JP2022018710A - Semiconductor material for thermoelectric conversion and thermoelectric conversion element using the same - Google Patents

Abstract

To provide a semiconductor material for thermoelectric conversion with low internal resistance and excellent thermoelectric properties, and a thermoelectric conversion element.SOLUTION: In a thermoelectric conversion semiconductor 11, a semiconductor material is a sintered body in which one or more low-resistance materials selected from the group consisting of metals, alloys, and metal compounds having a higher melting point and lower specific resistance than the semiconductor are dispersed as particles in a semiconductor made of FeSi2 containing dopants or Mg2SiSnGe material containing dopants. In addition, the thermoelectric conversion element uses the semiconductor material in at least one of a p-type semiconductor layer and an n-type semiconductor layer.SELECTED DRAWING: Figure 1

Description

The present invention relates to a semiconductor material for thermoelectric conversion and a thermoelectric conversion element using the same.

Due to the recent trend toward green society and the efficiency of energy use, power generation using waste heat from factory equipment, power generation equipment such as thermal power and nuclear power, and engines has attracted attention, and various technologies have been developed.
One of the power generation technologies is thermoelectric conversion using semiconductors, which has been put into practical use as a thermoelectric conversion element.

The largest engine for increasing the output and high conversion efficiency of a thermoelectric conversion element is a semiconductor material for thermoelectric conversion. For example, Patent Documents 1 to 3 and Non-Patent Document 1 disclose a part of the efforts. ing.

However, in the conventional thermoelectric conversion technology and the thermoelectric conversion element, the thermoelectric conversion efficiency and its output do not always satisfy the required values, and further improvement of the thermoelectric conversion efficiency and higher output are required.

Japanese Unexamined Patent Publication No. 2013-8747 Japanese Unexamined Patent Publication No. 2018-59160 Japanese Unexamined Patent Publication No. 2015-93788

Journal of Alloys Compounds, Volume 690, 5 January 2017, Pages 652-657

An object to be solved by the present invention is to provide a thermoelectric conversion semiconductor material and a thermoelectric conversion element having high thermoelectric conversion efficiency and thermoelectric conversion output, and to solve the problems described in the above background art.
Here, the thermoelectric conversion efficiency and thermoelectric conversion output are not modified, such as the composition of the semiconductor of the host responsible for thermoelectric conversion and the amount of dopant, so that the followability of the technologies developed so far and the production technology can be utilized. It is an object of the present invention to provide a high thermoelectric conversion semiconductor material and a thermoelectric conversion element.

The configuration of the present invention for solving the problem is shown below.
(Structure 1)
A sintered body in which one or more low resistance substances selected from the group consisting of metals, alloys and metal compounds, which have a higher melting point and a lower resistivity than the semiconductor, are dispersed as particles in a semiconductor made of FeSi ₂ containing a dopant. A semiconductor material for thermoelectric conversion consisting of.
(Structure 2)
The semiconductor for thermoelectric conversion according to Configuration 1, wherein the semiconductor is made of FeSi ₂ containing 1 or more selected from the group consisting of Ni, Co, Pt, Pd, B, Mn, Cr, V, Ti, Al, and P as a dopant. material.
(Structure 3)
In a semiconductor made of Mg ₂ SiSnGe-based material containing a dopant, one or more low resistance substances selected from the group consisting of metals, alloys and metal compounds having a higher melting point and a lower resistivity than the semiconductor were dispersed as particles. A semiconductor material for thermoelectric conversion made of a sintered body.
(Structure 4)
The dopants are Cu, Ag, Cd, Zn, Al, Ga, In, Au, Ni, Co, Fe, Li, Na, Ca, K, N, P, As, Sb, Bi, S, Se, Te, The semiconductor material for thermoelectric conversion according to the configuration 3, which is 1 or more selected from the group consisting of Cl, Br, and I.
(Structure 5)
The semiconductor is of the general formula A _2r Mg _2-2r (Si _{1-x-y Sn x} Gey) _1-s Bs (A and B are Cu, Ag, Cd, Zn, Al, Ga, In, Au, Ni). , Co, Fe, Li, Na, Ca, K, N, P, As, Sb, Bi, S, Se, Te, Cl, Br, I, one or more selected from the group, 0≤r <1, The semiconductor material for thermoelectric conversion according to the configuration 3 or 4, which comprises a material represented by 0 ≦ s ≦ 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1).
(Structure 6)
The semiconductor material for thermoelectric conversion according to any one of configurations 1 to 5, wherein the resistivity of the low resistivity material in the first half is 1/1000 or less of the resistivity of the semiconductor.
(Structure 7)
The low resistance substance is one or more selected from the group consisting of WSi ₂ , TiB ₂ , W, TaC, WC, ZrN, ZrB ₂ , HfB ₂ , VB ₂ , W ₂ B ₅ , LaB ₆ , TiSi ₂ , and MoSi ₂ . The semiconductor material for thermoelectric conversion according to any one of configurations 1 to 6.
(Structure 8)
The semiconductor material for thermoelectric conversion according to any one of configurations 1 to 6, wherein the low resistance substance is one or more selected from the group consisting of WSi ₂ and W.
(Structure 9)
The semiconductor material for thermoelectric conversion according to any one of configurations 1 to 8, wherein the volume fraction of the low resistance substance is 0.01% by volume or more and 2.5% by volume or less with respect to the semiconductor.
(Structure 10)
The semiconductor material for thermoelectric conversion according to any one of configurations 1 to 9, wherein the ratio of the number of atoms of the dopant to the semiconductor is 100 ppm or more and 5.3% or less.
(Structure 11)
The semiconductor material for thermoelectric conversion according to any one of configurations 1 to 10, wherein the semiconductor forms a grain boundary, and the low resistance substance exists between the grain boundaries of the semiconductor.
(Structure 12)
The p-type semiconductor layer and the n-type semiconductor layer are electrically connected, and at least one of the p-type semiconductor layer and the n-type semiconductor layer includes the semiconductor according to any one of configurations 1 to 11. , Thermoelectric conversion element.
(Structure 13)
The thermoelectric conversion element according to configuration 12, wherein the connection is made via electrodes.

