P-type thermoelectric material, manufacturing method thereof, and thermoelectric conversion element using the same

Abstract

To provide a p-type Fe2VAl-based thermoelectric material having a Seebeck coefficient (S) of 40 μV / K or more at 300 K or more but less than 350 K and a power factor (PF) of 1.4 mW / K2 m or more, a method for manufacturing the same, and a thermoelectric conversion element using the same.SOLUTION: A thermoelectric material according to the present invention contains an inorganic compound containing iron (Fe), vanadium (V), manganese (Mn), and aluminum (Al), and the inorganic compound has a Heusler structure, and its crystal orientation is preferentially oriented in the (110) plane, with an orientation degree of 98% or more.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to a p-type thermoelectric material, a method for producing the same, and a thermoelectric conversion element using the same. [Background technology]

[0002] Thermoelectric materials can convert heat into electricity using the Seebeck effect, and are therefore considered promising for use in energy conservation and as independent power sources for electronic devices. Typically, π-type thermoelectric modules are used, which are made by combining p-type and n-type thermoelectric elements in series, but thin-film thermoelectric elements, which are smaller in size and can be produced on a production line similar to the semiconductor process, are also attracting attention.

[0003] Thermoelectric materials using Heusler-type Fe2VAl-based alloys are particularly promising because they have the advantages of (1) high power factor at around room temperature, (2) being safe and inexpensive materials, and (3) having high mechanical strength.

[0004] FIG. 1 is a diagram showing the crystal structure of Fe2VAl.

[0005] Fe2VAl has a cubic crystal structure in space group Fm-3m (space group number 225 in the International Tables for Crystallography). This crystal structure is also called the Heusler structure or Fe2VAl structure. Fe (iron) occupies the 8c site, V (vanadium) occupies the 4b site, and Al (aluminum) occupies the 4a site. However, in reality, partial mutual substitution of the sites occurs. At high temperatures, complete site disordering occurs, resulting in a different space group. Known space groups include Pm-3m (space group number 221) and Im-3m (space group number 229). However, for simplicity, we will refer to structures with such mutual site substitution as the Fe2VAl structure (or Heusler structure).

[0006] Recently, there have been reports of thin films using Fe2VAl-based alloys as thermoelectric materials (see, for example, Non-Patent Document 1). According to Non-Patent Document 1, tungsten (W)-doped Fe2V 0.8 W 0.2 The Al thin film has a resistance of 10 to 40 mW / K at around room temperature. 2 It functioned as an n-type thermoelectric thin film, exhibiting a large power factor of up to m.

[0007] On the other hand, as for the p-type, which is the counterpart of the n-type, although there have been several reports on Fe2VAl-based alloys, no thin films exhibiting a large power factor have yet been obtained (see, for example, Non-Patent Documents 2 to 7).

[0008] According to Non-Patent Document 2, Fe2V 0.9 Ti 0.1 We report a thin film on a zirconia substrate by RF sputtering using an Al alloy target. X-ray diffraction revealed that the thin film had an Fe2VAl-type Heusler structure, with a particularly strong (422) peak, indicating that the film grew preferentially in the (211) direction. Thermoelectric property evaluation revealed that the thin film had p-type properties, with a maximum of 1 mW / K at around room temperature. 2 The power factor of m is shown.

[0009] According to Non-Patent Document 3, Fe2VAl, Fe2VAl 0.95 Si 0.05 We report a thin film on an MgO substrate by RF sputtering using a combination of V and V metal tips. In Non-Patent Document 3, a thin film oriented in the (100) direction with excellent crystallinity was obtained. Thermoelectric property evaluation revealed that this thin film had p-type properties, a Seebeck coefficient of approximately 20 μV / K, and a thermal conductivity of 1 mW / K. 2 It showed a power factor of less than m.

[0010] Non-Patent Document 4 reports a thin film prepared by DC sputtering using an Fe2VAl target. Specifically, in Non-Patent Document 4, the thin film was deposited on a MgO layer superimposed on a Si substrate, and had a (100) orientation. Thermoelectric property evaluation revealed that the thin film had p-type properties and a thermal conductivity of 1.13 mW / K 2 The power factor of m is shown.

[0011] Non-Patent Document 5 reports the deposition of a thin film of Fe2VAl on a MgAl2O4 (100) substrate by MBE using Fe, V, and Al as the deposition source. This thin film grows epitaxially in the (100) direction, and has a Seebeck coefficient of 40 μV / K and a lattice constant of 1.379 × 10 -5 Electrical resistance in Ωm, 0.12mW / K 2 The power factor of m is shown.

[0012] Non-Patent Document 6 reports on the improvement of p-type characteristics of thin films of Fe2VAl-based alloys. According to Non-Patent Document 6, when thin films with varying compositions were deposited on an MgO substrate by DC sputtering, the thermoelectric properties changed from n-type to p-type depending on the composition, and the maximum power factor in the p-type region was 1.0 mW / K. 2 The thickness of the thin film was m. Note that this thin film did not have any specific crystal orientation.

