KR100924054B1 - Thermoelectric material and method for producing same - Google Patents

Abstract

It is a thermoelectric material whose average particle diameter of a crystal | crystallization is 50 nm or less, and is a thermoelectric material whose relative density is 85% or more. Moreover, it is a manufacturing method of a thermoelectric material including the process of manufacturing a fine powder, and the process of sintering or fixing a fine powder under pressure of 1.0 kPa or more and 10 kPa or less.

Peltier element, gas atomization method, ball mill

Description

Thermoelectric material and its manufacturing method {THERMOELECTRIC MATERIAL AND METHOD FOR PRODUCING SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to thermoelectric materials constituting thermoelectric elements used for thermoelectric power generation by the Seebeck effect and direct cooling and heating by the Peltier effect. As the thermoelectric material used in this thermoelectric element, FeSi ₂ , MnSi _1.73, etc. are known, such as a Bi ₂ Te ₃ type, a skatellite type CoSb ₃ type intermetallic compound, a ZrNiSn having a half Whistler (MgAgAs) type structure, and the like.

Thermoelectric technologies such as thermoelectric power generation by the Seebeck effect and direct cooling and heating by the Peltier effect are compared to those using conventional compressors.

① Simple system configuration and compact size

② Do not use refrigerants such as fron

③ No moving parts, excellent durability, reliability and quietness

It has such features as a potentially very good technology. However, conventionally, the conversion efficiency of energy by thermoelectric elements is less than that of a system using a conventional compressor, and thus, they are only used as Peltier elements for cooling of LD used in high-performance CPUs and long-distance optical communications, portable refrigerators, and the like. In order to expand the field of application of this thermoelectric technology, it is necessary to improve the conversion efficiency, and therefore, it is necessary to improve the thermoelectric properties of the thermoelectric material.

The performance of the thermoelectric material is represented by the figure of merit expressed by the following equation.

Z = S ² / (ρ · κ)

S: Seebeck coefficient (V / K)

ρ: resistivity (Ωm)

κ: thermal conductivity (W / mK)

As a result, it can be seen that an increase in Seebeck coefficient and a decrease in specific resistance and thermal conductivity are effective for improving the performance of the thermoelectric material.

Seebeck coefficient is due to the electronic structure of the material, and is almost determined by the material and composition. Therefore, in order to increase the Seebeck coefficient, it is important to search the material system and optimize the doping type and amount. On the other hand, the specific resistance is influenced not only by the electronic structure but also by lattice vibration and impurities. In addition, the contribution of the lattice vibration is usually more than half in high-performance thermoelectric materials among the factors that determine the thermal conductivity. Therefore, in order to reduce specific resistance and thermal conductivity, it is thought that material engineering structure control is important.

The study of the performance improvement of the thermoelectric material conventionally performed was aimed at increasing the phonon scattering by refinement | miniaturization of a structure and introduction of an impurity for the purpose of reducing thermal conductivity. For example, Japanese Patent Application Laid-open No. 56-136635 discloses a method of obtaining a sintered compact having a high density and no gaps between particles by mixing and sintering ultrafine powder and two kinds of powders having a larger particle diameter. Moreover, as a manufacturing method of the ultrafine powder used as a raw material, the indication of the technique using the arc plasma sputtering method etc. to Unexamined-Japanese-Patent No. 2-27779 can be seen. Japanese Laid-Open Patent Publication No. 2000-252526 shows a method of producing a thermoelectric material by synthesizing fine powder of a raw material using a solution method or the like and sintering it. Japanese Unexamined Patent Application Publication No. 2000-349354 discloses a method of producing a thermoelectric material by preparing a fine powder using a mechanical alloying method and plasma sintering it.

In addition, Japanese Patent Application Laid-Open No. 10-209508 discloses a method for improving performance by setting the particle size to 50 nm or more and the carrier diffusion length, and discloses that performance decreases empirically when the particle size is less than 50 nm. . Although there is no mention of the cause of this performance deterioration, it is thought that the increase of an impurity and the fall of a relative density generate | occur | produce by making particle size small. In addition, Japanese Patent Laid-Open No. 2002-76452 discloses a thermoelectric conversion material in which crystals having a particle size distributed within a range of 0.5 nm to 100 nm are deposited or dispersed. However, in this thermoelectric conversion material, since crystals constituting the thermoelectric conversion material are deposited or dispersed, there is a problem that the relative density is lowered and the performance is lowered.