According to the present invention, it is possible to provide a thermoelectric conversion semiconductor material and a thermoelectric conversion element having high thermoelectric conversion efficiency and thermoelectric conversion output without modifying the composition of the thermoelectric semiconductor material and the amount of dopant.
In the present invention, since the composition and the amount of dopant of the thermoelectric semiconductor material to be the host follow the conventional technique, various existing techniques can be followed, and the existing production technique can also be utilized.

It is explanatory drawing which shows the schematic structure of the semiconductor material of this invention. It is explanatory drawing which shows the main part structure of a thermoelectric conversion element, (a) is a bird's-eye view, (b) is a sectional view. It is an SEM photograph of the semiconductor material of this invention. In the characteristic diagram showing the relationship between the weight ratio and the volume ratio of the material of the present invention, (a) is an n-type material and (b) is a p-type material. It is a characteristic figure which shows the WSi ₂ mixture amount dependence of the specific resistance of a FeSi ₂ thermoelectric semiconductor material. It is a characteristic figure which shows the dependence of the specific resistance of an n-type Mg ₂ SiSn-based thermoelectric semiconductor material with a low resistivity and a high melting point material mixture amount. It is a characteristic diagram which shows the dependence of the specific resistance of a p-type Mg ₂ SiSn-based thermoelectric semiconductor material with a low resistivity and a high melting point material mixture amount. FIG. 3 is a characteristic diagram showing the dependence of the Seebeck coefficient of the n-type Mg ₂ SiSn-based thermoelectric semiconductor material on the low resistance and high melting point material mixing amount. It is a characteristic diagram which shows the dependence of the Seebeck coefficient of a p-type Mg ₂ SiSn-based thermoelectric semiconductor material with a low resistance and a high melting point material mixture amount. It is a characteristic figure which shows the dependence of the electric performance index of an n-type Mg ₂ SiSn-based thermoelectric semiconductor material with the addition amount of a low resistance high melting point material. It is a characteristic figure which shows the dependence of the electric performance index of a p-type Mg ₂ SiSn-based thermoelectric semiconductor material with the addition amount of a low resistance high melting point material. It is a characteristic diagram which shows the temperature dependence of the electric and physical characteristics of an n-type Mg ₂ SiSn-based thermoelectric semiconductor material. Here, (a) is a Seebeck coefficient, (b) is a specific resistance, (c) is a thermal conductivity, and (d) is a dimensionless performance index ZT. It is a characteristic diagram which shows the temperature dependence of the electric and physical characteristics of a p-type Mg ₂ SiSn-based thermoelectric semiconductor material. Here, (a) is a Seebeck coefficient, (b) is a specific resistance, (c) is a thermal conductivity, and (d) is a dimensionless performance index ZT.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

(First Embodiment)
The first embodiment (Embodiment 1) relates to a semiconductor material for thermoelectric conversion.
Here, after explaining the thermoelectric conversion element in which the semiconductor material for thermoelectric conversion is used, the characteristics required for the semiconductor material for thermoelectric conversion in order to improve the performance, the material structure for obtaining the characteristics, and the manufacture thereof. The method will be described.

