Thermoelectric conversion material, thermoelectric conversion element, thermoelectric conversion module and optical sensor

Abstract

To provide a thermoelectric conversion material capable of improving the efficiency of thermoelectric conversion.SOLUTION: A thermoelectric conversion material contains, as a base material, iron, vanadium and aluminum. In an X-ray diffraction 2θ scan, the full width at half maximum (FWHM) of a peak at 2θ=44.5±2.5° is 3° to 7°.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a thermoelectric conversion material, a thermoelectric conversion element, a thermoelectric conversion module, and an optical sensor. [Background technology]

[0002] Techniques relating to Fe (iron)-V (vanadium)-Al (aluminum) based thermoelectric conversion materials have been disclosed (see, for example, Patent Document 1, Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-227755 [Non-patent literature]

[0004] [Non-Patent Document 1] B. Hinterleitner et al., “Thermoelectric performance of a metastable thin-film Heusler alloy”, Nature, Vol. 576,85-90(2019) [Non-patent document 2] Yukihiro Furuta et al., “Fe2VAl-Based Thermoelectric Thin Films Prepared by a Sputtering Technique”, abstract, Electric Journal of electronic materials, 43, p2157 (2014) [Non-patent document 3] Satoshi Hiroi et al., “Analyzing the Boundary Thermal Resistance of Epitaxially Grown Fe2VAl / W Layers by Picosecond Time-Domain Thermoreflectance”, abstract, Electric Journal of electronic materials, 43, p3113 (2018) Summary of the Invention [Problem to be solved by the invention]

[0005] Thermoelectric conversion materials are materials that convert temperature differences (thermal energy) into electricity. The power factor (hereinafter sometimes abbreviated as "PF"), which corresponds to the amount of power generated per unit temperature difference, is expressed by the following formula (1): In formula (1), S is the Seebeck coefficient, and σ is the electrical conductivity.

[0006] PF=S 2 ×σ (1)

[0007] In order to perform efficient thermoelectric conversion, it is important to increase the PF. If the PF can be increased, the efficiency of thermoelectric conversion can be improved.

[0008] Therefore, one of the objects is to provide a thermoelectric conversion material that can improve the efficiency of thermoelectric conversion. [Means for solving the problem]

[0009] The thermoelectric conversion material according to the present disclosure contains iron, vanadium, and aluminum as a base material, and has a half-width of a peak in a 2θ angle range of 44.5±2.5° in an X-ray diffraction 2θ measurement spectrum of 3° to 7°. [Effects of the Invention]

[0010] Such a thermoelectric conversion material can improve the efficiency of thermoelectric conversion. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing a cross section of a part of a thermoelectric conversion material according to the first embodiment. [Figure 2] FIG. 2 is a flowchart showing typical steps of a method for producing a thermoelectric conversion material according to the first embodiment. [Figure 3] FIG. 3 is a graph showing the relationship between the oxygen content (at %) derived from Samples 1 to 6 and ZT, which is the figure of merit. [Figure 4] FIG. 4 is a graph showing the relationship between the tungsten content (at %) derived from Samples 7 to 12 and ZT, which is the figure of merit. [Figure 5] FIG. 5 shows the XRD results for Sample 9. [Figure 6] FIG. 6 is a schematic diagram showing the structure of a π-type thermoelectric conversion element (power generation element) which is a thermoelectric conversion element. [Figure 7] FIG. 7 is a diagram showing an example of the structure of a power generation module. [Figure 8] FIG. 8 is a diagram showing an example of the structure of an infrared sensor. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Description of the embodiments of the present disclosure] (1) The thermoelectric conversion material according to the present disclosure contains iron, vanadium, and aluminum as a base material, and in the 2θ measurement spectrum of an X-ray diffraction, the half-width of a peak in the 2θ angle range of 44.5±2.5° is 3° or more and 7° or less.

[0013] The thermoelectric conversion material contains iron, vanadium, and aluminum as its base material, making it a metal, but with a pseudogap band structure near the Fermi level. The steep energy gradient of the density of states in this pseudogap region facilitates the realization of high thermoelectric properties. Furthermore, the half-width of the peak in the 2θ angle range of 44.5±2.5° in the X-ray diffraction 2θ measurement spectrum is 3° or more. This prevents excessive crystallinity and promotes amorphization. Therefore, an increase in thermal conductivity can be suppressed. Furthermore, the half-width of the peak in the 2θ angle range of 44.5±2.5° in the X-ray diffraction 2θ measurement spectrum is 7° or less. This prevents the short-range order of the atoms in the base material from being disrupted, resulting in a breakdown of the band structure. As a result, the thermoelectric conversion material can improve thermoelectric conversion efficiency.

[0014] (2) In the above (1), the thermoelectric conversion material may further contain oxygen and tungsten as a base material. When the thermoelectric conversion material contains oxygen and tungsten, the crystalline structure is easily broken down and the material becomes amorphous. This reduces the thermal conductivity of the thermoelectric conversion material and makes it easier to improve its thermoelectric properties. Therefore, the efficiency of thermoelectric conversion can be further improved.

[0015] (3) In the above (2), the oxygen content may be 4 at % or more and 27 at % or less with respect to the entire thermoelectric conversion material. By doing so, the oxygen content can be adjusted appropriately, and the amorphization can be promoted while suppressing an increase in electrical resistance due to oxidation. Therefore, the thermoelectric conversion efficiency can be more reliably improved.

