KR20180015356A - Bi-Te COMPOUND AND METHOD OF FORMING THE SAME - Google Patents

Abstract

Provided are a Bi-Te compound and method of forming the same. The Bi-Te compound has the following formula: Bi_2Te_3+x (0 < x < 1). The method for forming the Bi-Te compound includes a step of forming a Te nanorod, a step of forming a Bi precursor solution, and a step of reacting the Te nanorod and the Bi to form a Bi-Te nanotube.

Description

Bi-Te compound and method for forming the same [0002]

The present invention relates to a Bi-Te compound and a method of forming the same.

Thermoelectric technology is considered as a viable means for sustained power generation and energy storage because it allows direct conversion between heat and electricity. The thermoelectric conversion efficiency can be defined by the thermoelectric performance index.

Recently, thermoelectric materials having various structures such as AgPb _m SbTe _{m + 2} , SrTe-doped PbTe, Tl-doped PbTe, and Se-doped PbTe have been proposed. However, there is a demand for development of a new thermoelectric semiconductor compound with improved thermoelectric performance.

In order to solve the above problems, the present invention provides a Bi-Te compound having excellent physical properties.

The present invention provides a Bi-Te compound of novel composition.

The present invention provides a method for forming the Bi-Te compound.

Other objects of the present invention will become apparent from the following detailed description and the accompanying drawings.

The Bi-Te compound according to the embodiments of the present invention has the following chemical formula.

[Chemical Formula]

Bi ₂ Te _{3 + x} (0 &lt; x &lt; 1)

The Bi-Te compound may have phase uniformity. The Bi-Te compound may have a single melting point. The Bi-TE compound may have a hollow structure. The Bi-Te compound may have a nanotube shape, a nanoparticle shape, or a bulk pellet shape.

The Bi-Te compound may include a 7-fold atomic layer composed of Te-Bi-Te-Bi-Te-Bi-Te. The Bi-Te compound may include a Te-Bi-Te-Bi-Te-Te-Bi-Te atomic arrangement.

The Bi-Te compound may be an n-type thermoelectric semiconductor.

The formula may be a Bi ₂ Te _{3 .14.}

A method of forming a Bi-Te compound according to embodiments of the present invention includes forming a Te nanorod, forming a Bi precursor solution, and reacting the Te nanorod with Bi to form a Bi-Te nanotube .

The Te nano-rod may be combined with a PVP (polyvinylpyrrolidone) ligand. The reaction rate of Te and Bi can be controlled by the PVP ligand. In this reaction, the external diffusion of the Te ions by the PVP can proceed faster than the internal diffusion of the Bi ions.

The method for forming the Bi-Te compound may further include performing spark plasma sintering (SPS) on the Bi-Te nanotube. By the SPS, the Bi-Te compound can be formed into bulk pellets. The PVP ligand can be removed by the SPS.

The reaction may be carried out at a temperature of 150 to 170 ° C. The reaction may be carried out in ethylene glycol.

The Te nanorods may be formed by reacting a mixture of TeO _2, PVP, and KOH in ethylene glycol.

According to the embodiments of the present invention, a Bi-Te compound having a novel composition can be formed through controlling the reaction rate of Bi and Te. The Bi-Te compound may have excellent physical properties. The Bi-Te compound may have improved thermoelectric performance and power factor. The Bi-Te compound contains excess Te beyond the Bi-Te system state, but can have excellent stability. The Bi-Te compound may be formed in various shapes such as nanotubes, nanoparticles, and bulk pellets.