The main components of the thermoelectric conversion element are an n-type semiconductor material for thermoelectric power generation and a p-type semiconductor material for thermoelectric power generation, which are electrically connected in series.
The power generation output (electric power) P of the thermoelectric conversion element uses the thermoelectromotive voltage E generated in response to the temperature difference in the element portion made of the above semiconductor material and its internal resistance r.
P = E × E / (4r) (Equation 1)
It is represented by.
Therefore, one method of improving the power generation output P is to improve the thermoelectromotive voltage E and reduce the internal resistance r. However, in the thermoelectric conversion material made of a semiconductor, both the thermoelectromotive voltage E and the internal resistance r change depending on the amount of dopant and the material composition. There, in general, the effect of the thermoelectromotive voltage E and the internal resistance r is in a trade-off relationship, that is, when the thermoelectromotive voltage E increases, the internal resistance r also increases (conductance decreases), and when the thermoelectromotive voltage E decreases, the internal resistance r There is a relationship that it also goes down (conductance goes up).

In the present invention, basically, the semiconductor material itself that causes thermoelectric conversion is not modified, and as shown in FIG. 1, a sintered body in which low resistance particles 13 are dispersed in the semiconductor 12 is used as a thermoelectric conversion material. And said. With this structure and structure, the resistance of the thermoelectric conversion material 11 is suppressed and the internal resistance r is lowered. Here, the particles 13 are made of a substance having a melting point higher than that of the semiconductor 12 and a specific resistance significantly smaller than that of the semiconductor 12, and the particles 13 are formed at the grain interface of the semiconductor 12.
In this method, since the particles 13 are formed in a mixed form outside the host semiconductor 12, and the material itself of the semiconductor 12 is not modified, the thermoelectromotive voltage E is basically unchanged. On the other hand, the internal resistance r of the thermoelectric conversion material 11 decreases. Therefore, it becomes possible to supply a thermoelectric conversion material or a thermoelectric conversion element having a high power generation output P.

The semiconductor 12 is an iron disilicate (FeSi ₂ ) containing a dopant. Here, as the dopant, nickel (Ni), cobalt (Co), platinum (Pt), palladium (Pd), boron (B), manganese (Mn), chromium (Cr), vanadium (V), titanium (Ti). ), Aluminum (Al), Phosphorus (P), and one or more selected from the group. Here, the semiconductor 12 becomes an n-type semiconductor when nickel (Ni), cobalt (Co), boron (B), platinum (Pt), and palladium (Pd) are selected as dopants, and manganese (Mn) and chromium (Cr). ), Vanadium (V), titanium (Ti), aluminum (Al), phosphorus (P), and it becomes a p-type semiconductor.
Alternatively, the semiconductor 12 is a dimagnesium silicon tin germanium (Mg ₂ SiSnGe) -based material containing a dopant (Mg ₂ Si _{1-x-y Sn x} Gey (0 ≦ x ≦ 1,0 ≦ y ≦ 1)). .. Here, as the dopant, copper (Cu), silver (Ag), cadmium (Cd), zinc (Zn), aluminum (Al), gallium (Ga), indium (In), gold (Au), nickel (Ni). ), Cobalt (Co), Iron (Fe), Lithium (Li), Sodium (Na), Calcium (Ca), Potassium (K), Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb) ), Bismuth (Bi), Sulfur (S), Serene (Se), Tellurium (Te), Chlorine (Cl), Brom (Br), Indium (I). .. Here, the semiconductor 12 has copper (Cu), gold (Au), nickel (Ni), cobalt (Co), iron (Fe), antimony (Sb), bismuth (Bi), sulfur (S), and selenium as dopants. If (Se), tellurium (Te), chlorine (Cl), brom (Br), and arsenic (I) are selected, they become n-type semiconductors, which are silver (Ag), cadmium (Cd), zinc (Zn), and aluminum (Al). ), Gallium (Ga), Indium (In), Lithium (Li), Sodium (Na), Calcium (Ca), Potassium (K), Nitrogen (N), Phosphorus (P), Arsenic (As). It becomes a type semiconductor.
Examples of the Mg ₂ SiSnGe-based material containing a dopant include a material represented by the general formula A _2r Mg _2-2r (Si _{1-x-y Sn x} Gey) _1-s Bs. Here, A and B are dopant elements such as Cu, Ag, Cd, Zn, Al, Ga, In, Au, Ni, Co, Fe, Li, Na, Ca, K, N, P, As, Sb, Bi, One or more selected from the group consisting of S, Se, Te, Cl, Br, and I, and the relationship of 0 ≦ r <1, 0 ≦ s ≦ 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1. There is.

