JP2004363620A - Thermoelectric material, its manufacturing method and peltier module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric material capable of obtaining a high Seebeck coefficient with high homogeneity and reducing electric resistance by promoting the C-plane orientation of a Bi<SB>2</SB>Te<SB>3</SB>-based thermoelectric material, and also to provide a method for manufacturing the material and a peltier module. <P>SOLUTION: The method for manufacturing the thermoelectric material comprising steps of: at first, obtaining an ingot or its comminuted powder of which the composition is composed of at least one element selected from a group composed of Bi and Sb and at least one element selected from a group composed of Te and Se; and then forming a rhombohedral structure of the ingot or its comminuted powder by executing extrusion processing more than one time at an extrusion speed of 0.001-0.03 mm/minute so as to shear the ingot or its comminuted powder by using dies in which a pressurizing shaft and an extrusion shaft are not arranged on the same axis. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-performance thermoelectric material having an improved figure of merit, a method for manufacturing the same, and a Peltier module.

  The properties of the thermoelectric material are represented by the following equation 1 when the Seebeck coefficient is α (μ · V / K), the specific resistance is ρ (Ω · m), and the thermal conductivity is κ (W / m · K). It can be evaluated by the performance index Z.

  As shown in the above formula 1, in order to increase the figure of merit Z, it is effective to reduce the specific resistance ρ and the thermal conductivity κ. It is generally known that the smaller the grain size of the crystal grains, the lower the thermal conductivity κ. Further, when the number of passing crystals is reduced in the direction in which the heat flow and the current pass, the specific resistance decreases. That is, when the current or heat flow direction is defined in the direction in which the crystal grows, the figure of merit Z of the thermoelectric material increases.

As such a thermally conductive material, for example, Bi ₂ Te ₃ -based thermoelectric material is used. For example Bi ₂ Te ₃ -based thermoelectric material made of a sintered material, the solidified material is crushed will be produced by solidifying and molding by hot pressing or the like, during the solidification molding, pressure and vertical hot pressing A crystal orientation (a-axis) with low resistance grows in the direction, and a high figure of merit is obtained in this direction. Therefore, a thermoelectric element and a thermoelectric module including the plurality of thermoelectric elements are assembled by attaching electrodes so that a current flows in the a-axis direction. For this reason, in the production process of the thermoelectric material, it is important that the a-axes of the crystals are aligned, that is, that high orientation is imparted.

  2. Description of the Related Art Conventionally, a technique of manufacturing a thermoelectric material by an extrusion method in order to improve a figure of merit has been disclosed (see Patent Document 1). FIG. 16 is a cross-sectional view illustrating a method for manufacturing a thermoelectric material described in Patent Document 1. In the method for manufacturing a thermoelectric material described in Patent Document 1, as shown in FIG. 16, at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se A thermoelectric material (raw material) 101 having a composition including a seed element is extruded by a die 102 in the longitudinal direction of the raw material 101. At this time, the material 101 is heated by the heater 104 to soften it. As a result, the material 101 having the (001) plane (c-plane) direction aligned in one direction is extruded, so that the extruded material 103 has crystal grains refined while the c-plane direction is aligned in one direction. I do. Accordingly, the electrical resistivity ρ of the material 103 after extrusion does not change and the thermal conductivity κ of the material 103 after extrusion decreases as compared with the material 101 before extrusion. In such an extrusion method, the c-plane is slip-oriented by drawing.

  There is also a method in which a thermoelectric material is extruded into an L-shape to perform strong working by shearing processing, thereby imparting an orientation (see Non-Patent Document 1). FIG. 17 is a schematic cross-sectional view showing a shear addition extrusion method described in Non-Patent Document 1.

In the shear addition extrusion method described in Non-Patent Document 1, as shown in FIG. 17, a green compact of (Bi ₂ Te ₃ ) _0.2 (Sb ₂ Te ₃ ) _0.8 which is a p-type material is formed. Then, this green compact is processed by the extrusion die 110. The extrusion die 110 includes a cylindrical portion 110a whose central axis is in a vertical direction, and a horizontal portion 110b whose path is bent in a direction perpendicular to the cylindrical shape. Then, by pressing the green compact with the upper punch 111 inserted into the cylindrical portion 110a, the unidirectional orientation in the crystal direction due to the load of the shear stress and the rotation is applied to the green compact at the right angle portion of the path of the extrusion die 110. Induced.

  Further, there is disclosed a technique of crushing a thermoelectric material uniaxially in a direction orthogonal to a pressure axis (see Patent Document 2). FIG. 18 is a diagram showing hot upsetting forging in the method for producing a thermoelectric material of Patent Document 2. FIG. 18 (a) shows before upsetting forging, and FIG. 18 (b) shows after upsetting forging. It is a typical sectional view.

  In the method described in Patent Document 2, a solid solution ingot of a thermoelectric semiconductor is formed, and the ingot is pulverized and sintered under pressure. Thereafter, as shown in FIGS. 18A and 18B, a base 121, a cylindrical sleeve 122 having a rectangular parallelepiped cavity therein perpendicular to the base 121, and inserted through the cavity of the sleeve 122. The press-sintered powder sintered body 124 is inserted into the cavity of the sleeve 122 by using an upsetting device having a punch 123 formed so as to perform plastic deformation by hot plastic deformation. By stretching, the thermoelectric semiconductor material 125 is formed by a hot upsetting forging process in which the crystal grains of the powder crystal grains are oriented in a crystal orientation having an excellent figure of merit.

JP-A-11-163422 JP-A-10-178218 Collection of lectures of Japan Society of Powder and Powder Metallurgy Spring Meeting 2000, May 16, 2000, p. 197

  However, in the technique described in Patent Literature 1, the difference in the working degree increases in the circumferential direction, and a physical property distribution occurs. FIGS. 19A to 19C are diagrams showing the problems of the technology described in Patent Document 1. FIG. 19A is a schematic diagram showing a thermoelectric material in a die, and FIGS. 19C is a cross-sectional view and a schematic view showing the thermoelectric material at the position of the extruded portion shown in FIG. As shown in FIGS. 19 (a) and (b), there is a problem that the working degree near the material surface 130 in contact with the die in the extruded part is higher than the working degree in the central part. Further, the more the hard working is performed, the narrower the drawing diameter becomes, so that the yield decreases. Further, as shown in FIG. 19 (c), the extruded thermoelectric material rotates and its (001) plane (c plane) is arranged in the circumferential direction and is not arranged in one direction. However, there is a problem that a necessary low resistance value cannot be obtained.

