JP6923182B2 - Thermoelectric conversion materials and their manufacturing methods, thermoelectric power generation modules, and Perche coolers - Google Patents

Description

The present invention relates to a thermoelectric conversion technique, and more particularly to a thermoelectric conversion material and a method for manufacturing the same, a thermoelectric power generation module, and a Perche cooler.

Thermoelectric conversion directly converts thermal energy and electrical energy using a semiconductor device. The thermoelectric device generates electricity with a temperature gradient based on the Seebeck effect. Thermoelectric technology can recover waste heat generated in automobiles, thermal power plants, data centers, etc. to generate electricity, which will make a great contribution to overcoming the energy crisis and reducing the generation of carbon dioxide gas.

Thermoelectric cooling, on the other hand, uses the Perche effect to create a flow of heat as it consumes electrical energy. This phenomenon has come to be used more and more for cooling and refrigeration. Since the cooling device by the Perche effect has no moving parts, it has a long life, can be miniaturized, and is easy to carry.

Thermoelectric conversion requires a thermoelectric conversion material, and the performance of the material is represented by the dimensionless thermoelectric figure of merit ZT, where ZT = S ² T / (ρκ _total ). Here, S is the Seebeck coefficient of the thermoelectric conversion material, ρ is the electrical resistivity of the thermoelectric conversion material, κ _total is the thermal conductivity of the thermoelectric conversion material, and T is the absolute temperature.

There are two methods to improve the ZT of the thermoelectric conversion material, one is ^{to improve the power factor S 2} / ρ, and the other is to improve the thermal conductivity κ _total . To lower it. Over the last 15 years, many thermoelectric conversion materials have had their thermal conductivity κ _total significantly reduced by nanostructuring (thermal conductivity κ _total is _{represented by κ total} = κ _lat + κ _e , where κ _lat is. Lattice thermal conductivity, κ _e is electron thermal conductivity.). Nanostructuring is the embedding of nanoscale inclusions in bulk substrates, which can dramatically reduce _{thermal conductivity κ total by scattering short wavelength heat transport phonons.}

Currently, lead telluride (PbTe) has the highest performance as a thermoelectric conversion material, and the non-nanostructured material has a ZT value of approximately 1, which is improved by up to 50 to 70% by appropriate doping and nanostructured. (See, for example, Non-Patent Document 1).

The best approach to date for nanostructuring PbTe is a composite material with PbTe as the bulk substrate and embedded with matched or semi-matched nanoscale inclusions represented by structure AB. Here, A is an alkaline earth element composed of Be, Mg, Ca, Sr, Ba and Ra, and B is a chalcogen element composed of S, Se and Te (see, for example, Patent Document 1).

Composites and the mesoscale structure nanoscale precipitate formed was Pb _0.98 Na _0.02 composition of Te-6at% MgTe, in the composite material of the composition of _{Pb 0.98 Na 0.02 Te-8at%} SrTe that is nanostructured, ZT value 2 to 2.5 was obtained at 923K (see, for example, Non-Patent Documents 2 and 3). With these nanostructured PbTe materials, the device efficiency of the thermoelectric power generation module is 11% with a temperature difference of 590 K (see, for example, Non-Patent Document 4). These materials have achieved twice the device efficiency obtained in a thermoelectric power generation module using the commercially available thermoelectric conversion material Bi ₂ Te _{3 (see, for example, Non-Patent Document 5).}

International Publication No. 2011-037794

K. Biswas et al., “High-performance bulk thermoelectrics with all-scale hierarchical architectures”, Nature, 2012, Vol. 489, p.414-418 L. D. Zhao et al., “All-scale hierarchical thermoelectric: MgTe in PbTe facilitates valence band convergence and suppresses bipolar thermal transport for high performance”, Energy & Environmental Science, 2013, Vol. 6, p.3346-3355 Gangjian Tan et al., “Non-equilibrium processing leads to record high thermoelectric figure of merit in PbTe-SrTe”, Nature Communication, 2016, Vol. 7, Article No. 12167, p.1-9 Xiaokai Hu et al., “Power generation from nanostructured PbTe-based thermoelectric: comprehensive development from materials to modules”, Energy & Environmental Science, 2016, Vol. 9, p.517-529 Michihiro Ota, Jun Yamamoto, "Effective Utilization of Unused Thermal Energy by Thermoelectric Conversion", Energy and Resources, 2013, Vol. 34, No. 6, p.332-336

However, Be, Mg, Ca, Sr and Ba contained in the above-mentioned thermoelectric conversion material are not only difficult to store and handle before producing the material because they are easily oxidized and sensitive to humidity, but also are contained in PbTe. If so, the thermoelectric conversion material tends to deteriorate rapidly.

An object of the present invention has been made in view of the above problems, and an object of the present invention is to provide a thermoelectric conversion material having stable characteristics and high performance, a method for manufacturing the same, a thermoelectric power generation module, and a Perche cooler.

According to one aspect of the present invention, a thermoelectric conversion material containing a base material containing PbTe and at least one element (M) selected from the group consisting of C, Si, Ge and Sn in the base material. Provided are the thermoelectric conversion material comprising, including nanoprecipitates.

According to the above aspect, the thermoelectric conversion material is a material that is easily deteriorated by containing a nanoprecipitate having at least one element M selected from the group consisting of C, Si, Ge and Sn in the base material of PbTe. Since it does not contain, it exhibits stable properties and can provide a high-performance thermoelectric conversion material.

According to another aspect of the present invention, a method for producing a thermoelectric conversion material, which comprises Pb, Te, and at least one element (M) selected from the group consisting of C, Si, Ge and Sn. The production method is provided, which comprises a step of preparing a material containing the material and a step of heating and melting the prepared material in a vacuum to obtain a material containing the nanoprecipitate containing the M.

