Thermoelectric conversion material, thermoelectric conversion module, and heat flow sensor

Abstract

To provide a thermoelectric conversion material having high power generation performance at room temperature and a positive anomalous Nernst coefficient.SOLUTION: A thermoelectric conversion material according to an embodiment includes at least one of the crystal structures of MgZn2 type, MgCu2 type, and MgNi2 type, and has the anomalous Nernst effect.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a thermoelectric conversion material, a thermoelectric conversion module, and a heat flow sensor. [Background technology]

[0002] Thermoelectric conversion modules are being actively developed to utilize unused thermal energy. A well-known example of a thermoelectric conversion module is one that uses the Seebeck effect, which can generate voltage using a temperature gradient.

[0003] The Seebeck effect generates a voltage in the same direction as the temperature gradient, so thermoelectric conversion modules that utilize the Seebeck effect have a complex three-dimensional structure with π-type structures as their building blocks. This makes it difficult to make thermoelectric conversion modules that utilize the Seebeck effect large-area or film-like. Furthermore, thermoelectric conversion modules that utilize the Seebeck effect use rare materials, which poses the issue of high manufacturing costs. There are also issues with regard to toxicity.

[0004] In addition to thermoelectric conversion modules that utilize the Seebeck effect, thermoelectric conversion modules using thermoelectric conversion materials with the anomalous Nernst effect, which generates electromotive force due to the anomalous Nernst effect, have been proposed in recent years. The anomalous Nernst effect is a phenomenon in which, when a heat flow is passed through a magnetic material and a temperature difference is created, a voltage is generated in a direction perpendicular to both the magnetization direction and the temperature gradient.

[0005] The anomalous Nernst effect generates a voltage in a direction perpendicular to the temperature gradient. Therefore, a thermoelectric conversion module utilizing the anomalous Nernst effect can be deployed along the heat source, which has the advantage of making it easy to create a large surface area and a film.

[0006] For example, Patent Document 1 describes a thermoelectric conversion element having the anomalous Nernst effect, which has a Fermi energy E FThe thermoelectric conversion element is made of a ferromagnetic material having a band structure with a Weyl point in the vicinity of the ferromagnetic material, and has a thermoelectric mechanism that generates an electromotive force by the anomalous Nernst effect. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2019 / 009308 Summary of the Invention [Problem to be solved by the invention]

[0008] Materials such as Co2MnGa disclosed in Patent Document 1 exhibit high power generation performance at room temperature, but have the problem of using expensive raw materials such as Co. Therefore, there is a demand for materials that exhibit high power generation performance at room temperature. Furthermore, until now, there have been no materials with a relatively large anomalous Nernst coefficient at room temperature that has a positive sign. If there were a material with a positive anomalous Nernst coefficient, it would be possible to simplify the structure of a thermoelectric conversion module by combining it with a material with a negative sign. Therefore, there is a demand for materials with a positive anomalous Nernst coefficient.

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide a thermoelectric conversion material, a thermoelectric conversion module, and a heat flow sensor that have high power generation performance at room temperature and a positive anomalous Nernst coefficient. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention proposes the following means. <1> The thermoelectric conversion material of the first embodiment of the present invention has at least one of the crystal structures of MgZn2 type, MgCu2 type, and MgNi2 type, and has the anomalous Nernst effect. <2> A second aspect of the present invention is the thermoelectric conversion material of the first aspect, Composition formula AX 2+δA in the composition formula may be at least one element from Groups 2 to 6, X in the composition formula may be at least one element from Mn, Fe, Co, and Ni, and δ in the composition formula may be between −0.5 and 0.5. <3> A thermoelectric conversion module according to a third aspect of the present invention includes the thermoelectric conversion material according to the first or second aspect. <4> A fourth aspect of the present invention is a thermoelectric conversion module according to the third aspect, further comprising: a positive thermoelectric conversion material having a positive anomalous Nernst coefficient; a negative thermoelectric conversion material having an anomalous Nernst coefficient with a negative sign; Equipped with The positive thermoelectric conversion material may be the thermoelectric conversion material of embodiment 1 or 2. <5> A heat flow sensor according to a fifth aspect of the present invention may include the thermoelectric conversion module according to the third or fourth aspect. [Effects of the Invention]

