JPS63138789A - Manufacture of thermoelectric material - Google Patents

Abstract

PURPOSE:To mass-produce a thermoelectric material having a high performance index at low cost by a method wherein a plastic deformation is given so that its orientation property has a crystalline orientation having a superior performance index. CONSTITUTION:Bi2Te3 pulverized in -325 mesh is molded into a C.I.P and thereafter, the C.I.P is sintered at 400 deg.CX1H and is further heated to 500 deg.C and a hot rolling is performed to obtain a cube 1. When the X-ray diffraction of each surface after the rolling, that is, the respective X-ray diffractions of a plane 1a, end surfaces 1b and side surfaces 1c are measured, (006) and (0015) appear on the plane 1a and (110) becomes stronger on the end surfaces 1b and the side surfaces 1c. Accordingly, an orientation, with which a 'rt. angletri' direction coincides in a pushing-out direction, is through to be generated by rolling. Thereby, if a current is passed through in parallel to the plane 1a to a thermoelectric material, there is the same effect as that at a time when a current is passed through in the single crystal 'rt. angletri' direction and a high Z can be obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to thermoelectric materials such as leg materials for electronic cooling modules that utilize the Peltier effect or leg materials for power generation modules that utilize the Seebeck effect. This relates to a manufacturing method.

[Conventional technology]

The thermoelectric materials mentioned above include those having a rhombohedral structure, and Bi-Ta series, Bi-54 series, and the like are widely known.

These systems generally have a figure of merit Z (Z is a numerical value that indicates the performance of thermoelectric materials, and is α2/4, where α: Seebeck constant, σ: electrical conductivity, K: thermal conductivity) differs depending on the crystal direction. is known (for example, Akita, Onodera, et al., NationatTechF&ical Report
(Vol. 9, No. 1) Figure 5 shows the atomic arrangement of the 5/T4 system. In this figure, the trJor&aL direction (hereinafter referred to as the '/tri' direction) and this '/tr
It is explained that because the bonding forms of the crystals are different in the i'' direction and the vertical direction (hereinafter referred to as the 1-tri'' direction), there is a difference between Z in the ``/tri'' direction and Z in the l tri'' direction. There is. In FIG. 5, the diaphragm lines shown in the hexagonal unit cell are opposed to the rhombohedral unit cell. The black circle is 7
'g, white circles represent Bi.

The above-mentioned materials are manufactured into single crystals or crystals with a unidirectionally solidified structure with uniform crystal directions by the Bridgman method or the zone melt method.

Also, regarding Z, the bi-tri' direction is better in the Bi-Ta system, and the '/tri' direction is better in the B1m5h system.

[Problem that the invention seeks to solve]

The Bridgman method and the zone melt method shown in the above-mentioned conventional techniques have poor productivity and low fractionation, resulting in high costs and limited applications.

In order to solve the problem of high costs, an attempt was made to replace it with powder metallurgy.

In powder metallurgy, a polycrystalline material with random "/trs" and 1-tri" directions is formed, so there is a risk that Z is smaller than crystals produced by the Bridgman method or zone melting method.

[Measures to solve problems]

The present invention has been made in view of the above, and aims to provide a method for manufacturing thermoelectric materials that enables mass production of thermoelectric materials having a high performance index at low cost. The manufacturing method includes at least one step of applying plastic deformation so that the crystal orientation has an excellent figure of merit.

[For production]

Due to plastic deformation, an orientation occurs in which the direction of trL'' coincides with the direction of layered deformation.

〔Example〕

Examples of the present invention will be described below.

Example 1 Grind fe, Bi, Ta@C,1 to 325 mesh
, P (cold eye μ caric nine) after molding, 400
It was sintered at ℃×IE. It was further heated to 500° C. and hot rolled to obtain a cube 1 as shown in FIG. Each surface after the pressure end, that is, a plane! a, end surface IA.

When the X-ray diffraction of each side IC was measured, the results were as shown in Fig. 2A for the plane 1α, as shown in Fig. 2 for the end face 1b), and as shown in Fig. 2 (q) for the side IC.