According to the above aspect, heating is heated with at least one element M selected from the group consisting of lead (Pb), tellurium (Te), carbon (C), silicon (Si), germanium (Ge) and tin (Sn). By dissolving, a thermoelectric conversion material of a PbTe substrate having nanoprecipitates containing the element M can be obtained. Since this thermoelectric conversion material does not use a material that easily deteriorates, it is easy to handle, and the obtained thermoelectric conversion material has stable properties.

According to another aspect of the present invention, there is provided a thermoelectric power generation module including a thermoelectric conversion element having the thermoelectric conversion material of the above aspect.

According to the above aspect, by having the thermoelectric conversion material of the above aspect, a thermoelectric power generation module having stable characteristics and high power generation performance can be realized.

According to another aspect of the present invention, there is provided a Perche cooler comprising a thermoelectric cooling element having the thermoelectric conversion material of the above aspect.

According to the above aspect, by having the thermoelectric conversion material of the above aspect, a Perche cooler having stable characteristics and a high cooling capacity can be realized.

It is a transmission electron micrograph of a thermoelectric conversion material which concerns on 1st Embodiment of this invention. It is a high-angle scattering dark-field scanning transmission electron micrograph and an energy dispersive X-ray analysis image of the thermoelectric conversion material according to the first embodiment of the present invention. Other high-angle scattering dark-field scanning transmission electron micrographs and energy dispersive X-ray analysis images of the thermoelectric conversion material according to the first embodiment of the present invention. It is a powder X-ray diffraction pattern of the thermoelectric conversion material which concerns on 1st Embodiment of this invention. It is a flowchart which shows the manufacturing method of the thermoelectric conversion material which concerns on 1st Embodiment of this invention. It is a figure which shows the temperature dependence of the electrical resistivity of the Example and the comparative example of the thermoelectric conversion material which concerns on the 1st Embodiment of this invention. It is a figure which shows the temperature dependence of the Seebeck coefficient of the Example and the comparative example of the thermoelectric conversion material which concerns on the 1st Embodiment of this invention. It is a figure which shows the temperature dependence of the output factor of the Example and the comparative example of the thermoelectric conversion material which concerns on 1st Embodiment of this invention. (A) and (B) are diagrams showing the temperature dependence of the thermal conductivity and the lattice thermal conductivity of Examples and Comparative Examples of the thermoelectric conversion material according to the first embodiment of the present invention, respectively. It is a figure which shows the temperature dependence of the dimensionless thermoelectric figure of merit ZT of the Example and the comparative example of the thermoelectric conversion material which concerns on 1st Embodiment of this invention. It is the schematic of the thermoelectric power generation module which concerns on one Embodiment of this invention. It is the schematic of the Perche cooler which concerns on one Embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[First Embodiment]
The thermoelectric conversion material according to the first embodiment of the present invention is a lead (PbTe) tellurized thermoelectric conversion material containing a nanostructured Group 14 element, and has an extremely high dimensionless figure of merit ZT (about 2. 5) was obtained.

The thermoelectric conversion material according to the first embodiment is selected from the group consisting of Group 14 elements carbon (C), silicon (Si), germanium (Ge) and tin (Sn) in the base material of PbTe. Includes nanoprecipitates containing at least one element (hereinafter referred to as "M" or "element M"). By containing a very small amount of element M, nanoprecipitates of different shapes and sizes appear uniformly dispersed in the PbTe substrate, and the nanoprecipitates have various mean free paths. Is thought to scatter. In the examples described later, Ge, which is a Group 14 element, is contained as the element M. However, since the elements contained in the Group 14 element have similar electron arrangements, C, Si, and Sn are used instead of Ge. Even if any of them is contained, it is considered that the same effect as in the case of Ge can be obtained in the PbTe substrate, and further, it is considered that two or more kinds may be combined from Ge, C, Si, and Sn.

The thermoelectric conversion material according to the first embodiment is a P-type thermoelectric conversion material, and as acceptors, Group 1 elements (lithium (Li), sodium (Na), potassium (K)), Group 11 elements ( At least one element selected from the group consisting of copper (Cu), silver (Ag), gold (Au)) and Group 13 element (thallium (Tl)) (hereinafter referred to as "A" or "element A"). .) May be included. In the examples described later, the element A is Na, but instead of Na, elements other than Na, which is a Group 1 element, and Group 11 elements and Group 13 elements, which have an electronic structure similar to Na, may be contained. Well, with the element M, the lattice thermal conductivity can be reduced.

The thermoelectric conversion material according to the first embodiment is represented by, for example, a composition formula of _{Pb 1-xy} A _y M _{x Te.} Here, x and y represent the contents of the element M and the element A as atomic ratios with respect to the total amount of Pb, the element M and the element A, respectively.

It is preferable that the content x of the element M is greater than 0 and 0.015 or less, the content y of the element A is greater than 0 and 0.1 or less, and further, x is 0.002 or more and 0. It is preferably .012 or less, and more preferably x is 0.007 or more and 0.010 or less.

Further, in the composition of the thermoelectric conversion material having an atomic ratio of x described above, the element A is preferably Na and y is preferably 0.04. Thereby, the dimensionless thermoelectric figure of merit ZT can be improved.

Further, in the composition of the thermoelectric conversion material described above, it is particularly preferable that the element M is Ge.

FIG. 1 is a transmission electron micrograph of a thermoelectric conversion material according to the first embodiment of the present invention. The composition of this thermoelectric conversion material is Pb _0.953 Na _0.04 Ge _0.007 Te, which is a microscopic image of [001] axial orientation.