[0016] (4) In the above (2) or (3), the tungsten content may be 1.5 at% or more and 16.5 at% or less of the total thermoelectric conversion material. By doing so, the tungsten content can be adjusted appropriately, and the amorphization can be promoted while suppressing the collapse of the band structure. Therefore, the thermoelectric conversion efficiency can be more reliably improved.

[0017] (5) In any of (1) to (4) above, the ratio of the peak intensity of a peak in the 2θ angle range of 62.5±2.5° in the X-ray diffraction 2θ measurement spectrum to the peak intensity of a peak in the 2θ angle range of 44.5±2.5° in the X-ray diffraction 2θ measurement spectrum may be 0 or more and 0.06 or less. Such a thermoelectric conversion material has high amorphousness. Therefore, such a thermoelectric conversion material can reliably improve thermoelectric conversion efficiency.

[0018] (6) In any of the above (1) to (5), the thermoelectric conversion material may further include a silicon substrate. The base material may be disposed on the silicon substrate. By doing so, the silicon substrate is disposed as a substrate underlying the Fe-V-Al-based base material, which is the base material, and the base material can be easily made amorphous. This reduces the thermal conductivity of the thermoelectric conversion material, thereby further improving the thermoelectric conversion efficiency.

[0019] (7) A thermoelectric conversion element according to the present disclosure includes a thermoelectric conversion material section, a first electrode arranged in contact with the thermoelectric conversion material section, and a second electrode arranged in contact with the thermoelectric conversion material section and spaced apart from the first electrode. The material constituting the thermoelectric conversion material section is any one of the thermoelectric conversion materials (1) to (6) above, which has a p-type or n-type conductivity. In the thermoelectric conversion element according to the present disclosure, the material constituting the thermoelectric conversion material section is the thermoelectric conversion material described above. Therefore, the thermoelectric conversion element according to the present disclosure can achieve high thermoelectric conversion efficiency.

[0020] (8) The thermoelectric conversion module of the present disclosure includes the thermoelectric conversion element of the present disclosure (7). According to the thermoelectric conversion module of the present disclosure, by including the thermoelectric conversion element of the present disclosure that can achieve high thermoelectric conversion efficiency, it is possible to obtain a thermoelectric conversion module that can achieve high thermoelectric conversion efficiency.

[0021] (9) An optical sensor according to the present disclosure includes an absorber that absorbs light energy and a thermoelectric conversion material section connected to the absorber. The material constituting the thermoelectric conversion material section is any one of the thermoelectric conversion materials (1) to (6) above, which has a p-type or n-type conductivity. In the optical sensor according to the present disclosure, the material constituting the thermoelectric conversion material section is the thermoelectric conversion material described above. Therefore, a highly sensitive optical sensor can be provided.

[0022] [Details of the embodiments of the present disclosure] Next, embodiments of the thermoelectric conversion material of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference characters, and their description will not be repeated.

[0023] (Embodiment 1) A thermoelectric conversion material according to a first embodiment of the present disclosure will be described below. Fig. 1 is a schematic diagram showing a cross section of a portion of the thermoelectric conversion material according to the first embodiment.

[0024] Referring to FIG. 1, thermoelectric conversion material 11 in embodiment 1 includes base material 12 and silicon substrate 13. FIG. 1 is a cross-sectional view of silicon substrate 13 cut in the thickness direction. Base material 12 is disposed on substrate 13. Base material 12 includes Fe (iron), V (vanadium), and Al (aluminum). Base material 12 is an Fe-V-Al-based material. Base material 12 is formed as a film on Si (silicon) substrate 13.

[0025] In this embodiment, the thermoelectric conversion material 11 contains oxygen and tungsten as a base material. O (oxygen) is contained in the base material 12. The oxygen content is 4 at % or more and 27 at % or less with respect to the entire thermoelectric conversion material 11. The W (tungsten) content is 1.5 at % or more and 16.5 at % or less with respect to the entire thermoelectric conversion material 11.

[0026] Here, in the thermoelectric conversion material 11, the half-width of the peak in the 2θ angle range of 44.5±2.5° in the 2θ measurement spectrum of X-ray diffraction is 3° or more and 7° or less. A specific example of the 2θ angle in this case is 44.43°. Furthermore, in the thermoelectric conversion material 11, the ratio of the peak intensity of the peak in the 2θ angle range of 62.5±2.5° in the 2θ measurement spectrum of X-ray diffraction to the peak intensity of the peak in the 2θ angle range of 44.5±2.5° in the 2θ measurement spectrum of X-ray diffraction is 0 or more and 0.06 or less. A specific example of the 2θ angle in this case is 64.65°. These will be described in detail later.

[0027] The thermoelectric conversion material 11 according to the first embodiment can be manufactured, for example, by the following manufacturing method. FIG. 2 is a flowchart showing typical steps in the manufacturing method for the thermoelectric conversion material 11 according to the first embodiment. Referring to FIG. 2, in the manufacturing method for the thermoelectric conversion material 11 according to the first embodiment, a raw material preparation step is performed as step (S10). In this step (S10), a silicon substrate 13, specifically an n-type Si(100) substrate, is prepared. In addition, Fe, Al, V, and W, which are used to form a base material film, are prepared. The Fe, Al, V, and W elements may be prepared as a bulk substance of each element, or may be prepared as a compound containing any of Fe, Al, V, and W, such as Fe2VAl. Of course, both may be prepared. The amount of each element to be prepared is adjusted so that the desired composition of the thermoelectric conversion material 11 is finally achieved. In this embodiment, Fe2VAl and W are prepared as simple substances.

