Thermoelectric conversion material, thermoelectric conversion element, and method for manufacturing thermoelectric conversion material

Abstract

To provide a new thermoelectric conversion material that exhibits good thermoelectric conversion performance.SOLUTION: A thermoelectric conversion material is made of a CuxSe compound (1.9≤x≤2.6) in which Si oxide and Fe oxide are dispersed.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a thermoelectric conversion material, a thermoelectric conversion element, and a method for manufacturing a thermoelectric conversion material.

Background Art

[0002] A thermoelectric conversion material that converts heat into electricity can be used in a thermoelectric conversion element that generates electricity using waste heat. Such a thermoelectric conversion element is expected to be a power source for sensors installed in environments where power supply is difficult and as a next-generation power generation element. To realize a thermoelectric conversion element with a wide range of applications, in addition to reducing the use of toxic materials, it is useful to improve the thermoelectric conversion efficiency regardless of the form of the thermoelectric conversion material, such as bulk or thin film. Also, in order not to limit the operating temperature, it is useful to improve the thermoelectric conversion efficiency near room temperature.

[0003] One of the thermoelectric conversion materials is Bi2Te3. Bi2Te3 has a large dimensionless performance index zT indicating thermoelectric efficiency of about 0.85 and is excellent in thermoelectric conversion efficiency. However, Bi2Te3 has problems such as cost due to the scarcity of the Te element and toxicity of Te, and its spread has not progressed.

[0004] On the other hand, Cu2Se using Se, which is less toxic than Te, has attracted attention as a thermoelectric conversion material. For example, in Patent Document 1, a high performance index zT of up to about 0.6 at room temperature is obtained by a composite of a Cu2Se-based compound and an oxide.

[0005] However, in order to further expand the applications of thermoelectric conversion materials, a new thermoelectric conversion material that exhibits good thermoelectric conversion performance comparable to that of a composite of a Cu2Se-based compound and an oxide is desired.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] On one side, an object of the present invention is to provide a new thermoelectric conversion material exhibiting good thermoelectric conversion performance.

Means for Solving the Problems

[0008] According to one aspect, the thermoelectric conversion material is composed of a Cu x Se compound (1.9 ≦ x ≦ 2.6) in which Si oxide and Fe oxide are dispersed.

[0009] In the above thermoelectric conversion material, crystal grains of Cu2O or CuO may be formed on the surface of the Cu x Se compound.

[0010] In the above thermoelectric conversion material, the Si oxide may be uniformly distributed inside the Cu x Se compound.

[0011] In the above thermoelectric conversion material, the Fe oxide may be amorphous particles.

[0012] In the above thermoelectric conversion material, the crystal structure of the Cu x Se compound belongs to the cubic crystal system and may belong to at least one of the space groups Fm-3m and F-43m.

[0013] In the above thermoelectric conversion material, a plurality of voids may be formed inside the Cu x Se compound.

[0014] In the above thermoelectric conversion material, the Cu x Se compound may be in the form of a film.

[0015] According to one aspect, the thermoelectric conversion element is a Cu in which Si oxide and Fe oxide are dispersed xIt has a p-type thermoelectric conversion material made of a Se compound (1.9 ≦ x ≦ 2.6) and an n-type thermoelectric conversion material electrically connected in series with the p-type thermoelectric conversion material.

[0016] In the above thermoelectric conversion element, the Cu x Crystal grains of Cu2O or CuO may be formed on the surface of the Se compound.

[0017] In the above thermoelectric conversion element, the Si oxide may be uniformly distributed inside the Cu x Se compound.

[0018] In the above thermoelectric conversion element, the Fe oxide may be amorphous particles.

[0019] In the above thermoelectric conversion element, the Cu x Se compound may belong to the cubic crystal system and may belong to at least one of the space groups Fm-3m and F-43m.

[0020] In the above thermoelectric conversion element, the Cu x A plurality of voids may be formed inside the Se compound.

[0021] In the above thermoelectric conversion element, the Cu x Se compound may be in the form of a film.

[0022] According to one aspect, a method for manufacturing a thermoelectric conversion material includes forming a film of a Cu x Se compound (1.9 ≦ x ≦ 2.6) on a substrate by sputtering while covering a part of a target containing Cu2Se with a shutter having an FeSi2 film formed on its surface, and exposing the film to an oxygen-containing atmosphere.

Advantages of the Invention

[0023] According to the present invention, a new thermoelectric conversion material exhibiting good thermoelectric conversion performance can be provided.