With reference to FIG. 1, two different types of nanoprecipitates appear lattice-matched embedded in the crystals of the substrate, one of which, as shown in the dashed ellipse of (a). The other is a disk shape having a particle size (diameter) of 2 to 5 nm, and the other is a pseudo-sphere having a particle size (diameter) of 5 to 10 nm as shown in the broken line ellipse of (b). These nanoprecipitates can scatter phonons with a short mean free path.

In FIG. 2A, (i) is a high-angle scattering dark-field scanning electron micrograph, and (ii) and (iii) are energy dispersive X-ray analysis images of the thermoelectric conversion material according to the first embodiment of the present invention. The composition of this thermoelectric conversion material is Pb _0.953 Na _0.04 Ge _0.007 Te, which is sintered by the method described later, and is a microscope image of [220] axial orientation.

With reference to FIG. 2A, it can be seen that in (i), extremely large nanodepositions having a major axis of about 0.6 μm appear in the voids (pore) in the base material. According to (ii) of the energy dispersive X-ray analysis image, the nanoprecipitate has a phase containing Ge, and according to (iii), the nanoprecipitate does not contain Pb. Further, according to the study of the inventor, it is known that the nano-precipitate contains Na, and the nano-precipitate contains Ge-Na.

FIG. 2B is another high-angle scattering darkfield scanning electron micrograph (i) and energy dispersive X-ray analysis images, (ii) and (iii) of the thermoelectric conversion material according to one embodiment of the present invention. This thermoelectric conversion material is the same sample as in FIG. 2A.

With reference to FIG. 2B, (i) shows precipitates having a particle size of 5 nm to 100 nm in the substrate. According to (ii) of the energy dispersive X-ray (EDX) analysis image, nanoprecipitates having a particle size of at least 20 nm to 100 nm consist of a phase containing Ge, and according to (iii), those nanoprecipitates are Pb. It can be seen that it does not contain. Further, according to the study of the present inventor, it is known that the nano-precipitate contains Na, and that the nano-precipitate contains Ge-Na.

In these EDX analysis images, since the analysis of the precipitate having a particle size of 5 nm is near the detection limit of the apparatus, the content of Ge is not clearly shown, but the nanoprecipitate having a particle size of 20 nm to 100 nm is not clearly shown. Contains Ge-Na, and the transmitted electron microscope image of (i) shows that the nanodeposition having a particle size of 5 nm has the same shape as the nanodeposition having a particle size of 20 nm. It is presumed that the substance is also a precipitate having the same composition. Further, it is presumed that the disk-shaped precipitate having a particle size (diameter) of 2 to 5 nm in FIG. 1 is also a precipitate having the same composition.

Therefore, according to FIGS. 1, 2A and 2B, and the inventor's examination, the Ge-Na nanoprecipitates in the PbTe substrate have various particle sizes (particle size of 2 nm to 1 μm). It can efficiently scatter phonons with a wide range of mean free paths, from short to long mean free paths. In the specification, claims, drawings and abstracts of the present application, the term "nanoprecipitate" refers to various particle sizes precipitated in the crystals of a substrate, for example, particle sizes of 2 nm to 1 μm, as described above. Means a precipitate.

FIG. 3 is a powder X-ray diffraction pattern of the thermoelectric conversion material according to the first embodiment of the present invention. The composition of the thermoelectric conversion material according to one embodiment of the present invention is _{Pb 1-x-0.04 Na 0.04} Ge x Te (x = 0.007,0.01). Note that FIG. 3 also shows the diffraction pattern of the sample with x = 0 for comparison.

With reference to FIG. 3, in the powder X-ray diffraction pattern, only the peak of the face-centered cubic lattice structure (NaCl structure) appears, and the diffraction pattern due to the secondary phase does not appear. It can be seen that the [200] diffraction line, which is the highest intensity peak, shifts to the higher angle side as the Ge content increases, as shown by expanding to the upper right. This peak shift to the high angle side indicates a decrease in the lattice constant of PbTe, that is, a contraction of the lattice. According to the study of the present inventor, it is presumed that the contraction of the PbTe lattice causes Na atoms to be extruded from the PbTe lattice due to the presence of Ge atoms to generate Ge-Na nanoprecipitates in the PbTe substrate. doing.

The table below shows the hole concentration p and the hole mobility μ _h of the thermoelectric conversion materials (Pb _0.953 Na _0.04 Ge _0.007 Te and Pb _0.95 Na _0.04 Ge _{0.01 Te) according to the first embodiment.} Pb _0.96 Na _0.04 Te is shown for comparison

上記の表を参照するに、ＰｂＴｅ中に少量（０.７原子％）であってもＧｅが存在すると、格子中のドーパント（アクセプター）であるＮａの固溶度が減少する。その結果、Ｐｂ_0.96Ｎａ_0.04Ｔｅに対して、Ｐｂ_0.953Ｎａ_0.04Ｇｅ_0.007ＴｅおよびＰｂ_0.95Ｎａ_0.04Ｇｅ_0.01Ｔｅのホール濃度ｐがわずかに減少する。

With reference to the above table, the presence of Ge in PbTe even in a small amount (0.7 atomic%) reduces the solid solubility of Na, which is a dopant (acceptor) in the lattice. As a result, the hole concentration p of _{Pb 0.953} Na _0.04 Ge _0.007 Te and Pb _0.95 Na _0.04 Ge _0.01 Te is slightly reduced with respect to _{Pb 0.96} Na _{0.04 Te.}

The Ge-Na nanoprecipitate is contained consistently with the PbTe substrate. That is, the crystal lattice of the PbTe substrate and the crystal lattice of the Ge-Na nanoprecipitate are aligned or quasi-matched so that the electronic structure of the thermoelectric conversion material hardly changes with respect to the electronic structure of the PbTe substrate. doing. As a result, it is believed that charge carriers can easily move in the thermoelectric conversion material, which is a composite material, without being scattered by the matched nanoprecipitates. This means that, as shown in the above table, the hole mobilities (μ _h ) _{of the holes, which are charge carriers, are Pb 0.96} Na _0.04 Te, while Ge-added Pb _0.953 Na _0.04 Ge _0.007 Te and Pb _0.95. This is clear from the fact that _{Na 0.04} Ge _{0.01 Te has not changed significantly.}