The semiconductor 12 is manufactured by using a granular one. This prevents the elements of the particles 13 from being taken into the inside of the semiconductor 12 and changing the characteristics of the semiconductor 12, after forming the particles 13 at the grain interface of the semiconductor to lower the resistance of the thermoelectric conversion material 11. can do.

Examples of the size of the granular semiconductor include 1 μm or more and 75 μm or less, and specific examples include 38 μm to 75 μm. When the semiconductor is in the range of this size, the semiconductor 12 has a sufficient thermoelectric conversion function. On top of that, since the area of the grain interface is sufficient and a large number of particles 13 can be arranged, the resistance of the thermoelectric conversion material 11 can be significantly reduced. Moreover, mechanical problems such as cracking can be suppressed. It should be noted that this size can be defined by, for example, the average length of the longest portion measured by SEM or the like.

The ratio of the dopant to the semiconductor 12 is preferably 100 ppm or more and 5.3% or less in terms of atomic number ratio in order to obtain high thermoelectric conversion efficiency.
The semiconductor 12 is a semiconductor having a proven track record as a semiconductor material for thermoelectric conversion by itself.

As described above, the particle 13 is a substance having a melting point higher than that of the semiconductor 12 and a resistivity significantly smaller than that of the semiconductor 12, and can be one or more selected from the group consisting of metals, alloys and metal compounds.
The specific resistance of the particles 13 is preferably smaller than that of the semiconductor 12 by about 3 orders of magnitude or more. By reducing the specific resistance to 1/1000 or less, the internal resistance r of the thermoelectric conversion material 11 can be reduced to a necessary and sufficient level. The lower limit is not particularly limited, but a suitable material having a small resistivity is 7/10000 as compared with that of the semiconductor 12.

It is assumed that the melting point of the particles 13 is higher than the melting point of the semiconductor 12. It is preferably 1000 ° C. or higher, more preferably 2000 ° C. or higher, higher than the melting point of the semiconductor 12. By doing so, the elements of the particles 13 in the sintering process of the thermoelectric conversion material 11 are prevented from diffusing into the inside of the semiconductor 12, and the particles 13 are prevented from adversely affecting the characteristics of the semiconductor 12, and the heat of the semiconductor 12 is prevented. The trigger voltage E is held.

Here, specific examples of the particles 13 include tungsten diboride (WSi ₂ ), titanium diboride (TiB ₂ ), tungsten (W), tantalum carbide (TaC), tungsten carbide (WC), and zirconium diboride (ZrN). ), Zirconium diboride (ZrB ₂ ), hafnium diboride (HfB ₂ ), vanadium diboride (VB ₂ ), ditungsten pentabride (W2 _{B 5} ), lanthanum hexabride (LaB ₆ ), One or more selected from the group consisting of titanium diboride (TiSi ₂ ) and molybdenum diboride (MoSi ₂ ) can be mentioned.

These materials have a higher melting point than the semiconductor 12, and the resistivity is in the range of 7/10000 or more and 1/1000 or less as compared with the semiconductor 12. For reference, Table 1 shows a list of melting points, specific densities, and specific resistances of semiconductors useful as semiconductor 12, and Table 2 shows a list of melting points, specific densities, and specific resistances of the above-mentioned examples given as specific examples of particles 13.

The size of the particles 13 is preferably 50 nm or more and 2 μm or less. When the particles 13 are in the range of this size, they are sufficiently dispersed at the grain interface of the semiconductor 12, and the resistance of the thermoelectric conversion material 11 can be uniformly reduced.
The morphology of the particles 13 may be single or clustered.

The volume fraction of the particles 13 with respect to the semiconductor 12 is preferably 0.01% or more and 2.5% or less, more preferably 0.05% or more and 2.0% or less, and further preferably 0.1% or more and 1.5% or less. preferable.
By setting the volume ratio to 0.01% or more, the internal resistance r of the thermoelectric conversion material 11 can be lowered, and by setting the volume ratio to 0.05% or more, the internal resistance r can be remarkably lowered. By setting it to 1% or more, the internal resistance r can be further reduced. Further, when it is 2.5% or less, problems such as cracking of the thermoelectric conversion material 11 are less likely to occur, and when it is 2.0% or less, it is more difficult to crack. No cracking defects were observed below 1.5%.

