Thermoelectric conversion element and thermoelectric conversion device

Abstract

The present invention provides a thermoelectric conversion element composed of a first substance, a second substance, a third substance, a fourth substance or a fifth substance. The stoichiometric composition of the first substance (such as Fe3Al, etc.) is represented by the compositional formula Fe3X, where X is a typical element or a transition element; the second substance has an off-stoichiometric composition in which the composition ratio of Fe and X deviates from that of the first substance; the third substance (Nd 0.1 Fe 2.9 Ga, etc.) is a substance obtained by substituting a part of the Fe sites of the first substance or a part of the Fe sites of the second substance with a typical metal element or a transition element other than X; the fourth substance (Fe3Al 1‑x Ga x , etc.) is represented by the compositional formula Fe3M1 1‑x M2 x (0 < x < 1), where M1 and M2 are different typical elements; the fifth substance (Fe 2.9 Pt 0.1 Ga 0.9 Ge 0.1 , etc.) is a substance obtained by substituting a part of the Fe sites of the first substance with a transition element other than X and substituting a part of the X sites with a typical metal element other than X. The first substance, the second substance, the third substance, the fourth substance and the fifth substance exhibit an anomalous Nernst effect.

Description

Technical Field

[0001] The present invention relates to a thermoelectric conversion element and a thermoelectric conversion device including the thermoelectric conversion element. Background Art

[0002] As a thermoelectric mechanism that generates a voltage when a temperature gradient is applied to a substance, the Seebeck effect is known (for example, see Patent Document 1). However, in the thermoelectric mechanism using the Seebeck effect, materials that can be used at room temperature or higher are materials mainly made of bismuth, tellurium, lead, etc., which are highly toxic, so they are not suitable for practical use. In addition, they are mechanically fragile and have weak vibration resistance and do not have durability. Further, in the Seebeck effect, a voltage is generated in the same direction as the temperature gradient, so it is necessary to fabricate a three-dimensional and complex structure in which p-type modules and n-type modules are alternately provided in the vertical direction from the surface of the heat source, so the manufacturing cost is high. Also, it is difficult to expand such three-dimensional elements over a large area.

[0003] Similarly, as a thermoelectric mechanism that generates a voltage through a temperature gradient, the Anomalous Nernst effect is known. The Anomalous Nernst effect refers to a phenomenon in which a voltage is generated in a direction orthogonal to both the magnetization direction and the temperature gradient when a heat current is passed through a magnetic material to generate a temperature difference. In recent years, it has been found that by utilizing the topology of the electronic structure, the Nernst coefficient is much larger than the value (0.1 μV / K) known so far.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: International Publication WO2016 / 181777 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] However, so far, although various magnetic substances showing the Anomalous Nernst effect have been developed, there is a problem of increased cost because relatively expensive metals are used.

[0009] The present invention has been made in view of the above problems, and an object thereof is to provide a thermoelectric conversion element and a thermoelectric conversion device made of inexpensive and non-toxic materials.

[0010] Means for Solving the Problems

[0011] A thermoelectric conversion element according to an embodiment of the present invention is composed of the following substances: a first substance having a stoichiometric composition represented by the compositional formula Fe3X, where X is a typical element or a transition element; a second substance having a non-stoichiometric composition in which the composition ratio of Fe and the X deviates from the first substance; a third substance obtained by substituting a part of the Fe sites of the first substance or a part of the Fe sites of the second substance with a typical metal element or a transition element other than the X; a fourth substance having a compositional formula represented by Fe3M1 1-x M2 x (0 < x < 1), where M1 and M2 are different typical elements from each other; or a fifth substance obtained by substituting a part of the Fe sites of the first substance with a transition element other than X and substituting a part of the X sites with a typical metal element other than X. The first substance, the second substance, the third substance, the fourth substance, and the fifth substance exhibit an anomalous Nernst effect.

[0012] A thermoelectric conversion device according to an embodiment of the present invention includes a substrate and a power generation body provided on the substrate and having a plurality of thermoelectric conversion elements. Each of the plurality of thermoelectric conversion elements has a shape extending in one direction and is composed of the above-mentioned first substance, second substance, third substance, fourth substance, or fifth substance. The plurality of thermoelectric conversion elements are arranged in parallel in a direction perpendicular to the one direction and are electrically connected in series.

[0013] A thermoelectric conversion device according to another embodiment of the present invention includes the above-mentioned thermoelectric conversion element and a hollow member. The thermoelectric conversion element has a sheet-like structure or a wire and is provided so as to cover the outer surface of the hollow member.

[0014] Advantages of the Invention

[0015] According to the present invention, an anomalous Nernst effect can be exhibited by a thermoelectric conversion element composed of inexpensive and non-toxic substances. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram showing the crystal structure of D03-type Fe3X and the crystal structure of L12-type Fe3X.

[0017] Figure 2 is a schematic diagram for explaining the thermoelectric mechanism of the thermoelectric conversion element according to the present embodiment.

[0018] Figure 3 is a graph showing the temperature dependence of the Nernst coefficient of various metal materials.

[0019] Figure 4 is a graph obtained by normalizing the Nernst coefficient shown in Figure 3 with the Nernst coefficient at T = 300K.

[0020] Figure 5 It is a graph showing the magnetic field dependence of the Nernst coefficient at T = 300K for single crystals and polycrystals of Fe-Al alloys, and polycrystals of Fe-Al-V alloys.

[0021] Figure 6 It is a graph showing the temperature dependence of the Nernst coefficient for single crystals and polycrystals of Fe-Al alloys and polycrystals of Fe-Al-V alloys.

[0022] Figure 7 It is a perspective view showing the structure of a thermoelectric conversion device according to Example 1 of a thermoelectric conversion element having this embodiment.

[0023] Figure 8 It is a top view showing the structure of a thermoelectric conversion device according to Example 2 of a thermoelectric conversion element having this embodiment.

[0024] Figure 9 It is an external view showing the structure of a thermoelectric conversion device according to Example 3 of a thermoelectric conversion element having this embodiment.

[0025] Figure 10 It represents Fe3Pt, Fe3Ge, Fe3Al, Fe3Ga 0.5 Al 0.5 , Fe3Ga, and a graph showing the magnetic field dependence of the Nernst coefficient at T = 300K for Co2MnGa.

[0026] Figure 11 It is a graph showing the temperature dependence of the Nernst coefficient for Fe3Pt, Fe3Ge, Fe3Al, Fe3Ga, and Co2MnGa.

[0027] Figure 12A It is a graph showing the temperature dependence of the Nernst coefficient for Fe3Sn.

[0028] Figure 12B It is a graph showing the temperature dependence of the transverse thermoelectric conductivity for Fe3Sn.

[0029] Figure 13A It is a table showing the Nernst coefficient at T = 300K for the mixed crystal system of Fe3Si and Fe3Al.

[0030] Figure 13B It is a graph showing the Nernst coefficient at T = 300K for the mixed crystal system of Fe3Si and Fe3Al.

[0031] Figure 14A It is a table showing the Nernst coefficient at T = 300K for the mixed crystal system of Fe3Al and Fe3Ga.

[0032] Figure 14BIt is a graph showing the Nernst coefficient at T = 300K for a mixed crystal system of Fe3Al and Fe3Ga.

[0033] Figure 15 It is a graph showing the Nernst coefficient at T = 300K for Fe3Cu 1-x Ga x single crystals and polycrystals obtained by replacing a part of the Ga sites in Fe3Ga with Cu.

[0034] Figure 16A It is a graph showing the 0.1 Fe 2.9 X-ray diffraction patterns of Ga and Fe3Ga.

[0035] Figure 16B It is a graph showing the 0.1 Fe 2.9 magnetic field dependence of the magnetization of Ga at T = 300K.

