KR20220070669A - BiSbTe-based thermoelectric material with Gd-based oxide in which nanomaterials are dispersed in the matrix and method of manufacturing the same - Google Patents

Abstract

The present invention provides a BiSbTe-based thermoelectric material having excellent thermoelectric properties by including a Bi-containing nanomaterial dispersed in a BiSbTe-based base material. According to an embodiment of the present invention, the BiSbTe-based thermoelectric material includes gadolinium-based oxide dispersed in a Bi_aSb_bTe_c alloy (a in the Bi_aSb_bTe_c alloy is 0.4 to 0.6, b is 1.2 to 1.6, and c is 2.7 to 3.3).

Description

BiSbTe-based thermoelectric material with Gd-based oxide in which nanomaterials are dispersed in the matrix and method of manufacturing the same

The technical idea of the present invention relates to a thermoelectric material, and more particularly, to a hierarchical BiSbTe-based thermoelectric material including a gadolinium-based oxide provided as Gd _2-x Bi _x O ₃ in the BiSbTe-based thermoelectric material, and a method for manufacturing the same will be.

Thermoelectric devices are attracting attention because they can be applied in various ways in the field of energy conversion. For example, the energy conversion field includes power generation due to the Seebeck effect and active cooling due to the Peltier effect. The efficiency of these thermoelectric materials can be expressed using a dimensionless figure of merit.

Bi ₂ Te ₃ -based materials are widely used as thermoelectric devices at room temperature. Many studies are being conducted to improve the thermoelectric reaction of the Bi ₂ Te ₃ -based materials, for example, research is being conducted on process control, microstructure design, compositional precision control, and the like. In addition, Bi ₂ Te ₃ may be synthesized by physical and chemical methods. In general, the physical methods include evaporation, sputtering and spray pyrolysis and the like. The chemical methods include electrochemical deposition, electrolytic deposition, hydrothermal process, and solvothermal synthesis process. Chemical methods can precisely control particle size and particle size distribution, but are risky. On the other hand, physical methods can determine the microstructure and other properties of thermoelectric materials, but they depend entirely on the process temperature and pressure. Accordingly, there is an increasing demand for a thermoelectric material having increased thermoelectric properties and an improved method for manufacturing the thermoelectric material.

The technical problem to be achieved by the technical idea of the present invention is a hierarchical BiSbTe-based oxide containing a gadolinium-based oxide having excellent thermoelectric properties by including Gd _2-x Bi _x O ₃ (0<x<0.03) in a base material provided as a BiSbTe-based material. To provide a thermoelectric material and a method for manufacturing the same.

However, these tasks are exemplary, and the technical spirit of the present invention is not limited thereto.

The hierarchical BiSbTe-based thermoelectric material including a gadolinium-based oxide according to the technical spirit of the present invention for achieving the above technical object may include a gadolinium-based oxide dispersed in a Bi _a Sb _b Te _c alloy.

(In the Bi _a Sb _b Te _c alloy, a is 0.4 to 0.6, b is 1.2 to 1.6, and c is 2.7 to 3.3.)

In an embodiment of the present invention, the gadolinium-based oxide may be Gd _2-x Bi _x O ₃ (0<x<0.03).

In an embodiment of the present invention, the Bi _a Sb _b Te _c alloy may include Bi _0.5 Sb _1.5 Te ₃ .

In an embodiment of the present invention, the Gd _2-x Bi _x O ₃ nanoparticles may include Gd _1.98 Bi _0.02 O ₃ .

In an embodiment of the present invention, the Gd _2-x Bi _x O ₃ nanoparticles may be included in an amount of 1 to 3 wt% based on the total weight of the BiSbTe-based thermoelectric material.

In an embodiment of the present invention, the Gd _2-x Bi _x O ₃ nanoparticles may have a size in the range of 10 to 100 nm.

삼방정계 구조를 가질 수 있다.In one embodiment of the present invention, the BiSbTe-based thermoelectric material

It may have a trigonal structure.

A method for manufacturing a hierarchical BiSbTe-based thermoelectric material including a gadolinium-based oxide according to the technical idea of the present invention for achieving the above technical object is Bi _, Sb And forming a powder of the base material consisting of Te; forming a bismuth-containing gadolinium oxide powder; forming a composite mixed powder by mixing the powder of the base material and the bismuth-containing gadolinium oxide powder; ball milling the composite powder mixture; and spark plasma sintering of the composite mixed powder.

In one embodiment of the present invention, Bi _, Sb And forming the powder of the base material consisting of Te, Bi, Sb, and Te mixing in a stoichiometric composition to form a mixture; melting the mixture; and atomizing the molten mixture to form a powder of a base material composed of Bi _a Sb _b Te _c .

(In the Bi _a Sb _b Te _c alloy, a is 0.4 to 0.6, b is 1.2 to 1.6, and c is 2.7 to 3.3.)

In an embodiment of the present invention, the melting may be performed in an argon gas atmosphere using a high-frequency induction furnace, and the atomizing may be performed in a nitrogen atmosphere using a gas atomizer.

In one embodiment of the present invention, the forming of the bismuth-containing gadolinium oxide powder comprises: forming a mixed solution in which gadolinium nitride, a bismuth nitride precursor, and ethylene glycol are mixed; atomizing the mixed solution using an ultrasonic atomizer to form droplets; reacting the droplets in a quartz reactor at a temperature in the range of 850 to 950° C. to form a reactant; extracting powder from the reactant using a filter; and heat-treating the powder in an oxidizing atmosphere at a temperature in the range of 950 to 1050° C. to form the bismuth-containing gadolinium oxide powder.

In an embodiment of the present invention, the ball milling step includes a weight ratio of the milling balls to the composite mixed powder in the range of 10:1 to 20:1, a milling speed in the range of 500 to 1000 rpm, and 10 minutes to 30 minutes. It can be performed for a range of ball milling times.

In one embodiment of the present invention, the spark plasma sintering step may be performed at a temperature in the range of 400 to 500 ℃ and a pressure of 30 to 70 MPa.

In an embodiment of the present invention, the BiSbTe powder may include Bi _0.5 Sb _1.5 Te ₃ . The bismuth-containing gadolinium oxide powder may include Gd _1.98 Bi _0.02 O ₃ .

In the BiSbTe-based thermoelectric material including the Bi-containing nanomaterial dispersed in the base material and the manufacturing method thereof according to the technical concept of the present invention, Gd _1.98 Bi _0.02 O ₃ nanoparticles as a rare earth oxide containing bismuth using a simple chemical solution process Gd ₂ O ₃ nanoparticles can be easily formed as a rare earth oxide that does not contain ions and bismuth.

BiSbTe/Gd _1.98 Bi _0.02 O ₃ thermoelectric material formed by adding 2 wt% of Gd _1.98 Bi _0.02 O _{3 to} a BiSbTe-based base material increases electrical conductivity by increasing carrier concentration, whereas substitution of bismuth is Structure and charge carrier concentration can be preserved. In addition, the BiSbTe/Gd _1.98 Bi _0.02 O ₃ thermoelectric material increases the Seebeck coefficient due to an increase in effective mass by carrier energy filtering, whereas phonon scattering is reduced by the Gd _1.98 Bi _0.02 O ₃ nanoparticles. As it increases, the thermal conductivity is significantly reduced, and the thermal conductivity is reduced by about 9% compared to the BiSbTe-based base material. As a result, the BiSbTe/Gd _1.98 Bi _0.02 O ₃ thermoelectric material has a maximum figure of merit (ZT) of 0.87 at 300K, which is about 30% higher than that of the BiSbTe-based base material.

