Thermoelectric material, its manufacturing method, and thermoelectric power generation element

Abstract

To provide a thermoelectric material having excellent thermoelectric properties at room temperature, a method for manufacturing the same, and a thermoelectric generating element thereof.SOLUTION: A thermoelectric material according to an embodiment of the present invention includes an inorganic compound containing magnesium (Mg), antimony (Sb) and / or bismuth (Bi), copper (Cu), and optionally M (M is at least one element selected from the group consisting of selenium (Se) and tellurium (Te)), and the inorganic compound is represented by MgaSb2-b-cBibMcCud, and parameters a, b, c, and d satisfy 3≤a≤3.5, 0≤b≤2, 0≤c≤0.06, 0<d≤0.1, and b+c≤2.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a thermoelectric material, a manufacturing method thereof, and a thermoelectric power generation element, and more particularly to a thermoelectric material containing an Mg3Bi2-based thermoelectric material, a manufacturing method thereof, and a thermoelectric power generation element. [Background technology]

[0002] Even in Japan, where energy conservation has progressed particularly well compared to other countries in the world, approximately three-quarters of the primary energy supply is currently discarded as thermal energy in waste heat recovery. Under these circumstances, thermoelectric power generation elements are attracting attention as solid-state elements that can recover thermal energy and directly convert it into electrical energy.

[0003] Thermoelectric power generation elements are elements that directly convert energy into electricity, and have the advantage of being easy to maintain due to the lack of moving parts, as well as being highly scalable. For this reason, active research is being conducted into thermoelectric semiconductors as materials for use as power sources for IoT devices, etc.

[0004] For IoT power supply applications, practical use near room temperature is expected, but the thermoelectric material with the highest performance near room temperature is a Bi2Te3-based material, and the rarity of Te poses a problem for widespread practical use. However, there are few materials other than these Te compounds that offer relatively high performance at room temperature, which has been a problem, but Mg3Sb2-based materials have been raised as one candidate (see, for example, Patent Documents 1 and 2 and Non-Patent Document 1).

[0005] Non-patent document 1 describes Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 In this paper, we report a doped thermoelectric material in which the magnesium (Mg) site of the above-mentioned material is doped with Fe, Co, Hf, and Te (see, for example, Patent Document 1). According to Non-Patent Document 1, the parent phase is an Mg3Sb2 system with Mg 3.2 Sb 1.5 Bi 0.5 Te 0.01It is disclosed that by doping a small amount of the above-mentioned metal elements into the Mg site of the thermoelectric material, the electrical conductivity and Seebeck coefficient of the thermoelectric material are increased, and the figure of merit is improved.

[0006] Patent Document 1 describes Mg 3+m A a B b D 2-e E e wherein element A represents at least one element selected from the group consisting of Ca, Sr, Ba, and Yb, element B represents at least one element selected from the group consisting of Mn and Zn, the value of m is −0.39 or more and 0.42 or less, the value of a is 0 or more and 0.12 or less, the value of b is 0 or more and 0.48 or less, element D represents at least one element selected from the group consisting of Sb and Bi, element E represents at least one element selected from the group consisting of Se and Te, and the value of e is 0.001 or more and 0.06 or less.

[0007] Patent Document 2 describes Mg 3+m-a A a B 2-c-e C c E e wherein element A represents at least one element selected from the group consisting of Ca, Sr, Ba, Nb, Zn, and Al, element B represents at least one element selected from the group consisting of Sb and Bi, element C represents at least one element selected from the group consisting of Mn, Si, and Cr, element E represents at least one element selected from the group consisting of Se and Te, and the value of m is -0.1 or more and 0.4 or less, the value of a is 0 or more and 0.1 or less, the value of c is 0 or more and 0.1 or less, and the value of e is 0.01 or more and 0.06 or less.

[0008] Patent Documents 1 and 2 and Non-Patent Document 1 also disclose combinations of various materials, but the values ​​of the power factor and dimensionless figure of merit ZT at room temperature are particularly insufficient. Considering IoT power generation applications, the value of 14 μW cm at room temperature is -1 K -2It is expected that thermoelectric materials with high power factors exceeding 0.1 and dimensionless figure of merit ZT exceeding 0.3 will be developed. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2017 / 072982 [Patent Document 2] Japanese Patent Application Publication No. 2018-190953 [Non-patent literature]

[0010] [Non-Patent Document 1] Jun Mao et al., PNAS, 114(40), 10548-10553, 2017 Summary of the Invention [Problem to be solved by the invention]

[0011] In view of the above, an object of the embodiments of the present invention is to provide a thermoelectric material having excellent thermoelectric properties at room temperature, a method for producing the same, and a thermoelectric power generating element using the same. [Means for solving the problem]