1 schematically shows a process of forming a Bi-Te compound and a K-Bi-Te compound according to an embodiment of the present invention.
2 shows an image of a Bi-Te nanotube according to an embodiment of the present invention.
3 shows a STEM image and an EDS analysis result of a Bi-Te nanotube according to an embodiment of the present invention.
Fig. 4 shows a state diagram of the Bi-Te system.
5 is a TEM image of a K-Bi-Te nanotube according to an embodiment of the present invention.
Figure 6 shows K-Bi-Te bulk pellets according to embodiments of the present invention.
Referring to FIG. 6, the K-Bi-Te bulk pellets can be formed into various shapes through cutting and polishing after pressing the K-Bi-Te particles using the SPS.
7 shows a TGA graph of a Bi-Te compound and a K-Bi-Te compound according to embodiments of the present invention.
8 is an XRD graph of a Bi-Te compound, a K-Bi-Te compound and a Bi-Te compound according to comparative examples according to embodiments of the present invention.
9 shows a TGA graph of a Bi-Te compound, a K-Bi-Te compound, and a Bi-Te compound according to comparative examples according to embodiments of the present invention.
10 is a differential scanning calorimetry (DSC) analysis graph of a Bi-Te compound, a K-Bi-Te compound, and a Bi-Te compound according to comparative examples according to embodiments of the present invention.
11 shows Fourier transform infrared (FTIR) spectral analysis results of a K-Bi-Te bulk pellet according to an embodiment of the present invention.
12 is an X-ray diffraction (XRD) graph of a K-Bi-Te bulk pellet according to an embodiment of the present invention.
13 shows an SEM image of a K-Bi-Te bulk pellet according to an embodiment of the present invention.
14 shows a cross-sectional scanning TEM (STEM) image of a Bi-Te bulk pellet according to an embodiment of the present invention.
15 shows a STEM image of a K-Bi-Te bulk pellet according to an embodiment of the present invention.
Figure 16 shows an HAADF-STEM image of a K-Bi-Te bulk pellet (bulk KBT) according to one embodiment of the present invention.
17 shows the STEM-EDS analysis results of a K-Bi-Te bulk pellet (bulk KBT) according to an embodiment of the present invention.
Figure 18 shows an HAADF-STEM image of a K-Bi-Te bulk pellet (bulk KBT) according to one embodiment of the present invention.
FIG. 19 is a plot of Bi ₂ Te _{3 .14} bulk BT and K _0.06 Bi ₂ Te _3.18 bulk pellets (bulk KBT) according to embodiments of the present invention and Bi ₂ Te ₃ and K _{0. 02} Bi ₂ Te ₃ according to the temperature, and the Seebeck coefficient (S).
Figure 20 shows the electron concentration (n _e ) and mobility of the Bi ₂ Te _{3 .14} bulk BT and K _0.06 Bi ₂ Te _3.18 bulk pellets according to embodiments of the present invention mobility, μ _e ).
Figure 21 shows the electrical conductivity () and the Seebeck coefficient (K) of K _{0. 06} Bi ₂ Te _{3 .18} bulk KBT and Na _0.05 Bi ₂ Te _3.11 bulk pellets according to embodiments of the present invention S).
FIG. 22 is a graph showing the results of a comparison of the Bi ₂ Te _{3 .14} bulk BT and K _0.06 Bi ₂ Te _3.18 bulk pellets (bulk KBT) according to embodiments of the present invention and Bi ₂ Te ₃ and K _{0. 02} Bi ₂ Te ₃ according to the temperature.
FIG. 23 is a graph showing the results of a comparison between the Bi ₂ Te _{3 .14} bulk BT and K _0.06 Bi ₂ Te _3.18 bulk pellets according to embodiments of the present invention and Bi ₂ Te ₃ and K _{0. 02} Bi ₂ Te ₃ according to the temperature.
Figs. 24 and 25 are graphs showing the results of a comparison between the Bi ₂ Te _{3 .14} bulk BT and K _{0. 06} Bi ₂ Te _{3 .18} bulk pellets (bulk KBT) and comparative examples Total heat conductivity (κ _tot ) and lattice thermal conductivity (κ _latt ) of Bi ₂ Te ₃ and K _{0 .02} Bi ₂ Te ₃ with temperature are shown.

Hereinafter, the present invention will be described in detail with reference to examples. The objects, features and advantages of the present invention will be easily understood by the following embodiments. The present invention is not limited to the embodiments described herein, but may be embodied in other forms. The embodiments disclosed herein are provided so that the disclosure may be thorough and complete, and that those skilled in the art will be able to convey the spirit of the invention to those skilled in the art. Therefore, the present invention should not be limited by the following examples.

The "Bi-Te" or "Bi-Te compound" described herein refers to a compound comprising bismuth (Bi, bismuth) and tellurium (Te, tellurium). For example, "Bi-Te" or "Bi-Te compound" may be bismuth telluride. The term "A-Bi-Te" or "A-Bi-Te compound" refers to a compound containing an alkali metal (A), bismuth (Bi), and tellurium (Te) For example, "A-Bi-Te" or "A-Bi-Te compound" may be bismuth telluride doped with an alkali metal. The "K-Bi-Te" or "K-Bi-Te compound" may be potassium (K) doped bismuth telluride.

[ Bi - Te  compound]

The Bi-Te compound according to embodiments of the present invention may have the following formula (1).

[Chemical Formula 1]

Bi ₂ Te _{3 + x} (0 &lt; x &lt; 1)

The Bi-Te compound may be an n-type thermoelectric semiconductor. The Bi-Te compound may be homogeneous and pure phase. The Bi-Te compound may have a high phase homogeneity. In addition, the Bi-Te compound can have excellent thermal stability. Therefore, the Bi-Te compound may have improved thermoelectric performance than Bi ₂ Te ₃ .