It has been confirmed that the improvement of the thermal index of the thermoelectric material is achieved to some extent by the reduction of the thermal conductivity by a method such as miniaturization of the structure by using the above-mentioned ultrafine powder as a raw material or introduction of impurities. By making a microcrystal into a structure, scattering of a phonon increases and thermal conductivity decreases. However, the improvement in actual performance was limited. The reason for this is that ultrafine particle production technology and sintering technology have limitations, and production of a sintered body having a microcrystalline structure is impossible. In addition, since the refinement of the crystal usually involves an increase in the specific resistance, there are cases in which the increase in the figure of merit is not reached.

This invention solves the problem of the said prior art, and makes it a subject to provide a high performance thermoelectric material by reducing the thermal conductivity by minimizing the increase of the specific resistance of a thermoelectric material.

This invention is a thermoelectric material whose average particle diameter of a crystal | crystallization is 50 nm or less, and a thermoelectric material whose relative density of a thermoelectric material is 85% or more.

Here, in the EDS analysis of the grain boundary part of the thermoelectric material of this invention, it is preferable that the detection intensity of an impurity element is 1/5 or less of the intensity of the maximum detection intensity among the structural elements of a thermoelectric material.

Moreover, it is preferable that the specific resistance of the thermoelectric material of this invention is 1 * 10 <^{-3> (} ohm) m or less.

Moreover, it is preferable that the thermal conductivity of the thermoelectric material of this invention is 5 W / mK or less.

Moreover, it is preferable that the thermal conductivity of the thermoelectric material of this invention is 1 W / mK or less.

Moreover, this invention is a manufacturing method of the thermoelectric material containing the process of manufacturing a fine powder, and the process of sintering or solidifying these fine powders under the pressure of 1.0 kPa or more and 10 kPa or less.

Moreover, in the manufacturing method of the thermoelectric material of this invention, it is preferable to include the process of annealing the polycrystal after sintering or after solidification.

MEANS TO SOLVE THE PROBLEM As a result of carrying out research in order to overcome the said subject, when the average particle diameter of the crystal | crystallization which comprises a thermoelectric material is 50 nm or less, the knowledge of the fall of thermal conductivity is remarkable, and the increase of the specific resistance to it is acquired little, Alternatively, it has been found that reducing the inevitable impurities present in the grain boundaries is effective in reducing the specific resistance. In addition, the present inventors have found a manufacturing method capable of controlling the impurities present at the grain boundaries to a minimum and obtaining a microcrystalline structure, and completed the present invention based on these.

That is, the thermoelectric material according to the present invention is characterized in that the average particle diameter of the crystal is 50 nm or less. By controlling the average particle diameter of the crystal to 50 nm or less, the scattering of phonons in the sintered body can be promoted, the thermal conductivity can be suppressed low, and the performance of the thermoelectric material can be improved. The correlation between the average particle diameter of the crystal and the thermal conductivity of the thermoelectric material varies depending on the material. However, when the average particle diameter of the crystal is 50 nm or less, the effect of reducing the thermal conductivity becomes large. This is presumably because the average particle diameter of the crystal is sufficiently small with respect to the average free path of the phonon to promote scattering of the phonon and to lower the thermal conductivity of the thermoelectric material. In view of reducing the thermal conductivity of the thermoelectric material, the smaller the average particle diameter of the crystal is preferable, the minimum value of the average particle diameter of the crystal is in fact about 0.001 μm as a production limit. In addition, the average particle diameter of the crystal | crystallization of a thermoelectric material said here is an average value of the some crystallite (microcrystal which can be considered single crystal) size which comprises the crystal grain of one of the thermoelectric materials which can be confirmed by transmission electron microscope observation. Specifically, it calculated | required by the following method. That is, in any place of an image obtained by a transmission electron microscope (hereinafter referred to as a TEM), a straight line passing through 50 crystallites is subtracted, and the sum of the lengths across the crystallites divided by the number of crystallites 50 is determined. The obtained numerical value was called the average particle diameter of the crystal | crystallization of a thermoelectric material.

Moreover, it is preferable that it is 85% or more, and, as for the relative density of the thermoelectric material of this invention, it is more preferable that it is 90% or more. When the relative density of the thermoelectric material is less than 85%, the thermal conductivity of the thermoelectric material is slightly lowered. However, since the contact between the crystals required for electron conduction is small, the conductivity is drastically reduced and the performance is greatly reduced. Here, the relative density refers to the ratio of the volume of the portion excluding the voids from the thermoelectric material to the volume of the entire thermoelectric material.

