Magneto-thermoelectric materials

Abstract

The present invention relates to thermoelectric materials that exhibit a ZT of ≥ 0.3 and that are exposed to an external magnetic field of 0.01 T to 2 T, resulting in a ZT of ≥ 1.3 at a temperature of ≤ 300 K. More particularly, the present invention relates to thermoelectric materials that are at a temperature of ≤ 300 K under an applied external magnetic field of 0.01 T to 2 T, and that have a ZT of ≥ 10 at - 20 K. 4 cm 2 / Vs carrier mobility, and - 10 17 -10 20 / cm 3 and an effective mass ≦0.04 free electron mass, and a Fermi energy ≦100 meV. The present invention further relates to a method for making a thermoelectric material that exhibits a ZT value ≧1.3 at temperatures ≦300 K, which method is achieved in a low magnetic field of less than 2 T.

Description

[Technical Field]

[0001] The present invention relates to the technical field of topological magneto-thermoelectric materials. More particularly, the present invention relates to the enhanced thermoelectric performance of topological insulators or topological semimetals in the presence of a magnetic field. [Background technology]

[0002] Thermoelectric technology can convert heat into electricity and vice versa. Unlike well-established high-temperature waste heat recovery, very few materials have shown promising low-temperature cooling performance due to their small Seebeck coefficients, because the Seebeck coefficient of good thermoelectric materials varies linearly with temperature.

[0003] The Seebeck effect describes the generation of a thermoelectric voltage along a temperature gradient when a temperature gradient is applied to a sample. The Seebeck coefficient is defined as the reciprocal of the generated voltage divided by the temperature difference, i.e., S = -ΔV / ΔT. The Seebeck coefficient, along with electrical and thermal conductivity, is a key factor in high-performance thermoelectric materials.

[0004] Generally, the Seebeck coefficient is calculated by multiplying the effective mass (m * d , where m * d =g 2 / 3 m * , m * is the band effective mass and g is the degeneracy), and is proportional to the carrier concentration (n 2 / 3 ) is inversely proportional to the small mass band (m * ) which allows for maintaining both a high Seebeck coefficient and high electrical conductivity.

[0005] One material under consideration for thermoelectric device applications is bismuth, which is a weak topological insulator in a "hinge state" (Non-Patent Document 1). By alloying bismuth with, for example, antimony, the resulting Bi-Sb alloy can become semimetallic or remain an insulator, depending on the Bi:Sb ratio (Non-Patent Document 2).

[0006] Bismuth telluride and its solid solutions, such as (Bi-Sb)2Te3 and Bi2(Te-Se)3, are excellent topological insulators [Non-Patent Document 3] and excellent thermoelectric materials at room temperature [Non-Patent Document 4], and are therefore suitable for refrigeration applications around 300 K.

[0007] PbTe is an inverted-band semiconductor with a band gap of approximately 0.2 eV. Pure PbTe can be optimized by thallium doping, which achieves a ZT of 1.5 at 773 K [5]. By further alloying with SnTe, another topological insulator, Pb 1-x Sn x Te-based compounds have been produced, which have high mobility (>110000 cm at 5 K). 2 / Vs) [Non-Patent Document 6].

[0008] HgTe has a very small effective mass (0.02-0.03 free electron mass) and >10 when grown by MBE (molecular beam epitaxy). 6 cm 2 It is a topological semimetal with ultrahigh mobility of . / Vs. By further alloying it with CdTe, it can be tuned as a quantum spin Hall insulator. [Non-Patent Document 7]

[0009] Cd3As2 has ultra-high mobility (>10 7 cm 2 / Vs), maximum 3.3 10 18 / cm 3It is known as a 3D Dirac semimetal with a carrier concentration of 0.04, a free electron mass of 0.04, a Fermi energy of 46 meV, and colossal magnetoresistance at low temperatures [Non-Patent Documents 8, 9]. At the same time, the magnetic field response of the thermoelectric properties has also been reported, which can saturate below 2 T [Non-Patent Document 10]. A thermoelectric figure of merit (ZT) greater than 1 at 375 K has been reported in a magnetic field.

