N-type thermoelectric material, its manufacturing method, and thermoelectric power generation element

Abstract

To provide an n-type thermoelectric material having a dimensionless figure of merit (ZT) exceeding 1.4 at least at 850°C, a method for producing the same, and a thermoelectric power generation element. [Solution] The n-type thermoelectric material of the present invention comprises a composite containing a silicon germanium (SiGe)-based alloy to which phosphorus (P) and at least one substance selected from the group consisting of gallium phosphide (GaP) and gallium (Ga) have been added, and metal silicide particles dispersed in the SiGe-based alloy. The metal silicide particles may be a metal silicide represented by MSi2 (where M is at least one element selected from the group consisting of molybdenum (Mo), chromium (Cr), tungsten (W), cobalt (Co), and nickel (Ni)).

Description

[Technical Field]

[0001] The present invention relates to a silicon germanium (SiGe)-based n-type thermoelectric material, a method for producing the same, and a thermoelectric power generating 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 scalable. For this reason, active research is being conducted on thermoelectric semiconductors as materials for waste heat power generation, which contributes to carbon neutrality.

[0004] Silicon-germanium (SiGe)-based thermoelectric materials are known as n-type thermoelectric materials used in such thermoelectric power generation elements, and they operate stably under conditions of 600°C to 1050°C. In recent years, SiGe-based thermoelectric materials with improved dimensionless figure of merit ZT have been reported (e.g., Non-Patent Documents 1 to 3).

[0005] Non-Patent Document 1 reports that by forming MoSi2 in a silicon-germanium matrix to which phosphorus (P) is added, phonon scattering centers are generated, the thermal conductivity decreases, and ZT exceeds 1.0 at 700°C.

[0006] Non-Patent Documents 2 and 3 report that by adding phosphorus (P) and gallium phosphide (GaP) to a silicon-germanium matrix, the electrical conductivity and thermal conductivity are reduced, and ZT exceeds 1.0 at 900°C.

[0007] However, considering practical application, it is expected that n-type thermoelectric materials with ZT exceeding 1.4 at 850°C will be developed. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] K. Favier,Acta Materialia,64,2014,429-442 [Non-patent document 2] BACook et al., J. Appl. Phys., 78, 5474-5480, 1995 [Non-patent document 3] O.Yamashita,J.Appl.Phys.,89,6241-6246,2001 Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the above, an object of the present invention is to provide an n-type thermoelectric material having a dimensionless figure of merit (ZT) of more than 1.4 at least at 850° C., a method for producing the same, and a thermoelectric power generating element. [Means for solving the problem]

[0010] The n-type thermoelectric material according to the present invention comprises a composite containing a silicon germanium (SiGe)-based alloy to which phosphorus (P) and at least one substance selected from the group consisting of gallium phosphide (GaP) and gallium (Ga) have been added, and metal silicide particles dispersed in the SiGe-based alloy, thereby solving the above-mentioned problems. The metal silicide particles may be a metal silicide represented by MSi2 (wherein M is at least one element selected from the group consisting of molybdenum (Mo), chromium (Cr), tungsten (W), cobalt (Co), and nickel (Ni)). The metal silicide particles in the composite may satisfy the range of 0.5% to 2.5% by volume percentage. The content of the metal silicide particles in the composite may be in the range of 1% to 2% by volume. The composite has the composition formula Si a Ge b P c Ga d M e (M is at least one element selected from the group consisting of molybdenum (Mo), chromium (Cr), tungsten (W), cobalt (Co), and nickel (Ni), and satisfies a+b+c+d+e=1), and the parameters a, b, c, d, and e are 0.3≦a≦0.85 0.1≦b≦0.65 0.01≦c≦0.06 0.003≦d≦0.02 0.003≦e≦0.02 may be satisfied. The parameters a, b, c, d and e are 0.5≦a≦0.75 0.2≦b≦0.45 0.014≦c≦0.04 0.006≦d≦0.01 0.004≦e≦0.01 may be satisfied. The composite may be in a form selected from the group consisting of a powder, a sintered body, and a thin film. The composite may be in the form of the sintered body and may be composed of particles having an average particle size in the range of 100 nm to 500 nm. The sintered body may have pores with an average pore diameter in the range of 300 nm or more and 1500 nm or less. The composite is in the form of the powder and may further contain an organic material. The method for producing the above-mentioned n-type thermoelectric material according to the present invention includes mixing a raw material containing silicon (Si), a raw material containing germanium (Ge), a raw material containing gallium (Ga), a raw material containing phosphorus (P), and metal silicide particles to prepare a mixture, and firing the mixture, thereby solving the above-mentioned problem. Preparing the mixture comprises: Si powder as the silicon (Si)-containing raw material, Ge chunks as the germanium (Ge)-containing raw material, GaP chunks as the gallium (Ga)-containing raw material, and P chunks as the phosphorus (P)-containing raw material, Si α Ge β P γ (GaP) δ In the composition formula expressed as (α+β+γ+δ=1), the parameters α, β, γ, and δ are 0.7≦α≦0.75 0.22≦β≦0.27 0.005≦γ≦0.03 0.005≦δ≦0.025 may be mixed so as to satisfy the above. The preparation of the mixture may be such that the metal silicide particles in the mixture satisfy a volume percentage range of 0.5% to 2.5%. The firing may be performed at a temperature in the range of 900°C or higher and 1050°C or lower. The method may further comprise pulverizing the sintered body obtained by the firing. The method may further comprise mixing the powder with an organic material by grinding. The method may further include carrying out a physical vapor deposition method using the sintered body obtained by the firing. A thermoelectric power generating element according to the present invention includes at least an n-type thermoelectric material, which is the n-type thermoelectric material described above, thereby solving the above-mentioned problems. The thermoelectric element may include p-type thermoelectric materials connected in series alternately with the n-type thermoelectric materials. The p-type thermoelectric material is a BiSbTe-based, MgAgSb-based, SiGe-based, or LaFe3CoSb 12 , FeNbSb, HfCoSb, Yb 14 MnSb 11 , Cu2Se, Zn4Sb3, and AgSbSe systems. [Effects of the Invention]

