JP2003243729A - Thermoelectric material and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric material where power consumption at a high temperature can be reduced while a high performance index is maintained and to provide the manufacturing method. <P>SOLUTION: A pressure application face when a solidified molding is hot- pressed is restricted and a face vertical to the pressure application face is depressed with pressure. Crystal grains where a face C vertical to the applying direction of pressure are shifted to an expanding direction with the expansion of the solidified molding. The crystal grains where the face C is parallel to the applying direction of pressure are shifted to the expanding direction while they rotate by 90° with an axis (a) as a rotation axis. Thus, the face C of the crystal grains and the axis (a) are adjusted. In the thermoelectric material, an axis (c) is adjusted to a pressurizing axis direction at the time of swage molding. Since a direction parallel to the face C is that where specific resistance (ρ) is low, a Peltier element (a thermoelement) is assembled so that the direction becomes a conduction direction. Consequently, the high performance index (Z) can be obtained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric material applied to thermoelectric power generation, thermoelectric cooling and the like and a method for producing the same, and more particularly to a thermoelectric material capable of improving a figure of merit at high temperature and a method for producing the same.

[0002]

2. Description of the Related Art Thermoelectric materials include unidirectionally solidified materials and sintered materials. The unidirectionally solidified material is produced as follows. 13A to 13C are schematic views showing a method of manufacturing a conventional unidirectionally solidified material in the order of steps.

First, as shown in FIG. 13 (a), a raw material 101 is inserted into a quartz tube 102, the end of the quartz tube 102 is melted and cut, and the raw material 101 is sealed in the quartz tube 102. After that, as shown in FIG. 13B, the quartz tube 102 is put into the tubular furnace 103 to melt the raw material 101, and the stand 104 is placed.
The raw material melt is agitated by swinging the tubular furnace 103 rotatably supported by. Next, as shown in FIG. 13C, a temperature gradient is applied in the tubular furnace 103 to solidify the melt while orienting the crystal orientation. Thereby, a unidirectionally solidified material having a solidified structure extending in one direction is obtained.

The sintered material is obtained by crushing a solidified material,
Solidify by hot pressing or the like. In this case, since a low-resistance crystal orientation (a-axis) grows in a direction perpendicular to the pressure direction of the hot press, electrodes are attached to the thermoelectric element and the plurality of thermoelectric elements so that a current flows in the a-axis direction. Assemble the thermoelectric module consisting of elements.

FIG. 14 is a schematic view showing the crystal grains of the thermoelectric material to be solidified and molded and the hot pressing direction. When the thermoelectric material 1 is solidified by hot pressing, the a-axis side of the crystal structure of the crystal grain 2 grows in the direction orthogonal to the hot pressing direction, and the crystal structure of the crystal grain 2 extends in the direction parallel to the hot pressing direction. Grows on the c-axis side. Since the thermoelectric material generally has structural anisotropy, as shown in FIG. 14, by hot pressing, the growth proceeds in the a-axis direction rather than the c-axis direction of the crystal grains 2. As a result, the grain size of the crystal grain 2 grows to about several mm and the aspect ratio becomes 5 or more (for example, refer to Patent Document 1).

The crystal structure of such a thermoelectric material is
As shown in FIG. 15, it is considered to be a hexagonal crystal. In FIG. 15, the hexagonal surface shown by hatching is C
The surface.

Further, there is described a method in which powder obtained by crushing an ingot is sintered, and then the sintered body is subjected to upset forging (for example, refer to Patent Documents 2 to 4).

[0008]

[Patent Document 1] Japanese Patent Laid-Open No. 2000-232243
(Pages 2-5, 5-6)

[Patent Document 2] Japanese Patent Laid-Open No. 10-178218 (page 2-6, FIG. 1)

[Patent Document 3] JP-A-10-178219 (page 2-5, FIG. 1)

[Patent Document 4] Japanese Patent Laid-Open No. 11-261119 (page 2-3, FIG. 1)

[0009]

However, among the above-mentioned conventional thermoelectric materials, the unidirectionally solidified material has a crystal grain size of several meters.
Since it is more than m and is cleavable, it has the drawback of being brittle against mechanical impact. In addition, conventional thermoelectric materials are
High thermal conductivity. The figure of merit Z of a thermoelectric material is its Seebeck coefficient α (μ · V / K), specific resistance ρ (Ω · m),
When the thermal conductivity is κ (W / m · K), it is expressed as shown in the following mathematical formula 1.

