KR101051010B1 - Method of manufacturing p-type Bi-Sb-Te thermoelectric material - Google Patents

Abstract

The present invention relates to a method of manufacturing a p-type Bi-Sb-Te thermoelectric material. Concretely, Bi, Sb and Te are weighed and mixed so as to conform to the composition of Bi _x Sb _2-x Te ₃ (where x is 0 <x <2), charged into a tube and vacuum- step; An ingot manufacturing step of putting the tube sealed through the vacuum filling step into the furnace and stirring the mixture, and then cooling the furnace to produce an ingot; A crushing step of crushing the ingot produced in the ingot manufacturing step; A pulverizing step of pulverizing the pulverized powder through the pulverizing step; And a sintering step of subjecting the powder obtained through the pulverizing step to cold pressing and then heating and holding at a temperature of 450 ° C to 500 ° C and sintering the p-type Bi-Sb-Te based thermoelectric material. The thermoelectric material produced by the above method has a high performance index and can be widely used in various high-tech industrial fields such as electric / electronic, semiconductor, aerospace, environment, energy industry, and the like.

Thermoelectric materials, Bi, Sb, Te, Powder, Sintering temperature, Cold pressing, Performance index

Description

METHOD FOR MANUFACTURING OF P-TYPE Bi-Sb-Te BASED THERMOELECTRIC MATERIALS [0002]

 The present invention relates to a method of manufacturing a p-type Bi-Sb-Te thermoelectric material, and more particularly, to a method of manufacturing a p-type Bi-Sb-Te based thermoelectric material by forming a powder of a predetermined size range produced from an ingot obtained by using Bi, Sb and Te, And a method of manufacturing a p-type Bi-Sb-Te thermoelectric material for producing a thermoelectric material.

Generally, a thermoelectric material is an energy conversion material in which electrical energy is generated when a temperature difference is given between opposite ends of a material, and a temperature difference is generated between opposite ends of a material when electrical energy is given to the material.

Bi-Sb-Te thermoelectric materials are used as means for solving heat dissipation problems of highly integrated devices and various sensors due to excellent thermoelectric performance at room temperature, and they are mainly manufactured by one-way solidification method or single crystal growth method. However, a thermoelectric device using a casting method such as a one-direction solidification method or a single crystal growth method is disadvantageous in that it has a high cost due to an increase in a production cost due to a reduction in a recovery rate in processing and module manufacturing,

In order to overcome the problems of the above-mentioned casting method, studies on powder metallurgy processes which are excellent in mechanical strength and are expected to be advantageous in terms of performance and manufacturing cost, have been actively carried out. However, a method using a conventional powder size and a conventional sintering temperature It is difficult to control the densification of the structure, the grain size and the crystallographic anisotropy, and thus the thermoelectric performance.

Disclosure of Invention Technical Problem [8] In order to solve the above problems, it is an object of the present invention to provide a cemented carbide powder having excellent mechanical strength, And a method of manufacturing a p-type Bi-Sb-Te-based thermoelectric material which is advantageous in manufacturing cost.

In the present invention, Bi, Sb and Te are weighed and mixed so as to conform to the composition of Bi _x Sb _2-x Te ₃ (where x is 0 <x <2), charged into a tube and vacuum- step; An ingot manufacturing step of putting the tube sealed through the vacuum filling step into the furnace and stirring the mixture, and then cooling the furnace to produce an ingot; A crushing step of crushing the ingot produced in the ingot manufacturing step; A pulverizing step of pulverizing the pulverized powder through the pulverizing step; And a sintering step of subjecting the powder obtained through the pulverizing step to cold pressing and then heating and holding the powder at a temperature of 450 ° C to 500 ° C to sinter the p-type Bi-Sb-Te based thermoelectric material.

The present invention uses a powder of a predetermined size range obtained by pulverizing an ingot produced by using Bi, Sb and Te, and sintering at a predetermined temperature to improve the crystallographic orientation and to facilitate the densification and control of the structure, Provided is a method for producing a p-type Bi-Sb-Te thermoelectric material which is excellent in strength and which is advantageous in terms of performance and production cost. Therefore, the thermoelectric material manufactured according to the present invention has a high performance index and thus can be widely used in various high-tech industrial fields such as electric / electronic, semiconductor, aerospace, environment, energy industry, It can be widely used for cooling.

