JP7054925B2 - Thermoelectric conversion material - Google Patents

Description

The present invention relates to an alloy, a method for producing the alloy, a thermoelectric conversion material made of the alloy, and a thermoelectric conversion module using the thermoelectric conversion material.

In Japan, the rate of obtaining effective energy from the primary supply energy is only about 30%, and about 70% of the energy is finally discarded as heat in the atmosphere. In addition, heat generated by combustion in factories and waste incinerators is also discarded in the atmosphere without being converted into other energy. In this way, we human beings waste a great deal of heat energy and obtain only a small amount of energy from actions such as burning fossil energy.

In order to improve the energy acquisition rate, it is effective to make available the thermal energy that is wasted in the atmosphere. Generally, waste heat is released as high-temperature exhaust gas in factories and automobiles, but there is also low-temperature waste heat generated when liquefied natural gas is vaporized by heat exchange. Thermoelectric power generation, which directly converts this cold waste heat into electricity, is a promising technology.

Thermoelectric power generation utilizes the Zeebeck effect, and is an energy conversion method in which a potential difference is generated by creating a temperature difference between both ends of a thermoelectric conversion material to generate electricity. In this method, one end of the thermoelectric conversion material is placed in the low temperature part generated by the vaporization of liquefied natural gas, the other end is placed in the atmosphere at room temperature or in contact with the water tank, and the conductors are connected to both ends of each. Electricity can be obtained with, and there is no need for moving devices such as motors and turbines required for general power generation. Therefore, the cost is low, there is no exhaust gas, and power can be continuously generated until the thermoelectric conversion material deteriorates.

Another method of using thermoelectric conversion is to create a temperature difference between both ends of the thermoelectric conversion material by passing an electric current through it. For example, if the low temperature side of the thermoelectric conversion material is used, it can be used as a cooling element. This cooling method is called Pelche cooling. Cooling is essential for superconducting elements and infrared sensor elements. In particular, superconducting devices need to be cooled until the material is in a superconducting state. For that purpose, it is necessary to use liquid nitrogen, but using liquid as a refrigerant is complicated to handle and supply, and causes a problem in safety. Therefore, in the use of various sensors, a solid cooling element capable of cooling up to about 100 K is indispensable, and a Pelche cooling element due to a thermoelectric conversion effect is the most promising.

In this way, thermoelectric conversion is a technology that greatly contributes to the solution of energy problems and the spread of sensors necessary for the Internet of Things (IoT) society. For that purpose, a thermoelectric conversion material having high thermoelectric conversion efficiency and high durability is required.

So far, for example, Bi ₂ Te ₃ alloy has been reported as a substance exhibiting excellent thermoelectric conversion performance at low temperature (see Non-Patent Document 1 below). Bi ₂ Te ₃ is already on the market as a Pelche element, but its high performance temperature is around 250K to room temperature, and its efficiency is low for cooling and power generation at about 150K or less.

Furthermore, the performance of the thermoelectric conversion material is the dimensionless performance index ZT (= S ² T / (ρκ)) with respect to the thermoelectric conversion performance, where S, T, ρ, and κ are the Seebeck coefficient, absolute temperature, and electrical resistivity, respectively. , Thermal conductivity)), and in order to put the thermoelectric conversion material into practical use, it is necessary to increase the ZT value at, for example, about 300K. Then, in order to increase this ZT value, it is necessary to reduce the thermal conductivity at about 300 K.

C. J. Liu et al., Journal of Materials Chemistry, Vol. 22, pp. 4825-4831 (2012)

Under such circumstances, the present invention provides a novel alloy exhibiting excellent thermoelectric conversion characteristics, which has low thermal conductivity in an environment of about 300 K and low electrical resistivity at a low temperature of about 80 K. The main purpose is to do. Further, it is also an object of the present invention to provide a method for manufacturing the alloy, a thermoelectric conversion material made of the alloy, and a thermoelectric conversion module using the thermoelectric conversion material.

The present inventors have made diligent studies to solve the above problems. As a result, the composition formula: Bi _1-xy Sb _{x My (} in the formula, M is from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In. It is at least one element selected from the group consisting of 0.03 ≦ x ≦ 0.95 and 0.00 ≦ y ≦ 0.20), and has a plurality of rearrangements and a plurality of twin crystals in the crystal. It has been found that the alloy having at least one of the above has excellent thermal conductivity in an environment of about 300 K and low electrical resistivity in a low temperature of about 80 K, and exhibits excellent thermoelectric conversion characteristics.

