Thermoelectric conversion element and thermoelectric conversion device

Abstract

This thermoelectric conversion element comprises: a first substance (Fe3Al or the like) having a stoichiometric composition that is represented by the compositional formula Fe3X and in which X is a typical element or a transition element; a second substance having an off-stoichiometric composition in which the composition ratio of Fe and X deviates from that of the first substance; a third substance (Nd0.1Fe2.9Ga or the like) in which some of the Fe sites of the first substance or some of the Fe sites of the second substance are substituted with a typical metal element or a transition element other than X; a fourth substance (Fe3Al1 - xGax or the like) having a compositional formula represented by Fe3M11 - xM2x (0 < x < 1) and in which M1 and M2 are typical elements that differ from each other; or a fifth substance (Fe2.9Pt0.1Ga0.9Ge0.1 or the like) in which some of the Fe sites of the first substance are substituted with a transition element other than X and some of the X sites are substituted 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 abnormal 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 technology]

[0002] The Seebeck effect is known as a thermoelectric mechanism that generates a voltage when a temperature gradient is applied to a material (see, for example, Patent Document 1). However, in thermoelectric mechanisms using the Seebeck effect, materials that can be used above room temperature are primarily made from bismuth, tellurium, lead, or the like, which are highly toxic and therefore unsuitable for practical use. They are also mechanically fragile, susceptible to vibration, and lack durability. Furthermore, because the Seebeck effect generates a voltage in the same direction as the temperature gradient, it is necessary to fabricate a complex, three-dimensional structure in which p-type and n-type modules are alternately arranged in a direction perpendicular to the heat source surface, resulting in high manufacturing costs. Furthermore, it is difficult to deploy such three-dimensional elements over a large area.

[0003] Similarly, the anomalous Nernst effect is known as a thermoelectric mechanism that generates voltage due to a temperature gradient. The anomalous Nernst effect is a phenomenon in which, when a heat flow is passed through a magnetic material and a temperature difference is created, a voltage is generated in a direction perpendicular to both the magnetization direction and the temperature gradient. In recent years, it has been discovered that by utilizing the topology of the electronic structure, the Nernst coefficient can be increased much more than the previously known value (0.1 μV / K). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 181777 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although various magnetic materials showing an abnormal Nernst effect have been developed so far, there has been a problem of high cost because relatively expensive metals are used.

[0006] 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.

Means for Solving the Problems

[0007] The thermoelectric conversion element according to an embodiment of the present invention includes a first substance having a stoichiometric composition represented by the composition formula Fe3X, where X is a typical element or a transition element, a second substance having an off-stoichiometric composition in which the composition ratio of Fe and the X deviates from that of the first substance, 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 substituted with a typical metal element or a transition element other than the X, a fourth substance represented by the composition formula Fe3M1 1-x M2 x (0 < x < 1), where M1 and M2 are different typical elements from each other, or a fifth substance in which a part of the Fe sites of the first substance is substituted with a transition element other than X and a part of the X sites is substituted 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 abnormal Nernst effect.

[0008] The 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 made of the above-described 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.

[0009] The thermoelectric conversion device according to another embodiment of the present invention includes the above-described thermoelectric conversion element and a hollow member. The thermoelectric conversion element is a sheet-like structure or a wire and is provided so as to cover the outer surface of the hollow member.