[0010]

## EQU1 ## Z = α ² / (ρ × κ)

As is clear from the mathematical formula 1, when the thermal conductivity κ is high, the figure of merit Z is low. Therefore, when the thermal conductivity κ is high, there is a limit to the improvement in performance.

In the conventional thermoelectric material produced by the sintering method, the size of the powder is equal to the size of the crystal grain. Generally, the larger the grain size of the crystal grains, the larger the thermal conductivity κ and the smaller the specific resistance ρ, and the smaller the grain size, the smaller the thermal conductivity κ and the larger the specific resistance ρ. However, since the influence of the grain size is smaller in the specific resistance than the thermal conductivity, it is effective to refine the crystal grains in order to reduce the thermal conductivity κ for improving the performance index Z. Conventionally, since the powder grain size and the crystal grain size are the same, there is a limit to the refinement of the crystal grains. In addition, during pulverization, the powder surface is oxidized and impurities are mixed in, which increases the specific resistance, which lowers the figure of merit.

In addition, in the manufacturing method of upset forging, the powder obtained by crushing the ingot is sintered as it is, so the orientation inside the powder is low. For this reason,
The orientation of the solidified compact is low and the thermoelectric performance is not sufficient. Patent Document 3 also describes a method of enhancing the orientation by utilizing the slippage and cleavage planes of crystal grains, but when such a method is adopted, a large amount of strain occurs and the thermal conductivity κ decreases. At the same time, the specific resistance ρ increases. Although such a problem can be suppressed by high-temperature heat treatment and processing, grain growth unrelated to the orientation occurs.

Further, regarding the thermoelectric performance of the thermoelectric material described in Patent Document 1, the performance index Z itself is good,
Since the specific resistance ρ, which is easily affected by heat, is relatively high, its use at high temperatures is limited. That is, since the specific resistance ρ increases as the temperature increases, Joule heat generation increases. Further, the driving current is set by the manufacturer of the thermoelectric element. Therefore, the amount of heat absorbed by the thermoelectric element (Peltier element) is reduced and power consumption is increased. Therefore, in a high temperature environment where the temperature inside the package reaches 90 ° C., power consumption increases.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a thermoelectric material capable of reducing power consumption at high temperatures while maintaining a high figure of merit, and a method for manufacturing the same. And

[0016]

The thermoelectric material according to the present invention comprises 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. By applying pressure from one direction to a thermoelectric material having a composition consisting of elements, the a-axes of the crystal grains in the thermoelectric material are oriented parallel to the direction in which the pressure is applied, and the surface to which the pressure is applied is constrained. However, by performing upset forging in which pressure is applied from a direction perpendicular to the constrained surface, the thermoelectric material is spread and the C-plane of the crystal grains is rotated or slipped to reduce the pressure during upset forging. It is characterized in that it is oriented so as to be perpendicular to the application direction. In this specification, the a-axis is
The a-axis of the hexagonal crystal of the Bi-Te-based thermoelectric material.

The thermoelectric material is a molten metal having a composition of 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. It is preferable that the thin piece is unidirectionally solidified by rapid cooling and the a-axes of the crystal grains are aligned in the thickness direction of the thin piece.

The method for producing a thermoelectric material according to the present invention is based on Bi
1 for a thermoelectric material having a composition of at least one element selected from the group consisting of Sb and Sb and at least one element selected from the group consisting of Te and Se.
Applying a pressure from the direction to orient the a-axis of the crystal grains in the thermoelectric material parallel to the direction of applying the pressure; and a plane perpendicular to the constrained surface while constraining the surface to which the pressure is applied. By carrying out swaging forging in which pressure is applied from the direction, the thermoelectric material is spread to form C
And a step of orienting the surface by rotation or sliding so as to be perpendicular to the direction in which the pressure is applied during upset forging.

The thermoelectric material is a molten metal having a composition of 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 step of orienting the a-axis of the crystal grains parallel to the direction of applying the pressure is a unidirectionally solidified thin piece that is rapidly cooled and solidified, and the step of aligning the a-axis of the crystal grains in the thickness direction of the thin piece is performed. It is preferable to have.

Further, it is preferable that after the step of orienting the a-axis of the crystal grains parallel to the direction of applying the pressure, a step of heat-treating the thermoelectric material in a reducing gas atmosphere or an inert gas atmosphere is included.

