JPH10256611A - Thermoelectric conversion material and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substance exhibiting good thermoelectric characteristics over a wide temperature range from 100K or below to about 1000K. SOLUTION: The thermoelectric, conversion material contains at least one kind of first element selected from a group of Co, Rh and Ir, at least one kind of second element selected from a group of P, As and Sb, and at least one kind of light element selected from a group of B, C, N and O. Content of the light element is set at 0.001 at.% or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a thermoelectric conversion material used for a thermoelectric element.

[0002]

2. Description of the Related Art Increasing the efficiency of thermoelectric conversion materials has been an issue since the practical application of this technology began. In recent years, relatively organized research and development has been performed after a long slump. is there. One of the causes of this situation is the growing interest in energy and environmental issues. Thermoelectric power generation technology is strongly desired to be applied particularly as an effective utilization technology of unused thermal energy. It is expected to be applied not only to temperature control systems in IC manufacturing processes but also to refrigerators and air conditioners. The conversion efficiency of the thermoelectric conversion material is determined by a thermoelectric figure of merit Z that reflects the physical properties of each material, and this thermoelectric figure of merit is represented by the following equation (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 conducting component.

[0005] The higher the thermoelectric figure of merit, the better the thermoelectric conversion efficiency can be obtained. In other words, a material that is difficult to conduct heat, conducts electricity well, and has a large thermoelectromotive force becomes a high-efficiency material. Such a material has a characteristic that the thermal conductivity is small, the specific resistance is small, and the Seebeck effect is large. It is. At this time, the power generation conversion efficiency η (%)
Is expressed by the following equation (2) using the aforementioned thermoelectric figure of merit Z.

[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 formula (1) change depending on the temperature, Z also has temperature dependency, and the temperature at which the maximum value is obtained differs depending on the material. Therefore, in order to promote the efficiency of the thermoelectric conversion material, it is important that Z is large in the entire use temperature range, and a material that can increase ΔT is more advantageous.

Conventionally known thermoelectric conversion materials include Bi ₂ Te ₃ compounds, PbTe compounds, Si—Ge
Compounds, Fe-Si compounds, etc., but the material whose dimensionless figure of merit ZT, which is an index of thermoelectric properties, is very close to 1 is only a Bi ₂ Te ₃ compound, and the other materials have lower performance. I haven't. Although this Bi ₂ Te ₃ compound shows excellent performance, it tends to be unstable at high temperatures. For this reason, it is customary to use in a temperature range of 573K or lower, and has been used for electronic cooling rather than for power generation.

In order for a thermoelectric conversion material to be actually used for power generation utilizing waste heat such as a gas turbine, heat resistance up to about 1000K is required. Among the conventionally known materials, the Fe-Si compound is relatively stable and shows good performance even in this temperature range, but ZT =
It is on the order of 0.2, with very little power available.
Therefore, in order to obtain more electric power, a thermoelectric conversion material for power generation exhibiting excellent performance in a wide temperature range from room temperature to a relatively high temperature of about 1000 K is required. It is rare.

Recently, XY ₃ having a skutterudite structure
Compound (X is Co, Rh, Ir, Y is P, As, Sb)
Has attracted attention as a new thermoelectric conversion material. XY ₃
Among the compounds, CoSb ₃ , RhSb ₃ and IrSb
₃ Antimonide is a semiconductor having a unique band structure and carrier transport properties, and has excellent thermoelectric properties. Among the CoSb ₃ -based compounds, the materials exhibiting the most excellent thermoelectric properties at present are CoSb ₃ with Te, As and I
This is a compound represented by the following formula to which r is slightly added.

Co _0.97 Ir _0.03 Sb _2.81 Te _0.04 As _{0.15 Even with} this compound, ZT = 0.6 at 700K.
And does not reach the properties 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]

SUMMARY OF THE INVENTION As described above, Bi
Although ₂ Te ₃ compound shows excellent characteristics in the vicinity of 573K, and remains in use mainly for electronic cooling from very unstable at high temperatures, can not be used for the power generation heat resistance is required . On the other hand, a large number of thermoelectric conversion materials exhibiting excellent heat resistance, such as Fe—Si compounds, have been discovered, but the thermoelectric properties of any of these materials are Bi _2.
It is significantly inferior to the Te ₃ compound, and in order to obtain more power, a thermoelectric conversion material exhibiting excellent thermoelectric properties in a wide temperature range from a low temperature to a relatively high temperature is required.