The Bi-Te compound may have a nanotube shape, a nanopowder shape, or a bulk pellet shape.

[A- Bi - Te  compound]

The A-Bi-Te compound according to embodiments of the present invention may have the following formula (2).

(2)

A _y Bi ₂ Te _{3 + x} (wherein A is an alkali metal, 0 <x <1, 0 <y <0.1)

The A-Bi-Te compound may be an n-type thermoelectric semiconductor. The A-Bi-Te compounds, for example, may be a K-Bi-Te compound _{(K y Bi 2 Te 3 +} x). The A-Bi-Te compound may be homogeneous and pure phase. The A-Bi-Te compound may have a high phase homogeneity. In addition, the Bi-Te compound can have excellent thermal stability.

The A-Bi-Te compound may be formed by doping a Bi-Te compound with an alkali metal.

The A-Bi-Te compound may have a nanotube shape, a nanoparticle shape, or a bulk pellet shape.

The A-Bi-Te compound may have a high power factor and a thermoelectric figure of merit (ZT). For _{example, K 0. 06 Bi 2 Te 3} .18 is n- type thermoelectric semiconductor of Bi ₂ Te _{3 -} may have a power factor of _x Se _x is higher than a power factor of about 43㎼cm ^-1 K ^-2, 323K Lt; RTI ID = 0.0 &gt; ZT. &Lt; / RTI &gt;

According to embodiments of the present invention, it is possible to overcome the compositional limitations that are strictly controlled by the phase equilibrium through the nanochemical synthesis method and to stabilize the specific non-stoichiometric compounds . Thereby, a non-stoichiometric Bi-Te compound or A-Bi-Te compound having high phase uniformity and thermal stability can be formed. In contrast, the Bi-Te compound formed by the conventional high temperature solid phase reaction method may have a composition similar to that of the Bi-Te compound according to the embodiments of the present invention, including excess Te, It is decomposed by heating. Therefore, the Bi-Te compound formed by the conventional high-temperature solid-phase reaction method is inferior in phase uniformity and thermal stability to the Bi-Te compound according to the embodiments of the present invention.

1 schematically shows a process of forming a Bi-Te compound and a K-Bi-Te compound according to an embodiment of the present invention.

Referring to FIG. 1, Te nanorods are formed. The Te nanorods may have a diameter of about 50 nm and a length of about 1 m. The Te nanorods can be stabilized by bonding with polyvinylpyrrolidone (PVP). The Te nano-rod is reacted with Bi (NO ₃ ) ₃ to form a Bi ₂ Te _{3 .14} nanotube. Bi ₂ Te _{3 .14 The} reaction is carried out at a relatively low temperature of 160 ° C to stabilize the excess Te in the nanotubes. The PVP ligand bound to the Te nanorods can function as a diffusion barrier. The PVP ligand lowers the reaction rate between Bi ^{3 +} and Te ^{2 -} and may cause a Kirkendall effect. The external diffusion of Te ^{2 -} ions proceeds faster than the internal diffusion of Bi ^{3 +} ions, forming a hollow Bi ₂ Te _{3 .14} nanotube with stabilized excess Te. Bi ₂ Te _{3 .14} The chemical composition and excess Te of the nanotubes can be confirmed by ICP-AES (inductively coupled plasma atomic emission spectroscopy).

Bi ₂ Te _{3 .14} nanotubes can be consolidated to form a Bi ₂ Te _{3 .14} bulk BT. At this time, the remaining PVP can be removed.

The Bi ₂ Te _{3 .14} nanotubes are reacted with KOH to form K _{0 .07} Bi ₂ Te _{3 .14} nanotubes (KBT nanotubes). The reaction may be carried out in ethylene glycol to promote ion exchange reactions between potassium ions and PVP. K _0.07 Bi ₂ Te _3.14 The chemical composition and excess Te of nanotubes can be confirmed by ICP-AES.

K _{0. 07} Bi ₂ Te _{3 .14} nanotubes are integrated may be formed of a K _{0. 07} Bi ₂ Te _{3 .14} pellet bulk (bulk KBT). At this time, the remaining PVP can be removed.

Bi ₂ Te _{3 .14}  Nanotube Formation example

A precursor solution of Bi and a precursor solution of Te are formed. The Te precursor solution can be formed by reacting 2.394 g of TeO ₂ , 3 g of PVP, and 5.61 g of KOH in 150 ml of ethylene glycol. The Bi precursor solution can be formed by dissolving Bi (NO ₃ ) ₃ .5H ₂ O (bismuth nitrate pentahydrate) in 50 ml of ethylene glycol.