Effects of the Invention

[0010] According to the present invention, the anomalous Nernst effect can be realized by a thermoelectric conversion element using inexpensive and non-toxic materials. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing the crystal structure of D03-type Fe3X and the crystal structure of L12-type Fe3X. [Figure 2] 1 is a schematic diagram for explaining a thermoelectric mechanism of a thermoelectric conversion element according to an embodiment of the present invention. [Figure 3] 1 is a graph showing the temperature dependence of the Nernst coefficient in various metal materials. [Figure 4] 4 is a graph in which the Nernst coefficients shown in FIG. 3 are normalized by the Nernst coefficient at T=300K. [Figure 5] 1 is a graph showing the magnetic field dependence of the Nernst coefficient at T=300K for a single crystal and polycrystalline Fe—Al alloy, and a polycrystalline Fe—Al—V alloy. [Figure 6] 1 is a graph showing the temperature dependence of the Nernst coefficient of a single crystal and polycrystalline Fe—Al alloy, and a polycrystalline Fe—Al—V alloy. [Figure 7] 1 is a perspective view showing the configuration of a thermoelectric conversion device according to Example 1 that includes a thermoelectric conversion element of the present embodiment. [Figure 8] FIG. 10 is a plan view showing the configuration of a thermoelectric conversion device according to Example 2 that includes the thermoelectric conversion element of the present embodiment. [Figure 9] FIG. 10 is an external view showing the configuration of a thermoelectric conversion device according to Example 3 that includes the thermoelectric conversion element of the present embodiment. [Figure 10] 1 is a graph showing the magnetic field dependence of the Nernst coefficients of Fe3Pt, Fe3Ge, Fe3Al, Fe3Ga0.5Al0.5, Fe3Ga, and Co2MnGa at T=300K. [Figure 11] 1 is a graph showing the temperature dependence of the Nernst coefficients of Fe3Pt, Fe3Ge, Fe3Al, Fe3Ga, and Co2MnGa. [Figure 12A] 1 is a graph showing the temperature dependence of the Nernst coefficient of Fe3Sn. [Figure 12B] 1 is a graph showing the temperature dependence of the transverse thermoelectric conductivity of Fe3Sn. [Figure 13A] 1 is a table showing Nernst coefficients at T=300K for a mixed crystal system of Fe3Si and Fe3Al. [Figure 13B] 1 is a graph showing the Nernst coefficient at T=300K for a mixed crystal system of Fe3Si and Fe3Al. [Figure 14A] 1 is a table showing Nernst coefficients at T=300K for a mixed crystal system of Fe3Al and Fe3Ga. [Figure 14B] 1 is a graph showing the Nernst coefficient at T=300K for a mixed crystal system of Fe3Al and Fe3Ga. [Figure 15] 1 is a graph showing the Nernst coefficients at T=300K of Fe3Cu1-xGax single crystal and polycrystal obtained by substituting some of the Ga sites of Fe3Ga with Cu. [Figure 16A] 1 is a graph showing X-ray diffraction patterns of Nd0.1Fe2.9Ga and Fe3Ga. [Figure 16B] 1 is a graph showing the magnetic field dependence of magnetization of Nd0.1Fe2.9Ga at T=300K. [Figure 16C] 1 is a graph showing the magnetic field dependence of the Nernst coefficient at T=300 K for an Fe3Ga single crystal and an Nd0.1Fe2.9Ga polycrystalline body. [Figure 16D] 1 is a graph showing the magnetic field dependence of the Hall resistivity at T=300 K of an Fe3Ga single crystal and an Nd0.1Fe2.9Ga polycrystalline body. [Figure 17A] 1 is a graph showing X-ray diffraction patterns of Ho0.05Fe2.95Ga and Fe3Ga. [Figure 17B] 1 is a graph showing the magnetic field dependence of magnetization of Ho0.05Fe2.95Ga at T=300K. [Figure 18A] 1 is a graph showing X-ray diffraction patterns of Y0.05Fe2.95Ga and Fe3Ga. [Figure 18B] 1 is a graph showing the magnetic field dependence of magnetization of Y 0.05 Fe 2.95 Ga. [Figure 19A]1 is a graph showing the magnetic field dependence of magnetization of Tb0.05Fe2.95Ga. [Figure 19B] 19B is a graph enlarging the vicinity of the low magnetic field in FIG. 19A. [Figure 20A] 1 is a graph showing X-ray diffraction patterns of Tb0.03Fe2.97Ga and Fe3Ga. [Figure 20B] 1 is a graph showing the magnetic field dependence of magnetization of Tb0.03Fe2.97Ga at T=300K. [Figure 21A] 1 is a graph showing X-ray diffraction patterns of Fe3Ga0.8B0.2, Fe3Ga0.9B0.1, and Fe3Ga. [Figure 21B] 1 is a graph showing the magnetic field dependence of magnetization at T=300 K for a needle-shaped sample and a plate-shaped sample made of Fe3Ga0.8B0.2. [Figure 21C] 1 is a graph showing the magnetic field dependence of the magnetization of needle-shaped samples of Fe3Ga0.8B0.2 and Fe3Ga. [Figure 21D] 1 is a graph showing the magnetic field dependence of the magnetization of plate-shaped samples of Fe3Ga0.8B0.2 and Fe3Ga. [Figure 21E] 1 is a graph showing the magnetic field dependence of the Nernst coefficient of a plate-shaped sample of Fe3Ga0.8B0.2. [Figure 21F] 1 is a graph showing the magnetic field dependence of the Hall resistivity of a plate-shaped sample of Fe3Ga0.8B0.2. [Figure 22A] 1 is a graph showing X-ray diffraction patterns of Fe2.9Mn0.1Ga, Fe2.5Mn0.5Ga, Fe2MnGa, and Fe3Ga. [Figure 22B] 1 is a graph showing the magnetic field dependence of magnetization at T=300 K for needle-shaped samples of Fe2.9Mn0.1Ga and Fe2.5Mn0.5Ga. [Figure 23A] 1 is a graph showing X-ray diffraction patterns of Fe2.9Pt0.1Ga, Fe2.9Pt0.1Ga0.9Ge0.1, and Fe3Ga. [Figure 23B] 1 is a graph showing the magnetic field dependence of magnetization at T=300 K for needle-shaped samples of Fe2.9Pt0.1Ga and Fe2.9Pt0.1Ga0.9Ge0.1. [Figure 24] FIG. 1 is a schematic diagram for explaining the anomalous Nernst effect when a temperature gradient is applied in the in-plane direction of a thin film sample as a thermoelectric conversion element. [Figure 25] 1 is a 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 a thin film sample (Fe3Ga). [Figure 26] FIG. 1 is a schematic diagram for explaining the anomalous Nernst effect when a temperature gradient is applied in the direction perpendicular to the surface to a thin film sample as a thermoelectric conversion element. [Figure 27A] FIG. 1 is a schematic diagram for explaining a method for measuring the anomalous Nernst effect when a temperature gradient is applied to a thin film sample in the direction perpendicular to the surface. [Figure 27B] FIG. 1 is a schematic diagram for explaining a method for measuring the anomalous Nernst effect when a temperature gradient is applied to a thin film sample in the direction perpendicular to the surface. [Figure 28] 1 is a graph showing the measurement results of the anomalous Nernst effect when a temperature gradient is applied to a thin film sample (Fe3Ga) in the direction perpendicular to the surface. [Figure 29A] 10 is a graph showing the measurement results of the anomalous Nernst effect when a temperature gradient is applied in the direction perpendicular to the surface to a thin film sample of Fe3Ga obtained without annealing after film formation at room temperature. [Figure 29B] 29B is a graph enlarging the vicinity of the low magnetic field in FIG. 29A. [Figure 30] 10 is a graph showing the measurement results of the anomalous Nernst effect when a temperature gradient is applied in the perpendicular direction to a FeGa epitaxial film obtained by annealing after room temperature film formation and an FeGa amorphous film obtained by not annealing after room temperature film formation. DETAILED DESCRIPTION OF THE INVENTION

[0012] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings.

[0013] Among materials that exhibit the anomalous Nernst effect, the highest Nernst coefficient at room temperature to date is 6 μV / K, which the present inventors achieved in Co2MnGa (see Nature Physics 14, 1119-1124 (2018) and WO 2019 / 009308).

[0014] As described below, the present inventors have succeeded in achieving a Nernst coefficient approaching the highest value ever achieved with the binary Fe3Al system. The Clarke number, which represents the weight percentage of elements present near the Earth's surface, is known to be oxygen (O), silicon (Si), aluminum (Al), iron (Fe), and so on, in descending order. Because Fe and Al have relatively large Clarke numbers, they are very inexpensive and non-toxic materials. Furthermore, Fe3Al is chemically stable and has a high ferromagnetic transition temperature of approximately 700 K.

[0015] Figure 1 shows the crystal structure of Fe3X (X is a main group element or transition element) that can exhibit the anomalous Nernst effect. As shown in Figure 1, Fe3X can have a D03 type structure (a) or an L12 type structure (b).

[0016] The unit cell of the D03 structure (a) has eight body-centered cubic (bcc) subcells. In each subcell, Fe atoms (Fe(II)) occupy the corners, and each Fe(II) is shared by eight adjacent subcells. Four of the eight subcells have four Fe atoms (Fe(I)) at their body centers, and four X atoms occupy the body centers of the remaining four subcells. For example, the lattice constant a of Fe3Al in the D03 structure is 5.64 Å (see Physical Review B 66, 205203 (2002)).

[0017] The L12 structure (b) is a face-centered cubic (fcc) crystal structure in which Fe atoms are located at the face centers and X atoms are located at the corners.

[0018] For example, Fe3Al single crystals were produced by arc-melting Fe and Al in the 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 a few minutes to a few tens of minutes. Electron diffraction revealed that the produced Fe3Al single crystals were in an ordered phase (D03 phase (Fm-3m)).

[0019] On the other hand, polycrystalline Fe3Al was prepared by arc-melting Fe and Al in the appropriate ratio to prepare a polycrystalline sample, annealing the sample at a high temperature (e.g., 900°C), and then rapidly cooling it to room temperature within a few seconds. Based on 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.

[0020] Next, a thermoelectric conversion element and its thermoelectric mechanism according to an embodiment of the present invention will be described with reference to FIG.