  Further, in the technique described in Patent Document 2, since the starting material is obtained by pulverizing a solid solution ingot and sintering it under pressure, the crystal grain size is large and non-uniform, and the electric resistance is usually higher than that of the p-type. However, in the case of an n-type thermoelectric element having a high resistance, there is a problem that there is a limit in reducing the resistance.

Furthermore, in the techniques described in Patent Literatures 1 and 2 and Non-Patent Literature 1, in a thermoelectric material composed of (Bi, Sb) ₂ (Te, Se) ₃ , the n-type thermoelectric material has a performance index of 3.0 × 10 ^−3. It is extremely difficult to produce a material exceeding / K, and in particular, the electrical resistance ρ for use in optical communication components is 1.2 × 10 ⁻⁵ Ωm or less and the figure of merit is 3.0 × 10 ⁻³ / K. Very little material has been obtained.

  It is conventionally known that when comparing a p-type thermoelectric material and an n-type thermoelectric material, the n-type thermoelectric material has worse performance due to the characteristics of the material. That is, when the Seebeck coefficient is formed to be the same for the p-type and the n-type, the n-type thermoelectric material has a higher electric resistance than the p-type. If the electric resistance is the same, the Seebeck coefficient of the n-type becomes lower. However, in order to use it as a thermoelectric module, it is necessary to unify the thermoelectric properties including the Seebeck coefficient, electric resistance, and thermal conductivity. For this reason, the techniques described in Patent Literatures 1 and 2 and Non-Patent Literature 1 have a problem that it is difficult to manufacture an n-type thermoelectric material having excellent thermoelectric properties.

The present invention has been made in view of such a problem, and promotes the (001) plane orientation of a Bi ₂ Te ₃ -based thermoelectric material to reduce electric resistance, has excellent homogeneity, and is n-type. It is an object of the present invention to provide a thermoelectric material capable of obtaining a high Seebeck coefficient, a method for manufacturing the same, and a Peltier module.

  The thermoelectric material according to the first invention of the present application is an ingot having a composition including at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se, or an ingot thereof. An extruding process in which a crushed powder is subjected to a shearing process using a die in which a pressing axis and an extruding axis are not uniaxial is performed at least once at an extruding speed of 0.001 to 0.03 mm / min. It is characterized by having been done.

  In the extrusion process, a load smaller than the pressing load may be applied to the material to be extruded from a direction opposite to the extrusion direction.

  Further, the thermoelectric material of the present invention may be obtained by hot pressing in a direction orthogonal to the extrusion axis on a plane having a pressure axis and an extrusion axis after the extrusion processing, or the extrusion processing Is performed twice or more, and the cross-sectional area of the die outlet in the final extrusion step is made smaller than the cross-sectional area of the die inlet.

  Further, one or more elements selected from the group consisting of I, Cl, Hg, Br, Ag and Cu may be added to the thermoelectric material.

  Furthermore, crystal grains having an average particle diameter of 30 μm or less and having an angle between the extrusion axis and the [001] axis (c-axis) of 45 ° or less among all the crystal grains in a plane perpendicular to the extrusion direction. Can be set to 10% or less of the total crystal grain area.

  The method for producing a thermoelectric material according to the second invention of the present application includes a method of forming a composition comprising at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se. In the method for producing a thermoelectric material having, the ingot or the pulverized powder of the composition is subjected to at least one extrusion process of performing a shearing process using a die having a pressing axis and an extruding axis that are not coaxial. It is characterized by having.

  In the present invention, since the ingot or its pulverized powder is extruded with a die in which the pressure axis and the extrusion axis are not uniaxial, as in the case of using a flake obtained by the liquid quenching method, A high Seebeck coefficient α can be obtained by controlling the carrier concentration, and a high-performance thermoelectric material having a low electric resistance with a uniform (001) plane (c-plane) orientation can be obtained.

  In the extrusion process, a load smaller than the pressure load can be applied to the material to be extruded from a direction opposite to the extrusion direction.

  In the step of performing the extrusion process at least once, after the extrusion process, a hot press process may be performed on a plane having a pressing axis and an extrusion axis in a direction orthogonal to the extrusion axis.

  Further, in the step of performing the extrusion processing at least once, the extrusion processing is performed twice or more, and the cross-sectional area of the die outlet in the final extrusion step can be smaller than the cross-sectional area of the die inlet.

  Furthermore, the angle between the pressure axis and the extrusion axis in the extrusion process is preferably 60 to 150 °, and more preferably 90 to 120 °.

  Furthermore, in the extrusion process, the extrusion ratio ((cross-sectional area of die entrance) / (cross-sectional area of die exit)), which is a ratio of the cross-sectional area of the entrance of the die to the cross-sectional area of the exit of the die, is 4.5. Or more.

  Further, the processing temperature in the extrusion treatment is preferably from 300 to 600 ° C, more preferably from 320 to 450 ° C.

  Furthermore, the extrusion speed in the extrusion treatment is, for example, 0.01 to 1 mm / min.

  The Peltier module according to the third invention of the present application is characterized in that it has a thermoelectric element cut out of the above-mentioned thermoelectric material and energized in the direction with the lowest electric resistance.

  As described in detail above, according to the present invention, the ingot or the pulverized powder thereof is extruded with a die in which the pressing shaft and the extruding shaft are not coaxial, so that (001) A thermoelectric material having a uniform surface (c-plane) can be obtained, whereby the electric resistance can be reduced and a high-performance thermoelectric material can be obtained. Further, the performance can be improved without adding a special additive element, and the control of the additive element is unnecessary, so that the production is easy.

  Hereinafter, a thermoelectric material according to an embodiment of the present invention and a method for manufacturing the same will be specifically described with reference to the accompanying drawings. FIGS. 1A and 1B are a perspective view and a top view, respectively, schematically showing a thermoelectric material according to a first embodiment of the present invention.