From these results, the BiSbTe/Gd _1.98 Bi _0.02 O ₃ thermoelectric material formed by combining the BiSbTe-based base material and Gd _1.98 Bi _0.02 O ₃ , a rare earth oxide containing bismuth, can improve the thermoelectric properties of BiSbTe-based materials. Also, in the present invention, the inclusion of bismuth in gadolinium oxide can reduce the source of defects in the structure of the synthesized Gd ₂ O ₃ .

The above-described effects of the present invention have been described by way of example, and the scope of the present invention is not limited by these effects.

1 is a flowchart illustrating a method of manufacturing a BiSbTe-based thermoelectric material according to an embodiment of the present invention.
2 is a flowchart illustrating a step of forming a BiSbTe powder in the method for manufacturing the BiSbTe-based thermoelectric material of FIG. 1 according to an embodiment of the present invention.
3 is a flowchart illustrating a step of forming a bismuth-containing gadolinium oxide powder in the method for manufacturing the BiSbTe-based thermoelectric material of FIG. 1 according to an embodiment of the present invention.
4 is a schematic diagram illustrating an exemplary spray pyrolysis apparatus for performing the step of forming a bismuth-containing gadolinium oxide powder in a method for manufacturing a BiSbTe-based thermoelectric material according to an embodiment of the present invention.
5 is a transmission electron microscope photograph and EDS mapping photographs of Gd _1.98 Bi _0.02 O ₃ nanoparticles included in the BiSbTe-based thermoelectric material according to an embodiment of the present invention.
6 is a graph showing X-ray diffraction patterns of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.
7 is a transmission electron micrograph of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.
8 is a graph showing electrical conductivity according to temperature of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.
9 is a graph illustrating a Seebeck coefficient according to a temperature of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.
10 is a graph illustrating a power factor according to temperature of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.
11 is a graph illustrating thermal conductivity according to temperature of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.
12 is a graph showing lattice thermal conductivity according to temperature of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.
13 is a graph showing the figure of merit according to the temperature of the BiSbTe-based thermoelectric material according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are provided to more completely explain the technical idea of the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, The scope of the technical idea is not limited to the following examples. Rather, these embodiments are provided to more fully and complete the present disclosure, and to fully convey the technical spirit of the present invention to those skilled in the art. In this specification, the same reference numerals refer to the same elements throughout. Furthermore, various elements and regions in the drawings are schematically drawn. Accordingly, the technical spirit of the present invention is not limited by the relative size or spacing drawn in the accompanying drawings.

The efficiency of thermoelectric materials is given as a dimensionless figure of merit (ZT), and is expressed by Equation 1 below.

<Equation 1>

where σ is the electrical conductivity, S is the seebeck coefficient, (σS ² ) is the power factor, κ is the thermal conductivity, and T is the absolute temperature. .

According to Equation 1, the performance of the thermoelectric material can be increased as it has a high power factor and low thermal conductivity.

According to a recent study, when nano-structured nanoparticles are interposed in a BiSbTe-based base material, thermal conductivity is reduced, and a high figure of merit (ZT) can be achieved. In addition, according to another study, carrier scattering at the interfaces is generated through the energy filtering effect, and the power factor is increased by increasing the Seebeck coefficient, and consequently the figure of merit can be increased. In addition, in the case of the Bi ₂ Te ₃ nanocomposite, thermoelectric properties can be increased by dispersion through mechanical milling and coalescence by spark plasma sintering.

In order to increase the figure of merit of the thermoelectric material, there are several methods for reducing the thermal conductivity. For example, there is a method of incorporating nano-sized particles such as BN, ZrO ₂ , and C ₆₀ in a Bi ₂ Te ₃ material. In the study of Kim et al., the thermal conductivity was reduced by incorporating 4 wt% Ta ₂ O ₅ nanoparticles at room temperature, thus achieving a high figure of merit (ZT) of 1.38. In the study of Lu et al., using 1 mol% MnTe nanoparticles dispersed by ball milling for 3 hours, a figure of merit (ZT) of 1.37 was achieved at 348 K, which is pure Bi _0.52 Sb _1.48 Te ₃ showed an improvement of 10% compared to 1.24 of The increase in the figure of merit (ZT) by adding MnTe in the base material may increase the interfacial phonon scattering between the host and the nano-dispersion, thereby reducing the lattice thermal conductivity.

The technical idea of the present invention is to provide a hierarchical BiSbTe-based thermoelectric material including a gadolinium-based oxide dispersed in a Bi _a Sb _b Te _c alloy. (In the Bi _a Sb _b Te _c alloy, a is 0.4 to 0.6, b is 1.2 to 1.6, and c is 2.7 to 3.3.)

As used herein, the gadolinium-based oxide refers to nanoparticles in which gadolinium (Gd) is combined with oxygen (O), and the gadolinium-based oxide is a gadolinium-based oxide including a predetermined rare earth element (R) Ge _2-x R _x O ₃ ( 0<x<0.03).

The predetermined rare earth element (R) may include any one or more elements selected from the group consisting of bismuth (Bi), anion (Sb), and arsenic (As). In the present invention, an example in which bismuth (Bi) is included as the rare earth element will be described, but the present invention is not limited thereto.

According to an embodiment, when a certain amount of the gadolinium-based oxide containing the rare earth element is added, phonon scattering is increased to increase the power factor, and at the same time, thermal conductivity can be reduced, and the figure of merit can be improved.

On the other hand, when the rare earth is excessively contained in the gadolinium-based oxide, the carrier concentration may decrease, thereby reducing electrical conductivity. As a result, thermoelectric efficiency of the thermoelectric material may be reduced.

For this reason, in the gadolinium-based oxide (Ge _2-x R _x O ₃ ), x is preferably greater than 0 and less than 0.03, more preferably 0.01 to 0.02, even more preferably Gd _1.98 Bi _0.02 It may be provided as O ₃ .

That is, the present invention provides a thermoelectric material with excellent thermoelectric properties by forming Gd _1.98 Bi _0.02 O ₃ nanoparticles by a simple method and dispersing the Gd _1.98 Bi _0.02 O ₃ nanoparticles in a Bi _0.5 Sb _1.5 Te ₃ composite. will be.

According to an embodiment, the gadolinium-based oxide (Ge _2-x R _x O ₃ ) may be included in an amount of 1 to 3 wt% in the BiSbTe-based thermoelectric material.

When the gadolinium-based oxide powder is included in less than 1% by weight, the amount of the gadolinium-based oxide powder included in the base material is insufficient, so it is difficult to expect an effect of increasing the carrier concentration. In addition, it is difficult to expect improvement in electrical properties such as increased phonon scattering and reduced thermal conductivity due to the gadolinium-based oxide powder.

Conversely, when the gadolinium-based oxide powder exceeds 3 wt%, the gadolinium-based oxide in the base material is excessive and may act as an impurity that interferes with the flow of electrons in the base material. This may cause the electrical conductivity to decrease, which in turn may cause the figure of merit to decrease. For this reason, the gadolinium-based oxide is preferably included in an amount of 1 to 3 wt%, and more preferably 2 wt%.

