WO2012165855A2

WO2012165855A2 - Method of development for the enhancement of thermoelectric efficiency of thermoelectric material through annealing process

Info

Publication number: WO2012165855A2
Application number: PCT/KR2012/004260
Authority: WO
Inventors: Jong Min Lee
Original assignee: Lg Innotek Co., Ltd.
Priority date: 2011-05-30
Filing date: 2012-05-30
Publication date: 2012-12-06
Also published as: KR20120133009A; KR101853828B1; WO2012165855A3

Abstract

Provided is a thermoelectric nanowire and a method for improving thermoelectric efficiency thereof using heat treatment. Particularly, the method for improving thermoelectric efficiency of the thermoelectric nanowire includes a first process of synthesizing a nanowire of bismuth telluride (Bi₂Te₃) in a porous support; and a second process of receiving the nanowire of the bismuth telluride (Bi₂Te₃) in a sealing boat separated from an atmosphere and including inert gas to perform heat treatment while a tellurium powder fills the sealing boat. According to the present invention, heat treatment is performed using a sealing boat that is completely sealed in order to avoid a loss due to evaporation of a tellurium component by an increase in heat treatment temperature to improve crystallinity of a material including bismuth telluride, thus increasing thermoelectric efficiency.

Description

METHOD OF DEVELOPMENT FOR THE ENHANCEMENT OF THERMOELECTRIC EFFICIENCY OF THERMOELECTRIC MATERIAL THROUGH ANNEALING PROCESS

The present invention relates to a method of improving a thermoelectric efficiency of a thermoelectric material using heat treatment.

In accordance with the current energy crisis, an interest in thermoelectric material regarding efficient use of energy is growing. The thermoelectric material may be broadly classified into a material for a power generator and a material for cooling according to the purpose, and specifically may be used in a power generator for vehicles and to perform microcooling and cooling of laser diodes.

Efficiency of the thermoelectric material may be defined by the following equation of dimensionless ZT.

(S: seebeck coefficient, σ: electrical conductivity, κ: thermal conductivity)

Recently, methods for improving thermoelectric efficiency have been proposed from various angles.

Particularly, a seebeck coefficient and electrical conductivity need increasing while thermal conductivity is reduced in order to improve thermoelectric efficiency. The seebeck coefficient and the electrical conductivity is a function of a concentration of charge carrier of the thermoelectric material and are significantly affected by a crystalline structure.

An aspect of the present invention is directed to provide a technology for improving a seebeck coefficient of a thermoelectric material including bismuth telluride using heat treatment and a crystalline structure of the thermoelectric material to increase electrical conductivity, thus improving thermoelectric efficiency (performance efficiency) of a thermoelectric module including the thermoelectric material.

Another aspect of the present invention is directed to provide a process for performing a heat treatment process using a sealing boat that is completely sealed in order to avoid a loss due to evaporation of a tellurium component by an increase in heat treatment temperature to improve crystallinity of a thermoelectric material including bismuth telluride, thus increasing thermoelectric efficiency.

According to an embodiment of the present invention, a method for improving a thermoelectric efficiency of a thermoelectric material includes a first process of synthesizing the thermoelectric material including bismuth telluride (Bi₂Te₃); and a second process of receiving the thermoelectric material of the bismuth telluride (Bi₂Te₃) in a sealing boat separated from an atmosphere and including inert gas to perform heat treatment while a tellurium powder fills the sealing boat.

According to another embodiment of the present invention, a support includes a porous support; and a nanowire of bismuth telluride formed in the porous support using the method for improving a thermoelectric efficiency of a thermoelectric material and including the thermoelectric material having a chemical compositional ratio of Bi to Te of 2:3.

Furthermore, in this case, the porous support includes the thermoelectric material of porous alumina (Al₂O₃).

According to the present invention, a seebeck coefficient of a thermoelectric nanowire structure of bismuth telluride using heat treatment in an optimized temperature range and a crystalline structure of the nanowire structure may be improved to increase electrical conductivity, thus improving thermoelectric efficiency (performance efficiency) of a thermoelectric module having the nanowire structure.

Particularly, heat treatment is performed using a sealing boat that is completely sealed in order to avoid a loss due to evaporation of a tellurium component by an increase in heat treatment temperature to improve crystallinity of a material including bismuth telluride, thus increasing thermoelectric efficiency.