Brief Description of the Drawings

[0024]

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Mode for Carrying Out the Invention

[0025] (First Embodiment) In this embodiment, a new thermoelectric conversion material that exhibits good thermoelectric conversion performance comparable to a composite of a Cu2Se-based compound and an oxide is formed by a sputtering method. Therefore, the sputtering apparatus used in the sputtering method will be described.

[0026] Figure 1 is a cross-sectional view of the sputtering apparatus according to this embodiment. This sputtering apparatus 1 is an RF (Radio Frequency) magnetron sputtering apparatus, and includes a chamber 2, a sputter cathode 3, a shutter 4, a substrate holder 5, an exhaust pump 6, and an RF power supply 7.

[0027] The chamber 2 is a metal container that can be depressurized and houses the sputter cathode 3 and the substrate holder 5 inside. A supply pipe 13 is connected to the chamber 2, and a sputter gas such as argon gas is supplied from the supply pipe 13 to the chamber 2.

[0028] The sputter cathode 3 is an electrode fixed to the inner bottom surface of the chamber 2, and houses a target 10 inside. In this example, a metal cylinder whose axial direction extends vertically upward is used as the sputter cathode 3. The target 10 is a circular plate in a top view made of the thermoelectric material Cu2Se. The chamber 2 and the sputter cathode 3 are electrically insulated by an insulating member (not shown).

[0029] The shutter 4 is a metal plate fixed to the shaft 14, and a FeSi2 film 11 is formed on the surface facing the target 10 by the sputtering method in advance to a film thickness of 0.01 μm or more and 100 μm or less. The shaft 14 is rotatably inserted into the chamber 2, and the rotation angle is adjusted by a shaft drive unit 15 such as a motor. The shaft drive unit 15 is controlled by, for example, a computer.

[0030] The substrate holder 5 is a conductive component that holds the substrate 12 so as to face the target 10, and is fixed to the inner upper surface of the chamber 2. The substrate holder 5 incorporates a heater (not shown) for heating the substrate 12 in the range of room temperature (298K) or more and 1000K or less. Further, the chamber 2 and the substrate holder 5 are electrically insulated by an insulating member (not shown). The distance between the target 10 and the substrate 12 is not particularly limited, and can be, for example, a distance of 40 mm or more and 70 mm or less.

[0031] The exhaust pump 6 is a pump for evacuating the inside of the chamber 2. As an example, a turbo molecular pump or the like can be adopted as the exhaust pump 6. By the exhaust pump 6, the pressure inside the chamber 2 is set to, for example, 0.1 Pa or more and 1 Pa or less.

[0032] The RF power supply 7 is a power supply for applying RF power between the substrate holder 5 and the target 10, and is electrically connected to each of the substrate holder 5 and the sputter cathode 3. The frequency of the RF power supply 7 is, for example, 13.56 MHz, and the RF power is, for example, 30 W or more and 150 W or less.

[0033] According to such a sputtering apparatus 1, while evacuating the inside of the chamber 2 with the exhaust pump 6, a sputter gas is supplied from the gas supply pipe 13, and the sputter gas is made into plasma by the RF power supply 7. By opening the shutter 4 in this state, the surface of the target 10 is struck by the plasmaized sputter gas. As a result, Cu containing copper and selenium, which are the materials of the target 10 xA film 19 of a Se compound is formed on a substrate 12 as a thermoelectric conversion material to a thickness of 0.05 μm or more and 5000 μm or less. In the present embodiment, as will be described later, Cu that constitutes the film 19 x By setting the composition ratio x of the Cu x Se compound to 1.9 ≦ x ≦ 2.6, a film 19 exhibiting good thermoelectric conversion performance can be obtained.

[0034] Next, the operation of the shutter 4 will be described.

[0035] FIG. 2(a) is a top view of the shutter 4 in the closed state. The shutter 4 is substantially circular in size so as to cover all of the target 10 in a top view, and is rotatable in the direction A about the shaft 14. When film formation is not performed on the substrate 12 (see FIG. 1), the shutter 4 is closed as shown in FIG. 2(a) so as to cover all of the target 10 in a top view with the shutter 4.