  The thermoelectric material of the present embodiment is a liquid quenching method for a molten metal having a composition comprising at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se. The quenched and coagulated flakes are unidirectionally solidified by the liquid quenching method (LQ method), and a die having a pressing axis and an extruding axis not on one axis is used for the laminated flakes. Formed by performing an extrusion process (hereinafter, also simply referred to as "extrusion") once or a plurality of times, or an ingot of the above-described composition or a powder obtained by pulverizing the same. It is formed by performing one or more times of an extrusion process of performing a shearing process using a die in which the and the extrusion shaft are not coaxial. As shown in FIGS. 1A and 1B, the thermoelectric material 1 of the present embodiment has (001) plane (c plane) aligned in one direction. If the direction in which the thermoelectric material 1 is used is the direction indicated by the arrow A, the direction of the [001] axis (c-axis) is orthogonal to the direction in which the material is used, and the specific resistance of the thermoelectric material 1 is extremely small. Further, when a flake manufactured by the liquid quenching method is used, the thermoelectric material 1 is extremely fine and homogeneous, and has a high Seebeck coefficient α.

Further, one or more halogen elements such as I, Cl, Hg, Br, Ag or Cu may be added to the molten metal for forming the thermoelectric material 1 of the present embodiment. The halogen element is added, for example, with 0.1 mass% SbI to Bi, Te and Se, or added with, for example, 0.09 mass% HgBr ₂ for Bi, Sb, Te and Se. By adding I, Cl, Hg, Br, Ag and Cu, the carrier concentration can be controlled and the Seebeck coefficient can be improved.

  The molten metal can be obtained, for example, by the following method. First, the raw material powders of the above-mentioned elements are weighed so as to have a predetermined stoichiometric ratio, and then vacuum-sealed in a quartz glass tube. Next, this is heated and melted, stirred, and then solidified to obtain a raw material ingot. Then, a molten metal is obtained by melting the raw material ingot.

As the liquid quenching, any of a twin roll method, a single roll method, a gas atomizing method, and a rotating disk method may be employed. By this liquid quenching, a homogeneous flake or powder of the Bi ₂ Te ₃ -based thermoelectric material is obtained.

  Further, the thermoelectric material of the present example has an average particle size of 30 μm or less and, among all the crystal grains in a plane perpendicular to the extrusion direction, the extrusion measured by an Electron Back Scattering Pattern (hereinafter, referred to as EBSP). The ratio of the area occupied by crystal grains whose angle between the axis and the [001] axis (hereinafter referred to as the c-axis tilt angle) is 45 ° or less is 10% or less of the total crystal grain area. FIG. 2 is a schematic diagram showing a die in which the angle (die inclination angle) between the pressing shaft and the extrusion shaft is 90 °.

As shown in FIG. 2, the die inclination theta ₁ is 90 ° die 2 is composed of a pushing portion 2b provided in a direction orthogonal includes a pressing 2a which material is pressurized, the pressure portion 2a . That is, the pressure axis B and the extrusion axis C are perpendicular to each other. In this embodiment, the cross-sectional area of the extruded portion 2b is smaller than the cross-sectional area of the pressurized portion 2a. When the material of the pressing unit 2a is pressed by a punch (not shown) inserted from the upper surface of the pressing unit 2a, the material is pressed in the pressing axis B direction and extruded to the extruding unit 2b. Thereby, a shear stress is applied to the material, and the crystal direction of the material can be aligned by rotation from the pressing axis B to the extrusion axis C. The material extruded into the extruding portion 2b is extruded from the side surface of the die 2.

The thermoelectric material subjected to such an extrusion treatment has an average crystal grain size of 30 μm or less. Further, the [001] axis 3 relative to the total crystal grains in a plane perpendicular to the extrusion direction (direction of extrusion axis C), an angle (inclination angle of the c-axis) theta ₂ between the extrusion axis C is at 45 ° or less The area occupancy of the crystal grains is 10% or less.

The resistivity increases as the area occupancy increases when the inclination angle of the c-axis is 45 ° or less. If the area occupancy exceeds 10%, the specific resistance value of the thermoelectric material becomes higher than 1.2 × 10 ⁻⁵ Ωm. Therefore, it is preferable that the crystal grains having a c-axis tilt angle of 45 ° or less be 10% or less of all the crystal grains in a plane perpendicular to the extrusion direction.

  The inclination ratio of the c-axis can be measured by EBSP. In EBSP, the plane orientation of a sample can be determined by reading the distance (angle) between intersections of diffraction planes that appear with respect to a crystal structure observed by a scanning electron microscope (SEM). In the present invention, a thermoelectric material having a uniform crystal orientation is obtained by extrusion. However, when measuring the tilt angle of the c-axis by EBSP, the measurement surface of the thermoelectric material is polished and flattened.

  The diffraction line profile obtained by measuring the plane perpendicular to the extrusion direction by the X-ray diffraction method (2θ / θ method (diffractometer method)) indicates that the diffraction intensity of the (110) plane is larger than that of the (015) plane. Preferably, the strength is high. This is because good electrical characteristics can be obtained when the diffraction intensity of the (110) plane is higher than that of the (015) plane. A diffraction line profile obtained by measuring a plane parallel to the extrusion direction and a plane perpendicular to the extrusion direction in a plane defined by the pressing direction and the extrusion direction by an X-ray diffraction method is (006). It is preferable that the diffraction intensity of the (015) plane is larger than the diffraction intensity of the (015) plane, and the half width in rocking curve measurement of the (006) plane is 10 ° or less. By satisfying such conditions, good electrical characteristics can be obtained.

  In the present embodiment configured as described above, it is possible to obtain excellent thermoelectric properties not available in conventional materials. As described above, since it was difficult to produce an n-type thermoelectric material having excellent thermoelectric properties, in order to obtain an n-type thermoelectric material having the same thermoelectric performance as a p-type, it was necessary to reduce the resistance by using a p-type thermoelectric material. Alignment higher than thermoelectric materials is required. In addition, it is necessary to control the carrier concentration in order to improve the Seebeck coefficient, and it is necessary to refine the crystal grains of the thermoelectric material in order to reduce the thermal conductivity. However, in this embodiment, by manufacturing the starting material by the liquid quenching method, it is possible to finely control the carrier concentration without adding a halogen element. Then, since the pressing shaft and the extrusion shaft can be finely and strongly oriented by extrusion using a die in which the pressing shaft and the extrusion shaft are not uniaxial, even if the n-type thermoelectric material is used, the same performance as the p-type thermoelectric material can be obtained. Can be.