[0011] According to the above aspects of the present invention, it is possible to provide a thermoelectric conversion material, a thermoelectric conversion module, and a heat flow sensor that have high power generation performance at room temperature and exhibit the anomalous Nernst effect with a positive anomalous Nernst coefficient. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic diagram illustrating a thermoelectric mechanism using the thermoelectric conversion element of the first embodiment. [Figure 2A] FIG. 1 is a schematic diagram showing the MgZn2-type crystal structure. [Figure 2B] 1 is a schematic diagram showing the MgCu2-type crystal structure. [Figure 2C] 1 is a schematic diagram showing a MgNi2-type crystal structure. [Figure 3] FIG. 2 is a perspective view showing the configuration of a thermoelectric conversion module 10 according to a second embodiment. [Figure 4] FIG. 10 is a plan view showing the configuration of a thermoelectric conversion module 20 according to a third embodiment. [Figure 5] FIG. 10 is a plan view showing the configuration of a thermoelectric conversion module 20A according to a fourth embodiment. [Figure 6]1 is an external view showing the configuration of a thermoelectric conversion module 40 of the present embodiment. [Figure 7] FIG. 1 is a diagram showing the results of XRD analysis of Example 1. [Figure 8] FIG. 1 is a diagram showing the results of XRD analysis of Example 2. [Figure 9] FIG. 1 is a diagram showing the results of XRD analysis of Example 3. [Figure 10] FIG. 1 is a diagram showing the results of XRD analysis of Example 4. [Figure 11] FIG. 10 is a diagram showing the results of XRD analysis of Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0013] (First embodiment) The thermoelectric conversion material, thermoelectric conversion module, and heat flow sensor according to the present embodiment will be described in detail below with reference to the drawings. The drawings used in the following description may, for convenience, show characteristic parts in a schematic manner to make the features easier to understand, and the dimensional ratios of the components may not necessarily be the same as those in reality. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited thereto. Appropriate modifications can be made within the scope of the present invention.

[0014] (Thermoelectric materials 1) First, a thermoelectric conversion material 1 according to an embodiment of the present invention and its thermoelectric mechanism will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the configuration of a thermoelectric conversion material 1 according to a first embodiment.

[0015] The shape of the thermoelectric conversion material 1 according to this embodiment is not particularly limited. For example, as shown in FIG. 1 , the shape of the thermoelectric conversion material 1 is a rectangular parallelepiped having a predetermined thickness (length in the Z direction) and extending in one direction (the Y direction). Here, for example, it is assumed that the thermoelectric conversion material 1 is magnetized in the +Z direction or that a magnetic field is applied by a magnetic field application means (not shown). When a heat flow Q (∝ -∇T) flows in the +X direction through the thermoelectric conversion material 1, a temperature difference occurs in the +X direction. As a result, an electromotive force V (∝ M × (-∇T)) is generated in the thermoelectric conversion material 1 due to the anomalous Nernst effect in the cross product direction (the Y direction) perpendicular to both the direction of the heat flow Q (the +X direction) and the direction of the magnetization M or the magnetic field application (the +Z direction). In this case, the anomalous Nernst coefficient is considered positive when an electromotive force is generated in the +Y direction.

[0016] Thermoelectric conversion material 1 has at least one of the following crystal structures: MgZn2-type, MgCu2-type, and MgNi2-type. Possessing at least one of the following crystal structures allows for a high anomalous Nernst coefficient. Furthermore, it is easier to obtain a positive sign for the anomalous Nernst coefficient. A large anomalous Nernst coefficient results from a large virtual magnetic field generated in the band structure near the Fermi energy. The above crystal structure has a relatively high crystal symmetry, similar to a cubic or hexagonal crystal. High crystal symmetry is thought to result in a high anomalous Nernst coefficient because a large virtual magnetic field occurs periodically and frequently. Furthermore, the sign of the Nernst coefficient is determined by the scattering factor, regardless of the carrier type. The main scattering mechanisms of carriers are roughly three types: phonon scattering, ionized impurity scattering, and impact ionization scattering. Among these, when the contribution of ionized impurity scattering is large, the sign of the Nernst coefficient is positive, and when the contribution of phonon scattering is large, the sign of the Nernst coefficient is negative. It is presumed that by having at least one of the above crystal structures, ionized impurity scattering becomes dominant and the sign of the anomalous Nernst coefficient becomes positive. However, the effects are not limited to these.

