KR101683687B1 - Nanocomposite thermoelectric material and process for preparing the same - Google Patents

Abstract

The present invention relates to a method of manufacturing a semiconductor device comprising a first phase comprising Bi, Te and Se in a specific composition; And a secondary phase containing Cu and Te in a specific composition.
The nanocomposite thermoelectric material of the present invention exhibits an increased coefficient of thermal expansion and an increased coefficient of thermal expansion as well as an increased Seebeck coefficient, thus being useful for realizing high efficiency thermoelectric devices.

Description

TECHNICAL FIELD The present invention relates to a nanocomposite thermoelectric material and a process for preparing the nanocomposite thermoelectric material.

The present invention relates to a nanocomposite thermoelectric material, and more particularly, to a nanocomposite thermoelectric material including a primary phase and a secondary phase.

Thermoelectric phenomenon is a reversible and direct energy conversion phenomenon of heat and electricity, and is a phenomenon caused by the movement of electrons and / or holes in the thermoelectric material.

The thermoelectric effect is a Peltier effect in which heat is dissipated or absorbed at the contacts of dissimilar materials by an externally applied current to two dissimilar materials connected by the contacts, A Seebeck effect in which an electromotive force is generated from a temperature difference, and a Thomson effect in which heat is released or absorbed when a current flows in a material having a predetermined temperature gradient.

By using the heat transfer phenomenon, it is possible to convert heat generated from a computer, an automobile engine, and various industrial waste heat into electrical energy. By using the Peltier effect, various cooling systems that do not require a refrigerant can be realized. In recent years, interest in thermoelectric materials has been rising along with the growing interest in new energy development, recycling of waste energy, and environmental protection.

The energy conversion efficiency of the thermoelectric material showing the thermoelectric phenomenon is represented by a dimensionless figure of merit (ZT) of the following equation (1).

&Quot; (1) "

Where ZT is the figure of merit, S is the Seebeck coefficient, sigma is the electrical conductivity, T is the absolute temperature, and kappa is the thermal conductivity.

In order to increase the energy conversion efficiency, a thermoelectric material having a high Seebeck coefficient, a high electrical conductivity and a low thermal conductivity is required. However, since the Seebeck coefficient, the electrical conductivity and the thermal conductivity are generally not mutually influenced, It is not easy to realize a thermoelectric element having a high index, that is, a high efficiency.

On the other hand, since the nanostructure has a particle size smaller than that of the bulk material, the density of the grain boundaries is increased or the phase boundary is formed by the introduction of the nano-sized second phase. As a result, phonon scattering increases at the grain boundary and the phase boundary, The performance index can be improved by collapsing the trade-off between the whiteness factor and the electric conductivity from the quantum confinement effect or the carrier filtering effect.

Nanostructures can be, for example, superlattice thin films, nanowires, nanoplates, quantum dots, etc., but are difficult to manufacture or have poor performance indices in bulk. Thus, there is a need for a nanostructured material that is simple to fabricate and provides an improved figure of merit on the bulk.

The present inventors have studied a thermoelectric material capable of improving thermoelectric performance by simultaneously providing a low thermal conductivity and a high power factor (which is a value obtained by multiplying the square of the electric conductivity and the whiteness coefficient) As a primary phase; And a nanocomposite thermoelectric material including a secondary phase containing Cu and Te in a specific composition exhibit an increased effective heat transfer coefficient Can be used effectively.

Therefore, the present invention relates to a method of manufacturing a semiconductor device comprising a primary phase containing Bi, Te and Se in a specific composition; And a secondary phase containing Cu and Te in a specific composition, and a method for producing the same.

According to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: a first phase including Bi, Te, and Se, And a secondary phase containing Cu and Te and represented by the following general formula (2).

≪ Formula 1 >

Bi ₂ Te _{3 - y} Se _y (0.2 < y < 0.5)

(2)

Cu _z Te (1? Z? 2)

In one embodiment, the primary phase may further comprise Cu, in which case it may be represented by the following formula (3) or (4).