[0036] Figure 16C It is a graph showing the Nernst coefficient of Fe3Ga single crystals and 0.1 Fe 2.9 Ga polycrystals as a function of magnetic field at T = 300K.

[0037] Figure 16D It is a graph showing the Nernst coefficient of Fe3Ga single crystals and 0.1 Fe 2.9 Ga polycrystals as a function of magnetic field of the Hall resistivity at T = 300K.

[0038] Figure 17A It is a graph showing the 0.05 Fe 2.95 X-ray diffraction patterns of Ga and Fe3Ga.

[0039] Figure 17B It is a graph showing the 0.05 Fe 2.95 magnetic field dependence of the magnetization of Ga at T = 300K.

[0040] Figure 18A It is a graph showing the 0.05 Fe 2.95 X-ray diffraction patterns of Ga and Fe3Ga.

[0041] Figure 18B It is a graph showing the 0.05 Fe 2.95 magnetic field dependence of the magnetization of Ga.

[0042] Figure 19A It is a graph showing the 0.05 Fe 2.95Graph of the magnetic field dependence of the magnetization of Ga.

[0043] Figure 19B is a graph that magnifies and shows the region near the low magnetic field of Figure 19A .

[0044] Figure 20A is a graph showing the X-ray diffraction patterns of Tb 0.03 Fe 2.97 Ga and Fe3Ga.

[0045] Figure 20B is a graph showing the magnetic field dependence of the magnetization of Tb 0.03 Fe 2.97 Ga at T = 300 K.

[0046] Figure 21A is a graph showing the X-ray diffraction patterns of Fe3Ga 0.8 B 0.2 , Fe3Ga 0.9 B 0.1 and Fe3Ga.

[0047] Figure 21B are graphs respectively showing the magnetic field dependence of the magnetization of the needle-shaped specimen and the plate-shaped specimen composed of Fe3Ga 0.8 B 0.2 at T = 300 K.

[0048] Figure 21C is a graph showing the magnetic field dependence of the magnetization of Fe3Ga 0.8 B 0.2 and Fe3Ga in the needle-shaped specimen.

[0049] Figure 21D is a graph showing the magnetic field dependence of the magnetization of Fe3Ga 0.8 B 0.2 and Fe3Ga in the plate-shaped specimen.

[0050] Figure 21E is a graph showing the magnetic field dependence of the Nernst coefficient of Fe3Ga 0.8 B 0.2 in the plate-shaped specimen.

[0051] Figure 21F is a graph showing the magnetic field dependence of the Hall resistivity of Fe3Ga 0.8 B 0.2 in the plate-shaped specimen.

[0052] Figure 22A is a graph showing Fe 2.9 Mn 0.1 Ga, Fe 2.5 Mn 0.5Graph of the X-ray diffraction patterns of Ga, Fe2MnGa, and Fe3Ga.

[0053] Figure 22B Indicates Fe of the needle-shaped specimen 2.9 Mn 0.1 Ga and Fe 2.5 Mn 0.5 Graph of the magnetic field dependence of magnetization at T = 300 K for Ga and Fe

[0054] Figure 23A Indicates Fe 2.9 Pt 0.1 Ga, Fe 2.9 Pt 0.1 Ga 0.9 Ge 0.1 And graph of the X-ray diffraction patterns of Fe3Ga.

[0055] Figure 23B Indicates Fe of the needle-shaped specimen 2.9 Pt 0.1 Ga and Fe 2.9 Pt 0.1 Ga 0.9 Ge 0.1 Graph of the magnetic field dependence of magnetization at T = 300 K.

[0056] Figure 24 Schematic diagram for explaining the anomalous Nernst effect when a temperature gradient is applied in the in-plane direction of a thin-film specimen as a thermoelectric conversion element.

[0057] Figure 25 Graph showing the measurement results of the anomalous Nernst effect at T = 300 K when a temperature gradient is applied in the in-plane direction to the thin-film specimen (Fe3Ga).

[0058] Figure 26 Schematic diagram for explaining the anomalous Nernst effect when a temperature gradient is applied in the direction perpendicular to the plane of a thin-film specimen as a thermoelectric conversion element.

[0059] Figure 27A Schematic diagram for explaining the measurement method of the anomalous Nernst effect when a temperature gradient is applied in the direction perpendicular to the plane of a thin-film specimen.

[0060] Figure 27B Schematic diagram for explaining the measurement method of the anomalous Nernst effect when a temperature gradient is applied in the direction perpendicular to the plane of a thin-film specimen.

[0061] Figure 28 Graph showing the measurement results of the anomalous Nernst effect when a temperature gradient is applied in the direction perpendicular to the plane of the thin-film specimen (Fe3Ga).

[0062] Figure 29A This figure shows the measurement results of the anomalous Nernst effect when a temperature gradient is applied in the direction perpendicular to the plane of a thin film sample of Fe3Ga obtained without annealing after film formation at room temperature.

[0063] Figure 29B This is for Figure 29A a magnified view near the low magnetic field of

[0064] Figure 30 This figure shows the measurement results of the anomalous Nernst effect when a temperature gradient is applied in the direction perpendicular to the plane of an epitaxial film of Fe3Ga obtained after annealing and an amorphous film of Fe3Ga obtained without annealing after film formation at room temperature, respectively. Detailed implementation manners

[0065] Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

[0066] Among substances showing the anomalous Nernst effect, the highest value of the Nernst coefficient at room temperature achieved so far by the inventors of the present application is 6 μV / K achieved with Co2MnGa (see Nature Physics 14, 1119 - 1124 (2018) and International Publication WO2019 / 009308).

[0067] As will be described later, the inventors of the present application were able to achieve a Nernst coefficient close to the highest value achieved so far with binary Fe3Al. The Clark numbers representing the weight ratios of elements existing near the earth's surface are, in descending order, oxygen (O), silicon (Si), aluminum (Al), iron (Fe),.... Thus, since the Clark numbers of Fe and Al are relatively large, they are very inexpensive materials and are non-toxic. In addition, Fe3Al is also chemically stable, and the ferromagnetic transition temperature is as high as about 700 K.

[0068] Figure 1 The crystal structures of Fe3X (X is a typical element or a transition element) capable of exhibiting the anomalous Nernst effect are shown. As Figure 1 shown, Fe3X can adopt the D03-type structure (a) and the L12-type structure (b).

[0069] The unit cell of the D03 structure (a) has 8 body-centered cubic (bcc)-type sub-unit cells. In each sub-unit cell, Fe atoms (Fe(II)) occupy the corner points, and each Fe(II) is shared by 8 adjacent sub-unit cells. The body-centered points of 4 out of the 8 sub-unit cells are occupied by 4 Fe atoms (Fe(I)) respectively, and the body-centered points of the remaining 4 sub-unit cells are occupied by 4 X atoms respectively. For example, the lattice constant a of Fe3Al with the D03 structure is (See Physical Review B 66, 205203 (2002)).

[0070] The L12 structure (b) is a face-centered cubic (fcc)-type crystal structure with Fe atoms at the face-centered points and X atoms at the corner points.

[0071] For example, a single crystal of Fe3Al is prepared by arc melting Fe and Al in an appropriate ratio, growing the crystal by pulling using the Czochralski method, annealing the crystal at a low temperature (e.g., 500 °C), and slowly cooling it to room temperature over several minutes to several tens of minutes. According to electron beam diffraction, it is found that the prepared single crystal of Fe3Al is an ordered phase (D03 phase (Fm-3m)).

[0072] On the other hand, polycrystalline Fe3Al is prepared by arc melting an appropriate ratio of Fe and Al to make a polycrystalline sample, annealing the sample at a high temperature (e.g., 900 °C), and rapidly cooling it to room temperature within several seconds. According to the phase diagram, the prepared polycrystalline Fe3Al is considered to be a disordered phase (B2 phase (Pm-3m) or A2 phase (Im-3m)) or a mixed crystal with an ordered phase.