The above objects, features, and advantages will become more apparent from the following description taken in conjunction with the accompanying drawings. Hereinafter, the present invention will be described in detail.

In the present invention, Bi, Sb and Te are weighed and mixed so as to conform to the composition of Bi _x Sb _2-x Te ₃ (where x is 0 <x <2), charged into a tube and vacuum- step; An ingot manufacturing step of putting a tube sealed in the vacuum filling step into a furnace and stirring the resultant, and then cooling the ingot to produce an ingot; A crushing step of crushing the ingot produced in the ingot manufacturing step; A pulverizing step of pulverizing the pulverized powder through the pulverizing step; And a sintering step of subjecting the powder obtained through the pulverizing step to cold pressing and then heating and holding the powder at a temperature of 450 ° C to 500 ° C to sinter the p-type Bi-Sb-Te based thermoelectric material.

In the present invention, Bi, Sb and Te are weighed and mixed so as to conform to the composition of Bi _x Sb _2-x Te ₃ (where x is 0 <x <2), charged into a first tube, ; An ingot production step of charging the first pipe sealed through the vacuum filling step into the furnace and stirring the mixture, and then cooling the furnace to produce an ingot; A crushing step of crushing the ingot produced in the ingot manufacturing step; A pulverizing step of pulverizing the pulverized powder through the pulverizing step; An annealing step of charging the powder obtained through the pulverizing step into the second tube, filling and filling with hydrogen, and then heating and holding and annealing; And a sintering step of cold-pressing the powder subjected to the annealing step, and then sintering the powder by heating and holding at a temperature of 450 to 500 ° C to sinter the p-type Bi-Sb-Te-based thermoelectric material.

The vacuum sealing step is a preparation step for manufacturing an ingot. In one embodiment of the present invention, the vacuum filling step is performed by weighing Bi, Sb and Te so as to match the composition of Bi _x Sb _2-x Te ₃ (where x is 0 <x <2) (Or first tube), and then vacuum-sealed to about 10 ^-4 torr or less for inhibition of oxidation of the component element upon dissolution. The Bi, Sb and Te used are high purity (about 99.999%) But is not limited thereto.

The composition of Bi, Sb and Te is preferably Bi _x Sb _2-x Te ₃ (where x is 0 <x <2), more preferably Bi _0.5 Sb _1.5 Te ₃ , All the compositions of the p-type Bi-Sb-Te-based thermoelectric material can be used.

The tube and the first tube are preferably a quartz tube, a silica tube, or a Pyrex tube, but the present invention is not limited thereto.

The ingot manufacturing step is a step of manufacturing an ingot using the prepared material. In an embodiment of the present invention, in the ingot manufacturing step, the tube (or first tube) filled with the elements is charged into a furnace, stirred at about 700 ° C. to about 750 ° C. for 1 hour to 5 hours, However, the temperature range and stirring time are not limited thereto.

In one embodiment of the present invention, the melting temperature of Bi _0.5 Sb _1.5 Te ₃ is about 609 ° C and the ingot preparation step is generally carried out at a temperature about 100 ° C to about 150 ° C above the melting temperature, There may arise a problem that the volatilization of the component element is increased. The longer the melting time is, the more advantageous it is, and preferably about 2 hours, but it is not limited thereto.

The furnace is a furnace which can be used for the production of thermoelectric materials, and a rocking furnace is preferable, but not limited thereto.

The crushing step is a step of crushing the solidified ingot and thereafter carried out to facilitate the progress of the crushing step. In one embodiment of the present invention, the crushing step is performed using mortar in an inert atmosphere, such as a glove box under a nitrogen atmosphere, to prevent oxidation of the powder, but is not limited thereto . The crushing is preferably performed in a plate shape having a size ranging from 1 mm to 10 mm, but is not limited thereto.

The induction is an alumina mortar that can be used in the production of thermoelectric materials, Or zirconia mortar, but is not limited thereto.

