JPWO2018038146A1 - Thermoelectric material - Google Patents

Abstract

A novel alloy exhibiting excellent thermoelectric conversion characteristics is provided, which has low thermal conductivity in an environment at a temperature of about 300 K and low electrical resistivity at a low temperature of about 80 K. Composition formula: Bi1-x-ySbxMy (wherein, M is at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In A kind of element, expressed by 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20), and having at least one of a plurality of dislocations and a plurality of twins in a crystal, alloy.

Description

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

  In Japan, the yield rate of effective energy from primary supply energy is only about 30%, and about 70% of energy is finally discarded to the atmosphere as heat. In addition, heat generated by combustion is also discarded to the atmosphere without being converted to other energy in factories and waste incineration plants. In this way, we humans waste much heat energy and waste little energy from actions such as burning of fossil energy.

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

  Thermoelectric power generation is an energy conversion method that generates electric potential by causing a potential difference by providing a temperature difference at both ends of a thermoelectric conversion material, using the Seebeck effect. In this method, one end of the thermoelectric conversion material is placed in the low temperature part produced by the vaporization of the liquefied natural gas, the other end is placed in contact with the atmosphere or water tank at normal temperature, Electricity is obtained, and no moving devices such as motors or turbines necessary for general power generation are required at all. Therefore, the cost is low, there is no exhaust gas, and power generation can be continuously performed until the thermoelectric conversion material is deteriorated.

  Another way of using thermoelectric conversion is to make a temperature difference at both ends by supplying a current to the thermoelectric conversion material. 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 Peltier cooling. Cooling is essential for the superconducting element and the infrared sensor element. In particular, superconducting elements require cooling until the material is in the superconducting state. For that purpose, it is necessary to use liquid nitrogen, but using a liquid as a refrigerant makes handling and supply complicated, and also causes a problem in safety. Then, in use of various sensors, the solid cooling element which can be cooled to about 100 K is indispensable, and the Peltier cooling element by the thermoelectric conversion effect is the most promising.

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

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

Furthermore, the performance of the thermoelectric conversion material is the dimensionless figure of merit ZT (= S ² T / (ρ)) regarding thermoelectric conversion performance, where S, T, ρ, κ are Seebeck coefficient, absolute temperature, electrical resistivity, respectively) In order to put the thermoelectric conversion material into practical use, it is necessary to increase the ZT value at, for example, about 300K. And in order to raise this ZT value, it is necessary to reduce the heat conductivity in about 300K.

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, having a low thermal conductivity in an environment of about 300 K and a low electrical resistivity at a low temperature of about 80 K. The main purpose is to Furthermore, this invention also aims at providing the manufacturing method of the said alloy, the thermoelectric conversion material which consists of the said alloy, and the thermoelectric conversion module using the said thermoelectric conversion material.

The present inventors diligently studied to solve the above-mentioned problems. As a result, the compositional formula: Bi _1-xy Sb _x M _y (wherein M is from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In And at least one element selected from the group consisting of: 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20), and a plurality of dislocations and a plurality of twins in the crystal. It has been found that an alloy having at least one of the foregoing has excellent thermoelectric conversion characteristics in which the thermal conductivity in an environment at a temperature of about 300 K is low and the electrical resistivity at a low temperature of about 80 K is low.

  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 hitherto.

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

That is, the present invention provides the inventions of the aspects listed below.
Item 1. Composition formula: Bi in _1-xy Sb _x M _y (wherein, M is, Ti, V, Cr, Mn , Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and from the group consisting of In At least one element selected and represented by 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20), and at least one of a plurality of dislocations and a plurality of twins in the crystal Has an alloy.
Item 2. The alloy according to Item 1, having a thermal conductivity of 4.00 W / m · K or less at a temperature of 300 K.
Item 3. Composition formula: Bi in _1-xy Sb _x M _y (wherein, M is, Ti, V, Cr, Mn , Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and from the group consisting of In At least one element selected and 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. 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. The thermoelectric conversion material which consists of an alloy in any one of claim | item 1 -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 Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In, and at least one element selected from the group consisting of So that the molar ratio of 1) -x-y: x: y (where 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20), Step 1 of obtaining a metal composition in which an alloy, an intermetallic 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 is mixed,
Pressurizing the metal composition to obtain an alloy precursor;
A first heating and pressing step 3 of heating and pressing the alloy precursor under conditions of a temperature of 353 K to 573 K and a pressure of 5 MPa to 100 MPa to obtain an alloy;
Placing the alloy under a lower temperature and a lower pressure than the first heating and pressing step;
A second heating and pressing step of heating and pressing the alloy under conditions of a temperature of 353 K to 573 K and a pressure of 5 MPa to 100 MPa after the step 4;
A method of manufacturing an alloy, comprising:

