Method of manufacturing anomalous nernst effect element, and method of manufacturing thermoelectric conversion device

Abstract

To provide a method of manufacturing an anomalous Nernst effect element, with which an anomalous Nernst effect element that exhibits an excellent anomalous Nernst effect can be easily manufactured and an increase in capacity can be also achieved easily, and a method of manufacturing a thermoelectric conversion device using the same.SOLUTION: There is provided a method of manufacturing an anomalous Nernst effect element, including a step of sintering powder containing Co, Mn and Ga using a hot press method to prepare a sintered body. There is also provided a method of manufacturing a thermoelectric conversion device, including a step of manufacturing an anomalous Nernst effect element by the method of manufacturing an anomalous Nernst effect element.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing an anomalous Nernst effect element and a method for manufacturing a thermoelectric conversion device. [Background technology]

[0002] As a thermoelectric conversion device that generates a voltage based on a temperature gradient, one that utilizes the Seebeck effect is well known. In the Seebeck effect, a voltage is generated in the same direction as the temperature gradient, so thermoelectric conversion devices have a complex three-dimensional structure, making it difficult to make them large-area or film-like. In addition, they use highly toxic and rare materials, which make them brittle and vulnerable to vibration, and they also have high manufacturing costs.

[0003] In recent years, thermoelectric conversion devices have been proposed that use anomalous Nernst effect elements that generate electromotive force due to the anomalous Nernst effect. The anomalous Nernst effect is a phenomenon in which, when a heat flow is passed through a magnetic material, causing a temperature difference, a voltage is generated in a direction perpendicular to both the magnetization direction and the temperature gradient. Unlike the Seebeck effect, the anomalous Nernst effect generates a voltage perpendicular to the temperature gradient, so that a thermoelectric conversion device using the anomalous Nernst effect can be deployed along the heat source, which is advantageous for making it large-area and film-like. Furthermore, it is possible to select materials that are inexpensive, less toxic, and highly durable.

[0004] The indices for evaluating the anomalous Nernst effect are the anomalous Nernst coefficient, thermal conductivity, and electrical resistivity, as well as the dimensionless figure of merit ZT and power factor calculated from these.

[0005] The anomalous Nernst coefficient represents the thermoelectric voltage per Kelvin of temperature difference. The anomalous Nernst coefficient is expressed by the following equation (1). S ANE =ρ yy α yx -σyx ρ yy S SE …(1) S ANE : Anomalous Nernst coefficient ρ yy : Vertical resistance α yx : Transverse thermoelectric coefficient σ yx : Hall conductivity S SE : Seebeck coefficient

[0006] Transverse thermoelectric coefficient α yx is expressed by the following equation (2) (Mott's equation). α yx =-(π 2 / 3)·{(k B 2 T) / e}(∂σ yx / ∂ε) …(2) However, ∂σ yx / ∂ε is the value at the Fermi level. k B :Boltzmann constant ε: Energy e: elementary charge T: Absolute temperature

[0007] The dimensionless figure of merit ZT is expressed by the following formula (3). ZT=(S ANE 2 σ xx / κ yy )·T={S ANE 2 / (ρ xx ·κ yy )}·T …(3) σ xx : Electrical conductivity κ yy : Thermal conductivity ρ xx : Electrical resistivity

[0008] The anomalous Nernst effect has been reported in various materials such as Co2MnGa, Fe3Ga, Fe3Al, Mn3Ge, Mn3Sn, Mn2Ga, MnGe, Co, Fe, Nd2Mo2O7, Pt / Fe multilayer films, and L1-FePt alloys (see, for example, Non-Patent Documents 1 to 3 below). Among these materials, the one with the highest absolute value of the anomalous Nernst coefficient at present is Co2MnGa, with the highest reported data being 6.75-8μV / K. Note that these values ​​are for single crystals.

[0009] Although the above-mentioned anomalous Nernst effect has advantages over the Seebeck effect, the current amount of power generated by the anomalous Nernst effect using ordinary magnetic materials is still too small for full-scale practical use. Therefore, Patent Document 1 proposes a thermoelectric conversion element (anomalous Nernst effect element) made of Co2MnGa with a band structure having a Weyl point near the Fermi energy, as a material that produces a larger anomalous Nernst effect than ever before. The crystal structure of this Co2MnGa is a single crystal of the cubic system, and has a full Heusler system crystal structure.

[0010] On the other hand, in Patent Document 2, a Co2MnGa sintered body having an anomalous Nernst coefficient of 6.68 μV / K is produced by a spark plasma sintering (SPS) method. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. 2019 / 009308 [Patent Document 2] Patent Publication No. 2023-2425 [Non-patent literature]

[0012] [Non-Patent Document 1] Nature, 581(2000), 53 [Non-Patent Document 2] Nature physics, 14(2018), 1119 [Non-Patent Document 3] PHYSICAL REVIEW B, 101(2020), 180404(R) Summary of the Invention [Problem to be solved by the invention]

[0013] The thermoelectric conversion element described in the above Patent Document 1 exhibits excellent transverse thermoelectric power. However, when pulling up a single crystal of Co2MnGa, it takes time and power to raise the temperature to the melting point, and it also takes time to grow the crystal, so the manufacturing cost is high. In addition, since it is impossible to grow a single crystal of Co2MnGa near net, it needs to be cut, and shaping is also costly.