The pulverizing step is a step of pulverizing the pulverized ingot and thereafter carried out to facilitate the progress of the sintering step. In one embodiment of the present invention, the milling step is performed using a planetary mill or a ball mill, wherein the size of the milled powder may range from greater than 0 micrometers to less than 150 micrometers, More preferably in the range of more than 45 mu m, in the range of 45 mu m to 105 mu m, or in the range of more than 105 mu m and 150 mu m or less, and most preferably in the range of 45 mu m to 105 mu m.

If the size of the pulverized powder is out of the above range, it is difficult to sufficiently form sintering in the subsequent sintering step, so that it is difficult to manufacture a thermoelectric material. Even if a thermoelectric material is manufactured, the thermoelectric material can not have a fine layer structure, The mechanical properties and the thermoelectric performance may be deteriorated.

The sintering step is a step of tightly bonding the pulverized powder to each other to consolidate the powder. In one embodiment of the present invention, the sintering step comprises cold-pressing the pulverized powder or the pulverized and annealed powder in a vacuum of 10 ^-3 torr or less at a pressure of 40 MPa to 120 MPa, Lt; 0 &gt; C to about 500 &lt; 0 &gt; C, but is not limited thereto. In one embodiment of the present invention, the sintering step may be performed in a carbon mold, but is not limited thereto.

If the sintering temperature is less than 450 ° C., sintering may be incomplete and mechanical properties and thermoelectric performance of the thermoelectric material may be deteriorated. If the sintering temperature is higher than 500 ° C., porosity of the thermoelectric material due to volatilization of Te increases, There may be problems such as deterioration of its mechanical properties and thermoelectric performance.

The annealing step is a step of reducing the powdered powder in a hydrogen atmosphere to remove the oxide layer on the powder surface, thereby improving the sinterability and increasing the electrical conductivity of the pressure sintered body. In one embodiment of the present invention, the annealing step comprises charging the pulverized powder into a second tube, filling the tube with hydrogen at a pressure of about 200 torr to about 500 torr, heating the tube at about 340 ° C to about 400 ° C for about 10 hours For 15 hours, but is not limited thereto.

If the amount of hydrogen is insufficient in the annealing step, a reduction reaction can not be sufficiently performed, and if the amount of hydrogen is excessive, it may expand and explode at a high temperature. In addition, at a temperature lower than 340 deg. C, the activation energy is low, so that a very long period of hydrogen reduction is required. When the temperature exceeds 400 deg. C, the component element may volatilize during hydrogen reduction. The time of the annealing process is temperature dependent and is preferably, but not limited to, from about 10 hours to about 15 hours at a temperature of from about 340 ° C to about 400 ° C.

The second tube is preferably a pyrex tube, a quartz tube, or a silica tube as a tube that can be used for manufacturing thermoelectric materials, but is not limited thereto.

Example

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Example 1: Preparation of a p-type Bi-Sb-Te thermoelectric material using a powder having a size of less than 45 [mu] m and a sintering temperature of 450 [deg.

Bi, Sb and Te of high purity (about 99.999%) are mixed so as to have a composition of Bi _0.5 Sb _1.5 Te ₃ + 2% by weight Te to obtain a base material of the p-type thermoelectric material.

The base material was charged into a quartz tube and then vacuum-sealed at 10 ^-5 torr. The vacuum-enclosed quartz tube was charged into a locking furnace, stirred at 750 ° C for 2 hours, and then cooled to produce an ingot having a uniform composition. The ingot thus prepared was crushed into a 5 mm plate using a high-purity alumina-induction in a glove box in a nitrogen atmosphere. The crushed ingot was pulverized for 3 hours using a planetary mill to obtain a powder having a size exceeding 0 占 퐉 and less than 45 占 퐉. The pulverized powder was charged into a Pyrex glass tube and injected with H ₂ gas of 300 torr. The sealed Pyrex glass tube was subjected to annealing treatment in a salt bath at 380 캜 for 10 hours. The annealed powders were put into a carbon mold and cold pressed under a pressure of 98 MPa and a vacuum of 10 ^-4 torr and then heated at 450 ° C. for 20 hours to obtain a sintered body having a size of 14 mm × 17 mm × 9 mm A thermoelectric material was prepared. Hereinafter, this is referred to as a thermoelectric material A (450).