[0073] Next, reference will be made to Figure 2 the thermoelectric conversion element and its thermoelectric mechanism according to an embodiment of the present invention will be described.

[0074] The thermoelectric conversion element 1 according to the present embodiment is composed of a single crystal or polycrystal of Fe3X prepared by the above method. As Figure 2 shown, the thermoelectric conversion element 1 has a rectangular parallelepiped shape extending in one direction (y direction), has a predetermined thickness (length in the z direction), and is magnetized in the +z direction. When a heat current flows through the thermoelectric conversion element 1 in the +x direction, a temperature difference is generated in the +x direction. Thus, in the thermoelectric conversion element 1, due to the anomalous Nernst effect, an electromotive force is generated in the direction of the outer product orthogonal to both the direction of the heat current Q (+x direction) and the direction of magnetization M (+z direction) (y direction)

[0075] Figure 3 shows the result of comparing the Nernst coefficient (S yx ) of the thermoelectric conversion element 1 composed of a single crystal of Fe3Al with the Nernst coefficient of a thermoelectric conversion element composed of other metal materials, representing the temperature dependence of the Nernst coefficient. Figure 4 is a graph obtained by normalizing the Nernst coefficients of the respective metal materials shown in Figure 3 with the Nernst coefficient at T = 300 K.

[0076] In Figure 3 and Figure 4Among them, Fe3Al#1 represents the observation result of the thermoelectric conversion element 1 composed of a single crystal of a non-stoichiometric composition (Fe-rich, Al-poor) with a composition ratio of Fe and Al deviating from 3:1, and Fe3Al#2 represents the observation result of the thermoelectric conversion element 1 composed of a single crystal of a stoichiometric composition with a composition of Fe and Al of 3:1.

[0077] In addition, in Figure 3 and Figure 4 the data of L10-type MnGa, D0 22 type Mn2Ga, Co / Ni, FePd and FePt are based on the data disclosed in Appl. Phys. Lett. 106, 252405 (2015), and the data of Fe3O4 are based on the data disclosed in Physical Review B90, 054422 (2014). In addition, the data of Co2MnGa are based on the research of the inventors of the present application (Nature Physics 14, 1119-1124 (2018); International Publication WO2019 / 009308).

[0078] From Figure 3 and Figure 4 it can be seen that the absolute value of the Nernst coefficient |S yx | of Fe3Al#1 and Fe3Al#2 is larger than that of other metallic materials except Co2MnGa. In particular, the |S yx | of stoichiometric Fe3Al#2 is larger than that of non-stoichiometric Fe3Al#1, and is about 4 μV / K at room temperature (near T = 300K), and the |S yx | of Co2MnGa is ≈ 6 μV / K.

[0079] In addition, from Figure 3 and Figure 4 it can be seen that in the temperature range of 200K to 400K including room temperature, the S yx of non-stoichiometric Fe3Al#1 is hardly affected by temperature changes and is approximately a constant value.

[0080] Figure 5 represents the magnetic field dependence of the Nernst coefficient (S yx ) of single crystals (S1, S2) and polycrystals (P2) of Fe-Al alloys, and polycrystals (P1) of Fe-Al-V alloys at T = 300K, Figure 6 represents the temperature dependence of the Nernst coefficient of single crystals (S1, S2) and polycrystals (P2) of Fe-Al alloys, and polycrystals (P1) of Fe-Al-V alloys when a magnetic field B = 2T is applied.

[0081] In Figure 5 andFigure 6 in which, S1 and S2 respectively correspond to Figure 3 Fe3Al#2 and Fe3Al#1 shown in the figure. S1 represents the observation result when a magnetic field B parallel to

[001] is applied to the thermoelectric conversion element 1 and a heat flux Q parallel to

[010] flows through it. S2 represents the observation result when a magnetic field B parallel to

[001] is applied to the thermoelectric conversion element 1 and a heat flux Q parallel to

[210] flows through it.

[0082] In addition, in Figure 5 and Figure 6 P1 represents the observation result of the thermoelectric conversion element 1 composed of Fe 2.8 V 0.15 Al polycrystals obtained by substituting part of the Fe sites of Fe3Al with vanadium (V). P2 represents the observation result of the thermoelectric conversion element 1 composed of polycrystals with a stoichiometric composition of Fe and Al of 3:1.

[0083] From Figure 5 and Figure 6 it can be seen that, compared with single crystals (S1, S2), the absolute value of the Nernst coefficient |S yx | is larger. In addition, if polycrystals P1 and P2 are compared, it can be seen that the absolute value of |S yx | of polycrystal P2 of the stoichiometric binary system is larger than that of polycrystal P1 of the ternary system.

[0084] In addition, compared with single crystals (S1, S2), the Nernst coefficient of polycrystals (P1, P2) is almost not affected by temperature changes in the temperature range of 200K to 400K including room temperature (T = around 300K) and is approximately a constant value. Although the absolute value of |S yx | of polycrystals (P1, P2) is smaller than that of single crystals (S1, S2), the absolute value of |S yx | at room temperature is about 1.5 to 2.0 μV / K, and it can be said that it has reached the practical level of heat flux sensors, etc. In addition, as described above, polycrystals (P1, P2) are easier to fabricate than single crystals (S1, S2).

[0085] Next, a thermoelectric conversion device obtained by modularizing the thermoelectric conversion element of the present embodiment will be described.

[0086] Example 1

[0087] Figure 7The external structure of the thermoelectric conversion device 20 according to Embodiment 1 of the present embodiment is shown. The thermoelectric conversion device 20 has a substrate 22 and a power generation body 23 placed on the substrate 22. In the thermoelectric conversion device 20, when a heat flux Q flows from the substrate 22 side to the power generation body 23, a temperature difference in the heat flux direction is generated on the power generation body 23, and a voltage V is generated on the power generation body 23 due to the anomalous Nernst effect.

[0088] The substrate 22 has a first surface 22a on which the power generation body 23 is placed and a second surface 22b on the opposite side of the first surface 22a. Heat from a heat source (not shown) is applied to the second surface 22b.

[0089] The power generation body 23 has a plurality of thermoelectric conversion elements 24 and a plurality of thermoelectric conversion elements 25, each having an L-shaped three-dimensional shape and being made of the same material as the Figure 2 thermoelectric conversion element 1 shown. As Figure 7 shown, the plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 are alternately arranged side by side on the substrate 22 in a direction (y direction) perpendicular to their respective length directions (x direction). In addition, the number of the thermoelectric conversion elements 24 and the thermoelectric conversion elements 25 constituting the power generation body 23 is not limited.

[0090] In addition, the plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 are arranged such that the direction of magnetization M1 of the thermoelectric conversion element 24 is opposite to the direction of magnetization M2 of the thermoelectric conversion element 25. In addition, the plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 have Nernst coefficients of the same sign.

[0091] The thermoelectric conversion element 24 has a first end face 24a and a second end face 24b parallel to the length direction (x direction). The thermoelectric conversion element 25 has a first end face 25a and a second end face 25b parallel to the length direction (x direction). The first end face 25a of the thermoelectric conversion element 25 is connected to the second end face 24b of the adjacent thermoelectric conversion element 24, and the second end face 25b of the thermoelectric conversion element 25 is connected to the first end face 24a of the thermoelectric conversion element 24 adjacent on the opposite side. Therefore, the plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 are connected in series electrically. That is, the power generation body 23 is provided in a meandering shape on the first surface 22a of the substrate 22.

