Thermoelectric conversion material and thermoelectric conversion element using the same

Abstract

To provide a Cu2Se-based thermoelectric conversion material with excellent thermoelectric performance, and a thermoelectric conversion element based thereon.SOLUTION: A thermoelectric conversion material is a composite containing: a doped or undoped Cu2Se-based compound containing a substance represented by the general formula M12M2, where M1 is copper (Cu) and / or silver (Ag), and M2 is at least one selected from the group consisting of selenium (Se), sulfur (S), iron (Fe) and tellurium (Te); and an oxide containing M1, M2, and oxygen (O).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermoelectric conversion material and a thermoelectric conversion element using the same. [Background technology]

[0002] Thermoelectric materials, which generate electricity from waste heat, are expected to be used as autonomous power sources for sensors and as next-generation power generation materials. To develop these materials into a future power generation technology, it is important to improve their thermoelectric conversion efficiency, reduce the toxicity of the materials used, and diversify their applications from bulk to thin films. Furthermore, to maximize their applications, high performance at near-room temperature is desirable. Currently, Bi2Te3-based materials are the only commercially available materials. However, the toxicity of the Te element and the high cost associated with its scarcity hinder their widespread adoption. Meanwhile, non-toxic ubiquitous thermoelectric materials, while environmentally friendly, have a low non-dimensional figure of merit (zT), which indicates thermoelectric efficiency, making their widespread adoption difficult.

[0003] Among these, Cu2Se thermoelectric conversion material was positioned somewhere between them (see, for example, Non-Patent Document 1). According to Non-Patent Document 1, Cu2Se has a zT of approximately 0.15 in bulk near room temperature (Bi2Te3 is approximately 0.85), and is characterized by the lower toxicity of Se compared to Te. If the zT near room temperature could be improved, it would be preferable because it could replace Bi2Te3-based materials. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] H. Liu et al., Nature Materials 11, 422-425, 2012 Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above, an object of the present invention is to provide a Cu2Se-based thermoelectric conversion material having excellent thermoelectric performance, and a thermoelectric conversion element using the same. [Means for solving the problem]

[0006] The thermoelectric conversion material according to the present invention is a composite containing a doped or undoped Cu2Se-based compound containing a substance represented by the general formula M12M2 (wherein M1 is copper (Cu) and / or silver (Ag), and M2 is at least one selected from the group consisting of selenium (Se), sulfur (S), iron (Fe), and tellurium (Te)), and an oxide containing M1, M2, and oxygen (O), thereby solving the above-mentioned problems. The Cu2Se-based compound may belong to the cubic system and have F-43m symmetry. The oxide may be represented by the general formula M12[M2O3]O. The M1 may contain at least Cu, and the M2 may contain at least Se. The Cu2Se-based compound has the general formula Cu 2-x Ag x Se 1-y M3 y (wherein M3 is at least one selected from the group consisting of sulfur (S), iron (Fe), and tellurium (Te), and satisfies 0≦x<2 and 0≦y<1). The composite is Cu a Ag b Se c M3 d O e T f(wherein T is a dopant and is at least one element selected from the group consisting of rubidium (Rb), potassium (K), bismuth (Bi), lead (Pb), strontium (Sr), manganese (Mn), lanthanum (La), cobalt (Co), zinc (Zn), sodium (Na), yttrium (Y), holmium (Ho), cadmium (Cd), dysprosium (Dy), ytterbium (Yb), europium (Eu), hydrogen (H), chlorine (Cl), vanadium (V), mercury (Hg), lithium (Li), terbium (Tb), samarium (Sm), indium (In), and thallium (Tl), and in the formula, a+b+c+d+e+f=1), and the parameters a to f are respectively 0.5≦a≦0.8, 0.0≦b≦0.8 0.15≦c≦0.3, 0.0≦d≦0.3 0.01≦e≦0.1, and 0.0≦f≦0.05 may be satisfied. The parameters a to f are respectively: 0.7≦a≦0.8, 0.0≦b≦0.2 0.2≦c≦0.3, 0.0≦d≦0.1 0.01≦e≦0.03, and 0.0≦f≦0.01 may be satisfied. The parameters c and e are 2.5≦e / c≦3.5 may be satisfied. The parameters c and e are 2.8≦e / c≦3.2 may be satisfied. The parameters b, d and f may be zero. The oxide may belong to the cubic crystal system and have P213 symmetry. The content of the oxide in the composite may be in the range of more than 0% by volume and not more than 15% by volume. The content of the oxide in the composite may be in the range of 3% by volume to 10% by volume. The composite may further contain at least one substance selected from the group consisting of copper(I) oxide (CO), copper(II) oxide (CuO), selenium oxide, and a compound consisting of Cu and Se. The phase transition temperature of the composite may be in the range of 330K to 370K. The thermoelectric conversion element according to the present invention comprises p-type thermoelectric conversion materials and n-type thermoelectric conversion materials alternately connected in series, and the p-type thermoelectric conversion materials are the thermoelectric conversion materials described above, thereby solving the above-mentioned problems. [Effects of the Invention]