Te nanorods are formed. The Te nanorod can be formed by injecting 3 ml of NH ₂ NH ₂ .H ₂ O (hydrazine hydrate) into the Te precursor solution at 140 ° C and aging for 1 hour.

The Te nano rod mixed solution is heated to 160 캜 and the Bi precursor solution is added. The reaction mixture is aged for 30 to 60 minutes and cooled to room temperature. Precise control and reaction time of the Bi precursor solution is important for forming Bi ₂ Te _{3 .14} nanotubes. The Bi ₂ Te _{3 .14} nanotubes formed are collected by centrifugation at a speed of 13000 rpm and then washed several times with ethanol and distilled water.

K _{0. 07} Bi ₂ Te _{3 .14}  Nanotube Formation example

Bi ₂ Te _{3 .14} nanotubes are reacted with 0.2 M KOH in ethylene glycol solution at 140 ° C for 24 hours. During the reaction, the solution may be stirred vigorously. The formed K _0.07 Bi ₂ Te _3.14 nanotubes are washed with acetone and then dried under vacuum.

2 shows an image of a Bi-Te nanotube according to an embodiment of the present invention. 2A shows scanning electron microscopy (SEM) images of the Bi-Te nanotubes, and FIGS. 2B and 2C show TEM (transmission electron microscopy) images of the Bi-Te nanotubes . FIG. 3 shows a STEM (Scanning TEM) image and an EDS (dispersive X-ray spectroscopy) analysis result of a Bi-Te nanotube according to an embodiment of the present invention.

Referring to FIG. 2, the Bi ₂ Te _{3 .14} nanotube may have a polycrystalline nature consisting of nanoplates having a thickness of about 10 to 20 nm. The Bi ₂ Te _{3 .14} nanotubes may have a diameter of about 70-80 nm and a length of about 1 탆. Referring to FIG. 3, the Bi ₂ Te _3.14 nanotube has a hollow structure.

Fig. 4 shows a state diagram of the Bi-Te system.

4, the Bi-Te-based system, Bi: the stoichiometric range of Te 2: 2.98 ~ 2: is limited to 3.02 in, a Bi ₂ Te _{3 + x} by adding Te in an excess on a Bi ₂ Te ₃ compound It is very difficult to form. However, the nanochemical formation method according to embodiments of the present invention can easily form Bi ₂ Te _{3 + x} containing excess Te by using the reaction rate control at the atomic level.

5 is a TEM image of a K-Bi-Te nanotube according to an embodiment of the present invention.

5, the K _{0. 07} Bi ₂ Te _{3 .14} nanotubes may have a diameter and a length of about 1㎛ of about 70 ~ 80nm. The K _{0. 07} Bi ₂ Te _{3 .14} nanotubes have a hollow structure. Figure 5 is a diagram inserted in the K _{0. 07} Bi ₂ Te _{3 .14} shows a _.18 K _{0. 06} Bi ₂ Te ₃ particles are formed by incorporating nanotubes.

K _{0. 06} Bi ₂ Te _{3 .18} bulk pellets can be used for SPS (spark plasma sintering) formed by pressing the K _0.07 Bi ₂ Te _3.14 nanoparticles. The K _{0. 06} Bi ₂ Te _{3. 18} Bulk pellets may be pressed to form a high density by the SPS, and may have a diameter of about 13 mm and a thickness of about 6 to 7 mm, but are not limited in size and shape.

Figure 6 shows K-Bi-Te bulk pellets according to embodiments of the present invention.

Referring to FIG. 6, the K-Bi-Te bulk pellets can be formed into various shapes through cutting and polishing after pressing the K-Bi-Te particles using the SPS.

7 is a TGA (thermogravimetric analysis) graph of a Bi-Te compound and a K-Bi-Te compound according to embodiments of the present invention.

Referring to Figure 7, Bi ₂ Te _{3 .14} proceeds to nanotubes _{(BT nanotube) K 0. 07 Bi} 2 Te 3 .14 nanotubes, (KBT nanotube) the bulk K _{0. 07} Bi ₂ Te ₃ through _0.14 in And the PVP bound to the initial Te nanorod is removed.

For the comparative example, Bi ₂ Te ₃ , Bi ₂ Te _{3 .05} , and Bi ₂ Te _{3 .14} were formed by the high temperature solid phase reaction method. Bi ₂ Te ₃ , Bi ₂ Te _{3 .05} and Bi ₂ Te _{3 .14} according to the comparative examples and Bi ₂ Te _{3 .14} nanotube according to the embodiments of the present invention _{. 07} Bi ₂ Te _{3 .14} nanotubes (KBT nanotube), Bi ₂ Te _3.14 bulk BT, and K _{0. 06} Bi ₂ Te _{3 .18} bulk pellets (bulk KBT) were measured and compared. Hereinafter, the present invention will be described in detail with reference to the drawings.

