JP3477019B2 - Thermoelectric conversion material and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a thermoelectric conversion material used for a thermoelectric element.

[0002]

2. Description of the Related Art Improving the efficiency of thermoelectric conversion materials has been an issue since the commercialization of this technology began. In recent years, a relatively organized research and development has come out of the long stagnation period. is there. One of the causes of this situation is the growing interest in energy and environmental issues. It is strongly desired to apply the thermoelectric power generation technology as an effective utilization technology of unused thermal energy, and the thermoelectric cooling technology that is the inverse conversion is literally a CFC-free cooling / freezing technology for cooling electronic devices. It is expected to be applied to refrigerators and air conditioners as well as temperature control systems in IC manufacturing processes. The conversion efficiency of a thermoelectric conversion material is determined by a thermoelectric figure of merit Z that reflects the physical property values of each material, and this thermoelectric figure of merit is represented by the following mathematical expression (1).

[0003]

[Equation 1]

Where α is the Seebeck coefficient, ρ is the electrical resistivity, κ is the thermal conductivity, m ^* is the effective mass of electrons or holes, μ is the mobility, and κ _L is the lattice vibration of the total thermal conductivity. It is a heat conduction component.

The higher the thermoelectric figure of merit, the better the thermoelectric conversion efficiency. That is, a material that is hard to conduct heat, conducts electricity well, and has a large thermoelectromotive force becomes a high-efficiency material. Such a material has characteristics of low thermal conductivity, low specific resistance, and large Seebeck effect. Is. The power generation conversion efficiency η (%) at this time
Is expressed by the following mathematical expression (2) using the thermoelectric figure of merit Z described above.

[0006]

[Equation 2]

[0007] Here, [Delta] T is the temperature difference between the high temperature portion and the low temperature section, Z is the thermoelectric figure of merit of the material, the T _h is the absolute temperature of the high temperature portion. Since α, ρ, and κ in the above mathematical expression (1) change depending on temperature, Z also has temperature dependency, and the temperature at which it takes the maximum value also differs depending on the material. Therefore, in order to improve the efficiency of the thermoelectric conversion material, it is important that Z is large in the entire operating temperature range, and a material that can increase ΔT is more advantageous.

[0008] As the thermoelectric conversion materials known in the art, Bi ₂ Te ₃ compounds, PbTe compounds, Si-Ge
Compounds, Fe-Si compounds and the like can be mentioned, but the material having a dimensionless figure of merit ZT, which is an index of thermoelectric characteristics, extremely close to 1 is only the Bi ₂ Te ₃ compound, and other materials have performances lower than that. I haven't. Although this Bi ₂ Te ₃ compound exhibits excellent performance, it tends to become unstable at high temperatures. Therefore, it is usually used in a temperature range of 573 K or lower, and has been used for electronic cooling rather than for power generation.

In order for the thermoelectric conversion material to be actually used for power generation using waste heat of a gas turbine or the like, heat resistance up to around 1000 K is required. Among the conventionally known materials, the Fe-Si compound shows relatively stable and good performance even in this temperature range, but still ZT = 878K.
It is about 0.2 and the obtained electric power is very small.
Therefore, in order to obtain more electric power, a thermoelectric conversion material for power generation that exhibits excellent performance in a wide temperature range from room temperature to a relatively high temperature of about 1000 K is required, and the development of such a material is desired. It is rare.

Recently, XY ₃ having a skutterudite structure
Compound (X is Co, Rh, Ir, Y is P, As, Sb)
However, it is attracting attention as a new thermoelectric conversion material. XY ₃
Among the compounds, CoSb ₃ , RhSb ₃ and IrSb
₃ Antimonide is a semiconductor with a unique band structure and carrier transport properties, and has excellent thermoelectric properties. Of these CoSb ₃ -based compounds, the most excellent thermoelectric properties at present are CoSb ₃ containing Te, As and I.
It is a compound represented by the following formula with slight addition of r.

Co _0.97 Ir _0.03 Sb _2.81 Te _0.04 As _{0.15 Even with} this compound, ZT = 0.6 at 700K.
Therefore, it does not reach the characteristics of the Bi ₂ Te ₃ compound. If it is possible to impart properties comparable to the CoSb ₃ based compound Bi ₂ Te ₃ compound, CoSb ₃ based compound having excellent high-temperature stability compared to the Bi ₂ Te ₃ compounds, for power generation unprecedented It is expected to be put to practical use as a thermoelectric conversion material, and has great industrial value. Therefore, development of CoSb ₃ -based compounds having more excellent thermoelectric properties is desired.

[0012]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above, Bi
₂ Te ₃ compound shows excellent characteristics near 573 K, but it is mainly used for electronic cooling because it is very unstable at high temperature, and cannot be used for power generation requiring heat resistance. . On the other hand, many thermoelectric conversion materials having excellent heat resistance such as Fe-Si compounds have been discovered, but the thermoelectric properties of all materials are Bi ₂
It is significantly inferior to the Te ₃ compound, and in order to obtain more electric power, a thermoelectric conversion material exhibiting excellent thermoelectric properties in a wide temperature range from low temperature to relatively high temperature is required.