[0092] When heat is applied from a heat source to the second surface 22b of the substrate 22, the heat flux Q in the +z direction flows toward the power generation body 23. If a temperature difference is generated due to the heat flux Q, then due to the anomalous Nernst effect, in the thermoelectric conversion element 24, an electromotive force E1 is generated in the direction (-x direction) orthogonal to both the direction of the magnetization M1 (-y direction) and the direction of the heat flux Q (+z direction). In the thermoelectric conversion element 25, due to the anomalous Nernst effect, an electromotive force E2 is generated in the direction (+x direction) orthogonal to both the direction of the magnetization M2 (+y direction) and the direction of the heat flux Q (+z direction).

[0093] As described above, the thermoelectric conversion elements 24 and the thermoelectric conversion element 25 arranged in parallel are connected in series electrically, and thus, the electromotive force E1 generated in one thermoelectric conversion element 24 can be applied to the adjacent thermoelectric conversion element 25. Further, since the electromotive force E1 generated in one thermoelectric conversion element 24 and the electromotive force E2 generated in the adjacent thermoelectric conversion element 25 are in opposite directions, in each of the adjacent thermoelectric conversion elements 24 and the thermoelectric conversion element 25, the electromotive forces are added together, and the output voltage V can be increased.

[0094] In addition, as Figure 7 a modified example of the thermoelectric conversion device 20, it is also possible to employ a structure in which adjacent thermoelectric conversion elements 24 and thermoelectric conversion element 25 have Nernst coefficients with opposite signs to each other, and it is also possible to employ a structure in which the magnetization directions of a plurality of thermoelectric conversion elements 24 and a plurality of thermoelectric conversion elements 25 are the same (that is, the direction of the magnetization M1 and the direction of the magnetization M2 are the same).

[0095] Example 2

[0096] Figure 8 The top view of a thermoelectric conversion device 20A according to Example 2 of the present embodiment is shown. The thermoelectric conversion device 20A includes a plurality of rectangular parallelepiped thermoelectric conversion elements 1A having the same-sign Nernst coefficients as the power generation body 23A. Each thermoelectric conversion element 1A is made of the same material as the Figure 2 thermoelectric conversion element 1 shown. The plurality of thermoelectric conversion elements 1A are arranged in parallel on the substrate 22A in such a manner that the directions of the magnetization M are the same (y direction) in the direction (y direction) perpendicular to the length direction (x direction), and adjacent thermoelectric conversion elements 1A are connected by copper wirings 26, whereby the plurality of thermoelectric conversion elements 1A are connected in series electrically. The heat flux flows from the substrate 22A side toward the power generation body 23A (in the z direction). Since the thermoelectric conversion device 20A has a structure in which adjacent thermoelectric conversion elements 1A are connected via the copper wirings 26, it can be made more easily than the Figure 7 thermoelectric conversion device 20 of Example 1 shown.

[0097] Example 3

[0098] In a thermoelectric device based on the anomalous Nernst effect, since the directions of the temperature gradient, magnetization direction, and voltage are mutually orthogonal, a sheet-like thermoelectric conversion element can be fabricated.

[0099] Figure 9 FIG. shows the external structure of a thermoelectric conversion device 30 having a sheet-like thermoelectric conversion element 32 according to Embodiment 3. Specifically, the thermoelectric conversion device 30 includes a hollow member 31 and a long strip-like (band-like) sheet thermoelectric conversion element 32 wound so as to cover the outer surface of the hollow member 31. The thermoelectric conversion element 32 is made of the same material as the Figure 2 thermoelectric conversion element 1 shown. The magnetization direction of the thermoelectric conversion element 32 is parallel to the length direction (x direction) of the hollow member 31. If a heat flux is generated in a direction perpendicular to the length direction (x direction) of the hollow member 31 and a temperature gradient is generated from the inside to the outside of the hollow member 31, then due to the anomalous Nernst effect, a voltage V is generated along the length direction of the long thermoelectric conversion element 32 (a direction perpendicular to the magnetization direction and the heat flux direction).

[0100] In addition, in the Figure 9 thermoelectric conversion device 30, a structure in which a wire-shaped thermoelectric conversion element is wound around the hollow member 31 can also be adopted instead of the long strip-like sheet thermoelectric conversion element 32.

[0101] Here, in the Figures 7 - 9 , when the length in the length direction of the thermoelectric conversion element is L and the thickness (height) is H, the voltage generated by the anomalous Nernst effect is proportional to L / H. That is, the longer and thinner the thermoelectric conversion element, the greater the generated voltage. Therefore, by adopting a power generation body, wire, or long strip-like sheet thermoelectric conversion element in which a plurality of thermoelectric conversion elements are connected in series electrically, an improvement in the anomalous Nernst effect can be expected.

[0102] The thermoelectric conversion devices shown in Embodiments 1 to 3 can be applied in various ways. In particular, in the temperature range from room temperature to several hundred degrees Celsius, applications as an independent power source or a heat flux sensor for the Internet of Things (IoT) sensors can be expected.

[0103] For example, by applying the thermoelectric conversion device of the present embodiment to a heat flux sensor, it is possible to determine the quality of the heat insulation performance of a building. In addition, by providing a thermoelectric conversion device in an exhaust device of an automobile or the like, it is possible to generate electricity using the heat (waste heat) of exhaust gas, and the thermoelectric conversion device can be effectively used as an auxiliary power source. In addition, by arranging heat flux sensors in a mesh shape on the wall surface of a certain space, it is possible to identify the space of the heat flux and the heat source. This can be envisaged as, for example, high-precision temperature management for high-density crop cultivation or livestock growth, or an application for a driver detection system for autonomous driving. Furthermore, the heat flux sensor can also be used in indoor air-conditioning management and deep body temperature management in medicine. In addition, by forming the thermoelectric conversion element of the present embodiment into a powder or paste, its application in a wide range of fields can be expected.

[0104] In the present embodiment, although attention is paid to the voltage generated by the anomalous Nernst effect, the output voltage can be increased by the synergistic effect of the voltage generated by the Seebeck effect due to the temperature gradient, the Hall effect generated by the voltage based on the Seebeck effect, and the voltage generated by the anomalous Nernst effect.

[0105] In this way, according to the thermoelectric conversion element of the present embodiment, an anomalous Nernst effect can be exhibited by an alloy of Fe and Al, which is a material having a large Clark value, being inexpensive and non-toxic. In particular, by adjusting the composition ratio of Fe and Al to adopt a non-stoichiometric composition, or by adopting polycrystals as compared with the case of adopting single crystals, a thermoelectric conversion element in which the Nernst coefficient is insensitive to temperature changes in a wide range of 200K to 400K can be provided. As a result, in a heat flux sensor or the like using a material in which the Nernst coefficient changes greatly with temperature near room temperature, it is no longer necessary to provide a necessary temperature calibration circuit or thermometer, and the thermoelectric conversion device can be made cheaper.

[0106] In addition, in Figures 3 - 6 , although the thermoelectric conversion element is composed of an Fe-Al alloy or an Fe-Al-V alloy obtained by replacing a part of the Fe sites of the Fe-Al alloy with V, a transition element other than Al or a typical element, or a transition element other than V can also be adopted. That is, a first substance whose stoichiometric composition is represented by Fe3X (X is a typical element or a transition element), a second substance having a non-stoichiometric composition in which the composition ratio of Fe and X deviates from 3:1, a third substance in which a part of the Fe sites of the first substance or a part of the Fe sites of the second substance is replaced by a typical metal element or a transition element other than X, and a composition formula of Fe3M1 1-x M2 xIn the case of the expression (0 < x < 1), a fourth substance in which M1 and M2 are different typical elements, or a fifth substance obtained by substituting a part of the Fe sites of the first substance with a transition element other than X and substituting a part of the sites of X with a typical metal element other than X, the manifestation of the anomalous Nernst effect can also be expected. As candidates for X other than Al, Ga, Ge, Sn, Si, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Sc, Ni, Mn, or Co can be cited. As combinations of M1 and M2 constituting the fourth substance, for example, Ga and Al, Si and Al, Ga and B, etc. can be cited.

