KR101799164B1 - Au Included bismuth telluride thermoelectric composite and fabrication method thereof - Google Patents

Abstract

The present invention relates to a Bi ₂ Te ₃ thermoelectric composite material containing Au and a method of manufacturing the same. In order to produce an interface between Au and a semiconductor BT, a method of forming a Au- The present invention relates to a Bi ₂ Te ₃ based thermoelectric composite material containing Au, which is produced by a discharge plasma sintering method after co-crystal growth with nano dots, and a method of manufacturing the same.
The Bi ₂ Te ₃ thermocomposite material containing Au according to the present invention and its manufacturing method contribute to the improvement of the power factor and the reduction of the K lattice according to the energy filtering effect by the phonon scattering including Au nano materials, And it has an advantage of being able to manufacture a thermoelectric material having excellent thermoelectric properties and having high density and excellent thermoelectric properties by a bottom-up synthesis method and a discharge plasma sintering method.

Description

TECHNICAL FIELD [0001] The present invention relates to a bismuth telluride thermoelectric composite containing gold and a method of manufacturing the same,

The invention Bi ₂ a as Au on the Bi ₂ Te ₃ based thermoelectric composite material and a method for their preparation include, containing the Au can be used for bottom-up synthesis and spark plasma sintering method to produce a superior thermoelectric properties and high density of the thermoelectric material Te ₃ thermoelectric composite material and a method of manufacturing the same.

Thermoelectric power generation (TEG) is a key technology for harvesting clean energy and reducing GHG emissions. At this time, in general, the dimensionless thermoelectric performance index (ZT) of a material used for manufacturing a thermoelectric semiconductor is defined by the following formula, and it is essential to improve the performance of the thermoelectric material for the wide use of the TEG system.

ZT = s ㅇ S ² ㅇ T / k

Where S: Seebeck coefficient, sigma: electrical conductivity, k: total thermal conductivity at a given absolute temperature (T). Among the thermoelectric materials, Bi ₂ Te ₃ (BT) -based solid solutions such as p-type Bi ₂ -xSbxTe ₃ (BST) and n-type Bi ₂ Te ₃ -ySey (BTS) are known as the best materials among the thermoelectric materials used at room temperature have. Bi ₂ Te ₃ (BT) -based materials are now widely used in small or high density cooling systems, but they require high ZT to extend the range of applications from low levels of heat (<100 ° C) to include local cooling and power generation systems. A vibrating material is required.

Ingot of a Bi ₂ Te ₃ (BT) alloy is generally synthesized by a solid state reaction process requiring a high processing temperature (> 1000 K) and a long reaction time. On the other hand, a thermoelectric material in the form of a two-dimensional nanoplate or a one-dimensional nanowire can be synthesized by a simple and expandable bottom-up method at low temperatures. The sintered nano bulk of the synthesized nanoplate or nanowire has a lower lattice thermal conductivity than the nano bulk made from the ingot because of the enhanced phonon scattering at the high density grain boundaries. The performance of the ZT can be further improved by increasing the power factor (S2σ) through deformation of the electronic structure in such nano bulk.

This can be achieved by introducing a metal nanocomposite into the semiconductor thermoelectric material matrix and can lead to improved heat (reduced K grating) and electron (enhanced power factor) transport capability. The interface between the metal nanocrystals and the thermoelectric material matrix serves as an energy barrier or energy well for filtering carriers with low energy levels to induce carrier scattering as well as phonon scattering centers. The S-enhancement by carrier filtering has been experimentally verified by PbTe and III-V semiconductor materials consisting of thin film superlattice, nanogram and nano deposit.

Theoretically, band-banding at the metal-semiconductor (MS) interface forms a potential energy barrier to block low energy carriers. This 'carrier energy filtering' increases S for a given carrier concentration because the charge is moved by carriers with higher average energies.

The power factor can be increased or decreased by the barrier height of the metal semiconductor (MS) interface depending on the position of the semiconductor Fermi level with respect to the work function of the metal. However, although it is necessary to form a sophisticated metal-semiconductor junction in order to maximize the carrier filtering effect, there is insufficient research on the effect of band alignment on S and σ in a BT-based heterostructure system.

1. Korean Published Patent No. 2010-0138171 2. Korean Patent Publication No. 2014-0098353

The present invention been made according to the need as described above, a Bi ₂ Te ₃ based thermoelectric composite material comprising a Au according to the present invention is to provide a thermoelectric composite material having good thermal characteristics from the bottom up composite manner.

The present invention also provides a method for manufacturing a Bi ₂ Te ₃ thermoelectric composite material containing Au, which produces excellent thermoelectric properties and high-density thermoelectric materials by using a bottom-up synthesis method and a discharge plasma sintering method.

According to an aspect of the present invention, there is provided a Bi ₂ Te ₃ based thermoelectric material including Au, the Bi ₂ Te ₃ based thermoelectric material, and the Au 2N ₃ based thermoelectric material dispersed in the Bi ₂ Te ₃ based thermoelectric material. (nanoinclusion).