[0021] The thermoelectric conversion element 1 according to this embodiment is made of Fe3X single crystal or polycrystal produced by the above-described method. As shown in FIG. 2, the thermoelectric conversion element 1 has a rectangular parallelepiped shape extending in one direction (y direction), a predetermined thickness (length in the z direction), and is magnetized in the +z direction. When a heat flow Q (∝-∇T) flows in the +x direction through the thermoelectric conversion element 1, a temperature difference occurs in the +x direction. As a result, an electromotive force V (∝M × (-∇T)) is generated in the thermoelectric conversion element 1 in the cross product direction (y direction) 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.

[0022] Figure 3 shows the Nernst coefficient (S yx ) with the Nernst coefficients of thermoelectric conversion elements made from other metal materials, and shows the temperature dependence of the Nernst coefficient. Figure 4 is a graph in which the Nernst coefficients of the metal materials shown in Figure 3 are normalized by the Nernst coefficient at T = 300K.

[0023] In Figures 3 and 4, Fe3Al#1 represents the observation results for thermoelectric conversion element 1 made of a single crystal with an off-stoichiometric composition (Fe-rich, Al-poor) in which the Fe:Al composition ratio deviates from 3:1, and Fe3Al#2 represents the observation results for thermoelectric conversion element 1 made of a single crystal with a stoichiometric composition in which the Fe:Al composition ratio is 3:1.

[0024] 3 and 4, the L10 type MnGa, D0 22 The data for Mn2Ga, Co / Ni, FePd, and FePt are based on data disclosed in Appl. Phys. Lett. 106, 252405 (2015), the data for Fe3O4 are based on data disclosed in Physical Review B 90, 054422 (2014), and the data for Co2MnGa are based on research by the present inventors (Nature Physics 14, 1119-1124 (2018); WO 2019 / 009308).

[0025] From Figures 3 and 4, the absolute values ​​of the Nernst coefficients |S yx | is larger than that of other metallic materials except for Co2MnGa. In particular, |S of stoichiometric Fe3Al♯2 yx | is larger than that of off-stoichiometric Fe3Al♯1, and is about 4 μV / K at room temperature (T = around 300 K), yx It can be seen that the value is close to ≒ 6μV / K.

[0026] 3 and 4, the S of off-stoichiometric Fe3Al♯1 yx is hardly affected by temperature changes in the temperature range of 200K to 400K, which includes room temperature, and remains a nearly constant value.

[0027] Figure 5 shows the Nernst coefficients (S) at T = 300 K for single crystals (S1, S2) and polycrystals (P2) of Fe-Al alloys, and polycrystals (P1) of Fe-Al-V alloys. yx) is shown in Fig. 6, and the temperature dependence of the Nernst coefficient in single crystals (S1, S2) and polycrystalline (P2) of Fe-Al alloy, and in polycrystalline (P1) of Fe-Al-V alloy, when a magnetic field B = 2 T is applied, is shown in Fig. 7.

[0028] In Figures 5 and 6, S1 and S2 correspond to Fe3Al#2 and Fe3Al#1 shown in Figure 3, respectively. S1 represents the observation results when a magnetic field B parallel to

[0001] is applied to the thermoelectric conversion element 1 and a heat flow Q parallel to

[0010] is caused to flow. S2 represents the observation results when a magnetic field B parallel to

[0001] is applied to the thermoelectric conversion element 1 and a heat flow Q parallel to

[0210] is caused to flow.

[0029] 5 and 6, P1 represents Fe3Al in which some of the Fe sites are substituted with vanadium (V). 2.8 V 0.15 P1 shows the observation results for a thermoelectric conversion element 1 made of an Al polycrystalline body, and P2 shows the observation results for a thermoelectric conversion element 1 made of a polycrystalline body with a stoichiometric composition of Fe and Al at a ratio of 3:1.

[0030] 5 and 6, the single crystals (S1, S2) have a larger absolute value of the Nernst coefficient |S yx Furthermore, when comparing polycrystals P1 and P2, the stoichiometric binary polycrystal P2 has a larger |S than the ternary polycrystal P1. yx It can be seen that | is large.

[0031] Furthermore, the Nernst coefficients of the polycrystalline bodies (P1, P2) are less affected by temperature changes in the temperature range of 200K to 400K, including room temperature (near T = 300K), and are almost constant, compared to the single crystalline bodies (S1, S2). yx Although | is small, |S yx Since the value of | is approximately 1.5 to 2.0 μV / K, it can be said that this has reached a practical level for use in heat flow sensors, etc. Also, as mentioned above, polycrystalline bodies (P1, P2) are easier to fabricate than single crystalline bodies (S1, S2).

[0032] Next, a thermoelectric conversion device in which the thermoelectric conversion elements of this embodiment are modularized will be described. [Example]

[0033] 7 shows the external configuration of a thermoelectric converter 20 according to Example 1 of this embodiment. The thermoelectric converter 20 includes a substrate 22 and a power generator 23 placed on the substrate 22. In the thermoelectric converter 20, when a heat flow Q flows from the substrate 22 side toward the power generator 23, a temperature difference occurs in the power generator 23 in the direction of the heat flow, and a voltage V is generated in the power generator 23 due to the anomalous Nernst effect.

[0034] The substrate 22 has a first surface 22a on which the power generating body 23 is placed, and a second surface 22b opposite to the first surface 22a. Heat from a heat source (not shown) is applied to the second surface 22b.

[0035] The power generating body 23 has a plurality of thermoelectric conversion elements 24 and a plurality of thermoelectric conversion elements 25, each of which has an L-shaped three-dimensional shape and is made of the same material as the thermoelectric conversion element 1 shown in Fig. 2. As shown in Fig. 7, the plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 are arranged alternately in parallel on the substrate 22 in a direction (y direction) perpendicular to the longitudinal direction (x direction) of each. The number of thermoelectric conversion elements 24 and thermoelectric conversion elements 25 constituting the power generating body 23 is not limited.

[0036] The plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 are arranged so that the direction of magnetization M1 of the thermoelectric conversion elements 24 is opposite to the direction of magnetization M2 of the thermoelectric conversion elements 25. The plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 have Nernst coefficients of the same sign.

[0037] The thermoelectric conversion element 24 has a first end face 24a and a second end face 24b parallel to the longitudinal direction (x direction). The thermoelectric conversion element 25 has a first end face 25a and a second end face 25b parallel to the longitudinal 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 adjacent thermoelectric conversion element 24 on the opposite side. This electrically connects the plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 in series. That is, the power generation body 23 is provided in a serpentine shape on the first surface 22a of the substrate 22.

[0038] When heat is applied from a heat source to second surface 22b of substrate 22, heat flow Q flows in the +z direction toward power generator 23. When a temperature difference occurs due to heat flow Q, an electromotive force E1 is generated in thermoelectric conversion element 24 in a direction (-x direction) perpendicular to both the direction of magnetization M1 (-y direction) and the direction of heat flow Q (+z direction) due to the anomalous Nernst effect. In thermoelectric conversion element 25, an electromotive force E2 is generated in a direction (+x direction) perpendicular to both the direction of magnetization M2 (+y direction) and the direction of heat flow Q (+z direction) due to the anomalous Nernst effect.