[0011] The thermoelectric material of the present invention functions as an n-type thermoelectric material because it contains a silicon germanium (SiGe)-based alloy doped with phosphorus (P). Furthermore, the SiGe-based alloy is doped with at least one substance selected from the group consisting of gallium phosphide (GaP) and gallium (Ga), and metal silicide particles are dispersed therein. This suppresses thermal conductivity in the high-temperature range, enabling a dimensionless figure of merit (ZT) of greater than 1.4 at least at 850°C to be achieved while maintaining a power factor. Using such an n-type thermoelectric material in a thermoelectric generator can provide a highly efficient thermoelectric generator, particularly in the high-temperature range from 600°C to 950°C.

[0012] The method for producing a thermoelectric material of the present invention is highly industrially viable because it produces the above-mentioned thermoelectric material by mixing a raw material containing silicon (Si), a raw material containing germanium (Ge), a raw material containing gallium (Ga), a raw material containing phosphorus (P), and metal silicide particles to prepare a mixture, and then firing the mixture. [Brief explanation of the drawings]

[0013] [Figure 1] Flowchart showing the steps for producing the n-type thermoelectric material of the present invention [Figure 2] Schematic diagram showing a thermoelectric power generation element using the n-type thermoelectric material of the present invention. [Figure 3] Schematic diagram showing another thermoelectric power generation element using the n-type thermoelectric material of the present invention. [Figure 4] Figures showing SEM, EDS, and TEM images of the sample in Example 1 [Figure 5] Thermoelectric properties of the sample in Example 1 [Figure 6] Thermoelectric properties of the sample in Example 2 [Figure 7] Thermoelectric properties of the sample in Example 3 [Figure 8] Thermoelectric properties of the sample in Example 4 [Figure 9] Thermoelectric properties of the sample in Example 5 [Figure 10] Graph showing thermoelectric properties of the sample in Example 6 [Figure 11] Figure showing the thermoelectric characteristics of the sample of Example 7 [Figure 12] Figure showing the thermoelectric characteristics of the sample of Example 8

Best Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same elements are denoted by the same reference numerals, and the description thereof will be omitted. In this specification, a numerical range represented using "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value, respectively.

[0015] (Embodiment 1) The n-type thermoelectric material of the present invention contains a composite containing a silicon germanium (SiGe) alloy to which phosphorus (P) and at least one substance selected from the group consisting of gallium phosphide (GaP) and gallium (Ga) are added, and metal silicide particles dispersed therein. Since it contains an SiGe alloy, it functions as an n-type thermoelectric material in a high-temperature region. Furthermore, by adding P and GaP and / or Ga, and further dispersing metal silicide particles, a dimensionless figure of merit (ZT) exceeding 1.4 can be achieved at at least 850°C, and it functions as an excellent n-type thermoelectric material in the high-temperature range from 600°C to 950°C.

[0016] Each component will be described in detail. The SiGe alloy serving as the base material can be adopted without any compositional limitation as long as it is an alloy of silicon and germanium. The SiGe alloy can be represented by, for example, Si x Ge 1-x (0 < x < 1). The SiGe alloy is preferably represented by Si x Ge 1-x (0.2 ≤ x ≤ 0.45). Thereby, it can function as an excellent n-type thermoelectric material. The SiGe alloy is more preferably represented by Si x Ge 1-x (0.2 ≤ x ≤ 0.3). Thereby, it functions as a particularly excellent n-type thermoelectric material.

[0017] The SiGe alloy preferably has a diamond structure, which allows alloying of Si and Ge and allows it to function as an n-type thermoelectric material.

[0018] The P added to the SiGe alloy may be substituted for Si (silicon), and the GaP and Ga (gallium) added to the SiGe alloy may be dispersed in the SiGe.

