KR20120133009A - Method of development for the enhancement of thermoelectric efficiency of thermoelectric material through annealing process - Google Patents

Abstract

PURPOSE: Thermoelectric materials, a method for improving thermoelectric efficiency thereof, and a supporting body including the same are provided to improve crystallization of the thermoelectric material including bismuth telluride by performing heat treatment using a sealing container which is completely sealed up. CONSTITUTION: Thermoelectric materials including bismuth telluride is prepared. The thermoelectric materials are a nanowire structure or a bulk type structure. The thermoelectric materials including the bismuth telluride is accepted in a sealing container filled with inert gas. The sealed container for accepting the thermoelectric materials is sealed up through alumina paste. The sealed container is filled with tellurium powder and heat treatment is performed. [Reference numerals] (AA) Manufacturing porous(Al2O3) supporter; (BB) Anodizing method; (CC) Synthesizing Bi2Te3 nanorwire; (DD) Pulse electroplating method; (EE) Opening a sealing container; (FF) Filling Bi2Te3 nanowire + Te powder; (GG) Sealing a sealing container with Al paste; (HH) Glove Box; (II) Quartz Chamber; (JJ) Thermal process execution; (KK) 573K-673K

Description

Thermoelectric material, a method for improving the thermoelectric efficiency of the thermoelectric material and a support including the thermoelectric material {Method of development for the enhancement of thermoelectric efficiency of thermoelectric material through annealing process}

The present invention relates to a method for improving the thermoelectric efficiency of a thermoelectric material through heat treatment.

In recent years, interest in thermoelectric materials has been increasing for the efficient use of energy through the energy crisis. Thermoelectric materials can be broadly classified into power generators and cooling according to their purpose, and in detail, they can be used for cooling of automotive power generators, micro cooling, and laser diodes.

The efficiency of the thermoelectric material can be defined by the following equation, which is a dimensionless ZT value.

(S: 제백 계수,

: 전기전도도, κ: 열전도도)

(S: Seebeck coefficient,

: Electrical conductivity, κ: thermal conductivity)

Recently, methods for improving thermoelectric efficiency in terms of multiple angles have been reported.

In particular, in order to improve thermoelectric efficiency, it is necessary to increase the Seebeck coefficient and the electrical conductivity while simultaneously reducing the thermal conductivity. In general, the Seebeck coefficient and the electrical conductivity are a function of the carrier concentration of the thermoelectric material and are also affected by the crystal structure.

The present invention has been made to solve the above problems, an object of the present invention is to improve the Seebeck coefficient of the thermoelectric material including bismuth telluride and the crystal structure of the thermoelectric material through heat treatment Through the improvement of the electrical conductivity can be expected, based on this to provide a technology that can finally improve the thermoelectric efficiency (performance efficiency) of the thermoelectric module composed of such a thermoelectric material.

In particular, the present invention includes bismusteullide by performing a heat treatment using a sealed vessel (sealing boat) that is completely sealed in order to remove the loss due to the vaporization of the tellurium component lowered by the heat treatment temperature rise during this heat treatment process, It is another object of the present invention to provide a process for further improving the crystallinity improvement of the thermoelectric material and thereby improving the thermoelectric efficiency.

As a means for solving the above problems, the present invention comprises a first step of synthesizing a thermoelectric material comprising bismuth telluride (Bi ₂ Te ₃ ); And a second step of performing thermal treatment by receiving the bismuth telluride (Bi ₂ Te ₃ ) thermoelectric material from an external atmosphere and receiving an airtight container filled with an inert gas, wherein the second container is filled with tellurium powder. It is possible to provide a method for improving thermoelectric efficiency of a thermoelectric material including performing heat treatment.

In addition, the bismuth telrul fluoride (Bi ₂ Te ₃₎ The synthesis of thermoelectric material comprising a bismuth telrul fluoride (Bi ₂ Te ₃₎ improved thermal efficiency of the thermal conductive material step of synthesizing a nanowire structure in the porous support method Make it available. In this case, synthesizing the bismuth telluride (Bi ₂ Te ₃ ) nanowire structure in the above-described process, the nanowires may be synthesized by pulse plating on the porous alumina (Al ₂ O ₃ ) support. .

