KR102032194B1 - Composite thermoelectric material and preparation method thereof - Google Patents

Abstract

Composite thermoelectric materials and methods of making the same are disclosed. The composite thermoelectric material according to one embodiment includes a matrix of thermoelectric material and an alloy of carbon dispersed in the matrix.

Description

Composite thermoelectric material and its manufacturing method {COMPOSITE THERMOELECTRIC MATERIAL AND PREPARATION METHOD THEREOF}

The present disclosure relates to composite thermoelectric materials and methods of making the same.

Thermoelectric (TE) technology is an energy collection technology that is being developed as a renewable and sustainable energy source in response to global demand to reduce greenhouse gases causing global warming.

Thermoelectric technology is expected to play an important role in generating power from waste heat. Since the efficiency of a thermoelectric device is highly dependent on the performance of the thermoelectric material, high performance thermoelectric materials are very important in converting waste heat into electricity to generate power or using electricity to generate temperature differences to cool.

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

The coefficient of performance is defined as the power factor multiplied by the square of the electrical conductivity and the Seebeck coefficient multiplied by the temperature and then divided by the thermal conductivity. The electrical conductivity and the Seebeck coefficient have an inverse relationship with the carrier concentration, which makes it difficult to increase the performance coefficient.

For this reason, the performance factor was considered to have a limit of 1 for a long time. However, recent research has developed thermoelectric materials with performance coefficients above 1 by lowering thermal conductivity.

Korea Patent Publication No. 10-2014-0139908 (2014. 12. 08)

The embodiments described below provide composite thermoelectric materials with high coefficients of performance and techniques for making them.

The composite thermoelectric material according to one embodiment includes a matrix of thermoelectric material and an alloy 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 consisting of Chemical Formula 1 below.

[Formula 1]

Bi _2-a Sb _a Se _3-b Te _b (0≤a≤2, 0≤b≤3)

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

The graphene may include graphene peeled off from a tape, chemical vapor deposition (CVD) grown graphene, graphene oxide prepared by Hummers' method, and reduced graphene oxide. The carbon nanotubes may include single wall carbon nanotubes, double wall carbon nanotubes, and multiwall carbon nanotubes.

The carbon allotrope is in the composite thermoelectric material, based on the total volume of the composite thermoelectric material, up to 10% by volume (vol%), preferably in an amount of 0.1 vol% to 0.8 vol%, most preferably 0.4 May be included in an amount of vol%.

The grain size of the composite thermoelectric material may be smaller than the grain size of a pristine thermoelectric material that does not include the carbon allotrope.

The composite thermoelectric material may have a higher hole carrier mobility than the pristine thermoelectric material not containing the carbon allotrope.

The composite thermoelectric material may have a higher coefficient of performance (ZT) than a pristine thermoelectric material not containing the carbon allotrope.

According to one embodiment, a method of manufacturing a composite thermoelectric material includes: providing a pulverized thermoelectric material, mixing the pulverized thermoelectric material with a carbon allotrope powder to generate a mixed powder; Forming a ribbon by molding the mixed powder; pulverizing the ribbon; and sintering the pulverized ribbon to produce a matrix of thermoelectric material in which carbon allotrope is dispersed. do.

Providing the pulverized thermoelectric material may include generating an ingot of a thermoelectric material using the elemental material constituting the thermoelectric material as a starting material, and pulverizing the ingot of the thermoelectric material. It may include the step.

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

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

The rapid solidification method is a melt spinning method, a gas atomization method, a plasma deposition method, a centrifugal atomization method and a splat quenching method. It may be selected from the group consisting of.

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

The cooling may include cooling at a cooling rate of 10 ⁵ K / sec to 10 ⁷ K / sec.

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

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

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

Generating the matrix may include sintering the pulverized ribbon for 1 minute 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.