[0013] Non-Patent Document 7 reports the preparation of variously doped Fe2TiAl thin films on MgO substrates by magnetron sputtering. The Fe2TiAl-based alloy thin films are different in material system from Fe2VAl, but have the same crystal system. The thin films in Non-Patent Document 7 have a preferential orientation in the (00l) direction and a composition of Fe 2.01 Ti 0.56 V 0.67 Al 0.76 , Fe 2.18 Ti 0.73 Al 1.09 , Fe 1.99 Ti 0.66 Cr 0.45 Al 0.90 The thin film has an efficiency of 0.8 to 1.6 mW / K at around room temperature. 2 It had a power factor of m and exhibited p-type thermoelectric properties.

[0014] However, as shown in Non-Patent Document 8, the bulk of a Ti-doped Fe2VAl-based alloy has a thermal conductivity of 4 mW / K at around room temperature. 2 It has been reported that thin-film materials have a power factor of 1.4 mW / K. 2 There are no examples of a power factor of 1.4 mW / K or higher, whether it is a thin film material or a bulk material.2 There is a need for p-type thermoelectric materials with a power factor of m. [Prior art documents] [Non-patent literature]

[0015] [Non-Patent Document 1] B. Hinterleitner et al., Nature 576, 85, 2019 [Non-patent document 2] M. Mikami et al., Thin Solid Films, 518, 2010, 2796-2800 [Non-patent document 3] Y. Furuta et al., Journal of ELECTRONIC MATERIALS, Vol. 43, No. 6, 2014, 2157-2164 [Non-patent document 4] Nishide Satoshi et al., Journal of the Japan Institute of Metals, Vol. 76, No. 9, 2012, 541-545 [Non-patent document 5] S.Yamada et al., Applied Physics Express 10, 115802, 2017 [Non-patent document 6] N. Fukatani et al.,APPLIED PHYSICS LETTERS 112,033902,2018 [Non-Patent Document 7] Y. Kurosaki et al., AIP Advances 10, 115313, 2020 [Non-patent document 8] Y. Nishino et al., JOURNAL OF APPLIED PHYSICS 115, 123707, 2014 Summary of the Invention [Problem to be solved by the invention]

[0016] From the above, the object of the present invention is to provide a semiconductor laser having a Seebeck coefficient (S) of 40 μV / K or more at a temperature of 300 K or more but less than 350 K and a power factor (PF) of 1.4 mW / K. 2The present invention provides a p-type Fe2VAl-based thermoelectric material having a molecular weight of at least m, a method for producing the same, and a thermoelectric conversion element using the same. [Means for solving the problem]

[0017] The p-type thermoelectric material according to the present invention contains an inorganic compound containing iron (Fe), vanadium (V), manganese (Mn), and aluminum (Al), wherein the inorganic compound has a Heusler structure, the inorganic compound has a preferred crystal orientation in the (110) plane, and the degree of orientation of the preferred orientation is 98% or more, thereby solving the above-mentioned problems. The inorganic compound is Fe: 45 atomic% or more and 55 atomic% or less, V: 14.5 atom% or more and 20 atom% or less, Mn: 1.5 atomic % or more and 4 atomic % or less, and Al: 27 atomic% or more and 35 atomic% or less may be satisfied (provided that the total atomic % of Fe, V, Mn and Al is 100). The inorganic compound is Fe: 48.5 atomic% or more and 52 atomic% or less, V: 14.5 atom% or more and 18 atom% or less, Mn: 1.5 atomic % or more and 3 atomic % or less, and Al: 30 atomic% or more and 35 atomic% or less may be satisfied (provided that the total atomic % of Fe, V, Mn and Al is 100). The inorganic compound is Fe: 49.5 atomic% or more and 50.5 atomic% or less, V: 15 atomic% or more and 16.5 atomic% or less, Mn: 2 atomic % or more and 3 atomic % or less, and Al: 30 atomic% or more and 33 atomic% or less may be satisfied (provided that the total atomic % of Fe, V, Mn and Al is 100). The inorganic compound may further have a (111) diffraction peak in an X-ray diffraction pattern measured using Cu-Kα radiation. It may be a thin film. The thin film may be located on a substrate having an interatomic distance that is mismatched by 4% or more in absolute value from the Fe-Fe interatomic distance of the Heusler structure, or a substrate that does not have cubic symmetry. The substrate may be selected from the group consisting of lanthanum aluminate (LaAlO3), sapphire, strontium titanate (SrTiO3), and silicon. A method for producing a thin film p-type thermoelectric material according to the present invention includes forming a film on a substrate having an interatomic distance that is mismatched in absolute value by 4% or more from the Fe-Fe interatomic distance of the Heusler structure or on a substrate not having cubic symmetry by physical vapor deposition using a sintered body having a Heusler structure, the sintered body containing iron (Fe), vanadium (V), manganese (Mn), and aluminum (Al) as a target, the p-type thermoelectric material comprising an inorganic compound containing iron (Fe), vanadium (V), manganese (Mn), and aluminum (Al), the inorganic compound having a Heusler structure, the inorganic compound having a preferred crystal orientation in the (110) plane, the degree of orientation of the preferred orientation being 98% or more, thereby solving the above-mentioned problems. A thermoelectric conversion element according to the present invention includes at least a p-type thermoelectric material, which is the p-type thermoelectric material described above, thereby solving the above-mentioned problems. The thermoelectric element may include n-type thermoelectric materials connected in series alternately with the p-type thermoelectric materials. [Effects of the Invention]

