JP3203383B2 - Thermoelectric material and thermoelectric conversion element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric material and a thermoelectric conversion element used for a thermoelectric cooling device such as a refrigerator and a thermoelectric generator.

[0002]

2. Description of the Related Art As one of thermoelectric conversion elements, there is a thermocouple as a temperature measuring sensor. This thermocouple is formed by joining two different kinds of metals and semiconductors in pairs. When a temperature difference is applied to both ends of the thermocouple, an electromotive force corresponding to the temperature difference is generated. If one contact of the thermocouple is kept at a known temperature and the voltage between the two contacts is measured, this is a function of the temperature of the other contact.

[0003] Many devices have been proposed to obtain a large thermoelectromotive force by placing one contact at room temperature and placing the other contact at a high-temperature heat source by using the above phenomenon to increase the temperature difference between the two contacts. I have.

On the other hand, conversely, when a potential difference is applied between the two contacts of the thermocouple, a temperature difference corresponding to the potential difference is generated. For example, if the high-temperature side contact is kept at the ambient temperature, the low-temperature side contact will be lower in temperature than that, so that the low-temperature side contact can be directly cooled. Utilizing this phenomenon, it is applied to coolers such as portable refrigerators and computer CPUs.

At present, almost all thermoelectric materials used for thermoelectric power generation and thermoelectric cooling are semiconductors, and thermoelectric conversion elements have a configuration in which a p-type semiconductor and an n-type semiconductor are combined and joined.

A thermoelectric generator or a thermoelectric cooler using a thermoelectric conversion element has no mechanical driving part, so that it can be made noise-free and has a small configuration, and can be easily inspected and maintained. There are advantages. Therefore, as a device that is expected to be put to practical use as a device using a thermoelectric conversion element, there is, for example, a home refrigerator.

[0007] The performance of thermoelectric materials is usually Z = S ² / κρ
The superiority is compared by a performance index Z defined by. Here, S represents thermoelectric power called a Seebeck coefficient, κ represents thermal conductivity, and ρ represents electrical resistivity. ZT, which is a dimensionless version of Z, is also used as a figure of merit. Where T
Is the absolute temperature.

A thermoelectric conversion device using a thermoelectric material includes:
Examples of the refrigerator or the integrated circuit cooler of the computer as described above. These are all used near room temperature. Therefore, in evaluating the performance of a thermoelectric material, the ZT value near room temperature (about 300 K) is practically important.

1 (a) and 1 (b), temperature (K) is plotted on the horizontal axis, and figure of merit Z (× 10 ^-3 K ^-1 ) is plotted on the vertical axis.
FIG. 4 is a characteristic diagram showing a relationship between a figure of merit of a conventional semiconductor and temperature. FIG. 1A is a characteristic diagram of a p-type semiconductor, and FIG. 1B is a characteristic diagram of an n-type semiconductor.

As shown in FIGS. 1A and 1B, p
Exponent Z strongly depends on temperature for both n-type and n-type
Most of the semiconductors have a figure of merit Z at a maximum in the vicinity, and the figure of merit Z tends to increase as the temperature rises. As described above, since the figure of merit Z greatly changes depending on the temperature, it is not only that the figure of merit Z should just be high, but from the practical viewpoint, it is important that the Z value at room temperature is high. The semiconductor having the highest figure of merit near room temperature (300 K) is (B) in FIG.
i, Sb) ₂ Te _{3 is} a p-type semiconductor. Further, in FIG. 1B, it is an n-type semiconductor of Bi ₂ (Se, Te) ₃ . These are currently used in cooling devices at room temperature. Both semiconductors have a figure of merit Z near room temperature of about 2 × 10 ⁻³ K ⁻¹ and a ZT value of less than 1.

At present, thermoelectric materials exhibiting high thermoelectric performance near room temperature
As a material, "WM Kim and FD Ro"
si, Solid State Electron. 1
5,1121 (1972) "and" GD Maha.
n, Solid State Physics vol.
41, 81 (1998) ".
You. These documents include (Sb_TwoTe_Three)₇₂(Bi_TwoT
e_Three)_{twenty five}(Sb_TwoSe_Three)_ThreeA p-type semiconductor having a composition of
Exhibit a figure of merit of ZT = 1.02 (T = 300K)
Is disclosed. Also, (Sb_TwoTe_Three)_Five(Bi_TwoTe
_Three)₉₀(Sb_TwoSe _Three)_FiveAn n-type semiconductor having a composition of Z
It shows a figure of merit of T = 0.96 (T = 300K).
It has been disclosed.

[0012] In addition to the above-mentioned thermoelectric materials, it has been reported that amorphous thermoelectric materials also exhibit excellent thermoelectric performance.