[0017] The crystal structure of the MgZn2-type is shown in Figure 2A, and is a hexagonal symmetric crystal structure with C14 in Strukturbericht (SB) notation and space group P63 / mmc. The crystal structure of the MgCu2-type is shown in Figure 2B, and is a cubic symmetric crystal structure with C15 in SB notation and space group Fd3m. The crystal structure of the MgNi2-type is shown in Figure 2C, and is a hexagonal symmetric crystal structure with C36 in SB notation and space group P63 / mmc.

[0018] The thermoelectric conversion material 1 is not particularly limited as long as it has at least one crystal structure of MgZn2-type, MgCu2-type, or MgNi2-type, but may have two or more crystal structures among these. However, from the viewpoint of the merits and demerits of properties depending on the crystal structure, it is preferable that it has one crystal structure. The crystal structure of the thermoelectric conversion material 1 is not particularly limited as long as it is at least one of MgZn2-type, MgCu2-type, and MgNi2-type, but from the viewpoint of high crystal symmetry, MgCu2-type is more preferable.

[0019] The above-mentioned crystal structure can be identified by X-ray diffraction (XRD) analysis. For example, a sample is collected, and XRD measurement is performed to obtain a diffraction pattern. The obtained diffraction pattern can be compared with diffraction patterns in a known database for identification. For example, the Powder Diffraction File (PDF) provided by the International Centre for Diffraction Data (ICDD) can be used as a known database.

[0020] The thermoelectric conversion material 1 has the anomalous Nernst effect. Here, the anomalous Nernst effect is a phenomenon in which, when a heat flow is passed through a magnetic material and a temperature difference occurs, a voltage is generated in a direction perpendicular to both the magnetization (magnetic field) direction and the temperature gradient. The predetermined temperature range is, for example, 20°C to 100°C. The anomalous Nernst coefficient S of the thermoelectric conversion material 1 is ANE It is preferred that the sign of is positive.

[0021] "Anomalous Nernst coefficient S ANE " Anomalous Nernst coefficient S ANE is expressed by the following formula (1). yy means the longitudinal resistance. α in Equation (1) yx means the transverse thermoelectric coefficient. σ in Eq. (1) yx means the Hall conductivity. S in equation (1) SE means the Seebeck coefficient.

[0022] Transverse thermoelectric coefficient α yx is expressed by the following equation (2). Here, ∂σ in the following equation (2) yx / ∂ε is the value at the Fermi level. k in the following equation (2) B is the Boltzmann constant. In the following formula (2), ε means energy, and e means elementary charge. In the following formula (2), T means the absolute temperature (K) of the measurement sample.

[0023] S ANE =ρ yy α yx -σ yx ρ yy S SE ···(1) α yx =-(π 2 / 3)·{(k B 2 T) / e}(∂σ yx / ∂ε) (2)

[0024] "Method for measuring the anomalous Nernst coefficient" The anomalous Nernst coefficient S of the above-mentioned thermoelectric conversion material 1 ANEis measured, for example, as follows: A sample is cut into a flat plate (length L: 8 mm, width W: 2 mm, thickness t: 1 mm). One longitudinal end of the cut sample is heated with a heater, and the other longitudinal end is brought into contact with a heat sink, creating a temperature difference along the side L of the sample. A uniform temperature gradient is applied to the rectangular sample, and the temperature difference ΔT (K) is measured at two points spaced apart by L_temp (mm). A magnetic field is applied in a direction perpendicular to this temperature difference, and the voltage (V) generated at two points spaced apart by a distance W (mm) in a direction perpendicular to both the temperature difference and the magnetic field is measured. The anomalous Nernst coefficient S ANE The anomalous Nernst coefficient S is calculated using the following formula (3) based on the obtained voltage (V). ANE is calculated from the voltage when a magnetic flux density of 2 T is applied based on the following formula (3).

[0025] S ANE =(V / ΔT)×(L_temp / W)···(3)

[0026] Thermoelectric conversion material 1 is AX 2+δ It is preferable that the composition formula is represented by the following formula: A in the composition formula is preferably composed of at least one element selected from Groups 2 to 6. By doing so, the anomalous Nernst coefficient S ANE In the composition formula, A is preferably an element other than lanthanides and actinides, and more preferably at least one of Mg, Ca, Ti, Zr, Hf, Nb, Ta, W, Sc, and Y. Among these, Zr, Hf, Sc, and Y are more preferred from the viewpoint of high crystal symmetry.