An alloy having the above composition and having a thermal conductivity of 4.00 W / m · K or less at a temperature of 300 K is a novel compound which has not been known conventionally.

The present invention is an invention completed by further studies based on these findings.

That is, the present invention provides the inventions of the following aspects.
Item 1. Composition formula: Bi _1-xy Sb _{x My (} In the formula, M is from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In. At least one element of choice, represented by 0.03 ≤ x ≤ 0.95, 0.00 ≤ y ≤ 0.20), with at least one of a plurality of dislocations and a plurality of twins in the crystal. Has an alloy.
Item 2. Item 2. The alloy according to Item 1, which has a thermal conductivity of 4.00 W / m · K or less at a temperature of 300 K.
Item 3. Composition formula: Bi _1-xy Sb _{x My (} In the formula, M is from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In. It is at least one element selected, and is represented by 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20).
An alloy having a thermal conductivity of 4.00 W / m · K or less at a temperature of 300 K.
Item 4. Item 2. The alloy according to any one of Items 1 to 3, which has an electrical resistivity of 5.00 mΩcm or less at a temperature of 80 K.
Item 5. A thermoelectric conversion material comprising the alloy according to any one of Items 1 to 4.
Item 6. A thermoelectric conversion module comprising the thermoelectric conversion material according to Item 5.
Item 7. Bi, Sb, and M (where M is at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In. The molar ratio of 1) is 1-x-y: x: y (however, 0.03 ≦ x ≦ 0.95 and 0.00 ≦ y ≦ 0.20). Step 1 to obtain a metal composition obtained by mixing an alloy, an intermetal compound, or a solid solution composed of a simple substance of Bi metal, a simple substance of Sb metal, a simple substance of M metal, or at least two kinds of metals among these metals.
Step 2 of pressurizing the metal composition to obtain an alloy precursor, and
The first heating and pressurizing step 3 in which the alloy precursor is heated and pressurized under the conditions of a temperature of 353K to 573K and a pressure of 5MPa to 100MPa to obtain an alloy,
Step 4 of placing the alloy under a temperature and pressure lower than that of the first heating and pressurizing step, and
After the step 4, the second heating and pressurizing step of heating and pressurizing the alloy under the conditions of a temperature of 353K to 573K and a pressure of 5MPa to 100MPa,
A method of manufacturing an alloy.

According to the present invention, the composition formula: Bi _1-xy Sb _{x My (} in the formula, M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, It is at least one element selected from the group consisting of and In, and is represented by 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20), and has a plurality of rearrangements and twins in the crystal. Since it has at least one of the crystals, it has low thermal conductivity in an environment with a temperature of about 300 K and low electrical resistivity at a low temperature of about 80 K, and exhibits excellent thermoelectric conversion characteristics. Alloys can be provided.

Further, according to the present invention, the composition formula: Bi _1-xy Sb _{x My (} in the formula, M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, It is at least one element selected from the group consisting of Pb and In, and is represented by 0.03 ≦ x ≦ 0.95 and 0.00 ≦ y ≦ 0.20), and is 4.00 W at a temperature of 300 K. It is also possible to provide a novel alloy having a thermal conductivity of / m · K or less.

Further, according to the present invention, it is also possible to provide a method for producing the above-mentioned novel alloy, a thermoelectric conversion material made of the alloy, and a thermoelectric conversion module using the thermoelectric conversion material. The thermoelectric conversion material made of the alloy of the present invention can be used as an n-type or p-type thermoelectric conversion material depending on the composition and temperature. Specifically, since the alloy of the present invention has the low electrical resistivity and thermal conductivity as described above, it exhibits excellent power generation performance and cooling performance in a temperature range of, for example, about 80K to 300K. It can be an n-type or p-type thermoelectric conversion material. Further, by incorporating an n-type or p-type thermoelectric conversion material into a system as an n-type or p-type thermoelectric conversion element in a thermoelectric conversion module, liquefied natural gas that has been wasted by heat exchange with seawater or the like until now. It becomes possible to effectively utilize the cold energy from the above, and it becomes possible to use it as a solid cooling device capable of cooling to around 100 K by energizing the module.