[0012] In an embodiment of the present invention, the thermoelectric material comprises an inorganic compound containing magnesium (Mg), antimony (Sb) and / or bismuth (Bi), copper (Cu), and optionally M (wherein M is at least one element selected from the group consisting of selenium (Se) and tellurium (Te)), and the inorganic compound is Mg a Sb 2-b-c Bi b M c Cu d and the parameters a, b, c and d are 3≦a≦3.5, 0≦b≦2, 0≦c≦0.06, 0 <d≦0.1、および、 b+c≦2 The above problem is solved. The parameter d is 0.005≦d≦0.05 may be satisfied. The parameters a, b, c and d are 3≦a≦3.5, 0.2≦b≦0.7, 0≦c≦0.06, and 0.005≦d≦0.05 may be satisfied. The inorganic compound may have a La2O3 type structure and have space group P-3m1 symmetry. The Cu may be interstitially dissolved in the La2O3 type structure. The thermoelectric material may be n-type. The thermoelectric material may be in a form selected from the group consisting of a powder, a sintered body, and a thin film. The thermoelectric material may be in the form of a powder or a sintered body, and the inorganic compound may be composed of crystal grains having an average grain size in the range of 3.5 μm to 30 μm. The inorganic compound may be composed of crystal grains having an average grain size in the range of 4 μm to 20 μm. The thermoelectric material is in the form of a thin film, and the inorganic compound is composed of crystal grains having an average grain size in the range of 3.5 μm to 30 μm, and may further contain an organic material. In an embodiment of the present invention, the method for producing the thermoelectric material may include mixing a raw material containing magnesium (Mg), a raw material containing antimony (Sb) and / or a raw material containing bismuth (Bi), a raw material containing copper (Cu), and, if necessary, a raw material containing M (wherein M is at least one element selected from the group consisting of selenium (Se) and tellurium (Te)), to prepare a mixture, and sintering the mixture. The sintering may be spark plasma sintering. The discharge plasma sintering may be performed at a temperature range of 723 K or higher and 1173 K or lower, under a pressure of 30 MPa or higher and 100 MPa or lower, for a time of 1 minute or longer and 10 minutes or shorter. The method may further include pulverizing the sintered body obtained by the sintering. The method may further include mixing the powder obtained by the pulverizing and an organic material. The method may further include performing a physical vapor deposition method using the sintered body obtained by the sintering as a target. In an embodiment of the present invention, the thermoelectric power generation element includes a p-type thermoelectric material and an n-type thermoelectric material connected in series alternately, and the n-type thermoelectric material may be the above thermoelectric material. The above problem is solved.

Advantages of the Invention

[0013] In an embodiment of the present invention, the thermoelectric material includes an inorganic compound containing magnesium (Mg), antimony (Sb) and / or bismuth (Bi), copper (Cu), and optionally M (where M is an element selected from at least one of the group consisting of selenium (Se) and tellurium (Te)). The inorganic compound is represented by Mg a Sb 2-b-c Bi b M c Cu d and satisfies 3 ≦ a ≦ 3.5, 0 ≦ b ≦ 2, 0 ≦ c ≦ 0.06, 0 < d ≦ 0.1, and b + c ≦ 2. Thus, by adding Cu to an inorganic compound having Mg, Sb and / or Bi, and M as a matrix phase, an improvement in electrical conductivity at room temperature, an effective reduction in thermal conductivity, and a thermoelectric material with an improved figure of merit can be provided. Such a thermoelectric material is advantageous for a thermoelectric power generation element.

[0014] In an embodiment of the present invention, a method for producing a thermoelectric material includes mixing a raw material containing magnesium (Mg), a raw material containing antimony (Sb) and / or a raw material containing bismuth (Bi), a raw material containing copper (Cu), and, if necessary, a raw material containing M (wherein M is at least one element selected from the group consisting of selenium (Se) and tellurium (Te)), to prepare a mixture, and sintering this mixture to obtain the above-mentioned thermoelectric material, which is therefore highly versatile. [Brief explanation of the drawings]

[0015] [Figure 1A] 1 is a flowchart illustrating a process for manufacturing a thermoelectric material according to an embodiment of the present invention. [Figure 1B] Schematic diagram of Mg3(Sb,Bi)2-based crystals with La2O3-type structure [Figure 2A] Schematic diagram showing a thermoelectric power generation element (π-shaped) using a thermoelectric material in an embodiment of the present invention. [Figure 2B] Schematic diagram showing a thermoelectric generation element (U-shaped) using thermoelectric materials in an embodiment of the present invention. [Figure 2C] Schematic diagram showing thin film production using thermoelectric materials in an embodiment of the present invention. [Figure 2D] Schematic diagram showing powder, a powder compactor, a sintering furnace, and a sintered body using a thermoelectric material in an embodiment of the present invention. [Figure 3] Figure showing the appearance of the sample in Example 1 [Figure 4] 1 shows SEM images and EDS mapping of samples from Examples 1 to 5. [Figure 5] EBSD image of the sample in Example 2 [Figure 6] EBSD image of the sample in Example 5 [Figure 7] 1 shows XRD patterns of samples from Examples 1 to 5. [Figure 8] FIG. 10 shows the Cu addition amount dependence of the lattice constant of the samples of Examples 1 to 5. [Figure 9] Graph showing the temperature dependence of electrical conductivity of samples in Examples 1 to 5 [Figure 10]FIG. 10 shows the dependence of carrier concentration and mobility on the amount of Cu added in samples of Examples 1 to 5. [Figure 11] FIG. 1 shows the temperature dependence of the Seebeck coefficient of the samples of Examples 1 to 5. [Figure 12] FIG. 1 shows the temperature dependence of the electrical output factors of the samples of Examples 1 to 5. [Figure 13] FIG. 1 shows the temperature dependence of the total thermal conductivity of samples from Examples 1 to 5. [Figure 14] FIG. 1 shows the temperature dependence of the lattice thermal conductivity of samples in Examples 1 to 5. [Figure 15] FIG. 10 shows the temperature dependence of the dimensionless figure of merit ZT of the samples of Examples 1 to 5. [Figure 16] Graph showing the temperature dependence of electrical conductivity of samples in Examples 6 and 7 [Figure 17] FIG. 10 shows the temperature dependence of the Seebeck coefficient of the samples of Examples 6 and 7. [Figure 18] FIG. 1 shows the temperature dependence of the electrical output factors of the samples of Examples 6 and 7. [Figure 19] FIG. 10 shows the temperature dependence of the total thermal conductivity of samples from Examples 6 to 7. [Figure 20] FIG. 1 shows the temperature dependence of the lattice thermal conductivity of samples in Examples 6 and 7. [Figure 21] FIG. 10 shows the temperature dependence of the dimensionless figure of merit ZT of the samples of Examples 6 and 7. [Figure 22] FIG. 10 shows the temperature dependence of the electrical conductivity of samples in Examples 8 to 10. [Figure 23] FIG. 10 shows the temperature dependence of the Seebeck coefficient of the samples of Examples 8 to 10. [Figure 24] FIG. 10 is a diagram showing the temperature dependence of the electrical output factors of the samples of Examples 8 to 10. [Figure 25] FIG. 10 shows the temperature dependence of the total thermal conductivity of samples from Examples 8 to 10. [Figure 26] FIG. 10 shows the temperature dependence of the lattice thermal conductivity of samples in Examples 8 to 10. [Figure 27] FIG. 10 shows the temperature dependence of the dimensionless figure of merit ZT of the samples of Examples 8 to 10. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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.

