KR20190028944A - Method for manufacturing thermoelectric material - Google Patents

Abstract

The present invention relates to a thermoelectric material and, specifically, to a manufacturing method of a thermoelectric material for increasing dislocation density. The present invention relates to the manufacturing method of a thermoelectric material comprising: a step of manufacturing a bulk thermoelectric material using a thermoelectric material raw material; a step of manufacturing the bulk thermoelectric material into powder; a step of adding a metal additive selected from the thermoelectric material raw material to the powder; a step of forming an intermediate in which the metal additive is dispersed in the thermoelectric material; and a step of sintering the same at a temperature above a melting point of the metal additive.

Description

[0001] METHOD FOR MANUFACTURING THERMOELECTRIC MATERIAL [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric material, and more particularly, to a method of manufacturing a thermoelectric material for increasing a dislocation density.

The thermoelectric effect is a reversible, direct energy conversion between heat and electricity. Thermoelectric phenomenon is a phenomenon caused by the movement of charge carriers, ie, electrons and holes, in the material.

The Seebeck effect is a direct conversion of the temperature difference into electricity, and is applied to the power generation field by using the electromotive force resulting from the temperature difference between the two ends of the thermoelectric material. The Peltier effect is a phenomenon in which heat is generated at the upper junction and heat is absorbed at the lower junction when a current is passed through the circuit, And is applied to the cooling field. On the other hand, the Seebeck effect and the Phelthier effect are different from the Joule heating in that they are thermodynamically reversible.

Currently, thermoelectric materials are applied as active cooling system of semiconductor equipment and other electronic equipment which is difficult to solve the heat problem due to passive cooling system. It is impossible to solve with existing refrigerant gas compression system such as precision temperature control system applied to DNA research Demand in the field is expanding.

Thermoelectric cooling is a non-vibration, low-noise, environmentally friendly cooling technology that does not use refrigerant gas to cause environmental problems. With the development of high efficiency thermoelectric cooling materials, the application efficiency can be extended to general cooling applications such as commercial and household refrigerators and air conditioners.

In addition, when a thermoelectric material is applied to a portion where heat is emitted from an automobile engine or an industrial factory, it is possible to generate electricity by the temperature difference generated at both ends of the material, thereby attracting attention as one of the renewable energy sources.

The present invention has been proposed in order to satisfy the above-mentioned necessity, and it is an object of the present invention to provide a method of manufacturing a thermoelectric material capable of improving thermoelectric performance.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, unless further departing from the spirit and scope of the invention as defined by the appended claims. It will be possible.

In order to achieve the above object, the present invention provides a method of manufacturing a thermoelectric material, comprising the steps of: preparing a bulk thermoelectric material by using a thermoelectric material; Preparing the bulk thermoelectric material as a powder; Adding a metal additive selected from the thermoelectric material to the powder; Forming an intermediate in which the metal additive is dispersed in the thermoelectric material; And sintering at a temperature equal to or higher than the melting point of the metal additive.

Here, the thermoelectric material has a composition represented by the following formula (1)

≪ Formula 1 >

_{(TI) x (Bi 0 .5} Sb 1 .5- x Te 3 -y) 1-x

The TI may be a topological insulator.

In addition, the thermal material, the Bi _{0 .5} on the double structure including a second grain consisting of the first grains, and the geometric phase insulators (Topological Insulator) consisting of Sb _x Te _{3 -y 1 .5-} material Lt; / RTI >

In addition, the phase geometry nonconductor may include at least one of AgSbTe ₂ and Ag ₂ Te.

In the above formula (1), 0 <x? 0.4 and 0 <y? 0.5.

Here, the raw material may include Ag, Bi, Sb, and Te.

Here, the metal additive may be tellurium (Te).

Here, the metal additive may be contained in an amount of more than 20% by weight based on the raw material.

Here, the step of forming the intermediate may be carried out using a melting and rapid cooling apparatus.