[0028] Next, a film formation step is carried out as step (S20). In this step (S20), the silicon substrate 13 is heated at 700°C for 30 minutes or more, and then, while maintaining the heating, a W-containing Fe-V-Al film is formed by RF (Radio Frequency) magnetron sputtering. The film formation rate is 5 nm / min, and in this embodiment, a film of 230 nm is formed. Ar (argon) gas is used for sputtering. In addition, the background oxygen concentration (oxygen partial pressure) is adjusted to 1.0 x 10 to achieve the desired oxygen content.-1 Pa (Pascal) or more 1.0 x 10 -3 The pressure is adjusted to a range of not more than Pa. In this way, base material 12 is formed as a film on silicon substrate 13. In this way, thermoelectric conversion material 11 in the first embodiment is obtained.

[0029] The thermoelectric conversion material 11 contains iron, vanadium, and aluminum as the base material 12, and thus is a metal, but has a pseudogap band structure near the Fermi level. The steep energy gradient of the density of states in this pseudogap region facilitates the realization of high thermoelectric properties. Furthermore, the half-width of the peak in the 2θ angle range of 44.5±2.5° in the X-ray diffraction 2θ measurement spectrum is 3° or more. This prevents excessive crystallinity and promotes amorphization. Therefore, an increase in thermal conductivity can be suppressed. Furthermore, the half-width of the peak in the 2θ angle range of 44.5±2.5° in the X-ray diffraction 2θ measurement spectrum is 7° or less. This prevents the short-range order of the atoms in the base material 12 from being disrupted, thereby preventing the band structure from collapsing. As a result, the thermoelectric conversion material 11 can improve thermoelectric conversion efficiency.

[0030] In this embodiment, the thermoelectric conversion material 11 contains oxygen and tungsten as a base material. When the thermoelectric conversion material 11 contains oxygen and tungsten, the crystalline structure is easily broken down and the material is easily made amorphous. This reduces the thermal conductivity of the thermoelectric conversion material 11, making it easier to improve the thermoelectric properties. This can further improve the efficiency of thermoelectric conversion.

[0031] In this embodiment, the oxygen content is 4 at % or more and 27 at % or less with respect to the entire thermoelectric conversion material 11. Therefore, by adjusting the oxygen content, it is possible to promote amorphization while suppressing an increase in electrical resistance due to oxidation, and therefore it is possible to appropriately improve the thermoelectric conversion efficiency.

[0032] In this embodiment, the tungsten content is 1.5 at % or more and 16.5 at % or less with respect to the entire thermoelectric conversion material 11. Therefore, by appropriately adjusting the tungsten content, it is possible to promote amorphization while suppressing the collapse of the band structure, and therefore it is possible to appropriately improve the thermoelectric conversion efficiency.

[0033] In this embodiment, the ratio of the peak intensity of the peak in the 2θ angle range of 62.5±2.5° in the X-ray diffraction 2θ measurement spectrum to the peak intensity of the peak in the 2θ angle range of 44.5±2.5° in the X-ray diffraction 2θ measurement spectrum is 0 or more and 0.06 or less. Such thermoelectric conversion material 11 has high amorphousness. Therefore, such thermoelectric conversion material 11 can reliably improve the thermoelectric conversion efficiency.

[0034] In this embodiment, the thermoelectric conversion material 11 includes a silicon substrate 13. The base material 12 is disposed on the silicon substrate 13. Therefore, by disposing the silicon substrate 13 as a substrate underlying the Fe-V-Al-based base material, the base material 12 can be easily made amorphous. This reduces the thermal conductivity of the thermoelectric conversion material 11, thereby further improving the thermoelectric conversion efficiency.

[0035] The physical properties of the obtained thermoelectric conversion material 11 can be measured, for example, by the following method. The content ratio of elements greater than 0.1 at% can be measured, for example, by EDX (Energy Dispersive X-ray spectrometry). EDX was measured by taking a TEM (Transmission Electron Microscope) image of a portion of the thermoelectric conversion material 11. The TEM image was taken using a JEM-2800 (manufactured by JEOL Ltd.) under measurement conditions of an acceleration voltage of 200 kV, a probe size of 0.5 nm, and a CL aperture of 3. The conditions for detecting atoms by EDX were an EDX (manufactured by Thermo Fisher Scientific K.K.) under measurement conditions of a spot size of 0.5 nm, a CL aperture of 3, a mapping analysis mode, and a 20-minute analysis time. The content ratio of elements less than 0.1 at% can be measured, for example, by SIMS (Secondary Ion Mass Spectroscopy). Specifically, the measurement was performed using ADEPT-1010 manufactured by ULVAC, Inc., and the ion source used for the measurement was CsR + ions for the element R.

