)
From the above formulas (1) to (4), it can be seen that the thermoelectric conversion efficiency of the thermoelectric conversion material improves as the performance index and the temperature difference between the high temperature end and the low temperature end increase.

By the way, the thermoelectric conversion materials that have been studied so far include Bi ₂ Te ₃ system, PbTe system, GeTe-AgSbTe ₂ system, SiGe system, Fe ₂ Si system, Zn ₄ Sb ₃ system, B ₄ C system, scooter. There are LaFe ₄ Sb ₁₂ , LaFe ₃ CoSb ₁₂ and Yb _0.15 Co ₄ Sb ₁₂ series materials having a terdite structure, NaCo ₂ O ₄ , Ca ₃ Co ₄ O ₉ , Bi ₂ Sr ₂ Co ₂ O ₈ series oxides, etc. .

Among these, only the Bi ₂ Te ₃ system is put into practical use. Bi ₂ Te ₃ -based thermoelectric conversion elements have been developed mainly for use in a low temperature range, but their applications are limited to Peltier elements having a low thermoelectric conversion efficiency of less than 10% and a small space utility.
Further, as a thermoelectric conversion material that can be used in the middle temperature range, a skutterudite CoSb _3- based thermoelectric conversion material is being developed. In order to improve the thermoelectric performance, a Co _1-x M _x Sb ₃ material in which Co is partially substituted with Pd, Pt, Ru, Rh (indicated by M in the chemical formula) has been developed, and its production method has also been studied. (See Patent Documents 1-9).

However, these material systems generally have a large thermal conductivity and a dimensionless figure of merit ZT is small, so that they have not been put into practical use at present.
In order to reduce the thermal conductivity of CoSb _3- based materials, Slack et al. Proposed the concept of “Phonon Glass and Electron Crystal” and developed a skutterudite thermoelectric conversion material using the rattling effect. In 1997, Slack et al. Reported that skutterudite compounds LaFe ₄ Sb ₁₂ and CeFe ₄ Sb ₁₂ had good p-type thermoelectric performance in the middle temperature range, and then LaFe in which Fe was partially substituted with Co or the like. ₃ CoSb ₁₂ materials have been developed, and various methods for producing these materials have been studied (see Patent Documents 10-17). As a result, although the dimensionless figure of merit ZT of the p-type thermoelectric conversion material was 0.8, the performance was still insufficient as a practical material.

In 2000, Nolas et al. Discovered that Yb _x Co ₄ Sb ₁₂ (0 <x ≦ 1) had good n-type thermoelectric performance, and its dimensionless figure of merit ZT was reported to be 0.7. Yes.
Conventionally, when manufacturing these thermoelectric conversion materials, first, a molten material is produced by a melting method. That is, the raw materials weighed based on the target chemical composition are put in a crucible and melted, and then cooled to obtain a molten product. Next, the melted material is further pulverized, or atomized after melting in the course of the melting process to obtain a fine powder having the desired composition. Thereafter, these fine powders are used as raw materials by using a solid-phase molding method such as a hot press method or a discharge plasma sintering method.

Here, with reference to the Co—Sb phase diagram of FIG. 6, a solidification process until a melted material obtained by a conventional melting method is obtained by using a CoSb ₃ material as an example.
First, raw materials are weighed for the purpose of producing CoSb ₃ , melted to the melting point or higher, and held at point (A) in the figure. When cooled as it is, first, at a temperature T ₀ (T ₀ > 1000 ° C.),
(1) L ₀ (Liquid phase 0) → β-CoSb T ₀ > 1000 ° C.
Β-CoSb begins to precipitate due to the reaction. As the temperature is further cooled, the amount of β-CoSb deposited increases, and at a temperature T _A = 931 ° C.,
(2) L ₁ (Liquid phase 1) + β-CoSb → γ-CoSb ₂ T _A = 931 ° C.
Γ-CoSb ₂ is produced from liquid phase 1 and β-CoSb by the peritectic reaction. In yet a temperature _T B = 876 ° C. When the temperature decreases, due to the gamma-CoSb ₂ and a liquid phase ₂ (3) _L 2 (liquid phase _{2) + γ-CoSb 2 →} δ-CoSb 3 T B = 876 ℃
By the peritectic reaction, δ-CoSb ₃ that is the target phase is produced, and when it is cooled as it is to room temperature, a melted material of δ-CoSb ₃ that is the target phase is obtained.