[0036] On the other hand, FIG. 2(b) is a top view of the shutter 4 during film formation. As shown in FIG. 2(b), during film formation, a film is formed on the substrate 12 (see FIG. 1) while covering a part 10a of the target 10 with the shutter 4 in a top view. As a result, since the FeSi2 film 11 (see FIG. 1) is exposed to the plasmaized sputter gas, iron and silicon that constitute the FeSi2 film 11 are scattered into the chamber 2, and the film 19 can be doped with trace amounts of iron (Fe) and silicon (Si).

[0037] The inventor of the present application formed the film 19 by variously changing the film formation conditions and investigated the thermoelectric conversion performance of the film 19. The investigation will be described below.

[0038] FIG. 3 is a diagram showing the film formation conditions of each sample of the film 19 used in the investigation. In this investigation, films 19 according to Examples 1 to 5 in which the RF power of the RF power supply 7 and the substrate temperature were different were formed. Regarding the RF power, it was 60 W in Examples 1 and 2, 80 W in Example 3, 100 W in Example 4, and 120 W in Example 5. Regarding the substrate temperature, it was 298 K (room temperature) in Example 1 and 773 K in Examples 2 to 5.

[0039] Also, in all of Examples 1 to 5, a quartz (SiO2) substrate with a size of 25 mm × 16 mm and a thickness of 0.5 mm in plan view was used as the substrate 12. Further, argon gas with a purity of 99.999% or more was used as the sputtering gas. Furthermore, the distance between the target 10 and the substrate 12 was set to 55 mm, and the pressure in the chamber 2 was set to 0.4 Pa. And as the target 10, a Cu2Se target manufactured by High Purity Chemical Co., Ltd. was used. The diameter of the target 10 was 50 mm, and the thickness was 6 mm. Additionally, an FeSi2 film 11 was previously formed on the shutter 4 to a film thickness of 3 μm.

[0040] And, in top view, the percentage of the area of a part 10a of the target 10 (see Fig. 2(b)) to the total area of the target 10 was set to 5%.

[0041] Furthermore, after forming the film 19, the substrate 12 was taken out of the chamber 2 and the film 19 was exposed to the atmosphere, thereby introducing oxygen in the atmosphere into the film 19. Note that the atmosphere is an example of an oxygen-containing atmosphere.

[0042] Fig. 4 is a graph obtained by investigating the relationship between the temperature and the electrical conductivity of the film 19. For the measurement of the electrical conductivity, SBA 458 Nemesis manufactured by Nitchi Japan Co., Ltd. was used. As shown in Fig. 4, among Examples 1 to 5, the electrical conductivity at each temperature was the largest in Example 1 and the smallest in Example 2. Also, in Examples 2 to 4, the electrical conductivity was maximum around 350 K.

[0043] Fig. 5 is a graph obtained by investigating the relationship between the temperature and the Seebeck coefficient of the film 19. For the measurement of the Seebeck coefficient, SBA 458 Nemesis manufactured by Nitchi Japan Co., Ltd. was used. As shown in Fig. 5, among Examples 1 to 5, the Seebeck coefficient at each temperature was the smallest in Example 1 and the largest in Example 5. Also, in Examples 2 to 4, the Seebeck coefficient was minimum around 350 K.

[0044] Figure 6 is a graph obtained by investigating the relationship between the temperature of the film 19 and the power factor. The power factor PF is defined by the following formula (1) using the electrical conductivity σ (Figure 4) and the Seebeck coefficient S (Figure 5).

[0045]

Equation

[0046] As shown in Figure 6, among Examples 1 to 5, the power factor at each temperature was the largest in Example 5. Also, in Examples 2 to 4, the power factor was minimized around 350K.

[0047] Figure 7 is a graph obtained by investigating the relationship between the RF power during film formation and the thermal conductivity of the film 19. For the measurement of thermal conductivity, ai-Phase manufactured by EyePhase Co., Ltd. was used. As shown in Figure 7, among Examples 1 to 5, the thermal conductivity of Example 5 with the largest RF power was the smallest. Also, comparing Example 1 and Example 2 with the same RF power, Example 2 with a higher substrate temperature had a higher thermal conductivity than Example 1.

[0048] Figure 8 is a graph obtained by investigating the relationship between the RF power during film formation and the performance index zT of the film 19 at room temperature (298K). The performance index zT is a dimensionless index defined by the following formula (2).

[0049]

Equation

[0050] Note that in formula (2), S, T, σ, and κ are the Seebeck coefficient, absolute temperature, electrical conductivity, and thermal conductivity, respectively.