[0027] Composition formula AX 2+δ In the formula, X preferably comprises at least one of Mn, Fe, Co, and Ni. From the viewpoint of the Clarke number (which represents the proportion of elements present near the Earth's surface in weight percent), 2+δ More preferably, X in the formula is Fe.

[0028] Composition formula AX 2+δIt is preferable that δ in the formula is between -0.5 and 0.5. The stable crystal structure may change depending on the value of δ. For example, if A is Hf, when δ is greater than 0.3, the MgZn2 type structure is stable, and when δ is less than 0.3, the MgCu2 type structure is stable.

[0029] The thermoelectric conversion material 1 is preferably a Laves phase intermetallic compound. A Laves phase intermetallic compound is a type of size factor compound that is formed when the atomic radius ratio of two types of atoms (here, a large atom A and a small atom X) that make up the intermetallic compound is close to 1.225. When the thermoelectric conversion material 1 is a Laves phase intermetallic compound, it has a high anomalous Nernst coefficient S ANE Furthermore, the anomalous Nernst coefficient S ANE It is easy to make the sign of .

[0030] The thickness of the thermoelectric conversion material 1 is preferably 1.0 mm or more. By making the thickness 1.0 mm or more, the amount of current generated can be increased within a predetermined temperature range.

[0031] Thermoelectric conversion material 1 exhibiting the anomalous Nernst effect can be produced by known methods such as arc melting. Alternatively, thin films can be produced using methods such as sputtering, vacuum deposition, or chemical vapor deposition (CVD). It may be single crystal or polycrystalline. Furthermore, since it is a very stable substance, the crystals can be crushed into powder and used to produce ink. By selecting the elements A and X and adjusting the value of δ, the crystal structure of thermoelectric conversion material 1 can be at least one of MgZn2-type, MgCu2-type, and MgNi2-type crystal structures. The raw materials are prepared using the composition formula AX 2+δ By blending the components so as to satisfy the above condition, it becomes easier to obtain at least one of the crystal structures of MgZn2-type, MgCu2-type, and MgNi2-type.

[0032] The thermoelectric conversion material 1 according to the first embodiment has been described above. The thermoelectric conversion material 1 has at least one of MgZn2-type, MgCu2-type, and MgNi2-type crystal structures and has the anomalous Nernst effect, so that the sign is positive and the anomalous Nernst coefficient SANE It has.

[0033] The magnetic field applying means (not shown) is, for example, an electromagnet. In the thermoelectric conversion material 1, a magnetic field is applied by the magnetic field applying means, but if there is residual magnetization, the magnetic field applying means may not be necessary.

[0034] (Second embodiment) Next, a thermoelectric conversion module including the thermoelectric conversion material of this embodiment will be described. Fig. 3 shows the external configuration of a thermoelectric conversion module 10 according to this embodiment. The thermoelectric conversion module 10 includes a substrate 12 and a power generation body 13 placed on the substrate 12. In the thermoelectric conversion module 10, when a heat flow Q flows from the substrate 12 toward the power generation body 13, a temperature difference occurs in the power generation body 13 in the direction of the heat flow, and a voltage V is generated in the power generation body 13 due to the anomalous Nernst effect.

[0035] The substrate 12 has a first surface 12a on which the power generating body 13 is placed and a second surface 12b opposite to the first surface 12a. Heat from a heat source is applied to the second surface 12b. The material of the substrate 12 is not particularly limited as long as it can transfer heat. Examples of materials for the substrate 12 include MgO, Si, and Al2O3.

[0036] The power generating body 13 has a plurality of thermoelectric conversion elements 14 and a plurality of thermoelectric conversion elements 15, each of which has an L-shaped three-dimensional shape and is made of the above-described thermoelectric conversion material 1. As shown in Fig. 3, the plurality of thermoelectric conversion elements 14 and the plurality of thermoelectric conversion elements 15 are arranged alternately in parallel on the substrate 12 in a direction (Y direction) perpendicular to the longitudinal direction (X direction) of each of the elements. Note that the number of thermoelectric conversion elements 14 and thermoelectric conversion elements 15 constituting the power generating body 13 is not limited.