Example 2 Instead of the rolling process shown in Example IK, extrusion was carried out to obtain a cylindrical body 2 as shown in FIG. When X-ray diffraction was measured on the side surface 2α and end surface 2b of the cylindrical body 2 after extrusion molding, the results were as shown in FIG. 4(b) on the side surface 2a.

Comparative Example 1 Bi! shown in FIG. The xN diffraction (Cu target) fα, line) of the close-packed surface 3 of the T single crystal was measured, and the results were as shown in FIG.

Comparative Example 2-325) C,1
After molding, it was sintered at 400°C x IB. As shown in Fig. 7, the sintered body was cut without strain into a cube 4 with a 2cIx angle, and the X-ray diffraction of each of its plane 4α, end surface 4A, and side surface 4C was measured. 8(b) on the end surface 4b, and 8(b) on the side surface 4c.
The result is as shown in Figure 0.

In the above Examples and Comparative Examples, FIG. 6 showing the experimental results of Comparative Example 1 shows the diffraction angle 2θ on the horizontal axis and the X-ray diffraction intensity on the vertical axis. Since the relationship between the diffraction angle and the interplanar spacing when α is used for a Cu target is known, the interplanar spacing of each peak is determined, and then B* and A of T shown in the attached table are calculated.
The results of determining the plane index of each peak based on the values on the STM card are also added in parentheses. In Comparative Example 1, the closest-packed plane 3 of the single crystal was measured, so the diffraction results recorded only plane indices (006), (0015) and reflections from the closest-packed plane.

In the experimental results of Comparative Example 2, the reflection of the surface with strong diffraction intensity shown in the attached ASTM card (015), (+010
), (+10), (205), etc. are recorded.

This indicates that there is no particular surface on the measurement surface, and since the results are the same for each of the three surfaces measured, the produced sintered body is as shown in Figure 9. It is concluded that it is a polycrystalline body with extremely random crystal orientation.

When rolling is performed as shown in Example 1, the plane 1a has (
006), (0015), end face 1b and side face I
C has a strong (110). Figure 10 shows (00
6), (0015), and (+10) planes are shown.

Therefore, by rolling, 1 soil tri” in the extrusion direction
It appears that alignment with matching directions occurs as shown in FIG.

As a thermoelectric material, when current is applied parallel to the plane 1α, it has the same effect as when electricity is applied in the 1× direction of a single crystal.
High Z can be obtained.

Similarly, in Example 2, an orientation in which the 1/3'' direction coincides with the extrusion direction occurs (FIG. 12).

As a thermoelectric material, a high value of 2 can be obtained by applying current parallel to the extrusion direction.

Similar effects can be obtained by applying plastic deformation in a uniaxial direction in processes other than pressure treatment and extrusion processes. Thermoelectric materials (such as BiSb) having nine rhombohedral structures are also effective.

〔Effect of the invention〕

According to the present invention, thermoelectric materials having a high figure of merit can be mass-produced at low cost.

[Brief explanation of the drawing]

Figures 1 and 3 are 1. A perspective view showing the molded body obtained in the second example, Fig. 2), (B), (Q is an X1m diffraction diagram of each surface of the molded body obtained in the first example, Figures 4 (a) and (b) are X-ray diffraction diagrams of each surface of the next molded product obtained in the second example, and Figure 5 is the Bit T gs O single M
Crystal O'ilA formula diagram, fg6 diagram bar't(7) Xi1
1 is a diffraction diagram, FIG. 7 is a perspective view of a molded body molded by a conventional molding method, and FIG. 8 is an X-ray diffraction diagram of each side of a conventional molded body. FIGS. 9, 10, 11, and 12 are schematic diagrams showing the crystal orientation of each molded body.

Claims (3)

[Claims] (1) A method for producing a thermoelectric material using a rhombohedral structure, the method comprising at least one step of plastically deforming the material so that it has orientation in a crystal orientation with an excellent figure of merit. . (2) The method for producing a thermoelectric material according to claim 1, which comprises a rolling step. (3) The method for producing a thermoelectric material according to claim 1, which comprises an extrusion step.