Anomalous nernst effect element and method of manufacturing the same, and thermoelectric conversion device

Abstract

To suppress the thermal conductivity of thermoelectric materials made of an alloy.SOLUTION: An anomalous Nernst effect element 1 includes a sintered body 2 containing Co, Mn and Ga, and the porosity of the sintered body 2 is 20% or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In recent years, a thermoelectric conversion device using an anomalous Nernst effect element that generates an electromotive force due to the anomalous Nernst effect has been proposed (see, for example, Patent Document 1 below). The anomalous Nernst effect is a phenomenon in which, when a heat flow is passed through a magnetic material to generate a temperature difference, a voltage is generated in a direction perpendicular to both the magnetization direction and the temperature gradient.

[0003] Similarly, a well-known thermoelectric conversion device that generates voltage from a temperature gradient is one that uses the Seebeck effect. With the Seebeck effect, a voltage is generated in the same direction as the temperature gradient, so the thermoelectric conversion device has a complex three-dimensional structure, making it difficult to make it large-area or into a film. In addition, highly toxic and rare materials are used, making them brittle and vulnerable to vibration, and they also have issues such as high manufacturing costs.

[0004] On the other hand, in the anomalous Nernst effect, a voltage is generated in a direction perpendicular to the temperature gradient, so that a thermoelectric conversion device using this anomalous Nernst effect can be developed along the heat source, which is advantageous for making it large-area and film-like. Furthermore, it is possible to select inexpensive, less toxic, and highly durable materials.

[0005] Various materials have been reported that exhibit the anomalous Nernst effect, including Co2MnGa, Fe3Ga, Fe3Al, Mn3Ge, Mn3Sn, Mn2Ga, MnGe, Co, Fe, Nd2Mo2O7, Pt / Fe multilayers, and L1-FePt alloys. Among these, the one with the highest absolute value of the anomalous Nernst coefficient is Co2MnGa, and the highest reported data is 6.75-8μV / K. Note that these values ​​are for single crystals.

[0006] The indices for evaluating anomalous Nernst materials 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. The anomalous Nernst coefficient means the thermoelectromotive force per 1 K of temperature difference.

[0007] Anomalous Nernst coefficient S ANE is expressed by the following formula (1). S ANE =ρ yy α yx -σ yx ρ yy S SE …(1) ρ yy : Vertical resistance α yx : Transverse thermoelectric coefficient σ yx : Hall conductivity S SE : Seebeck coefficient

[0008] In addition, the transverse thermoelectric coefficient α yx is expressed by the following formula (2). α yx =-(π 2 / 3)·{(k B 2 T) / e}(∂σ yx / ∂ε) (Mott's law) …(2) However, ∂σ yx / ∂ε is the value at the Fermi level. k B :Boltzmann constant ε: Energy e: elementary charge T: Absolute temperature

[0009] 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

[0010] Since alloy thermoelectric conversion materials are metals, they have a high thermal conductivity, making it difficult to create a temperature difference within the material, and there are concerns that the temperature gradient that is formed is small and that the heat flow through the thermoelectric conversion module becomes too large. It is necessary to create a thermoelectric conversion module using a thermoelectric conversion material with a thermal conductivity that can make maximum use of the temperature difference and heat flow environment in which it will be installed. [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(2020), 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] Although the above-mentioned anomalous Nernst effect has an advantage over the Seebeck effect, the current amount of power generated by the anomalous Nernst effect using a normal magnetic material is still too small for full-scale practical use.

[0014] Therefore, the above-mentioned 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 can bring about a larger anomalous Nernst effect than conventional materials. The crystal structure of this Co2MnGa is a single crystal of the cubic system and has a full Heusler system crystal structure.

[0015] On the other hand, the thermoelectric conversion element described in the above Patent Document 1 exhibits excellent transverse thermoelectric power, but when pulling up the single crystal of Co2MnGa, it takes time and power to raise the temperature to the melting point. In addition, it is known that the manufacturing cost is high because of the time required for crystal growth. In addition, since it is impossible to grow the single crystal of Co2MnGa near net, it needs to be cut, and shape processing is also costly.

[0016] Sintered bodies do not require raising the temperature above the melting point, so they require less power and time than single crystal growth, and the required high-temperature holding time is also shorter. In particular, sintering under pressures of 1 MPa or less not only does not require the introduction of special equipment, but can also be produced in existing electric furnaces. It is also a common and easy sintering method. Furthermore, sintered bodies can be near-net sintered, which is expected to reduce costs for shape processing.

[0017] Generally, a sintered body refers to a body that is sintered by forming raw material powder in a mold and then firing it in an electric furnace at atmospheric pressure or under pressure, or by a hot press method, a hot isostatic pressing method (HIP) method, a spark plasma sintering method (SPS) method, a microwave sintering method, or the like.

[0018] Recently, new sintering methods such as flash sintering have been reported. Sintered bodies are produced by various methods, but those that are sintered at a temperature lower than the inherent melting point of the material are called sintered bodies.

[0019] Sintered bodies are classified as polycrystalline bodies. When a material is heated to a temperature higher than the melting point in the single crystal growth method, and then rapidly cooled, the atomic arrangement cannot be regularized in time, and the material becomes polycrystalline. This also falls under the category of polycrystalline bodies, but is not called a sintered body.