[0039] As described above, the thermoelectric conversion elements 24 and 25 arranged in parallel are electrically connected in series, so that the electromotive force E1 generated in one thermoelectric conversion element 24 can be applied to the adjacent thermoelectric conversion element 25. Furthermore, 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, the electromotive forces of the adjacent thermoelectric conversion elements 24 and 25 are added together, and the output voltage V can be increased.

[0040] As a modified example of the thermoelectric conversion device 20 of FIG. 7, a configuration may be adopted in which adjacent thermoelectric conversion elements 24 and 25 have Nernst coefficients of opposite signs, and the plurality of thermoelectric conversion elements 24 and the plurality of thermoelectric conversion elements 25 are arranged so that their magnetization directions are the same (i.e., so that the direction of magnetization M1 and the direction of magnetization M2 are the same). [Example]

[0041] FIG. 8 shows a plan view of a thermoelectric converter 20A according to Example 2 of this embodiment. The thermoelectric converter 20A includes, as a power generating body 23A, a plurality of rectangular parallelepiped thermoelectric conversion elements 1A having the same Nernst coefficient. Each thermoelectric conversion element 1A is made of the same material as the thermoelectric conversion element 1 shown in FIG. 2. The plurality of thermoelectric conversion elements 1A are arranged in parallel on a substrate 22A in a direction (y direction) perpendicular to the longitudinal direction (x direction) so that the magnetization M is oriented in the same direction (y direction). Adjacent thermoelectric conversion elements 1A are connected by copper wiring 26, thereby electrically connecting the plurality of thermoelectric conversion elements 1A in series. Heat flows from the substrate 22A toward the power generating body 23A (z direction). Because the thermoelectric converter 20A has a configuration in which adjacent thermoelectric conversion elements 1A are connected via copper wiring 26, it can be fabricated more easily than the thermoelectric converter 20 of Example 1 shown in FIG. 7. [Example]

[0042] In the thermoelectric mechanism based on the anomalous Nernst effect, the temperature gradient, the magnetization direction, and the voltage direction are perpendicular to each other, making it possible to fabricate a thin sheet-like thermoelectric conversion element.

[0043] FIG. 9 shows the external configuration of a thermoelectric converter 30 according to Example 3, which includes a sheet-like thermoelectric conversion element 32. Specifically, the thermoelectric converter 30 includes a hollow member 31 and a long, sheet-like (tape-like) thermoelectric conversion element 32 wrapped around the outer surface of the hollow member 31. The thermoelectric conversion element 32 is made of the same material as the thermoelectric conversion element 1 shown in FIG. 2. The magnetization direction of the thermoelectric conversion element 32 is parallel to the longitudinal direction (x-direction) of the hollow member 31. When a heat flow occurs in a direction perpendicular to the longitudinal 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, a voltage V is generated along the longitudinal direction of the long thermoelectric conversion element 32 (a direction perpendicular to the magnetization direction and the heat flow direction) due to the anomalous Nernst effect.

[0044] In the thermoelectric converter 30 of FIG. 9, instead of the long sheet-like thermoelectric conversion element 32, a configuration in which a wire thermoelectric conversion element is wound around the hollow member 31 may be employed.

[0045] 7 to 9, where L is the longitudinal length of the thermoelectric conversion element and H is the thickness (height), the voltage generated by the anomalous Nernst effect is proportional to L / H. In other words, the longer and thinner the thermoelectric conversion element, the greater the generated voltage. Therefore, by using a power generator in which multiple thermoelectric conversion elements are electrically connected in series, or a wire or long sheet-shaped thermoelectric conversion element, it is possible to expect an improvement in the anomalous Nernst effect.

[0046] The thermoelectric converters shown in Examples 1 to 3 can be used in a variety of applications. In particular, they are expected to be used as a standalone power source or heat flow sensor for Internet of Things (IoT) sensors in the temperature range from room temperature to several hundred degrees Celsius.

[0047] For example, by applying the thermoelectric conversion device of this embodiment to a heat flow sensor, it is possible to determine the quality of the thermal insulation performance of a building. Furthermore, by installing a thermoelectric conversion device in the exhaust system of an automobile or the like, it is possible to generate electricity using the heat (waste heat) of the exhaust gas, and the thermoelectric conversion device can be effectively used as an auxiliary power source. Furthermore, by arranging heat flow sensors in a mesh pattern on the wall surface of a space, it is possible to spatially recognize heat flows and heat sources. This is expected to be applied, for example, to high-precision temperature control for high-density crop cultivation and livestock breeding, and as a driver detection system for autonomous driving. Furthermore, heat flow sensors can also be used in indoor air conditioning management and deep body temperature management in medicine. Furthermore, by making the thermoelectric conversion element of this embodiment into a powder or paste, it is expected to be applicable to a wide range of fields.

[0048] In this embodiment, attention is focused on the voltage generated by the anomalous Nernst effect, but it is possible to increase the output voltage through the synergistic effect of the voltage generated by the Seebeck effect due to the temperature gradient, the Hall effect generated based on the voltage created by the Seebeck effect, and the voltage generated by the anomalous Nernst effect.

[0049] As described above, the thermoelectric conversion element of this embodiment can exhibit the anomalous Nernst effect using an alloy of Fe and Al, which is an inexpensive, non-toxic material with a large Clarke number. In particular, by adjusting the composition ratio of Fe and Al to adopt an off-stoichiometric composition, or by using a polycrystalline material rather than a single crystal, a thermoelectric conversion element can be provided that is insensitive to temperature changes over a wide range of Nernst coefficients from 200 K to 400 K. This eliminates the need for a temperature calibration circuit or thermometer, which are required in heat flow sensors and the like that use materials whose Nernst coefficients change significantly with temperature near room temperature, thereby enabling thermoelectric conversion devices to be produced at lower cost.

[0050] 3 to 6, the thermoelectric conversion element is made of an Fe-Al alloy or an Fe-Al-V alloy in which part of the Fe sites of the Fe-Al alloy is substituted with V, but a transition element or typical element other than Al, or a transition element other than V may also be used. That is, a first substance whose stoichiometric composition is represented by Fe3X (X is a typical element or transition element), a second substance whose composition ratio of Fe to X is off-stoichiometric and deviates from 3:1, a third substance in which part of the Fe sites of the first substance or part of the Fe sites of the second substance is substituted with a typical metal element or transition element other than X, a third substance whose composition formula is Fe3M1 1-x M2 xIn the case of a fourth substance represented by (0 < x < 1), where 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 transition elements other than X and substituting a part of the sites of X with typical metal elements other than X, the manifestation of the anomalous Nernst effect can also be expected. Candidates for X other than Al include Ga, Ge, Sn, Si, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Sc, Ni, Mn, or Co. Examples of the combination of M1 and M2 constituting the fourth substance include Ga and Al, Si and Al, Ga and B, etc.