Recently, CoSb ₃ compounds have been attracting attention as promising substances, but their thermoelectric properties are only ZT = 0.6 at 700 K, which is still smaller than that of Bi ₂ Te ₃ compounds, and ZT = 1. Further improvements aimed at are necessary. In particular, CoSb ₃ compounds have a thermoelectric figure of merit Z
Since the thermal conductivity, which is one of the three factors that control the thermal conductivity, is significantly higher than that of the Bi ₂ Te ₃ compound, it is an important issue to reduce the thermal conductivity.

The present invention has been made in order to solve such a problem, and an object thereof is to provide a thermoelectric conversion material exhibiting excellent thermoelectric properties in a very wide temperature range of about 100K to 1000K. . Another object of the present invention is to provide a manufacturing method capable of manufacturing a thermoelectric conversion material having excellent thermoelectric properties.

[0015]

In order to solve the above-mentioned problems, the present invention provides at least one first element selected from the group consisting of Co, Rh, and Ir, and P, As,
And at least one second element selected from the group consisting of Sb, and at least one light element selected from the group consisting of B, C, N, and O, and containing said light element Provided is a thermoelectric conversion material, characterized in that the amount is 0.001 at% or more.

Further, the present invention is selected from the group consisting of P, As and Sb in the tubular member composed of at least one kind of first element selected from the group consisting of Co, Rh and Ir. The method comprises the steps of filling a substance composed of at least one kind of second element to obtain a rod-shaped member, drawing the rod-shaped member to obtain a wire-shaped member, and subjecting the wire-shaped member to heat treatment. A method for producing a thermoelectric conversion material is provided.

Furthermore, the present invention provides a thin film formed of at least one first element selected from the group consisting of Co, Rh and Ir, and at least one second thin film selected from P, As and Sb. A step of laminating a thin film formed of an element to obtain a laminated body having the thin film formed of the first element as a surface, a step of rolling the laminated body, and a laminated body after the rolling. Provided is a method for producing a thermoelectric conversion material, which comprises a step of performing heat treatment.

The present invention will be described in detail below. The thermoelectric conversion material of the present invention basically has a skutterudite structure, and a specific element is added to this structure.

Here, the skutterudite structure will be described by taking the CoSb ₃ phase as an example. The CoSb ₃ phase is stable below 1043 K, is formed by a peritectic reaction containing the CoSb ₂ phase and the Sb phase, and has an Im3 type crystal structure represented by the CoAs ₃ phase as shown in FIG. There is. As shown, this structure is a cubic lattice containing a total of 32 atoms of 8 Co atoms and 24 Sb atoms in a unit cell.

At this time, the Sb atom is in a unique crystal state, and six antimony rings formed from four Sb atoms are formed in the unit cell. Since the unit lattice is formed by eight small lattices, when the antimony ring is formed only in the six small lattices, the unit lattice contains two voids in which the antimony ring does not exist.

The thermoelectric conversion material of the present invention is obtained by adding at least one element selected from B, C, N and O to a compound having such a structure. Light elements such as B, C, N and O used herein are generally known as interstitial elements and are located to fill the lattice gaps in the compound. Even in the CoSb ₃ phase, these light elements infiltrate so as to fill the gaps in the lattice.

Therefore, these elements also invade two voids in which the antimony ring peculiar to the skutterudite structure does not exist, and a dense structure without voids is formed. In such a structure, the presence of light elements filled in the voids suppresses phonon scattering and significantly reduces thermal conductivity. In addition, the performance index can be significantly improved by taking advantage of the high mobility that the original structure has.

In the skutterudite structure which is the basis of the thermoelectric conversion material of the present invention, Co, Rh and I are used.
The ratio of at least one element selected from r and at least one element selected from P, As and Sb is
It is preferably about 1: 2.5 to 1: 3.5,
In the case of 1: 3, the most excellent thermoelectric property can be obtained.

The light elements such as B, C, N, and O added here form an interstitial solid solution in the substance and therefore do not change the original crystal structure. Therefore, Co, Rh
And at least one element selected from Ir and P,
A substance showing extremely good thermoelectric characteristics by adding a predetermined amount or more of light elements such as B, C, N and O while maintaining the ratio of at least one element selected from As and Sb within the above range. Is obtained.

The thermoelectric conversion material of the present invention contains at least one element selected from Co, Rh and Ir and P and As.
And at least one element selected from Sb can be used, for example, by a sintering method, an arc melting method, or a gradient solidification method. It is a simple and appropriate method to use the high temperature sintering method for the powder which has been subjected to the preliminary heat treatment and has been subjected to the solid phase reaction.

In the present invention, the higher the purity of the raw material is, the better the thermoelectric conversion material can be obtained. However, if it has a purity of 99.9% or more, it is 99.99.
The characteristics superior to those of the B, C, N and O-free substances produced using 99% or more of the raw materials can be obtained.

The thermoelectric conversion material of the present invention can be manufactured, for example, as follows. That is, first, each powder, which is weighed in a predetermined amount so as to have the above-mentioned mixing ratio, is sufficiently stirred by hand mixing in a V mixer or an agate mortar. When B or C is used as the light element to be added, a predetermined amount of the powder is added and sufficiently stirred with the materials previously mixed to obtain a mixed powder. In addition, N and O are
After the additive-free substance is produced, it can be added to the material by heat treatment in the atmosphere.

An alumina tube is filled with the mixed powder obtained as described above, and the quartz tube is vacuum-sealed. At this time, the degree of vacuum is preferably 1 × 10 ⁻³ Pa or more in order to suppress excessive oxidation of the raw material powder.