[0007] The thermoelectric conversion material according to the present invention is a composite containing a doped or undoped CuSe-based compound and an oxide containing the elements that constitute the compound and oxygen (O). Because it contains a CuSe-based compound, known as a thermoelectric conversion material, as its main component, it exhibits thermoelectric performance. In particular, by forming a composite with an oxide, it can become a thermoelectric conversion material with an improved figure of merit zT. Such a thermoelectric conversion material can be applied to thermoelectric conversion elements. [Brief explanation of the drawings]

[0008] [Figure 1] Schematic diagram showing a crystal represented by Cu2[SeO3]O [Figure 2] 1 is a diagram schematically illustrating a thermoelectric conversion element according to the present invention; [Figure 3] Schematic diagram of COSCOS (thin film manufacturing equipment) [Figure 4] 1 shows SEM images of the surface of the thin film of Example 5 at various magnifications. [Figure 5] Graph showing XPS spectra of thin films of Examples 1 to 5 [Figure 6] EDX mapping of the surface of the thin film in Example 5 [Figure 7] 1 shows an SEM image and an EBSD image of a cross section of the thin film of Example 5. [Figure 8] Figure showing the FFT diffraction pattern of the thin film of Example 5 [Figure 9] Figure 1 shows FFT diffraction patterns of the thin film in Example 5 under different tilt conditions. [Figure 10] 10A and 10B show FFT diffraction patterns of the thin film of Example 5 under different tilt conditions. [Figure 11] Graph showing the thermal conductivity of thin films in Examples 1 to 5 at room temperature [Figure 12] FIG. 10 shows the temperature dependence of the power factor of the thin films of Examples 1 to 5. [Figure 13] FIG. 1 shows the temperature dependence of the figure of merit of the thin films of Examples 1 to 5. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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. (Embodiment 1) In the first embodiment, a thermoelectric conversion material and a method for producing the same according to the present invention will be described.

[0010] The thermoelectric conversion material of the present invention is a composite of a CuSe-based compound as a main component and an oxide containing the elements constituting the compound and oxygen (O). The present inventors have found that the thermoelectric properties of the CuSe-based compound are improved by being composited with the oxide.

[0011] In this specification, a Cu2Se-based compound contains a substance represented by the general formula M12M2 (where M1 is copper (Cu) and / or silver (Ag), and M2 is at least one selected from the group consisting of selenium (Se), sulfur (S), iron (Fe), and tellurium (Te). All of these are known as thermoelectric conversion materials.

[0012] A representative Cu2Se compound is a substance represented by Cu2Se, where M1 is Cu and M2 is Se. Cu2Se is known as a p-type thermoelectric material, and its crystal structure belongs to the cubic system and has the symmetry of the space group F-43m (number 216 in the International Tables for Crystallography). Preferably, the lattice constants a = b = c satisfy 0.5845 ± 0.05 nm. Within this range, the crystal structure is stable and excellent thermoelectric performance is exhibited.

[0013] It is known that Cu2Se-based compounds undergo a reversible phase transition near 400 K. The phase transition causes carrier scattering, increases the Seebeck coefficient, and decreases the thermal conductivity, resulting in an improvement in the figure of merit (dimensionless figure of merit) zT after the phase transition. The thermoelectric conversion material of the present invention is a composite of a Cu2Se-based compound and an oxide containing the elements that constitute the compound and oxygen (O), and therefore can shift the phase transition temperature of the Cu2Se-based compound to a lower temperature. As a result, the thermoelectric performance at lower temperatures, such as room temperature, can be improved.

[0014] Furthermore, Cu2Se-based compounds may be doped (doped) or undoped (undoped) to control the conduction type or to achieve a desired conductivity. Undoped Cu2Se-based compounds are known as p-type thermoelectric conversion materials, but adding a dopant can improve the conductivity or control the conduction type.

[0015] Such dopants include at least one element selected from the group consisting of rubidium (Rb), potassium (K), bismuth (Bi), lead (Pb), strontium (Sr), manganese (Mn), lanthanum (La), cobalt (Co), zinc (Zn), sodium (Na), yttrium (Y), holmium (Ho), cadmium (Cd), dysprosium (Dy), ytterbium (Yb), europium (Eu), hydrogen (H), chlorine (Cl), vanadium (V), mercury (Hg), lithium (Li), terbium (Tb), samarium (Sm), indium (In), and thallium (Tl). These dopants are commonly used in CuSe-based compounds and can replace part of the M1 or M2 elements in the general formula above. The amount of dopant added is not particularly limited as long as the crystal structure of the Cu2Se-based compound is maintained, but may be, for example, 5% or less.