[0051] As shown in Figure 8, the performance index zT of Examples 1 to 5 at room temperature (298K) was generally in the range of 0.2 to 0.6, and it was revealed that a performance index comparable to that of a composite of a Cu2Se-based compound and an oxide was obtained.

[0052] In particular, in Examples 2 to 5 where the substrate temperature during the film formation of the film 19 was higher than room temperature, the performance index zT was greater than that in Example 1 where the substrate temperature was room temperature. From this, it became clear that increasing the substrate temperature above room temperature is effective in improving the performance index zT.

[0053] Furthermore, in Examples 3 to 5 where the RF power was 80 W or more, the performance index zT exceeded 0.4. Therefore, it became clear that it is preferable to set the RF power to 80 W or more in order to obtain a performance index zT exceeding 0.4.

[0054] Also, the performance index zT of Example 5 is very high at 0.6. This is presumably because in Example 5, the Seebeck coefficient S of the numerator of Equation (2) is high (see Figure 5), and the thermal conductivity κ of the denominator of Equation (1) is small (see Figure 7).

[0055] Next, the EDS (Energy Dispersive X-ray Spectroscopy) spectra obtained to identify the composition of the film 19 according to each example will be described.

[0056] Figures 9(a), 10(a), 11(a), 12(a), and 13(a) are surface SEM (Scanning Electron Microscope) images of the films 19 according to Examples 1 to 5, respectively, from which the EDS spectra were obtained. For obtaining the surface SEM images, a Schottky field emission type scanning electron microscope JSM-7900F manufactured by JEOL Ltd. was used.

[0057] Also, Figures 9(b), 10(b), 11(b), 12(b), and 13(b) are the EDS spectra of the films 19 according to Examples 1 to 5, respectively. For obtaining the EDS spectra, an energy dispersive X-ray analyzer JED-2300 Analysis Station Plus manufactured by JEOL Ltd. was used. The horizontal axis of the EDS spectra indicates the energy (keV) of the X-rays emitted from the film 19, and the vertical axis indicates the intensity (arbitrary unit) of the X-rays.

[0058] Figure 14 shows the composition of the film 19 obtained from the results of FIGS. 9(b), 10(b), 11(b), 12(b), and 13(b). Here, the concentrations of oxygen (O), silicon (Si), iron (Fe), copper (Cu), and selenium (Se) in the film 19 are shown in atomic percent. Also, the composition ratio of copper and selenium is shown in FIG. 14 as well. The concentration of each element was calculated from the intensity of the characteristic X-ray of each element that appeared in the EDS spectrum. For example, the quantification of the characteristic X-ray can be performed in advance using a standard sample for an energy dispersive X-ray analyzer, and the concentration of each element can be calculated by comparing it with the intensity of the characteristic X-ray of the standard sample.

[0059] Among the respective elements, copper (Cu) and selenium (Se) are derived from the target 10. Also, silicon (Si) and iron (Fe) are derived from the FeSi2 film 11 formed on the surface of the shutter 4. And oxygen (O) was incorporated into the film 19 by exposing the film 19 to the atmosphere after film formation.

[0060] Also, the film thickness measured by a crystal oscillator film thickness meter (not shown) installed in the chamber 2 is also shown in FIG. 14.

[0061] As shown in FIG. 14, in Examples 1 to 5, the composition ratio of copper and selenium is 1.9 or more and 2.6 or less, which is a value deviated from the stoichiometric composition of "2" of Cu2Se. This is because iron (Fe) and silicon (Si) derived from the FeSi2 film 11 were incorporated into the film 19. Since FeSi2 itself is also a good thermoelectric conversion material, by doping a small amount of this into the film 19 to make the composition ratio of copper and selenium 1.9 or more and 2.6 or less, it is considered that a performance index zT (see FIG. 8) comparable to that of a composite of a Cu2Se-based compound and an oxide could be realized in Examples 1 to 5.

[0062] In particular, in this embodiment, as shown in FIG. 2(b), while covering a part 10a of the target 10 with the shutter 4, the FeSi2 film 11 (see FIG. 1) of the shutter 4 is struck with a sputtering gas to dope the film 19 with iron and silicon. Thereby, it is possible to prevent the film 19 from being excessively doped with iron and silicon, and it is possible to reduce the possibility that the thermoelectric conversion performance of the film 19 is degraded by excessive iron and silicon.

