Thermoelectric material having a networked heterostructure that provides improved thermoelectric efficiency and method for preparing the same

Abstract

A simple and scalable method for preparing networked heterostructures in nanoscale thermoelectric materials is disclosed. The preparation method includes oscillating a molten form of component B together with a nanomaterial of component A in an inert environment, followed by controlled solidification. A honeycomb-like network of component B with voids filled by component A forms a nanoscale heterostructure B / A, where components A and B may be metals, semiconductors, or insulators. A method for improving the thermoelectric figure of merit (ZT) by quantum confinement effects and polarity reversal by carrier injection from a barrier layer in the nanoscale heterostructure is also disclosed. Formula D δ / Bi x S 2-x D y M 3-y ZT > 2 is demonstrated in both p-type and n-type metal-semiconductor bulk heterostructures. Methods for improving ZT are also applicable to semiconductor-semiconductor heterostructures and superlattice structures. High ZT materials are used in power generation, Peltier cooling and refrigeration, thermal infrared detection and imaging, and thermal infrared displays.

Description

[Technical Field]

[0001] This invention relates to thermoelectric materials, and more particularly to the development and efficiency improvement methods for thermoelectric materials. [Background technology]

[0002] Pure metals in bulk form are not considered suitable candidates for thermoelectric purposes because their differences in chemical potential are negligible. Initially, intermetallic materials such as nickel-chromium, nickel-aluminum, platinum-rhodium, and constantan were used as thermoelectric materials, particularly in temperature-measuring thermocouples. However, their low thermoelectric conversion efficiency limited their range of applications.

[0003] With technological advancements, highly doped semiconductors have established their position through their ability to generate n-type and p-type thermoelectric phenomena resulting from shifts in the Fermi level (chemical potential in metals) due to variations in doping type. The efficiency of semiconductor thermoelectric materials is far superior to that of intermetallic alloys due to the band gap value that governs the operating temperature, the symmetrical positions of the Fermi levels between p-type and n-type materials that form thermocouples instead of pairing with copper, which is the baseline for the Seebeck coefficient, and the reduced lattice thermal conductivity value.

[0004] Most research and development attempts ultimately shifted to semiconductors as potential thermoelectric materials. Bismuth-antimony chalcogenides were established as suitable thermoelectric materials for applications above room temperature due to the parameters dominated by their preferred components.

[0005] The thermoelectric efficiency parameter of a material is established as the figure of merit (ZT), where ZT = (S 2 The power factor (σ / κ)T is defined as (where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature). Therefore, Z is determined by the ratio of the power factor (PF) to κ, where the power factor is PF = S 2It is defined as σ. The value of ZT remained approximately 1 for decades until research and development was revived by theoretical predictions regarding ZT improvement due to quantum confinement in prior art {LD Hicks and MS Dresselhause, "Thermoelectric figure of merit of a one-dimensional conductor," Phys. Rev. B 47, 16631 (1993) and "Effect of quantum-well structures on thermoelectric figure of merit," Phys. Rev. B 47, 12727 (1993)}.

[0006] Experimental reports on achieving ZT improvement through quantum confinement include: quantum wells {LD Hicks et al., "Experimental study of the effect of quantum-well structure on thermoelectric figure of merit," Phys. Rev. B 53, R10493 (1996); U.S. Patent No. 7,400,050 B2}, quantum nanowires {J. Heremans and CM Thrush, "Thermoelectric power of bismuth nanowires," Phys. Rev. 59, 12579 (1999); Yu-Ming Lin et al., "Transport properties of Bi nanowire array," Appl. Phys. Lett. 76, 3944 (2000); Yu-Ming Lin et al., "Semimetal-semiconductor transition in Bi 1-x S x"Alloy nanowires and their thermoelectric properties" Appl. Phys. Lett. 81, 2403 (2002); U.S. Patent Application Publication No. 2014 / 0024202 A1), and superlattice {TC Harman et al., "Quantum dot superlattice thermoelectric materials and devices" Science 297, 2229 (2002); Hiromichi Ohta et al., "Giant thermoelectric Seebeck coefficient of a two-dimensional electron gas in SrTiO3" Nat. Mat. 6, 129 (2007); JC Caylor et al., "Developing PbTe-based superlattice structures with enhanced thermoelectric performance" IEEE ICT, 492 (2005); S. Ghamaty et al., "Quantum well thermoelectric devices and applications" IEEE ICT 563 (2003); U.S. Patent Application Publication No. 2011 / 0062420 These are limited to: A1; U.S. Patent Application Publication No. 2007 / 0084499; A1; U.S. Patent No. 5,550,387 dated August 27, 1996; U.S. Patent No. 5,436,467 dated July 25, 1995; U.S. Patent No. 9,136,456; B2; U.S. Patent No. 7,400,050; B2; U.S. Patent No. 8,569,710; B2; PCT International Patent Publication No. 03 / 096438; A2; PCT International Patent Publication No. 01 / 17035; A1; PCT International Patent Publication No. 98 / 42033; PCT International Patent Publication No. 98 / 42034. These structures require complex and costly technologies such as molecular beam epitaxy (MBE) for development. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] U.S. Patent No. 7,400,050 B2

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[0008]

Non-licensed literature 1

[0009] The object of this disclosure is to provide an easily expandable method for obtaining thermoelectric heterostructure materials having a nanoscale heterostructure in a honeycomb-like network configuration at the nanoscale during bulk synthesis.

[0010] Another objective of this disclosure is to realize both p-type and n-type thermoelectric heterostructure materials by the same process.

[0011] Another object of this disclosure is to obtain a thermoelectric heterostructure material having improved thermoelectric efficiency.

[0012] Another object of this disclosure is to provide a thermoelectric heterostructure material having an improved Seebeck coefficient, increased electrical conductivity, reduced thermal conductivity, and an improved figure of merit. [Means for solving the problem]

[0013] According to an embodiment, a method for obtaining a networked heterostructure nanomaterial by synthesis is disclosed. The method includes the step of mixing the nanomaterial powder of component A with the powder of component B at a ratio selected from the range of 95:05 to 75:25 to obtain the mixture. The method further includes the step of heating the obtained mixture under vacuum to melt component B in the mixture and at the same time rocking the mixture during heating. The method further includes the step of quenching the heated mixture in air to obtain a quenched mixture. The method further includes the step of grinding the quenched mixture containing components A and B into a powdered form. The method further includes the step of filling the powdered form of the quenched mixture into a pre-designed die. The method further includes the step of solidifying the powdered form of the quenched mixture by sintering in an exhaust chamber to obtain a networked heterostructure nanomaterial.