[0018] The p-type thermoelectric material of the present invention contains an inorganic compound containing iron (Fe), vanadium (V), manganese (Mn), and aluminum (Al) and has a Heusler structure, so it functions as a thermoelectric material. In particular, the crystal orientation of the inorganic compound is preferentially oriented in the (110) plane, and the degree of orientation is controlled to 98% or more. Therefore, in the temperature range of 300K or more but less than 350K, the Seebeck coefficient (S) is 40 μV / K or more and the power factor (PF) is 1.4 mW / K. 2By applying the p-type thermoelectric material of the present invention, it is possible to provide an excellent thermoelectric conversion element in the temperature range of 300 K or more and less than 350 K, particularly in the temperature range near room temperature (273 K or more and 310 K or less). [Brief explanation of the drawings]

[0019] [Figure 1] Diagram showing the crystal structure of Fe2VAl [Figure 2] A flowchart showing the steps for producing a thin-film thermoelectric material as a p-type thermoelectric material of the present invention. [Figure 3] 1 is a diagram showing a thermoelectric conversion element of the present invention; [Figure 4] XRD pattern of the thin film of Example 1 [Figure 5] XRD pattern of the thin film of Example 2 [Figure 6] 1 shows the XRD pattern of the thin film of Example 3. [Figure 7] 1 shows the XRD pattern of the thin film of Example 4. [Figure 8] 1 shows the XRD pattern of the thin film of Example 5. [Figure 9] FIG. 1 shows the temperature dependence of the electrical resistance (ρ) of the thin films of Examples 1 to 6. [Figure 10] FIG. 1 shows the temperature dependence of the Seebeck coefficient (S) of the thin films of Examples 1 to 6. [Figure 11] FIG. 10 shows the temperature dependence of the power factor (PF) of the thin films of Examples 1 to 6. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that like elements are designated by like numbers and their description will be omitted.

[0021] (Embodiment 1) In the first embodiment, a p-type thermoelectric material of the present invention and a method for producing the same will be described in detail.

[0022] The p-type thermoelectric material of the present invention contains an inorganic compound containing iron (Fe), vanadium (V), manganese (Mn), and aluminum (Al), and has the Heusler structure shown in Figure 1. That is, since it is an inorganic compound in which Mn is added to an Fe2VAl-based alloy, it functions as a p-type thermoelectric material. Furthermore, the crystal orientation of the inorganic compound is preferentially oriented in the (110) plane, and the degree of orientation of this preferred orientation is 98% or more. As a result, in the temperature range of 300K or more but less than 350K, the Seebeck coefficient (S) is 40μV / K or more, and the power factor (PF) is 1.4mW / K. 2 It can exhibit excellent thermoelectric properties of 0.1m or more.

[0023] The degree of preferred orientation is preferably 98.5% or more. This can improve the thermoelectric properties. The degree of preferred orientation is more preferably 99% or more. This can further improve the thermoelectric properties. The upper limit of the degree of orientation may be 100%, but as long as it is 98% or more, other orientations may be included to the extent that they do not impair the thermoelectric properties. For example, the inorganic compound may further have a (111) diffraction peak in an X-ray diffraction pattern measured using Cu-Kα radiation.

[0024] In this specification, the degree of preferred orientation of the (110) plane is calculated as follows: For a target sample, the 2θ value, which is the angle between the incident X-ray and the detector, is fixed to the value of the (220) peak (approximately 44.38°), and a rocking curve is measured. Next, the half-width of the (220) peak of the obtained rocking curve is defined as D, and the degree of orientation is calculated using the following formula. Orientation degree={(180-D) / 180}*100

[0025] The inorganic compound is preferably Fe: 45 atomic% or more and 55 atomic% or less, V: 14.5 atom% or more and 20 atom% or less, Mn: 1.5 atomic % or more and 4 atomic % or less, and Al: 27 atomic% or more and 35 atomic% or less (However, the total atomic percentage of Fe, V, Mn, and Al must be 100.) This stabilizes the Heusler structure, further increasing the degree of preferred orientation of the (110) plane, and improving the thermoelectric properties.

[0026] The inorganic compound is more preferably Fe: 48.5 atomic% or more and 52 atomic% or less, V: 14.5 atom% or more and 18 atom% or less, Mn: 1.5 atomic % or more and 3 atomic % or less, and Al: 30 atomic% or more and 35 atomic% or less (However, the total atomic percentage of Fe, V, Mn, and Al is 100.) This further stabilizes the Heusler structure, further increases the degree of preferred orientation of the (110) plane, and improves the thermoelectric properties.

[0027] In the inorganic compound, more preferably Fe: 49.5 atomic% or more and 50.5 atomic% or less, V: 15 atomic% or more and 16.5 atomic% or less, Mn: 2 atomic % or more and 3 atomic % or less, and Al: 30 atomic% or more and 33 atomic% or less (However, the total atomic percentage of Fe, V, Mn, and Al is 100.) This further stabilizes the Heusler structure, further increases the degree of preferred orientation of the (110) plane, and in the wide temperature range of 300K to 400K, the Seebeck coefficient (S) is 70μV / K or more and the power factor (PF) is 2mW / K. 2 In particular, at room temperature (273K to 310K), the Seebeck coefficient (S) is 80μV / K or more and the power factor (PF) is 4mW / K or more. 2 It is possible to provide a p-type thermoelectric material having thermoelectric properties of m or more.