[0107] For example, the anomalous Nernst effect is also manifested in Fe-Ge alloys, Fe-Ga alloys, and Fe-Ga-Al alloys. Figure 10 Shows Fe3Pt, Fe3Ge, Fe3Al, Fe3Ga 0.5 Al 0.5 , the magnetic field dependence of the Nernst coefficient (S yx ) of Fe3Ga and Co2MnGa at T = 300 K, Figure 11 Shows the temperature dependence of the Nernst coefficient of Fe3Pt, Fe3Ge, Fe3Al, Fe3Ga, and Co2MnGa.

[0108] In Figure 10 and Figure 11 , Fe3Ge represents the observation result when a magnetic field B parallel to the a-axis is applied to the thermoelectric conversion element 1 composed of a hexagonal Fe3Ge single crystal and a heat current Q parallel to the c-axis flows. Fe3Al represents the observation result when a magnetic field B parallel to

[001] is applied to the thermoelectric conversion element 1 composed of a cubic Fe3Al single crystal and a heat current Q parallel to

[110] flows. Fe3Ga represents the observation result when a magnetic field B parallel to

[110] is applied to the thermoelectric conversion element 1 composed of a cubic Fe3Ga single crystal and a heat current Q parallel to [1 - 11] flows. In addition, in Figure 10 , Fe3Ga 0.5 Al 0.5 represents the observation result when a magnetic field B parallel to

[110] is applied to the thermoelectric conversion element 1 composed of Fe3Ga 0.5 Al 0.5 single crystal and a heat current Q parallel to [1 - 11] flows. Furthermore, in Figure 10 and Figure 11In this case, Fe3Pt represents the observation result when a magnetic field B parallel to

[110] is applied to the thermoelectric conversion element 1 composed of a Fe3Pt single crystal, and a heat current Q parallel to [1-10] flows. Co2MnGa represents the observation result when a magnetic field B parallel to

[001] is applied to the thermoelectric conversion element 1 composed of a Co2MnGa single crystal, and a heat current Q parallel to

[110] flows.

[0109] From Figure 10 and Figure 11 it can be seen that compared with the Fe3Al single crystal, the Fe3Ge single crystal has a smaller |S yx |, but compared with the Fe3Pt single crystal, it has a larger |S yx |. At room temperature, the |S yx | exceeds 2.0 μV / K, reaching the practical level of heat current sensors and the like. In addition, for the ternary Fe3Ga 0.5 Al 0.5 single crystal, compared with the Fe3Al single crystal, its |S yx | is larger, about 5.0 μV / K at room temperature. In addition, the |S yx | of the Fe3Ga single crystal at room temperature significantly exceeds 5.0 μV / K, showing a value close to the highest value (6 μV / K) achieved by the Co2MnGa single crystal so far. In addition, an anomalous Nernst effect is also confirmed in the hexagonal Fe3Ga single crystal.

[0110] In addition, from Figure 11 it can be seen that compared with the single crystals of Fe3Pt and Co2MnGa, the temperature change of the Nernst coefficient of each single crystal of Fe3Ge, Fe3Al, and Fe3Ga is slow in the temperature range of 200 K to 400 K.

[0111] The Fe-Sn alloy also exhibits an anomalous Nernst effect. Figure 12A shows the temperature dependence of the Nernst coefficient of a hexagonal Fe3Sn polycrystal synthesized by melting and annealing in an arc furnace for one week at 805 degrees Celsius. In addition, Figure 12B shows the temperature dependence of the transverse thermoelectric conductivity α [A / Km] estimated by the anomalous Nernst effect of this Fe3Sn at a magnetic field B = 2 T. From these experimental data, it can be seen that the value of the Nernst coefficient |S yx | of the Fe3Sn polycrystal increases to more than 3 μV / K above room temperature.

[0112] Next, polycrystals of a mixed crystal system among three polycrystals (Fe3Si, Fe3Al, and Fe3Ga) are fabricated, and the measurement results of the anomalous Nernst effect are described.

[0113] Figure 13A and Figure 13BIndicates the Nernst coefficient of polycrystals of the mixed crystal system of Fe3Si and Fe3Al, Fe3Si 1-x Al x (0 ≤ x ≤ 1) at T = 300 K. Here, Figure 13A The Fe3Si shown 0.67 Al 0.4 is a soft magnetic material called Sendust (Fe-Si-Al soft magnetic alloy). From Figure 13A and Figure 13B it can be seen that, excluding Fe3Si 0.3 Al 0.7 , when the content of Al increases, the Nernst coefficient |S yx | increases.

[0114] Figure 14A and Figure 14B show the Nernst coefficient of polycrystals of the mixed crystal system of Fe3Al and Fe3Ga, Fe3Al 1-x Ga x (0 ≤ x ≤ 1) at T = 300 K. Figure 14B Also shown is the Nernst coefficient of a single crystal of Fe3Al 1-x Ga x prepared at a crystal growth rate of 20 mm / h. From Figure 14A and Figure 14B it can be seen that, compared with polycrystals, the Nernst coefficient |S yx | of the single crystal is larger. For both the single crystal and polycrystals, excluding Fe3Al 0.25 Ga 0.75 in polycrystals, when the content of Ga increases, the Nernst coefficient |S yx | increases.

[0115] Figure 15 Represents the Nernst coefficient of single crystals and polycrystals (0.6 < x ≤ 1) of Fe3Cu obtained by replacing a part of the Ga sites in Fe3Ga with Cu 1-x Ga x at T = 300 K. The single crystal of Fe3Cu 1-x Ga x is also prepared at a crystal growth rate of 20 mm / h. From Figure 15 it can be seen that in the single crystal of Fe3Cu 1-x Ga x , when the content of Cu increases and the content of Ga decreases, the Nernst coefficient |S yx | decreases. However, even when x = 0.7, it exceeds 3 μV / K, indicating that it has reached a practical level.

[0116] Next, with reference to Figures 16A - 20B , the experimental results of doping Nd, Ho, Y, and Tb in Fe3Ga will be described.

[0117] Figure 16A show the X-ray diffraction patterns of Nd 0.1 Fe 2.9 Ga and Fe3Ga, Figure 16B show the magnetic field dependence of the magnetization of Nd 0.1 Fe 2.9 Ga at T = 300 K. As can be seen from Figure 16A Nd 0.1 Fe 2.9 Ga maintains a crystal structure roughly the same as that of Fe3Ga. In addition, according to Figure 16B Nd 0.1 Fe 2.9 Ga reaches a saturation magnetization of 4.08 μ B / F.U. at 500 Oe, and the coercive force is hardly visible.

[0118] Figure 16C show the magnetic field dependence of the Nernst coefficient of single-crystal Fe3Ga and polycrystalline Nd 0.1 Fe 2.9 Ga at T = 300 K. In addition, Figure 16D show the magnetic field dependence of the Hall resistivity of single-crystal Fe3Ga and polycrystalline Nd 0.1 Fe 2.9 Ga at T = 300 K. As can be seen from Figure 16C Nd 0.1 Fe 2.9 the Nernst coefficient |S yx | of polycrystalline Ga is less than that of single-crystal Fe3Ga, but exceeds 3 μV / K, reaching the practical level. In addition, as can be seen from Figure 16D the magnetic field dependence of the Hall resistivity ρ 0.1 Fe 2.9 of single-crystal Fe3Ga and polycrystalline Nd yx Ga is almost the same.

[0119] Figure 17A show the X-ray diffraction patterns of Ho 0.05 Fe 2.95 Ga and Fe3Ga, Figure 17B show the magnetic field dependence of the magnetization of Ho 0.05 Fe 2.95 Ga at T = 300 K. As can be seen from Figure 17A Ho 0.05 Fe 2.95 Ga maintains a crystal structure roughly the same as that of Fe3Ga. In addition, according to Figure 17B Ho 0.05 Fe 2.95 Ga reaches a saturation magnetization of 4.8 μ at 2 TB / F.U., the coercivity is hardly visible.