[0019] The metal silicide particles are not particularly limited as long as they are formed by a reaction between metal and silicon, except for SiGe alloys. For example, they are represented by MSi2 (where M is at least one element selected from the group consisting of molybdenum (Mo), chromium (Cr), tungsten (W), cobalt (Co), and nickel (Ni)). These metal silicide particles, when dispersed in a SiGe alloy, can suppress the thermal conductivity and improve the power factor (PF) and the dimensionless figure of merit (ZT). Among these, the metal silicide particles are preferably MoSi2 and / or WSi2. These are advantageous for improving the dimensionless figure of merit (ZT) in the high-temperature range.

[0020] The average particle size of the metal silicide particles is preferably 70 nm or less. There is no particular lower limit, but it may be 10 nm or more due to ease of availability. By setting the particle size in this range, phonons can be effectively scattered and thermal conductivity can be reduced. The average particle size of the metal silicide particles is more preferably in the range of 45 nm to 55 nm.

[0021] The content of the metal silicide particles in the composite is preferably in the range of 0.5% to 2.5% by volume. Within this range, they are dispersed in the SiGe alloy, suppressing the thermal conductivity and improving the power factor (PF) and dimensionless figure of merit (ZT). The content of the metal silicide particles is more preferably in the range of 0.75% to 2.25% by volume, and even more preferably in the range of 1% to 2%. This activates phonon scattering, reducing the thermal conductivity in the high-temperature range and favoring an improvement in the dimensionless figure of merit (ZT).

[0022] The amount of P added to the composite is preferably in the range of 1 at% to 5 at% and more preferably in the range of 1.2 at% to 4 at%. Within this range, P can be substituted for Si and improve the thermoelectric properties. Note that when GaP is added in addition to P, the amount of P added includes the amount of P in GaP.

[0023] The amount of Ga added to the composite is preferably in the range of 0.3 at% to 1.5 at% and more preferably in the range of 0.5 at% to 1 at%. This range can improve the thermoelectric properties. Note that, when GaP is added in addition to Ga, the amount of Ga added includes the amount of Ga in GaP.

[0024] The composite preferably has the formula Si a Ge b P c Ga d M e (M is at least one element selected from the group consisting of molybdenum (Mo), chromium (Cr), tungsten (W), cobalt (Co), and nickel (Ni), and satisfies a+b+c+d+e=1), and the parameters a, b, c, d, and e are 0.3≦a≦0.85 0.1≦b≦0.65 0.01≦c≦0.06 0.003≦d≦0.02 0.003≦e≦0.02 As a result, it exhibits excellent thermoelectric properties in the high temperature range.

[0025] The parameters a, b, c, d and e are more preferably: 0.5≦a≦0.75 0.2≦b≦0.45 0.014≦c≦0.04 0.006≦d≦0.01 0.004≦e≦0.01 As a result, it exhibits particularly excellent thermoelectric properties in the high temperature range, and can achieve a dimensionless figure of merit (ZT) of over 1.4 at 850°C.

[0026] The n-type thermoelectric material of the present invention 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 conversion elements with excellent thermoelectric properties in the high temperature range.

[0027] Generally, powder may include crushed particles or powder. A powder compact can be formed by compressing powder using a press, such as a powder compactor. A powder compact is a powder compact formed by compressing powder into a specific 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 as the heating time increases. This phenomenon is called sintering, and the product obtained by sintering is called a sintered body. A thin film is a thin film and may include a layer formed by condensation of a gas phase on a solid surface.

[0028] When the n-type thermoelectric material is a powder or sintered body, the powder or sintered body may be composed of crystal grains with an average grain size in the range of 100 nm to 500 nm. This reduces grain boundary scattering of charge carriers, suppresses thermal conductivity in the high-temperature range, and achieves a high dimensionless figure of merit. The powder or sintered body may more preferably be composed of crystal grains with an average grain size in the range of 100 nm to 300 nm. The crystal grains constituting the powder and sintered body may have lattice defects. Such lattice defects include, for example, line defects and twin crystals. Lattice defects increase phonon scattering, reducing thermal conductivity.

[0029] The average particle size was determined by randomly selecting images of particles observed with a scanning electron microscope (e.g., FESEM, Hitachi SU8000), measuring the particle size (major axis) of 100 particles using Image J (ver. 1.53k: open-source, public domain image processing software), and averaging the results.

[0030] In particular, when the n-type thermoelectric material is a sintered body, the sintered body may have pores with an average pore diameter in the range of 300 nm to 1500 nm. This activates phonon scattering and reduces thermal conductivity. The sintered body may have pores with an average pore diameter in the range of 800 nm to 1000 nm. Here, the average pore diameter is determined by randomly selecting images of particles observed with a scanning electron microscope (e.g., FESEM, Hitachi SU8000), measuring the particle diameters (major diameters) of 100 particles using Image J (ver. 1.53k: open-source, public domain image processing software), and averaging the results.