1 shows an example of a method of manufacturing a composite thermoelectric material according to one embodiment.
FIG. 2 shows an example of the melt spinning method shown in FIG. 1.
3A shows an example of a scanning electron microscope (SEM) image of the ribbon contact surface shown in FIG. 2.
3B shows an example of an SEM image of the ribbon free surface shown in FIG. 2.
FIG. 3C shows an example of an SEM image of reduced graphene oxide (RGO) dispersed in the ribbon shown in FIG. 2.
4A shows an example of an SEM image of the fracture surface of a thermoelectric material pellet without carbon allotrope.
4B shows an example of an SEM image of the fracture surface of a composite thermoelectric material pellet containing 0.1 volume percent RGO.
4C shows an example of an SEM image of the fracture surface of a composite thermoelectric material pellet with 0.4% by volume of RGO.
4D shows an example of an SEM image of the fracture surface of a composite thermoelectric material pellet with 0.8% volume 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.
6A shows an example of the result of performing Raman spectroscopy on a carbon allotrope.
6B shows an example of the results of performing Raman spectroscopy on a composite thermoelectric material.
7A shows an example of the temperature dependence of the electrical conductivity of a composite thermoelectric material according to the carbon allotrope volume percentage.
7B shows an example of changes in carrier concentration and mobility of the composite thermoelectric material according to carbon allotrope volume percentage.
7C shows an example of the temperature dependence of the Seebeck Coefficient of the composite thermoelectric material according to the carbon allotrope volume percentage.
7D shows an example of the temperature dependence of the Power Factor of the composite thermoelectric material according to the carbon allotrope volume percentage.
8A shows the temperature dependence of the thermal conductivity of a composite thermoelectric material according to the volume percentage of carbon allotrope.
8B shows the temperature dependence of the lattice thermal conductivity of the composite thermoelectric material according to the volume percentage of carbon allotrope.
8C shows the temperature dependence of the coefficient of performance of the composite thermoelectric material according to the volume percentage of carbon allotrope.

Specific structural or functional descriptions of the embodiments according to the inventive concept disclosed herein are merely illustrated for the purpose of describing the embodiments according to the inventive concept, and the embodiments according to the inventive concept. These may be embodied in various forms and are not limited to the embodiments described herein.

Embodiments according to the inventive concept may be variously modified and have various forms, so embodiments are illustrated in the drawings and described in detail herein. However, this is not intended to limit the embodiments in accordance with the concept of the present invention to specific embodiments, and includes modifications, equivalents, or substitutes included in the spirit and scope of the present invention.

Terms such as first or second may be used to describe various components, but the components should not be limited by the terms. The terms are only for the purpose of distinguishing one component from another component, for example, without departing from the scope of the rights according to the inventive concept, the first component may be called a second component, Similarly, the second component may also be referred to as the first component.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected to or connected to that other component, but it may be understood that other components may be present in between. Should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between. Expressions describing relationships between components, such as "between" and "immediately between" or "directly neighboring", 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. Singular expressions include plural expressions unless the context clearly indicates otherwise. As used herein, the terms "comprise" or "have" are intended to designate that the stated feature, number, step, operation, component, part, or combination thereof is present, but one or more other features or numbers, It is to be understood that it does not exclude in advance the possibility of the presence or addition of steps, actions, components, 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. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art, and are not construed in ideal or excessively formal meanings unless expressly defined herein. Do not.

Hereinafter, exemplary 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 numerals in the drawings denote like elements.

FIG. 1 illustrates an example of a method of manufacturing a composite thermoelectric material, and FIG. 2 illustrates an example of a melt spinning method illustrated in FIG. 1.

1 and 2, the composite thermoelectric material may be manufactured using a Bi (bismuth) -Te (tellurium) based thermoelectric material. The thermoelectric material may include 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 Formula 1 below:

[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 . It} can be ₆₄ Te ₃ .

The method of manufacturing a composite thermoelectric material may include providing a pulverized thermoelectric material. Providing the pulverized thermoelectric material may include generating an ingot of the thermoelectric material using the elemental material constituting the thermoelectric material as a starting material, and grinding the ingot of the thermoelectric material. .