[0014] On the other hand, the SPS method used in Patent Document 2 is a method in which powder is filled into an electrically conductive mold, pressure is applied from above and below, and electricity is passed through, and the driving force for sintering is electromagnetic energy from the current and discharge energy from self-heating, in addition to pressure and temperature. This makes it possible to increase temperature quickly, sinter quickly, and sinter in a short time. However, because the SPS method is a relatively new and specialized method, the introduction of equipment into companies has not progressed much, and the production of large-volume sintered bodies using the SPS method is still in its infancy.

[0015] The present invention has been made in consideration of the above circumstances, and has an object to provide a method for easily manufacturing an anomalous Nernst effect element that exhibits an excellent anomalous Nernst effect and that can easily be made large-capacity, and a method for manufacturing a thermoelectric conversion device using the same. [Means for solving the problem]

[0016] In order to achieve the above object, the present invention provides the following means. [1] A method for manufacturing an anomalous Nernst effect element, comprising the step of sintering a powder containing Co, Mn, and Ga by a hot press method to produce a sintered body. [2] The method for producing an anomalous Nernst effect element according to [1], wherein in the above step, the sintering temperature is 700°C or higher and 1100°C or lower. [3] The method for producing an anomalous Nernst effect element according to [1] or [2], wherein in the step, the applied pressure is 30 MPa or more and 130 Pa or less. [4] The method for producing an anomalous Nernst effect element according to any one of [1] to [3], wherein in the step, the sintering time is 24 hours or less. [5] The method for producing an anomalous Nernst effect element according to any one of [1] to [4], wherein the sintered body has crystal grains containing Co, Mn and Ga. [6] The method for manufacturing the anomalous Nernst effect element according to [5], wherein the crystal grains have a Heusler structure. [7] The method for producing an anomalous Nernst effect element according to [5] or [6], wherein the average grain size of the crystal grains is 8 μm or more and 30 μm or less. [8] The method for producing an anomalous Nernst effect element according to any one of [5] to [7], wherein the standard deviation of the grain size of the crystal grains is 1 μm or more and 12 μm or less. [9] The method for producing an anomalous Nernst effect element according to any one of [1] to [8], wherein the absolute value of the anomalous Nernst coefficient of the sintered body is 5 μV / K or more at 300 K.

[10] A method for producing a thermoelectric conversion device, comprising the step of producing an anomalous Nernst effect element by the method for producing an anomalous Nernst effect element according to any one of [1] to [9]. Effect of the Invention

[0017] According to the present invention, it is possible to provide a method for easily manufacturing an anomalous Nernst effect element that exhibits an excellent anomalous Nernst effect and that can easily increase the capacity, and a method for manufacturing a thermoelectric conversion device using the same. [Brief description of the drawings]

[0018] [Figure 1] 1 is an SEM image of the sintered body of Example 3. [Diagram 2] FIG. 4 is a crystal grain size analysis image of the SEM image of FIG. 3. [Diagram 3] FIG. 1 is a schematic diagram showing the crystal structure of Co2MnGa. [Figure 4] 1 is a schematic perspective view showing a configuration of a thermoelectric conversion device according to a first embodiment. [Diagram 5] FIG. 4 is a schematic perspective view showing the configuration of a thermoelectric conversion device according to a second embodiment. [Figure 6] FIG. 11 is a schematic perspective view showing the configuration of a thermoelectric conversion device according to a third embodiment. [Figure 7] FIG. 11 is a schematic plan view showing the configuration of a thermoelectric conversion device according to a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In addition, the drawings used in the following description may show characteristic parts in a schematic manner for the sake of convenience in order to make the characteristics easier to understand, and the dimensional ratios of each component may not necessarily be the same as in reality. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited to them, and may be appropriately modified and implemented within the scope of the present invention.

[0020] In a manufacturing method of an anomalous Nernst effect element according to an embodiment of the present invention, a powder (raw material powder) containing Co, Mn, and Ga is sintered by hot pressing to produce a sintered body.

[0021] A "sintered body" refers to a material in which raw material powder is sintered at a temperature lower than the material's inherent melting point. Sintered bodies are generally produced by forming raw material powder in a mold and sintering it under atmospheric pressure or under pressure. Sintered bodies are classified as polycrystalline bodies. When a material is heated to a temperature higher than its melting point using the single crystal growth method to become molten, and then rapidly cooled, the atomic arrangement cannot be regularized in time, resulting in a polycrystalline product. This product also falls under the category of polycrystalline bodies, but is not called a sintered body.

[0022] The raw material powder is not particularly limited as long as it contains Co, Mn, and Ga, and may contain other elements such as Fe, Ni, Si, C, O, and N. In particular, a powder of Co2MnGa is preferable. The sintering by the hot pressing method can be carried out using a known hot pressing device. In the hot pressing method, the raw material powder is filled into a mold and heated together with the mold while applying pressure in one axial direction, resulting in a high-density sintered body. The mold may be, for example, a carbon mold. For heating, various heaters such as a resistance heating type and a high-frequency induction heating type can be used. The sintering atmosphere is generally an inert gas atmosphere such as Ar or N2. In order to produce a high-density sintered body, it is preferable that the sintering temperature is high and that the pressure applied during sintering is large.

[0023] The sintering temperature is preferably 700° C. or higher, more preferably 750° C. or higher, even more preferably 800° C. or higher, and particularly preferably 850° C. or higher. By setting the sintering temperature to 750° C. or higher, sintering can be continued until the final sintering, the sintered density is improved, and a high-density sintered body can be produced.