The volume fraction of the particles 13 with respect to the semiconductor 12 can be obtained from image observation using SEM or the like, or can be calculated by separately obtaining a calibration curve of the weight ratio and the volume ratio. In the method using the calibration curve of the weight ratio and the volume ratio, the volume fraction can be controlled by the weight ratio of the preparation according to the calibration curve.
For reference, FIG. 4 shows the relationship between the volume fraction and the weight ratio of the particles 13 with respect to the semiconductor 12. A nearly linear relationship is recognized between the two.

The thermoelectric conversion material 11 is manufactured as follows.
First, a predetermined amount of semiconductor powder having the composition of the semiconductor 12 containing the dopant and the powder of the particles 13 are prepared and mixed.
Then, the mixture is sintered using a hot press or the like, and the thermoelectric conversion material 11 made of the sintered body is manufactured. For example, in the case of hot pressing, the sintering conditions include a pressure of 50 MPa or more and 100 MPa or less, a temperature of 650 ° C. or more and 1200 ° C. or less, and an hour of 60 minutes or more and 5 hours or less. As the sintering method, in addition to hot pressing, a discharge plasma sintering method, an ultra-high pressure sintering method, or the like can also be used.

In Non-Patent Document 1, a result of mixing CrSi ₂ powder, which is a semiconductor material, and WSi ₂ powder to prepare a sintered body by a pulse current sintering method and examining its electrical characteristics is reported. There is. In this paper, CrSi ₂ of the thermoelectric material becomes Cr _1-x W _x Si ₂ compound by adding WSi ₂ , and Cr-rich hexagonal (CrW) Si ₂ phase and W-rich tetragonal (WCr) Si ₂ A phase is generated and the grain size of the CrSi ₂ phase is reduced. From a different point of view, this method is a method when the CrSi ₂ semiconductor is changed to another compound.
On the other hand, the present invention is characterized in that the composition of the semiconductor 12 and the mixed powder does not change. That is, in the present invention, FeSi ₂ and Mg ₂ SiSnGe-based semiconductors, which have a sufficient track record in high-quality technology and high-efficiency production technology as thermoelectric semiconductor materials, are followed.
Therefore, the semiconductor material for thermoelectric conversion of the present invention has a feature that it is possible to supply a product having sufficiently high quality and productivity by utilizing the technology, knowledge, equipment, etc. accumulated so far. ..

(Second embodiment)
The second embodiment (the second embodiment) relates to a thermoelectric conversion element using a semiconductor material according to the first embodiment.

In thermal power generation and engines, much of the energy is wasted as waste heat. A thermoelectric conversion element using a semiconductor is an element that recovers heat energy such as waste heat and directly converts it into useful electric energy, and has features such as ease of maintenance and good scalability due to the absence of moving parts. ..

The thermoelectric conversion element is an element having a structure in which an n-type semiconductor and a p-type semiconductor are electrically connected. When this connection is made via electrodes, n-type semiconductors and p-type semiconductors can be arranged side by side, which is characterized by high productivity and easy compactness of thermoelectric conversion elements. You may connect directly.
The thermoelectric conversion element 31 is, for example, between the electrode 34 (34a) on the low temperature side and the electrode 34 (34b) on the high temperature side, as shown in FIG. 2, which is a configuration diagram of the main part thereof. It is an element having a structure in which an n-type semiconductor 32 and a p-type semiconductor 33 are electrically arranged in series via electrodes. Here, FIG. 2A is a bird's-eye view, and FIG. 2B is a sectional view.
In the second embodiment, the thermoelectric conversion semiconductor described in the first embodiment is used for at least one of the n-type semiconductor 32 and the p-type semiconductor 33. That is, an n-type semiconductor or a p-type semiconductor in which FeSi ₂ or Mg ₂ SiSnGe-based material containing a dopant is used as a host semiconductor portion and particles having a low resistivity and a high melting point are formed at the grain interface of the semiconductor portion is used.
Since these semiconductors can supply high output power with high conversion efficiency, the thermoelectric conversion element 31 becomes a high output thermoelectric conversion element having high thermoelectric conversion efficiency. Here, it is preferable to use the thermoelectric conversion semiconductor described in the first embodiment for both the n-type semiconductor 32 and the p-type semiconductor 33. In this way, the thermoelectric conversion element 31 becomes a high-output thermoelectric conversion element having extremely high thermoelectric conversion efficiency.