[0031] The porosity of the sintered body may be in the range of 1% to 10%. This range allows for reduced thermal conductivity while maintaining electrical conductivity. The porosity is more preferably in the range of 5% to 10%. Note that the porosity is the percentage of the volume of the pores in the external volume of the sintered body, where the external volume is taken as 1, and is calculated using a specific gravity measuring device.

[0032] The thermoelectric material of the present invention may be in the form of a thin film, which may be a crystalline thin film formed by physical vapor deposition, as described below, or a thin film containing the above-mentioned powder.

[0033] When the thermoelectric material of the present invention 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 thermoelectric material film.

[0034] 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.

[0035] Next, an exemplary method for producing such an n-type thermoelectric material of the present invention will be described. FIG. 1 is a flowchart showing the steps for producing an n-type thermoelectric material of the present invention.

[0036] Step S110: A mixture is prepared by mixing a raw material containing silicon (Si), a raw material containing germanium (Ge), a raw material containing gallium (Ga), a raw material containing phosphorus (P), and metal silicide particles. Step S120: The mixture obtained in step S110 is fired. The n-type thermoelectric material of the present invention can be obtained by the above-mentioned steps S110 and S120. Each step will be described in detail below.

[0037] In step S110, the Si-containing raw material may be Si metal alone, or an oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride of Si. The Ge-containing raw material may be Ge metal alone, or a silicide, oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride of Ge. The Ga-containing raw material may be Ga metal alone, or an oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride of Ga. The P-containing raw material may be P alone, or an oxide, carbonate, nitride, oxynitride, chloride, fluoride, or oxyfluoride of P. Note that Ge silicide can be used as the Si-containing raw material and the Ge-containing raw material.

[0038] Gallium phosphide (GaP) may be used as the Ga-containing raw material or the P-containing raw material. The metal silicide particles are preferably at least one element selected from the group consisting of molybdenum (Mo), chromium (Cr), tungsten (W), cobalt (Co), and nickel (Ni). From the standpoint of mixability and handling, the raw material is preferably in the form of powder, grains, or small lumps.

[0039] In step S110, the metal elements in the raw material mixture are selected to have the following composition formula: Si a Ge b P c Ga d M e (M is at least one element selected from the group consisting of molybdenum (Mo), chromium (Cr), tungsten (W), cobalt (Co), and nickel (Ni), and satisfies a+b+c+d+e=1), and the parameters a, b, c, d, and e are 0.3≦a≦0.85 0.1≦b≦0.65 0.01≦c≦0.06 0.003≦d≦0.02 0.003≦e≦0.02 This results in the above-mentioned n-type thermoelectric material.

[0040] The parameters a, b, c, d and e are more preferably: 0.5≦a≦0.75 0.2≦b≦0.45 0.014≦c≦0.04 0.006≦d≦0.01 0.004≦e≦0.01 This results in an n-type thermoelectric material that exhibits particularly excellent thermoelectric properties in the high temperature range and can achieve a dimensionless figure of merit (ZT) of over 1.4 at 850°C.

[0041] For example, in step S110, when Si powder is used as the Si-containing raw material, Ge chunks are used as the Ge-containing raw material, GaP chunks are used as the Ga-containing raw material, and P chunks are used as the P-containing raw material, Si α Ge β P γ (GaP) δ In the composition formula represented by (α+β+γ+δ=1), the parameters α, β, γ, and δ are 0.5≦α≦0.75 0.22≦β≦0.27 0.005≦γ≦0.03 0.005≦δ≦0.025 This allows the above-mentioned n-type thermoelectric material to be obtained.

[0042] In step S110, the metal silicide particles in the mixture preferably satisfy the range of 0.5% to 2.5% by volume percentage, which allows them to be dispersed in the SiGe alloy. The metal silicide particles more preferably satisfy the range of 1% to 2% by volume percentage, which allows them to be dispersed in the SiGe alloy and improve the thermoelectric properties.

[0043] The mixture obtained in step S110 may be uniformly mixed by mechanical milling using a ball mill or the like, and then molded by pressing or the like. For example, the mixture may be compressed at a pressure in the range of 5 MPa to 10 MPa to obtain a compact. The mechanical milling may be performed, for example, in an argon atmosphere for 1 hour to 24 hours.

[0044] 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 pulse current sintering, but is preferably performed 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 additive.

[0045] The firing is preferably carried out at a temperature ranging from 900°C to 1050°C. This promotes sintering. For example, when SPS is employed, the firing is preferably carried out at a temperature ranging from 900°C to 1050°C under a pressure of from 30 MPa to 100 MPa for from 1 minute to 30 minutes. Under these conditions, the thermoelectric material of the present invention, which is the sintered body described above, can be obtained with a high yield. The sintering time is more preferably from 1 minute to 10 minutes, and even more preferably from 2 minutes to 5 minutes. This generates lattice distortion, further improving electrical conductivity in the medium temperature range and providing an n-type thermoelectric material with improved thermoelectric performance.