In addition, the step of forming the intermediate may include: charging the thermoelectric material powder and the metal additive into a tube having a nozzle; Melting the thermoelectric material powder and the metal additive in a liquid state; And discharging the molten material to a rotating plate to form particles in the form of a ribbon.

The sintering step may be a spark plasma sintering method.

In addition, the sintering may be performed so that the metal additive is eluted to the outside to form a dislocation.

According to the embodiment of the present invention, it is possible to provide a thermoelectric material having improved thermoelectric performance.

Specifically, as the electric conductivity increases and the thermal conductivity decreases, a thermoelectric material having a significantly improved performance index ZT of the thermoelectric material can be obtained.

The effects obtained by the present invention are not limited to the above-mentioned effects, and other effects not mentioned can be clearly understood by those skilled in the art from the following description will be.

1A to 1C are diagrams showing the microstructure of thermoelectric materials for improving the figure of merit ZT of the thermoelectric material.
2 is a schematic view showing a microstructure of a thermoelectric material having an interface formed by each of different types of phase insulators formed according to an embodiment of the present invention.
3 is a schematic diagram for explaining the potential shown in Fig.
4 is a flowchart showing a method of manufacturing a thermoelectric material according to an embodiment of the present invention.
5 is an X-ray diffraction (XRD) measurement spectrum of a bulk thermoelectric material according to an embodiment of the present invention.
6 is a high magnification transmission electron microscope (TEM) photograph of a bulk thermoelectric material according to an embodiment of the present invention.
7 is a scanning electron microscopy (SEM) photograph of an intermediate according to an embodiment of the present invention.
8 is an enlarged view of a portion A in Fig.
9 is a high magnification transmission electron microscope (TEM) photograph of a thermoelectric material produced by sintering according to an embodiment of the present invention.
FIGS. 10 to 13 are graphs showing characteristics of thermoelectric materials manufactured according to embodiments of the present invention, according to temperature. FIG.

The composition of the thermoelectric material used for cooling or heat pump in the vicinity of room temperature (300K) is generally (Bi _a Sb _1-a ) ₂ (Te _c Se _1-c ) ₃ , and the performance of the polycrystalline bulk material The index (ZT) is about 1 at 300K. The performance of the thermoelectric material can be represented by a figure of merit (ZT) defined as Equation 1, commonly referred to as a dimensionless figure of merit.

In Equation (1), S is the Seebeck coefficient (which means the thermoelectric power generated by the temperature difference per 1 ° C), σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity. S ² ? Constitutes a power factor. In order to increase the figure of merit (ZT) of the thermoelectric material as shown in equation (1) above Seebeck (Seebeck) coefficient (S) and electrical conductivity (σ), that is, power factor (S ² σ is increased and the thermal conductivity ( κ) should be reduced.

However, since the Jacobian coefficient and the electric conductivity have a relationship of exchange-canceling relation, the other value decreases as the value increases as the carrier or electron concentration increases. For example, metals with high electrical conductivity have low Seebeck coefficients, and insulating materials with low electrical conductivity have high Seebeck coefficients. The exchange counterbalance relationship between the Seebeck coefficient and the electric conductivity is a great limitation in increasing the power factor.

1A to 1C are diagrams showing the microstructure of a thermoelectric material applied to the present invention to improve the performance index ZT of the thermoelectric material.

In order to improve the performance index ZT of the thermoelectric material, nanostructures such as a superlattice thin film, a nanowire, and a quantum dot are formed to increase a Seebeck coefficient by a quantum confinement effect Or an attempt is made to lower the thermal conductivity by the concept of Phonon Glass Electron Crystal (PGEC).

First, the quantum confinement effect is a concept of increasing the density of states (DOS) of carriers in the material by the nanostructure and increasing the effective mass and raising the Seebeck coefficient. At this time, the correlation between the electrical conductivity and the Seebeck coefficient collapses and the electrical conductivity does not change much even if the Seebeck coefficient is increased.