[0014] According to an embodiment, a heterostructure thermoelectric nanomaterial is disclosed. The heterostructure thermoelectric nanomaterial includes a heterostructure of the formula Bi x Sb 2-x D y M 3-y / D δ where Bi x Sb 2-x D y M 3-y is component A, D is component B, the elements D and M are selected from the group of Te, Se, S, and the values of x, y, and δ are in the range of 0 to 3.

[0015] In an embodiment, the nanostructure of the heterostructure thermoelectric nanomaterial forms a networked heterostructure morphology at the nanoscale in the range of 1 nm to 10 nm, component B has a honeycomb-like networked structure with voids therein, and the voids are filled with component A.

[0016] In an embodiment, the concept of improving the thermoelectric efficiency of the networked heterostructure includes quantum confinement in the metal layer or semiconductor layer of component B, a band offset for quantum confinement obtained by the semiconductor thermoelectric nanomaterial barrier layer of component A, and carrier injection from the barrier layer of component A to the quantum well layer of component B for obtaining a thermoelectric heterostructure of different polarities.

[0017] In this embodiment, the maximum value of the figure of merit (ZT) is p-type tellurium / Sb 2-x Bi x For Te3 heterostructures, the coefficient is 2.1 at around room temperature.

[0018] In this embodiment, the maximum value of the figure of merit (ZT) is n-type tellurium / Bi2Te 3-x Se x For heterostructures, the value is 2.6 at around room temperature.

[0019] To better understand exemplary embodiments of this technology, the following description, interpreted in relation to the accompanying drawings, is to be used. [Brief explanation of the drawing]

[0020] [Figure 1] This figure shows a flowchart of a method according to an exemplary embodiment of the present disclosure. [Figure 2] This is a photograph of a solidified pellet with a heterostructure. [Figure 3] This figure shows a high-resolution transmission electron microscope (HR-TEM) image of a heterostructured sample at a 100 nm scale, illustrating the honeycomb-like network of component B and the voids filled with component A according to embodiments of the present disclosure. [Figure 4] This figure shows an HR-TEM image of a heterostructured sample at a 50 nm scale, illustrating the honeycomb-like network of component B and the voids filled with component A according to the embodiments of this disclosure. [Figure 5] This figure shows an HR-TEM image of a heterostructured sample at a 5 nm scale, showing a small number of quintuples and a small number of atomic layers of component B according to embodiments of the present disclosure. [Figure 6] This figure shows an HR-TEM image of a heterostructured sample at a 5 nm scale, showing a few quintuplets and a few atomic layers of component B at a different location in the image, according to an embodiment of the present disclosure. [Figure 7]This figure shows a graph representation of the measured Seebeck coefficient (S) of the Teδ / BixSb2-xTe3 heterostructure as a function of temperature for different values ​​of δ, according to embodiments of the present disclosure. [Figure 8] This figure shows a graph representation of the measured electrical conductivity (σ) of the Teδ / BixSb2-xTe3 heterostructure as a function of temperature for different values ​​of δ, according to embodiments of the present disclosure. [Figure 9] This figure shows a graph of the calculated power factor (S2σ) from measured values ​​of S and σ of the Teδ / BixSb2-xTe3 heterostructure as a function of temperature for different values ​​of δ, according to embodiments of the present disclosure. [Figure 10] This figure shows a graph of the measured thermal diffusivity of the Teδ / BixSb2-xTe3 heterostructure as a function of temperature for different values ​​of δ, according to embodiments of the present disclosure. [Figure 11] This figure shows a graph of calculated values ​​of thermal conductivity from measured values ​​of thermal diffusivity, specific heat, and solid density of the Teδ / BixSb2-xTe3 heterostructure as a function of temperature for different values ​​of δ, according to embodiments of the present disclosure. [Figure 12] This figure shows a graph of the calculated figure of merit from the power factor and thermal conductivity of the Teδ / BixSb2-xTe3 heterostructure as a function of temperature for different values ​​of δ, according to embodiments of the present disclosure. [Figure 13] This figure shows a graph of the temperature dependence of (a) hole mobility and (b) carrier concentration of the optimal performance composition of a p-type Teδ / BixSb2-xTe3 heterostructure according to an embodiment of the present disclosure. [Figure 14(a)] This figure shows a graph of the measured Hall resistance and longitudinal resistance of the Teδ / BixSb2-xTe3 heterostructure as a function of the applied magnetic field at room temperature, according to an embodiment of the present disclosure. [Figure 14(b)] This figure shows a graph of the measured Hall resistance and longitudinal resistance of the Teδ / BixSb2-xTe3 heterostructure as a function of the applied magnetic field at room temperature, according to an embodiment of the present disclosure. [Figure 15]This figure shows a graph representation of the measured Seebeck coefficient (S) of the Teδ / Bi2Te3-ySey heterostructure as a function of temperature for different values ​​of δ, according to embodiments of the present disclosure. [Figure 16] This figure shows a graph representation of the measured electrical conductivity (σ) of the Teδ / Bi2Te3-ySey heterostructure as a function of temperature for different values ​​of δ, according to embodiments of the present disclosure. [Figure 17] This figure shows a graph of the calculated power factor (S2σ) from measured values ​​of S and σ of the Teδ / Bi2Te3-ySey heterostructure as a function of temperature for different values ​​of δ, according to embodiments of the present disclosure. [Figure 18] This figure shows a graph of the measured thermal diffusivity of the Teδ / Bi2Te3-ySey heterostructure as a function of temperature for different values ​​of δ, according to embodiments of the present disclosure. [Figure 19] This figure shows a graph of calculated values ​​of thermal conductivity from measured values ​​of thermal diffusivity, specific heat, and solid density of the Teδ / Bi2Te3-ySey heterostructure as a function of temperature for different values ​​of δ, according to embodiments of the present disclosure. [Figure 20] This figure shows a graph of the calculated figure of merit from the power factor and thermal conductivity of the Teδ / Bi2Te3-ySey heterostructure as a function of temperature for different values ​​of δ, according to embodiments of the present disclosure. [Figure 21] This figure shows a graph of the temperature dependence of (a) hole mobility and (b) carrier concentration of an optimal performance composition of an n-type Teδ / Bi2Te3-ySey heterostructure according to an embodiment of the present disclosure. [Figure 22(a)] This figure shows a graph of the measured Hall resistance and longitudinal resistance of the Teδ / Bi2Te3-ySey heterostructure as a function of the applied magnetic field at room temperature, according to an embodiment of the present disclosure. [Figure 22(b)] This figure shows a graph of the measured Hall resistance and longitudinal resistance of the Teδ / Bi2Te3-ySey heterostructure as a function of the applied magnetic field at room temperature, according to an embodiment of the present disclosure. [Modes for carrying out the invention]

[0021] The following description includes numerous specific details for illustrative purposes and to provide a complete understanding of the disclosure. However, it will be apparent to those skilled in the art that the disclosure can be implemented without these specific details.