[0017] (Embodiment 1) In an embodiment of the present invention, the thermoelectric material comprises an inorganic compound containing magnesium (Mg), antimony (Sb) and / or bismuth (Bi), copper (Cu), and optionally M (wherein M is at least one element selected from the group consisting of selenium (Se) and tellurium (Te)).

[0018] Inorganic compounds include Mg a Sb 2-b-c Bi b M c Cu d The parameters a to d are expressed as follows: 3≦a≦3.5, 0≦b≦2, 0≦c≦0.06, 0 <d≦0.1、および、 b+c≦2 By using such a composition, the thermoelectric material may be configured as a whole, such as an inorganic compound having a composition in which an inorganic compound consisting of Mg, Sb and / or Bi, and M is used as a parent phase and Cu is added to the parent phase. In this way, a thermoelectric material can be provided that has improved electrical conductivity, particularly at room temperature (a temperature range of 273 K or higher and 320 K or lower), effectively reduced thermal conductivity, and an improved figure of merit. In an embodiment of the present invention, by satisfying the above-mentioned composition, the thermoelectric material can function as an n-type thermoelectric material having electrons as carriers.

[0019] The inorganic compound matrix is ​​preferably Mg a Sb 2-b-c Bi b M cand Cu may be added thereto. Here, the parent phase is preferably an Mg3Sb2-based crystal, has a La2O3-type structure, and belongs to the P-3m1 space group (164th in the International Tables for Crystallography). In this specification, "-3" represents "3 with an overbar."

[0020] The Mg3Sb2 system is composed of the above elements (e.g., Mg, Sb, Bi, Se, Te), and may have the above crystal structure (e.g., La2O3 type structure) and space group (e.g., P-3m1 space group). Other than that, there are no particular limitations, but examples include Mg3Sb2, Mg 3.2 (Sb,Bi)2, Mg 3.2 Examples include ((Sb,Bi),M)2. When written as (Sb,Bi), it means that Sb and Bi occupy the site where Sb and Bi occupy without distinction, and when written as ((Sb,Bi),M), it means that Sb and / or Bi and M occupy the site where Sb and / or Bi occupy without distinction. Here, M is at least one element selected from the group consisting of Se and Te. Mg 3.2 Exemplary compositions of (Sb,Bi)2 include Mg 3.2 Sb 1.5 Bi 0.5 There is Mg 3.2 Exemplary compositions of ((Sb,Bi),M) include Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 These may all have the above-mentioned crystal structure and space group, and the so-called excess components may constitute so-called defects in a part of the crystal structure, and may impart properties such as n-type to the inorganic compound as a whole.

[0021] In the examples of the present invention, the Mg3Sb2-based crystal has a La2O3-type structure and belongs to the P-3m1 space group. Figure 1B shows a schematic diagram of the crystal structure of an Mg3Sb2-based crystal. The constituent elements of the Mg3Sb2-based crystal may be replaced by other elements or may form solid solutions as interstitial atoms (e.g., Cu). In such cases, the lattice constants may change, but the atomic positions determined by the crystal structure, the sites occupied by the atoms, and their coordinates are unlikely to change significantly enough to break the chemical bonds between the backbone atoms. In the examples of the present invention, the inorganic compound obtained can be determined to be an Mg3Sb2-based crystal if the lattice constants determined by Rietveld analysis of the X-ray diffraction or neutron diffraction results in the P-3m1 space group are within ±5% of the theoretical values ​​(a = 4.582 Å, b = 4.582 Å, c = 7.244 Å).

[0022] In the present embodiment, Mg a Sb 2-b-c Bi b M cThe matrix phase represented by may be a Mg3Sb2-based crystal, but Sb and Bi may be completely mutually substitutable. For example, the Mg3Sb2-based crystal may include a Mg3Bi2 crystal structure. For example, the parameter b may include 0 and be greater than or equal to that. It may be 0.2 or more. It may also be 2 or less. It may also be 0.7 or less. Also, c representing the component amount of M(Se and / or Te) may include 0 and be greater than or equal to that. It may be 0.06 or less. The addition of M may endow an inorganic compound having some properties without causing destruction of the crystal structure of the Mg3Sb2-based crystal of the matrix phase. The parameter d representing the component amount of Cu is greater than 0. More preferably, it may be 0.001 or more, and may be 0.005 or more. The parameter d is 0.1 or less, but preferably may be 0.05 or less, 0.025 or less. Also, it may satisfy the range of 0 < d ≦ 0.1, and preferably may satisfy the range of 0.005 ≦ d ≦ 0.05. Within such a range, the electrical conductivity at room temperature can be further improved, the thermal conductivity can also be further reduced, and the figure of merit can be improved. The parameter d more preferably may satisfy the range of 0.005 ≦ d ≦ 0.025. Within this range, the figure of merit at room temperature can be improved.

[0023] The parameters a to d are preferably 3 ≦ a ≦ 3.5, 0.2 ≦ b ≦ 0.7, 0 ≦ c ≦ 0.06, and, 0.005 ≦ d ≦ 0.05 is satisfied. By making it such a composition, the electrical conductivity at room temperature can be further improved, the thermal conductivity can also be further reduced, and the figure of merit can be improved.

[0024] It is believed that Cu atoms are preferably interstitially dissolved in the La2O3-type structure. It has generally been thought that elements added to Mg3Sb2-based crystals substitute for some of the elements that make up the crystal structure, and that this also affects the crystal structure of the resulting inorganic compound. However, the present inventors have discovered that adding Cu can promote grain growth and grain boundary modification of the material. Such grain growth and grain boundary modification contribute to the carrier scattering mechanism, reducing scattering at relatively low temperatures such as room temperature (below 500 K), which is thought to reduce electrical resistance at room temperature, improve electrical conductivity, and potentially improve thermoelectric performance.