JP-A-8-186294 Japanese Patent Laid-Open No. 9-64422 JP-A-9-260728 JP-A-10-303468 Japanese Patent Laid-Open No. 11-40860 Japanese Patent Laid-Open No. 11-40861 Japanese Patent Laid-Open No. 11-40862 Japanese Patent Laid-Open No. 11-46020 JP-A-11-150307 JP 2000-252526 A JP 2001-196647 A JP 2002-33526 A JP 2002-33527 A JP 2002-246656 A JP 2002-246657 A JP 2003-218410 A JP 2004-76046 A

  However, in the production process of the conventional thermoelectric conversion material described above, when producing a melted material by a melting method, the raw material is melted and then cooled to obtain a melted material. Due to the inherent characteristic that the volume is reduced during solidification, a porous structure with many voids is formed instead of a dense structure, as will be described in detail later. As a result, there is a problem that the electrical resistivity is increased and the thermoelectric conversion performance is lowered.

The reason why a porous tissue is formed will be described.
Table 1 below shows the density and molar volume of substances related to the reactions (1) to (3) described above. In other words, Table 1 shows the density and molar volume of the substance related to the production of CoSb ₃ .

Based on this, as shown in Table 2 below, the volume change before and after the reaction in the peritectic reaction of (2) and the peritectic reaction of (3) is determined. Table 2 shows the volume change in the CoSb ₃ production reaction.

That is, the volume due to peritectic reaction -2.6Cm ³ / mol by peritectic reaction (2), reduces the -0.1Cm ³ / moles of volume by peritectic reaction (3), in particular (2) It can be seen that the reduction is large.

If the peritectic reaction of (2) or (3) above occurs uniformly like a liquid-liquid reaction, the volume is reduced as a whole, so that a porous structure is not obtained. However, since these reactions are solid-liquid reactions, the progress of the reaction largely depends on the initial tissue shape of the solid, and it is difficult to reduce the volume of the entire material uniformly. For this reason, it becomes easy to form a partially porous tissue.
Therefore, in order to produce a dense material in the conventional manufacturing method, the raw material of the thermoelectric conversion material is once prepared by the conventional melting method and then further densified by using a hot press method, a discharge plasma sintering method, or the like. It was. However, such a method has a problem that the number of manufacturing processes increases and sufficient thermoelectric performance cannot be obtained and the manufacturing cost is increased.

The present invention has been made in view of such problems, and is an n-type Yb—Co—Sb thermoelectric conversion material, Yb _x Co _y Sb, which is dense and has high thermoelectric conversion performance at a low production cost. It is an object of the present invention to provide a method for producing a _z- based thermoelectric conversion material and an n-type skutterudite-based Yb—Co—Sb thermoelectric conversion material.

In order to achieve the above object, an n-type Yb-Co-Sb thermoelectric conversion material according to claim 1 of the present invention is an n-type Yb-Co-Sb system having a skutterudite structure manufactured by a melting method. The thermoelectric conversion material has a density of 7.4 g / cm ³ or more and a dimensionless figure of merit ZT (Z: figure of merit, T: absolute temperature) indicating thermoelectric conversion performance is 0.6 or more. .

The Yb _x Co _y Sb _z- based thermoelectric conversion material according to claim 2 of the present invention is such that the content x of Yb in the n-type Yb—Co—Sb thermoelectric conversion material according to claim 1 is 0 <x ≦. 1. It was manufactured by a melting method in which the Co content y was 3.5 ≦ y ≦ 4.5 and the Sb content z was 10 ≦ z ≦ 15.

