Magnetothermoelectric material

Abstract

The invention relates to a thermoelectric material which exhibits a ZT of > = 0.3 and which results in a ZT of > = 1.3 when exposed to an external magnetic field of 0.01 T-2T at a temperature of < = 300 K. More specifically, the invention relates to a thermoelectric material under an applied magnetic field of 0.01 T-2 T at a temperature of < = 300 K, where the material comprises:-a three-dimensional topological insulator or topological semimetal-a carrier mobility at 20 K > = 104 cm2 / Vs, and-a carrier concentration of 1017-1020 / cm3, and-an effective mass of < = 0.04 mass of free electrons, and-a Fermi energy of < = 100 meV. The invention also relates to a method for producing a thermoelectric material which exhibits a ZT value of > = 1.3 at a temperature of < = 300 K and which is implemented in a low magnetic field of less than 2 T.

Description

Technical Field

[0001] The present invention relates to the technical field of topological magnetothermoelectric 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 Art

[0002] Thermoelectric technology can convert heat into electricity or vice versa. Different from well-established high-temperature waste heat recovery, due to the small Seebeck coefficient, very few materials show promising low-temperature cooling performance because the Seebeck coefficient in good thermoelectric materials is proportional to temperature.

[0003] The Seebeck effect describes the generation of a thermal 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, together with electrical conductivity and thermal conductivity, is a key factor for high-performance thermoelectric materials.

[0004] Generally, the Seebeck coefficient is proportional to the density of the state effective mass (m ＊ d , where m * is the band effective mass and g is the degeneracy), and is inversely proportional to the carrier concentration (n 2 / 3 ) in a given system. So far, an effective way to obtain good thermoelectric performance is to have a high degeneracy (g) of a small mass band (m * ), which can maintain a high Seebeck coefficient and high electrical conductivity.

[0005] One material considered for thermoelectric device applications is bismuth. Bismuth is a weak topological insulator in the "hinge state" (Aggarwal, L. et al. Nat Commun 12, 4420 (2021)). By alloying bismuth with, for example, antimony, the resulting Bi-Sb alloy can become a semimetal or remain an insulator, depending on the Bi:Sb ratio (R. Wolfe, G. E. Smith, Appl. Phys. Lett. 1, 5 (1962)).

[0006] Bismuth telluride and its solid solutions such as (Bi-Sb)2Te3 and Bi2(Te-Se)3 are good topological insulators at room temperature [Chen, Y. L. et al. Science 5937, 178-181 (2009)] and good thermoelectric materials [Heremans, J., Cava, R. & Samarth, N. Nat. Rev. Mater. 2, 17049 (2017)], and thus are suitable for refrigeration applications at about 300K.

[0007] PbTe is a band-inverted semiconductor with a bandgap of ~0.2 eV. Pure PbTe can be optimized by doping thallium, which achieves a ZT of 1.5 at 773 K [Heremans, J.P. et al. Science 321, 5888, 554 - 557 (2008)]. By further alloying with SnTe, another topological insulator, the Pb 1-x Sn x Te system is produced, which is called a massive Dirac semimetal with a high mobility (>110000 cm 2 / Vs at 5 K) [Liang, T et al. Nat Commun 4, 2696 (2013)].

[0008] HgTe is a topological semimetal with a very small effective mass (0.02 - 0.03 free electron masses) and, when grown by MBE (molecular beam epitaxy), has an ultrahigh mobility of >10 6 cm 2 / Vs. By further alloying with CdTe, it can be tuned into a quantum spin Hall insulator M. et al. Science 318.5851 766 - 770 (2007)].

[0009] Cd3As2 is known as a 3D Dirac semimetal with an ultrahigh mobility (>10 7 cm 2 / Vs), a carrier concentration of up to 3.3·10 18 / cm 3 , a free electron mass greater than 0.04 free electron masses, a Fermi energy greater than 46 meV, and a giant magnetoresistance at low temperatures [Liang, T.et al. Nature Mater 14, 280–284 (2015), H.Wang et al. MagneticField-Enhanced Dirac Semimetal Concentrations, Adv.Funct.Mater.2019, 29, 1902437]. At the same time, a magnetic field response of the thermoelectric properties has also been reported, which can saturate below 2 T [Liang, T etal. Phys.Rev.Lett. 118, 136601 (2017)]. A thermoelectric figure of merit (ZT) greater than 1 has been reported at 375 K in a magnetic field.