[0025] The presence of interstitial Cu atoms in the solid solution can be determined by measuring the changes in the a-axis and c-axis lattice constants of the resulting inorganic compound using powder X-ray diffraction. If Mg3Sb2-based crystals are identified from the resulting inorganic compound and the lattice constants (e.g., a, c) determined by Rietveld analysis are larger than those of the corresponding inorganic compound without Cu, it may be possible to determine that Cu has formed an interstitial solid solution.

[0026] In an embodiment of the present invention, the thermoelectric material may be in a form selected from the group consisting of powder, sintered body, and thin film, which allows it to be applied to various thermoelectric power generation elements that exhibit high thermoelectric performance at room temperature.

[0027] In the embodiments of the present invention, when the thermoelectric material is a powder or a sintered body, the inorganic compound may be composed of crystal grains having an average grain size in the range of 3.5 μm to 30 μm. This can enhance the scattering effect, improve the electrical conductivity at room temperature, and improve the thermoelectric performance. More preferably, the inorganic compound may be composed of crystal grains having an average grain size in the range of 4 μm to 20 μm. This can further enhance the scattering effect, improve the electrical conductivity at room temperature, and reduce the thermal conductivity despite the larger grain size, thereby further improving the thermoelectric performance. Even more preferably, the inorganic compound may be composed of crystal grains having an average grain size in the range of 4 μm to 10 μm.

[0028] In this specification, the average grain size of crystal grains is analyzed and calculated using image analysis software (HKL CHANNEL5, HKL Tango, ver. 5.12.72.0, Oxford Instruments) attached to an electron backscatter diffraction (EBSD) measuring device.

[0029] In embodiments of the present invention, the thermoelectric material may be in the form of a thin film. The thin film may be a crystalline thin film formed by physical vapor deposition, as described below, or may be a thin film containing the above-mentioned powder. Here, the term "powder" generally refers to powder that has been crushed into small pieces or powder. A powder compact can be formed by pressing the powder using a press, such as a powder compactor. Generally, a powder compact refers to a powder compressed into a predetermined shape. When heated at a temperature below the melting point of the powder components, the contact surfaces of the powder particles adhere to each other, and the powder compact shrinks and densifies with increasing heating time. This phenomenon is called sintering, and the product obtained by sintering can also be called a sintered body. The term "thin film" refers to a thin film and may include a layer formed by condensation of a gas phase on a solid surface.

[0030] In an embodiment of the present invention, when the thermoelectric material is a film containing an inorganic compound powder, the powder is mixed with an organic material and processed into a film. In this case, the organic material can be at least one selected from the group consisting of poly(3,4-ethylenedioxythiophene)polystyrenesulfonate (PEDOT:PSS), poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT), polyaniline (PANI), tetrathiafulvalene (TTF), and benzodifurandione paraphenylenevinylidene (BDPPV). These organic materials can provide a flexible film-like thermoelectric material.

[0031] In this case, the powder content is not particularly limited as long as a film can be formed, but the powder content is preferably in the range of 4% by mass to 80% by mass, more preferably 4% by mass to 50% by mass, even more preferably 4% by mass to 10% by mass, and even more preferably 4% by mass to 7% by mass, relative to the organic material. This allows for a flexible film with thermoelectric performance.

[0032] In the embodiments of the present invention, the thermoelectric material can have improved electrical conductivity and effectively reduced thermal conductivity, particularly at room temperature, thereby improving the figure of merit. The addition of Cu does not impair the inherently excellent figure of merit of Mg3Sb2-based materials at high temperatures (e.g., 573 K).

[0033] Next, an exemplary method for producing a thermoelectric material in accordance with this embodiment of the present invention will be described. FIG. 1A is a flow chart illustrating a process for fabricating a thermoelectric material in accordance with an embodiment of the present invention.

[0034] Step S110: A raw material containing magnesium (Mg), a raw material containing antimony (Sb) and / or a raw material containing bismuth (Bi), a raw material containing copper (Cu), and, if necessary, a raw material containing M (wherein M is at least one element selected from the group consisting of selenium (Se) and tellurium (Te)) are mixed to prepare a mixture. Step S120: The mixture obtained in step S110 is fired.

[0035] In the embodiment of the present invention, the thermoelectric material is obtained by the above-mentioned steps S110 and S120. Each step will be described in detail.

[0036] In step S110, the Mg-containing raw material may be Mg metal alone, or a silicide, oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride of Mg. The Sb-containing raw material may be Sb metal alone, or a silicide, oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride of Sb. The Bi-containing raw material may be Bi metal alone, or a silicide, oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride of Bi. The Cu-containing raw material may be Cu metal alone, or a silicide, oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride of Cu. The M-containing raw material may be M metal alone, or a silicide, oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride of M. The raw materials are preferably in the form of powder, granules or small lumps from the viewpoint of mixability and handling.

[0037] In step S110, the metal elements in the raw materials are selected from the group consisting of Mg a Sb 2-b-c Bi b M c Cu d where the parameters a, b, c, and d are 3≦a≦3.5, 0≦b≦2, 0≦c≦0.06, 0 <d≦0.1、および、 b+c≦2 The preferable parameters are as described above, and therefore the explanation will be omitted.

[0038] In step S120, sintering may be performed by any method, such as spark plasma sintering (SPS), hot press sintering (HP), hot isostatic pressing (HIP), cold isostatic pressing (CIP), or Paltz current sintering, but preferably by spark plasma sintering (SPS), which allows for the production of a sintered body with suppressed grain growth in a short time without using a sintering aid.

[0039] SPS may be preferably performed at a temperature of 723 K to 1173 K under a pressure of 30 MPa to 100 MPa for 1 minute to 10 minutes. In an embodiment of the present invention, under these conditions, the above-mentioned sintered thermoelectric material can be obtained with a good yield.