According to the thermoelectric conversion material according to the first embodiment, the thermoelectric conversion material includes at least one element M selected from the group consisting of C, Si, Ge and Sn, and as acceptors, Group 1 elements, eleventh elements. By including a nanoprecipitate having at least one element A selected from the group consisting of group elements and group 13 elements in the base material of PbTe, a higher dimensionless thermoelectric performance index ZT than before can be achieved. Since it does not contain a material that easily deteriorates, it is possible to realize a P-type thermoelectric conversion material that exhibits stable characteristics.

FIG. 4 is a flowchart showing a method for producing a thermoelectric conversion material according to the first embodiment of the present invention.

Hereinafter, a method for producing a thermoelectric conversion material according to the first embodiment of the present invention will be described with reference to FIG.

First, a material containing lead (Pb), tellurium (Te) and at least one element (M) selected from the group consisting of carbon (C), silicon (Si), germanium (Ge) and tin (Sn). Is prepared and sealed (S110). Specifically, powders or particles of Pb, Te and element M having a purity of 99.999% or more or 99.9999% or more are prepared, weighed so as to have the following composition, and placed in a nitrogen atmosphere. Mix, put in a quartz tube, exhaust and seal. The purity of the material is the same for the elements described below.

The composition of the above materials may be prepared in a molar ratio of Te: Pb: M = 1: 1-x: x, where x may be greater than 0 and 0.015 or less. Here, M is at least one element M selected from the group consisting of C, Si, Ge and Sn, as described above. x is preferably 0.002 or more and 0.012 or less, and more preferably 0.007 or more and 0.010 or less. As a result, a dimensionless thermoelectric figure of merit ZT higher than the conventional one can be obtained.

Further, as acceptors (lactones), Group 1 elements (lithium (Li), sodium (Na), potassium (K)), Group 11 elements (copper (Cu), silver (Ag), gold (Au)) and At least one element (A) selected from the group consisting of Group 13 elements (Tl) is added. The composition is prepared with a molar ratio of Te: Pb: M: A = 1: 1-x-y: x: y, y is preferably greater than 0 and 0.1 or less, and y is 0.04. Is more preferable. Note that x is selected from the above range.

The material is then heated and melted to give an ingot containing the nanoprecipitates (S120). Specifically, the quartz tube in which the material is sealed is heated at a high temperature equal to or higher than the temperature at which PbTe melts (1197K) for several hours, and slowly cooled to room temperature to obtain an ingot. As a result, a thermoelectric conversion material in which nanostructures are precipitated can be obtained. The heating temperature is preferably 1207 K or higher.

After S120, the ingot may be powdered and sintered under pressure, if necessary, such as homogenizing the composition in the ingot or randomizing the crystal orientation (S130). Specifically, the ingot is ground in a mortar to form a polycrystalline powder, filled in a graphite die having an inner diameter of 10 mm or 15 mm, and pressurized and heated in one direction by a discharge plasma sintering (SPS) device. This SPS treatment is carried out at a pressure of 25 MPa, for example, in a temperature range of 723K to 1147K for 1 hour to 1.5 hours. As a result, a sintered body having a diameter of 10 mm or 15 mm having a density of 99% of the density of the bulk material can be obtained.

According to the method for producing a thermoelectric conversion material according to the first embodiment, it consists of a group consisting of lead (Pb), tellurium (Te), carbon (C), silicon (Si), germanium (Ge) and tin (Sn). By heating and melting at least one selected element M and the element A of the dopant as an acceptor, a thermoelectric conversion material of a PbTe substrate having nanoprecipitates containing the elements M and A can be obtained. Since no material that easily deteriorates is used, it is easy to handle, and the obtained thermoelectric conversion material has stable properties.

[Example 1]
First, the single element material is weighed, Pb (6.0480 g) (Osaka Asahi Metal, purity 99.99999%), Te (3.9080 g) (Osaka Asahi Metal, purity 99.99999%), Ge. (0.0160 g) (manufactured by High Purity Chemical Laboratory, purity 99.999%) and Na (0.0280 g) (manufactured by Sigma-Aldrich, purity 99.95%) are prepared, mixed in a nitrogen atmosphere, and quartz tube. The mixture was placed in a container, ^{exhausted to 7 × 10 -3} Pa, and sealed. Next, the material enclosed in the quartz tube was heated at 1.2 K / min, heated at 1323 K for 10 hours, and then cooled to room temperature over time. As a result, an ingot of 9.9980 g of Pb _0.953 Na _0.04 Ge _0.007 Te was obtained.

Next, the ingot was powdered in a dairy pot, and the crystal structure was confirmed by the powder X-ray diffraction pattern and the transmission electron micrograph of the powder (see FIGS. 3 and 1, respectively). Furthermore, it was confirmed by a high-angle scattering dark-field scanning transmission electron microscope and an energy dispersive X-ray analyzer that Ge-Na nanoprecipitates in the PbTe substrate were even formed (see FIG. 2A).

Next, the powdered Pb _0.953 Na _0.04 Ge _0.007 Te material was filled into graphite dies with inner diameters of 10 mm and 15 mm, pressurized by 30 MPa in one direction by a discharge plasma sintering (SPS) device, and pressed at 773 K for 1 hour 30. Heated for minutes. _{As a result, Pb 0.953} Na _0.04 Ge _0.007 Te sintered bodies having a diameter of 10 mm and 15 mm having a density of 98% or more of the bulk density of this material were obtained.