[0010] ZrTe5 is a Dirac semimetal with a Lifschiz transition around 100 K. It has a valence of >5×10 at 2 K. 5 cm 2 It is the only known 3D quantum Hall system with a mobility of 1 / Vs [Non-Patent Document 11]. Appropriate field response can be achieved well below 2 T in both electrical and thermoelectric transport properties [Non-Patent Document 12]. Excellent thermoelectric performance can be expected around 100 K.

[0011] WTe2 is known as a type-II Weyl semimetal with perfect electron-hole compensation

[13] . WTe2 is the first reported giant magnetoresistance system due to its high electron and hole mobility. It also exhibits giant Nernst and magnetic Seebeck signals

[14] . [Prior art documents] [Non-patent literature]

[0012] [Non-Patent Document 1] Aggarwal, L. et al., Nat Commun 12, 4420(2021) [Non-patent document 2] R. Wolfe, GE Smith, Appl. Phys. Lett. 1, 5 (1962) [Non-patent document 3] Chen, YL et al., Science 5937, 178-181 (2009) [Non-patent document 4] Heremans, J., Cava, R. and Samarth, N. Nat. Rev. Mater. 2, 17049 (2017) [Non-Patent Document 5] Heremans, JP et al., Science 321, 5888, 554-557 (2008) [Non-patent document 6] Liang, T et al., Nat Commun 4, 2696 (2013) [Non-Patent Document 7] Konig, M. et al., Science 318.5851 766-770(2007) [Non-patent document 8] Liang, T. et al., Nature Mater 14, 280-284 (2015) [Non-Patent Document 9] H. Wang et al., Magnetic Field-Enhanced Dirac Semimetal Concentrations, Adv.Funct.Mater.2019, 29, 1902437 [Non-Patent Document 10] Liang, T et al., Phys.Rev.Lett.118, 136601 (2017) [Non-Patent Document 11] Tang, F. et al., Nature 569, 537-541 (2019) [Non-Patent Document 12] Galeski, S. et al., Nat Commun 12, 3197(2021) [Non-Patent Document 13] Ali, M. et al., Nature 514, 205-208 (2014) [Non-Patent Document 14] Pan, Y. et al., Nat Commun 13, 3909(2022) Summary of the Invention [Problem to be solved by the invention]

[0013] It was an object of the present invention to provide a thermoelectric material having improved thermoelectric properties compared to known thermoelectric materials, particularly at temperatures ≦300 K. A particular object was to improve the thermoelectric properties of topological thermoelectric materials that already exhibit a ZT of ≧0.3 at temperatures ≦300 K. An even more challenging object was to provide a thermoelectric compound having - At temperatures ≦300K - in magnetic fields below 2T - A ZT value of ≥ 1.3 should be provided. [Means for solving the problem]

[0014] The present inventors have discovered that the thermoelectric properties of known thermoelectric compounds, particularly those already possessing a ZT of ≥ 0.3, can be increased to ≥ 1.3 at temperatures around or below room temperature, i.e., ≤ 300 K, preferably ≤ 290 K, and even more preferably ≤ 280 K, by exposing these thermoelectric compounds to an external magnetic field. It was surprising that the application of even a low magnetic field in the range of 0.01 T to 2 T resulted in such a dramatic increase in ZT.

[0015] In preferred embodiments, the thermoelectric properties of topological materials are improved. Topology refers to relativistic effects in heavy element compounds. Due to the dispersion of electronic bands, the outer shells of heavy elements may have lower energy than the inner shells of light elements (e.g., the Bi 6p band versus the Se 4p band in Bi2Se3). In this case, band inversion can occur, resulting in changes in properties such as the conductance quantum or Berry curvature, which can be explained by integers. Common topological materials are topological insulators and topological semimetals, both of which have been reported to have surface states, small effective masses, high mobilities, and strong field responses of their transport properties. Therefore, the unique band signatures of topological materials provide an ideal platform for improved thermoelectric materials. Band inversion in topological systems not only generates topological integers but also modifies the electronic structure of the topological material. Band inversion shifts the conduction band minimum and valence band maximum from high to low symmetry points, which can generate higher degeneracy. At the same time, intense Ek dispersion at the crossing point of the two bands arises in pockets with small band mass and high mobility, which is most pronounced in topological semimetals such as Dirac and Weyl semimetals. Such high-mobility electrons can exhibit a strong response to external magnetic fields, making topological insulators and topological semimetals ideal candidates for magnetothermoelectric materials.