Next, the enclosed quartz tube is heat-treated at a temperature not higher than the melting point of the substance to cause a solid phase reaction. The condition of this heat treatment is 500 to 1150K, 0.1
It may be about 100 hours, and usually 873K for about 24 hours is sufficient.

The reaction product aggregated by the solid phase reaction is crushed in an agate mortar, powdered again, and then sintered by hot pressing at a temperature below the melting point of the substance. The sintering conditions at this time are as follows: press pressure 0.1 to 300 MPa, 500 to
It may be 1150 K for about 0.1 to 10 hours, and for example, if treatment is performed at 40 MPa and 873 K for 1 hour,
A substance having a density of 99% or more of the theoretical density is obtained.
Further, the atmosphere at this time may be an Ar atmosphere instead of a vacuum.

When N or O is used as the light element, after the additive-free material is produced in the above-mentioned step, the nitrogen content or the oxygen content is, for example, 500 to
0.001a by heat treatment at about 1150K
A thermoelectric conversion material containing these elements at a content of t% or more can be obtained.

In order to achieve the object of the present invention,
Light elements such as B, C, N and O must be added in a proportion of 0.001 at% or more, but their contents are not impaired because the characteristics originally possessed by the CoSb ₃ phase etc. are not impaired. Is desired to be at most 60 at% or less.

The thermoelectric conversion material of the present invention produced in this manner exhibits remarkably excellent thermoelectric characteristics as compared with the conventional materials to which B, C, N and O are not added. In addition, Co, R
at least one element selected from h and Ir;
When a thermoelectric conversion material is produced by a usual method such as an arc melting method using at least one element selected from P, As and Sb and a mixture of these elements, a material having a target composition is obtained. Is difficult. this is,
Due to the high vapor pressure of P, As and Sb,
This is because part of it evaporates during heating.

By using the method of the present invention, it is possible to prevent evaporation of high vapor pressure substances such as P, As and Sb and to accurately obtain a target composition, and to reduce light elements such as B, C, N and O. A thermoelectric conversion material having excellent thermoelectric properties can be obtained without adding it.

The method for producing the thermoelectric conversion material of the present invention will be described in detail below. The first manufacturing method of the present invention is
A tubular member formed of a low vapor pressure substance such as Rh and Ir is used, and a high vapor pressure substance such as P, As and Sb is filled in the tubular member, drawn, and then heat treated.

The first manufacturing method will be described with reference to FIGS. First, as shown in FIG. 2, a rod-shaped member 3 is obtained by filling a tubular member 1 formed of a low vapor pressure substance with a high vapor pressure substance 2 in accordance with an atomic equivalent ratio of a target substance. At this time, as described above, it is preferable to set the dimensions and the like of the tubular member so that the ratio of the low vapor pressure substance to the high vapor pressure substance is 1: 2.5 to 1: 3.5. That is, the outer diameter and the inner diameter of the tubular member 1 can be determined according to the intended composition.

The tubular member 1 used is, for example, C
It may be formed of one element of o, Rh or Ir, or may be an alloy composed of two or more elements. Similarly, the high vapor pressure substance 2 filled in the tubular member 2
Also, P, As, and Sb can be used alone or two or more kinds of elements can be used. The high vapor pressure substance 2 can be in any state, but if it is in the shape of a rod or a powder, it is easy to handle and the workability is improved.

If an alloy is used as at least one of the tubular member 1 and the substance 2 to be filled in the tubular member 1, a thermoelectric conversion material composed of a ternary or higher multi-component substance can be produced by the same method.

Then, the rod-shaped member 3 obtained by filling the high-vapor-pressure substance 2 in the tubular member 1 is subjected to wire drawing to form a thin wire-shaped member 4 as shown in FIG. The thickness of the wire-shaped member 4 is preferably as thin as possible in order to shorten the heat treatment time after processing, specifically, 500 μm.
It is desired that it is about m or less. This is because the thinner the wire, the shorter the element diffusion distance required for the reaction, and the desired substance can be produced by a short-time heat treatment.

The wire-shaped member 4 which has been subjected to wire drawing is heat-treated at an appropriate temperature to obtain a wire-shaped substance 5 as shown in FIG. The condition of the heat treatment is, for example, 500
It can be set to about 1150K and 0.1 to 3.6ks.

In the first method of the present invention, the high vapor pressure substance 2
Since it is filled in the tubular member 1 made of a low vapor pressure substance, it is not directly exposed to the outside atmosphere, and the evaporation of the high vapor pressure substance can be prevented. That is, the composition of the obtained substance does not substantially deviate from the composition ratio of the raw materials mixed first, and the characteristics of the substance are not impaired.

The wire-like substance 5 obtained in the above process
Is cut into an appropriate length, a plurality of them are bundled as shown in FIG. 5, and a heat treatment of about 500 to 1150 K is performed, whereby a bulk material 7 as shown in FIG. 6 can be manufactured. At this time, in order to obtain a bulk material with high density,
It is desired that the heat treatment is performed by applying a pressure of about 1 to 300 MPa.

Next, the second manufacturing method of the present invention will be described. A second manufacturing method of the present invention is a method in which a thin film formed of a high vapor pressure substance is sandwiched between thin films formed of a low vapor pressure substance, rolled, and then heat treated.