[0120] Figure 18A Shows Y 0.05 Fe 2.95 X-ray diffraction patterns of Ga and Fe3Ga, Figure 18B Shows Y 0.05 Fe 2.95 Magnetic field dependence of the magnetization of Ga. From Figure 18A It can be seen that Y 0.05 Fe 2.95 Ga maintains a crystal structure roughly the same as that of Fe3Ga. In addition, from Figure 18B It can be seen that Y 0.05 Fe 2.95 Ga reaches a saturation magnetization of 3.28 μ B / F.U. at 500 Oe and has a coercivity of about 20 Oe.

[0121] Figure 19A Shows the magnetic field dependence of the magnetization of Tb 0.05 Fe 2.95 Ga prepared using a single arc furnace, Figure 19B Shows the enlarged view of the low magnetic field region of Figure 19A . From Figure 19A and Figure 19B It can be seen that Tb 0.05 Fe 2.95 Ga reaches a saturation magnetization of 7.5 μ B / F.U. at 2 T and has a coercivity of about 40 Oe.

[0122] Figure 20A Shows the X-ray diffraction pattern of Tb 0.03 Fe 2.97 Ga prepared using a four-arc furnace and the X-ray diffraction pattern of Fe3Ga, Figure 20B Shows the magnetic field dependence of the magnetization of Tb 0.03 Fe 2.97 Ga at T = 300 K. From Figure 20A It can be seen that Tb 0.03 Fe 2.97 Ga maintains a crystal structure roughly the same as that of Fe3Ga. In addition, according to Figure 20B Tb 0.03 Fe 2.97 Ga reaches a saturation magnetization of 6.9 μ B / F.U. at 2 T and the coercivity is hardly visible.

[0123] In addition, in Figures 16A - 17B and Figures 19A - 20BAmong them, the anomalous Nernst effect of a substance (a third substance) obtained by replacing a part of the Fe sites of Fe3Ga with Nd, Ho, or Tb is shown. However, anomalous Nernst effect can also be expected for other third substances obtained by replacing with other lanthanide elements (such as Gd, etc.).

[0124] Next, with reference to Figures 21A - 23B , the experimental results of doping B, Mn, or Pt in Fe3Ga will be described.

[0125] First, the experimental results of doping B in Fe3Ga will be described. Figure 21A Shows Fe3Ga 0.8 B 0.2 , Fe3Ga 0.9 B 0.1 and the X-ray diffraction patterns of Fe3Ga. From this, it can be seen that Fe3Ga 0.8 B 0.2 and Fe3Ga 0.9 B 0.1 maintain a crystal structure roughly the same as that of Fe3Ga. In addition, it can be seen from energy-dispersive X-ray analysis (EDX) (omitted from the illustration) that B as an additive appears near the boundary of Fe3Ga.

[0126] Figure 21B Respectively show the magnetic field dependence of the magnetization of the needle-shaped specimen and the plate-shaped specimen composed of Fe3Ga 0.8 B 0.2 at T = 300K. Figure 21B The needle-shaped specimen shown in is magnetized in the length direction, and a magnetic field is applied parallel to the length direction. Figure 21B The plate-shaped specimen shown in is magnetized in the in-plane direction, and a magnetic field is applied in the direction perpendicular to the plane. In this way, in the plate-shaped specimen, the magnetization direction is perpendicular to the magnetic field direction. Therefore, in order to initiate magnetization along the magnetic field direction, a strong magnetic field needs to be applied. From Figure 21B it can be seen that if a strong magnetic field is applied, in the plate-shaped specimen, the magnetization only changes slightly linearly, but in the needle-shaped specimen with magnetization in the direction parallel to the magnetic field, the magnetization changes greatly, and obvious hysteresis appears.

[0127] Figure 21C Shows the magnetic field dependence of the magnetization of the needle-shaped specimen of Fe3Ga 0.8 B 0.2 and Fe3Ga. Figure 21C The needle-shaped specimen shown in is magnetized in the length direction, and a magnetic field is applied parallel to the magnetization direction. Since the magnetization direction and the magnetic field direction are parallel, both Fe3Ga and Fe3Ga 0.8 B 0.2 saturate the magnetization with relatively weak magnetic fields (about 400 Oe and about 800 Oe respectively). According toFigure 21C , shows more obvious hysteresis in Fe3Ga 0.8 B 0.2 than in Fe3Ga. The coercivity relative to Fe3Ga is about 10 Oe, and that of Fe3Ga 0.8 B 0.2 is about 35 Oe.

[0128] Figure 21D shows the magnetic field dependence of the magnetization of the plate-shaped specimens of Fe3Ga 0.8 B 0.2 and Fe3Ga. Figure 21D The plate-shaped specimens shown are magnetized in the in-plane direction, and a magnetic field is applied in the direction perpendicular to the plane. Since the magnetization direction and the magnetic field direction are perpendicular, a relatively strong magnetic field is required to initiate magnetization in the direction perpendicular to the plane. The magnetization of both Fe3Ga and Fe3Ga 0.8 B 0.2 increases linearly up to a magnetic field of over 3 kOe, and the hysteresis is weak. In fact, for Fe3Ga, the coercivity is hardly visible. On the other hand, according to the enlarged view near the low magnetic field ( Figure 21D inserted figure), Fe3Ga 0.8 B 0.2 has a coercivity of about 35 Oe.

[0129] Figure 21E shows the magnetic field dependence of the Nernst coefficient of the plate-shaped specimens of Fe3Ga 0.8 B 0.2 , Figure 21F shows the magnetic field dependence of the Hall resistivity of the plate-shaped specimens of Fe3Ga 0.8 B 0.2 . Figure 21E and Figure 21F The plate-shaped specimens shown are magnetized in the in-plane direction and a magnetic field is applied in the direction perpendicular to the plane, similar to Figure 21D . In Figure 21F , the data points when the magnetic field increases from -2 T to +2 T are represented by circles, while the data points when the magnetic field decreases from +2 T to -2 T are represented by squares. As can be seen from Figure 21E , the Nernst coefficient |S 0.8 B 0.2 | of Fe3Ga yx reaches 4 μV / K, showing about 80% of the value of the Nernst coefficient (4.9 μV / K: refer to Figure 14A and Figure 14B ) of polycrystalline Fe3Ga.

[0130] Thus, by replacing a part of the Ga sites in Fe3Ga with B, the coercivity increases, and the Nernst coefficient can ensure about 80% of the value of Fe3Ga. Therefore, it can be said that Fe3Ga0.8 B 0.2 It is advantageous for the fabrication of a thermopile that can be realized under zero magnetic field.

[0131] Next, the experimental results of doping Mn into Fe3Ga are described. Figure 22A Shows Fe 2.9 Mn 0.1 Ga, Fe 2.5 Mn 0.5 Ga, Fe2MnGa and Fe3Ga X-ray diffraction patterns, Figure 22B Shows the Fe of the needle-shaped specimen 2.9 Mn 0.1 Ga and Fe 2.5 Mn 0.5 Magnetic field dependence of magnetization at T = 300K of Ga. Figure 22B The needle-shaped specimen shown is magnetized in the length direction, and a magnetic field is applied parallel to the magnetization direction.

[0132] From Figure 22A It can be seen that Fe 2.9 Mn 0.1 Ga and Fe 2.5 Mn 0.5 Ga maintains a crystal structure roughly the same as that of Fe3Ga. In addition, according to Figure 22B Fe 2.9 Mn 0.1 Ga shows a large magnetization but hardly any hysteresis. On the other hand, Fe 2.5 Mn 0.5 Ga shows a small hysteresis and has a coercive force of about 10 Oe (the same as the coercive force of Fe3Ga of the needle-shaped specimen shown in Figure 21C ), but the magnetization is significantly suppressed compared to Fe 2.9 Mn 0.1 Ga.