The method for producing an n-type skutterudite-based Yb-Co-Sb thermoelectric conversion material according to claim 3 of the present invention is the n-type Yb-Co-Sb-based thermoelectric conversion material according to claim 1 or claim in the production method _{of Yb} x _Co y Sb _z system for producing a thermoelectric conversion material n- type skutterudite Yb-CoSb thermoelectric conversion material according to claim 2, CoSb or CoSb _2, Yb, Co, and Sb raw material The raw material is heated and dissolved in a temperature range of 875 ° C. to 1000 ° C. and then cooled to obtain a thermoelectric conversion material.

According to the method for producing an n-type skutterudite-based Yb-Co-Sb thermoelectric conversion material according to claim 3, the n-type Yb-Co-Sb-based thermoelectric conversion material according to claim 1, or claim 2 Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) -based thermoelectric conversion material can be densely produced only by a melting method, It becomes possible to provide a thermoelectric conversion material having a dimensionless figure of merit equal to or higher than that when using the solid-phase molding method.

  In order to realize this, in the present invention, the solidification characteristics of the n-type skutterudite-based Yb-Co-Sb thermoelectric conversion material by melting method are analyzed in detail, and the replenishment of the melt accompanying the volume reduction and reduction during solidification It was clarified that the deficiency was the cause of porous tissue formation. A precise thermoelectric conversion material can be produced by suppressing the volume reduction at the time of solidification, or by making the whole volume proceed uniformly rather than partially even if this volume reduction reaction occurs.

All n-type skutterudite-based Yb—Co—Sb thermoelectric conversion materials are formed by a peritectic reaction. The phase diagram of these materials is similar to the CoSb ₃ phase diagram given above as an example in FIG. By adding Yb element, the CoSb ₃ phase becomes Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15). As a result of thermal analysis and composition analysis, Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) is the following (similar to the above three reactions (1) to (3) ( 4) to (6) are formed by the solidification process, and the peritectic reaction temperature of (5) and (6) is almost equal to {reaction temperature of (2) and (3)} in the case of CoSb _three- phase formation. I found that it has not changed.

(4) L ₀ (Liquid phase 0) → (Yb solid solution) β-CoSb T ₀ > 1000 ° C.
(5) [Peritectic reaction A]
L ₁ (Liquid phase 1) + (Yb solid solution) β-CoSb → (Yb solid solution) γ-CoSb ₂
T _A = 930 ° C.
(6) [Peritectic reaction B]
L ₂ (liquid phase 2) + (Yb solid solution) γ-CoSb ₂ → YbxCoySbz
T _B = 875 ° C
Hereinafter, the reaction (5) is referred to as the peritectic reaction A, and the reaction (6) is referred to as the peritectic reaction B. The peritectic reaction A is similar to the peritectic reaction B as in the volume change shown in Table 2 above. In the reaction having a larger volume reduction ratio than the volume before the reaction, the volume after the reaction becomes smaller and the porous structure is generated.

By the way, an n-type skutterudite-based Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) thermoelectric conversion material is manufactured using a conventional melting method. In this case, if the volume reduction reaction in the peritectic reaction A occurs uniformly throughout, it does not result in a porous state. However, since this reaction is a solid-liquid reaction, it is difficult to occur uniformly and partially. A volume reduction reaction takes place, resulting in a porous state.

  As a result of examining this cause in detail, when the primary (Yb solid solution) β-CoSb phase is precipitated from the melt (liquid phase 0) by the reaction of (4), the (Yb solid solution) β-CoSb primary phase Is formed in a skeleton-like structure, and the melt is not sufficiently replenished in the next peritectic reaction A, so that the volume is partially reduced and becomes a porous state instead of a uniform volume reduction reaction. It has been found. Therefore, in order to produce a dense material, the key point is how to prevent the primary crystal phases from being connected to each other in a skeleton form.

According to the present invention, in the melting method according to claims 1 to 3, the maximum melting temperature (Tmax) at the time of melting is controlled to be equal to or lower than the liquidus temperature, so that the phase configuration after dissolution and the solidification process Changes to eliminate the cause of the porous state formation, and the dense n-type skutterudite system Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) A thermoelectric conversion material can be manufactured.