  Next, as a second embodiment of the present invention, a method for manufacturing the thermoelectric material according to the first embodiment will be described.

In the second embodiment, first, at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se are (Bi, Sb) _2. (Te, Se) An ingot of _three compositions is produced, and then solidified rapidly by a liquid quenching method from a molten metal to produce a flake having a (001) plane (c plane) unidirectionally solidified (hereinafter, referred to as a rapidly cooled foil). Next, hydrogen reduction and sintering are performed. After that, an extrusion process of performing a shearing process using a die in which the pressure axis and the extrusion axis are not on one axis is performed once or a plurality of times. Thereafter, a heat treatment is performed to obtain a thermoelectric material.

According to the second embodiment, the (001) plane is aligned in one direction by extrusion using a die in which the pressure axis and the extrusion axis are not uniaxial, using Bi ₂ Te ₃ thin film produced by the liquid quenching method. be able to. Therefore, the electric resistance can be reduced, and the output factor (power factor (PF)) represented by the Seebeck coefficient α / specific resistance ρ can be increased. Furthermore, since the quenched foil of the starting material has a homogeneous and fine structure, the thermal conductivity of the thermoelectric material is low, and high strength is obtained.

  FIG. 3A is a schematic diagram illustrating an extrusion method of the second embodiment, and FIG. 3B is a schematic diagram illustrating a conventional extrusion method. In this example, since the extrusion process is performed by a die in which the pressing axis and the extrusion axis are not on one axis, as shown in FIG. 3A, it is possible to obtain an oriented structure in which the (001) plane is aligned in the same direction. Can be. On the other hand, as shown in FIG. 3B, in the conventional extruded material, the c-plane is oriented by sliding the c-plane by drawing, so that the c-axis is oriented toward the center axis of the cylinder of the die. At the same time, the degree of processing increases in the circumferential direction, and the degree of processing near the surface becomes higher than the degree of processing at the center, resulting in a distribution of physical properties.

Further, if the composition of the starting material is such that Te / Se is 2.5 / 0.5 to 2.7 / 0.3, the temperature characteristics are good. FIG. 4 is a graph showing the temperature characteristics of the (Bi, Sb) ₂ (Te, Se) ₃ composition, with the horizontal axis representing the temperature and the vertical axis representing the rate of change of the output factor. The output factor change rate indicates a change rate when the output factor at room temperature (25 ° C.) is set to 1. As shown in FIG. 4, in a temperature range of −20 to 100 ° C. actually used as an LD module or the like, the output factor of Te / Se is 2.5 / 0.5 to 2.7 / 0.3. high.

  Next, a method for manufacturing a thermoelectric material according to the second embodiment will be described in more detail. In the extrusion process described above, the die used in the present embodiment does not have the pressing shaft and the extrusion shaft on one axis. Thereby, extrusion processing can be performed by adding shearing processing. It is preferable that the angle between the pressing axis and the extrusion axis of the die (hereinafter, referred to as the die inclination angle) is 60 to 150 °. If the die inclination angle is less than 60 °, there is a possibility that an extruded material having a good shape may not be obtained. Conversely, if the die inclination angle exceeds 150 °, the effect of the shearing process cannot be sufficiently obtained. This is because there are times. Further, it is more preferable that the die inclination angle is 90 to 120 °. In this embodiment, a die having a dice inclination of 60 to 150 degrees can be used in addition to the dice inclination of 90 degrees shown in FIG. A tapered portion (die angle) in a die used for so-called extrusion processing is provided, and the material is squeezed at a bent portion where the pressing shaft and the extrusion shaft intersect.

  Further, the processing temperature at the time of the extrusion treatment is preferably 300 to 600 ° C. If the processing temperature is lower than 300 ° C., the electric resistance may increase without sintering and densification of the thermoelectric material. If the processing temperature exceeds 600 ° C., the thermoelectric material may be melted. Because there is.

Table 1 below shows the relationship between the extrusion conditions (die tilt angle and processing temperature) in the extrusion treatment, the crystal grain size, and the performance index Z. In addition, all of these materials were formed by using a material having a composition of Bi _1.9 Sb _0.1 Te _2.6 Se _0.4 and extruding at an extrusion ratio of 6.54 and an extrusion speed of 0.1 mm / min. .

The lower the processing temperature of the extrusion process and the smaller the inclination angle of the die, the greater the load required for the processing, and the more likely it is to cause clogging. In addition, as the processing temperature is higher, the growth of the recrystallized composition becomes remarkable, and the orientation is lost. Further, when the processing temperature exceeds 600 ° C., the melting point of the thermoelectric material may be exceeded. This lowers the figure of merit of the thermoelectric material. Therefore, it is preferable that the die inclination angle is 60 to 150 ° and the processing temperature is 300 to 600 ° C. More preferably, the die inclination angle is 90 to 120 ° and the processing temperature is 320 to 450 ° C. Thereby, a high figure of merit Z of 3.0 × 10 ⁻³ / K or more can be obtained.

  In the extrusion process, the extrusion ratio ((cross-sectional area of die entrance) / (cross-sectional area of die exit)), which is the ratio of the area of the die entrance to the area of the exit of the die, is preferably 4.5 or more. When the extrusion process is performed twice or more, the extrusion ratio in the final extrusion step is preferably 4.5 or more. FIGS. 5A and 5B are schematic diagrams showing dies having an extrusion angle of 135 ° and an extrusion ratio of 1 and an extrusion ratio of 4, respectively. The dies shown in FIGS. 5A and 5B are dies of a type in which pressure is applied from above and pushed out to the side. Therefore, a die inlet is provided on the upper surface of the die, and a die outlet is provided on the side surface of the die. When a die having a high extrusion ratio, that is, a die having an extrusion ratio of 1 shown in FIG. 5A and a die having an extrusion ratio of 4 shown in FIG. It becomes finer, the orientation improves, and the relative density of the thermoelectric material increases.

