KR20220152723A - Thermoelectric snte nanocomposite with ternary-compound coating layer and preparing method thereof - Google Patents

Abstract

The present invention relates to a thermoelectric element including a ternary material coating layer and a manufacturing method thereof. The thermoelectric element includes a binary chalcogenide material core and a ternary material coating layer. Therefore, the thermoelectric element generates an energy filtering effect due to a significant energy potential barrier between the binary chalcogenide material core and the ternary material coating layer to increase a Seebeck coefficient of the thermoelectric element and increase a thermoelectric performance figure accordingly.

Description

Thermoelectric material including ternary material coating layer and manufacturing method thereof

The present application relates to a thermoelectric material including a ternary material coating layer, and a manufacturing method thereof.

A thermoelectric element is an element capable of directly converting heat and electricity, and has been used in the field of waste heat recovery systems and the like. Since PbTe alloy thermoelectric materials have an excellent thermoelectric figure of merit in a medium temperature range, they have been widely used in the field of waste heat recovery, and recently, research on thermoelectric materials composed of eco-friendly elements such as SnTe has been actively conducted.

On the other hand, the conversion efficiency of a thermoelectric element can be expressed as zT=S ² σT/(κ _L +κ _e ) as a function of a dimensionless index called thermoelectric figure of merit (S: Seebeck coefficient, σ: electrical conductivity, κ _L : lattice thermal conductivity, κ _e : electronic thermal conductivity). As a strategy for improving the thermoelectric figure of merit, increasing the power factor (S ² σ) or decreasing the thermal conductivity (κ _L +κ _e ) has been proposed. However, since the Seebeck coefficient and electrical conductivity have an inverse relationship, it is difficult to increase the power factor. From the Boltzmann transport equation of Equation 1 below, the Seebeck coefficient is a function of density of state (DOS, D(E)), scattering time (τ(E)), and Fermi-Dirac distribution can be derived as:

[Equation 1]

.

.

where E is the electron energy, τ is the scattering time, D is the density of states, and F is the Fermi-Dirac distribution function. The denominator of Equation 1 is the electrical conductivity. Therefore, it is very difficult to simultaneously improve the Seebeck coefficient and electrical conductivity in bulk materials.

In addition, many nanotechnological attempts have been made to improve the Seebeck coefficient while minimizing the electrical conductivity. The Seebeck coefficient can be improved by adjusting D(E) and τ(E) near the Fermi level, and the adjustment of D(E) can be performed by resonance doping or quantum confinement effect, and τ(E ) can be controlled by the energy filtering effect. The energy filtering may be induced by a potential barrier of embedded nanoparticle impurities. In addition, dispersed nanoparticle impurities have been reported as one of the effective ways to reduce κ _L by acting as effective phonon scatterers for short- and medium-wavelength phonons. However, in the structure in which nanoparticle impurities are dispersed, only some carriers have a chance to meet the barrier, so the energy filtering effect is low, and the density is not high enough to serve as a phonon scattering agent.

Paper Impact of energy filtering and carrier localization on the thermoelectric properties of granular semiconductors, Journal of Solid State Chemistry 2012, 193, 19-25.

The present application intends to provide a thermoelectric material including a binary chalcogenide material core and a ternary material coating layer.

However, the problem to be solved by the present application is not limited to the above-mentioned problem, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

A first aspect of the present application is a thermoelectric material including a binary chalcogenide material core and a ternary material coating layer, wherein the ternary material coating layer includes a chalcogen material, a first substitution material, and a second substitution material, wherein the The first substitution material and the second substitution material provide a thermoelectric material different from the metal of the binary chalcogenide material.

A second aspect of the present application provides a step of preparing a binary chalcogenide material core, preparing a ternary material precursor including a first substitution material precursor and a second substitution material precursor, and the binary chalcogenide material core and A method for producing a thermoelectric material is provided, comprising mixing the ternary material precursor and subjecting the precursor to a cation substitution reaction to obtain a thermoelectric material.

A thermoelectric material according to embodiments of the present disclosure includes a binary chalcogenide material core and a ternary material coating layer, and energy is filtered due to a significant energy potential barrier between the binary chalcogenide material core and the ternary material coating layer. As a result of the effect, the Seebeck coefficient of the thermoelectric material is improved, and thus the thermoelectric figure of merit is improved.

A thermoelectric material according to embodiments of the present disclosure includes a binary chalcogenide material core and a ternary material coating layer, and coherent phonon scattering occurs due to a mismatch in acoustic impedance between the binary chalcogenide material core and the ternary material coating layer. This is enhanced to reduce the lattice thermal conductivity of the thermoelectric material and thereby improve the thermoelectric figure of merit.

The thermoelectric material according to embodiments of the present disclosure is characterized in that the energy filtering effect and the coherent phonon scattering enhancing effect are effectively generated by uniformly forming the ternary material coating layer on the surface of the binary chalcogenide material core.