[0016] As a result of the above, we have discovered that the Seebeck coefficient can be enhanced by an applied magnetic field, especially in three-dimensional topological insulators or topological semimetals, while simultaneously reducing the electrical and thermal conductivity, leading to a dramatic improvement in the thermoelectric figure of merit, ZT.

[0017] As mentioned above, band inversion in topological insulators and topological semimetals can generate highly degenerate, low-effective-mass pockets with low carrier concentrations, which then result in a low Seebeck coefficient. In semiclassical terms, enhancement can be achieved in topological semimetals / insulators by applying an external magnetic field: the Seebeck coefficient increases under applied magnetic field at low field strengths (μB<1, where μ is the mobility and B is the applied field) and saturates at high field strengths (μB≫1). The electrical resistivity increases with applied field, which implies that the electrical conductivity decreases with applied field (σ=1 / ρ). According to the Wiedemann-Franz law, the thermal conductivity should also decrease with applied field. The figure of merit, ZT, is given by the equation ZT=S 2 The Seebeck term S can be calculated by T / ρκ, where S is the Seebeck coefficient, ρ is the resistivity, κ is the thermal conductivity, and T is the absolute temperature. 2 As long as the gain in is greater than the increase in the resistivity term ρ, a finite improvement in ZT is achieved.

[0018] Based on the above findings, we hypothesize and confirm that the thermoelectric properties of known thermoelectric compounds, especially those already possessing a ZT of ≥ 0.3, can be increased to ≥ 1.3 at or even below room temperature by exposing these thermoelectric compounds to an external magnetic field that can be as low as 0.01 T to 2 T; these improved thermoelectric compounds are referred to as magnetothermoelectric compounds.

[0019] More specifically, application of the above theoretical principles has led to the discovery that ideal candidates for improved thermoelectric materials are three-dimensional topological insulators or topological semimetals with high carrier mobilities that can benefit from larger gains in the magnetic Seebeck coefficient. Additionally, appropriate doping of these candidates can result in improved thermoelectric performance of up to 150% compared to the same undoped topological insulator or topological semimetal.

[0020] Preferred candidates for three-dimensional topological insulators or topological semimetals that meet the above requirements are alloys or compounds selected from all topological insulators or topological semimetals, including but not limited to: -Bi-Sb alloys, Bi2Te3, Bi2Se3, HgTe, SnTe, PbTe, Cd3As2, WTe2, and ZrTe5.

[0021] By doping these topological insulators / semimetals with trace amounts of either p-type or n-type dopants, the position of the Fermi energy can be effectively shifted toward the conduction / valence band for optimal carrier concentrations for good thermoelectric materials. At room temperature or even below, the best thermoelectric performance can be achieved by applying a magnetic field with an applied field strength of 0.01 T to 2 T to the best zero-field performing crystals.

[0022] The accompanying drawings are included to provide a more detailed understanding of the invention. The drawings illustrate exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention. [Brief explanation of the drawings]

[0023] [Figure 1] Figure 1 shows the clear enhancement of the Seebeck coefficient in topological materials, exemplified by selected systems Bi2Te3 and Bi-Sb alloys. [Figure 2] FIG. 1 shows the magnetic field dependence of the thermoelectric transport properties of Te-doped Bi0.88Sb0.12 alloy from 0 to 2 T in the temperature range of 20 K to 300 K. [Figure 3] FIG. 10 shows the Hall response of Te-doped Bi0.88Sb0.12 alloy from 20 K to 300 K with resolved carrier concentration and mobility. [Figure 4] FIG. 10 shows the magnetic field dependence of ZT in Te-doped Bi0.88Sb0.12 alloy with a temperature-dependent peak ZT. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention provides topological magnetic thermoelectric compounds that are thermoelectric compounds that exhibit a ZT of ≥ 0.3 at temperatures ≤ 300 K, preferably ≤ 290 K, even more preferably ≤ 280 K, and that upon exposure to an external magnetic field of 0.01 T to 2 T, preferably 0.01 T to 1 T, more preferably 0.01 T to 0.5 T, result in a ZT of ≥ 1.3, preferably ZT > 1.7, and more preferably ZT > 2.0.

