JP2008227321A - Thermoelectric conversion material and thermoelectric conversion module using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric conversion material which has a large nondirectional performance index ZT as a material containing a half-Heusler compound as a main phase while maintaining a high Seebeck coefficient and low resistivity, and a thermoelectric conversion module using the same. <P>SOLUTION: The thermoelectric conversion material is formed which is represented as composition formula (Ti<SB>p</SB>Zr<SB>Q</SB>Hf<SB>R</SB>)<SB>x</SB>Ni<SB>Y</SB>(Sn<SB>1-S</SB>Sb<SB>S</SB>)<SB>1-X-Y</SB>(P+Q+R=1, 0.3≤P≤0.7, 0<Q<1, 0<R<1, 0.003<S<0.01, 0.30≤X≤0.35, and 0.30≤Y≤0.35) and includes as a main phase the phase that an MgAgAs type crystal structure has, and the thermoelectric conversion module is formed using the thermoelectric conversion material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thermoelectric conversion material and a thermoelectric conversion module using the same.

  In recent years, interest in the thermoelectric conversion module using the Peltier effect, which is a chlorofluorocarbon-free cooling device, has increased due to the heightened awareness of global environmental problems. Similarly, in order to reduce carbon dioxide emissions, there is an increasing interest in thermoelectric conversion devices using the Seebeck effect that provide power generation systems using unused waste heat energy. Each of these thermoelectric conversion devices includes a thermoelectric conversion module in which p-type thermoelectric conversion materials and n-type thermoelectric conversion materials are alternately connected in series.

  A thermoelectric conversion module using the Peltier effect or Seebeck effect is generally formed by alternately connecting a p-type material containing a p-type thermoelectric conversion material and an n-type material containing an n-type thermoelectric conversion material in series. ing. Currently, many thermoelectric conversion materials used near room temperature use Se-containing Bi-Te single crystals or polycrystals because of their high efficiency. Moreover, Pb-Te system is used for the thermoelectric conversion material used at a temperature higher than room temperature because of its high efficiency.

  However, Se (selenium) and Pb (lead) used in these thermoelectric conversion modules are toxic and harmful to the human body and are not preferable from the viewpoint of global environmental problems. Furthermore, Te (tellurium) has very little reserves on the earth and has difficulty in supply as a resource. For this reason, harmless materials that replace Bi-Te and Pb-Te materials have been studied. In view of such a point, a material (hereinafter referred to as a half-Heusler material) having a main phase of a phase having an MgAgAs-type crystal structure (hereinafter referred to as an MgAgAs-type crystal phase) has attracted attention.

  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).

On the other hand, there is a performance index Z as a parameter indicating the conversion efficiency of the thermoelectric conversion material, which is expressed by the following formula (1).
Z = α ² / (ρ · κ) (1)
In the above formula (1), α is the Seebeck coefficient of the thermoelectric conversion material, ρ is the electrical resistivity of the thermoelectric conversion material, and κ is the thermal conductivity of the thermoelectric conversion material. Α ² / ρ in Equation (1) is called a power factor.

  Z has the dimension of the reciprocal of temperature, and when this figure of merit Z is multiplied by the absolute temperature T, 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 thermoelectric conversion efficiency increases as the ZT increases. As can be seen from the above equation (1), in order to realize a thermoelectric conversion material having a high ZT value, a thermoelectric conversion material having a higher Seebeck coefficient α, a lower electrical resistivity ρ, and a lower thermal conductivity κ. Is required.

Among the half-Heusler materials described above, (Ti, Hf, Zr) -Ni-Sn-based materials have high thermoelectric properties and are promising as thermoelectric conversion materials. For example, in (Ti _0.50 Zr _0.25 Hf _0.25 ) Ni (Sn _0.990 Sb _0.010 ) in which a part of Sn is replaced with Sb, the dimensionless figure of merit is reported as 1.22. This exceeds the dimensionless figure of merit 1.0 of Bi-Te system (Patent Document 1). However, development of a thermoelectric conversion material having a larger ZT is desired.
J. et al. Phys. : Condens. Matter 11, 1697-1709 (1999) JP 2004-356607 A

  The present invention relates to a (Ti, Hf, Zr) -Ni-Sn half-Heusler material, a thermoelectric conversion material having a dimensionless figure of merit ZT larger than that of a conventional (Ti, Hf, Zr) -Ni-Sn half-Heusler material, and It is providing the thermoelectric conversion module using this.