In addition, unlike the above-mentioned, to synthesize the bismuth telluride (Bi ₂ Te ₃ ) thermoelectric material, the bismuth (Bismuth), tellurideum (Tellurium) powder to form a nano-size Bi-Te-based powder, The Bi-Te-based powder may be processed and synthesized into a bulk type structure. In this case, processing the Bi-Te-based powder and synthesizing it into a bulk structure may be implemented as a bulk-type structure by injecting the Bi-Te-based powder into a mold and hot pressing.

In addition, the heat treatment of the second process may be performed at 573.15K to 673.15K. In addition, the preparation process for the heat treatment, the preparation process for receiving the bismuth telluride (Bi ₂ Te ₃ ) thermoelectric material is isolated from the external atmosphere and filled with inert gas in a sealed container to be performed in a space blocked from the external atmosphere. Can be. In particular, in this case, the inert gas of the second process may be any one of helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Can be.

In the second process, the sealed container containing the thermoelectric material may be sealed through an alumina paste.

In addition, the heat treatment of the second process may be performed in a quartz chamber filled with nitrogen.

In addition, the thermoelectric material containing bismuth telluride (Bi ₂ Te ₃ ) is prepared by the method of claim 1 to perform heat treatment by isolating the external atmosphere, the chemical composition ratio of Te: Bi is Bi: Te = 2: 3 Satisfactory, the thermoelectric material may be a nanowire structure or a bulk structure.

In addition, the bismuth telluride (Bi ₂ Te ₃ ) nanowires, made of a single crystal, may be a thermoelectric material having a hexagonal Bi ₂ Te ₃ phase of the (205), (110), (0015) direction. . Further, in this case, the growth direction of the nanowire may be a direction perpendicular to the c-axis [00ℓ].

The above-described thermoelectric material according to the present invention includes a porous support; and bismustrilide nanowires prepared by claim 1 formed in the porous support; wherein the bismustrilide nanowires have a chemical composition ratio of Te: Bi It may be formed of a support including a thermoelectric material satisfying Bi: Te = 2: 3.

In this case, the porous support may include a thermoelectric material which is porous alumina (Al ₂ O ₃ ).

According to the present invention, the electrical conductivity is expected to be improved by improving the sebeck coefficient of the bismuth telluride thermoelectric nanowire structure and the crystal structure of the nanowire structure through heat treatment at an optimized temperature range. Based on this, the thermoelectric efficiency (performance efficiency) of the thermoelectric module finally composed of nanowire structures can be expected.

In particular, heat treatment is performed by using a sealed vessel that is completely sealed to remove the loss due to vaporization of the telluride component due to an increase in the heat treatment temperature, thereby further improving and improving the crystallinity of the bismuthulelide material. This also has the effect of improving the thermoelectric efficiency.

1 and 2 are flowcharts according to first and second embodiments of a method for improving thermoelectric efficiency of bismuth telluride thermoelectric nanowires according to the present invention.
3 is a schematic diagram of the morphology change of the bismuth telluride nanowire structure during the heat treatment process according to a preferred embodiment of the present invention.
4, 5 and 6 are EDX graphs showing the chemical composition ratio inside the nanowires during the heat treatment process.
7 and an EDX graph showing Seebeck coefficient data measured through a heat treatment process at a specific temperature, and FIG. 8 is a transmission electron microscope (TEM) showing crystallinity of the nanowire structure.
FIG. 9 shows the Seebeck coefficient of the nanowires heat-treated at each temperature, analyzed by SAED.
10 and 11 are graphs showing the chemical composition ratio of the bismuth telluride nanowires according to the heat treatment temperature in the experimental conditions of FIG. 2.
FIG. 11 is a graph showing the change of Seebeck coefficient of bismuth telluride according to the heat treatment temperature in the second experimental example under the experimental conditions of FIG. 2.
12 is an image showing that the crystallinity of the bismuth telluride nanospheres is improved to a single crystal according to the heat treatment temperature in the second experimental example.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration and operation according to the present invention. In the description with reference to the accompanying drawings, the same components are given the same reference numerals regardless of the reference numerals, and duplicate description thereof will be omitted. The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The present invention provides a bismuth telluride thermoelectric material capable of improving thermoelectric efficiency by heat treating a thermoelectric material (thermoelectric nanowire or bulk structure) including bismuth telluride at a specific temperature, and improving thermoelectric efficiency thereof. The main idea is to provide a method. Hereinafter, the thermoelectric material in the present invention is a concept encompassing a material containing Bi ₂ Te ₃ , such as a nanowire structure, a bulk structure (Pellet, Ingot), or a film structure.