[0020] The above-mentioned Patent Document 2 reports the production of a Co2MnGa sintered body by spark plasma sintering. Sintering is performed in a vacuum atmosphere of about 1 Pa by applying 90 MPa, and the temperature program is to raise the temperature to 650°C and hold it for 10 minutes, then raise the temperature to 750°C and hold it for another 10 minutes. With this method, a material with an absolute value of the anomalous Nernst coefficient of 6.68 μV / K is produced. However, this requires the introduction of special equipment called spark plasma sintering, and the manufacturing method has the drawback of being difficult to manufacture in large quantities. Furthermore, the thermal conductivity of the sample manufactured by this method is 26 W / K·m, which is higher than that of single crystal Co2MnGa, and the problem of high thermal conductivity, which is a drawback of alloy-based thermoelectric materials, has not been resolved.

[0021] The present invention has been proposed in light of the above-mentioned conventional circumstances, and has an object to provide an anomalous Nernst effect element that can be manufactured more inexpensively by a general and easy sintering method, in which specific voids are present, thereby significantly suppressing thermal conductivity and making it easier to process into a shape, as well as a manufacturing method thereof, and a thermoelectric conversion device using such an anomalous Nernst effect element. [Means for solving the problem]

[0022] In order to achieve the above object, the present invention provides the following means. [1] An anomalous Nernst effect element comprising a sintered body containing Co, Mn, and Ga, the sintered body having a porosity of 20% or more. [2] The anomalous Nernst effect element according to [1], wherein the sintered body has a Heusler structure. [3] The anomalous Nernst effect element according to [1] or [2], wherein the sintered body has an electrical resistivity of 200 μΩ·cm or more. [4] The anomalous Nernst effect element according to any one of [1] to [3], wherein the anomalous Nernst coefficient of the sintered body has an absolute value of 1.0 μV / K or more. [5] A method comprising the steps of preparing a compact containing a powder containing Co, Mn, and Ga, After the above step, the powder is sintered at a sintering temperature of 700° C. to 1100° C. under a pressure of 1 MPa or less. [6] The method for producing an anomalous Nernst effect element according to [5], wherein in the step, a mixture of the powder and ethanol is uniaxially pressurized at 10 MPa to 200 MPa, and then sintered under the pressure. [7] The method for producing an anomalous Nernst effect element according to [5], wherein in the step, the powder is filled into a mold, uniaxially pressed at 10 MPa to 200 MPa, and then sintering is carried out under the pressure while the powder is filled into the mold. [8] The method for producing an anomalous Nernst effect element according to [5], wherein in the step, the mixture of the powder and the binder is uniaxially pressurized at 10 MPa to 200 MPa, and then sintered under the pressure. [9] A device comprising any one of the anomalous Nernst effect elements according to [1] to [4], A thermoelectric conversion device, wherein the sintered body has a thermal conductivity of 15 W / K·m or less.

[10] A thermoelectric conversion device that performs thermoelectric conversion by using any one of the anomalous Nernst effect elements according to [1] to [4].

[11] The thermoelectric conversion device according to [9] or

[10] , wherein the absolute value of the anomalous Nernst coefficient of the sintered body is 1.0 μV / K to 10 μV / K at 10° C. to 50° C. Effect of the Invention

[0023] As described above, according to each of the above aspects of the present invention, it is possible to provide an anomalous Nernst effect element that can be easily shaped and manufactured more inexpensively by introducing voids using a common and easy sintering method, as well as a manufacturing method thereof, and a thermoelectric conversion device using such an anomalous Nernst effect element. [Brief description of the drawings]

[0024] [Figure 1] 1 is a schematic diagram showing a configuration of an anomalous Nernst effect element according to a first embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic diagram showing the crystal structure of Co2MnGa. [Diagram 3] FIG. 4 is a schematic diagram showing the configuration of a thermoelectric conversion device according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing the configuration of a thermoelectric conversion device according to a third embodiment of the present invention. [Diagram 5] FIG. 11 is a plan view showing the configuration of a thermoelectric conversion device according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] 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.

[0026] [First embodiment] (Anomalous Nernst effect element) First, as a first embodiment of the present invention, an anomalous Nernst effect element 1 shown in FIG. 1 will be described.

[0027] Fig. 1 is a schematic diagram showing the configuration of the anomalous Nernst effect element 1. Fig. 2 is a schematic diagram showing the crystal structure of Co2MnGa.

[0028] The anomalous Nernst effect element 1 of this embodiment is a sintered body containing Co, Mn, and Ga, as shown in FIG. 1. As long as it contains Co, Mn, and Ga, there is no particular limitation, and it may contain Fe, Ni, Si, C, O, N, etc. For example, the sintered body 2 may contain many voids depending on the progress of sintering, and the progress of sintering may be limited to the initial sintering or intermediate sintering stage. Moreover, even such a sintered body has a Heusler structure containing Co, Mn, and Ga.

[0029] The sintered body 2 contains Co, Mn, and Ga, and is, for example, a ferromagnetic material of Co2MnGa having a full Heusler structure of L21 type cubic crystal. As shown in FIG. 2, the unit cell of the L21 structure consists of four face-centered cubic lattices (fcc), and in the lattice coordinates, Co atoms are located at (1 / 4, 1 / 4, 1 / 4) and (3 / 4, 3 / 4, 3 / 4), Mn atoms are located at (0, 0, 0), and Ga atoms are located at (1 / 2, 1 / 2, 1 / 2). The crystal structure of Co2MnGa can be determined by various diffraction methods such as X-ray diffraction.