The above and other aspects, features and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIGS. 1 and 2 are flowcharts of a method for improving thermoelectric efficiency of a thermoelectric nanowire of bismuth telluride according to first and second embodiments of the present invention;

FIG. 3 is a view showing a morphology change of a nanowire structure of bismuth telluride during a heat treatment process according to a preferable embodiment of the present invention;

FIGS. 4, 5 and 6 are EDX graphs showing a chemical compositional ratio of an internal side of the nanowire during the heat treatment process;

FIG. 7 is an EDX graph showing seebeck coefficient data measured using the heat treatment process at a predetermined temperature;

FIG. 8 is a picture of TEM (transmission electron microscope) showing crystallinity of the nanowire structure;

FIG. 9 is a graph showing a seebeck coefficient obtained using analysis of crystallinity of the nanowire heat treated at a predetermined temperature using SAED;

FIGS. 10 and 11 are graphs showing a chemical compositional ratio of an internal side of the nanowire of bismuth telluride according to a heat treatment temperature under an experimental condition of FIG. 2;

FIG. 11 is a graph showing a change in seebeck coefficient of bismuth telluride according to the heat treatment temperature under the experimental condition of FIG. 2 in experimental example 2; and

FIG. 12 is an image showing an improvement of crystallinity of a nanostructure of bismuth telluride into a single crystal according to the heat treatment temperature in experimental example 2.

Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Wherever possible, the same reference numerals will be used to refer to the same elements throughout the specification, and a duplicated description thereof will be omitted. It will be understood that although the terms “first”, “second”, etc. are used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element.

The present invention provides a thermoelectric material of bismuth telluride and a method for improving thermoelectric efficiency of the thermoelectric material including heat treating the thermoelectric material (a thermoelectric nanowire or a bulk type of structure) including bismuth telluride at a predetermined temperature. Hereinafter, the thermoelectric material of the present invention includes a material including Bi₂Te₃, such as a nanowire structure, a bulk type of structure (pellet and ingot), and a film type of structure.

1. First embodiment

Particularly, FIG. 1 is a flowchart of a process for improving thermoelectric efficiency of the thermoelectric material according to the present invention, and a process regarding a nanowire of the thermoelectric material including Bi₂Te₃, such as a nanowire structure, a bulk type of structure (pellet and ingot), and a film type of structure is described in the first embodiment. The present invention includes synthesizing the nanowire of bismuth telluride (Bi₂Te₃) in a porous support, and heat treating the nanowire of bismuth telluride (Bi₂Te₃) in an inert atmosphere. That is, the method for improving thermoelectric efficiency of the thermoelectric nanowire according to the present invention includes a process for forming the porous support, and a process for synthesizing the nanowire structure in the porous support and performing the heat treatment process to maximize a seebeck coefficient.

Particularly, in the process, a porous alumina (Al₂O₃) template may be used as the porous support, and it is preferable to perform the process for synthesizing the nanowire of bismuth telluride (Bi₂Te₃) in an inert atmosphere, that is, an inert container filled with any one gas selected from helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn), and the process is performed in an inert atmosphere of argon in the present embodiment.

Furthermore, in the present invention, the seebeck coefficient may be maximized using the heat treatment after the nanowire of bismuth telluride (Bi₂Te₃) is synthesized, and particularly the heat treatment may be preferably performed at a temperature in the range of 423 to 475 K. However, the Te component is evaporated at a temperature other than the above heat treatment temperature range to reduce thermoelectric efficiency and, more particularly, tellurium (Te) is evaporated during the heat treatment process at a temperature other than the above heat treatment temperature range to reduce the seebeck coefficient, thus reducing thermoelectric efficiency.

With reference to FIG. 2, in respects to the result of the heat treatment at each temperature after the nanowire is synthesized in the porous support, the seebeck coefficient of the nanowire at the heat treatment temperature of 423 K is slightly increased 57 μV/K as compared to the seebeck coefficient of the nanowire before the heat treatment, and the seebeck coefficient is increased to 62 μV/K as the heat treatment temperature is increased to 475 K. That is, the single crystal nanowire is formed at 423 to 475 K, the seebeck coefficient is increased to 57 to 62 μV/K, the tellurium crystallite is formed in the nanowire at 523 K to cause Bi₄Te₅-Te morphology separation, and a known stoichiometric composition of Bi₂Te₃ is changed through an intermediate of Bi₄Te₅ (523 K) to Bi₄Te₃ in a Bi-rich state at 673 K due to melting of the tellurium crystallite and evaporation of the tellurium component.