[0025] More specifically, the present invention provides: - ≧10 4 cm 2 / Vs, preferably ≥ 5 × 10 4 cm 2 / Vs, more preferably ≥ 10 5 cm 2 / Vs (at 20 K) carrier mobility, and - 10 17 -10 20 / cm 3 carrier concentration of, and a small effective mass of ≦0.04, preferably ≦0.02, more preferably ≦0.01 free electron mass, and - have a Fermi energy of ≦100 meV, preferably ≦50 meV, more preferably ≦30 meV A thermoelectric material is provided that includes a three-dimensional topological insulator or topological semimetal, with Seebeck enhancement at temperatures ≦300 K, preferably ≦290 K, and even more preferably ≦280 K, under an applied external magnetic field of 0.01 T to 2 T, preferably 0.01 T to 1 T, and more preferably 0.01 T to 0.5 T. The lower limit of 0.01 T is chosen to indicate that the applied external magnetic field is greater than the Earth's (natural) magnetic field, which is approximately 25 to 65 μT. Therefore, to clearly distinguish from the Earth's magnetic field, the minimum applied external magnetic field is set to ≧0.01 T.

[0026] To discover three-dimensional topological insulators or topological semimetals that meet the current basic criteria of candidates for improved thermoelectric materials, for example, the inorganic crystal structure database, FIZ Karlsruhe (ICSD; https: / / icsd.fiz-karlsruhe.de), could serve as a source, eventually in combination with the Bilbao crystallographic server (http: / / www.cryst.ehu.es / ).

[0027] The ICSD is a chemical database that aims to contain information on all inorganic crystal structures (with atomic coordinates) published since 1913, including pure elements, minerals, metals, and intermetallic compounds. As of October 2022, the ICSD will contain over 270,000 entries and will be updated twice a year.

[0028] The Bilbao Crystallographic Server is an open-access website that provides online crystallographic databases and programs aimed at analyzing, calculating, and visualizing structural and mathematical crystallography, solid state physics, and structural chemistry. Of particular interest is the "TQC" (Topological Quantum Chemistry) page on the Bilbao Crystallographic Server, which can provide band representations for space groups.

[0029] For example, thanks to the database above, we select a topological insulator or topological semimetal that is already close to the following target properties: - ≧10 4 cm 2 / Vs, preferably ≥ 5 × 10 4 cm 2 / Vs, more preferably ≥ 10 5 cm 2 / Vs (at 20 K) carrier mobility, and - 10 17 -10 20 / cm 3 carrier concentration of, and a small effective mass of ≦0.04, preferably ≦0.02, more preferably ≦0.01 free electron mass, and A Fermi energy of ≦100 meV, preferably ≦50 meV, more preferably ≦30 meV.

[0030] The reason for starting with a topological insulator or topological semimetal is that in topological materials, band inversions always exist. These inverted bands can result in very small effective mass, high degeneracy, and high mobility. On the other hand, in nontopological materials, the bands are generally heavier than in topological materials, and as a result, the heavy bands have lower mobility and weaker magnetic field response. Materials with inherently small band effective mass but high mobility can still be within the scope of this invention, even if they are nontopological.

