JP2007173799A - Thermoelectric conversion material and thermoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric conversion material having a large dimensionless performance index ZT by maintaining a high Seebeck coefficient and low resistivity and fully reducing thermal conductivity, in a material with a half-Heusler compound as a main phase. <P>SOLUTION: The thermoelectric conversion material is expressed by a composition formula (2) (Ln<SB>d</SB>(Ti<SB>a2</SB>Zr<SB>b2</SB>Hf<SB>c2</SB>)<SB>1-d</SB>)<SB>x</SB>Ni<SB>y</SB>Sn<SB>100-x-y</SB>and has an MgAgAs type crystal structure, where x and y satisfy the conditions of 30≤x≤35 and 30≤y≤35, Ln is at least one type selected from a group comprising Y and rare earth elements, and a2, b2, c2 and d satisfy the conditions of 0≤a2≤1, 0≤b2≤1, 0≤c2≤1, a2+b2+c2=1, and 0<d≤0.3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermoelectric conversion material, and more particularly to a thermoelectric conversion material having a half-Heusler compound having a MgAgAs type crystal structure as a main phase, and a thermoelectric conversion element using the same.

  In recent years, interest in thermoelectric cooling elements using the Peltier effect, which is freonless cooling, has increased due to the heightened awareness of global environmental problems. Interest in thermoelectric generators that directly convert unused waste heat energy into electrical energy to reduce carbon dioxide emissions from global warming issues is also increasing.

  As the p-type and n-type thermoelectric cooling materials and thermoelectric power generation materials used for such thermoelectric conversion elements, a Bi-Te single crystal structure or a polycrystal structure is often used because of its high efficiency. In thermoelectric materials used under conditions higher than room temperature, Pb—Te-based materials are used for both p-type and n-type because of their high efficiency.

  Pb (lead) contained in the Pb—Te-based material is toxic and harmful to the human body and is not preferable from the viewpoint of global environmental problems. Bi-Te-based materials generally contain Se as an impurity, which is also an element that is toxic and harmful to the human body. Se is not preferable from the viewpoint of global environmental problems. Furthermore, Te used in such a material system has a very small reserve on the earth, and there is a difficulty in supply in terms of resources. For this reason, there is a demand for thermoelectric conversion materials that have higher efficiency and are harmless than Bi—Te materials and Pb—Te materials.

  The half-Heusler compound is represented by the chemical formula ABX, is an intermetallic compound having a cubic MgAgAs type crystal structure, and has a structure in which B atoms are inserted into the NaCl type crystal lattice of AX. A compound having such a structure has a high Seebeck coefficient at room temperature. For example, TiNiSn is reported to be −142 μV / K, ZrNiSn is −176 μV / K, and HfNiSn is reported to be −124 μV / K (for example, Non-Patent Document 1). reference).

  In addition, the figure of merit Z of the thermoelectric conversion material is expressed by the following formula (1).

Z = α ² σ / κ (1)
In the above formula (1), α is the Seebeck coefficient of the thermoelectric conversion material, σ is the conductivity of the thermoelectric conversion material, and κ is the heat conductivity of the thermoelectric conversion material. The reciprocal of conductivity σ is expressed as electrical resistivity ρ.

  Z has a dimension of the reciprocal of temperature, and when this figure of merit Z is multiplied by absolute temperature, it becomes a dimensionless value. This value ZT is called a dimensionless figure of merit and has a correlation with the thermoelectric conversion efficiency of the thermoelectric conversion material, and the higher the ZT, the greater the thermoelectric conversion efficiency.

That is, a material that is less likely to pass heat, passes electricity more, and has a higher thermoelectromotive force becomes a more efficient thermoelectric conversion material. For example, the dimensionless figure of merit of the Bi-Te system having the largest dimensionless figure of merit among currently known materials is about 1.0 at 300K.

  The half-Heusler compound ZrNiSn described above has a high Seebeck coefficient of −176 μV / K at room temperature, but has a high resistivity at room temperature of 11 mΩcm and a high thermal conductivity of 8.8 W / mK. For this reason, the dimensionless figure of merit ZT is as small as 0.010, and it is reported that the thermoelectric conversion efficiency is small. For TiNiSn and HfNiSn, the thermoelectric conversion efficiency is even smaller, about 0.007 for TiNiSn, and only 0.005 for HfNiSn.

On the other hand, for example, HoPdSb has been reported as a half-Heusler compound containing a rare earth (see, for example, Non-Patent Document 2). This HoPdSb has a Seebeck coefficient of 150 μV / K at room temperature and a thermal conductivity of 6 W / mK, which is slightly smaller than ZrNiSn, but still has a resistivity as large as 9 mΩcm. Ho _0.5 Er _0.5 PdSb _1.05 , Er _0.25 Dy _0.75 Pd _1.02 Sb, and Er _0.25 Dy _0.75 PdSb _1.05 have a low dimensionless figure of merit at room temperature, reported as 0.04, 0.03, and 0.02, respectively. ing.
J. et al. Phys. : Condens. Matter 11 1697-1709 (1999) Appl. Phys. Lett. 74, 1414-1417 (1999)

  In view of the above problems, the present invention is a thermoelectric conversion having a large dimensionless figure of merit ZT by sufficiently reducing the thermal conductivity while maintaining a high Seebeck coefficient and a low resistivity in a material having a half-Heusler compound as a main phase. It is an object to provide a material and a thermoelectric conversion element using the material.

  A method for producing a thermoelectric conversion material according to one embodiment of the present invention is a method for producing a thermoelectric conversion material containing a phase having a MgAgAs type crystal structure, wherein an alloy powder having a composition represented by the following composition formula (2) is used. It has the process of integrally forming by a sintering method.

_{(Ln d (Ti a2 Zr b2} Hf c2) 1-d) x Ni y Sn 100-xy composition formula (2)
(In the composition formula (2), Ln is at least one selected from the group consisting of Y and rare earth elements, 0 ≦ a2 ≦ 1, 0 ≦ b2 ≦ 1, 0 ≦ c2 ≦ 1, a2 + b2 + c2 = 1, 0 <D ≦ 0.3, 30 ≦ x ≦ 35, 30 ≦ y ≦ 35.)
A thermoelectric conversion material according to another aspect of the present invention is a method for producing a thermoelectric conversion material containing a phase having an MgAgAs type crystal structure, and sintering an alloy powder having a composition represented by the following composition formula (3) It has the process of integrally forming by a method.

Ln1 _X Ni _Y Sb _100-XY composition formula (3)
(In the composition formula (3), Ln1 is at least one selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U, and 30 ≦ X ≦ 35. 30 ≦ Y ≦ 35.)
A thermoelectric conversion material according to another aspect of the present invention is a method for producing a thermoelectric conversion material containing a phase having an MgAgAs type crystal structure, and sintering an alloy powder having a composition represented by the following composition formula (4) It has the process of integrally forming by a method.

_{(Ln2 p Y 1-p)} X Ni Y Sb 100-XY composition formula (4)
(Ln2 is at least one selected from Sc, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U, and 0.001 ≦ P ≦ 0.999, 30 ≦ X ≦ 35. 30 ≦ Y ≦ 35.)
A thermoelectric conversion element according to one embodiment of the present invention includes p-type thermoelectric conversion materials and n-type thermoelectric conversion materials alternately connected in series, and at least one of the p-type thermoelectric conversion material and the n-type thermoelectric conversion material is It is preferable to include a thermoelectric conversion material manufactured by a manufacturing method in which the alloy powder is integrally formed by a sintering method.

  According to the present invention, in a material having a half-Heusler compound as a main phase, the heat conductivity is sufficiently reduced while maintaining a high Seebeck coefficient and a low resistivity, and a thermoelectric conversion material having a large dimensionless figure of merit ZT, And a thermoelectric conversion element using the same can be provided.

  Embodiments of the present invention will be described below.

  Generally, heat conduction is divided into phonons, that is, due to propagation of crystal lattice vibrations, and conductive carriers, ie, due to movement of free electrons. Therefore, the thermal conductivity κ is expressed by the following formula (2).