[0030] When a magnetic field is applied to the sintered body 2, the anomalous Nernst effect generates a normal Nernst effect proportional to the magnitude of the magnetic field, which can increase the thermoelectric power. Therefore, a magnetic field may be applied to the sintered body 2 during actual use.

[0031] In this specification, the sintered body 2 with many voids at the initial or intermediate sintering stage refers to a sintered body with a porosity of 20% or more. With an increase in voids, the conduction of phonons is hindered, and the thermal conductivity can be reduced. The porosity of the sintered body 2 is more preferably 30% or more. The porosity is preferably 50% or less. If the porosity is 50% or less, the strength of the sintered body can be maintained. The porosity refers to the ratio of the volume of voids to the total volume of the sintered body 2. The porosity of the sintered body 2 can be evaluated by the Archimedes method described later.

[0032] The relative density of the sintered body 2 may be 50% or more, or may be 80% or less.

[0033] The porosity and relative density of the sintered body 2 can be obtained by Archimedes' method. The Archimedes' method is explained below. 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, the density of the sintered body 2 is {A / (AB)} x 100 (%).

[0034] The relative density of the sintered body 2 can be calculated from the ratio of the theoretical density of the material constituting the sintered body 2 to the density of the sintered body 2 obtained by the Archimedes method. For example, in the case of single crystal Co2MnGa, the theoretical density (8.39 g / cm 3 ) can be obtained from the ratio of the density of the sintered body 2 to the density of the sintered body 2.

[0035] The voids in the sintered body 2 can be calculated by (100-relative density) (%). For example, the void ratio of a sintered body 2 with a relative density of 80% is 20%.

[0036] The electrical resistivity ρ of the sintered body 2 is preferably 200 μΩ·cm or more. By introducing voids, the electrical resistivity ρ of the sintered body 2 being 200 μΩ·cm or more makes it easier to suppress the thermal conductivity of the sintered body 2 to 15 W / K·m or less. The electrical resistivity ρ of the sintered body 2 may be 1000 μΩ·cm or less. The electrical resistivity ρ can be measured by a four-terminal method.

[0037] The thermal conductivity κ of the sintered body 2 is preferably 15 W / K·m or less. More preferably, the thermal conductivity κ of the sintered body 2 is 5 W / K·m or less. The thermal conductivity κ of the sintered body 2 may be 0.1 W / K·m or more. The thermal conductivity κ of the sintered body 2 can be measured by applying pulsed heat to one end of the sintered body 2 and analyzing the relaxation process of the temperature difference generated in the sintered body 2.

[0038] At 10℃~50℃, the anomalous Nernst coefficient S of sintered body 2 ANE The absolute value of the anomalous Nernst coefficient S of the sintered body 2 is preferably 1.0 μV / K or more. ANEThe absolute value of the anomalous Nernst coefficient S of the sintered body 2 at 10° C. to 50° C. may be 10 μV / K or less. ANE It is more preferable that the absolute value of is 1.0 μV / K to 10 μV / K.

[0039] Anomalous Nernst coefficient S ANE is expressed by the following equation (4). S ANE =(V / ΔT)×(L_temp / W) …(4)

[0040] Anomalous Nernst coefficient S of sintered body 2 ANE can be measured by the following method. A flat sample for evaluation (for example, length L=8 mm, width W=1.5 mm, thickness t=1 mm) is cut out from the sintered body 2. One end of this sample is heated with a heater, and a heat sink is placed in contact with the other end while a temperature difference is applied along the length of the sample. This gives a uniform temperature gradient to the rectangular sample, and the temperature difference ΔT at two points separated by L_temp is measured. A magnetic field is applied in a direction perpendicular to this temperature difference ΔT, and the voltage V generated at two points separated by a distance W is measured in a direction perpendicular to both the temperature difference and the magnetic field. The anomalous Nernst coefficient S ANE can be calculated from the voltage V when a magnetic field of 2 Tesla is applied, using the above formula (4).

[0041] When measuring the anomalous Nernst coefficient, the surface of the sintered body 2 may be roughly polished with #800 waterproof abrasive paper, then medium polished with a 1 μm alumina suspension, and further mirror polished with a 0.3 μm alumina suspension.

[0042] 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. However, if the relative density is low and the porosity is large, it may be impossible to polish to a glossy state by mirror polishing, in which case polishing may be terminated with medium polishing.

[0043] As shown in FIG. 1, the anomalous Nernst effect element 1 of this embodiment has a rectangular parallelepiped sintered body 2 extending in one direction (the y direction in this embodiment), has a thickness of 0.1 μm or more in the thickness direction (the z direction in this embodiment), and is magnetized in the +z direction.

[0044] In the anomalous Nernst effect element 1 of this embodiment, when a heat flow Q flows through the sintered body 2 in a 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.

[0045] As a result, in the sintered body 2, 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. As a result, the anomalous Nernst effect element 1 of this embodiment can perform thermoelectric conversion as a thermoelectric conversion element.