8 is an X-ray diffraction (XRD) graph of a Bi-Te compound and a K-Bi-Te compound according to embodiments of the present invention and a Bi-Te compound according to a comparative example.

Referring to FIG. 8, Bi ₂ Te _{3 .05} and Bi ₂ Te _{3 .14} according to the comparative examples show peaks at 23 ° corresponding to the (001) reflction of hexagonal tellurium, examples of the Bi ₂ Te _{3 .14} nanotubes (BT nanotube) and K _{0. 07} Bi ₂ Te _{3 .14} nanotubes, (KBT nanotube) according to does not show a peak at 23 °. This indicates that the Bi-Te compound and the K-Bi-Te compound according to the embodiments of the present invention include excess Te but are pure or highly homogeneous.

9 shows a TGA graph of a Bi-Te compound, a K-Bi-Te compound, and a Bi-Te compound according to comparative examples according to embodiments of the present invention.

Referring to FIG. 9, Bi ₂ Te _{3 .05} and Bi ₂ Te _{3 .14} according to the comparative examples show weight loss from 680 K, but Bi ₂ Te _{3 .14} bulk pellets according to embodiments of the present invention bulk BT) and K _0.06 Bi ₂ Te _3.18 bulk pellets show little weight loss even at high temperatures above 680K. This means that Bi ₂ Te _{3 .05} and Bi ₂ Te _{3 .14} according to the comparative examples decompose excess tellurium having a melting point of 720K.

10 is a differential scanning calorimetry (DSC) analysis graph of a Bi-Te compound, a K-Bi-Te compound, and a Bi-Te compound according to comparative examples according to embodiments of the present invention.

Referring to FIG. 10, the Bi ₂ Te _{3 .14} bulk BT and K _{0. 06} Bi ₂ Te _{3 .18} bulk pellets (bulk KBT) according to embodiments of the present invention and the biologically Bi ₂ Te ₃ exhibits a single melting behavior at 851K, 848K and 859K, respectively, whereas Bi ₂ Te _{3 .05} and Bi ₂ Te _{3 .14} according to the comparative examples exhibit additional melting at 687.5K and 688K, respectively Multiple melting behavior is shown. This is consistent with the TGA graph.

The Bi ₂ Te _{3 .14} bulk BT and K _{0. 06} Bi ₂ Te _{3 .18} bulk pellets according to embodiments of the present invention include excess Te and potassium (K) Thermal stability and phase uniformity. This means that the nanochemical formation method of the Bi-Te compound and the A-Bi-Te compound according to the embodiments of the present invention enables the synthesis of an amphoteric compound that does not conform to the state diagram of the constituent elements.

11 shows Fourier transform infrared (FTIR) spectral analysis results of a K-Bi-Te bulk pellet according to an embodiment of the present invention.

Referring to FIG. 11, K _{0. 06} Bi ₂ Te _{3 .18} bulk pellets formed after spark plasma sintering (SPS) contain residual organics that are considered serious problems of solution treated materials for thermoelectric applications I never do that.

12 is an X-ray diffraction (XRD) graph of a K-Bi-Te bulk pellet according to an embodiment of the present invention.

Referring to FIG. 12, the XRD pattern of the K _0.06 Bi ₂ Te _3.18 bulk pellet taken in the in-plane direction is shown in the out-of-plane direction Exhibit a high preferred orientation of (001) reflection relative to the XRD pattern taken. This means that the one-dimensional nanotubes are well-aligned to form a two-dimensional arrangement perpendicular to the pressing direction of the SPS.

13 shows an SEM image of a K-Bi-Te bulk pellet according to an embodiment of the present invention. 13A is an SEM image in an in-plane direction and FIG. 13B is an SEM image in an out-of-plane direction.

Referring to Figure _{13, K 0. 06 Bi 2 Te} 3 .18 pellet has a bulk (bulk KBT) is highly clove morphology (highly oriented morphology) as the single crystal.

Figure 14 shows a cross-sectional scanning TEM image of a Bi-Te bulk pellet according to an embodiment of the present invention, and Figure 15 shows a STEM image of a K-Bi-Te bulk pellet according to an embodiment of the present invention. . 14 and 15 are high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images.

Referring to FIG. 14, the Bi-Te bulk BT shown below the [-100] axis shows a moderate structural dislocation that grows along the in-plane direction indicated by the white arrows. However, referring to FIG. 15, a K-Bi-Te bulk pellet (bulk KBT) contains significant lattice degeneration along the in-plane direction, including merged lattices and antisites of Te and Bi considerable lattice modulation. It is preferred that the potassium cation is located around the Te-rich region and can be judged to induce severe structural deformation.