Second, the concept of PGEC is a concept that blocks the movement of phonons responsible for heat transfer and does not interfere with the movement of charge carrier electrons, thereby reducing the thermal conductivity without lowering the electrical conductivity. That is, among the phonons and the charge carrier electrons that transfer heat from the high temperature side to the low temperature side of the thermoelectric material, the progress of the phonon is hindered by phonon scattering (phonon scattering), and the charge carrier electrons are advanced without clogging. Therefore, although the thermal conductivity is reduced by phonon scattering, the electric conductivity by the charge carrier electrons can be reduced.

These techniques are specifically described with reference to the drawings of the thermoelectric material microstructure.

FIG. 1A is a diagram showing the microstructure of the nanocomposite body thermoelectric material 10. FIG. In the nanocomposite body thermoelectric material 10, the value of ZT can be improved by reducing the size of the grain 11 of the thermoelectric material. The grain 11 may have a diameter of 20 to 100 nanometers.

Since the phonon scattering phenomenon occurs when phonons pass through grain boundaries (grain boundaries) 12, the effect of lowering the thermal conductivity as the size of the grain 11 is reduced is generated. On the other hand, the transfer of the charge carrier electrons can minimize the change in the electrical conductivity since the influence of the electrons passing through the grain boundary 12 is relatively small. Accordingly, as shown in FIG. 1A, in a thermoelectric material having a nanocomposite structure, the ZT value of the thermoelectric material can be improved by the PGEC concept.

1B is a diagram showing the microstructure of the deposition type thermoelectric material 20 in which the value of ZT is improved through precipitation of a predetermined material 21 on the grain boundary 12.

The material 21 deposited on the grain boundary 12 has the effect of improving the electrical conductivity while generating phonon scattering and improving the ZT value of the entire deposition type thermoelectric material 20. [

1C is a diagram showing the microstructure of a hierarchical structure thermoelectric material 30 through process diversification.

The hierarchical structure means that another grain is formed in the grain 11 to cause phonon scattering with respect to the large phonon through the large grain 11 and phonon scattering with respect to the small phonon through the small grain 31 . The thermal conductivity of the thermoelectric material can be reduced through the induced phonon scattering.

According to the microstructure as described above, a structure for lowering the thermal conductivity is generally focused. As described above, in the method of controlling the thermal conductivity only and changing the ZT value, there is a limit that the change value of the ZT value can only be insignificant.

Another concrete method for implementing the PGEC concept is to make the superlattice of the PbSeTe layer on PbTe or the superlattice of Bi ₂ Te ₃ and Sb ₂ Te ₃ to form a superlattice, . However, such a superlattice is not suitable for practical thermoelectric power generation and cooling because it requires an artificially thin film process, which is expensive and requires only a few hundred nanometers even if the thickness of the thin film is made thick.

Therefore, the microstructure of the thermoelectric material proposed in one embodiment of the present invention proposes a structure capable of not only lowering the thermal conductivity through the nanostructure but also improving the electric conductivity and the Seebeck coefficient.

One of the main strategies for reducing the thermal conductivity is to realize a microstructure capable of effectively scattering the phonons responsible for heat transfer through nanostructuring as shown in FIG. 1A. The grain boundary 12 is an interface effective for phonon scattering, and it is possible to reduce the lattice thermal conductivity by decreasing the grain size and increasing the density of the grain boundary 12. In recent years, there has been a tendency for technology to manufacture nano-sized thermoelectric material particles such as nanoparticles, nanowires, and nano plates by using the material development strategy.

On the other hand, since the electrical conductivity and the Seebeck coefficient are exchange-canceled as described above, it is difficult to improve both numerical values at once. The reason for the exchange-offset relationship between the Seebeck coefficient and the electrical conductivity is that the Seebeck coefficient and the electrical conductivity property are difficult to control simultaneously in the sample bulk. However, if the generation channels of the Seebeck coefficient and the electric conductivity can be biased, their exchange-offset relationship will be broken. In other words, if the electric conductivity comes out from the surface of the sample and the higher the value of the Seebeck coefficient in the bulk, the higher the Seebeck coefficient and the higher the electrical conductivity, the better.