[0010] ZrTe5 is a Dirac semimetal with a Lifshiz transition at around 100 K. It is called the only 3D quantum Hall system with >5×10 at 2 K 5cm 2 Mobility per Vs [Tang.F, etal. Nature 569, 537–541 (2019)]. In terms of electrical and thermoelectric transport properties, a suitable field response can be achieved well below 2 T [Galeski, S., et al. Nat Commun 12, 3197 (2021)]. Optimal thermoelectric performance can be expected at around 100 K.

[0011] WTe2 is known as a type-II Weyl semimetal, which has perfect compensation between electrons and holes [Ali, M. et al Nature 514, 205–208 (2014)]. WTe2 is the first reported giant magnetoresistance system due to its high electron and hole mobilities. It also shows large Nernst and magnetic Seebeck signals [Pan, Y. et al. Nat Commun 13, 3909 (2022)].

[0012] Object of the Invention

[0013] The object of the present invention is to provide a thermoelectric material having improved thermoelectric properties (compared to known thermoelectric materials), especially at temperatures ≤ 300 K. A specific object is to improve the thermoelectric properties of topological thermoelectric materials that have shown a ZT ≥ 0.3 at temperatures ≤ 330 K. As an even more challenging object, a thermoelectric compound should be provided having the following properties:

[0014] – Exhibiting a ZT value ≥ 1.3

[0015] – In a magnetic field below 2 T

[0016] – At a temperature ≤ 300 K. Summary of the Invention

[0017] The inventors have found that by exposing known thermoelectric compounds to an external magnetic field, the thermoelectric properties of these thermoelectric compounds (especially those that already have a ZT ≥ 0.3) can be increased to ≥ 1.3 at temperatures near or below room temperature (i.e., at temperatures ≤ 300 K, preferably ≤ 290 K, even more preferably ≤ 280 K). Surprisingly, even applying a low magnetic field in the range of 0.01 T - 2 T results in such a significant increase in ZT.

[0018] In a preferred embodiment, the thermoelectric properties of topological materials are improved. Topology involves the relativistic effects of heavy element compounds. Due to the dispersion of the electronic energy bands, the outer shells of heavy elements can have lower energies than the inner shells of light elements (e.g., the Bi 6p energy band in Bi2Se3 relative to the Se 4p energy band). In this case, band inversion can occur, which can lead to changes in properties, such as the conductance quantum or Berry curvature, which can be described by integers. Common topological materials are topological insulators and topological semimetals, both of which are reported to have surface states, small effective masses, high mobilities, and strong field responses of their transport properties. Thus, 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 changes the electronic structure of topological materials. For band inversion, the minimum of the conduction band and the maximum of the valence band shift from high-symmetry points to lower-symmetry points, which can result in a higher degeneracy. At the same time, the sharp E-k dispersion at the crossing of the two energy bands gives rise to pockets with small band masses and high mobilities, which is most prominent in topological semimetals such as Dirac and Weyl semimetals. Such high-mobility electrons can exhibit a strong response to an external magnetic field, making topological insulators and topological semimetals ideal candidates for magnetothermoelectric materials.

[0019] As a result of the above, the inventors have found that, especially in three-dimensional topological insulators or topological semimetals, the Seebeck coefficient can be increased by an applied magnetic field, while at the same time, the electrical conductivity and thermal conductivity are decreased. This leads to a remarkable increase in the thermoelectric figure of merit ZT.

[0020] As described above, band inversion in topological insulators and topological semimetals can produce pockets with high degeneracy, low carrier concentration, and low effective mass, which then results in a low Seebeck coefficient. In the semiclassical picture, enhancement can be achieved in topological semimetals / insulators by applying an external magnetic field, where the Seebeck coefficient increases at low field strengths (μB < 1, μ is the mobility, B is the applied field) and saturates at high field strengths (μB >> 1) under the applied magnetic field. The resistivity increases with the applied field, which means that the electrical conductivity decreases with the applied field (σ = 1 / ρ), and by the Wiedemann-Franz Law, the thermal conductivity should also decrease with the applied field. The figure of merit ZT can be calculated by the equation ZT = S 2 T / ρκ, where S is the Seebeck coefficient, ρ is the resistivity, κ is the thermal conductivity, and T is the absolute temperature. As long as the gain of the Seebeck term S 2 is greater than the gain of the resistivity term ρ, a finite enhancement of ZT is achieved.