[0037] The thermoelectric conversion elements 14 and the thermoelectric conversion elements 15 are arranged such that the direction of magnetization M1 of the thermoelectric conversion elements 14 is opposite to the direction of magnetization M2 of the thermoelectric conversion elements 15. The thermoelectric conversion elements 14 and the thermoelectric conversion elements 15 have anomalous Nernst coefficients S ANEThe thermoelectric conversion elements 14 and 15 can be made of the same material as the thermoelectric conversion material 1 of the present disclosure.

[0038] One end (-Y side) of one side surface (-X side) in the longitudinal direction (Y direction) of thermoelectric conversion element 14 is defined as first end surface 14a, and the other end (+Y side) of the other side surface (+X side) is defined as second end surface 14b. The other end (+Y side) of one side surface (-X side) in the longitudinal direction (Y direction) of thermoelectric conversion element 15 is defined as first end surface 15a, and one end (-Y side) of the other side surface (+X side) is defined as second end surface 15b.

[0039] The first end surface 15a of the thermoelectric conversion element 15 is connected to the second end surface 14b of the thermoelectric conversion element 14 adjacent on the -Y side, and the second end surface 15b of the thermoelectric conversion element 15 is connected to the first end surface 14a of the thermoelectric conversion element 14 adjacent on the opposite side (+Y side). This electrically connects the multiple thermoelectric conversion elements 14 and the multiple thermoelectric conversion elements 15 in series. That is, the power generation body 13 is provided in a serpentine shape on the first surface 12a of the substrate 12. The thermoelectric conversion elements 14 and the thermoelectric conversion elements 15 are insulated from each other except for the connection points.

[0040] When heat is applied from a heat source to second surface 12b of substrate 12, heat flow Q flows in the +Z direction toward power generator 13. When a temperature difference occurs due to heat flow Q, an electromotive force E1 is generated in thermoelectric conversion element 14 in a direction (+Y direction) perpendicular to both the direction of magnetization M1 (-X direction) and the direction of heat flow Q (+Z direction) due to the anomalous Nernst effect. In thermoelectric conversion element 15, an electromotive force E2 is generated in a direction (-Y direction) perpendicular to both the direction of magnetization M2 (+X direction) and the direction of heat flow Q (+Z direction) due to the anomalous Nernst effect.

[0041] As described above, the thermoelectric conversion elements 14 and 15 arranged in parallel are electrically connected in series, so that the electromotive force E1 generated in one thermoelectric conversion element 14 can be applied to the adjacent thermoelectric conversion element 15. Furthermore, since the electromotive force E1 generated in one thermoelectric conversion element 14 and the electromotive force E2 generated in the adjacent thermoelectric conversion element 15 are in opposite directions, the electromotive forces of the adjacent thermoelectric conversion elements 14 and 15 are added together, and the output voltage V can be increased.

[0042] As a modification of the thermoelectric conversion module 10 shown in FIG. 3, the adjacent thermoelectric conversion elements 14 and 15 have anomalous Nernst coefficients S ANE and a configuration in which the plurality of thermoelectric conversion elements 14 and the plurality of thermoelectric conversion elements 15 are arranged so that their magnetization directions are the same (i.e., so that the direction of magnetization M1 and the direction of magnetization M2 are the same).

[0043] For example, the anomalous Nernst coefficient S ANE The thermoelectric conversion material 1 described above can be used as a thermoelectric conversion material in which the sign of is positive (hereinafter, sometimes referred to as a "positive thermoelectric conversion material").

[0044] In addition, the anomalous Nernst coefficient S ANE As a thermoelectric conversion material in which the sign of is negative (hereinafter, sometimes referred to as a "negative thermoelectric conversion material"), known thermoelectric conversion materials can be used. Examples of negative thermoelectric conversion materials include Co2MnGa, Fe3Ga, Fe3Al, and Fe3Sn.

[0045] (Third embodiment) Next, a thermoelectric conversion module 20 according to a third embodiment will be described. Fig. 4 shows a plan view of the thermoelectric conversion module 20 according to this embodiment. The thermoelectric conversion module 20 has a power generating body 23, and the anomalous Nernst coefficient S ANE The thermoelectric conversion element 24 has a plurality of rectangular parallelepiped thermoelectric conversion elements 24. Each thermoelectric conversion element 24 is made of the thermoelectric conversion material 1 described above.