In one embodiment of the present invention, a topological insulator (TI), hereinafter referred to as a phase insulator, is used to simultaneously realize high Seebeck coefficient and electrical conductivity. A phase insulator is a material that is bulk insulated due to strong spin-orbital bonding and time-reversal symmetry, but whose surface is not topologically stable. This means that electrons can move only through the surface of the sample, and the phenomenon that the sample surface of the non-conductive material is metallic is called a "topological metallic state". If the electrons move through the metal layer formed on the surface of the phase insulator, the electric conductivity of the thermoelectric material can be improved. Hereinafter, the microstructure of a specific thermoelectric material according to an embodiment of the present invention will be described.

2 is a schematic view showing a microstructure of a thermoelectric material having an interface formed by each of different types of phase insulators formed according to an embodiment of the present invention. 3 is a schematic diagram for explaining the potential shown in Fig.

The microstructure of the nanocomposite thermoelectric material shown in FIG. 2 has a phase separation (hereinafter referred to as &quot; second grain &quot;) of a first material grain (hereinafter referred to as first grain) 201 and a second material grain 201 phase separation. A method of manufacturing a microstructure according to an embodiment of the present invention will be described below in detail.

At least one of the first material and the second material constituting the nanocomposite thermoelectric material according to an embodiment of the present invention may be at least one selected from the group consisting of Bi-Te, Pb-Te, Co-Sb, Si- And may include at least one Fe-Si-based material. The thermoelectric material of the Pb-Te system may be a material containing both Pb and Te and containing other elements. The Co-Sb thermoelectric material may be a material containing one element of Co and Fe and Sb. The thermoelectric material of the Si-Ge system may be a material containing both Si and Ge. More specific examples of such materials include Bi _{0 .5} Sb _{1 .5} Te ₃ , Bi ₂ Te ₃ alloy, CsBi ₄ Te ₆ , CoSb ₃ , PbTe alloy, Zn ₄ Sb ₃ , Zn ₄ Sb ₃ alloy, Na _x CoO ₂ , CeFe _3.5 Co _0.5 Sb ₁₂ , Bi ₂ Sr ₂ Co ₂ O _y , Ca ₃ Co ₄ O ₉ , or Si _0.8 Ge _0.2 alloy. However, thermoelectric materials are not limited to these materials.

At least one of the first and second materials of an embodiment of the present invention may comprise a phase insulator.

At least one of the first and second materials of an embodiment of the present invention may include a semiconductor having a large energy gap.

The thermoelectric material according to one embodiment of the present invention can lead to a significant increase in the ZT value in that it can control thermal conductivity, electrical conductivity and whitening coefficient, respectively.

First, the thermoelectric material according to an embodiment of the present invention can lower the thermal conductivity through the nanostructure. As described above in the nanocomposite microstructure of FIG. 1A, the nanostructure is effective in lowering the thermal conductivity because it can cause phonon scattering in the grain boundary 12. The thermoelectric material according to an embodiment of the present invention can lower the thermal conductivity through the nanostructure formed of the first and second grains.

Second, the thermoelectric material according to one embodiment of the present invention can increase the electrical conductivity through the "topological metallic state" of the phase insulator. Since the metal state having high mobility is formed in the grain boundary 12, which can be called the surface of the phase insulator, the electric conductivity of the thermoelectric material can be greatly increased.

Third, in one embodiment of the present invention, the use of a material having a large energy gap as a sample bulk can improve the Seebeck coefficient. If the Seebeck coefficient is improved, a higher power factor can be expected. As the energy gap of the first and second materials forming the first and second grains respectively becomes larger, the Seebeck coefficient becomes higher, so that the Seebeck coefficient value will be improved when the first and second materials are made of the nonconductor. This is because an insulator is a substance having a large energy gap.

In one embodiment of the present invention, a dislocation (D) formed by a lattice mismatch between atoms is formed at a high density in the crystal grain and at the interface 202. When the thermoelectric material is manufactured, electrons flow smoothly through the interface of the phase insulator and the electric conductivity increases. Phonons (P) are scattered due to the dislocations (D) existing in the fine crystal grains and inside the crystal grains, The performance ZT can be improved.