[0036] The electrical conductivity and Seebeck coefficient were measured using a thermoelectric property measurement device (RZ2001i, manufactured by Ozawa Scientific Co., Ltd.). The measurement method is as follows: First, the thermoelectric conversion material is fixed between a pair of quartz jigs so that it bridges the gap, and the atmosphere is heated in a resistance heating furnace. One end of the quartz jigs is left hollow, and nitrogen gas is passed through it to cool one end of the thermoelectric conversion material. This creates a temperature difference in the thermoelectric conversion material. For the thermoelectric conversion material, a platinum-platinum-rhodium thermocouple (R thermocouple) is used to measure the temperature difference between two points on the surface of the thermoelectric conversion material. A voltmeter is connected to the thermocouple to measure the voltage generated by the temperature difference between the two points. This allows the generated voltage relative to the temperature difference to be measured, which can then be used to estimate the Seebeck coefficient of the material. Resistance is measured using the four-terminal method. That is, two electric wires are connected to the outside of two platinum wires connected to the voltmeter. A current is passed through the wire, and the voltage drop is measured using the internal voltmeter. In this way, the resistance value of the thermoelectric conversion material is measured using the four-terminal method. The conductivity is derived from the measured resistance value. The PF is then calculated based on the obtained conductivity and Seebeck coefficient using the above formula (1).

[0037] Furthermore, the obtained thermoelectric conversion material 11 was evaluated by XRD (X-ray diffraction) to determine its crystallinity and the presence of an Fe-Si phase in the Fe-V-Al base material 12. For XRD, a Bruker D8 Advance was used as the apparatus, with an incident angle of 1°, 2θ measurement from 20° to 70°, Cu Ka radiation (λ=1.5418 Å), and a Ni filter with a thickness of 0.02 mm, and a Gaussian function was fitted to the detected peaks using the least squares method.

[0038] Here, the conversion efficiency η of the temperature difference (thermal energy) into electrical energy using a thermoelectric conversion material is given by the following equation (2):

[0039] η=ΔT / T h (M-1) / (M+T c / T h )···(2)

[0040] η is the conversion efficiency, ΔT is T h and T c The difference between T h is the temperature on the hot side, T c is the temperature on the lower side, and M is (1+ZT) 1 / 2 , ZT=α 2 ST / κ and ZT are dimensionless figures of merit, α is the Seebeck coefficient, S is the electrical conductivity, and κ is the thermal conductivity. The conversion efficiency is a monotonically increasing function of ZT. A high ZT value in the thermoelectric conversion material 11 indicates high thermoelectric conversion efficiency.

[0041] (Example) Here, a number of thermoelectric conversion materials with different oxygen content rates were prepared. The results are shown in Table 1. Sample 1 has an oxygen content rate of 0.1 at%. Sample 2 has an oxygen content rate of 0.5 at%. Sample 3 has an oxygen content rate of 6.2 at%. Sample 4 has an oxygen content rate of 14.5 at%. Sample 5 has an oxygen content rate of 24.8 at%. Sample 6 has an oxygen content rate of 30.1 at%. The composition of the thermoelectric conversion materials was as follows: (Fe2V 0.96 Al1W 0.04 ) x O 1-x It is as follows.

[0042] The crystallinity was evaluated using an X-ray diffractometer, an Empyrean manufactured by Malvern-Panalytical. The tube used was a copper tube with Kα1 radiation. To eliminate the influence of the substrate, the measurement method used the 2θ method, in which the incident angle to the sample was fixed at a shallow angle and the detector angle 2θ relative to the sample surface was varied. The measurement conditions were: the applied voltage and current to the tube were 40 kV and 40 mA, respectively; the X-ray incident angle to the sample was fixed at 2.0°; the detector angle 2θ was scanned from 10° to 120° in 0.02° increments; and the intensity of the X-rays scattered from the sample was obtained.

[0043] For each sample, the full width at half maximum (FWHM)1 of the peak in the 2θ angle range of 44.5±2.5° in the 2θ measurement spectrum of X-ray diffraction, the peak intensity (PI)1, the peak intensity (PI)2 of the peak in the 2θ angle range of 62.5±2.5° in the 2θ measurement spectrum of X-ray diffraction, the ratio of peak intensity (PI) to peak intensity (PI2 / PI), and ZT were calculated. ZT was the value at room temperature (25°C). The same applies to ZT hereinafter.

[0044] Fig. 3 is a graph showing the relationship between the oxygen content (at%) derived from Samples 1 to 6 and ZT, which is a figure of merit. In Fig. 3, the plotted data for Samples 1 to 6 are connected by lines. In Fig. 3, the horizontal axis represents the oxygen content (at%), and the vertical axis represents ZT. The thick horizontal line indicates the plot where ZT is 3.5.

[0045] [Table 1]

[0046] 3, Samples 3, 4, and 5 in particular have a ZT of 3.5 or more, which indicates particularly excellent thermoelectric conversion characteristics. That is, by setting the oxygen content to 4 at % or more and 27 at % or less with respect to the entire thermoelectric conversion material 11, it is possible to more reliably improve the thermoelectric conversion efficiency.

[0047] Next, a number of thermoelectric conversion materials were prepared with varying tungsten content ratios. The results are shown in Table 2. Sample 7 has a tungsten content ratio of 0 at %. In other words, no tungsten is included. Sample 8 has a tungsten content ratio of 2 at %. Sample 9 has a tungsten content ratio of 4 at %. Sample 10 has a tungsten content ratio of 7 at %. Sample 11 has a tungsten content ratio of 15 at %. Sample 12 has a tungsten content ratio of 20 at %. The thermoelectric conversion materials had the following composition: (Fe2V 1-y Al1W y ) 0.95 O 0.05 It is as follows.