Next, the electrical resistivity of this sintered body is ρ (μΩ m), the Seebeck coefficient S (μVK ^-1 ), the thermal conductivity κ _total (WK ^-1 m ^-1 ), and the lattice thermal conductivity κ _lat (WK ^-1). m ^-1 ) was measured in the temperature range of 300K to 920K. Moreover, the output factor and the dimensionless thermoelectric figure of merit were obtained from these results.

[Example 2]
Weighing the single element materials Pb (6.0360 g), Te (3.9130 g), Ge (0.0220 g), and Na (0.0280 g), Pb _0.95 Na _0.04 Ge _0.01 Te in the same manner as in Example 1. A sintered body having the composition of (1) was prepared and measured.

[Example 3]
Weighing the single element materials Pb (6.0170 g), Te (3.9210 g), Na (0.0330 g), and Ge (0.280 g), Pb _0.945 Na _0.04 Ge _0.015 Te in the same manner as in Example 1. A sintered body having the composition of the above was prepared. Next, the electrical resistivity ρ (μΩ m) and the Seebeck coefficient S (μVK ^-1 ) of this sintered body were measured at a temperature of 300 K to 920 K. In addition, output factors were obtained from these results.

[Comparison example]
The single element materials Pb (6.0750 g), Te (3.8970 g), and Na (0.0280 g) were weighed to prepare a sintered body having a composition of _{Pb 0.96} Na _{0.04 Te in the same manner as in Example 1.} , The measurement was performed.

FIG. 5 is a diagram showing the temperature dependence of the electrical resistivity of the examples and comparative examples of the thermoelectric conversion material according to the first embodiment of the present invention.

With reference to FIG. 5, it can be seen that the electrical resistivity ρ is higher in the compositions of Examples 1, 2 and 3 over the entire temperature range of 300K to 920K than in Comparative Examples. From the relationship of 1 / ρ = p × e × μ _h , it can be seen that the electrical resistivity of Examples 1, 2 and 3 is higher than that of Comparative Example due to the lower Hall concentration p. Here, μ _h is the hole mobility, and e is an elementary charge.

FIG. 6 is a diagram showing the temperature dependence of the Seebeck coefficient of Examples and Comparative Examples of the first embodiment of the present invention.

With reference to FIG. 6, the Seebeck coefficient S is proportional to ^{m * T (π / 3p) 2/3.} Here, m * is the effective carrier mass, T is the temperature, and p is the hole concentration. From this relationship, it can be seen that the Seebeck coefficient S increases as the Hall concentration p decreases in Examples 1, 2 and 3 over the entire temperature range of 300K to 920K as compared with Comparative Examples.

FIG. 7 is a diagram showing the temperature dependence of the output factors of the examples and comparative examples of the first embodiment of the present invention.

With reference to FIG. 7, for the output factor (S ² / ρ), Examples 1 and 2 are more prominent than Comparative Examples over the entire temperature range of 300K to 920K, as the increase in S cancels out the decrease in ρ. It can be seen that there is no significant change. Example 3 is slightly reduced, but not so large. It can be seen that the Ge-Na nanoprecipitate has a very small effect on ^{the output factor (S 2 / ρ) of the PbTe substrate.}

8 (A) and 8 (B) are diagrams showing the temperature dependence of the thermal conductivity and the lattice thermal conductivity of Examples and Comparative Examples of the thermoelectric conversion material according to the first embodiment of the present invention, respectively. ..

With reference to FIGS. 8A and 8B _{, Examples 1 and 2 have comparative thermal conductivity (κ total} ) and lattice thermal conductivity (κ _lat ) over a temperature range of 300K to 860K. It is reduced by 30% to 20% compared to the example. The lowest lattice thermal conductivity (κ _lat ^{) was 0.31 WK -1} m ^-1 at a temperature of 700 K in Example 1. It is considered that this is because phonon scattering from Ge-Na nanoprecipitates of various sizes and shapes is effective. Although no measurement results have been obtained in Example 3, it is estimated that the measurement results are similar to those in Examples 1 and 2.

FIG. 9 is a diagram showing the temperature dependence of the dimensionless thermoelectric figure of merit ZT of Examples and Comparative Examples of the thermoelectric conversion material according to the first embodiment of the present invention.

With reference to FIG. 9, in Examples 1 and 2, the dimensionless thermoelectric figure of merit ZT is much higher in the range of 300K to 920K than in Comparative Example, and is 2.0 or more from 700K to 850K. You can see that. In particular, it can be seen that Example 1 shows a maximum value of 2.5 at 720K, while the maximum value (810K) of Comparative Example is 1.76. Since the measurement result of the thermal conductivity was not obtained in Example 3, the dimensionless thermoelectric figure of merit ZT was not calculated, but it is estimated to be about the same as in Examples 1 and 2.

This is because the crystal lattice of the base material and the crystal lattice of Ge-Na nanoprecipitates of various sizes and shapes are partially or sufficiently crystallographically aligned, which affects electron transport. On the other hand, it is considered that the Ge-Na nanoprecipitate effectively scatters phonons, which increases the dimensionless thermoelectric performance index ZT.

[Second Embodiment]
The thermoelectric conversion material according to the second embodiment of the present invention is the same as the thermoelectric conversion material according to the first embodiment described above, and is a Group 14 element in a substrate containing PbTe, C, Si, Ge. , Sn contains nanoprecipitates containing at least one element M selected from the group.

The thermoelectric conversion material according to the second embodiment is an N-type thermoelectric conversion material, and is at least one selected from group 17 elements chlorine (Cl), bromine (Br) and iodine (I), which are donors. It may contain one element (hereinafter, referred to as "X").