[0024] On the other hand, the sintering temperature is preferably 1100°C or less, and more preferably 1050°C or less. By setting the sintering temperature to 1100°C or less, evaporation of elements can be suppressed and composition deviation can be prevented. In addition, since it is below the melting point, abnormal grain growth due to melt can be suppressed. Furthermore, when sintering is performed in a carbon mold, seepage from the mold during sintering can be suppressed. Furthermore, since sintering is a reaction below the melting point, there is no need to raise the temperature until the inside becomes molten, and power consumption and sintering time can be suppressed. The above lower limit value and the above upper limit value can be combined as appropriate.

[0025] The applied pressure is preferably 30 MPa or more, more preferably 40 MPa or more, even more preferably 50 MPa or more, and most preferably 55 MPa or more. By setting the applied pressure to the above lower limit or more, the sintering density can be increased to suppress the generation of voids, and the crystal grain size can be increased.

[0026] On the other hand, the applied pressure is preferably 130 MPa or less, more preferably 120 MPa or less, further preferably 110 MPa or less, and most preferably 105 MPa or less. By keeping the applied pressure below the upper limit, damage to the mold during hot press sintering can be prevented, and the crystal grain size can be prevented from becoming too large. The upper limit value and the lower limit value can be combined as appropriate.

[0027] The sintering time is preferably 24 hours or less, more preferably 20 hours or less, even more preferably 16 hours or less, and particularly preferably 14 hours or less. By setting the sintering time to 24 hours or less, abnormal grain growth can be suppressed. In addition, power consumption can also be suppressed.

[0028] On the other hand, the sintering time is preferably 0.5 hours or more, and more preferably 1 hour or more. By setting the sintering time to the above-mentioned time or more, the sintering can be completed up to the final sintering. The upper limit value and the lower limit value can be combined as appropriate.

[0029] After sintering, the obtained sintered body may be subjected to processing such as cutting, machining, polishing, milling, etc.

[0030] The sintered body obtained by the manufacturing method of this embodiment is a magnetic body containing Co, Mn, and Ga, and can be used as an anomalous Nernst effect element. The sintered body typically has crystal grains containing Co, Mn, and Ga.

[0031] An example of a sintered body is shown in Figures 1 and 2. Figure 1 is a scanning electron microscope (SEM) image by secondary electrons of the surface of a sintered body produced in Example 3 (sintering temperature 1000°C) described later. Figure 2 is a crystal grain size analysis image of the SEM image of Figure 1. In the crystal grain size analysis image, the crystal grains in the SEM image are distinguished by image processing. The sintered body of this example is composed of a large number of crystal grains, as shown in FIGS.

[0032] From the viewpoint of the electronic structure derived from the crystal structure, the crystal grains preferably have a Heusler structure, and more preferably have a full Heusler structure of an L21 type cubic crystal made of Co2MnGa as shown in FIG. The unit cell of the L21 structure consists of four face-centered cubic (fcc) lattices, as shown in Figure 3, with Co atoms at (1 / 4, 1 / 4, 1 / 4) and (3 / 4, 3 / 4, 3 / 4), Mn atoms at (0, 0, 0), and Ga atoms at (1 / 2, 1 / 2, 1 / 2) in the lattice coordinates. The crystal structure can be determined by various diffraction methods, such as X-ray diffraction.

[0033] The average grain size of the crystal grains is preferably 8 μm or more, more preferably 10 μm or more, and even more preferably 12 μm or more. By making the average grain size of the crystal grains 8 μm or more, the following phenomenon is suppressed, and the anomalous Nernst coefficient of the entire sintered body is less likely to decrease. That is, a sintered body is composed of crystal grains and grain boundaries that exist between the grains. Grain boundaries are spaces where the orientation of crystal grains changes, and because the elemental arrangement is disturbed, the elemental composition of the crystal grains near the grain boundaries deviates from the Co2MnGa composition. This portion where the composition is shifted is composed of a material with a low anomalous Nernst coefficient, and the anomalous Nernst coefficient is locally reduced in that portion only. Therefore, the anomalous Nernst coefficient of the entire sintered body is ultimately reduced. Grain boundaries have these negative effects, but by setting the average grain size of the crystal grains to 8 μm or more, these negative effects can be reduced; the increase in grain boundaries is suppressed; the number of parts with low anomalous Nernst coefficients does not increase; and the anomalous Nernst coefficient of the entire sintered body is less likely to decrease.

[0034] On the other hand, the average grain size of the crystal grains is preferably 30 μm or less, and more preferably 26 μm or less. By setting the average grain size to 30 μm or less, there is no need to cause abnormal grain growth, and therefore there is less need to raise the sintering temperature above the melting point or to extend the sintering time. This reduces the possibility that the composition of the sintered body will deviate from that of the raw material powder. It also reduces the time required for production and power consumption. The upper limit value and the lower limit value can be combined as appropriate.

[0035] The standard deviation of the grain size of the crystal grains is preferably 1 μm or more, and more preferably 6 μm or more. By making the standard deviation of the grain size of the crystal grains 1 μm or more, the need to keep the standard deviation of the grain size of the raw material powder very small is reduced, and manufacturing processes such as pulverization and precision classification can be omitted, thereby simplifying the process.

[0036] On the other hand, the standard deviation of the grain size is preferably 12 μm or less, and more preferably 11 μm or less. By making the standard deviation of the grain size 12 μm or less, abnormal grain growth can be suppressed. In addition, the sintering temperature is not too high and the sintering time is not too long, so that power consumption can be suppressed and production efficiency can be improved. Furthermore, by setting the appropriate sintering temperature and sintering time, the possibility that the composition of the sintered body will deviate from that of the raw material powder can be suppressed. The upper limit value and the lower limit value can be combined as appropriate.

[0037] The grain size of the crystal grains is measured by mirror-polishing the surface of the sintered body and then observing it with a SEM.