Recently, CoSb ₃ -based compounds have attracted interest as promising substances, but their thermoelectric properties are only 0.6 at 700 K, still smaller than Bi ₂ Te ₃ compounds, and ZT = 1. Further improvements are needed. In particular, the CoSb ₃ -based compound has a thermoelectric figure of merit Z
Since the thermal conductivity, which is one of the three factors governing the thermal conductivity, is significantly higher than that of the Bi ₂ Te ₃ compound, reducing the thermal conductivity has become an important issue.

The present invention has been made to solve such a problem, and an object of the present invention 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 production method capable of producing a thermoelectric conversion material having excellent thermoelectric properties.

[0015]

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

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

Further, 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 a thin film formed of at least one second element selected from P, As and Sb. Stacking a thin film formed of an element, and obtaining a laminate in which the thin film formed of the first element is a surface, a step of rolling the laminate, and a laminate after the rolling. Provided is a method for producing a thermoelectric conversion material, comprising a step of performing a heat treatment.

Hereinafter, the present invention will be described in detail. 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 with reference to the CoSb ₃ phase as an example. The CoSb ₃ phase is stable at 1043 K or lower, is formed by a peritectic reaction including 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. I have. As shown in the figure, this structure is a cubic lattice including a total of 32 atoms of 8 Co atoms and 24 Sb atoms in a unit cell.

At this time, the Sb atoms are 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 of eight small lattices, if an antimony ring is formed only in six small lattices, two voids in which no antimony ring exists are included in the unit lattice.

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 here are generally known as interstitial elements and are located so as to fill the lattice gaps in the compound. Even in the CoSb ₃ phase, these light elements penetrate so as to fill the lattice gap.

Therefore, these elements also penetrate into two voids where no antimony ring peculiar to the skutterudite structure does not exist, and a dense structure having no voids is formed. In such a structure, the presence of the light element filled in the voids suppresses phonon scattering and greatly reduces the thermal conductivity. In addition to that, the advantage of the inherent mobility of the structure is large, so that the figure of merit can be greatly improved.

In the skutterudite structure which is the basis of the thermoelectric conversion material of the present invention, Co, Rh and I
The ratio of at least one element selected from r to 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 characteristics can be obtained.

Light elements such as B, C, N, and O added here do not change the original crystal structure because they are interstitially dissolved in the substance. Therefore, Co, Rh
And at least one element selected from Ir and Ir,
A substance exhibiting extremely good thermoelectric properties by adding a predetermined amount of light elements such as B, C, N and O while maintaining the ratio of at least one element selected from As and Sb in the above-mentioned range. Is obtained.

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

In the present invention, a higher-purity raw material can be used to obtain a thermoelectric conversion material exhibiting better characteristics, but if it has a purity of 99.9% or more, it is basically 99.99%.
Better properties can be obtained than B, C, N and O-free substances prepared using raw materials of 99% or more.

The thermoelectric conversion material of the present invention can be manufactured, for example, as follows. That is, first, each powder weighed in a predetermined amount so as to have the above-described 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 the mixture is sufficiently stirred with the previously blended material to obtain a mixed powder. In addition, N and O are
After producing the additive-free substance, it can be added to the material by performing a heat treatment in the atmosphere.

The mixed powder obtained as described above is filled in an alumina tube, and further sealed in a quartz tube by vacuum. The degree of vacuum at this time is preferably 1 × 10 ⁻³ Pa or more in order to suppress excessive oxidation of the raw material powder.

Next, the sealed quartz tube is subjected to a heat treatment at a temperature lower than the melting point of the substance to cause a solid phase reaction. The conditions of this heat treatment are 500-1150K, 0.1
Approximately 100 hours may be sufficient, and approximately 24 hours at 873K is usually sufficient.

The reaction product agglomerated by the solid-phase reaction is pulverized in an agate mortar, powdered again, and then sintered by hot pressing at a temperature lower than the melting point of the substance. The sintering conditions at this time are as follows: a pressing pressure of 0.1 to 300 MPa, 500 to
It suffices that the pressure is about 1150K and about 0.1 to 10 hours.
A substance having a density of 99% or more of the theoretical density is obtained.
The atmosphere at this time may be an Ar atmosphere other than the vacuum.