In the present invention, swaging forging is performed on a thermoelectric material whose a-axis is aligned in one direction by pressing, while pressing the pressing surface and applying pressure from a direction perpendicular to the restricted surface. Therefore, the thermoelectric material spreads in a direction perpendicular to the pressing direction of the swaging forging and perpendicular to the unconstrained surface. Along with this spreading, the C-planes including the a-axis of each crystal grain are arranged in parallel with each other. Therefore, the orientation of the c-axis becomes extremely high, and the performance index can be improved by assembling the thermoelectric element with the direction of the low specific resistance as the current-carrying direction, and the consumption at high temperature can be maintained while maintaining the high performance index. It becomes possible to reduce the power.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. A foil of thermoelectric material can be produced by a liquid quenching method, and the produced foil itself may be fine like a powder. If it is not fine, the obtained foil is crushed into powder. In this way, the thermoelectric material powder obtained by the liquid quenching method has high-density strains and defects introduced therein. In this quenched foil, when heat treatment is performed in a reducing atmosphere of hydrogen gas, or during solidification molding such as hot pressing or extrusion molding, fine recrystallized grains become powder (foil) with nuclei of strain or defects. Is deposited inside. Since the grain boundary (interface) of the crystal grains has a lower impurity concentration than the interface between the pulverized powders, the phonon scattering due to the grain boundary is increased and the thermal conductivity (ratio) is increased while keeping the specific resistance (ρ) low. κ) can be reduced. Thereby, the figure of merit (Z) can be significantly improved.

Further, in the crystal utilizing the strain in the quenched foil, the major axis is biased in the direction parallel to the pressing direction during solidification forming, and the minor axis is biased in the direction perpendicular to the pressing direction to obtain an aspect ratio. It has a characteristic that it grows as a crystal grain having a large ratio or recrystallizes. In this case, the resistivity (ρ) value in the major axis direction is significantly lower than the resistivity (ρ) value in the minor axis direction, so that the figure of merit in this direction is high. Further, if the C planes are aligned parallel to the pressing direction, the specific resistance ρ further decreases and the figure of merit Z increases. Therefore, when assembling a thermoelectric conversion element into a thermoelectric conversion element, it is necessary to attach electrodes so that a current flows in a direction parallel to the pressurizing direction at the first solidification molding (primary solidification molding), that is, the long axis direction. is necessary.

In this embodiment, Bi, Sb and Te are used.
Although the thermoelectric material manufactured by adding Se to the composition consisting of is used, the same effect can be obtained by using thermoelectric materials having other various compositions. For example, in the present invention, as the thermoelectric material, a material composed of either one or both of Bi and Sb and one or both of Te and Se can be used. As the thermoelectric material, in addition to the above composition, I, Cl, Hg, B
It is also possible to use those to which at least one element selected from the group consisting of r, Ag and Cu is added.

Next, a method for manufacturing a thermoelectric material according to an embodiment of the present invention will be described. FIG. 1 is a flowchart showing a method for manufacturing a thermoelectric material according to an embodiment of the present invention.

In this embodiment, first, the raw material B
i, Sb, Te and Se are weighed (step S
1), as shown in FIG. 2A, this raw material 41 is inserted into the ampoule 42 (step S2). In addition, at the time of this encapsulation, after the raw material 41 is put into the ampoule 42, the inside of the ampoule 42 is evacuated, and the inside of the ampoule 42 is kept in a vacuum state or an inert gas is introduced. )
The mouth of the ampoule 42 is sealed off as shown in FIG. afterwards,
As shown in FIG. 2C, the ampoule 42 is placed at 600 to 7
The raw material 41 is melted by being placed in a tubular furnace 43 at 00 ° C., the tubular furnace 43 is rotatably supported by a stand 44, and is swung like a cradle to stir the raw material melt. Then, the melt is cooled and solidified. In this way, an ingot is manufactured (step S3).

FIG. 3 is a diagram showing a method for producing powder of thermoelectric material by the liquid quenching method. While rotating the copper roll 12, the molten metal 13 of thermoelectric material stored in a quartz nozzle 11 having a slit or a plurality of holes formed in the tip thereof at its tip 15 is pressurized by Ar gas and supplied. As a result, the molten metal 13 comes into contact with the copper roll 12 and is rapidly cooled, and becomes a quenched thin ribbon 14 which is sent out by the rotation of the roll 12 (step S4).