To form the composite having such a characteristic, in the embodiment of the present invention, the thermoelectric material Bi _{0 .5} Sb _{1 .5} Te ₃ base material (the first material) of the hetero thermally non-conductive material or phase (second material) in the Is phase-separated to exhibit interfacial phase storage stability, thereby providing a thermoelectric material having a composition represented by the following formula (1).

In the above formula (1), TI is any material having a "topology insulator" or phase insulator property, and may include at least one of AgSbTe ₂ and Ag ₂ Te. x is the molar ratio of TI.

The thermoelectric material of the present invention may be a P-type thermoelectric semiconductor. That is, the thermoelectric semiconductor may be a semiconductor in which a hole acts as a majority carrier.

In addition, an intermediate is formed by using a metal additive as one of the thermoelectric materials, and is melted during sintering, so that a dislocation (D) formed by a lattice misfit between atoms is formed inside the crystal grain and at the interface It can be formed at a high density.

According to one embodiment of the present invention, Te may have a stoichiometric deficiency.

According to one embodiment of the present invention, Sb may have a stoichiometric deficiency.

According to one embodiment of the invention, the compounds made from the composition of formula 1 is x-ray diffraction (x-ray diffraction) non-conductive phase (TI) and Bi _{0 .5} Sb _{1 .5} may exist a dual phase of Te ₃ are mixed on have.

According to an embodiment of the present invention, it is preferable that the thermoelectric material has a density corresponding to 70% to 100% of the theoretical density.

Hereinafter, a manufacturing method for realizing the fine structure of FIG. 2 will be briefly described.

First, an ingot raw material made of the composition of the formula (1) is made into a rapidly cooled material (intermediate) in the form of ribbons through a rapid solidification process device.

Next, the bulk material can be produced through a Spark Plasma Sintering apparatus capable of heating and cooling the ribbon-shaped intermediate to produce fine-sized crystal grains formed with phase insulators.

At this time, when a bulk material is made by adding a metal additive having a low melting temperature in the production of a ribbon-shaped material as an intermediate, a dislocation (D) in which a lattice misfit is formed as shown in FIG. And is formed at a high density. That is, the potential D is formed not only at the interface 202 of the thermoelectric material but also inside the crystal grains.

When the thermoelectric material is manufactured, electrons flow smoothly through the phase insulator interface, and the electric conductivity increases. The phonon is scattered by the fine grains and the dislocations (D) existing at the inside of the grains and at the interface, .

Here, a metal additive for forming dislocation (D) is added with a certain amount (0 to 30% by weight) of a tellurium (Te) material having a lower melting temperature than the ingot raw material. Such a metal additive is used in a sintering process for producing a bulk And is discharged outside to confuse the atomic arrangement inside the thermoelectric material to form a misfit dislocation in the atomic arrangement. Such a metal additive may be any one material selected from thermoelectric material raw materials.

4 is a flowchart showing a method of manufacturing a thermoelectric material according to an embodiment of the present invention.

Hereinafter, a method for manufacturing a thermoelectric material according to an embodiment of the present invention will be described in detail with reference to FIG.

In order to manufacture the above-mentioned thermoelectric material, first, a bulk thermoelectric material (for example, ingot) is manufactured using the raw material for thermoelectric material (S10). At this time, the raw material may include Ag, Bi, Sb, and Te.

First, the raw materials are mixed in the molar ratio according to the composition of the thermoelectric material, charged into a quartz tube, and vacuum sealed.

Thereafter, it is charged into a melting furnace, melted at a high temperature of about 1,000 ° C., and cooled to room temperature to produce an ingot.

The bulk thermoelectric material (ingot) thus produced is pulverized into powder form (S20). For example, the ingot can be made into a powder form by a ball milling process.

A certain amount of metal additive is added thereto (S30). These metal additives may be any one or more of the materials selected from the thermoelectric material. Further, the metal additive may be a substance having a lower melting point than the ingot.