In some embodiments of the present invention, the diameter of the Au nanocomposite may be 10 to 20 nm or less.

In some embodiments of the present invention, the thermoelectric composite may have a dimensionless thermoelectric performance index (ZT) of at least 0.6 at 450K.

In some embodiments of the present invention, the thermoelectric composite may have a power factor of at least 1.8 mWm &lt; ^-1 &gt; K &lt; ^-2 &gt; at 450K.

According to an aspect of the present invention, there is provided a method for manufacturing a Bi ₂ Te ₃ thermoelectric composite material including Au, which comprises adding a tellurium oxide, an organic solvent, a coupling agent, and Au-nano dots, Nanotube; preparing a Au-nano-dot / BT (Bi ₂ Te ₃ ) -nanotube by mixing and reacting a Bi precursor solution with a solution containing the Te-nano- Nanotubes / BT-nanotubes to form a sintered body.

In some embodiments of the present invention, the step of forming the sintered body may be performed using Spark Plasma Sintering (SPS).

In some embodiments of the present invention, the diameter of the Au-nano-dot may be 10 nm or less.

In some embodiments of the present invention, the content of the Au-nano dot may be 1 to 5 mol%.

In some embodiments of the present invention, the Au-nano-point may be prepared by preparing an Au solution which is heated while stirring gold chloride hydrate dissolved in distilled water, mixing trisodium citrate dehydrate dissolved in the high-temperature Au solution And heating the mixed solution and then cooling to room temperature.

In some embodiments of the present invention, the thickness of the Te nanorods may be 20 nm or less.

In some embodiments of the present invention, the tellurium oxide may be any one of TeO ₂ , TeO, TeO ₃ , Te ₂ O _5, and Te ₄ O ₉ .

In some embodiments of the present invention, the organic solvent is selected from the group consisting of ethylene glycol, oleic acid, oleylamine, hexadecane, ethylenediamine, dimethylform And may be one or more selected from the group consisting of dimethylformamide, pyridine, and acetone.

In some embodiments of the present invention, the coupling agent is selected from the group consisting of polyviny pyrrolidone, polyvinylalcohol, cetyl-trimethyl-ammonium-bromide, ethylene diaminotetraacetic acid May be any one of ethylenediaminotetraacetic acid disodium salt and sodium dodecyl-benzene-sulfonate.

The Bi ₂ Te ₃ thermoelectric composite containing Au according to the present invention contributes to the improvement of the power factor and the reduction of the K lattice according to the effect of energy filtering by the phonon scattering including the Au nanocomposite material, Lt; / RTI &gt;

The Bi ₂ Te ₃ based thermoelectric composite material containing Au according to the present invention can produce a thermoelectric material having high density and excellent thermoelectric properties by a bottom-up synthesis method and a discharge plasma sintering method.

The effects of the present invention described above are exemplarily described, and the scope of the present invention is not limited by these effects.

FIG. 1 is a cross-sectional view of an embodiment of Au / Bi ₂ Te ₃ and Bi / Bi ₂ Te ₃ interface It is a band diagram.
2 is a schematic view showing a method of synthesizing an Au-nano-dot / Bi ₂ Te ₃ nanotube hybrid according to an embodiment of the present invention.
3 (a) and 3 (b) are SEM images of Bi ₂ Te ₃ nanotubes according to an embodiment of the present invention.
3 (c) is a TEM image of an Au-nano-dot having a diameter of 10 nm or less according to an embodiment of the present invention.
3 (d) is a TEM image of a Te nano rod having a thickness of 20 nm or less according to an embodiment of the present invention.
3 (e) is an SEM image of an Au-nano-dot / BT-nanotube according to an embodiment of the present invention.
3 (f) is an image showing the tube shape of the BT-nanotube according to the embodiment of the present invention.
3 (g) and 3 (h) are EDS mapping showing the distribution of Au (red) / Bi (green) according to the embodiment of the present invention.
4 (a) is a STEM image and EDS mapping of an Au-nano-dot / BT-nanotube composite according to an embodiment of the present invention.
FIG. 4 (b) is an image showing Au nanostructures having a diameter of 20 nm or less and included in the matrix according to the embodiment of the present invention.
4 (c) is an HRTEM image of an Au-nano-dot / BT-nanotube composite according to an embodiment of the present invention.
4 (d) is an image showing an Au-nano-dot seed pattern in the BT matrix according to an embodiment of the present invention.
5 is a graph showing an XRD pattern of an Au-nano-dot / BT-nanotube composite according to an embodiment of the present invention.
6 is an image showing a fracture profile of a sintered 4 mol% Au-nano-dot / BT-nanotube composite according to an embodiment of the present invention.
FIG. 7 is a graph showing the thermoelectric characteristics of Bi ₂ Te ₃ , Au-nano-dot / BT-nanotube composite and Au-doped samples according to an embodiment of the present invention.
8 is a graph showing the whitening coefficients of Au-nano-dot / BT-nanotube, Au-doped BT-nanotube, and BT-nanotube according to an embodiment of the present invention.
9 is a band diagram of Au / BT and Cu / BT according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be apparent to those skilled in the art that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. The scope of technical thought is not limited to the following examples. Rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will fully convey the scope of the invention to those skilled in the art. As used herein, the term "and / or" includes any and all combinations of one or more of the listed items. The same reference numerals denote the same elements at all times. Further, the various elements and regions in the drawings are schematically drawn. Accordingly, the technical spirit of the present invention is not limited by the relative size or spacing drawn in the accompanying drawings.