In the thermoelectric material according to the present invention, in the EDS analysis of the grain boundary part of the thermoelectric material, the detection intensity of the impurity element is preferably 1/5 or less of the strength of the maximum detection intensity among the constituent elements of the thermoelectric material. Since the specific resistance of the thermoelectric material can be suppressed by pressing the impurities at the grain boundaries at a low level, the performance of the thermoelectric material can be further improved. Since impurities present at the grain boundaries contribute to scattering of phonons and are effective in reducing the thermal conductivity of the thermoelectric material, they are preferably present slightly. However, on the other hand, since there is an adverse effect of remarkably inhibiting the electrical conduction between the particles constituting the grain boundary, it is preferably very small. Here, when the detection intensity of the impurity element is 1/5 or less of the strength of the maximum detection intensity among the constituent elements of the thermoelectric material, the amount of impurity element is not detected when the EDS analysis of the grain boundary part is less than the detection limit of the machine. It also includes. In addition, EDS analysis is an analysis by an energy-dispersive X-ray analyzer.

In the thermoelectric material according to the present invention, the specific resistance thereof is preferably 1 × 10 ⁻³ Ωm or less. This is because the above-described performance index can be increased when the specific resistance of the thermoelectric material is reduced. At the same time, the smaller the thermal conductivity of the thermoelectric material is to improve the figure of merit, so the thermal conductivity of the thermoelectric material of the present invention is preferably 5 W / mK or less. Moreover, when the thermal conductivity of the thermoelectric material of this invention is 1 W / mK or less, it is more preferable at the point which can improve the performance index of a thermoelectric material further. The thermal conductivity of the thermoelectric material is a value that varies depending on the type of thermoelectric material, the amount of impurities, the crystal structure, etc., but in the manufacturing method of the present invention, it can be adjusted within the above range (5 W / mK or less or 1 W / mK or less). .

The thermoelectric material according to the present invention uses a manufacturing method including a step of producing a fine powder and a step of sintering or solidifying the fine powder under a pressure of 0.5 Pa or more and 10 Pa or less, preferably 1.0 Pa or more and 10 Pa or less. Are manufactured.

As a fine powder used for this invention, the particle | grains of an average particle diameter of 50 nm or less can be used, for example. This is because when the particles having an average particle diameter of 50 nm or less are used, a thermoelectric material having an average particle diameter of 50 nm or less can be obtained.

In addition, the fine powder preferably contains secondary particles having a size of 0.1 μm to 100 μm in which crystallites having an average particle diameter of 50 nm or less are bonded and adhered thereto. This is because in the case of obtaining a microcrystalline structure such as the thermoelectric material of the present invention, since the particle size of the particles required is very small, the activity is high, and the surface of the particles is easily contaminated with impurities by oxidation or the like.

In addition, the fine powder preferably includes particles containing dislocations. In the case where the particles contain dislocations or defects, recrystallization starting from dislocations or defects can be produced in the sintering or solidification step or in the heat treatment applied before and after, and the thermoelectric material of the present invention can be made into a microcrystalline structure. to be. Herein, particles containing dislocations refer to particles having a crystallinity of 70% or less due to X-ray diffraction, including defects and defects.

The total scattering intensity of X-rays, and precisely the intensity of coherent scattering except Compton scattering, is always constant regardless of the ratio between amorphous and crystalline. Therefore, the degree of crystallization by X-ray diffraction is, for example, the ratio (%) of the scattering intensity of the X-rays of the crystalline portion of the particle including the potential with respect to the scattering intensity of the X-rays of the particles which are 100% crystalline, or the particles which are 100% amorphous. It can be calculated | required by the value (%) which subtracted from 100 the ratio (%) of the scattering intensity | strength of the X-ray of the amorphous part of the particle | grains containing the electric potential with respect to the scattering intensity | strength of X-ray.