This is an example of a schematic diagram of a thermoelectric conversion module using the alloy of the present invention as a p-type and n-type thermoelectric conversion material. It is a graph which shows the powder X-ray diffraction pattern measured at room temperature about the alloy (sintered body) obtained in Example 1. FIG. It is an example of a schematic diagram showing the outline of a sample holder and wiring for measuring Seebeck coefficient, electrical resistivity, and thermal conductivity. FIG. 4A shows an alloy (sintered body) obtained in Example 1 (i) and Comparative Example 1 (ii), and FIG. 4B shows a comparative example with Example 45 (iii). 2 is a graph showing the temperature dependence of the Seebeck coefficient at temperatures of 80K to 300K for each of the alloys (sintered bodies) obtained in 2 (iv). FIG. 5A shows an alloy (sintered body) obtained in Example 1 (i) and Comparative Example 1 (ii), and FIG. 5B shows a comparative example with Example 45 (iii). It is a graph which shows the temperature dependence of the electrical resistivity in the temperature 80K-300K about the alloy (sintered body) obtained in 2 (iv). FIG. 6A shows an alloy (sintered body) obtained in Example 1 (i) and Comparative Example 1 (ii), and FIG. 6B shows a comparative example with Example 45 (iii). 2 is a graph showing the temperature dependence of thermal conductivity at temperatures of 80K to 300K for each of the alloys (sintered bodies) obtained in 2 (iv). It is a transmission electron micrograph of the alloy (sintered body) obtained in Example 1 (i) and Comparative Example 1 (ii) (in the photograph (i) of FIG. 7, (a) shows the dislocation location. , (B) indicate the location of twins).

The first alloy of the present invention has a composition formula: Bi _1-xy Sb _{x My (} in the formula, M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn. , Pb, and In, at least one element selected from the group, 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20), and in the crystal. It is characterized by having at least one of a plurality of dislocations and a plurality of twins.

Further, the second alloy of the present invention has a composition formula: Bi _1-xy Sb _{x My (} where M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge). , Sn, Pb, and In, at least one element selected from the group, 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20), and a temperature of 300K. Is characterized by having a thermal conductivity of 4.00 W / m · K or less.

Hereinafter, the alloy of the present invention will be described in detail.

The alloy of the present invention has a composition represented by the composition formula _: Bi _1-xy Sb _x My. In the composition formula, M is at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In. The alloy of the present invention may not have M (ie, y = 0). The type of the metal M contained in the alloy is preferably 0 to 5, more preferably 0 to 3, and even more preferably 0 to 1.

The M is not particularly limited as long as it is the above, but preferably Pb, Sn, In, Ge and the like can be mentioned.

The alloy of the present invention is in a state in which Sb, which is an essential element, and M, which is an optional element, are substituted at the element positions of Bi, which is the parent material, and is a rhombic crystal (trigonal) system (spatial group) similar to Bi. It is a metal compound (metal material) having a crystal structure of R_3m). As will be described later, the alloy can be said to be a sintered body because it is manufactured by heating and pressurizing a simple substance of metal or the like.

The alloy of the present invention has a negative Seebeck coefficient or a positive Seebeck coefficient by adjusting the composition (that is, the amount of substitution of Sb and M with respect to the Bi crystal and the type of M) and the operating temperature condition. Have. That is, the positive or negative of the Seebeck coefficient can be controlled by appropriately adjusting the composition and the temperature conditions. For example, when a negative Seebeck coefficient is exhibited when a temperature difference is generated at both ends of the alloy, the potential generated by the thermoelectromotive force is higher on the high temperature side than on the low temperature side, and as an n-type thermoelectric conversion material. Shows the characteristics of. On the other hand, when the positive Seebeck coefficient is shown, the potential generated by the thermoelectromotive force is higher on the low temperature side than on the high temperature side, and exhibits the characteristics as a p-type thermoelectric conversion material.

The first alloy of the present invention has at least one of a plurality of dislocations and a plurality of twins in the crystal. Here, in the present invention, the dislocation in the crystal means a linear lattice defect due to the displacement of the crystal plane. Further, in the present invention, the twin crystal in the crystal means a crystal in which different crystals are joined in the crystal axis orientation. In the first alloy of the present invention, by having dislocations and twins in the crystal, phonons that transfer heat are effectively scattered, so that the thermal conductivity at, for example, 300K is effectively reduced. It is 00 W / m · K or less. Further, since dislocations and twins in the crystal have a small effect on the electrical resistivity, the first alloy of the present invention shows a low value of 5.00 mΩcm or less even at a low temperature of 80 K, for example. ing.