According to the present invention, a novel method for preparing rare earth oxides containing bismuth is proposed, and the preparation of rare earth oxides containing bismuth (2% by weight of Gd _1.98 Bi _0.02 O ₃ ) into p-type Bi _0.5 Sb _1.5 Te ₃ based composites. to analyze the effect. Interestingly, the rare earth oxide with bismuth dispersed in the BiSbTe (2 wt% Gd _1.98 Bi _0.02 O ₃ ) has increased phonon scattering compared to the rare earth oxide without bismuth (2 wt% Gd ₂ O ₃ ). As a result, the power factor can be increased and the thermal conductivity can be reduced at the same time, and consequently the figure of merit can be increased.

In the present invention, Gd ₂ O ₃ was selected from among the rare earth oxides as the dispersant. The reason is that the Gd ₂ O ₃ has various properties such as high mechanical strength and a large optical bandgap. In fact, gadolinium has not been found naturally as a pure metal to date, the most common chemical being found as trivalent gadolinium oxide (Gd ³⁺ ). The oxide can also be used in other important applications, such as magnetic resonance, fluorescence imaging, and doping control of heat-treated nanocomposites. By controlling the lattice disorder during growth through spray pyrolysis, bismuth-containing nanomaterials and bismuth-free nanomaterials can be prepared. These nanomaterials can be dispersed in Bi _0.5 Sb _1.5 Te ₃ by combining ball milling and spark plasma sintering.

1 is a flowchart illustrating a method ( S100 ) of manufacturing a BiSbTe-based thermoelectric material according to an embodiment of the present invention.

Referring to FIG. 1 , the method for manufacturing the BiSbTe-based thermoelectric material ( S100 ) includes forming a powder of a base material including Bi, Sb and Te ( S110 ); Forming a bismuth-containing gadolinium oxide powder (S120); mixing the powder of the base material and the bismuth-containing gadolinium oxide powder to form a composite mixed powder (S130); ball milling the composite powder mixture (S140); and sintering the composite mixed powder with spark plasma (S150).

First, the step (S110) of forming a powder of the base material including the Bi, Sb and Te is performed.

FIG. 2 is a flowchart illustrating a step (S110) of forming a powder of a base material including Bi, Sb, and Te in the method (S100) of manufacturing the BiSbTe-based thermoelectric material of FIG. 1 according to an embodiment of the present invention.

Referring to FIG. 2 , the step of forming the powder of the base material including Bi, Sb, and Te (S110) in the above is a step of forming a mixture by mixing Bi, Sb, and Te in a stoichiometric composition (S111) ; melting the mixture (S112); and atomizing the molten mixture to form the BiSbTe powder (S113).

The melting step ( S112 ) may be performed in an argon gas atmosphere using a high-frequency induction furnace.

The atomizing step (S113) may be performed in a nitrogen gas atmosphere using a gas atomizer, and as a result, powder of the base material including Bi, Sb and Te may be formed in the above. The powder of the base material may be provided as Bi _0.5 Sb _1.5 Te ₃ , but this is exemplary and the technical spirit of the present invention is not limited thereto.

Subsequently, the step of forming the bismuth-containing gadolinium oxide powder of FIG. 1 ( S120 ) is performed.

3 is a flowchart illustrating a step (S120) of forming a bismuth-containing gadolinium oxide powder in the method (S100) of manufacturing the BiSbTe-based thermoelectric material of FIG. 1 according to an embodiment of the present invention.

Referring to FIG. 3 , the step of forming the bismuth-containing gadolinium oxide powder (S120) includes forming a mixed solution in which gadolinium nitride, a bismuth nitride precursor, and ethylene glycol are mixed (S121); Atomizing the mixed solution using an ultrasonic atomizer to form droplets (droplet) (S122); forming a reactant by reacting the droplets at a temperature in the range of 850 to 950° C. in a quartz reactor (S123); extracting powder from the reactant using a filter (S124); and heat-treating the powder in an oxidizing atmosphere at a temperature in the range of 950 to 1050° C. to form the bismuth-containing gadolinium oxide powder (S125).

The gadolinium nitride, bismuth nitride precursor, and ethylene glycol are exemplary, and the technical spirit of the present invention is not limited thereto.

4 is a schematic diagram illustrating an exemplary spray pyrolysis apparatus for performing the step (S120) of forming bismuth-containing gadolinium oxide powder in the method for manufacturing a BiSbTe-based thermoelectric material according to an embodiment of the present invention.

Referring to FIG. 4 , in the spray pyrolysis apparatus, Gd _1.98 Bi _0.02 O ₃ nanoparticles may be formed as the bismuth-containing gadolinium oxide powder, and Gd ₂ O ₃ may be formed as a comparative example.

The mixed solution is transferred using a peristatic pump, and a carrier gas such as air is transferred through a separate path and charged into an ultrasonic nebulizer. The carrier gas is delivered at a flow rate of about 45 L/min. The ultrasonic atomizer may have six vibrators of 1.7 MHz and may be cooled by cooling water. In the ultrasonic atomizer, the mixed solution is atomized to form droplets. The droplets are charged into a quartz reactor maintained at a temperature in the range of 850 to 950° C. by air at a flow rate of 40 L/min, and react to form reactants. The dimensions of the quartz reactor may for example have a diameter of 55 mm and a length of 150 cm. The reactant is powdered by a Teflon bag filter. The residue may be discharged into a hood and filtered by a trap.

Referring back to FIG. 1 , a step ( S130 ) of forming a composite powder mixture by mixing the powder of the base material and the bismuth-containing gadolinium oxide powder is performed. At this time, as described above, the bismuth-containing gadolinium oxide powder is preferably included in an amount of 1 to 3% by weight based on the total amount of the composite mixed powder. As described above, when the gadolinium-based oxide powder is included in less than 1% by weight, It is difficult to expect the effect of increasing the carrier concentration because the amount of gadolinium-based oxide powder included in the base material is insufficient, and electrical properties such as increased phonon scattering and reduced thermal conductivity are expected due to the gadolinium-based oxide powder hard to do

Conversely, when the gadolinium-based oxide powder exceeds 3 wt%, the gadolinium-based oxide in the base material is excessive and may act as an impurity that interferes with the flow of electrons in the base material. This may cause the electrical conductivity to decrease, which in turn may cause the figure of merit to decrease. For this reason, the gadolinium-based oxide is preferably included in an amount of 1 to 3 wt%, and more preferably 2 wt%.

Then, the step (S140) of ball milling the composite mixed powder of FIG. 1 is performed. The ball milling step (S140) is performed for a weight ratio of the milling ball to the composite mixed powder in the range of 10:1 to 20:1, a milling speed in the range of 500 to 1000 rpm, and a ball milling time in the range of 10 to 30 minutes. can be

Then, the spark plasma sintering step (S150) of the composite mixed powder of FIG. 1 is performed. The spark plasma sintering (S150) may be performed at a temperature in a range of 400 to 500°C and a pressure in a range of 30 to 70 MPa for 1 to 20 minutes.

BiSbTe-based thermoelectric material according to the technical spirit of the present invention, BiSbTe-based base material; and Gd _2-x Bi _x O ₃ (0<x<0.03) nanoparticles dispersed in the BiSbTe-based base material.