1 is, in one embodiment of the present application, a schematic diagram of the mechanism of a cation substitution reaction.
2 is a transmission electron microscope (TEM) picture of a CuInTe ₂ /SnTe nanostructure in one embodiment of the present application.
3a is a high-resolution TEM photograph obtained by enlarging and measuring the crystal grain interface (coating layer) of the CuInTe ₂ /SnTe nanostructure in one embodiment of the present application.
Figure 3b is, according to an embodiment of the present application, a fast Fourier transform (FFT) pattern photograph of the crystal grain interface (coating layer) of the CuInTe ₂ /SnTe nanostructure.
Figure 4a, in one embodiment of the present application, CuInTe ₂ /SnTe nanostructure XRD measurement results.
Figure 4b is a schematic diagram of the crystal structures of CuInTe ₂ and SnTe in one embodiment of the present application.
5 is a compositional analysis result using STEM-EDS (Scanning TEM-Electron Dispersive Spectroscopy) of a CuInTe ₂ /SnTe nanostructure in one embodiment of the present application.
6a is a resistivity graph of CuInTe ₂ /SnTe nanostructures according to one embodiment of the present application.
Figure 6b is a Seebeck coefficient graph of CuInTe ₂ /SnTe nanostructures according to one embodiment of the present application.
Figure 6c is a power factor graph of the CuInTe ₂ /SnTe nanostructure according to one embodiment of the present application.
6d is a schematic diagram showing a band diagram of CuInTe ₂ and SnTe of the CuInTe ₂ /SnTe nanostructure in one embodiment of the present application.
Figure 6e is, according to an embodiment of the present application, a CuInTe ₂ /SnTe nanostructure is a resistivity graph.
6 f is a Seebeck coefficient graph of CuInTe ₂ /SnTe nanostructures according to an embodiment of the present application.
6g is a power factor graph of CuInTe ₂ /SnTe nanostructures according to one embodiment of the present application.
Figure 7a is a thermal conductivity graph of the CuInTe ₂ /SnTe nanostructure according to one embodiment of the present application.
Figure 7b is a lattice thermal conductivity graph of CuInTe ₂ /SnTe nanostructures according to one embodiment of the present application.
Figure 7c is a thermal conductivity graph of the CuInTe ₂ /SnTe nanostructure according to one embodiment of the present application.
Figure 8a is a thermoelectric figure of merit graph of CuInTe ₂ /SnTe nanostructures according to one embodiment of the present application.
FIG. 8B is a graph showing a comparison of the thermoelectric figure of merit between the CuInTe ₂ /SnTe nanostructure and the thermoelectric structure of the prior literature according to one embodiment of the present application.
8 c is a thermoelectric figure of merit graph of a CuInTe ₂ /SnTe nanostructure according to one embodiment of the present application.

Hereinafter, with reference to the accompanying drawings, embodiments and embodiments of the present application will be described in detail so that those skilled in the art can easily practice the present invention. However, the present disclosure may be embodied in many different forms and is not limited to the implementations and examples described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout this specification, when a part is said to be "connected" to another part, this includes not only the case of being "directly connected" but also the case of being "electrically connected" with another element in between. do.

Throughout the present specification, when a member is said to be located “on” another member, this includes not only a case where a member is in contact with another member, but also a case where another member exists between the two members.

Throughout the present specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated.

As used herein, the terms "about," "substantially," and the like are used at or approximating that number when manufacturing and material tolerances inherent in the stated meaning are given, and are intended to assist in the understanding of this disclosure. Accurate or absolute figures are used to prevent undue exploitation by unscrupulous infringers of the stated disclosure.

The term "step of" or "step of" used throughout the present specification does not mean "step for".

Throughout this specification, the term "combination(s) of these" included in the expression of the Markush form means one or more mixtures or combinations selected from the group consisting of the components described in the expression of the Markush form, It means including one or more selected from the group consisting of the above components.

Throughout this specification, reference to "A and/or B" means "A or B, or A and B".

Throughout the present specification, the description of "cation substitution reaction" means that the metal of the thermoelectric material is replaced with a metal different from the metal of the thermoelectric material during the manufacturing process of the thermoelectric material, and cation substitution means a different metal to be substituted. means

Hereinafter, embodiments of the present application have been described in detail, but the present application may not be limited thereto.

A first aspect of the present application is a thermoelectric material including a binary chalcogenide material core and a ternary material coating layer, wherein the ternary material coating layer includes a chalcogen material, a first substitution material, and a second substitution material, wherein the The first substitution material and the second substitution material provide a thermoelectric material different from the metal of the binary chalcogenide material.

In one embodiment of the present application, the first substitution material and the second substitution material of the ternary material coating layer may be cation substitution products of the binary chalcogenide material. Specifically, the ternary material coating layer may be formed by replacing the metal of the binary chalcogenide material with the first substitution material and the second substitution material through a cation exchange reaction on the surface of the binary chalcogenide material core. have.

In one embodiment of the present application, the first substitution material may include one or more selected from Cu, Cs, and Ag, and the second substitution material includes one or more selected from Bi, Sb, Ga, and In. It may be, but may not be limited thereto.

In one embodiment of the present application, the first substitution material and the second substitution material may be selected in consideration of the solubility product (K _SP ). Specifically, the solubility product between the first substituted material and the second substituted material and the chalcogenide material may be smaller than the solubility product of the binary chalcogenide material. More specifically, the solubility product (K _SP ) is a thermodynamic factor that can predict a cation substitution reaction, and the solubility product of the binary chalcogenide material is higher than the solubility product of the first substituted material and the second substituted material and the chalcogenide material. As the solubility product of liver is small, the metal of the binary chalcogenide material is spontaneously substituted with the first substitution material and the second substitution material, so that the ternary material coating layer can be formed on the surface of the core of the binary chalcogenide material. have.