[0028] There is no particular limitation on the form of the inorganic compound, and it may be a thin film or a bulk single crystal.

[0029] When the inorganic compound is a thin film, the thickness of the thin film is preferably 100 nm or more. This allows for preferential orientation in the (110) plane, resulting in a high degree of orientation. The thickness of the thin film is more preferably 200 nm or more, and even more preferably 250 nm or more and 10 μm or less.

[0030] The thin film may be located on a substrate. There are no particular limitations on the substrate as long as the thin film has a preferred orientation in the (110) plane, but preferred are substrates with an interatomic distance that is mismatched by 4% or more in absolute value from the Fe-Fe atomic distance in the Heusler structure, or substrates that do not have cubic symmetry. If such a substrate is used, the thin film located thereon will have a preferred orientation in the (110) plane. There is no particular upper limit on the mismatch, but a mismatch of up to 10% in absolute value is allowed.

[0031] Examples of substrates with interatomic distances that are mismatched by an absolute value of 4% or more from the Fe-Fe atomic distance in the Heusler structure include lanthanum aluminate (LaAlO3), strontium titanate (SrTiO3), and silicon.Since the mismatch with the (100) plane of these substrates exceeds 4% in absolute value, it is easy to obtain thin films oriented in the (110) plane rather than the (100) plane.

[0032] Substrates that do not have cubic symmetry are incompatible with the cubic Heusler structure. An example of such a substrate is sapphire (Al2O3), which produces thin films oriented in the (110) plane on the (0001) plane (c-plane).

[0033] The thickness of the substrate is not particularly limited, but may be in the range of 1 μm to 1 mm, which makes it easy to handle and allows the provision of a thin thermoelectric conversion element as described below.

[0034] Next, a method for producing the p-type thermoelectric material of the present invention will be described. FIG. 2 is a flowchart showing the steps for producing a thin film thermoelectric material as a p-type thermoelectric material of the present invention.

[0035] The manufacturing method of the present invention includes the following steps, by which a thin film thermoelectric material is obtained. Step S210: Using a sintered body containing iron (Fe), vanadium (V), manganese (Mn), and aluminum (Al) and having a Heusler structure as a target, a film is formed by physical vapor deposition on a substrate having an interatomic distance that is mismatched by 4% or more in absolute value from the Fe-Fe atomic distance of the Heusler structure, or on a substrate that does not have cubic symmetry.

[0036] The sintered body is prepared, for example, by mixing a raw material containing iron (Fe), a raw material containing vanadium (V), a raw material containing manganese (Mn), and a raw material containing aluminum (Al), and firing the mixture.

[0037] The Fe-containing raw material may be Fe metal alone, or may be an oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride of Fe. The V-containing raw material may be V metal alone, or may be V oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride. The Mn-containing raw material may be Mn metal alone, or may be Mn oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride. The Al-containing raw material may be Al metal alone, or may be Al oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride. The raw materials are preferably in the form of powder, granules, or small chunks from the viewpoints of mixability and handling.

[0038] The metal elements in the raw materials are Fe: 45 atomic% or more and 55 atomic% or less, V: 14.5 atom% or more and 20 atom% or less, Mn: 1.5 atomic % or more and 4 atomic % or less, and Al: 27 atomic% or more and 35 atomic% or less (where the total atomic % of Fe, V, Mn and Al is 100). The preferred composition is as described above, and therefore will not be described here.

[0039] Sintering may be performed by any method, such as spark plasma sintering (SPS), hot press sintering (HP), hot isostatic pressing (HIP), cold isostatic pressing (CIP), or pulse current sintering, but is preferably performed by spark plasma sintering (SPS). This allows for the production of a sintered body with suppressed grain growth in a short time without using a sintering aid. The sintering temperature may be, for example, in the range of 1073 K to 1473 K.

[0040] The sintered body thus obtained is used as a target to perform physical vapor deposition, which may be a known method such as resistance heating evaporation, electron beam thermal vapor deposition (EBPVD), pulsed laser deposition (PLD), molecular beam epitaxy (MBE), ion plating, ion beam evaporation, or sputtering.

[0041] Growth conditions vary depending on the physical vapor deposition method selected. For example, if sputtering is used as the physical vapor deposition method, an inert gas such as argon can be used as the sputtering gas, and the substrate temperature can be set to a range of 723K or higher and 1073K or lower.

[0042] As described above, the substrate may be a substrate having an interatomic distance that is mismatched by 4% or more in absolute value from the Fe-Fe interatomic distance of the Heusler structure, or a substrate that does not have cubic symmetry, such as lanthanum aluminate (LaAlO), sapphire, strontium titanate (SrTiO), silicon, etc.

[0043] After the film formation, it is preferable to age the film at the film formation temperature for 1 hour to 24 hours, which stabilizes the crystal structure of the thin film and allows it to be preferentially oriented in the (110) plane.

[0044] By extending the deposition time, a bulk single crystal may be obtained instead of a thin film. Alternatively, when obtaining a bulk single crystal, known single crystal growth techniques may be employed, such as the Czochralski method (CZ method) using Fe metal, V metal, Mn metal, and Al metal satisfying the above-mentioned composition as raw materials, or the floating zone method (FZ method) using the above-mentioned sintered body as a raw material rod.

