KR20190080425A - Composite thermoelectric material and preparation method thereof - Google Patents

Abstract

Disclosed are a composite thermoelectric material and a manufacturing method thereof. According to one embodiment, the composite thermoelectric material comprises: a matrix of a thermoelectric material; and an allotrope of carbon dispersed in the matrix. Therefore, an objective of the present invention is to provide the composite thermoelectric material having a high coefficient of performance and a technique for manufacturing the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite thermoelectric material,

The present disclosure relates to a composite thermoelectric material and a method of manufacturing the same.

ThermoElectric (TE) technology is an energy harvesting technology that is being developed as a renewable and sustainable energy source to meet the global demand to reduce greenhouse gases that cause global warming.

Thermoelectric technology is expected to play an important role in generating electricity using abandoned waste heat. Since the efficiency of a thermoelectric device greatly depends on the performance of a thermoelectric material, a high-performance thermoelectric material is very important for generating electricity by converting waste heat into electricity or generating a temperature difference using electricity.

The performance of the thermoelectric material is determined by the ZT value, which is a dimensionless figure of merit. However, there are many difficulties in manufacturing a thermoelectric material having a high ZT value.

The performance factor is defined as the power factor times the square of the electrical conductivity and the square of the Seebeck coefficient times the temperature divided by the thermal conductivity. Here, since the electric conductivity and the Seebeck coefficient are in inverse proportion to the carrier concentration, it is difficult to increase the coefficient of performance.

For this reason, the coefficient of performance was considered to have a limit of 1 over a long period of time. Recent research, however, has shown that thermoelectric materials with performance coefficients exceeding 1 are being developed by lowering the thermal conductivity.

Korean Published Patent No. 10-2014-0139908 (Dec. 08, 2014)

The embodiments described below provide a composite thermoelectric material having a high coefficient of performance and a technique for manufacturing the same.

A composite thermoelectric material according to one embodiment includes a matrix of a thermoelectric material and an allotrope of carbon dispersed in the matrix.

The thermoelectric material may include a Bi-Sb-Se-Te based thermoelectric material.

The Bi-Sb-Se-Te based thermoelectric material may include a material having the following formula (1).

[Chemical Formula 1]

Bi _2-a Sb _a Se _3-b Te _b (0? A? 2, 0? _{B? 3} )

The carbon isotope may be selected from graphene and carbon nanotubes.

The graphene may include graphene peeled off by tape, graphene grown by CVD (Chemical Vapor Deposition), graphene oxide produced by Hummer's method, and reduced graphene oxide The carbon nanotubes may include single wall carbon nanotubes, double wall carbon nanotubes, and multiwall carbon nanotubes.

The carbon isotope is added to the composite thermoelectric material in an amount of 10 vol% or less, preferably 0.1 vol% to 0.8 vol%, and most preferably 0.4 vol% or less, based on the total volume of the composite thermoelectric material. vol%. < / RTI >

The grain size of the composite thermoelectric material may be smaller than the grain size of the pristine thermoelectric material not containing the carbon isotope.

The composite thermoelectric material may have a higher hole carrier mobility than the pristine thermoelectric material that does not include the carbon isotope.

The composite thermoelectric material may have a higher coefficient of performance (ZT) than a pristine thermoelectric material that does not include the carbon isotope.

A method of making a composite thermoelectric material according to an embodiment includes the steps of providing a pulverized thermoelectric material, mixing the pulverized thermoelectric material with an isotropic carbon powder to produce a mixed powder, Forming a ribbon of the mixed powder to form a ribbon; pulverizing the ribbon; and sintering the pulverized ribbon to produce a matrix of thermoelectric materials in which the carbon isotope is dispersed do.

The step of providing the pulverized thermoelectric material includes the steps of generating an ingot of a thermoelectric material by using an element material constituting the thermoelectric material as a starting material and pulverizing the ingot of the thermoelectric material, .

The carbon isotope may be selected from graphene and carbon nanotubes.

The step of forming the ribbon may be performed using a rapid solidification method.

The rapid solidification method can be performed by a melt spinning method, a gas atomization method, a plasma deposition method, a centrifugal atomization method, and a splat quenching method Can be selected from the group consisting of.

The step of forming the ribbon is performed using a melt spinning method, and the melt spinning method may include a step of melting the mixed powder and a step of cooling the molten mixed powder.

The cooling step may include cooling to a cooling rate of 10 < ⁵ > K / sec to 10 < ⁷ > K / sec.

The step of pulverizing the ribbon may include pulverizing the ribbon using a dry grinding method.