[0051] For example, the anomalous Nernst effect also appears in Fe-Ge alloys, Fe-Ga alloys, and Fe-Ga-Al alloys. In Fig. 10, Fe3Pt, Fe3Ge, Fe3Al, Fe3Ga 0.5 Al 0.5 and Fe3Ga and Co2MnGa's Nernst coefficient (S yx ) as a function of magnetic field at T = 300 K is shown, and in Fig. 11, the temperature dependence of the Nernst coefficient of Fe3Pt, Fe3Ge, Fe3Al, Fe3Ga, and Co2MnGa is shown.

[0052] In Figs. 10 and 11, Fe3Ge represents the observation results 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 is passed. Fe3Al represents the observation results when a magnetic field B parallel to

[0001] is applied to the thermoelectric conversion element 1 composed of a cubic Fe3Al single crystal and a heat current Q parallel to

[0110] is passed. Fe3Ga represents the observation results when a magnetic field B parallel to

[0110] is applied to the thermoelectric conversion element 1 composed of a cubic Fe3Ga single crystal and a heat current Q parallel to [1-11] is passed. Also, in Fig. 10, Fe3Ga 0.5 Al 0.5 is Fe3Ga 0.5 Al 0.510 and 11 show the observation results when a magnetic field B parallel to the

[0110] direction is applied to a thermoelectric conversion element 1 made of a single crystal, and a heat flow Q parallel to the [1-11] direction is passed through it. Furthermore, in Figures 10 and 11, Fe3Pt shows the observation results when a magnetic field B parallel to the

[0110] direction is applied to a thermoelectric conversion element 1 made of an Fe3Pt single crystal, and a heat flow Q parallel to the [1-10] direction is passed through it, and Co2MnGa shows the observation results when a magnetic field B parallel to the

[0001] direction is applied to a thermoelectric conversion element 1 made of a Co2MnGa single crystal, and a heat flow Q parallel to the

[0110] direction is passed through it.

[0053] 10 and 11, the Fe3Ge single crystal has a higher |S yx Although | is smaller, |S yx | is large, and |S at room temperature yx | exceeds 2.0 μV / K, which is sufficient for practical use in heat flow sensors. 0.5 Al 0.5 The single crystal has a higher |S yx | is large, and is approximately 5.0 μV / K at room temperature. Furthermore, |S yx The value of | easily exceeds 5.0 μV / K, approaching the highest value (6 μV / K) achieved to date for a Co2MnGa single crystal. The anomalous Nernst effect has also been confirmed in a hexagonal Fe3Ga single crystal.

[0054] Furthermore, it can be seen from FIG. 11 that the Nernst coefficients of the single crystals of Fe3Ge, Fe3Al and Fe3Ga change more slowly with temperature in the temperature range of 200K to 400K than the single crystals of Fe3Pt and Co2MnGa.

[0055] The anomalous Nernst effect also appears in Fe-Sn alloys. Figure 12A shows the temperature dependence of the Nernst coefficient of a hexagonal Fe3Sn polycrystalline body obtained by melting and synthesizing the polycrystalline body in an arc furnace, followed by annealing at 805 degrees Celsius for one week. Figure 12B also shows the temperature dependence of the transverse thermoelectric conductivity α [A / Km] of this Fe3Sn in a magnetic field B = 2 T, estimated by the anomalous Nernst effect. From these experimental data, it can be seen that the Fe3Sn polycrystalline body exhibits a Nernst coefficient |S yx It can be seen that | has increased to more than 3 μV / K.

[0056] Next, we will explain the results of producing polycrystals of a mixed crystal system between three polycrystals (Fe3Si, Fe3Al, and Fe3Ga) and measuring the anomalous Nernst effect.

[0057] 13A and 13B show the mixed crystal system Fe3Si of Fe3Si and Fe3Al. 1-x Al x The Nernst coefficients at T = 300 K for the polycrystalline Fe3Si (0 ≤ x ≤ 1) shown in Figure 13A are shown. 0.67 Al 0.4 is a soft magnetic material called Sendust. From Figures 13A and 13B, Fe3Si 0.3 Al 0.7 With the exception of yx It can be seen that | increases.

[0058] 14A and 14B show the mixed crystal system Fe3Al of Fe3Al and Fe3Ga. 1-x Ga x Figure 14B shows the Nernst coefficients at T = 300 K for the polycrystalline Fe3Al (0 ≤ x ≤ 1) produced at a crystal growth rate of 20 mm / h. 1-x Ga x The Nernst coefficient of the single crystal is also shown. From Figures 14A and 14B, the Nernst coefficient |S yx | is large, and both single crystal and polycrystalline Fe3Al 0.25 Ga 0.75 Except for polycrystalline materials, the Nernst coefficient |Syx It can be seen that | increases.

[0059] In Fig. 15, Fe3Cu obtained by substituting part of the Ga sites in Fe3Ga with Cu 1-x Ga x The Nernst coefficients of single crystals and polycrystals (0.6 < x ≤ 1) at T = 300 K of Fe3CuGa are shown. 1-x Ga x The single crystals were also fabricated at a crystal growth rate of 20 mm / h. From Fig. 15, Fe3CuGa 1-x Ga x For the single crystals of Fe3CuGa, it can be seen that as the Cu content increases and the Ga content decreases, the Nernst coefficient |S yx | decreases. However, even at x = 0.7, it exceeds 3 μV / K, indicating that it has reached the practical level.

[0060] Next, referring to Figs. 16A to 20B, the experimental results of doping Fe3Ga with Nd, Ho, Y, and Tb will be described.

[0061] In Fig. 16A, Nd 0.1 Fe 2.9 The X-ray diffraction patterns of Ga and Fe3Ga are shown, and in Fig. 16B, the magnetic field dependence of the magnetization of Nd 0.1 Fe 2.9 Ga at T = 300 K is shown. From Fig. 16A, it can be seen that Nd 0.1 Fe 2.9 Ga maintains almost the same crystal structure as Fe3Ga. Also, from Fig. 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 observable.

[0062] In Fig. 16C, the magnetic field dependence of the Nernst coefficients of Fe3Ga single crystals and Nd 0.1 Fe 2.9 Ga polycrystals at T = 300 K are shown. Also, in Fig. 16D, the magnetic field dependence of the Hall resistivity of Fe3Ga single crystals and Nd 0.1 Fe 2.9 Ga polycrystals at T = 300 K are shown. From Fig. 16C, Nd0.1 Fe 2.9 Nernst coefficient |S of Ga polycrystalline yx Although the value of | is smaller than that of the Fe3Ga single crystal, it exceeds 3 μV / K, which is a practical level. 0.1 Fe 2.9 Hall resistivity ρ of Ga polycrystalline yx It can be seen that the magnetic field dependence of shows almost the same behavior.

[0063] In Figure 17A, Ho 0.05 Fe 2.95 17B shows the X-ray diffraction patterns of Ga and Fe3Ga, and 0.05 Fe 2.95 The magnetic field dependence of the magnetization of Ga at T = 300 K is shown in Fig. 17A. 0.05 Fe 2.95 It can be seen that Ga maintains almost the same crystal structure as Fe3Ga. 0.05 Fe 2.95 Ga has a saturation magnetization of 4.8μ at 2T. B / FU, and almost no coercive force is observed.