[0048] For each sample, the half-width of the peak in the 2θ angle range of 44.5 ± 2.5° in the 2θ measurement spectrum of X-ray diffraction, the peak intensity of the peak in the 2θ angle range of 44.5 ± 2.5° in the 2θ measurement spectrum of X-ray diffraction, the peak intensity of the peak in the 2θ angle range of 62.5 ± 2.5° in the 2θ measurement spectrum of X-ray diffraction, the ratio of the peak intensity of the peak in the 2θ angle range of 62.5 ± 2.5° in the 2θ measurement spectrum to the peak intensity of the peak in the 2θ angle range of 44.5 ± 2.5° in the 2θ measurement spectrum of X-ray diffraction, and ZT were calculated in the same manner as in Table 1.

[0049] FIG. 4 is a graph showing the relationship between the tungsten content (at%) and the figure of merit (ZT) derived from Samples 7 to 12. In FIG. 4, the plotted values ​​for Samples 7 to 12 are connected by lines. In FIG. 4, the horizontal axis represents the tungsten content (at%), and the vertical axis represents ZT. The thick horizontal line represents the plot where ZT is 3.5. FIG. 5 shows the XRD results for Sample 9. In FIG. 5, the peak indicated by arrow D1 is a peak in the 2θ angle range of 44.5±2.5° in the 2θ measurement spectrum of X-ray diffraction. In FIG. 5, the peak indicated by arrow D2 is a peak in the 2θ angle range of 62.5±2.5° in the 2θ measurement spectrum of X-ray diffraction. In FIG. 5, the line indicated by arrow 14 shows the XRD results for Sample 9. For comparison, the line indicated by arrow 15 shows the XRD results for a sample with high crystallinity that does not exhibit high thermoelectric conversion efficiency.

[0050] [Table 2]

[0051] 4 and 5, Samples 8, 9, 10, and 11 have ZT values ​​of 3.5 or more, and exhibit particularly excellent thermoelectric conversion characteristics. That is, by setting the tungsten content to 1.5 at % or more and 16.5 at % or less with respect to the entire thermoelectric conversion material 11, it is possible to more reliably improve the thermoelectric conversion efficiency.

[0052] Next, several thermoelectric conversion materials that did not contain tungsten were prepared. The results are shown in Table 3. Sample 13 did not contain tungsten and had an oxygen content of 0 at %. Sample 14 did not contain tungsten and had an oxygen content of 22 at %. The composition of the thermoelectric conversion materials was (Fe2VAl) 1-x O x It is as follows.

[0053] For each sample, the following were calculated in the same manner as shown in Table 1: the half-width FWHM1 of the peak in the 2θ angle range of 44.5±2.5° in the 2θ measurement spectrum of X-ray diffraction, the peak intensity PI1 of the peak in the 2θ angle range of 44.5±2.5° in the 2θ measurement spectrum of X-ray diffraction, the peak intensity PI2 of the peak in the 2θ angle range of 62.5±2.5° in the 2θ measurement spectrum of X-ray diffraction, the ratio of peak intensity PI1 to peak intensity PI2 (PI2 / PI1), and ZT.

[0054] [Table 3]

[0055] Referring to Table 3, Samples 13 and 14, which do not contain W, have a full width at half maximum (FWHM1) of less than 3 and high crystallinity, resulting in high thermal conductivity. This results in low thermoelectric properties (ZT). This is because W inhibits the atomic bonding of FeV2Al during film formation, causing it to become amorphous.

[0056] (Embodiment 2) Next, a power generating element will be described as one embodiment of a thermoelectric conversion element using the thermoelectric conversion material according to the present disclosure.

[0057] 6 is a schematic diagram showing the structure of a π-type thermoelectric conversion element (power generation element) 21, which is a thermoelectric conversion element in this embodiment. Referring to Fig. 6, the π-type thermoelectric conversion element 21 includes a p-type thermoelectric conversion material part 22, which is a first thermoelectric conversion material part, an n-type thermoelectric conversion material part 23, which is a second thermoelectric conversion material part, a high-temperature side electrode 24, a first low-temperature side electrode 25, a second low-temperature side electrode 26, and wiring 27.

[0058] The material constituting the p-type thermoelectric conversion material section 22 is the thermoelectric conversion material of the first embodiment, whose composition has been adjusted to have a p-type conductivity. Examples of p-type dopants (acceptors) include Ti (titanium) and Zr (zirconium). The thermoelectric conversion material constituting the n-type thermoelectric conversion material section 23 is the thermoelectric conversion material of the first embodiment, whose composition has been adjusted to have an n-type conductivity. Examples of n-type dopants (donors) include Si (silicon), Ge (germanium), Mo (molybdenum), Co (cobalt), and Pt (platinum).