The dry milling may be selected from the group consisting of ball milling, attrition milling, high energy milling, zet milling and mortar milling.

The sintering may include spark plasma sintering or hot press sintering.

The step of producing the matrix may comprise sintering the pulverized ribbon for 1 to 10 minutes under at least one of a temperature condition of 300 ° C to 800 ° C, a pressure condition of 1 Pa to 100 Pa and a vacuum condition have.

Fig. 1 shows an example of a method for producing a composite thermoelectric material according to one embodiment.
Fig. 2 shows an example of the melt spinning method shown in Fig.
FIG. 3A shows an example of a scanning electron microscope (SEM) image of the ribbon contact surface shown in FIG.
FIG. 3B shows an example of a SEM image of the ribbon free surface shown in FIG.
Figure 3C shows an example of a SEM image of reduced graphene oxide (RGO) dispersed in the ribbon shown in Figure 2.
4A shows an example of a SEM image of a fracture surface of a thermoelectric material pellet not containing carbon isotopes.
4B shows an example of a SEM image of a fracture surface of a composite thermoelectric material pellet containing 0.1 volume percent of RGO.
4C shows an example of a SEM image of the fracture surface of a composite thermoelectric material pellet containing 0.4 volume percent of RGO.
Figure 4d shows an example of a SEM image of the fracture surface of a composite thermoelectric material pellet containing 0.8 volume percent RGO.
5 shows an example of an X-ray diffraction (XRD) pattern performed in a direction perpendicular to the spark plasma sintering direction of the composite thermoelectric material.
FIG. 6A shows an example of a result of performing Raman spectroscopy on a carbon isotope.
FIG. 6B shows an example of the result of performing Raman spectroscopy on the composite thermoelectric material.
7a shows an example of the temperature dependence of the electrical conductivity of the composite thermoelectric material according to the carbon isotope volume percentage.
7B shows an example of the change in carrier concentration and mobility of the composite thermoelectric material according to the carbon isotope volume percentage.
FIG. 7C shows an example of the temperature dependence of the Seebeck coefficient of the composite thermoelectric material according to the percentage of the carbon isotope volume.
7d shows an example of the temperature dependence of the power factor of the composite thermoelectric material according to the carbon isotope volume percentage.
8a shows the temperature dependence of the thermal conductivity of the composite thermoelectric material according to the volume percentage of the carbon isotope.
Figure 8b shows the temperature dependence of the lattice thermal conductivity of the composite thermoelectric material according to the volume percentage of the carbon isotope.
Figure 8c shows the temperature dependence of the coefficient of performance of the composite thermoelectric material according to the volume percentage of the carbon isotope.

It is to be understood that the specific structural or functional descriptions of embodiments of the present invention disclosed herein are presented for the purpose of describing embodiments only in accordance with the concepts of the present invention, May be embodied in various forms and are not limited to the embodiments described herein.

Embodiments in accordance with the concepts of the present invention are capable of various modifications and may take various forms, so that the embodiments are illustrated in the drawings and described in detail herein. However, it is not intended to limit the embodiments according to the concepts of the present invention to the specific disclosure forms, but includes changes, equivalents, or alternatives falling within the spirit and scope of the present invention.

The terms first, second, or the like may be used to describe various elements, but the elements should not be limited by the terms. The terms may be named for the purpose of distinguishing one element from another, for example without departing from the scope of the right according to the concept of the present invention, the first element being referred to as the second element, Similarly, the second component may also be referred to as the first component.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between. Expressions that describe the relationship between components, for example, "between" and "immediately" or "directly adjacent to" should be interpreted as well.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms "comprises ", or" having ", and the like, are used to specify one or more of the features, numbers, steps, operations, elements, But do not preclude the presence or addition of steps, operations, elements, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the meaning of the context in the relevant art and, unless explicitly defined herein, are to be interpreted as ideal or overly formal Do not.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, the scope of the patent application is not limited or limited by these embodiments. Like reference symbols in the drawings denote like elements.

Fig. 1 shows an example of a method for producing a composite thermoelectric material according to one embodiment, and Fig. 2 shows an example of a melt spinning method shown in Fig.

Referring to FIGS. 1 and 2, the composite thermoelectric material may be manufactured using a thermoelectric material based on Bi (bismuth) -Te (tellurium). The thermoelectric material may comprise a Bi-Sb (antimony) -Te based thermoelectric material.