[0031] To approach the desired target properties mentioned above, the preselection of a topological insulator or a topological semimetal can be further refined by making the topological bands more pronounced, as well as by doping. The former can be achieved by providing alloys. For example, by adding Sb to Bi, or SnTe to PbTe, or Bi2Se3 to Bi2Te3. Taking the Bi-Sb system as an example, pure Bi has a 3 × 10 17 / cm 3 After alloying with Sb, the Bi-Sb system becomes a topological insulator, which meets the requirements of the present invention. Similarly, PbTe is an inverted-band semiconductor with a large effective mass of 0.2 free electron masses. By adding SnTe, it becomes a semimetal with an effective mass of 110,000 cm at 5 K. 2 / Vs and approx. 80,000 cm at 20 K 2The topological semimetal / insulator transforms into a topological crystalline insulator with a mobility of . / Vs. The achieved state of the topological semimetal / insulator can be used to further tune the properties through doping. For example, the use of Te to dope Bi results in one excess electron per dopant. This indicates that the carrier concentration of the topological insulator / semimetal can be precisely controlled, tuning the carrier concentration to an optimal value (which is material-dependent) to achieve the best thermoelectric performance when an external field is applied, in order to push the topological insulator / semimetal to its best figure of merit.

[0032] The Bi-Sb alloy is used here as a non-limiting example to demonstrate the principles of the present invention. Bi has an effective mass of 0.001 free electron mass and a densitometric value of 5 × 10 at 20 K. 6 cm 2 It has been reported that Bi alloys exhibit mobilities exceeding 1000 kJ / Vs. Therefore, Bi alloys are favorable candidates for thermoelectric performance in magnetic fields.

[0033] The application of the inventive principles described above can be applied to all topological insulators and topological semimetals, including, but not limited to, Bi2Te3, Bi2Se3, HgTe, SnTe, PbTe, Cd3As2, WTe, and ZrTe5. Two or more compounds can always be alloyed to achieve desired band parameters and transport properties.

[0034] By appropriately doping either p-type or n-type dopants into the obtained topological insulator or topological semimetal, the position of the Fermi energy can be effectively shifted towards the conduction / valence band, and an extra carrier density can be achieved, which in turn leads to the best thermoelectric performance.

[0035] Examples of tuning / doping topological insulators or topological semimetals selected from the list above are Bi2Te3 and Sb2Te3 (= p-type alloy), Bi2Te3 and Bi2Se3 (= n-type alloy), PbTe and SnTe (= p-type alloy), or Bi alloyed with Sb and doped with Te (= n-type doping); i.e. -Bi 2-x Sb x Te3(x~1.5) p-type alloy -Bi 1-x Sb x (0≦x≦1)+Te, alloy and n-type doped - Bi2Te2Se n-type alloy, or - Pb 1-x Sn x Te(0,2≦x≦0.4) p-type alloy For example, Bi 1-x Sb x In the above, the dopant is preferably Te, which is preferably present in a mole fraction of 0.01% or less. 1-x Sb x Doped into alloys, i.e., Bi 1-x Sb x +yTe, y≦0.01% (based on Bi). The generation of thermoelectric properties in a magnetic field requires the application of a finite external magnetic field to the system. For practical applications, the magnetic field should preferably be as low as possible, which, in turn, requires high electron mobility and, therefore, an ultralow effective mass of the selected system. Surprisingly, the above-described topological insulators or topological semimetals can already exhibit enhanced Seebeck coefficients under the influence of external magnetic fields of only 0.01 T to 2 T (e.g., achievable with electromagnets), preferably 0.01 T to 1 T (e.g., achievable with rare-earth-containing permanent magnets), and more preferably 0.01 T to 0.5 T (e.g., achievable with rare-earth-free permanent magnets). The lower limit of the applied external magnetic field of 0.01 T is chosen to indicate that the applied external magnetic field is greater than the Earth's (natural) magnetic field, which is approximately 25 to 65 μT. Therefore, to clearly distinguish it from the Earth's magnetic field, the minimum applied external magnetic field is preferably set to ≧0.01 T.

[0036] In such an applied magnetic field, the Seebeck coefficient is significantly enhanced compared to the zero-field value, but the electrical resistivity does not increase by the same amount as the square of the Seebeck coefficient. The thermal conductivity decreases progressively with applied field; as a result, the thermoelectric performance is greatly enhanced.