[0045] (Embodiment 2) In the second embodiment, a thermoelectric conversion element using a thin film as the p-type thermoelectric material of the present invention described in the first embodiment will be described.

[0046] FIG. 3 is a diagram showing a thermoelectric conversion element of the present invention.

[0047] Thermoelectric conversion element 300 according to the present invention includes at least p-type thermoelectric material 320, which is the p-type thermoelectric material of the present invention described in embodiment 1. Here, the p-type thermoelectric material is a thin film, and thermoelectric conversion element 300 is a planar thermoelectric conversion element.

[0048] In detail, the thermoelectric conversion element 300 comprises an insulating substrate 310, a p-type thermoelectric material 320 and an n-type thermoelectric material 330 disposed thereon, and electrodes 340 connecting them. Although three pairs of thermoelectric materials are shown in FIG. 3, the number of pairs is not limited to this. The thermoelectric conversion element 300 of the present invention uses a thermoelectric thin film, making it possible to provide a compact, thin, and therefore high-density, lightweight device.

[0049] The insulating substrate 310 may be any of the above-mentioned substrates, particularly lanthanum aluminate (LaAlO), sapphire, strontium titanate (SrTiO), and silicon, which allows the p-type thermoelectric material 320 to be preferentially oriented in the (110) plane and exhibit excellent thermoelectric properties.

[0050] The n-type thermoelectric material 330 is not particularly limited, but preferably has an absolute value of 40 μV / K or more and a power factor (PF) of 1.4 mW / K in the temperature range of 300 K or more and less than 350 K. 2It has thermoelectric properties of m or more. Such n-type thermoelectric material 330 includes, for example, Fe2VAl 1-x Si x (0 < x < 1), Fe2V 1+x Al 1-x (0 < x < 1), etc.

[0051] The electrode 340 is not particularly limited as long as it electrically connects the p-type thermoelectric material 320 and the n-type thermoelectric material 330. Exemplarily, it is a chromium (Cr) layer, a nickel (Ni) layer, a platinum (Pt) layer, etc. These materials are known as electrode materials.

[0052] The thermoelectric conversion element 300 of the present invention operates as follows. In FIG. 3, the thermoelectric conversion element 300 of the present invention is installed in an environment where the electrode in the upper part of the paper surface is at a high temperature and the electrode in the lower part of the paper surface is at a lower temperature than that. Then, when the electrodes at the ends of the thermoelectric conversion element 300 are connected to an external circuit (not shown) such as an external measuring instrument, a voltage is generated by the Seebeck effect, and a current flows as shown by the arrow in FIG. 3. Specifically, electrons in the n-type thermoelectric material 330 obtain thermal energy from the electrode 340 on the high-temperature side, move to the electrode on the low-temperature side, and release thermal energy there. On the other hand, holes in the p-type thermoelectric material 320 obtain thermal energy from the electrode on the high-temperature side, move to the electrode on the low-temperature side, and release thermal energy there, and a current flows.

[0053] The thermoelectric conversion element 300 of the present invention is manufactured by combining known lithography techniques and film-forming techniques of n-type thermoelectric materials after manufacturing the p-type thermoelectric material 320 on the substrate 310 by the method of FIG. 2.

[0054] In FIG. 3, the π-type thermoelectric conversion element 300 is used for explanation, but it may also be a U-type thermoelectric conversion element (not shown). Also in this case, the p-type thermoelectric material of the present invention and known n-type thermoelectric materials are alternately and electrically connected to be configured.

[0055] 3 has been described using the n-type thermoelectric material 330, a metal material or another p-type thermoelectric material may be used instead of the n-type thermoelectric material 330. For example, when a metal material is used instead of the n-type thermoelectric material 330, the metal material may be the same material as the electrode 340. When another p-type thermoelectric material is used instead of the n-type thermoelectric material 330, the p-type thermoelectric material may be a material having a Seebeck coefficient smaller than the Seebeck coefficient of the p-type thermoelectric material 320 of the present invention. Even with this configuration, thermal energy can be efficiently converted into electricity as described above.

[0056] The present invention will now be described in detail using specific examples, but it should be noted that the present invention is not limited to these examples. [Example]

[0057] [Example 1] In Example 1, Fe2V 0.8 Mn 0.2 Al 1.0 A thermoelectric material was produced as a thin film with a thickness of 500 nm using a target represented by the formula:

[0058] 20% Mn-doped Fe2V 0.8 Mn 0.2 Al 1.0 The metal raw materials Fe (manufactured by Sigma-Aldrich), V (manufactured by Furuuchi Chemical Co., Ltd.), Mn (manufactured by Furuuchi Chemical Co., Ltd.), and Al (manufactured by Furuuchi Chemical Co., Ltd.) were weighed out so as to satisfy the above composition formula, and melted by arc melting to obtain a molten ingot (20 g).