According to the present invention, the compositional formula: Bi in _1-xy Sb _x M _y (wherein, M is, Ti, V, Cr, Mn , Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, And at least one element selected from the group consisting of and 0.03 and represented by 0.03 ≦ x ≦ 0.95 and 0.00 ≦ y ≦ 0.20), and a plurality of dislocations and Novel thermal conductivity is excellent because it has at least one of the crystals, so that the thermal conductivity in an environment at a temperature of about 300 K is low, and the electrical resistivity at a low temperature of about 80 K is low. An alloy can be provided.

Further, according to the present invention, a composition formula: Bi _{1 -xy} Sb _x M _y (where, M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, At least one element selected from the group consisting of Pb and In, which is represented by 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20), and at a temperature of 300 K, 4.00 W It is also possible to provide new alloys having a thermal conductivity of less than / m · K.

  Furthermore, according to the present invention, it is possible to provide a method for producing the above novel alloy, a thermoelectric conversion material comprising the alloy, and a thermoelectric conversion module using the thermoelectric conversion material. The thermoelectric conversion material comprising 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 such 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 80 K to 300 K. It can be an n-type or p-type thermoelectric conversion material. Furthermore, by incorporating n-type or p-type thermoelectric conversion material into the system as an n-type or p-type thermoelectric conversion element in a thermoelectric conversion module, liquefied natural gas which has been discarded by heat exchange up to now in seawater etc. It is possible to effectively utilize the cold energy from the above, and it is possible to utilize as a solid cooling device capable of cooling to around 100 K by energizing the module.

It is an example of the schematic diagram of the thermoelectric conversion module which used the alloy of this invention as 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 the schematic diagram which shows the outline of the sample holder and wiring which measure a Seebeck coefficient, an electrical resistivity, and thermal conductivity. FIG. 4 (a) shows the alloy (sintered body) obtained in Example 1 (i) and Comparative Example 1 (ii), FIG. 4 (b) shows Example 45 (iii) and Comparative Example It is a graph which shows the temperature dependence of the Seebeck coefficient in the temperature of 80 K-300 K, respectively about the alloy (sintered body) obtained by 2 (iv). FIG. 5 (a) shows the alloy (sintered body) obtained in Example 1 (i) and Comparative Example 1 (ii), FIG. 5 (b) shows Example 45 (iii) and Comparative Example It is a graph which shows the temperature dependence of the electrical resistivity in the temperature of 80 K-300 K about the alloy (sintered body) obtained by 2 (iv). 6 (a) shows the alloy (sintered body) obtained in Example 1 (i) and Comparative Example 1 (ii), FIG. 6 (b) shows Example 45 (iii) and Comparative Example It is a graph which shows the temperature dependence of thermal conductivity in temperature 80 K-300 K, respectively about the alloy (sintered body) obtained by 2 (iv). It is a transmission electron micrograph of the alloy (sintered body) obtained in Example 1 (i) and Comparative Example 1 (ii) ((a) in FIG. 7 shows the location of dislocations. , (B) shows the location of twins).

The first alloy of the present invention has a composition formula: Bi _{1 -xy} Sb _x M _y (where, M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn And at least one element selected from the group consisting of Pb, and In, wherein 0.03 ≦ x ≦ 0.95, and 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.

Furthermore, the second alloy of the present invention has a composition formula: Bi _{1 -xy} Sb _x M _y (where, M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge And at least one element selected from the group consisting of Sn, Pb, and In, wherein 0.03 ≦ x ≦ 0.95, and 0.00 ≦ y ≦ 0.20), and the temperature 300 K In the above, the thermal conductivity is 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 M _y . 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 alloys of the present invention may not have M (i.e., y = 0). Moreover, as a kind of metal M contained in an alloy, it is preferable that it is 0-5 types, It is more preferable that it is 0-3 types, It is still more preferable that it is 0-1 types.

  M is not particularly limited as long as it is as described above, but Pb, Sn, In, Ge and the like are preferably 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 position of the parent material Bi, and a rhombohedral (trigonal) system similar to Bi (space group It is a metal compound (metal material) which has a crystal structure of R_3 m). As will be described later, the alloy can be said to be a sintered body because it is manufactured by heating and pressing a single metal or the like.