Hereinafter, the present invention will be described in more detail by way of examples, but these examples are given here only for the purpose of assisting the understanding of the present invention, and the present invention is not limited thereto.

(Example 1)
In Example 1, a sintered body obtained by mixing WSi ₂ powder with FeSi ₂ powder to which an n-type dopant was added was prepared by using a hot press, and its resistivity was measured.
The details of the manufacturing process of the sintered body are shown below.
First, FeSi ₂ powder (purity: 99% manufactured by Fukuda Metal Foil Powder Industry Co., Ltd.) to which cobalt (Co) was added was prepared, and WSi ₂ powder (purity: 99% manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was prepared. ) And weighed so as to be the predetermined weight%. Here, the average particle size of the FeSi ₂ powder and the WSi ₂ powder is 7 μm and 2 to 5 μm, respectively. These powders were mixed in an inclined planetary ball mill (Plant M2-3F manufactured by Nagao System Co., Ltd.) at room temperature in an argon atmosphere. The mixing time was 20 minutes. As shown in Table 1, the melting point and resistivity of WSi ₂ are about 1.4 times and 1/640 times that of FeSi ₂ , respectively.
Next, the mixture was hot-pressed to prepare a sintered body. The conditions for hot pressing were a pressure of 50 MPa, a temperature of 1174 ° C., and 30 minutes. The mixing ratio is 0 to 0.1 mol%.
After hot pressing, heat treatment to make β phase was performed at 800 ° C. for 20 hours.

The resistivity ρ of the obtained sintered body at room temperature was measured by the four-probe method.
As shown in FIG. 5, the resistivity ρ monotonically decreased from about 8.5 μΩm of the unmixed sample to about 5.1 μΩm of the 0.1 mol% mixed sample as the mixing ratio increased. From this result, it was confirmed that the specific resistance of the sintered body was significantly reduced by the addition of the high melting point and low resistivity particles.

(Example 2)
In Example 2, a plurality of sintered bodies obtained by mixing WSi ₂ or W with a Mg ₂ SiSnGe-based material were prepared, and their electrical and physical properties were evaluated.

The first sintered body is an example of an n-type semiconductor, which is a powder having a composition of Mg ₂ Si _0.4625 Sn _0.4625 Sb _0.075 and WSi ₂ (manufactured by Wako Pure Chemical Industries, Ltd., purity: 99). %) Or W powder (manufactured by Nippon Shinkinzoku Co., Ltd., purity 99.9%) was sealed in a glass tube and mixed by applying rotation to prepare a sintered body using a hot press. The conditions for hot pressing were a pressure of 80 MPa, a temperature of 780 ° C., and 5 hours.
The second sintered body is an example of a p-type semiconductor, in which a powder having a composition of Mg _1.97 Ag _0.25 Li _0.05 Si _0.25 Sn _0.75 and WSi ₂ or W powder are placed in a glass tube. It was sealed, mixed by rotation, and a sintered body was prepared using a hot press. The conditions for hot pressing were a pressure of 80 MPa, a temperature of 650 ° C., and 4 hours.

The resistivity ρ of the first and second sintered bodies at room temperature are shown in FIGS. 6 and 7, respectively. The Seebeck coefficient α at room temperature is shown in FIGS. 8 and 9, respectively, and the electrical figure of merit PW calculated from the Seebeck coefficient α and the specific resistance ρ is shown in FIGS. 10 and 11, respectively.

The resistivity ρ of Mg ₂ Si _0.4625 Sn _0.4625 Sb _0.075 of the n-type semiconductor which is the first sintered body is 2.34 in the unmixed sample in which WSi ₂ or W powder is not mixed. It is × ^10-5 Ωm, but 1.12 × ^10-5 Ωm (2 wt% (2 wt%)) for WSi ₂ mixed sample, 1.01 × ^10-5 Ωm (4 wt%) for WSi 2 mixed sample, and W mixed sample. It was significantly reduced to 8.96 × 10 ^-6 Ωm (2% by weight) and 2.42 × 10 ^-6 Ωm (4% by weight), and the effect of mixing was remarkable.
The resistivity ρ of Mg _1.97 Ag _0.025 Li _0.005 Si _0.25 Sn _0.75 of the p-type semiconductor which is the second sintered body is 2.09 × 10 ^-5 Ωm in the unmixed sample. However, in the WSi ₂ mixed sample, it decreased slightly to 2.00 × ^10-5 Ωm (2% by weight) and 1.92 × ^10-5 Ωm (4% by weight). On the other hand, in the W mixed sample, it decreased significantly to 1.41 × ^10-5 Ωm.