삼방정계 구조를 가질 수 있다.The BiSbTe-based base material may include Bi _0.5 Sb _1.5 Te ₃ . The Gd _2-x Bi _x O ₃ nanoparticles may include Gd _1.98 Bi _0.02 O ₃ nanoparticles. The Gd _2-x Bi _x O ₃ nanoparticles may be included in an amount of 1 to 3 wt%, preferably 2 wt%, based on the total weight of the BiSbTe-based thermoelectric material. The Gd _2-x Bi _x O ₃ nanoparticles may have a size in the range of 10 to 100 nm. The Gd _1.98 Bi _0.02 O ₃ nanoparticles may be configured as spheroid-shaped aggregates. The BiSbTe-based thermoelectric material is

It may have a trigonal structure.

Experimental example

Hereinafter, an experimental example according to a technical embodiment of the present invention will be described. However, the technical spirit of the present invention is not limited to the following experimental examples.

Hereinafter, "BiSbTe" refers to Bi _0.5 Sb _1.5 Te ₃ , and when described alone, refers to a Bi _0.5 Sb _1.5 Te ₃ material in which the following gadolymium-based nanomaterials are not dispersed. “BiSbTe/Gd ₂ O ₃ ” refers to a material in which 2 wt% of Gd ₂ O ₃ nanomaterials are dispersed in Bi _0.5 Sb _1.5 Te ₃ . “BiSbTe/Gd _1.98 Bi _0.02 O ₃ ” refers to a material in which 2 wt% of Gd _1.98 Bi _0.02 O ₃ nanomaterials are dispersed in Bi _0.5 Sb _1.5 Te ₃ .

[Production Example 1]

BiSbTe-based nanoparticles production

Bi, Sb, and Te as elements of high purity (99.99%, Alfa Aesar) were mixed in a stoichiometric composition to form a mixture. The mixture was charged into a graphite crucible and melted in an argon gas atmosphere using a high-frequency induction furnace. Then, the molten material melted in a nitrogen atmosphere was atomized using a gas atomizer. Accordingly, Bi _0.5 Sb _1.5 Te ₃ nanoparticles were formed as a powder.

[Production Example 2]

Gd _1.98 Bi _0.02 O ₃ Nanoparticle Manufacturing

Meanwhile, Gd ₂ O ₃ nanoparticles and Gd _1.98 Bi _0.02 O ₃ nanoparticles were formed by spray pyrolysis as follows. As starting materials, Gd(NO ₃ ) ₃ , Bi(NO ₃ ) ₃ , and C ₂ H ₆ O ₂ were used, and they were mixed to a desired composition to form a mixed solution. For example, the mixed solutions are prepared by dissolving 0.3 M of gadolinium nitride (Gd(NO ₃ ) ₃ ) in pure water, and 0.375 M of a bismuth nitride precursor (Bi(NO ₃ ) ₃ ) and ethylene glycol; C ₂ H ₆ O ₂ ) was prepared by dissolving. The mixed solutions were atomized using an ultrasonic atomizer to form droplets. The droplets are moved into a quartz reactor maintained at a temperature of about 900° C. by air at a flow rate of 40 L/min. Finally, the powder was extracted by a Teflon bag filter installed at the end of the quartz reactor. The powder was heat-treated at about 1000° C. for 3 hours in an oxidizing atmosphere. Accordingly, Gd _1.98 Bi _0.02 O ₃ nanoparticles were prepared.

[Production Example 3]

Gd _1.99 Bi _0.01 O ₃ Nanoparticle Manufacturing

In Preparation Example 2, gadolinium nitride (Gd(NO ₃ ) ₃ ) was mixed with 0.3 M, and the bismuth nitride precursor (Bi(NO ₃ ) ₃ ) was mixed with 0.18 M. All processes were performed in the same manner as in Preparation Example 1, Gd _1.99 Bi _0.01 O ₃ nanoparticles were prepared.

[Comparative Preparation Example 1]

Gd ₂ O ₃ Nanoparticle Manufacturing

In Preparation Example 2, all processes except for Bi(NO ₃ ) ₃ in the starting material were performed in the same manner as in Preparation Example 2 to form Gd ₂ O ₃ nanoparticles.

[Example 1]

BiSbTe-based nanoparticles prepared in Preparation Example 1, that is, Bi _0.5 Sb _1.5 Te ₃ nanoparticles and Gd _1.98 Bi _0.02 O ₃ nanoparticles prepared in Preparation Example 2 were synthesized, and then mixed by gas atomizing to obtain Bi _0.5 A BiSbTe/Gd _1.98 Bi _0.02 O ₃ composite powder in which Sb _1.5 Te ₃ nanoparticles and Gd _1.98 Bi _0.02 O ₃ nanoparticles are mixed was formed. At this time, Gd _1.98 Bi _0.02 O ₃ nanoparticles were mixed to be included in an amount of 2% by weight based on the entire composite mixed powder.

Then, each of the BiSbTe/Gd _1.98 Bi _0.02 O ₃ composite mixed powder was ball milled. The ball milling was mechanically milled in a zirconia vessel having a zirconia milling medium charged into a planetary ball mill operating in a glove box under a very pure argon atmosphere. In the above ball milling, a weight ratio of the milling balls to the composite mixed powder of 15:1, a milling speed of 800 rpm, and a ball milling time of 20 minutes were performed.

Finally, the composite mixed powders were sintered using a spark plasma sintering (SPS) method at a temperature of 450° C. and a pressure of 50 MPa for 10 minutes to prepare BiSbTe/Gd _1.98 Bi _0.02 O ₃ .

[Example 2]

In Example 1, Bi _0.5 Sb _1.5 Te ₃ prepared in Preparation Example 2 and Gd _1.99 Bi _0.01 O ₃ nanoparticles prepared in Preparation Example 3 were synthesized in the same manner as in Preparation Example 1, except for synthesizing the nanoparticles. to prepare BiSbTe/Gd _1.99 Bi _0.01 O ₃ .

[Comparative Example 1]

Bi _0.5 Sb _1.5 Te ₃ prepared in Preparation Example 1 is prepared.

[Comparative Example 2]

BiSbTe/Gd ₂ O ₃ was prepared in the same manner as in Preparation Example 1 except for synthesizing Gd ₂ O ₃ nanoparticles in Bi _0.5 Sb _1.5 Te ₃ prepared in Comparative Preparation Example 1 in Example 1 manufacture

[Comparative Example 3]

All processes were performed in the same manner as in Preparation Example 1, except that the Gd _1.98 Bi _0.02 O ₃ nanoparticles were mixed to be included in an amount of 0.5 wt % based on the total amount of the composite mixed powder.

[Comparative Example 4]

All processes were performed in the same manner as in Preparation Example 1, except that the Gd _1.98 Bi _0.02 O ₃ nanoparticles were mixed in an amount of 5% by weight based on the total amount of the composite mixed powder.

Examples and Comparative Examples prepared according to the above-described process are shown in Table 1 below. Hereinafter, the thermoelectric materials prepared in Examples 1 to 2 and Comparative Examples 1 to 4 are defined as BiSbTe-based thermoelectric materials.

base material gadolinium oxide mixing ratio chemical formula Example 1 Preparation Example 1 Preparation 2 2% by weight BiSbTe/Gd _1.98 Bi _0.02 O ₃ Example 2 Preparation Example 1 Preparation 3 2% by weight BiSbTe/Gd _1.99 Bi _0.01 O ₃ Comparative Example 1 Preparation Example 1 - - BiSbTe Comparative Example 2 Preparation Example 1 Comparative Preparation Example 1 2% by weight BiSbTe/Gd ₂ O ₃ Comparative Example 3 Preparation Example 1 Preparation 2 0.5% by weight BiSbTe/Gd _1.98 Bi _0.02 O ₃ Comparative Example 4 Preparation Example 1 Preparation 2 5% by weight BiSbTe/Gd _1.98 Bi _0.02 O ₃

Characterization of BiSbTe-based thermoelectric materials

X-ray diffraction characteristics of the BiSbTe-based thermoelectric material were analyzed at room temperature using an X-ray spectrometer (Rigaku, MiniFlex-600, Japan) having high-energy monochromatic CuK _α radiation and a K _β filter.