1. First Embodiment

In particular, referring to Figure 1, which is a flow chart of a process for improving the thermoelectric efficiency of the thermoelectric material according to the present invention, a thermoelectric containing Bi ₂ Te ₃ , such as nanowire structure, bulk structure (Pellet, Ingot), film type structure, etc. The process will be described using nanowires as a first embodiment of the material. The present invention comprises synthesizing bismuth telluride (Bi ₂ Te ₃ ) nanowires in a porous support and heat-treating the bismuth telluride (Bi ₂ Te ₃ ) nanowires in an inert atmosphere. That is, the thermoelectric efficiency improvement method of the thermoelectric nanowire according to the present invention, first, the process of forming a porous support, and synthesize the nanowire structure inside the porous support, and then can maximize the Seebeck coefficient through the heat treatment process It can be implemented as a process.

In particular, in the above-described process, the porous support may use a porous alumina (Al ₂ O ₃ ) template, and the process of synthesizing bismuth telluride (Bi ₂ Te ₃ ) nanowires is an inert atmosphere, that is, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn) is preferably carried out in an inert space formed of any one of the gases, in one embodiment is formed of argon It will be described as an example that proceeds in an inert atmosphere.

In addition, in the present invention, after synthesis of bismuth telluride (Bi ₂ Te ₃ ) nanowires, the Seebeck coefficient may be maximized through heat treatment, and particularly, the heat treatment temperature may be performed at a temperature range of 423 to 475 K. have. However, if the temperature is out of the heat treatment temperature range, the Te component may evaporate to cause a deadly problem in which the thermoelectric efficiency is lowered. This leads to a drop in thermoelectric efficiency.

Referring to FIG. 2, after synthesis of the nanowires in the porous support, the heat treatment results according to the respective temperatures are shown. The Seebeck coefficient of the nanowires having a heat treatment temperature of 423K is slightly increased than the Seebeck coefficient of the nanowires before the heat treatment. 57 μV / K, and as the heat treatment temperature is increased to 475 K, the Seebeck coefficient increases to 62 μV / K. That is, single crystal nanowires are realized at 423 ~ 475K, and the Seebeck coefficient is increased to 57μV / K ~ 62μV / K, and then, at 523K, Tellurium crystallite is formed inside the nanowires to separate Bi ₄ Te ₅ -Te shape. was phenomenon is found, 673K in the state Bi ₄ Te ₅ (523K) goes through an intermediate process, Bi ₄ Te ₃ to the Bi-rich in the conventional stoichiometric composition of Bi ₂ Te ₃ to the evaporation of the melting phenomenon and Tellurium component of Tellurium crystallite Will change to

As a result, when the annealing temperature was increased to 523 K, the Seebeck coefficient of the nanowires rapidly decreased to 19 μV / K and decreased by about 64%. When the annealing temperature was increased again to 673K, the Seebeck coefficient increased slightly to 29 μV / K. The surface area exposed is large due to the morphological properties of the nanowires depending on the temperature of the heat treatment, which causes a lot of vaporization of the tellurium (Te) component. Will lead to Furthermore, the Seebeck coefficient leads to a decrease in Seebeck coefficient due to heat treatment under conditions not optimized as a function of the charge concentration of the thermoelectric material, especially when the annealing temperature is increased from 523K to 673K. Recrystallization of the (Te) component slightly improves the crystallinity, but the Seebeck coefficient increases slightly, but this does not lead to an increase in thermoelectric efficiency.

2. Second Embodiment

As described above in the first embodiment, in the thermoelectric efficiency improvement method of the thermoelectric nanowire according to the present invention, heat treatment is performed at a temperature range of 423 to 475 K, and at this temperature, tellurium vaporization proceeds in the heat treatment process. As described above, the Seebeck coefficient falls. Therefore, the present embodiment implements an embodiment that can extend the temperature limit for the increase in thermoelectric efficiency through the process shown in FIG. 2 particularly to solve this problem.

As shown in FIG. 3, the process according to the present invention is a first process of synthesizing bismuth telluride (Bi ₂ Te ₃ ) nanowires in a porous support and the bismuth telluride (Bi ₂ Te ₃ ) nanowires in an external atmosphere. And a second step of carrying out heat treatment by receiving an inert gas-filled hermetically sealed container. In particular, the above-mentioned second process is characterized in that the heat treatment is carried out by filling the tellurium powder in the airtight container.