[0040] Furthermore, the obtained sintered body may be pulverized by mechanical milling such as a ball mill, thereby obtaining a powdered thermoelectric material in the embodiment of the present invention.

[0041] In the embodiment of the present invention, the thus obtained powdered thermoelectric material can be mixed with an organic material to provide a flexible thermoelectric material. In this case, the organic material and the mixing ratio described above can be used.

[0042] Alternatively, the resulting sintered body may be used as a target for physical vapor deposition, which in the present embodiment provides a thin film of a thermoelectric material.

[0043] (Embodiment 2) In the second embodiment, a thermoelectric power generating element using the thermoelectric material described in the first embodiment will be described as an example of the present invention.

[0044] FIG. 2A is a schematic diagram showing a thermoelectric power generation element (π-shaped) using a thermoelectric material in an example of the present invention.

[0045] In an embodiment of the present invention, the thermoelectric power generating element 200 includes a pair of n-type and p-type thermoelectric materials 210 and 220, and electrodes 230 and 240 at their respective ends. The electrodes 230 and 240 electrically connect the n-type and p-type thermoelectric materials 210 and 220 in series.

[0046] Here, the p-type thermoelectric material 210 is not particularly limited, but preferably has high thermoelectric performance (for example, ZT of 0.4 to 1.6) at 500 K or less, particularly at room temperature. Illustrative examples of the p-type thermoelectric material 210 include BiSbTe-based, MgAgSb-based, and AgSbSe-based materials. An exemplary composition of a BiSbTe-based material is, for example, Bi 0.5 Sb 1.5 Te3, Bi 0.4 Sb 1.6 Te3. Exemplary compositions of the MgAgSb system include, for example, MgAgSb, MgAg 0.965 Ni 0.005 Sb 0.99 An exemplary composition of the AgSbSe system is, for example, AgSbSe2. Note that these are examples and are not limiting.

[0047] On the other hand, in the examples of the present invention, the n-type thermoelectric material 220 is the thermoelectric material described in embodiment 1. In the examples of the present invention, the thermoelectric material exhibits excellent thermoelectric properties, particularly at room temperature, and is therefore advantageous for waste heat recovery.

[0048] The electrodes 230, 240 may be made of a common electrode material, such as Fe, Ag, Al, Ni, or Cu.

[0049] 2A shows a state in which a chip made of n-type thermoelectric material 210 is joined by solder or the like to an electrode 240 on the low-temperature side, and an opposite end of the chip of n-type thermoelectric material 210 is joined by solder or the like to an electrode 230 on the high-temperature side. Similarly, a chip made of p-type thermoelectric material 220 is joined by solder or the like to an electrode 230 on the high-temperature side, and an opposite end of the chip of p-type thermoelectric material 220 is joined by solder or the like to an electrode 240 on the low-temperature side.

[0050] In an embodiment of the present invention, when the thermoelectric power generating element 200 is placed in an environment where the electrode 230 is at a high temperature and the electrode 240 is at a lower temperature than the electrode 230 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 order of the electrode 240, the n-type thermoelectric material 210, the electrode 230, and the p-type thermoelectric material 220, as shown by the arrows in Fig. 2A. In detail, the electrons in the n-type thermoelectric material 210 obtain thermal energy from the electrode 230 on the high-temperature side, move to the electrode 240 on the low-temperature side, and release the thermal energy there. In response, the holes in the p-type thermoelectric material 220 obtain thermal energy from the electrode 230 on the high-temperature side, move to the electrode 240 on the low-temperature side, and release the thermal energy there. This is the principle by which a current flows.

[0051] In the examples of the present invention, the thermoelectric material described in the first embodiment is used as the n-type thermoelectric material 210. This allows for the realization of a thermoelectric power generation element 200 with a particularly large power generation capacity at room temperature (275 K to 320 K). Furthermore, when the thermoelectric material in the examples of the present invention is a powder or film containing an inorganic compound with an Mg3Sb2-based parent phase to which Cu atoms have been added, or a thin film obtained using a sintered body of the above inorganic compound as a target, a flexible thermoelectric power generation module can be provided as an IoT power source. For example, Figure 2C illustrates how a sintered body of this inorganic compound is used as a target 300 and sputtered with argon 320 to deposit inorganic compound particles 330 onto a substrate 310, forming a thin film 340. Needless to say, this thin film 340 can be peeled off from the substrate 310 using existing technology to form a separate film. For example, Figure 2D illustrates powder 350 of this inorganic compound. This powder 350 is compressed by a powder compactor 370 to obtain a green compact 360, and the green compact 380 is placed in a sintering furnace 390 and sintered to obtain a sintered body 400.

[0052] In the embodiment of the present invention, if a thermoelectric material is used, a thermoelectric power generation element 200 with a large amount of power generation at room temperature can be provided, but in the embodiment of the present invention, the thermoelectric power generation element 200 is not limited to use in a temperature range higher than room temperature (for example, 573 K, etc.). Since the thermoelectric power generation element 200 exhibits a high dimensionless figure of merit (ZT) even in a high temperature range, it goes without saying that a thermoelectric power generation element with a large amount of power generation can be provided.

[0053] 2A has been described using a π-shaped thermoelectric power generation element, but in an embodiment of the present invention, the thermoelectric material may be used in a U-shaped thermoelectric power generation element (FIG. 2B). In this case, in an embodiment of the present invention, n-type thermoelectric material 210 and p-type thermoelectric material 220 made of thermoelectric materials are directly connected at junction 215 on the high-temperature side. Low-temperature electrodes 240a and 240b may each be electrically connected to the low-temperature electrodes of separate U-shaped thermoelectric power generation elements.

[0054] 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]

[0055] [Raw materials] In the following examples, Mg (powder, purity 99.99%, manufactured by Sigma-Aldrich Japan LLC), Sb (powder, purity 99.99%, manufactured by Sigma-Aldrich Japan LLC), Bi (powder, purity 99.99%, manufactured by Sigma-Aldrich Japan LLC), Te (powder, purity 99.99%, manufactured by Sigma-Aldrich Japan LLC), and, if necessary, Cu (powder, purity 99.99%, manufactured by Sigma-Aldrich Japan LLC) were used.