When N or O is used as the light element, the additive-free substance is prepared in the above-described steps, and then, in an atmosphere having a nitrogen partial pressure or an oxygen partial pressure of 10 Pa or less, for example, 500 to 500 Pa.
0.001a by heat treatment of about 1150K
A thermoelectric conversion material containing these elements at a content of t% or more can be obtained.

Incidentally, in order to achieve the object of the present invention,
B, C, light elements such as N and O, it is necessary to add at a ratio of more than 0.001 at%, in order not to impair the properties CoSb ₃ equality has originally their content Is desired to be suppressed to 60 at% or less at the maximum.

The thermoelectric conversion material of the present invention produced in this manner exhibits remarkably excellent thermoelectric characteristics as compared with the conventional material to which B, C, N and O are not added. Note that Co, R
at least one element selected from h and Ir;
When a thermoelectric conversion material is manufactured by using only at least one element selected from P, As, and Sb by a normal method such as an arc melting method using a mixture of these, a material having a desired composition is obtained. It is difficult. this is,
Due to the high vapor pressure of P, As, Sb, etc.,
This is because a part thereof 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, thereby achieving a target composition accurately, and to reduce light elements such as B, C, N, and O. A thermoelectric conversion material having good thermoelectric properties can be obtained without adding.

Hereinafter, the method for producing the thermoelectric conversion material of the present invention will be described in detail. The first manufacturing method according to the present invention comprises Co,
A tubular member made of a low vapor pressure substance such as Rh and Ir is used, filled with a high vapor pressure substance such as P, As, and Sb, drawn, and then subjected to heat treatment.

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 high-vapor-pressure substance 2 into a tubular member 1 formed of a low-vapor-pressure substance in accordance with an atomic equivalence ratio of a target substance. At this time, it is preferable to set the dimensions and the like of the tubular member so that the ratio between the low vapor pressure substance and the high vapor pressure substance is 1: 2.5 to 1: 3.5 as described above. That is, the outer diameter and the inner diameter of the tubular member 1 can be determined according to the desired composition.

The tubular member 1 used is, for example, C
It may be formed from one kind of element of o, Rh or Ir, or may be an alloy composed of two or more kinds of elements. Similarly, the high vapor pressure substance 2 filled in the tubular member 2
However, P, As, and Sb can be used alone or in combination of two or more. The high vapor pressure substance 2 can be in any state, but if it is in the form of a rod or 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 therein, a thermoelectric conversion material composed of a ternary or more multi-element material can be produced in the same manner.

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

The wire-like member 4 thus drawn is subjected to a heat treatment at an appropriate temperature to obtain a wire-like substance 5 as shown in FIG. The condition of the heat treatment is, for example, 500
１1150 K, about 0.1 to 3.6 ks.

In the first method of the present invention, the high vapor pressure substance 2
Is filled in the tubular member 1 made of a substance having a low vapor pressure, so that it is not directly exposed to the outside atmosphere, so that evaporation of the substance having a high vapor pressure can be prevented. In other words, the composition of the obtained substance hardly deviates from the composition ratio of the raw materials initially mixed, and the characteristics of the substance are not impaired.

The wire-like substance 5 obtained in the above-described step
Is cut into a suitable length, a plurality of pieces are bundled as shown in FIG. 5, and a heat treatment of about 500 to 1150 K is performed to produce a bulk material 7 as shown in FIG. At this time, in order to obtain a bulk material with high density,
It is desired that the heat treatment be performed under a pressure of about 1 to 300 MPa.

Next, a second manufacturing method of the present invention will be described. A second manufacturing method of the present invention is a method of sandwiching a thin film formed of a high vapor pressure substance between thin films formed of a low vapor pressure substance, rolling, and then performing a heat treatment.

A 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 the weight ratio of a target substance.

The thin film 10 formed of a low vapor pressure substance may be formed of, for example, 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 from a high vapor pressure substance
Also contains 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 system or more 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: 1: It is preferable to set the 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 to the member 13 in which the adhesion between the films is increased by rolling, to produce a rolled plate-like member 14 as shown in FIG. At this time, the thickness of the member 13 obtained by rolling is preferably thinner in consideration of the heat treatment time after the working, and for example, is preferably about 500 μm or less. This is because the thinner the thin film, the shorter the element diffusion distance required for the reaction to be, so that the target substance can be manufactured by a short heat treatment.