[0046] The resulting sintered body may then be pulverized by mechanical milling such as a ball mill, thereby obtaining the thermoelectric material of the present invention in the form of a powder.

[0047] A flexible thermoelectric material can be provided by mixing the thus obtained powdered thermoelectric material of the present invention with an organic material. In this case, the organic material and mixing ratio described above can be used.

[0048] Alternatively, the obtained sintered body may be used as a target to carry out physical vapor deposition, thereby providing a thin film made of the thermoelectric material of the present invention.

[0049] (Embodiment 2) In the second embodiment, a thermoelectric generating element using the thermoelectric material of the present invention described in the first embodiment will be described.

[0050] FIG. 2 is a schematic diagram showing a thermoelectric power generating element using the n-type thermoelectric material of the present invention.

[0051] A thermoelectric power generating element 200 according to the present invention includes an n-type thermoelectric material 210 and electrodes 220, 230 at each end of the n-type thermoelectric material 210. The n-type thermoelectric material 210 is the n-type thermoelectric material of the present invention described in the first embodiment.

[0052] The electrodes 220, 230 may be made of a common electrode material, illustratively Fe, Ag, Al, Ni, Cu, or the like.

[0053] FIG. 2 shows a state in which a chip made of n-type thermoelectric material 210 is joined to an electrode 230 on the low-temperature side by solder or the like, and the opposite end of the chip of n-type thermoelectric material 210 is joined to an electrode 220 on the high-temperature side by solder or the like.

[0054] When the thermoelectric power generation element 200 of the present invention is placed in an environment where the electrode 220 is at a high temperature and the electrode 230 is at a lower temperature than the electrode 220, and the end electrodes are connected to an electric circuit or the like, a voltage is generated due to the Seebeck effect, and a current flows in the order of the electrode 230, the n-type thermoelectric material 210, and the electrode 220, as shown by the arrows in Figure 2. More specifically, the current flows based on the principle that electrons in the n-type thermoelectric material 210 obtain thermal energy from the electrode 220 on the high-temperature side, move to the electrode 230 on the low-temperature side, and release the thermal energy there. Such a thermoelectric power generation element 200 may be called a single-element power generation element.

[0055] Since the n-type thermoelectric material of the present invention described in the first embodiment is used as the n-type thermoelectric material 210, even the thermoelectric power generation element 200 of a single element module exhibits excellent energy conversion efficiency in the high temperature range.

[0056] FIG. 3 is a schematic diagram showing another thermoelectric power generating element using the n-type thermoelectric material of the present invention.

[0057] Another thermoelectric power generating element 300 according to the present invention includes a pair of n-type and p-type thermoelectric materials 310 and 320, and electrodes 330 and 340 at their respective ends. The electrodes 330 and 340 electrically connect the n-type and p-type thermoelectric materials 310 and 320 in series.

[0058] The n-type thermoelectric material 310 is the thermoelectric material of the present invention described in embodiment 1. The n-type thermoelectric material of the present invention exhibits excellent performance in the high temperature range and is effective for converting waste heat into energy.

[0059] Here, the p-type thermoelectric material 320 is not particularly limited, but preferably has high thermoelectric performance (for example, ZT of 0.4 to 1.6) in the high temperature range from room temperature to 950° C. For example, the p-type thermoelectric material 320 may be a BiSbTe-based material, an MgAgSb-based material, an SiGe-based material, or a LaFe3CoSb-based material. 12 , FeNbSb, HfCoSb, Yb 14 MnSb 11 , Cu2Se, Zn4Sb3, AbSbSe systems, etc.

[0060] An exemplary composition of the BiSbTe system 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, MgAg 0.965 Ni 0.005 Sb 0.99 An exemplary composition of the SiGe system is, for example, Si 0.724 Ge 0.241 P 0.025 An exemplary composition of the FeNbSb system is FeNb 1-x Sb x (0.06≦x≦0.2). An exemplary composition of the AgSbSe system is, for example, AgSbSe2. Note that these are examples and are not limiting.

[0061] The electrodes 330, 340 may be made of a common electrode material, such as Fe, Ag, Al, Ni, or Cu.

[0062] When the thermoelectric power generation element 300 of the present invention is placed in an environment where the electrode 330 is at a high temperature and the electrode 340 is at a lower temperature than the electrode 330, 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 340, the n-type thermoelectric material 310, the electrode 330, and the p-type thermoelectric material 320, as shown by the arrows in Figure 3.

[0063] The high-temperature side temperature of the thermoelectric power generation element 300 of the two-pair module is controlled by the stability of the p-type thermoelectric material 320, so that, for example, by using a p-type thermoelectric material (e.g., MgAgSb) that has high performance in the low temperature range below 300°C, it is possible to provide a thermoelectric power generation element that operates from room temperature to a low temperature range. Such a thermoelectric power generation element 300 may be called a two-pair power generation element.

