JP2018152521A - Thermoelectric conversion material and method of producing the same, thermoelectric power generation module, and peltier cooler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a thermoelectric conversion material having stable characteristics and also having a high dimensionless thermoelectric figure of merit ZT and a method of producing the same; a thermoelectric power generation module; and a Peltier cooler.SOLUTION: The present disclosure provides a thermoelectric conversion material including: a substrate including PbTe; and nanoprecipitates including at least one element (M) selected from the group consisting of C, Si, Ge, and Sn in the substrate. The thermoelectric conversion material may include at least one element (A) selected from the group consisting of group 1 elements, group 11 elements, and group 13 elements, and also may include at least one element (X) selected from group 17 elements. A method of producing a thermoelectric conversion material, a thermoelectric power generation module, and a Peltier cooler are further disclosed.SELECTED DRAWING: Figure 1

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 Peltier cooler.

  Thermoelectric conversion directly converts thermal energy and electrical energy using a semiconductor device. The thermoelectric device generates power by a temperature gradient based on the Seebeck effect. Thermoelectric technology can generate electricity by recovering waste heat generated in automobiles, thermal power plants, data centers, etc., and thus greatly contributes to overcoming the energy crisis and reducing the generation of carbon dioxide gas.

  On the other hand, thermoelectric cooling uses the Peltier effect to create a flow of heat with the consumption of electrical energy. This phenomenon has been increasingly used for cooling and refrigeration. Since the cooling device using the Peltier 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 expressed by a dimensionless thermoelectric figure of merit ZT, which is 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 for improving the ZT of the thermoelectric conversion material, one of which is to improve the power factor S ² / ρ, and the other is to increase the thermal conductivity κ _total . Is to lower. Over the past 15 years, many thermoelectric conversion materials have been significantly reduced in thermal conductivity κ _total due to nanostructuring (the thermal conductivity κ _total is expressed as κ _total = κ _lat + κ _e , κ _lat is Lattice thermal conductivity, κ _e is the electronic thermal conductivity.) Nanostructuring is the embedding of nanoscale inclusions in a bulk substrate, which could 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 ZT value of the material that has not been nanostructured is improved to approximately 1 to 50% by appropriate doping and nanostructuring, compared to approximately 1 (See, for example, Non-Patent Document 1).

  To nanostructure PbTe, the best approach so far is a composite material with PbTe as the bulk substrate and embedded nanoscale inclusions that are matched or quasi-matched 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).

In a composite material with a composition of Pb _0.98 Na _0.02 Te-6 at% MgTe in which nanoscale precipitates are formed in a mesoscale structure or a composite material with a composition of nanostructured Pb _0.98 Na _0.02 Te-8 at% SrTe, the ZT value Is 923K and 2 to 2.5 is obtained (for example, see Non-Patent Documents 2 and 3). With these nanostructured PbTe materials, a device efficiency of the thermoelectric power generation module of 11% is obtained at a temperature difference of 590 K (for example, see Non-Patent Document 4). These materials achieve twice the device efficiency obtained with a thermoelectric power generation module using a 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 and Satoshi Yamamoto, “Effective Utilization of Unused Thermal Energy Progressed by Thermoelectric Conversion”, Energy and Resources, 2013, Vol. 34, No. 6, pp. 332-336

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

  An object of the present invention is to provide a thermoelectric conversion material having a stable characteristic and a high performance, a manufacturing method thereof, a thermoelectric power generation module, and a Peltier cooler.

  According to one aspect of the present invention, there is provided a base material containing PbTe, which is a thermoelectric conversion material, and at least one element (M) selected from the group consisting of C, Si, Ge, and Sn in the base material. The said thermoelectric conversion material containing the nanoprecipitate containing is provided.

  According to the above aspect, the thermoelectric conversion material is a material that easily deteriorates by including in the PbTe base material a nanoprecipitate having at least one element M selected from the group consisting of C, Si, Ge, and Sn. Therefore, stable characteristics are exhibited and a high-performance thermoelectric conversion material can be provided.

  According to another aspect of the present invention, there is provided a method for producing a thermoelectric conversion material, comprising: Pb, Te, and at least one element (M) selected from the group consisting of C, Si, Ge, and Sn. There is provided the above manufacturing method, comprising: preparing a material including the material; and heating and dissolving the prepared material in a vacuum to obtain a material including the nanoprecipitate including the M.