[0016] The oxide in the thermoelectric conversion material of the present invention contains M1, M2, and oxygen (O). The inventors have discovered that the thermoelectric properties are improved by combining the above-mentioned Cu2Se-based compound with the above-mentioned oxide. Although the mechanism is unknown, it is believed that this is due to the contribution of the new band structure that the oxide possesses.

[0017] The content of the oxide containing M1, M2, and oxygen (O) in the composite is not particularly limited, but may be in the range of more than 0% by volume and not more than 15% by volume. This range can improve thermoelectric performance. The content of the oxide containing M1, M2, and oxygen (O) is preferably in the range of 3% by volume or more and 10% by volume or less. This range can shift the phase transition temperature of the Cu2Se-based compound to a lower temperature, thereby significantly improving the thermoelectric performance at room temperature. The content of the oxide containing M1, M2, and oxygen (O) is more preferably in the range of 4% by volume or more and 8% by volume or less. From this perspective, the amount of the oxide as the main component of the Cu2Se-based compound should be at least 85% by volume, preferably more than 90%, and more preferably more than 92% but less than 96%.

[0018] The oxide containing M1, M2, and oxygen (O) is preferably represented by the general formula M12[M2O3]O. The oxide represented by M12[M2O3]O was discovered by the present inventors and confirmed to be a novel crystal through crystal structure analysis. By combining a Cu2Se-based compound with an oxide represented by M12[M2O3]O, the figure of merit zT at room temperature can be dramatically improved.

[0019] FIG. 1 is a schematic diagram showing a crystal represented by Cu2[SeO3]O.

[0020] As a result of structural analysis of Cu2[SeO3]O crystal, where M1 is Cu and M2 is Se, an oxide represented by M12[M2O3]O, the crystal structure model shown in Figure 1 was obtained.

[0021] The Cu2[SeO3]O crystal was found to belong to the cubic crystal system, have the symmetry of the P213 space group (number 198 in the International Tables for Crystallography), and occupy the crystal parameters and atomic coordinate positions shown in Table 1.

[0022] [Table 1]

[0023] In Table 1, the lattice constants a, b, and c indicate the lengths of the axes of the unit cell, and α, β, and γ indicate the angles between the axes of the unit cell. The atomic coordinates indicate the position of each atom in the unit cell, with values ​​between 0 and 1, based on the unit cell. This crystal contains Cu, Se, and O atoms, and analysis results showed that Cu exists in two types of sites, Cu1 and Cu2. Analysis results also showed that Se exists in two types of sites, Se1 and Se2. Furthermore, analysis results showed that O exists in four types of sites, O1 to O4.

[0024] M12[M2O3]O crystals have the same crystal structure as Cu2[SeO3]O crystals. M1 is Cu and / or Ag. M2 is at least one element selected from the group consisting of Se, S, Fe, and Te. Such crystals can also have improved thermoelectric performance when combined with Cu2Se-based compounds.

[0025] The thermoelectric conversion material of the present invention can be identified by X-ray diffraction or neutron diffraction as a composite of a Cu2Se-based compound and M12[M2O3]O crystals.

[0026] M1 preferably contains Cu, and M2 preferably contains Se. In one embodiment of this case, the thermoelectric conversion material of the present invention is a composite of at least doped or undoped CuSe as a CuSe-based compound and at least Cu[SeO]O crystals as an oxide. By forming the composite, excellent thermoelectric performance can be exhibited even when the Se content is reduced, which is advantageous for reducing environmental impact and also enables cost reduction.

[0027] In one embodiment of this case, the thermoelectric conversion material of the present invention is a doped or undoped CuSe-based compound having the general formula Cu 2-x Ag x Se 1-y M3 y (wherein M3 is at least one selected from the group consisting of sulfur (S), iron (Fe), and tellurium (Te), and satisfies 0≦x<2 and 0≦y<1).

[0028] In one embodiment of this case, in the thermoelectric conversion material of the present invention, the composite may contain at least one substance selected from the group consisting of copper(I) oxide (CO), copper(II) oxide (CuO), selenium oxide, and a compound consisting of Cu and Se. The compound consisting of Cu and Se may be any compound containing Cu and Se, such as CuSe, CuSe, or CuSe. Such substances are preferred because they do not reduce thermoelectric performance. The amount of these substances contained may preferably be 3% by volume or less.

[0029] M1 is more preferably Cu, and M2 is more preferably Se. In this case, the thermoelectric conversion material of the present invention is a composite of doped or undoped CuSe and Cu[SeO]O crystals. This allows it to exhibit a high figure of merit at room temperature. Furthermore, since the Se content can be reduced compared to single-phase CuSe thermoelectric conversion materials, it is possible to reduce environmental impact and costs.