  The alloy of the present invention has a negative Seebeck coefficient or a positive Seebeck coefficient by adjusting it to the composition (that is, the substitution amount of Sb and M and the type of M with respect to Bi crystal) and the use temperature conditions. Have. That is, by adjusting the composition and temperature conditions appropriately, it is possible to control the positive and negative of the Seebeck coefficient. For example, when a temperature difference is generated at both ends of the alloy and the negative Seebeck coefficient is indicated, 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 Show the characteristics of On the other hand, when a positive Seebeck coefficient is exhibited, 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 a crystal. Here, in the present invention, dislocation within a crystal means linear lattice defects due to deviation of crystal planes. Further, in the present invention, the twin crystal in a crystal means that different crystals are joined in the crystal axis orientation. In the first alloy of the present invention, by having dislocations or twins in the crystal, the phonons that transfer heat are effectively scattered, so the thermal conductivity at 300 K, for example, is effectively reduced; It is less than 00 W / m · K. In addition, since dislocations and twins in the crystal have little influence on the electrical resistivity, the first alloy of the present invention exhibits a low value of 5.00 mΩcm or less even for the electrical resistivity under 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, further preferably 1.95 W / M · K or less can be mentioned.

  Furthermore, 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, and still more preferably 0.60 mΩcm or less.

  From the same point of view, the electrical resistivity of the alloy of the present invention at 300 K 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 made into an n-type thermoelectric conversion material or a p-type thermoelectric conversion material by adjusting the composition and the temperature condition in the use environment.

  Furthermore, the thermoelectric conversion material can be made into n-type or p-type thermoelectric conversion element by combining multiple thermoelectric conversion materials which consist of an alloy of the present invention, and it can be used as a thermoelectric conversion module using these. An example of a schematic view 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 the structure 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, an electrode 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 80 K to 300 K. N-type or p-type thermoelectric conversion material. Furthermore, by incorporating an n-type or p-type thermoelectric conversion material into the system as an n-type or p-type thermoelectric conversion element in a thermoelectric conversion module, for example, liquefaction which has hitherto been discarded by heat exchange in seawater etc. It becomes possible to effectively utilize the cold energy from the natural gas, and by energizing the module it is possible to use as a solid cooling device capable of cooling to around 100K.

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

Step 1: Bi, Sb, and M (where M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In) The molar ratio of one kind of element) is a mixing ratio of 1-xy: x: y (however, 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20) As described above, a process of obtaining a metal composition in which an alloy, an intermetallic 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 is mixed. Step of pressing the metal composition obtained in Step 1 to obtain an alloy precursor Step 3: The alloy precursor obtained in Step 2 is heated and pressed under conditions of temperature 353 K to 573 K and pressure 5 MPa to 100 MPa To obtain an alloy, the first heating and pressing step Process of placing the alloy obtained in Step 3 under a lower temperature and pressure than the first heating and pressing process Step 5: After Step 4, the alloy is heated to a temperature of 353 K to 573 K and a pressure of 5 MPa to 100 MPa. The second heating and pressurizing step of heating and pressurizing under the conditions

  First, in step 1, the 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 not only Bi metal alone, Sb metal alone and M metal alone, but also an alloy, an intermetallic compound, or a solid solution composed of at least two 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 method for pressurizing the metal composition is not particularly limited, and examples thereof include a mechanical alloying method, a melting or solid phase reaction method. In the mechanical alloying method, for example, the metal composition is placed in a crucible or a container made of stainless steel, and balls made of the same material as the container and having an arbitrary diameter (for example, about 2 mm to 2 cm) are put in an appropriate number It is a method of alloying using the collision energy between spheres and a metal composition (preferably powder) or by utilizing the collision energy of the spheres by rotating and oscillating the container. In addition, in the method of melting or solid phase reaction, powder, granular, plate or the like may be used as the metal composition. Step 2 is preferably performed in vacuum or under an inert gas such as argon.