[0038] Specifically, first, the surface of the sintered body is roughly polished with #800 waterproof abrasive paper, then it is medium polished with a 1 μm alumina suspension, and further mirror polished with a 0.3 μm alumina suspension. The particle size of the waterproof abrasive paper and the alumina in the alumina suspension used during polishing are not necessarily limited to these. Also, if sufficient mirror polishing has been completed, the above-mentioned mirror polishing does not need to be performed. On the other hand, after the above-mentioned mirror polishing, flat milling may be further performed. Next, the surface of the sintered body is observed using secondary electrons and backscattered electrons from an SEM. A total of six images are taken at a magnification of 500 times for each sample, and the grain size is measured by analyzing each image.

[0039] For the crystal grains of the sintered body, SEM observation images are taken using secondary electrons and backscattered electrons, and then the SEM images are used to calculate the average grain size and standard deviation of the grain size. Specifically, one SEM image is divided into individual grains for each pixel. At this time, grains around the edges of the image are removed. The area of ​​each divided grain is calculated using image processing, and a circle with an area equal to that of each grain is determined. For one sample, the average grain size and standard deviation of the grain size are calculated from the diameters of all circles in the six SEM images measured, excluding the circles near the edges of the images.

[0040] The theoretical density of single crystal Co2MnGa (8.39 g / cm 3 ) vs. density of sintered body (g / cm 3 ) (hereinafter also referred to as relative density) is preferably 86% or more, more preferably 90% or more, and even more preferably 95% or more. When the relative density is equal to or more than the lower limit, the anomalous Nernst coefficient tends to be better. The upper limit of the relative density of the sintered body 2 is not particularly limited, but is, for example, 110%, taking into account the effect of measurement error.

[0041] The density of the sintered body is determined by Archimedes' method. Specifically, the mass A of the sample in air is weighed using a weighing scale. Next, the sample is submerged in pure water, and the reading on the weighing scale at that time is taken as B. The mass of the sample is A, and according to Archimedes' law, (AB) is the volume of the sample. Therefore, {A / (AB)} x 100(%) is the density of the sintered body.

[0042] The value calculated by (100-relative density) (%) can be regarded as the porosity of the sintered body. For example, a sintered body with a relative density of 80% has a porosity of 20%.

[0043] Anomalous Nernst coefficient S of sintered bodies ANE From the viewpoint of thermoelectric conversion efficiency, the absolute value of is preferably 5 μV / K or more at 300 K, and more preferably 5.5 μV / K or more.

[0044] Anomalous Nernst coefficient S of sintered bodies ANE is measured as follows: A flat sample (e.g., length L = 8 mm, width W = 1.5 mm, thickness t = 1 mm) is cut out from the sintered body. One end of the sample in the longitudinal direction is heated with a heater, and the other end is brought into contact with a heat sink, creating a temperature difference along the longitudinal direction of the sample. This creates a uniform temperature gradient in the rectangular sample, and the temperature difference ΔT (K) at two points separated by L_temp is measured. A magnetic field of 2 Tesla is applied in a direction perpendicular to the direction of this temperature difference, and the voltage V generated at two points separated by a distance W in a direction perpendicular to both the temperature difference and the magnetic field is measured, and the anomalous Nernst coefficient S is calculated using the following equation (4). ANE Calculate the value of S ANE =(V / ΔT)×(L_temp / W) …(4)

[0045] Electrical resistivity ρ of sintered body xx From the viewpoint of improving the dimensionless figure of merit ZT and suppressing the internal resistance of the thermoelectric device, the dielectric constant is preferably 200 μΩ·cm or less at 300 K, and more preferably 150 μΩ·cm or less.

[0046] Electrical resistivity ρ of sintered body xx is the anomalous Nernst coefficient S ANE The same sample used for the measurement is measured by the four-terminal method.

[0047] From the viewpoint of improving the dimensionless figure of merit ZT, the thermal conductivity κ of the sintered body is preferably 50 W / Km or less at 300 K, and more preferably 35 W / Km or less.

[0048] The thermal conductivity κ of a sintered body is determined by the anomalous Nernst coefficient S ANE and electrical resistivity ρ xx It can be determined by applying a pulse of heat to one end of the same sample used in the measurement of , and analyzing the relaxation process of the temperature difference generated in the sample. The direction of the heat flow when measuring the thermal conductivity κ is the same as that of the electrical resistivity ρ xx The direction of the current shall be the same as that applied when measuring the

[0049] The dimensionless figure of merit ZT of the sintered body is preferably 0.01% or more at 300K, and more preferably 0.03% or more, from the viewpoint of thermoelectric conversion efficiency.

[0050] The dimensionless figure of merit ZT of a sintered body is calculated by multiplying the anomalous Nernst coefficient S ANE , electrical resistivity ρ xx , and the thermal conductivity κ, according to the above formula (3).

[0051] In the manufacturing method of the anomalous Nernst effect element of this embodiment, an anomalous Nernst effect element exhibiting an anomalous Nernst effect equivalent to that of a single crystal exhibiting a high anomalous Nernst coefficient can be manufactured by sintering, which is a more general and easier method than growing a single crystal. Since there is no need to raise the temperature above the melting point during production of sintered bodies, it requires less power and time than single crystal growth, and the required high temperature holding time is also shorter. In addition, sintered bodies can be near-net sintered, which is expected to reduce costs for shaping. Furthermore, among various known sintering methods, the hot press method is an established and highly reliable method for sintering under pressure, and sintering equipment using the hot press method is widely available in companies. Therefore, the hurdle for practical use is lower than that of SPS. In addition, the hot press method can produce sintered bodies with a larger capacity (for example, 500 x 500 x 500 mm) than can be produced by the spark plasma sintering method. 3 It is possible to produce sintered bodies of the above types.