The thermoelectric conversion material according to the second embodiment is represented by, for example, a composition formula of _{Pb 1-x} M _x Te _1-z X _z. Here, x represents the atomic ratio of the element M to the total amount of Pb and the element M, and it is preferable that x is larger than 0 and 0.015 or less. It is more preferable that x is 0.002 or more and 0.012 or less, and it is particularly preferable that x is 0.007 or more and 0.010 or less.

z represents the atomic ratio of donor X to the total amount of Te and donor X, and z is preferably greater than 0 and less than 0.01. z is more preferably 0.002 or more and 0.006 or less, and z is particularly preferably 0.004.

In the composition of the thermoelectric conversion material described above, it is particularly preferable that the element M is Ge.

The thermoelectric conversion material according to the second embodiment is considered to have the same crystal structure (NaCl structure) as the thermoelectric conversion material of the first embodiment described above, and has the same element M as that of the first embodiment. It is considered that the nanoprecipitate has the same action and effect on the PbTe substrate by containing the amount. As a result, the same high dimensionless thermoelectric figure of merit ZT as in the first embodiment can be achieved, and an N-type thermoelectric conversion material exhibiting stable characteristics can be realized because it does not contain a material that easily deteriorates.

A method for producing a thermoelectric conversion material according to a second embodiment of the present invention will be described. The method for producing the thermoelectric conversion material according to the second embodiment is described in place of the element A in the step (S110) of preparing the material in the flowchart of FIG. 4 showing the method for producing the thermoelectric conversion material according to the first embodiment. As a donor, at least one element (X) selected from Group 17 elements (Cl, Br, I) is added. The addition of this element X is, for example, addition of the 17th group element (Cl, Br, I) alone, or the addition of the 17th group element (Cl, Br, I) including Te, Pb and the element M. Compounds such as PbCl ₂ , PbBr ₂ , and PbI ₂ are used as starting materials. Other than this, the method is the same as the method for producing the thermoelectric conversion material according to the first embodiment, and the description thereof will be omitted. The formulation in the step of preparing the material is prepared in a molar ratio of Te: Pb: M: X = 1-z: 1-x: x: z. The addition amount z of the element X is preferably greater than 0 and 0.01 or less, more preferably z is 0.002 or more and 0.006 or less, and particularly preferably z is 0.004. preferable.

According to the method for producing a thermoelectric conversion material according to the second embodiment, it consists of a group consisting of lead (Pb), tellurium (Te), carbon (C), silicon (Si), germanium (Ge) and tin (Sn). Nano containing elements M and X by heating and melting at least one selected element M and a compound of element X or element X as a donor and one of Pb, Te, and element M. A thermoelectric conversion material of a PbTe substrate having a precipitate is obtained. Since no material that easily deteriorates is used, it is easy to handle, and the obtained thermoelectric conversion material has stable properties.

[Thermoelectric power generation module]
FIG. 10 is a schematic view of a thermoelectric power generation module according to an embodiment of the present invention.

With reference to FIG. 10, the thermoelectric power generation module 10 according to the embodiment of the present invention includes a P-type thermoelectric conversion element 21, an N-type thermoelectric conversion element 22, a P-type thermoelectric conversion element 21, and an N-type thermoelectric conversion element 22. It has an electrode 30 that contacts one side of each of the above, an electrode 41 that contacts the other side of the P-type thermoelectric conversion element 21, and an electrode 42 that contacts the other side of the N-type thermoelectric conversion element 22.

The P-type thermoelectric conversion element 21 may have the thermoelectric conversion material of the first embodiment described above, or may have a known P-type thermoelectric conversion material.

The N-type thermoelectric conversion element 22 may have the thermoelectric conversion material of the second embodiment described above, or may have a known N-type thermoelectric conversion material.

The electrodes 30, 41, and 42 are made of metal, and a known metal material can be used.

The thermoelectric power generation module 10 is a carrier of a portion of the P-type thermoelectric conversion element 21 and the N-type thermoelectric conversion element 22 that come into contact with the electrodes 30 by bringing the high-temperature body into contact with the electrodes 30 and the low-temperature body with the electrodes 41 and 42. The concentrations (hole concentration and electron concentration, respectively) increase, and the carriers diffuse to the electrodes 41 and 42, respectively. As a result, a current flows from the electrode 42 to the electrode 41 via the N-type thermoelectric conversion element 22, the electrode 30, and the P-type thermoelectric conversion element 21, and a positive voltage is generated in the electrode 42 with respect to the electrode 41. This makes it possible to generate electricity.

According to the present embodiment, since the P-type thermoelectric conversion element 21 has the thermoelectric conversion material of the first embodiment, the thermoelectric power generation module 10 having stable characteristics and high power generation performance can be realized. Further, since the N-type thermoelectric conversion element 22 has the thermoelectric conversion material of the second embodiment, the thermoelectric power generation module 10 having stable characteristics and high power generation performance can be realized. Furthermore, by having the P-type thermoelectric conversion element 21 of the thermoelectric conversion material of the first embodiment and the N-type thermoelectric conversion element 22 of the thermoelectric conversion material of the second embodiment, the characteristics are stable and the power generation performance is higher. The thermoelectric power generation module 10 can be realized.

[Pelche cooler]
FIG. 11 is a schematic view of a Pelche cooler according to an embodiment of the present invention.

With reference to FIG. 11, the Perche cooler 50 according to the embodiment of the present invention includes a P-type thermoelectric conversion element 21, an N-type thermoelectric conversion element 22, a P-type thermoelectric conversion element 21, and an N-type thermoelectric conversion element 22. An electrode 30 that contacts one side of the P-type thermoelectric conversion element 21, an electrode 41 that contacts the other side of the P-type thermoelectric conversion element 21, an electrode 42 that contacts the other side of the N-type thermoelectric conversion element 22, and electrodes 41 and 42. It has a power supply unit 60 which is connected to the electrode 41 and applies a positive voltage to the electrode 41 and a negative voltage to the electrode 42. Since the P-type thermoelectric conversion element 21, the N-type thermoelectric conversion element 22, and the electrodes 30, 41, and 42 are the same as those shown in FIG. 10, they are designated by the same reference numerals and detailed description thereof will be omitted. ..