That is, in order to avoid the vaporization of the telluride component by removing the heat treatment method described above in the first embodiment, a sample of bismuth tellulite nanowires is synthesized, and the structure capable of completely sealing the nanowire sample before heat treatment ( The container is then sealed in a 'sealing boat', and the sealed container is sealed using an alumina paste after storage. In particular, it is more preferable to fill the hermetic container with tellurium powder before sealing.

In addition, the preparation before the heat treatment is more preferably performed in a space such as a glove box filled with Ar to prevent contact with the atmosphere.

3. Experimental Example and Comparative Example

Hereinafter, the variation of the Seebeck coefficient for the thermoelectric efficiency improvement method involving the heat treatment process according to the present invention will be described through an experimental example.

(1) Experimental Example 1

The preferred heat treatment temperature range of the present invention is to perform a heat treatment of the lower limit of 423K in the range of 423 ~ 475K, and then it will be described through a comparison result in the range of 523K, 673K.

First, in the experimental example related to the first embodiment of the present invention, the porous alumina template was prepared by a two-step anodization method under an applied voltage of 40V and oxalic acid of 0.3M. Subsequently, bismuth telluride nanowires were continuously synthesized in the porous alumina template by a pulse electroplating method with 5 ms on time and 50 ms off time. Finally, the bismuth telluride membrane was overgrown by overflowing the upper portion of the porous alumina template. film) was formed.

In particular, in this case, the synthesized nanowires have a diameter of 50 nm and a length of 20 μm. The bismuth telluride nanowires synthesized on the porous alumina template were subjected to a heat treatment process for 4 hours in an inert atmosphere at respective temperatures of 423, 523, and 673K.

The crystallinity of the nanowires was analyzed by XRD, HRTEM (High Resolution Transmission Electron Microscopy) and SAED (Selected Area Transmission Electron Microscopy), and the chemical composition of the nanowires heat-treated at each temperature was analyzed by EDX. For the above analysis, the selective dissolution of the porous alumina template allowed the nanowires to be dispersed in the TEM grid.

Subsequently, in order to measure the Seebeck coefficient, after the Au (gold) layer was deposited through a mask, copper blocks were contacted at both ends, and then a Peltier element was contacted to apply a temperature difference of 15K at both ends. Through this measurement, the generated electric potential was finally able to measure the Seebeck coefficient of the nanowires finally heat-treated at the respective temperatures.

The results for the Seebeck coefficient of the nanowires measured through the above results are as follows.

Figure 4 shows the change in the composition of the bismuth telluride according to the heat treatment, referring to the graph it was confirmed that the complex bismuth oxygen layer and the tellurium oxygen layer was formed on the surface of the synthesized bismuth telluride nanowires. This can lead to the result that an oxide layer is formed on the surface of the nanowire from the result of detecting the oxygen component only at the upper and lower portions of the measurement region, as in the EDX results.

In addition, Figure 5 shows a comparison of the chemical composition ratio of the nanowires heat-treated at each temperature. The chemical composition ratio represents the ratio of Te / Bi. As the heat treatment temperature increases, the chemical composition ratio decreases, which shows a decrease in the tellurium content as the heat treatment temperature increases. This is due to the fact that Tellurium crystallite is formed inside the nanowire at 523K, and Bi ₄ Te ₅ -Te shape separation phenomenon occurs. Throughout the Bi ₄ Te ₅ (523K) in the middle course Bi ₂ Te ₃ it is due to the result that is replaced by the Bi ₄ Te ₃ in the Bi-rich state.

Therefore, as a result of heat treatment on bismuth telluride in the present invention, it can be seen that the probability of vaporization phenomenon occurs during the heat treatment process due to the high vapor pressure of the tellurium component, and furthermore, the nanowires have a relative surface area when compared to bulk materials or thin films. It can be seen that this phenomenon becomes larger because of the large size. However, at the heat treatment temperature 423K, as shown, the molar ratio between Te / Bi is 0.8-1.5, indicating a stable state, which means that the width of the component change is very small and reliability can be ensured.