[0022] Any reference in this specification to “one embodiment” or “embodiment” means that certain features, structures, or characteristics described in relation to an embodiment are included in at least one embodiment of this disclosure. The phrase “in an embodiment” appearing in various parts of this specification does not necessarily refer to the same embodiment, nor does a separate or alternative embodiment exclude other embodiments. Furthermore, various features are described that may be shown in some embodiments but not in others. Similarly, various requirements are described that may be required in some embodiments but not in others.

[0023] Furthermore, the following description includes many details for illustrative purposes, but those skilled in the art will understand that many variations and / or modifications to such details are within the scope of this disclosure. Similarly, many of the features of this disclosure are described with respect to or in relation to each other, but those skilled in the art will understand that many of these features can be provided independently of the others. Accordingly, this description of the disclosure is made without prejudice to the generality of the disclosure and without imposing limitations on the disclosure.

[0024] This disclosure relates to a method for obtaining heterostructured thermoelectric nanomaterials and networked heterostructured nanomaterials having metal-semiconductor heterostructures. The method is also applicable to semiconductor-semiconductor, metal-insulator, and semiconductor-insulator heterostructures. Such heterostructures, having a network of nanoscale quantum well layers similar to a honeycomb structure and filled with a barrier layer material, are used in applications requiring quantum confinement and electrical transport. The method of the present invention for preparing thermoelectric heterostructured materials is readily extensible. Application areas of such novel forms are generally electronic devices, particularly thermoelectric devices.

[0025] Figure 1 shows a flowchart of Method 100 for obtaining a networked heterostructure nanomaterial from components A and B.

[0026] In step 102, the powder of nanomaterial component A is mixed with the powder of component B. Components A and B can be selected from the group including metals, semiconductors, and insulators. In the embodiment, component A may be a metal, semiconductor, or insulator, and component B may be a metal or semiconductor. Furthermore, component A can be selected from highly doped semiconductor thermoelectric nanomaterials. In the embodiment, component A is 1 cm 3 10 19 ~1cm 3 10 21 A p-type highly doped semiconductor nanomaterial or an n-type highly doped semiconductor nanomaterial having a carrier concentration in the range of is selected. In the embodiments described above, the selection of components A and B is carried out in such a way that the melting point of component A is higher than the melting point of component B. Furthermore, components A and B may be selected such that component B has a lower chemical potential than the corresponding component A. In the embodiments, after components A and B have been selected, the selected components A and B are mixed in a ratio that can vary from 95:05 to 75:25 to obtain the mixture.

[0027] Regarding step 102 described above, in one example, component B is selected from the group including tellurium, bismuth, and zinc, and component A is Bi2Te 3-x Se x It is selected as such, where x is in the range of 0.1 to 1.

[0028] In another exemplary embodiment, component B is selected from the group comprising tellurium, bismuth, and zinc, and component A is Sb 2-x Bi x Te3 is selected, where x is in the range of 0.1 to 1.

[0029] In another exemplary embodiment, component B is selected from the group comprising Bi2Te3 and Sb2Te3, and component A is selected from the group comprising Bi2Se3, Bi2S3, Sb2Se3, and Sb2S3.

[0030] In step 104, the mixture obtained by mixing components A and B as described above is heated under exhaust gas at the melting point of component B. Simultaneously, the mixture is agitated while heating. In one example, the mixture is heated to a temperature at which component A remains solid and only component B melts. The agitation of component A and liquefied component B is carried out in a quartz ampoule for a period of 1 to 5 hours. Thus, in step 104, one solid raw material and one liquid raw material are agitated.

[0031] In step 106, the heated mixture is rapidly cooled in air to obtain a quenched mixture. In one example, the quenched mixture is collected by breaking open a quartz ampoule.

[0032] In step 108, the rapidly cooled mixture of components A and B is pulverized to obtain a powdered form of the rapidly cooled mixture. In one example, the rapidly cooled mixture is powdered using conventional pulverization techniques.

[0033] In step 110, the powdered form of the rapidly cooled mixture is filled into a pre-designed die. In this embodiment, the graphite die has an inner diameter in the range of 10 mm to 40 mm.

[0034] In step 112, the powdered form of the quenched mixture is solidified in a die by sintering the mixture in an exhaust chamber to obtain a networked heterostructure nanomaterial. In one example, the die is made from graphite or tungsten carbide. In one example, the die is made from part of other suitable die materials, and the die material can be selected according to the pressure and temperature requirements of the solidification. In one embodiment, the powdered form of the quenched mixture is solidified in a discharge plasma sintering (SPS) machine. In one example, solidification may be carried out in a conventional DC hot press or an indirectly heated hot press. In one example, solidification is carried out at a pressure in the range of 20 MPa to 100 MPa and at a temperature near the melting point of component B. In one embodiment, during the sintering process, any excess amount of component B, if present, is discharged from the graphite die to obtain a high-density pellet. A photograph of the solidified pellet is shown in Figure 2.

[0035] In step 112, controlled solidification is performed such that component B, which was liquefied in the oscillating step 104, spreads around the nanomaterial particles of component A, forming a honeycomb-like network structure at the nanoscale during solidification.

[0036] The present invention also discloses heterostructured thermoelectric nanomaterials. In the embodiments, the networked heterostructured thermoelectric nanomaterial is of the formula Bi x S 2-x D y M 3-y / D δ It may be both a p-type and an n-type metal-semiconductor bulk heterostructure, where Bi x S 2-x D y M 3-y is component A, and D is component B. Components D and M are selected from the group Te, Se, and S, and the values ​​of x, y, and δ are in the range of 0 to 3. In this embodiment, the values ​​of x, y, and δ are in the range of 0.1 to 1.

[0037] In the embodiment, component A may be selected from highly doped semiconductor thermoelectric nanomaterials. In the embodiment, component A is 1 cm 3 10 19 ~1cm 3 10 21A p-type highly doped semiconductor nanomaterial or an n-type highly doped semiconductor nanomaterial having a carrier concentration in the range of [range] is selected.