[0046] The thermoelectric conversion elements 24 are arranged in parallel on the substrate 22 so that the direction of magnetization M is the same (Y direction) in a direction (Y direction) perpendicular to the longitudinal direction (X direction). One end (+X side) of a thermoelectric conversion element 24 is connected to the other end (-X side) of an adjacent thermoelectric conversion element 24 on the -Y side by copper wiring 26, so that the thermoelectric conversion elements 24 are electrically connected in series. Examples of materials for the substrate 22 include MgO, Si, and Al2O3, but are not particularly limited.

[0047] The heat flow is from the substrate 22 side toward the power generation body 23 (in the +Z direction). The thermoelectric conversion module 20 has a configuration in which adjacent thermoelectric conversion elements 24 are connected via copper wiring 26, and therefore can be manufactured more easily than the thermoelectric conversion module 10 shown in FIG.

[0048] (Fourth embodiment) Next, a thermoelectric conversion module 20A according to a fourth embodiment will be described. Fig. 5 shows a plan view of the thermoelectric conversion module 20A according to this embodiment. The thermoelectric conversion module 20A has a power generating element 23A having a positive anomalous Nernst coefficient S ANE and a plurality of rectangular parallelepiped thermoelectric conversion elements 24A having a negative anomalous Nernst coefficient S ANE The thermoelectric conversion element 24A has a plurality of rectangular parallelepiped thermoelectric conversion elements 24B each having a thickness of 1000 Å. The thermoelectric conversion element 24A is made of the above-mentioned thermoelectric conversion material 1. The thermoelectric conversion element 24B may be made of Co2MnGa, Fe3Ga, Fe3Al, Fe3Sn, or the like.

[0049] The plurality of thermoelectric conversion elements 24A and the plurality of thermoelectric conversion elements 24B are arranged in parallel on the substrate 22 so that the direction of magnetization M is the same (+Y direction) in a direction (Y direction) perpendicular to the longitudinal direction (X direction). One end (+X side) of the thermoelectric conversion element 24A is connected to one end (+X side) of the thermoelectric conversion element 24B adjacent to it on the -Y side by copper wiring 26, and the other end (-X side) of the thermoelectric conversion element 24B is connected to the other end (-X side) of the thermoelectric conversion element 24A adjacent to it on the -Y side by copper wiring 26, thereby electrically connecting the plurality of thermoelectric conversion elements 24A and the plurality of thermoelectric conversion elements 24B in series. Examples of materials for the substrate 22 include, but are not limited to, MgO, Si, and Al2O3.

[0050] The heat flow is from the substrate 22 side toward the power generation body 23 (in the +Z direction). The thermoelectric conversion module 20 has a configuration in which adjacent thermoelectric conversion elements 24A and 24B are connected via copper wiring 26, and therefore can be manufactured more easily than the thermoelectric conversion module 20 shown in FIG.

[0051] (Fifth embodiment) 6 shows the external configuration of a thermoelectric conversion module 40 according to this embodiment. The thermoelectric conversion module 40 includes a hollow member 42 and a long sheet-like (tape-like) thermoelectric conversion element 44 that is wrapped around and covers the outer surface of the hollow member 42. The thermoelectric conversion element 44 is made of the thermoelectric conversion material 1 described above.

[0052] The magnetization of the thermoelectric conversion element 44 is parallel to the longitudinal direction (X direction) of the hollow member 42. When a heat flow occurs from the inside to the outside of the hollow member 42 and a temperature gradient occurs due to the heat flow, a voltage V is generated along the longitudinal direction of the long thermoelectric conversion element 44 (a direction perpendicular to the direction of magnetization and the direction of heat flow) due to the anomalous Nernst effect.

[0053] In the thermoelectric conversion module 40 of FIG. 6, instead of the long sheet-like thermoelectric conversion elements 44, a configuration in which wire thermoelectric conversion elements are wound around the hollow member 42 may be employed.

[0054] 3 to 6, if the longitudinal length of the thermoelectric conversion element is L and the thickness (height) is H, the voltage generated by the anomalous Nernst effect is proportional to L / H. In other words, the longer and thinner the thermoelectric conversion element, the greater the generated voltage. Therefore, by using a power generator in which multiple thermoelectric conversion elements are electrically connected in series, or a wire or long sheet-shaped thermoelectric conversion element, it is possible to expect an improvement in the anomalous Nernst effect.