κ = κ _ph + κ _el formula (2)
The numerical expression (2), κ _ph is the lattice thermal conductivity, kappa _el is the electron thermal conductivity.

The electronic thermal conductivity κ _el is expressed by the following formula (3) according to the Biedemann Franz rule.

κ _el = LTσ Formula (3)
In the above mathematical formula (3), σ is electrical conductivity, T is absolute temperature, and L is a Lorentz factor, which is represented by the following mathematical formula (4).

^{L = (π 2/3)} (kB / e) 2 (4)
In the above formula (4), kB is the Boltzmann constant (1.38 × 10 ⁻²³ J / K), and e is the charge amount of electrons (−1.60 × 10 ⁻¹⁹ C).

Therefore, the Lorentz factor is a constant, and its value is 2.44 × 10 ⁻⁸ V ² / K ² . As shown in the above formula (3), since the electronic thermal conductivity κ _el is proportional to the absolute temperature and the electrical conductivity, it is necessary to reduce the electrical conductivity in order to reduce the electronic thermal conductivity at the same temperature. There is.

  However, as can be seen from the equation (1), the conductivity must be increased in order to increase the dimensionless figure of merit ZT. Therefore, it is not possible to reduce the electronic thermal conductivity to reduce the overall thermal conductivity κ, thereby increasing the dimensionless figure of merit. Further, as can be seen from the above formula (3), if the conductivity is not temperature dependent and constant with respect to temperature change, the electronic thermal conductivity increases in proportion to the temperature. Therefore, even if the lattice thermal conductivity is not temperature-dependent and constant, the overall thermal conductivity κ increases from the above formula (2) as the temperature increases, and the dimensionless figure of merit decreases. End up.

From the above, in order to reduce the overall thermal conductivity κ and increase the dimensionless figure of merit ZT, it is important how to reduce the lattice thermal conductivity _κph . The lattice thermal conductivity greatly depends on the type of crystal lattice and the constituent elements, and can be lowered by disturbing the regularity of the lattice. In MNiSn having a half-Heusler structure, when Ti, Zr, and Hf are used alone as M, the lattice thermal conductivity is 6.7 to 9.3 W / mK.

  As a result of intensive studies, the present inventors have found that the thermal conductivity can be further reduced by introducing atomic radius irregularity of atoms at the A site in the MNiSn having the half-Heusler structure shown in FIG. In FIG. 1, reference numerals 1, 2, and 3 represent an A element (M), a B element (Ni), and an X element (Sn), respectively, and a reference numeral 4 represents a void.

  Specifically, by making the atoms at the A site contain all of Ti, Zr, and Hf, phonon scattering due to nonuniformity in atomic radius and atomic weight, and nonuniformity in crystal lattice size occur. Thus, the thermal conductivity can be greatly reduced.

  Furthermore, the present inventors have made it clear that making the atoms at the A site contain all of Ti, Zr, and Hf has a sharp change in the electron density distribution in the vicinity of the Fermi surface and is effective in increasing the Seebeck coefficient. I found it.

  That is, the n-type thermoelectric conversion material according to one embodiment of the present invention is characterized in that a main phase is a phase represented by the following composition formula (1) and having an MgAgAs crystal structure.

(Ti _a1 Zr _b1 Hf _c1 ) _x Ni _y Sn _100-xy composition formula (1)
In order for the atoms at the A site to contain all of Ti, Zr, and Hf, a1, b1, and c1 in the composition formula (1) must be larger than zero. Therefore, the numerical values of a1, b1, and c1 are defined as 0 <a1 <1, 0 <b1 <1, 0 <c1 <1, and a1 + b1 + c1 = 1. Even more preferably, 0.1 <a1 <0.9, 0.1 <b1 <0.9, 0
. 1 <c1 <0.9 and a1 + b1 + c1 = 1.

  Further, in order to increase the volume occupancy of the phase having the MgAgAs type crystal structure and obtain a high Seebeck coefficient, x and y are defined in the ranges of 30 ≦ x ≦ 35 and 30 ≦ y ≦ 35, respectively. More preferable ranges of x and y are 33 ≦ x ≦ 34 and 33 ≦ y ≦ 34.

  Furthermore, the present inventors paid attention to a rare earth element having an atomic radius larger than any element of Ti, Zr, and Hf. Since rare earth elements easily form an alloy phase with Ni or Sn, a reduction in thermal conductivity due to this is expected. As a result of earnest investigation based on such knowledge, the present inventors selected a part of M in the half-Heusler compound MNiSn (X = Ti, Zr, Hf) from the group consisting of Y and rare earth elements. It has been found that the thermal conductivity can be greatly improved by substituting with at least one element.

  That is, an n-type thermoelectric conversion material according to another aspect of the present invention is characterized in that a main phase is a phase represented by the following composition formula (2) and having an MgAgAs-type crystal structure.

_{(Ln d (Ti a2 Zr b2} Hf c2) 1-d) x Ni y Sn 100-x-y composition formula (2)
Ln is at least one element selected from the group consisting of Y and rare earth elements, and the rare earth elements include all elements from La of atomic number 57 to Lu of atomic number 71 in the periodic table. . Considering the melting point and the atomic radius, Er, Gd, and Nd are particularly preferable as Ln.

  Ln is an element effective for reducing the thermal conductivity as described above. The effect is exhibited even in a small amount, but in order to further reduce the thermal conductivity, the blending amount of Ln should be 0.1 atomic% or more of the total amount of Ln and (Ti, Zr, Hf). preferable. When the amount of Ln exceeds 30 atomic% of the total amount of Ln and (Ti, Zr, Hf), precipitation of a phase other than the phase having the MgAgAs crystal structure, for example, the LnSn3 phase becomes remarkable. The Seebeck coefficient may be deteriorated. For this reason, the value of d is defined within the range of 0 <d ≦ 0.3, and more preferably within the range of 0.001 ≦ d ≦ 0.3.

  In the composition formula (2), Ti, Zr and Hf are not necessarily all present simultaneously. For this reason, a2, b2, and c2 are within the ranges of 0 ≦ a2 ≦ 1, 0 ≦ b2 ≦ 1, 0 ≦ c2 ≦ 1, and a2 + b2 + c2 = 1.

In order to increase the volume occupancy of the phase having the MgAgAs type crystal structure and obtain a high Seebeck coefficient, x and y are set in a range of 30 ≦ x ≦ 35 and 30 ≦ y ≦ 35. In the half-Heusler compound, a large Seebeck coefficient is observed when the total number of valence electrons is around 18. For example, the outer electron arrangement in ZrNiSn is Zr (5d ² 6s ² ), Ni (3d ⁸ 4s ² ), Sn (5s ² 5p ² ), and the total number of valence electrons is 18. Similarly, TiNiSn and HfNiSn have 18 valence electrons.

On the other hand, when a part of Ti, Zr, and Hf is substituted with a rare earth element as represented by the above composition formula (2), the rare earth elements excluding Ce, Eu, and Yb are (5d ¹ 6s ² ), The total number of valence electrons may deviate from 18. Therefore, it is possible to compensate for this by appropriately adjusting x and y.

  In the aforementioned composition formulas (1) and (2), part of Ti, Zr and Hf is substituted with at least one element selected from the group consisting of V, Nb, Ta, Cr, Mo and W. Also good. These elements can be used alone or in combination of two or more to substitute a part of Ti, Zr and Hf. By such substitution, it is possible to adjust the total valence electron number in the MgAgAs phase, which is the main phase, and increase the Seebeck coefficient and the conductivity. As described above, in the half-Heusler compound, a large Seebeck coefficient is observed when the total number of valence electrons is around 18. Therefore, the total number of valence electrons is adjusted by using these substitution elements and rare earth elements in combination. It is effective. However, the substitution amount is preferably 30 atomic percent or less of the total amount of Ti, Zr, and Hf. If it exceeds 30 atomic%, the precipitation of phases other than the phase having the MgAgAs type crystal structure becomes prominent, and the Seebeck coefficient may be deteriorated.