The power supply unit 60 is not particularly limited as long as the DC voltage source can sufficiently supply the current.

In the Pelche cooler 50, the current supplied by the power supply unit 60 flows from the electrode 42 in the order of the N-type thermoelectric conversion element 22, the electrode 30, the P-type thermoelectric conversion element 21, and the electrode 41, so that the cooling target on the electrode 30 side is Heat is absorbed from an object, and in the P-type thermoelectric conversion element 21, holes absorb energy on the electrode 30 side and release it on the electrode 41 side, and in the N-type thermoelectric conversion element 22, electrons absorb energy on the electrode 30 side and the electrode 42. By releasing energy on the side, the object to be cooled can be cooled.

According to the present embodiment, by having the thermoelectric conversion material of the first embodiment in the P-type thermoelectric cooling element 21, the Perche cooler 50 having stable characteristics and high cooling capacity can be realized. Further, by having the thermoelectric conversion material of the second embodiment in the N-type thermoelectric conversion element 22, the Perche cooler 50 having stable characteristics and high cooling capacity can be realized. Further, by having the P-type thermoelectric conversion element 21 of the thermoelectric conversion material of the first embodiment and the N-type thermoelectric conversion element 22 of the thermoelectric conversion material of the second embodiment, the characteristics are stable and the cooling capacity is higher. The Pelche cooler 50 can be realized.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment, and various modifications and changes can be made within the scope of the present invention described in the claims. It is possible. It goes without saying that the thermoelectric conversion material of the present invention, a method for producing the same, and a thermoelectric power generation module can be applied to various heat sources such as automobiles, thermal power plants, data centers, and the like. Needless to say, the Perche cooler of the present invention can cool various objects.

The following additional notes will be further disclosed with respect to the above description.
(Appendix 1) Thermoelectric conversion material
Substrate containing PbTe and
A nanoprecipitate containing at least one element (M) selected from the group consisting of C, Si, Ge and Sn in the substrate, and
The thermoelectric conversion material including.
(Appendix 2) The thermoelectric conversion material according to Appendix 1, wherein the thermoelectric conversion material contains at least one element (A) selected from the group consisting of Group 1 elements, Group 11 elements and Group 13 elements.
(Appendix 3) The thermoelectric conversion material is _{represented by the composition formula of Pb 1-xy} A _y M _x Te, and x and y are the atomic ratios of M and A to the total amount of Pb, M and A, respectively. The thermoelectric conversion material according to Appendix 2, wherein x is greater than 0 and 0.015 or less, and y is greater than 0 and 0.1 or less.
(Appendix 4) The thermoelectric conversion material according to Appendix 3, wherein x is 0.002 or more and 0.012 or less.
(Appendix 5) The thermoelectric conversion material according to Appendix 3, wherein x is 0.007 or more and 0.010 or less.
(Supplementary note 6) The thermoelectric conversion material according to any one of Supplementary note 3 to 5, wherein A is Na and y is 0.04.
(Supplementary note 7) The thermoelectric conversion material according to any one of Supplementary notes 1 to 6, wherein M is Ge.
(Appendix 8) The thermoelectric conversion material according to any one of Appendix 1 to 7, wherein the thermal conductivity is 1.3 WK ^-1 m ^{-1 or less from 700 K to 900 K.}
(Supplementary note 9) The thermoelectric conversion material according to any one of Supplementary notes 1 to 8, wherein the dimensionless thermoelectric figure of merit ZT is 2.0 or more from 700K to 850K.
(Supplementary Note 10) The thermoelectric conversion material according to any one of Supplementary note 1 to 9, wherein the nanoprecipitate has a particle size of 2 nm to 1 μm.
(Appendix 11) The thermoelectric conversion material according to Appendix 1, wherein the thermoelectric conversion material contains at least one element (X) selected from Group 17 elements.
(Appendix 12) The thermoelectric conversion material is _{represented by the composition formula of Pb 1-x} M _x Te _1-z X _z , x represents the atomic ratio of M to the total amount of Pb and M, and x is 0. The thermoelectric conversion material according to Appendix 11, wherein z is greater than or equal to 0.015, z represents the atomic ratio of X to the total amount of Te and X, and z is greater than 0 and less than or equal to 0.01.
(Appendix 13) The thermoelectric conversion material according to Appendix 12, wherein z is 0.002 or more and 0.006 or less.
(Supplementary note 14) The thermoelectric conversion material according to Supplementary note 12, wherein z is 0.004.
(Supplementary note 15) The thermoelectric conversion material according to any one of Supplementary note 12 to 14, wherein x is 0.002 or more and 0.012 or less.
(Supplementary note 16) The thermoelectric conversion material according to any one of Supplementary notes 12 to 15, wherein x is 0.007 or more and 0.010 or less.
(Supplementary note 17) The thermoelectric conversion material according to any one of Supplementary notes 12 to 16, wherein M is Ge.
(Supplementary Note 18) The thermoelectric conversion material according to any one of Supplementary note 11 to 17, wherein the nanoprecipitate has a particle size of 2 nm to 1 μm.
(Appendix 19) A method for producing a thermoelectric conversion material.
A step of preparing a material containing Pb, Te, and at least one element (M) selected from the group consisting of C, Si, Ge and Sn.
The step of heating and melting the prepared material in a vacuum to obtain a material containing the nanoprecipitate containing M, and
The production method.
(Appendix 20) In the preparation step,
The production method according to Appendix 19, wherein the material is prepared in a molar ratio of Te: Pb: M = 1: 1-x: x, where x is greater than 0 and less than or equal to 0.015.
(Supplementary note 21) The production method according to Supplementary note 20, wherein x is 0.002 or more and 0.012 or less.
(Supplementary note 22) The production method according to Supplementary note 20, wherein x is 0.005 or more and 0.010 or less.
(Appendix 23) In the preparation step, the material further comprises at least one element (A) selected from the group consisting of Group 1 elements, Group 11 elements and Group 13 elements.
The following item of Appendix 20 to 22, wherein the preparation is made in a molar ratio of Te: Pb: M: A = 1: 1-xy: x: y, and y is greater than 0 and 0.1 or less. How to make.
(Appendix 24) In the preparation step, the material further contains at least one element (X) selected from Group 17 elements, and Te: Pb: M: X = 1-z: 1-x: x. : The production method according to any one of Appendix 20 to 22, wherein the preparation is made in a molar ratio of z, and z is greater than 0 and 0.01 or less.
(Supplementary note 25) The production method according to any one of Supplementary note 19 to 24, wherein the material is heated to a temperature of 1207 K or higher in the melting step.
(Appendix 26) A step of crushing the material obtained by the dissolution step into powder and sintering under pressure, and a step of sintering.
The production method according to any one of Supplementary note 19 to 25, further comprising.
(Supplementary note 27) A thermoelectric power generation module comprising a thermoelectric conversion element having the thermoelectric conversion material according to any one of Supplementary notes 1 to 18.
(Supplementary note 28) A thermoelectric power generation module comprising a P-type thermoelectric conversion element having the thermoelectric conversion material according to any one of Supplementary note 2 to 10.
(Supplementary note 29) A thermoelectric power generation module comprising an N-type thermoelectric conversion element having the thermoelectric conversion material according to any one of Supplementary notes 11 to 18.
(Appendix 30) A Perche cooler comprising a thermoelectric conversion element having the thermoelectric conversion material according to any one of Supplements 1 to 18.
(Appendix 31) A Perche cooler comprising a P-type thermoelectric conversion element having the thermoelectric conversion material according to any one of Appendix 2 to 10.
(Appendix 32) A Perche cooler comprising an N-type thermoelectric conversion element having the thermoelectric conversion material according to any one of Supplements 11 to 18.