[0064] In Figure 18A, Y 0.05 Fe 2.95 The X-ray diffraction patterns of Ga and FeGa are shown in FIG. 18B. 0.05 Fe 2.95 The magnetic field dependence of the magnetization of Ga is shown in Figure 18A. 0.05 Fe 2.95 It can be seen that Ga maintains almost the same crystal structure as Fe3Ga. 0.05 Fe 2.95 Ga has a saturation magnetization of 3.28μ at 500 Oe. B / FU and has a coercive force of about 20 Oe.

[0065] Figure 19A shows the Tb 0.05 Fe 2.95 19A and 19B show the magnetic field dependence of the magnetization of Ga, and FIG. 19B shows an enlarged graph of the low magnetic field region of FIG. 19A.0.05 Fe 2.95 Ga has a saturation magnetization of 7.5μ at 2T. B / FU and has a coercive force of about 40 Oe.

[0066] Figure 20A shows the Tb 0.03 Fe 2.97 The X-ray diffraction patterns of Ga and Fe3Ga are shown in Figure 20B. 0.03 Fe 2.97 The magnetic field dependence of the magnetization of Ga at T=300K is shown in Figure 20A. 0.03 Fe 2.97 It can be seen that Ga maintains almost the same crystal structure as Fe3Ga. 0.03 Fe 2.97 Ga has a saturation magnetization of 6.9μ at 2T. B / FU, and almost no coercive force is observed.

[0067] 16A to 17B and 19A to 20B show the anomalous Nernst effect of a substance (third substance) obtained by substituting a part of the Fe site of FeGa with Nd, Ho, or Tb, but a similar anomalous Nernst effect can be expected in other third substances obtained by substituting other lanthanoids (e.g., Gd).

[0068] Next, with reference to FIGS. 21A to 23B, the results of experiments in which Fe3Ga was doped with B, Mn, or Pt will be described.

[0069] First, the experimental results of doping Fe3Ga with B will be explained. 0.8 B 0.2 , Fe3Ga 0.9 B 0.1 The X-ray diffraction patterns of Fe3Ga and Fe3Ga are shown. 0.8 B 0.2 and Fe3Ga 0.9 B 0.1It can be seen that the crystal structure is almost the same as that of Fe3Ga. Furthermore, energy dispersive X-ray analysis (EDX) (not shown) reveals that the additive B appears near the boundary of Fe3Ga.

[0070] In Figure 21B, Fe3Ga 0.8 B 0.2 The magnetic field dependence of magnetization at T = 300 K is shown for needle-shaped and plate-shaped samples. The needle-shaped sample (cylindrical sample) shown in Figure 21B is magnetized in the longitudinal direction, and a magnetic field is applied parallel to the longitudinal direction. The plate-shaped sample shown in Figure 21B is magnetized in the in-plane direction, and a magnetic field is applied perpendicular to the plane. Because the magnetization direction and the magnetic field direction are perpendicular to the plate-shaped sample, a strong magnetic field is required to raise the magnetization in the direction of the magnetic field. Figure 21B shows that when a strong magnetic field is applied, the magnetization of the plate-shaped sample changes only slightly linearly, while the magnetization of the needle-shaped sample, which has magnetization parallel to the magnetic field, changes significantly, revealing clear hysteresis.

[0071] Fig. 21C shows the needle-shaped sample of Fe3Ga 0.8 B 0.2 The magnetic field dependence of the magnetization of Fe3Ga and Fe3Ga is shown in Figure 21C. The needle-shaped sample shown in Figure 21C is magnetized in the longitudinal 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 The magnetization is saturated at relatively weak magnetic fields (approximately 400 Oe and 800 Oe, respectively). 0.8 B 0.2 The hysteresis is more obvious in Fe3Ga than in Fe3Ga, and the coercive force of Fe3Ga is about 10 Oe, while that of Fe3Ga 0.8 B 0.2 The coercive force is approximately 35 Oe.

[0072] Figure 21D shows the Fe3Ga plate sample. 0.8 B 0.2The magnetic field dependence of the magnetization of Fe3Ga and Fe3Ga is shown in Fig. 21D. The plate-shaped sample shown in Fig. 21D is magnetized in the in-plane direction, and a magnetic field is applied in the perpendicular direction. Since the magnetization direction and the magnetic field direction are perpendicular, a strong magnetic field is required to raise the magnetization in the perpendicular direction. 0.8 B 0.2 The magnetization increases linearly up to a magnetic field exceeding 3 kOe, and the hysteresis is weak. In fact, almost no coercivity is observed for Fe3Ga. On the other hand, the enlarged view near the low magnetic field (insert in Figure 21D) shows that Fe3Ga 0.8 B 0.2 has a coercivity of about 35 Oe.

[0073] Figure 21E shows the Fe3Ga plate sample. 0.8 B 0.2 Fig. 21F shows the magnetic field dependence of the Nernst coefficient of the plate-shaped sample Fe3Ga 0.8 B 0.2 21E and 21F show the magnetic field dependence of the Hall resistivity of Fe3Ga. The plate-shaped samples shown in Fig. 21E and 21F are magnetized in the in-plane direction, as in Fig. 21D, and the magnetic field is applied perpendicular to the plane. In Fig. 21F, the data plots when the magnetic field is increased from -2 T to +2 T are shown by circles, and the data plots when the magnetic field is decreased from +2 T to -2 T are shown by squares. Fig. 21E shows that Fe3Ga 0.8 B 0.2 Nernst coefficient of |S yx reaches 4 μV / K, which is approximately 80% of the Nernst coefficient of the Fe 3 Ga polycrystalline body (4.9 μV / K: see FIGS. 14A and 14B).

[0074] In this way, by substituting part of the Ga site of Fe3Ga with B, the coercive force increases and the Nernst coefficient can be secured at about 80% of that of Fe3Ga. 0.8 B 0.2 This is advantageous for fabricating a thermopile that can be realized in zero magnetic field.

[0075] Next, we will explain the experimental results of doping Fe3Ga with Mn. 2.9 Mn0.1 Ga, Fe 2.5 Mn 0.5 The X-ray diffraction patterns of Ga, Fe2MnGa, and Fe3Ga are shown in Fig. 22B. 2.9 Mn 0.1 Ga and Fe 2.5 Mn 0.5 This shows the magnetic field dependence of the magnetization of Ga at T = 300 K. The needle-shaped sample shown in Figure 22B is magnetized in the longitudinal direction, and a magnetic field is applied parallel to the magnetization direction.