[0038] In this embodiment, the nanostructure of the heterostructured thermoelectric nanomaterial forms a networked heterostructure morphology on a nanoscale in the range of 1 nm to 10 nm. Component B has a honeycomb-like networked structure with voids between it, and the voids are filled with component A.

[0039] In the embodiment, the particle size of component A in the heterostructured thermoelectric nanomaterial is in the range of 5 nm to 10 nm on the nanoscale. In the embodiment, the size of the component B layer in the heterostructured thermoelectric material is in the range of 1 nm to 5 nm on the nanoscale.

[0040] In this embodiment, the quantum well layer of component B is tellurium, zinc, or bismuth, and the barrier layer of component A is Sb 2-x Bi x By using Te3, it is possible to obtain p-type networked heterostructure thermoelectric nanomaterials with improved efficiency.

[0041] In this embodiment, the quantum well layer of component B is tellurium, zinc, or bismuth, and the barrier layer of component A is Bi2Te 3-x Se x By using this method, it is possible to obtain n-type networked heterostructure thermoelectric nanomaterials with improved efficiency.

[0042] In this embodiment, p-type tellurium / Sb 2-x Bi x For the Te3 heterostructure, the maximum Seebeck coefficient obtained is 343.8 μV / K at around room temperature. The maximum electrical conductivity obtained is p-type tellurium / Sb 2-x Bi x For Te3 heterostructures, the temperature is 6.5 × 10⁻¹⁶ at around room temperature. 4 The power factor is S / m. The maximum value of the power factor obtained is p-type tellurium / Sb 2-x Bi x For a Te3 heterostructure, the current is 7.6 mW / mK at around room temperature. 2Therefore, the minimum value of the thermal conductivity obtained is p-type tellurium / Sb 2-x Bi x For the Te3 heterostructure, the resistance is 1.06 W / mK at around room temperature. The maximum value of the obtained ZT (figure of merit) is p-type tellurium / Sb 2-x Bi x For Te3 heterostructures, the value is 2.1 at around room temperature. The average value of the obtained ZT (figure of merit) is p-type tellurium / Sb 2-x Bi x For Te3 heterostructures, the coefficient is 1.3 in the temperature range from room temperature to 250°C. Furthermore, quantum confinement is p-type tellurium / Sb 2-x Bi x For Te3 heterostructures, this is confirmed by a quantization plateau in Hall resistance and a longitudinal resistance peak that decreases as a function of the applied magnetic field at room temperature, which correlates with the structure.

[0043] In this embodiment, n-type tellurium / Bi2Te 3-x Se x For heterostructures, the maximum Seebeck coefficient obtained is (negative) 199.8 μV / K near room temperature. The maximum electrical conductivity obtained is n-type tellurium / Bi2Te 3-x Se x For heterostructures, 1.5 × 10⁻¹⁰ units are obtained at around room temperature. 5 The power factor is S / m. The maximum value of the power factor obtained is n-type tellurium / Bi2Te 3-x Se x For heterostructures, the reaction is 6.1 mW / mK at around room temperature. 2 Therefore, the minimum value of the thermal conductivity obtained is n-type tellurium / Bi2Te 3-x Se x For heterostructures, the figure of merit (ZT) is 0.71 W / mK at room temperature. The maximum obtainable figure of merit (ZT) is n-type tellurium / Bi2Te 3-x Se x For heterostructures, the figure of merit (ZT) is 2.6 at around room temperature. The average value of the obtained figure of merit (ZT) is n-type tellurium / Bi2Te 3-x Se x For heterostructures, the coefficient is 2.0 in the temperature range from room temperature to 250°C. Furthermore, quantum confinement is observed in n-type tellurium / Bi2Te 3-x Se xFor heterostructures, this is confirmed by a quantization plateau in Hall resistance and a longitudinal resistance peak that decreases as a function of the applied magnetic field at room temperature, which correlates with the structure.

[0044] In the embodiment, the heterostructure of the thermoelectric material obtained by method 110 exhibits an improved Seebeck coefficient, increased electrical conductivity, decreased thermal conductivity, and consequently an improved figure of merit. The sign of the Seebeck coefficient of the thermoelectric material heterostructure may be determined by the sign of the Seebeck coefficient of component A. An improvement in the Seebeck coefficient and / or electrical conductivity is obtained, and therefore a very good improvement in the power factor is obtained by the quantum confinement effect. Furthermore, both n-type and p-type thermoelectric heterostructure materials can be realized by method 100.

[0045] In the embodiment, improved figures of merit are shown for both p-type and n-type thermoelectric heterostructure materials in the same material system simply by changing the polarity of the semiconductor barrier layer. Method 100 provides a pair of materials for practical and efficient thermoelectric devices and discloses knowledge of carrier injection from the barrier layer to the quantum well layer for thermoelectric transport properties.

[0046] In the embodiment, quantum confinement in the heterostructure produced by method 100 is shown by a quantum well layer in the range of several nanometers in transmission electron microscopy. Furthermore, improved power factors are shown in thermoelectric measurements and observations of the quantum Hall effect. Quantum confinement occurs in the metal or semiconductor layer of component B. In addition, a band offset occurs with respect to the quantum confinement obtained by the semiconductor thermoelectric nanomaterial barrier layer of component A. Therefore, a decrease in thermal conductivity is obtained due to a band offset value higher than the typical phonon energy. Furthermore, in this method, carrier injection occurs from the barrier layer of component A to the quantum well layer of component B, resulting in thermoelectric heterostructures of different polarities.

[0047] High-resolution transmission electron microscopy (HR-TEM) of thin sections taken from the solidified pellet reveals heterostructures with unique morphologies at the nanoscale. The 100 nm scale HR-TEM image in Figure 3 shows a honeycomb-like structure of component B, with the voids in the structure filled by component A. More detailed structural information is available in the 50 nm scale HR-TEM image shown in Figure 4.

[0048] Atomic-level details of the heterostructure are shown in the 5 nm scale HR-TEM images in Figures 5 and 6. These figures show a quintuple layer containing identical atomic layers of component B and different groups of atoms repeating within the crystal lattice of component A. The layer size specification of several nanometers demonstrates the formation of a 2D heterostructure. As a result, the method for forming the networked heterostructure of this disclosure is demonstrated.