Alternatively, instead of performing the rolling process, a pressure of about 0.1 to 300 MPa is applied to the laminated body 12 in which the thin film 11 made of the high vapor pressure substance is sandwiched by the thin film 10 made of the low vapor pressure substance while applying 500 to 1150 K , 0.1 ~
A heat treatment of about 3.6 ks may be performed. Even in the case of rolling, if the member 13 after the rolling is subjected to a heat treatment under the same conditions, a good substance with less defects can be obtained.

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, the high vapor pressure substance is prevented from evaporating, a material having a composition according to the composition ratio of the raw material can be obtained, and the characteristics of the substance are not impaired.

Further, as shown in FIG.
By increasing the number of 0s and 11s to form the laminate 15 and performing a heat treatment under the same conditions as described above, a 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 can be imparted over a wide temperature range. Further, in the method of the present invention, it is possible to prevent the evaporation of the high vapor pressure substance during the heat treatment and to produce a material having the same composition as the raw material, so that the thermoelectric conversion having good thermoelectric properties without impairing the intrinsic properties of the substance. Material can be manufactured.

[0052]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to 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 (both having a purity of 9)
9.9%, particle size of 325 mesh or less), 99% purity,
B powder having a particle size of 325 mesh or less is mixed with C in an atomic equivalent ratio.
o: Sb: B = 1: 3: 1 was mixed. After sufficiently stirring the obtained mixture using a V mixer, the mixed powder was accommodated in an alumina tube and further vacuum-sealed in a quartz tube. At this time, the degree of vacuum was 1 × 10 ⁻⁶ Pa.

Next, the sealed quartz tube was placed at 873K for 24 hours.
A solid-phase reaction was performed by performing a preliminary heat treatment for an hour. The reaction product agglomerated by the solid-phase reaction was pulverized using an agate mortar to obtain a powder again, and then sintered by hot pressing at a temperature equal to or lower than the melting point of the substance. The sintering conditions at this time were 1 × 1
Press pressure 40 MPa, 873 K in a vacuum of 0 ^-6 Pa,
1 hour. When the density of the fabricated sample was measured,
It was 99% or more of the theoretical density.

The sintered body was cut into a cross section of 2 cm ² and a height of 1 c.
After processing into a columnar shape of m, the low-temperature side was fixed at 40K and the high-temperature side was gradually heated to give a temperature difference, and the open-end voltage and the internal resistance were measured. When the Seebeck coefficient α and the specific resistance ρ of the substance were measured from the measured values, the results were as follows.

[0055] Next, as a result of measuring the thermal conductivity κ by the laser flash method, κ = 8.0 [W / mK] at 350 K,
At 700K, κ was 3.9 [W / mK].

From the above results, the thermoelectric performance index Z of the thermoelectric conversion material of this example at 350K is Z = 0.001058 [K
^-1 ], and at 700K, Z = 0.001846 [K ^-1 ].
Therefore, the dimensionless figure of merit ZT is ZT = 0.703 at 350K and ZT = 1.29 at 700K.
It becomes 2. From 40K to 1000K as one measurement,
The measurement was repeated 30 times, but no change was observed in the characteristics. In addition, even if the same measurement was performed after holding at 1000 K for 1 hour, no change was observed in the characteristics.

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

[0058] From the above results, the figure of merit Z of this material is Z = 0.0002893 [K ⁻¹ ] at 350K, and Z = 7000028K.
0.0003353 [K ^-1 ]. Therefore, the dimensionless figure of merit ZT is ZT = 0.113,700 at 350K.
In K, ZT was 0.2347, and it was found that the thermoelectric conversion material of the present invention to which B powder was added exhibited better thermoelectric properties. (Example 2) Sb powder was purified to have a purity of 99.9% and a particle size of 325.
The raw material powders were mixed, stirred, heat-treated and solid-phase reacted in the same manner as in Example 1 except that the powder was changed to a P powder having a mesh size or less.

Then, a sintered body was prepared in the same manner as in Example 1 and the density was measured.
% Or more. Further, the open-end voltage and the internal resistance of the sample prepared in the same manner as described above were measured, and the Seebeck coefficient α, the specific resistance ρ, and the heat conduction coefficient κ of the substance were measured from the measured values. Each was as follows.