To produce ingots of thermoelectric materials, high purity (99.999%) elemental Bi, Sb, Te granules can be metered according to the chemical formula of the thermoelectric material to be prepared. For example, the amount of Bi, Sb, Te is represented by the formula Bi _{0 . 36} Sb _{1 .} It can be weighed to ₆₄ Te 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 create an ingot of thermoelectric material.

The method of manufacturing a composite thermoelectric material can include pulverizing an ingot of a thermoelectric material. The method of manufacturing a composite thermoelectric material may include mixing the pulverized thermoelectric material with the carbon allotrope powder to produce the mixed powder 10. The carbon allotrope may comprise graphene and carbon nanotubes. Graphene does not diffuse in the mother phase, which is advantageous for producing the secondary phase.

For example, the ingot of the thermoelectric material is pulverized and then mixed with the reduced graphene oxide (RGO) nanopowder reduced for 1 hour using a spex-mill to produce a mixed powder 10. Can be.

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

Forming the ribbon 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 may form particles of various shapes in addition to the ribbon form. For example, the spherical particles may be formed by molding the mixed powder using the rapid solidification method.

Rapid solidification method is a group consisting of melt spinning method, gas atomization method, plasma deposition method, centrifugal atomization method and splat quenching method It may be selected from. For example, the rapid solidification method may be a melt spinning method.

Forming the ribbon may be performed using a melt spinning method, which may include melting the mixed powder and cooling the molten mixed powder.

Forming the ribbon 50 may be performed by cold forming the mixed powder 10. For example, the mixed powder 10 may be cold compacted by a hydraulic press and then injected into a graphite mold 20 having a 0.4 mm diameter nozzle.

The mixed powder 10 injected into the graphite mold 20 may be melt spun to form nanostructures and a homogeneous mixture of RGO and BST.

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

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

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

The method of manufacturing a composite thermoelectric material may include pulverizing a ribbon, and sintering the pulverized ribbon to generate a matrix of thermoelectric materials in which carbon allotrope is dispersed.

Crushing the ribbon may include using a dry crushing method. The dry grinding method may be selected from the group consisting of ball milling, attrition milling, high energy milling, jet milling and mortar bowl grinding. For example, the ribbon 50 can be milled using a mortar and pestle.

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

The step of producing a matrix of thermoelectric material in which the carbon allotrope is dispersed may be performed for 1 minute 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. Sintering) may be included.

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

Graphene can reduce grain size by preventing diffusion between parent grains during the sintering process. Graphene can improve the thermoelectric performance of composite thermoelectric materials by increasing mobility and lowering lattice thermal conductivity while maintaining charge concentrations.

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

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 an SEM image of the ribbon free surface shown in FIG. 2, and FIG. 3C is shown in FIG. An example of an SEM image of the RGO dispersed in the ribbon is shown.

3A-3C, FIGS. 3A-3C show Bi _{0 . 36} Sb _{1 .} An image of a ribbon 50 produced from a mixed powder of ₆₄ Te ₃ and RGO is shown. Due to the turbulent flow of the molten thermoelectric material in the melt spinning process, a composite thermoelectric material comprising carbon allotrogen uniformly dispersed in a matrix of thermoelectric material can be obtained.

The high cooling rate (10 ⁵ K / sec to 10 ⁷ K / sec) in the melt spinning process allows the carbon allotrope to be uniformly dispersed in the matrix of thermoelectric material. Carbon allotrope with high charge mobility can cause the matrix of thermoelectric material to have high charge mobility. In addition, as the boundary between the thermoelectric material and the carbon allotrope increases due to the combination of the carbon allotrope and the thermoelectric material, scattering of phonons may increase.