Figure 16 shows an HAADF-STEM image of a K-Bi-Te bulk pellet (bulk KBT) according to one embodiment of the present invention. In Fig. 16, the pink arrow indicates Te and the yellow arrow indicates Bi.

Referring to FIG. 16, the excess Te is located in the interlayer space to fuse individual Bi ₂ Te ₃ . An extended 7-septuple atomic layer consisting of [Bi ₃ Te ₄ ] (Te-Bi-Te-Bi-Te-Bi-Te) along the ideal quintuple atomic layer is frequently observed do.

17 shows the STEM-EDS analysis results of a K-Bi-Te bulk pellet (bulk KBT) according to an embodiment of the present invention. In Fig. 17, yellow indicates Bi and red indicates Te.

Referring to FIG. 17, a Te-Te-Bi-Te-Bi-Te-Te-Bi-Te atomic arrangement is shown, with the Te atom layer replacing the Bi atom layer to form a Te-Te bond (white arrow). The formation of the Te-Te atomic layer reduces the net negative charge of the K-Bi-Te bulk pellet (bulk KBT) and the Bi-Te bulk pellet (bulk BT) and stabilizes the excess Te.

As described above, the nanochemical formation method according to the embodiments of the present invention can control the reaction rate between the Te nanorod and the Bi source so that the Bi-Te compound and the Bi-Te compound, which contain excessive Te beyond the state diagram, A-Bi-Te compound can be formed.

Figure 18 shows an HAADF-STEM image of a K-Bi-Te bulk pellet (bulk KBT) according to one embodiment of the present invention.

Referring to FIG. 18, potassium ions may be disposed at interstitial sites (blue arrows) and interlayer sites (orange arrows) of Bi ₂ Te ₃ layers, respectively.

For the comparative example, Bi ₂ Te ₃ and K _{0 .0} Bi ₂ Te ₃ were formed by the high temperature solid phase reaction method. Bi ₂ Te ₃ and K _{0. 02} Bi ₂ Te ₃ according to the above comparative examples and Bi ₂ Te _{3 .14} bulk BT and K _{0. 06} Bi ₂ Te ₃ according to embodiments of the present invention _{. 18} Bulk pellets (bulk KBT) were measured and compared. The thermoelectric properties were measured in the in-plane direction after SPS treatment of all samples according to the above embodiments and comparative examples. Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 19 is a plot of Bi ₂ Te _{3 .14} bulk BT and K _0.06 Bi ₂ Te _3.18 bulk pellets (bulk KBT) according to embodiments of the present invention and Bi ₂ Te ₃ and K _{0. 02} Bi ₂ Te ₃ according to the temperature, and the Seebeck coefficient (S).

Referring to Figure 19, Bi ₂ Te _{3 .14} bulk BT and K _{0. 06} Bi ₂ Te _{3 .18} bulk pellets (bulk KBT) according to embodiments of the present invention and other Bi ₂ Te ₃ represents a negative value in the temperature range of 300 to 470 K, indicating that the former is the main charge carrier. In addition, the K _{0. 06} Bi ₂ Te _{3 .18} pellet bulk (bulk KBT) is shown and the n- type behavior, the K _{0. 02} Bi ₂ Te ₃ denotes a p- type behavior.

Figure 20 shows the electron concentration (n _e ) and mobility of the Bi ₂ Te _{3 .14} bulk BT and K _0.06 Bi ₂ Te _3.18 bulk pellets according to embodiments of the present invention mobility, μ _e ).

Referring to Figure _{20, K 0. 06 Bi 2 Te} 3 .18 pellet bulk (bulk KBT) is a value of electron concentration (n _e) at a temperature of 300K by introducing the potassium is about 3.14 × 10 ¹⁹ ~ 4.63 × 10 increased to ¹⁹ cm ^-3, and the mobility (μ _e) value of about 142 ~ 171cm ² V ^-1 s ^{- 1} increases. This means that potassium functions as an electron donor.