That is, when the maximum dissolution temperature Tmax is controlled in the temperature range of 875 ° C. to 930 ° C., the primary crystal phase (Yb solid solution) β-CoSb itself forming a skeleton structure is not formed in the liquid phase, and the volume is reduced before and after the reaction. (Yb solid solution) γ-CoSb ₂ is formed directly from the liquid phase without the peritectic reaction A having a large change. For this reason, the factor of the porous state formation is completely eliminated, and the dense n-type skutterudite system Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) A thermoelectric conversion material can be manufactured.

Furthermore, when the maximum melting temperature Tmax is controlled within a temperature range of 930 ° C. to 1000 ° C. (liquidus temperature or lower), by limiting the starting material to at least one of CoSb and CoSb ₂ , When the crystal phase (Yb solid solution) β-CoSb is formed, the skeletons connected to each other can not be formed. Thus, when peritectic reaction A occurs, the melt necessary for the reaction is smoothly replenished, a uniform volume reduction reaction occurs as a whole, and a porous state is not formed, so a dense n-type skutterudite system Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) thermoelectric conversion material can be manufactured.

  Further, in the method for producing an n-type skutterudite-based Yb—Co—Sb thermoelectric conversion material of the present invention, there are many production processes such as a conventional hot press method and a discharge plasma sintering method, and the production cost is high. Therefore, an n-type skutterudite-based Yb—Co—Sb thermoelectric conversion material with high density and high thermoelectric conversion performance can be produced at a low production cost.

As described above, according to the present invention, an n-type Yb-Co-Sb thermoelectric conversion material, a Yb _x Co _y Sb _z thermoelectric conversion material, which is dense and has high thermoelectric conversion performance at a low production cost, There is an effect that a method for producing an n-type skutterudite-based Yb-Co-Sb thermoelectric conversion material can be provided.

Embodiments of the present invention will be described below.
(Embodiment)
The n-type skutterudite-based Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) thermoelectric conversion according to claims 1 to 3 of the present invention In order to manufacture the material by densifying the material, it is desirable to control the maximum melting temperature Tmax to a temperature range of 875 ° C. to 930 ° C. as described above. If the maximum dissolution temperature Tmax is within the temperature range of 875 ° C. to 930 ° C., a dense n-type skutterudite system Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) A thermoelectric conversion material can be produced.

More desirably, the maximum melting temperature Tmax is set to around 900 ° C. After realizing the two-phase coexistence state of L ₂ (liquid phase 2) and (Yb solid solution) γ-CoSb ₂ by dissolving and holding the raw material in the temperature range of 875 ° C. to 930 ° C., the target If the temperature is lower than 875 ° C. for forming the thermoelectric conversion material, for example, kept at 870 ° C., the peritectic reaction B proceeds sufficiently, and dense Yb _x Co _y Sb _z (0 <x ≦ 1, 3 0.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) A thermoelectric conversion material can be obtained. Here, the manufacturing method for controlling the maximum melting temperature Tmax within the temperature range of 875 ° C. to 930 ° C. is defined as melting method 1. Melting method 1 does not limit the type of starting material at the time of melting, such as a simple metal or a compound.

Further, when the maximum melting temperature Tmax is controlled in the temperature range of 930 ° C. to 1000 ° C., the n-type skutterudite system Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) In order to manufacture a thermoelectric conversion material by densification, it is desirable to limit the starting material to include at least one of CoSb or CoSb ₂ . After realizing the two-phase coexistence state of β-CoSb phase and L ₀ (liquid phase 0) that are not connected to each other by dissolving and holding the raw material in the temperature range of 930 ° C. to 1000 ° C., for example, up to 870 ° C. If the temperature is lowered and held, the peritectic reaction B proceeds sufficiently, and the dense n-type skutterudite system Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) A thermoelectric conversion material can be obtained. Here, a manufacturing method for controlling the maximum melting temperature Tmax to a temperature range of 930 ° C. to 1000 ° C. is defined as a melting method 2.