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

Since the volume percentage of carbon allotrope dispersed in the composite thermoelectric material is very low, it is not easy to find the carbon allotrope dispersed in the composite thermoelectric material as shown in FIG. 3C. Carbon allotropees are 1 to 5 micrometers in size and can be rarely found on free surfaces. When the carbon allotrope and thermoelectric material are mixed, the carbon allotrope can float in the matrix of the thermoelectric material due to the low molecular weight of the carbon allotrope.

4A shows an example of an SEM image of the fracture surface of a composite thermoelectric material pellet not including carbon allotrope, and FIG. 4B is an SEM image of the fracture surface of a composite thermoelectric material pellet containing 0.1 volume percent carbon allotrope. 4C shows an example of an SEM image of the fracture surface of a composite thermoelectric material pellet containing 0.4 volume percent carbon allotrope, and FIG. 4D shows a fracture surface of the composite thermoelectric material pellet containing 0.8 volume percentage carbon allotrope. An example of an SEM image is shown.

4A-4D, the composite thermoelectric material includes a matrix of thermoelectric material and an alloy of carbon dispersed in the matrix. The thermoelectric material may include a Bi-Sb-Te (BST) based thermoelectric material. For example, BST (Bi-Sb-Te) based thermoelectric materials are Bi _{0 . 36} Sb _{1 . And 64} Te ₃ .

Carbon allotrope may include graphene and carbon nanotubes. Graphene may include graphene peeled off from tape, chemical vapor deposition (CVD) grown graphene, graphene oxide produced by Hummer's method and reduced graphene oxide (RGO). have. Carbon nanotubes may include single wall carbon nanotubes, double wall carbon nanotubes, and multiwall carbon nanotubes.

The carbon allotrope may be included in the composite thermoelectric material in a volume percentage (vol.%) Of 10 or less. The grain size of the composite thermoelectric material may be small compared to the grain size of the pristine thermoelectric material without carbon allotrope.

4a to 4c are Bi _{0 . 36} Sb _{1 . The} image of the fracture surface of the composite thermoelectric material produced using ₆₄ Te ₃ and RGO as the carbon allotrope is shown. Bi _{0 .36} Sb _1.64 Te fracture surface of the composite thermal transfer material comprising a dispersion of ₃ to RGO matrix Bi ₂ Te grain (grain) of the _third polycrystalline typical microstructure of plate-like (plate-shape) indicating the material of the base Has

Bi ₀ combined with RGO _{. 36} Sb _{1 .} The grain size of ₆₄ Te ₃ is based on pristine Bi _{0 . 36} Sb _{1 . It} may be smaller than the grain size of ₆₄ Te ₃ . Bi ₀ combined with RGO _{. 36} Sb _{1 .} The average grain size of ₆₄ Te ₃ decreases to 29.4 um, 25.1 um, 20.1 um and 19.7 um as the volume percentage of RGO increases to 0 vol.%, 0.1 vol.%, 0.4 vol.%, 0.8 vol.%. Can be. Grain size can be measured by averaging the sizes of ten or more grains.

That is, the composite thermoelectric material including the RGO has a smaller grain size than the pristine thermoelectric material without the RGO, and the grain size of the composite thermoelectric material may be controlled by adjusting the ratio of RGO.

As the grain size becomes smaller, scattering at the grain boundary can be increased, resulting in lower lattice thermal conductivity (k _lat ).

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.

5, Bi _{0 . 36} Sb _{1 .} The XRD pattern of ₆₄ Te ₃ may represent basic diffraction peaks showing Sb ₂ Te ₃ of a rhombohedral structure without impurity peaks. The degree of anisotropy of the XRD sample can be calculated as the ratio of the peak intensity of the 006 plane (I ₀₀₆ / I ₀₁₅ ) to the peak intensity of the 015 plane. The calculated degree of anisotropy can have a value between 0.04 and 0.06 and all composite thermoelectric materials can have a small anisotropy.

Since the degree of anisotropy does not vary significantly with the percentage of volume of RGO, the addition of RGO is Bi _{0 . 36} Sb _{1 .} It can be seen that the crystal structure of ₆₄ Te ₃ hardly changes.