From the viewpoint of further enhancing the thermoelectric conversion characteristics of the alloy, the thermal conductivity of the alloy of the present invention at a temperature of 300 K is preferably 4.00 W / m · K or less, more preferably 3.00 W / m · K or less. More preferably, it is 2.50 W / m · K or less.

From the same viewpoint, the thermal conductivity of the alloy of the present invention at a temperature of 80 K is preferably 3.50 W / m · K or less, more preferably 2.50 W / m · K or less, still more preferably 1.95 W. / M · K or less can be mentioned.

Further, from the same viewpoint, the electrical resistivity of the alloy of the present invention at a temperature of 80 K is preferably 5.00 mΩcm or less, more preferably 1.00 mΩcm or less, still more preferably 0.60 mΩcm or less.

From the same viewpoint, the electrical resistivity of the alloy of the present invention at 300K is preferably 2.50 mΩcm or less, more preferably 1.00 mΩcm or less, still more preferably 0.50 mΩcm or less.

The alloy of the present invention can be suitably used as a thermoelectric conversion material. As described above, the alloy of the present invention can be an n-type thermoelectric conversion material or a p-type thermoelectric conversion material by adjusting the composition and the temperature conditions in the usage environment.

Further, by combining a plurality of thermoelectric conversion materials made of the alloy of the present invention, the thermoelectric conversion material can be an n-type or p-type thermoelectric conversion element, and these can be used to form a thermoelectric conversion module. An example of a schematic diagram of such a thermoelectric conversion module is shown in FIG. The structure of the thermoelectric conversion module shown in FIG. 1 is the same as that of a known thermoelectric conversion module, and is composed of a substrate material, a p-type thermoelectric conversion material, an n-type thermoelectric conversion material, electrodes, and the like.

More specifically, since the alloy of the present invention has the low electrical resistivity and thermal conductivity as described above, it exhibits excellent power generation performance and cooling performance in a temperature range of, for example, about 80K to 300K. It can be an n-type or p-type thermoelectric conversion material. Further, by incorporating the n-type or p-type thermoelectric conversion material into the system as an n-type or p-type thermoelectric conversion element in the thermoelectric conversion module, for example, liquefaction that has been previously discarded by heat exchange in seawater or the like. It is possible to effectively use the cold energy from natural gas, and it is possible to use it as a solid cooling device that can cool down to around 100K by energizing the module.

The method for producing the alloy of the present invention is not particularly limited, and for example, it can be suitably produced by a method including the following steps 1 to 5.

Step 1: Bi, Sb, and M (where M is at least selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In. The molar ratio of (a kind of element) is a mixture ratio of 1-xy: x: y (provided that 0.03 ≦ x ≦ 0.95 and 0.00 ≦ y ≦ 0.20). Step 2: Obtaining a metal composition obtained by mixing an alloy, an intermetal compound, or a solid solution composed of a single Bi metal, a single Sb metal, a single M metal, or at least two of these metals. Step 3: The alloy precursor obtained in Step 2 is heated and pressurized under the conditions of a temperature of 353K to 573K and a pressure of 5MPa to 100MPa. First heating and pressurizing step to obtain an alloy Step 4: The alloy obtained in Step 3 is placed at a lower temperature and lower pressure than in the first heating and pressurizing step Step 5: After Step 4. , A second heating and pressurizing step of heating and pressurizing the alloy under the conditions of a temperature of 353K to 573K and a pressure of 5MPa to 100MPa.

First, in step 1, raw materials of Bi, Sb, and M are prepared so as to have the same composition as the target alloy composition, and these raw materials are mixed to obtain a metal composition. Examples of the raw material include a simple substance of Bi metal, a simple substance of Sb metal, a simple substance of M metal, and an alloy, an intermetal compound, or a solid solution composed of at least two kinds of these metals. The form of the raw material is not particularly limited, but is preferably in the form of powder.