FIG. 6 shows that for a material having a composition of Bi _1.9 Sb _0.1 Te _2.6 Se _0.4 , the abscissa indicates the extrusion ratio ((cross-sectional area at die entrance) / (cross-sectional area at die exit)). FIG. 3 is a graph showing the relationship between the extrusion ratio and the relative density, with the relative density taken on the vertical axis. The relative density was determined by setting the density of Bi ₂ Te ₃ described in the ASTM (JCPDS) card of 7.858 g / cm ³ to 100%.

  The thermoelectric material preferably has a relative density of 98% or more because the electrical resistance increases when the relative density is low. As shown in FIG. 6, when the extrusion ratio is 4.5 or more, a relative density of 98% or more can be obtained. Therefore, the extrusion ratio is preferably set to 4.5 or more. In the case where the extrusion is performed twice or more, the extrusion ratio is 4.5 or more only in the final extrusion process, and even if the extrusion ratio is less than 4.5 in the previous extrusion process, the relative density is 98% or more. Obtainable.

  Further, in the case of performing the extrusion process twice or more, it is preferable that the direction of the thermoelectric material inserted into the die for the second time is one of the two directions described below. FIGS. 7A and 7B are schematic diagrams showing a thermoelectric material to be inserted into the die of the present embodiment. As shown in FIG. 7A, a material 20 having a square cross section is inserted from a square entrance provided on the upper surface of the die 24, and the material 20 is extruded from a lateral exit. In FIG. 7, the surface parallel to the pressing axis of the material 20 in contact with the die at the position furthest away from the die outlet is denoted by 13, and the surfaces parallel to the other pressing axes are clockwise 14, 11, and 12, respectively. I do. The first material insertion direction is the same as that of the first extrusion process when the first extrusion process is performed, and the surfaces 11 to 14 parallel to the extrusion direction of the material 20 are in contact with the die 24 when the second extrusion process is performed. , That is, the surface in contact with the die at the position furthest away from the die outlet is the surface 13 of the material 20. Thereby, the crystal grains of the material 20 can be elongated in the orientation direction. As the insertion direction of the second material, in the first extrusion process, the insertion direction of the material 20 is set to the direction shown in FIG. 7A, and in the second extrusion process, as shown in FIG. The material 20 is inserted in such a manner that the opposing surface 11 of the surface 13 of the material 20 from which the material 20 has been extruded at the first time is in contact with the die at the position farthest from the die outlet in the second extrusion process. That is, the second material 20 is inserted into the die with the orientation of the first material 20 rotated by 180 °. Thereby, the orientation can be provided without changing the crystal grain size of the material 20.

  The performance index is higher when the extrusion process is performed twice or more than when the extrusion process is performed once. FIG. 8 is a graph showing the relationship between the number of extrusion processes on the horizontal axis and the average crystal grain size and the maximum shear stress on the vertical axis. In FIG. 8, ● indicates the average crystal grain size, and X indicates the maximum shear stress. The results shown in FIG. 8 show that after filling the flakes of the raw material into a mold (die) in which the pressing shaft and the extruding shaft make an inclination angle of 90 °, the pressing shaft speed was reduced to 0 in an Ar atmosphere at a temperature of 450 ° C. It is the one when extrusion processing was performed while performing shear deformation at 0.03 mm / min. As shown in FIG. 8, as the number of times of the extrusion process increases, the crystal grains become finer and the maximum shear stress increases.

  Furthermore, when the dies are changed between the first extrusion process and the second extrusion process, the cross-sectional area of the outlet of the die used in the first process is the same as the cross-sectional area of the inlet of the die used in the second process, and the second process is performed. It is preferable to squeeze by extrusion.

  Further, the extrusion speed in the extrusion treatment is preferably 0.01 to 1 mm / min. Further, the extrusion speed is more preferably 0.05 to 0.2 mm / min. This is because if the extrusion speed is less than 0.01 mm / min, the processing time is long and the production efficiency decreases, and if the extrusion speed exceeds 1 mm / min, the extrusion load increases and the density tends to decrease. Because.

  Table 2 below shows the relationship between the extrusion speed and the figure of merit. In addition, Table 2 shows the measured values of the thermoelectric materials extruded using a die having an extrusion temperature of 450 ° C. and a die inclination angle of 90 °.

As shown in Table 2, when the extrusion speed is 0.01 to 1 mm / min, a high figure of merit is obtained, and when the extrusion speed is 0.05 to 0.2 mm min, 3.0 × 10 3 A performance index of ⁻³ / K or more can be obtained.

  Furthermore, after the extrusion process, there is a step of performing a hot press process by a discharge plasma sintering method (SPS) or forging in a direction perpendicular to the extrusion axis on a plane having a pressure axis and an extrusion axis, for example, in an Ar atmosphere. Is preferred. FIG. 9 is a graph showing the electrical properties of an n-type thermoelectric material manufactured by the method of the present invention, with the horizontal axis representing the Seebeck coefficient α and the vertical axis representing the specific resistance (electrical resistivity) ρ.

In FIG. 9, ○ indicates a hot pressed (HP) material, Δ indicates an extruded material, and X indicates electrical properties of a material subjected to hot pressing after extrusion. The hot-pressed material indicated by 示 す was solidified and formed by a hot-press apparatus using a quenched foil piece prepared by the same liquid quenching method as that in the second embodiment for comparison. The extruded material indicated by Δ is the one produced according to the second embodiment, and is obtained by extruding a rapidly cooled foil piece under the conditions of a die inclination angle of 90 ° C., a processing temperature of 450 ° C., and an extrusion speed of 0.1 mm / min. . Further, the material indicated by x is obtained by further performing a hot press treatment on the extruded material indicated by △. FIG. 9 shows the results of measurement using a material of Bi _1.9 Sb _0.1 Te _2.6 Se _0.4 .

In FIG. 9, the output factor (PF) represented by (Seebeck coefficient α) / (specific resistance ρ) is expressed by P.F. F. = 3.0, 3.5, 4.0 (× 10 ⁻³ W / (K ² m)). The output factor corresponds to a numerical value obtained by dividing the figure of merit Z = α ² / (ρ × κ) by the thermal conductivity κ, and represents thermoelectric characteristics. The output factor is preferably as large as possible, and shows the same electrical characteristics on the same straight line.