The dimensionless figure of merit ZT is theoretically considered to have no fundamental limit, and various thermoelectric materials are being researched and developed. Taking thermoelectric cooling as an example, it is said that a home refrigerator using a thermoelectric material can compete with a home refrigerator using a conventional compressor if the value of ZT at room temperature is around 3.

[0014]

However, taking thermoelectric cooling as an example, the thermoelectric cooling performance that can be achieved by the above-described conventional thermoelectric material is clearly inferior in efficiency to the cooling performance using a compressor. . For this reason, conventional thermoelectric materials have been limited only to applications where reliability and convenience are more important than economics. Further, an amorphous thermoelectric material which is conventionally said to have high thermoelectric performance has a problem that it may deteriorate over time and has poor reliability.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thermoelectric material exhibiting a higher performance index ZT at room temperature than conventional thermoelectric materials and having no fear of deterioration. To provide.

Another object of the present invention is to provide a thermoelectric conversion element having the above thermoelectric material and having excellent thermoelectric conversion performance.

[0017]

The present invention uses the following means in order to solve the above problems.

(1) The general formula CeAM (where A is N
one element selected from the group consisting of i, Rh, and Pt, and M represents one element selected from the group consisting of Bi, Sb, As, and Sn); A p-type semiconductor thermoelectric material that is a crystal substituted with an acceptor element.

(2) General formula XQR (where X is one element of Yb or Sm element, Q is one element selected from the group consisting of Ni, Rh and Pt, R is Bi,
N represents an element selected from the group consisting of Sb, As, and Sn), and is a crystal in which a part of the element X is substituted with a donor element.

(3) The general formula CeAM (where A is N
one element selected from the group consisting of i, Rh, and Pt, and M represents one element selected from the group consisting of Bi, Sb, As, and Sn); A p-type semiconductor thermoelectric material which is a crystal substituted with an acceptor element, and a general formula XQR (where X is one of Yb or Sm elements, and Q is Ni, Rh and Pt)
One element selected from the group consisting of: R is Bi, S
b, represents one element selected from the group consisting of As and Sn), and comprises an n-type semiconductor thermoelectric material which is a crystal in which part of the element X is substituted with a donor element. element.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a p-type semiconductor thermoelectric material according to the present invention will be described in detail.

This p-type semiconductor thermoelectric material has the general formula CeA
It is a crystal in which a compound represented by M has a basic skeleton and a part of Ce element is substituted by an acceptor element. In the above general formula, A is any one element of Ni, Rh and Pt. M is any one element of Bi, Sb, As or Sn.

As the acceptor element, La, Y, S
Elements such as c can be cited, and combinations thereof may be used. Among the acceptor elements, La is preferable. La is preferable because the ionic radius of La and the ionic radius of Ce are close to each other, so that the crystal structure is not disturbed. The substitution amount of the acceptor element is preferably 0.5 to 5 atomic% of the Ce element amount. By setting the substitution amount in the above-mentioned range, the carrier concentration can be improved so that the thermoelectric performance can be significantly improved.

An ordinary semiconductor has the property that the electrical resistivity increases as the thermoelectric power increases. However, the p-type semiconductor thermoelectric material has a characteristic that the electrical resistivity does not increase even if the thermoelectric power increases, and thus shows a remarkably high figure of merit. In addition, it shows a high dimensionless figure of merit near room temperature. Furthermore, since it is a crystalline body, there is no possibility of deterioration like an amorphous thermoelectric material.

The p-type semiconductor thermoelectric material of the present invention can be produced by, for example, growing a single crystal by the Bridgman method. In the Bridgman method, first, each element having the above composition is dissolved in an arc melting furnace or the like to obtain a polycrystalline compound as a raw material. Next, this raw material is vacuum-sealed in a tube made of a high melting point metal such as molybdenum or tungsten. continue,
The tube is set in a heating furnace such as a high-frequency induction heating furnace, and is moved vertically to be single-crystallized, thereby obtaining the p-type semiconductor thermoelectric material.

Next, the n-type semiconductor thermoelectric material according to the present invention will be described in detail.

This n-type semiconductor thermoelectric material has the general formula XQR
Is a crystal in which a compound represented by is used as a basic skeleton, and a part of the X element is substituted with a donor element. In the above general formula, X is a Yb or Sm element. Q is Ni, R
h or any one of Pt. R is B
i, Sb, As, and Sn are any one of the elements.

Lu, Y, Zr, H
Elements such as f can be mentioned, and combinations thereof may be used. Among the above-mentioned donor elements, it is preferable to be the Lu element or the Y element. Lu element or Y element is preferable because the ionic radius of these elements and Yb
This is because the crystal structure is not disturbed because the ionic radii of Sm and Sm are close.