[0133] Next, the experimental results of doping Pt into Fe3Ga are described. Figure 23A Shows Fe 2.9 Pt 0.1 Ga, Fe 2.9 Pt 0.1 Ga 0.9 Ge 0.1 And Fe3Ga X-ray diffraction patterns, Figure 23B Shows the Fe of the needle-shaped specimen 2.9 Pt 0.1 Ga and Fe 2.9 Pt 0.1 Ga 0.9 Ge 0.1 Magnetic field dependence of magnetization at T = 300K of.Figure 23B The needle-shaped sample shown is magnetized in the longitudinal direction, and a magnetic field is applied parallel to the magnetization direction.

[0134] It is known from Figure 23A that Fe 2.9 Pt 0.1 Ga and Fe 2.9 Pt 0.1 Ga 0.9 Ge 0.1 maintain a crystal structure substantially the same as that of Fe3Ga. Additionally, according to Figure 23B , Fe 2.9 Pt 0.1 Ga hardly shows magnetic hysteresis. On the other hand, Fe 2.9 Pt 0.1 Ga 0.9 Ge 0.1 shows a small magnetic hysteresis and has a coercive force of about 8 Oe. That is, it is known that by substituting Ge for a part of the Ga sites in Fe 2.9 Pt 0.1 Ga, the coercive force increases.

[0135] As described above, when substituting a part of the Ga sites in Fe3Ga with B, an increase in the coercive force was also observed (refer to Figure 21C and Figure 21D ), so it can be considered that the substitution of the Ga sites has an impact on the magnetic properties.

[0136] Next, referring to Figures 24 - 30 , an embodiment in which the thermoelectric conversion element 1 is a thin film will be described. In the following embodiments, the thermoelectric conversion element 1 is composed of a first substance having a composition formula of Fe3X or a second substance having a non-stoichiometric composition in which the composition ratio of Fe to X deviates from that of the first substance, but is not limited thereto.

[0137] First, the method for fabricating the thin film will be described. Hereinafter, an example of fabricating a thin film by sputtering is shown, but the method for fabricating the thin film is not limited. For example, Molecular Beam Epitaxy (MBE) method, Chemical Vapor Deposition (CVD), Pulsed Laser Deposition (PLD), electroplating method, etc. can also be used.

[0138] For example, in the fabrication of Fe3Ga thin films, first, using a DC magnetron sputtering apparatus, a process of discharging a target composed of Fe and Ga in a composition ratio of 3:1 is carried out at room temperature, and a thin film doped with Ga in Fe is fabricated on a

[001] -oriented magnesium oxide (MgO) substrate. The Fe3Ga sample formed at room temperature is a polycrystalline thin film. After film formation, without breaking the vacuum, annealing is performed at 500 °C for 30 minutes, thereby enabling the fabrication of a

[001] -oriented epitaxial film. Thus, the Fe3Ga thin film is a

[001] -oriented epitaxial film fabricated on a

[001] -oriented MgO substrate.

[0139] In addition, an anti-oxidation layer composed of MgO is provided on the outermost surface of the thin film. In addition, as the anti-oxidation layer, in addition to MgO, a coating layer that prevents general oxidation of Al, Al2O3, SiO2, etc. can also be used. In addition, a buffer layer between the thin film and the substrate or a coating layer on the outermost surface of the thin film is not necessarily required.

[0140] As the T / S distance (distance between the target and the substrate), in the above fabrication method, it is preferably 15 cm to 20 cm in the sputtering apparatus. However, in the case of using other fabrication methods, the T / S distance can also be set in the range of 5 cm to 40 cm.

[0141] Due to the influence of the reverse magnetic field, it is difficult for a ferromagnetic material to make the magnetization direction perpendicular to the temperature difference consistent, so it is difficult to obtain a voltage under zero magnetic field. However, if it is thinned as described above, the contribution of the reverse magnetic field in the direction perpendicular to the plane of the thin film becomes larger. On the other hand, in the in-plane direction, the effect of the reverse magnetic field is approximately zero. Thus, the magnetization is stable in the in-plane direction.

[0142] Next, with reference to Figure 24 a method for measuring the anomalous Nernst effect when a temperature gradient is applied to the thin film sample as the thermoelectric conversion element 1 in the in-plane direction will be described. To measure such an anomalous Nernst effect, for example, the Figure 24 shown cuboid-shaped structure is used. In the Figure 24 structure, a thin film (Fe3X thin film) sample with a thickness of 50 nm is laminated on a MgO substrate with a thickness of 500 μm, and a MgO coating layer with a thickness of 5 nm is laminated on the thin film sample. The length in the length direction of this structure is 9 mm, and the length in the width direction is 2 mm. A thermocouple is provided along the length direction on the thin film sample, and the interval between the thermocouples is 6 mm.

[0143] As described above, the thin film sample is magnetized in the in-plane direction. As Figure 24 shown, when a magnetic field is applied to the thin film sample in the direction perpendicular to the plane, the magnetization starts in the direction perpendicular to the plane. When a heat flux Q flows along the length direction of the thin film sample, a temperature difference ΔT (= T2 - T1) is generated. Thus, related to Figure 2Similarly, through the anomalous Nernst effect, an electromotive force V is generated in a direction orthogonal to both the direction of the heat flux Q and the direction of magnetization (perpendicular to the plane). yx .

[0144] Figure 25 Indicates Figure 24 The measurement results of the anomalous Nernst effect when the thin film sample shown is Fe3Ga (magnetic field dependence of the Nernst coefficient at T = 300 K). As can be seen from Figure 25 It can be seen that the Nernst coefficient |S yx | of Fe3Ga is 4.0 μV / K.

[0145] In Figure 24 and Figure 25 , an example of applying a temperature gradient in the in-plane direction to the thin film sample is shown. However, as Figure 26 shown, when a temperature gradient is applied to the thin film sample in the direction perpendicular to the plane, an anomalous Nernst effect can also be obtained. That is, when the thin film sample as the thermoelectric conversion element 1 is magnetized in the in-plane direction (x direction), if the heat flux Q flows relative to the thin film sample in the direction perpendicular to the plane (z direction), an electromotive force V is generated in the direction orthogonal to both the direction of the heat flux Q and the direction of magnetization M.

[0146] To measure such an anomalous Nernst effect, for example, the structure shown in Figure 27A is used. In the structure of Figure 27A , a silicone pad with a thickness of 500 μm is provided on a heat sink made of Cu, a MgO substrate with a thickness of 500 μm is laminated on the silicone pad, a thin film sample with a thickness of 50 nm is laminated on the MgO substrate, and a MgO capping layer with a thickness of 5 nm is laminated on the thin film sample. Voltage terminals are provided at both ends in the length direction of the MgO capping layer, and the voltage terminals are connected to both end portions in the length direction of the thin film sample. Thus, as Figure 27B shown, the electromotive force V generated in the length direction of the thin film sample due to the anomalous Nernst effect can be measured yx .

[0147] A silicone gasket with a thickness of 500 μm is laminated on the MgO capping layer, a copper plate with a thickness of 1 mm is laminated on the silicone gasket, and a resistance heater (ceramic heater) is provided on the copper plate. Thermocouples are provided at the upper end of the MgO capping layer and the lower end of the MgO substrate. Using the thermocouples, the temperature gradient ΔT in the direction perpendicular to the plane [00 - 1] generated from the upper end of the MgO capping layer through the thin film sample to the lower end of the MgO substrate can be measured using the heat flux from the ceramic heater all . In Figure 27A and Figure 27B , the magnetization direction of the thin film sample and the direction of the applied magnetic field

[110] are parallel.