[0063] In order to dope the film 19 with an appropriate amount of iron and silicon, it is preferable that the percentage of the ratio of the area of the part 10a in the top view to the entire area of the target 10 is 0.1% or more and 30% or less. The range of the percentage of the ratio is set as above because outside this range, the doping amount of iron and silicon may be insufficient or excessive, making it difficult to improve the thermoelectric conversion characteristics of the film 19.

[0064] Next, the XRD (X-ray Diffraction) spectrum of the film 19 will be described.

[0065] FIGS. 15 to 18 are diagrams showing the XRD spectra of the film 19 according to Examples 1 to 4, respectively. FIGS. 19 and 20 are diagrams showing the XRD spectra of the film 19 according to Example 5. The horizontal axis in FIGS. 15 to 20 indicates the diffraction angle of X-rays, and the vertical axis indicates the intensity of the diffracted X-rays.

[0066] The XRD spectrum was obtained using a SmartLab manufactured by Rigaku Corporation. Here, a CuKα tube was used, and the X-ray output was set to 45 kV and 200 mA. The divergence slit was set to automatic, and a high-speed one-dimensional X-ray detector (D / teX Ultra 250) was used as the detector. The operating range of the diffraction angle was set to 5° or more and 90° or less, and the reading width of the diffracted X-rays was set to 0.01°.

[0067] In FIGS. 15 to 20, the diffraction planes of various materials are indicated by dotted lines. Each diffraction plane is also accompanied by the material and its crystal structure. For example, "Cu2Se(m)" indicates a monoclinic Cu2Se crystal.

[0068] As shown in FIG. 15, in Example 1, many diffraction peaks originating from Cu2Se appear. 1.8 Diffraction peaks due to Se also appear.

[0069] On the other hand, as shown in FIG. 16, in Example 2, Cu 1.82 Several diffraction peaks originating from Se and Cu 1.8 Several diffraction peaks attributable to Se appear. On the other hand, the intensity of the diffraction peak attributable to Cu2Se is lower than in Example 1. Furthermore, a diffraction peak attributable to CuO is also seen near 40°.

[0070] 17, a similar tendency to that of Example 2 (FIG. 16) is also seen in Example 3. Furthermore, in Example 3, not only the diffraction peak of CuO but also the diffraction peak of CuO appears around 62°, which indicates that the oxidation of Cu is more promoted than in Example 2.

[0071] As shown in FIG. 18, the same tendency as in Example 3 (FIG. 17) is observed in Example 4. Furthermore, in Example 4, Cu 1.8 The diffraction peaks due to Se are stronger than in Example 3 (FIG. 17).

[0072] Furthermore, as shown in FIG. 19, in Example 5, Cu 1.8 The intensity of the diffraction peak derived from Se is stronger than in Examples 2 to 4.

[0073] Fig. 20 is a diagram in which the scale of the vertical axis is enlarged in Fig. 19. As shown in Fig. 20, in Example 5, the diffraction peaks derived from monoclinic Cu2Se crystals disappear.

[0074] From the above results, it can be seen that the Cu2Se crystals are Cu in the order of Example 1, Example 2, Example 3, Example 4, and Example 5. 1.82 Se crystal, Cu 1.8 It was found that the order of the Se crystals changed and the oxidation of copper was promoted.

[0075] In addition, in Example 5, since the diffraction peaks derived from the monoclinic Cu2Se crystal have disappeared, the stress inside the Cu2Se crystal has been released, resulting in the generation of Cu 1.8 Se crystals and Cu 1.82 Se crystals, and these crystals may have increased the performance index zT of Example 5 as shown in Fig. 8.

[0076] Next, the investigation results regarding the appearance of the film 19 will be described.

[0077] Figs. 21(a) and (b) are cross-sectional SEM images of the film 19 according to Example 2 and Example 5, respectively. For obtaining the cross-sectional SEM images, Thermo Scientific Scios2 HiVac manufactured by FEI Electron Optics in the Netherlands was used. In this cross-sectional SEM image, the higher the film density, the brighter it appears, and the lower the film density, the darker it appears. In particular, the black areas indicate voids.

[0078] As shown in Figs. 21(a) and (b), it was revealed that a plurality of voids 19a indicated in black were formed in the film 19 in both Example 2 and Example 5. In this embodiment, the RF power was changed in the range of 60 W to 120 W as shown in Fig. 3, and Example 2 and Example 5 adopted the maximum value and the minimum value in this range, respectively. Therefore, it can be inferred that voids 19a are similarly formed in the film 19 in Examples 3 and 4 where the RF power is between Example 2 and Example 5. Also, since Example 1 has the same RF power as Example 2, it can be inferred that voids 19a are formed in the film 19 in the same manner as Example 2.