[0060] From the above results, the thermoelectric figure of merit Z of this substance was 350K
Z = 0.0005696 [K ^-1 ] at 700 K, Z at 700 K
= 0.001316 [K ^-1 ]. Accordingly, the dimensionless figure of merit ZT is ZT = 0.994,7 at 350K.
At 00K, ZT = 0.9211. 40K-1
One measurement was performed up to 000 K, and the measurement was repeated 30 times, but no change was observed in the characteristics. Also, 10
Even if the same measurement was performed after holding at 00K for 1 hour, no change was observed in the characteristics.

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 B powder was not added, and the Seebeck coefficient, the specific resistance and the thermal conductivity were measured. Were as follows.

[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.
003435 [K ⁻¹ ]. Therefore, the dimensionless figure of merit Z
T was ZT = 0.0343 at 350K and ZT = 0.2404 at 700K, and it was found that the thermoelectric conversion material of the present invention to which B powder was added exhibited more excellent thermoelectric properties. (Example 3) Co powder and Sb powder (both having a purity of 9)
9.9%, particle size 325 mesh or less) and purity 99.9.
9% and a 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 described above, and then heat-treated to cause a solid phase reaction.

The reaction product agglomerated by the solid-phase reaction was pulverized by the same method as in the above-mentioned Example 1 to obtain a powder, and further sintered 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 was cut into a cross section 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, the results were as follows, respectively.

[0065] From the above results, the thermoelectric performance index Z of the thermoelectric conversion material of this example is Z = 0.0008066 [K ⁻¹ ], 70 at 350K.
At 0K, Z = 0.001451 [K ^-1 ]. Therefore, the dimensionless figure of merit ZT is 0.3T at 350K.
ZT = 1.016 at 2,823,700K.
One measurement was performed from 40K to 1000K, and the measurement was repeated 30 times, but no change was observed in the characteristics.
In addition, even if the same measurement was performed after holding at 1000 K for 1 hour, no change was observed in the characteristics.

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 no C powder was added, and the Seebeck coefficient, the specific resistance and the thermal conductivity were measured. And at 700K, respectively.

[0067] From the above results, the figure of merit Z of this material is Z = 0.0002893 [K ⁻¹ ] at 350K, and Z = 7000028K.
0.0003353 [K ^-1 ]. Therefore, the dimensionless figure of merit ZT is ZT = 0.113,700 at 350K.
At K, ZT = 0.2347, which indicates 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 (both having a purity of 9)
9.9% and a particle size of 325 mesh or less) were mixed at a ratio such that the atomic equivalent ratio Co: Sb = 1: 3. After stirring the obtained powder in the same manner as in Example 1 described above,
Heat treatment was performed to cause a solid phase reaction.

The reaction product agglomerated by the solid phase reaction is pulverized in the same manner as in Example 1 except that the vacuum pressure is adjusted to 1 × 10 ⁻⁵ Pa to obtain a powdery product, and further sintered under the same conditions. When a sample was prepared and its density was measured, it was
% Or more.

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

This sintered body was cut into a cross section of 2 cm ² and a height of 1 c.
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. The results were as follows at 350 K and 700 K, respectively.

[0071] From the above results, the thermoelectric performance index Z of the thermoelectric conversion material of this example is Z = 0.001013 [K ⁻¹ ], 70 at 350K.
At 0K, Z = 0.002167 [K ^-1 ]. Therefore, the dimensionless figure of merit ZT is 0.3T at 350K.
At 3544 and 700K, ZT = 1.517.
One measurement was performed from 40K to 800K, and the measurement was repeated 30 times, but no change was observed in the characteristics. In addition, even if the same measurement was performed after holding at 800K for 1 hour, no change was observed in the characteristics.

On the other hand, as a comparative example of this example, a CoSb ₃ compound containing no O was prepared in the same manner 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. 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 = 7000028K.
0.0003353 [K ^-1 ]. Therefore, the dimensionless figure of merit ZT is ZT = 0.113,700 at 350K.
In K, ZT was 0.2347, and it was found that the thermoelectric property of the thermoelectric conversion material of the present invention containing O was superior to that of the oxygen-free substance. (Example 5) A 99.999% pure tubular member having an outer diameter of 3 mm and an inner diameter of 2.5 mm was made of 99.9999% Co.
A 999% Sb powder having a diameter of 10 to 44 μm was filled so that the atomic equivalent of Co: Sb = 1: 3 to obtain a rod-shaped member.