[0059] The p-type thermoelectric conversion material section 22 and the n-type thermoelectric conversion material section 23 are arranged side by side with a gap between them. The high-temperature side electrode 24 is arranged so as to extend from one end 31 of the p-type thermoelectric conversion material section 22 to one end 32 of the n-type thermoelectric conversion material section 23. The high-temperature side electrode 24 is arranged so as to contact both one end 31 of the p-type thermoelectric conversion material section 22 and one end 32 of the n-type thermoelectric conversion material section 23. The high-temperature side electrode 24 is arranged so as to connect one end 31 of the p-type thermoelectric conversion material section 22 to one end 32 of the n-type thermoelectric conversion material section 23. The high-temperature side electrode 24 is made of a conductive material, for example, a metal. The high-temperature side electrode 24 is in ohmic contact with the p-type thermoelectric conversion material section 22 and the n-type thermoelectric conversion material section 23.

[0060] The first low-temperature side electrode 25 is arranged in contact with the other end 33 of the p-type thermoelectric conversion material part 22. The first low-temperature side electrode 25 is arranged apart from the high-temperature side electrode 24. The first low-temperature side electrode 25 is made of a conductive material, for example, a metal. The first low-temperature side electrode 25 is in ohmic contact with the p-type thermoelectric conversion material part 22.

[0061] The second low-temperature side electrode 26 is arranged in contact with the other end 34 of the n-type thermoelectric conversion material part 23. The second low-temperature side electrode 26 is arranged apart from the high-temperature side electrode 24 and the first low-temperature side electrode 25. The second low-temperature side electrode 26 is made of a conductive material, for example, a metal. The second low-temperature side electrode 26 is in ohmic contact with the n-type thermoelectric conversion material part 23.

[0062] The wiring 27 is made of a conductor such as metal, etc. The wiring 27 electrically connects the first low-temperature side electrode 25 and the second low-temperature side electrode 26 together.

[0063] In the π-type thermoelectric conversion element 21, for example, when a temperature difference is created such that one end 31 of the p-type thermoelectric conversion material section 22 and one end 32 of the n-type thermoelectric conversion material section 23 are at a high temperature, and the other end 33 of the p-type thermoelectric conversion material section 22 and the other end 34 of the n-type thermoelectric conversion material section 23 are at a low temperature, p-type carriers (holes) move from one end 31 to the other end 33 in the p-type thermoelectric conversion material section 22. At this time, n-type carriers (electrons) move from one end 32 to the other end 34 in the n-type thermoelectric conversion material section 23. As a result, a current flows through the wiring 27 in the direction of arrow I. In this way, the π-type thermoelectric conversion element 21 generates electricity through thermoelectric conversion using the temperature difference. That is, the π-type thermoelectric conversion element 21 is a power generation element.

[0064] The thermoelectric conversion material of the first embodiment, which can achieve a high ZT, is used as the material for forming the n-type thermoelectric conversion material portion 23. As a result, the π-type thermoelectric conversion element 21 is a highly efficient power generating element.

[0065] In the above embodiment, a π-type thermoelectric conversion element has been described as an example of the thermoelectric conversion element of the present disclosure, but the thermoelectric conversion element of the present disclosure is not limited to this. The thermoelectric conversion element of the present disclosure may be a thermoelectric conversion element having another structure, such as an I-type (uni-leg) thermoelectric conversion element.

[0066] (Embodiment 3) A power generation module serving as a thermoelectric conversion module can be obtained by electrically connecting a plurality of π-type thermoelectric conversion elements 21. The power generation module 41, which is a thermoelectric conversion module of this embodiment, has a structure in which a plurality of π-type thermoelectric conversion elements 21 are connected in series.

[0067] FIG. 7 is a diagram illustrating an example of the structure of a power generation module. Referring to FIG. 7, a power generation module 41 according to this embodiment includes a p-type thermoelectric conversion material portion 22, an n-type thermoelectric conversion material portion 23, low-temperature-side electrodes 25 and 26 corresponding to the first low-temperature-side electrode 25 and the second low-temperature-side electrode 26, a high-temperature-side electrode 24, a low-temperature-side insulator substrate 28, and a high-temperature-side insulator substrate 29. The low-temperature-side insulator substrate 28 and the high-temperature-side insulator substrate 29 are made of ceramic such as alumina. The p-type thermoelectric conversion material portion 22 and the n-type thermoelectric conversion material portion 23 are arranged alternately. The low-temperature-side electrodes 25 and 26 are arranged in contact with the p-type thermoelectric conversion material portion 22 and the n-type thermoelectric conversion material portion 23, similar to the π-type thermoelectric conversion element 21 described above. The high-temperature-side electrode 24 is arranged in contact with the p-type thermoelectric conversion material portion 22 and the n-type thermoelectric conversion material portion 23, similar to the π-type thermoelectric conversion element 21 described above. The p-type thermoelectric conversion material section 22 is connected to the adjacent n-type thermoelectric conversion material section 23 on one side by a common high-temperature electrode 24. The p-type thermoelectric conversion material section 22 is also connected to the adjacent n-type thermoelectric conversion material section 23 on a side different from the one side by common low-temperature electrodes 25, 26. In this way, all of the p-type thermoelectric conversion material sections 22 and n-type thermoelectric conversion material sections 23 are connected in series.

[0068] The low-temperature-side insulator substrate 28 is arranged on the main surface side opposite to the side in contact with the p-type thermoelectric conversion material section 22 and the n-type thermoelectric conversion material section 23 of the plate-shaped low-temperature-side electrodes 25, 26. One low-temperature-side insulator substrate 28 is arranged for each of the plurality (all) of low-temperature-side electrodes 25, 26. The high-temperature-side insulator substrate 29 is arranged on the side opposite to the side in contact with the p-type thermoelectric conversion material section 22 and the n-type thermoelectric conversion material section 23 of the plate-shaped high-temperature-side electrode 24. One high-temperature-side insulator substrate 29 is arranged for each of the plurality (all) of high-temperature-side electrodes 24.