[0056] [Example 1 to Example 10] In Examples 1 to 5, the general formula Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 Cu d The raw materials were mixed so as to satisfy the formula (d = 0, 0.005, 0.01, 0.025, 0.05) to produce thermoelectric materials. 3.2 Sb0.5 Bi 1.498 Te 0.002 Cu 0.01 In Examples 8 to 10, the raw materials were mixed so as to satisfy the general formula Mg 3.2 Sb 0.5 Bi 1.495 Te 0.005 Cu 0.01 The raw materials were mixed so as to satisfy the above requirements, and a thermoelectric material was produced.

[0057] Each raw material powder was weighed to satisfy the composition shown in Table 1, loaded into a stainless steel ball mill container in a glove box, and mixed in a ball mill for 5 hours. The mixture was then sintered at 973 K for 5 minutes using a spark plasma sintering apparatus (SPS, manufactured by SPS Syntex, Inc., SPS-1080 System). Specifically, the mixture was loaded into a graphite sintering die (inner diameter 10 mm, height 30 mm) and subjected to a uniaxial stress of 60 MPa at a heating rate of 100 K / min at a sintering temperature of 973 K, maintaining the temperature for 5 minutes. Sintered compacts were thus obtained. Samples 1 to 5 satisfied the compositions of d = 0.005, d = 0.01, d = 0.025, d = 0.05, and d = 0, respectively, while samples 6 to 10 satisfied the compositions described above.

[0058] The sintered bodies were observed. Surface observations were also performed using a scanning electron microscope (SEM, JEOL Ltd., JSM-7800F) equipped with an electron backscatter diffraction detector (EBSD) and an energy dispersive X-ray spectrometer (EDS), and the average grain size was determined. The average grain size was calculated using the image analysis software described above. The results are shown in Figures 3 to 6 and Table 2.

[0059] The resulting fired body was wet-ground using ethanol in an agate mortar. The ground particles were sieved through a mesh (45 μm opening), and only particles with a particle size of 45 μm or less that passed through the mesh were extracted. The particles were identified using powder X-ray diffraction (Rigaku Corporation, SmartLab3) and their composition was analyzed using X-ray fluorescence analysis (Horiba, Ltd., EMAX Evolution EX). The X-ray diffraction results are shown in Figures 7 and 8.

[0060] The sintered compacts were cut into rectangular parallelepipeds measuring 1.5 mm × 1.5 mm × 9 mm using a high-speed cutter, and their electrical conductivity and thermoelectric properties were measured. Electrical conductivity was measured using the DC four-terminal method. Thermoelectric properties, such as the Seebeck coefficient and thermal conductivity, were measured using the steady-state temperature difference method using a thermoelectric property measurement and evaluation device (ZEM-3, manufactured by Advance Riko Co., Ltd.) and a thermal conductivity evaluation device (HyperflashXXX, manufactured by Netsch), respectively. Measurements were performed in a helium gas atmosphere over a temperature range from room temperature to 800 K. The electrical power factor was calculated from the thermoelectric power obtained from the electrical conductivity or electrical resistivity and the Seebeck coefficient, and the dimensionless figure of merit (ZT) was calculated from the Seebeck coefficient, electrical conductivity, and thermal conductivity. These results are shown in Figures 9 to 15 and Table 3, and are described below.

[0061] For simplicity, the manufacturing conditions for samples in Examples 1 to 10 are summarized in Table 1. All samples in Examples 1 to 10 were sintered at a stress of 60 MPa. Examples 1 to 5 were sintered at a sintering temperature of 973 K (700°C) for 5 minutes. Examples 6 and 8 were sintered at a sintering temperature of 973 K (700°C) for 10 minutes, Examples 7 and 9 were sintered at a sintering temperature of 1023 K (750°C) for 10 minutes, and Example 10 was sintered at a sintering temperature of 1073 K (800°C) for 10 minutes. These results are explained below.

[0062] [Table 1]

[0063] FIG. 3 is a diagram showing the appearance of the sample of Example 1.

[0064] As shown in Figure 3, the sample of Example 1 was a disk-shaped sintered body with a diameter of 10 mm and a thickness of 2 mm. Although not shown, the other samples also had similar shapes.

[0065] FIG. 4 shows SEM images and EDS mapping of the samples of Examples 1 to 5.

[0066] Figures 4(A) to (E) show SEM images of the samples of Example 5 and Examples 1 to 4, respectively, and Figure 4(F) shows EDS mapping of the sample of Example 2. Figures 4(A) to (E) show that the addition of Cu clearly caused grain growth, and as the amount of Cu added increased, the grain size also increased. Figure 4(F) shows the grayscale image, confirming that Mg, Bi, and Sb are uniformly distributed throughout the sample.

[0067] FIG. 5 shows an EBSD image of the sample of Example 2. FIG. 6 shows an EBSD image of the sample of Example 5.

[0068] Figures 5 and 6 show grain mapping and grain size histograms along with inverse pole point (IPF) maps. According to Figures 5 and 6, the average grain size of the sample in Example 5 without Cu addition was 3.24 μm, while that of the sample in Example 2 with Cu addition was 4.57 μm. The EBSD and SEM images suggest that the samples in Examples 1, 3, and 4 with Cu addition consist of inorganic compounds with average grain sizes between 4 μm and 6 μm. It was also found that the addition of Cu increased the average grain size by more than 40%. Furthermore, the average grain size tended to increase as the amount of Cu added increased.

[0069] FIG. 7 shows XRD patterns of the samples of Examples 1 to 5. As shown in FIG. FIG. 8 is a diagram showing the Cu addition amount dependence of the lattice constants of the samples of Examples 1 to 5. In FIG.