[0052] A thermoelectric conversion device can be constructed using the anomalous Nernst effect element manufactured by the manufacturing method of the anomalous Nernst effect element of this embodiment. In the thermoelectric conversion device, the anomalous Nernst effect element functions as a thermoelectric conversion element. Hereinafter, the thermoelectric conversion device will be described with reference to an embodiment.

[0053] [First embodiment] FIG. 4 is a schematic perspective view showing the configuration of the thermoelectric conversion device according to the first embodiment. A thermoelectric conversion device 10 according to this embodiment includes an anomalous Nernst effect element 1, as shown in FIG. The anomalous Nernst effect element 1 is manufactured by the above-mentioned method for manufacturing an anomalous Nernst effect element, and is made of a sintered body.

[0054] In the thermoelectric conversion device 10 of this embodiment, as shown in FIG. 4, a rectangular anomalous Nernst effect element 1 extending in one direction (Y direction in this embodiment) has a thickness of 0.1 μm or more in the thickness direction (Z direction in this embodiment) and is magnetized in the +Z direction.

[0055] In the thermoelectric conversion device 10 of this embodiment, when a heat flow Q flows through the anomalous Nernst effect element 1 in another direction (+X direction in this embodiment) perpendicular to the direction of magnetization M (+Z direction), a temperature difference ΔT is generated in the +X direction.

[0056] As a result, in the anomalous Nernst effect element 1, an electromotive force is generated in a direction (Y direction in this embodiment) perpendicular to both the direction of the heat flow Q (+X direction) and the direction of the magnetization M (+Z direction) due to the anomalous Nernst effect. This allows the anomalous Nernst effect element 1 to perform thermoelectric conversion as a thermoelectric conversion element.

[0057] In addition, when a magnetic field is applied to the anomalous Nernst effect element 1, the anomalous Nernst effect adds a normal Nernst effect proportional to the magnitude of the magnetic field, and the thermoelectric power may increase, so a magnetic field may be applied to the anomalous Nernst effect element 1 during actual use. The means for applying the magnetic field is not particularly limited as long as it is capable of applying a magnetic field in a direction perpendicular to the direction in which the temperature difference occurs and the direction in which the electromotive force is generated. Examples of the means for applying the magnetic field include a permanent magnet and an electromagnet.

[0058] Second Embodiment FIG. 5 is a schematic perspective view showing the configuration of a thermoelectric conversion device according to the second embodiment. A thermoelectric conversion device 20 according to this embodiment includes a substrate 21 and a power generating body 22 disposed on the substrate 21, as shown in FIG.

[0059] The substrate 21 has a first surface 21a on which the power generating body 22 is disposed, and a second surface 21b opposite to the first surface 21a. Heat from a heat source (not shown) is applied to the second surface 21b. There is no particular limitation on the material of the substrate 21. The material of the substrate 21 is preferably one having high thermal conductivity. Examples of the material of the substrate 21 include AlN, Al2O3, MgO, and BN.

[0060] The power generating body 22 has a plurality of first anomalous Nernst effect elements 23 and a plurality of second anomalous Nernst effect elements 24. The first anomalous Nernst effect element 23 and the second anomalous Nernst effect element 24 can be basically the same as the anomalous Nernst effect element 1 described above.

[0061] The multiple first anomalous Nernst effect elements 23 and the multiple second anomalous Nernst effect elements 24 extend in one direction (the X direction in this embodiment) within the plane of the first surface 21a and are arranged alternately in another direction (the Y direction in this embodiment) that intersects (is perpendicular to) this one direction.

[0062] The first anomalous Nernst effect element 23 has a first connection part 23a protruding from one end side (-X side) in one direction (X direction) toward one side (-Y side) in the other direction (Y direction). On the other hand, the second anomalous Nernst effect element 24 has a second connection part 24a protruding from the other end side (+X side) in the one direction (X direction) toward one side (-Y side) in the other direction (Y direction).

[0063] The first anomalous Nernst effect element 23 is electrically connected to one end side (-X side) in one direction (X direction) of the second anomalous Nernst effect element 24 via a first connection part 23a. On the other hand, the second anomalous Nernst effect element 24 is electrically connected to the other end side (+X side) in one direction (X direction) of the first anomalous Nernst effect element 23 via a second connection part 24a.

[0064] As a result, in the power generating body 22, the first anomalous Nernst effect element 23 and the second anomalous Nernst effect element 24 adjacent to each other are electrically connected in series, so that the power generating body 22 has a meandering shape as a whole.

[0065] In the power generating body 22, the first anomalous Nernst effect element 23 and the second anomalous Nernst effect element 24 are arranged such that the direction of magnetization M1 of the first anomalous Nernst effect element 23 (-Y direction in this embodiment) and the direction of magnetization M2 of the second anomalous Nernst effect element 24 (+Y direction in this embodiment) are opposite to each other. Furthermore, the first anomalous Nernst effect element 23 and the second anomalous Nernst effect element 24 have anomalous Nernst coefficients of the same sign.

[0066] In the thermoelectric conversion device 20 of this embodiment having the above-mentioned configuration, when a heat flow Q flows from a heat source on the second surface 21b side of the substrate 21 toward the power generating body 22, a temperature difference in the direction of the heat flow occurs in the power generating body 22, and a voltage V is generated in the power generating body 22 due to the anomalous Nernst effect.