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

  According to the other aspect of this invention, a thermoelectric power generation module provided with the thermoelectric conversion element which has the thermoelectric conversion material of the said aspect is provided.

  According to the said aspect, by having the thermoelectric conversion material of the said aspect, the thermoelectric power generation module of the stable power generation performance of the characteristic is realizable.

  According to the other aspect of this invention, a Peltier cooler provided with the thermoelectric conversion element which has the thermoelectric conversion material of the said aspect is provided.

  According to the said aspect, by having the thermoelectric conversion material of the said aspect, the Peltier cooler of the high cooling capacity with the stable characteristic is realizable.

It is a transmission electron micrograph of the thermoelectric conversion material which concerns on the 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. It is another high angle scattering dark field scanning transmission electron micrograph and energy dispersive X-ray analysis image 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 the 1st Embodiment of this invention. It is a flowchart which shows the preparation methods 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 electrical resistivity of the Example of a thermoelectric conversion material which concerns on the 1st Embodiment of this invention, and a comparative example. It is a figure which shows the temperature dependence of the Seebeck coefficient of the Example of the thermoelectric conversion material which concerns on the 1st Embodiment of this invention, and a comparative example. It is a figure which shows the temperature dependence of the output factor of the Example of the thermoelectric conversion material which concerns on the 1st Embodiment of this invention, and a comparative example. (A) And (B) is a figure which shows the temperature dependence of the thermal conductivity of the Example of a thermoelectric conversion material which concerns on the 1st Embodiment of this invention, and a comparative example, respectively, and a lattice thermal conductivity, respectively. It is a figure which shows the temperature dependence of the dimensionless thermoelectric figure of merit ZT of the Example of the thermoelectric conversion material which concerns on the 1st Embodiment of this invention, and a comparative example. It is the schematic of the thermoelectric power generation module which concerns on one Embodiment of this invention. It is the schematic of the Peltier cooler concerning one embodiment of the present 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 telluride (PbTe) thermoelectric conversion material containing a nanostructured group 14 element, and has an extremely high dimensionless thermoelectric 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 carbon (C), silicon (Si), germanium (Ge) and tin (Sn), which are group 14 elements in the PbTe base material. And a nanoprecipitate containing at least one element (hereinafter referred to as “M” or “element M”). By including a very small amount of element M, nanoprecipitates of different shapes and various sizes appear uniformly dispersed in the PbTe substrate, and the nanoprecipitates have various mean free paths. Is thought to scatter. In an example described later, the element M includes the group 14 element Ge, but the elements included in the group 14 element have similar electron arrangements, so that instead of Ge, C, Si, and Sn are included. Even if any of them is included, it is considered that the same effect as in the case of Ge can be obtained in the PbTe substrate, and further, two or more kinds of Ge, C, Si, and Sn may be combined.

  The thermoelectric conversion material according to the first embodiment is a P-type thermoelectric conversion material. As an acceptor, a group 1 element (lithium (Li), sodium (Na), potassium (K)), a group 11 element ( 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”) .). In the examples described later, the element A is Na. However, instead of Na, the element A may include elements other than the group 1 element Na, group 11 elements and group 13 elements having an electronic structure similar to Na. Well, together 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 elements M and A with respect to the total amount of Pb, the element M, and the element A, respectively, in an atomic ratio.

  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 preferably greater than 0 and 0.1 or less, and x is 0.002 or more and 0 or less. It is preferably 0.012 or less, and more preferably, x is 0.007 or more and 0.010 or less.

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

  Furthermore, in the composition of the thermoelectric conversion material described above, the element M is particularly preferably Ge.

FIG. 1 is a transmission electron micrograph 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 a microscopic image of the [001] axis orientation.

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

FIG. 2A 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 microscopic image of [220] axial orientation.

  Referring to FIG. 2A, it can be seen that (i) shows nanoprecipitates having a very large major axis of about 0.6 μm in the pores in the substrate. According to (ii) of the energy dispersive X-ray analysis image, the nanoprecipitate has a phase containing Ge, and (iii) shows that the nanoprecipitate does not contain Pb. Further, according to the inventors' investigation, it has been found that the nanoprecipitate contains Na, and the nanoprecipitate contains Ge-Na.