In the melting method 1 and the melting method 2, the heating method is not limited. For example, any method such as electric furnace heating, high-frequency melting heating, and other heating methods may be used. In order to perform dissolution uniformly in the melting method 1 and the melting method 2, stirring the melt is employed as an auxiliary means. The stirring method is not particularly limited as long as the solid phase and liquid phase in the melt can be made uniform.
The n-type skutterudite-based Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) thermoelectric conversion material obtained by any method becomes dense. The density was 7.4 g / cm ³ or more. The relationship between the Seebeck coefficient, electrical resistivity, thermal conductivity and temperature was measured, and the dimensionless figure of merit ZT at each temperature was calculated. As a result, the dimensionless figure of merit ZT was 0 in the temperature range of room temperature to 600 ° C. Reached 7 or more.

Further, in the melting method 1 and the melting method 2, the material is an n-type skutterudite-based Yb _x Co _y Sb _z (0 <x ≦ 1, 3.5 ≦ y ≦ 4.5, 10 ≦ z ≦ 15) thermoelectric. For example, n-type or p-type in which part or all of Co is substituted with Fe, and part of Yb is substituted with an alkaline earth metal element such as Ca, Sr or Ba. It can also be applied to thermoelectric conversion materials.

  Next, the present invention will be specifically described below with reference to examples. Hereinafter, a method for producing an n-type skutterudite-based Yb—Co—Sb thermoelectric conversion material according to claims 1 to 3 in the case of using the melting method 1 and its thermoelectric conversion performance will be described.

(Example 1)
Using Yb, Co, and Sb simple metals as starting materials, Yb: Co: Sb = 1: 9.0820: 56.922 in a weight ratio of pure metals Yb, Co, and Sb are placed in an alumina crucible, and inert gas In an atmosphere, it was heated and melted to a maximum temperature of 900 ° C. using an electric furnace and held for 6 hours. Then, after holding at 800 ° C. for 24 hours, at 650 ° C. for 12 hours, and further at 550 ° C. for 6 hours, and then cooled to room temperature, the microstructure microscope of the Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material in FIG. As shown in the photograph, a dense Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material without a porous state having a density of 7.48 g / cm ³ could be obtained.

Using a thermoelectric performance evaluation apparatus, the Seebeck coefficient, electrical resistivity, and thermal conductivity of the thermoelectric conversion material described above were measured in a temperature range of room temperature to 600 ° C., and a dimensionless figure of merit was calculated. These results are shown in FIGS. As can be seen from FIG. 5, the dimensionless figure of merit ZT reached 0.7 in the temperature range of 400 to 500 ° C.
However, FIG. 2 is a relationship diagram between the Seebeck coefficient of Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material and temperature, and FIG. 3 is a relationship diagram between the electrical resistivity of Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material and temperature. , 4 _Yb 0.15 _Co 4 _{Sb 12} thermal conductivity and the relationship diagram between the temperature of the thermoelectric conversion material, Figure 5 is a dimensionless figure of merit ZT and temperature of _Yb 0.15 _Co 4 _{Sb 12} thermoelectric conversion material It is a relationship diagram.

(Example 2)
A single metal of Yb, Co, Fe, and Sb is used as a starting material, and pure metals Yb, Co, Fe, and Sb are mixed at a weight ratio of Yb: Co: Fe: Sb = 1: 4.2572: 0.2689: 28.461. The raw material is put in an alumina crucible, heated and dissolved in an inert gas atmosphere to a maximum temperature of 900 ° C. in an electric furnace, held for 6 hours, then held at 800 ° C. for 24 hours, 650 ° C. for 12 hours, and further 550 ° C. for 6 hours. Each was held and then cooled to room temperature.

As a result, a dense Yb _0.3 Co _3.75 Fe _0.25 Sb ₁₂ thermoelectric conversion material having a density of 7.50 g / cm ³ and having no porous state could be obtained. Furthermore, when the dimensionless figure of merit in this material was calculated in the temperature range of room temperature to 600 ° C. using a thermoelectric performance evaluation apparatus, the dimensionless figure of merit ZT reached a maximum of 0.8 in the temperature range of 400 to 500 ° C.