[0046] (Method of manufacturing anomalous Nernst effect element) Next, a method for manufacturing the anomalous Nernst effect element 1 of this embodiment will be described. When manufacturing the anomalous Nernst effect element 1 of this embodiment, a powder containing Co, Mn, and Ga or a powder compact thereof is sintered to produce a sintered body 2. Specifically, the manufacturing method of the anomalous Nernst effect element according to this embodiment includes a step of producing a compact containing a powder containing Co, Mn, and Ga, and after the step of producing the compact, the powder containing Co, Mn, and Ga is sintered at a sintering temperature of 700° C. to 1100° C. under a pressure of 1 MPa or less.

[0047] (Process for producing a molded body) A compact is prepared that includes a powder containing Co, Mn, and Ga.

[0048] "Powder" The powder is not particularly limited as long as it contains Co, Mn, and Ga, and may be, for example, Co2MnGa, Co2MnAl, Co2MnIn, Mn3Ga, Mn3Ge, Fe2NiGa, CoTiSb, CoVSb, CoCrSb, CoMnSb, TiGa2Mn, and preferably, any one or more of Co2MnGa powder. As the powder containing Co, Mn, and Ga, Co2MnGa powder is preferable.

[0049] In this specification, examples of the molded body containing the powder containing Co, Mn, and Ga include a pressed powder molded body made of only the powder, a molded body made of a mixture of the powder and a molding assistant such as a solvent or a binder, etc. A method for producing the molded body will be described below.

[0050] The first method for producing a compact includes filling a mixture of ethanol and a powder containing Co, Mn, and Ga as raw material powders into a mold (e.g., a non-magnetic metal mold), applying uniaxial pressure at 10 to 200 MPa, releasing the pressure, and removing the mixture from the mold to produce a compact. The uniaxial pressure can be performed using a known press. For example, a compact can be produced by applying uniaxial pressure to the mixture filled in the mold and then releasing the pressure of the press. The holding time after applying pressure is, for example, more than 0 seconds and 1 hour or less. By mixing ethanol, it becomes easier to maintain the compact under a pressure of 1 MPa or less. In the case of the first production method, in the step of producing a compact, a mixture of powder and ethanol is uniaxially pressed at 10 MPa to 200 MPa, and then sintering under a pressure of 1 MPa or less, as described below, to obtain a sintered body 2.

[0051] The second method for producing a compact includes filling a mold (e.g., a carbon mold) with a powder containing Co, Mn, and Ga as raw material powders, applying uniaxial pressure at 10 to 200 MPa, and then releasing the pressure to produce a compact. The time for which pressure is applied is, for example, more than 0 seconds and not more than 1 hour. In the case of the second production method, in the step of producing a compact, the powder is filled into a mold, and after applying uniaxial pressure at 10 MPa to 200 MPa, sintering is performed under a pressure of 1 MPa or less with the powder filled into the mold, as described below, to obtain a sintered body 2.

[0052] The third method for producing a molded body is to fill a mold (e.g., a non-magnetic metal mold) with a mixture (binder mixed powder) of powder containing Co, Mn, and Ga as raw material powders and a binder, and then release the pressure to produce a molded body. The holding time after pressurization is, for example, more than 0 seconds and 1 hour or less. By mixing the binder and the powder, it is possible to easily maintain the molded body under a pressure of 1 MPa or less. In the case of the third production method, in the step of producing a molded body, the mixture of the powder and the binder is uniaxially pressed at 10 MPa to 200 MPa, and then sintered under a pressure of 1 MPa or less, as described below, to obtain a sintered body 2.

[0053] The binder used in the third method for producing a molded body is not particularly limited as long as it is a binder used for sintering. For example, the binder material may be acrylic resin, modified polyvinyl alcohol, etc. As the binder, Oricox (registered trademark) KC-1700P (Kyoeisha Chemical Co., Ltd.), Oricox (registered trademark) KC-500 (Kyoeisha Chemical Co., Ltd.), Z-300 (Mitsubishi Chemical Co., Ltd.), etc. may be used.

[0054] The binder is preferably mixed at a concentration of 2 to 10% by weight based on the total mass of the raw material powder. By mixing at a concentration of 2 to 10% by weight based on the total mass of the raw material powder, the shape of the molded body can be maintained under a pressure of 1 MPa or less, and the degree of voids in the sintered body 2 can be modulated.

[0055] (Sintering under pressure of 1MPa or less) Next, the powder containing Co, Mn, and Ga is sintered at a sintering temperature of 700°C to 1100°C at a pressure of 1 MPa or less. This makes it possible to produce a sintered body 2 containing Co, Mn, and Ga with a desired shape and size by a general and easy method. Specifically, the molded body produced in the above process is sintered at a sintering temperature of 700°C to 1100°C at a pressure of 1 MPa or less. The sintering pressure is 1 MPa or less, preferably 500 kPa or less, more preferably 200 kPa or less, further preferably 110 kPa or less, and particularly preferably 105 kPa or less. The lower limit is not particularly limited, but is, for example, 0.1 kPa or more.

[0056] Sintering at 1 MPa or less allows for the introduction of voids into the material because the pressure during sintering is low. The introduction of voids is expected to have the effect of lowering thermal conductivity, suppressing the heat flow passing through the material, and increasing the temperature difference or temperature gradient within the material.