[0055] The thermoelectric conversion modules shown in Figures 3 to 6 can be used in a variety of applications, particularly in the temperature range from room temperature to several hundred degrees Celsius, as a standalone power source or heat flow sensor for Internet of Things (IoT) sensors.

[0056] For example, by applying the thermoelectric conversion module of this embodiment to a heat flow sensor, it is possible to determine the quality of the thermal insulation performance of a building. Furthermore, by installing a thermoelectric conversion module in the exhaust system of an automobile or the like, it is possible to generate electricity using the heat (waste heat) of the exhaust gas, and the thermoelectric conversion module can be effectively used as an auxiliary power source. Furthermore, by arranging heat flow sensors in a mesh pattern on the wall surface of a space, it is possible to spatially recognize heat flows and heat sources. This is expected to be applied, for example, to high-precision temperature control for high-density crop cultivation and livestock breeding, and as a driver detection system for autonomous driving. Furthermore, heat flow sensors can also be used in indoor air conditioning management and deep body temperature management in medicine. Furthermore, by making the thermoelectric conversion element of this embodiment into a powder or paste, it is expected to be applicable to a wide range of fields.

[0057] In this embodiment, attention is focused on the voltage generated by the anomalous Nernst effect, but it is possible to increase the output voltage through the synergistic effect of the voltage generated by the Seebeck effect due to the temperature gradient, the Hall effect generated based on the voltage created by the Seebeck effect, and the voltage generated by the anomalous Nernst effect.

[0058] The thermoelectric conversion module of this embodiment can also be given a function of temperature modulation (particularly cooling) by supplying power, like a Peltier element.

[0059] The technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. In addition, the components in the above-described embodiments can be replaced with well-known components as appropriate, and the above-described modifications can be combined as appropriate, without departing from the spirit of the present invention. [Example]

[0060] The effects of the present invention will be made clearer by the following examples. Note that the present invention is not limited to the following examples and can be practiced with appropriate modifications within the scope of the present invention.

[0061] Example 1 Tablet-shaped Zr (purity 99.2%) and needle-shaped Fe (purity 99.9%) were weighed in a 1:2 molar ratio and melted in a small arc melting furnace (ACM-C01P) manufactured by Daia Vacuum Co., Ltd. to obtain a ZrFe2 ingot. After melting with an arc current of 150 A, the current was reduced to 0 A within 5 seconds and the ingot was rapidly cooled to produce the ingot. The XRD analysis results shown in Figure 7 confirmed that the ingot had an MgCu2-type crystal structure.

[0062] Example 2 Sponge-like Hf (98% purity) and needle-like Fe (99.9% purity) were weighed in a 1:2 molar ratio and melted in a small arc melting furnace (ACM-C01P) manufactured by Daia Vacuum Co., Ltd. to obtain an HfFe2 ingot. After melting with an arc current of 150 A, the current was reduced to 0 A within 5 seconds and the ingot was rapidly cooled to produce the ingot. The XRD analysis results shown in Figure 8 confirmed that the ingot had an MgCu2-type crystal structure.

[0063] Example 3 Sponge-like Hf (98% purity) and needle-like Fe (99.9% purity) were weighed in a 1:2 molar ratio and melted in a small arc melting furnace (ACM-C01P) manufactured by Daia Vacuum Co., Ltd. to obtain an HfFe2 ingot. After melting with an arc current of 150 A, the current was slowly reduced to 0 A over 30 seconds, and the ingot was slowly cooled to produce an ingot. The XRD analysis results shown in Figure 9 confirmed the presence of two types of crystal structures: MgCu2 and MgZn2.

[0064] Example 4 Sponge-like Hf (purity 98%) and needle-like Fe (purity 99.9%) were weighed in a molar ratio of 1:2.33 and melted in a small arc melting furnace (ACM-C01P) manufactured by Daia Vacuum Co., Ltd. to produce HfFe 2.33 An ingot of 150 A was obtained. After melting with an arc current of 150 A, the current was slowly reduced to 0 A over 30 seconds, and the ingot was slowly cooled to produce an ingot. The XRD analysis results shown in Figure 10 confirmed that the ingot had an MgZn2-type crystal structure.