In one embodiment of the present application, the first substitution material and the second substitution material may be selected in consideration of the HSAB (hard and soft acid and bases) theory. Specifically, according to the theory of hard and soft acid and bases (HSAB), hard acid cations bind strongly to hard bases, and soft acid cations strongly bind to soft bases. It can be inferred that As an example, when the binary chalcogenide material is SnTe and the ternary material is CuInTe ₂ , copper acetate (Cu(Ac) ₂ ), indium acetate (In(Ac) ₃ ), and oleic acid When a solution containing oleylamine (OLA) is mixed with SnTe, a cation substitution reaction between Sn and Cu and In cations may occur on the SnTe surface. According to the HSAB theory, since the copper acetate and indium acetate are easily ionized, Cu ²⁺ and In ³⁺ are easily generated, and Sn ²⁺ of the SnTe is a strong acid, so the implanted metal (Cu ²⁺ and In ³⁺ ) Since it forms a more stable acid-base pair with acetate (Ac ^- ) than Acetate, it can easily form a metal acetate complex.

In one embodiment of the present application, the ternary material may include one or more selected from CuInTe ₂ , AgInTe ₂ , CuBiTe ₂ , AgBiTe ₂ , CuSbTe ₂ , and AgSbTe ₂ .

In one embodiment of the present application, the diameter of the binary chalcogenide material core may be about 100 nm to about 3000 nm, but may not be limited thereto. Specifically, the diameter of the binary chalcogenide material core is about 100 nm to about 3000 nm, about 100 nm to about 2000 nm, about 100 nm to about 1000 nm, about 200 nm to about 3000 nm, about 200 nm to about 2000 nm, or about 200 nm to about 1000 nm, but may not be limited thereto.

In one embodiment of the present application, the thickness of the ternary material coating layer may be about 3% to about 20% of the core diameter of the binary chalcogenide material, but may not be limited thereto. Specifically, the thickness of the ternary material coating layer is about 3% to about 20%, about 3% to about 15%, about 3% to about 10%, about 4% to about 20% of the core diameter of the binary chalcogenide material. %, about 4% to about 15%, about 4% to about 10%, about 5% to about 20%, about 5% to about 15%, or about 5% to about 10%. When the thickness of the ternary material coating layer is out of the above range, a problem in which the coherent scattering effect of phonons is degraded may occur.

In one embodiment of the present application, the coating layer of the ternary material may be a uniform layer formed by uniformly aggregating nanoparticles of the ternary material.

In one embodiment of the present application, the crystal structure of the ternary material may be similar to that of the binary chalcogenide material. As an example, when the binary chalcogenide material is SnTe and the ternary material is CuInTe ₂ , the SnTe has an FCC rock salt structure in which the space group containing Te ^2- anion is Fm3m, It can be confirmed that the CuInTe ₂ has a tetragonal structure in which a space group is I42d. Therefore, tetragonal CuInTe ₂ is a structure in which Te anions form an FCC cage and Cu ⁺ and In ³⁺ cations are in tetrahedral sites, and it can be confirmed that the structure is similar to the SnTe crystal structure.

In one embodiment of the present application, the thermoelectric material further includes at least one selected from Bi, Ag, Cu, Cr, Sb, Zn, Se, S, In, Cd, Mg, Hg, Mn, and Ca as a dopant. It may be, but may not be limited thereto. Specifically, the dopant creates a resonance state near the Fermi level of the binary chalcogenide material, or reduces the valence band offset and increases the Seebeck coefficient. can play a role

In one embodiment of the present application, the binary chalcogenide material is at least one selected from SnTe, SnSe, SnS, PbTe, PbSe, PbS, ZnTe, ZnSe, ZnS, ZnO, GeTe, Cu ₂ Te, and Cu ₂ Se It may include, but may not be limited thereto.

In one embodiment of the present application, in the thermoelectric material, an energy potential barrier may be formed between the binary chalcogenide material core and the ternary material coating layer, and the size of the energy potential barrier is about 100 meV to about 200 meV It may be, but may not be limited thereto. Specifically, the size of the energy potential barrier is about 100 meV to about 200 meV, about 100 meV to about 190 meV, about 100 meV to about 180 meV, about 100 meV to about 170 meV, about 100 meV to about 160 meV, It may be about 100 meV to about 150 meV, about 100 meV to about 140 meV, about 100 meV to about 130 meV, about 100 meV to about 120 meV, or about 100 meV to about 110 meV, but may not be limited thereto. .

In one embodiment of the present application, the energy potential barrier formed between the binary chalcogenide material core and the ternary material coating layer may block conduction carriers to generate an energy filtering effect. The energy filtering effect results in an enhancement of the Seebeck coefficient, and calculation of the Seebeck coefficient enhancement may be performed based on the Boltzmann transport equation.

In one embodiment of the present application, coherent phonon scattering is enhanced due to the acoustic impedance mismatch between the binary chalcogenide material core and the ternary material coating layer, thereby reducing the lattice thermal conductivity of the thermoelectric material and thus improving the thermoelectric figure of merit. can Specifically, when a traveling phonon phase passes through the ternary material coating layer, a phonon phase delay occurs due to a difference in acoustic impedance between the binary chalcogenide material core and the ternary material coating layer, and such multiple The phase delay of phonons causes interference, which can lead to strong phonon scattering. Since the coherent phonon scattering creates a short phonon mean free path in a wide phonon spectrum, it can act as a strong advantage in the thermoelectric field.