Example 2: Fabrication of p-type Bi-Sb-Te thermoelectric material using a powder having a size of less than 45 [mu] m and a sintering temperature of 500 [deg.

A sintered body having a size of 14 mm x 17 mm x 9 mm, that is, a thermoelectric material was prepared in the same manner as in Example 1, except that the sintering temperature was 500 캜. Hereinafter, this is referred to as thermoelectric material A (500).

Example 3: Fabrication of p-type Bi-Sb-Te thermoelectric material using powders having a size ranging from 45 μm to 105 μm and sintering temperature of 450 ° C.

In the same manner as in Example 1 except that the crushed ingot was pulverized for 10 hours using a ball mill to obtain a powder having a size ranging from 45 탆 to 105 탆, a size of 14 mm x 17 mm x 9 mm Sintered body, i.e., a thermoelectric material, was prepared. Hereinafter, this is referred to as thermoelectric material B (450).

Example 4: Fabrication of p-type Bi-Sb-Te thermoelectric material using powders having a size ranging from 45 μm to 105 μm and sintering temperature 500 ° C.

A sintered body having a size of 14 mm x 17 mm x 9 mm, i.e., a thermoelectric material, was prepared in the same manner as in Example 3, except that the sintering temperature was 500 占 폚. Hereinafter, this is referred to as thermoelectric material B (500).

Example 5: Fabrication of a p-type Bi-Sb-Te thermoelectric material using a powder having a size in the range of more than 105 μm and not more than 150 μm and a sintering temperature of 450 ° C.

In the same manner as in Example 1 except that the crushed ingot was pulverized for 10 hours using a ball mill to obtain a powder having a size in a range of more than 105 탆 and not more than 150 탆, Sized sintered body, that is, a thermoelectric material was prepared. Hereinafter, this is referred to as thermoelectric material C (450).

Example 6: Fabrication of a p-type Bi-Sb-Te thermoelectric material using a powder having a size ranging from more than 105 μm to 150 μm or less and a sintering temperature of 500 ° C.

A sintered body having a size of 14 mm x 17 mm x 9 mm, i.e., a thermoelectric material, was prepared in the same manner as in Example 5, except that the sintering temperature was 500 占 폚. Hereinafter, this is referred to as thermoelectric material C (500).

Comparative Example 1: Fabrication of p-type Bi-Sb-Te thermoelectric material using powders having a size exceeding 150 μm and sintering temperature of 500 ° C.

The sintered compact having a size of 14 mm x 17 mm x 9 mm was produced in the same manner as in Example 2, except that the crushed ingot was pulverized for 10 hours using a ball mill to obtain powder having a size exceeding 150 mu m. That is, a thermoelectric material. Hereinafter, this is referred to as thermoelectric material D (500).

Comparative Example 2: Fabrication of a p-type Bi-Sb-Te thermoelectric material using powders having a size ranging from 45 μm to 105 μm and a sintering temperature of 400 ° C.

A sintered body having a size of 14 mm x 17 mm x 9 mm, that is, a thermoelectric material was manufactured in the same manner as in Example 3, except that the sintering temperature was 400 占 폚. Hereinafter, this is referred to as thermoelectric material B (400).

Comparative Example 3: Fabrication of a p-type Bi-Sb-Te thermoelectric material using powders having a size ranging from 45 μm to 105 μm and a sintering temperature of 550 ° C.

A sintered body having a size of 14 mm x 17 mm x 9 mm, i.e., a thermoelectric material, was prepared in the same manner as in Example 3, except that the sintering temperature was 550 占 폚. Hereinafter, this is referred to as thermoelectric material B (550).