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

  Referring to FIG. 2B, (i) shows a precipitate 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 are composed of phases containing Ge. According to (iii), these nanoprecipitates are Pb. It is understood that it does not contain. Moreover, according to examination of this inventor, it turns out that Na is contained in the nano precipitate, and it turns out that the nano precipitate contains Ge-Na.

  In these EDX analysis images, since the analysis of precipitates with a particle size of 5 nm is near the detection limit of the apparatus, the inclusion of Ge is not clearly shown, but nanoprecipitates with a particle size of 20 nm to 100 nm are not shown. And the transmission electron microscope image of (i) shows that the nanoprecipitate having a particle size of 5 nm has the same shape as the nanoprecipitate having a particle size of 20 nm. The product is also estimated to be a precipitate having the same composition. Furthermore, it is presumed that the disk-shaped precipitate having a particle diameter (diameter) of FIG. 1 of 2 to 5 nm is also a precipitate having the same composition.

  Thus, according to FIG. 1, FIG. 2A and FIG. 2B, and the inventors' investigation, the Ge—Na nanoprecipitates in the PbTe substrate span a variety of particle sizes (2 nm to 1 μm particle size) It is possible to efficiently scatter phonons having a wide range of mean free paths from short mean phonons to long phonons. In the specification, claims, drawings and abstract of the present application, the term “nanoprecipitate” refers, as described above, to various particle sizes precipitated in the crystals of the substrate, for example from 2 nm to 1 μm. 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 the embodiment of the present invention is Pb _1-x-0.04 Na _0.04 Ge _x Te (x = 0.007, 0.01). FIG. 3 also shows a diffraction pattern of a sample with x = 0 for comparison.

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

The following table shows the hole concentration p and the hole mobility mu _h of the thermoelectric conversion material according to the first embodiment (Pb _0.953 Na _0.04 Ge _0.007 Te and _{Pb 0.95 Na 0.04 Ge 0.01 Te)} . 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。

Referring to the above table, even if Ge is present in a small amount (0.7 atomic%) in PbTe, the solid solubility of Na as a dopant (acceptor) in the lattice decreases. 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 decreased with respect to Pb _0.96 Na _0.04 Te.

Ge-Na nanoprecipitates are included consistently with the PbTe substrate. That is, the crystal lattice of the PbTe base material and the crystal lattice of the Ge—Na nanoprecipitate are aligned or quasi-aligned so that the electronic structure of the thermoelectric conversion material hardly changes relative to the electronic structure of the PbTe base material. doing. As a result, it is considered that the charge carriers can easily move in the thermoelectric conversion material that is a composite material without being scattered by the aligned nanoprecipitates. As shown in the above table, this indicates that the hole mobility (μ _h ) of holes as charge carriers is Pb _0.953 Na _0.04 Ge _0.007 Te and Pb _{0.95 with} Ge added to Pb _0.96 Na _0.04 Te. This is evident 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 a group 1 element, an eleventh element as an acceptor. By including a nanoprecipitate having at least one element A selected from the group consisting of a group element and a group 13 element in a PbTe substrate, a dimensionless thermoelectric figure of merit ZT higher than conventional can be achieved. Since the material does not easily deteriorate, a P-type thermoelectric conversion material exhibiting stable characteristics can be realized.

  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, preferably having a purity of 99.999% or more or 99.9999% or more, are prepared, weighed so as to have the following composition, and in a nitrogen atmosphere Mix, evacuate and enclose in a quartz tube. The purity of the material is the same for the elements described below.

  The above materials are mixed at a molar ratio of Te: Pb: M = 1: 1−x: x, where x may be greater than 0 and not greater than 0.015. 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 from 0.002 to 0.012, and more preferably from 0.007 to 0.010. Thereby, a dimensionless thermoelectric figure of merit ZT higher than the conventional one can be obtained.

  Further, as an acceptor (dopant), a group 1 element (lithium (Li), sodium (Na), potassium (K)), a group 11 element (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 blending is prepared at a molar ratio of Te: Pb: M: A = 1: 1-xy: x: y, and y is preferably greater than 0 and 0.1 or less, and y is 0.04. More preferably. Note that x is selected from the above-described range.

  Next, the material is heated and melted to obtain an ingot containing nanoprecipitates (S120). Specifically, the quartz tube in which the material is sealed is heated for several hours at a high temperature equal to or higher than the temperature at which PbTe melts (1197 K), and gradually cooled to room temperature to obtain an ingot. Thereby, the thermoelectric conversion material in which the nanostructure is deposited is obtained. The heating temperature is preferably 1207K or higher.