[0067] That is, when heat is applied from a heat source to the second surface 21b of the substrate 21, a heat flow Q flows in the +Z direction toward the power generator 22. At this time, in the first anomalous Nernst effect element 23, an electromotive force E1 is generated in a direction (-X direction) perpendicular to both the direction of the magnetization M1 (-Y direction) and the direction of the heat flow Q (+Z direction). On the other hand, in the second anomalous Nernst effect element 24, an electromotive force E2 is generated in a direction (+X direction) perpendicular to both the direction of the magnetization M2 (+Y direction) and the direction of the heat flow Q (+Z direction).

[0068] In the power generating body 22, the first anomalous Nernst effect element 23 and the second anomalous Nernst effect element 24, which are adjacent to each other, are electrically connected in series, so that the electromotive force E1 generated in the first anomalous Nernst effect element 23 and the electromotive force E2 generated in the second anomalous Nernst effect element 24 are added together, making it possible to increase the output voltage V.

[0069] In the thermoelectric conversion device 20 of this embodiment, the temperature gradient, the magnetization direction, and the voltage direction are perpendicular to each other, so that it is possible to use the first anomalous Nernst effect element 23 and the second anomalous Nernst effect element 24 that are thin sheets.

[0070] Here, if the length in the longitudinal direction of the first anomalous Nernst effect element 23 and the second anomalous Nernst effect element 24 are L and the thickness (height) is H, the voltage V generated by the anomalous Nernst effect is proportional to L / H. That is, the longer and thinner the first anomalous Nernst effect element 23 and the second anomalous Nernst effect element 24 are, the larger the obtained voltage V becomes.

[0071] Therefore, in the thermoelectric conversion device 20 of this embodiment, by adopting a power generating body 22 in which the above-mentioned adjacent first anomalous Nernst effect element 23 and second anomalous Nernst effect element 24 are electrically connected in series, a further increase in voltage V can be expected due to an improved anomalous Nernst effect.

[0072] In addition to the above-mentioned configuration, the thermoelectric conversion device 20 may also adopt a configuration in which, for example, the first anomalous Nernst effect element 23 and the second anomalous Nernst effect element 24 have anomalous Nernst coefficients of opposite signs to each other, and are arranged so that the direction of magnetization M1 of the first anomalous Nernst effect element 23 and the direction of magnetization M2 of the second anomalous Nernst effect element 24 are the same.

[0073] Third embodiment FIG. 6 is a schematic perspective view showing the configuration of a thermoelectric conversion device according to the third embodiment. 6, a thermoelectric conversion device 30 of this embodiment includes a substantially cylindrical hollow member 31 and a long sheet-like anomalous Nernst effect element 32 spirally wound around the outer circumferential surface of the hollow member 31. The anomalous Nernst effect element 32 can be basically the same as the anomalous Nernst effect element 1. The anomalous Nernst effect element 32 is magnetized in a direction parallel to the axial direction (x direction) of the hollow member 31. When making a spiral sintered body by hot pressing as shown in Figure 6, for example, a cylindrical object is made during sintering, and then cut. Alternatively, since hot pressing allows for near-net sintering, it is possible to sinter into a cylindrical shape and then cut it out. Alternatively, multiple pieces like tiles, like cylindrical parts, are made and then joined together. A spiral sintered body can be made by these processes.

[0074] In the thermoelectric conversion device 30 of this embodiment, when the inside of the hollow member 31 is hotter than the outside, the heat flow P flows from the inside to the outside of the hollow member 31, causing a temperature gradient (temperature difference) from the inside to the outside of the hollow member 31, and a voltage V is generated in the anomalous Nernst effect element 32 due to the anomalous Nernst effect. That is, in the anomalous Nernst effect element 32, an electromotive force is generated along the longitudinal direction of the anomalous Nernst effect element 32 (the direction perpendicular to both the magnetization direction and the heat flow direction).

[0075] In the thermoelectric conversion device 30 of this embodiment, the temperature gradient, the magnetization direction, and the voltage direction are perpendicular to one another, so that it is possible to use a thin sheet-like anomalous Nernst effect element 32 .

[0076] Therefore, in the thermoelectric conversion device 20 of this embodiment, by adopting the long sheet-like anomalous Nernst effect element 32 wound in a spiral shape around the outer peripheral surface of the hollow member 31 described above, a further increase in the voltage V can be expected due to an improved anomalous Nernst effect.

[0077] [Fourth embodiment] FIG. 7 is a schematic plan view showing the configuration of a thermoelectric conversion device according to the fourth embodiment. A thermoelectric conversion device 40 of this embodiment includes a substrate 41 and a power generating body 42 disposed on the substrate 41, as shown in FIG.

[0078] The substrate 41 has a first surface 41a on which the power generating body 42 is disposed, and a second surface 41b opposite to the first surface 41a. Heat from a heat source (not shown) is applied to the second surface 41b.

[0079] The power generating body 42 has a plurality of anomalous Nernst effect elements 45 and wiring 46 . The anomalous Nernst effect element 45 can be basically the same as the anomalous Nernst effect element 1. The anomalous Nernst effect elements 45 are arranged in parallel on the substrate 41 in a direction (X direction) perpendicular to the extension direction (Y direction) so that the directions of the magnetization M1A are the same (-X direction).

[0080] One end of the wiring 46 is electrically connected to one end side (-Y side) of the anomalous Nernst effect element 45, and the other end is electrically connected to the other end side (+Y side) of another adjacent anomalous Nernst effect element 45. As a result, the anomalous Nernst effect elements 45 are electrically connected in series. There are no particular limitations on the material of the wiring 46 as long as it is conductive. For example, the material of the wiring 46 may be metal such as Au, Ag, Cu, or Al.