(3)

Cu _x Bi ₂ Te _{3 - y} Se _y (0 <x <0.03, 0.2 <y <0.5)

&Lt; Formula 4 >

Bi _{2 - x} Cu _x Te _{3 - y} Se _y (0 <x <0.03, 0.2 <y <0.5)

In one embodiment, the secondary phase may be represented by CuTe or Cu ₂ Te, and may exist in a structure selected from the group consisting of orthorhombic, cubic, and hexagonal systems.

In one embodiment, the secondary phase may have an average particle size of 1 to 300 nm and may be included in an amount of 0.1 to 3.0 parts by weight based on 100 parts by weight of the primary phase.

According to an aspect of the present invention, there is also provided a method of preparing a nanocomposite powder, comprising: (a) preparing a nanocomposite raw material powder; And (b) sintering the nanocomposite raw material powder obtained in step (a) to obtain a nanocomposite type thermoelectric material.

According to the present invention, a primary phase containing Bi, Te and Se in a specific composition; And a secondary phase containing Cu and Te in a specific composition are formed in a nanoinclusion form in a secondary phase in a matrix of primary phase, Phase boundary surface. In addition to exhibiting increased Seebeck coefficient due to carrier filtering effect due to band bending at the phase boundary, the phase boundary is reduced by phonon scattering at the phase boundary, It is found that the increase of the Seebeck coefficient and the decrease of the thermal conductivity simultaneously show the improved performance index characteristic by showing the thermal conductivity.

Therefore, the nanocomposite thermoelectric material of the present invention can be usefully used in thermoelectric devices requiring high thermoelectric efficiency.

FIG. 1 is a schematic view schematically showing a Cu _x Bi ₂ Te _{3 - y} Se _y matrix and a secondary phase Cu ₂ Te nanoinclusion structure, which are the primary phases of the nanocomposite body thermoelectric material of the present invention.
2 is a transmission electron microscope (TEM) image showing the microstructure (Cu _x Bi ₂ Te _{3 - y} Se _y matrix and Cu ₂ Te nanocomposite) of the thermoelectric material produced in Example 1.
3 is an enlarged TEM image showing the microstructure (Cu _x Bi ₂ Te _{3 - y} Se _y matrix and Cu ₂ Te nanocomposite) of the thermoelectric material produced in Example 1.
FIG. 4 is a selected area electron diffraction (TEM-SAED) image showing the Bi ₂ Te _{3 - y} Se _y structure and the Cu ₂ Te hexagonal structure of the thermoelectric material prepared in Example 7.
Fig. 5 shows the results of electrical conductivity measurements of the thermoelectric materials prepared in Comparative Examples and Examples 1 to 6. Fig.
6 shows the results of Seebeck coefficient measurements of the thermoelectric materials prepared in Comparative Examples and Examples 1 to 6.
FIG. 7 shows the results of the power factor measurement of the thermoelectric materials prepared in Comparative Examples and Examples 1 to 6.
FIG. 8 shows the results of thermal conductivity measurements of the thermoelectric materials prepared in Comparative Examples and Examples 1 to 6. FIG.
Fig. 9 shows the results of the measurement of the figure of merit (ZT) of the thermoelectric material produced in Comparative Example and Examples 1 to 6.

According to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: a first phase including Bi, Te, and Se, And a secondary phase containing Cu and Te and represented by the following general formula (2).

&Lt; Formula 1 >

Bi ₂ Te _{3 - y} Se _y (0.2 < y < 0.5)

(2)

Cu _z Te (1? Z? 2)

The nanocomposite thermoelectric material is dispersed in a state in which a secondary phase which is a nano-sized nano-containing substance on the first order of n-type semiconductor characteristics constituting the matrix is embedded and thereby a new interface is formed and a substantially nanostructure is introduced Effect. Therefore, the scattering of phonons at the interface increases, and the thermal conductivity can be lowered. In addition, since the nanocomposite thermoelectric material has different compositions of the first phase and the second phase, it is possible to selectively transport the carriers by controlling the composition of the first phase and the second phase. That is, it is possible to control the size of the energy barrier at the primary phase / secondary phase interface by adjusting the composition of the primary phase and the secondary phase. By adjusting the size of the energy barrier, a carrier filtering effect can be obtained which selectively transports only carriers having a large contribution to the power factor S ² ?. The carrier filtering effect increases the Seebeck coefficient, and consequently the figure of merit can be improved.