[0030] In one embodiment, the composite of the present invention comprises Cu a Ag b Se c M3 d O e T f (wherein T is a dopant and is at least one element selected from the group consisting of Rb, K, Bi, Pb, Sr, Mn, La, Co, Zn, Na, Y, Ho, Cd, Dy, Yb, Eu, H, V, Hg, Li, Tb, Sm, In, and Tl, and in the formula, a+b+c+d+e+f=1), and the parameters a to f are respectively 0.5≦a≦0.8, 0.0≦b≦0.8 0.15≦c≦0.3, 0.0≦d≦0.3 0.01≦e≦0.1, and 0.0≦f≦0.05 In this case, a composite of a doped or undoped Cu2Se-based compound and M12[M2O3]O crystal is formed, which exhibits excellent thermoelectric performance.

[0031] The parameters a to f are preferably respectively: 0.7≦a≦0.8, 0.0≦b≦0.2 0.2≦c≦0.3, 0.0≦d≦0.1 0.01≦e≦0.03, and 0.0≦f≦0.01 In this case, a composite of a doped or undoped Cu2Se-based compound and M12[M2O3]O crystals is formed, and the content of M12[M2O3]O crystals falls within the above range, thereby exhibiting excellent thermoelectric performance.

[0032] The parameters c and e are preferably 2.5≦e / c≦3.5 As a result, the M12[M2O3]O crystal contains Cu2[SeO3]O crystal, which provides excellent thermoelectric performance.

[0033] The parameters c and e are more preferably: 2.8≦e / c≦3.2 As a result, the M12[M2O3]O crystal contains Cu2[SeO3]O crystal, and the above content is satisfied, so that excellent thermoelectric performance is exhibited.

[0034] The parameters b, d, and f may be 0. This allows the thermoelectric conversion material of the present invention to become a composite of Cu2Se and Cu2[SeO3]O crystals, thereby achieving a reduction in environmental load and cost reduction.

[0035] As described above, the thermoelectric conversion material of the present invention can have an improved figure of merit at room temperature by controlling the composition. For example, when the thermoelectric conversion material of the present invention is in the form of a thin film, zT=0.6 has been confirmed at room temperature, and when it is in the form of a bulk material, an even higher figure of merit can be achieved.

[0036] Furthermore, as described above, by controlling the composition, the thermoelectric conversion material of the present invention can have a phase transition temperature lower than 400 K, but preferably has a phase transition temperature in the temperature range of 330 K to 370 K. As a result, it can exhibit excellent thermoelectric performance, particularly at room temperature.

[0037] The thermoelectric conversion material of the present invention may be in the form of a thin film or a bulk material, and the form may be appropriately selected depending on the application.

[0038] Next, an exemplary method for producing the thermoelectric conversion material of the present invention will be described. First, a manufacturing method for the case where the thermoelectric conversion material of the present invention is a bulk body will be described. A raw material containing an M1 element (M1 is copper (Cu) and / or silver (Ag)), a raw material containing an M2 element (M2 is at least one selected from the group consisting of selenium (Se), sulfur (S), iron (Fe), and tellurium (Te)), and optionally a raw material containing a T element (T is rubidium (Rb), potassium (K), bismuth (Bi), lead (Pb), strontium (Sr), manganese (Mn), lanthanum (La), cobalt (Co), zinc (Zn), sodium (Na), and the like. The SiO2 nanoparticles can be obtained, for example, by mixing and firing at least one element selected from the group consisting of ammonium (Na), yttrium (Y), holmium (Ho), cadmium (Cd), dysprosium (Dy), ytterbium (Yb), europium (Eu), hydrogen (H), chlorine (Cl), vanadium (V), mercury (Hg), lithium (Li), terbium (Tb), samarium (Sm), indium (In), and thallium (Tl) so as to satisfy the above-mentioned composition formula.

[0039] The raw material containing the M1 element and the raw material containing the M2 element may be the M1 metal alone and the M2 metal alone, respectively. Alternatively, for example, an oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride of M1, or an oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride of M2 may also be used.

[0040] The raw material containing the T element may be the T metal alone, excluding hydrogen, or may be an oxide, carbonate, nitride, oxynitride, chloride, fluoride or oxyfluoride of T.

[0041] The calcination may be performed by heating the mixture of raw materials to a temperature at which the mixture reacts, illustratively in the temperature range of 1073 K to 1773 K. When the mixture of raw materials contains oxygen, the calcination is preferably performed in an inert atmosphere of nitrogen or a rare gas such as argon or helium, or in a vacuum. When the mixture of raw materials does not contain oxygen, the calcination may be performed in an inert atmosphere with an adjusted oxygen concentration or in a vacuum. The calcination time varies depending on the calcination temperature, but illustratively is in the range of 30 minutes to 48 hours. The temperature rise rate is not particularly limited, but can be in the range of 5 K / hour to 20 K / hour. In this manner, the thermoelectric conversion material of the present invention in bulk form is obtained.

[0042] Prior to firing, the mixture of raw materials may be molded. This is preferable because it accelerates the reaction. Press molding may be used for such molding. After firing, the fired body may be rapidly cooled. This results in a uniform fired body.