[0037] As mentioned above, topological materials likely exhibit band inversion and also band gaps subject to spin-orbit coupling. Because spin-orbit coupling is a relatively small perturbation in the electronic structure, the energy gap is often very small, on the order of 100 meV. At such small gaps, intrinsic excitations of both electrons and holes can be detrimental to thermoelectric performance. Therefore, topological materials are preferably limited to thermoelectric applications below room temperature, i.e., temperatures ≦300 K, preferably ≦290 K, and even more preferably ≦280 K.

[0038] Manufacturing method Thermoelectric materials according to the present invention can be manufactured in the same manner as conventional thermoelectric materials. For example, module manufacturing using a Bi-Sb alloy begins with growing a crystal using the "horizontally moving melting zone technique," using a pre-molten mixture of elements (e.g., Bi and Sb) in the desired stoichiometric ratio as feed and seed crystals, then cutting the target crystal into small parallelepipeds, which are then joined into a series of blocks. These blocks are then placed between two thick plates, e.g., made of ceramic, preferably with contacts prepared for the blocks to maintain a uniform temperature gradient. Doping can be achieved by simply adding dopants to the initial alloy / compound mixture before starting the melting process described above.

[0039] application The thermoelectric materials of the present invention can be used, for example, as or in refrigerators, called "thermoelectric coolers" or "Peltier coolers", or for power generation by thermoelectric generators, or in solar thermal energy generation.

[0040] Example The present invention provides Bi with uniform element distribution at 2 K to 300 K using an external magnetic field of 0 T to 2 T. 0.88 Sb 0.12 This is explained in more detail below with reference to the example of a Te-doped single crystal of the alloy. 0.88 Sb 0.12 It should be emphasized that this is not the only example of such an achievement: any Bi-Sb alloy, semiconducting or semimetallic, would have a similar response, provided the carrier concentrations are within reasonable limits.

[0041] In the example, the crystals were grown using Bi as a seed. 0.97 Sb 0.03 Polycrystalline and Bi as feed 0.88 Sb 0.12 The polycrystals are grown using the horizontal moving molten zone technique. A moving system using a motor and heating coils is used for the moving molten zone process. Both the seed and feed polycrystals are grown at 700°C. o The resulting polycrystal is a cylinder, which is then transferred into a larger ampoule. Careful control of the current applied to the heating coil ensures that only the seed melts at the start of crystal growth. A motor pushes the ampoule with the crystal at a speed of 1 mm / h to ensure excellent quality of the target crystal. The resulting grown crystal is then placed in a scanning electron microscope for energy dispersive X-ray spectroscopy examination to determine the exact ratio of Bi to Sb.

[0042] A general example of field enhancement in the Seebeck coefficient of topological insulators / semiconductors is shown in Figure 1. Bi2Te3 and undoped Bi-Sb alloy are used as examples to illustrate the effect of magnetic field. Between the two, Bi-Sb alloy has a stronger field dependence, which is shown in low magnetic fields. To better illustrate the present invention, the Bi-Sb system is used for further presentation.

[0043] 10 ppm Te-doped Bi at 20K to 300K0.88 Sb 0.12 The field dependence of the resistivity ρ, Seebeck coefficient S, and thermal conductivity κ for the alloy is shown in Figure 2. All three properties show a strong field dependence over the entire temperature range. In particular, below 100 K, a global minimum in resistivity is observed, along with a platform observed in the Seebeck coefficient. At the same time, the thermal conductivity decreases rapidly with field below 1 T and saturates above 1 T.

[0044] The Hall resistivity at various temperatures up to 2 T, along with the resolved carrier concentration and averaged mobility, are shown in Figure 3. Hall measurements are taken simultaneously with the thermoelectric transport properties for one sample. The Hall coefficient, which is the slope of the Hall resistance versus the magnetic field, gradually decreases with temperature as a result of thermal excitations within the insulator. The resolved carrier density is shown for the undoped topological insulator Bi 0.88 Sb 0.12 Much higher than 3 × 10 17 / cm 3 This indicates the effectiveness of doping. The mobility at low temperature is 60m 2 / Vs, allowing for a very strong response of all transport properties to external fields. The effective mass is 0.008 free electron mass, and the Fermi energy is at 25 meV.