  Next, in step 3, a first heating and pressing step of heating and pressing the alloy precursor obtained in step 2 under conditions of temperature 353 K to 573 K and pressure 5 MPa to 100 MPa to obtain an alloy Do. At this time, the alloy precursor to be subjected to step 3 is preferably in the form of powder. For heating and pressing, for example, a powdery alloy precursor is formed into a plate (for example, a disk) by uniaxial pressing, then the plate is put into a mold made of carbon, and a pressing shaft is placed on the plate surface. There is a method in which the alloy precursor is sintered and alloyed by heating under the condition of pressure 5MPa to 100MPa and heating at temperature 353K to 573K in that state so that

  The method of heating and pressing in step 3 is not particularly limited, but for example, a hot press method of heating by heat transfer from a heating element, energization of a carbon mold and conduction sintering of heating by heat generation by electrical resistance Law etc.

  As heating temperature in the process 3, Preferably about 443K-503K is mentioned. Moreover, as pressure, Preferably about 10 MPa-about 80 MPa are mentioned. Further, the heating and pressurizing time is not particularly limited, but preferably about 5 minutes to 60 minutes, more preferably about 10 minutes to 30 minutes.

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

  Next, in step 4, the alloy obtained in step 3 is put under a lower temperature and lower pressure than the first heating and pressing step of step 3. The temperature at this time is not particularly limited, but preferably about 283 K to 353 K, more preferably about 293 K to 313 K. 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 time under which the temperature and pressure are lower than in the first heating and pressurizing step in step 3 is not particularly limited, but is preferably about 1 hour to 72 hours, more preferably about 1 hour to 24 hours. It can be mentioned. Typically, the alloy obtained in step 3 is placed at normal temperature (about 25 ° C.) under normal pressure, and allowed to cool naturally until the alloy reaches normal temperature, and the second heating and pressing in step 5 described later The process can be performed.

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

  In the second heating and pressurizing step of step 5, the alloy cooled in step 4 is again heated and pressurized under conditions of a temperature of 353 K to 573 K and a pressure of 5 MPa to 100 MPa. In the second heating and pressing step, the alloy obtained in step 3 is not crushed, and it is placed in a mold capable of sintering a substance that is about 1.1 to 2 times larger than the diameter of the alloy, and heated and pressurized. It is preferred to do. Thereby, the alloy is easily plastically deformed, the diameter is increased, the thickness is reduced, and an alloy having at least one of a plurality of dislocations and a plurality of twins in a crystal is preferably obtained.

  As a heating temperature in a 2nd heating-pressing process, Preferably about 443K-503K is mentioned. Moreover, as pressure, Preferably about 10 MPa-about 80 MPa are mentioned. Further, the heating and pressurizing time is not particularly limited, but preferably about 5 minutes to 60 minutes, more preferably about 10 minutes to 30 minutes. The heating temperature and pressure in the second heating and pressing step may be the same as or different from the first heating and pressing step in step 3, respectively.

  As the method of heating and pressurizing in step 5, the same method as in step 3 can be mentioned. In addition, after step 5, step 4 and step 5 may be repeated twice or more.

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

  Hereinafter, the present invention will be described in detail by showing 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 diameter: 100 mesh) were used as a Bi source and an Sb source, respectively, and measurement was performed so that Bi: Sb (element ratio) = 0.88: 0.12. The powder was placed in a cylindrical zirconia (zirconium dioxide) container having a volume of 250 cm ³ . Thereto, zirconia balls having a diameter of 5 mm and 10 mm were placed in a weight of about 10 times the weight of the raw material powder. At this time, the number of balls of the two types was the same. The container containing the raw material powder and the balls was placed in a glove box filled with argon gas, and the inside of the container was argon-sealed using a lid that can be sealed. The container was attached to an apparatus (Flitch made Pulverisette 6) having a rotation mechanism, and mixing was performed at a rotational speed of 500 revolutions per minute. The mixing was carried out for 30 minutes to stop the temperature rise due to the collision of the ball and the container, and then stopped for 20 minutes, and the mixing for another 30 minutes was repeated. In total, it was mixed for 10 hours and 30 minutes. By this mixing, an alloy of bismuth and antimony (in the present invention, an alloy precursor) was produced. In addition, generally, this alloy manufacturing method is called a mechanical alloying method.