  A part of Ni in the composition formula (1) or (2) may be substituted with at least one element selected from the group consisting of Mn, Fe, Co, and Cu. These elements can be used alone or in combination of two or more to replace a part of Ni. By such substitution, it is possible to increase the Seebeck coefficient and conductivity by adjusting the total number of valence electrons in the MgAgAs phase that is the main phase. In general, the amount of substitution is desirably limited to 50 atomic% or less of Ni. In particular, when substituting with Cu, if the amount of substitution is too large, the formation of the MgAgAs phase may be hindered.

  Furthermore, a part of Sn in the composition formula (1) or (2) may be substituted with at least one element selected from the group consisting of As, Sb, Bi, Ge, Pb, Ga, and In. These elements can be used alone or in combination of two or more to replace a part of Sn. By such substitution, it is possible to increase the Seebeck coefficient and conductivity by adjusting the total number of valence electrons in the MgAgAs phase that is the main phase. However, the element substituting Sn is particularly preferably Sb or Bi in consideration of toxicity, toxicity, and material cost. The amount of substitution is preferably 30 atomic percent or less of Sn. When it exceeds 30 atomic%, precipitation of a phase other than the phase having the MgAgAs type crystal structure becomes remarkable, which may cause deterioration of the Seebeck coefficient.

  Although the n-type thermoelectric conversion material has been described above, the same theory can be applied to the p-type thermoelectric conversion material. It has been found by the present inventors that the power factor is increased by using Ni as compared with the case where Pd is used as the B element.

  A p-type thermoelectric conversion material according to one embodiment of the present invention is represented by the following composition formula (3), and is characterized in that a phase having an MgAgAs-type crystal structure is a main phase.

_{Ln1 X Ni Y Sb 100-X} -Y composition formula (3)
Corresponding to the crystal structure shown in FIG. 1, A element 1 corresponds to Ln1, B element 2 corresponds to Ni, and X element 3 corresponds to Sb.

  In the composition formula (3), Ln1 is at least one element selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, and U. In order to increase the volume occupancy of the phase having the MgAgAs type crystal structure and obtain a high Seebeck coefficient, X and Y are respectively defined in the ranges of 30 ≦ X ≦ 35 and 30 ≦ Y ≦ 35. More preferable ranges of X and Y are 33 ≦ X ≦ 34 and 33 ≦ Y ≦ 34.

  In order to cause nonuniformity in the size of the crystal lattice and greatly reduce the thermal conductivity, it is preferable to contain Y as a part of Ln1.

  A p-type thermoelectric conversion material according to another embodiment of the present invention is represented by the following composition formula (4) and is characterized in that a phase having an MgAgAs-type crystal structure is a main phase.

_{(Ln2 P Y 1-P)} X Ni Y Sb 100-X-Y composition formula (4)
Corresponding to the crystal structure shown in FIG. 1, A element 1 is Ln2 and Y, B element 2 is Ni, and X element 3 is Sb.

  In the composition formula (4), Ln2 is at least one element selected from Sc, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, and U. In order to increase the volume occupancy of the phase having the MgAgAs type crystal structure and obtain a high Seebeck coefficient, P, X and Y are 0.001 ≦ P ≦ 0.999, 30 ≦ X ≦ 35, 30 ≦ Y. Each is defined in a range of ≦ 35. More preferable ranges of P, X, and Y are 0.01 ≦ P ≦ 0.99, 33 ≦ X ≦ 34, and 33 ≦ Y ≦ 34.

  The p-type thermoelectric conversion material represented by the composition formula (4) described above requires Y, and this Y decreases the thermal conductivity. Therefore, the figure of merit can be further increased.

  In the above composition formula (3) or (4), a part of Ln1 or Ln2 is composed of Ti, Zr, Hf, La, Ce, Pr, Nd, Sm, Eu, Be, Mg, Ca, Sr, and Ba. It may be substituted with at least one element selected from the group. These elements can be used alone or in combination of two or more to substitute a part of Ln1 or Ln2. By such substitution, it is possible to increase the conductivity by adjusting the total number of valence electrons in the main phase MgAgAs phase. In particular, substitution with a divalent element such as Be, Mg, Ca, Sr, or Ba results in substitution of trivalent Ln1 and Ln2 with a divalent element, thus forming an electrical hole. The

  Since the thermoelectric conversion material of this embodiment is p-type, it is effective for increasing the carrier concentration and increasing the conductivity. However, the substitution amount is preferably about 30 atomic% or less of the total amount of Ln1 or Ln2. If it exceeds about 30 atomic%, precipitation of a phase other than the phase having the MgAgAs type crystal structure becomes prominent, and the Seebeck coefficient may be deteriorated.

  In the composition formula (3) or (4), a part of Ni is V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Rh, Ir, Pd, Pt, Cu, Ag, It may be substituted with at least one element selected from the group consisting of Au and Zn. These elements can be used alone or in combination of two or more, and a part of Ni can be substituted. By such substitution, it is possible to increase the Seebeck coefficient and conductivity by adjusting the total number of valence electrons in the MgAgAs phase that is the main phase. In particular, substitution with an element having a smaller number of outer shell valence electrons than Ni, such as Co, Rh, and Ir, is effective in forming electrical holes, increasing carrier concentration, and increasing conductivity. is there.

  However, the amount of substitution is preferably limited to 30 atomic% or less of Ni. If it exceeds 30 atomic%, the precipitation of phases other than the phase having the MgAgAs type crystal structure becomes prominent, and the Seebeck coefficient may be deteriorated.

  Furthermore, in the composition formula (3) or (4), a part of Sb is substituted with at least one element selected from the group consisting of Al, Si, Ga, Ge, As, In, Sn, Pb, and Bi. May be. These elements can be used alone or in combination of two or more to replace a part of Sb. By such substitution, it is possible to increase the Seebeck coefficient and conductivity by adjusting the total number of valence electrons in the MgAgAs phase that is the main phase. In particular, substitution with an element having a smaller number of outer valence electrons than Sb, such as Si, Ge, Sn, and Pb, increases the carrier concentration due to the formation of electrical holes, and increases the conductivity. It is effective for increase.

  However, the amount of substitution is desirably limited to 30 atomic% or less of Sb. If it exceeds 30 atomic%, the precipitation of phases other than the phase having the MgAgAs type crystal structure becomes prominent, and the Seebeck coefficient may be deteriorated. Further, substituting Sb with Bi replaces with an element having a larger atomic radius and a larger atomic weight, which increases the phonon scattering effect and is effective in lowering the lattice thermal conductivity.

  The thermoelectric conversion material concerning embodiment of this invention can be manufactured by the following methods, for example.

  First, an alloy containing a predetermined amount of each element is produced by arc melting or high frequency melting. In producing the alloy, a liquid quenching method such as a single roll method, a twin roll method, a rotating disk method, or a gas atomizing method, or a method using a solid phase reaction such as a mechanical alloying method may be employed. Methods such as the liquid quenching method and the mechanical alloying method are advantageous in that the crystal phase constituting the alloy is refined and the solid solution region of the element in the crystal phase is expanded. For this reason, thermal conductivity can be reduced significantly.

  Alternatively, it is possible to produce an alloy by hot pressing the raw metal powder without going through the melting process as described above.

  The produced alloy may be heat-treated as necessary. This heat treatment makes the alloy single phase and the crystal grain size is also controlled, so that the thermoelectric characteristics can be further enhanced. Steps such as melting, liquid quenching, mechanical alloying and heat treatment are preferably performed in an inert atmosphere such as Ar from the viewpoint of preventing oxidation of the alloy.