Bi ₂ Te ₃ based thermoelectric composite material containing the Au according to the present invention includes a Bi ₂ Te ₃ based thermoelectric material, and the Bi ₂ Te ₃ based thermoelectric the Au nano-dispersed in the material within the wealth (nanoinclusion). The thermoelectric composite according to the present invention can induce an electron energy filtering effect by including an Au nano-scale material in an n-type BT matrix. The work function of Au, which ranges from 5.31 to 5.47 eV according to the crystal plane, is suitable for electron affinity (4.5 EV) and BT work function (5.3 EV). FIG. 1 is a cross-sectional view of an embodiment of Au / Bi ₂ Te ₃ and Bi / Bi ₂ Te ₃ interface It is a band diagram. The potential barrier (V _B ) for Bi / Bi ₂ Te ₃ is about 0.2 eV and the potential barrier (V _B ) for Au / Bi _{2 Te 3} is about 0.1 eV. As shown in Figure 1, the energy potential barrier (V _B ) for energy filtering is expected to be about 0.1 eV. This is theoretically predicted optimally for power factor improvement.

Compared to undoped monocrystalline BT, the polycrystalline stoichiometric compound BT is n-type. The n-type electrical properties of the thermoelectric composite according to the present invention are consistent with the bottom-up synthesized nanostructured BT compound. Au addition can have three effects. First, Au doped to Bi site forms a point defect (Au _Bi ^2- ) and generates holes. Second, the occupation of the interstitial site produces a donor of Au _i ⁺ . Au is present in the interstitial position between the two quintet (intercalation) to achieve an electrical connection (electrical connection) to a decrease in carrier mobility (μ) increases with k _lat. Third, Au can be precipitated as a nano deposit at the matrix and / or crystal boundaries. In this case, the heterointerface between the Au nanocomposite and the BT-based matrix is created. This heterointerface can act as a phonon scattering center as well as an energy barrier for carriers, thereby improving the thermoelectric property ZT.

The diameter of the Au nanocomposite may be 10 to 20 nm or less. At a given volumetric content, the smaller the secondary particles, the greater the interface concentration, which can simultaneously increase the phonon scattering and carrier filtering probabilities. However, when the diameter of the particles is 10 nm or less, the melting point of the Au nanoparticles falls below the bulk Au (1337 k), so that the Au particles of too small size are hard to remain in the secondary phase. Au nanopores with an average diameter of 10 nm or less may be selected as seeds for crystal growth of the BT nanotubes, and the nanostructures in the sintered matrix may be 10-20 nm in size.

The thermoelectric composite can have a dimensionless thermoelectric performance index (ZT) of at least 0.6 at 450 K and a power factor of at least 1.8 mWm ^-1 K ^-2 at 450 K. The BT (Bi ₂ Te ₃ ) thermocomposite material in which the Au nanocomposite material is distributed according to the present invention contributes to the improvement of the power factor and the reduction of k _latt according to the effect of energy filtering by the phonon scattering in the presence of the Au nanocomposite material, Overall improvement is shown.

2 is Au- nano / BT (Bi ₂ Te ₃₎ according to an embodiment of the present _invention is a schematic diagram showing a nanotube hybrid synthesis. In order to generate the interface between the metal Au and the semiconductor BT, the Au-NDs can be fabricated by the discharge plasma sintering method after the Au-NDs are crystallized in the crystal growth of BT-nanotubes using the bottom-up synthesis method.

As shown in FIG. 2, the method for manufacturing a Bi ₂ Te ₃ thermoelectric composite material containing Au according to the present invention includes steps of forming a Te-nano rod, forming Au-nano dot / BT-nanotube and forming a sintered body .

In the step of forming the Te-nano-rods, a tellurium oxide, an organic solvent, a coupling agent, and an Au-nano-dot may be added and mixed and reacted to form a Te-nano rod. The thickness of the Te nanorod may be 20 nm or less, and the Te nanorod grows using the Au nanopore as a seed.

The diameter of the Au-nano-dot may be 10 nm or less. At a given volume, the smaller the secondary particles, the greater the interface concentration, which can simultaneously increase the phonon scattering and carrier filtering probabilities.