  Next, the obtained alloy powder is placed in a carbon mold capable of firing a disk-shaped sample with a diameter of 10 mm, and direct current is supplied to the carbon mold for heating while applying uniaxial pressurization of 30 MPa in vacuum. (Electric 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 under normal pressure (about 1 atm) at room temperature (about 25 ° C.) and naturally cooled to about room temperature. Next, the alloy is put into a carbon mold capable of producing a disk-shaped sintered body having a diameter of 15 mm without crushing, and the pressure and baking temperature and time are 30 MPa and 200 MPa under the same conditions as the above conditions. It baked again as 5 degreeC for 5 minutes. Thereby, the sintered body was plastically deformed and the diameter was enlarged 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 source. The obtained X-ray diffraction pattern is shown in FIG. According to Miller indexing of each diffraction peak, the alloy obtained in Example 1 has the same rhombohedral (trigonal) crystal system as the metal bismuth simple substance, and part of the bismuth element is antimony It was confirmed that the alloy was substituted.

  In addition, 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 observed in the crystals of the alloys of Examples 2 to 92. In Examples 1 to 92, these dislocations and twins were observed at a plurality of locations, respectively. On the other hand, neither dislocations nor twins were observed in Comparative Examples 1 and 2.

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

  The respective 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 is confirmed that each of them has the same rhombohedral (trigonal) crystal system as that of metal bismuth alone, and is an alloy in which a part of the bismuth element is substituted by antimony and each additive element. did it.

Comparative example 2
Bi: Pb: Sb (element ratio) = 0.77: 0.05: 0 using a Bi metal source, an Sb source, and a bismuth metal powder, an antimony metal powder, and a lead metal powder (particle size 100 mesh) as the Pb source, respectively. Weighed to .18. These powders were placed in a cylindrical zirconia (zirconium dioxide) container having a volume of 250 cm ³ . Thereto, zirconia balls having a diameter of 5 mm and 10 mm were placed in a weight of about 10 times the weight of the raw material powder. At this time, the number of balls of the two types was the same. The container containing the raw material powder and the balls was placed in a glove box filled with argon gas, and the inside of the container was argon-sealed using a lid that can be sealed. The container was attached to an apparatus (Flitch made Pulverisette 6) having a rotation mechanism, and mixing was performed at a rotational speed of 500 revolutions per minute. The mixing was carried out for 30 minutes to stop the temperature rise due to the collision of the ball and the container, and then stopped for 20 minutes, and the mixing for another 30 minutes was repeated. In total, it was mixed for 10 hours and 30 minutes. An alloy of bismuth and antimony was produced by this mixing (mechanical alloying method). The alloy powder was placed in a carbon mold capable of firing a disk-shaped sample with a diameter of 10 mm, and while applying uniaxial pressure of 30 MPa in vacuum, DC current was applied to the carbon mold to heat it (electricity 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 The Seebeck coefficient, the electrical resistivity, and the thermal conductivity of each of the alloys (samples) obtained in Examples 1 to 92 and Comparative Examples 1 and 2 were measured by the following method. Since all of them are low-temperature measurements, they were measured using liquid helium by the thermal transport option (TTO) of a physical property measuring apparatus (PPMS) manufactured by Quantum Design. The results are shown in Tables 1 to 4 and Figs.

Seebeck coefficient The sample was formed into a rectangular solid (Fig. 3 (a)) having a cross section of about 3.5 mm square and a length of about 8 mm, and both ends in the lengthwise direction were fixed to the sample holder using a conductive epoxy adhesive. (Same (b)). A heater (resistor) (the same (c)) is attached to one of the holder portions, and a temperature difference can be given to both ends of the sample. The temperature measuring resistor (the same (e)) and the voltage measurement terminal (the same (f)) were connected to two places (the same (d)) between the two ends of the sample with a conductive epoxy adhesive. The temperature difference between the two points due to heating and the thermoelectromotive force are measured by the temperature measuring resistor and the voltage measuring 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 the measurement was performed in the range of 80 to 300K. Tables 1-4 show the values of the Seebeck coefficients at 80K and 300K.

Electrical Resistivity A sample is formed into a rectangular parallelepiped having 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-mentioned Seebeck coefficient measurement. Holders at both ends become current terminals of the AC power supply (same (g)). An alternating current is applied, and the voltage is measured with a voltage measurement terminal connected with a conductive epoxy-based adhesive at two points between both ends of the sample, and a phase-sensitive detector is used to generate a weak voltage signal An accurate electrical resistance R was measured, and an electrical resistivity ρ = R × A / L was obtained from sample dimensions (cross sectional area A, distance L between terminals). Tables 1 to 4 show the electrical resistivity (mΩ cm) at 80 K and 300 K.