The microstructure of the bulk sample of the BiSbTe-based thermoelectric material was analyzed using a scanning electron microscope (FESEM-MIRA-LMH II, TESKAN) equipped with an energy-dispersive X-ray spectrometer (EDS).

Thermoelectric properties such as Seebeck coefficient and electrical conductivity of the BiSbTe-based thermoelectric material were measured in a range of 300 to 500 K using a thermoelectric measurement system (TEP-1000, Seepel).

The thermal diffusivity (D) of the BiSbTe-based thermoelectric material was measured using a laser flash method (Netzsch LFA 457 system).

The specific heat capacity (C _p ) of the BiSbTe-based thermoelectric material was measured using a thermal analyzer (Perkin Elmer DSC-8000). Then, the thermal conductivity (κ) was calculated using the relational expression of κ = dC _p D . Here, "d" is the density of the sample measured by Archimedes principle.

The carrier concentration (n _c ) and mobility (μ _c ) of the BiSbTe-based thermoelectric material were measured using a Hall measurement system (Ecopia HMS-3000).

Transmission electron microscope analysis of bulk samples of the BiSbTe-based thermoelectric material was performed using a JEOL 2010 high-resolution transmission electron microscope (JEOL 2010 HRTEM).

Results and discussion

5 is a transmission electron microscope photograph and EDS mapping photographs of Gd _1.98 Bi _0.02 O ₃ nanoparticles included in the BiSbTe-based thermoelectric material according to an embodiment of the present invention.

Referring to FIG. 5 , gadolinium (Ga) and oxygen (O) are uniformly distributed in Gd _1.98 Bi _0.02 O ₃ nanoparticles, and bismuth (Bi) is uniformly distributed in a very small amount in the nanoparticles. can be known

6 is a graph showing X-ray diffraction patterns of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.

Referring to FIG. 6 , X-ray diffraction patterns for BiSbTe, Gd ₂ O ₃ powder, Gd _1.98 Bi _0.02 O ₃ powder, BiSbTe/Gd ₂ O ₃ , and BiSbTe/Gd _1.98 Bi _0.02 O ₃ are shown. “BST” refers to BiSbTe.

삼방정계(rhombohedral) 구조를 가짐을 알 수 있다.Gd ₂ O ₃ diffraction peaks indicated by JCPDF # 12-0797 appear in Gd ₂ O ₃ powder and Gd _1.98 Bi _0.02 O ₃ powder, but Gd ₂ O ₃ or Gd _1.98 Bi _0.02 O ₃ is bonded to the BiSbTe-based base material, respectively. The diffraction peaks do not appear in BiSbTe/Gd ₂ O ₃ and BiSbTe/Gd _1.98 Bi _0.02 O ₃ . Instead, in BiSbTe/Gd ₂ O ₃ , and BiSbTe/Gd _1.98 Bi _0.02 O ₃ , peaks corresponding to the BiSbTe-based base material indicated by JCPDF#49-1713 appear. That is, the BiSbTe-based base material, the BiSbTe/Gd ₂ O ₃ , and the BiSbTe/Gd _1.98 Bi _0.02 O ₃ as a whole

It can be seen that it has a rhombohedral structure.

7 is a transmission electron micrograph of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.

Referring to FIG. 7 , (a) is a low magnification transmission electron micrograph of a BiSbTe/Gd _1.98 Bi _0.02 O ₃ nanocomposite, and (b) and (c) are high magnifications of Gd _1.98 Bi _0.02 O ₃ dispersed in a BiSbTe-based base material. These are transmission electron micrographs, and (d) is a high-resolution transmission electron micrograph of the area indicated in (c). (d) shows the Fourier transform diffraction pattern of Gd _1.98 Bi _0.02 O ₃ .

It can be seen that the Gd _1.98 Bi _0.02 O ₃ nanoparticles have a polygonal shape and are found in many dispersoids having a size of about 300 nm. Interfaces between the BiSbTe-based base material and the Gd _1.98 Bi _0.02 O ₃ nanoparticles are clearly visible. The Gd _1.98 Bi _0.02 O ₃ nanoparticles are mainly observed at grain boundaries.

Then, the interface between the BiSbTe-based base material and the Gd _1.98 Bi _0.02 O ₃ nanoparticles was analyzed. As shown in (d) of FIG. 7 , the interfaces between the BiSbTe-based base material and the Gd _1.98 Bi _0.02 O ₃ nanoparticles were clearly seen. It can be seen that the reflections appearing in the Fourier transform diffraction pattern are due to the Gd _1.98 Bi _0.02 O ₃ nanoparticles. Accordingly, it can be seen that the Gd _1.98 Bi _0.02 O ₃ particles are well dispersed in the BiSbTe-based base material. It is analyzed that these interfaces and nanocrystal grain boundaries increase phonon scattering and decrease thermal conductivity.

The properties of the BiSbTe-based thermoelectric material were measured, and specifically, the carrier concentration (n, unit is 10 ¹⁹ cm ^-3 ) and carrier mobility (μ) at room temperature for Examples 1 to 2 and Comparative Examples 1 to 5. , the unit is 10 ² cm ² V ^-1 s ^-1 ) was measured and shown in Table 2 below.

Furtherance carrier concentration
(n,cm ^-3 ) carrier mobility
(μ,cm ² V ^-1 s ^-1 ) Example 1 BiSbTe/Gd _1.98 B _0.02 O ₃ 1.32 2.365 Example 2 BiSbTe/Gd _1.99 B _0.01 O ₃ 1.230 2.318 Comparative Example 1 BiSbTe 0.866 2.73 Comparative Example 2 BiSbTe/Gd ₂ O ₃ 1.136 2.28 Comparative Example 3 BiSbTe/Gd _1.98 B _0.02 O ₃ 1.062 2.675 Comparative Example 4 BiSbTe/Gd _1.98 B _0.02 O ₃ 0.926 2.62

Referring to Table 2, the BiSbTe-based thermoelectric materials prepared in Examples 1 and 2 in which the bismuth (Bi) content satisfies 0<x<0.03 maintains the same level without significant change in carrier concentration and mobility. can check that

Specifically, the carrier concentration was increased by 0.364 to 0.454 cm ^-3 compared to Comparative Example 1 not containing the gadolinium oxide, and from 0.094 to 0.184 cm ^-3 compared to Comparative Example 2 containing Gd ₂ O ₃ . increased.

On the other hand, the carrier mobility was reduced to 2.365 cm ² V ^-1 s ^-1 and 2.315 cm ² V ^-1 s ^-1 compared to the 2.73 cm ² V ^-1 s ^-1 of Comparative Example 1. The reason for the decrease in carrier mobility is nano-dispersed Gd _1.98 B _0.02 O ₃ and It is analyzed that carriers are scattered due to Gd _1.99 B _0.01 O ₃ . That is, the Gd _1.98 B _0.02 O ₃ and Due to Gd _1.99 B _0.01 O ₃ , the carrier concentration is increased but carrier mobility is decreased, which means that the electrical conductivity determined by the combination thereof increases.