A second aspect of the present application provides a step of preparing a binary chalcogenide material core, preparing a ternary material precursor including a first substitution material precursor and a second substitution material precursor, and the binary chalcogenide material core and A method for producing a thermoelectric material is provided, comprising mixing the ternary material precursor and subjecting the precursor to a cation substitution reaction to obtain a thermoelectric material.

In one embodiment of the present application, the step of preparing the binary chalcogenide material core may be to form the binary chalcogenide material core into a powder form, but may not be limited thereto.

In one embodiment of the present application, the step of preparing a ternary material precursor including the first substitution material precursor and the second substitution material precursor is preparing the ternary material precursor in a solution phase, oxygen and moisture of the solution It may include removing, but may not be limited thereto. Specifically, the ternary material precursor solution contains oleylamine (OLA), oleic acid, trioctyl phosphine (TOP), and tributyl phosphine (TBP) as organic ligands. It may contain one or more selected from among, and may contain one or more selected from octadecene (1-octadecene, 1-ODE), methyl cyclohexane, and toluene as a solvent, may not be limited thereto.

In one embodiment of the present application, the first substitution material precursor and the second substitution material precursor include at least one selected from acetate-based, bromide-based, and iodide-based However, it may not be limited thereto. As an example, the first substitution material precursor may be copper acetate (Cu(Ac) ₂ ), and the second substitution material precursor may be indium acetate (In(Ac) ₃ ), but may not be limited thereto.

In one embodiment of the present application, the cation substitution reaction may be performed in consideration of the solubility product. Specifically, the solubility product (K _SP ) is a thermodynamic factor that can predict a cation substitution reaction, and the solubility product between the first substituted material and the second substituted material and the chalcogen material is compared to the solubility product of the binary chalcogenide material. By being small, the metal of the binary chalcogenide material is spontaneously substituted with the first substitution material and the second substitution material, so that the ternary material coating layer can be formed on the surface of the binary chalcogenide material core.

In one embodiment of the present application, the cation substitution reaction may be performed in consideration of the HSAB (hard and soft acid and bases) theory. Specifically, according to the theory of hard and soft acid and bases (HSAB), hard acid cations bind strongly to hard bases, and soft acid cations strongly bind to soft bases. It can be inferred that As an example, when the binary chalcogenide material is SnTe and the ternary material is CuInTe ₂ , copper acetate (Cu(Ac) ₂ ), indium acetate (In(Ac) ₃ ), and oleic acid When a solution containing oleylamine (OLA) is mixed with SnTe, a cation substitution reaction between Sn and Cu and In cations may occur on the SnTe surface. According to the HSAB theory, since the copper acetate and indium acetate are easily ionized, Cu ²⁺ and In ³⁺ are easily generated, and Sn ²⁺ of the SnTe is a strong acid, so the implanted metal (Cu ²⁺ and In ³⁺ ) Since it forms a more stable acid-base pair with acetate (Ac ^- ) than Acetate, it can easily form a metal acetate complex.

In one embodiment of the present application, the amount of the first substitution material precursor and the second substitution material precursor may be n moles and m moles, respectively, with respect to 1 mole of the binary chalcogenide material, and n and m are each independently It may be an integer of 1 to 6, but may not be limited thereto. Specifically, the content of the precursor of the first substituted material and the second substituted material is 1 to 6 moles, 1 to 5 moles, 1 to 4 moles, and 1 mole, respectively, based on 1 mole of the binary chalcogenide material. to 3 moles, 1 to 2 moles, 2 to 6 moles, 2 to 5 moles, 2 to 4 moles, 2 to 3 moles, 3 to 6 moles, 3 to 5 moles, 3 to 4 moles mole, 4 moles to 6 moles, 4 moles to 5 moles, or 5 moles to 6 moles, but may not be limited thereto.

In one embodiment of the present application, n may be an integer equal to or smaller than m. When the n is equal to the m, the Seebeck coefficient of the thermoelectric material may be the highest, and when the n is slightly smaller than the m, the reliability of the thermoelectric material may be high. Specifically, the ratio (n:m) of the n and the m may be 3:5 to 5:5.

In one embodiment of the present application, the cation substitution reaction may be performed by mixing and heating the binary chalcogenide material core and the ternary material precursor, but may not be limited thereto.

In one embodiment of the present application, the cation substitution reaction may be carried out at a temperature range of about 180 ° C to about 250 ° C, but may not be limited thereto. Specifically, the cation substitution reaction is about 180 ℃ to about 250 ℃, about 180 ℃ to about 240 ℃, about 180 ℃ to about 230 ℃, about 180 ℃ to about 220 ℃, about 180 ℃ to about 210 ℃, about 180 °C to about 200 °C, about 180 °C to about 190 °C, about 190 °C to about 250 °C, about 190 °C to about 240 °C, about 190 °C to about 230 °C, about 190 °C to about 220 °C, about 190 °C to About 210°C, about 190°C to about 200°C, about 200°C to about 250°C, about 200°C to about 240°C, about 200°C to about 230°C, about 200°C to about 220°C, about 200°C to about 210°C °C, about 210 °C to about 250 °C, about 210 °C to about 240 °C, about 210 °C to about 230 °C, about 210 °C to about 220 °C, about 220 °C to about 250 °C, about 220 °C to about 240 °C, It may be performed in a temperature range of about 220 ° C to about 230 ° C, about 230 ° C to about 250 ° C, about 230 ° C to about 240 ° C, or about 240 ° C to about 250 ° C, but may not be limited thereto.