The thermoelectric material may include Bi-Sb-Te-Se (selenium). The thermoelectric material may include one represented by the following formula (1)

[Chemical Formula 1]

Bi _{2 - a} Sb _a Se _{3 - b} Te _b (0? A? 2, 0? _{B? 3} )

In one embodiment, the thermoelectric material is Bi _{0 . 36} Sb _{1 . 64} Te ₃ .

A method of making a composite thermoelectric material may include providing a pulverized thermoelectric material. The step of providing the pulverized thermoelectric material may include the steps of producing an ingot of the thermoelectric material with the element material constituting the thermoelectric material as a starting material and pulverizing the ingot of the thermoelectric material .

To produce an ingot of thermoelectric material, a high purity (99.999%) elemental phase Bi, Sb, Te granules can be metered to the formula of the thermoelectric material to be produced. For example, the amounts of Bi, Sb and Te are expressed by the formula Bi _{0 . 36} Sb _{1 . 64} Te < / RTI > ₃ .

The prepared raw materials are loaded into a quartz ampule and sealed under vacuum. The quartz ampoule is heated at 1373 K for 4 hours and then quenched with water to produce an ingot of thermoelectric material.

The composite thermoelectric material manufacturing method may include pulverizing the ingot of the thermoelectric material. The method of making a composite thermoelectric material may include mixing the pulverized thermoelectric material with the carbon isotope powder to produce a blended powder 10. The carbon isotope may include graphene and carbon nanotubes. The graphene does not diffuse into the parent phase, which is advantageous for the production of the secondary phase.

For example, after the ingot of the thermoelectric material is pulverized, it is mixed with the reduced powdered nano powder (RGO) for 1 hour by using a spex-mill to produce a mixed powder 10 .

The method for manufacturing a composite thermoelectric material may include mixing powdered pulverized thermoelectric material with an isotropic carbon powder to produce a mixed powder, and molding the mixed powder to form a ribbon.

The step of forming the ribbons 50 may be performed using a rapid solidification method. The step of forming the ribbon by molding the mixed powder according to the rapid solidification method can form particles of various shapes in addition to the ribbon shape. For example, spherical particles may be formed by molding a mixed powder using a rapid solidification method.

The rapid solidification method includes a group consisting of a melt spinning method, a gas atomization method, a plasma deposition method, a centrifugal atomization method, and a splat quenching method ≪ / RTI > For example, rapid solidification can be a melt spinning process.

The step of forming the ribbon is performed by using the melt spinning method, and the melt spinning method may include a step of melting the mixed powder and a step of cooling the molten mixed powder.

The step of forming the ribbons 50 may be performed by cold-molding the mixed powder 10. For example, the mixed powder 10 may be cold compacted with a hydraulic press and then injected into a graphite mold 20 having a nozzle of 0.4 mm diameter.

The blended powder 10 injected into the graphite mold 20 can be melt spinned to form a homogeneous mixture of nanostructuring and RGO and BST.

For example, in a melt spinning process, a Cu (copper) wheel (wheel or roller) 40 is rotated at 1000 rpm and the cold compacted powder can be melted by the induction 30. The ribbon 50 can be formed by melt spinning processing.

The ribbon 50 exhibits an amorphous structure at the contact surface and a crystalline nanostructure at the free surface. The crystalline nanostructure may have a width of 200 to 300 nm. The contact surface may refer to the surface in contact with the copper wheel 40, and the free surface may refer to the opposite surface of the contact surface.

The molten mixed powder 10 can be cooled to form the ribbon 50. [ The step of cooling the molten mixed powder 10 may include cooling to a cooling rate of 10 ⁵ K / sec to 10 ⁷ K / sec.

The method of making a composite thermoelectric material may include pulverizing the ribbon and sintering the pulverized ribbon to produce a matrix of thermoelectric materials in which the carbon isotope is dispersed.

The step of pulverizing the ribbon may comprise using a dry grinding method. The dry grinding method may be selected from the group consisting of ball milling, attrition milling, high energy milling, zet milling and mortar milling. For example, the ribbon 50 may be pulverized using a mortar and pestle.

Sintering may include spark plasma sintering or hot press sintering. For example, sintering may be spark plasma sintering.

The step of producing a matrix of the thermoelectric material in which the carbon isotope is dispersed is carried out under conditions of a temperature of 300 to 800 DEG C, a pressure condition of 1 Pa to 100 Pa and a vacuum condition for 1 minute to 10 minutes, ). ≪ / RTI >

For example, the pulverized ribbon 50 can be sintered for 3 minutes at a temperature condition of 753 K and a pressure of 60 MPa. The pulverized ribbon 50 may be spark plasma sintered to form a pellet comprising a matrix of thermoelectric materials in which the carbon isotope is dispersed. The formed pellets may have a diameter of 12.5 mm and a size of 10 mm.