The thermoelectric conversion material according to one embodiment of the present invention is
Composition formula (Ti _P Zr _Q Hf _R ) _X Ni _Y (Sn _1-S Sb _S ) _1-XY (P + Q + R = 1, 0.3 ≦ P ≦ 0.7, 0 <Q <1, 0 <R <1 0.003 <S <0.01, 0.30 ≦ X ≦ 0.35, 0.30 ≦ Y ≦ 0.35), and a phase having an MgAgAs type crystal structure (MgAgAs type crystal phase) is a main phase.

  The inventors of the present invention have intensively studied to achieve the above object. As a result, Sb is added to the (Ti, Hf, Zr) -Ni-Sn half-Heusler material, and the content is set to a specific range, that is, a range exceeding 0.003 atomic% and not exceeding 0.01 atomic%. In addition, by adjusting the content of other constituent elements so that the entire crystal structure becomes an MgAgAs type crystal phase, it exhibits a very high Seebeck coefficient, and as a result, an extremely high dimensionless figure of merit ZT is obtained. It has been found. Therefore, a thermoelectric conversion material having a large dimensionless figure of merit ZT and a thermoelectric conversion module using the same can be provided by configuring the thermoelectric conversion material from such a material.

  The thermoelectric conversion module according to one aspect of the present invention is characterized in that the thermoelectric conversion material is composed of a p-type thermoelectric conversion material and an n-type thermoelectric conversion material. Specifically, the first electrode; A p-type thermoelectric conversion material having one end connected to the first electrode, a second electrode connected to the other end of the p-type thermoelectric conversion material, and an n-type having one end connected to the second electrode A thermoelectric conversion module comprising a thermoelectric conversion material and a third electrode connected to the other end of the n-type thermoelectric conversion material, wherein at least one of the p-type thermoelectric conversion material and the n-type thermoelectric conversion material is the thermoelectric conversion material. It is characterized by comprising a conversion material.

  As described above, according to the present invention, the (Ti, Hf, Zr) -Ni-Sn half-Heusler material has a dimensionless figure of merit ZT larger than that of the conventional (Ti, Hf, Zr) -Ni-Sn half-Heusler material. A thermoelectric conversion material and a thermoelectric conversion module using the same can be provided.

  Hereinafter, modes for carrying out the present invention will be described.

(Thermoelectric conversion material)
The thermoelectric conversion material according to an embodiment of the present invention is:
Composition formula: (Ti _P Zr _Q Hf _R ) _X Ni _Y (Sn _1-S Sb _S ) _1-XY (2)
(Where P + Q + R = 1, 0.3 ≦ P ≦ 0.7, 0 <Q <1, 0 <R <1, 0.003 <S <0.01, 0.30 ≦ X ≦ 0.35, 0.30 ≦ Y ≦ 0.35) The main phase is a phase that is expressed and has an MgAgAs type crystal structure (MgAgAs type crystal phase).

  FIG. 1 shows the crystal structure of a half-Heusler compound ABX having a cubic system and MgAgAs type structure. In FIG. 1, reference numerals 1, 2, and 3 represent an A site element, a B site element, and an X site element, respectively, and reference numeral 4 represents a vacancy site. The MgAgAs type crystal structure has a crystal structure in which B site atoms are inserted into a NaCl type crystal lattice formed by A site atoms and X site atoms. Ni-based half-Heusler compounds using Ni as the B-site atom need to adjust the number of valence electrons per atom to a value close to 6 in order to improve thermoelectric characteristics by increasing the Seebeck coefficient. Ni has 10 valence electrons. Therefore, Ti, Zr, and Hf with 4 valence electrons are used for the A site atom. Further, Sn is used as the X site atom.

  Next, a thermoelectric conversion material (Ni-based half-Heusler material) according to an embodiment of the present invention will be described in detail. In the thermoelectric conversion material of this embodiment, the MgAgAs type crystal phase (half-Heusler phase) is a phase that bears thermoelectric properties, and this is the main phase. Here, the main phase refers to a phase having the largest volume occupancy with respect to the total amount of all the crystal phases and amorphous phases constituting the thermoelectric conversion material. When the volume content of the half-Heusler phase is 50% or more, high thermoelectric characteristics can be obtained, and more preferably 90% or more.