6 and 7, black spots (crystallites) are irregularly formed in the nanowires heat-treated at 523K, and this part is purely a tellurium component through EDX analysis. It was confirmed that the composition was composed of, and in other nanowire parts, a decrease in the content of tellurium was also found. However, when the heat treatment temperature was increased to 673K, black spots (crystallites) disappeared. However, as the heat treatment temperature was increased, black spot decomposition occurred and dissolved. In the chemical composition of the nanowires heat-treated at 623K, a continuous reduction of the tellurium (Te) component was found.

8 illustrates the results of analyzing the crystallinity of the nanowires at 423K, 523K, and 673K through the SAED in the above-described experiment.

Referring to the illustrated figure, referring to images processed at respective temperatures of 423K, 523K, and 673K, in the SAED of the nanowires heat-treated at 423K, nanowires are composed of single crystals, and bright spots are shown ( 205), (110) and (0015) hexagonal Bi ₂ Te ₃ Evidence shows that it consists of phases. In addition, it also shows that the growth direction of the nanowire was made in a direction perpendicular to the c-axis [00ℓ].

The crystallinity of the nanowires with the heat treatment temperature of 523K is shown in the form of a ring, which shows that the nanowires are made of polycrystals, and through the information of each bright spot, ( 0027) shows the Bi ₄ Te ₅ phase and tellurium (Te) crystalline complex. This is because polycrystalline nanowires are composed of Bi ₄ Te ₅ and Te.

When the temperature of the heat treatment finally reached 673K, it was found that the nanowires were composed of single crystalline again, and grew in the direction perpendicular to the c-axis as in 423K, (003), (009), ( 0021) and hexagonal Bi ₄ Te ₃ phase.

The change from polycrystal to single crystal when the heat treatment temperature is increased from 523K to 623K can be understood as the recrystallization of the tellurium (Te) component, through the black spot vaporization of pure tellurium. It can be concluded that the transition to the most stable state, Bi ₄ Te ₃ phase. It can be seen that the bismuth telluride thin film synthesized at 600K by molecular beam epitaxy is in conflict with the result of forming the Bi ₄ Te ₃ phase.

As a result, the change in crystallinity and components at 523K, 623K temperature does not lead to an improvement in the thermoelectric efficiency of bismuth telluride, the preferred heat treatment range of the present invention can maximize the thermoelectric efficiency at 423K ~ 475K.

In particular, these results can be seen in the graph of the change in Seebeck coefficient of the bismuth telluride nanowires according to the heat treatment temperature according to FIG.

Referring to the drawings, the measured Seebeck coefficients all show positive values, which is evidence that the bismuth telluride nanowires synthesized under the above experimental conditions are in the form of P-type, and also due to the excess of the bismuth component. The resulting hole is the charge concentration of the majority (major).

In this case, the Seebeck coefficient of nanowires with a heat treatment temperature of 423 K was measured to be 57 μV / K, slightly higher than the Seebeck coefficient of nanowires before heat treatment, which improved crystallinity rather than the effect of a decrease in charge concentration through heat treatment at 423 K. This is the result. In addition, the improvement of the Seebeck coefficient is increased from 475K to 62μV / K, it can be seen that this leads to a sharp increase in the thermoelectric efficiency.

However, when the annealing temperature was increased to 523K, the nanowire backing coefficient rapidly decreased to 19 μV / K and decreased by about 64%. When the annealing temperature was increased again to 673K, the Seebeck coefficient increased slightly to 29 μV / K, which is a much lower value than before the heat treatment.

Taken together, as the heat treatment temperature increases, vaporization occurs due to the high vapor pressure of the tellurium (Te) component, resulting in the formation of pure tellurium (Te) and Bi ₄ Te ₅ phase from 523K, 623K At higher temperatures, pure tellurium decomposes and recrystallizes into Bi ₄ Te ₃ phase, and at the same time the vaporization of the tellurium causes the chemical composition of the conventional nanowires (Bi _2). The collapse of Te ₃ ) leads to a decrease in Seebeck coefficient. Accordingly, the method for improving the thermoelectric efficiency of the bismuth telluride thermoelectric nanowire according to the present invention may be implemented by maximizing the Seebeck coefficient by performing heat treatment at a temperature range of 423 to 475K. Afterwards, as the heat treatment temperature increases, a slight increase in the Seebeck coefficient is slightly recrystallized due to the recrystallization of the tellurium (Te) component, but the Seebeck coefficient increases slightly, but this does not lead to an increase in the thermoelectric efficiency.