Graphene can reduce the grain size by preventing grain-to-grain diffusion during sintering. The graphene can improve the thermoelectric performance of the composite thermoelectric material by increasing the mobility and reducing the lattice thermal conductivity while maintaining the charge density.

The composite thermoelectric material manufacturing method exemplified herein can be applied to various thermoelectric materials such as skutterudite, half-Heusler, and PbTe.

Fig. 3A shows an example of a scanning electron microscope (SEM) image of the ribbon contact surface shown in Fig. 2, Fig. 3B shows an example of a SEM image of the ribbon free surface shown in Fig. 2, Lt; RTI ID = 0.0 > RGO < / RTI >

Referring to Figure 3a-3c, Figure 3a to 3c are Bi _{0. 36} Sb _{1 . 64} < / RTI > Te ₃ and RGO. Due to the turbulent flow of the melted thermoelectric material in the melt spinning process, a composite thermoelectric material comprising carbon isotope homogeneously dispersed in a matrix of thermoelectric materials can be obtained.

The carbon isoterms can be uniformly dispersed in the matrix of the thermoelectric material due to the high cooling rate (10 ⁵ K / sec to 10 ⁷ K / sec) in the melt spinning process. A carbon isotope having a high charge mobility can cause a matrix of thermoelectric materials to have a high charge mobility. Also, as the boundary between the thermoelectric material and the carbon isotope increases due to the combination of the carbon isotope and the thermoelectric material, the scattering of the phonon may increase.

The ribbon 50 formed by the melt spinning process may have different microstructures, distinguished by a contact surface and a free surface. As shown in FIGS. 3A and 3B, the contact surface has an amorphous phase due to the high cooling rate, but the free surface can have a crystal structure of 200 to 300 nm width.

Since the volume percentage of carbon isotope dispersed in the composite thermoelectric material is very low, it is not easy to find a carbon isotope dispersed in the composite thermoelectric material as shown in FIG. 3C. The carbon isotope is from 1 to 5 micrometers in size and can be found infrequently on a free surface. When carbon isotopes and thermoelectric materials are mixed, carbon isotopes can float in the matrix of thermoelectric materials due to the low molecular weight of the carbon isotopes.

4A shows an example of a SEM image of a fracture surface of a composite thermoelectric material pellet containing a carbon isotope, and FIG. 4B shows an SEM image of a fracture surface of a composite thermoelectric material pellet containing a 0.1 vol. 4C shows an example of a SEM image of the fracture surface of a composite thermoelectric material pellet containing 0.4 volume percent carbon isotope, and FIG. 4D shows an example of a SEM image of a fracture cross section of a composite thermoelectric material pellet containing 0.8 volume percent carbon isotope ≪ / RTI >

Referring to Figures 4a to 4d, a composite thermoelectric material includes a matrix of thermoelectric material and an allotrope of carbon dispersed in a matrix. The thermoelectric material may include a thermoelectric material based on BST (Bi-Sb-Te). For example, a BST (Bi-Sb-Te) based thermoelectric material is Bi _{0 . 36} Sb _{1 . 64} Te ₃ .

The carbon isotope may include graphene and carbon nanotubes. The graphene may comprise graphene stripped with a tape, CVD (Chemical Vapor Deposition) grown graphene, graphene oxide made with the Hummer's method and reduced graphene oxide (RGO). have. The carbon nanotubes may include single wall carbon nanotubes, double wall carbon nanotubes, and multiwall carbon nanotubes.

The carbon isotope may be included in the composite thermoelectric material in a volume fraction (vol.%) Of less than 10. The grain size of the composite thermoelectric material may be smaller than the grain size of a pristine thermoelectric material that does not contain carbon isotopes.

Figs. 4A to 4C are diagrams showing the relationship between Bi _{0 . 36} Sb _{1 . 64} Te ₃ and using RGO as the carbon isotope. The fracture profile of the composite thermoelectric material containing RGO dispersed in the matrix of Bi _{0 .36} Sb _1.64 Te ₃ is a plate-shaped grain showing the typical microstructure of the Bi ₂ Te ₃ -based polycrystalline material, .