The fine powder used in the present invention can be produced using a mechanical grinding method such as a ball mill, a gas atomizing method in a vacuum or in an inert atmosphere, or a production process of the fine powder by thermal plasma. The mechanical grinding method is a method for grinding particles by, for example, shearing force acting between the ball or the port of the ball mill. In this method, when the particle diameter becomes small, secondary particles to which crystallites are bonded and fixed by the pressure received from the ball or the pot can be formed, or dislocations or defects can be introduced into the particles constituting the fine powder. The gas atomizing method is a method that can reduce the amount of impurities compared to mechanical grinding methods such as ball mills, and rapidly cools the particles in the form of droplets by blowing gas out of the particles in the molten state. Can be obtained. In addition, the production process of the fine powder by thermal plasma is a method of obtaining fine and many defect-containing particles by quenching and condensing the raw material of the fine powder by high temperature plasma.

The defects or defects introduced by these methods become a starting point of recrystallization during sintering, form a microstructure, and become a scattering source of phonon in the sintered body, resulting in an effect of lowering the thermal conductivity of the thermoelectric material.

And the fine powder prepared by the above-mentioned method etc. is sintered or solidified under the pressure of 0.5 Pa or more and 10 Pa or less, Preferably it is 1.0 Pa or more and 10 Pa or less. This is for sintering or solidifying the fine powder without causing excessive grain growth and at high density. In order to obtain a high-density thermoelectric material without causing grain growth, a crushing process by pressurization and a densification process by a slipping process between particles and a plastic flow process are required. In the case of sintering or solidifying the fine powder at a pressure of less than 0.5 kPa, the slipping process between the particles does not proceed, so that it is difficult to obtain a high-density thermoelectric material. In addition, when sintering or solidifying the fine powder at a pressure of less than 1.0 kPa, it is also related to the shear strength of the particles constituting the fine powder, but crushing of the particles constituting the fine powder does not proceed, thereby obtaining a high-density thermoelectric material. It tends to be difficult. On the other hand, when the fine powder is sintered or solidified at a pressure of more than 10 kPa, a high-density thermoelectric material can be obtained without causing grain growth, but the cost of sintering or solidification increases rapidly and the volume of the thermoelectric material obtained Also becomes smaller. In the present invention, sintering refers to a phenomenon in which two or more particles are bonded by heating. In addition, in this invention, solidification means the phenomenon which two or more particle | grains couple | bond with the phenomenon other than sintering.

In addition, the sintering or solidifying step of the fine powder is preferably performed at a temperature of 25% or more and 60% or less of the lowest melting point T1 (K) among the melting points of the materials constituting the fine powder in absolute temperature display. When the temperature of the sintering or solidification process of the fine powder is less than 25% of T1, the fine powder tends to be difficult to sinter or solidify, and when the temperature is higher than 60% of T1, rapid grain growth tends to occur.

Moreover, in the manufacturing method of the thermoelectric material of this invention, it is preferable to include the process of annealing the polycrystal after sintering or after solidification. The present inventors have found that the heat treatment (annealing) of a polycrystalline body after sintering or after solidification to a predetermined temperature improves the performance of the thermoelectric material in a state in which grain growth is suppressed. By annealing, the effect of removing the distortion of the grain boundary in the polycrystal after sintering or solidification can be obtained, and unlike the usual annealing, the effect of hardly showing grain growth in the polycrystal after sintering or solidification is also obtained. Tend to be.

Here, it is preferable that annealing is performed at 45% or more and 65% or less of melting | fusing point T2 (K) among the melting points of the material which comprises the polycrystal after sintering or solidification. When annealing is performed at less than 45% of the melting point T2, the effect of removing distortion of grain boundaries and the like tends to be difficult to be obtained. Moreover, when annealing is performed at temperature higher than 65% of the said melting | fusing point T2, there exists a tendency for the thermal conductivity of a thermoelectric material to rise significantly by rapid grain growth, and the performance of a thermoelectric material falls.

In the thermoelectric material production method of the present invention, the step of producing the fine powder and the step of sintering or solidifying the fine powder are preferably performed in an inert gas atmosphere or a vacuum atmosphere. This is because impurities hardly mix in the thermoelectric material.

EMBODIMENT OF THE INVENTION Hereinafter, the specific form of this invention is demonstrated by an Example.