[0064] Furthermore, when the n-type thermoelectric material of the present invention is a powder made of a composite containing a silicon germanium (SiGe) alloy to which phosphorus (P) and at least one substance selected from the group consisting of gallium phosphide (GaP) and gallium (Ga) have been added, and metal silicide particles dispersed therein, or a film containing the powder, or when the thermoelectric material of the present invention is a thin film obtained by targeting a sintered body made of the composite, it is possible to provide a flexible thermoelectric power generation module as an IoT power source.

[0065] 3, the n-type thermoelectric material of the present invention may be used in a U-shaped thermoelectric power generation element (not shown). In this case as well, the n-type thermoelectric material of the present invention and a known p-type thermoelectric material are electrically connected alternately in series.

[0066] 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]

[0067] [Raw materials] In the following examples, Si (powder, purity 5N-10N, particle size 45 μm, manufactured by Sigma-Aldrich Japan LLC), Ge (lump, purity 5N, size 0.5 mm-1 mm, manufactured by Sigma-Aldrich Japan LLC), P (lump, purity 2N, size 0.1 mm-0.5 mm, manufactured by Sigma-Aldrich Japan LLC), GaP (lump, purity 3N, size 0.1 mm-0.5 mm, manufactured by Sigma-Aldrich Japan LLC), MoSi2 (powder, purity 4N, particle size 50 nm, manufactured by Sigma-Aldrich Japan LLC), and WSi2 (powder, purity 4N, particle size 50 nm, manufactured by Sigma-Aldrich Japan LLC) were used.

[0068] [Example 1 to Example 8] In Examples 1 to 8, composites containing a silicon germanium (SiGe) alloy with added phosphorus (P), gallium phosphide (GaP), and gallium (Ga) and MoSi2 or WSi2 as metal silicide particles dispersed therein were synthesized, and their thermoelectric properties were evaluated.

[0069] According to Table 1, Si powder as a silicon (Si)-containing raw material, Ge chunks as a germanium (Ge)-containing raw material, GaP chunks as a gallium (Ga)-containing raw material, P chunks as a phosphorus (P)-containing raw material, and MoSi2 / WSi2 powder as metal silicide particles were mixed to prepare a mixture (step S110 in FIG. 1). For example, in Example 1, Si powder, Ge chunks, P chunks, and GaP chunks were mixed (total 10 g) in the molar ratio shown in Table 1, and MoSi2 powder was mixed therewith. At this time, the ratio (volume ratio) of the mixture of Si powder, Ge chunks, P chunks, and GaP chunks to MoSi2 powder was 99:1.

[0070] The mixture was then pulverized using a ball mill (SPEX SamplePrep LLC, Ball Mill 8000D). Steel balls were used as pulverizing balls, and the mixture was placed in a ball mill container at a ratio (volume ratio) of 1:5. The ball mill container was sealed in an argon atmosphere, and pulverization was carried out for 12 hours.

[0071] The pulverized mixture was fired (step S120 in FIG. 1). The mixture was compacted in a press (pressure 10 MPa) to obtain a green body. The size of the green body was 10 mm in diameter and 8 mm in thickness. The pulverized mixture was handled in a glove box.

[0072] The compact was placed in a graphite sintering die (inner diameter 10 mm, height 30 mm) and sintered using a spark plasma sintering apparatus (SPS, manufactured by SPS Syntex, Inc., SPS-1080 system) under the sintering conditions shown in Table 1. The degree of vacuum inside the spark plasma sintering apparatus was maintained at 1 Pa to 2 Pa, the temperature was increased at a rate of 25°C / min, and the temperature was maintained at 952°C or 900°C for 3 minutes, after which it was allowed to cool for 15 minutes and the sintered compact was removed.

[0073] The appearance of the sintered body was observed. The microstructure and composition of the sintered body were evaluated using a scanning electron microscope (FESEM, Hitachi SU8000) and an atomic resolution electron microscope (STEM, JEM-ARM300F) equipped with an energy dispersive spectrometer (EDS, XFlash FlatQUAD 5060F). The EDS acceleration voltage was 300 keV. The sintered body was wet-ground using ethanol in an agate mortar. After grinding, the particles of the sintered body 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 an X-ray diffractometer (Rigaku Corporation, Rigaku SmartLab 9kW).

[0074] The sintered bodies were cut into rectangular parallelepipeds measuring 1 cm x 1 cm x 0.3 cm 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 (Advance Riko Co., Ltd., ZEM-3) and a thermal conductivity evaluation device (NETZSCH, LFA467 Hyperflash), respectively. Measurements were performed in a helium gas atmosphere over a temperature range from room temperature to 850°C. 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.

[0075] For simplicity, the manufacturing conditions for the samples of Examples 1 to 8 are summarized in Table 1, and the above results will be explained.