  The volume occupancy is obtained by, for example, mirror-polishing the surface of the thermoelectric conversion material, then using an electron microscope, identifying the half-Heusler phase using electron diffraction and energy dispersive X-ray analysis, and determining from the area occupancy. Although it is strictly known, for convenience, the sintered body is pulverized and subjected to powder X-ray diffraction to identify the generated phase, and the diffraction line intensity derived from the half-Heusler phase is larger than the diffraction line intensity derived from other crystal phases. Can be determined.

  In realizing a Ni-based half-Heusler material having a half-Heusler phase as a main phase, the values of X and Y in the formula (2) are both in the range of 0.30 to 0.35. In equation (2), if the total amount of (Ti, Zr, Hf) represented by X and the amount of Ni represented by Y deviate from the above ranges, the amount of precipitation of phases other than the half-Heusler phase increases, and the thermoelectric In particular, the Seebeck coefficient α is deteriorated. More preferably, the values of X and Y are in the range of 0.33 to 0.34.

  In order to increase the thermoelectric conversion characteristics of Ni-based half-Heusler materials, it is important to optimize the ratio of Ti, Zr, and Hf. In the thermoelectric conversion material of this embodiment, the value of P in the expression (2) representing the Ti amount is in the range of 0.3 to 0.7 (0.3 ≦ P ≦ 0.7). Within this range, the thermoelectric properties of the Ni-based half-Heusler material, in particular, the Seebeck coefficient α increases, and the thermal conductivity κ decreases. When the Ti amount P is smaller than 0.3, or when the Ti amount P is larger than 0.7, the Seebeck coefficient α is decreased, and the dimensionless figure of merit ZT is decreased.

  Further, the Zr content and the Hf content must be such that the content ratios Q and R satisfy 0 <Q <1, 0 <R <1, respectively, preferably 0.1 ≦ Q ≦ 0.6 and 0.1 ≦ R ≦. 0.6.

  In order to increase the thermoelectric conversion characteristics of the Ni-based half-Heusler material, it is important to replace a part of Sn occupying the X site with Sb in FIG. In the thermoelectric conversion material of this embodiment, the value of S in the equation (2) representing the Sb amount is in a range exceeding 0.003 and not exceeding 0.010 (0.003 <S <0.010). This is due to the following reason.

The composition of a Ni-based half-Heusler material in which a part of Sn is not substituted with Sb is represented by the following formula.
Composition formula: (Ti _P Zr _Q Hf _R ) _X Ni _Y Sn _1-XY (3)
(Where P + Q + R = 1, 0 ≦ P ≦ 1, 0 ≦ Q ≦ 1, 0 ≦ R ≦ 1, 0.30 ≦ X ≦ 0.35, 0.30 ≦ Y ≦ 0.35)

  In the Ni-based half-Heusler material in which part of Sn represented by the formula (3) is not substituted with Sb, a band gap exists between the valence band and the conduction band in the vicinity of the Fermi surface. Therefore, the resistivity ρ is large, and the dimensionless figure of merit ZT is not so large as can be seen from the equation (1). As described above, the valence of Sn is tetravalent. On the other hand, the valence of Sb is pentavalent. When a part of Sn is substituted with Sb as represented by the formula (2), conductive carriers are generated due to substitution with elements having different valences, and the resistivity is lowered. The resistivity decreases as S increases in equation (2).

However, the carrier concentration and the Seebeck coefficient α have the relationship of equation (4).
Z = (k _B / e) (A + ln2 (2 pm*k _B T) ^1.5 / h ³ n) (4)
Here, k _B, e, A, m *, T, h, and n are Boltzmann constant, electron charge, scattering term, effective mass, temperature, Planck constant, and carrier concentration, respectively. As can be seen from the equation (4), the Seebeck coefficient α decreases as the carrier concentration n increases.

A value obtained by dividing the square of the Seebeck coefficient α by the resistivity is referred to as a power factor (hereinafter referred to as PF). Equation (1) can be written as follows.
Z = PF / κ (5)

As the carrier concentration n increases, both the resistivity ρ and the Seebeck coefficient α decrease. However, since the dependence of ρ and α on n is not linear, the power factor has a maximum value at a certain carrier concentration. As a result of the study by the present inventors, in the formula (2), the value of S is within a range exceeding 0.003 and not exceeding 0.010 (0.003 <S <0.010), which is a large power factor compared with the conventional Ni-based half-Heusler material. It has been found that a thermoelectric conversion material having a dimensionless figure of merit can be obtained as compared with a conventional Ni-based half-Heusler material. As an example, FIG. 2 shows the Sb amount S dependence of the dimensionless figure of merit ZT of (Ti _0.4 Zr _0.3 Hf _0.3 ) Ni (Sn _{1 -S} Sb _S ).