[0057] Introducing voids during sintering means limiting the sintering stage to the initial or intermediate stage, and this can be achieved by sintering at 1 MPa or less. Sintered bodies containing Co, Mn, and Ga that have reached the initial or intermediate stage can maintain the same Heusler structure as a Co2MnGa single crystal.

[0058] The sintering is preferably performed in an atmosphere of an inert gas such as Ar or N2.

[0059] The sintering time can be appropriately set depending on the size of the sample. For example, the sintering time is 1 hour or more. More preferably, the sintering time is 3 hours or more.

[0060] The sintering temperature is 700° C. or higher. The sintering temperature is preferably 800° C. or higher. More preferably, the sintering temperature is higher than 850° C.

[0061] By setting the sintering temperature to over 850°C, the raw material powders can be bonded together by sintering. By completing the sintering at the initial or intermediate stage, voids can be introduced into the sintered body 2, and the voids can suppress the thermal conductivity.

[0062] The sintering temperature is preferably 1100° C. or less, and more preferably 950° C. or less.

[0063] By setting the sintering temperature at 1100°C or less, it is possible to suppress the evaporation of elements and prevent compositional deviation. In addition, because it is below the melting point, abnormal grain growth due to the melt can be suppressed. Furthermore, when sintering is performed inside a carbon mold, it is possible to suppress seepage from the mold during sintering. Because 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.

[0064] In this embodiment, the temperature inside the electric furnace can be measured by, for example, a type B thermocouple (platinum-rhodium).

[0065] As described above, the anomalous Nernst effect element and the manufacturing method thereof of the present embodiment can obtain an anomalous Nernst effect equivalent to that of an anomalous Nernst effect material that exhibits a high absolute value of the anomalous Nernst coefficient, and can be manufactured more inexpensively and easily by a more general and simpler sintering method, making it easier to process the shape.

[0066] Second Embodiment (Thermoelectric conversion device) Next, as a second embodiment of the present invention, a thermoelectric conversion device 20 shown in FIG. 3 will be described. FIG. 3 is a schematic diagram showing the configuration of the thermoelectric conversion device 20. As shown in FIG.

[0067] As shown in FIG. 3, a thermoelectric conversion device 20 of this embodiment includes a substrate 21 and a power generating body 22 disposed on the substrate 21.

[0068] 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.

[0069] The power generating body 22 has a plurality of first thermoelectric conversion elements 23 and a plurality of second thermoelectric conversion elements 24. For the first thermoelectric conversion elements 23 and the second thermoelectric conversion elements 24, the same elements as those used in the anomalous Nernst effect element 1 described above can be basically used.

[0070] The multiple first thermoelectric conversion elements 23 and the multiple second thermoelectric conversion elements 24 extend in one direction (x direction in this embodiment) within the plane of the first surface 21a and are arranged alternately in another direction (y direction in this embodiment) that intersects (orthogonal in this embodiment) with this one direction.

[0071] The first thermoelectric conversion element 23 has a first connection portion 23a protruding from one end side (-x side) in one direction (x direction) toward one side (-y side) in the other direction (y direction). Meanwhile, the second thermoelectric conversion element 24 has a second connection portion 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).

[0072] The first thermoelectric conversion element 23 is electrically connected to one end side (-x side) in one direction (x direction) of the second thermoelectric conversion element 24 via the first connection part 23a. On the other hand, the second thermoelectric conversion element 24 is electrically connected to the other end side (+x side) in one direction (x direction) of the first thermoelectric conversion element 23 via the second connection part 24a.

[0073] As a result, the power generating body 22 has a meandering shape as a whole, with the first thermoelectric conversion element 23 and the second thermoelectric conversion element 24 adjacent to each other being electrically connected in series.

[0074] The power generation body 22 is arranged such that the direction of magnetization M1 of the first thermoelectric conversion element 23 (-y direction in this embodiment) and the direction of magnetization M2 of the second thermoelectric conversion element 24 (+y direction in this embodiment) are opposite to each other. Furthermore, the first thermoelectric conversion element 23 and the second thermoelectric conversion element 24 have Nernst coefficients of the same sign.

[0075] In the thermoelectric conversion device 20 of this embodiment having the above-mentioned configuration, when a heat flow Q flows from 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.

[0076] 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 generation body 22. At this time, in the first thermoelectric conversion 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 thermoelectric conversion 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).

[0077] In the power generation body 22, the first thermoelectric conversion element 23 and the second thermoelectric conversion element 24, which are adjacent to each other, are electrically connected in series, so that the electromotive force E1 generated in the first thermoelectric conversion element 23 and the electromotive force E2 generated in the second thermoelectric conversion element 24 are added together, making it possible to increase the output voltage V.

[0078] 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 thermoelectric conversion element 23 and the second thermoelectric conversion element 24 that are thin sheets.

[0079] Here, assuming that the length in the longitudinal direction of the first thermoelectric conversion element 23 and the second thermoelectric conversion element 24 is L and the thickness (height) is H, the voltage V generated by the anomalous Nernst effect is proportional to L / H. In other words, the longer and thinner the first thermoelectric conversion element 23 and the second thermoelectric conversion element 24 are, the larger the obtained voltage V becomes.