[0070] As shown in Figure 7, the diffraction peaks in the XRD patterns of the samples of Examples 1 to 5 all matched those of the Mg2Sb3 phase, indicating that the samples of Examples 1 to 5 were inorganic compounds with a La2O3 structure and P-3m1 space group symmetry. Composition analysis confirmed that the composition of each sample matched the starting composition. As shown in Figure 8, the addition of Cu increased both the a-axis and c-axis. In general, the atomic diameter of Cu is not larger than that of Mg or Sb. This indicates that Cu is an interstitial solid solution, not a substitutional solid solution.

[0071] Therefore, it was shown that the samples of Examples 1 to 4 contain inorganic compounds in which Cu is added to an inorganic crystal having a La2O3 type structure containing Mg, Sb, Bi, and Te as the host crystal.

[0072] [Table 2]

[0073] Fig. 9 is a graph showing the temperature dependence of the electrical conductivity of the samples of Examples 1 to 5. Fig. 16 is a graph showing the temperature dependence of the electrical conductivity of the samples of Examples 6 and 7, and Fig. 22 is a graph showing the temperature dependence of the electrical conductivity of the samples of Examples 8 to 10.

[0074] 9, it was found that the electrical conductivity of the samples of Examples 1 to 4 to which Cu was added was higher than that of the sample of Example 5 to which Cu was not added, and that the increase was particularly remarkable around room temperature. The samples of Examples 1 to 4 had electrical conductivity (electrical resistivity) sufficient for use as thermoelectric materials, and had temperature dependence. Furthermore, focusing on the electrical conductivity at room temperature, it was found that by controlling the amount of Cu added, the electrical conductivity at room temperature could be increased to approximately 5×10 4 (Ωm) -1 16 to 27 show the sintering temperature in degrees Celsius, with 700 in Figs. 16 to 21 being Example 6 and 750 being Example 7, and 700 in Figs. 22 to 27 being Example 8, 750 being Example 9, and 800 being Example 10. According to Fig. 16, the electrical conductivity increases slightly as the sintering temperature increases, and similarly according to Fig. 22, the electrical conductivity increases slightly as the sintering temperature increases.

[0075] FIG. 10 is a diagram showing the Cu addition amount dependence of the carrier concentration and mobility of the samples of Examples 1 to 5. In FIG.

[0076] According to Figure 10, as the amount of Cu added increases, the carrier concentration and mobility also tend to increase. In particular, when focusing on mobility, the addition of Cu increases the carrier concentration to 100 cm 2 V -1 s-1 This is thought to be due to the advantageous carrier scattering mechanism caused by the interstitial solid solution of Cu.

[0077] 11, 17, and 23 are diagrams showing the temperature dependence of the Seebeck coefficients of the samples of Examples 1 to 5, Examples 6 to 7, and Examples 8 to 10. FIG.

[0078] As shown in FIG. 11, all samples were confirmed to be n-type conductive with a large Seebeck coefficient of 170 μV / K or more. Surprisingly, despite the improvement in electrical conductivity due to the addition of Cu, the magnitude of the Seebeck coefficient was not impaired. As shown in FIG. 17, all samples were confirmed to be n-type conductive with a large Seebeck coefficient of 220 μV / K or more. As shown in FIG. 23, all samples were confirmed to be n-type conductive with a large Seebeck coefficient of 160 μV / K or more.

[0079] Fig. 12 is a graph showing the temperature dependence of the electric output factors of the samples of Examples 1 to 5. Fig. 18 is a graph showing the temperature dependence of the electric output factors of the samples of Examples 6 and 7. Fig. 24 is a graph showing the temperature dependence of the electric output factors of the samples of Examples 8 to 10.

[0080] According to FIG. 12, it was found that the electrical output factors (power factors) of the samples of Examples 1 to 4 to which Cu was added were dramatically increased in the low temperature range of 300 K to 400 K compared to that of the sample of Example 5 to which Cu was not added. For example, the electrical output factor (21.03 μW cm ) of the sample of Example 2 at room temperature (300 K) was 21.03 μW cm . -1 K -2 ) and that of the sample of Example 5 (7.16 μW cm -1 K -2 ), the increase was approximately three times. This means that the device is suitable for recovering waste heat as a power source for various thermoelectric cooling applications and IoT devices, and can provide a thermoelectric power generation element for consumer use. According to Fig. 18 and Fig. 24, the same results as in Examples 1 to 4 were obtained.

[0081] Fig. 13 is a graph showing the temperature dependence of the total thermal conductivity of samples of Examples 1 to 5. Fig. 19 is a graph showing the temperature dependence of the total thermal conductivity of samples of Examples 6 and 7. Fig. 25 is a graph showing the temperature dependence of the total thermal conductivity of samples of Examples 8 to 10. Fig. 14 is a graph showing the temperature dependence of the lattice thermal conductivity of samples of Examples 1 to 5. Fig. 20 is a graph showing the temperature dependence of the lattice thermal conductivity of samples of Examples 6 and 7. Fig. 26 is a graph showing the temperature dependence of the lattice thermal conductivity of samples of Examples 8 to 10.

[0082] According to FIG. 13, the addition of Cu slightly reduced the total thermal conductivity. The Lorentz number L was calculated, and the electronic thermal conductivity was subtracted from the total thermal conductivity to determine the lattice thermal conductivity. As shown in FIG. 14, in the relatively low temperature range below 400 K, the lattice thermal conductivity of the samples of Examples 1 to 4, which contained Cu, was significantly lower than that of the sample of Example 5, which did not contain Cu. For example, when comparing the lattice thermal conductivity of the sample of Example 2 with that of the sample of Example 5 over the entire temperature range measured, the lattice thermal conductivity of the sample of Example 2 was reduced by 20 to 30%. According to FIGS. 19 and 25 and FIGS. 20 and 26, similar results to those of Examples 1 to 4 were obtained.