  Next, the alloy is pulverized by a ball mill, a brown mill, a stamp mill or the like to obtain an alloy powder, and the alloy powder is integrally formed by a hot pressing method or a sintering method such as an SPS method. From the viewpoint of preventing oxidation of the alloy, the integral molding is preferably performed in an inert atmosphere such as Ar. Subsequently, the thermoelectric conversion material concerning embodiment of this invention is obtained by processing the obtained molded object into a desired dimension. The shape and dimensions of the molded body can be selected as appropriate. For example, it can be a cylindrical shape having an outer shape of 0.5 to 10 mmφ and a thickness of 1 to 30 mm, or a rectangular parallelepiped shape of (0.5 to 10 mm) × (0.5 to 10 mm) × thickness (1 to 30 mm). .

  The thermoelectric conversion element concerning embodiment of this invention can be manufactured using the thermoelectric conversion material obtained in this way. FIG. 2 is a schematic cross-sectional view showing an example of the configuration.

  In the thermoelectric conversion element shown in FIG. 2, the n-type semiconductor thermoelectric conversion material 9 and the p-type semiconductor thermoelectric conversion material 8 according to the embodiment of the present invention are arranged in parallel. Electrodes 10a and 10b are respectively arranged on the upper surfaces of the n-type thermoelectric conversion material 9 and the p-type thermoelectric conversion material 8, and the upper insulating substrate 11a is connected to the outside thereof. The lower surfaces of the n-type thermoelectric conversion material 9 and the p-type thermoelectric conversion material 8 are connected by an electrode 10c supported by the lower insulating substrate 11b.

  When a temperature difference is given between the upper and lower insulating substrates 11a and 11b to make the upper side low and the lower side high, the p-type semiconductor thermoelectric conversion material 8 has a positive charge. The hole 14 moves to the lower temperature side (upper side), and the electrode 10b has a higher potential than the electrode 10c. On the other hand, inside the n-type semiconductor thermoelectric conversion material 9, electrons 15 having negative charges move to the low temperature side (upper side), and the electrode 10c has a higher potential than the electrode 10a.

  As a result, a potential difference is generated between the electrode 10a and the electrode 10b. As shown in FIG. 2, when the upper side is at a low temperature and the lower side is at a high temperature, the electrode 10b is a positive electrode and the electrode 10a is a negative electrode.

  As shown in FIG. 3, a plurality of p-type thermoelectric conversion materials 8 and n-type thermoelectric conversion materials 9 are alternately connected in series to obtain a higher voltage than the structure shown in FIG. Can be secured.

  The above-described thermoelectric conversion element 16 can be applied to a thermal battery. An example of the configuration is shown in FIG. As shown in the drawing, when the upper side of the electric conversion element 16 is set to a low temperature and the lower side is set to a high temperature, a potential difference is generated in the termination electrode 19 of the thermoelectric conversion element 16. When a load 20 is connected to the electrode 19a and the electrode 19b, a current 21 flows in the direction of the arrow shown in the figure and functions as a thermal battery.

  Or the thermoelectric conversion element mentioned above is applicable to a cooler. An example of the configuration is shown in FIG. As shown in the figure, a DC current 23 is passed in the direction of the arrow in the figure using a DC power source 22 on the termination electrode 19 of the thermoelectric conversion element 16. As a result, the upper side of the thermoelectric conversion element 16 becomes high temperature, and one lower side becomes low temperature and functions as a cooler.

  The thermoelectric conversion material of the present invention will be described in detail below with reference to examples.

Example I
In this example, an n-type thermoelectric conversion material will be described.

(Example I-1)
99.9% purity Ti, 99.9% purity Zr, 99.9% purity Hf, 99.99% purity Ni, and 99.99% purity Sn were prepared as raw materials. It was weighed so as to be (Ti _0.3 Zr _0.35 Hf _0.35 ) NiSn.

The weighed raw materials were mixed, loaded into a copper-cooled copper hearth in an arc furnace, and evacuated to a vacuum of 2 × 10 −3 Pa. Thereafter, high-purity Ar having a purity of 99.999% was introduced to -0.04 MPa, and arc-dissolved in a reduced pressure Ar atmosphere. After melting, the metal lump obtained by quenching with a water-cooled copper hearth was vacuum-sealed in a quartz tube at a high vacuum of 10 ⁻⁴ Pa or less and heat-treated at 1073 K for 72 hours.

  The obtained metal lump was pulverized and molded at a pressure of 50 MPa using a mold having an inner diameter of 20 mm. The obtained molded body was filled in a carbon mold having an inner diameter of 20 mm, and pressure sintered at 80 MPa and 1200 ° C. for 1 hour in an Ar atmosphere to obtain a disk-shaped sintered body having a diameter of 20 mm.

  When this sintered body was examined by a powder X-ray diffraction method, it was confirmed that the sintered body was mainly composed of a phase having an MgAgAs type crystal structure.

  Moreover, when the composition of the obtained sintered body was analyzed by ICP emission spectroscopy, it was confirmed that the composition was almost a predetermined composition.

  The obtained sintered body was evaluated for thermoelectric properties by the following method.

(1) The resistivity sintered body was cut into 2 mm × 0.5 mm × 18 mm, electrodes were formed, and measurement was performed by a direct current four-terminal method.

(2) Seebeck coefficient The sintered body was cut into 4 mm × 1 mm × 0.5 mm, a temperature difference of 2 ° C. was applied to both ends thereof, the electromotive force was measured, and the Seebeck coefficient was obtained.

(3) The thermal conductivity sintered body was cut into φ10 mm × t2.0 mm, and the thermal diffusivity was measured by a laser flash method. Separately, specific heat was determined by DSC measurement. The density of the sintered body was obtained by the Archimedes method, and the thermal conductivity was calculated from these.

  Using the resistivity, Seebeck coefficient, and thermal conductivity values obtained in this way, the dimensionless figure of merit ZT was obtained by the above formula (1). The resistivity, Seebeck coefficient, lattice thermal conductivity, and dimensionless figure of merit at 300K and 700K are as follows.

300K: Resistivity 8.62 × 10 ⁻³ Ωcm
Seebeck coefficient -333μV / K
Lattice thermal conductivity 3.05W / mK
ZT = 0.12
700K: resistivity 2.35 × 10 ⁻³ Ωcm
Seebeck coefficient -328μV / K
Lattice thermal conductivity 1.95W / mK
ZT = 1.20
The temperature dependence of the dimensionless figure of merit ZT of the thermoelectric conversion material produced in Example I-1 is shown as curve a in FIG. As shown in the figure, a dimensionless figure of merit ZT of about 1.21 is obtained at the maximum.

  As already explained, the maximum value of the dimensionless figure of merit ZT for existing thermoelectric conversion materials is 1.0 for Bi-Te based materials. In this example, since the composition was (Ti0.3Zr0.35Hf0.35) NiSn, a high-performance thermoelectric conversion material exceeding this was obtained.

(Comparative Example I-1)
Zr with a purity of 99.9%, Hf with a purity of 99.9%, Ni with a purity of 99.99%, and Sn with a purity of 99.99% are prepared as raw materials so that the composition formula becomes Zr0.5Hf0.5NiSn. Weighed. Using the weighed raw material powder, a sintered body was produced by the same method as in Example I-1, and the thermoelectric characteristics were evaluated by the same method. The resistivity, Seebeck coefficient, lattice thermal conductivity, and dimensionless figure of merit at 300K and 700K are as follows.

300K: Resistivity 9.6 × 10 −3 Ωcm
Seebeck coefficient -180μV / K
Lattice thermal conductivity 3.95W / mK
ZT = 0.02
700K: resistivity 2.3 × 10 −3 Ωcm
Seebeck coefficient -272 μV / K
Lattice thermal conductivity 3.49W / mK
ZT = 0.53
The temperature dependence of the dimensionless figure of merit ZT of the thermoelectric conversion material produced in (Comparative Example I-1) is shown as a curve c in FIG. It can be seen that the dimensionless figure of merit ZT remains at about 0.54 at the maximum.

Thus, in the case of the composition of Zr _0.5 Hf _0.5 NiSn, a high-performance thermoelectric conversion material exceeding 1.0 of the Bi—Te based material was not obtained.