Detailed descriptions of portions overlapping with the first aspect of the present application have been omitted, but the description of the first aspect of the present application can be equally applied even if the description is omitted in the second aspect of the present application.

Hereinafter, the present application will be described in more detail using examples, but the following examples are only illustrative to aid understanding of the present application, and the content of the present application is not limited to the following examples.

[Example]

<Example 1: CuInTe ₂ / Fabrication of SnTe nanostructures>

1) CuInTe in a mixed solution of 25 mL of oleylamine (OLA) (Alfa Aesar, 70%, tech grade) and 175 mL of octadecene (1-octadecene, 1-ODE) (Alfa Aesar, 90%, tech grade) After dissolving copper acetate (Cu(Ac) ₂ ) and indium acetate (In(Ac) ₃ ) (Sigma-Aldrich, hydrate, 98% reagent grade), which are precursors of ₂ , in a 500 mL three-necked flask (three-neck flask) flask) at 100 ° C., and oxygen and moisture were removed for 1 hour under vacuum conditions. Cu(Ac) ₂ and In(Ac) ₃ were added in ratios of 1 mole, 3 moles, 5 moles, and 7 moles, respectively, to 1 mole of SnTe to make nanostructured samples coated with precursors of various mole ratios. The nanostructure sample was named CG-Cu:In/x:y according to the molar ratio of Cu(Ac) ₂ and In(Ac) ₃ precursors (x: molar ratio of copper acetate, y: molar ratio of indium acetate) . In addition, 3 moles and 5 moles of Cu(Ac) ₂ and In(Ac) ₃ were added to 1 mole of SnTe, respectively (CG-Cu:In/3:5), and Cu(Ac) ₂ and In(Ac) ₃ 5 moles and 3 moles of (CG-Cu:In/3:5) were added to prepare nanostructure samples.

2) 6 g of ball-milled SnTe powder was added to the solution of 1) and heated to 180° C. to proceed with a cation exchange reaction. After the reaction was completed, the dark-colored solution was cooled from the air to room temperature, and the precipitate was washed with toluene and acetone and collected by centrifugation. The precipitate was dried under vacuum conditions for 12 hours to prepare CuInTe ₂ /SnTe powder.

3) The CuInTe ₂ /SnTe powder prepared in 2) was annealed at 450° C. for 30 minutes in a vacuum condition to remove residual organic matter. The annealed powder was sintered in a hot-press at 600° C. for 1 hour to make pellets, which were annealed again at 550° C. and then cut into appropriate shapes for measurement.

The Cu(Ac) ₂ and In(Ac) ₃ were selected as the easiest precursor among eco-friendly elements in consideration of the solubility product (K _SP ) and the HSAB theory. The solubility product (K _SP ) was considered as the driving force of the cation exchange process. The solubility product is the equilibrium constant between the solid and dissolved states of an ion in solution. The spontaneity of the cation substitution reaction can be predicted through the difference in solubility between the host chalcogenide metal and the introduced chalcogenide metal. It can be predicted that a chalcogenide metal having a K _SP lower than Sn will spontaneously form a metal chalcogenide coating layer on the surface of SnTe through a cation exchange process that dissolves Sn ²⁺ cations. Table 1 below is a table showing solubility products for various chalcogenide metals mentioned by GD Moon et al. Considering K _SP , Bi, Ag, Cu, Cd, Hg, Pb, Pt, In and Sb can be considered as candidates for the spontaneous cation substitution reaction of SnTe. Pearson's theory of hard and soft acids and bases (HSAB) was used as a tool to predict the interactions of solvents, ligands and ions. From the HSAB theory, hard acid cations (eg Zn ²⁺ , Sn ²⁺ ) bind more strongly with strong bases (eg I ^- ), and weak acids (eg Cd ²⁺ , Ag ⁺ , Cu ⁺ ) It can be deduced that cations bind strongly with weak bases (eg Ac ^- ). Referring to FIG. 1, in the cation substitution reaction of SnTe with CuInTe ₂ , cations can be easily released and Sn ²⁺ is more reactive with Ac ⁻ than ingoing metals (Cd ²⁺ , Ag ⁺ and Cu ⁺ ). It is a reaction favored by weak acid complexes such as Cd ²⁺ , Ag ⁺ and Cu ⁺ acetate, as they form more stable acid-base pairs. The high affinity of host cations (Sn ²⁺ ) and ligands (OLA, Ac ⁻ ) can allow cations to be released from the particle surface. Here, Cu(Ac) ₂ and In(Ac) ₃ were selected due to toxicity concerns. Referring to Table 1 below, although In ³⁺ is considered a strong acid, it can be confirmed that K _SP is significantly lower than Sn ²⁺ .