[0076] [Table 1]

[0077] FIG. 4 shows an SEM image, an EDS image, and a TEM image of the sample of Example 1.

[0078] In Figure 4, (A) is an SEM image, (B) is an EDS image, and (C) to (E) are TEM images. According to Figure 4(A), the sample of Example 1 was a sintered body made of particles with a particle size of 100 nm to 300 nm, and had pores with a pore size of 300 nm to 1000 nm. The average particle size was 190 nm, and the average pore size was 900 nm. As shown in Table 2, it was confirmed that the samples of Examples 2 to 8 were also sintered bodies made of particles with an average particle size of 100 nm to 500 nm, and had pores with an average pore size of 300 nm to 1500 nm. The porosity of the sample of Example 1 was 7%, and the porosities of the samples of Examples 2 to 8 all fell within the range of 5% to 10%.

[0079] Figure 4(B) is shown in grayscale, with bright areas indicating the location of MoSi2 particles. Figure 4(B) reveals that the MoSi2 particles are uniformly distributed in the base material, with a particle size of 50 nm. The dark areas in the grayscale reveal the distribution of Si and Ge, indicating a SiGe-based compound. Another EDS image (not shown) of Example 1 reveals the presence of P, Ga, and GaP. From this, it is inferred that the GaP masses were partially decomposed into P and Ga. Those skilled in the art will understand that, depending on the reaction temperature, the decomposition of GaP can be suppressed to produce a SiGe-based alloy with P and GaP added, or that GaP can be completely decomposed to produce a SiGe-based alloy with P and Ga added.

[0080] As shown in Table 2, the samples of Examples 1 to 8 have the composition formula Si a Ge b P c Ga d M e where the parameters a, b, c, d and e are 0.5≦a≦0.75 0.2≦b≦0.45 0.014≦c≦0.04 0.006≦d≦0.01 0.004≦e≦0.01 It was confirmed that the following was satisfied.

[0081] The TEM images in Figures 4(C) and 4(D) reveal the presence of line defects and twin lattice defects in the L1 and L2 regions of the base material of the sample in Example 1. Lattice fringes are observed in the TEM image in Figure 4(E).

[0082] Furthermore, XRD confirmed that the samples of Examples 1 to 8 had a diamond structure, and as shown in Table 2, the base material SiGe was an alloy having a diamond structure.

[0083] [Table 2]

[0084] From the above, it has been shown that the method of Figure 1 can produce a composite containing a silicon germanium (SiGe)-based alloy to which phosphorus (P) and gallium phosphide (GaP) and / or gallium (Ga) have been added, and MoSi2 or WSi2 as metal silicide particles dispersed therein.

[0085] FIG. 5 is a diagram showing the thermoelectric properties of the sample of Example 1. FIG. 6 is a graph showing the thermoelectric properties of the sample of Example 2. FIG. 7 is a graph showing the thermoelectric properties of the sample of Example 3. FIG. 8 is a diagram showing the thermoelectric properties of the sample of Example 4. FIG. 9 is a diagram showing the thermoelectric properties of the sample of Example 5. FIG. 10 is a diagram showing the thermoelectric properties of the sample of Example 6. FIG. 11 is a diagram showing the thermoelectric properties of the sample of Example 7. FIG. 12 is a diagram showing the thermoelectric properties of the sample of Example 8.

[0086] Figures 5(A) to 12(A) are graphs showing the temperature dependence of the Seebeck coefficient and electrical resistivity. Figures 5(B) to 10(B) are graphs showing the temperature dependence of the thermal conductivity and dimensionless figure of merit (ZT). Figures 11(B) to 12(B) are graphs showing the temperature dependence of the power factor (PF).

[0087] [Table 3]

[0088] The electrical resistance of the samples of Examples 1 to 8 tended to increase as the temperature increased, but slightly decreased at a temperature of 700°C. On the other hand, the Seebeck coefficient of the samples of Examples 1 to 8 was a negative value, and tended to increase in absolute value as the temperature increased, but slightly decreased at a temperature of 700°C.

[0089] The thermal conductivity of the samples of Examples 1 to 8 showed a tendency to decrease as the temperature increased, and although it increased slightly above a temperature of 700° C., the thermal conductivity at higher temperatures was significantly suppressed.

[0090] The dimensionless figure of merit ZT of the samples of Examples 1 to 8 increased as the temperature increased, and all exceeded 1.4 at a temperature of 850°C, as shown in Table 2. In particular, Examples 1, 3, 5, 6, and 8 exhibited a dimensionless figure of merit ZT of 1.7 or more at a temperature of 850°C.