Bi ₀ combined with RGO _{. 36} Sb _{1 .} The grain size of ₆₄ Te ₃ is the pristine Bi _{0 . 36} Sb _{1 . 64} Te ₃ grain size. Bi ₀ combined with RGO _{. 36} Sb _{1 .} The average grain size of ₆₄ Te ₃ decreased to 29.4 μm, 25.1 μm and 20.1 μm 19.7 μm as the volume percentages of RGO increased to 0 vol.%, 0.1 vol.%, 0.4 vol.% And 0.8 vol.%, Respectively . The grain size can be measured by averaging the sizes of ten or more grains.

That is, the composite thermoelectric material containing RGO has a smaller grain size than the Pristine thermoelectric material not including RGO, and the grain size of the composite thermoelectric material can be controlled by controlling the ratio of RGO.

As the grain size decreases, the scattering at the grain boundary increases, and the lattice thermal conductivity (k _lat ) can be lowered.

5 shows an example of an X-ray diffraction (XRD) pattern performed in a direction perpendicular to the spark plasma sintering direction of the composite thermoelectric material.

Referring to FIG. 5, Bi _{0 . 36} Sb _{1 .} The XRD pattern of ₆₄ Te ₃ can represent the fundamental diffraction peaks of Sb ₂ Te ₃ of a rhombohedral structure with no impurity peak. The degree of anisotropy of the XRD sample can be calculated as the ratio of the peak intensity of the 006 plane to the peak intensity of the 015 plane (I ₀₀₆ / I ₀₁₅ ). The calculated degree of anisotropy may have a value of 0.04 to 0.06 and all the composite thermoelectric materials may have a small anisotropy.

It is seen that in accordance with the volume percentage of RGO unless anisotropic degree is very different, the addition of RGO Bi _{0. 36} Sb _{1 .} It can be seen that does not substantially change the crystalline structure of ₆₄ Te _3.

FIG. 6A shows an example of a result of Raman spectroscopy performed on a carbon isotope, and FIG. 6B shows an example of a result of Raman spectroscopy performed on a composite thermoelectric material.

6A and 6B, the crystallinity of the carbon isotope and the composite thermoelectric material can be measured. For example, the carbon isotope is RGO and the composite thermoelectric material is Bi _{0 . 36} Sb _{1 . 64} Te ₃ matrix.

The Raman spectroscopy results of Figures 6a and 6b can represent typical peaks of carbon based materials. G peak (~ 1350 cm ^{- 1)} and the D peak (~ 1600 cm ^{- 1)} can be derived from each of the graphite (graphite) structure and a carbon defect (defective carbon).

Bi _{0 in} which RGO and RGO are dispersed _{. 36} Sb _{1 .} The I _G / I _D values of the ₆₄ Te ₃ matrix can have 1.06 and 1.16, respectively. The crystallinity of the Bi _0.36 Sb _1.64 Te ₃ matrix in which the RGO is dispersed in the heating process in the melt spinning process can be improved. The improvement of the crystallinity can lead to an increase in electrical conductivity (σ).

7a shows an example of the temperature dependence of the electrical conductivity of the composite thermoelectric material according to the carbon isotope volume percentage.

Referring to FIG. 7A, the performance of the thermoelectric material is determined by a dimensionless coefficient of performance ZT. ZT can be expressed by Equation (1).

Where S denotes the electrical conductivity, S denotes the Seebeck coefficient, T denotes the absolute temperature, and k denotes the thermal conductivity.

Further, the power factor PF can be defined as in Equation (2).

In order to produce good thermoelectric materials, it should be possible to have low thermal conductivity with high electrical conductivity and Seebeck coefficient. However, since the electric conductivity and the Seebeck coefficient of the thermoelectric material have an inverse relationship with the carrier concentration, it may be difficult to improve the power factor of the thermoelectric material.

The thermal conductivity (k) is determined by the sum of the lattice thermal conductivity k _lat and the electronic thermal conductivity k _el as shown in Equation (3). The electronic thermal conductivity K _el can be calculated by the Wiedemann-Franz law as shown in equation (4).

Where L is the Lorenz number.

The graph of Fig. 7A shows the electrical conductivity when the volume percentage of RGO is 0, 0.1, 0.4, and 0.8. When the temperature is increased from room temperature to 473K, the semiconductor behavior deteriorates and the electrical conductivity σ decreases. The electrical conductivity increased to 1395 S / cm, 1407 S / cm and 1580 S / cm, respectively, as the volume percentage of RGO increased to 0, 0.1 and 0.4 at room temperature.