In the nanocomposite thermoelectric material, the secondary phase may be present in the intragrain of the primary phase. The secondary phase may also exist in the grain boundary of the primary phase, but the secondary phase may be present in the primary phase to further increase the scattering of the phonon. The secondary phase may be formed by excess deposition of a compound containing a transition metal in the course of sintering the composite raw material powder.

In one embodiment, the primary phase may further comprise Cu and may be represented by the following formula (3) or (4).

(3)

Cu _x Bi ₂ Te _{3 - y} Se _y (0 <x <0.03, 0.2 <y <0.5)

&Lt; Formula 4 >

Bi _{2 - x} Cu _x Te _{3 - y} Se _y (0 <x <0.03, 0.2 <y <0.5)

Cu may be present in an intercalation form when the first phase further comprising Cu is expressed as in Formula 3, and in the case where it is represented by Formula 4, it may be mixed with Bi-site doped &lt; / RTI &gt;

In one embodiment, the secondary phase may be represented by CuTe or Cu ₂ Te. When the second phase is represented by CuTe, it may exist in an orthorhombic structure. When the second phase is represented by Cu ₂ Te, it may exist in a cubic or hexagonal structure. May exist in a hexagonal structure.

In the nanocomposite thermoelectric material, a nano-sized secondary phase means a secondary phase having an average particle size of less than 1 μm. For example, the average particle diameter of the secondary phase may be 1 to 900 nm, preferably 1 to 500 nm, and more preferably 1 to 300 nm. The nanocomposite thermoelectric material can provide a further improved figure of merit in the above average particle size range.

In one embodiment, the secondary phase may be contained in an amount of 0.1 to 3.0 parts by weight based on 100 parts by weight of the primary phase, preferably 0.1 to 1.0 part by weight based on 100 parts by weight of the primary phase, more preferably 100 parts by weight of the primary phase 0.4 to 0.6 parts by weight based on the total weight of the composition. The nanocomposite thermoelectric material can provide a further improved figure of merit in the above content range.

The nanocomposite thermoelectric material can provide a significantly improved ZT value compared to the conventional n-type thermoelectric material by the nano-sized quadratic structure dispersed in the primary phase and the specific composition. That is, the nanocomposite thermoelectric material may have a figure of merit (ZT) of 0.5 or more at 300K to 450K, and more particularly, it may have an enhanced index of performance over a thermoelectric material containing no primary phase at room temperature .

The nanocomposite thermoelectric material of the present invention is formed in the form of a nano-containing substance in a secondary phase in a primary phase matrix to form an increased phase boundary between the primary phase and the secondary phase. In this phase boundary, It shows enhanced Jeckheck coefficient due to filtering effect and reduced thermal conductivity due to phonon scattering at this phase boundary. It shows enhanced performance index characteristics by simultaneously increasing the Seebeck coefficient and reducing the thermal conductivity.

The nanocomposite thermoelectric material may be bulk. The bulk nanocomposite thermoelectric material may be a pressurized sinter produced by pressing and sintering a composite base material powder.

According to an aspect of the present invention, there is also provided a method of preparing a nanocomposite powder, comprising: (a) preparing a nanocomposite raw material powder; And (b) sintering the nanocomposite raw material powder obtained in step (a) to obtain a nanocomposite type thermoelectric material.

In the step (a), the nanocomposite raw material powder for preparing the nanocomposite thermoelectric material is prepared.