[0069] Wiring 27 is connected to high-temperature side electrode 24 or low-temperature side electrodes 25, 26 that contact p-type thermoelectric conversion material section 22 or n-type thermoelectric conversion material section 23 located at both ends of p-type thermoelectric conversion material section 22 and n-type thermoelectric conversion material section 23 connected in series. When a temperature difference is created such that high-temperature side insulator substrate 29 side is high temperature and low-temperature side insulator substrate 28 side is low temperature, current flows in the direction of arrow I through p-type thermoelectric conversion material section 22 and n-type thermoelectric conversion material section 23 connected in series, as in the case of above-mentioned π-type thermoelectric conversion element 21. In this way, power generation is achieved in power generation module 41 by thermoelectric conversion utilizing the temperature difference.

[0070] (Fourth embodiment) Next, an infrared sensor, which is an optical sensor, will be described as another embodiment of a thermoelectric conversion element using the thermoelectric conversion material according to the present disclosure.

[0071] Fig. 8 is a diagram showing an example of the structure of infrared sensor 51. Referring to Fig. 8, infrared sensor 51 includes a p-type thermoelectric conversion material part 52 and an n-type thermoelectric conversion material part 53 arranged adjacent to each other. P-type thermoelectric conversion material part 52 and n-type thermoelectric conversion material part 53 are formed on substrate 54.

[0072] The infrared sensor 51 includes a substrate 54, an etching stop layer 55, an n-type thermoelectric conversion material layer 56, and an n + The semiconductor device includes an n-side ohmic contact layer 57, an insulator layer 58, a p-type thermoelectric conversion material layer 59, an n-side ohmic contact electrode 61, a p-side ohmic contact electrode 62, a heat absorption pad 63, an absorber 64, and a protective film 65.

[0073] The substrate 54 is made of an insulator such as silicon dioxide. A recess 66 is formed in the substrate 54. The etching stop layer 55 is formed to cover the surface of the substrate 54. The etching stop layer 55 is made of an insulator such as silicon nitride. A gap is formed between the etching stop layer 55 and the recess 66 of the substrate 54.

[0074] The n-type thermoelectric conversion material layer 56 is formed on the main surface of the etching stop layer 55 opposite to the substrate 54. The thermoelectric conversion material constituting the n-type thermoelectric conversion material layer 56 is the thermoelectric conversion material of the first embodiment. + The n-type ohmic contact layer 57 is formed on the main surface of the n-type thermoelectric conversion material layer 56 opposite to the etching stop layer 55. + The n-type ohmic contact layer 57 is doped with n-type impurities that generate n-type carriers (electrons), which are majority carriers. + The conductivity type of the ohmic contact layer 57 is n-type.

[0075] n + An n-side ohmic contact electrode 61 is disposed so as to be in contact with the center of the main surface of the n-type ohmic contact layer 57 opposite to the n-type thermoelectric conversion material layer 56. The n-side ohmic contact electrode 61 is + The n-type ohmic contact layer 57 is made of a material that can make ohmic contact with the n-type ohmic contact layer 57, such as a metal. + An insulator layer 58 made of an insulator such as silicon dioxide is disposed on the main surface of the n-type ohmic contact layer 57 opposite to the n-type thermoelectric conversion material layer 56. The insulator layer 58 is disposed on the n-side ohmic contact electrode 61 on the p-type thermoelectric conversion material portion 52 side. + The ohmic contact layer 57 is disposed on the major surface of the ohmic contact layer 57 .

[0076] n + A protective film 65 is further disposed on the main surface of the n-type ohmic contact layer 57 opposite the n-type thermoelectric conversion material layer 56. The protective film 65 is disposed on the n-side ohmic contact electrode 61 opposite the p-type thermoelectric conversion material layer 52. + The n-type ohmic contact layer 57 is disposed on the main surface of the n-type ohmic contact layer 57. + On the main surface of the n-type ohmic contact layer 57 opposite to the n-type thermoelectric conversion material layer 56, another n-side ohmic contact electrode 61 is arranged on the opposite side to the n-side ohmic contact electrode 61 with a protective film 65 sandwiched therebetween.

[0077] n of the insulator layer 58 +A p-type thermoelectric conversion material layer 59 is disposed on the main surface opposite to the p-type ohmic contact layer 57 .

[0078] A protective film 65 is disposed in the center of the main surface of the p-type thermoelectric conversion material layer 59 opposite the insulator layer 58. A pair of p-side ohmic contact electrodes 62 are disposed on the main surface of the p-type thermoelectric conversion material layer 59 opposite the insulator layer 58, sandwiching the protective film 65 therebetween. The p-side ohmic contact electrodes 62 are made of a material, such as a metal, that can make ohmic contact with the p-type thermoelectric conversion material layer 59. Of the pair of p-side ohmic contact electrodes 62, the p-side ohmic contact electrode 62 on the n-type thermoelectric conversion material portion 53 side is connected to the n-side ohmic contact electrode 61.