FIG. 4 is a schematic diagram showing the growth direction of crystal grains in a quenched thin piece. A quenching thin piece 31 is formed on the surface of the cooling roll 30, crystals grow in a direction away from the roll surface (thickness direction of foil), and have a major axis D in this direction,
Crystal structure 32 having a minor axis d in a direction parallel to the roll surface
Is obtained. Regarding the shape and orientation of the crystal in the quenched thin piece 31, the direction of the long axis D is originally parallel to the C plane. Then, when stress is applied to the quenched thin piece 31 in a direction parallel to the major axis, a crystal structure 33 which is a hexagonal crystal and whose C-plane is parallel to the pressing direction is obtained.

Taking the case of the liquid quenching method (single roll method) as shown in FIG. 3 as an example, when the molten metal of the thermoelectric material is cooled on the surface of the cooling roll to form a quenched ribbon, the molten metal is cooled. The part on the front surface side is first cooled, and then the part which is separated from the cooling roll is sequentially cooled. Therefore, a temperature gradient occurs in which the roll surface side is low in temperature and becomes higher in temperature as it moves away from it. Therefore, the crystal grains grow in a direction away from the roll surface, and have a long axis D in this direction and a short axis d in a direction parallel to the roll surface, and have a large aspect ratio. In the quenched ribbon 14, a large number of crystal grains having the major axis are arranged in parallel with the thickness direction. That is, the C plane of each crystal grain is parallel to the thickness direction of the quenched ribbon 14, and the thickness direction of the quenched ribbon 14 is the direction of low resistance in this material.

Further, by controlling the temperature of the molten metal during the rapid cooling, the crystallographic orientation in which the thermoelectric material grows can be controlled. As shown in FIG. 5, the hexagonal a-axis is parallel to the thickness direction of the quenched thin piece 31. And C-plane are also aligned.

Next, if necessary, the quenched ribbon 14 obtained by quenching by the liquid quenching method shown in FIG. 3 is heat-treated in hydrogen gas or Ar gas (hydrogen reduction treatment or annealing treatment: step S5). To do. This heat treatment condition is, for example,
The temperature is 400 ° C. and the time is 8 hours. FIG. 6A is a sectional view showing the structure of the quenched ribbon 14 before heat treatment, and FIG. 6B is a sectional view showing the structure of the quenched ribbon 14 after heat treatment. As shown in FIG. 6A, in the structure before the heat treatment, that is, in the structure as rapidly solidified, a large amount of chill crystals 52 are present on the surface of the quenched ribbon 14 in addition to the crystal grains 51 extending in the thickness direction. On the other hand, the heat treatment causes the chill crystals 52 to disappear, as shown in FIG. Further, during the heat treatment, Te atoms and Se atoms in the quenched ribbon 14 are segregated on the surface due to grain boundary diffusion. This is an improvement in sinterability,
Effective for improving carrier mobility.

Thereafter, the thin strip 14 is crushed if necessary,
Classify and make the particle size uniform. Then, a thin strip (foil) 14 having an appropriate grain size range is loaded while being stacked in a prismatic mold (not shown), and a pressure P is applied in the axial direction in a state where the side surface is restrained by the heated heat. And hot press. In addition, in the ribbon 14 obtained by liquid quenching, as shown in FIG.
Since the a-axis (C plane) of each crystal grain is aligned in the thickness direction of the ribbon 14, the pressure P during hot pressing is applied parallel to the a-axis. As a result of this hot pressing, a prismatic solidified compact having a crystal structure having crystal grains whose major axis is aligned in the pressing direction (pressing direction) and whose minor axis is aligned in the direction orthogonal to the pressing direction is obtained (primary solidification). Molding) (step S6).

Strains and defects have been introduced into the quenched flakes produced by the liquid quenching method. When the rapidly cooled flakes are crushed or solidified by hot pressing or the like without crushing, grain growth of crystal grains occurs, or this strain or defect serves as nuclei to precipitate recrystallized grains. The recrystallized grains can be crystal grains with a large aspect ratio having a major axis in a direction parallel to the pressing direction during solidification molding and a minor axis in a direction perpendicular to the pressing direction.