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

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

The Raman spectroscopy results of FIGS. 6A and 6B may represent typical peaks of a carbon based material. 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).

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

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

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

Where s represents electrical conductivity, S represents Seebeck coefficient, T represents absolute temperature, and k represents thermal conductivity.

In addition, the power factor PF may be defined as in Equation 2.

To make a good thermoelectric material, it must be able to have high electrical conductivity and Seebeck coefficient and low thermal conductivity. However, since the electrical conductivity and Seebeck coefficient of the thermoelectric material are inversely related to the carrier concentration, it can be difficult to improve the power factor of the thermoelectric material.

Thermal conductivity k is determined by the sum of lattice thermal conductivity k _lat and electron thermal conductivity k _el , as shown in Equation 3 below. The electronic thermal conductivity K _el may be calculated by the Wiedemann-Franz law as shown in Equation 4.

Where L is the Lorentz number.

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

Due to the high electrical conductivity of the RGO, the composite thermoelectric material in which the RGO is dispersed may have a higher electrical conductivity than the pristine thermoelectric material without the RGO. However, if the volume percentage of the RGO is not good dispersion, it can be seen that when the volume percentage of the RGO is 0.8, the electrical conductivity slightly decreases 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 may be expressed as in Equation 5.

Where p and e represent hall carrier concentration and electron charge, respectively. The hole carrier mobility (mo) may be obtained by using Equation 6.

7B shows examples of changes in carrier concentration and mobility of the composite thermoelectric material depending on the volume percentage of carbon allotrope.

Referring to FIG. 7B, the composite thermoelectric material may have a higher hole carrier mobility than the pristine thermoelectric material not including the carbon allotrope.

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

The hole carrier mobility of the composite thermoelectric material can be greatly improved by combining with a carbon allotrope having a high carrier mobility. If the volume percentage of RGO is 0.1, Pristine Bi ₀ without RGO _{. 36} Sb _{1 .} Carrier mobility similar to ₆₄ Te ₃ can be exhibited, and when the RGO volume percentage is 0.8, the carrier mobility can be lower than that of Pristine Bi _0.36 Sb _1.64 Te ₃ due to poor dispersion of RGO.

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

7C shows an example of the temperature dependence of the Seebeck Coefficient of the composite thermoelectric material according to the carbon allotrope volume percentage.

Referring to FIG. 7C, it can be seen that the Seebeck coefficient of Bi _0.36 Sb _1.64 Te ₃ is changed when the volume percentage of the RGO is changed to 0, 0.1, 0.4, and 0.8. It can be seen that the majority carrier is a hole because the Seebeck coefficient is positive in all samples.

Seebeck coefficient increases with increasing temperature, which may be due to thermal excitation of minor carriers at high temperatures. The Seebeck coefficient at room temperature can be 170, 172, 171, 166 uV / K when the volume percentage of RGO is 0, 0.1, 0.4, 0.8, respectively. It can be seen that the Seebeck coefficient has similar values even if the RGO volume percentage changes.

The composite thermoelectric material produced by the composite thermoelectric material manufacturing method has a high electrical conductivity due to improved hole mobility and the Seebeck coefficient may not only have a constant value, but also scale in terms of a one pot synthesis method. It may be advantageous for scale-up processes.

7D shows an example of the temperature dependence of the Power Factor of a composite thermoelectric material according to the volume percentage of carbon allotrope.

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 of 46 × 10 ⁻⁴ W / mK ² when the volume percentage of RGO is 0.4 at room temperature. If the volume percentages of RGO are 0, 0.1 and 0.8, the power factors are 40 × 10 ^-4 W / mK ² , respectively. 42 × 10 ⁻⁴ W / mK ² and 47 × 10 ⁻⁴ W / mK ² . The optimal RGO volume percentage is 0.4, which can have a 20% improvement in power factor compared to Pristine Bi _0.36 Sb _1.64 Te ₃ without RGO.