Due to the high electrical conductivity of RGO, RGO - dispersed composite thermoelectric materials can have higher electrical conductivity than Pristine thermoelectric materials without RGO. However, it can be seen that when the volume percentage of RGO is high, the dispersion may not be good. Therefore, it can be seen that when the volume percentage of RGO is 0.8, the electrical conductivity is slightly reduced to 1333 S / cm at room temperature.

The carrier concentration of the samples can be estimated using the Hall Coefficient R _H. The Hall coefficient can be expressed by Equation (5).

Here, p and e represent a hole carrier concentration and an electron charge, respectively. The hole carrier mobility () can be obtained using Equation (6).

FIG. 7B shows an example of changes in carrier concentration and mobility of the composite thermoelectric material according to the volume percentage of the carbon isotope.

Referring to FIG. 7B, the composite thermoelectric material may have a higher hole carrier mobility than the pristine thermoelectric material that does not include the carbon isotope.

7B, the carrier concentration and the mobility of the composite thermoelectric material can be shown. At room temperature, the carrier concentration is constant according to the volume percentage of RGO, but the mobility increases from 223 cm ² / Vs to 253 cm ² / Vs as the volume percentage of RGO increases from 0 to 0.4.

The hole carrier mobility of the composite thermoelectric material can be greatly improved by being combined with the carbon isotope having a high carrier mobility. When the volume percentage of RGO is 0.1, Pristine Bi _{0 . 36} Sb _{1 . 64} Te ₃ and the RGO volume fraction of 0.8 may have a lower carrier mobility than Pristin Bi _0.36 Sb _1.64 Te ₃ due to the poor dispersion of RGO.

The electrical conductivity σ (T) with temperature can follow the exponential rule of T ^-1.5 in the temperature range from room temperature to 473K, which may indicate that the hole carrier transmission is dominated by acoustic phonon scattering.

FIG. 7C shows an example of the temperature dependence of the Seebeck coefficient of the composite thermoelectric material according to the percentage of the carbon isotope volume.

Referring to FIG. 7C, the change in the Seebeck coefficient of Bi _0.36 Sb _1.64 Te ₃ is found when the volume percentage of RGO changes to 0, 0.1, 0.4, and 0.8. It can be seen that the major carrier is a hole, since the whiteness factor has a positive value in all samples.

As the temperature increases, the Seebeck coefficient increases, which may be due to thermal excitation of the minor carriers at high temperatures. At room temperature, the Seebeck coefficient can be 170, 172, 171, 166 uV / K when the volume percentages of RGO are 0, 0.1, 0.4 and 0.8, respectively. It can be seen that the Seebeck coefficient has a similar value even if the RGO volume percentage changes.

The composite thermoelectric material produced by the method of preparing a composite thermoelectric material has a high electric conductivity due to an improved hole mobility and has a constant value of the Seebeck coefficient, Scale-up process.

7D shows an example of the temperature dependence of the power factor of the composite thermoelectric material according to the volume percentage of the carbon isotope.

Referring to FIG. 7D, it can be seen that the power factor decreases with increasing temperature. It can be seen that the power factor has the highest value at 46 × 10 ^-4 W / mK ² when the volume percentage of RGO is 0.4 at room temperature. When the volume percentage of RGO is 0, 0.1, and 0.8, respectively, the power factor is 40 × 10 ^-4 W / mK ² , 42 × 10 ^-4 W / mK ² , and 47 × 10 ^-4 W / mK ² , respectively. The optimal RGO volume percentage is 0.4 and can have a 20% power factor improvement over Pristine Bi _0.36 Sb _1.64 Te ₃ without RGO.

8a shows the temperature dependence of the thermal conductivity of the composite thermoelectric material according to the volume percentage of the carbon isotope.

Referring to FIG. 8A, the thermal conductivity shows a similar value depending on the temperature regardless of the volume percentage of RGO, and shows a bipolar conduction which decreases with increasing temperature and slightly increases at high temperature . A sample of Bi _0.36 Sb _1.64 Te _{3 in} which RGO was dispersed was Pristine Bi _{0 . 36} Sb _{1 . It} has a lower thermal conductivity than the ₆₄ Te ₃ sample.

From the assumption of a single parabolic band (SPB) model having acoustic phonon scattering, the Lorentz number can be calculated using the Fermi integral of Equations (7) and (8).

Here, F _n (ξ) and ξ may correspond to Fermi integral and reduced Fermi energy (E _F -E _C ) / k _T , respectively, and r for acoustic phonon scattering may correspond to -1 / 2 < / RTI > The Lorentz number can be calculated as shown in Equation (9) using Equation (7) and Equation (8).