The content of the Au-nano dot may be 1 to 5 mol%. The electrical conductivity value can be increased due to the formation of the electron carrier by introducing the Au-nano-dot, but as the concentration of Au-nano-dot increases, the electrical conductivity decreases due to the substitution of a part of the Au- - The nano dots may be excellent in electric conductivity when the content is 1.0 to 5.0 mol%.

The Au-nanoparticles can be synthesized by a microemulsion method. The Au-nano-point may be prepared by preparing an Au solution which is heated while stirring gold chloride hydrate dissolved in distilled water, mixing trisodium citrate dehydrate dissolved in the high-temperature Au solution, heating the mixed solution, And then cooling the mixture to a temperature of at least &lt; RTI ID = 0.0 &gt;

The tellurium oxide TeO _2, TeO, TeO _3, Te ₂ O ₅ and Te ₄ O _9, and of the number of days any one of the organic solvents include ethylene glycol (ethyelene glycol), oleic acid (oleic acid), oleyl amine the coupling agent may be at least one selected from the group consisting of oleylamine, hexadecane, ethylenediamine, dimethylformamide, pyridine, and acetone, Polyvinyl pyrrolidone, polyvinylalcohol, cetyl-trimethyl-ammonium-bromide, ethylenediaminotetraacetic acid disodium salt and sodium dodecylbenzene sulphonate dodecyl-benzene-sulfonate).

The step of forming the Au-nano-dot / BT-nanotube may include forming a Au-nano-dot / BT-nanotube by mixing and reacting a Bi precursor solution with a solution containing the Te-nano rod. Nanotubes are formed by diffusion of Bi into Te nanorods through an alloying reaction.

The forming of the sintered body may be performed by sintering the Au-nano-dot / BT-nanotube to form a sintered body. At this time, the sintered body forming step may be performed using Spark Plasma Sintering (SPS). A high density polycrystalline bulk thermoelectric material can be manufactured by a discharge plasma sintering method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, details of the present invention will be described with reference to examples and experimental examples.

1. Materials Preparation

_{TeO 2 (Alfa Aesar, 99.9995%} ), NaOH (DaeJung, 98%), PVP (Sigma Aldrich), ethyleneglycol (DaeJung, 99.5%), hydrazine monohydrate (Junsei, 98%), bismuth nitrate hydrate (Sigma Aldrich, 99.99% ), gold chloride hydrate (Sigma Aldrich, 99.999%), and trisodium citrate dehydrate (Daejung, 99%) were used.

2. Au-nano dot synthesis

First, 0.039 g of gold chloride hydrate was dissolved in 100 mL of distilled water and heated to 90 DEG C with stirring. 0.235 g of trisodium citrate dehydrate was dissolved in 20 mL of distilled water and poured into the heated Au solution. The mixed solution was heated at 100 占 폚 for 10 minutes. The dark red suspension produced here was cooled to room temperature.

3. Synthesis of Au-nano-dot / BT-nanotube composite

During bottom-up synthesis of BT-nanotubes, liquid Au-nano-dot solutions were added at different ratios, and in the BT-nanotube growth process, close contact between the Au-nanoparticles and the BT-nanotubes Lt; RTI ID = 0.0 &gt; interface. &Lt; / RTI &gt;

BT-nanotubes were grown by a two-step solution phase reaction. The nanorods were first grown using Au-nanoparticles as seeds, and BT-nanotubes were formed by diffusion of Bi into Te-nanorods through an alloying reaction.

In order to form Te nanorods, 70 mL of ethylene glycol was placed in a three-neck flask while blowing N ₂ , followed by 1.0 g of polyvinylpyrrolidone (PVP, Mw ~ 40,000) in the presence of Au- 2.1 g of KOH, and 1.115 g of TeO ₂ powder (99.9995%). The mixture was heated to 120 ° C while being protected with nitrogen, and 2.25 mL of hydrazine monohydrate was added as a reducing agent.

A uniform Te-nanorod was formed after 40 minutes. The Bi precursor solution was prepared by adding 2.265 g of Bi (NO ₃ ) ₃ .5H ₂ O, 0.15 g of PVP and 2.25 mL of hydrazine monohydrate in 15 mL of ethyleneglycol. The BT nanotubes were prepared by injecting a Bi precursor solution prepared at 120 ° C into a Te-nanorod solution prepared above.

After further reaction for 40 minutes, Au-nanoparticles / BT-nanotubes were obtained. The remaining surfactants and reagents were removed by stirring the suspension in anhydrous ethanolic solution containing 10 vol% hydrazine monohydrate.

Au-nanoparticles / BT-nanotube powders were obtained by washing with anhydrous ethanol and acetone and centrifugation / drying. The obtained powders were loaded in a graphite die, and the sintered specimens were obtained by spark plasma sintering (SPS).