[0081] A first electrode 43 is electrically connected to one end of the power generating body 42, and a second electrode 44 is electrically connected to the other end.

[0082] The material of the first electrode 43 is not particularly limited as long as it has conductivity. For example, the material of the first electrode 43 may be metals such as Au, Ag, Cu, and Al. The material of the second electrode 44 is not particularly limited as long as it has conductivity. For example, the material of the second electrode 44 may be metals such as Au, Ag, Cu, and Al.

[0083] There is no particular limitation on the arrangement of the first electrode 43 and the second electrode 44. However, if there is a difference in temperature between the first electrode 43 and the second electrode 44, the Seebeck effect will be superimposed in addition to the anomalous Nernst effect, so that for the heat flow sensor, the first electrode 43 and the second electrode 44 are preferably arranged so that they are at the same distance from the heat source.

[0084] In the thermoelectric conversion device 40 of this embodiment having the above-mentioned configuration, when a heat flow Q flows from a heat source on the second surface 41b side of the substrate 41 toward the power generating body 42, a temperature difference occurs in the power generating body 42 in the heat flow direction (+Z direction), and a voltage V is generated in the power generating body 42 due to the anomalous Nernst effect. The thermoelectric conversion device 40 can be manufactured more easily than the thermoelectric conversion device 20 because the adjacent anomalous Nernst effect elements 45 are connected via the wiring 46 .

[0085] The present invention is not necessarily limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the anomalous Nernst effect element 1 can be applied not only to the thermoelectric conversion devices 10, 20, 30, and 40 described above, but also to various other devices. For example, by providing the anomalous Nernst effect element 1 in a heat flow sensor, it is possible to judge whether the thermal insulation performance of a building is good or bad.

[0086] Furthermore, by providing the thermoelectric conversion devices 10, 20, 30 in an exhaust system of a motorcycle or the like, it is possible to generate electricity using the heat (waste heat) of the exhaust gas, and the thermoelectric conversion devices 10, 20, 30, 40 can be effectively used as auxiliary power sources.

[0087] In addition, in the above embodiment, attention was focused on the voltage generated by the anomalous Nernst effect, but it is possible to increase the output voltage by the synergistic effect of the voltage caused by the Seebeck effect generated by 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.

[0088] Furthermore, the anomalous Nernst effect element of this embodiment can function not only as the thermoelectric conversion element described above, but also as the opposite function to that of a thermoelectric conversion element, that is, the function of temperature modulation (particularly cooling) by supplying electric power like a Peltier element.

[0089] In the above embodiment, it has been described that the sintered body made of Co2MnGa mentioned above brings about a larger anomalous Nernst effect than conventional ones. However, other than Co2MnGa, other candidate substances that may have the potential to enhance the anomalous Nernst effect include sintered bodies of Fe3Ga, Fe3Al, Co2MnAl, Co2MnIn, Mn3Ga, Mn3Ge, Fe2NiGa, CoTiSb, CoVSb, CoCrSb, CoMnSb, TiGa2Mn, etc. EXAMPLES

[0090] 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 appropriately modified and implemented without departing from the gist of the present invention.

[0091] (Examples 1 to 4) A sintered body of Co2MnGa was produced by hot pressing. In producing the sintered body, the raw powder of Co2MnGa was filled into a carbon mold in the electric furnace of the hot pressing device, and the carbon mold was heated while applying pressure in one axial direction to sinter the raw powder. In order to minimize oxygen and water vapor in the electric furnace during sintering, the electric furnace was degassed before sintering, and then the Ar gas was restored to atmospheric pressure. This process was repeated three times. Sintering was performed in an Ar atmosphere while flowing Ar gas. The sintering temperature and the pressure applied during sintering were the values ​​shown in Table 1. The sintering program was to increase the temperature from 600°C to the target sintering temperature at a rate of 15°C / min, hold the temperature for 3 hours after reaching the target sintering temperature, and then naturally cool. For sintering temperatures below 900°C, a type C thermocouple is used, between 900°C and 1100°C, both a type C thermocouple and a radiation thermometer (CHINO IR-CZH7T6) are used, and for temperatures above 1100°C, only the radiation thermometer is used. The temperature in the uniform heating area of ​​the electric furnace is constant within a temperature range of ±10°C, and a thermocouple is placed in the space to measure the temperature, or a graphite block is placed and the temperature is measured with a radiation thermometer, and this temperature is taken as the furnace temperature. Therefore, there is a time lag between the temperature in the uniform heating area and the central temperature in the carbon mold, and it takes about 15 minutes for the central temperature of the mold to follow the temperature in the uniform heating area for a Φ50mm mold. The time lag also varies depending on the amount of sample filled and the size of the mold being used. The following measurements were carried out on the obtained sintered body, and the results are shown in Table 1.

[0092] <Relative density> The density of the sintered body was measured by the Archimedes method, and the theoretical density of single crystal Co2MnGa (8.39 g / cm 3 ) was calculated as the relative density.