Thermal Conductivity The sample is formed into a rectangular parallelepiped having 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-mentioned Seebeck coefficient measurement. By heating the sample with a fixed amount of heat from the heater attached to the sample holder, and measuring the time-dependent change in temperature difference with a resistance temperature detector connected at two points between the two 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 80 K and 300 K.

  As shown in FIGS. 4 to 6, in Example 1, n-type thermoelectric characteristics and in Example 45 p-type thermoelectric characteristics are shown, and in the present invention, the composition and the like of the alloy are adjusted. , And n-type and p-type thermoelectric conversion materials.

  In Examples 1 and 45, after performing the first heating and pressing step of heating and pressing the metal composition at a predetermined temperature and pressure, the alloy is heated to a temperature lower than that of the first heating and pressing step. And a second heating and pressurizing step of heating and pressurizing at a predetermined temperature and pressure under a low pressure. On the other hand, in Comparative Examples 1 and 45 having the same composition as in Examples 1 and 45, only the first heating and pressing step is performed. Therefore, it can be said that the density of the alloy of Examples 1 and 45 is higher than that of 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 enhanced. However, in Examples 1 to 92, the thermal conductivity at 300 K is significantly lower than 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 cooling and depressurization, and therefore, in the crystal of the alloy. It can be understood that at least one of a plurality of dislocations and twins is formed (see FIG. 7), and as a result, the thermal conductivity is significantly reduced (Tables 1 to 4). In fact, in the alloys of Comparative Examples 1 and 2, plural dislocations and twins were not observed in the crystal (see FIG. 7). Also, for example, as shown in FIG. 6, the alloys of Examples 1 and 45 have heat at 80 K to 300 K more than Comparative Examples 1 and 2 having the same composition in either n-type or p-type, respectively. The conductivity was significantly lower.

Thus, the compositional formula: Bi _{1 -xy} Sb _x M _y (where, M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In And at least one element selected from the group consisting of: 0.03 ≦ x ≦ 0.95, 0 ≦ y0.00 ≦ y ≦ 0.20), and a plurality of dislocations and a plurality of dislocations in the crystal. It is understood that an alloy having at least one of twins has excellent thermal conductivity and low thermal conductivity in an environment at a temperature of 300 K and low electric resistivity at a low temperature of 80 K. On the other hand, in Comparative Example 1 having the composition but not having 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 The conductivity was also high, and it was revealed that the thermoelectric conversion performance was inferior to the alloys of Examples 1 to 92. In addition, the alloy of Comparative Example 2 having no plurality of dislocations or twins in the crystal has low electrical resistivity at a low temperature of 80 K, but high thermal conductivity in an environment at a temperature of 300 K. It turned out that it is inferior to thermoelectric conversion performance compared with the alloy of Examples 1-92.

Claims (7)

Composition formula: Bi in _1-xy Sb _x M _y (wherein, M is, Ti, V, Cr, Mn , Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and from the group consisting of In At least one element selected and represented by 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20), and at least one of a plurality of dislocations and a plurality of twins in the crystal Has an alloy.   The alloy according to claim 1, having a thermal conductivity of 4.00 W / m · K or less at a temperature of 300K. Composition formula: Bi in _1-xy Sb _x M _y (wherein, M is, Ti, V, Cr, Mn , Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and from the group consisting of In At least one element selected and 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.   The alloy according to any one of claims 1 to 3, which has an electrical resistivity of 5.00 mΩcm or less at a temperature of 80K.   The thermoelectric conversion material which consists of an alloy in any one of Claims 1-4.   A thermoelectric conversion module, comprising the thermoelectric conversion material according to claim 5. Bi, Sb, and M (where M is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Te, Ge, Sn, Pb, and In, and at least one element selected from the group consisting of So that the molar ratio of 1) -x-y: x: y (where 0.03 ≦ x ≦ 0.95, 0.00 ≦ y ≦ 0.20), Step 1 of obtaining a metal composition in which an alloy, an intermetallic 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 is mixed,
Pressurizing the metal composition to obtain an alloy precursor;
A first heating and pressing step 3 of heating and pressing the alloy precursor under conditions of a temperature of 353 K to 573 K and a pressure of 5 MPa to 100 MPa to obtain an alloy;
Placing the alloy under a lower temperature and a lower pressure than the first heating and pressing step;
A second heating and pressing step of heating and pressing the alloy under conditions of a temperature of 353 K to 573 K and a pressure of 5 MPa to 100 MPa after the step 4;
A method of manufacturing an alloy, comprising:

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