[0079] The p-side ohmic contact electrode 62 and the n-side ohmic contact electrode 61 are connected to each other. + An absorber 64 is disposed so as to cover the main surface opposite the n-type ohmic contact layer 57. The absorber 64 is made of, for example, titanium. A heat absorption pad 63 is disposed so as to be in contact with the p-side ohmic contact electrode 62 on the side not connected to the n-side ohmic contact electrode 61. In addition, a heat absorption pad 63 is disposed so as to be in contact with the n-side ohmic contact electrode 61 on the side not connected to the p-side ohmic contact electrode 62. Au (gold) / Ti (titanium), for example, is used as a material for forming the heat absorption pad 63. That is, the absorber 64 and the n-type thermoelectric conversion material layer 56 are thermally connected. The absorber 64 and the p-type thermoelectric conversion material layer 59 are thermally connected.

[0080] When infrared rays are irradiated onto the infrared sensor 51, the absorber 64 absorbs the infrared energy. As a result, the temperature of the absorber 64 rises. Meanwhile, the temperature rise of the heat absorption pad 63 is suppressed. Therefore, a temperature difference is generated between the absorber 64 and the heat absorption pad 63. Then, in the p-type thermoelectric conversion material layer 59, p-type carriers (holes) move from the absorber 64 side toward the heat absorption pad 63 side. Meanwhile, in the n-type thermoelectric conversion material layer 56, n-type carriers (electrons) move from the absorber 64 side toward the heat absorption pad 63 side. Then, the infrared rays are detected by extracting a current generated as a result of the carrier movement from the n-side ohmic contact electrode 61 and the p-side ohmic contact electrode 62.

[0081] In infrared sensor 51 of the present embodiment, the thermoelectric conversion material of embodiment 1 is used as the thermoelectric conversion material that constitutes n-type thermoelectric conversion material layer 56. As a result, infrared sensor 51 is a highly sensitive infrared sensor.

[0082] (Other embodiments) In the above embodiment, the thermoelectric conversion material is manufactured by depositing a base material on a silicon substrate, but this is not limited to this. The thermoelectric conversion material may be manufactured by depositing a base material on another substrate, or the thermoelectric conversion material may not include a silicon substrate.

[0083] In the above-described embodiment, the thermoelectric conversion material may be configured to contain neither oxygen nor tungsten.

[0084] It should be understood that the embodiments disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is defined not by the above description but by the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0085] 11 Thermoelectric conversion materials 12 Base material 13 Silicon substrate 14,15 Arrows D1, D2 arrows 21 π-type thermoelectric conversion element 22,52 p-type Thermoelectric Materials Department 23,53 n-Type Thermoelectric Materials Department 24 High temperature side electrode 25 1st low temperature side electrode (low temperature side electrode) 26 2nd low temperature side electrode (low temperature side electrode) 27, 42, 43 Wiring 28 Low temperature side insulator substrate 29 High temperature side insulator substrate 31, 32, 33, 34 End 41 Thermoelectric conversion module 51 Infrared sensor 54 PCB 55 Etching stop layer 56 n-type thermoelectric conversion material layer 57n + Ohmic contact layer 58 Insulator Layer 59 p-type thermoelectric conversion material layer 61 n-side ohmic contact electrode 62 p-side ohmic contact electrode 63 Heat absorption pad 64 Absorber 65 Protective film 66 Recess I arrow.

Claims

1. The base material includes iron, vanadium, and aluminum, A thermoelectric conversion material, in which the half-width of a peak in a 2θ angle range of 44.5±2.5° in an X-ray diffraction 2θ measurement spectrum is 3° or more and 7° or less.

2. Oxygen and The thermoelectric conversion material according to claim 1 , further comprising tungsten as the base material.

3. 3. The thermoelectric conversion material according to claim 2, wherein the oxygen content is 4 at % or more and 27 at % or less with respect to the entire thermoelectric conversion material.

4. 4. The thermoelectric conversion material according to claim 2, wherein the content of the tungsten is 1.5 at % or more and 16.5 at % or less with respect to the entire thermoelectric conversion material.

5. 3. The thermoelectric conversion material according to claim 1, wherein a ratio of a peak intensity of a peak in a 2θ angle range of 62.5±2.5° in an X-ray diffraction 2θ measurement spectrum to a peak intensity of a peak in a 2θ angle range of 44.5±2.5° in an X-ray diffraction 2θ measurement spectrum is 0 or more and 0.06 or less.

6. further comprising a silicon substrate; The thermoelectric conversion material according to claim 1 or 2, wherein the base material is disposed on the silicon substrate.

7. Thermoelectric Materials Department, a first electrode disposed in contact with the thermoelectric conversion material portion; a second electrode in contact with the thermoelectric conversion material portion and disposed apart from the first electrode, 3. A thermoelectric conversion element, comprising the thermoelectric conversion material according to claim 1 or 2, wherein the material constituting the thermoelectric conversion material portion has a conductivity type of p-type or n-type.

8. A thermoelectric conversion module comprising the thermoelectric conversion element according to claim 7 .

9. an absorber that absorbs light energy; a thermoelectric conversion material portion connected to the absorber, 3. The optical sensor according to claim 1, wherein the material constituting the thermoelectric conversion material portion is a thermoelectric conversion material having a conductivity type of p-type or n-type.

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