[0059] The molten ingot was pulverized in an argon atmosphere using a tungsten carbide planetary ball mill to obtain raw material powder. The raw material powder was refined to pass through a 50 μm sieve. This raw material powder was packed into a high-strength graphite die and sintered by spark plasma sintering to produce a target. The sintering conditions were a vacuum atmosphere, a pressure of 60 MPa, a temperature of 1273 K, and 10 minutes. The target obtained in this way was disk-shaped, 50 mm in diameter and 4 mm thick.

[0060] Using an RF magnetron sputtering method, the target was sputtered under the sputtering conditions shown in Table 1, and a film was formed on a lanthanum aluminate substrate (LaAlO3, manufactured by Crystal GmbH, (100) plane, thickness 0.5 mm).

[0061] The composition of the obtained thin film of Example 1 was evaluated by energy dispersive spectroscopy (EDS), and the crystal structure was identified by X-ray diffraction. The thermoelectric properties of the thin film of Example 1 were measured using a thermoelectric property evaluation device (ZEM3, manufactured by Advance Riko Co., Ltd.).

[0062] [Example 2] In Example 2, Fe2V 0.8 Mn 0.2 Al 1.0 A thermoelectric material was produced as a thin film with a thickness of 300 nm using a target represented by the formula: Example 2. The process was the same as in Example 1 except that the sputtering time was controlled so as to obtain a thickness of 300 nm, so a detailed explanation will be omitted. The thin film of Example 2 was evaluated using EDS, XRD, and for its thermoelectric properties in the same manner as in Example 1.

[0063] [Example 3] In Example 3, Fe2V 0.8 Mn 0.2 Al 1.0 A thermoelectric material was produced as a thin film with a thickness of 200 nm using a target represented by the formula: Example 3. The process was the same as in Example 1 except that the sputtering time was controlled so that the thickness was 200 nm, so a detailed explanation will be omitted. The thin film of Example 3 was evaluated using EDS, XRD, and for its thermoelectric properties in the same manner as in Example 1.

[0064] [Example 4] In Example 4, Fe2V 0.8 Mn 0.2 Al 1.0 A thermoelectric material was produced as a thin film with a thickness of 200 nm using a target represented by the formula (1). The procedure was the same as in Example 1 except that the sputtering time was controlled so that the thickness was 100 nm, so a detailed explanation will be omitted. The thin film of Example 4 was evaluated using EDS, XRD, and for its thermoelectric properties in the same manner as in Example 1.

[0065] [Example 5] In Example 5, Fe2V0.8 Mn 0.2 Al 1.0 A thermoelectric material was produced as a thin film with a thickness of 300 nm using a target represented by the formula: Example 5 is the same as Example 2 except that the substrate was changed from LaAlO to sapphire (AlO, manufactured by Crystal GmbH, (0001) plane (c-plane), thickness 0.5 mm), and therefore a description thereof will be omitted.

[0066] [Example 6] In Example 6, Fe2V 0.8 Mn 0.2 Al 1.0 A thermoelectric material was produced as a thin film with a thickness of 300 nm using a target represented by the formula: Example 6 is the same as Example 2 except that the substrate was changed to strontium titanate (SrTiO3, manufactured by K&R Creations, (100) plane, thickness 0.5 mm), and therefore a description thereof will be omitted.

[0067] For simplicity, the experimental conditions are summarized in Table 1, and the results are shown in FIGS. 4 to 11 and Tables 2 to 4, and will be explained collectively.

[0068] [Table 1]

[0069] FIG. 4 shows the XRD pattern of the thin film of Example 1. FIG. 5 shows the XRD pattern of the thin film of Example 2. FIG. 6 shows the XRD pattern of the thin film of Example 3. FIG. 7 shows the XRD pattern of the thin film of Example 4. FIG. 8 shows the XRD pattern of the thin film of Example 5.

[0070] 4(A) to 7(A) show that all the thin films have a Heusler structure. The XRD patterns of all the thin films show a clear peak at (220), indicating a (110) preferred orientation. The XRD patterns of the thin films of Examples 1 and 2 also show a (111) diffraction peak. Although not shown, the thin films of Examples 5 and 6 also show a clear peak at (220).

[0071] Figures 4(B) to 7(B) and 8 show rocking curves (θ scans) for the (220) peak of the thin films of Examples 1 to 5. Specifically, the 2θ value (the angle between the incident X-ray and the detector) was fixed at the (220) peak value (approximately 44.38°), and the sample was tilted to evaluate the vertical crystal orientation of the thin films. Figures 4(B) to 7(B) and 8 all show a clear peak in the rocking curves for the (220) peak, indicating that the thin films have a preferred orientation in the (220) plane (equivalent to a preferred orientation in the (110) plane). Furthermore, as the film thickness decreased, the peak of the (220) rocking curve tended to broaden.

[0072] Here, the half width of the peak in the (220) rocking curve was taken as D, and the degree of orientation was calculated by the following formula. Orientation degree={(180-D) / 180}*100 Table 2 shows the (220) half-width and degree of orientation of the thin films of Examples 1 to 6. The degrees of orientation of the thin films of Examples 1 to 3 were 98% or more, which was higher than that of the thin film of Example 4.

[0073] [Table 2]

[0074] 8 and Table 2, the degree of orientation of the thin film in Example 5 was also 98% or more. Although not shown, the degree of orientation of the thin film in Example 6 was also 98% or more. Therefore, even when the substrate was sapphire (Al2O3, c-plane) or SrTiO3, a film with a preferred orientation to the (110) plane and an orientation degree of over 98% was obtained.