  As is clear from FIG. 2 and the like, the Sb amount is preferably set so that the content ratio S satisfies 0.004 ≦ S ≦ 0.008.

(Method for producing thermoelectric conversion material)
The thermoelectric conversion material of the present invention can be produced, for example, by the following method.
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.

  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 sintered by an atmospheric pressure sintering method, a hot press sintering method, an SPS method, or the like. From the viewpoint of preventing oxidation of the alloy, the sintering 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 sintered compact into a desired dimension. The shape and dimensions of the thermoelectric conversion material according to the embodiment of the present invention can be appropriately selected. 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). .

(Thermoelectric conversion module)
Next, a thermoelectric conversion module according to an embodiment of the present invention will be described. In the thermoelectric conversion module, the above-described thermoelectric conversion material is used as at least one of a p-type thermoelectric conversion material and an n-type thermoelectric conversion material.

  FIG. 3 is a schematic cross-sectional view for explaining the power generation principle of the thermoelectric conversion module. In the thermoelectric conversion module shown in FIG. 3, 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. 3, 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.

  Although not shown in particular, even when the positions of the electrodes 10a and 10b and the electrode 10c are switched, the insulating substrate 11a is set to a high temperature, and the insulating substrate 11b is set to a low temperature, the same movement of holes and electrons is performed. And a potential difference is generated between the electrodes 10a and 10b.

  FIG. 4 is a schematic configuration diagram illustrating an example of a thermoelectric conversion module according to an embodiment of the present invention. As shown in FIG. 4, in the thermoelectric conversion module 16 of this embodiment, a plurality of p-type thermoelectric conversion materials 8 and n-type thermoelectric conversion materials 9 are alternately connected in series, and the thermoelectric conversion module as shown in FIG. It has a structure that includes multiple units. In this case, as is apparent from FIG. 4, the electrodes 10a and 10b have a structure shared by adjacent units.

  The thermoelectric conversion module 16 shown in FIG. 4 has a configuration in which units as shown in FIG. 3 are connected in series. Therefore, the power generation amount from the thermoelectric conversion module 16 is generated by the unit shown in FIG. The power generation amount is multiplied by the number of units. Therefore, a higher voltage than that of the structure shown in FIG.

(Application of thermoelectric conversion module)
The above-described thermoelectric conversion module 16 can be applied to a thermal battery. FIG. 5 is a cross-sectional configuration diagram schematically illustrating an example of the thermal battery. As shown in FIG. 5, when the upper side of the thermoelectric conversion module 16 is set to a low temperature and the lower side is set to a high temperature, a potential difference is generated between the termination electrodes 19 a and 19 b of the thermoelectric conversion module 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.

  In addition, the thermoelectric conversion module mentioned above can also be used not only for the electric power generation use which converts heat into electric power, but for the heating or cooling use which converts electricity into heat. FIG. 6 is a cross-sectional configuration diagram illustrating an example of a heating / cooling apparatus using the thermoelectric conversion module. As shown in the figure, a DC current 23 is passed in the direction of the arrow in the figure using a DC power supply 22 to the termination electrode 19 of the thermoelectric conversion module 16. As a result, heat dissipation occurs on the upper side of the thermoelectric conversion module 16, and heat absorption occurs on the lower side. Accordingly, the object to be processed can be heated by arranging the object to be processed on the heat radiation side. Or by arrange | positioning a to-be-processed object to the heat absorption side, it can cool by taking away heat from a to-be-processed object.

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

(Example 1)
99.9% purity Ti, 99.9% purity Zr, 99.9% purity Hf, 99.99% purity Ni, and 99.99% purity Sn are prepared as raw materials, and this is represented by the composition formula (Ti _0.4 Zr _0.3 Hf _0.3 ) Ni ( Sn _0.994 Sb _0.006 ). 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 99.99% was introduced to -40 kPa, and arc-dissolved in a reduced pressure Ar atmosphere.

  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, only diffraction lines mainly derived from the MgAgAs type crystal phase (half-Heusler phase) were observed. After the surface of this sintered body is mirror-polished, the volume occupancy of the half-Heusler phase is 99% or more as a result of obtaining the area occupancy using electron diffraction and energy dispersive X-ray analysis using an electron microscope. there were.