The second manufacturing method will be described with reference to FIGS. First, as shown in FIG. 7, a laminate 12 is obtained by sandwiching a thin film 11 formed of a high vapor pressure substance between thin films 10 formed of a low vapor pressure substance according to a weight ratio of a target substance.

The thin film 10 formed of a low vapor pressure substance may be formed of one kind of element such as Co, Rh or Ir, or may be an alloy composed of two or more kinds of elements. Similarly, a thin film 11 formed of a high vapor pressure material
Also, P, As, Sb alone, or 2
Alloys composed of more than one type of element can be used. That is, if an alloy is used as at least one of the thin film 10 formed of a low vapor pressure element and the thin film 11 formed of a high vapor pressure element, a thermoelectric conversion material composed of a ternary or higher multi-component system can be manufactured. .

The composition ratio of the obtained material can be adjusted by changing the thickness of the thin films 10 and 11, but as described above, the ratio of the low vapor pressure substance to the high vapor pressure substance is 1 :. It is preferable to set the film thickness of each thin film so as to be 2.5 to 1: 3.5.

A member 12 in which a thin film 11 formed of a high vapor pressure substance is sandwiched between thin films 10 formed of a low vapor pressure substance.
Is subjected to a heat treatment on the member 13 whose adhesion between the films has been improved by rolling to produce a rolled plate-shaped member 14 as shown in FIG. At this time, the thickness of the member 13 obtained by rolling is preferably thin in consideration of the heat treatment time after processing, and is preferably about 500 μm or less, for example. This is because the thinner the thickness of the thin film, the shorter the element diffusion distance required for the reaction, so that the target substance can be produced by a short heat treatment.

Alternatively, instead of carrying out rolling, a laminated body 12 in which a thin film 11 made of a high vapor pressure substance is sandwiched by a thin film 10 made of a low vapor pressure substance is applied at a pressure of about 0.1 to 300 MPa while 500 to 1150K. , 0.1
You may perform heat processing of about 3.6 ks. Even when the rolling process is performed, a good substance with fewer defects can be obtained by subjecting the member 13 after the rolling process to the heat treatment under the same conditions.

In the second method of the present invention, since the thin film containing the high vapor pressure substance is sandwiched between the thin films containing the low vapor pressure substance, the area of the high vapor pressure substance exposed on the surface is extremely small. Even during the heat treatment, the area affected by the outside atmosphere is very small. Therefore, during the heat treatment, evaporation of the high vapor pressure substance is prevented, a material having a composition according to the composition ratio of the raw materials can be obtained, and the characteristics of the substance are not impaired.

The thin film 1 to be laminated as shown in FIG.
If the laminated body 15 is formed by increasing the number of sheets of 0 and 11, and heat treatment is performed under the same conditions as described above, the bulk material 16 as shown in FIG. 11 can be manufactured.

Since the thermoelectric conversion material of the present invention contains a predetermined amount of a light element, excellent thermoelectric properties could be imparted over a wide temperature range. Further, according to the method of the present invention, it is possible to prevent evaporation of a high vapor pressure substance during heat treatment, and to manufacture a material in accordance with the raw material composition, so that thermoelectric conversion having good thermoelectric properties without impairing the original properties of the substance. The material can be manufactured.

[0052]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in more detail below by showing Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples. (Example 1) Co powder and Sb powder (purity 9
9.9%, particle size 325 mesh or less) and purity 99%,
B powder having a particle size of 325 mesh or less is mixed with C in an atomic equivalent ratio.
The mixture was mixed at a ratio of o: Sb: B = 1: 3: 1. The obtained mixture was sufficiently stirred using a V mixer, then the mixed powder was placed in an alumina tube and further vacuum-sealed in a quartz tube. At this time, the degree of vacuum was 1 × 10 ⁻⁶ Pa.

Then, the enclosed quartz tube was placed at 873K for 24 hours.
A solid phase reaction was carried out by pre-heat treatment for an hour. The reaction product agglomerated by the solid phase reaction was pulverized using an agate mortar to re-powder, and then sintered by hot pressing at a temperature below the melting point of the substance. The sintering conditions at this time are 1 × 1
Press pressure 40 MPa, 873K, in a vacuum of 0 ^-6 Pa,
It was one hour. When the density of the prepared sample was measured,
It was 99% or more of the theoretical density.

This sintered body had a cross-sectional area of 2 cm ² and a height of 1 c.
After being processed into a cylindrical shape of m, the low temperature side was fixed at 40 K and the high temperature side was gradually heated to give a temperature difference, and the open circuit voltage and the internal resistance were measured. The Seebeck coefficient α and the specific resistance ρ of the substance were measured from the measured values and were as follows.

[0055] Then, the thermal conductivity κ was measured by the laser flash method. As a result, κ = 8.0 [W / mK] at 350K,
At 700 K, κ = 3.9 [W / mK].

From the above results, the thermoelectric figure of merit Z of the thermoelectric conversion material of this example is 350 = 350K, Z = 0.001058 [K
⁻¹ ], at 700 K, Z = 0.001846 [K ⁻¹ ].
Therefore, the dimensionless figure of merit ZT is ZT = 0.3703 at 350K and ZT = 1.29 at 700K.
It becomes 2. 40K to 1000K is one measurement,
The measurement was repeated 30 times, but no change was observed in the characteristics. Further, no change was observed in the characteristics even when the same measurement was carried out after holding at 1000 K for 1 hour.