However, when forming an intermediate as described below, it may be a substance capable of forming dislocation D in the lattice or at the interface. For example, if the melting point is low enough to melt before forming solid crystals, dislocation D can not be formed inside the lattice or at the interface.

The metal additive may be included in an amount of more than 20 to 25% by weight based on the raw material. The metal additive may also be tellurium (Te).

Next, in the state where the powder and the metal additive are mixed, an intermediate is formed using a melting and rapid cooling apparatus (S40). Such an intermediate may be a ribbon-like material. Such an intermediate may be formed by dispersing a metal additive in a thermoelectric material.

In the rapid cooling process, a material is charged into a quartz tube having a narrow nozzle size, and is melted by induction heating. Then, gas pressure is applied to the copper rotary plate which rotates at high speed and is instantaneously discharged to cool and solidify.

That is, the process of forming such an intermediate may include a process of charging thermoelectric material powder and a metal additive into a tube having nozzles, a process of melting such thermoelectric material powder and metal additives in a liquid state, and discharging the melted material onto a rotating plate And forming a ribbon-shaped particle.

Thereafter, the intermediate material is sintered to produce a thermoelectric material (S50). At this time, the sintering temperature may be higher than the melting point of the metal additive.

During sintering, the ribbon-like material is made of a thermoelectric material in a bulk form using a spark plasma sintering method using a carbon mold, that is, a spark plasma device.

That is, when the ribbon-shaped material is made into a powder state again or a ribbon-shaped material is charged into the carbon mold and then a DC current is supplied while being pressurized, a sparked plasma is generated between the powder particles and instantaneously heated to a high temperature, Sintering is performed.

In such a sintering process, the metal additive may be eluted to the outside to form a dislocation. That is, this sintering process may be for the metal additive to be eluted to the outside to form a dislocation.

Generally, a thermoelectric material, which is usually formed in a polycrystalline form, is produced by a ball milling process after the ingot is manufactured to a powder of several to several tens of microns in size, and then is manufactured by a hot press process. However, such a general process has a limitation in reducing the grain size of the bulk material because of the slow cooling rate, and it may be difficult to form a dislocation using a metal additive.

Then, the bulk thermoelectric material is cut and processed into a desired shape to observe the thermoelectric properties (Seebeck coefficient, electrical conductivity, thermal conductivity) and microstructure.

Hereinafter, specific embodiments of the present invention will be described in detail.

1. Ingot manufacturing

5 is an X-ray diffraction (XRD) measurement spectrum of a bulk thermoelectric material according to an embodiment of the present invention. 6 is a high-magnification transmission electron microscope (TEM) photograph of a bulk thermoelectric material according to an embodiment of the present invention.

In order to produce a bulk thermoelectric material, Ag, Bi, Sb and Te were quantitatively measured at a molar ratio in accordance with a composition ratio of Ag _{0 .2} Bi _{0 .5} Sb _{1 .4} Te _{2 .9} and put into a quartz tube. Vacuum seal at a pressure of ^-5 torr.

Since the melting point of Ag ₂ Te is 960 ° C, a vacuum-sealed quartz tube is placed in an electric furnace, and the temperature is gradually raised to 1,050 ° C, maintained at 1,050 ° C for 12 hours, and cooled.

The microstructure of the bulk thermoelectric material (ingot material) produced through this process is shown in FIG.

Figure 5 is a phase separation in the Bi _{0 .5} Sb _{1 .5} Te ₃ with Ag ₂ Te on the X-ray diffraction (X-ray diffraction, XRD) phase separation and the measurement results, Fig. 6 Bi _{0 .5} Sb _{1 .5} Te ₃ (TEM) observation of a high-power transmission electron microscope (Ag ₂ Te).

Even when 5 and 6, you can see the AgSbTe ₂ and Bi _{0 .5} Sb _{1 .5} different from the result of separation Te ₃ of the ingot material.

2. Bulk thermoelectric material manufacturing

7 is a scanning electron microscopy (SEM) photograph of an intermediate according to an embodiment of the present invention. 8 is an enlarged view of a portion A in Fig.