Therefore, when solidifying the quenched thin piece (powder), it is pressed in the direction parallel to the thickness direction of the quenched ribbon, that is, in the direction parallel to the long axis of the crystal grains in the quenched ribbon, and at the time of solidification molding. If the long axes of the recrystallized grains that are generated are aligned in the pressing direction,
As a result, a solidified compact having a crystal structure in which the major axis direction of the crystal grains is aligned in the direction parallel to the pressing direction is obtained.

Further, in this embodiment, as described above, Te atoms and S atoms are formed on the surface of the quenched ribbon 14 by the heat treatment.
Since the e-atoms are segregated, these atoms are easily diffused between the quenched ribbons 14 and are easily solidified and molded.

After that, upsetting is performed on the solidified compact (step S7). FIG. 8 is a schematic view showing a method of upsetting. When performing the swaging forging, first, as shown in FIG. 8A, the pressure applying surface 61a of the solidified molded body 61 during hot pressing is constrained, and the pressure applying surface 61 is restrained.
The surface perpendicular to a is pressed with pressure P2. As a result,
The solidified molded body 61 extends in a direction parallel to the pressure application surface 61a and the surface to which the pressure P2 is applied.

9 to 11 are schematic diagrams showing changes in the orientation of the crystal grains as the solidified compact 61 is spread. 9 to 11, (a) shows a state before spreading, (b)
And (c) show the state after spreading. In FIG. 9A, the X axis indicates the pressure application direction of upset forging, the Y axis indicates the spreading direction, and the Z axis indicates the pressure application direction during hot pressing.
Further, FIG. 9 shows a change when viewed from a direction inclined with respect to the application direction of the pressure P2 (X-axis direction), and FIG. 10 shows a change when viewed from the application direction of the pressure P2 (X-axis direction). 11 shows the change when viewed from the direction (Z-axis direction) perpendicular to the constraining surface (pressure applying surface 61a). Solidified compact 6
With the spread of No. 1, the crystal grains 62 whose C-plane is perpendicular to the application direction of the pressure P2 (X-axis direction) are shown in FIGS.
As shown in (b), the application direction of the pressure P2 (X-axis direction)
While the C and C planes remain vertical, one side of the C plane rotates so as to be parallel to the Y axis, and further shifts in the spreading direction (Y axis direction). Alternatively, as shown in FIGS. 10 (c) and 11 (c), the C plane does not rotate and the C plane does not rotate while the application direction (X-axis direction) of the pressure P2 and the C plane remain vertical. It is oriented so that one side is parallel to the Z axis and is offset in the spreading direction (Y axis direction). On the other hand, crystal grains 6 whose C plane is parallel to the direction of application of pressure P2
3 rotates 90 ° so that the direction of application of the pressure P2 and the C-plane are perpendicular to each other, and as shown in FIGS. 10 (b) and 10 (b), one side of the C-plane is the Y-axis. It rotates so that it becomes parallel, and it shifts in the spreading direction (Y-axis direction). Alternatively, FIG.
As shown in (c) and FIG. 11 (c), one side of the C plane is Z
It is oriented so that it is parallel to the axis and is offset in the spreading direction (Y-axis direction). As a result, as shown in FIGS. 9 to 11, the C planes and a-axes of the respective crystal grains are aligned.

In the thermoelectric material thus obtained, the c-axis is aligned in the pressing axis direction during upset forging. That is, the C planes are aligned in the spreading direction during upsetting. C
Since the direction parallel to the plane is the direction where the specific resistance (ρ) is low,
A high performance index (Z) can be obtained by assembling the Peltier device (thermoelectric device) so that this direction is the energization direction. Further, such a thermoelectric element can be used for optical communication, for example, and is extremely effective as a Peltier element that has low Joule heat and low power consumption even when used in a package having a high temperature.

Further, in this embodiment, since the chill crystals in the quenched ribbon 14 are eliminated by heat treatment, the thermoelectric material obtained as a result has high sinterability and excellent mechanical strength, and orientation Is further improved. That is, when heat treatment is not performed as in the conventional case, the chill crystals existing on the surface of the quenched ribbon grow irregularly during the subsequent hot pressing. In fact, when observing the structure of the thermoelectric material produced by such a method, the crystal grains obtained by the growth of chill crystals are present at the interface of the quenched ribbon, not the crystal grains with high orientation. The orientation of is disturbed. Therefore, this region serves as a deformation resistance during sintering, and the sinterability is low. On the other hand, when heat treatment is performed as in this example, strain during quenching is relaxed, chill crystals disappear, deformation resistance during sintering (hot pressing) is significantly relaxed, and sinterability is improved. Is improved. In addition, since chill crystals cannot grow, high orientation can be obtained. Further, as described above, T during heat treatment
The sinterability is also improved by the diffusion of e atoms and Se atoms.