[0091] From the above, it was shown that a composite containing a silicon germanium (SiGe) alloy to which phosphorus (P) and gallium phosphide (GaP) and / or gallium (Ga) have been added, and metal silicide particles dispersed therein, functions as an n-type thermoelectric material. In particular, the n-type thermoelectric material of the present invention exhibits excellent thermoelectric properties, with thermal conductivity suppressed in the high temperature range of 600°C to 1050°C, and a dimensionless figure of merit ZT exceeding 1.3. [Industrial Applicability]

[0092] The n-type thermoelectric material of the present invention has excellent thermoelectric performance in the high-temperature range of 600°C to 1050°C 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 be used to provide flexible thermoelectric generation elements as IoT power sources. [Explanation of symbols]

[0093] 200, 300 Thermoelectric power generation element 210, 310 n-type thermoelectric materials 220, 230, 330, 340 electrodes 320 p type thermoelectric material

Claims

1. a silicon germanium (SiGe)-based alloy to which phosphorus (P) and at least one substance selected from the group consisting of gallium phosphide (GaP) and gallium (Ga) are added; Metal silicide particles dispersed in the SiGe-based alloy; 1. An n-type thermoelectric material comprising a composite containing:

2. The metal silicide particles are MSi ２ 2. The n-type thermoelectric material according to claim 1, wherein the n-type thermoelectric material is a metal silicide represented by the formula:

3. The n-type thermoelectric material according to claim 1 or 2, wherein the metal silicide particles in the composite satisfy a volume percentage range of 0.5% to 2.5%.

4. The n-type thermoelectric material according to claim 3 , wherein the content of the metal silicide particles in the composite satisfies the range of 1% to 2% by volume.

5. The composite has the composition formula Si ａ Ge ｂ P ｃ Ga ｄ M ｅ (M is at least one element selected from the group consisting of molybdenum (Mo), chromium (Cr), tungsten (W), cobalt (Co), and nickel (Ni), and a+b+c+d+e=1 is satisfied), and the parameters a, b, c, d, and e are 0.3≦a≦0.85 0.1≦b≦0.65 0.01≦c≦0.06 0.003≦d≦0.02 0.003≦e≦0.02 The n-type thermoelectric material according to any one of claims 1 to 4, which satisfies the following:

6. The parameters a, b, c, d and e are 0.5≦a≦0.75 0.2≦b≦0.45 0.014≦c≦0.04 0.006≦d≦0.01 0.004≦e≦0.01 The n-type thermoelectric material according to claim 5 , which satisfies the following:

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

8. the composite is in the form of the sintered body; 8. The n-type thermoelectric material according to claim 7, which consists of particles having an average particle size in the range of 100 nm to 500 nm.

9. The n-type thermoelectric material according to claim 7 or 8, wherein the sintered body has pores with an average pore diameter in the range of 300 nm to 1500 nm.

10. the complex is in the form of a powder; The n-type thermoelectric material of claim 7 , further comprising an organic material.

11. Mixing a raw material containing silicon (Si), a raw material containing germanium (Ge), a raw material containing gallium (Ga), a raw material containing phosphorus (P), and metal silicide particles to prepare a mixture; baking the mixture; A method for producing the n-type thermoelectric material according to any one of claims 1 to 10, comprising:

12. Preparing the mixture comprises: Si powder as the silicon (Si)-containing raw material, Ge chunks as the germanium (Ge)-containing raw material, GaP chunks as the gallium (Ga)-containing raw material, and P chunks as the phosphorus (P)-containing raw material, Si α Ge β P γ (GaP) δ In the composition formula expressed as (α+β+γ+δ=1), the parameters α, β, γ, and δ are ０．５≦α≦０．７５ ０．２２≦β≦０．２７ 0.005≦γ≦0.03 0.005≦δ≦0.025 The method according to claim 11, wherein the mixing is carried out so as to satisfy the above.

13. The method according to claim 11 or 12, wherein preparing the mixture comprises the metal silicide particles in the mixture satisfying a volume percentage range of 0.5% to 2.5%.

14. The method according to any one of claims 11 to 13, wherein the firing comprises firing the mixture at a temperature in the range of 900°C or higher and 1050°C or lower.

15. The method according to any one of claims 11 to 14, further comprising pulverizing the sintered body obtained by the firing.

16. 16. The method of claim 15, further comprising mixing the powder with an organic material by said grinding.

17. The method according to any one of claims 11 to 14, further comprising carrying out a physical vapor deposition method using the sintered body obtained by the firing.

18. A thermoelectric power generating element including at least an n-type thermoelectric material, A thermoelectric power generation element, wherein the n-type thermoelectric material is the n-type thermoelectric material according to any one of claims 1 to 10.

19. 20. The thermoelectric generator of claim 18, comprising p-type thermoelectric materials connected in series alternating with the n-type thermoelectric materials.

20. The p-type thermoelectric material is a BiSbTe-based, MgAgSb-based, SiGe-based, LaFe ３ CoSb １２ , FeNbSb, HfCoSb, Yb １４ MnSb １１ , Cu ２ Se, Zn ４ Sb ３ 20. The thermoelectric power generating element according to claim 19, wherein the thermoelectric power generating element is selected from the group consisting of AgSbSe-based materials and AgSbSe-based materials.

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