Ag _{0 .2} Bi _{0 .5} Sb _{1 .4} Te _{2 .9} The ingot material made from the material composition is made into a powder of several to several tens of microns in size by a milling process.

Thereafter, 20 to 25 wt% of tellurium (Te) powder as a metal additive is mixed with the matrix composition powder, and then an intermediate is formed by using a rapid cooling device.

That is, pellets having a diameter of 10 to 15 mm and a height of 10 mm or more are made into a ribbon by a rapid cooling device, and then put into a quartz tube having a nozzle size of about 0.3 to 0.4 mm in diameter.

Thereafter, the powder is melted by induction heating, and then discharged to a copper rotary plate having a diameter of 300 mm which is rotated at a high speed by applying pressure, thereby cooling and solidifying the mixture, whereby a ribbon-shaped intermediate in which metal additives are precipitated can be obtained.

At this time, when the rotary plate is rotated at 2800 to 3200 rpm, a ribbon-shaped material having a thickness of about 1 탆 to 100 탆 is obtained. Such a ribbon-like material is obtained by dispersing a metal additive in a thermoelectric material, and a thermoelectric material and a metal additive may be formed in a size of several tens of nanometers to several hundreds of nanometers by the effect of quenching.

For example, if a ribbon-shaped material is made by using a rapid cooling apparatus including Ag _{0 .2} Bi _{0 .5} Sb _{1 .4} Te _{2 .9} as a thermoelectric matrix and Te as a metal additive, The shape can be formed as shown in Figs. 7 and 8. Fig.

Ag _{0 .2} Bi _{0 .5} Sb _{1 .4} Te _{2 .9} When an excessive amount of a metal additive such as Te is added to the melt, eutectic decomposition occurs in the crystallization process, and Te precipitates. Part B of Fig. 8 shows a state in which Te is precipitated by eutectic decomposition.

At this time, the position at which Te is precipitated is uniformly dispersed in the crystal grains, and may be shaped like Te particles embedded in the resin surface as shown in FIGS. This may be a good condition for increasing the interface density of Bi _{0 .5} Sb _{1 .5} Te ₃ / Te containing a high density of misfit dislocations as described above.

3. Sintering

9 is a high magnification transmission electron microscope (TEM) photograph of a thermoelectric material produced by sintering according to an embodiment of the present invention.

As described above, the ribbon-shaped intermediate produced by the rapid cooling and solidification method is pulverized by using a rapid cooling apparatus, and then subjected to pressure sintering using a spark plasma sintering method.

The pressure sintering is carried out by charging the material into a carbon mold having an inner diameter of 10 mm, holding the material at a temperature of 450 to 500 DEG C for 3 minutes, and then air-cooling it. At this time, the thickness of the sample used is 10 mm.

When hot pressing thermal _{matrix, Bi 0 .5 Sb 1 .5 Te} 3 / Te In order for the interface to become semi-matched, the sintering temperature may be above the melting point of the metal additive tellurium.

For example, the sintering temperature may be at a temperature above the melting point of the metal additive, for example, at a temperature above the melting point to about (melting point + 30) ° C.

At atmospheric pressure, the melting point of tellurium is 449.57 ^° C, and the melting point is somewhat lowered under pressure. It can be understood that it is necessary to tellurium starts the crystallization according to the crystal plane of the then turned into a liquid phase _{(Liquid Phase), Bi 0 .5} Sb 1 .5 Te 3.

Since tellurium is a liquid phase in pressure sintering, a certain amount can be eluted to the outside, and the pressure applied in the pressure sintering process can be about 30 Mpa or more, for example, in the range of 40 to 100 MPa.

As a result of TEM observation of the microstructure of the bulk thermoelectric material produced by this method, dislocation was observed not only at the grain boundary interface 202 but also inside the grain as shown in FIG. In Fig. 9, arrows indicate positions of dislocations located inside the crystal grains.

4. Characteristic evaluation result

FIGS. 10 to 13 are graphs showing characteristics of thermoelectric materials manufactured according to embodiments of the present invention, according to temperature. FIG.