It is preferable that the atmosphere during the upsetting is such that the oxygen concentration is 5000 ppm or less and the dew point is -20 ° C. or less.

The method for obtaining the foil or powder having the orientation inside the crystal by the liquid quenching method includes, for example, the single roll method and the gas atomizing method, but the present invention is not limited thereto.

Further, with respect to the degree of working in the swaging forging, it is preferable that the variation is about 50 to 90%.

Next, the results of producing thermoelectric materials under various conditions and determining their thermoelectric characteristics will be described. First, the thermoelectric materials having various compositions are manufactured, and the direction parallel to the pressing direction at the time of the first hot pressing (primary solidification molding) is
The figure of merit Z was calculated from the specific resistance ρ, the thermal conductivity κ and the Seebeck coefficient α. The results are shown in Tables 1 to 20 below. Tables 1 and 2 show the composition of each thermoelectric material, and Tables 3 and 4 show the values of the specific resistance ρ, the thermal conductivity κ, the Seebeck coefficient α, and the figure of merit Z when the reduction treatment is performed, Table 5
And Table 6 shows the specific resistance ρ when no reduction treatment is performed,
The values of thermal conductivity κ, Seebeck coefficient α and figure of merit Z are shown.

Example No. In 1 to 7, compounded to each composition
Thin slices or powders are made from the ingots by the liquid quenching method.
Manufactured and subjected to reduction treatment in a hydrogen atmosphere at 400 ° C for 10 hours
And then stack the foils in the thickness direction of the foil (parallel to the C surface).
Direction) as the pressing direction.
Then, a solidified molded body was produced. Also, do not perform reduction processing
A solidified compact was also produced. Furthermore, the hot press of the solidified compact
Pressure is applied from one direction while restraining the pressing surface during
Upsetting was performed by adding. Hot pre
For the space, use a carbide die and set the atmosphere to Ar atmosphere.
It was Further, the shape of the solidified molded body is such that each side has a length of 50 mm.
Cube, 0.5 (t / cm^Two) Pressure to P-type thermoelectric
Material is 380 ℃ for 1 hour, N-type thermoelectric material is 450 ℃
Application was continued for 1 hour. In addition, in upset forging, carbide
Using a die, 0.8 (t / cm ^Two) Pressure is 400
Continue to apply for 5 hours at ℃, the amount of change in the pressing direction during forging is 55
%. In addition, regarding the atmosphere during upsetting,
Elementary concentration shall be 5000ppm or less
Has a dew point temperature of −20 ° C. or lower. Figure 12 shows the forging
It is a schematic diagram which shows the amount of change of a pressure direction. Dimension in Figure 12
For method a and b, change amount is calculated by b / a × 100
Can be

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

[0049]

[Table 5]

[0050]

[Table 6]

As shown in these results, in each of the examples, by performing the predetermined upset forging, the specific resistance (ρ) decreased while maintaining the high performance index (Z). That is, these treatments yielded a thermoelectric material suitable for use at high temperatures.

[0052]

As described in detail above, according to the present invention,
The thermoelectric material spreads in a direction perpendicular to the pressing direction of upset forging and perpendicular to the unconstrained surface, and the C-planes including the a-axis of each crystal grain are parallel to each other with this spreading. Since the c-axis is extremely aligned, the figure of merit can be improved by assembling the thermoelectric element with the direction in which the specific resistance is low as the conducting direction.
As a result, it is possible to reduce power consumption at high temperature while maintaining a high figure of merit.

[Brief description of drawings]

FIG. 1 is a flowchart showing a method for manufacturing a thermoelectric material according to an example of the present invention.

2 (a) to 2 (c) are views showing a method for producing an ingot in the example of the present invention.

FIG. 3 shows a method for producing a powder of thermoelectric material by a liquid quenching method.

FIG. 4 is a schematic diagram showing a growth direction of crystal grains in a quenched thin piece.

FIG. 5 is a schematic diagram showing a relationship between a pressing direction and a C surface.