The Seebeck coefficient α at room temperature was -177.3 μV / K for the unmixed sample and -153.2 μV / K (2% by weight) for the WSi ₂ mixed sample in the first sintered body (n-type sample). It is 181.0 μV / K (4% by weight), -128.2 μV / K (2% by weight) and -127.4 μV / K (4% by weight) in the W mixed sample, and it is as the mixing ratio increases. There was a tendency to decrease.
In the second sintered body (p-type sample), the unmixed sample was 128.7 μV / K, and the WSi ₂ mixed sample was 134.4 μV / K (2% by weight) and 152.2 μV / K (4% by weight). In the W mixed sample, it was 137.4 μV / K (2% by weight) and 155.7 μV / K (4% by weight), and the Seebeck coefficient α at room temperature was increased by mixing WSi ₂ and W.

The calculated electrical performance index PW was 1.39 mW / mK ² for the unmixed sample and 2.03 mW / mK ² (2% by weight) for the WSi ₂ mixed sample in the first sintered body. It is .82 mW / mK ² (4% by weight), 1.93 mW / mK ² (2% by weight) for the W mixed sample, and 1.78 mW / mK ² (4% by weight) for the W mixed sample, which is the maximum compared to the unmixed sample. The performance was improved by 46%.
In the second sintered body, 0.95 mW / mK ² for the unmixed sample, 1.04 mW / mK ² (2% by weight), 1.11 mW / mK ² (4% by weight), W for the WSi ₂ mixed sample. The mixed sample had 1.11 mW / mK ² (2% by weight) and 1.21 mW / mK ² (4% by weight), and the performance was improved by up to 27% as compared with the unmixed sample.
Here, the fact that the electrical performance index PW is increased by mixing WSi ₂ and W with a high melting point and a low resistivity means that the thermoelectric power generation output P is significantly increased.

The temperature dependence of the thermoelectric characteristics in the first sintered body is shown in FIG. 12, and the temperature dependence of the thermoelectric characteristics in the second sintered body is shown in FIG.
The Seebeck coefficient α in the first sintered body (n-type sample) tends to increase in absolute value as the temperature rises. The Seebeck coefficient α of the unmixed sample showed the maximum absolute value at about 700 K and decreased above that temperature. However, the Seebeck coefficient α of the mixed sample was smaller than that of the unmixed sample in the measurement temperature range (FIG. 12 (a)).

On the other hand, the Seebeck coefficient α in the second sintered body (p-type sample) showed no significant difference between the unmixed sample and the mixed sample, and showed the maximum value at around 550 K (FIG. 13 (a)).

The temperature dependence of the specific resistance ρ increases with increasing temperature in all samples, and in the n-type sample, which is the first sintered body, the mixed sample significantly decreases in the measurement temperature range as compared with the unmixed sample ( FIG. 12 (b)), in the p-type sample which is the second sintered body, the true region was reached at about 550 K or higher and decreased linearly (FIG. 13 (b)).
Here, the first sintered body mixed with 4% by weight WSi ₂ has a higher resistivity ρ than that mixed with 2% by weight WSi ₂ , but this is the inside of the first sintered body mixed with 4% by weight WSi ₂ . It is probable that it was caused by the increase in resistance due to the cracks that occurred in. The crack was confirmed by SEM.

In the first sintered body, which is an n-type sample, the temperature dependence of the thermal conductivity κ was large only in the sample mixed with 4 wt% WSi ₂ , and the other mixed samples and the unmixed sample were almost the same (). FIG. 12 (c)).
On the other hand, in the second sintered body, which is a p-type sample, the unmixed sample was small, and the mixed sample was almost the same for all the samples, but larger than the unmixed sample (FIG. 13 (c)).

The maximum value of the dimensionless performance index ZT = (α ² T / ρκ) calculated from the Seebeck coefficient α, temperature T, specific resistance ρ, and thermal conductivity κ is found in the first sintered body (n-type sample). The 4 wt% WSi ₂ mixed sample is the smallest, the other mixed samples are larger than the unmixed sample (0.8), and the 4 wt% WSi sample is 1.25 and 1.6 than the unmixed sample. It was doubled (Fig. 12 (d)).
In the second sintered body (p-type sample), the specific resistance ρ became smaller, but the Seebeck coefficient α also became smaller, and the thermal conductivity κ was almost the same, so the maximum value of the dimensionless performance index ZT was none. The mixed sample and the mixed sample were almost the same (FIG. 13 (d)).