(Examples I-2 to I-21, Comparative Examples I-2 to I-3)
Thermoelectric conversion materials having various compositions represented by the composition formula (Ti _a1 Zr _b1 Hf _c1 ) NiSn were produced in the same manner as in Example 1 described above. About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated similarly to the above, and the obtained result is put together in following Table 1. FIG. Table 1 also shows the results of the above-mentioned (Example I-1) and (Comparative Example I-1).

  As shown in Table 1, each of the thermoelectric conversion materials containing three kinds of elements of Ti, Zr, and Hf and having various compositions represented by the above composition formula (1) has good thermoelectric conversion characteristics. It was recognized that In contrast, Comparative Examples I-1, I-2, and I-3 that do not contain any of Ti, Zr, and Hf clearly show that the dimensionless figure of merit ZT is inferior in the results of Table 1. Has been.

(Examples I-22 to I-45)
A part of Ti, Zr, and Hf in the thermoelectric conversion material represented by the composition formula (Ti _0.3 Zr _0.35 Hf _0.35 ) NiSn prepared in Example I-1 described above is substituted with V, Nb, A thermoelectric conversion material represented by a composition formula ((Ti _0.3 Zr _0.35 Hf _0.35 ) _1-e X _e ) NiSn was produced by substituting with at least one element selected from the group of Ta.

Specifically, a thermoelectric conversion material was produced by the same method as in (Example I-1) except that V, Nb, or Ta as X was further added at the substitution element amount e shown in Table 2 below. About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated similarly to the above, and the obtained result is put together in following Table 2. FIG.

Furthermore, a part of Ti, Zr, and Hf in the thermoelectric conversion material represented by the composition formula (Ti _0.5 Zr _0.25 Hf _0.25 ) NiSn is at least one element selected from the group of V, Nb, and Ta. To produce a thermoelectric conversion material represented by the composition formula ((Ti _0.5 Zr _0.25 Hf _0.25 ) _1-e X _e ) NiSn.

Specifically, a thermoelectric conversion material was produced in the same manner as in (Example I-1) except that V, Nb, or Ta as X was further added in a substitution element amount e shown in Table 3 below. About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated similarly to the above, and the obtained result is put together in following Table 3. FIG.

As shown in Table 2, thermoelectrics having various compositions represented by the composition formula ((Ti _0.3 Zr _0.35 Hf _0.35 ) _1-e X _e ) NiSn, (X = V, Nb, Ta). All conversion materials were found to have good thermoelectric conversion characteristics. As shown in Table 3, the thermoelectrics of various compositions represented by the composition formula ((Ti _0.5 Zr _0.25 Hf _0.25 ) _1-e X _e ) NiSn, (X = V, Nb, Ta) Both conversion materials were also found to have good thermoelectric conversion properties.

  The temperature dependence of the dimensionless figure of merit ZT of the thermoelectric conversion material produced in (Example I-31) is shown as a curve b in the graph of FIG. The thermoelectric conversion material of (Example I-31) has a dimensionless figure of merit ZT higher than that of the thermoelectric conversion material of Example 1. This is presumably because the carrier concentration increased and the resistivity decreased due to the substitution of tetravalent Ti, Zr, and Hf with pentavalent Ta.

  Further, in the thermoelectric conversion material in which a part of Ti, Zr and Hf in the thermoelectric conversion materials produced in Examples I-2 to I-18 is substituted with at least one element selected from the group of V, Nb and Ta Similarly, good thermoelectric conversion characteristics were confirmed.

  Furthermore, a part of Ti, Zr and Hf in the thermoelectric conversion materials produced in Examples I-1 to I-18 are substituted with at least one element selected from the group consisting of Cr, Mo and W. Moreover, it was confirmed that the thermoelectric conversion characteristics are also good.

(Examples I-46 to I-53)
A part of Ni in the thermoelectric conversion material represented by the composition formula (Ti _0.3 Zr _0.35 Hf _0.35 ) NiSn prepared in Example I-1 described above was substituted with Cu, and the composition formula ( the thermoelectric conversion material represented by _{Ti 0.3 Zr 0.35 Hf 0.35) Ni} 1-f Cu f Sn was manufactured.

A thermoelectric conversion material was prepared by the same method as in Example I-1 except that Cu was further added in the amount of substitution element f shown in Table 4 below. About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated similarly to the above, and the obtained result is put together in following Table 4.

Further, a part of Ni in the thermoelectric conversion material represented by the composition formula (Ti _0.5 Zr _0.25 Hf _0.25 ) NiSn is substituted with Cu, and the composition formula (Ti _0.5 Zr _0.25 Hf _{0 .25} ) A thermoelectric conversion material represented by Ni _1-f Cu _f Sn was produced.

A thermoelectric conversion material was produced by the same method as in Example I-1 except that Cu was further added in the amount f of the substitution element shown in Table 5 below. About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated similarly to the above, and the obtained result is put together in following Table 5. FIG.

As shown in Table 4, the thermoelectric conversion materials having various compositions represented by the composition formula (Ti _0.3 Zr _0.35 Hf _0.35 ) Ni _{1 -f} Cu _f Sn are all good thermoelectric conversion characteristics. It was found to have As shown in Table 5, the thermoelectric conversion materials having various compositions represented by the composition formula (Ti _0.5 Zr _0.25 Hf _0.25 ) Ni _{1 -f} Cu _f Sn are all good thermoelectric conversion characteristics. It was found to have

  Moreover, it was confirmed that the thermoelectric conversion material in which a part of Ni in the thermoelectric conversion materials produced in Examples I-2 to I-18 was substituted with Cu also had good thermoelectric properties.

  Furthermore, thermoelectric conversion materials obtained by substituting a part of Ni in the thermoelectric conversion materials produced in Examples I-1 to I-18 with at least one element selected from the group consisting of Mn, Fe, and Co are also thermoelectric conversion materials. The conversion characteristics were confirmed to be good as well.

(Examples I-54 to I-69)
Part of Sn in the thermoelectric conversion material represented by the composition formula (Ti _0.3 Zr _0.35 Hf _0.35 ) NiSn prepared in Example I-1 is selected from the group consisting of Sb and Bi. By substituting with at least one element, a thermoelectric conversion material represented by a composition formula (Ti _0.3 Zr _0.35 Hf _0.35 ) NiSn _1-g X _g was produced.

Specifically, a thermoelectric conversion material was produced in the same manner as in Example I-1, except that Sb or Bi as X was further added at the substitution element amount g shown in Table 6 below. About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated similarly to the above, and the obtained result is put together in following Table 6. FIG.

Furthermore, a part of Sn in the thermoelectric conversion material represented by the composition formula (Ti _0.5 Zr _0.25 Hf _0.25 ) NiSn is substituted with at least one element selected from the group consisting of Sb and Bi, A thermoelectric conversion material represented by a composition formula (Ti _0.53 Zr _0.25 Hf _0.25 ) NiSn _1-g X _g was produced.

Specifically, a thermoelectric conversion material was produced in the same manner as in Example I-1, except that Sb or Bi as X was further added at the substitution element amount g shown in Table 7 below. About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated similarly to the above, and the obtained result is put together in following Table 7. FIG.

As shown in Table 6, the thermoelectric conversion materials having various compositions represented by the composition formula (Ti _0.3 Zr _0.35 Hf _0.35 ) NiSn _1-g X _g (X = Sb, Bi) Were also found to have good thermoelectric conversion characteristics. As shown in Table 7, the thermoelectric conversion materials having various compositions represented by the composition formula (Ti _0.5 Zr _0.25 Hf _0.25 ) NiSn _1-g X _g (X = Sb, Bi) Were also found to have good thermoelectric conversion characteristics.

  In addition, in the thermoelectric conversion material in which a part of Sn in the thermoelectric conversion materials produced in Examples I-2 to I-18 is substituted with at least one element selected from the group of Sb and Bi, the same is good. It was confirmed to have thermoelectric properties.