[0080] Therefore, in the thermoelectric conversion device 20 of this embodiment, by adopting a power generating body 22 in which the above-mentioned adjacent first thermoelectric conversion element 23 and second thermoelectric conversion element 24 are electrically connected in series, a further increase in voltage V can be expected due to an improved anomalous Nernst effect.

[0081] In addition to the above-mentioned configuration, the thermoelectric conversion device 20 may also adopt a configuration in which, for example, the first thermoelectric conversion element 23 and the second thermoelectric conversion element 24 have Nernst coefficients of opposite signs to each other and are arranged so that the direction of magnetization M1 of the first thermoelectric conversion element 23 and the direction of magnetization M2 of the second thermoelectric conversion element 24 are the same.

[0082] Third embodiment (Thermoelectric conversion device) Next, as a third embodiment of the present invention, for example, a thermoelectric conversion device 30 shown in the drawings will be described. FIG. 4 is a schematic diagram showing the configuration of the thermoelectric conversion device 30. When the spiral thermoelectric conversion element 32 shown in FIG. 4 is produced by sintering under a pressure of 1 MPa or less, a cylindrical object is produced during sintering, and then the cylindrical object is cut to produce the spiral thermoelectric conversion element 32. Alternatively, since near-net sintering is possible under a pressure of 1 MPa or less, the spiral thermoelectric conversion element 32 can be produced by sintering the object into a cylindrical shape and cutting it out. Alternatively, the spiral thermoelectric conversion element 32 can be produced by producing a plurality of tile-shaped thermoelectric conversion elements, such as a part of a cylindrical shape, and connecting the produced tile-shaped thermoelectric conversion elements to each other.

[0083] 4, a thermoelectric conversion device 30 of this embodiment includes a substantially cylindrical hollow member 31 and a long sheet-like thermoelectric conversion element 32 spirally wound around the outer circumferential surface of the hollow member 31. The thermoelectric conversion element 32 may be basically the same as the anomalous Nernst effect element 1. The thermoelectric conversion element 32 is magnetized in a direction parallel to the axial direction (x direction) of the hollow member 31.

[0084] 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, creating a temperature gradient (temperature difference) from the inside to the outside of the hollow member 31, and a voltage V is generated in the thermoelectric conversion element 32 due to the anomalous Nernst effect. That is, in the thermoelectric conversion element 32, an electromotive force is generated along the longitudinal direction of the thermoelectric conversion element 32 (the direction perpendicular to both the magnetization direction and the heat flow direction).

[0085] In the thermoelectric conversion device 30 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 a thin sheet-like thermoelectric conversion element 32.

[0086] Therefore, in the thermoelectric conversion device 20 of this embodiment, by adopting a long sheet-like thermoelectric conversion element 32 wound in a spiral shape around the outer peripheral surface of the hollow member 31 described above, a further increase in voltage V can be expected due to an improved anomalous Nernst effect.

[0087] [Fourth embodiment] Next, a thermoelectric conversion device 100B according to a fourth embodiment will be described. Fig. 5 is a plan view of the thermoelectric conversion device 100B. The thermoelectric conversion device 100B includes a substrate 30 and a power generation body 40B disposed on the substrate 30.

[0088] (Power generating body 40B) The power generating body 40B has a plurality of thermoelectric conversion elements 45 and wiring 50.

[0089] "Thermoelectric conversion element 45" The thermoelectric conversion elements 45 can be basically the same as the anomalous Nernst effect element 1. The thermoelectric conversion elements 45 are arranged in parallel on the substrate 30 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).

[0090] "Wiring 50" In the thermoelectric conversion device 100B, one end of the wiring 50 is electrically connected to one end side (-Y side) of the thermoelectric conversion element 45, and the other end is electrically connected to the other end side (+Y side) of another adjacent thermoelectric conversion element 45. This electrically connects the thermoelectric conversion elements 45 in series. The material of the wiring 50 is not particularly limited as long as it is conductive. For example, the material of the wiring 50 may be metal such as Au, Ag, Cu, or Al.

[0091] (1st electrode 11A) In the thermoelectric conversion device 100B, the first electrode 11A is electrically connected to one end of the power generation body 40B. The material of the first electrode 11A is not particularly limited as long as it has electrical conductivity. For example, the material of the first electrode 11A may be a metal such as Au, Ag, Cu, or Al.

[0092] (2nd electrode 12A) In the thermoelectric conversion device 100B, the second electrode 12A is electrically connected to the other end of the power generation body 40B. The material of the second electrode 12A is not particularly limited as long as it has electrical conductivity. For example, the material of the second electrode 12A may be a metal such as Au, Ag, Cu, or Al.

[0093] The heat flow Q flows from the substrate 30 side to the power generation body 40B side (flows in the +Z direction). The thermoelectric conversion device 100B can be manufactured more easily than the thermoelectric conversion device 20 because adjacent thermoelectric conversion elements 45 are connected via wiring 50.

[0094] 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 to various devices, not just the thermoelectric conversion devices 20, 30, and 100B described above. For example, by providing the anomalous Nernst effect element 1 in a heat flow sensor, it is possible to determine whether the thermal insulation performance of a building is good or bad.

[0095] Furthermore, by providing the thermoelectric conversion device 20, 30, 100B 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 device 20, 30 can be effectively used as an auxiliary power source.

[0096] 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 generated by the Seebeck effect caused by the temperature gradient and the voltage generated by the anomalous Nernst effect.