Specifically, 10 to 13 are prepared by the embodiments of the present and the Bi _{0 .5} Sb _{1 .5} Te ₃ of the stoichiometric composition characteristic of the sample manufactured by the conventional method (indicated by the dashed line, squares) invention The characteristics of the thermoelectric material (solid line and triangle) are compared.

Figs. 10 to 13 show the characteristic value (ZT), the electric conductivity, the Seebeck coefficient and the thermal conductivity, respectively.

The electrical conductivity and the Seebeck coefficient were measured simultaneously using ULVAC ZEM-3 and the thermal conductivity was calculated from the thermal diffusivity measured with ULVAC TC-9000H (Laser Flash method).

From the results, it can be seen that there is almost no change in the Seebeck coefficient (FIG. 12) when the thermoelectric performance index ZT and the respective characteristic values are measured at 50 ° C.

However, the electrical conductivity (Fig. 11) increased significantly from 0.40 to 0.74 at 50 캜, where the thermal conductivity (Fig. 13) decreased from 0.93 to 0.84.

Therefore, referring to FIG. 10, the performance index ZT of the thermoelectric material was greatly improved from 0.9 to 1.6.

The reason for this is as follows: As a result of observation of microstructure, grain size decreased from 20 microns to 7 microns in average grain size compared to the prior art, phonons were scattered due to dislocations formed inside and at the interface between grains, Phase and Bi _{0 .5} Sb _{1 .5} Te matrix interface were formed by the phase interfacial effect to improve the electric conductivity by improving the electric conductivity by smoothly flowing electrons.

It should be noted that the embodiments of the present invention disclosed in the present specification and drawings are only illustrative of specific examples for the purpose of understanding and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention are possible in addition to the embodiments disclosed herein.

200: first grain 201: second grain
202: Interface

Claims (12)

A method of manufacturing a thermoelectric material,
Preparing a bulk thermoelectric material using the thermoelectric material;
Preparing the bulk thermoelectric material as a powder;
Adding a metal additive selected from the thermoelectric material to the powder;
Forming an intermediate in which the metal additive is dispersed in the thermoelectric material; And
And sintering at a temperature equal to or higher than the melting point of the metal additive. The thermoelectric material according to claim 1,
Having a composition represented by the following formula (1)
&Lt; Formula 1 >
_{(TI) x (Bi 0.5 Sb} 1.5-x Te 3-y) 1-x
Wherein the TI is a topological insulator. 3. The thermoelectric material according to claim 2,
Thermally, characterized in that with a double structure on the a second grain consisting of the _{Bi 0 .5 Sb 1 .5- x Te} 3 -y first material grains and the geometric phase insulators (Topological Insulator) consisting of Method of manufacturing a material. 3. The method of claim 2,
The geometric phase is non-conductive, AgSbTe ₂ and the method of producing a thermal transfer material comprising at least one of Ag ₂ Te. The thermoelectric material of claim 2, wherein 0 <x? 0.4 and 0 <y? 0.5. The method of manufacturing a thermoelectric material according to claim 1, wherein the raw material comprises Ag, Bi, Sb, and Te. The method of manufacturing a thermoelectric material according to claim 1, wherein the metal additive is tellurium (Te). The method of claim 1, wherein the metal additive is present in an amount of more than 20% by weight of the raw material. The method of claim 1, wherein the forming of the intermediate is performed using a melting and rapid cooling apparatus. 10. The method of claim 9, wherein forming the intermediate comprises:
Charging the thermoelectric material powder and the metal additive into a tube having nozzles;
Melting the thermoelectric material powder and the metal additive in a liquid state; And
And discharging the molten material onto a rotating plate to form ribbon-shaped particles. The method of manufacturing a thermoelectric material according to claim 1, wherein the sintering step uses spark plasma sintering. The method of manufacturing a thermoelectric material according to claim 1, wherein the sintering step is performed so that the metal additive is eluted to the outside to form a dislocation.

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