[0045] The field-dependent ZT is shown in Figure 4. In the presence of an external magnetic field between 80K and 100K, the highest ZT value reaches 2.3 at about 0.3T. A high ZT of >2 can be achieved in a wide temperature range from 80K to 200K. For high ZT at high temperatures, the optimum field gradually increases from 0.3T at 80K to 1.5T at 200K. The thermoelectric parameter ZT is given by ZT = (S 2 / ρκ)T, where S, ρ, κ, and T are the Seebeck coefficient, resistivity, thermal conductivity, and temperature, respectively.

Claims

1. 1. A thermoelectric material under an applied external magnetic field of 0.01 T to 2 T at a temperature of ≦300 K, the material comprising: - ≥ 10 at 20K ４ cm ２ / Vs carrier mobility, and -10 １７ -10 ２０ / cm ３ carrier concentration of, and - effective mass ≦ ​​0.04 free electron mass, and - have a Fermi energy of ≦100 meV, - Three-dimensional topological insulator or topological semimetal The thermoelectric material comprising:

2. The thermoelectric material is doped with a p-type or n-type dopant. - Three-dimensional topological insulator, or - Three-dimensional topological semimetals The thermoelectric material of claim 1 , wherein

3. The thermoelectric material is a Bi-Sb alloy, Bi ２ Te ３ , Bi ２ Se ３ , PbTe, SnTe HgTe, Cd ３ As ２ , ZrTe ５ , and WTe ２ 3. The thermoelectric material according to claim 1, which is a three-dimensional topological insulator or a three-dimensional topological semimetal selected from the group consisting of:

4. The thermoelectric material is Bi １－ｘ Sb ｘ The thermoelectric material of any one of claims 1 to 3, wherein +yTe, y≦0.01% (based on Bi).

5. 1. A thermoelectric material that exhibits a ZT of ≥ 0.3 when, and while, not exposed to a magnetic field of ≥ 0.01 T, wherein the material is at a temperature of ≤ 300 K and is under the influence of an external magnetic field of 0.01 T to 2 T, resulting in a ZT of ≥ 1.

3.

6. The thermoelectric material according to any one of claims 1 to 5, wherein the material is under the influence of an external magnetic field of 0.01T to 1.0T, preferably 0.01T to 0.5T.

7. 1. A method of making a thermoelectric material that exhibits a ZT value of ≧1.3, comprising the steps of selecting a thermoelectric material that possesses a ZT of ≧0.3 when not exposed to a magnetic field of ≧0.01 T, and then exposing the thermoelectric material to an external magnetic field of 0.01 T to 2 T at a temperature of ≦300 K.

8. The thermoelectric material is doped with p-type or n-type dopants - Three-dimensional topological insulator, or - Three-dimensional topological semimetals The method of claim 7, wherein

9. Thermoelectric materials include Bi-Sb alloys and Bi ２ Te ３ , Bi ２ Se ３ , PbTe, SnTe, HgTe, Cd ３ As ２ , ZrTe ５ , and WTe ２ 9. The method of claim 7 or 8, wherein the three-dimensional topological insulator or three-dimensional topological semimetal is selected from the group consisting of:

10. The thermoelectric material is Bi １－ｘ Sb ｘ The method according to any one of claims 7 to 9, wherein +yTe, y≦0.01% (based on Bi).

11. Use of the thermoelectric material according to any one of claims 1 to 6 as or in a refrigerator.

12. Use of the thermoelectric material according to any one of claims 1 to 6 for generating electricity by means of a thermoelectric generator.

13. Use of the thermoelectric material according to any one of claims 1 to 6 in solar thermal energy generation.

14. A refrigerator comprising the thermoelectric material according to any one of claims 1 to 6.

15. A generator comprising the thermoelectric material according to any one of claims 1 to 6.

16. A solar energy generator comprising the thermoelectric material according to any one of claims 1 to 6.

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