[0076] From Figure 22A, Fe 2.9 Mn 0.1 Ga and Fe 2.5 Mn 0.5 It can be seen that Ga maintains almost the same crystal structure as Fe3Ga. 2.9 Mn 0.1 Although Ga shows a large magnetization, it shows almost no hysteresis. 2.5 Mn 0.5 Ga exhibits small hysteresis and has a coercivity of about 10 Oe (same as the coercivity of the Fe3Ga needle sample shown in Figure 21C), while Fe 2.9 Mn 0.1 It can be seen that the magnetization is significantly suppressed compared to Ga.

[0077] Next, we will explain the experimental results of doping Pt into Fe3Ga. 2.9 Pt 0.1 Ga, Fe 2.9 Pt 0.1 Ga 0.9 Ge 0.1 and FeGa, and Fig. 23B shows the X-ray diffraction patterns of the needle-shaped sample Fe 2.9 Pt 0.1 Ga and Fe 2.9 Pt 0.1 Ga 0.9 Ge 0.1 23B shows the magnetic field dependence of the magnetization at T=300 K. The needle-shaped sample shown in FIG. 23B is magnetized in the longitudinal direction, and a magnetic field is applied parallel to the magnetization direction.

[0078] From Figure 23A, Fe2.9 Pt 0.1 Ga and Fe 2.9 Pt 0.1 Ga 0.9 Ge 0.1 It can be seen that the crystal structure of Fe3Ga is almost the same as that of Fe3Ga. 2.9 Pt 0.1 Ga shows almost no hysteresis. 2.9 Pt 0.1 Ga 0.9 Ge 0.1 exhibits small hysteresis and has a coercivity of about 8 Oe. 2.9 Pt 0.1 It can be seen that the coercive force is increased by substituting some of the Ga sites of Ga with Ge.

[0079] As mentioned above, an increase in coercivity was observed when some of the Ga sites of Fe3Ga were substituted with B (see Figures 21C and 21D), which suggests that the substitution of Ga sites affects the magnetic properties.

[0080] 24 to 30, an embodiment in which the thermoelectric conversion element 1 is a thin film will be described. In the following embodiment, the thermoelectric conversion element 1 is made of a first substance having a composition formula Fe3X or a second substance having an off-stoichiometric composition in which the composition ratio of Fe and X is shifted from that of the first substance, but is not limited thereto.

[0081] First, a method for producing a thin film will be described. In the following, an example in which a thin film is produced by sputtering will be shown, but the method for producing a thin film is not limited thereto, and other methods such as molecular beam epitaxy (MBE), chemical vapor deposition (CVD), pulsed laser deposition (PLD), plating, etc. may also be used.

[0082] For example, in the fabrication of Fe3Ga thin films, a target consisting of a 3:1 Fe:Ga composition was first discharged in a DC magnetron sputtering system at room temperature to form a thin film of Fe doped with Ga on a magnesium oxide (MgO) substrate with a

[0001] orientation. The Fe3Ga sample formed at room temperature is a polycrystalline thin film, but by annealing it at 500°C for 30 minutes without breaking the vacuum after deposition, an epitaxial thin film with a

[0001] orientation can be fabricated. In this way, the Fe3Ga thin film is a

[0001] -oriented epitaxial thin film fabricated on a

[0001] -oriented MgO substrate.

[0083] In addition, an oxidation prevention layer made of MgO is provided on the outermost surface of the thin film. Note that, in addition to MgO, a cap layer made of a general material that prevents oxidation, such as Al, Al2O3, or SiO2, can also be used as the oxidation prevention layer. Note that a buffer layer between the thin film and the substrate and a cap layer on the outermost surface of the thin film are not necessarily required.

[0084] In the above-described manufacturing method, the T / S distance (distance between the target and the substrate) is preferably 15 cm to 20 cm in a sputtering apparatus, but even when other manufacturing methods are used, the T / S distance may be in the range of 5 cm to 40 cm.

[0085] With ferromagnetic materials, it is difficult to align the magnetization direction perpendicular to the temperature difference due to the influence of the demagnetizing field, making it difficult to obtain a voltage in zero magnetic field. However, when the film is thinned as described above, the contribution of the demagnetizing field in the direction perpendicular to the film's surface increases, while the effect of the demagnetizing field in the in-plane direction becomes almost zero. This stabilizes the magnetization in the in-plane direction.

[0086] Next, with reference to FIG. 24, a method for measuring the anomalous Nernst effect when a temperature gradient is applied in the in-plane direction to a thin film sample serving as a thermoelectric conversion element 1 will be described. To measure such an anomalous Nernst effect, for example, a rectangular parallelepiped structure as shown in FIG. 24 is used. In the structure of FIG. 24, a 50 nm-thick thin film (Fe3X thin film) sample is stacked on a 500 μm-thick MgO substrate, and a 5 nm-thick MgO cap layer is stacked on the thin film sample. The length of this structure in the longitudinal direction is 9 mm and the width is 2 mm. Thermocouples are provided in the thin film sample in the longitudinal direction, with the thermocouples spaced 6 mm apart.

[0087] As mentioned above, the thin film sample is magnetized in the in-plane direction. As shown in Figure 24, when a magnetic field is applied perpendicular to the surface of the thin film sample, the magnetization rises in the perpendicular direction. When a heat flow Q flows in the longitudinal direction of the thin film sample, a temperature difference ΔT (= T2 - T1) occurs. As a result, as in Figure 2, an electromotive force V is generated in a direction perpendicular to both the direction of the heat flow Q and the direction of magnetization (perpendicular to the surface) due to the anomalous Nernst effect. yx occurs.

[0088] The measurement results of the anomalous Nernst effect when the thin film sample shown in FIG. 24 is Fe3Ga (magnetic field dependence of the Nernst coefficient at T=300K) are shown in FIG. 25. From FIG. 25, the Nernst coefficient |S yx It can be seen that | indicates 4.0 μV / K.

[0089] 24 and 25 show examples in which a temperature gradient is applied to a thin film sample in the in-plane direction, but the anomalous Nernst effect can also be obtained when a temperature gradient is applied to a thin film sample in the direction perpendicular to the plane, as shown in Fig. 26. That is, the thin film sample serving as the thermoelectric conversion element 1 is magnetized in the in-plane direction (x direction), and when a heat flow Q is applied to this thin film sample in the direction perpendicular to the plane (z direction), an electromotive force V is generated in the direction (y direction) perpendicular to both the direction of the heat flow Q and the direction of the magnetization M.

[0090] To measure this anomalous Nernst effect, for example, a structure shown in FIG. 27A is used. In the structure of FIG. 27A, a 500 μm thick silicone pad is provided on a Cu heat sink, a 500 μm thick MgO substrate is laminated on the silicone pad, a 50 nm thick thin film sample is laminated on the MgO substrate, and a 5 nm thick MgO cap layer is laminated on the thin film sample. Voltage terminals are provided on both longitudinal ends of the MgO cap layer, and these voltage terminals are connected to both longitudinal ends of the thin film sample. As a result, as shown in FIG. 27B, an electromotive force V generated in the longitudinal direction of the thin film sample by the anomalous Nernst effect is yx can be measured.