  Further, when the composition of the obtained sintered body was analyzed by ICP emission spectroscopy, it was confirmed to be a predetermined composition. The obtained sintered body was evaluated for thermoelectric properties by the following method.

(1) resistivity ρ
The sintered body was cut into 1 mm × 0.5 mm × 18 mm, electrodes were formed, and measurement was performed by a direct current four-terminal method.
(2) Seebeck coefficient α
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 α was determined.
(3) Thermal conductivity κ
The sintered body was cut into φ10 mm × t2.0 mm, and the thermal diffusivity was measured by a laser flash method. Separately, the specific heat was obtained by DSC measurement. The density of the sintered body was determined by the Archimedes method, and the thermal conductivity κ was calculated from these results.

Using the values of resistivity ρ, Seebeck coefficient α, and thermal conductivity κ thus obtained, the dimensionless figure of merit ZT was obtained by the above equation (1). The resistivity ρ, Seebeck coefficient α, lattice thermal conductivity κ, and dimensionless figure of merit ZT at 293K and 713K are as follows.
293K: Resistivity 1.08 × 10 ⁻³ Ωcm
Seebeck coefficient -216μV / K
Thermal conductivity 3.28W / mK
ZT = 0.38
713K: Resistivity 1.25 × 10 ^-3 Ωcm
Seebeck coefficient -291μV / K
Thermal conductivity 3.17W / mK
ZT = 1.52

  As described above, the dimensionless figure of merit ZT of 1.52 at the maximum was obtained for the thermoelectric conversion material produced in Example 1. As already explained, the maximum value of the dimensionless figure of merit ZT for the existing Ni-based half-Heusler material is 1.22. In this example, a high-performance thermoelectric conversion material significantly exceeding this was obtained.

(Comparative Example 1)
99.9% Ti, 99.9% pure Zr, 99.9% pure Hf, purity of 99.99% Ni, 99.99% purity of Sn was prepared as a raw material, which composition formula _{(Ti 0.4 Zr 0.3 Hf 0.3)} Ni (Sn _0.990 Sb _0.010 ). Using the weighed raw material powder, a sintered body was produced in the same manner as in Example 1. When this sintered body was examined by a powder X-ray diffraction method, only diffraction lines mainly derived from the MgAgAs type crystal phase were observed. Further, when the composition of the obtained sintered body was analyzed by ICP emission spectroscopy, it was confirmed to be a predetermined composition. A dimensionless figure of merit was determined from the resistivity ρ, Seebeck coefficient α, and thermal conductivity κ at 293K and 713K in the same manner as in Example 1.

293K: Resistivity 0.57 × 10 ⁻³ Ωcm
Seebeck coefficient -150μV / K
Thermal conductivity 4.20W / mK
ZT = 0.28
713K: Resistivity 0.96 × 10 ^-3 Ωcm
Seebeck coefficient -230μV / K
Thermal conductivity 3.30W / mK
ZT = 1.19
Thus, it can be seen that the maximum value of the dimensionless figure of merit ZT of the thermoelectric conversion material produced in Comparative Example 1 remains at 1.19.

(Examples 2-60, Comparative Examples 2-44)
Composition formula _{(Ti P Zr Q Hf R)} Ni (Sn 1-S Sb S) thermoelectric conversion material of various composition represented by, was prepared by the same manner as in Example 1 above. As a result of examining these sintered bodies by the powder X-ray diffraction method, only diffraction lines mainly derived from the MgAgAs type crystal phase were observed in all compositions. Further, when the composition of the obtained sintered body was analyzed by ICP emission spectroscopy, it was confirmed to be a predetermined composition. For each thermoelectric conversion material, a dimensionless figure of merit ZT at 713K was determined from the resistivity ρ, Seebeck coefficient α, and thermal conductivity κ by the same method as in Example 1. The obtained results are summarized in Table 1 and Table 2 below. Tables 1 and 2 also show the results of Example 1 and Comparative Example 1 described above.

  As is apparent from Table 1, the Ti amount P in Examples 1 to 60 is in the range of 0.3 to 0.7, and the Sb amount S exceeds 0.003 and does not exceed 0.0010, particularly the Sb content S is 0.004 ≦ S ≦ 0.008. Each thermoelectric conversion material has a dimensionless figure of merit ZT at 713K of 1.20 or more and excellent thermoelectric conversion characteristics. On the other hand, as shown in Comparative Examples 2 to 4 and 44, Ti amount P is 0.3 to 0.7. Thermoelectric conversion materials outside the range have a dimensionless figure of merit ZT at 713K of 1.20 or less even when the Sb content S is in the range of more than 0.003 and not more than 0.0010. Further, as shown in Comparative Examples 1 and 5 to 43, even when the Ti amount P is within the range of 0.3 to 0.7, the thermoelectric conversion material having the Sb amount S of 0.003 or less or 0.0010 or more is dimensionless at 713K. It can be seen that the figure of merit ZT is as small as 1.20 or less.