The substitution amount is preferably 0.5 to 5 atomic% of the X element amount. By setting the substitution amount in the above range, a carrier concentration that can significantly improve thermoelectric performance can be obtained.

The n-type semiconductor thermoelectric material has a characteristic that the electrical resistivity does not increase even if the thermoelectric power increases. Therefore, it shows a significantly high figure of merit. Also, it shows a high dimensionless figure of merit ZT even near room temperature. Furthermore, since it is a crystalline body, there is no risk of deterioration as in an amorphous thermoelectric material.

The n-type semiconductor thermoelectric material of the present invention can be obtained by growing a compound having the above composition by arc melting or the like into a single crystal by, for example, the Bridgman method.

Next, the thermoelectric conversion element according to the present invention will be described in detail.

This thermoelectric conversion element has the above-mentioned p-type semiconductor thermoelectric material and n-type semiconductor thermoelectric material. A thermoelectric cooling device incorporating such a thermoelectric conversion element provided with such p-type and n-type semiconductor thermoelectric materials will be described below with reference to FIG.

The thermoelectric conversion element has, for example, an n-type semiconductor thermoelectric material 2 and a p-type semiconductor thermoelectric material 3 which are arranged adjacent to each other, for example, in the form of a rectangular block.
Is joined to the endothermic electrode 4. The other end of the n-type semiconductor thermoelectric material 2 is joined to the heating-side electrode 5a. The heating-side electrode 5a is connected to the positive side of the power supply 1 via a conductive wire. The other end of the p-type semiconductor thermoelectric material 3 is joined to the heating-side electrode 5b.
The heating-side electrode 5b is connected to the negative side of the power supply 1 via a conductive wire.

It should be noted that the thermoelectric cooling device is not limited to the case where one thermoelectric conversion element is provided as shown in FIG. 2, and a large number of thermoelectric conversion elements may be connected in series. With such a configuration, a thermoelectric cooling device that can further improve the cooling efficiency can be obtained. Further, by connecting the thermoelectric conversion elements in a cascade of a plurality of stages, a thermoelectric cooling device capable of further lowering the cooling temperature on the heat absorption side can be obtained.

In the thermoelectric cooling device shown in FIG.
When a voltage is applied to each of the thermoelectric materials 2 and 3, electrons, which are majority carriers in the n-type semiconductor thermoelectric material 2, move to the heating-side electrode 5 a to carry heat. At the same time, holes which are majority carriers in the p-type semiconductor thermoelectric material 3 also move to the heat-generating electrode 5b to carry heat. At this time, since the p-type and n-type semiconductor thermoelectric materials 2 and 3 each have a high figure of merit, it is possible to cause a large temperature difference between both the heat-absorbing side electrode 4 and the heat-generating side electrodes 5a and 5b. . Therefore, high cooling performance can be realized on the heat absorption side of the thermoelectric cooling device incorporating the thermoelectric conversion element of the present invention shown in FIG.

The electrodes 4 and 5 are desirably made of a material having as small an electrical resistivity as possible and having a high thermal conductivity. If the electric resistance is small, the energy loss due to Joule heat can be suppressed, and if the thermal conductivity is large, the amount of heat can be quickly transferred when absorbing or generating heat. Examples of the material for the electrodes 4 and 5 include copper and aluminum.

It should be noted that the thermoelectric generator can be used as a thermoelectric generator capable of extracting electric power by providing a temperature difference between the heat absorbing side electrode 4 and the heat generating side electrodes 5a and 5b in FIG.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail.

Example 1 First, each element of Ce, La, Rh and Sb was converted to Ce.
Each was weighed so as to have an atomic ratio satisfying the composition formula of _0.99 La _0.01 RhSb.

Next, these weighed elements were arc-melted in a pure argon atmosphere. Since Sb loses transpiration during melting, 1% of the Sb weight was added before arc melting to compensate for this.

Subsequently, the sample obtained by arc melting was sealed in a crucible made of a high melting point metal, and a single crystal of a p-type semiconductor having the above composition was prepared by the Bridgman method.

With respect to the obtained single crystal of Ce _0.99 La _0.01 RhSb, the electric resistivity ρ, the thermal conductivity κ, and the thermoelectric power S were measured at a temperature of 300 K, respectively, and the figure of merit ZT was examined. As a result, ZT was found to be 1.05, indicating excellent thermoelectric performance.

Example 2 The elements of Yb, Y, Ni, and As were converted to Yb _0.99 Y _0.01 N
Each was weighed so as to have an atomic ratio satisfying the composition formula of iAs.

Next, these weighed elements were arc-melted in a pure argon atmosphere. Otherwise, a single crystal of the above composition formula was prepared in the same manner as in Example 1 to obtain an n-type semiconductor thermoelectric material.