[0079] The voids 19a play a role in reducing the thermal conductivity κ of the film 19 and increasing the performance index zT in Equation (2). Therefore, one of the factors that enabled a large performance index zT to be achieved in each of Examples 1 to 5 as shown in Fig. 8 is considered to be the voids 19a.

[0080] Next, the investigation results regarding the crystal structure of the film 19 will be described.

[0081] Figs. 22(a) and (b) are electron diffraction images of the film 19 according to Example 2 and Example 5, respectively. To obtain the electron diffraction images, an atomic resolution electron microscope JEM-ARM300F GRAND ARM manufactured by JEOL Ltd. was used. When analyzing this electron diffraction image, it became clear that both films 19 of Example 2 and Example 5 belong to the cubic crystal and belong to at least one of the space groups of Fm-3m and F-43m. However, "-" indicates an overline of the number immediately following it. For the same reason as in Figs. 21(a) and (b), in Examples 3 and 4 where the RF power is between Example 2 and Example 5, and in Example 1 where the RF power is the same as that of Example 2, it can be inferred that the crystal structure of the film 19 belongs to the cubic crystal and belongs to at least one of the space groups of Fm-3m and F-43m.

[0082] Next, the investigation results regarding the texture of the surface of the film 19 will be described. Figs. 23(a), (b), Figs. 24(a), (b), and Figs. 25(a), (b) are surface SEM images of the film 19 according to Example 1, Example 2, and Example 5, respectively. To obtain this surface SEM image, an S-3700 manufactured by Hitachi High-Technologies Corporation was used.

[0083] As shown in Figs. 23(a), (b), Figs. 24(a), (b), and Figs. 25(a), (b), all films 19 of Example 1, Example 2, and Example 5 are dense aggregates of microcrystals, and the texture caused by the microcrystals appears on the surface.

[0084] Fig. 26 is a STEM (Scanning Transmission Electron Microscope) image of a cross-section near the surface of the film 19 according to Example 5. Note that to obtain the STEM image, an atomic resolution electron microscope JEM-ARM300F GRAND ARM manufactured by JEOL Ltd. was used.

[0085] As shown in Fig. 26, on the surface of the film 19 according to Example 5, minute triangular protrusions 19b are formed in a cross-sectional view. The inventor of the present application obtained a count map of EDS for each element in the protrusion 19b in order to confirm the composition of the protrusion 19b according to Example 5.

[0086] FIG. 27 is a count map of EDS for each element of the protrusion 19b according to Example 5. The count map is a map showing the intensity distribution of characteristic X-rays of each element measured by EDS, and indicates that the brighter the site, the more the target element is contained. To obtain the count map, an energy dispersive X-ray analyzer JED-2300 Analysis Station Plus manufactured by JEOL Ltd. was used. Here, count maps of each of copper (Cu), oxygen (O), selenium (Se), iron (Fe), and silicon (Si) were obtained.

[0087] As shown in FIG. 27, it was revealed that the protrusion 19b contains a large amount of copper (Cu) and oxygen (O), and hardly contains selenium (Se), iron (Fe), and silicon (Si) other than these.

[0088] According to the measurement results of electron beam diffraction, a diffraction pattern specific to the Cu2O crystal was observed in the protrusion 19b. Also, according to the measurement results of XRD, diffracted X-rays specific to the CuO crystal were observed in the protrusion 19b. Thereby, it became clear that the protrusion 19b is a crystal grain of Cu2O or CuO.

[0089] Among Examples 1 to 5, the protrusion 19b could be clearly confirmed only in Example 5. Therefore, it is presumed that the reason why the performance index ZT of the film 19 according to Example 5 is significantly larger than those of Examples 1 to 4 as shown in FIG. 8 is also related to the action of this protrusion 19b.

[0090] Next, the investigation results regarding the distribution of each element in the film 19 will be described.

[0091] FIGS. 28 to 30 are count maps of EDS of the film 19 according to Example 1, Example 2, and Example 5, respectively. Using the same apparatus as in FIG. 27, count maps of each of copper (Cu), oxygen (O), selenium (Se), iron (Fe), and silicon (Si) were obtained. As described in FIG. 27, the brighter the site in each count map, the more the target element is contained.