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

Referring to FIG. 8A, it can be seen that thermal conductivity shows a similar value with temperature regardless of the volume percentage of RGO, decreases with increasing temperature, and shows bipolar conduction which slightly increases at high temperature. . Bi _0.36 Sb _1.64 Te ₃ samples with RGO dispersed prestin Bi _{0 . 36} Sb _{1 .} Lower thermal conductivity compared to ₆₄ Te ₃ samples.

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

Where F _n (ξ) and ξ can correspond to Fermi integration and reduced Fermi energy ((E _F -E _C ) / kT), respectively, and r for acoustic phonon scattering is -1 / May be two. Using the equations (7) and (8), the Lorentz number can be calculated as shown in equation (9).

The Lorentz number calculated according to Equation 9 may range from 1.61 × 10 ⁻⁹ WΩ / K ² to 1.69 × 10 ⁻⁹ WΩ / K ² at room temperature to 473K.

8B shows the temperature dependence of the lattice thermal conductivity of the composite thermoelectric material according to the volume percentage of carbon allotrope.

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

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

8C shows the temperature dependence of the coefficient of performance of the composite thermoelectric material according to the volume percentage of carbon allotrope.

Referring to FIG. 8C, it can be seen that the composite thermoelectric material has a higher coefficient of performance (ZT) compared to a pristine thermoelectric material that does not include a carbon allotrope.

The value of the maximum coefficient of performance increases as the volume percentage of the RGO increases to 0, 0.1, 0.4, and it can be seen that the maximum coefficient of performance is 1.16 at a temperature of 393 K when the volume percentage is 0.4. In all samples, the coefficient of performance shows a similar trend with temperature. This similar trend means that RGO bonds did not affect the electronic band structure of the thermoelectric material.

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

High purity Bi (99.999%, 5N Plus), Sb (99.999%, 5N Plus) and Te (99.999%, 5N Plus) granules were obtained by Bi _{0 . 36} Sb _{1 .} Weighed as starting material according to the formula of ₆₄ Te ₃ . An excess of 1 wt% Te was added to compensate for Te volatilization. Raw materials were loaded into quartz ampoules and sealed in vacuo. The ampoule was heated at 1373 K for 4 hours and quenched to yield an ingot.

The ingot was crushed and the ingot ground for 1 hour with a spex-mill was mixed with RGO nanopowder (purchased at graphene-supermarket.com). The mixed powder was injected into a 0.4 mm diameter graphite mold.

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

As shown in FIG. 2, the ribbon 50 formed through melt spinning had an amorphous structure at the contact surface CS and a crystalline nanostructure (200-300 nm wide) at the free surface FS. The melt spun ribbon was ground into 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 in a direction perpendicular to the compression plane direction of spark plasma sintering. The result is shown in FIG. The microstructure was examined by SEM (JSM-7600F, JEOL). 6A and 6B, the crystallinity of RGO and sintered samples was measured with Raman spectroscopy.

As shown in FIG. 7A, electrical conductivity (σ) was measured at 473 K temperature using a four point probe method with a ZEM-3 device (ULVAC-RIKO), and the results are shown in FIG. 7C. Similarly, Seebeck coefficients (S) were 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). As shown in FIG. 8A, thermal conductivity (k) was measured by laser-flash analysis using Netzsch LFA 457. The physical properties are summarized in Table 1 below.

Characteristics: 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

Although the embodiments have been described by the limited embodiments and the drawings as described above, various modifications and variations are possible to those skilled in the art from the above description. For example, the described techniques may be performed in a different order than the described method, and / or components of the described systems, structures, devices, circuits, etc. may be combined or combined in a different form than the described method, or other components. Or even if replaced or substituted by equivalents, an appropriate result can be achieved.

Therefore, other implementations, other embodiments, and equivalents to the claims are within the scope of the claims that follow.