In consideration of the potential anisotropic properties of the thermoelectric material elements of the Bi ₂ Te ₃ material, polycrystalline bulk samples in the form of thick discs (10 mm diameter by SPS for 2 minutes at a pressure of 30 MPa and a temperature of 360 캜 in a vacuum state, , Thickness: 13 mm). A polycrystalline bulk sample of high density (96% or more of the density in theory) was obtained.

4. Microstructure and phase identification of Au-nano-dot / BT-nanotube composite

Nano-dots, BT-nanotubes, and Te-nanorod intermediates obtained after solution synthesis were analyzed. As shown in Figs. 3 (a) to 3 (d), the Au nanoparticles were synthesized by a microemulsion method and used as seeds for Te-nanorod crystal growth. It then reacts with the Te-nanorod Bi-solution to form BT nanocrystals.

3 (a) and 3 (b) are SEM (scanning electron microscope) images of Bi ₂ Te ₃ nanotubes according to an embodiment of the present invention, TEM image of Au-nano-dot. FIG. 3 (d) is a TEM image of a Te nanorod having a thickness of 20 nm or less according to an embodiment of the present invention, showing uniform formation of the intermediate product, Te-nanorod, obtained after the first step of solution- Show.

FIG. 3 (e) is a SEM image of Au-nano-dot / BT-nanotube according to an embodiment of the present invention, EDS mapping showing the distribution of Bi (green). As shown in Figs. 3 (e) to 3 (h), the uniform dispersion of the secondary phase (Au-nano dot) is also observed in the aggregated BT-nanotubes. FIG. 3 (f) is an image showing a tube shape of a BT-nanotube according to an embodiment of the present invention, wherein BT has a rough surface shape of a polycrystalline tube.

As shown in Fig. 3 (b), after the Bi alloy process, the average diameter of the BT-nanotubes increases from about 20 nm (Te-nanorod) to 100 nm although the size distribution is not narrow. As shown in Fig. 3 (d), unlike Te-nano-rods with smooth surfaces, BT-nanotubes exhibit very rough surfaces. As shown in Fig. 3 (d), although the Te-nano-rods are monocrystalline, the final BT-nanotubes clearly show polycrystalline properties having several crystalline domains.

4 (a) is a scanning transmission electron microscope (STEM) image and EDS mapping of an Au-nano-dot / BT-nanotube composite according to an embodiment of the present invention, Is an image showing Au nanostructures having a diameter of 20 nm or less. FIG. 4 (c) is a high-resolution transmission electron microscope (HRTEM) image of an Au-nano-dot / BT-nanotube composite according to an embodiment of the present invention, Nano-dot seed pattern of Au. The nanocomposites were identified as Au based on EDS analysis. According to Fig. 4 (b), Au nanoparticle size increases to 20 nm after the crystal growth process of Te nanorods due to Ostwald ripening of Au nanoparticles.

As shown in Fig. 2 (b), the small Au nanoparticles on the surface of the Te-nanorod are dissolved so that the Te-nanorod can grow into larger particles. The migration of the Au-nanoparticles prefer the tip of the Te-rod and leads to growth in that direction, because this location has a higher surface energy and a lower surfactant capping effect It is easy to access.

As shown in FIG. 3 (e), it can be seen that the globular spheres appearing in white contrast in the STEM image are located at the end of the BT-NT. Selective growth at the tip of the Te-nanorod can help uniform diffusion of Au-nanoparticles in a thermoelectric matrix. The HRTEM image of FIG. 4 (c) shows that Au-NDs with well-resolved lattice fringes are included in the BT matrix. The size is 10 to 20 nm as shown in Figs. 4 (b) and 4 (c), which is larger at the Au-nano-dot in Fig. 3 (c).

5 is a graph showing an XRD pattern of an Au-nano-dot / BT-nanotube composite according to an embodiment of the present invention. The electron diffraction pattern for the selected region confirms that the Au-nanoparticles of the single crystal are included in the matrix. 5 shows a typical X-ray diffraction (XRD) pattern of Au-nanoparticles / BT-nanotubes after solution-based synthesis, which is a pristine Te phase (JCPDS no. 36- 1452) and the pristine BT image (JCPDS no. 15-0863). According to XRD patterns and EDS (energy dispersive X-ray spectroscopy) analysis, the BT-nanotubes after the two-step process have a Te-rich Bi ₂ Te ₃ phase.

Due to the low volume fraction of Au (<1.0 vol.%), There was no trace of Au in the XRD pattern. In comparison of the XRD patterns of the sintered sample and its powder, the crystal phase changes from Te-enriched Bi ₂ Te ₃ to pure Bi ₂ Te ₃ form and oxidation does not occur in the second-phase forming step (Au-nanoparticles are excluded ). No particular orientation orientation was found, which means high disorder of Bi ₂ Te ₃ nanograms.