(2) Experimental Example 2

In the second experimental example, it is possible to implement the process conditions for overcoming the increase in the Seebeck coefficient for improving the thermoelectric efficiency as described above in the second embodiment having limitations due to the heat treatment temperature.

To this end, in order to prevent evaporation of the telluride component by removing the conventional heat treatment method, pre-heating telelylium powder (powder) was added to the heat-sealing boat before the heat treatment of the bismuth telluride nanostructure sample. In addition, the sealing boat containing the above-mentioned sample was completely sealed using an alumina paste. In particular, this sample preparation process is performed in a glove box filled with Ar to prevent contact with the atmosphere. Process conditions of the heat treatment are carried out at a temperature of 423K, 473K, 523K, 573K, 623K, 673K, heat treatment time was carried out for 4 hours in a quartz chamber filled with nitrogen.

FIG. 10 is a result graph according to the above-described process conditions, and shows the molar ratio between the atoms of Bi and Te, FIG. 10 (a) shows the molar ratio before heat treatment, and (b) shows the molar ratio after 623K heat treatment. will be. Comparing with this, even though the heat treatment temperature is greatly increased, it can be seen that the amount of the tellurium component is almost unchanged before and after the heat treatment, because the vaporization of the tellurium component is prevented.

FIG. 11 is a graph showing change in Seebeck coefficient of bismuth telluride according to the heat treatment temperature in Experimental Example 2. FIG.

Referring to the illustrated graph, it can be seen that the Seebeck coefficient shows the maximum value around 350 degrees (623K), and the Seebeck coefficient increases even at the heat treatment temperature which is greatly increased in the temperature range of the first embodiment, especially 573K to 673K. It can be seen that the Seebeck coefficient increases up to three times in the interval. That is, the process of the second embodiment according to the present invention completely prevents the evaporation of the tellurium component, and improves the Seebeck coefficient value of the bismuth telluride nanostructure through an improved heat treatment process. Improvements in crystallinity can also be expected to improve electrical conductivity, which in turn can lead to improvements in ZT values, the thermoelectric efficiency (performance index) index.

12 is an image showing that the crystallinity of the bismuth telluride nanospheres is improved to a single crystal according to the heat treatment temperature in the second experimental example.

(3) Third Experimental Example

In the third experimental example, unlike the nanowire structure shown in the first and second exemplary embodiments, the method of improving the thermoelectric efficiency according to the present invention is applied to the bulk structure (Pellet, Ingot), that is, the bulk Bi-Te material. Let's explain.

_{30g Bi 0 .25 Sb 0 .75 Te} 3 of p-type Bi-Te-based bulk (bulk) type pellets during manufacture of the experimental conditions (pellet) is as follows. In the present invention, the synthesis of Be-Sb-Te powder using bismuth, antimony, and tellurium will be described as an example.

Specifically, 20.89, 36.52 and 76.56 g of bismuth, antimony and tellurium powders having a purity of 5N (99.999%) were respectively inserted into glass quartz. In order to prevent the contact of the seal (torque) was completely sealed (sealing). Heat treatment at 800 ° C for 10 hours for the polymerization of each compound followed by ball-milling and 45 μm sieve of Bi-Sb of nano grain size -Te powder can be obtained.

After the Bi-Sb-Te powder is inserted into a graphite mold, a bulk sample in a pellet form may be obtained by hot pressing. Hot pressing experimental conditions are 420 ° C, 200M Pa, 30min.

The heat treatment of the synthesized pellet-type bulk sample was carried out in the same manner as in the first and second embodiments, in which tellurium powder was added and nitrogen-filled after being inserted into a sealing boat sealed with alumina paste. Heat treatment was performed up to 623K in a quartz chamber. Since the surface area is relatively lower than that of the nanostructure, the increase of the Seebeck coefficient is lower than three times, but still increases by more than 50%, thereby improving thermoelectric efficiency.

The thermoelectric material manufactured according to the improved method of the above-described second embodiment and the second experimental example, even if the sample prepared under the present patent conditions is bulk or nanostructure, in the case of bulk type scrape powder of Pellet through TEM EDX analysis The internal structural chemical composition ratio can be determined. That is, as shown in FIG. 10, it can be seen that the atomic percentages of Bi and Te are constant at 40%: 60%. It can be seen that the stoichiometric composition is maintained because the heat treatment under the present patent conditions. Accordingly, the thermoelectric material implemented through the heat treatment process of the second embodiment is preferably formed of Bi: Te = 2: 3 composition in the EDX analysis.