Specifically, referring to FIG. 8 showing the electrical conductivity according to the temperature of the BiSbTe-based thermoelectric material, Example 1 (BiSbTe/Gd _1.98 Bi _0.02 O ₃ ), Comparative Example 1 (BiSbTe), and Comparative Example 2 (BiSbTe/Gd ₂ O) ₃ ) Electrical conductivity according to temperature is shown. In all cases, the electrical conductivity tended to decrease with increasing temperature. Specifically, at 450K or less, the electrical conductivity was decreased as the temperature increased. On the other hand, at 450K or higher, the electrical conductivity tends to slightly increase with an increase in temperature, especially in the BiSbTe/Gd ₂ O ₃ . This trend is analyzed because the material changes from a degenerate semiconducting behavior to an intrinsic semiconducting behavior.

In addition, it can be seen that when gadolinium (Gd) oxide is added, a change in electrical conductivity occurs. Compared to the BiSbTe, the BiSbTe/Gd ₂ O ₃ exhibited a decrease in electrical conductivity by about half or less over all temperature ranges. However, the BiSbTe/Gd _1.98 Bi _0.02 O ₃ in which bismuth was added to the Gd oxide exhibited an increase in electrical conductivity over all temperature ranges, compared to the BiSbTe, and the degree of this increase increased as the temperature increased. It can be seen that there is a decreasing trend with Therefore, when Gd ₂ O ₃ is added to the BiSbTe-based base material, electrical conductivity is greatly reduced, but when Gd _1.98 Bi _0.02 O ₃ is added to the BiSbTe-based base material, the electrical conductivity is higher than that of the BiSbTe-based base material. was also increased. This causes a difference in electrical conductivity, as described above.

In FIG. 8 , the maximum electrical conductivity of the BiSbTe is about 350Ω ^-1 cm ^-1 at 300K, the BiSbTe/Gd ₂ O ₃ is about 190Ω ^-1 cm ^-1 at 300K, and the BiSbTe/Gd _1.98 Bi _0.02 O ₃ is 393 Ω ^-1 cm ^-1 at 300 K.

BiSbTe/Gd _1.98 Bi _0.02 O ₃ Since BiSbTe/Gd ₂ O ₃ includes bismuth substituted, the bismuth substitution may preserve the overall structure and charge carrier concentration. However, even in the case of substituting a very small amount of bismuth, the properties of the atomic structure may be affected. That is, in the case of the nanoparticles of Gd _1.98 Bi _0.02 O ₃ , the disorder of the atomic size may be reduced, and other transport mechanisms of charge carriers may occur, and thus BiSbTe/Gd _1.98 Bi _0.02 O ₃ may be increased. It may have electrical conductivity and at the same time have an increased Seebeck coefficient. On the other hand, compared to the BiSbTe/Gd _1.98 Bi _0.02 O ₃ , the BiSbTe/Gd ₂ O ₃ suppresses the movement of charge carriers, and thus electrical conductivity is reduced.

On the other hand, although not disclosed in the drawings, Comparative Examples 3 and 5 in which Gd1.98Bi0.02O3 nanoparticles were mixed to be included in 0.5% by weight based on the total amount of the composite mixed powder and Comparative Example 4 in which the nanoparticles were mixed to be included in 5% by weight Also, the Gd1.98Bi0 .02O3 It can be seen that the carrier concentration was reduced compared to Examples 1 and 2.

Specifically, Comparative Example 3 has a carrier concentration of 1.062 cm-3 and a carrier mobility of 2.675 cm2V-1s-1. This means that the carrier concentration was reduced to 0.168 to 0.258 cm -3 compared to Examples 1 and 2, whereas the carrier mobility was increased by 0.31 to 0.357 cm 2 V -1s -1 .

Comparative Example 4 has a carrier concentration of 0.926 cm ^-3 and a carrier mobility of 2.62 cm ² V ^-1 s ^-1 . This means that, compared to Examples 1 and 2, the carrier concentration decreased from 0.304 to 0.394 cm ^-3 , while the carrier concentration was increased from 0.255 to 0.302 cm ² V ^-1 s ^-1 . The reason for this difference is that, as described above, in Comparative Example 3, less than 1% by weight of the gadolinium-based oxide powder was included, so that the degree of increase in the carrier concentration was insufficient. On the other hand, in Comparative Example 4, the Gd _1.98 Bi _0.02 O ₃ was excessively contained, and it rather acted as an impurity preventing electron movement.

9 is a graph illustrating a Seebeck coefficient according to a temperature of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.

Referring to FIG. 9 , Seebeck coefficients according to temperature are shown for BiSbTe, BiSbTe/Gd ₂ O ₃ , and BiSbTe/Gd _1.98 Bi _0.02 O ₃ . In all cases, the Seebeck coefficient increased slightly in the temperature range of 300 to 350K, and the Seebeck coefficient decreased with increasing temperature above 350K.

For a denatured semiconductor, the Seebeck coefficient S is expressed by Equation 2 below.

<Equation 2>

where k _B is the Boltzmann constant, m ^* is the effective mass, h is the Planck constant, and T is the absolute temperature.

According to Equation 2, it can be seen that the Seebeck coefficient S decreases as the carrier concentration n increases. The increase in carrier concentration may be due to excited minor carriers. Thus, it is explained that as the temperature increases, the total carrier concentration increases, and thus the Seebeck coefficient decreases with increasing temperature. The BiSbTe/Gd _1.98 Bi _0.02 O ₃ has a maximum Seebeck coefficient of 255.67 μVK ⁻¹ at room temperature (300K), which is slightly increased compared to the BiSbTe.

As shown in Table 2, compared to the BiSbTe, the BiSbTe/Gd ₂ O ₃ and the BiSbTe/Gd _1.98 B _0.02 O ₃ have relatively large carrier concentrations, so according to Equation 2, the BiSbTe/Gd ₂ O ₃ and the Seebeck coefficient of BiSbTe/Gd _1.98 B _0.02 O ₃ should be smaller than the Seebeck coefficient of BiSbTe. However, in reality, the Seebeck coefficients of the BiSbTe/Gd ₂ O ₃ and the BiSbTe/Gd _1.98 B _0.02 O ₃ were relatively larger. It is analyzed that these different results are due to the increase of the Seebeck coefficient by the increase of the effective mass. The effective mass (m ^* ) increases as Gd ₂ O ₃ nanoparticles or Gd _1.98 Bi _0.02 O ₃ nanoparticles are incorporated into the BiSbTe-based base material, and this increase is due to energy-dependent scattering or energy filtering. This increased effective mass increases the Seebeck coefficient. Therefore, it is analyzed that the BiSbTe/Gd ₂ O ₃ and the BiSbTe/Gd _1.98 B _0.02 O ₃ have a higher Seebeck coefficient than the BiSbTe due to an increase in effective mass.

10 is a graph showing a power factor according to temperature of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.