[0075] On the other hand, Non-Patent Document 5 reports that a (100)-oriented Fe2VAl film can be obtained on the (100) plane of an MgAl2O4 substrate. Furthermore, Non-Patent Document 6 reports that a (100)-oriented Fe2VAl film can be obtained on the (001) plane of an MgO substrate. 1-x Si x The reason why the Fe2VAl film has a preferred (100) orientation on these substrates is thought to be that the interatomic distance between oxygen atoms in the substrate is close to the interatomic distance between iron atoms in the Fe2VAl film, which has a Heusler structure, and that this results in good lattice matching with the (100) plane. Based on this idea, the lattice matching of MgAl2O4 is 99%, and that of MgO is 103%.

[0076] The lattice matching of LaAlO3 is 93%, and that of SrTiO3 is 95.7%, both of which have low matching with the Fe-Fe interatomic distance in the Heusler structure. Therefore, it is thought that by using a substrate with such low matching, a thin film with a preferred orientation in the (110) plane rather than the (100) plane was obtained.

[0077] Since Al2O3 is not a cubic crystal, it is thought that it has low conformity with the (100) plane of the Heusler structure, resulting in a thin film with a preferred orientation to the (110) plane.

[0078] Therefore, it was shown that a thin film with a Heusler structure preferentially oriented in the (110) plane can be obtained by using a substrate with an interatomic distance that is mismatched by 4% or more in absolute value from the Fe-Fe interatomic distance (2.88 Å) of the Heusler structure, or by using a substrate that does not have cubic symmetry.

[0079] [Table 3]

[0080] Furthermore, according to Table 3, it was found that the thin films of Examples 1 to 3 and 5 all reflect the composition of the targets and are inorganic compounds containing iron (Fe), vanadium (V), manganese (Mn) and aluminum (Al). Although not shown in the table, it was also confirmed that the thin film of Example 6 is an inorganic compound containing Fe, V, Mn and Al.

[0081] From the above, it was demonstrated that the method shown in Figure 2 can be used to obtain a thin film consisting of an inorganic compound with a Heusler structure containing iron (Fe), vanadium (V), manganese (Mn), and aluminum (Al), which is preferentially oriented in the (110) plane and has an orientation degree of 98% or more, on a substrate with an interatomic distance that is mismatched by 4% or more in absolute value from the Fe-Fe interatomic distance (2.88 Å) of the Heusler structure, or on a substrate that does not have cubic symmetry.

[0082] Furthermore, according to Table 3, the thin films of Examples 1 to 3 and 5 have the following properties: Fe: 45 atomic% or more and 55 atomic% or less, V: 14.5 atom% or more and 20 atom% or less, Mn: 1.5 atomic % or more and 4 atomic % or less, and Al: 27 atomic% or more and 35 atomic% or less It was confirmed that the material was composed of inorganic compounds that satisfied the above condition (provided that the total atomic percentage of Fe, V, Mn and Al was 100).

[0083] FIG. 9 is a graph showing the temperature dependence of the electrical resistance (ρ) of the thin films of Examples 1 to 6. FIG. 10 is a graph showing the temperature dependence of the Seebeck coefficient (S) of the thin films of Examples 1 to 6. As shown in FIG. FIG. 11 is a graph showing the temperature dependence of the power factor (PF) of the thin films of Examples 1 to 6.

[0084] [Table 4]

[0085] 9 to 11, it was found that all samples were substantially stable, with no temperature dependence of the electrical resistance, Seebeck coefficient, or power factor, within the measured temperature range (300 K to 425 K). Furthermore, all samples had a positive Seebeck coefficient, confirming that they were p-type thermoelectric thin films.

[0086] 9 to 11 and Table 4, the thin films of Examples 1 to 3, 5 and 6, in which the degree of orientation of the (110) plane is 98% or more, have a Seebeck coefficient of 40 μV / K or more and a Seebeck coefficient of 1.4 mW / K or more in the range of 300 K or more and less than 350 K. 2 m or more, it was found to be an excellent p-type thermoelectric thin film.

[0087] Specifically, the thin films of Examples 1 and 2 have a large Seebeck coefficient of about 100 μV / K at room temperature (305 K) and a low dc current of 4 mW / K. 2 On the other hand, the thin film of Example 4, which had an orientation degree of less than 98%, exhibited a power factor of 0.8 mW / K at room temperature. 2 The power factor was m, and no improvement in the thermoelectric properties was observed.

[0088] From this, it can be seen that an inorganic compound containing Fe, V, Mn, and Al and having a Heusler structure has a Seebeck coefficient of 40 μV / K or more in the range of 300 K or more but less than 350 K, and a Seebeck coefficient of 1.4 mW / K or more. 2 It was shown that in order to function as a p-type thermoelectric material that satisfies a power factor of m or more, it is essential that the (110) plane orientation is 98% or more. In addition, it was found that in the case of thin films, a film thickness of more than 100 nm is preferable.