Example 3 Each element of Yb, Y, Rh, and Sb was _converted to Yb _0.995 Y
Each was weighed so as to have an atomic ratio satisfying the composition formula of _0.005 RhSb. Otherwise, a single crystal of the above composition formula was prepared in the same manner as in Example 1 to obtain an n-type semiconductor thermoelectric material.

Example 4 Each element of Yb, Lu, Pt and Sb was _converted to Yb _0.995 L
Each was weighed so as to have an atomic ratio satisfying the composition formula of u _0.005 PtSb. Otherwise, a single crystal of the above composition formula was prepared in the same manner as in Example 1 to obtain an n-type semiconductor thermoelectric material.

Example 5 Each element of Sm, Y, Ni and As was converted to Sm _0.99 Y _0.01 N
Each was weighed so as to have an atomic ratio satisfying the composition formula of iAs. Otherwise, a single crystal of the above composition formula was prepared in the same manner as in Example 1 to obtain an n-type semiconductor thermoelectric material.

Example 6 Each element of Sm, Lu, Pt, and Sb was _converted to Sm _0.995 L
Each was weighed so as to have an atomic ratio satisfying the composition formula of u _0.005 PtSb. Otherwise, a single crystal of the above composition formula was prepared in the same manner as in Example 1 to obtain an n-type semiconductor thermoelectric material.

With respect to the single crystal of each n-type semiconductor thermoelectric material obtained in Examples 2 to 6, the electrical resistivity ρ, the thermal conductivity κ, and the thermoelectric power S at a temperature of 300 K were measured, and a figure of merit Z
T was examined. The results are shown in Table 1 below.

[0051]

[Table 1]

As shown in Table 1, it was confirmed that the single crystal of any of the n-type semiconductor thermoelectric materials had a high figure of merit and exhibited excellent thermoelectric performance near room temperature.

Example 7 Using the single crystal of the p-type semiconductor thermoelectric material obtained in Example 1 and the single crystal of the n-type semiconductor thermoelectric material obtained in Examples 2 to 6, the thermoelectric element shown in FIG. A cooling device was manufactured. As the power source 1, a 6 V DC power source was used. Each electrode and the semiconductor thermoelectric material were joined with a silver paste. In the thermoelectric cooling device thus configured, the temperature difference between the two electrodes of the heat-absorbing electrode 4 and the heat-generating electrode 5a (or the heat-generating electrode 5b) was measured at 300K. Table 2 shows the results.

[0054]

[Table 2]

It was confirmed that a very large temperature difference of 29 or 30 K was generated in any combination of thermoelectric conversion elements, and it was found that the thermoelectric conversion element had excellent thermoelectric conversion performance at room temperature.

[0056]

As described above, according to the present invention,
Dimensionless figure of merit Z near room temperature, which is important for practical use
P-type and n-type semiconductor thermoelectric materials exhibiting high T values are provided. Moreover, since the thermoelectric material of the present invention is crystalline,
There is no risk of deterioration as in the case of an amorphous thermoelectric material. Further, by using these thermoelectric materials, a thermoelectric conversion element exhibiting excellent thermoelectric conversion performance at room temperature is provided.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the temperature and the performance index of conventional p-type semiconductor thermoelectric materials and n-type semiconductor thermoelectric materials.

FIG. 2 is a view schematically showing a thermoelectric cooling device according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Power supply 2 ... n-type semiconductor thermoelectric material 3 ... p-type semiconductor thermoelectric material 4 ... Heat absorption side electrode 5a, 5b ... Heat generation side electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 35/18 H01L 35/20 H01L 35/32 H01L 35/34 C22C 30/00

Claims (3)

(57) [Claims] 1. The general formula CeAM (where A is Ni, R
one element selected from the group consisting of h and Pt, M
Represents one element selected from the group consisting of Bi, Sb, As and Sn), and is a crystal in which part of the Ce element is replaced with an acceptor element. Thermoelectric material. 2. A general formula XQR (where X is one element of Yb or Sm element, and Q is Ni, Rh and Pt)
One element selected from the group consisting of: R is Bi, S
an element selected from the group consisting of b, As, and Sn), wherein the element X is a crystal in which part of the element X is substituted with a donor element. 3. The general formula CeAM (where A is Ni, R
one element selected from the group consisting of h and Pt, M
Represents one element selected from the group consisting of Bi, Sb, As, and Sn), a p-type semiconductor thermoelectric material that is a crystal in which part of the Ce element is replaced with an acceptor element, Formula XQR (where X is one element of Yb or Sm element, Q is one element selected from the group consisting of Ni, Rh and Pt, and R is Bi, Sb, As and S
n, which represents one element selected from the group consisting of n), and an n-type semiconductor thermoelectric material which is a crystal in which a part of the element X is substituted by a donor element. Conversion element.