Therefore, when the heat treatment temperature is increased to 523 K, the seebeck coefficient of the nanowire is rapidly reduced to 19 μV/K by about 64%. Furthermore, when the heat treatment temperature is increased again to 673 K, the seebeck coefficient is slightly increased to 29 μV/K. The surface area exposed due to a morphological characteristic of the nanowire depending on the heat treatment temperature is large to evaporate a large amount of the tellurium (Te) component, accordingly, the chemical composition of the nanowire becomes non-uniform, thus reducing the seebeck coefficient. Moreover, the seebeck coefficient as a function of a charge concentration of the thermoelectric material is reduced due to the heat treatment under the non-optimized condition. Particularly, when the heat treatment temperature is increased from 523 K to 673 K, the seebeck coefficient is slightly increased due to recrystallization of the tellurium (Te) component to slightly improve the crystallinity, not increasing thermoelectric efficiency.

2. Second embodiment

In the method for improving thermoelectric efficiency of the thermoelectric nanowire according to the first embodiment of the present invention, the heat treatment is performed at a temperature in the range of 423 to 475 K, and tellurium is evaporated to reduce the seebeck coefficient at a temperature other than the temperature range. Therefore, in the second embodiment, a description of extension of a limit of the temperature regarding an increase in thermoelectric efficiency using a process of FIG. 2 is given to avoid the reduction.

In FIG. 3, the process according to the present invention includes a first process of synthesizing the nanowire of bismuth telluride (Bi₂Te₃) in a porous support and a second process of receiving the nanowire of the bismuth telluride (Bi₂Te₃) in a sealing boat separated from an atmosphere and including inert gas to perform heat treatment. Particularly, in the second process, the heat treatment is performed in the sealing boat filled with tellurium powder.

That is, unlike the heat treatment process of the first embodiment, the nanowire sample of bismuth telluride is synthesized, and received in a structure that is completely sealed (hereinafter, referred to as 'sealing boat') before the heat treatment, and the sealing boat is then sealed using an alumina paste to prevent the evaporation of the tellurium component. Particularly, it is more preferable to fill the sealing boat with the tellurium powder before the sealing.

Furthermore, it is more preferable to perform a preparation process before the heat treatment in a container such as a glove box filled with Ar to prevent a contact with the atmosphere.

3. Experimental example and comparative example

A description is given of a change in seebeck coefficient depending on the method for improving thermoelectric efficiency including the heat treatment process according to the present invention below.

(1) Experimental example 1

The preferable range of the heat treatment temperature of the present invention is 423 to 475 K, the heat treatment is performed at the temperature of the lower limit of 423 K, and the results at the temperatures of 523 K and 673 K are given for comparison.

First, in the experimental example regarding the first embodiment of the present invention, the porous alumina template was produced using the two-step anodization process in the 0.3 M oxalic acid under the condition of application voltage of 40 V. Subsequently, the nanowire of bismuth telluride was synthesized in the porous alumina template using the pulse electroplating process to which the on time of 5 ㎳ and the off time of 50 ㎳ were applied, and the bismuth telluride overgrown film was formed over the porous alumina template.

Particularly, in this case, the synthesized nanowire had the diameter of 50 ㎚ and the length of 20 ㎛. The nanowire of bismuth telluride synthesized in the porous alumina template was heat treated at the temperatures of 423 K, 523 K, and 673 K in an inert atmosphere for 4 hours.

The crystallinity of the nanowire was analyzed using the XRD, the HRTEM (high resolution transmission electron microscopy), and the SAED (selected area transmission electron microscopy), and the chemical composition of the nanowire heat treated at each temperature was analyzed using the EDX. Only the nanowire was dispersed in the TEM grid using the selective dissolution of the porous alumina template to perform the analysis.

The Au (gold) layer was deposited using the mask, the copper blocks came into contact with both ends thereof and then with the peltier element to cause a difference of 15 K in temperature of both ends, thus measuring the seebeck coefficient. The electric potential thusly formed was measured to measure the seebeck coefficient of the nanowire heat treated at each temperature.