[0092] As shown in Fig. 28, in Example 1, the bright parts of oxygen (O) and iron (Fe) appear at substantially the same position. As a result, it became clear that particles of Fe oxides such as FeO were dispersed in the film 19. Further, according to the XRD spectra of Figs. 15 to 20, no diffraction X-rays peculiar to Fe oxide crystals appeared. Therefore, it became clear that the particles of Fe oxide were dispersed in the film 19 in an amorphous state.

[0093] In addition, no distinct pattern appeared in the count map of silicon (Si), and it was also found that silicon (Si) was uniformly distributed in the film 19. In particular, since there is no dark part of silicon (Si) in the bright part of oxygen (O), it can also be seen that silicon (Si) is present at the site where oxygen (O) is present. From this result, it also became clear that Si oxides such as SiO were dispersed in the film 19.

[0094] On the other hand, as shown in Fig. 29, in Example 2, no distinct pattern appeared in the count maps of copper (Cu), oxygen (O), selenium (Se), iron (Fe), and silicon (Si), and it became clear that these elements were uniformly distributed in the film 19.

[0095] In particular, since oxygen (O) is also present where silicon (Si) is present, it can be seen that Si oxides are uniformly distributed in the film 19. Similarly, since oxygen (O) is also present where iron (Fe) is present, it can also be seen that Fe oxides are uniformly distributed in the film 19.

[0096] Further, as shown in Fig. 30, in Example 5, fine bright parts appear in the count maps of oxygen (O) and iron (Fe) respectively. These bright parts are substantially the same for oxygen (O) and iron (Fe) respectively. As a result, similar to Example 1, it became clear that Fe oxides were dispersed in the film 19.

[0097] Furthermore, since oxygen (O) is also present where silicon (Si) is present, it can be seen that Si oxides are uniformly distributed in the film 19 similar to Example 1.

[0098] As described above, it has become clear that in the film 19 according to this embodiment, the Si oxide and the Fe oxide are dispersed. In particular, it has also become clear that the Si oxide is uniformly distributed inside the film 19.

[0099] (Second Embodiment) In this embodiment, a thermoelectric conversion element including the film 19 according to the first embodiment will be described.

[0100] FIG. 31 is a perspective view of the thermoelectric conversion element according to this embodiment. The thermoelectric conversion element 200 is an element that generates electricity by applying a temperature difference, and includes a base material 210, a p-type thermoelectric conversion film 220, an n-type thermoelectric conversion film 230, a first electrode 241, and a second electrode 242.

[0101] The base material 210 may be a rigid substrate such as a glass substrate, a metal substrate, or a ceramic substrate, or may be a flexible sheet such as a polymer sheet. Hereinafter, the direction parallel to the surface of the base material 210 is defined as the first direction X1, and the direction intersecting the first direction on the surface is defined as the second direction X2.

[0102] The p-type thermoelectric conversion film 220 is a film 19 of a Cu x Se compound (1.9 ≦ x ≦ 2.6) and is in a strip shape extending along the first direction X1.

[0103] Further, the n-type thermoelectric conversion film 230 is a thin film of an n-type thermoelectric conversion material and is in a strip shape extending along the first direction X1. The material of the n-type thermoelectric conversion film 230 is not particularly limited. For example, thin films such as carbon nanotubes, fullerenes, Bi2(Se, Te)3, PbTe, SiGe, GaP, Gd2Se3, and FeSi2 can be adopted as the n-type thermoelectric conversion film.

[0104] In this example, the p-type thermoelectric conversion film 220 and the n-type thermoelectric conversion film 230 are alternately arranged at intervals along the second direction X2.

[0105] The first electrode 241 and the second electrode 242 are conductive films that electrically connect the ends of the adjacent p-type thermoelectric conversion films 220 and n-type thermoelectric conversion films 230, respectively, and electrically connect the thermoelectric conversion films 220 and 230 in series. For example, thin films such as aluminum (Al), nickel (Ni), platinum (Pt), and indium tin oxide (ITO) can be employed as the electrodes 241 and 242. In this example, the first electrode 241 is arranged at intervals along the second direction X2, and the second electrode 242 is arranged at intervals along the second direction X2.

[0106] Such a thermoelectric conversion element 200 is called a π-type thermoelectric conversion element. In a π-type thermoelectric conversion element, by applying a temperature difference between the first electrode 241 and the second electrode 242, an electromotive force V is generated by the Seebeck effect.