Referring again to FIGS. 19 and 20, the electron carrier concentration is the Bi ₂ Te _{3 .14} pellet bulk (bulk BT) of the K _{0. 06} Bi ₂ Te _{3 .18} pellet bulk (bulk KBT) at a temperature of 300K Concentration is 1.5 times larger than the concentration, but the Seebeck coefficient (S) is almost equal to -182 K ^-1 . The absolute value of the Seebeck coefficient of the Bi ₂ Te _{3 .14} bulk BT and the K _{0. 06} Bi ₂ Te _{3 .18} bulk pellet is the Seebeck coefficient (S) of Bi ₂ Te ₃ , Which is much larger than the absolute value of-135 K ^-1 . In addition, the K _{0. 06} Bi ₂ Te _{3 .18} absolute value of the Seebeck coefficient of the pellet the bulk (bulk KBT) is reduced at higher temperatures while increase to 350K. This potassium contained in K _{0. 06} Bi ₂ Te _{3 .18} pellet bulk (bulk KBT) formed in accordance with the nano-chemical formation method according to the embodiments of the present invention exhibit a unique behavior, which is the K _{0. 06} Bi ₂ Te _{3 .18} Bulk pellets (bulk KBT) can not be formed by conventional methods.

Figure 21 shows the electrical conductivity () and the Seebeck coefficient (K) of K _{0. 06} Bi ₂ Te _{3 .18} bulk KBT and Na _0.05 Bi ₂ Te _3.11 bulk pellets according to embodiments of the present invention S).

Referring to Figure 21, the Na _{0. 05} Bi ₂ Te _{3 .11} bulk pellets (bulk NaBT) can be formed in the same manner as the K _0.06 Bi ₂ Te _3.18 bulk pellet (bulk KBT). The Na _0.05 Bi ₂ Te _3.11 bulk pellet (bulk NaBT) has negative Shek coefficient values over the entire temperature range and exhibits n-type behavior. In addition, the Na _{0. 05} Bi ₂ Te _{3 .11} bulk pellet (bulk NaBT) showed that the electrical conductivity change with temperature was not larger than that of K _{0. 06} Bi ₂ Te _{3 .18} bulk pellet (bulk KBT).

FIG. 22 is a graph showing the results of a comparison of the Bi ₂ Te _{3 .14} bulk BT and K _0.06 Bi ₂ Te _3.18 bulk pellets (bulk KBT) according to embodiments of the present invention and Bi ₂ Te ₃ and K _{0. 02} Bi ₂ Te ₃ according to the temperature.

Referring to FIG. 22, the Bi ₂ Te _{3 .14} bulk BT and K _{0. 06} Bi ₂ Te _{3 .18} bulk pellets (bulk KBT) according to embodiments of the present invention and other Bi ₂ Te ₃ decreases as the temperature increases. Wherein at a temperature of _{300K K 0. 06 Bi 2 Te 3} .18 bulk pellets about 711Scm the electrical conductivity of the Bi ₂ Te _{3 .14} pellet bulk (bulk BT) The ionic conductivity is about 1265Scm ^-1 of (bulk KBT) ^{- 1} is almost twice as large. This is due to greater than the K _{0. 06} Bi ₂ Te _{3 .18} pellet bulk density and the electron mobility which the Bi ₂ Te _{3 .14} pellet bulk (bulk BT) of (bulk KBT). In contrast, K _{0. 02} electrical conductivity of the Bi ₂ Te ₃ is significantly decreased than about 1142 Scm ^-1 in the electric conductivity of the Bi ₂ Te ₃ is about 448Scm ^-1.

FIG. 23 is a graph showing the results of a comparison between the Bi ₂ Te _{3 .14} bulk BT and K _0.06 Bi ₂ Te _3.18 bulk pellets according to embodiments of the present invention and Bi ₂ Te ₃ and K _{0. 02} Bi ₂ Te ₃ according to the temperature.

Referring to Figure 23, the K _{0. 06} Bi ₂ Te _{3 .18} bulk power factor of the pellets (bulk KBT) is that after reaching the maximum value of about 42.8㎼cm ^-1 K ^-2 temperature increase at a temperature of 323K as . The K _{0. 06} Bi ₂ Te _{3 .18} pellet bulk (bulk KBT) is in a temperature range of 300 ~ 480K can have more than about 22㎼cm ^{-1 -2} K factor. The K _{0. 06} Bi ₂ Te _{3 .18} power factor of bulk pellets (bulk KBT) is shown to be much greater than the power factor of the Bi ₂ Te ₃ and K _{0. 02} Bi ₂ Te _3. In addition, the K _{0. 06} Bi ₂ Te _{3. 18} bulk PKT is greater than the power factor of the Bi ₂ Te _3.14 bulk BT, which has a similar Seebeck coefficient (S) to that of the Bi ₂ Te _3.14 bulk pellet. The K _{0. 06} Bi ₂ Te _{3 .18} bulk pellet (bulk BTT) is greater than the electrical conductivity of the Bi ₂ Te _{3 .14} bulk BT.