This rod-shaped member was drawn to a diameter of 10
After processing into a wire shape of 0 μm, a heat treatment of 86.4 ks was performed at 873 K in a vacuum of 1 × 10 ⁻⁷ Pa. The composition of the cross section of the wire-like member after the heat treatment was analyzed by EDX. % Co-75 at. % S
b, and no portion where Co or Sb was segregated and concentrated was found. Further, the heat-treated member was pulverized into a powder and analyzed by XRD.
It was found to be sb ₃ compound single phase.

As a result of measuring the Seebeck coefficient governing the thermoelectric properties of the CoSb ₃ compound thus obtained, 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 produced 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%)
And Co: Sb = 1: 3, and sufficiently stirred in an agate mortar. Thereafter, the pressure is reduced to 1 × 10 ⁻⁷ Pa
While applying a pressure of × 10 ⁷ Pa, 8 at 873K
A heat treatment of 6.4 ks was performed. The composition of the cross section of the heat-treated member was analyzed by EDX.
at. % Co-75 at. Although the target composition was% Sb, the concentration of Sb decreased as approaching the surface, and the Sb concentration significantly decreased at the outermost surface.

[0077] Further, when the heat-treated member was then ground to a powder XRD analysis, in addition CoS of CoSb ₃ phase
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 governing the thermoelectric properties of the substance thus obtained, it showed a maximum value at 403 K, which was 180 μV / K, indicating that the thermoelectric conversion material produced by the method of the present invention had a maximum value of 180 μV / K. In comparison, the thermoelectric properties were significantly inferior. (Example 6) First, using at least 99.9999% pure Co and 99.9999% pure Ir, 50 at. % Co
-50 at. % Ir alloy, outer diameter 3 mm, inner diameter 2.
A 5 mm tubular member was produced. On the other hand, purity 99.999
9% of As and Sb powders were mixed in a mixing ratio of 1: 1 in terms of atomic equivalent, and sufficiently stirred to obtain a mixed powder, and the mixed powder was placed in the above tubular member in atomic% (Co, Ir). : (A
(s, Sb) = 1: 3 to obtain a rod-shaped member.

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

Further, the heat-treated member is pulverized into powder,
XRD analysis revealed that the constituent phase of this member was a (Co, Ir) (As, Sb) ₃ single phase having a skutterudite structure. As a result of measuring the Seebeck coefficient which governs the thermoelectric properties of the substance thus obtained, 42
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 prepared by a powder high-temperature sintering method. Specifically, first, Co powder, Ir powder, As
Powder and Sb powder (both in diameter 10-44 μm, purity 99.9999%) in atomic% Co: Ir: A
The mixture was mixed so that s: Sb = 1: 1: 3: 3, and sufficiently stirred in an agate mortar to obtain a mixed powder. Next, 1 × 1 ⁻² was added to the obtained mixed powder in an argon atmosphere of 1 × 10 ⁻² Pa.
While applying a pressure of 0 ⁷ Pa, 86 at 873K.
A heat treatment of 4 ks was performed.

When the cross section of the heat-treated member was subjected to composition analysis by EDX, the central part in the plane was 12.5 at. % Co
-12.5 at. % Ir-37.5 at. % As-3
7.5 at. % Sb was the target composition,
As approaching the surface, the concentrations of As and Sb decreased, and at the outermost surface, the concentrations of As and Sb significantly decreased.

Further, when the heat-treated member was pulverized into a powder and subjected to XRD analysis, it was found that, in addition to the (Co, Ir) (As, Sb) ₃ phase having a skutterudite structure, (Co, I)
r) The presence of (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.

When the Seebeck coefficient governing the thermoelectric properties of the substance thus obtained was measured, it was 150 μV / K at 423 K, and the thermoelectric properties were significantly higher than those of the thermoelectric conversion material manufactured by the method of the present invention described above. Was inferior. Example 7 46 thin films of 24.96 μm in thickness formed of Ir having a purity of 99.9999% and a purity of 99.99999
% Sb and a thin film 45 having a thickness of 205.05 μm
Are prepared and alternately laminated so that the front and back surfaces become Ir, and a thickness of about 1 in which Ir: Sb = 1: 3 in atomic equivalent.
A 0 mm laminate was produced.