(Example 3)
Yb, Ca, Co, Fe, Sb simple metal starting material, Yb: Ca: Co: Fe: Sb = 1: 0.0772: 4.2572: 0.2689: 28.461 Yb, Ca, Co, Fe and Sb raw materials are put in an alumina crucible, heated and dissolved in an inert gas atmosphere to a maximum temperature of 900 ° C. in an electric furnace, held for 6 hours, then held at 800 ° C. for 24 hours, 650 ° C. For 12 hours and further at 550 ° C. for 6 hours, and then cooled to room temperature.

Then, a dense Yb _0.3 Ca _0.1 Co _3.75 Fe _0.25 Sb ₁₂ thermoelectric conversion material having a density of 7.51 g / cm ^{3 and} having no porous state could be obtained. Furthermore, when the dimensionless figure of merit in this material was calculated in the temperature range of room temperature to 600 ° C. using a thermoelectric performance evaluation apparatus, the dimensionless figure of merit ZT reached 1.1 at the maximum in the temperature range of 400 to 500 ° C.

Example 4
Yb, Sr, Co, Fe, Sb simple metal starting material, Yb: Sr: Co: Fe: Sb = 1: 0.1688: 4.2572: 0.2689: 28.461 The raw materials of Yb, Sr, Co, Fe, and Sb are put into an alumina crucible, heated and dissolved in an inert gas atmosphere to a maximum temperature of 900 ° C. in an electric furnace, held for 6 hours, then held at 800 ° C. for 24 hours, 650 ° C. For 12 hours and further at 550 ° C. for 6 hours, and then cooled to room temperature.

As a result, a dense Yb _0.3 Sr _0.1 Co _3.75 Fe _0.25 Sb ₁₂ thermoelectric conversion material having a density of 7.52 g / cm ^{3 and} having no porous state could be obtained. Furthermore, when the dimensionless figure of merit in this material was calculated in the temperature range of room temperature to 600 ° C. using a thermoelectric performance evaluation apparatus, the dimensionless figure of merit ZT reached a maximum of 0.8 in the temperature range of 400 to 500 ° C.

(Example 5)
Yb, Ba, Co, Fe, Sb simple metal starting material, Yb: Ba: Co: Fe: Sb = 1: 0.2645: 4.2572: 0.2689: 28.461 The raw materials of Yb, Ba, Co, Fe, and Sb are put in an alumina crucible, heated and dissolved in an inert gas atmosphere up to a maximum temperature of 900 ° C. in an electric furnace, held for 6 hours, then at 800 ° C. for 24 hours, 650 ° C. For 12 hours and further at 550 ° C. for 6 hours, and then cooled to room temperature.

Thus, a dense Yb _0.3 Ba _0.1 Co _3.75 Fe _0.25 Sb ₁₂ thermoelectric conversion material having a density of 7.54 g / cm ^{3 and} having no porous state could be obtained. Furthermore, when a dimensionless figure of merit in this material was calculated in the temperature range of room temperature to 600 ° C. using a thermoelectric performance evaluation apparatus, the dimensionless figure of merit ZT reached a maximum of 0.9 in the temperature range of 400 to 500 ° C.

(Example 6)
In this example, a method for producing a Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material according to claims 1 to 3 when the melting method 2 is used and the thermoelectric conversion performance thereof will be described.

CoSb ₂ compound, Yb, Sb simple metal as a starting material, Yb: CoSb ₂ : Sb = 1: 46.6101: 18.7641 by weight ratio Pure metal Yb, Sb raw material and CoSb ₂ compound raw material are alumina Put in a crucible and heat and melt to a maximum temperature of 1000 ° C by heating in an inert gas atmosphere, hold for 2 hours, then 900 ° C for 6 hours, 800 ° C for 24 hours, and 650 ° C for 12 hours, Furthermore, it hold | maintained at 550 degreeC for 6 hours, respectively. When cooled to room temperature, a dense Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material having a density of 7.45 g / cm ³ and having no porous state could be obtained.