[0091] A 500 μm thick silicone pad is layered on the MgO cap layer, and a 1 mm thick copper plate is layered on the silicone pad. A resistive heater (ceramic heater) is placed on the copper plate. Thermocouples are placed at the top of the MgO cap layer and the bottom of the MgO substrate. The thermocouples are used to measure the temperature gradient ΔT in the perpendicular direction ([00-1]) from the top of the MgO cap layer through the thin film sample to the bottom of the MgO substrate due to the heat flow from the ceramic heater. all In Figures 27A and 27B, the direction of magnetization of the thin film sample and the direction of the applied magnetic field

[0110] are parallel.

[0092] Figure 28 shows the measurement results (magnetic field dependence of electromotive force) of the anomalous Nernst effect at 300 K when the thin film sample shown in Figures 27A and 27B is Fe3Ga. From Figure 28, it can be seen that, unlike the bulk sample, the thin film sample Fe3Ga has an electromotive force of 19.8 μV even in zero magnetic field, which is almost the same as the value in a saturated magnetic field. In addition, the coercive force of the thin film sample Fe3Ga is approximately 40 Oe.

[0093] In this measurement, the temperature difference measured by the thermocouple in the direction perpendicular to the surface is ΔT all = 1.5K. Here, the temperature gradient of the thin film sample itself, ∇T filmSince it is difficult to accurately estimate ∇T, the measurement results shown in Figure 25 will be used, 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 perpendicular direction. The Nernst coefficient (4.0 μV / K) of Fe3Ga shown in Figure 25 is film Assuming that this method is also applicable to thin films, the temperature gradient acting in the direction perpendicular to the surface of a 50 nm thin film sample of Fe3Ga can be estimated to be 0.9 K / mm.

[0094] In the above-mentioned thin film fabrication method, annealing is performed after film formation at room temperature. However, even in polycrystalline or amorphous thin films obtained without annealing after film formation at room temperature, the same degree of anomalous Nernst effect as that of annealed thin film samples can be obtained, as will be shown below.

[0095] Thin film fabrication without annealing is easier and can be used for flexible films. Furthermore, while the fabrication of the epitaxial film described above required a <0001> oriented MgO substrate, the fabrication of polycrystalline or amorphous films does not require any substrate.

[0096] The material of the substrate is not limited, and in addition to MgO, Si, Al2O3, PET, polyimide, etc. can be used.

[0097] Fig. 29A shows the measurement results (magnetic field dependence of electromotive force) of the anomalous Nernst effect at T = 300 K when a temperature gradient is applied in the perpendicular direction as shown in Fig. 26 to a thin film sample Fe3Ga fabricated on an MgO substrate without annealing after film formation at room temperature, and Fig. 29B shows an enlarged graph of the vicinity of the low magnetic field in Fig. 29A. In Figs. 29A and 29B, as in Figs. 27A and 27B, the thickness of the thin film sample Fe3Ga is 50 nm, and the temperature gradient in the perpendicular direction measured by the thermocouple is ΔT all =1.5K (3K / mm).

[0098] 30 shows the measurement results of the anomalous Nernst effect (magnetic field dependence of electromotive force) when a temperature gradient is applied in the perpendicular direction for an Fe3Ga epitaxial film obtained by annealing after room temperature film formation, and an Fe3Ga amorphous film obtained by not annealing after room temperature film formation. The measurement results for the amorphous film in Fig. 30 correspond to the measurement results shown in Fig. 29A and Fig. 29B, and the measurement results for the epitaxial film in Fig. 30 correspond to the measurement results for Fe3Ga shown in Fig. 28.

[0099] 29A, 29B, and 30 show that the electromotive force of the amorphous film is almost equal to that of the epitaxial film under a high magnetic field, and is about half that of the epitaxial film under zero magnetic field. In other words, the Fe3Ga amorphous thin film sample fabricated by room temperature deposition has a Nernst coefficient of about 2 μV / K under zero magnetic field.

[0100] In the above-described embodiment (FIGS. 24 to 30), an example was shown in which the thickness of the thin film was 50 nm, but the thickness of the thin film is not limited, and may be 10 μm or less, more preferably 1 μm or less.

[0101] As described above, according to the embodiment of FIGS. 24 to 30, a thin film made of Fe3Ga is used as the thermoelectric conversion element 1, so that the anomalous Nernst effect can be obtained with an inexpensive material. Furthermore, by making the thermoelectric conversion element 1 thin, it is possible to fabricate a thermoelectric conversion element 1 that exhibits a large anomalous Nernst effect even in zero magnetic field. Furthermore, the anomalous Nernst effect can be obtained whether the thermoelectric conversion element 1 is single crystalline, polycrystalline, or amorphous. Furthermore, because film formation at room temperature is possible, a thin film can be fabricated even on a flexible substrate that is vulnerable to heat. [Explanation of symbols]

[0102] 1, 1A, 24, 25, 32 Thermoelectric conversion element 20, 20A, 30 Thermoelectric conversion device 22, 22A board 23, 23A power generating unit 31 Hollow member

Claims

1. The composition formula is Fe ３ a first material of stoichiometric composition represented by X, wherein X is Ga, Ge, Sn, or Si; Fe ３ Fe-Al-V alloys in which part of the Fe site of Al is replaced with V, or Fe ３ a third material which is an alloy in which a part of the Fe site of Ga is substituted with Mn, Y, Pt or a lanthanide; The composition formula is Fe ３ M1 １－ｘ M2 ｘ (0<x<1), and the combination of M1 and M2 is Si and Al, Al and Ga, Cu and Ga, or Ga and B; or Fe ３ a fifth material in which a portion of the Fe site of Ga is substituted with Pt and a portion of the Ga site is substituted with Ge; A thermoelectric conversion element, wherein the first material, the third material, the fourth material, and the fifth material exhibit the anomalous Nernst effect when an external magnetic field is applied, and Fe3Ga exhibits the anomalous Nernst effect in zero magnetic field when it is a thin film having a thickness of 10 μm or less, and the absolute value of the Nernst coefficient of the anomalous Nernst effect is 1.5 μV / K or more.

2. 2. The thermoelectric conversion element according to claim 1, wherein the polycrystalline Fe-Al-V alloy has a Nernst coefficient that is constant in a temperature range of 200K to 400K.

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

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

5. The thermoelectric conversion element according to claim 1 , wherein the first material, the third material, the fourth material, or the fifth material is amorphous.

6. A substrate; a power generating 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 made of the same material as the thermoelectric conversion element according to any one of claims 1 to 5; The thermoelectric conversion device, wherein the plurality of thermoelectric conversion elements are arranged in parallel in a direction perpendicular to the one direction and are electrically connected in series.

7. The thermoelectric conversion device according to claim 6 , wherein the plurality of thermoelectric conversion elements are arranged in a serpentine pattern.

8. The thermoelectric conversion element according to any one of claims 1 to 5, a hollow member; The thermoelectric conversion element is a sheet-like structure or a wire material, and is provided so as to cover the outer surface of the hollow member.

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