[0043] The sintered body thus obtained may be crushed and sintered to provide the thermoelectric conversion material of the present invention as a sintered body. For example, the sintered body is crushed and molded into a predetermined shape, and the molded body is then subjected to sintering at a pressure of 10 MPa to 100 MPa and a temperature of 1073 K to 1273 K°C. The sintering time may be 5 minutes to 12 hours. Sintering may be performed by a conventional hot press method, pulse current sintering method, or spark plasma sintering (SPS). The resulting sintered body may be molded (shaped) using a high-speed cutter or the like and used as a thermoelectric conversion element (which may also be called a thermoelectric conversion module) or a target for film formation, as described below.

[0044] Next, a manufacturing method for the thermoelectric conversion material of the present invention when it is a thin film will be described. The thermoelectric conversion material of the present invention can be manufactured by physical vapor deposition. For example, the above-mentioned sintered body or a sintered body of a Cu2Se-based compound may be used as a target, or a target consisting of an M1 element (M1 is copper (Cu) and / or silver (Ag)), a target consisting of an M2 element (M2 is at least one selected from the group consisting of selenium (Se), sulfur (S), iron (Fe), and tellurium (Te)), and, if necessary, a target consisting of a T element (T is rubidium (Rb), potassium (K), bismuth (Bi), lead (Pb), strontium (Sr), manganese (Mn), lanthanum (La), cobalt (Co), zinc (Zn), or the like may be used. The semiconductor laser can be manufactured using at least one element selected from the group consisting of zinc (Zn), sodium (Na), yttrium (Y), holmium (Ho), cadmium (Cd), dysprosium (Dy), ytterbium (Yb), europium (Eu), hydrogen (H), chlorine (Cl), vanadium (V), mercury (Hg), lithium (Li), terbium (Tb), samarium (Sm), indium (In), and thallium (Tl), excluding hydrogen and chlorine, by sputtering, resistance heating evaporation, electron beam evaporation, molecular beam epitaxy, or ion plating.

[0045] For example, when a sputtering method is employed, the thermoelectric conversion material as a thin film of the present invention can be produced on a desired substrate by setting sputtering conditions such as a sputtering gas pressure of Ar or the like in the range of 0.1 Pa to 1 Pa, a substrate temperature in the range of room temperature (298 K) to 1000 K, an RF output in the range of 30 W to 150 W, and a target-substrate distance in the range of 40 mm to 70 mm.

[0046] (Embodiment 2) In the second embodiment, a thermoelectric conversion element using the thermoelectric conversion material described in the first embodiment will be described. FIG. 2 is a diagram schematically showing a thermoelectric conversion element according to the present invention.

[0047] 2 shows a thermoelectric conversion element 200 in which the thermoelectric conversion material of the present invention is in the form of a thin film. The thermoelectric conversion element 200 according to the present invention comprises at least the thermoelectric conversion material of the present invention. The thermoelectric conversion material of the present invention is as described above, and therefore further description will be omitted.

[0048] Specifically, the thermoelectric conversion element 200 according to the present invention includes a pair of p-type and n-type thermoelectric conversion materials 220 and 230, and electrodes 240 at the ends of each of these materials. The p-type and n-type thin-film thermoelectric conversion materials 220 and 230 are electrically connected in series by the electrodes 240. The pair of p-type and n-type thin-film thermoelectric conversion materials 220 and 230, and the electrodes 240, are located on a substrate 210. As described above, the substrate 210 is selected from the group consisting of a flexible polymer substrate, a glass substrate, a metal substrate, a ceramic substrate, and a semiconductor substrate. If the substrate 210 is a flexible polymer substrate, the thermoelectric conversion element 200 can be a flexible sheet-type thermoelectric conversion element.

[0049] Here, the p-type thin-film thermoelectric conversion material 220 is the thin-film thermoelectric conversion material of the present invention. The n-type thin-film thermoelectric conversion material 230 is not particularly limited, but examples include carbon nanotubes, fullerenes, Bi2(Se,Te)3, PbTe, SiGe, GaP, Gd2Se3, and FeSi2. These materials are known as n-type thermoelectric conversion materials and can be in the form of a thin film.

[0050] The electrode 240 can be made of a common electrode material, illustratively Al, Ni, Cu, Pt, indium tin oxide (ITO), or the like.

[0051] When the thermoelectric conversion element 200 of the present invention is placed in an environment where one of the electrodes 240 is on the high temperature side and the other of the electrodes 240 is on the low temperature side, and the end electrodes are connected to an electric circuit or the like, a voltage is generated by the Seebeck effect, and a current flows in the following order: one of the electrodes 240, the n-type thin-film thermoelectric conversion material 230, the other electrode 240, and the p-type thin-film thermoelectric conversion material 220. In detail, the electrons in the n-type thermoelectric conversion material 230 obtain thermal energy from the high temperature side electrode 240, move to the low temperature side electrode 240, and release the thermal energy there; in response, the holes in the p-type thin-film thermoelectric conversion material 220 obtain thermal energy from the high temperature side electrode 240, move to the low temperature side electrode 240, and release the thermal energy there.