The number of Lorentz calculated according to Equation (9) can range from 1.61 × 10 ^-9 WΩ / K ² to 1.69 × 10 ^-9 WΩ / K ² in a range of from room temperature to 473K.

Figure 8b shows the temperature dependence of the lattice thermal conductivity of the composite thermoelectric material according to the volume percentage of the carbon isotope.

Referring to FIG. 8B, the lattice thermal conductivity k _lat can be calculated using the calculated Lorentz number. If the volume percentage of the 0.4 value RGO lowest lattice thermal conductivity at 374 K can be confirmed that represents the 0.63 W / mK, which pristine Bi _{0. 36} Sb _{1 . The} value can be 11% lower than the lattice thermal conductivity value (0.71 W / mK) of ₆₄ Te ₃ .

The reduction in the lattice thermal conductivity value may be due to the enhanced scattering effect at the interface between the carbon isotope and the thermoelectric material and the reduced grain size. In samples with a high RGO volume percentage, the lattice thermal conductivity may increase due to poor dispersion of RGO.

Figure 8c shows the temperature dependence of the coefficient of performance of the composite thermoelectric material according to the volume percentage of the carbon isotope.

Referring to FIG. 8C, it can be seen that the composite thermoelectric material has a higher coefficient of performance (ZT) than a pristine thermoelectric material containing no carbon isotope.

The maximum performance factor increases as the RGO volume percentage increases to 0, 0.1 and 0.4, and the maximum performance factor is 1.16 at a temperature of 393 K when the volume percentage is 0.4. The coefficient of performance in all samples tends to be similar with temperature. This similar trend means that the RGO bond did not affect the electronic band structure of the thermoelectric material.

By combining thermoelectric material and carbon isotope, high hole carrier mobility can be achieved and low lattice thermal conductivity due to enhanced phonon boundary scattering can be achieved.

Highly pure Bi (99.999%, 5N Plus) , Sb (99.999%, 5N Plus) and Te (99.999%, 5N Plus) a granule (granule) Bi _{0. 36} Sb _{1 . 64} Te ₃ as starting materials. An excess of 1 wt% Te was further added to compensate for Te volatilization. The raw materials were loaded into a quartz ampule and sealed under vacuum. The ampoule was heated at 1373 K for 4 hours and quenched to obtain an ingot.

The ingot was pulverized and milled for 1 hour with spex-mill, and the ingot was mixed with RGO nano powder (purchased from graphene-supermarket.com). The blended powder was injected into a 0.4 mm diameter graphite mold.

Using the apparatus shown in Fig. 1, a melt-spinning treatment was performed to obtain a homogeneous, nanostructured RGO / BST mixture. The copper wheel was rotated at 1000 rpm in the melt spinning process, and the cold compacted powder was melted by induction.

As shown in FIG. 2, the ribbon 50 formed through melt spinning had a crystalline nanostructure (200-300 nm width) at the free surface (FS) with an amorphous structure at the contact surface (CS). The fused spinning ribbon was pulverized with a powder and spark plasma sintering (SPS) was performed at 753 K, 60 MPa for 3 minutes. The sintered pellets had a diameter of 12.5 mm and a height of 10 mm.

Spark plasma sintered samples were subjected to X-ray diffraction (XRD, New D8 Advance, Bruker, Cu Kα) measurements perpendicularly and horizontally to the compression plane direction of the spark plasma sintering. The results are shown in Fig. Microstructures were investigated with SEM (JSM-7600F, JEOL). In addition, as shown in Figs. 6A and 6B, the crystallinity of RGO and sintered samples was measured with Raman spectroscopy.

As shown in FIG. 7A, the electric conductivity () was measured at a temperature of 473 K using a four point probe method with a ZEM-3 apparatus (ULVAC-RIKO), and the results shown in FIG. Likewise, the Seebeck coefficient (S) was measured. As shown in FIG. 7B, carrier concentration and mobility (μ) were measured using a Hall effect measurement system (HT-Hall, ResiTest 8300, Toyo Corporation). Thermal conductivity (k) was measured by laser-flash analysis using Netzsch LFA 457, as shown in Figure 8A. These properties are summarized in Table 1 below.