  Furthermore, a thermoelectric conversion material in which a part of Sn in the thermoelectric conversion materials produced in Examples I-1 to I-18 is substituted with at least one element selected from the group consisting of As, Ge, Pb, Ga, and In. Moreover, it was confirmed that the thermoelectric conversion characteristics are also good.

(Examples I-70 to I-93)
Formula _{(Ln d (Ti a2 Zr b2} Hf c2) 1-d) x Ni y Sn 100-x-y (Ln at least one element is Er, selected from the group consisting of Gd, and Nd, 0 ≦ a2 ≦ 1, 0 ≦ b2 ≦ 1, 0 ≦ c2 ≦ 1, a2 + b2 + c2 = 1, 035, 30 ≦ y ≦ 35) were produced by the same method as in Example (I-1) described above. . About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated similarly to the above, and the obtained result is put together in following Table 8.

As shown in Table 8, the composition formula (Ln _d (Ti _a2 Zr _b2 Hf _c2 ) _1-d ) _x Ni _y Sn _100-xy (Ln is at least selected from the group consisting of Er, Gd, and Nd) 1 type of element, 0 ≦ a2 ≦ 1, 0 ≦ b2 ≦ 1, 0 ≦ c2 ≦ 1, a2 + b2 + c2 = 1, 0d ≦ 0.3, 30 ≦ x ≦ 35, 30 ≦ y ≦ 35) These thermoelectric conversion materials were found to have good thermoelectric conversion characteristics.

(Examples I-94 to I-105)
Formula _{(Ln d (Ti a2 Zr b2} Hf c2) 1-d) x Ni y Sn 100-x-y (Ln is at least one element selected from the group consisting of Er, Gd and Nd, 0 ≦ a2 ≦ 1 , 0 ≦ b2 ≦ 1, 0 ≦ c2 ≦ 1, a2 + b2 + c2 = 1, 05, 30 ≦ y ≦ 35), a part of (TiaZrbHfc) is selected from the group of V, Nb, Ta By substituting with at least one element, a thermoelectric conversion material represented by a composition formula (Ln _d (Ti _a2 Zr _b2 Hf _c2 ) _1-d ) _x Ni _y Sn _100-xy was produced.

Specifically, V, Nb or Ta as X was further added at a blending amount e shown in Table 6 below, and a thermoelectric conversion material was produced by the same method as in (Example I-1). About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated like the above. The results for the thermoelectric conversion material containing Er as Ln are summarized in Table 9 below.

As shown in Table 9, in the composition formula (Ln _d (Ti _a2 Zr _b2 Hf _c2 ) _1-d ) _x Ni _y Sn _100-xy , Ln = Er, a2 = 0.3, b2 = 0. The thermoelectric conversion materials having various compositions represented by 35, c2 = 0.35, x = y = 33.3 have good thermoelectric conversion characteristics when V, Nb or Ta is contained as X. It was recognized that

  Further, in the above-described composition formula, good thermoelectric conversion characteristics were also confirmed in the thermoelectric conversion material containing Gd or Nd as Ln.

  Furthermore, the thermoelectric conversion material containing V, Nb, or Ta as X also had good thermoelectric properties regardless of the element contained as Ln.

(Examples I-106 to I-109)
Formula _{(Ln d (Ti a2 Zr b2} Hf c2) 1-d) x Ni y Sn 100-x-y (Ln is at least one element selected from the group consisting of Er, Gd and Nd, 0 ≦ a2 ≦ 1 in the thermoelectric conversion material represented by 0 ≦ b2 ≦ 1,0 ≦ c2 ≦ 1, a2 + b2 + c2 = 1,05,30 ≦ y ≦ 35), and substituting a part of Ni with Cu, composition formula _(Ln d ( to prepare a _{Ti a2 Zr b2 Hf c2) 1} -d) x (Ni 1-f Cu f) thermoelectric conversion material represented by _{y Sn 100-x-y.}

Specifically, Cu was further added at a blending amount f shown in Table 10 below, and a thermoelectric conversion material was produced by the same method as in Example I-1. About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated like the above. The results for the thermoelectric conversion material containing Er as Ln are summarized in Table 10 below.

As shown in Table 10, in the composition formula _{(Ln d (Ti a2 Zr b2} Hf c2) 1-d) x (Ni 1-f Cu f) thermoelectric conversion material represented by _{y Sn 100-x-y,} Ln = Er, a2 = 0.3, b2 = 0.35, c2 = 0.35, x = y = 33.3 The thermoelectric conversion materials having various compositions all have good thermoelectric conversion characteristics. It was recognized that

  Further, in the above-described composition formula, good thermoelectric conversion characteristics were also confirmed in the thermoelectric conversion material containing Gd or Nd as Ln.

  Furthermore, the thermoelectric conversion material in which a part of Ni is substituted with Mn, Fe, or Co instead of Cu also has good thermoelectric properties regardless of the element contained as Ln.

(Examples I-110 to I-117)
Formula _{(Ln d (Ti a2 Zr b2} Hf c2) 1-d) x Ni y Sn 100-x-y (Ln is at least one element selected Er, Gd, from Nd, 0 ≦ a2 ≦ 1,0 ≦ In the thermoelectric conversion material represented by b2 ≦ 1, 0 ≦ c2 ≦ 1, a2 + b2 + c2 = 1, 035), a part of Sn is substituted with at least one element selected from the group of Sb and Bi, and the composition formula (Ln _d a _{(Ti a2 Zr b2 Hf c2)} 1-d) x Ni y (Sn 1-g X g) a thermoelectric conversion material represented by _100-x-y was prepared.

Specifically, Bi or Sb as X was further added at a blending amount g shown in Table 11 below, and a thermoelectric conversion material was produced in the same manner as in Example I-1. About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated like the above. The results for the thermoelectric conversion material containing Er as Ln are summarized in Table 11 below.

As shown in Table 11, in the composition formula _{(Ln d (Ti a2 Zr b2} Hf c2) 1-d) x Ni y (Sn 1-g X g) a thermoelectric conversion material represented by _100-x-y, Ln = Er, (X = Sb, Bi), a2 = 0.3, b2 = 0.35, c2 = 0.35, x = y = 33.3 It was found to have good thermoelectric conversion characteristics.

  Moreover, the thermoelectric conversion material in which Gd or Nd is contained as Ln in the above composition was confirmed to have good thermoelectric conversion characteristics.

  Furthermore, the thermoelectric conversion material containing As, Ge, Pb, Ga, or In as X also had good thermoelectric properties regardless of the element contained as Ln.

(Example I-118)
A thermoelectric conversion element as shown in FIG. 3 was produced using CeCoFe ₃ Sb ₁₂ as the p-type thermoelectric conversion material and using the thermoelectric conversion material of Example I-30 as the n-type thermoelectric conversion material.

Each p-type and n-type thermoelectric conversion material is cut out to 3.0 mm square and 10.0 mm in height, each of 60 pieces, all 120 pieces are arranged alternately in p and n so that it becomes 10 columns x 12 rows, 120 pieces in total Were connected in series with a silver electrode plate. Furthermore, an aluminum nitride sintered body plate was bonded to the other surface of the silver electrode plate, that is, the surface opposite to the surface where the thermoelectric conversion element was bonded, and a current lead wire was bonded to the termination electrode to produce a thermoelectric conversion element.

  About the obtained thermoelectric conversion element, the high temperature side was 570 degreeC and the low temperature side was 55 degreeC, and the electric power generation characteristic was evaluated. The internal resistance under this temperature condition was 2.22Ω. As a load, the power generation characteristics were measured under matching load conditions in which a load of 2.22Ω which is the same as the internal resistance of the thermoelectric conversion module was connected. As a result, the generated voltage was 5.0 V, a current of 3.24 A flowed, and a power of 16.2 W was obtained, confirming power generation.

Example II
In this example, a p-type thermoelectric conversion material will be described.

Example II-1
Y having a purity of 99.9%, Er having a purity of 99.9%, Ni having a purity of 99.99%, and Sb having a purity of 99.99% were prepared as raw materials, which were represented by the composition formula Y _0.5 Er _0.5 Weighed to become NiSb.