10 Thermoelectric power generation module 21 P-type thermoelectric conversion element 22 N-type thermoelectric conversion element 30, 41, 42 Electrodes 50 Perche cooler 60 Power supply unit

Claims (13)

It is a thermoelectric conversion material
Substrate containing PbTe and
At least one element (M) selected from the group consisting of C, Si, Ge and Sn in the substrate and at least one selected from the group consisting of Group 1 elements, Group 11 elements and Group 13 elements. only contains a nano-precipitates, the including One of the elements and the (a),
It is represented by the composition formula of Pb _1-xy A _y M _{x Te.}
x and y represent the atomic ratios of M and A to the total amount of Pb, M and A, respectively, x is 0.002 or more and 0.012 or less, and y is greater than 0 and 0.1. The thermoelectric conversion material described below. The thermoelectric conversion material according to claim 1, wherein y is 0.04. The thermoelectric conversion material according to claim 1, wherein x is 0.007 or more and 0.010 or less, and y is 0.04. The thermoelectric conversion material according to any one of claims 1 to 3, wherein the element M is Ge. The thermoelectric conversion material according to any one of claims 1 to 4, wherein the element A is Na. The thermoelectric conversion material according to any one of claims 1 to 5, wherein the thermal conductivity is 1.3 WK ^-1 m ^{-1 or less from 700 K to 900 K.} Dimensionless thermoelectric figure of merit ZT is over from 700K to 850K, Ri der 2.0 or more, and up to 2.5, the thermoelectric conversion material according to any one of claims 1 to 6. The thermoelectric conversion material, instead of the element A, looking containing at least one element (X) is selected from among Cl, Br and I is a group 17 element,
It is represented by the composition formula of Pb _1-x M _x Te _1-z X _z , where x represents the atomic ratio of M to the total amount of Pb and M, and when x is 0.002 or more and 0.012 or less. The thermoelectric conversion material according to claim 1, wherein z represents the atomic ratio of X to the total amount of Te and X, and z is greater than 0 and 0.01 or less. The thermoelectric conversion material according to any one of claims 1 to 8 , wherein the nanoprecipitate has a particle size of 2 nm to 1 μm. It is a method of manufacturing a thermoelectric conversion material.
It was selected from the group consisting of at least one element (M) selected from the group consisting of Pb, Te, C, Si, Ge and Sn, and the group consisting of Group 1 elements, Group 11 elements and Group 13 elements. A step of preparing a material containing at least one element (A) , prepared in a molar ratio of Te: Pb: M: A = 1: 1-xy: x: y, where x is 0. The preparation step , which is 002 or more and 0.012 or less, and y is greater than 0 and 0.1 or less.
The production method comprising the steps of heating and melting the prepared material in a vacuum to obtain a material containing nanoprecipitates containing the element M and the element A. In the preparation step, the material contains at least one element (X) selected from the Group 17 elements Cl, Br and I in place of the element (A), and Te: Pb: M: The production method according to claim 10, wherein the preparation method is prepared with a molar ratio of X = 1-z: 1-x: x: z, and z is greater than 0 and 0.01 or less. A thermoelectric power generation module comprising a thermoelectric conversion element having the thermoelectric conversion material according to any one of claims 1 to 9. A Perche cooler comprising a thermoelectric cooling element having the thermoelectric conversion material according to any one of claims 1 to 9.

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