Properties \ RGO content 0 vol. % 0.1 vol. % 0.4 vol. % 0.8 vol. % σ (RT) 1395 S / cm 1407 S / cm 1580 S / cm 1333 S / cm S (RT) 170 uV / K 172 uV / K 171 uV / K 166 uV / K μ (RT) 223 cm ² / Vs 219 cm ² / Vs 253 cm ² / Vs 210 cm ² / Vs PF (RT) 40 × 10 ^-4 W / mK ² 42 × 10 ^-4 W / mK ² 46 × 10 ^-4 W / mK ² 37 × 10 ^-4 W / mK ² k _lat (347K) 0.71 W / mK 0.68 W / mK 0.63 W / mK 0.67 W / mK ZT (393K) 1.01 1.11 1.16 1.02

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI > or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (20)

A matrix of thermoelectric material; And
Allotrope of carbon dispersed in the matrix,
/ RTI >
The method according to claim 1,
The thermo-
A composite thermoelectric material comprising a Bi-Sb-Se-Te based thermoelectric material.
3. The method of claim 2,
The Bi-Sb-Se-Te based thermoelectric material,
A composite thermoelectric material comprising a material represented by the following formula (1).
Formula 1
Bi _{2 - a} Sb _a Se _{3 - b} Te _b (0? A? 2, 0? _{B? 3} )
The method according to claim 1,
The above-
Graphene, and carbon nanotubes.
Composite thermoelectric materials.
5. The method of claim 4,
The graphene
Tape-graphene graphene, CVD (Chemical Vapor Deposition) grown graphene, graphene oxide prepared by the Hummer's method, and reduced graphene oxide,
The carbon nanotubes may include,
Including single-walled carbon nanotubes, double-walled carbon nanotubes and multi-walled carbon nanotubes
Composite thermoelectric materials.
The method according to claim 1,
The above-
The composite thermoelectric material is contained in an amount of 10 vol.% Or less
Composite thermoelectric materials.
The method according to claim 1,
The grain size of the composite thermoelectric material is smaller than the grain size of a pristine thermoelectric material not containing the carbon isotope
Composite thermoelectric materials.
The method according to claim 1,
In the composite thermoelectric material,
The material having a higher hole carrier mobility than the pristine thermoelectric material containing no carbon isotope
Composite thermoelectric materials.
The method according to claim 1,
Wherein the composite thermoelectric material has a higher coefficient of performance (ZT) than the pristine thermoelectric material that does not include the carbon isotope
Composite thermoelectric materials.
Providing a pulverized thermoelectric material;
Mixing the pulverized thermoelectric material with an isotopic carbon powder to produce a mixed powder;
Shaping the mixed powder to form a ribbon;
Pulverizing the ribbon; And
Sintering the pulverized ribbon to produce a matrix of thermoelectric materials in which the carbon isotope is dispersed
≪ / RTI >
11. The method of claim 10,
Wherein providing the pulverized thermoelectric material comprises:
Generating an ingot of a thermoelectric material by using an element material constituting the thermoelectric material as a starting material; And
Pulverizing the ingot of the thermoelectric material;
≪ / RTI >
11. The method of claim 10,
Wherein the carbon isotope is selected from graphene and carbon nanotubes
A method for manufacturing a composite thermoelectric material.
11. The method of claim 10,
Wherein forming the ribbon comprises:
Which is carried out using the rapid solidification method
A method for manufacturing a composite thermoelectric material.
14. The method of claim 13,
In the rapid solidification method,
And is selected from the group consisting of a melt spinning method, a gas atomization method, a plasma deposition method, a centrifugal atomization method, and a splat quenching method.
A method for manufacturing a composite thermoelectric material.
15. The method of claim 14,
Wherein forming the ribbon comprises:
Is performed using the melt spinning method,
In the melt spinning method,
Melting the mixed powder; And
Cooling the molten mixed powder
≪ / RTI >
16. The method of claim 15,
Wherein the cooling step comprises:
Cooling to a cooling rate of 10 ⁵ K / sec to 10 ⁷ K / sec
≪ / RTI >
11. The method of claim 10,
Wherein the step of grinding the ribbon comprises:
Pulverizing the ribbon using a dry grinding method
≪ / RTI >
18. The method of claim 17,
In the dry grinding method,
And is selected from the group consisting of ball milling, attrition milling, high energy milling, zet milling and mortar milling.
A method for manufacturing a composite thermoelectric material.
11. The method of claim 10,
Preferably,
Spark plasma sintering or hot press sintering.
≪ / RTI >
11. The method of claim 10,
Wherein generating the matrix comprises:
Sintering the pulverized ribbon for 1 minute to 10 minutes under at least one of a temperature condition of 300 DEG C to 800 DEG C, a pressure condition of 1 Pa to 100 Pa and a vacuum condition
≪ / RTI >

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