The weighed raw materials were mixed, loaded into a water-cooled copper hearth in an arc furnace, and evacuated to a vacuum degree of 2 × 10 ⁻³ Pa. Thereafter, high-purity Ar having a purity of 99.999% was introduced to -0.04 MPa, and arc-dissolved in a reduced pressure Ar atmosphere. After melting, the metal lump obtained by quenching with a water-cooled copper hearth was vacuum-sealed in a quartz tube at a high vacuum of 10 ⁻⁴ Pa or less and heat-treated at 1073 K for 72 hours.

  The obtained metal lump was pulverized and molded at a pressure of 50 MPa using a mold having an inner diameter of 20 mm. The obtained molded body was filled in a carbon mold having an inner diameter of 20 mm, and pressure sintered at 80 MPa and 1200 ° C. for 1 hour in an Ar atmosphere to obtain a disk-shaped sintered body having a diameter of 20 mm.

  When this sintered body was examined by a powder X-ray diffraction method, it was confirmed that the sintered body was mainly composed of a phase having an MgAgAs type crystal structure.

  Moreover, when the composition of the obtained sintered body was analyzed by ICP emission spectroscopy, it was confirmed that the composition was almost a predetermined composition.

  The obtained sintered body was evaluated for thermoelectric properties by the following method.

(1) The resistivity sintered body was cut into 2 mm × 0.5 mm × 18 mm, electrodes were formed, and measurement was performed by a direct current four-terminal method.

(2) Seebeck coefficient The sintered body was cut into 4 mm × 1 mm × 0.5 mm, a temperature difference of 2 ° C. was applied to both ends thereof, the electromotive force was measured, and the Seebeck coefficient was obtained.

(3) The thermal conductivity sintered body was cut into φ10 mm × t2.0 mm, and the thermal diffusivity was measured by a laser flash method. Separately, specific heat was determined by DSC measurement. The density of the sintered body was obtained by the Archimedes method, and the thermal conductivity was calculated from these.

  Using the resistivity, Seebeck coefficient, and thermal conductivity values obtained in this way, the dimensionless figure of merit ZT was obtained by the above formula (1). The resistivity, Seebeck coefficient, lattice thermal conductivity, and dimensionless figure of merit at 300K and 700K are as follows.

300K: Resistivity 47.5 × 10 ⁻³ Ωcm
Seebeck coefficient 351μV / K
Lattice thermal conductivity 3.18W / mK
ZT = 0.02
700K: Resistivity 2.82 × 10 ⁻³ Ωcm
Seebeck coefficient 311μV / K
Lattice thermal conductivity 1.79 W / mK
ZT = 1.04
The temperature dependence of the dimensionless figure of merit ZT of the thermoelectric conversion material produced in Example II-1 is shown as a curve d in FIG. As shown in the figure, a dimensionless figure of merit ZT of about 1.05 is obtained at the maximum.

As already explained, the maximum value of the dimensionless figure of merit ZT for existing thermoelectric conversion materials is 1.0 for Bi-Te based materials. In this example, since the composition was Y _0.5 Er _0.5 NiSb, a high-performance thermoelectric conversion material exceeding this was obtained. In this example, since the B element of the half-Heusler compound ABX is Ni, the power factor can be increased.

(Comparative Example II-1)
Y having a purity of 99.9%, Er having a purity of 99.9%, Pd having a purity of 99.99%, and Sb having a purity of 99.99% are prepared as raw materials so that the composition formula is Y0.5Er0.5PdSn. Weighed out. Using the weighed raw material powder, a sintered body was produced by the same method as in Example II-1, and the thermoelectric characteristics were evaluated by the same method. The resistivity, Seebeck coefficient, lattice thermal conductivity, and dimensionless figure of merit at 300K and 700K are as follows.

300K: Resistivity 29.0 × 10 −3 Ωcm
Seebeck coefficient 155μV / K
Lattice thermal conductivity 2.97W / mK
ZT = 0.00
700K: resistivity 2.1 × 10 −3 Ωcm
Seebeck coefficient 190μV / K
Lattice thermal conductivity 1.29 W / mK
ZT = 0.57
In this comparative example, since the element B of the half-Heusler compound ABX is Pd, a high-performance thermoelectric conversion material exceeding 1.0 of the Bi—Te material could not be obtained.

(Examples II-2 to II-31)
Thermoelectric conversion of various compositions represented by the composition formula (Ln3 _S Ln4 _1-S ) NiSb (Ln3, Ln4 are different elements selected from Y, Gd, Tb, Dy, Ho, Er, Yb) The material was produced by the same method as in Example II-1. About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated similarly to the above, and the obtained result is put together in following Table 12. In addition, it shows in Table 12 similarly about Example II-1.

As shown in Table 12, the compositional formula (Ln3 _S Ln4 _1-S ) NiSb (Ln3, Ln4 are various elements selected from Y, Gd, Tb, Dy, Ho, Er, Yb) It was confirmed that all the thermoelectric conversion materials having the composition described above have good thermoelectric conversion characteristics.

(Examples II-32 to II-51)
A part of Y and Er in the thermoelectric conversion material represented by the composition formula Y0.5Er0.5NiSb prepared in Example II-1 described above is at least one selected from the group of Be, Mg, Ca, Sr, and Ba. A thermoelectric conversion material represented by a composition formula (Y _0.5 Er _0.5 ) _1-a X _a NiSb (X = Be, Mg, Ca, Sr, Ba) was substituted with an element in Example II-1. It was produced by the same method.

About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated, and the obtained result is shown in following Table 13.

As shown in Table 13, the thermoelectric conversion materials represented by the composition formula (Y _0.5 Er _0.5 ) _1-a X _a NiSb (X = Be, Mg, Ca, Sr, Ba) are all good. It was recognized that it has a good thermoelectric conversion characteristic. That is, in the composition in which a part of Ln3 and Ln4 of the thermoelectric conversion materials of Examples II-2 to II-31 is substituted with at least one element selected from the group of Be, Mg, Ca, Sr, and Ba. It was confirmed to have good thermoelectric properties.

(Examples II-52 to II-63)
A part of Ni in the thermoelectric conversion material represented by the composition formula Y _0.5 Er _0.5 NiSb is substituted with at least one element selected from the group of Co, Rh, Ir, and the composition formula (Y _0.5 A thermoelectric conversion material represented by Er _0.5 ) Ni _1-b Z _b Sb (Z = Co, Rh, Ir) was produced in the same manner as in Example II-1.

About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated, and the obtained result is shown in following Table 14.

As shown in Table 14, all the thermoelectric conversion materials represented by the composition formula (Y _0.5 Er _0.5 ) Ni1-bZbSb (Z = Co, Rh, Ir) have good thermoelectric conversion characteristics. It was recognized that That is, even in a composition in which a part of Ni of the thermoelectric conversion material of Examples II-2 to II-31 is substituted with at least one element selected from the group of Co, Rh, and Ir, good thermoelectric characteristics are similarly obtained. It was confirmed to have.

  The temperature dependence of the dimensionless figure of merit ZT of the thermoelectric conversion material produced in Example II-53 is shown as a curve e in the graph of FIG. The thermoelectric conversion material of Example II-53 has a dimensionless figure of merit ZT higher than the thermoelectric conversion material of Example II-1. This is presumably because the carrier concentration increased and the resistivity decreased because the 10-valent Ni was replaced with the 9-valent Co.

(Examples II-64 to II-79)
A part of Sb in the thermoelectric conversion material represented by the composition formula Y _0.5 Er _0.5 NiSb is substituted with at least one element selected from the group consisting of Si, Ge, Sn, and Pb. _A thermoelectric conversion material represented by _0.5 Er _0.5 ) NiSb _1-c T _c (T = Si, Ge, Sn, Pb) was produced in the same manner as in Example II-1.

About each thermoelectric conversion material, the characteristic in 300K and 700K was evaluated, and the obtained result is shown in following Table 15.