[0148] Figure 28 shows Figure 27A and Figure 27B The measurement results of the anomalous Nernst effect (magnetic field dependence of electromotive force) at 300 K when the thin film sample shown is Fe3Ga. From Figure 28 it can be seen that, different from the bulk sample, the thin film sample Fe3Ga also has an electromotive force of 19.8 μV in zero magnetic field, which is approximately the same as the value in the saturation magnetic field. In addition, the coercive force of the thin film sample Fe3Ga is about 40 Oe.

[0149] In this measurement, the temperature difference in the direction perpendicular to the plane obtained by the thermocouple is ΔT all = 1.5 K. Here, since it is difficult to accurately estimate the temperature gradient of the thin film sample itself Therefore, the measurement results shown Figure 25 are applied, that is, the measurement results when a temperature gradient is applied in the in-plane direction of the thin film sample and a magnetic field is applied in the direction perpendicular to the plane. Figure 25 The Nernst coefficient (4.0 μV / K) of Fe3Ga shown can also be applied to the case where the temperature gradient applied in the direction perpendicular to the plane of the 50-nm thin film sample Fe3Ga can be estimated to be 0.9 K / mm.

[0150] In the above thin film manufacturing method, annealing is performed after film formation at room temperature. However, in polycrystalline or amorphous thin films obtained without annealing after film formation at room temperature, as shown below, an anomalous Nernst effect comparable to that of the thin film sample obtained after annealing can also be obtained.

[0151] If annealing is not performed, thin film manufacturing becomes simple and it can also be used for flexible thin films. In addition, in the production of the epitaxial film, a

[001] -oriented MgO substrate is required, but in the production of polycrystalline or amorphous films, the substrate is not limited.

[0152] There is no restriction on the material of the substrate. In addition to MgO, Si, Al2O3, PET, polyimide, etc. can also be used.

[0153] Figure 29A It shows the measurement results of the anomalous Nernst effect (magnetic field dependence of electromotive force) at T = 300 K when a temperature gradient is applied in the direction perpendicular to the plane of the thin film sample Fe3Ga fabricated on a MgO substrate without annealing after film formation at room temperature, Figure 26 as shown Figure 29B shows a magnified view of the vicinity of low magnetic field for Figure 29A . In Figure 29A and Figure 29B , it is also the same as Figure 27A and Figure 27BSimilarly, the thickness of the thin film sample of Fe3Ga is 50 nm, and the temperature gradient in the direction perpendicular to the surface obtained by the thermocouple is ΔT all = 1.5 K (3 K / mm).

[0154] In addition, Figure 30 The measurement results of the anomalous Nernst effect (magnetic field dependence of electromotive force) when a temperature gradient is applied in the direction perpendicular to the surface are shown for the epitaxial film of Fe3Ga obtained by annealing after film formation at room temperature and the amorphous film of Fe3Ga obtained without annealing after film formation at room temperature, respectively. Figure 30 The measurement results of the amorphous film in Figure 29A and Figure 29B correspond to the measurement results shown, Figure 30 The measurement results of the epitaxial film in Figure 28 correspond to the measurement results of Fe3Ga shown.

[0155] From Figure 29A , Figure 29B and Figure 30 , it can be seen that the electromotive force of the amorphous film is roughly the same as that of the epitaxial film at high magnetic fields, and is about half of the electromotive force of the epitaxial film at zero magnetic field. That is, in the amorphous thin film sample of Fe3Ga fabricated by film formation at room temperature, a Nernst coefficient of about 2 μV / K is obtained at zero magnetic field.

[0156] In addition, in the above-described embodiment ( Figures 24 - 30 ), an example in which the thickness of the thin film is set to 50 nm is shown, but the thickness of the thin film is not limited and may be 10 μm or less, more preferably 1 μm or less.

[0157] As described above, according to the embodiment of Figures 24 - 30 , since the thin film made of Fe3Ga is used as the thermoelectric conversion element 1, the anomalous Nernst effect can be obtained with an inexpensive material. In addition, by thinning the film, a thermoelectric conversion element 1 that exhibits a large anomalous Nernst effect even at zero magnetic field can be fabricated. Furthermore, the anomalous Nernst effect can be obtained regardless of whether the thermoelectric conversion element 1 is a single crystal, polycrystal, or amorphous. In addition, since film formation can be performed at room temperature, a thin film can also be fabricated on a flexible substrate with poor heat resistance.

[0158] Explanation of symbols

[0159] 1, 1A, 24, 25, 32: Thermoelectric conversion elements;

[0160] 20, 20A, 30: Thermoelectric conversion devices;

[0161] 22, 22A: Substrates;

[0162] 23, 23A: Power generation bodies;

[0163] 31: Hollow member.

Claims

1. A thermoelectric conversion element composed of a first substance, a third substance, a fourth substance, or a fifth substance, wherein, the first substance has a stoichiometric composition represented by the compositional formula Fe3X, where X is Al, Ga, Ge, Sn, or Si, and the composition ratio of Fe and X is 3:1; The third substance is Fe obtained by replacing a part of the Fe sites in Fe3Al with V. 2.8 V 0.15 The polycrystal of Al, or the alloy obtained by replacing a part of the Fe sites in Fe3Ga with Mn, Y, Pt, or a lanthanide element, namely Fe 2.9 Mn 0.1 Ga, Fe 2.5 Mn 0.5 Ga, Fe2MnGa, Y 0.05 Fe 2.95 Ga, Fe 2.9 Pt 0.1 Ga, Nd 0.1 Fe 2.9 Ga, Ho 0.05 Fe 2.95 Ga, Tb 0.05 Fe 2.95 Ga, Tb 0.03 Fe 2.97 Any one of Ga; The fourth substance is Fe3Si 1-x Al x polycrystals of, Fe3Al 1-y Ga y polycrystals of, Fe3Cu 1-z Ga z single crystals or polycrystals of, Fe3Ga 0.8 B 0.2 or, Fe3Ga 0.9 B 0.1 where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0.6 < z ≤ 1; The fifth substance is Fe obtained by replacing part of the Fe sites of Fe3Ga with Pt and replacing part of the Ga sites with Ge 2.9 Pt 0.1 Ga 0.9 Ge 0.1 , the first substance, the third substance, the fourth substance, and the fifth substance exhibit an anomalous Nernst effect.

2. The thermoelectric conversion element according to claim 1, wherein, The Nernst coefficient of the polycrystal of 2.8 Fe 0.15 V Al is constant in the temperature range of 200K to 400K.

3. The thermoelectric conversion element according to claim 1, wherein, The first substance, the third substance, the fourth substance, or the fifth substance is a single crystal.

4. The thermoelectric conversion element according to claim 1, wherein, The first substance, the third substance, the fourth substance, or the fifth substance is a polycrystal.

5. The thermoelectric conversion element according to claim 1, wherein, The first substance is amorphous.

6. The thermoelectric conversion element according to any one of claims 1 to 5, wherein, The thermoelectric conversion element is a thin film with a thickness of 10 μm or less.

7. A thermoelectric conversion device, comprising: a substrate; and a power generation body disposed on the substrate and having a plurality of thermoelectric conversion elements, each of the plurality of thermoelectric conversion elements has a shape extending in one direction and is composed of the same substance as the thermoelectric conversion element according to any one of claims 1-6, the plurality of thermoelectric conversion elements are arranged side by side in a direction perpendicular to the one direction and are electrically connected in series.

8. The thermoelectric conversion device according to claim 7, wherein, The plurality of thermoelectric conversion elements are arranged in a serpentine shape.

9. A thermoelectric conversion device, comprising: the thermoelectric conversion element according to any one of claims 1-6; and a hollow member, the thermoelectric conversion element is in a sheet structure or a wire and is disposed so as to cover the outer surface of the hollow member.

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