In the case of the nanostructure to which the thermoelectric efficiency improving method according to the present invention is applied, the internal chemical composition ratio can be known through TEM EDX analysis in the form of nanowires, nanotubes, and nanodots.

In the foregoing detailed description of the present invention, specific examples have been described. However, various modifications are possible within the scope of the present invention. The technical idea of the present invention should not be limited to the embodiments of the present invention but should be determined by the equivalents of the claims and the claims.

TEM: Transmission Electron Microscope
Seebeck coefficient: Seebeck coefficient

Claims (16)

A first step of synthesizing a thermoelectric material including bismuth telluride (Bi ₂ Te ₃ );
And a second step of performing a heat treatment by receiving the bismuth telluride (Bi ₂ Te ₃ ) thermoelectric material from an external atmosphere and receiving a sealed container filled with an inert gas.
Method of improving the thermoelectric efficiency of the thermoelectric material comprising filling the closed container with tellurium powder heat treatment.

The method according to claim 1,
Synthesizing a thermoelectric material including the bismuth telluride (Bi ₂ Te ₃ ),
A method of improving thermoelectric efficiency of thermoelectric materials, which is a process of synthesizing bismuth telluride (Bi ₂ Te ₃ ) nanowire structures in a porous support.
The method according to claim 2,
Synthesizing the bismuth telluride (Bi ₂ Te ₃ ) nanowire structure,
Method for improving the thermoelectric efficiency of the thermoelectric material in which the nanowires are synthesized by the pulsed plating method on the porous alumina (Al ₂ O ₃ ) support.
The method according to claim 1,
Synthesizing the bismuth telluride (Bi ₂ Te ₃ ) thermoelectric material,
Bismuth and Tellurium powder are heat-treated to form nano-size Bi-Te powder,
Process to improve the thermoelectric efficiency of the thermoelectric material is synthesized by processing the Bi-Te-based powder into a bulk type (bulk type) structure.
The method of claim 4,
By processing the Bi-Te-based powder synthesized into a bulk structure,
Injecting the Bi-Te-based powder into a mold and implementing a bulk structure through hot pressing method of the thermoelectric efficiency of the thermoelectric material.
The method according to claim 2 or 4,
Performing the heat treatment of the second process,
How to improve thermoelectric efficiency of thermoelectric materials performed at 573.15K ~ 673.15K.
The method of claim 6,
The bismuth telluride (Bi ₂ Te ₃ ) is a method of improving the thermoelectric efficiency of the thermoelectric material is isolated from the external atmosphere and the preparation process for receiving the inert gas-filled sealed container is carried out in a space blocked from the external atmosphere.
The method of claim 7,
Inert gas of the second step,
A method of improving thermoelectric efficiency of a thermoelectric material formed of any one selected from helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).
The method according to claim 1,
In the second step,
The hermetic container containing the thermoelectric material is a thermoelectric efficiency improvement method of the thermoelectric material sealed (sealing) through the alumina paste.
The method according to claim 9,
The second step of the heat treatment is a method of improving the thermoelectric efficiency of the thermoelectric material is carried out in a quartz chamber filled with nitrogen (Quartz chamber).
A thermoelectric material including bismuth telluride (Bi ₂ Te ₃ ) is prepared by the method of claim 1 to perform heat treatment by isolating the external atmosphere,
Thermoelectric material whose chemical composition ratio of Te: Bi satisfies Bi: Te = 2: 3.
The method of claim 11,
The thermoelectric material is a nanowire structure or a bulk structure.
The method of claim 11,
The bismuth telluride (Bi ₂ Te ₃ ) nanowires,
A thermoelectric material consisting of a single crystal and having a hexagonal Bi ₂ Te ₃ phase in the directions (205), (110), and (0015).
The method according to claim 13,
The growth direction of the nanowires is a thermoelectric material perpendicular to the c-axis [00ℓ].
Porous support;
Including; bismustelluride nanowires prepared by claim 1 formed in the porous support;
The bismustelluride nanowire includes a thermoelectric material having a chemical composition ratio of Te: Bi that satisfies Bi: Te = 2: 3.
The method according to claim 15,
The porous support is a support comprising a thermoelectric material of porous alumina (Al ₂ O ₃ ).

Images