[0049] The heterostructured solidified pellets are cut to the appropriate shape and dimensions for thermoelectric measurements while maintaining their orientation. Electrical conductivity and Seebeck coefficient are measured simultaneously. The accuracy of the system is verified using bismuth telluride according to the NIST SRM 3451 standard. Thermal diffusivity is measured using a standard laser flash apparatus compliant with the ASTM 1461 standard. Specific heat is measured using a differential scanning calorimeter with sapphire NIST SRM 720 standard material. Room temperature density is determined using an Archimedes apparatus with the standard density of 99.9% ethanol. Thermal conductivity is calculated by multiplying the measured values ​​of thermal diffusivity, specific heat, and density. Power factor and figure of merit values ​​are calculated from the aforementioned measurement data.

[0050] The measured Seebeck coefficients of the heterostructured samples are much higher than the corresponding values ​​for components A and B. Furthermore, the temperature dependence of the Seebeck coefficients does not correspond to that of components A and B. Therefore, completely unique functional properties are obtained. This supports the formation of a heterostructure of components A and B, rather than simply the formation of a composite.

[0051] The measured electrical conductivity of heterostructured samples is much higher than the corresponding value for component A and approaches the corresponding high value for component B. Samples with ideal semiconductor Seebeck coefficient values ​​exhibit electrical conductivity values ​​in the semimetallic region.

[0052] The measured values ​​of the Seebeck coefficient and electrical conductivity indicate that the conventional relationship between the Seebeck coefficient and electrical conductivity, generally known as the Pisarenko relation, is broken. In heterostructures, the Seebeck coefficient and electrical conductivity improve. This leads to an improved power factor (S 2 The calculated value of σ) has improved, which is clear evidence of quantum confinement in the heterostructure produced by the method of the present invention.

[0053] While the measured thermal diffusivity may show a slight increase, this can be controlled by appropriately selecting the content of components A and B. Specific heat is a bulk property, and the averaging effect of the corresponding values ​​of components A and B may help control its value to some extent. The resulting calculated thermal conductivity value is held at the corresponding value of component B, which is much lower than the corresponding value of component A in their bulk forms.

[0054] The sign change of the Seebeck coefficient (p-type or n-type) in the heterostructure of components A and B is observed in accordance with the change in the type of carrier in component A. This indicates a charge injection mechanism that realizes both n-type and p-type thermoelectric heterostructures in the same material system.

[0055] By selecting the type of carrier in component A to improve the power factor, controlling the value of thermal conductivity, and changing the type, improved figure of merit values ​​of more than 2 were demonstrated in both n-type and p-type heterostructures. Therefore, improved efficiency thermoelectric heterostructures of both p-type and n-type are demonstrated in the same class of material systems with nearly identical temperature dependence of thermoelectric properties.

[0056] Knowledge of improving thermoelectric efficiency in heterostructures is demonstrated in this invention using networked heterostructures. This knowledge is valid for all kinds of heterostructures, including superlattices, quantum wells, quantum wires, quantum dots, and combinations thereof.

[0057] Knowledge of improving thermoelectric efficiency in a heterostructure is demonstrated in the present invention by using component A as a semiconductor material and component B as a metal. This knowledge is effective for semiconductor, metal and insulator components A and B, and combinations thereof.

[0058] Knowledge of improving thermoelectric efficiency in a heterostructure is demonstrated in the present invention by using the size parameters and band offset values of components A and B. This knowledge is effective for optimized values of the size specifications of the quantum wells and barriers, and optimized values of the band offset by suitable selection of components A and B, and combinations thereof.

Example

[0059] The following examples are given as illustrations of the present disclosure and should not be construed as limiting the scope of the present disclosure. It should be understood that both the foregoing general description and the following detailed description are merely illustrative and explanatory and are intended to provide further description of the subject matter. The present disclosure is demonstrated for a heterostructure Bi x Sb 2-x D y M 3-y / D δ by using the semiconductor of Formula I: Bi x Sb 2-x D y M 3-y as component A and metal D as component B. In Formula I, the elements D and M can be selected from chalcogenides Te, Se and S.

[0060] (Example 1: Te δ / Bi x Sb 2-x Te3 heterostructure) A highly doped p-type semiconductor Bi x Sb 2-x Te3 nanomaterial is used as component A, and Te powder is used as component B. Other options for component B with respect to this component A material are Bi, Zn, Sn, In, and Bi x Sb 2-xOther such metals and semiconductors having a melting point lower than that of Te3 may also be used.

[0061] Bi x Sb 2-x Mix the Te3 nanomaterial powder and the Te powder together and fill them into a quartz ampoule. The values of x and δ are both in the range of 0.25 to 1. After evacuating the ampoule and purging it with an inert gas, seal it under evacuation conditions using a conventional LPG-oxygen mixed flame. Place this sealed ampoule in a rocking tube furnace and heat it at about 400 °C to melt Te without affecting Bi x Sb 2-x Te3. Rock the mixer of this molten Te and Bi x Sb 2-x Te3 for 1 hour to 5 hours and then rapidly cool it in air. Collect the specimens obtained by breaking the ampoule and powderize them by a conventional pulverization method.

[0062] Fill the powdered specimen from the previous process into a graphite die. Use a graphite die with an inner diameter of 10 mm to 40 mm, which may be any value according to the requirements of the sample size. Tungsten carbide and other suitable die materials can be used according to the requirements of the pressure and temperature of the solidification process. The powdered specimen inside the graphite is solidified by a spark plasma sintering (SPS) machine. This solidification is carried out in a pressure range of 25 MPa to 100 MPa, at a temperature near the melting point of Te, i.e., 400 °C, and for a time of 2 minutes to 15 minutes. Instead of SPS, other similar machines such as a direct current hot press (DCHP), an indirect heating hot press, etc. can also be used for solidification. In this solidification process, an excessive amount of Te is discharged from the graphite die according to the value of δ.

[0063] A solid specimen with a thickness in the range of 2 mm to 15 mm is produced according to the requirements in the solidification process. Any thickness may be used according to the requirements and the availability of resources. The solid specimen is cut into different sizes and shapes for various thermoelectric measurements and Hall measurements while maintaining its directionality. Thin slices are also taken from the solid specimen for HR-TEM imaging.

[0064] HR-TEM images are shown in Figures 3 to 6. These figures show the honeycomb-like network configuration of Te. δ / Bi 0.5 S 1.5 Te3 heterostructure, and Bi x S 2-x This shows the formation of voids in a network filled with Te3 nanomaterial. Te can be identified by the same type of atomic layer in Figures 5 and 6, and Bi x S 2-x Te3 can also be identified in these figures by a quintuple layer of multiple types of atoms. This is Te by the method of the present invention. δ / Bi x S 2-x This demonstrates the formation of a Te3 networked heterostructure.