The result of the seebeck coefficient of the nanowire measured from the above results is described below.

FIG. 4 shows a change in component of bismuth telluride depending on the heat treatment, and from the shown graph, it was confirmed that the complex of the bismuth oxygen layer and the tellurium oxygen layer was formed on the surface of the synthesized nanowire of bismuth telluride. Like the EDX result, from the result of the detection of the oxygen component only on the upper and the lower sides of the measured part, it can be seen that the oxygen layer is formed on the surface of the nanowire.

Furthermore, FIG. 5 shows comparison of the chemical compositional ratios of the nanowire heat treated at each temperature. The chemical compositional ratio is a Te/Bi ratio. The chemical compositional ratio is reduced as the heat treatment temperature is increased, which means that the tellurium component is reduced as the heat treatment temperature is increased. That is, this is because the tellurium crystallite is formed in the nanowire at 523 K to cause Bi₄Te₅-Te morphology separation, and because a known stoichiometric composition of Bi₂Te₃ is changed through an intermediate of Bi₄Te₅ (523 K) to Bi₄Te₃ in a Bi-rich state at 673 K due to melting of the tellurium crystallite and evaporation of the tellurium component.

Therefore, from the result of the heat treatment of bismuth telluride according to the present invention, it can be seen that a possibility of evaporation is increased during the heat treatment process due to high vapor pressure of the tellurium component, which is caused by the relatively larger surface area of the nanowire as compared to the bulk material or the thin film. However, the molar ratio of Te/Bi atoms is 0.8 to 1.5 at the heat treatment temperature of 423 K, which means a stable state and that reliability is obtained because of a very narrow range of change of the component.

From FIGS. 6 and 7, it can be seen that black spots (crystallite) are irregularly formed in the nanowire heat treated at 523 K, including only the tellurium (Te) component confirmed by the EDX analysis, and that the tellurium component is reduced in the other nanowires. However, when the heat treatment temperature is increased to 673 K, the black spots (crystallite) are removed, which is because the black spots are decomposed and dissolved as the heat treatment temperature is increased, in terms of the chemical composition of the nanowire heat treated at 623 K, the tellurium (Te) component is continuously reduced.

FIG. 8 shows the results of the crystallinity of the nanowire at 423 K, 523 K, and 673 K in the experiment analyzed using the SAED.

With reference to the images treated at the temperatures of 423 K, 523 K, and 673 K in the drawing, from the SAED of the nanowire heat treated at 423 K, it can be seen that the nanowire has a single crystal and a hexagonal Bi₂Te₃ phase in (205), (110), and (0015) directions as shown in bright spots. Moreover, a growth direction of the nanowire is perpendicular to a c-axis [00ℓ].

The ring form of crystallinity of the nanowire at the heat treatment temperature of 523 K means that the nanowire has a polycrystal, and from information of the bright spots, it can be seen that the nanowire includes the complex of the Bi₄Te₅ phase in (0011) and (0027) directions and the tellurium (Te) crystallinity. This is because the polycrystalline nanowire includes Bi₄Te₅ and Te.

When the heat treatment temperature finally approaches 673 K, the nanowire has the single crystal, and like at 423 K, the nanowire grows in a direction perpendicular to the c-axis and has the hexagonal Bi₄Te₃ phase in (003), (009), and (0021) directions.

When the heat treatment temperature is increased from 523 K to 623 K, changing of the polycrystal to the single crystal may be understood by recrystallization of the tellurium (Te) component, and the crystal is changed to the Bi₄Te₃ phase in the most stable state due to the black spot evaporation of pure tellurium. It can be seen that this result conflicts with the result that the bismuth telluride thin film synthesized at 600 K using the molecular beam epitaxy has the Bi₄Te₃ phase.

Therefore, a change in crystallinity and component at the temperature of 523 K and 623 K does not improve thermoelectric efficiency of bismuth telluride, and thermoelectric efficiency is maximized at the preferable heat treatment temperature of 423 to 475 K according to the present invention.

Particularly, this result can be confirmed from the graph showing a change in seebeck coefficient of the nanowire of bismuth telluride depending on the heat treatment temperature in FIG. 9.

With reference to the drawing, all the measured seebeck coefficients have the positive values, which is the evident showing that the nanowire of bismuth telluride synthesized under the above experiment condition has a P-type form, and that holes form a major charge concentration due to the excessive amount of bismuth component.