Test Example 1: Crystal structure and anisotropy analysis of the thermoelectric material prepared above

For the crystal structure and anisotropy analysis of the thermoelectric materials prepared in Examples 1 to 6, X-ray diffraction (XRD) spectroscopy was used to observe cross-sections perpendicular to the cold pressing direction and in a horizontal direction. An XRD spectrum obtained from a plane parallel to the cold pressing direction of the thermoelectric materials A 500, B 500 and C 500 is shown in Fig. 3, and an XRD spectrum obtained from a plane perpendicular to the cold pressing direction is shown in Fig. .

The intensity of the (0 0 6), (0 0 15) and (0 0 18) peaks in FIG. 4 is much greater than the intensity of the same peak in FIG. 3, (0 0 21) peaks can be confirmed. This means that the prepared thermoelectric material has a rhombohedral crystal structure and has anisotropy, and thus has excellent thermoelectric properties.

The XRD spectra of the thermoelectric materials A 450, B 450 and C 450 show the same tendency as the XRD spectra of the thermoelectric materials A 500, B 500 and C 500.

Test Example 2: Microstructure and density analysis of the thermoelectric material prepared above

The microstructure of the fracture surface of the thermoelectric material was analyzed by SEM.

SEM images of the fracture surfaces of the thermoelectric materials A 500, B 500 and C 500 are shown in Fig. 6 shows an SEM image of the fracture surface of the thermoelectric material D (500).

As shown in FIG. 5, it can be seen that the crystal grains of the thermoelectric materials A 500, B 500 and C 500 have a layered structure.

As shown in FIG. 6, it can be seen that the crystal grains of the thermoelectric material D (500) do not form a fine layered structure and have large pores. The thermal conductivity of the thermoelectric material D 500 is low due to the large pores and large pores present in the thermoelectric material D 500, B (500) and C (500).

Thus, it can be confirmed that the size of the pulverized powder significantly affects the microstructure and performance of the thermoelectric material.

The size of the grain of the thermoelectric material produced at the sintering temperature of 450 ° C was smaller than that of the thermoelectric material produced at the sintering temperature of 500 ° C. In addition, the density of the thermoelectric material produced at the sintering temperature of 500 캜 was smaller than that of the thermoelectric material produced at the sintering temperature of 450 캜. This is because the volatilization of Te is accelerated as the sintering temperature is increased.

The density D (g / cm 3) of the thermoelectric material was measured by using Archimedes' principle after immersing the sample in a liquid paraffin solution,

C is the weight (g) in water of the waterproofed sample, and ρ is the weight of the water at the test temperature (room temperature). In the equation, A is the weight of the sample in grams, B is the weight of the water- Density (g / cm &lt; 3 &gt;).

.

The relative densities of the thermoelectric materials produced at the sintering temperature of 450 캜 or at the sintering temperature of 500 캜 are shown in Table 1 below.

The relative density of the thermoelectric materials A 450, A 500, B 450, B 500, C 450 and C 500 Thermoelectric material Relative density (%) A (450) 78 A (500) 73 B (450) 87 B (500) 85 C (450) 86 C (500) 83

Test Example 3: Electrical conductivity analysis of the thermoelectric material prepared above

The electrical resistivity ρ was measured using a four-probe tester, and the electric conductivity was calculated using the measured resistivity. The thermoelectric material thus prepared was subjected to regular polishing to have a size of 3 × 3 × 12 μm Thermoelectric materials were used.

The resistivity p is determined by applying a current I through the electrodes at both ends of the thermoelectric material and measuring a drop voltage V _r between the two probes,

(Where S is the cross-sectional area of the thermoelectric material and L is the spacing of the probe).

.

Since the thermoelectric semiconductor has a very low electrical resistivity, it is necessary to increase the current density in order to obtain a high V _r . However, when the current applied to the thermoelectric semiconductor is increased, Peltier heat is generated at the junction of the electrode and the thermoelectric material, And the thermal conductivity generated in this case affects the voltage drop, and an error occurs in the electrical resistivity measurement. Therefore, it is possible to perform precise measurement only by minimizing the influence of the Peltier effect. Therefore, a high-speed repeat measurement method was used in which a voltage drop was measured while passing a current of 10 mA through the Pt wire attached with solder (35Bi-65In) at both ends of the thermoelectric material for less than 1 second.

The results of the electrical conductivity analysis are shown in Fig.