6 is an image showing a fracture profile of a sintered 4 mol% Au-nano-dot / BT-nanotube composite according to an embodiment of the present invention. As shown in FIG. 6, all of the sintered samples have a well crystallized and void-free structure, which is consistent with the high density (> 96%) of the samples. As can be seen in Figure 6 (b), the fracture profile of the single-phase Bi ₂ Te ₃ bulk shows that the nanograms with high aspect ratios were sintered without a definite orientation orientation of the grain. Random orientation reduces the diffusion of cracks in the bottom surface, which is often seen in n-type BTS / BT ingots or pressure sintered samples, which can lead to improved mechanical strength.

Anisotropic grains have a small thickness of about 20 to 30 nm, which is smaller than BT-nanotubes having a thickness of about 100 nm. This may be due to the depression of polycrystalline BT-nanotubes with hollow form, which contributes to a decrease in k _latt due to phonon boundary scattering.

5. Measurement of thermoelectric properties of Au-nano-dot / BT-nanotube composite

In order to measure the accurate thermoelectric properties, measurements of S, σ, and K values were made perpendicular to the SPS pressure direction. S and sigma values were measured using ULVAC ZEM-3 at 300-480K. The K value (K = ρ _s C _p λ) was calculated by measuring the sample density (ρ _s ), heat capacity (C _p ) and thermal diffusivity (λ). The sample density (ρ _s ) was determined in terms of dimension and mass, and λ was measured in a vacuum state using a laser-flash method (TC-9000, ULVAC, Japan). The C _p value at low temperature (100 to 390 K) was measured using a Quantum Design PPMS system, and the C _p value was a constant, which was estimated by Dulong-Petit's law of 0.157 Jg ^-1 K ^-1 .

6. Measurement results of thermoelectric properties of Au-nano-dot / BT-nanotube composite

FIG. 7 is a graph showing the thermoelectric characteristics of Bi ₂ Te ₃ , Au-nano-dot / BT-nanotube composite, and Au-doped samples according to an embodiment of the present invention. 7 (a) and 7 (b) show the temperature dependence of S and σ measured in the synthesized components, respectively. As Au is added to the Au-doped Bi ₂ Te ₃ sample, the σ value decreases, suggesting that a portion of the Au substitutes for Bi.

Table 1 below shows the whiteness coefficient (S), electrical conductivity (σ), mobility (μ) and carrier concentration (n) at room temperature for pure BT, Au-nano dot / BT- The results are shown in Table.

Samples Whitening Factor (S)
(μV K ^-1 ) Electrical Conductivity (σ)
( S cm ^-1 ) Mobility (μ)
(cm ² V ^-1 s ^-1 ) Carrier concentration (n)
(10 ¹⁹ cm ^-3 ) Comparative Example 1 IT -169 664 162 2.5 Example 1 1.0 mol%
Au-BT -121 1234 145 5.3 Example 2 2.0 mol%
Au-BT -138 1018 135 4.7 Example 3 4.0 mol%
Au-BT -155 837 119 4.4 Example 4 5.0 mol%
Au-BT -159 778 113 4.3 Comparative Example 2 1.0 mol% Au-doped BT -189 586 158 2.3 Comparative Example 3 2.0 mol% Au-doped BT -196 541 159 2.1

As Table 1 shows, all Au nanoparticles / BT-nanotube composites have higher n and sigma values than pure BT. However, the n-value of Au-nanoparticles / BT-nanotubes decreases with Au-nanoparticle content, indicating that some of the Au-nano-dots replace Bi. During the sintering process at 360 ° C, Au nanoparticles smaller than 10 nm in diameter can be melted and melted.

Thus, Au diffuses into the BT matrix and forms point defects (Au _Bi ^2- ), which results in a decrease in n value due to the p-type doping effect. The larger Au nanoparticles remaining in the BT matrix are shown in Figures 4 (b) and (c). On the other hand, as the Au-nano-dot concentration increases, the mobility (μ) generally decreases because of the electron scattering between the Au-nano-dot at the hetero-interface and the BT matrix.

As Au nanoparticle concentration increases from 1.0 mol.% To 5.0 mol.% In Au-nano-dot / BT-nanotube composite, the sigma value decreases and the S value increases. The value of sigma at room temperature is 778 to 1018 S / cm at 2.0 to 5.0 mol.%, Which is reduced at 1230 S / cm at 1.0 mol.%.

On the other hand, the absolute value of S increased from 121 μV / K to 159 μV / K as the Au nanoparticle concentration increased from 1.0 to 5.0 mol /%. This may be due to the energy filtering effect due to the heterointerface between the Au-nano-dot and the BT matrix as the value of n decreases.

In addition, the temperature dependence of σ, S and power factor values in Au-nanopart / BT-nanotube samples shows a significant difference between Au-doped and pure BT samples. In Au-doped samples (without nano-deposits), the | S | value decreases as the temperature increases from 300K to 500K.

However, all Au-nanoparticles / BT-nanotube samples constantly increase in temperature between 300 and 500K. Therefore, the compositions show the maximum power factor and ZT value as the temperature increases in Au doped samples than in pure BT, and this property is more beneficial to TEG than pure BT or conventional BTS.