  Using a thermoelectric performance evaluation apparatus, the Seebeck coefficient, electrical resistivity, and thermal conductivity of the thermoelectric conversion material described above were measured in a temperature range of room temperature to 600 ° C., and a dimensionless figure of merit was calculated. These results are shown in FIGS. As shown in FIG. 5, the dimensionless figure of merit ZT reached 0.7 even in the temperature range of 400 to 500 ° C.

(Comparative example)
In this comparative example, a conventional melting method of Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material and its thermoelectric performance will be described.

Using Yb, Co, and Sb simple metals as starting materials, Yb: Co: Sb = 1: 9.0820: 56.922 in a weight ratio of pure metals Yb, Co, and Sb are placed in an alumina crucible, and inert gas In an atmosphere, heating and melting to a temperature above the liquidus by heating in an electric furnace, for example, to 1200 ° C., holding for 2 hours, gradually cooling, 900 ° C. for 6 hours, 800 ° C. for 24 hours, 650 ° C. for 12 hours Held for 6 hours at 550 ° C. When cooled to room temperature, a non-dense porous Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material having a density of 7.0 g / cm ³ was obtained as shown in FIG.

  Using a thermoelectric performance evaluation apparatus, the Seebeck coefficient, electrical resistivity, and thermal conductivity of the thermoelectric conversion material described above were measured in a temperature range of room temperature to 600 ° C., and a dimensionless figure of merit was calculated. These results are shown in FIGS. As can be seen from FIGS. 2 to 5, there was no significant difference between the dense material and the porous material with respect to the Seebeck coefficient, but the electrical resistivity due to the porous state became considerably large, and the heat conduction The rate was slightly reduced by the contribution of the porous. Therefore, the maximum value of the dimensionless figure of merit ZT was reduced to 0.35, which was half that of the dense material.

As apparent from the above results, the melting method of the n-type skutterudite-based Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material provided by the present invention can obtain thermoelectric performance superior to that of the conventional melting method. . The manufacturing method provided by the present invention is applicable not only to Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion materials but also to all n-type skutterudite-based Yb—Co—Sb thermoelectric conversion materials.
However, although the present invention has been described in detail based on the form of the invention specifically shown above, the present invention is not limited to the above contents, and all modifications and changes can be made without departing from the scope of the present invention. It can be changed.

It is a microphotograph of _Yb 0.15 _Co 4 _{Sb 12} thermoelectric conversion material according to the embodiment of the present invention. It is a graph showing the relationship between the Seebeck coefficient and temperature of Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material. It is a graph showing the relationship between electrical resistivity and temperature Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material. It is a graph showing the relationship between thermal conductivity and temperature of Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material. It is a graph showing the relationship between dimensionless figure of merit ZT and temperature of Yb _0.15 Co ₄ Sb ₁₂ thermoelectric conversion material. It is a Co-Sb system phase diagram.

Claims (3)

In an n-type Yb-Co-Sb-based thermoelectric conversion material having a skutterudite structure manufactured by a melting method, the density is 7.4 g / cm ³ or more, and a dimensionless figure of merit ZT (Z N-type Yb—Co—Sb thermoelectric conversion material, characterized by having a figure of merit, T: absolute temperature) of 0.6 or more. In the n-type Yb-Co-Sb-based thermoelectric conversion material according to claim 1, the Yb content x is 0 <x ≦ 1, the Co content y is 3.5 ≦ y ≦ 4.5, and the Sb content is A Yb _x Co _y Sb _z- based thermoelectric conversion material manufactured by a melting method in which the amount z is 10 ≦ z ≦ 15. N- type Yb-Co-Sb based thermoelectric conversion material according to claim 1, or preparing the _Yb x _Co y Sb _z based thermoelectric conversion material according to claim 2 n- type skutterudite Yb-Co- In the method for producing a Sb thermoelectric conversion material, CoSb or CoSb ₂ , Yb, Co, Sb is used as a raw material. The raw material is heated and dissolved in a temperature range of 875 ° C. to 1000 ° C. A method for producing an n-type skutterudite-based Yb-Co-Sb thermoelectric conversion material, characterized by obtaining a conversion material.

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