Next, in step 2, the metal composition obtained in step 1 is pressurized to obtain an alloy precursor. The pressurizing method of the metal composition is not particularly limited, and examples thereof include a mechanical alloying method and a method of melting or solid-phase reaction. In the mechanical alloying method, for example, a metal composition is placed in a container made of amber or stainless steel, and an appropriate number of spheres made of the same material as the container and having an arbitrary diameter (for example, about 2 mm to 2 cm) are placed. This is a method of alloying a container between a sphere and a metal composition (preferably powder) by rotating and oscillating the container, or by utilizing the collision energy between the spheres. Further, in the method of melting or solid-phase reaction, the metal composition may be in the form of powder, granule, plate or the like. The step 2 is preferably performed in vacuum or under an inert gas such as argon.

Next, in step 3, the first heating and pressurizing step of heating and pressurizing the alloy precursor obtained in step 2 under the conditions of a temperature of 353K to 573K and a pressure of 5MPa to 100MPa to obtain an alloy is performed. conduct. At this time, the alloy precursor used in step 3 is preferably in the form of powder. For heating and pressurization, for example, a powdery alloy precursor is molded into a plate shape (for example, a disk shape) by uniaxial pressurization, the plate is placed in a carbon mold, and a pressurizing shaft is applied to the surface of the plate. A method of pressurizing under the condition of a pressure of 5 MPa to 100 MPa and heating at a temperature of 353 K to 573 K in that state to sinter the alloy precursor and alloying the alloy precursor can be mentioned.

The method of heating and pressurizing in step 3 is not particularly limited, but for example, a hot press method of heating by heat transfer from a heating element, an energization sintering method in which a carbon mold is energized and heated by heat generated by electric resistance. The law etc. can be mentioned.

The heating temperature in the step 3 is preferably about 443K to 503K. The pressure is preferably about 10 MPa to 80 MPa. Further, the time for heating and pressurizing is not particularly limited, but is preferably about 5 to 60 minutes, and more preferably about 10 to 30 minutes.

Step 3 is preferably carried out under an inert gas such as argon.

Next, in step 4, the alloy obtained in step 3 is placed at a lower temperature and lower pressure than in the first heating and pressurizing step of step 3. The temperature at this time is not particularly limited, but is preferably about 283K to 353K, and more preferably about 293K to 313K. The pressure at this time is preferably about atmospheric pressure (about 0.1 MPa) to about 1 MPa, and more preferably about atmospheric pressure to about 0.2 MPa. The period of keeping the temperature and pressure lower than that of the first heating and pressurizing step of the step 3 is not particularly limited, but is preferably about 1 hour to 72 hours, more preferably about 1 hour to 24 hours. Can be mentioned. Typically, the alloy obtained in step 3 is placed at room temperature (about 25 ° C.) under normal pressure and naturally cooled until the alloy reaches room temperature, and then the second heating and pressurizing in step 5 described later is performed. The process can be performed.

Next, in step 5, after step 4, a second heating and pressurizing step of heating and pressurizing the alloy under the conditions of a temperature of 353K to 573K and a pressure of 5MPa to 100MPa is performed. By performing the step 5, the alloy of the present invention can be suitably produced.

In the second heating and pressurizing step of the step 5, the alloy cooled in the step 4 is heated and pressurized again under the conditions of a temperature of 353K to 573K and a pressure of 5MPa to 100MPa. In the second heating and pressurizing step, the alloy obtained in step 3 is not crushed, but is placed in a mold capable of sintering a substance 1.1 to 2 times larger than the diameter of the alloy and heated and pressurized. It is preferable to do so. As a result, an alloy in which the alloy is easily plastically deformed, has a large diameter, is thin in thickness, and has a plurality of dislocations and at least one of a plurality of twins in the crystal is preferably obtained.

The heating temperature in the second heating and pressurizing step is preferably about 443K to 503K. The pressure is preferably about 10 MPa to 80 MPa. Further, the time for heating and pressurizing is not particularly limited, but is preferably about 5 to 60 minutes, and more preferably about 10 to 30 minutes. The heating temperature and pressure in the second heating and pressurizing step may be the same as or different from those in the first heating and pressurizing step of step 3, respectively.

Examples of the heating and pressurizing methods in step 5 include the same methods as in step 3. Further, after the step 5, the steps 4 and 5 may be repeated twice or more.

Step 5 is preferably carried out under an inert gas such as argon.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the examples.