As described above, from the improvement of the electric figure of merit PW at room temperature, when used near room temperature, the output performance of thermoelectric power generation is improved by mixing the particles 13. Since there is a great demand for IoT power supplies near room temperature, it is expected that they will be greatly utilized as an industry.

Since the semiconductor material for thermoelectric conversion and the thermoelectric conversion element using the semiconductor material for thermoelectric conversion according to the present invention are elements that directly convert heat having a high thermoelectric conversion output into electricity, they are expected to be widely used in industry such as waste heat recovery. Will be done.

11: Thermoelectric conversion semiconductor 12: Semiconductor 13: Particles (particles of low resistance)
14: Grain interface 31: Thermoelectric power generation element 32: n-type semiconductor 33: p-type semiconductor 34: Electrode 35: Current

Claims (13)

A sintered body in which one or more low resistance substances selected from the group consisting of metals, alloys and metal compounds, which have a higher melting point and a lower resistivity than the semiconductor, are dispersed as particles in a semiconductor made of FeSi ₂ containing a dopant. A semiconductor material for thermoelectric conversion consisting of. The thermoelectric conversion according to claim 1, wherein the semiconductor is made of FeSi ₂ containing 1 or more selected from the group consisting of Ni, Co, Pt, Pd, B, Mn, Cr, V, Ti, Al, and P as a dopant. Semiconductor material. In a semiconductor made of Mg ₂ SiSnGe-based material containing a dopant, one or more low resistance substances selected from the group consisting of metals, alloys and metal compounds having a higher melting point and a lower resistivity than the semiconductor were dispersed as particles. A semiconductor material for thermoelectric conversion made of a sintered body. The dopants are Cu, Ag, Cd, Zn, Al, Ga, In, Au, Ni, Co, Fe, Li, Na, Ca, K, N, P, As, Sb, Bi, S, Se, Te, The semiconductor material for thermoelectric conversion according to claim 3, which is 1 or more selected from the group consisting of Cl, Br, and I. The semiconductor is of the general formula A _2r Mg _2-2r (Si _{1-x-y Sn x} Gey) _1-s Bs (A and B are Cu, Ag, Cd, Zn, Al, Ga, In, Au, Ni). , Co, Fe, Li, Na, Ca, K, N, P, As, Sb, Bi, S, Se, Te, Cl, Br, I, one or more selected from the group, 0≤r <1, The semiconductor material for thermoelectric conversion according to claim 3 or 4, which comprises a material represented by 0 ≦ s ≦ 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1). The semiconductor material for thermoelectric conversion according to any one of claims 1 to 5, wherein the resistivity of the low resistivity material in the first half is 1/1000 or less of the resistivity of the semiconductor. The low resistance substance is one or more selected from the group consisting of WSi ₂ , TiB ₂ , W, TaC, WC, ZrN, ZrB ₂ , HfB ₂ , VB ₂ , W ₂ B ₅ , LaB ₆ , TiSi ₂ , and MoSi ₂ . The semiconductor material for thermoelectric conversion according to any one of claims 1 to 6. The semiconductor material for thermoelectric conversion according to any one of claims 1 to 6, wherein the low resistance substance is one or more selected from the group consisting of WSi ₂ and W. The semiconductor material for thermoelectric conversion according to any one of claims 1 to 8, wherein the volume fraction of the low resistance substance is 0.01% by volume or more and 2.5% by volume or less with respect to the semiconductor. The semiconductor material for thermoelectric conversion according to any one of claims 1 to 9, wherein the ratio of the number of atoms of the dopant to the semiconductor is 100 ppm or more and 5.3% or less. The semiconductor material for thermoelectric conversion according to any one of claims 1 to 10, wherein the semiconductor forms a grain boundary, and the low resistance substance exists between the grain boundaries of the semiconductor. The p-type semiconductor layer and the n-type semiconductor layer are electrically connected, and at least one of the p-type semiconductor layer and the n-type semiconductor layer includes the semiconductor according to any one of claims 1 to 11. There is a thermoelectric conversion element. The thermoelectric conversion element according to claim 12, wherein the connection is made via electrodes.

Images