(First embodiment)

As the thermoelectric material, FeSi ₂ was selected as a raw material and easy to obtain, and the effect of the present invention was verified. Commercially available FeSi ₂ powder (particle diameter of 10 to 20 μm) was sealed with iron balls in an iron pot, and the resultant was placed in an inert gas atmosphere by Ar substitution, followed by grinding by a planetary ball mill for 10 hours. The secondary particle diameter of the FeSi ₂ powder after grinding | pulverization confirmed that it was 0.5-2 micrometers by SEM observation. The size of the crystallites was determined from the integral width of the XRD measurement of the FeSi ₂ powder (Hall's method) and found to be 5 to 10 nm (average particle diameter of the crystallites 8 nm). Furthermore, this FeSi ₂ powder was filled and sealed with a capsule made of Ni in an Ar glove box, and sintered at 700 ° C. for 30 minutes under a pressure of 3 Pa. The XRD measurement after sintering confirmed that the sintered compact was a FeSi ₂ single phase. As a result of TEM observation of the sintered compact structure, the average particle diameter of the crystal | crystallization which comprises a sintered compact was 15 nm. In addition, the relative density of the sintered compact was 93%.

From this sintered compact, the disk-shaped sample of diameter 10mm and thickness 1mm was produced, and the thermal conductivity was measured by the laser flash method, and it was 0.98 W / mK.

(First Comparative Example)

As a 1st comparative example, since the said powder was used as it is, it sintered at 200 Mpa and 1150 degreeC for 1 hour, and since the high temperature phase transformed by sintering was returned to a low temperature phase, heat processing was performed at 800 degreeC for 10 hours. Although the sintered body is also confirmed to be the single-phase FeSi ₂ by the XRD measurement, and the sample was the thermal conductivity of the same disk-shaped sintered body it is created from a 10 W / mK.

(2nd Example)

A sintered body was produced in the same process as in Example 1 except that the grinding time by the ball mill was 5 hours, and the average particle diameter and thermal conductivity of the crystals constituting the sintered body were measured. The results are shown in Table 1 below. In Table 1, number 4 is the result of the second embodiment, and number 5 is the result of the first embodiment. In addition, the average particle diameter of the crystallite after ball mill grinding was 35 nm. The results shown in Table 1 show that the thermal conductivity significantly decreased when the grain size of the sintered compact structure was 0.05 µm or less.

(2nd comparative example)

Except having made grinding | pulverization time by the ball mill into 0 hour, 1 hour, and 2 hours, the sintered compact was created in the same process as Example 1, and the average particle diameter and thermal conductivity of the crystal | crystallization which comprise a sintered compact were measured. The results are shown in Table 1 below. In addition, in Table 1, the thing which set the grinding time by the ball mill to 0 hours as the number 1 and the 1 hour was made into the number 2 and the 2 hours was made into the number 3. In addition, the average particle diameter of the crystallite after ball mill grinding was 5 micrometers or more (number 1), 0.9 micrometer (number 2), and 85 nm (number 3), respectively.

Results of the first to second examples and the second comparative example number Ball mill time (hr) Average particle diameter of sintered body (㎛) Thermal Conductivity (W / mK) One 0 20 10 2 One One 6.4 3 2 0.1 3.9 4 5 0.05 2.0 5 10 0.015 0.98

(Third Embodiment)

The sample of the magnitude | size of 1 mm x 1 mm x 15 mm was cut out from the sintered compact of 1st Example (No. 5 of Table 1), and the specific resistance by the 4-terminal method was measured. Moreover, the EDS analysis of the grain boundary part of the sintered compact was performed, and the constituent element was identified. In addition, two kinds of sintered bodies were prepared: ball milling in air without ar substitution under the same condition as No. 5 (No. 6) and filling of the Ni capsule before sintering in the air (No. 7). As described above, specific resistance measurement and EDS analysis were performed. The results are shown in Table 2.

From this result, it turned out that the grain boundary impurity (an oxide in this case) has a big influence on a specific resistance, and even a fine crystal structure can reduce specific resistance by reducing an impurity.

Results of the third example number Ball mill time (hr) Resistivity (Ωm) 0 Peak Strength by EDS ※ 5 10 9 × 10 ^-4 0.15 6 10 5 × 10 ^-3 0.30 7 10 1.5 × 10 ^-3 0.25

* Relative intensity when K α of Si which is the table peak is set to 1.

(Example 4)

Fe powder and Si powder were mixed and melted, and the fine powder was produced using the gas atomization method in vacuum. He atom with high cooling capacity was used for atomization, and gas pressure was set to 100 kgf / cm <2>. When this powder was observed using SEM, the particle diameter was 5-20 micrometers. In addition, the size of crystallites was determined to be 2 to 10 nm (average particle diameter of 7 nm) by XRD measurement.