[0021] Based on the above findings, it is hypothesized and confirmed that by exposing known thermoelectric compounds, especially those already having a ZT of ≥0.3, to an external magnetic field that can be as low as 0.01T–2T, the thermoelectric properties of these thermoelectric compounds can be improved to ≥1.3 at room temperature or even below room temperature; these improved thermoelectric compounds are referred to as magnetothermoelectric compounds.

[0022] More specifically, the application of the above theoretical principle leads to the following findings: Ideal candidates for improved thermoelectric materials are three-dimensional topological insulators or topological semimetals with high carrier mobility, which can benefit from a greater gain in the magnetic Seebeck coefficient. Additionally, compared to the same undoped topological insulator or topological semimetal, appropriately doping these candidates can result in an improved thermoelectric performance of up to 150%.

[0023] 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:

[0024] - Bi-Sb alloys, Bi2Te3, Bi2Se3, HgTe, SnTe, PbTe, Cd3As2, WTe2, and ZrTe5.

[0025] By doping trace amounts of p-type or n-type dopants into these topological insulators / semimetals, the position of the Fermi energy can be effectively shifted towards the conduction band / valence band, towards the optimal carrier concentration for a good thermoelectric material. By applying a magnetic field with an applied field strength of 0.01T–2T to the optimal zero-field performance crystal, the optimal thermoelectric performance can be achieved at room temperature or even below room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings are included to provide a more detailed understanding of the present invention. The drawings illustrate exemplary embodiments of the present invention and, together with the description, are used to explain the principles of the present invention.

[0027] Figure 1 Showing a significant enhancement of the Seebeck coefficient in topological materials; taking the selected systems Bi2Te3 and Bi-Sb alloy as examples.

[0028] Figure 2 Showing Te-doped Bi 0.88 Sb 0.12 The magnetic field dependence of the thermoelectric transport properties of the alloy from 0 to 2T in the temperature range of 20K to 300K.

[0029] Figure 3 Showing Te-doped Bi 0.88 Sb 0.12 The Hall response of the alloy, as well as the resolved carrier concentration and mobility.

[0030] Figure 4 Show Te-doped Bi 0.88 Sb 0.12 The field dependence of ZT in the alloy, with a temperature-dependent peak ZT. Detailed implementation mode

[0031] The present invention provides a topological magnetothermoelectric compound, which is a thermoelectric compound that exhibits a ZT of ≥0.3 at a temperature of ≤300 K, preferably ≤290 K, and even more preferably ≤280 K, and a ZT of ≥1.3 when exposed to an external magnetic field of 0.01 T–2 T, preferably 0.01 T–1 T, and more preferably 0.01 T–0.5 T. Preferably, ZT > 1.7 and more preferably ZT > 2.0.

[0032] More specifically, the present invention provides a thermoelectric material comprising:

[0033] – A three-dimensional topological insulator or topological semimetal

[0034] – Carrier mobility ≥10 4 cm 2 / Vs, preferably ≥5×10 4 cm 2 / Vs, more preferably ≥10 5 cm 2 / Vs (at 20 K), and

[0035] – A carrier concentration of 10 17 -10 20 / cm 3 and

[0036] – A small effective mass of ≤0.04 free electron mass, preferably ≤0.02, and more preferably ≤0.01 free electron mass, and

[0037] – Fermi energy of ≤100 meV, preferably ≤50 meV, and more preferably ≤30 meV.

[0038] At a temperature of ≤300 K, preferably ≤290 K, and even more preferably ≤280 K, there is a Seebeck enhancement under an applied magnetic field of 0.01 T–2 T, preferably 0.01 T–1 T, and more preferably 0.01 T–0.5 T. The lower limit of 0.01 T is selected to indicate that the applied magnetic field is destined to be greater than the Earth's (natural) magnetic field, which is about 25 μT–65 μT. Therefore, to clearly distinguish from the Earth's magnetic field, the minimum applied magnetic field is set to ≥0.01 T.

[0039] To find three-dimensional topological insulators or topological semimetals that match the current basic criteria for candidates for improved thermoelectric materials for, e.g., the Inorganic Crystal Structure Database, FIZ Karlsruhe (ICSD; https: / / icsd.fiz-karlsruhe.de), in combination with the Bilbao Crystallographic Server (http: / / www.cryst.ehu.es / ) can be used as a source.