[0093] <Average grain size, grain size standard deviation> First, the surface of the sintered body was roughly polished with #800 waterproof abrasive paper, then moderately polished with 1 μm alumina suspension, and further mirror-polished with 0.3 μm alumina suspension. Next, the surface of the sintered body was observed using secondary electrons and backscattered electrons of an SEM. Then, a total of six images of 228.7 μm wide x 157 μm long were taken at 500 times magnification for each sample, and the grain size was measured by analyzing each image, and the average grain size (average grain size) and standard deviation (standard deviation of grain size) of the grain size were calculated. To calculate the average crystal grain size and standard deviation of crystal grain size, one SEM image was divided into individual grains for each pixel. Grains around the edges of the image were removed. The area of ​​each divided grain was calculated using image processing, and a circle with an area equivalent to that of each grain was determined. For one sample, the average crystal grain size and standard deviation of grain size were calculated from the diameters of all circles in the six SEM images measured, excluding the circles near the edges of the images.

[0094] <Anomalous Nernst coefficient S ANE > A flat plate-shaped sample (length L = 8 mm, width W = 1.5 mm, thickness t = 1 mm) for evaluation was cut out from the sintered body. Using the Thermal Transport Option of a Physical Property Measurement System manufactured by Quantum Design, heat was injected in a pulsed manner from one end of the sample in the longitudinal direction at a temperature of 300 K, and a heat sink was placed in contact with the other end, thereby creating a temperature difference along the longitudinal direction of the sample. The temperature difference ΔT was measured at two points separated by L_temp (4 to 8 mm) on the sample. A magnetic field of 2 Tesla was also applied in a direction perpendicular to the direction of this temperature difference and perpendicular to the surface of the sample, and the voltage V generated at two points separated by a distance W in a direction perpendicular to both the temperature difference and the magnetic field was measured, and the anomalous Nernst coefficient S was calculated using the above formula (4). ANE The value was calculated.

[0095] <Electrical resistivity ρ xx > Anomalous Nernst coefficient S ANEThe electrical resistivity ρ was measured by the four-terminal method at a temperature of 300K for the same sample used in the measurement of xx was measured.

[0096] <Thermal conductivity κ> Anomalous Nernst coefficient S ANE and electrical resistivity ρ xx For the same sample used in the measurement of (a), pulsed heat was applied to one end of the sample at 300 K using the Thermal Transport Option of a Physical Property Measurement System manufactured by Quantum Design, and the thermal conductivity κ was obtained by analyzing the relaxation process of the temperature difference generated in the sample. The direction of the heat flow when measuring the thermal conductivity κ is the same as that of the electrical resistivity ρ xx The direction of the current was the same as that of the current applied during the measurement.

[0097] <Dimensionless figure of merit ZT> The anomalous Nernst coefficient S ANE , electrical resistivity ρ xx The dimensionless figure of merit ZT was calculated by the above formula (3) using the values ​​of the thermal conductivity κ and the thermal conductivity κ.

[0098] (Comparative Examples 1 to 2) The single crystals of Co2MnGa described in Non-Patent Document 2 and Non-Patent Document 3 were used as Comparative Examples 1 and 2. Note that a single crystal refers to a single crystal on the scale of nm, μm, mm, or cm. For each single crystal, the anomalous Nernst coefficient S ANE , electrical resistivity ρ xx The thermal conductivity κ and dimensionless figure of merit ZT were measured. The results are shown in Table 1.

[0099] [Table 1]

[0100] As shown by the above results, the sintered bodies of Examples 1 to 4 exhibited the anomalous Nernst effect and dimensionless figure of merit ZT at the same levels as those of a single crystal of Co2MnGa. [Industrial Applicability]

[0101] According to the present invention, an anomalous Nernst effect element having a high anomalous Nernst coefficient can be manufactured by hot pressing, which is an established, highly reliable, and widely used sintering method. The hot pressing method allows the production of a large-capacity sintered body, is easy to shape, and allows the sintered body to be manufactured at a low cost. [Explanation of symbols]

[0102] Reference Signs List 1... anomalous Nernst effect element (sintered body), 10... thermoelectric conversion device, 20... thermoelectric conversion device, 21... substrate, 22... power generation body, 23... first anomalous Nernst effect element, 24... second anomalous Nernst effect element, 30... thermoelectric conversion device, 31... hollow member, 32... anomalous Nernst effect element

Claims

1. A method for manufacturing an anomalous Nernst effect element, comprising the step of sintering a powder containing Co, Mn, and Ga by a hot press method to produce a sintered body.

2. 2. The method for producing an anomalous Nernst effect element according to claim 1, wherein the sintering temperature in said step is 700° C. or more and 1100° C. or less.

3. 2. The method for producing an anomalous Nernst effect element according to claim 1, wherein the applied pressure in said step is 30 MPa or more and 130 MPa or less.

4. 2. The method for producing an anomalous Nernst effect element according to claim 1, wherein in said step, the sintering time is 24 hours or less.

5. The method for producing an anomalous Nernst effect element according to claim 1 , wherein the sintered body has crystal grains containing Co, Mn and Ga.

6. The method for producing an anomalous Nernst effect element according to claim 5 , wherein the crystal grains have a Heusler structure.

7. 6. The method for producing an anomalous Nernst effect element according to claim 5, wherein the average grain size of the crystal grains is 8 [mu]m or more and 30 [mu]m or less.

8. 6. The method for producing an anomalous Nernst effect element according to claim 5, wherein the standard deviation of the grain size of the crystal grains is 1 [mu]m or more and 12 [mu]m or less.

9. 2. The method for producing an anomalous Nernst effect element according to claim 1, wherein the absolute value of the anomalous Nernst coefficient of said sintered body is 5 [mu]V / K or more at 300K.

10. A method for manufacturing a thermoelectric conversion device, comprising the step of manufacturing an anomalous Nernst effect element by the method for manufacturing an anomalous Nernst effect element according to any one of claims 1 to 9.

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