This powder was filled and sintered in the same manner as in the first embodiment. TEM observation of the obtained sintered compact showed that the crystal grain diameter of this sintered compact was 5-20 nm (average particle diameter 15 nm). Moreover, it was 0.94 W / mK when the heat conductivity of this sintered compact was measured similarly to Example 1, and was measured. It can be seen from this that the gas atomization method is also a suitable method for producing a sintered body having a microcrystalline structure.

(Third comparative example)

A sintered body was produced in the same manner as in the first example except that the sintering was carried out at 0.2 kPa and 700 ° C. for 30 minutes. Thus, when the sintering temperature was set at 1000 ° C., the relative density became 90% and a sintered compact having a certain degree of strength could be obtained. As a result of measuring the thermal conductivity of the sintered compact, it was 5.9 W / mK, and the specific resistance was 8x10 <^-4> ohm. Therefore, outside the range of the sintering conditions of the present invention, a thermoelectric material having the desired microcrystalline structure of the present invention could not be obtained.

(Example 5)

The sintered bodies obtained in Examples 1 and 2 were made of 670 K (45% of melting point T2), 800 K (54% of melting point T2), 960 K (65% of melting point T2). It annealed in Ar atmosphere for 1 hour at temperature. As a result, the sintered compacts annealed at 670 K and 800 K improved the electrical conductivity by 1.3 times and 1.5 times, respectively, while the thermal conductivity remained unchanged. As a result of the electron microscope observation, it was confirmed that the crystal grain size of the sintered compact did not change before and after annealing. The sintered body annealed at 960 K increased the electrical conductivity by 2 times and the thermal conductivity by 1.5 times, respectively.

The sintered compact obtained by the 1st Example and the 2nd Example was annealed for 1 hour at 600K (41% of melting | fusing point T2) and 1030K (70% of melting | fusing point T2) in Ar atmosphere. The sintered body annealed at 600 K had no change in both thermal conductivity and electrical conductivity, and no change was observed in the structure even under an electron microscope observation. On the other hand, all of the sintered bodies annealed at 1030 K have doubled their electrical conductivity, but the thermal conductivity is about 6 W / mK, which is 3 times (for the second embodiment) to 6 times (for the first embodiment) compared to the annealing. As a result, the figure of merit decreased.

(Example 6)

The thermoelectric materials other than FeSi ₂ were also examined in the same manner as in the first to fourth embodiments. The results are reported in Table 3 below (number 8 to number 19). In addition, the Seebeck coefficient had little dependence on the particle size, and therefore is not described in Table 3. It was found that the thermoelectric material having the desired microcrystalline structure of the present invention can be obtained by the sintering conditions of the present invention. In addition, it was found that the thermoelectric material of the present invention having an average particle diameter of 50 nm or less and a relative density of 85% or more tends to lower both the relative resistivity and the values of room temperature (25 ° C) thermal conductivity.

Examination result of Example 6 number Material system Ball mill time (hr) Sintering Temperature (℃) Sintering pressure Average particle diameter of sintered body (㎛) Relative Density (%) EDS Impurity Oxygen Peak Intensity Ratio Relative resistivity (compared with HP: times) Room temperature thermal conductivity (W / mK) 8 ZnO 4 900 One 0.05 89 - 1.00 10 9 ZnO 4 900 3 0.035 93 - 0.98 8 10 ZnO 4 820 5 0.023 96 - 1.03 4.8 11 CoSb ₃ 10 600 One 0.050 85 0.03 0.98 4 12 CoSb ₃ 10 600 3 0.030 90 0.03 0.95 3.5 13 CoSb ₃ 10 500 10 0.025 98 0.04 0.87 3.1 14 Zn ₄ Sb ₃ 8 250 2 0.010 100 0.01 1.00 0.36 15 Zn ₄ Sb ₃ 8 250 5 0.010 100 0.01 1.02 0.35 16 Mg ₂ Si 4 400 3 0.020 100 0.08 0.95 1.4 17 MnSi _1.75 4 400 3 0.020 100 0.05 0.97 1.6 18 ZrNiSn 10 700 5 0.027 100 0.03 0.98 4.7 19 ZrNiSn 10 700 10 0.010 100 0.03 1.05 3.8

(4th comparative example)

To the other of the sixth embodiment with respect to the thermoelectric material of the non-FeSi _2, the sintered body prepared by the manufacturing conditions shown in Table 4, and were subjected to the examination such as the first to fourth embodiments. The results are shown in Table 4 (No. 20 to No. 37). As shown in Table 4, in the fourth comparative example manufactured under conditions different from the sixth example, no single sintered body having an average particle diameter of 50 nm or less and a relative density of 85% or more was obtained. In addition, the sintered compacts (Nos. 20 to 37) of the fourth comparative example tended to decrease in that both the specific resistance and the room temperature thermal conductivity were superior to those of the sintered compacts (numbers 8 to 19) of the sixth example.