As shown in Table 15, the thermoelectric conversion material represented by the composition formula (Y _0.5 Er _0.5 ) NiSb _1-c T _c (T = Si, Ge, Sn, Pb) is good. It was found to have thermoelectric conversion properties. Even in the composition in which a part of Sb of the thermoelectric conversion materials of Examples II-2 to II-31 was substituted with at least one element selected from the group of Si, Ge, Sn, and Pb, good thermoelectric characteristics were similarly obtained. It was confirmed to have.

(Example II-80)
The thermoelectric conversion material of Example II-53 is used as the p-type thermoelectric conversion material, and the composition formula (Ti _0.3 Zr _0.35 Hf _0.35 ) _0.99 Ta _0.1 is used as the n-type thermoelectric conversion material. A thermoelectric conversion element as shown in FIG. 3 was produced using a thermoelectric conversion material having a composition represented by NiSn. This n-type thermoelectric conversion material corresponds to Example I-31.

  Each p-type and n-type thermoelectric conversion material is cut out to 3.0 mm square and 10.0 mm in height, each of 60 pieces, all 120 pieces are arranged alternately in p and n so that it becomes 10 columns x 12 rows, 120 pieces in total Were connected in series with a SUS410 electrode plate. Furthermore, an aluminum nitride sintered body plate was bonded to the other surface of the silver electrode plate, that is, the surface opposite to the surface where the thermoelectric conversion element was bonded, and a current lead wire was bonded to the termination electrode to produce a thermoelectric conversion element.

  About the obtained thermoelectric conversion element, the high temperature side was 570 degreeC and the low temperature side was 55 degreeC, and the electric power generation characteristic was evaluated. The internal resistance under this temperature condition was 1.51Ω. The power generation characteristics were measured under matched load conditions in which a load of 1.51Ω, which is the same as the internal resistance of the thermoelectric conversion module, was connected as a load. As a result, the generated voltage was 5.68 V, a current of 3.76 A flows, electric power of 21.3 W was obtained, and it was confirmed that the thermal battery had good power generation characteristics.

(Example II-81)
A thermoelectric conversion element was produced in the same manner as in Example II-80 described above except that the n-type thermoelectric conversion material was changed to Ce _0.2 (Co _0.97 Pd _0.03 ) ₄ Sb ₁₂ . The n-type thermoelectric conversion material used here is a conventional material and does not have a half-Whistler compound as a main phase.

  About the obtained thermoelectric conversion element, the electric power generation characteristic was evaluated on the same conditions as the above-mentioned. The internal resistance under this temperature condition was 1.23Ω. The power generation characteristics were measured under matched load conditions in which a load of 1.23Ω, which is the same as the internal resistance of the thermoelectric conversion module, was connected as a load. As a result, the generated voltage was 4.87 V, a current of 3.96 A flowed, 19.3 W of power was obtained, and power generation was confirmed.

(Conventional example)
A thermoelectric conversion element was produced in the same manner as in Example II-81 described above except that the p-type thermoelectric conversion material was changed to CeCoFe ₃ Sb ₁₂ . The p-type thermoelectric conversion material used here is a conventional material and does not have a half-Whistler compound as a main phase.

  About the obtained thermoelectric conversion element, the electric power generation characteristic was evaluated on the same conditions as the above-mentioned. The internal resistance under this temperature condition was 1.43Ω. As a load, power generation characteristics were measured under matching load conditions in which a load of 1.43Ω which is the same as the internal resistance of the thermoelectric conversion module was connected. As a result, the generated voltage was 4.80 V, and a current of 3.37 A flowed. The power remained at 16.1W.

The schematic diagram showing the structure of half-Heusler ABX. The schematic diagram showing the thermoelectric conversion element concerning one Embodiment of this invention. The schematic diagram showing the thermoelectric conversion element concerning other embodiment of this invention. The schematic diagram showing the thermoelectric conversion element concerning other embodiment of this invention. The schematic diagram showing the thermoelectric conversion element concerning other embodiment of this invention. The graph showing the temperature dependence of the dimensionless figure of merit of the thermoelectric conversion material concerning one embodiment of the present invention. The graph showing the temperature dependence of the dimensionless figure of merit of the thermoelectric conversion material concerning other embodiments of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... A element, 2 ... B element, 3 ... X element, 4 ... Hole, 8 ... p-type thermoelectric conversion material, 9 ... n-type thermoelectric conversion material, 10, 19 ... Electrode, 11 ... Insulating substrate, 14 ... Hall, 15 ... electron, 16 ... thermoelectric conversion element, 20 ... load, 21 ... current, 22 ... DC power supply, 23 ... current.

Claims (10)

A method for producing a thermoelectric conversion material containing a phase having an MgAgAs crystal structure,
A method for producing a thermoelectric conversion material comprising a step of integrally forming an alloy powder having a composition represented by the following composition formula (2) by a sintering method.
_{(Ln d (Ti a2 Zr b2} Hf c2) 1-d) x Ni y Sn 100-xy composition formula (2)
(In the composition formula (2), Ln is at least one selected from the group consisting of Y and rare earth elements, 0 ≦ a2 ≦ 1, 0 ≦ b2 ≦ 1, 0 ≦ c2 ≦ 1, a2 + b2 + c2 = 1, 0 <D ≦ 0.3, 30 ≦ x ≦ 35, 30 ≦ y ≦ 35.) A part of Ti, Zr, and Hf in the composition formula (2) is substituted with at least one element selected from the group consisting of V, Nb, Ta, Cr, Mo, and W. Item 2. A method for producing a thermoelectric conversion material according to Item 1. The part of Ni in the composition formula (2) is substituted with at least one element selected from the group consisting of Mn, Fe, Co, and Cu. The method for producing a thermoelectric conversion material according to Item. A part of Sn in the composition formula (2) is substituted with at least one element selected from the group consisting of As, Sb, Bi, Ge, Pb, Ga and In. 4. The thermoelectric conversion material according to any one of 3 above. A method for producing a thermoelectric conversion material containing a phase having an MgAgAs crystal structure,
A method for producing a thermoelectric conversion material comprising a step of integrally forming an alloy powder having a composition represented by the following composition formula (3) by a sintering method.
Ln1 _X Ni _Y Sb _100-XY composition formula (3)
(In the composition formula (3), Ln1 is at least one selected from Sc, Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U, and 30 ≦ X ≦ 35. 30 ≦ Y ≦ 35.) A method for producing a thermoelectric conversion material containing a phase having an MgAgAs crystal structure,
A method for producing a thermoelectric conversion material comprising a step of integrally forming an alloy powder having a composition represented by the following composition formula (4) by a sintering method.
_{(Ln2 p Y 1-p)} X Ni Y Sb 100-XY composition formula (4)
(Ln2 is at least one selected from Sc, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, U, and 0.001 ≦ P ≦ 0.999, 30 ≦ X ≦ 35. 30 ≦ Y ≦ 35.) A part of Ln1 in the composition formula (3) or a part of Ln2 in the composition formula (4) is Ti, Zr, Hf, La, Ce, Pr, Nd, Sm, Eu, Be, Mg, Ca, Sr, The method for producing a thermoelectric conversion material according to claim 5 or 6, wherein the thermoelectric conversion material is substituted with at least one selected from the group consisting of Ba. A part of Ni in the composition formula (3) or (4) is from V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn. The method for producing a thermoelectric conversion material according to claim 5, wherein the thermoelectric conversion material is substituted with at least one selected from the group consisting of: A part of Sb in the composition formula (3) or (4) is substituted with at least one selected from the group consisting of Al, Si, Ga, Ge, As, In, Sn, Pb, and Bi. The thermoelectric conversion material manufacturing method according to any one of claims 5 to 8. It includes a p-type thermoelectric conversion material and an n-type thermoelectric conversion material alternately connected in series, and at least one of the p-type thermoelectric conversion material and the n-type thermoelectric conversion material is in any one of claims 1 to 9. The thermoelectric conversion element characterized by including the thermoelectric conversion material manufactured by the thermoelectric conversion material manufacturing method of description.

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