[0052] In the present invention, the thermoelectric conversion material of the present invention described in the first embodiment can be used as the p-type thin-film thermoelectric conversion material 220, thereby realizing a thermoelectric conversion element 200 that is flexible and can follow the bending of the element. Furthermore, the use of the thermoelectric conversion material of the present invention also provides excellent thermoelectric performance, particularly in the low-temperature range of 200°C or less, and therefore allows the provision of flexible thermoelectric conversion elements as wearable devices and IoT power sources that utilize body heat and waste heat.

[0053] In this way, the thermoelectric conversion element of the present invention preferably comprises the thermoelectric conversion material of the present invention (p-type thermoelectric conversion material in FIG. 2) and a thermoelectric conversion material of a different conductivity type (n-type thermoelectric conversion material in FIG. 2), which can be alternately connected in series.

[0054] 2, a π-type thermoelectric conversion element is used for explanation, but the thermoelectric conversion material of the present invention may also be used in a U-type thermoelectric conversion element (not shown). In this case as well, n-type thermoelectric conversion materials and p-type thermoelectric conversion materials made of the thermoelectric conversion material of the present invention are alternately connected electrically in series.

[0055] 2 has been described using the n-type thin-film thermoelectric conversion material 230, a metal material or another p-type thin-film thermoelectric conversion material may be used instead of the n-type thin-film thermoelectric conversion material 230. For example, when a metal material is used instead of the n-type thin-film thermoelectric conversion material 230, the metal material may be the same material as the electrode 240. When a p-type thin-film thermoelectric conversion material is used instead of the n-type thin-film thermoelectric conversion material 230, another thermoelectric conversion material of the present invention having a Seebeck coefficient different from, and preferably smaller than, the Seebeck coefficient of the thermoelectric conversion material of the present invention used for the p-type thin-film thermoelectric conversion material 220 can be used. 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 to Example 5] In Examples 1 to 5, a CuSe target in which M1 is Cu and M2 is Se was used to produce the thermoelectric conversion material of the present invention as a thin film by a sputtering method using a Combinatorial Sputter Coating System (COSCOS) (see, for example, Convertec 2008.3).

[0058] FIG. 3 is a diagram showing a schematic diagram of COSCOS (thin film manufacturing equipment).

[0059] The COSCOS (thin-film manufacturing equipment 300) includes at least a vacuum chamber 310 with a gas inlet and a gas outlet, a CuSe target 330, and a substrate holder for mounting a substrate 340. It also includes a power supply 350 connecting the substrate 340 and the CuSe target 330. In FIG. 3, a shutter 360 is provided above the CuSe target 330. The substrate holder is equipped with a heating means. The substrate holder or the targets are configured to be rotatable so that each target is positioned directly below the substrate 340. The targets are attached to a sputtering source. Furthermore, the COSCOS is equipped with an external control device (not shown) that automatically controls the rotation of the substrate holder, the vacuum pumping system, the sputtering gas pressure, the substrate temperature, the bias voltage, the target-substrate distance, and the opening and closing of the shutter.

[0060] A Cu2Se target (diameter: 50 mm, thickness: 6 mm, manufactured by Kojundo Chemical Co., Ltd.) was placed in the vacuum chamber 310.

[0061] The substrates used were alumina (Al2O3) coated substrates for thermoelectric property evaluation (size: 10mm x 10mm x 0.3mm, manufactured by LINSEIS) and quartz substrates (size: 25mm x 16mm x 0.5mm). They were cleaned and placed on a substrate holder (capable of holding up to 14 substrates). The target-substrate distance was fixed at 55mm. Ar gas (purity 99.999% or higher) was connected to the vacuum chamber, and the film thickness was monitored using a quartz crystal microbalance (QCM). The experimental conditions shown in Table 2 were registered in an external control device, and thin films were produced fully automatically.

[0062] [Table 2]

[0063] The thin films of Examples 1 to 5 were observed using a scanning electron microscope (SEM, Hitachi High-Tech Innovations Corporation, S-3700) equipped with an energy dispersive X-ray spectrometer (EDX). The observation results are shown in Figure 4. The chemical bonding state and atomic concentration on the surface and deep inside of the thin films of Examples 1 to 5 were evaluated using an X-ray photoelectron spectrometer (ULVAC-PHI, Quanterea SXM). The results are shown in Figure 5 and Table 3.

[0064] The cross-sectional appearances of the thin films of Examples 1 to 5 were observed by SEM, and elemental analysis was performed by EDX. The results are shown in Figure 6. The cross-sectional appearances and electron backscatter diffraction (EBSD) images of the thin films of Examples 1 to 5 were observed by SEM. The results are shown in Figure 7.