[0097] 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.

[0098] In the above embodiment, it has been described that the sintered body 2 containing Co, Mn, and Ga provides a larger anomalous Nernst effect than conventional sintered bodies. However, other than sintered bodies containing Co, Mn, and Ga (e.g., Co2MnGa), examples of substances that may enhance the anomalous Nernst effect include sintered bodies 2 such as Fe3Ga, Fe3Al, Co2MnAl, Co2MnIn, Mn3Ga, Mn3Ge, Fe2NiGa, CoTiSb, CoVSb, CoCrSb, CoMnSb, and TiGa2Mn. EXAMPLES

[0099] The effects of the present invention will be more clearly understood by the following examples. Note that the present invention is not limited to the following examples, and can be modified as appropriate without departing from the spirit and scope of the present invention.

[0100] In this example, a sintered body of Co2MnGa was produced by uniaxially molding the raw material powder of Co2MnGa while changing the sintering temperature and then sintering it at 0.1 MPa.

[0101] The sintered body with "ethanol mixed" listed in the compacting method in Table 1 (ethanol mixed sintered body) was produced by mixing the raw material powder with ethanol, moistening it, filling it into a non-magnetic metal mold, applying a uniaxial pressure of 10 to 200 MPa and holding it for 10 seconds to 5 minutes, removing it from the metal mold as a green body (compressed powder body), and sintering it at 0.1 MPa (sintered body of experiment No. 4).

[0102] The sintered body (carbon-mold filled sintered body) described as "carbon mold filling" in the powder compacting method in Table 1 was produced by the following method. The powder was filled into a carbon mold, uniaxially pressurized at 10 to 200 MPa, and held for 10 seconds to 5 minutes to produce a compact (green compact). Carbon mold filling sintering differs from ethanol mixed sintering in that the filled powder was not removed from the carbon mold, but was sintered with the carbon mold at 0.1 MPa to produce a sintered body (sintered body of experiment No. 5).

[0103] The sintered body (binder-mixed sintered body A) described as binder mixed (Oricox KC-1700P) in the powder compacting method in Table 1 was produced by the following method. A mixture was produced by mixing the raw material powder with a binder (Oricox KC-1700P, Kyoeisha Chemical Co., Ltd.) at a concentration of 2 to 10% by weight based on the total mass of the raw material powder. The produced mixture was filled into a non-magnetic metal mold and subjected to uniaxial pressure of 10 to 200 MPa, and held for 10 seconds to 5 minutes to produce a green body (green body). The green body removed from the mold was sintered at 0.1 MPa to produce a sintered body (sintered body of experiment No. 6).

[0104] The sintered body (binder-mixed sintered body B) described as binder mixed (Z-300) in the powder compacting method in Table 1 was produced by the following method. The raw material powder was mixed with a binder (Z-300, Mitsubishi Chemical Corporation) at a concentration of 2 to 10% by weight based on the total mass of the raw material powder. The produced mixture was filled into a non-magnetic metal mold and uniaxially pressed at 10 to 200 MPa, and held for 10 seconds to 5 minutes to produce a green body (green body). The green body removed from the mold was sintered at 0.1 MPa to produce a sintered body (sintered body of experiment No. 7).

[0105] Sintering under a pressure of 1MPa or less involved degassing the electric furnace to 20-40Pa before sintering in order to minimize oxygen and water vapor in the furnace, and then restoring the N2 gas pressure to 0.1MPa. This process was repeated three times. Sintering conditions were an N2 atmosphere with N2 gas flowing at 5-10L / min. The sintering program involved heating up to 1000°C at 10°C / min, holding at 1000°C for 3 hours, and then naturally cooling.

[0106] The sintered compacts were cut and polished to the desired shape, and anomalous Nernst measurements were performed.

[0107] Anomalous Nernst coefficient S ANE , electrical resistivity ρ xx The thermal conductivity κ and the thermal conductivity κ were obtained as follows. A flat plate-shaped sample (for example, length L=8 mm, width W=1.5 mm, thickness t=1 mm) for evaluation was cut out from the sintered body 2, and then, using the Thermal Transport Option of a Physical Property Measurement System manufactured by Quantum Design, one end of the sample was brought into contact with a heater at a temperature of 300 K to inject pulsed heat, and the other end was brought into contact with a heat sink, thereby applying a temperature difference along the length of the sample. The temperature difference ΔT between two points separated by L_temp on the sample was measured. A magnetic field was also applied in a direction perpendicular to 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. The anomalous Nernst coefficient S ANE was calculated from the voltage V when a magnetic field of 2 Tesla was applied, using the above formula (4). The results are shown in Table 1.

[0108] Electrical resistivity ρ xx The results are shown in Table 1.

[0109] The thermal conductivity κ was obtained by applying pulsed heat to one end of the sample using the Thermal Transport Option of the Physical Property Measurement System manufactured by Quantum Design, and analyzing the relaxation process of the temperature difference generated in the sample. The results are shown in Table 1.

[0110] And these anomalous Nernst coefficients S ANE , electrical resistivity ρ xx The dimensionless figure of merit ZT was calculated using the values ​​of the thermal conductivity κ and the thermal conductivity κ according to the above formula (3). The results are shown in Table 1.