[0107] In the present embodiment, since the film 19 having a figure of merit zT at room temperature comparable to that of a composite of a Cu2Se-based compound and an oxide is employed as the p-type thermoelectric conversion film 220, the thermoelectric conversion element 200 can generate electricity even with a slight amount of waste heat around body temperature. Thereby, the thermoelectric conversion element 200 generates electricity from various waste heats in the environment and can drive IoT devices such as sensors with the electric power.

[0108] Note that in the above, the film 19 according to the first embodiment is used for the π-type thermoelectric conversion element 200, but the present embodiment is not limited thereto. For example, the film 19 according to the first embodiment may be used for a U-type thermoelectric conversion element.

[0109] Furthermore, a metal film may be used instead of the n-type thermoelectric conversion film 230. In this case, as the material of the metal film, for example, the same materials as those of the electrodes 241 and 242 can be employed.

[0110] Also, instead of the n-type thermoelectric conversion film 230, a thermoelectric conversion film having a Seebeck coefficient different from that of the p-type thermoelectric conversion film 220 may be employed.

Explanation of Reference Numerals

[0111] 1... Sputtering apparatus, 2... Chamber, 3... Sputtering cathode, 4... Shutter, 5... Substrate holder, 6... Exhaust pump, 7... RF power supply, 10... Target, 10a... Part, 11... FeSi2 film, 12... Substrate, 13... Gas supply pipe, 14... Shaft, 15... Shaft drive unit, 19... Film, 19a... Part, 19b... Protrusion, 200... Thermoelectric conversion element, 210... Substrate, 220... p-type thermoelectric conversion film, 230... n-type thermoelectric conversion film, 241... First electrode, 242... Second electrode.

Claims

1. Cu in which SiOx and FeOx are dispersed ｘ A thermoelectric conversion material comprising a Se compound (1.9 ≤ x ≤ 2.6).

2. The above-mentioned Cu ｘ On the surface of the Se compound, crystal grains of Cu ２ O or CuO are formed. The thermoelectric conversion material according to claim 1.

3. The Si oxide is the Cu ｘ The thermoelectric conversion material according to claim 1 or claim 2, wherein the Si oxide is uniformly distributed inside the Se compound.

4. The thermoelectric conversion material according to claim 1 or claim 2, wherein the Fe oxide is amorphous particles.

5. The above-mentioned Cu ｘ The thermoelectric conversion material according to claim 1 or claim 2, wherein the crystal structure of the Se compound belongs to the cubic system and belongs to at least one of the space groups of Fm-3m and F-43m.

6. The above-mentioned Cu ｘ The thermoelectric conversion material according to claim 1 or claim 2, in which a plurality of voids are formed inside the Se compound.

7. The above-mentioned Cu ｘ The thermoelectric conversion material according to claim 1 or claim 2, wherein the CuSe compound is in a film form.

8. Cu in which SiOx and Fe oxide are dispersed ｘ a p-type thermoelectric conversion material composed of a Se compound (1.9 ≤ x ≤ 2.6), and An n-type thermoelectric conversion material electrically connected in series with the p-type thermoelectric conversion material, and a thermoelectric conversion element having the same.

9. The above-mentioned Cu ｘ On the surface of the Se compound, crystal grains of Cu ２ O or CuO are formed, and the thermoelectric conversion element according to claim 8.

10. The Si oxide is the Cu ｘ The thermoelectric conversion element according to claim 8 or claim 9, wherein the Si oxide is uniformly distributed inside the Se compound.

11. The thermoelectric conversion element according to claim 8 or claim 9, wherein the Fe oxide is amorphous particles.

12. The above-mentioned Cu ｘ The thermoelectric conversion element according to claim 8 or claim 9, wherein the crystal structure of the Se compound belongs to the cubic system and belongs to at least one of the space groups of Fm-3m and F-43m.

13. The Cu ｘ The thermoelectric conversion element according to claim 8 or claim 9, in which a plurality of voids are formed inside the Se compound.

14. The Cu ｘ Se compound is in the form of a film, the thermoelectric conversion element according to claim 8 or claim 9.

15. FeSi on the surface ２ A shutter with a film formed thereon covers a part of a target containing Cu ２ A CuSe compound (1.9 ≤ x ≤ 2.6) film is formed on a substrate by sputtering while covering a part of the target containing CuSe ｘ and forming a film of CuSe compound (1.9 ≤ x ≤ 2.6). Exposing the film to an oxygen-containing atmosphere, and a method for manufacturing a thermoelectric conversion material including the same.

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