[0065] Te in a temperature range from room temperature to 250°C δ / Bi x S 2-x By using Te3 heterostructure samples measuring 8mm-10mm (length) x 3mm-4mm (width) x 1mm-2mm (thickness), the Seebeck coefficient and electrical conductivity are measured simultaneously. These measurements against typical δ values ​​are plotted in Figures 7 and 8, respectively. x S 2-x Compared to Te3 (δ=0), the Seebeck coefficient improves in heterostructures. The electrical conductivity remains the same at low temperatures as Bi. x S 2-x The power factor decreases compared to Te3 (δ=0). The improvement in the Seebeck coefficient is more significant than the decrease in electrical conductivity. As a result, the power factor improves, which is plotted in Figure 9. The obtained peak power factor value is 7.5 mW / mK 2 Such a high power factor is Te δ / Bi x S 2-x This supports the quantum confinement effect in Te3 heterostructures.

[0066] Using a laser flash device, Te is heated in a temperature range from room temperature to 250°C. δ / Bi x S 2-xThe thermal diffusivity was measured using a 12.7 mm (diameter) × 1 mm to 2 mm thick Te3 heterostructure sample and plotted in Figure 10. Specific heat was measured using a differential scanning calorimeter in the temperature range from room temperature to 250°C. Density was measured at room temperature and assumed to be relatively constant in the temperature range from room temperature to 250°C in order to calculate thermal conductivity. The thermal conductivity value calculated by multiplying the measured values ​​of thermal diffusivity, specific heat, and density is plotted in Figure 11.

[0067] The power factor and thermal conductivity values ​​at each temperature are used to calculate the figure of merit, which is then plotted in Figure 12. δ / Bi x S 2-x The Te3 heterostructure exhibits an improved figure of merit of 2.3. The highest average figure of merit obtained for this heterostructure was 1.3, while the peak value was 2.15. δ / Bi x S 2-x Table 1 summarizes the thermoelectric parameter values ​​for this highest mean figure of merit composition in the Te3 heterostructure.

[0068] [Table 1]

[0069] The electrical transport characteristics in a magnetic field were tested using a 4-probe van der Pau configuration with samples measuring 8mm-10mm × 8mm-10mm × 0.7mm-0.9mm in size. Measurements were performed in a 9kG magnetic field with a constant current of 5mA in a temperature range from room temperature to 250°C. To realistically estimate the transport characteristics of these bulk samples, resistivity and Hall voltage were measured while averaging with respect to shape and current reversal. The oven containing the samples was evacuated and purged with helium for stable measurement conditions. Calculated values ​​of Hall mobility and carrier concentration were used for p-type Te δ / Bi x S 2-x The Te3 heterostructure is plotted in Figure 13.

[0070] p-type Te δ / Bi x S 2-x The Te3 heterostructure exhibits improved mobility at room temperature, which decreases at higher temperatures. Simultaneously, the carrier concentration increases with increasing temperature, making it ideal for bulk thermoelectric materials. 19 cm -3 It is within the range.

[0071] Using a Hall measurement system, Te δ / Bi x S 2-x Magnetic transport measurements will be performed on Te3 heterostructure samples measuring 8mm-10mm (length) x 8mm-10mm (width) x 0.5mm-0.9mm (thickness). Hall resistance (R xy ) shows a plateau in the Landau level, and longitudinal resistance measurement (R xx ) showed a dip at the start of the Landau Plateau as a function of the applied magnetic field. Figure 14 shows R xy and R xx The function of R is plotted as a function of the applied magnetic field at room temperature. It is shown that the quantized Hole plateau correlates with the decreasing longitudinal resistance. This correlation is more evident in Figure 14(a) for a single peak, supporting the presence of a 2D transport contribution. xy Landau Plateau and R xx This correlation in the position of the dip in Te δ / Bi x S 2-x This demonstrates the observation of the quantum Hall effect in Te3 heterostructures, and how this relates to the Te produced in the present invention. δ / Bi x S 2-x To establish the role of quantum size effects in improving thermoelectric efficiency in Te3 heterostructures.

[0072] (Example 2: Te δ / Bi2Te 3-y Se y (Heterostructure) Highly doped n-type semiconductor Bi2Te 3-y Se yLet the nanomaterial be component A and the Te powder be component B. Other options for component B relative to component A are Bi, Zn, Sn, In, and Bi2Te. 3-y Se y Other such metals and semiconductors may have melting points lower than that of the other metal.

[0073] Bi2Te 3-y Se y The nanomaterial powder and Te powder are mixed together and filled into a quartz ampoule. The values ​​of y and δ are both in the range of 0.25 to 1. The ampoule is evacuated, purged with an inert gas, and then sealed under evacuated conditions using a conventional LPG-oxygen mixed flame. This sealed ampoule is placed in an oscillating tube furnace and heated to approximately 400°C to produce Bi2Te 3-y Se y To melt Te without affecting Bi2Te. 3-y Se y The mixer is agitated for 1 to 5 hours and then rapidly cooled in air. The test samples obtained by breaking the ampoules are collected and powdered using conventional pulverization methods.

[0074] The powdered specimen from the previous process is loaded into a graphite die. A graphite die with an inner diameter of 10 mm to 40 mm is used, which may be any value depending on the required sample size. Tungsten carbide and other suitable die materials can be used depending on the pressure and temperature requirements of the solidification process. The powdered specimen inside the graphite is solidified using a discharge plasma sintering (SPS) machine. This solidification is carried out at a pressure range of 25 MPa to 100 MPa, a temperature near the melting point of Te, i.e., 400°C, and for a time of 2 to 15 minutes. In addition to SPS, other similar machines such as DCHP and indirect heating hot presses can also be used for solidification. In this solidification process, an excess amount of Te is discharged from the graphite die depending on the value of δ.

[0075] Solid specimens with thicknesses ranging from 2 mm to 15 mm are produced as required by the solidification process. Any thickness may be used depending on the requirements and resource availability. The solid specimens are cut into different sizes and shapes for various thermoelectric and Hall measurements while maintaining orientation.

[0076] Te in a temperature range from room temperature to 250°C δ / Bi2Te 3-y Se y By using heterostructured samples measuring 8mm-10mm (length) x 3mm-4mm (width) x 1mm-2mm (thickness), the Seebeck coefficient and electrical conductivity are measured simultaneously. These measurements against typical δ values ​​are plotted in Figures 15 and 16, respectively. 3-y Se y Compared to (δ=0), the Seebeck coefficient improves in the heterostructure. The electrical conductivity remains the same as Bi2Te. 3-y Se y The power factor improves compared to (δ=0). The power factor improves due to the improvement in the Seebeck coefficient and electrical conductivity, and this is plotted in Figure 17. The obtained peak power factor value is 7.0 mW / mK 2 Such a high power factor is Te δ / Bi2Te 3-y Se y This supports the quantum confinement effect in heterostructures.