Specifically, a precursor of a thermoelectric material (for example, a raw material metal) is mixed at a predetermined ratio, and the resultant is placed in a quartz tube and vacuum-sealed. The resultant is melted at 800 to 1200 ° C for 1 to 5 hours, To 700 ° C for 0.5 to 2 hours and then quenched with a coolant such as water to produce an ingot thermoelectric semiconductor.

After mixing the thermoelectric semiconductor ingot with a secondary phase precursor (for example, a starting metal) at a predetermined ratio, the mixture is pulverized at 100 to 2000 rpm for 0.1 to 10 minutes in a high energy ball mill, A rapid solidification method may be performed to produce a composite raw material powder in the form of a ribbon.

The rapid solidification method may be performed by a conventional rapid solidification method such as a melt spinning method, a gas atomization method, a plasma deposition method, a centrifugal atomization method, And a splat quenching method. Preferably, the method may be performed by a melt spinning method. However, the present invention is not limited thereto and may be used in the art in the rapid solidification method Anything that can be done is possible. Industrial rapid mass scaling of nanocomposite thermoelectric materials is possible by using the rapid solidification method. Improved physical properties can be obtained even when a general solidification method other than the rapid solidification method is used.

In the rapid solidification process, for example, a melt spinning process, the mixed raw material is heated to a melting point or higher to form a liquid state, and is passed through a nozzle at a high speed of 1000 to 5000 rpm in a vacuum or inert atmosphere chamber at a room temperature of from 0.1 bar to less than 1 bar And the mixture is ejected by a rotating Cu wheel to obtain a ribbon-like base material.

Thereafter, the ribbon-like composite material is pulverized by ball milling, attrition milling, high energy milling, zet milling, mortar or the like But is not limited to them. Any method can be used as a method for producing powders by pulverizing raw materials by a dry method, as long as they can be used in the technical field.

Alternatively, the composite raw material powder may be prepared by gas atomization. In the gas atomization method, a mixture obtained by mixing the thermoelectric semiconductor ingot and a secondary phase precursor (for example, a starting metal) at a predetermined ratio is molded to prepare a mixed raw material in the form of a molded product. The mixed raw material is heated to a temperature higher than the melting point to form a liquid state, and rapidly injected into a vacuum or argon atmosphere at room temperature through a nozzle to quench the mixture to obtain spherical composite raw material powder.

The step (b) is a step of sintering the nanocomposite raw material powder obtained in the step (a) to obtain a nanocomposite type thermoelectric material.

The sintering can be performed by a commonly used sintering process, and can be obtained, for example, by pressure sintering. Specifically, the composite raw material powder can be produced by a hot press method in which a mold having a predetermined shape is added and molded at a high temperature, for example, about 300 to 580 캜 and a high pressure, for example, about 30 to 300 MPa. For example, the composite raw material powder can be produced by a spark plasma sintering method in which a material is sintered in a short time by energizing about 50 to 500 A under a high-voltage condition at a high-voltage current, for example, a pressure of about 30 to 300 MPa have. For example, it can be produced by a hot-pouring method in which a raw material powder of a thermosensitive material of nanocomposite body is extruded and sintered at a high temperature, for example, about 300 to 580 ° C during press forming.

The sintering may be performed at a temperature of 300 to 580 캜, a pressure of 1 to 100 Pa and a vacuum for 1 to 10 minutes by using a spark plasma sintering method, And may be suitably changed within a range capable of improving the performance index of the nanocomposite thermoelectric material.

The nanocomposite thermoelectric material produced by the sintering process may have a density of about 70-100% of the theoretical density. The theoretical density is calculated by dividing the molecular weight by the atomic volume and can be evaluated as a lattice constant. For example, it may have a density of about 95 to 100% and thus exhibit an increased electrical conductivity.

Since the bulk nanocomposite thermoelectric material can be manufactured in various forms, a thin and highly efficient thermoelectric device of 1 mm or less can be realized. The nanocomposite thermoelectric material is easy to manufacture in a bulk phase and has a high performance index in a bulk phase, and thus has a high commercial potential.

During the sintering process, a secondary phase is precipitated to form a nanocomposite thermoelectric material.