Test result of the fourth comparative example number Material system Ball mill time (hr) Sintering Temperature (℃) Sintering pressure Average particle diameter of sintered body (㎛) Relative Density (%) EDS Impurity Oxygen Peak Intensity Ratio Relative resistivity (compared with HP: times) Room temperature thermal conductivity (W / mK) 20 ZnO 4 1400 0.1 5 82 - 1.00 42 21 ZnO 4 1300 0.8 1.5 84 - 1.00 30 22 ZnO 4 750 0.5 - Smile - - - 23 ZnO 4 850 0.5 0.02 73 - 32.00 18 24 ZnO 4 850 0.1 0.04 66 - 126.00 7 25 ZnO 4 1050 0.5 0.07 80 - 15.00 20 26 ZnO 4 1100 0.8 0.09 86 - 5.70 25 27 CoSb ₃ 10 800 Atmospheric pressure - Smile 0.03 - - 28 CoSb ₃ 10 800 0.1 1.4 90 0.03 1.00 7.5 29 CoSb ₃ 10 800 0.3 1.2 92 0.04 0.91 7 30 CoSb ₃ 10 650 0.9 0.075 85 0.04 3.20 7 31 CoSb ₃ 10 600 0.9 0.045 77 0.03 10.30 4.5 32 CoSb ₃ 10 600 0.8 0.05 78 0.04 14.50 5.5 33 Zn ₄ Sb ₃ 8 500 0.1 One 97 <0.01 1.00 0.7 34 Mg ₂ Si 4 600 0.1 One 98 0.08 1.00 2.3 35 MnSi _1.75 4 600 0.1 One 97 0.05 1.00 3.2 36 ZrNiSn 10 850 0.1 1.2 97 0.03 1.00 10 37 ZrNiSn 10 850 0.5 0.9 98 0.03 1.02 9

In Tables 3 and 4, the material system indicates the composition of the material constituting the thermoelectric material, and ZnO (No. 8 to No. 10 and No. 20 to No. 26) in Tables 3 and 4 represents Al in Zn. Doped% is used.

In addition, EDS impurity oxygen peak intensity ratio shows the ratio with which detection intensity is the largest by EDS analysis. In the case where the material system is ZnO (number 8 to number 10, number 20 to number 26), since oxygen is not an impurity, the impurity oxygen peak intensity ratio by EDS is "-".

In addition, the value of relative resistivity is shown by the ratio with respect to the value at the time of hot press (HP) sintering under pressure of 0.1 kPa. When the value of relative resistivity is 1.0 or less, it shows that the resistivity falls.

As described above, the thermoelectric material of the present invention and the method of manufacturing the thermoelectric material of the present invention can achieve a decrease in thermal conductivity by minimizing the increase in specific resistance, and improve the thermoelectric performance.

In addition, the present invention can be applied in addition to the material adopted in the embodiment, and can contribute to the improvement of the performance of existing thermoelectric materials.

Claims (7)

The thermoelectric material whose average particle diameter of a crystal | crystallization is 50 nm or less, and the relative density of the said thermoelectric material is 85% or more, The thermoelectric material characterized by the above-mentioned. The thermoelectric material according to claim 1, wherein in the EDS analysis of the grain boundary portion of the thermoelectric material, the detection intensity of the impurity element is 1/5 or less of the strength of the maximum detection intensity among the constituent elements of the thermoelectric material. The thermoelectric material according to claim 1, wherein the specific resistance is 1 × 10 ⁻³ Ωm or less. The thermoelectric material according to claim 1, wherein the thermal conductivity is 5 W / mK or less. The thermoelectric material according to claim 1, wherein the thermal conductivity is 1 W / mK or less. And a step of producing a fine powder, and a step of sintering or solidifying the fine powder under a pressure of 1.0 Pa or more and 10 Pa or less. The method of manufacturing a thermoelectric material according to claim 6, further comprising annealing the polycrystal after the sintering or after the solidification.