On the other hand, as a comparative example of this example, a CoSb ₃ compound was prepared in the same manner as described above except that the B powder was not added, and the Seebeck coefficient, the specific resistance and the thermal conductivity were measured and found to be 350K and 700K. The following were each.

[0058] From the above results, the figure of merit Z of this material is Z = 0.0002893 [K ⁻¹ ] at 350K and Z = at 700K.
It becomes 0.0003353 [K ^-1 ]. Therefore, the dimensionless figure of merit ZT is ZT = 0.0113,700 at 350K.
In K, ZT was 0.2347, and it was found that the thermoelectric conversion material of the present invention to which the B powder was added exhibited superior thermoelectric characteristics. (Example 2) Sb powder having a purity of 99.9% and a particle size of 325
The raw material powders were mixed, stirred and heat-treated in the same manner as in Example 1 except that the powder was changed to a P powder having a mesh size or smaller to cause a solid phase reaction.

Then, a sintered body was prepared in the same manner as in Example 1 above, and its density was measured. As a result, the theoretical density of 99 was obtained.
% Or more. Further, the open end voltage and the internal resistance of the sample produced in the same manner as above were measured, and the Seebeck coefficient α, the specific resistance ρ, and the thermal conductivity coefficient κ of the substance were measured from the measured values, and at 350K and 700K. They were as follows.

[0060] From the above results, the thermoelectric figure of merit Z of this substance is 350K
At Z = 0.0005696 [K ⁻¹ ], at 700K Z
= 0.001316 [K ^-1 ]. Therefore, the dimensionless figure of merit ZT is ZT = 0.1994,7 at 350K.
At 00K, ZT = 0.92111. 40K-1
The measurement was repeated 30 times up to 000K, but no change was observed in the characteristics. Also, 10
No change was observed in the characteristics even when the same measurement was performed after holding at 00K for 1 hour.

On the other hand, as a comparative example of this example, a CoP ₃ compound was prepared in the same manner as described above except that the B powder was not added, and the Seebeck coefficient, the specific resistance and the thermal conductivity were measured. The following were each.

[0062] From the above results, the figure of merit Z of this material is Z = 0.000098 [K ⁻¹ ] at 350K and Z = 0.0 at 700K.
[0034] [K ^-1 ]. Therefore, the dimensionless figure of merit Z
T was ZT at 350K, 0.03 at 700K, and ZT was 0.2404 at 700K, and it was found that the thermoelectric conversion material of the present invention to which the B powder was added exhibits superior thermoelectric characteristics. (Example 3) Co powder and Sb powder (purity 9
9.9%, particle size 325 mesh or less) and purity 99.9
9% and C powder having a particle size of 325 mesh or less were mixed in a ratio such that Co: Sb: C = 24: 72: 4 in atomic equivalent ratio. The obtained powder was stirred in the same manner as in Example 1 above, then heat-treated, and solid-phase reacted.

The reaction product agglomerated by the solid phase reaction was pulverized in the same manner as in Example 1 to obtain a powder, which was then fired under the same conditions to prepare a sample, and its density was measured. However, it was 99% or more of the theoretical density.

This sintered body had a cross-sectional area of 2 cm ² and a height of 1 cm.
When the Seebeck coefficient α, the specific resistance ρ, and the thermal conductivity κ were measured in the same manner as in Example 1,
At 350K and 700K, respectively, it was as follows.

[0065] From the above results, the thermoelectric figure of merit Z of the thermoelectric conversion material of this example is 350 = 350, and Z = 0.0008066 [K ⁻¹ ], 70
At 0K, Z = 0.001451 [K ^-1 ]. Therefore, the dimensionless figure of merit ZT is ZT = 0.
At 2823 and 700K, ZT = 1.016.
Although 40K to 1000K was set as one measurement and the measurement was repeated 30 times, no change was observed in the characteristics.
Further, no change was observed in the characteristics even when the same measurement was carried out after holding at 1000 K for 1 hour.

On the other hand, as a comparative example of this example, a CoSb ₃ compound was prepared in the same manner as above except that the C powder was not added, and the Seebeck coefficient, the specific resistance and the thermal conductivity were measured. And at 700 K were as follows respectively.

[0067] From the above results, the figure of merit Z of this material is Z = 0.0002893 [K ⁻¹ ] at 350K and Z = at 700K.
It becomes 0.0003353 [K ^-1 ]. Therefore, the dimensionless figure of merit ZT is ZT = 0.0113,700 at 350K.
In K, ZT = 0.2347, which shows that the thermoelectric properties of the thermoelectric conversion material of the present invention to which the C powder is added are superior to the non-added substance. (Example 4) Co powder and Sb powder (purity 9
9.9%, particle size 325 mesh or less) were mixed in a ratio such that Co: Sb = 1: 3 in atomic equivalent ratio. After stirring the obtained powder in the same manner as in Example 1 above,
It heat-processed and solid-phase-reacted.

The reaction product aggregated by the solid phase reaction was pulverized into a powder by the same method as in Example 1 except that the vacuum pressure was set to 1 × 10 ⁻⁵ Pa, and further baked under the same conditions. A sample was prepared by measuring the density of the sample,
% Or more.