The laminate thus produced was cold-rolled perpendicularly to the lamination plane to obtain a laminate having a thickness of about 2.5 mm. Further, a vacuum of 1 × 10 ⁻⁷ Pa was applied to the laminate after rolling. Heat treatment at 873K for 86.4ks. The composition of the cross section of the heat-treated member was analyzed by EDX. % Ir-75 at. % Sb, where no Ir or Sb segregated and concentrated.

When the heat-treated member was pulverized into a powder and analyzed by XRD, the constituent phase of this member was IrSb
It was found to be _three single phases. As a result of measuring the Seebeck coefficient that governs the thermoelectric properties of the substance thus obtained,
It shows the maximum value at 573K, and the value is 260 μV /
It was K.

On the other hand, as a comparative example of this example, a compound of Ir and Sb was prepared 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
The mixture was mixed so that r: Sb = 1: 3, and sufficiently stirred in an agate mortar to obtain a mixed powder. Next, 1
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.

The composition of the cross section of the heat-treated member was analyzed by EDX. % Ir-7
5 at. Although the target composition was% Sb, the concentration of Sb decreased as approaching the surface, and the Sb concentration decreased remarkably at the outermost surface. Further, when the heat-treated member was pulverized into a powder and analyzed by XRD, the 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 governing the thermoelectric properties of the material thus obtained, the maximum value was shown at 593 K, which was 180 μV / K, which was the thermoelectric element produced by the method of the present invention described above. Thermoelectric properties were remarkably inferior to the conversion material. (Example 8) Co and Rh (both having a purity of 99.9999)
% At 50 at. % C
o-50 at. 46% Rh alloy thin film, As and Sb
(All thickness 99.9999%)
50at. % As-50 at. % Sb
Forty-five thin films are prepared and alternately laminated with (As, Sb) so that (Co, Rh) is 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 and having a thickness of 3 was prepared. To laminate prepared, to obtain about 2.0mm thick laminate is subjected to vertically cold rolling in the laminating direction, and further, 1 × 10 ^-2 to stack after rolling
86.4k at 873K in an argon atmosphere of Pa
s.

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

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

The cross section of the heat-treated member was subjected to composition analysis by EDX. % Co
-12.5 at. % Rh-37.5 at. % As-3
7.5 at. % Sb was the target composition,
As approaching the surface, the concentrations of As and Sb decreased, and at the outermost surface, the concentrations of As and Sb significantly decreased.

When the heat-treated member was pulverized into a 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.

As a result of measuring the Seebeck coefficient governing the thermoelectric properties of the substance obtained as described above, it was 180 μV / K at 423 K, which was significantly higher than that of the thermoelectric conversion material produced by the method of the present invention described above. Was inferior.

[0095]

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

[Brief description of the drawings]

FIG. 1 is a schematic view of a skutterudite structure which is a crystal structure of a CoSb ₃ -based 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-like member after wire drawing has been performed on the member shown in FIG. 2;

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

FIG. 5 is a schematic diagram showing a state in which members after the wire drawing shown in FIG. 3 are bundled;

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.

FIG. 8 is a perspective view showing a state after rolling processing is performed on the member shown in FIG. 7;

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

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Tubular member which consists of low vapor pressure substance 2 ... High vapor pressure substance 3 ... Bar-shaped member 4 ... Wire-shaped member 5 ... Thermoelectric conversion material of this invention 6 ... Aggregate of wire-shaped members 4 7 ... Thermoelectric conversion material of this invention DESCRIPTION OF SYMBOLS 10 ... Low vapor pressure substance thin film 11 ... High vapor pressure substance thin film 12 ... Thin film laminated body 13 ... Thin film rolled body 14 ... Thermoelectric conversion material of the present invention 15 ... Laminated body of thin film laminated body 16 ... Thermoelectric conversion material of the present invention

Claims (3)

[Claims] 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 And at least one light element selected from the group consisting of C, N and O, wherein 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, wherein at least one type selected from the group consisting of P, As, and Sb is contained in the tubular member. A step of obtaining a rod-shaped member by filling a substance composed of the second element, a step of drawing the rod-shaped member to obtain a wire-shaped member,
And a method for producing a thermoelectric conversion material, comprising a step of subjecting the wire-like member to a 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 a thin film formed of at least one kind of second element selected from P, As, and Sb. Laminated with the thin film,
A method for producing a thermoelectric conversion material, comprising: a step of obtaining a laminate having a surface on which a thin film formed of the element is formed; a step of rolling the laminate; and a step of performing a heat treatment on the laminate after the rolling.