2 is a transmission electron microscope (TEM) photograph of a CuInTe ₂ /SnTe nanostructure. It can be confirmed from a and b of FIG. 2 that a coating layer is formed at the grain interface, and from c) of FIG. 2, it can be seen that nanoparticles having a size of several tens of nm are agglomerated to form a coating layer.

Figure 3a is a high-resolution TEM photograph of an enlarged crystal grain interface (coating layer) of CuInTe ₂ /SnTe nanostructure, and Figure 3b is a fast Fourier transform (FFT) pattern photograph of region a of Figure 3 4a is a result of XRD measurement of the CuInTe ₂ /SnTe nanostructure. The CuInTe ₂ and SnO ₂ phases were confirmed from b of FIG. 3 , which is consistent with the observed results of the CuInTe ₂ and SnO ₂ phases in the XRD data of FIG. 4a . Referring to FIG. 4b, it can be confirmed that the strong peak of XRD is clearly consistent with the FCC rock salt structure of SnTe having a space group Fm3m containing Te ^2- anion. However, around 25 ^o and 40 ^o (2θ), a weak peak of tetragonal CuInTe ₂ of space group I42d was observed. Through this, it was confirmed that the tetrahedral CuInTe ₂ has a similar crystal structure to SnTe, and the Te anion has an FCC structure in which Cu ⁺ and In ³⁺ cations are located at tetrahedral sites.

5 is a result of composition analysis using STEM-EDS (Scanning TEM-Electron Dispersive Spectroscopy) of CuInTe ₂ /SnTe nanostructures, and the CuInTe ₂ coating layer contains most of Cu, In, and Te atoms similar to the molar ratio of CuInTe ₂ showed In summary, from the high-resolution TEM, FFT pattern, and EDS analysis results, it was confirmed that a uniform coating layer composed of CuInTe ₂ nanoparticles was formed through a cation exchange reaction at SnTe grain boundaries.

<Experimental Example 1: CuInTe ₂ / Measurement of electrical properties of SnTe nanostructures>

The electrical properties of the CuInTe ₂ /SnTe nanostructure sample and the uncoated SnTe sample prepared with various mole ratio precursors prepared in Example 1 were measured (FIG. 6). Specifically, 1 mole and 1 mole (CG-Cu:In/1:1), ₃ moles and ₃ moles (CG-Cu:In/ 3:3), 5 moles and 5 moles (CG-Cu:In/5:5), 7 moles and 7 moles (CG-Cu:In/7:7), 3 moles and 5 moles (CG-Cu:In /3:5), and 5 mol and 3 mol (CG-Cu:In/5:3) were added to fabricate nanostructure samples coated with various mole ratios of the precursor. 6 a and e are resistivity graphs, b and f of FIG. 6 are Seebeck coefficient graphs, c and g of FIG. 6 are power factor graphs, and d of FIG. 6 are band diagrams of CuInTe ₂ and SnTe. It is also a model. Resistivity and Seebeck coefficient showed a clear trend with the precursor molar ratio. It was confirmed that the resistance and Seebeck coefficient of the CuInTe ₂ /SnTe nanostructure were improved compared to uncoated SnTe, and specifically, it was confirmed that the resistance and Seebeck coefficient increased as the mole ratio of the precursor increased.

In the Hall effect measurement results of Table 2 below, it was shown that the carrier concentration and mobility of the CuInTe ₂ /SnTe nanostructure were reduced compared to uncoated SnTe. This is mainly due to the energy filtering effect caused by the conduction carrier blocking by the potential barrier of CuInTe ₂ , and the increase of the Seebeck coefficient also occurs due to the energy filtering by the potential barrier of CuInTe ₂ . Referring to d of FIG. 6 , SnTe has a narrow band gap of 180 meV, but CuInTe ₂ has a band gap of about 1 eV. Through modeling of the Seebeck coefficient, the potential barrier can be predicted to be about 100 meV.

Specifically, the calculation of the Seebeck coefficient enhancement was performed based on Boltzmann's transport equation. Referring to b of FIG. 6, the black solid line is the calculation result of SnTe without a coating layer. In order to model the energy filtering by the CuInTe ₂ coating layer, reference was made to Equation 2 in the literature describing the transmission probability through the potential barrier between heterophases:

[Equation 2]

.

.

In Equation 2, E _B is the barrier height, m ^* is the effective mass, and w _B is the barrier thickness (coating layer thickness). The transmission probability T _B is obtained as the integral of the Fermi-Dirac integral of Equation 1. The results are shown in Figure 6b. A barrier height of about 100 meV was most suitable for the CG-Cu:In/7:7 nanostructured sample. The above results indicate that the potential barrier height between CuInTe ₂ and SnTe is about 100 meV. However, varying the coating layer thickness (W _b ) made negligible differences in the calculations. For the calculation of the Seebeck coefficient, the fitting parameter fraction factor (f _v ) was used. The fraction factor is a value obtained by assuming the number of coated crystal grains relative to the total number of crystal grains. In the case of the CG-Cu:In/5:5 sample, the f _v value is 0.7, and in the case of the CG-Cu:In/7:7 sample, Calculation with an f _v value of 1 was the best fit. Therefore, it was confirmed that the improvement of the Seebeck coefficient was due to energy filtering through the CuInTe ₂ coating layer. Due to the Seebeck coefficient enhancement, the power factor of the CG-Cu:In/5:5 sample increased from about 1.8 mW/mK ² for uncoated SnTe to about 2.1 mW/mK ² .