As shown in FIG. 7, the electrical conductivity of the thermoelectric material prepared at the sintering temperature of 500 ° C. is higher than that of the thermoelectric material prepared at the sintering temperature of 450 ° C. This is because the thermoelectric material prepared at the sintering temperature of 500 캜 has a larger hole concentration. At a higher temperature, a hole having a higher hole concentration causes the volatilization of Te during sintering, and the volatilization is caused by Bi _Te and Sb _Te As well as the formation of antistructural defects. This confirms the correlation between hole concentration and electrical conductivity.

It can be also seen that the electrical conductivity is greatly influenced by the size of the pulverized powder. The prepared thermoelectric material A had the lowest hole concentration, and thus had a lower electrical conductivity than the thermoelectric materials B and C prepared above. Low hole concentration is believed to be due to oxygen formed on the powder surface. That is, oxygen replaces Te atoms present at a ratio of [O ₂ ] ^1/2 , thereby increasing the electron concentration of the Bi-Te-based thermoelectric material, which decreases the hole concentration. Since the prepared thermoelectric material B has a high hole concentration and a low porosity, it has a higher electric conductivity than the thermoelectric material C prepared above.

The hole concentration and hole mobility of the thermoelectric material produced from the hole coefficient data are shown in Table 2 below.

 The hole concentration and hole mobility of the thermoelectric materials A 450, A 500, B 450, B 500, C 450 and C 500 Thermoelectric material Hole concentration (m ^-3 ) Hole mobility (m 2 / s · V) A (450) 0.439 x 10 ²⁵ 5.182 × 10 ^-2 A (500) 0.617 x 10 ²⁵ 4.120 x 10 ^-2 B (450) 0.770 × 10 ²⁵ 4.635 × 10 ^-2 B (500) 1.059 × 10 ²⁵ 3.604 × 10 ^-2 C (450) 0.677 × 10 ²⁵ 4.731 × 10 ^-2 C (500) 0.899 × 10 ²⁵ 4.079 x 10 ^-2

Test Example 4: Seebeck coefficient analysis of the thermoelectric material prepared above

The thermal conductivity was analyzed using a thermoelectric material having a size of 5 x 5 x 5 mm by subjecting the thermoelectric material prepared above to normal polishing.

After measuring the electromotive force generated by applying a temperature difference to both ends of the thermoelectric material having the size of 5 x 5 x 5 mm,

DELTA V is the difference in electromotive force between both ends of the thermoelectric material produced by the applied temperature difference, DELTA T is the temperature difference between both ends of the thermoelectric material prepared above, and? _Cu is about -2 ㎶ / K.)

The thermoelectric performance of the thermoelectric material was calculated. The results are shown in Fig.

In all of the thermoelectric materials prepared above, the thermal conductivity has a positive sign, which means that the charge causing electric conduction is positive. It can be confirmed that the thermoelectric performance of the thermoelectric material produced was greatly influenced by the hole concentration. Thermoelectric material A (450) exhibited the highest thermal conductivity due to the lowest hole concentration. It is also confirmed that the thermal conductivity of the thermoelectric material produced at a sintering temperature of 500 ° C is smaller than that of a thermoelectric material produced at a sintering temperature of 450 ° C.

The thermoelectric power? Of the thermoelectric material produced is represented by the following formula:

(Wherein, κ _B is Boltzmann's constant, e is the charge, r is the case of the scatter factor (lattice scattering is r = 0, if the impurity scattering is r = 2 Im), m ^* is the effective mass, h is Planck's constant , and n _c is the charge concentration.)

.

The above equation shows that the thermoelectric power a is greatly influenced by the charge concentration and the scattering factor r. The thermal conductivity of thermoelectric material C was smaller than that of thermoelectric material B, although the thermoelectric material C had a relatively low hole concentration. This implies that the scattering factor value of the thermoelectric material C is smaller than the scattering factor value of the thermoelectric material B.