Example 1 and Comparative Example 1
Bismuth metal powder and antimony metal powder (particle size 100 mesh) were used as Bi source and Sb source, respectively, and weighed so that Bi: Sb (element ratio) = 0.88: 0.12. The powder was placed in a cylindrical zirconia (zirconium dioxide) container with a capacity of 250 cm ³ . Zirconia balls having diameters of 5 mm and 10 mm were placed therein so as to be about 10 times the weight of the raw material powder. At this time, the number of the two types of balls was the same. The container containing the raw material powder and the sphere was placed in a glove box filled with argon gas, and the inside of the container was sealed with argon using a sealable lid. This container was attached to a device having a rotation mechanism (Pulveristte 6 manufactured by Fritsch), and mixing was performed at a rotation speed of 500 rotations per minute. In order to suppress the temperature rise due to the collision between the sphere and the container, the mixing was carried out for 30 minutes, then stopped for 20 minutes, and the mixing was repeated for another 30 minutes. A total of 10 hours and 30 minutes was mixed. This mixing produced an alloy of bismuth and antimony (alloy precursor in the present invention). Generally, this alloy manufacturing method is called a mechanical alloying method.

Next, the obtained alloy powder was placed in a carbon mold capable of firing a disk-shaped sample having a diameter of 10 mm, and a direct current was applied to the carbon mold while applying a uniaxial pressurization of 30 MPa in a vacuum to heat the carbon mold. (Current current sintering method). The firing temperature and time were 200 ° C. and 5 minutes. The alloy (sintered body) obtained here was used as the alloy of Comparative Example 1.

Next, the obtained alloy was placed at room temperature (about 25 ° C.) and under normal pressure (about 1 atm), and naturally cooled to about room temperature. Next, the alloy was placed in a carbon mold capable of producing a disk-shaped sintered body having a diameter of 15 mm without crushing, and the pressure, firing temperature, and time were the same as in the previous conditions, 30 MPa, 200 in vacuum. It was fired again at ° C for 5 minutes. As a result, the sintered body was plastically deformed and the diameter was expanded to 15 mm. The alloy (sintered body) produced here was used as the alloy of Example 1.

The alloy obtained in Example 1 was pulverized by pulverization, and X-ray diffraction measurement was performed at room temperature using copper as a target of an X-ray generation source. The obtained X-ray diffraction pattern is shown in FIG. The alloy obtained in Example 1 by mirror indexing of each diffraction peak has the same rhombic crystal (trigonal) crystal system as the simple substance of metal bismuth, and a part of the bismuth element is made of antimony. It was confirmed that it was a substituted alloy.

Further, transmission electron micrographs of the alloys obtained in Example 1 and Comparative Example 1 are shown in FIGS. 7 (i) and 7 (ii). In FIG. 7 (i), (a) shows dislocations in the crystal, and (b) shows twins. Similar dislocations and twins were confirmed in the crystals of the alloys of Examples 2 to 92. Further, in Examples 1 to 92, these dislocations and twins were observed at a plurality of places, respectively. On the other hand, in Comparative Examples 1 and 2, neither dislocations nor twins were observed.

Examples 2-92
An alloy was obtained in the same manner as in Example 1 except that the powder of each metal alone was used as the metal source so as to have the composition shown in Table 1. At the time of energization sintering, the firing temperature was appropriately adjusted according to the composition so that melting did not occur in the temperature range of 453K to 523K.

The alloys obtained in Examples 2 to 92 were also subjected to X-ray diffraction analysis in the same manner as in Example 1. As a result, it was confirmed that all of them have the same rhombic crystal (trigonal) crystal system as the simple substance of metal bismuth, and that some of the bismuth elements are substituted with antimony and each additive element. did it.

Comparative Example 2
Bismuth metal powder, antimony metal powder, and lead metal powder (particle size 100 mesh) are used as Bi source, Sb source, and Pb source, respectively, and Bi: Pb: Sb (element ratio) = 0.77: 0.05: 0. Weighed to be .18. These powders were placed in a cylindrical zirconia (zirconium dioxide) container with a capacity of 250 cm ³ . Zirconia balls having diameters of 5 mm and 10 mm were placed therein so as to be about 10 times the weight of the raw material powder. At this time, the number of the two types of balls was the same. The container containing the raw material powder and the sphere was placed in a glove box filled with argon gas, and the inside of the container was sealed with argon using a sealable lid. This container was attached to a device having a rotation mechanism (Pulveristte 6 manufactured by Fritsch), and mixing was performed at a rotation speed of 500 rotations per minute. In order to suppress the temperature rise due to the collision between the sphere and the container, the mixing was carried out for 30 minutes, then stopped for 20 minutes, and the mixing was repeated for another 30 minutes. A total of 10 hours and 30 minutes was mixed. By this mixing (mechanical alloying method), an alloy of bismuth and antimony could be produced. The alloy powder was placed in a carbon mold capable of firing a disk-shaped sample having a diameter of 10 mm, and a direct current was applied to the carbon mold while applying a uniaxial pressurization of 30 MPa in a vacuum (current sintering method). .. The firing temperature and time were 200 ° C. and 5 minutes. The obtained alloy (sintered body) was used as the alloy of Comparative Example 2.