In this case, the seebeck coefficient of the nanowire at the heat treatment temperature of 423 K is measured to be 57 μV/K slightly increased as compared to the seebeck coefficient of the nanowire before the heat treatment, which is not caused by a reduction in charge concentration during the heat treatment at 423 K but by an improvement in crystallinity. Moreover, the seebeck coefficient is increased to 62 μV/K at 475 K, which means that thermoelectric efficiency is rapidly increased.

However, when the heat treatment temperature is increased to 523 K, the seebeck coefficient of the nanowire is rapidly reduced to 19 μV/K by about 64%. Furthermore, when the heat treatment temperature is increased to 673 K, the seebeck coefficient is slightly increased to 29 μV/K but this corresponds to a value that is significantly lower than that before the heat treatment.

To sum up, when the heat treatment temperature is increased, evaporation occurs due to high vapor pressure of the tellurium (Te) component, the nanowire includes pure tellurium (Te) and the Bi₄Te₅ phase at 523 K, the pure tellurium component is decomposed at a high temperature of 623 K to be converted into the Bi₄Te₃ phase of the single crystalline component due to the recrystallization while the chemical composition (Bi₂Te₃) of the known nanowire is broken due to the evaporation of the tellurium component, thus reducing the seebeck coefficient. Therefore, in the method for improving thermoelectric efficiency of the thermoelectric nanowire of bismuth telluride according to the present invention, the heat treatment is performed at the temperature of 423 to 475 K to maximize the seebeck coefficient. When the heat treatment temperature is increased, crystallinity is slightly improved due to recrystallization of the tellurium (Te) component to slightly increase the seebeck coefficient but not to increase thermoelectric efficiency.

(2) Experimental example 2

Experimental example 2 provides the process condition for overcoming the fact that an increase in seebeck coefficient for improving thermoelectric efficiency has a limit depending on the heat treatment temperature in the second embodiment.

Unlike a known heat treatment process, the tellurium powder is added to the sealing boat for heat treatment before the nanostructure sample of bismuth telluride is heat treated, and the sealing boat including the sample is completely sealed using an alumina paste to prevent the evaporation of the tellurium component. Particularly, the sample preparation process is performed in the glove box filled with Ar to prevent a contact with the atmosphere. With respect to the process condition of the heat treatment, the heat treatment is performed at the temperature of 423 K, 473 K, 523 K, 573 K, 623 K, and 673 K for 4 hours in the quartz chamber filled with nitrogen.

FIG. 10 is a result graph according to the process condition, showing a molar ratio of atoms of Bi and Te, FIG. 10A shows the molar ratio before the heat treatment, and FIG. 10B shows the molar ratio after the heat treatment at 623 K. From comparison of FIGS. 10A and 10B, it can be seen that even though the heat treatment temperature is largely increased, the amounts of tellurium components are almost the same as each other before and after the heat treatment, which is because the tellurium component is prevented from evaporating.

FIG. 11 is a graph showing a change in seebeck coefficient of bismuth telluride according to the heat treatment temperature in experimental example 2.

From the graph, it can be seen that the seebeck coefficient has the maximum value at about 350°C (623 K), the seebeck coefficient is increased even at the heat treatment temperature that is far higher than the temperature of the first embodiment, and particularly, the seebeck coefficient is increased up to three times in the range of 573 to 673 K. That is, the tellurium component is completely prevented from evaporating using the process of the second embodiment according to the present invention, and the seebeck coefficient of the nanostructure of bismuth telluride and crystallinity are improved using the improved heat treatment process to improve electrical conductivity, thus improving a ZT value as an index of thermoelectric efficiency (performance index).

(3) Experimental example 3

In experimental example 3, unlike the nanowire structures of the first and the second embodiments, a description is given of application of a bulk type of structure (pellet and ingot), that is, a bulk type of Bi-Te material to the method for improving thermoelectric efficiency according to the present invention.

When 30 g of the p-type Bi-Te bulk pellet of Bi_0.25Sb_0.75Te₃ is produced, the experimental condition is as follows. In the present invention, synthesis of the Be-Sb-Te powder using bismuth, antimony, and tellurium is described as an example thereof.