[0040] The ICSD is a chemical database that attempts to contain information on all inorganic crystal structures published since 1913, including pure elements, minerals, metals, and intermetallic compounds (with atomic coordinates). As of October 2022, the ICSD contains over 270,000 entries and is updated twice a year.

[0041] The Bilbao Crystallographic Server is an open-access website that provides online crystallographic databases and programs designed to analyze, calculate, and visualize problems in 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 of space groups.

[0042] For example, topological insulators or topological semimetals that are already close to the target properties are selected with the aid of the above databases:

[0043] – Carrier mobility ≥ 10 4 cm 2 / Vs, preferably ≥ 5 × 10 4 cm 2 / Vs, more preferably ≥ 10 5 cm 2 / Vs (at 20 K), and

[0044] – Carrier concentration of 10 17 -10 20 / cm 3 , and

[0045] – Small effective mass of ≤ 0.04 free electron mass, preferably ≤ 0.02, more preferably ≤ 0.01 free electron mass, and

[0046] – Fermi energy of ≤ 100 meV, preferably ≤ 50 meV, more preferably ≤ 30 meV.

[0047] The reason for starting with topological insulators or topological semimetals is that in topological materials, there are always band inversions. These inverted bands can lead to extremely small effective masses, high degeneracy, and high mobility. On the other hand, in non-topological materials, the bands are generally heavier than those in topological materials, making such heavy bands have lower mobility and weaker field responses. Materials with inherently small effective band masses but high mobility, even non-topological materials, can still be within the scope of the present invention.

[0048] To further approach the above desired target properties, the preselection of topological insulators or topological semimetals can be further refined by making the topological bands more prominent and by doping. The former can be achieved by providing alloys. For example, by adding Sb to Bi, or by adding SnTe to PbTe, or by adding Bi2Se3 to Bi2Te3. Taking the Bi-Sb system as an example, pure Bi is a semimetal with electron and hole concentrations of 3×10 17 / cm 3 . After alloying with Sb, the Bi-Sb system becomes a topological insulator, which meets the prerequisites of the present invention. Similarly, PbTe is a band-inverted semiconductor with a large effective mass of 0.2 free electron mass. By adding SnTe, it becomes a topological crystalline insulator that has a mobility of more than 110,000 cm 2 / Vs at 5K and a mobility of ∼80,000 cm 2 / Vs at 20K. Through the achieved state of topological semimetal / insulator, the properties can be further adjusted via doping. For example, doping Bi with Te results in one excess electron per dopant. This shows that the carrier concentration of topological insulators / semimetals can be precisely controlled, adjusted to the optimal value (which is material-dependent), and the best thermoelectric performance can be obtained when an external field is applied to push the topological insulator / semimetal to its optimal value.

[0049] The Bi-Sb alloy is used here as a non-limiting example to demonstrate the principle of the present invention. It is reported that the effective mass of Bi is 0.001 free electron mass and it exhibits a mobility of more than 5×10 6 cm 2 / Vs at 20K. Therefore, Bi alloys belong to the preferred candidates with thermoelectric properties in a magnetic field.

[0050] The application of the above invention principle can be implemented to all topological insulators and topological semimetals, including but not limited to Bi2Te3, Bi2Se3, HgTe, SnTe, PbTe, Cd3As2, WTe2, and ZrTe5. One can always alloy two or more compounds together to achieve the desired band parameters and transport properties.

[0051] By appropriately doping a p-type or n-type dopant into the obtained topological insulator or topological semimetal, the position of the Fermi energy can be effectively shifted towards the conduction band / valence band and a high-quality carrier density can be achieved, which then results in optimal thermoelectric properties.

[0052] Examples of modulating / doping topological insulators or topological semimetals selected from the above list are: Bi2Te3 and Sb2Te3 (= p-type alloying), Bi2Te3 and Bi2Se3 (= n-type alloying), PbTe and SnTe (= p-type alloying), or alloying Bi and Sb and doping with Te (= n-type doping); that is,

[0053] -Bi 2-x Sb x Te3(x~1.5) p-type alloying

[0054] -Bi 1-x Sb x (0 ≤ x ≤ 1) + Te alloying and n-type doping

[0055] -Bi2Te2Se n-type alloying, or

[0056] -Pb 1-x Sn x Te(0.2 ≤ x ≤ 0.4) p-type alloying

[0057] For example, in Bi 1-x Sb x the dopant is preferably Te, which is preferably doped into the Bi 1-x Sb x alloy at a molar fraction of less than or equal to 0.01%, that is, Bi 1-x Sb x + yTe, y ≤ 0.01% (based on Bi).