The effect of the overall electrical transport is illustrated in Figure 7 (f), which shows the power factor of different compositions depending on temperature. 2.0 or 4.0 mol.% Au nanoparticles / BT nanotube composite exhibits the highest power factor near 450K.

The inclusion of the Au-nano dot (2.0 mol.% Au) in the Au-nano-dot / BT-nanotube composite sample synthesized through the process of growing the BT-nanotube with the Au- At 450 K, the electrical conductivity increased by about 105%, and the | S | value decreased by only 3%.

This increased the power factor (2.3 mWm ^-1 K ^-2 ) by 92% compared to the pure sample (1.2 mW m ^-1 K ^-2 ) by the improvement of the S value through the carrier filtering effect at 450 K. At 300K, the power factor of Au-nanoparticles / BT-nanotubes is 27% higher than the maximum value of the pure sample (1.8 mWm ^-1 K ^-2 ).

8 is a graph showing a Seebeck coefficient (S) according to carrier concentration (n) of Au-nano-dot / BT-nanotube, Au-doped BT-nanotube and pure BT- to be. The S values are compared with the known Pt / BTS, Bi / BTS, Cu / BTS, and S-doped BT values. To determine the difference in electron transport behavior in Au-nano-dot / BT-nanotube and Au-doped samples, the effective density md * of state density (DOS) at 300 K was calculated and shown in FIG. md * was estimated using the following formula.

Where k _B , e, and h are the Boltzmann constant, the basic charge amount, and the Planck constant, respectively.

Figure 8 shows S measured at 300K as a function of n (Pisarenko plot). The solid line md * = 0.8,1.00,1.2m ₀ was calculated in the circumstances, the nest Au- md * value by the nano-dots is about 0.75m ₀ (pure BT- nanotubes) at about 1.0m ₀ (2.0mol. % Au-nanoparticles / BT-nanotubes). Au doped samples also show slightly increased md * values compared to pure samples.

The reason for the higher md * values in the samples doped with Au-nanoparticles / BT-nanotubes and Au is believed to be the deformation of the electronic structure due to the doping of the Au-nano-dots and Au, A larger | S | value may have appeared.

8 shows that the S-n points of the Au-nanoparticles / BT-nanotube nanocomposites in this study are at a higher position than the previously known n-type BT-based materials. The samples show larger md * values compared to Cu / BTS, S doped BT and show larger or similar md * values than BiT containing Bi nanostructured BTS with Pt nanostructures.

9 is a band diagram of Au / BT and Cu / BT according to an embodiment of the present invention. No potential barrier for energy filtering was formed at the Cu / BT interface. 9, when the work function value of the metal is larger than the work function value of BT, the V _B value is approximately the work function (metal) -buy function (BT). Pt has a high work function (5.65 eV) than Au, and therefore the potential barrier (V _B of about 0.25 eV) of V _B in Pt / BT interface is greater than the potential barrier (V _B of about 0.1 eV) in the Au / BT do. Potential barriers optimized for power factor improvement have been estimated to be close to 0.1 eV. For metals with smaller work function values than BT, the formation of potential barriers depends on the situation.

When the BT matrix contains Cu, the energy filtering effect is not exhibited. This may be due to the fact that V _B is not formed according to the work function (4.5 to 5.1 eV) of Cu as shown in Fig. On the other hand, as shown in FIG. 1, in the case of the Bi / BT interface, the work function value (4.3 eV) of Bi is smaller than the work function value of BT, and the V _B value is approximately the work function (BT) It can be effective for the rise of S.

Figs. 7 (c) and 7 (e) show the K and K _latt values of the BT samples having different Au-nanoparticle contents according to temperature. The total thermal conductivity is _composed of an electron thermal conductivity (K _ele = KK _latt ), K _latt and a bipolar thermal conductivity (K _bp ), and K _bp is generally negligible at room temperature. Thus, K _latt can be obtained by taking K _ele as K in K.

However, in the Au-doped BT system, the bipolar portions can not be neglected at high temperatures (> 350 K) as shown in Figures 7 (c) and 7 (e) This is in contrast to the case. Based on the Wiedemann-Franz law, K _ele can be approximated by the correlation of Ke = LσT. Here, the L (Lorentz constant) value of BT and Au-nanoparticles / BT-nanotubes is assumed to be 2.0 × 10 ^-8 V ² K ^-2 at 300K.