Test Example 5: Thermal conductivity analysis of the thermoelectric material prepared above

The thermal conductivity of the thermoelectric material was measured. The thermal conductivity was measured using a thermoelectric material having a size of 5 x 5 x 5 mm by subjecting the thermoelectric material prepared above to normal polishing, and a transparent SiO 2 having a thermal conductivity similar to the thermal conductivity of the Bi ₂ Te ₃ thermoelectric material ₂ (1.36 W / mK) was used as a standard sample using a static comparative method. In this case, it was measured under vacuum of 5 × 10 ^-5 torr in order to minimize the effect of convection, and a thin thermocouple of 75 μm in diameter was used to block the heat escaping to the thermocouple. The results are shown in Fig.

The thermal conductivity κ shows a tendency similar to the above-mentioned electric conductivity, and the magnitude of the thermal conductivity indicates the order of the thermoelectric material B> the thermoelectric material C> the thermoelectric material A, and the thermal conductivity of the thermoelectric material manufactured at the sintering temperature of 500 ° C. is 450 Which is higher than the thermal conductivity of the thermoelectric material prepared at sintering temperature of.

Thermal conductivity κ consists of electron thermal conductivity κ _el and phonon thermal conductivity κ _ph . That is, κ = κ _el + κ _ph can be expressed as shown in FIG.

The above-mentioned κ _el is represented by the following formula by Wiedemann-Franz law:

(Where L ₀ is the Lorentz number and? Is the electrical resistivity).

.

κ _el is a factor related to charge transfer in thermal conductivity κ and is proportional to electrical conductivity. κ _ph is not influenced by the charge concentration n _c and is greatly affected by phonon scattering. For a Bi ₂ Te ₃ thermoelectric material, when the charge concentration n _c is about 10 ²⁵ m ^-3 , κ _ph has a contribution of about 75% of the total thermal conductivity κ.

Test Example 6: Analysis of the figure of merit of the thermoelectric material prepared above

The performance index Z of the thermoelectric material was calculated using the data measured in the above test examples. The results are shown in Fig.

The figure of merit Z is given by the formula:

Where? Is the thermal conductivity,? Is the electrical conductivity, and? Is the thermal conductivity.

.

In order to obtain high thermoelectric efficiency, a thermoelectric material having a large figure of merit is required to obtain a high thermoelectric efficiency. In order to obtain a thermoelectric material having a high figure of merit, the value of thermoelectric power and electric conductivity is large, The value of conductivity should be small.

As shown in FIG. 11, it can be seen that the thermoelectric material according to the present invention has a large figure of merit, and in particular, the thermoelectric material B (450) has the largest figure of merit. This indicates that the thermoelectric material manufactured according to the present invention has better performance than the thermoelectric material produced by the conventional manufacturing method.

On the other hand, the performance indexes of the thermoelectric materials B (400) and B (550) prepared in Comparative Examples 2 and 3 were 1.72 10 ^-3 / K and 1.83 10 ^-3 / K, respectively. That is, the thermoelectric materials B 400 and B 550 have a significantly smaller figure of merit than the thermoelectric material according to the present invention.

As a result, it can be seen that the sintering temperature greatly influences the performance index of the thermoelectric material.

1 is a photograph showing an ingot in a quartz tube manufactured according to an embodiment of the present invention.

2 (a), B 450 (FIG. 2 (b), and C 450 (FIG. 2 (c)), thermoelectric material A 450 FIG.

3 (a), B (500) (Fig. 3 (b), and 500 (Fig. 3 (c)) thermoelectric materials A And the XRD spectrum obtained from the horizontal plane of the cold pressing direction.

4 (a), B (500) (Fig. 4 (b), and 500 (Fig. 4 (c)) thermoelectric materials A Is an XRD spectrum obtained from a plane perpendicular to the cold pressing direction.

5 (a), B (500) (FIG. 5 (b), and 500 (FIG. 5 (c)) thermoelectric materials A Fig.

6 is an SEM image of the fracture surface of the thermoelectric material D (500) produced according to Comparative Example 1. Fig.

FIG. 7 is a schematic view of a thermoelectric material A 450 and A 500 (FIG. 7 (a)), B 450 and B 500 (FIG. 7 (b)), C (450) and C (500) (Fig. 7 (c)).