[0065] Example 5 Tablet-shaped Zr (purity 99.2%) and needle-shaped Fe (purity 99.9%) were weighed in a molar ratio of 1:2.33 and melted in a small arc melting furnace (ACM-C01P) manufactured by Daia Vacuum Co., Ltd. to produce ZrFe 2.33 An ingot of 150 A was obtained. After melting with an arc current of 150 A, the current was slowly reduced to 0 A over 30 seconds, and the ingot was slowly cooled to produce an ingot. The XRD analysis results shown in Figure 11 confirmed that the ingot had an MgCu2-type crystal structure.

[0066] (Comparative Example 1) Co, Mn, and Ga were weighed in a 2:1:1 molar ratio and melted in an arc furnace to obtain a Co2MnGa polycrystalline ingot. The resulting polycrystalline ingot was then melted again in the arc furnace, and a tungsten rod was placed in contact with the molten liquid to grow a single crystal by the pulling method. XRD analysis confirmed that the material had a full Heusler structure with an L21 cubic crystal structure.

[0067] <XRD Measurement> For each of Examples 1 to 5, XRD measurements were performed at an interval of 0.02°, and the above results were obtained. The apparatus and conditions used were as follows. Apparatus: Rigaku fully automatic multi-purpose X-ray diffractometer SmartLab SE X-ray source: CuKα Accelerating voltage: 40 kV Current: 50 mA Kβ cut-off method: Ni filter

[0068] <Evaluation of Anomalous Nernst Coefficient> A sample in the shape of a flat plate (length L = 8 mm, width W = 2 mm, thickness t = 1 mm) was cut out from an ingot obtained in an arc furnace, and the two surfaces of L×W and the two surfaces of L×t were mirror-polished to obtain a sample for evaluation. One end in the length direction of the sample was heated with a heater, and a heat sink was brought into contact with the other end in the length direction to create a temperature difference in the length direction of the sample. The temperature difference was set to 3 to 7 K. The evaluation temperatures are summarized in Table 1. The evaluation temperatures were in the range of room temperature (20 to 35°C). Along the length L direction on the sample, temp thermocouples were installed at two points separated by about L (4 mm), the temperature difference ΔT was measured, a magnetic field with a magnetic flux density of -2T to 2T was applied in the thickness t direction, the voltage V generated between two points of the width W was measured, and the anomalous Nernst coefficient S ANE was calculated from the above formula (3).

[0069] Anomalous Nernst coefficient S ANE was calculated based on the above formula (3) from the voltage when a magnetic flux density of 2T was applied. The anomalous Nernst coefficients S of Examples 1 to 5 ANE are shown in Table 1. The anomalous Nernst coefficients S of Examples 1 to 5 ANE had a positive sign, and their absolute values were 0.3 μV / K or more. Therefore, it was found that the thermoelectric conversion module using the thermoelectric conversion material showing the anomalous Nernst effect of the examples exhibited excellent power generation performance at room temperature. On the other hand, the thermoelectric conversion material of Comparative Example 1 did not have at least one of the crystal structures of the MgZn2 type, MgCu2 type, and MgNi2 type, so the sign of the anomalous Nernst coefficient was negative.

[0070] [Table 1] [Explanation of symbols]

[0071] 1 thermoelectric conversion material, 10 thermoelectric conversion module, 12 substrate, 13 power generation body, 14 thermoelectric conversion element, 15 thermoelectric conversion element, 20, 20A thermoelectric conversion module, 22 substrate, 23, 23A power generation body, 24, 24A, 24B thermoelectric conversion element, 40 thermoelectric conversion module, 42 hollow member, 44 thermoelectric conversion element

Claims

1. MgZn ２ Mold, MgCu ２ Mold, MgNi ２ A thermoelectric conversion material having at least one crystal structure of the type and exhibiting the anomalous Nernst effect.

2. Composition formula AX ２＋δ is expressed as In the composition formula, A is composed of at least one element from Groups 2 to 6, In the composition formula, X is at least one of Mn, Fe, Co, and Ni, 2. The thermoelectric conversion material according to claim 1, wherein δ in the composition formula is −0.5 or more and 0.5 or less.

3. A thermoelectric conversion module comprising the thermoelectric conversion material according to claim 1 or 2.

4. a positive thermoelectric conversion material having a positive anomalous Nernst coefficient; a negative thermoelectric conversion material having an anomalous Nernst coefficient with a negative sign; Equipped with The thermoelectric conversion module according to claim 3 , wherein the positive thermoelectric conversion material is the thermoelectric conversion material.

5. A heat flow sensor comprising the thermoelectric conversion module according to claim 3 .

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