  As shown in FIG. 9, since the hot-pressed material has a poor degree of orientation, the Seebeck coefficient is high, but the electrical resistance is high. For this reason, P. F. (Output factor) is as small as 3.0 or less. On the other hand, the electrical resistivity of the extruded material manufactured according to the second example shown by Δ and × is low. Further, the material subjected to the hot press treatment after the extrusion treatment has a lower electric resistivity. This is to maintain the crystal orientation obtained by extrusion by hot-pressing the extruded material on a plane having a pressure axis and an extrusion axis in a direction perpendicular to the extrusion axis. This is because the organization can be made more precise.

  Table 3 below shows the relationship between the hot pressing conditions and the performances of the materials subjected to hot pressing after extrusion. In Table 3, the orientation ratio indicates the (006) intensity of each material when the (006) peak intensity in the powder X-ray diffraction of the extruded material (△ in FIG. 9) is 100, and the density ratio indicates the extruded material. Indicates the density of each material when the density of the extruded material is 100, and the performance ratio indicates the performance index of each material when the performance index of the extruded material is 100.

  Although hydrogen reduction of the flakes after the liquid quenching and before the extrusion treatment is not always necessary, for example, by performing the reduction treatment in a hydrogen atmosphere at 400 ° C., the electrical resistance of the thermoelectric material can be reduced. Table 4 below shows a comparison result of each property related to the presence or absence of reduction.

  As shown in Table 4, the specific resistance was reduced by about 20% by performing the hydrogen reduction, and the figure of merit was improved by about 10%.

Also, at the time of the extrusion treatment, it is not always necessary to laminate the flakes, but when the liquid quenching is performed by employing a roll quenching method such as a twin roll method and a single roll method, since the flakes are obtained, By laminating the flakes so as to be aligned in the thickness direction, the processing pressure in the extrusion process can be reduced. This is because the resistance is reduced by lamination since the c-plane of the crystal is aligned in the thickness direction of the foil (flake). FIG. 10 is a graph showing the relationship between the presence or absence of lamination and the extrusion load by a bar graph. As shown in FIG. 10, when lamination was performed, the extrusion load was 9.31 kN / cm ² (0.95 t weight / cm ² ), whereas when the lamination was not performed, the extrusion load was 1.147 kN / cm ^{2. 2} (1.17 tons / cm ² ).

Furthermore, during the extrusion process, it is preferable to apply a load smaller than the load on the pressing shaft to the material from a direction opposite to the extrusion direction (discharge direction) on the extrusion shaft. FIG. 11 is a schematic diagram showing a state in which a load is applied from a direction opposite to the extrusion direction. For example, when the extrusion process is performed using a die 24 having an inlet having a cross-sectional area of 19.6 cm ² and an outlet having a cross-sectional area of 4 cm ² , as shown by an arrow 31, 0.3 (mm) under a temperature condition of 450 ° C. / Min), a load of 4.9 kN / cm ² may be applied to the material 20 from the opposite direction to the extrusion direction as indicated by an arrow 32.

  By applying such a load, the structure can be further densified while maintaining the crystal orientation, similarly to the hot press treatment.

  Next, as a third embodiment of the present invention, a method of manufacturing the thermoelectric material according to the first embodiment will be described.

In the third embodiment, an ingot having a composition of (Bi, Sb) ₂ (Te, Se) ₃ is pulverized to obtain a powder having the above composition, and is subjected to hydrogen reduction and sintering. Thereafter, similarly to the second embodiment, the extrusion process of performing the shearing process using a die in which the pressure axis and the extrusion axis are not on one axis is performed once or a plurality of times. Thereafter, a heat treatment is performed to obtain a thermoelectric material.

  Thus, the third embodiment is such that the object to be extruded is an ingot or a crushed powder thereof, and the object to be extruded is a unidirectional solidified material obtained by liquid quenching. However, the other steps are the same as in the second embodiment. Therefore, similarly to the second embodiment, a high Seebeck coefficient α can be obtained, and a high-performance thermoelectric material having a uniform (001) plane orientation and low electric resistance can be obtained. Further, as compared with the second embodiment, although the homogeneity of the non-extruded material is slightly inferior, it is not necessary to perform liquid quenching, so that the number of steps is greatly reduced.

  In the case of using the ingot pulverized powder in the third embodiment, for example, after filling the pulverized powder into a mold (die) having a pressing axis and an extruding axis inclined at 90 °, the temperature is increased to 450 ° C. Extrusion may be performed in a Ar atmosphere at a temperature of 0.03 mm / min with shearing deformation at a pressing shaft speed of 0.03 mm / min.

When a pulverized powder is used, it is preferable to perform a reduction treatment in an H ₂ atmosphere at 400 ° C., for example, before the extrusion treatment. This is because, compared to ingots, since the specific surface area of the pulverized powder is large, oxidation is more likely to occur. Such oxidation causes an increase in the electric resistance. By performing the reduction treatment, such an increase in the electric resistance can be prevented.

  Further, similarly to the second embodiment, it is possible to change and adjust various conditions such as the presence or absence of reduction and the application of a load from the opposite direction during the extrusion process.

  Next, a method of manufacturing a Peltier module from the thermoelectric material manufactured according to the above-described embodiment will be described. FIG. 12 is a perspective view showing a planar Peltier module. FIG. 13 is a flowchart illustrating a method for manufacturing a planar Peltier module. As shown in FIG. 12, for example, the planar Peltier module 120 is configured by sandwiching thermoelectric elements 121 having Cu electrodes 122 and 122 above and below an insulating substrate 123.

  As shown in FIG. 13, a method of manufacturing such a planar Peltier module 120 is divided into a material processing step of manufacturing the thermoelectric element 121 and a substrate step of manufacturing the insulating substrate 123.

  In the material processing step, first, for example, the thermoelectric material 1 is manufactured according to the second embodiment. Next, the thermoelectric material 1 is cut into a disk shape whose plane is perpendicular to the extrusion axis, and electroless Ni (+ Au) plating is performed. Furthermore, the thermoelectric element 121 is manufactured by cutting these into a quadrangular prism shape.