As shown in FIGS. 7 (c) and 7 (e), the dispersion of Au nanoparticles in the high temperature range significantly reduces K _latt . The lowest value of bulk BT containing 2.0 mol% Au-NDs is lowered from 450 K to 0.47 Wm ^-1 K ^-1 . This is the value of the pure bulk BT ^- is much lower than that (0.73 Wm ^-1 K ^1). At 300 K, the minimum value of Au-nanoparticles / BT-nanotubes is 78% as compared to the pure sample (0.60 Wm ^-1 K ^-1 ). The remarkable reduction of K _latt value with increasing Au content is believed to be due to the strong scattering effect of phonons in the presence of Au nanoparticles. Considering the size of the dispersed Au nanoparticles (10-20 nm), phonons with short or medium mean free path (3-100 nm) were effectively scattered by the Au nanoparticles.

Fig. 7 (d) shows the dimensionless figure of merit ZT calculated for all bulk samples. ZT values in bulk BT with Au-nanoparticle dispersions were found to increase with increasing temperature, which is different from the trend in single-phase bulk BT.

The dispersion of Au nanoparticles leads to a marked increase in the ZT value, which means that the ZT maximum in bulk BT with 2.0 nm.% Dispersed Au nanodevices ranges from 480 K to 0.95, which is less than the value in the BT matrix 67 percent higher. This result shows that the diffusion of Au nanoparticles in BT-based materials shows a significant increase in thermoelectric properties over all temperature ranges when the Au-nanoparticle content is properly controlled.

In the Au-nano-dot / BT-nanotube thermoelectric composite according to the present invention, the Au-nano dot is synthesized by a microemulsion method, and the interface between the Au and the semiconductor BT of the metal is formed by a bottom- The Au-NDs can be fabricated using the discharge plasma sintering method after the co-crystallization of Au-NDs in the crystal growth of &lt; RTI ID = 0.0 &gt;

The ZT value increases markedly with the dispersion of Au nanoparticles, and the maximum value of ZT in bulk BT with 2.0 mol.% Au nanodispersion dispersed from 480K to 0.95. In the Au-nano-dot / BT-nanotube thermoelectric composite according to the present invention, the ZT value of 0.95 is about 67% higher than that of pure Bi ₂ Te ₃ , and the hot press sintering of the ball- Type BTS sample synthesized through the method of the present invention does not exceed the maximum value (ZT = 1.04), but the ZT value of the thermoelectric material manufactured by the bottom-up synthesis method is not nearly 0.95.

The power factor improvement (27%) and the reduction of the K lattice (22%) according to the energy filtering effect by phonon scattering in the presence of Au-nanoparticle nanoparticles in the Au nanoparticles / BT- Contributing to the overall improvement of ZT.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. And will be apparent to those skilled in the art.

Claims (13)

delete delete delete delete Adding a tellurium oxide, an organic solvent, a coupling agent, and an Au-nano-point, mixing and reacting to form a Te-nano rod;
Nanotube / BT (Bi ₂ Te ₃ ) -nanotube by mixing a Bi precursor solution with a solution containing the Te-nano-rod and reacting it; And
The Au- nano / BT- nanotubes sintering method to prepare a Bi ₂ Te ₃ based thermoelectric composite material comprises Au this includes forming the sintered body.
6. The method of claim 5,
Wherein forming the sintered body comprises:
A method for manufacturing a Bi ₂ Te ₃ thermoelectric composite material containing Au, which is carried out using Spark Plasma Sintering (SPS).
6. The method of claim 5,
Au- the diameter of the nano-dots is 10 nm or less of Au Bi ₂ Te ₃ based thermoelectric composite material manufacturing method comprising a.
6. The method of claim 5,
Au- the content of the nano-dots is 1 to 5 mol% of Au of Bi ₂ Te ₃ based thermoelectric composite material manufacturing method comprising a.
6. The method of claim 5,
The Au-
Preparing an Au solution which is heated while stirring gold chloride hydrate dissolved in distilled water;
Au solution into trisodium citrate dehydrate; And
Wherein the mixed heating a solution containing the Au to the following synthesis, including the step of cooling to room temperature, Bi ₂ Te ₃ based thermoelectric composite material manufacturing method.
6. The method of claim 5,
The thickness Te of the nanorod is not more than 20nm Au of Bi ₂ Te ₃ based thermoelectric composite material manufacturing method comprising a.
6. The method of claim 5,
The tellurium oxide _{TeO 2, TeO, TeO 3,} Te 2 O 5 and Te ₄ O ₉ any one of Au the Bi ₂ Te ₃ containing the composite material of the thermoelectric method.
6. The method of claim 5,
The organic solvent may be at least one selected from the group consisting of ethylene glycol, oleic acid, oleylamine, hexadecane, ethylenediamine, dimethylformamide, pyridine, A method for manufacturing a Bi ₂ Te ₃ thermoelectric composite material containing Au of at least one selected from acetone.
6. The method of claim 5,
The coupling agent may be selected from the group consisting of polyviny pyrrolidone, polyvinylalcohol, cetyl-trimethyl-ammonium-bromide, ethylenediaminotetraacetic acid disodium salt, A method for manufacturing a Bi ₂ Te ₃ thermoelectric composite material containing Au, which is any one of sodium dodecyl-benzene-sulfonate.

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