To be specific, after 20.89 g, 36.52 g, and 76.56 g of powders of bismuth, antimony, and tellurium having the purity of 5 N (99.999%) were added to the glass quartz, the quartz was completely sealed using the torque to prevent a contact with the atmosphere. After the heat treatment is performed at 800°C for 10 hours to alloy the constitutional compounds, Bi-Sb-Te powder having a nanograin size is obtained using ball-milling and a sieve of 45 μm.

The Bi-Sb-Te powder as a basic material is added to a graphite mold to obtain a bulk type of pellet sample using a hot pressing process. The experimental condition of the hot pressing includes 420°C, 200 MPa, and 30 min.

The bulk type of pellet sample was heat treated in the quartz chamber filled with nitrogen to 623 K after the tellurium powder was added using the same process as the first and the second embodiments and provided to the sealing boat sealed using the alumina paste. Since the surface area of the pellet sample is relatively lower than that of the nanostructure, the seebeck coefficient is increased by 50% or more and less than three times to improve thermoelectric efficiency.

Even when the sample of the thermoelectric material produced using the improved method of the second embodiment and experimental example 2 under the present patent condition is a bulk type or a nanostructure type, in the case of the bulk type, the powder of the pellet is scrapped to obtain a chemical compositional ratio of an internal structure using a TEM EDX analysis. That is, from FIG. 10, it can be seen that an atomic percentage of Bi and Te is maintained at a ratio of 40%:60%. The stoichiometric composition is maintained because the heat treatment is performed under the present patent condition. Therefore, it is preferable that the thermoelectric material formed using the heat treatment process of the second embodiment has a compositional ratio of Bi to Te of 2:3, as a result of EDX analysis.

In the case of the nanostructure to which the method for improving thermoelectric efficiency according to the present invention is applied, the internal chemical compositional ratio may be obtained using a nanowire type, a nanotube type, or a nanodot type of TEM EDX analysis and is 2:3.

While the invention has been shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.

Claims

A method for improving a thermoelectric efficiency of a thermoelectric material, comprising:

a first process of synthesizing the thermoelectric material comprising bismuth telluride (Bi₂Te₃); and

a second process of performing heat treatment of the thermoelectric material in a sealing boat which is separated from an atmosphere and filled with inert gas wherein the sealing boat receives a tellurium powder.
The method of claim 1, wherein the synthesizing of the thermoelectric material comprising the bismuth telluride (Bi₂Te₃) comprises a process of synthesizing a nanowire structure of the bismuth telluride (Bi₂Te₃) in a porous support.
The method of claim 2, wherein the synthesizing of the nanowire structure of the bismuth telluride (Bi₂Te₃) is synthesizing the nanowire in the porous support of alumina (Al₂O₃) using a pulse plating process.
The method of claim 1, wherein the synthesizing of the thermoelectric material including the bismuth telluride (Bi₂Te₃) includes heat treating bismuth and tellurium powders to form a nano-sized Bi-Te powder, and processing the Bi-Te powder to synthesize a bulk type structure.
The method of claim 4, wherein the processing of the Bi-Te powder to synthesize the bulk type of structure includes adding the Bi-Te powder to a mold to form the bulk type of structure using a hot pressing.
The method of claim 2 or 4, wherein the heat treatment is performed at 573.15 K to 673.15 K.
The method of claim 1, wherein the inert gas is selected from a group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).
The method of claim 1, wherein the sealing boat is sealed using an alumina paste.
The method of claim 8, wherein the heat treatment is performed in a quartz chamber filled with nitrogen.
A thermoelectric material produced using the method of claim 1 having a chemical compositional ratio of Bi to Te is 2:3.
The thermoelectric material of claim 10, wherein the thermoelectric material has a nanowire structure or a bulk type structure.
The thermoelectric material of claim 10, wherein a nanowire of the bismuth telluride (Bi₂Te₃) is form of a single crystal, and comprises a hexagonal Bi₂Te₃ phase in (205), (110), and (0015) directions.
The thermoelectric material of claim 12, wherein a growth direction of the nanowire is perpendicular to a c-axis [00ℓ].
A support comprising:

a porous support; and

a nanowire of bismuth telluride formed using the method according to claim 1 in the porous support and having the chemical compositional ratio of Bi to Te of 2:3.
The support of claim 14, wherein the porous support comprises the thermoelectric material of porous alumina (Al₂O₃).