The obtained sample was subjected to heat treatment at 1023 K for 1 hour in an oxygen partial pressure atmosphere of 10 Pa and then subjected to compositional analysis. As a result, the atomic equivalent ratio of Co: Sb: O =
It was 24.5: 73.5: 2.

This sintered body had a cross-sectional area of 2 cm ² and a height of 1 c.
When processed into a columnar shape of m and the Seebeck coefficient α, the specific resistance ρ, and the thermal conductivity κ were measured in the same manner as in Example 1, they were as follows at 350K and 700K.

[0071] From the above result, the thermoelectric figure of merit Z of the thermoelectric conversion material of this example is Z = 0.01013 [K ⁻¹ ], 70 at 350K.
At 0K, Z = 0.002167 [K ^-1 ]. Therefore, the dimensionless figure of merit ZT is ZT = 0.
ZT = 1.517 is obtained at 3544 and 700K.
Although 40K to 800K was set as one measurement and the measurement was repeated 30 times, no change was observed in the characteristics. In addition, no change was observed in the characteristics even when the same measurement was performed after holding at 800 K for 1 hour.

On the other hand, as a comparative example of this example, a CoSb ₃ compound containing no O was prepared by the same method as described above except that the heat treatment was not performed in an oxygen atmosphere, and the Seebeck coefficient, the specific resistance and the thermal conductivity were measured. I went to 35
At 0K and 700K, respectively, it was as follows.

[0073] From the above results, the figure of merit Z of this material is Z = 0.0002893 [K ⁻¹ ] at 350K and Z = at 700K.
It becomes 0.0003353 [K ^-1 ]. Therefore, the dimensionless figure of merit ZT is ZT = 0.0113,700 at 350K.
In K, ZT was 0.2347, and it was found that the thermoelectric conversion material of the present invention containing O is superior to the oxygen-free substance. (Example 5) Purity of 99.9 in a tubular member made of Co having a purity of 99.9999% and having an outer diameter of 3 mm and an inner diameter of 2.5 mm.
Sb powder of 999% and a diameter of 10 to 44 μm was filled so as to have an atomic equivalent of Co: Sb = 1: 3 to obtain a rod-shaped member.

This rod-shaped member was drawn to have a diameter of 10
After processing into a wire of 0 μm, a heat treatment of 86.4 ks was performed at 873 K in a vacuum of 1 × 10 ⁻⁷ Pa. When the composition of the cross section of the wire-like member after heat treatment was analyzed by EDX, it was found to be 25 at. % Co-75 at. % S
b, and no location where Co or Sb was segregated and concentrated was found. Moreover, when the heat-treated member was pulverized into powder and subjected to XRD analysis, it was found that the constituent phase of this member was Co.
It was found that the Sb ₃ compound had a single phase.

The Seebeck coefficient, which controls the thermoelectric properties of the CoSb ₃ compound thus obtained, was measured and found to be 37
The maximum value was shown at 3K, and the value was 300 μV / K.

On the other hand, as a comparative example of this example, a compound of Co and Sb was prepared by a powder high temperature sintering method. Specifically, first, Co powder and Sb powder (both having a diameter of 1
0-44 μm, purity 99.9999%) atomic%
Then, they were mixed so that Co: Sb = 1: 3, and sufficiently stirred in an agate mortar. After that, 1 in a vacuum of 1 × 10 ⁻⁷ Pa
8 at 873K while applying a pressure of × 10 ⁷ Pa
A heat treatment of 6.4 ks was performed. When the composition of the cross section of the heat-treated member was analyzed by EDX, it was found that
at. % Co-75 at. Although the target composition was% Sb, the concentration of Sb decreased as it approached the surface, and the Sb concentration significantly decreased on the outermost surface.

When the heat-treated member was pulverized into powder and subjected to XRD analysis, it was found that CoSb ₃ phase and CoS
The presence of the b ₂ phase was confirmed. This phenomenon in which the amount of Sb decreases is presumed to be due to evaporation of Sb during the heat treatment.

As a result of measuring the Seebeck coefficient controlling the thermoelectric properties of the substance thus obtained, the maximum value was shown at 403 K, but the value was 180 μV / K, which was the same as that of the thermoelectric conversion material produced by the method of the present invention. The thermoelectric properties were remarkably inferior to those of the above. (Example 6) First, using Co of 99.9999% purity and Ir of 99.9999% purity, 50 at. % Co
-50 at. % Ir alloy, outer diameter 3 mm, inner diameter 2.
A 5 mm tubular member was prepared. On the other hand, purity 99.999
9% As and Sb powder were mixed at a mixing ratio of 1: 1 in atomic equivalent and thoroughly stirred to obtain a mixed powder, which was atomically (Co, Ir) in the tubular member. : (A
s, Sb) = 1: 3 was filled to obtain a rod-shaped member.

This rod-shaped member was drawn to a diameter of 10
After processing into a wire of 0 μm, a heat treatment of 86.4 ks was performed at 873 K in an argon atmosphere of 1 × 10 ⁻² Pa. When the composition of the cross section of the heat-treated member was analyzed by EDX, 12.5 at. % Co-12.
5 at. % Ir-37.5 at. % As-37.5a
t. % Sb, and no location where Co, Ir, As or Sb was segregated and concentrated was found.