Referring to FIG. 10 , power factors according to temperature are shown for BiSbTe, BiSbTe/Gd ₂ O ₃ , and BiSbTe/Gd _1.98 Bi _0.02 O ₃ . in all cases. The power factor decreased as the temperature increased. Compared with the BiSbTe, the BiSbTe/Gd ₂ O ₃ exhibited a small value for the power factor over all temperature ranges. On the other hand, the BiSbTe/Gd _1.98 Bi _0.02 O ₃ showed a high power factor over all temperature ranges. At room temperature (300K), it was approximately 12% larger. This increasing tendency of the power factor decreased with increasing temperature.

As shown in Equation 1 above, the power factor is proportional to the electrical conductivity and the Seebeck coefficient. Therefore, it can be seen that the increased power factor of BiSbTe/Gd _1.98 Bi _0.02 O ₃ is due to an increase in Seebeck coefficient and an increase in electrical conductivity. The maximum value of the power factor of the BiSbTe/Gd _1.98 Bi _0.02 O ₃ is about 2.57 x 10 ^-3 Wm ^-1 K ^-1 at 300K.

11 is a graph illustrating thermal conductivity according to temperature of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.

Referring to FIG. 11 , the thermal conductivity according to temperature for BiSbTe, BiSbTe/Gd ₂ O ₃ and BiSbTe/Gd _1.98 Bi _0.02 O ₃ is shown. In all cases, the thermal conductivity increased with increasing temperature. Compared with the BiSbTe, the BiSbTe/Gd ₂ O ₃ and BiSbTe/Gd _1.98 Bi _0.02 O ₃ showed that the thermal conductivity decreased over all temperature ranges, and the difference in the thermal conductivity became larger as the temperature increased. In addition, the BiSbTe/Gd ₂ O ₃ and the BiSbTe/Gd _1.98 Bi _0.02 O ₃ exhibited almost similar thermal conductivity over all temperature ranges. The thermal conductivity of BiSbTe/Gd _1.98 Bi _0.02 O ₃ was 0.89 W/mK at room temperature (300K), which was 9% lower than that of BiSbTe 0.98 W/mK.

In general, heat conduction of a material is conducted through electrons or heat is conducted through lattice vibrations, and the total thermal conductivity (κ) of the material is expressed by Equation 3 below.

<Equation 3>

κ = κ _e + κ _l

Here, κ _e is the electronic thermal conductivity and κ _l is the lattice thermal conductivity.

In general, the electronic thermal conductivity (κ _e ) may be calculated by Equation 4, which is a Wiedemann-Franz law.

<Equation 4>

κ _e = LσT

Here, L is the Lorentz number, σ is the electrical conductivity, and T is the absolute temperature.

The Lorentz number is shown in Table 2, and can be calculated by Equation 5.

<Equation 5>

Here, L is the Lorentz number (unit is 10 ^-8 WΩK ^-2 ), S is the Seebeck coefficient (μVK ^-1 ).

Referring to Table 2, since the BiSbTe/Gd ₂ O ₃ and the BiSbTe/Gd _1.98 Bi _0.02 O ₃ have higher carrier concentrations than the BiSbTe, the BiSbTe/Gd ₂ O ₃ and the BiSbTe/Gd The electronic thermal conductivity of _1.98 Bi _0.02 O ₃ is expected to be greater or almost the same as that of BiSbTe. Therefore, according to Equation 3, the reduction in the thermal conductivity of BiSbTe/Gd ₂ O ₃ and BiSbTe/Gd _1.98 Bi _0.02 O ₃ compared to the BiSbTe is mainly due to the decrease in lattice thermal conductivity (κ _l ). do.

12 is a graph showing lattice thermal conductivity according to temperature of a BiSbTe-based thermoelectric material according to an embodiment of the present invention.

Referring to FIG. 12 , the lattice thermal conductivity as a function of temperature for BiSbTe, BiSbTe/Gd ₂ O ₃ and BiSbTe/Gd _1.98 Bi _0.02 O ₃ is shown. In all cases, the lattice thermal conductivity increased with increasing temperature. Compared with the BiSbTe, the lattice thermal conductivity of BiSbTe/Gd ₂ O ₃ and BiSbTe/Gd _1.98 Bi _0.02 O ₃ was decreased over all temperature ranges, and the difference in the lattice thermal conductivity became larger as the temperature increased. appear. In addition, the BiSbTe/Gd ₂ O ₃ and the BiSbTe/Gd _1.98 Bi _0.02 O ₃ exhibit almost similar lattice thermal conductivity trends over all temperature ranges, and the lattice thermal conductivity of the BiSbTe/Gd _1.98 Bi _0.02 O ₃ was all decreased compared to the BiSbTe/Gd ₂ O ₃ over the temperature range.

This decrease in lattice thermal conductivity is analyzed to be due to increased phonon scattering by Gd ₂ O ₃ nanoparticles or Gd _1.98 Bi _0.02 O ₃ nanoparticles incorporated into the BiSbTe base. In particular, the lattice thermal conductivity (κ ₁ ) of the BiSbTe/Gd _1.98 Bi _0.02 O ₃ at room temperature (300K) is 0.70 W/mK, which is 14% smaller than that of the BiSbTe 0.81 W/mK. On the other hand, the electronic thermal conductivity (κ _e ) of BiSbTe/Gd _1.98 Bi _0.02 O ₃ at room temperature (300K) is slightly higher than that of the BiSbTe-based base material, which is due to the increased electrical conductivity (σ). In addition, the interfaces of Gd _1.98 Bi _0.02 O ₃ are randomly dispersed in Bi _0.5 Sb _1.5 Te ₃ , can achieve carrier transport, and are also similar to the interfaces in the nanostructured bulk (Bi, Sb) ₂ Te ₃ . It may have very low thermal conductivity.

13 is a graph showing the figure of merit according to the temperature of the BiSbTe-based thermoelectric material according to an embodiment of the present invention.

Referring to FIG. 13 , dimensionless figure of merit (ZT) according to temperature for BiSbTe, BiSbTe/Gd ₂ O ₃ , and BiSbTe/Gd _1.98 Bi _0.02 O ₃ are shown. In all cases, the figure of merit showed a tendency to decrease with increasing temperature. Specifically, at 350 K or less, the figure of merit slightly increased as the temperature increased. On the other hand, above 350K, the figure of merit was decreased as the temperature increased. Compared to the BiSbTe, the BiSbTe/Gd ₂ O ₃ showed a small figure of merit over all temperature ranges. On the other hand, the BiSbTe/Gd _1.98 Bi _0.02 O ₃ showed a large figure of merit over all temperature ranges.

The BiSbTe/Gd _1.98 Bi _0.02 O ₃ exhibited a maximum figure of merit of 0.87 at room temperature (300K), which is an increase of about 30% compared to the BiSbTe. As such, it is analyzed that the increase in figure of merit is due to the increased power factor and decreased thermal conductivity.