Claims (20)

A matrix of thermoelectric material having a composition of Bi _2-a Sb _a Te ₃ (0 <a ≦ ₂ ); And
Allotropes of carbon dispersed in the matrix
As a composite thermoelectric material comprising,
The composite thermoelectric material is a p-type semiconductor.
delete delete The method of claim 1,
The carbon allotrope,
Selected from graphene and carbon nanotubes
Composite thermoelectric materials.
The method of claim 4, wherein
The graphene,
It includes graphene peeled off with tape, chemical vapor deposition (CVD) grown graphene, graphene oxide and reduced graphene oxide produced by Hummer's method,
The carbon nanotubes,
Containing single wall carbon nanotubes, double wall carbon nanotubes and multiwall carbon nanotubes
Composite thermoelectric materials.
The method of claim 1,
The carbon allotrope,
It is contained in the composite thermoelectric material in an amount of 10 vol.% Or less
Composite thermoelectric materials.
The method of claim 1,
The grain size of the composite thermoelectric material is small compared to the grain size of a pristine thermoelectric material that does not contain the carbon allotrope.
Composite thermoelectric materials.
The method of claim 1,
The composite thermoelectric material,
Compared to the pristine thermoelectric material that does not include the carbon allotrope, it has a higher hole carrier mobility.
Composite thermoelectric materials.
The method of claim 1,
The composite thermoelectric material has a higher coefficient of performance (ZT) compared to a pristine thermoelectric material that does not contain the carbon allotrope.
Composite thermoelectric materials.
Providing a pulverized thermoelectric material, wherein the thermoelectric material is Bi _2-a Sb _a Te ₃ (0 <a ≦ 2);
Mixing the pulverized thermoelectric material with a carbon allotrope powder to produce a mixed powder;
Molding the mixed powder to form a ribbon;
Pulverizing the ribbon; And
Sintering the pulverized ribbon to produce a matrix of thermoelectric material in which carbon allotrope is dispersed
As a composite thermoelectric material manufacturing method comprising:
The composite thermoelectric material produced is a p-type semiconductor, composite thermoelectric material manufacturing method.
The method of claim 10,
Providing the pulverized thermoelectric material,
Creating an ingot of the thermoelectric material using the elemental material constituting the thermoelectric material as a starting material; And
Pulverizing the ingot of the thermoelectric material;
Composite thermoelectric material manufacturing method comprising a.
The method of claim 10,
The carbon allotrope is selected from graphene and carbon nanotubes
Method for manufacturing composite thermoelectric materials.
The method of claim 10,
Forming the ribbon,
Is performed using a rapid solidification method
Method for manufacturing composite thermoelectric material.
The method of claim 13,
The rapid solidification method,
Selected from the group consisting of melt spinning method, gas atomization method, plasma deposition method, centrifugal atomization method and splat quenching method
Method for manufacturing composite thermoelectric material.
The method of claim 14,
Forming the ribbon,
Is carried out using the melt spinning method,
The melt spinning method,
Melting the mixed powder; And
Cooling the molten mixed powder
Composite thermoelectric material manufacturing method comprising a.
The method of claim 15,
The cooling step,
Cooling to a cooling rate of 10 ⁵ K / sec to 10 ⁷ K / sec
Composite thermoelectric material manufacturing method comprising a.
The method of claim 10,
Crushing the ribbon,
Grinding the ribbon using a dry grinding method
Composite thermoelectric material manufacturing method comprising a.
The method of claim 17,
The dry grinding method,
Ball milling, attrition milling, high energy milling, jet milling, and mortar grinding
Method for manufacturing composite thermoelectric material.
The method of claim 10,
The sintering is,
Spark plasma sintering or hot press sintering
Composite thermoelectric material manufacturing method comprising a.
The method of claim 10,
Generating the matrix,
Sintering the pulverized ribbon for 1 minute to 10 minutes under at least one of a temperature condition of 300 ° C to 800 ° C, a pressure condition of 1Pa to 100Pa and a vacuum condition
Composite thermoelectric material manufacturing method comprising a.

Images