[0077] Using a laser flash device, Te is heated in a temperature range from room temperature to 250°C. δ / Bi2Te 3-y Se y The thermal diffusivity was measured using a heterostructured sample measuring 12.7 mm (diameter) x 1 mm to 2 mm thick, and plotted in Figure 18. Specific heat was measured using a differential scanning calorimeter in the temperature range from room temperature to 250°C. Density was measured at room temperature and assumed to be relatively constant in the temperature range from room temperature to 250°C for the purpose of calculating thermal conductivity. The thermal conductivity value calculated by multiplying the measured values ​​of thermal diffusivity, specific heat, and density is plotted in Figure 19.

[0078] The power factor and thermal conductivity values ​​at each temperature are used to calculate the figure of merit, which is then plotted in Figure 20. δ / Bi2Te 3-y Se y In the heterostructure, an improved figure of merit value of 2.6 is observed. The highest average figure of merit value obtained with this heterostructure is 2.0. δ / Bi2Te 3-y Se y The thermoelectric parameter values ​​for this highest mean figure of merit composition in the heterostructure are summarized in Table 2.

[0079] [Table 2]

[0080] The electrical transport characteristics in a magnetic field were tested using a 4-probe van der Pau configuration with samples measuring 8mm-10mm × 8mm-10mm × 0.7mm-0.9mm in size. Measurements were performed in a 9kG magnetic field with a constant current of 5mA in a temperature range from room temperature to 250°C. To realistically estimate the transport characteristics of these bulk samples, resistivity and Hall voltage were measured while averaging with respect to shape and current reversal. The oven containing the samples was evacuated and purged with helium for stable measurement conditions. Calculated values ​​of Hall mobility and carrier concentration were used for n-type Te δ / Bi2Te 3-y Se y This is plotted in Figure 21.

[0081] n-type Te δ / Bi2Te 3-y Se y In the case of a heterostructure, the carrier concentration is 10 20 cm -3 This is observed within a very high range. Furthermore, it shows little temperature dependence. The hole mobility of this material is very low compared to that reported for the constituent materials of heterostructures. Moreover, it shows little temperature dependence. The decrease in mobility in n-type heterostructures may be related to increased carrier-carrier scattering at such high carrier concentrations.

[0082] Using a Hall measurement system, Te δ / Bi2Te 3-y Se y Magnetic transport measurements will be performed on heterostructured samples measuring 8mm-10mm (length) x 8mm-10mm (width) x 0.5mm-0.9mm (thickness). Hall resistance (R xy ) shows a plateau in the Landau level, and longitudinal resistance measurement (R xx ) showed a dip at the starting point of the Landau Plateau as a function of the applied magnetic field. Figure 22 shows R as a function of the applied magnetic field at room temperature. xy and R xx The graph is plotted. It is shown that the quantized hole plateau correlates with decreasing longitudinal resistance. This correlation is more evident in Figure 22(a) for a single peak, supporting the presence of a 2D transport contribution. xy Landau Plateau and R xx This correlation in the position of the dip in Te δ / Bi x S 2-x The quantum Hall effect in the Te3 heterostructure was observed. This demonstrated the Te produced in the present invention. δ / Bi2Te 3-y Se y To establish the role of quantum size effects in improving thermoelectric efficiency in heterostructures.

Claims

1. A method (100) for obtaining networked heterostructure nanomaterials by synthesis, a. A step of obtaining a mixture by mixing the nanomaterial powder of component A with the powder of component B in a ratio selected from the range of 95:05 to 75:25 (102), b. The obtained mixture is heated under vacuum (104) to melt component B in the mixture, and at the same time the mixture is shaken during heating. c. A step of rapidly cooling the heated mixture in air (106) to obtain a rapidly cooled mixture, d. A step of grinding the rapidly cooled mixture containing components A and B into a powdered form of the rapidly cooled mixture (108) e. A step of filling a pre-designed die with the powdered form of the rapidly cooled mixture (110), and f. A process to obtain a networked heterostructure nanomaterial by solidifying the powdered form of the rapidly cooled mixture by sintering it in an exhaust chamber (112). Method (100), including the method (100).

2. The method according to claim 1 (100), further comprising the step of selecting component A and component B from the group including metals, semiconductors, and insulators.

3. The method according to claim 1 (100), further comprising the step of selecting components A and B such that the melting point of component A is greater than the melting point of component B.

4. A step of selecting component B from the group including tellurium, bismuth, and zinc, and component A is Bi ２ Te ３－ｘ See ｘ The method according to claim 1 (100), further comprising the step of selecting as such, wherein x is in the range of 0.1 to 1.

5. A step of selecting component B from the group including tellurium, bismuth, and zinc, and a step of selecting component A from Sb ２－ｘ Bi ｘ Te ３ The method according to claim 1 (100), further comprising the step of selecting as such, wherein x is in the range of 0.1 to 1.

6. Step of selecting component B from the group containing Bi ２ Te ３ and Sb ２ Te ３ and step of selecting component A from the group containing Bi ２ Se ３ Bi ２ S ３ Sb ２ Se ３ and Sb ２ S ３ The method (100) according to claim 1, further comprising the step of selecting from the group containing.

7. Formula Bi ｘ Sb ２－ｘ D ｙ M ３－ｙ / D δ It has a heterostructure, Bi ｘ Sb ２－ｘ D ｙ M ３－ｙ A heterostructured thermoelectric nanomaterial in which is component A, D is component B, elements D and M are selected from the group Te, Se, and S, and the values ​​of x, y, and δ are in the range of 0 to 3.

8. The heterostructured thermoelectric nanomaterial according to claim 7, wherein the values ​​of x, y, and δ are in the range of 0.1 to 1.

9. The heterostructured thermoelectric nanomaterial according to claim 7, wherein the nanostructure of the heterostructured thermoelectric nanomaterial forms a networked heterostructure morphology on a nanoscale in the range of 1 nm to 10 nm, and component B has a honeycomb-like networked structure with voids between them, and the voids are filled with component A.

10. The heterostructured thermoelectric nanomaterial according to claim 7, comprising a layer of component B having a size in the range of 1 nm to 5 nm.