Hereinafter, the present invention will be described in more detail through examples and test examples. However, the following examples and test examples are provided for illustrating the present invention, and the scope of the present invention is not limited thereto.

Example  One. Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3}  + Cu ₂ Te ( Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3} Of 0.1% by weight)

Cu, Bi, Te, and Se, which are raw metals, were mixed in a composition ratio so as to obtain a thermoelectric semiconductor having a composition formula of Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3} to prepare a mixture. 20 g of the prepared mixture was placed in a quartz tube and vacuum-sealed. The resultant mixture was melted at 1000 ° C for 3 hours, maintained at 600 ° C for 1 hour, quenched using water at room temperature, To produce an ingot-type thermoelectric semiconductor.

4.32 g of Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3 in an} ingot form, 0.0021 g of metallic Cu and 0.0022 g of metallic Te were prepared and then heated at 1,425 rpm for 2 minutes using a high energy ball mill The powder was uniformly pulverized.

The obtained powder was melt-spinned as follows to prepare a ribbon-shaped composite raw material. The composite material was melted in a molten spinning chamber and ejected onto a Cu wheel through a nozzle. The inside of the chamber was an argon atmosphere, the chamber pressure was 0.4 bar, and the rotation speed of the Cu wheel was 4000 rpm. The ribbons (length of about 10 mm, width of about 2 mm, thickness of about 5 탆) produced by the melt spinning were pulverized in a mortar to prepare a composite raw material powder.

Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 . 3} and Cu-Te compound was sintered at 500 ° C for 2 minutes under a pressure of 30 MPa and a vacuum condition using Spark Plasma Sintering method to prepare a composite thermoelectric material. The microstructure of the thermoelectric material thus prepared was photographed by a transmission electron microscope (TEM) and shown in Fig. 2 and Fig.

As shown in FIG. 2, in the thermoelectric material produced, the structure of the Cu _x Bi ₂ Te _{3 - y} Se _y matrix and the structure of the Cu ₂ Te nanocomposite in the matrix can be confirmed. Further, as shown in Fig. 3, the enlarged microstructure of the Cu ₂ Te nanocomposite can be confirmed. The overall composition of the prepared thermoelectric material was determined by inductively coupled plasma (ICP) analysis. As a result, Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3} + Cu ₂ Te (Cu _{0 .01} Bi ₂ Te _{2 0.7} was 0.1% by weight of Se _{0 .3).}

Example  2. Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3}  + Cu ₂ Te ( Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3} Of 0.2% by weight)

A composite thermoelectric material was prepared in the same manner as in Example 1 except that 4.32 g of Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3 in an} ingot form, 0.0043 g of metal Cu and 0.0044 g of metal Te were used.

Example  3. Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3}  + Cu ₂ Te ( Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3} 0.4% &lt; / RTI &gt; weight ratio)

A composite thermoelectric material was prepared in the same manner as in Example 1, except that 4.32 g of Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3 in an} ingot form, 0.0086 g of metal Cu and 0.0087 g of metal Te were used.

Example  4. Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3}  + Cu ₂ Te ( Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3} Of 0.6% by weight)

A composite thermoelectric material was prepared in the same manner as in Example 1 except that 4.32 g of Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3 in an} ingot form, 0.0126 g of metal Cu and 0.0128 g of metal Te were used.

Example  5. Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3}  + Cu ₂ Te ( Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3} Of 0.8% by weight)

Composite thermoelectric materials were prepared in the same manner as in Example 1, except that 4.32 g of Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3 in an} ingot form, 0.0172 g of metal Cu and 0.0174 g of metal Te were used.

Example  6. Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3}  + Cu ₂ Te ( Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3} Of 1.0% by weight)

A composite thermoelectric material was prepared in the same manner as in Example 1, except that 4.32 g of Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3 in an} ingot form, 0.0215 g of metal Cu and 0.0217 g of metal Te were used.