6A is a sectional view showing the structure of the quenched ribbon 14 before heat treatment, and FIG. 6B is a sectional view showing the structure of the quenched ribbon 14 after heat treatment.

FIG. 7 is a schematic diagram showing the orientation of crystal grains in the ribbon 14 obtained by liquid quenching.

FIG. 8 is a schematic view showing a swaging forging method.

FIG. 9 is a schematic diagram showing changes in the orientation of crystal grains (when viewed from a direction inclined with respect to the application direction of the pressure P2) due to the spreading of the solidified compact 61, (a) before spreading And (b) and (c) are schematic diagrams showing a state after spreading.

FIG. 10 is a schematic diagram showing a change in orientation of crystal grains (when viewed from the direction of application of pressure P2) due to spreading of the solidified compact 61, (a) showing a state before spreading, (b) And (c) is a schematic diagram which shows the state after spreading.

FIG. 11 is a schematic diagram showing a change in orientation of crystal grains (when viewed from a direction perpendicular to a constraining surface) due to spreading of the solidified compact 61, (a) showing a state before spreading. , (B) and (c) are schematic views showing a state after spreading.

FIG. 12 is a schematic diagram showing the amount of change in the pressing direction during forging, where (a) is before processing and (b) is after processing.

13A to 13C are schematic views showing a method of manufacturing a conventional unidirectionally solidified material in the order of steps.

FIG. 14 is a schematic diagram showing crystal grains of a thermoelectric material to be solidified and molded and hot pressing directions.

FIG. 15 is a diagram showing a crystal structure of a Bi—Te based thermoelectric material.

[Explanation of symbols]

1; thermoelectric material, 2; crystal grain, 11; quartz nozzle,
12: Copper roll, 13: Molten metal, 14: Quenched foil strip,
15; top part, 30; chill roll, 31; quenching flakes,
32, 33; crystal structure, 41, 101; raw material, 4
2, 102; ampoule, 43, 103; tubular furnace, 4
4, 104; stand, 51, 62, 63; crystal grain,
52; chill crystal, 61; solidified compact

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[Procedure amendment]

[Submission date] December 17, 2002 (2002.12.
17)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22C 28/00 C22C 28/00 Z H01L 35/34 H01L 35/34 F term (reference) 4K018 AA40 AB10 AC01 BA20 BC06 EA03 EA04 EA43 FA09 FA14 HA08 KA32

Claims (5)

[Claims] 1. 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 from one direction. By applying pressure, the a-axes of the crystal grains in the thermoelectric material are oriented parallel to the direction in which the pressure is applied, and while constraining the surface to which the pressure is applied, pressure is applied from a direction perpendicular to the constrained surface. By applying upset forging, the thermoelectric material is spread and the C-plane of the crystal grains is oriented by rotation or sliding so as to be perpendicular to the direction in which the pressure is applied during upsetting forging. A thermoelectric material characterized in that 2. The thermoelectric material comprises at least one element selected from the group consisting of Bi and Sb, and Te and S.
A thin piece obtained by unidirectionally solidifying a molten metal having a composition consisting of at least one element selected from the group consisting of e, in which the a-axes of the crystal grains are aligned in the thickness direction of the thin piece. The thermoelectric material according to claim 1, wherein: 3. 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 from one direction. Applying a pressure to orient the a-axes of the crystal grains in the thermoelectric material parallel to the direction in which the pressure is applied; and, while constraining the surface to which the pressure is applied, from a direction perpendicular to the constrained surface. A step of spreading the thermoelectric material by performing a swaging forging to apply a pressure, and orienting the C-plane of the crystal grains by rotation or sliding so as to be perpendicular to the direction in which the pressure is applied during the swallowing forging; A method for producing a thermoelectric material, comprising: 4. The thermoelectric material comprises at least one element selected from the group consisting of Bi and Sb, and Te and S.
A thin piece obtained by unidirectionally solidifying a molten metal having a composition consisting of at least one element selected from the group consisting of e, in which the a-axis of the crystal grains is oriented parallel to the direction in which the pressure is applied. The method for producing a thermoelectric material according to claim 4, wherein the step includes a step of aligning the a-axes of the crystal grains in the thickness direction of the flakes. 5. A step of heat-treating the thermoelectric material in a reducing gas atmosphere or an inert gas atmosphere after the step of orienting the a-axis of the crystal grains parallel to the pressure application direction. The method for producing a thermoelectric material according to claim 4 or 5.