Measurement of Thermoelectric Conversion Characteristics For each of the alloys (samples) obtained in Examples 1 to 92 and Comparative Examples 1 and 2, the Seebeck coefficient, electrical resistivity, and thermal conductivity were measured by the following methods, respectively. Since all of them are low temperature measurements, they were measured using liquid helium by the thermal transport option (TTO) of the physical characteristic measuring device (PPMS) manufactured by Quantum Design. The results are shown in Tables 1 to 4 and FIGS. 4 to 6.

-Seebeck coefficient A sample was formed into a rectangular parallelepiped (Fig. 3 (a)) with a cross section of about 3.5 mm square and a length of about 8 mm, and both ends in the length direction were fixed to the sample holder using a conductive epoxy adhesive. (Same as (b)). A heating heater (resistor) (same as (c)) is attached to one of the holder portions, and a temperature difference can be created at both ends of the sample. A resistance temperature detector (same (e)) and a voltage measuring terminal (same (f)) were connected to two places (same (d)) between both ends of the sample with a conductive epoxy adhesive. The temperature difference between two points due to heating and the thermoelectromotive force are measured with a resistance temperature detector and a voltage measurement terminal to obtain the Seebeck coefficient. The sample holder on which the sample was mounted was placed in a sample chamber whose temperature could be adjusted by liquid helium and an electric heater, and measurement was performed in the range of 80 to 300 K. Tables 1 to 4 show the values of the Seebeck coefficient at 80K and 300K.

-Electrical resistivity A sample is formed into a rectangular parallelepiped with a cross section of about 3.5 mm square and a length of about 8 mm, and fixed to the sample holder in the same manner as in the above Seebeck coefficient measurement. The holders at both ends serve as current terminals for AC power (same as (g)). An alternating current is applied, the voltage is measured at two voltage measurement terminals connected to both ends of the sample with a conductive epoxy adhesive, and a phase-sensitive detector is used to detect a weak voltage signal. The accurate electric resistance R was measured, and the electrical resistivity ρ = R × A / L was obtained from the sample dimensions (cross-sectional area A, distance between terminals L). Tables 1 to 4 show electrical resistivity (mΩcm) at 80K and 300K.

-Thermal conductivity The sample is formed into a rectangular parallelepiped with a cross section of about 3.5 mm square and a length of about 8 mm, and fixed to the sample holder in the same manner as the above Seebeck coefficient measurement. By heating the sample with a constant amount of heat from the heating heater attached to the sample holder, and measuring the change over time of the temperature difference with a temperature measuring resistor connected to two places between both ends of the sample with a conductive epoxy adhesive. The thermal conductivity K was calculated, and the thermal conductivity κ = K × L / A was obtained from the sample dimensions. Tables 1 to 4 show the thermal conductivity (W / m · K) at 80K and 300K.

As shown in FIGS. 4 to 6, Example 1 shows an n-type thermoelectric characteristic, and Example 45 shows a p-type thermoelectric characteristic. In the present invention, the composition of the alloy and the like are adjusted. , N-type and p-type thermoelectric conversion materials.

Further, in Examples 1 and 45, after the first heating and pressurizing step of heating and pressurizing the metal composition at a predetermined temperature and pressure is performed, the temperature of the alloy is lower than that of the first heating and pressurizing step. A second heating and pressurizing step of heating and pressurizing at a predetermined temperature and pressure was performed. On the other hand, in Comparative Examples 1 and 45 having the same composition as Examples 1 and 45, only the first heating and pressurizing step is performed. Therefore, it can be said that the alloys of Examples 1 and 45 have a higher density than the alloys of Comparative Examples 1 and 2.