Further, the heat-treated member is pulverized into powder,
As a result of XRD analysis, it was found that the constituent phase of this member was a (Co, Ir) (As, Sb) ₃ single phase having a skutterudite structure. The Seebeck coefficient, which controls the thermoelectric properties of the material thus obtained, was measured.
The maximum value was shown at 3K, and the value was 280 μV / K.

On the other hand, as a comparative example of this example, compounds of Co, Ir, As and Sb were produced by a powder high temperature sintering method. Specifically, first, Co powder, Ir powder, As
Powder and Sb powder (both diameter 10 to 44 μm, purity 99.9999%) in atomic% Co: Ir: A
The mixture was mixed so that s: Sb = 1: 1: 3: 3, and sufficiently mixed in an agate mortar to obtain a mixed powder. Then, 1 x 1 was added to the obtained mixed powder in an argon atmosphere of 1 x 10 ^-2 Pa.
While applying a pressure of 0 ⁷ Pa, 86.
Heat treatment was performed for 4 ks.

The composition of the cross section of the member after the heat treatment was analyzed by EDX. As a result, the central portion within the surface was 12.5 at. % Co
-12.5 at. % Ir-37.5 at. % As-3
7.5 at. Although the composition was intended to be% Sb,
The concentrations of As and Sb decreased as they approached the surface, and the As and Sb concentrations decreased significantly on the outermost surface.

Further, the heat-treated member was pulverized into a powder form and subjected to XRD analysis. As a result, in addition to the (Co, Ir) (As, Sb) ₃ phase having a skutterudite structure, (Co, I)
The presence of r) (As, Sb) ₂ phase was confirmed. This phenomenon in which the amount of As or Sb decreases is presumed to be due to evaporation of As or Sb during the heat treatment.

The Seebeck coefficient, which controls the thermoelectric properties of the substance thus obtained, was measured and found to be 150 μV / K at 423 K, which is significantly higher than the thermoelectric conversion materials produced by the method of the present invention shown above. It was inferior. (Example 7) 46 thin films with a thickness of 24.96 μm formed of Ir with a purity of 99.9999% and a purity of 99.9999.
% Sb thin film 45 with a thickness of 205.05 μm
1 and 2 are prepared and are alternately laminated so that the front and back surfaces are Ir, and the atomic equivalent is Ir: Sb = 1: 3.
A 0 mm laminate was prepared.

By cold rolling the produced laminated body perpendicularly to the laminating surface, a laminated body having a thickness of about 2.5 mm was obtained, and the laminated body after rolling was further subjected to a vacuum of 1 × 10 ⁻⁷ Pa. Heat treatment was performed at 873K for 86.4ks. When the composition of the cross section of the heat-treated member was analyzed by EDX, it was found to be 25 at. % Ir-75 at. % Sb, and no portion where Ir or Sb was segregated and concentrated was found.

When the heat-treated member was pulverized into powder and subjected to XRD analysis, the constituent phase of this member was IrSb.
It was found to be ₃ monophasic. As a result of measuring the Seebeck coefficient that controls the thermoelectric properties of the material thus obtained,
It shows the maximum value at 573K, and the value is 260μV /
It was K.

On the other hand, as a comparative example of this example, a compound of Ir and Sb was produced by a powder high temperature sintering method. Specifically, first, Ir powder and Sb powder (both having a diameter of 10
˜44 μm, purity 99.9999%) in atomic equivalent I
The mixture was mixed so that r: Sb = 1: 3, and sufficiently mixed in an agate mortar to obtain a mixed powder. Then add 1 to this mixed powder.
While applying a pressure of 1 × 10 ⁷ Pa in a vacuum of × 10 ^-7 Pa, it was heat-treated at 86.4ks at 873 K.

When the composition of the cross section of the heat-treated member was analyzed by EDX, it was found that the in-plane central portion was 25 at. % Ir-7
5 at. Although the target composition was% Sb, the Sb concentration decreased as it approached the surface, and the Sb concentration significantly decreased on the outermost surface. In addition, when the heat-treated member was pulverized into powder and subjected to XRD analysis, it was found that IrS
The presence of the IrSb ₂ phase in addition to the b ₃ phase was confirmed. This phenomenon in which the amount of Sb decreases is presumed to be due to evaporation of Sb during the heat treatment.

As a result of measuring the Seebeck coefficient which controls the thermoelectric properties of the material thus obtained, the maximum value was found at 593K, and the value was 180 μV / K, which was the thermoelectric element produced by the method of the present invention shown above. The thermoelectric properties were significantly inferior to the conversion material. (Example 8) Co and Rh (both having a purity of 99.9999)
%) With a thickness of 25.11 μm of 50 at. % C
o-50 at. 46% Rh alloy thin films, As and Sb
Thickness 1 made from (purity 99.9999% for each)
60.55 μm 50 at. % As-50 at. % Sb
45 thin films were prepared, and (As, Sb) were alternately laminated so that (Co, Rh) became the front and back surfaces, and Co: Rh: As: Sb = 1: 1: 3: in atomic equivalent. A laminated body having a thickness of about 8.4 mm was manufactured. The produced laminated body is cold-rolled perpendicularly to the laminating direction to obtain a laminated body having a thickness of about 2.0 mm, and the laminated body after rolling is further subjected to 1 × 10 ^-2.
86.4k at 873K in an argon atmosphere of Pa
s heat treatment.