  In the substrate process, an alumina substrate is used as the insulating substrate 123. First, the alumina substrate is metallized, and electroless Ni plating is applied to the metallized portion. Next, the Cu electrode 122 is soldered to the alumina substrate. Thus, the insulating substrate 123 is manufactured.

  Then, after assembling the thermoelectric element 121 manufactured by the above-described material processing step and the insulating substrate 123, the thermoelectric element 121 and the Cu electrode 122 are soldered. Further, by connecting the leads to the thermoelectric elements 121 arranged at both ends, the planar Peltier module 120 is completed.

  As shown in FIG. 14, a Peltier module manufactured by such a method can reduce power consumption by about 20% as compared with a module manufactured from a conventional thermoelectric element.

  Hereinafter, the thermoelectric material of the present invention is actually manufactured, and its effect will be described. An example of a method for producing the produced n-type thermoelectric material will be described below.

Bi, Sb, Te and Se were weighed and mixed so that the element ratio became Bi _1.9 Sb _0.1 Te _2.6 Se _0.4 . The obtained mixed powder was weighed in a vacuum atmosphere in a quartz glass tube, melted and mixed at a temperature of 680 ° C. for 1 hour, and solidified. This alloy was rapidly solidified from 800 ° C. using a single-roll type liquid quenching apparatus to produce a sample slice. Next, the sample flake was sealed in a quartz glass tube in an H ₂ atmosphere and subjected to a deoxygenation treatment. Then, after laminating the obtained deoxidized flakes, they were cold-rolled at 9.8 kN / cm ² to produce pellets for extrusion treatment.

  Thereafter, the pellets for extrusion treatment were extruded at a processing temperature of 450 ° C., an extrusion speed of 0.1 mm / min, an Ar atmosphere, a die extrusion ratio of 4.5, and a die angle of 90 ° (sample No. 2). .

Further, the sample No. Extrusion pellets formed in the same manner as in Example 2 were extruded at a processing temperature of 450 ° C., an extrusion speed of 0.1 mm / min, an Ar atmosphere, a die extrusion ratio of 4.5, and a die angle of 90 °. Thereafter, the sample after the extrusion treatment was subjected to a hot press treatment at 9.8 kN / cm ² , 450 ° for 90 minutes in a direction perpendicular to the extrusion shaft in a plane formed by the extrusion shaft and the pressure shaft ( Sample No. 7).

  Further, the sample No. The pellets for extrusion treatment formed in the same manner as in Example 2 were subjected to four extrusion treatments at a temperature of 450 ° C., an extrusion speed of 0.1 mm / min, an Ar atmosphere, a die extrusion ratio of 1, and a die angle of 120 °. Next, the sample was subjected to shearing treatment extrusion at a processing temperature of 380 ° C., an extrusion speed of 0.1 mm / min, an Ar atmosphere, a die extrusion ratio of 4.5, and a die angle of 90 ° (sample No. 8).

  In the same manner as these samples, thermoelectric materials having various compositions and extrusion treatment conditions were prepared. In addition, as a comparative example, pellets for extrusion were subjected to hot press processing instead of shearing extrusion processing (Sample Nos. 11 and 12). The composition and manufacturing conditions of the obtained thermoelectric material are shown in Table 5 below. In addition, about what performed the extrusion process several times, the extrusion ratio shows the extrusion ratio in the last extrusion process. Thereafter, the Seebeck coefficient α, the specific resistance ρ, and the thermoelectric coefficient κ of each obtained thermoelectric material were measured, and the output factor and the performance index Z were calculated. The area occupancy of crystal grains having a c-axis tilt angle of 45 ° or less among the crystal grains in a cross section perpendicular to the extrusion axis was measured by EBSP. Further, the ratio of the diffraction intensity of the (110) plane to the diffraction intensity of the (015) plane in the diffraction line profile of the plane perpendicular to the extrusion direction (hereinafter, I (100) / I (015)) was determined by the X-ray diffraction method. Was. The results are shown in Table 6 below.

As shown in Table 6, the sample No. manufactured by the method of the present example was used. 1 to 10 show good thermoelectric properties. In particular, for sample Nos. With dice inclination angles of 90 and 120 °. 1 to 5 show extremely good thermoelectric properties. Further, the sample No. As shown in 2 to 8 and 10, when the composition of the material is Te / Se of 2.6 / 0.4 to 3.0 / 0, the specific resistance is 1.2 × 10 ⁻⁵ Ωm or less. Showed low values. In addition, for sample No. Sample No. 7 shows only the extrusion process. The figure of merit was higher than that of No. 2. Furthermore, the sample No. Sample No. 8 is a sample of one extrusion process. The figure of merit was higher than that of No. 5. Further, the sample No. In No. 6, since the dice inclination was large, sufficient orientation was not obtained, and the area occupancy of crystal grains having a c-axis inclination of 45 ° or less exceeded 10%, and the figure of merit was slightly lowered. Further, the sample No. In No. 9, since the extrusion ratio was as small as 1.96, the figure of merit slightly decreased.

  In FIG. 15, the vertical axis indicates the area distribution ratio, and the horizontal axis indicates the inclination angle of the 001 axis in a cross section orthogonal to the extrusion axis of the thermoelectric material. FIG. 2 is a graph showing the distribution of the inclination angle of the c-axis in FIG. In FIG. The measurement result of sample No. 2 is indicated by ●. Among the production conditions of 2, the measurement results of those obtained by changing only the processing temperature to 380 ° C. are indicated by ○. As shown in FIG. 15, the distribution of the thermoelectric material manufactured by the method of the present invention in which the c-axis tilt angle is 45 ° or less is extremely small.

On the other hand, the sample No. 11 and 12 have low figures of merit. Sample No. Sample No. 11 had a specific resistance higher than 1.2 × 10 ⁻⁵ Ωm, and the sample no. In No. 12, although the specific resistance was low, the figure of merit was low. In these samples, the area occupied by crystal grains having a tilt angle of the 001 axis exceeding 45 ° is high.