8 shows a thermoelectric material A 450 and A 500 (FIG. 8 (a)), B 450 and B 500 (FIG. 8 (b)), C (450) and C (500) (Fig. 8 (c)).

9 shows the thermoelectric material A 450 and A 500 (Fig. 9 (a)), B 450 and B 500 (Fig. 9 (b)), C 450 and C 500 (Fig. 9 (c)).

10 shows the thermoelectric materials A 450 and A 500 (FIG. 10 (a)), B 450 and B 500 (FIG. 10 (b)), K _el , and kappa _ph of C (450) and C (500) (Fig. 10 (c)).

11 shows the thermoelectric material A 450 and A 500 (FIG. 11 (a)), B 450 and B 500 (FIG. 11 (b)), C (450) and C (500) (Fig. 11 (c)).

Claims (15)

Bi, Sb and Te are weighed and mixed so as to conform to the composition of Bi _x Sb _2-x Te ₃ (where x is 0 < x < 2), charged into a tube, and then vacuum-sealed; An ingot manufacturing step of putting the tube sealed through the vacuum filling step into the furnace and stirring the mixture, and then cooling the furnace to produce an ingot; A crushing step of crushing the ingot produced in the ingot manufacturing step; A pulverizing step of pulverizing the pulverized powder through the pulverizing step to a size of 45 mu m to 105 mu m; And a sintering step of cold-pressing the powder obtained through the pulverizing step in a vacuum of 10 ^-3 torr or less under a pressure of 40 MPa to 120 MPa and then heating and holding at a temperature of 450 ° C to 500 ° C for sintering. Type Bi-Sb-Te based thermoelectric material. Bi, Sb and Te are weighed and mixed so as to conform to the composition of Bi _x Sb _2-x Te ₃ (where x is 0 <x <2), charged into a first tube, and vacuum- ; An ingot production step of charging the first pipe sealed through the vacuum filling step into the furnace and stirring the mixture, and then cooling the furnace to produce an ingot; A crushing step of crushing the ingot produced in the ingot manufacturing step; A pulverizing step of pulverizing the pulverized powder through the pulverizing step to a size of 45 mu m to 105 mu m; An annealing step of charging the powder obtained through the pulverizing step into the second tube, filling and filling with hydrogen, and then heating and holding and annealing; And And a sintering step of cold-pressing the powder subjected to the annealing step in a vacuum of 10 ^-3 torr or less under a pressure of 40 MPa to 120 MPa and then heating and holding it at a temperature of 450 ° C to 500 ° C for sintering, A method for manufacturing a Bi-Sb-Te thermoelectric material. 3. The method according to claim 1 or 2, The tube, the first tube and the second tube may be quartz tubes, silica tubes, or pyrex tubes A method for producing a p-type Bi-Sb-Te thermoelectric material. 3. The method according to claim 1 or 2, The ingot manufacturing step is a step of stirring the ingot at 700 ° C. to 750 ° C. for 1 hour to 5 hours, A method for producing a p-type Bi-Sb-Te thermoelectric material. 3. The method according to claim 1 or 2, In the above, A method for producing a p-type Bi-Sb-Te thermoelectric material. 3. The method according to claim 1 or 2, The step of crushing is a step of crushing in an inert atmosphere in a glove box using induction A method for producing a p-type Bi-Sb-Te thermoelectric material. The method according to claim 6, The inert atmosphere is a nitrogen atmosphere A method for producing a p-type Bi-Sb-Te thermoelectric material. The method according to claim 6, The induction may be an alumina-induced or zirconia-induced A method for producing a p-type Bi-Sb-Te thermoelectric material. 3. The method according to claim 1 or 2, The pulverizing step is a step of pulverizing using a planetary mill or a ball mill A method for producing a p-type Bi-Sb-Te thermoelectric material. 3. The method of claim 2, In the annealing step, hydrogen is injected into the second tube filled with the powder obtained through the pulverization step at a pressure of 200 torr to 500 torr and maintained at 340 to 400 ° C for 10 to 15 hours A method for producing a p-type Bi-Sb-Te thermoelectric material. delete delete delete delete delete

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