11. The heterostructured thermoelectric nanomaterial according to claim 7, comprising particles of component A having a size in the range of 5 nm to 10 nm.

12. The concept of improving the thermoelectric efficiency of networked heterostructures is a. Quantum confinement in the metal or semiconductor layer of component B, b. Band offset for quantum confinement obtained by the semiconductor thermoelectric nanomaterial barrier layer of component A, and c. Carrier injection from the barrier layer of component A to the quantum well layer of component B in order to obtain thermoelectric heterostructures of different polarities. A heterostructured thermoelectric nanomaterial according to claim 7, comprising:

13. The heterostructured thermoelectric nanomaterial according to claim 7, wherein the chemical potential of component B is lower than the chemical potential of component A.

14. Component A is 1 cm ３ 10 １９ ~1 cm ３ 10 ２１ A heterostructured thermoelectric nanomaterial according to claim 7, selected from the group comprising p-type highly doped semiconductor nanomaterials and n-type highly doped semiconductor nanomaterials having carrier concentrations in the range of .

15. The heterostructured thermoelectric nanomaterial according to claim 7, wherein the sign of the Seebeck coefficient of the heterostructure is determined by the sign of the Seebeck coefficient of component A.

16. The heterostructured thermoelectric nanomaterial according to claim 7, wherein an improvement in the Seebeck coefficient and / or electrical conductivity is obtained for the heterostructured thermoelectric nanomaterial, and an improvement in the power factor is obtained by quantum confinement in the heterostructured thermoelectric nanomaterial.

17. The heterostructured thermoelectric nanomaterial according to claim 7, wherein the decrease in thermal conductivity is obtained by a band offset value higher than the typical phonon energy.

18. A p-type networked heterostructure is obtained, where component B is selected from the group including tellurium, zinc, and bismuth to form a quantum well layer of component B, and component A is Sb to form a barrier layer of component A. ２－ｘ Bi ｘ Te ３ A heterostructured thermoelectric nanomaterial according to claim 7, selected as such.

19. p-type tellurium / Sb ２－ｘ Bi ｘ Te ３ A heterostructured thermoelectric nanomaterial according to claim 18, wherein the material has a heterostructure.

20. An n-type networked heterostructure is obtained, where component B is selected from the group including tellurium, zinc, and bismuth to form a quantum well layer of component B, and component A is selected from the group including tellurium, zinc, and bismuth to form a barrier layer of component A. ２ Te ３－ｘ See ｘ A heterostructured thermoelectric nanomaterial according to claim 7, selected as such.

21. n-type tellurium / Bi ２ Te ３－ｘ See ｘ A heterostructured thermoelectric nanomaterial according to claim 20, wherein the material has a heterostructure.

22. The maximum value of the p-type Seebeck coefficient is p-type tellurium / Sb ２－ｘ Bi ｘ Te ３ The heterostructured thermoelectric nanomaterial according to claim 19, wherein the heterostructure has a voltage of 343.8 μV / K at room temperature.

23. The maximum value of electrical conductivity is p-type tellurium / Sb ２－ｘ Bi ｘ Te ３ For heterostructures, 6.5 × 10⁻¹⁰ units are obtained at around room temperature. ４ A heterostructured thermoelectric nanomaterial according to claim 19, wherein the S / m ratio is S / m.

24. The maximum power factor is p-type tellurium / Sb ２－ｘ Bi ｘ Te ３ For heterostructures, the reaction temperature is 7.6 mW / mK at around room temperature. ２ The heterostructured thermoelectric nanomaterial according to claim 19.

25. The minimum value of thermal conductivity is p-type tellurium / Sb ２－ｘ Bi ｘ Te ３ The heterostructured thermoelectric nanomaterial according to claim 19, wherein the heterostructure has a thermoelectric voltage of 1.06 W / m·K at room temperature.

26. The maximum value of the figure of performance (ZT) is p-type tellurium / Sb ２－ｘ Bi ｘ Te ３ The heterostructure thermoelectric nanomaterial according to claim 19, wherein the heterostructure has a coefficient of 2.1 at room temperature.

27. The average value of the performance index (ZT) is p-type tellurium / Sb ２－ｘ Bi ｘ Te ３ The heterostructure thermoelectric nanomaterial according to claim 19, wherein the ratio for the heterostructure is 1.3 in the temperature range from room temperature to 250°C.

28. Quantum confinement is p-type tellurium / Sb ２－ｘ Bi ｘ Te ３ The heterostructured thermoelectric nanomaterial according to claim 19, which is confirmed by a quantization plateau in the Hall resistance and a longitudinal resistance peak that decreases as a function of the applied magnetic field at room temperature that correlates with the heterostructure.

29. The maximum value of the n-type Seebeck coefficient is tellurium / Bi ２ Te ３－ｘ See ｘ The heterostructured thermoelectric nanomaterial according to claim 21, wherein the heterostructure has a (negative) voltage of 199.8 μV / K at room temperature.

30. The maximum value of electrical conductivity is n-type tellurium / Bi ２ Te ３－ｘ See ｘ For heterostructures, 1.5 × 10⁻¹⁰ at around room temperature. ５ The heterostructured thermoelectric nanomaterial according to claim 21, wherein the S / m ratio is S / m.

31. The maximum power factor is n-type tellurium / Bi ２ Te ３－ｘ See ｘ For heterostructures, the reaction temperature is 6.1 mW / mK at around room temperature. ２ The heterostructured thermoelectric nanomaterial according to claim 21.

32. The minimum value of the thermal conductivity is n-type tellurium / Bi ２ Te ３－ｘ See ｘ The heterostructured thermoelectric nanomaterial according to claim 21, wherein the heterostructure has a thermoelectric voltage of 0.71 W / m·K at room temperature.

33. The maximum value of the figure of performance (ZT) is n-type tellurium / Bi ２ Te ３－ｘ See ｘ The heterostructure thermoelectric nanomaterial according to claim 21, wherein the heterostructure has a coefficient of 2.6 at room temperature.

34. The average value of the performance index (ZT) is n-type tellurium / Bi ２ Te ３－ｘ See ｘ The heterostructure thermoelectric nanomaterial according to claim 21, wherein the heterostructure has a coefficient of 2.0 in the temperature range from room temperature to 250°C.

35. Quantum confinement is n-type tellurium / Bi ２ Te ３－ｘ See ｘ The heterostructured thermoelectric nanomaterial according to claim 21, which is confirmed by a quantization plateau in the Hall resistance and a longitudinal resistance peak that decreases as a function of the applied magnetic field at room temperature that correlates with the heterostructure.

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