That is, in Examples 1 to 92, since the density is increased in the second heating and pressurizing step, it is considered that the thermal conductivity is also increased. However, in Examples 1 to 92, the thermal conductivity at 300K is significantly lower than that in Comparative Examples 1 and 2. This is because in Examples 1 to 92, in addition to the first heating and pressurizing step, the second heating and pressurizing step is performed after further cooling and depressurizing, so that the inside of the alloy crystal is contained. It can be understood that at least one of the plurality of dislocations and twins was formed (see FIG. 7), and as a result, the thermal conductivity was significantly reduced (Tables 1 to 4). In fact, in the alloys of Comparative Examples 1 and 2, a plurality of dislocations and twins were not observed in the crystals (see FIG. 7). Further, for example, as shown in FIG. 6, the alloys of Examples 1 and 45 have the same composition in both n-type and p-type, respectively, and the heat at 80K to 300K is higher than that of Comparative Examples 1 and 2. The conductivity was significantly lower.

Thus, the composition formula: Bi _1-xy Sb _{x My (} in the formula, M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In. It is at least one element selected from the group consisting of 0.03 ≦ x ≦ 0.95, 0 ≦ y0.00 ≦ y ≦ 0.20), and has a plurality of rearrangements and a plurality of rearrangements in the crystal. It can be seen that the alloy having at least one of the twin crystals has excellent thermal conductivity in an environment of 300 K and low electrical resistivity in a low temperature of 80 K, and exhibits excellent thermoelectric conversion characteristics. On the other hand, in Comparative Example 1 which has the composition but does not have a plurality of dislocations or twins in the crystal, the electrical resistivity at a low temperature of 80 K is high, and the heat in an environment of a temperature of 300 K is high. It was clarified that the conductivity was high and the thermoelectric conversion performance was inferior to that of the alloys of Examples 1 to 92. Further, for the alloy of Comparative Example 2 which does not have a plurality of dislocations or twins in the crystal, the electrical resistivity at a low temperature of 80 K is low, but the thermal conductivity is high in an environment of a temperature of 300 K. It was clarified that the thermoelectric conversion performance was inferior to that of the alloys of Examples 1 to 92.

Claims (4)

Composition formula: Bi _{1 -x -y} Sb _x My ₍ In the formula, M is at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, and Te. It is an element of 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20), and has a plurality of dislocations and at least one of a plurality of twins in the crystal.
It has a thermal conductivity of 4.00 W / m · K or less at a temperature of 300 K.
A sintered body having an electrical resistivity of 5.00 mΩcm or less at a temperature of 80 K. A thermoelectric conversion material comprising the sintered body according to claim 1. A thermoelectric conversion module comprising the thermoelectric conversion material according to claim 2. It is a manufacturing method of a sintered body.
The sintered body has a composition formula: Bi _{1 -x -y} Sb _x My ₍ in the formula, M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, It is at least one element selected from the group consisting of Pb and In, and is represented by 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20), and a plurality of rearrangements in the crystal. And a sintered body having at least one of a plurality of twin crystals, having a thermal conductivity of 4.00 W / m · K or less at a temperature of 300 K, and an electrical resistivity of 5.00 mΩ cm or less at a temperature of 80 K. can be,
Bi, Sb, and M (where M is at least one element selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In. The molar ratio of 1) is 1-x-y: x: y (however, 0.03 ≦ x ≦ 0.95 and 0.00 ≦ y ≦ 0.20). Step 1 to obtain a metal composition obtained by mixing an alloy, an intermetal compound, or a solid solution composed of a simple substance of Bi metal, a simple substance of Sb metal, a simple substance of M metal, or at least two kinds of metals among these metals.
Step 2 of pressurizing the metal composition to obtain a sintered precursor,
The first heating and pressurizing step 3 of heating and pressurizing the sintered body precursor under the conditions of a temperature of 353 K to 573 K and a pressure of 5 MPa to 100 MPa to obtain a sintered body,
Step 4 of placing the sintered body under a temperature and pressure lower than that of the first heating and pressurizing step, and
After the step 4, the second heating and pressurizing step of heating and pressurizing the sintered body under the conditions of a temperature of 353K to 503K and a pressure of 5MPa to 100MPa, and a second heating and pressurizing step.
A method for manufacturing a sintered body.

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