(A) and (b) are the perspective view and the top view which show typically the thermoelectric material concerning the Example of this invention, respectively. It is a schematic diagram which shows the dice in which the angle (die inclination angle) which a press axis | shaft and an extrusion axis make is 90 degrees. (A) is a schematic diagram showing an extrusion method of an example of the present invention, and (b) is a schematic diagram showing a conventional extrusion method. FIG. 4 is a graph showing temperature characteristics of a (Bi, Sb) ₂ (Te, Se) ₃ composition, with the horizontal axis representing temperature and the vertical axis representing the rate of change in output factor. (A) And (b) is a schematic diagram which shows the dice | dies of the extrusion ratio 1 and the extrusion ratio 4, respectively, which have a dice | tilt angle of 135 degrees. FIG. 4 is a graph showing the relationship between the extrusion ratio and the relative density, with the horizontal axis representing the extrusion ratio ((cross-sectional area at the die entrance) / (cross-sectional area at the die exit)) and the vertical axis representing the relative density. (A) And (b) is a schematic diagram which shows the thermoelectric material inserted in the dice | dies of the Example of this invention. FIG. 3 is a graph showing the relationship between the number of extrusion processes on the horizontal axis and the average crystal grain size and the maximum shear stress on the vertical axis. FIG. 4 is a graph showing the electrical properties of an n-type thermoelectric material manufactured by the method of the present invention, with the horizontal axis representing the Seebeck coefficient α and the vertical axis representing the specific resistance (electrical resistivity) ρ. It is a graph which shows the relationship between the presence or absence of lamination and an extrusion load with a bar graph. It is a schematic diagram which shows a mode that a load is applied from a direction opposite to the extrusion direction. It is a perspective view showing a plane type Peltier module. It is a flowchart figure which shows the manufacturing method of a planar Peltier module. It is a graph which shows the relationship between the kind of Peltier module and power consumption with a bar graph. FIG. 9 is a graph showing the 001-axis tilt distribution of a thermoelectric material produced by the method of the present invention, with the vertical axis representing the area distribution ratio, and the horizontal axis representing the 001-axis tilt angle in a cross section orthogonal to the extrusion axis of the thermoelectric material. is there. FIG. 9 is a cross-sectional view illustrating a method for manufacturing a thermoelectric material described in Patent Document 1. It is a typical sectional view showing the shear addition extrusion method of nonpatent literature 1. It is a figure which shows the hot upsetting forging in the manufacturing method of the thermoelectric material of patent document 2, (a) is a typical cross section before upsetting forging, (b) is after upsetting forging. (A) and (b) are diagrams showing problems of the technology described in Patent Document 1, (a) is a schematic diagram showing a material in a die, and (b) and (c) are (a) 3A and 3B are a cross-sectional view and a schematic view, respectively, showing an extruded portion shown in FIG.

Explanation of reference numerals

101; material 101
102; die 103; material 104; heater 110; extrusion die 110a; cylindrical portion 110b; horizontal portion 111; upper punch 121; base 122; sleeve 123; punch 124; powder sintered body 125;

Claims (15)

A pressing shaft and an extruder are used for an ingot having a composition comprising at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se, or a pulverized powder thereof. It is characterized in that it is obtained by performing at least one extrusion process in which an extrusion speed of 0.001 to 0.03 mm / min is performed by performing an extrusion process in which a shearing process is performed using a die whose axis is not coaxial. Thermoelectric material. The thermoelectric material according to claim 1, wherein a load smaller than a pressing load is applied to the material to be extruded from a direction opposite to the extrusion direction in the extrusion process. 3. The method according to claim 1, wherein the extrusion processing is performed by hot pressing in a direction orthogonal to the extrusion axis on a plane having a pressure axis and an extrusion axis after the extrusion processing. Thermoelectric material. 3. The thermoelectric material according to 1 or 2, wherein the thermoelectric material is obtained by performing the extrusion process twice or more and making a cross-sectional area of a die outlet smaller than a cross-sectional area of a die inlet in a final extrusion step. 5. The thermoelectric device according to claim 1, wherein one or more elements selected from the group consisting of I, Cl, Hg, Br, Ag, and Cu are added. 6. material. Of the total crystal grains in a plane having an average particle diameter of 30 μm or less and orthogonal to the extrusion direction, the ratio of the area occupied by the crystal grains having an angle of 45 ° or less between the extrusion axis and the [001] axis is all The thermoelectric material according to any one of claims 1 to 5, wherein the thermoelectric material has a crystal grain area of 10% or less. In the method for producing a thermoelectric material having a composition comprising at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se, an ingot having the composition A step of subjecting the pulverized powder to at least one extrusion treatment in which a shearing process is performed using a die in which the pressure axis and the extrusion axis are not on one axis. The method for manufacturing a thermoelectric material according to claim 7, wherein a load smaller than a pressing load is applied to the material to be extruded from a direction opposite to an extrusion direction in the extrusion process. The step of performing the extrusion process at least once includes, after the extrusion process, a step of performing a hot press process in a direction orthogonal to the extrusion axis on a plane having a pressure axis and an extrusion axis. Item 9. The method for producing a thermoelectric material according to Item 7 or 8. 10. The step of performing the extrusion process at least once, wherein the extrusion process is performed twice or more, and a cross-sectional area of a die outlet in the final extrusion step is smaller than a cross-sectional area of a die inlet. The method for producing a thermoelectric material according to claim 1. The method for manufacturing a thermoelectric material according to any one of claims 7 to 10, wherein in the extrusion process, an angle formed by the pressing shaft and the extrusion shaft is 60 to 150 °. In the extrusion treatment, an extrusion ratio ((cross-sectional area of die entrance) / (cross-sectional area of die exit)), which is a ratio of a cross-sectional area of an entrance of the die to a cross-sectional area of an exit of the die, is 4.5 or more. The method for producing a thermoelectric material according to any one of claims 7 to 11, wherein: The method for producing a thermoelectric material according to any one of claims 7 to 12, wherein the extrusion process has a processing temperature of 300 to 600 ° C. The method for producing a thermoelectric material according to any one of claims 7 to 13, wherein the extrusion process has an extrusion speed of 0.01 to 1 mm / min. A Peltier module comprising a thermoelectric element cut from the thermoelectric material according to any one of claims 1 to 6, and energized in a direction having the lowest electric resistance.

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