As a result, when comparing the BiSbTe/Gd ₂ O ₃ and the BiSbTe/Gd _1.98 Bi _0.02 O ₃ in the BiSbTe-based system, it can be seen that the BiSbTe/Gd _1.98 Bi _0.02 O ₃ thermoelectric performance is excellent. In the BiSbTe/Gd _1.98 Bi _0.02 O ₃ , the increased thermoelectric performance is due to the increased phonon scattering due to dispersion by the bismuth (Bi)-rare earth oxide, that is, Gd _1.98 Bi _0.02 O ₃ nanoparticles contained in the BiSbTe-based base material. is analyzed as On the other hand, it can be seen that the overall structure type and charge carrier concentration are preserved even when the bismuth is substituted. The inclusion of bismuth in gadolinium oxide can provide the effect of reducing the source of defects in the structure of the synthesized Gd ₂ O ₃ .

conclusion

According to the present invention, bismuth-free rare earth oxide Gd ₂ O ₃ and bismuth-containing rare earth oxide Gd _1.98 Bi _0.02 O ₃ were successfully prepared using spray pyrolysis. Then, by using a combined ball milling and spark plasma sintering process, p-type BiSbTe, BiSbTe/Gd ₂ O ₃ and BiSbTe/Gd _1.98 Bi _0.02 O ₃ were successfully prepared.

As the Gd _1.98 Bi _0.02 O ₃ nanoparticles were incorporated into the BiSbTe-based base material, electrical conductivity and Seebeck coefficient were simultaneously increased, and it is analyzed that this increase is due to energy-dependent scattering and an increase in carrier concentration. In addition, since the Gd ₂ O ₃ nanoparticles and the Gd _1.98 Bi _0.02 O ₃ nanoparticles are well dispersed in the BiSbTe-based base material, additional carrier transport can be induced.

In addition, by mixing the Gd _1.98 Bi _0.02 O ₃ nanoparticles in an amount of 1 to 3 wt % based on the total weight of the BiSbTe-based thermoelectric material, the carrier concentration may be increased to exhibit an inclusion effect. Phonon scattering was increased by the Gd ₂ O ₃ nanoparticles and the Gd _1.98 Bi _0.02 O ₃ nanoparticles, and thus the thermal conductivity was reduced, and the thermal conductivity was reduced by about 9% compared to the BiSbTe-based base material. As a result, the BiSbTe/Gd _1.98 Bi _0.02 O ₃ had a maximum figure of merit of about 0.87, which was about 30% higher than that of the BiSbTe-based base material at room temperature (300K).

On the other hand, when less than 1 wt% of Gd _1.98 Bi _0.02 O ₃ nanoparticles are mixed, the amount of Gd _1.98 Bi _0.02 O ₃ nanoparticles mixed is reduced, thereby reducing the Seebeck coefficient and power factor of the thermoelectric material as well as thermal conductivity. This causes the performance index to deteriorate. In addition, when the Gd _1.98 Bi _0.02 O ₃ nanoparticles exceed 3% by weight, the Gd _1.98 Bi _0.02 O ₃ nanoparticles may act as impurities to reduce electrical conductivity.

From these results, BiSbTe/Gd _1.98 Bi _0.02 O ₃ having Gd oxide containing bismuth can provide superior thermoelectric performance compared to BiSbTe/Gd ₂ O ₃ having Gd oxide containing bismuth, more preferably Preferably, the Gd _1.98 Bi _0.02 O ₃ is mixed with 1 to 3% by weight BiSbTe/Gd _1.98 Bi _0.02 O ₃ , even more preferably 1 to 2 wt% of Gd _1.98 Bi _0.02 O ₃ is mixed BiSbTe/Gd _1.98 Bi _0.02 O ₃ It can be used as an additive to BiSbTe-based materials. Accordingly, by alloying bismuth telluride and its alloy with a bismuth-containing rare earth (RE) metal, the thermoelectric properties of the target material may be improved.

The technical spirit of the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and it is the technical spirit of the present invention that various substitutions, modifications and changes are possible within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in the art to which this belongs.

Claims (12)

A hierarchical BiSbTe-based thermoelectric material comprising a gadolinium-based oxide dispersed in a Bi _a Sb _b Te _c alloy.
(In the Bi _a Sb _b Te _c alloy, a is 0.4 to 0.6, b is 1.2 to 1.6, and c is 2.7 to 3.3.) The method of claim 1,
The gadolinium-based oxide is Gd _2-x Bi _x O ₃ (0<x<0.03), a hierarchical BiSbTe-based thermoelectric material comprising a gadolinium-based oxide. The method of claim 1,
The gadolinium-based oxide is a Bi _a Sb _b Te _c hierarchical thermoelectric material comprising a gadolinium-based oxide, characterized in that it is dispersed as nanoparticles in the alloy BiSbTe. 3. The method of claim 2,
The Gd _2-x Bi _x O ₃ nanoparticles are included in an amount of 1 to 3% by weight based on the total weight of the BiSbTe-based thermoelectric material, the hierarchical BiSbTe-based thermoelectric material including a gadolinium-based oxide. 5. The method of claim 4,
The Gd _2-x Bi _x O ₃ nanoparticles have a size of 10 to 100 nm, a hierarchical BiSbTe-based thermoelectric material comprising a gadolinium-based oxide. The method of claim 1,
The BiSbTe-based thermoelectric material is a hierarchical BiSbTe-based thermoelectric material including a gadolinium-based oxide having a trigonal structure. Forming a powder of a base material consisting of Bi, Sb and Te;
forming a bismuth-containing gadolinium oxide powder;
forming a composite mixed powder by mixing the powder of the base material and the bismuth-containing gadolinium oxide powder;
ball milling the composite powder mixture; and
A method of manufacturing a hierarchical BiSbTe-based thermoelectric material containing a gadolinium-based oxide, including; sintering the composite mixed powder with spark plasma. 8. The method of claim 7,
The step of forming the powder of the base material consisting of Bi, Sb and Te is,
mixing Bi, Sb, and Te in a stoichiometric composition to form a mixture;
melting the mixture; and
A method of manufacturing a hierarchical BiSbTe-based thermoelectric material containing a gadolinium-based oxide, including; atomizing the molten mixture to form a powder of a base material composed of the Bi _a Sb _b Te _c alloy.
(In the Bi _a Sb _b Te _c alloy, a is 0.4 to 0.6, b is 1.2 to 1.6, and c is 2.7 to 3.3.) 9. The method of claim 8,
The melting step is performed in an argon gas atmosphere using a high-frequency induction furnace,
The atomizing step is performed in a nitrogen atmosphere using a gas atomizer, a method of manufacturing a hierarchical BiSbTe-based thermoelectric material containing a gadolinium-based oxide. 8. The method of claim 7,
Forming the bismuth-containing gadolinium oxide powder comprises:
forming a mixed solution of gadolinium nitride, a bismuth nitride precursor, and ethylene glycol;
atomizing the mixed solution using an ultrasonic atomizer to form droplets;
reacting the droplets in a quartz reactor at a temperature ranging from 850 to 950° C. to form a reactant;
extracting powder from the reactant using a filter; and
Heating the powder in an oxidizing atmosphere at a temperature in the range of 950 to 1050° C. to form the bismuth-containing gadolinium oxide powder; Method for producing a hierarchical BiSbTe-based thermoelectric material including a gadolinium-based oxide 8. The method of claim 7,
The step of ball milling,
A layer comprising gadolinium-based oxide, carried out for a weight ratio of milling balls to composite mixed powder ranging from 10:1 to 20:1, a milling speed ranging from 500 to 1000 rpm, and a ball milling time ranging from 10 minutes to 30 minutes A method for manufacturing a red BiSbTe-based thermoelectric material. 8. The method of claim 7,
The spark plasma sintering step,
A method for producing a hierarchical BiSbTe-based thermoelectric material comprising a gadolinium-based oxide, which is performed at a temperature in the range of 400 to 500° C. and a pressure in the range of 30 to 70 MPa.

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