[0058] Generating thermoelectric properties in a magnetic field requires applying a finite external magnetic field to the system. For practical applications, the magnetic field should preferably be as low as possible, which on the other hand requires a high mobility of the electrons in the system and thus an ultra-low effective mass of the selected system. Surprisingly, the above topological insulators or topological semimetals have shown an enhanced Seebeck coefficient under the influence of an external magnetic field of only 0.01 T - 2 T (e.g., achievable using an electromagnet), preferably 0.01 T - 1 T (e.g., achievable using a rare-earth-containing permanent magnet), more preferably 0.01 T - 0.5 T (e.g., achievable using a rare-earth-free permanent magnet). The lower limit of the applied magnetic field is selected as 0.01 T in order to show that the applied magnetic field is destined to be greater than the (natural) magnetic field of the Earth, which is about 25 - 65 μT. Therefore, in order to clearly distinguish from the Earth's magnetic field, the minimum applied magnetic field is preferably set to ≥ 0.01 T.

[0059] In such an applied magnetic field, the Seebeck coefficient is significantly increased compared to the zero-field value, while the increase in resistivity is different from the increase in the square of the Seebeck coefficient. The thermal conductivity gradually decreases with the applied field; as a result, the thermoelectric performance is greatly improved.

[0060] As described above, topological materials exhibit band inversion and most likely also exhibit a band gap that can withstand spin-orbit coupling. Since spin-orbit coupling is a relatively small perturbation in the electronic structure, the band gap is usually very small, on the order of 100 meV. Due to this small band gap, the intrinsic excitations of electrons and holes may be detrimental to the thermoelectric performance. Therefore, topological materials are preferably limited to thermoelectric applications at room temperature and below, i.e., limited to temperatures ≤ 300 K, preferably ≤ 290 K, and even more preferably ≤ 280 K.

[0061] Manufacturing method

[0062] The manufacturing of the thermoelectric material according to the present invention can be similar to that of conventional thermoelectric materials. For example, manufacturing a module with a Bi-Sb alloy can start from growing a crystal. For example, using a pre-melted mixture of elements (such as Bi and Sb) with the desired stoichiometric ratio as the feed and seed crystal, adopting the "horizontal moving zone melting technique", and then cutting the target crystal into small parallelepipeds, which can then be connected in series as a block. Then, these blocks can be placed between two plates made of, for example, ceramics, preferably using contact parts prepared for the blocks to maintain a uniform temperature gradient. Doping can be achieved by simply adding a dopant to the initial alloy / compound mixture before starting the above melting process.

[0063] Applications

[0064] The thermoelectric material of the present invention can be used, for example, as or in a refrigerator (referred to as a "thermoelectric cooler" or "Peltier cooler"), or for power generation using a thermoelectric generator, or for solar thermal power generation.

[0065] Examples

[0066] The following explains the present invention in more detail with reference to an example of a Te-doped Bi 0.88 Sb 0.12 alloy single crystal, which has a uniform elemental distribution under an external magnetic field of 0 T - 2 T between 2 K - 300 K. Also, it should be emphasized that Bi 0.88 Sb 0.12 is not the only example of such an achievement. Any Bi-Sb alloy (semiconducting or semi-metallic) will have a similar response as long as the carrier concentration is within a reasonable range.

[0067] In this example, a crystal is grown using the horizontal moving zone melting technique, using Bi 0.97 Sb0.03 Polycrystals are used as seeds, and Bi is used 0.88 Sb 0.12 Polycrystals are used as feedstock. A moving system with a motor and heating coils is used for the moving melt zone process. Both the seed and feed polycrystals are prepared by melting a stoichiometric mixture of Bi and Sb in a quartz ampoule at 700 °C and then quenching. The resulting polycrystals are cylinders, which are transferred to a larger ampoule. The current applied to the heating coils is carefully controlled to ensure that only the seed melts at the start of crystal growth. The motor pushes the ampoule with the crystal at a rate of 1 mm / h to ensure good quality of the target crystal. The resulting grown crystal is loaded into a scanning electron microscope for energy-dispersive X-ray spectroscopy testing to determine the exact ratio of Bi to Sb.