When the composition of the cross-section of the heat-treated member was analyzed by EDX, it was found to be uniformly 12.5 at. % Co-1
2.5 at. % Rh-37.5 at. % As-37.5
at. % Sb, and no location where Co, Rh, As or Sb was segregated and concentrated was found. Also, when the heat-treated member was pulverized into powder and subjected to XRD analysis,
The constituent phase of this member has a skutterudite structure (C
o, Rh) (As, Sb) ₃ single phase was found. As a result of measuring the Seebeck coefficient controlling the thermoelectric properties of the thus obtained substance, the maximum value was shown at 473 K, and the value was 260 μV / K.

On the other hand, as a comparative example of this example, compounds of Co, Rh, As and Sb were prepared by a powder high temperature sintering method. Specifically, first, Co powder, Rh powder, As
Powder and Sb powder (both diameter 10-44 μm, purity 99.999%) in atomic equivalent Co: Rh: As: S
The mixture was mixed so that b = 1: 1: 3: 3, and sufficiently mixed in an agate mortar to obtain a mixed powder. Then, this mixed powder was subjected to a heat treatment of 86.4 ks at 873 K while applying a pressure of 1 × 10 ⁷ Pa in an argon atmosphere of 1 × 10 ^-2 Pa.

When the composition of the cross section of the heat-treated member was analyzed by EDX, the central portion in the surface was 12.5 at. % Co
-12.5 at. % Rh-37.5 at. % As-3
7.5 at. Although the composition was intended to be% Sb,
The concentrations of As and Sb decreased as they approached the surface, and the As and Sb concentrations decreased significantly on the outermost surface.

Further, when the heat-treated member was pulverized into powder and subjected to XRD analysis, it was found that in addition to the (Co, Rh) (As, Sb) ₃ phase having a skutterudite structure, (Co, R
h) The presence of the (As, Sb) ₂ phase was confirmed. This phenomenon in which the amount of As or Sb decreases is presumed to be due to evaporation of As or Sb during the heat treatment.

The Seebeck coefficient, which controls the thermoelectric properties of the substance thus obtained, was measured and found to be 180 μV / K at 423 K, which is significantly higher than the thermoelectric conversion materials produced by the method of the present invention shown above. It was inferior.

[0095]

As described above, according to the present invention,
Provided is a thermoelectric conversion material which exhibits excellent thermoelectric properties in a wide temperature range from low temperature to relatively high temperature. Such a material is a high-performance material that can be used not only for cooling elements but also for power generation using waste heat, and its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a skutterudite structure which is a crystal structure of a CoSb ₃ compound.

FIG. 2 is a perspective view showing a rod-shaped member processed by the method of the present invention.

FIG. 3 is a perspective view showing a wire-shaped member after the member shown in FIG. 2 has been subjected to wire drawing.

FIG. 4 is a perspective view showing an example of a thermoelectric conversion material of the present invention.

5 is a schematic view showing a state in which the members after the wire drawing process shown in FIG. 3 are bundled together.

FIG. 6 is a perspective view showing another example of the thermoelectric conversion material of the present invention.

FIG. 7 is a perspective view showing a laminated member processed by the method of the present invention.

8 is a perspective view showing a state after the member shown in FIG. 7 is rolled.

FIG. 9 is a perspective view showing an example of a thermoelectric conversion material of the present invention.

10 is a perspective view showing a state in which several members shown in FIG. 8 are stacked.

FIG. 11 is a perspective view showing another example of the thermoelectric conversion material of the present invention.

[Explanation of symbols]

1. Tubular member made of low vapor pressure substance 2 ... High vapor pressure substance 3 ... Bar-shaped member 4 ... Wire-like member 5 ... Thermoelectric conversion material of the present invention 6 ... Aggregate of wire-like members 4 7 ... Thermoelectric conversion material of the present invention 10 ... Low vapor pressure substance thin film 11 ... High vapor pressure substance thin film 12 ... Thin film laminate 13 ... Thin film rolling body 14 ... Thermoelectric conversion material of the present invention 15 ... Laminate of thin film laminate 12 16 ... Thermoelectric conversion material of the present invention

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B21B 1/22 B21C 1/00 B32B 15/01 H01L 35/34

Claims (3)

(57) [Claims] 1. At least one first element selected from the group consisting of Co, Rh and Ir, at least one second element selected from the group consisting of P, As and Sb, and B. , C, N and O, and at least one light element selected from the group consisting of C, N and O, and the content of the light element is 0.001 at% or more. 2. A tubular member composed of at least one first element selected from the group consisting of Co, Rh and Ir, and at least one selected from the group consisting of P, As and Sb. Filling a substance composed of the second element to obtain a rod-shaped member, drawing the rod-shaped member to obtain a wire-shaped member,
And a method for producing a thermoelectric conversion material, which comprises a step of subjecting the wire-shaped member to heat treatment. 3. A thin film formed of at least one kind of first element selected from the group consisting of Co, Rh and Ir, and at least one kind of second element selected from P, As and Sb. The laminated thin film, and the first
A method for producing a thermoelectric conversion material, comprising: a step of obtaining a laminated body having a thin film formed of the element as a surface, a step of rolling the laminated body, and a step of heat-treating the laminated body after the rolling.