[0065] For the thin films of Examples 1 to 5, a transmission electron microscope (TEM, JEM-2100F, manufactured by JEOL Ltd.) was used to measure FFT diffraction patterns by the fast Fourier transform (FFT) method. The crystalline phases of the thin films were identified from the FFT diffraction patterns, and the content of the crystalline phases was calculated from the identification results and the results of elemental analysis. These results are shown in Figures 8 to 10 and Table 4.

[0066] The thermal resistance and electrical resistivity of the thin films of Examples 1 to 5 were measured using an ω-method nano-thin film thermal conductivity meter (see, for example, Japanese Patent No. 5598813) and a resistivity meter using the four-terminal method, respectively. The thermal conductivity and electrical conductivity were calculated from the obtained thermal resistance and electrical resistivity. The Seebeck coefficient, as a thermal property of the thin films of Examples 1 to 5, was measured using a steady-state temperature difference method with an integrated thermoelectric performance evaluation device (LINSEIS). The figure of merit zT was calculated from these measurement results. These results are shown in Figures 11 to 13 and Table 5.

[0067] The above results will be summarized. FIG. 4 shows SEM images of the surface of the thin film of Example 5 at various magnifications.

[0068] 4, it was found that the thin film of Example 5 was a dense aggregate of microcrystals. Although not shown, the thin films of Examples 1 to 4 also had a similar appearance.

[0069] FIG. 5 shows XPS spectra of the thin films of Examples 1 to 5.

[0070] 5, it was found that the thin films of Examples 1 to 5 mainly contained a CuSe phase. Although not shown, the presence of adsorbed oxygen was confirmed on the surfaces of the thin films of Examples 1 to 5, and peaks derived from CuO, CuO, and SeO were confirmed.

[0071] FIG. 6 shows an EDX mapping diagram of the surface of the thin film of Example 5.

[0072] The EDX mapping diagrams are shown in grayscale, with bright areas indicating the presence of the corresponding elements in each diagram. It was found that Cu, Se, and oxygen (O) were uniformly distributed throughout the thin film without agglomeration. Carbon (C) and platinum (Pt) are carbon and a surface coating for surface protection, respectively. The thin films of Examples 1 to 4 also had a thickness of approximately 10 μm, and Cu, Se, and oxygen (O) were uniformly distributed. According to a cross-sectional SEM image (not shown), the thickness of the thin film of Example 5 was 13.25 μm. Similarly, the thicknesses of the thin films of Examples 1 to 4 determined from the cross-sectional SEM images are summarized in Table 3.

[0073] [Table 3]

[0074] As shown in Table 3, the thin films of Examples 1 to 5 contain Cu a Ag b Se c M3 d O e T f When expressed by the composition formula, the parameters b, d, and f are 0, and the parameters a, c, and e are respectively: 0.5≦a≦0.8, 0.15≦c≦0.3, and 0.01≦e≦0.1 In detail, 0.7≦a≦0.8, 0.2≦c≦0.3, and 0.01≦e≦0.03 It was found that

[0075] FIG. 7 shows an SEM image and an EBSD image of the cross section of the thin film of Example 5.

[0076] According to Figure 7, voids were observed on the substrate (quartz substrate) side of the thin film of Example 5, but the surface side was a dense thin film. We believe that these voids are due to the effects of crystallization, which involves volume changes due to repeated phase transitions. Furthermore, as explained with reference to Figure 4, the thin film of Example 5 is composed of microcrystals, but it was found that the grain size of the crystal grains on the substrate side was small and that the crystal grains grew larger toward the surface side. Furthermore, according to the EBSD image, the crystal grains exhibited various grayscales, indicating that the thin film of Example 5 was polycrystalline. Although not shown, the thin films of Examples 1 to 4 were also polycrystalline, consisting of crystal grains that grew from the substrate side toward the surface side.

[0077] FIG. 8 shows the FFT diffraction pattern of the thin film of Example 5. FIG. 9 shows FFT diffraction patterns of the thin film of Example 5 under different tilt conditions. FIG. 10 shows FFT diffraction patterns of the thin film of Example 5 under different tilt conditions.

[0078] Figures 8 to 10(A) show FFT diffraction patterns under various tilt conditions for the thin film of Example 5. Figures 8 to 10(B) show the results of fitting the FFT diffraction patterns of Figures 8 to 10(A) with Cu2Se, which belongs to a cubic crystal system and has the symmetry of space group F-43m (number 216 in the International Tables for Crystallography), and it was found that some spots fit well.

[0079] Figures 8 to 10(C) show the results of fitting the FFT diffraction patterns in Figures 8 to 10(A) with Cu2[SeO3]O, which belongs to a cubic crystal system and has the symmetry of the P213 space group (number 198 in the International Tables for Crystallography). It was found that the remaining spots other than the spots fitted in (B) fit well. This Cu2[SeO3]O crystal was discovered by the present inventors and confirmed to be a new crystal by crystal structure analysis. The peaks derived from CuO, Cu2O, and SeO, which were very slightly observed in XPS, are presumed to be due to the new crystal.