[0111] The anomalous Nernst coefficient S ANE , electrical resistivity ρ xx The measurements of the electrical resistivity ρ and thermal conductivity κ were performed on the same cut sample. xx The direction of the electric current applied during the measurement of the thermal conductivity κ was the same as the direction of the heat flow applied during the measurement of the thermal conductivity κ. The measurement was performed at 300K.

[0112] The relative density and porosity were measured by the Archimedes method, and the results are shown in Table 1.

[0113] As comparative examples, Table 1 shows the results of a single crystal of Co2MnGa (Non-Patent Documents 2 (Experiment No. 1) and 3 (Experiment No. 2)) and a high-pressure sintered body by spark plasma sintering (SPS) (Experiment No. 3). Here, a single crystal is a large single crystal of μm or more, while a sintered body means an aggregate of many crystals of nm, μm, or mm scale. In Table 1, blanks in the sintering method, sintering temperature, and sintering time columns indicate that no sintering was performed. Blanks in the relative density and porosity columns indicate that the body is a single crystal. Blanks in the compaction method column in Table 1 indicate that no compaction was performed. In the sintering method column in Table 1, "atmospheric pressure sintering" means that sintering was performed under a pressure of 0.1 MPa.

[0114] The porosity of the samples sintered under a pressure of 1 MPa or less was 29.6% for the ethanol-mixed sintered body (Experiment No. 4), 24.7% for the carbon-type filled sintered body (Experiment No. 5), 42.7% for the binder-mixed sintered body A (Experiment No. 6), and 37.6% for the binder-mixed sintered body B (Experiment No. 7).

[0115] The relative densities of the samples sintered under a pressure of 1 MPa or less were 70.4% for the ethanol-mixed sintered body (Experiment No. 4), 75.3% for the carbon-type filled sintered body (Experiment No. 5), 57.3% for the binder-mixed sintered body A (Experiment No. 6), and 62.4% for the binder-mixed sintered body B (Experiment No. 7).

[0116] As shown in Table 1, the thermal conductivity of the Co2MnGa sintered body satisfying the conditions of the present invention was significantly suppressed by containing about 25 to 43% voids. The thermal conductivity of the single crystal was 21 to 22 W / K·m, and that of the SPS sintered body was 26 W / K·m. The thermal conductivity of the ethanol-mixed sintered body (Experiment No. 4) and the carbon-type filled sintered body (Experiment No. 5) was suppressed by nearly half, and that of the binder-mixed sintered body (Experiment No. 6 and Experiment No. 7) was suppressed by more than 80%. The absolute value of the anomalous Nernst coefficient of the ethanol-mixed sintered body (Experiment No. 4), the carbon-type filled sintered body (Experiment No. 5), the binder-mixed sintered body A (Experiment No. 6), and the binder-mixed sintered body B (Experiment No. 7) was 1.0 μV / K to 10 μV / K at 10°C to 50°C in a magnetic field of 2 Tesla.

[0117] A small thermal conductivity means that a large temperature difference or temperature gradient can be created within the sample, making it suitable as a thermoelectric conversion material when it is desired to suppress heat flow or to create a large temperature difference or temperature gradient.

[0118] [Table 1] [Explanation of symbols]

[0119] Reference Signs List 1 anomalous Nernst effect element 2 sintered body 20 thermoelectric conversion device 21 substrate 22 power generation body 23 first thermoelectric conversion element 24 second thermoelectric conversion element 30 thermoelectric conversion device 31 hollow member 32 thermoelectric conversion element

Claims

1. A sintered body containing Co, Mn, and Ga, The anomalous Nernst effect element has a porosity of 20% or more of the sintered body.

2. 2. The anomalous Nernst effect element according to claim 1, wherein the sintered body has a Heusler structure.

3. 2. The anomalous Nernst effect element according to claim 1, wherein the electrical resistivity of said sintered body is 200 μΩ·cm or more.

4. 2. The anomalous Nernst effect element according to claim 1, wherein the absolute value of the anomalous Nernst coefficient of said sintered body is 1.0 μV / K or more.

5. The method includes the steps of preparing a compact including a powder containing Co, Mn, and Ga, After the above step, the powder is sintered at a sintering temperature of 700° C. to 1100° C. under a pressure of 1 MPa or less.

6. 6. The method for producing an anomalous Nernst effect element according to claim 5, wherein in the step, a mixture of the powder and ethanol is uniaxially pressurized at 10 MPa to 200 MPa, and then sintered under the pressure.

7. 6. The method for manufacturing an anomalous Nernst effect element according to claim 5, wherein in the step, the powder is filled into a mold, uniaxially pressed at 10 MPa to 200 MPa, and then sintering is performed under the pressure while the powder is filled into the mold.

8. 6. The method for producing an anomalous Nernst effect element according to claim 5, wherein in the step, the mixture of the powder and the binder is uniaxially pressed at 10 MPa to 200 MPa, and then sintered under the pressure.

9. The anomalous Nernst effect element according to claim 1 is provided, The sintered body has a thermal conductivity of 15 W / K·m or less.

10. A thermoelectric conversion device that performs thermoelectric conversion using the anomalous Nernst effect element according to claim 1.

11. 11. The thermoelectric conversion device according to claim 10, wherein the absolute value of the anomalous Nernst coefficient of the sintered body is 1.0 μV / K to 10 μV / K at 10° C. to 50° C.

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