<Experimental Example 2: CuInTe ₂ /Measurement of thermal properties of SnTe core cell nanostructure>

The thermal properties of the CuInTe ₂ /SnTe nanostructure sample and the uncoated SnTe sample prepared with various mole ratio precursors prepared in Example 1 were measured (FIG. 7). 7A and C are thermal conductivity graphs, and FIG. 7B is a lattice thermal conductivity graph. The total thermal conductivity of all coated particle samples was decreased compared to that of uncoated SnTe. To divide the total thermal conductivity (κ _t ) by the electron and phonon contributions, the Wiedemann Franz law, κ _e = LσT, was used and the electronic thermal conductivity (κ _e ) was subtracted from the total thermal conductivity (κ _total ). The lattice thermal conductivity (κ _L ) was greatly reduced as shown in FIG. According to Cahill's model, the minimum thermal conductivity of SnTe is known to be 0.44 W/mK. According to b of FIG. 7 , the lattice thermal conductivity of most of the nanostructure samples of the present application was about 0.4 to about 1.5 W/mK, and the lattice thermal conductivity at the highest temperature was close to the minimum thermal conductivity. This decrease in lattice thermal conductivity is presumed to be due to coherent phonon scattering. When the impurity phase is located at the grain boundary, when the phase of a traveling phonon passes through the impurity, the phase delay of the phonon occurs due to the difference in acoustic impedance between the impurity and the parent material, and the phase delay of these multiple phonons causes interference. It can cause phonon scattering. The coherent phonon scattering creates a short phonon mean free path in a wide phonon spectrum, which can act as a strong advantage in the thermoelectric field. As shown in b of FIG. 7, the reduction in lattice thermal conductivity of the grain-coated sample was consistent with the theoretical calculation results of the present inventors. In addition, referring to b of FIG. 7, the thermal conductivity calculated based on the Klemens theory of a heterogeneous medium containing SnTe and CuInTe ₂ was found to be similar to or much higher than that of SnTe, indicating that the thermal conductivity of CuInTe ₂ was higher than that of SnTe. because it is high Therefore, the decrease in lattice thermal conductivity of the grain-coated CuInTe ₂ /SnTe nanostructures cannot be explained using traditional composite theory, and the ultra-low lattice thermal conductivity values can be assumed to be due to coherent phonon scattering.

<Experimental Example 3: CuInTe ₂ /Measurement of thermoelectric figure of merit (zT) of SnTe nanostructures>

The thermoelectric figure of merit (zT) of the CuInTe ₂ /SnTe nanostructure sample and the uncoated SnTe sample prepared with various mole ratio precursors prepared in Example 1 was calculated based on the measured values of Experimental Examples 1 and 2 (Fig. 8). 8a is a graph of the thermoelectric figure of merit, and the thermoelectric figure of merit of the CuInTe ₂ /SnTe core cell nanostructure is 1.68 at 823K and an average of 0.7 in the measured temperature range, confirming that it has the highest value in the corresponding material and temperature range. . The thermoelectric figure of merit increased from the CG-Cu:In/1:1 sample to the CG-Cu:In/5:5 sample, with the CG-Cu:In/7:7 sample having a low power factor (1.8 mW/mK at 823K). ² ), the thermoelectric figure of merit was lower than that of CG-Cu:In/5:5. The high electrical resistivity of CG-Cu:In/7:7 resulted in a low power factor comparable to uncoated SnTe. Thus, the CG-Cu:In/5:5 sample had the highest thermoelectric figure of merit value of 1.68 at 823K. In addition, from the results of repeated measurements of thermal conductivity and Seebeck coefficient at different times, the range of change in the data of the CG-Cu:In/5:5 sample and the CG-Cu:In/3:5 sample was found to be CG-Cu:In /5:3 samples were confirmed. Therefore, it was confirmed that the physical properties of the thermoelectric material were more stable when the Cu and In contents were the same or when the Cu content was slightly less than the In content, compared to when the Cu content was greater than the In content. Comparison of the thermoelectric figure of merit with the thermoelectric structures of other prior literature is shown in FIG. 8(b). The Zt value at 823 K of the CuInTe ₂ /SnTe core cell nanostructure was the highest in the list. The SnTe nanostructure in which CdS or Cu ₂ Te nanopowder was dispersed had a lower thermoelectric figure of merit than the CuInTe ₂ /SnTe core cell nanostructure. This suggests that the structure of the grain-coated CuInTe ₂ /SnTe core cell nanostructure is more efficient in improving the thermoelectric figure of merit than the conventional SnTe nanostructure in which nanopowder is dispersed. As an example for equivalent comparison, SnTe nanostructures in which CuInTe ₂ nanopowders were dispersed recorded a thermoelectric figure of merit of 1.0 zT at 873K, but a total thermal conductivity of 2.0 W/mK at 873K and 1.09 W/mK at 823K. It was significantly higher than the Example value of. This suggests that structural differences can lead to improvements in thermoelectric performance. Referring to b of FIG. 8, compared to the prior art CdTe/SnTe coated particles, the zT value at 823K and the average zT value at the temperature gradient (about 370K to about 823K) of the CuInTe ₂ /SnTe nanostructure of the present application are You can check higher. In addition, it can be seen that the average zT value in the temperature gradient (about 370K to about 823K) of the CuInTe ₂ /SnTe nanostructure of the present application is higher than that of the thermoelectric structure of other prior literature.