[0083] Fig. 15 is a graph showing the temperature dependence of the dimensionless figure of merit ZT of the samples of Examples 1 to 5. Fig. 21 is a graph showing the temperature dependence of the dimensionless figure of merit ZT of the samples of Examples 6 and 7. Fig. 27 is a graph showing the temperature dependence of the dimensionless figure of merit ZT of the samples of Examples 8 to 10.

[0084] According to Fig. 15, it was found that the ZT of the samples of Examples 1 to 4 to which Cu was added was higher than that of the sample of Example 5 to which Cu was not added. In particular, this tendency was remarkable in the relatively low temperature range of 400 K or less for the samples of Examples 1 to 4 to which Cu was added, and it was found that they achieved high values ​​of 0.4 or more at room temperature. It was confirmed that the original ZT of Mg3Sb2 was substantially maintained even with the addition of Cu in the high temperature range above 400 K. According to Fig. 21 and Fig. 27, results similar to those of Examples 1 to 4 were obtained.

[0085] The above thermoelectric properties are summarized in Table 3. In Table 3, "E" represents a power of 10.

[0086] [Table 3]

[0087] Table 3 shows that the samples in Examples 1 to 4, which contained Cu, had high electrical conductivity at room temperature and improved figures of merit. It was also shown that the Cu content (d value) was preferably in the range of 0.005≦d≦0.05, with a range of 0.005≦d≦0.025 being particularly preferable. Furthermore, in Examples 6 to 10, the power factor at room temperature, which is formed by the Seebeck coefficient and electrical conductivity, was larger and enhanced than in Examples 1 to 5. This is because the composition ratio of Bi in Examples 6 to 10 was higher than that of Sb (see Table 1), narrowing the band gap and achieving particularly high electrical conductivity without significantly impairing the Seebeck coefficient at room temperature. Furthermore, although the total thermal conductivity was high, the lattice thermal conductivity was relatively low. It is generally believed that thermal conduction is categorized into two types: thermal conduction due to the transfer of heat associated with the movement of charged particles such as electrons, and thermal conduction due to the transmission of lattice vibrations, which does not involve the movement of such particles. In thermoelectric elements that generate voltage based on a temperature difference, it is said that low thermal conductivity and high electrical conductivity are preferable. That is, it is believed that such a preferable state was obtained in Examples 6 to 10. For example, in consideration of the power factor, it is preferable to increase the composition ratio of Bi relative to Sb, with b>1 being more preferable, b≧1.2 being even more preferable, and b≧1.4 being even more preferable. [Industrial Applicability]

[0088] In the embodiments of the present invention, the thermoelectric material has excellent thermoelectric performance, particularly at around room temperature, and can function as a substitute for Bi2Te3-based materials, and is used in thermoelectric cooling devices and power generation devices used in various electrical devices. In particular, if it is made into a thin film, it can provide a flexible thermoelectric generation element as a power source for IoT. [Explanation of symbols]

[0089] 200 Thermoelectric power generation element 210 n-type thermoelectric materials 220 p type thermoelectric material 230, 240 electrode

Claims

1. an inorganic compound containing magnesium (Mg), antimony (Sb), bismuth (Bi), copper (Cu), and tellurium (Te); The inorganic compound is Mg ａ Sb ２－ｂ－ｃ Bi ｂ Te ｃ Cu ｄ is expressed as The parameters a, b, c and d are 3≦a≦3.5, 0.2≦b, 0.002≦c≦0.06, 0.001<d≦0.1, and b + c < 2 Fulfilling The inorganic compound is La ２ O ３ It has a structure of the type 1, and has symmetry of the space group P-3m1, Cu is the same as the La ２ O ３ n-type, which is an interstitial solid solution in the n-type structure; It has a power factor of more than 14 μWcm −1 K −2 at room temperature; A thermoelectric material having a dimensionless figure of merit ZT greater than 0.

3.

2. The parameter d is 0.005≦d≦0.05 The thermoelectric material according to claim 1 , wherein

3. The parameters a, b, c and d are 3≦a≦3.5, 0.2≦b≦0.7, 0.002≦c≦0.06, and 0.005≦d≦0.05 The thermoelectric material according to claim 1 or 2, which satisfies the following:

4. 4. The thermoelectric material according to claim 1, wherein the thermoelectric material is in a form selected from the group consisting of a powder, a sintered body, and a thin film.

5. the thermoelectric material is in the form of a powder or a sintered body; The thermoelectric material according to claim 4 , wherein the inorganic compound is composed of crystal grains having an average grain size in the range of 3.5 μm to 30 μm.

6. The thermoelectric material according to claim 5 , wherein the inorganic compound is composed of crystal grains having an average grain size in the range of 4 μm to 20 μm.

7. the thermoelectric material is in the form of a thin film; the inorganic compound is composed of crystal grains having an average grain size in the range of 3.5 μm or more and 30 μm or less, The thermoelectric material of claim 4 further comprising an organic material.

8. mixing a raw material containing magnesium (Mg), a raw material containing antimony (Sb), a raw material containing bismuth (Bi), a raw material containing copper (Cu), and a raw material containing tellurium (Te) to prepare a mixture; sintering the mixture; and A method for producing the thermoelectric material according to any one of claims 1 to 7, comprising:

9. The method of claim 8 , wherein the sintering comprises spark plasma sintering.

10. The method according to claim 9, wherein the spark plasma sintering is performed at a temperature of 723 K or higher and 1173 K or lower, under a pressure of 30 MPa or higher and 100 MPa or lower, for a time of 1 minute or higher and 10 minutes or lower.

11. The method according to any one of claims 8 to 10, further comprising pulverizing the sintered body obtained by the sintering.

12. The method of claim 11, further comprising mixing the powder obtained by grinding with an organic material.

13. The method according to any one of claims 8 to 10, further comprising carrying out a physical vapor deposition method using the sintered body obtained by sintering as a target.

14. A thermoelectric power generation element comprising p-type thermoelectric materials and n-type thermoelectric materials alternately connected in series, wherein the n-type thermoelectric materials are the thermoelectric materials according to any one of claims 1 to 7.

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