[0089] In addition, the substrate is not limited to LaAlO3, and even if it is Al2O3 or SrTiO3, an inorganic compound containing Fe, V, Mn, and Al, having a Heusler structure, and satisfying a degree of orientation of the (110) plane of 98% or more, has a Seebeck coefficient of 40 μV / K or more in the range of 300 K or more but less than 350 K, and has a thermal conductivity of 1.4 mW / K. 2 It was shown that it functions as a p-type thermoelectric material with a power factor of m or more.

[0090] From the above, an inorganic compound containing iron (Fe), vanadium (V), manganese (Mn), and aluminum (Al), having a Heusler structure, and preferentially oriented to the (110) plane with an orientation degree of 98.6% or more, has a Seebeck coefficient (S) of 40 μV / K or more and a power factor (PF) of 1.4 mW / K in the temperature range of 300 K or more and less than 350 K. 2 It was shown that it functions as a p-type thermoelectric material with a molecular weight of m or more.

[0091] In particular, the following composition (where the total atomic percentage of Fe, V, Mn, and Al is 100): Fe: 49.5 atomic% or more and 50.5 atomic% or less, V: 15 atomic% or more and 16.5 atomic% or less, Mn: 2 atomic % or more and 3 atomic % or less, and Al: 30 atomic% or more and 33 atomic% or less The thin films of Examples 1 and 2 made of inorganic compounds satisfying the above condition have a large Seebeck coefficient of about 100 μV / K at room temperature (305 K) and a low-temperature resistance of 4 mW / K. 2 It was shown that the material functions as an excellent p-type thermoelectric material, exhibiting a large power factor exceeding m. [Industrial Applicability]

[0092] The p-type thermoelectric material of the present invention has excellent thermoelectric performance, particularly at around room temperature, and is therefore suitable for use in thermoelectric cooling devices and power generation devices used in various electrical devices. In particular, because it can be made into a thin film, it can be used to provide flexible thermoelectric conversion elements as IoT power sources. [Explanation of symbols]

[0093] 300 Thermoelectric conversion element 310 Insulating substrate 320 p type thermoelectric material 330 n-type thermoelectric material 340 electrode

Claims

1. Contains an inorganic compound containing iron (Fe), vanadium (V), manganese (Mn), and aluminum (Al), the inorganic compound has a Heusler structure, The inorganic compound has a crystal orientation preferentially oriented in the (110) plane, A p-type thermoelectric material, wherein the degree of preferred orientation is 98% or more.

2. The inorganic compound is Fe: 45 at% or more and 55 at% or less, V: 14.5 at% or more and 20 at% or less, Mn: 1.5 atomic % or more and 4 atomic % or less, and Al: 27 at% or more and 35 at% or less 2. The p-type thermoelectric material according to claim 1, wherein the total atomic percentage of Fe, V, Mn, and Al is 100.

3. The inorganic compound is Fe: 48.5 at% or more and 52 at% or less, V: 14.5 at% or more and 18 at% or less, Mn: 1.5 atomic % or more and 3 atomic % or less, and Al: 30 at% or more and 35 at% or less 3. The p-type thermoelectric material according to claim 2, wherein the total atomic percentage of Fe, V, Mn, and Al is 100.

4. The inorganic compound is Fe: 49.5 atomic% or more and 50.5 atomic% or less, V: 15 at% or more and 16.5 at% or less, Mn: 2 atomic % or more and 3 atomic % or less, and Al: 30 at% or more and 33 at% or less 4. The p-type thermoelectric material according to claim 3, wherein the total atomic percentage of Fe, V, Mn, and Al is 100.

5. 2. The p-type thermoelectric material according to claim 1, wherein the inorganic compound further has a (111) diffraction peak in an X-ray diffraction pattern measured using Cu-Kα radiation.

6. 10. The p-type thermoelectric material of claim 1, wherein the p-type thermoelectric material is a thin film.

7. 7. The p-type thermoelectric material according to claim 6, wherein the thin film is located on a substrate having an interatomic distance that is mismatched by 4% or more in absolute value from the Fe-Fe interatomic distance of a Heusler structure, or a substrate that does not have cubic symmetry.

8. The substrate is made of lanthanum aluminate (LaAlO ３ ), sapphire, strontium titanate (SrTiO ３ 8. The p-type thermoelectric material of claim 7, wherein the p-type thermoelectric material is selected from the group consisting of: silicon, arsenic ...

9. 1. A method for producing a thin film p-type thermoelectric material, comprising: The p-type thermoelectric material is Contains an inorganic compound containing iron (Fe), vanadium (V), manganese (Mn), and aluminum (Al), the inorganic compound has a Heusler structure, The inorganic compound has a crystal orientation preferentially oriented in the (110) plane, The degree of preferential orientation is 98% or more, A sintered body containing the iron (Fe), the vanadium (V), the manganese (Mn), and the aluminum (Al) and having a Heusler structure is used as a target, and a film is formed by physical vapor deposition on a substrate having an interatomic distance that is mismatched by 4% or more in absolute value from the Fe-Fe interatomic distance of the Heusler structure, or on a substrate that does not have cubic symmetry. The method includes:

10. A thermoelectric conversion element including at least a p-type thermoelectric material, A thermoelectric conversion element, wherein the p-type thermoelectric material is the p-type thermoelectric material according to any one of claims 1 to 8.

11. The thermoelectric conversion element according to claim 10 , comprising n-type thermoelectric materials connected in series alternately with the p-type thermoelectric materials.

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