In summary, the thermoelectric CuInTe ₂ /SnTe core cell nanostructure having a grain-coated structure in this example was synthesized by forming a CuInTe ₂ layer by cation substitution on the surface of SnTe particles. The HSAB theory, the thermodynamic factor and the structural similarity of the two heterophases were found to be important in the cation substitution process. The thermoelectric performance of the CuInTe ₂ /SnTe core cell nanostructure was improved by carrier energy filtering and coherent phonon scattering induced by the coated grain boundaries. The potential barrier by the CuInTe ₂ coating layer improves the Seebeck coefficient by scattering low-energy carriers (holes). According to calculations based on the Boltzmann transport equation, the barrier height between SnTe and CuInTe ₂ is about 100 meV. The Seebeck coefficient of the grain-coated CuInTe ₂ /SnTe nanocomposite was improved by about 40% to about 50% compared to that of uncoated SnTe. The power factor improved from about 1.8 to about 2.1 mW/mK ² for the CG-Cu:In/5:5 nanocomposite. The lattice thermal conductivity decreased in uncoated SnTe due to enhanced phonon scattering by the interference of wave-like phonons. Acoustic impedance mismatch between the CuInTe ₂ coating layer and the SnTe base material causes a phonon phase delay and causes multi-phonon interference. The lattice thermal conductivity of the grain-coated CuInTe ₂ /SnTe core cell nanostructure was recorded as about 1.4 to about 0.4 W/mK, which is an almost minimum thermal conductivity. Due to the significant reduction in lattice thermal conductivity by coherent phonon scattering, the total thermal conductivity of the grain-coated CuInTe ₂ /SnTe core-cell nanostructure was recorded as about 1.09 W/mK at 823 K, which is significantly lower than that of SnTe. The thermoelectric figure of merit of the CG-Cu:In/5:5 nanocomposite was 1.68 at 823K, more than twice that of uncoated SnT. It was confirmed that the tremendous functional enhancement of the grain-coated CuInTe ₂ /SnTe core cell nanostructures occurred due to the synergistic effect of carrier energy filtering and coherent phonon scattering.

The above description of the present application is for illustrative purposes, and those skilled in the art will understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present application. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may also be implemented in a combined form.

The scope of the present application is indicated by the following claims rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and equivalent concepts thereof should be construed as being included in the scope of the present application. .

Claims (13)

A thermoelectric material comprising a binary chalcogenide material core and a ternary material coating layer,
The ternary material coating layer includes a chalcogen material, a first substitution material, and a second substitution material,
The first substituted material and the second substituted material are different from the metal of the binary chalcogenide material,
thermoelectric material.
According to claim 1,
The thermoelectric material, wherein the first substitution material and the second substitution material of the ternary material coating layer are cation substitution products of the binary chalcogenide material.
According to claim 1,
The first substitution material includes one or more selected from Cu, Cs, and Ag, and the second substitution material includes one or more selected from Bi, Sb, Ga, and In.
According to claim 1,
The ternary material includes at least one selected from CuInTe ₂ , AgInTe ₂ , CuBiTe ₂ , AgBiTe ₂ , CuSbTe ₂ , and AgSbTe ₂ .
According to claim 1,
The thermoelectric material, wherein the thickness of the ternary material coating layer is 3% to 20% of the diameter of the core of the binary chalcogenide material.
According to claim 1,
The thermoelectric material further comprises at least one selected from Bi, Ag, Cu, Cr, Sb, Zn, Se, S, In, Cd, Mg, Hg, Mn, and Ca as a dopant.
According to claim 1,
The binary chalcogenide material includes at least one selected from SnTe, SnSe, SnS, PbTe, PbSe, PbS, ZnTe, ZnSe, ZnS, ZnO, GeTe, Cu ₂ Te, and Cu ₂ Se, a thermoelectric material .
According to claim 1,
An energy potential barrier is formed between the binary chalcogenide material core and the ternary material coating layer,
The size of the energy potential barrier is 100 meV to 200 meV, the thermoelectric material.
preparing a binary chalcogenide material core;
preparing a ternary material precursor including a first substitution material precursor and a second substitution material precursor; and
Obtaining a thermoelectric material by mixing the binary chalcogenide material core and the ternary material precursor and subjecting to a cation substitution reaction
Including, a method for manufacturing a thermoelectric material.
According to claim 9,
Wherein the first substitution material precursor and the second substitution material precursor include at least one selected from an acetate-based, a bromide-based, and an iodide-based method for manufacturing a thermoelectric material .
According to claim 9,
The method for producing a thermoelectric material, wherein the amounts of the first substitution material precursor and the second substitution material precursor are n moles and m moles, respectively, with respect to 1 mole of the binary chalcogenide material:
Wherein n and m are each independently an integer of 1 to 6.
According to claim 9,
The method of manufacturing a thermoelectric material, wherein the cation substitution reaction is performed by mixing and heating the binary chalcogenide material core and the ternary material precursor.
According to claim 9,
The cation substitution reaction is a method for producing a thermoelectric material that is performed in a temperature range of 180 ° C to 250 ° C.

Images