Example  7. Bi ₂ Te _{2 .7} Se _{0 .3}  + Cu ₂ Te ( Bi ₂ Te _{2 .7} Se _{0 .3} Of 0.2% by weight)

A composite thermoelectric material was prepared in the same manner as in Example 1, except that 4.32 g of Bi ₂ Te _{2 .7} Se _{0 .3 in an} ingot form, 0.0043 g of a metal Cu and 0.0044 g of a metal Te were used.

The microstructure of the prepared thermoelectric material was confirmed by selected area electron diffraction (TEM-SAED), and the result is shown in FIG. As shown in FIG. 4, it can be confirmed that the thermoelectric material prepared is a Bi ₂ Te _{2 .7} Se _{0 .3} structure and a Cu ₂ Te hexagonal structure.

Comparative Example . Cu _{0 .01} Bi ₂ Te _{2 .7} Se _{0 .3} Manufacturing

Was prepared in the _{Cu 0 .01 Bi 2 Te 2 .7} Se 0 .3 thermal conductive material in the same way as in Example 1, except that the Cu metal and metal Te.

Test Example  1. Electrical Conductivity and Of the Seebeck coefficient  Measure

The electrical conductivity and the Seebeck coefficient of the thermoelectric materials prepared in Comparative Examples and Examples 1 to 6 were measured using ULVAC-RIKO ZEM-3, and the results are shown in FIG. 5 and FIG. 6, respectively. As shown in FIGS. 5 and 6, the composite thermoelectric materials of Examples 1 to 6 containing Cu ₂ Te, as compared with Comparative Examples not containing Cu ₂ Te, exhibited low electric conductivity and high Seebeck coefficient, It can be seen that as the content of Cu ₂ Te increases, the Seebeck coefficient increases.

Test Example  2. Thermal conductivity, Power factor  And performance index ( ZT )

The thermal conductivity was calculated from the measured thermal diffusivity using ULVAC TC-9000H (Laser Flash method) and is shown in FIG. The power factor and thermoelectric performance index ZT calculated from the above results are shown in FIGS. 7 and 9, respectively.

As shown in FIG. 8, as the content of Cu ₂ Te in the composite thermoelectric material increases, the thermal conductivity decreases. Particularly, it is confirmed that the degree of reduction is remarkable at room temperature.

Further, as shown in Fig. 9, the composite thermoelectric materials of Examples 1 to 6 containing Cu ₂ Te exhibited a higher figure of merit (ZT) than the comparative example not containing Cu ₂ Te, As the content of Cu ₂ Te increases, the figure of merit (ZT) increases. In particular, in Examples 3 and 4, the increase in the figure of merit at room temperature is remarkably excellent.

Claims (8)

A primary phase represented by the following formula (3) or (4); And
The secondary phase represented by Cu ₂ Te
Wherein the secondary phase exists in a hexagonal system structure. The nanocomposite body thermoelectric material according to claim 1,
(3)
Cu _x Bi ₂ Te _3-y Se _y (0 <x <0.03, 0.2 <y <0.5)
&Lt; Formula 4 &gt;
Bi _2-x Cu _x Te _3-y Se _y (0 <x <0.03, 0.2 <y <0.5). delete delete delete delete The nanocomposite thermoelectric material according to claim 1, wherein the secondary phase has an average particle size of 1 to 300 nm. The nanocomposite thermoelectric material according to claim 1, wherein the secondary phase is included in an amount of 0.1 to 3.0 parts by weight based on 100 parts by weight of the primary phase. (a) preparing a nanocomposite raw material powder comprising a thermoelectric semiconductor of the following chemical formula (3) or a chemical formula (4) and a metal of Cu ₂ Te composition; And
(b) sintering the nanocomposite raw material powder obtained in the step (a) to obtain a nanocomposite type thermoelectric material
A method for producing a nanocomposite thermoelectric material comprising:
(3)
Cu _x Bi ₂ Te _3-y Se _y (0 <x <0.03, 0.2 <y <0.5)
&Lt; Formula 4 &gt;
Bi _2-x Cu _x Te _3-y Se _y (0 <x <0.03, 0.2 <y <0.5).

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