[0068] Figure 1 General examples of field enhancement in the Seebeck coefficient of topological insulator / semiconductors are shown. Bi2Te3 and undoped Bi-Sb alloys are used as examples to illustrate the effect of magnetic fields. Among the two, the Bi-Sb alloy has a strong field dependence, which is shown at lower fields. To better illustrate the present invention, the Bi-Sb system is used for further demonstration.

[0069] Figure 2 Bi doped with 10 ppm Te is shown 0.88 Sb 0.12 The field dependence of the resistivity ρ, Seebeck coefficient S, and thermal conductivity κ in the alloy from 20 K to 300 K is shown. All three of these properties show strong field dependence over the entire temperature range. In particular, below 100 K, a global minimum in resistivity is observed with a plateau observed in the Seebeck coefficient. At the same time, the thermal conductivity decreases rapidly with field below 1 T and saturates above 1 T.

[0070] Figure 3 The Hall resistivity up to 2 T at various temperatures is shown, along with the resolved carrier concentration and average mobility. Hall measurements are performed simultaneously with the thermoelectric transport properties on one sample. The Hall coefficient is the slope of the Hall resistivity with respect to the magnetic field, and due to thermal excitation in the insulator, the Hall coefficient decreases gradually with temperature. The resolved carrier density is approximately 3×10 17 / cm 3 , much higher than that of undoped topological insulator Bi 0.88 Sb 0.12 , thus demonstrating the effectiveness of doping. The mobility at low temperatures reaches 60 m 2 / Vs, allowing for a very strong response of all transport properties to an external field. The effective mass is 0.008 free electron masses and the Fermi energy is 25 meV.

[0071] Figure 4Shows the field-dependent ZT. In the presence of an external magnetic field, between 80K and 100K, the highest ZT value reaches 2.3 at ~0.3T. High ZT > 2 can be obtained over a wide temperature range (from 80K to 200K). For high ZT at higher temperatures, the optimal magnetic field gradually increases from 0.3T at 80K to 1.5T at 200K. The thermoelectric parameter ZT is calculated by ZT = (S 2 / ρκ)T, where S, ρ, κ, and T are the Seebeck coefficient, electrical resistivity, thermal conductivity, and temperature, respectively.

Claims

1. A thermoelectric material, at a temperature of ≤300K under an applied magnetic field of 0.01T–2T, wherein the material comprises: – A three-dimensional topological insulator or topological semimetal – Carrier mobility ≥ 10 4 cm 2 / Vs, and –10 17 -10 20 / cm 3 carrier concentration, and – An effective mass of ≤0.04 free electron masses, and – A Fermi energy of ≤100 meV.

2. The thermoelectric material according to claim 1, wherein the thermoelectric material is a three-dimensional topological – insulator, or – A semimetal, doped with a p-type or n-type dopant.

3. The thermoelectric material according to claim 1 or 2, wherein the thermoelectric material is a three-dimensional topological insulator or three-dimensional topological semimetal selected from: Bi-Sb alloy, Bi2Te3, Bi2Se3, PbTe, SnTe, HgTe, Cd3As2, ZrTe5 and WTe2, or an alloy thereof.

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

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

3.

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

7. A method of manufacturing a thermoelectric material that exhibits a ZT value of ≥1.3, the method comprising the steps of: selecting a thermoelectric material that has a ZT of ≥0.3 when not exposed to a magnetic field of ≥0.01T, and then exposing the thermoelectric material to an external magnetic field of 0.01T - 2T at a temperature of ≤300K.

8. The method according to claim 7, wherein the thermoelectric material is a three-dimensional topological – insulator, or – A semimetal, doped with a p-type or n-type dopant.

9. The method according to claim 7 or 8, wherein the thermoelectric material is a three-dimensional topological insulator or three-dimensional topological semimetal selected from: Bi-Sb alloy, Bi2Te3, Bi2Se3, PbTe, SnTe, HgTe, Cd3As2, ZrTe5 and WTe2, or an alloy thereof.

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

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

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

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

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

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

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

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