[0080] This indicates that the thin film of Example 5 is a composite of the CuSe (space group F-43m) phase and the Cu[SeO]O phase. Similarly, the thin films of Examples 1 to 4 were also confirmed to be composites of the CuSe (space group F-43m) phase and the Cu[SeO]O phase.

[0081] [Table 4]

[0082] As shown in Table 4, the thin films of Examples 2 to 5 were found to be composites of the Cu2Se (space group F-43m) phase and the Cu2[SeO3]O phase, and the content of the Cu2[SeO3]O phase in the composite was 15% by volume or less, more specifically, 3% by volume or more and 10% by volume or less.

[0083] FIG. 11 is a diagram showing the thermal conductivities of the thin films of Examples 1 to 5 at room temperature. FIG. 12 is a diagram showing the temperature dependence of the power factors of the thin films of Examples 1 to 5. In FIG. FIG. 13 is a diagram showing the temperature dependence of the figures of merit of the thin films of Examples 1 to 5. In FIG.

[0084] 11, the thermal conductivities of the thin films of Examples 1 to 5 were in the range of 1.2 W / mK or more and 1.5 W / mK or less. Although not shown, the Seebeck coefficients of the thin films of Examples 1 to 5 were measured at room temperature (25°C) and were found to be 11 μV / K, 36 μV / K, 32 μV / K, 40 μV / K, and 42 μV / K, respectively, indicating positive Seebeck coefficients and confirming p-type conductivity.

[0085] 12, it was found that the thin films of Examples 1 to 5 were able to achieve high power factors in the measurement temperature range and functioned as p-type thermoelectric conversion materials. Focusing particularly on the thin films of Examples 2 to 5, they exhibited excellent thermoelectric performance at low temperatures near room temperature. This is believed to be due to the shift of the CuSe phase transition temperature (400 K) to around 350 K by combining with the CuSeO phase. Meanwhile, the thin film of Example 1 exhibited superior thermoelectric performance at higher temperatures than the thin film of Example 2, but no shift in the phase transition temperature was observed at lower temperatures. This is believed to be due to the film quality of the thin film of Example 1 being inferior to that of Examples 2 to 5, as it was formed at room temperature.

[0086] FIG. 13 shows the results of calculating the figure of merit zT using the thermal conductivity at room temperature. Surprisingly, for the thin film of Example 5, zT was 0.6 at room temperature (25°C). This value is the same as that of the bulk material shown in Non-Patent Document 1. (about 0.15) Therefore, if the thermoelectric conversion material of the present invention is used in bulk instead of in a thin film, an even larger zT can be achieved, surpassing that of Bi2Te3-based thermoelectric materials (zT at room temperature is 0.85).

[0087] [Table 5]

[0088] The above results demonstrate that the thermoelectric conversion material of the present invention is suitable for recovering low-temperature heat of 600 K or less, and can provide a thermoelectric conversion element for consumer use. [Industrial Applicability]

[0089] The thermoelectric conversion material of the present invention has a high figure of merit ZT that surpasses that of Bi2Te3-based thermoelectric materials, and is therefore used in thermoelectric cooling devices and power generation devices used in various electrical devices. In particular, because it can also be provided as a thin film material, it can be used to provide flexible thermoelectric conversion elements as power sources for wearable devices and IoT devices. [Explanation of symbols]

[0090] 200 Thermoelectric conversion element 210, 340 board 220 p-type thermoelectric materials 230 n-type thermoelectric materials 240 electrodes 300 Thin film manufacturing equipment 310 Vacuum Chamber 330 Cu2Se target 350 power supply 360 Shutter

Claims

1. Doped or undoped Cu ２ Se and Cu 2 [SeO 3 ]O oxide and is a complex containing A thermoelectric conversion material, wherein the content of the oxide in the composite is in the range of more than 0 vol % and not more than 15 vol %.

2. The oxide belongs to the cubic system and has a P2 １ The thermoelectric conversion material according to claim 1 , having a symmetry of 3.

3. 3. The thermoelectric conversion material according to claim 1, wherein the content of the oxide in the composite is in the range of 3% by volume or more and 10% by volume or less.

4. The complex may be copper(I) oxide (CO), copper(II) oxide (Cu ２ 4. The thermoelectric conversion material according to claim 1, further comprising at least one substance selected from the group consisting of Cu, SiO, selenium oxide, and compounds consisting of Cu and Se.

5. 5. The thermoelectric conversion material according to claim 1, wherein the phase transition temperature of the composite is in the range of 330 K or more and 370 K or less.

6. A thermoelectric conversion element comprising a p-type thermoelectric conversion material and an n-type thermoelectric conversion material alternately connected in series, wherein the p-type thermoelectric conversion material is the thermoelectric conversion material according to any one of claims 1 to 5.

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