Figs. 24 and 25 are graphs showing the results of a comparison between the Bi ₂ Te _{3 .14} bulk BT and K _{0. 06} Bi ₂ Te _{3 .18} bulk pellets (bulk KBT) and comparative examples Total heat conductivity (κ _tot ) and lattice thermal conductivity (κ _latt ) of Bi ₂ Te ₃ and K _{0 .02} Bi ₂ Te ₃ with temperature are shown.

Referring to Figure 24, the K _{0. 06} Bi ₂ Te _{3 .18} appears to be the lowest total thermal conductivity of bulk pellets (bulk KBT). The K _{0. 06} Bi ₂ Te _{3 .18} Bulk Pellets total thermal conductivity of about 1.30Wm ^-1 K ^-1, and a minimum value of about 1.25Wm ^-1 K ^-1 at a temperature of 350K in a temperature of 300K in the (bulk KBT) to be. The total thermal conductivity of the Bi ₂ Te _{3 .14} bulk BT is about 1.57 W m ^-1 K ^-1 at a temperature of 300 K and about 1.53 W m ^-1 K ^-1 at a temperature of 350 K.

Referring to Figure 25, wherein at a temperature of _{300K K 0. 06 Bi 2 Te 3} .18 pellet bulk lattice thermal conductivity is from about 0.66Wm ^-1 K of (bulk KBT) ^- wherein the Bi ₂ Te _{3 .14} bulk pellets ¹ (bulk BT) appears to be much lower than the approximately 1.21Wm ^-1 K ^-1 lattice thermal conductivity. This is due to the various structural displacements caused by the doped potassium.

Fig. 26 is a graph showing the results of a comparison of Bi ₂ Te _{3 .14} bulk BT and K _0.06 Bi ₂ Te _3.18 bulk pellets (bulk KBT) according to embodiments of the present invention and Bi ₂ Te ₃ and K _{0. 02} Bi ₂ Te ₃ according to the temperature.

Referring to FIG. 26, the K _{0. 06} Bi ₂ Te _{3 .18} bulk pellet (bulk KBT) has the highest thermoelectric performance index. Thermoelectric figure of merit of the K _{0. 06} Bi ₂ Te _{3 .18} pellet bulk (bulk KBT) is about 1.0 at a temperature of 300K, it is increased at a temperature of 350K to about 1.14 of the maximum value. The K _{0. 06} Bi ₂ Te _{3 .18} pellet bulk (bulk KBT) may have about 0.6 or more thermoelectric figure of merit over a temperature range of 300 ~ 480K.

Hereinafter, specific embodiments of the present invention have been described. 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 by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

Claims (18)

A Bi-Te compound having the formula:
[Chemical Formula]
Bi ₂ Te _{3 + x} (0 &lt; x &lt; 1) The method according to claim 1,
Wherein the Bi-Te compound has phase uniformity. The method according to claim 1,
Wherein the Bi-Te compound has a single melting point. The method according to claim 1,
The Bi-Te compound has a hollow structure. The method according to claim 1,
Wherein the Bi-Te compound has a nanotube shape, a nanoparticle shape, or a bulk pellet shape. The method according to claim 1,
Wherein the Bi-Te compound comprises a 7-fold atomic layer composed of Te-Bi-Te-Bi-Te-Bi-Te. The method according to claim 1,
Wherein the Bi-Te compound comprises a Te-Bi-Te-Bi-Te-Te-Bi-Te atomic arrangement. The method according to claim 1,
The Bi-Te compound is an n-type thermoelectric semiconductor. The method according to claim 1,
Wherein the formula is Bi ₂ Te _{3 .14} . Forming a Te nanorod;
Forming a Bi precursor solution; And
And reacting the Te nanorod and the Bi to form a Bi-Te nanotube. 11. The method of claim 10,
The Te nano-
Wherein a polyvinylpyrrolidone (PVP) ligand is bound to the substrate. 12. The method of claim 11,
Wherein the reaction rate of the Te and Bi is controlled by the PVP ligand. 13. The method of claim 12,
Wherein the external diffusion of the Te ions proceeds faster than the internal diffusion of the Bi ions by the PVP in the reaction. 12. The method of claim 11,
Further comprising performing spark plasma sintering (SPS) on the Bi-Te nanotube,
Wherein the Bi-Te compound is formed of bulk pellets by the SPS. 15. The method of claim 14,
Wherein the PVP ligand is removed by the SPS. 11. The method of claim 10,
Wherein the reaction is carried out at a temperature of 150 to 170 ° C. 11. The method of claim 10,
Wherein the reaction is carried out in ethylene glycol. 11. The method of claim 10,
The Te nano-
TeO _2, PVP, and a method of forming a Bi-Te compound being formed by reacting a mixture of KOH in ethylene glycol.

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