(Example 61)
Co-based thermoelectric conversion material ((TI, Zr, Hf) Co (Sb, Sn)) is used as the p-type thermoelectric conversion material, and the composition formula (Ti _0.4 Zr _0.3 Hf _0.3 ) Ni ( A thermoelectric conversion module as shown in FIG. 5 was produced using a thermoelectric conversion material having a composition represented by Sn _0.994 Sb _0.006 ). The n-type thermoelectric conversion material corresponds to Example 1.

  Each p-type and n-type thermoelectric conversion material is cut out to 2.7mm square and 3.0mm height, 72 pieces each, 144 pieces in total are arranged in 12 rows x 12 rows, p and n alternately, 144 pieces in total are copper The electrode plates were connected in series. Furthermore, a silicon nitride sintered body plate was bonded to the other surface of the copper electrode plate, that is, the surface opposite to the surface to which the thermoelectric conversion module was bonded, and a current lead wire was bonded to the termination electrode to produce a thermoelectric conversion module.

  About the obtained thermoelectric conversion module, the high temperature side was 603 degreeC and the low temperature side was 43 degreeC, and the electric power generation characteristic was evaluated. The internal resistance under this temperature condition was 1.59Ω. As a load, the power generation characteristics were measured under a matched load condition in which a load of 1.59Ω which is the same as the internal resistance of the thermoelectric conversion module was connected. As a result, the generated voltage was 7.24 V, a current of 4.56 A flowed, 33.0 W of power was obtained, and it was confirmed that the thermal battery had good power generation characteristics.

  While the present invention has been described in detail based on the above specific examples, the present invention is not limited to the above specific examples, and various modifications and changes can be made without departing from the scope of the present invention.

It is a schematic diagram showing the structure of half-Heusler ABX. 5 is a graph showing the Sb content S dependence of a dimensionless figure of merit ZT of a thermoelectric conversion material having a composition of (Ti _0.4 Zr _0.3 Hf _0.3 ) Ni (Sn _{1 -S} Sb _S ). It is a schematic sectional drawing for demonstrating the electric power generation principle of a thermoelectric conversion module. It is a schematic block diagram which shows an example of the thermoelectric conversion module based on one Embodiment of this invention. It is a section lineblock diagram showing roughly an example of a thermal battery to which a thermoelectric conversion module based on one embodiment of the present invention is applied. It is a section lineblock diagram showing roughly an example of a heating cooling device to which a thermoelectric conversion module based on one embodiment of the present invention is applied.

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 ... electronic, 16 ... thermoelectric conversion module, 20 ... load, 21 ... current, 22 ... DC power supply, 23 ... current.

Claims (5)

Composition formula (Ti _P Zr _Q Hf _R ) _X Ni _Y (Sn _1-S Sb _S ) _1-XY (P + Q + R = 1, 0.3 ≦ P ≦ 0.7, 0 <Q <1, 0 <R <1 0.003 <S <0.01, 0.30 ≦ X ≦ 0.35, 0.30 ≦ Y ≦ 0.35), and the phase having the MgAgAs type crystal structure is the main phase.   The thermoelectric conversion material according to claim 1, wherein in the composition formula, the Sb content S is 0.004 ≦ S ≦ 0.008.   3. The thermoelectric conversion material according to claim 1, wherein in the composition formula, the Zr content Q is 0.1 ≦ Q ≦ 0.6.   The thermoelectric conversion material according to claim 1, wherein in the composition formula, the Hf content R is 0.1 ≦ R ≦ 0.6. A first electrode; a p-type thermoelectric conversion material having one end connected to the first electrode; a second electrode connected to the other end of the p-type thermoelectric conversion material; and one end being the second electrode A thermoelectric conversion module comprising: an n-type thermoelectric conversion material connected to the second electrode; and a third electrode connected to the other end of the n-type thermoelectric conversion material.
The said n-type thermoelectric conversion material consists of the thermoelectric conversion material as described in any one of Claims 1-4, The thermoelectric conversion module characterized by the above-mentioned.

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