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

  According to the method for producing a thermoelectric conversion material according to the first embodiment, lead (Pb), tellurium (Te), carbon (C), silicon (Si), germanium (Ge), and tin (Sn). A PbTe-based thermoelectric conversion material having nanoprecipitates including the elements M and A is obtained by heating and dissolving the selected at least one element M and the dopant element A as an acceptor. Since a material that easily deteriorates is not used, it is easy to handle, and the obtained thermoelectric conversion material has stable characteristics.

[Example 1]
First, a single element material was weighed, Pb (6.0480 g) (manufactured by Osaka Asahi Metal, purity 99.9999%), Te (3.9080 g) (manufactured by Osaka Asahi Metal, purity 99.9999%), Ge (0.0160 g) (manufactured by High-Purity Chemical Laboratory, purity 99.999%), Na (0.0280 g) (manufactured by Sigma-Aldrich, purity 99.95%) were prepared and mixed under a nitrogen atmosphere, and a quartz tube And evacuated to 7 × 10 ⁻³ Pa. Next, the temperature of the material enclosed in the quartz tube was raised at 1.2 K / min, heated at 1323 K for 10 hours, and then cooled to room temperature over time. As a result, 9.9980 g of Pb _0.953 Na _0.04 Ge _0.007 Te ingot was obtained.

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

Next, the powdered Pb _0.953 Na _0.04 Ge _0.007 Te material was filled in a graphite die having an inner diameter of 10 mm and a diameter of 15 mm, and 30 MPa was pressed in one direction by a discharge plasma sintering (SPS) apparatus, and then at 773 K for 1 hour 30 Heated for minutes. As a result, a Pb _0.953 Na _0.04 Ge _0.007 Te sintered body having a diameter of 10 mm and a diameter of 15 mm having a density of 98% or more of the bulk density of the material was obtained.

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

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

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

[Comparative example]
A single element material Pb (6.0750 g), Te (3.8970 g) and Na (0.0280 g) were weighed, and a sintered body having a composition of Pb _0.96 Na _0.04 Te was prepared 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.

Referring to FIG. 5, it can be seen that the electrical resistivity ρ is higher in the compositions of Examples 1, 2 and 3 than in the comparative example over the entire temperature range of 300K to 920K. It can be seen that 1 / [rho = p × implemented from the relationship e × mu _h by hole concentration p is lower Example 1, 2 and 3 are electrical resistivity than the comparative example is higher. Here, μ _h is the hole mobility, and e is the elementary charge.

  FIG. 6 is a diagram showing the temperature dependence of the Seebeck coefficient in the examples and comparative examples of the first embodiment of the present invention.

Referring to FIG. 6, the Seebeck coefficient S is proportional to m * T (π / 3p) ^2/3 . Here, m * is a carrier effective mass, T is a temperature, and p is a hole concentration. From this relationship, it can be seen that the Seebeck coefficient S increases with the decrease of the hole concentration p in Examples 1, 2, and 3 compared to the comparative example in the entire temperature range of 300K to 920K.

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

Referring to FIG. 7, the power factor (S ² / ρ) shows that the increase in S cancels the decrease in ρ, so that in the entire temperature range of 300 K to 920 K, Examples 1 and 2 are significant over the comparative example. There is no significant change. Example 3 is slightly lower, but not so large. This shows that the Ge—Na nanoprecipitate has a very small effect on the output factor (S ² / ρ) of the PbTe substrate.

  FIGS. 8A and 8B are diagrams showing the temperature dependence of the thermal conductivity and lattice thermal conductivity of the examples and comparative examples of the thermoelectric conversion material according to the first embodiment of the present invention, respectively. .

Referring to FIGS. 8A and 8B, the thermal conductivity (κ _total ) and lattice thermal conductivity (κ _lat ) are over the temperature range of 300 K to 860 K, and Examples 1 and 2 are compared. Compared to the example, it is reduced by 30% to 20%. The lowest lattice thermal conductivity (κ _lat ) was 0.31 WK ⁻¹ m ⁻¹ in Example 1 at a temperature of 700 K. This is presumably because phonon scattering from Ge—Na nanoprecipitates of various sizes and shapes is effective. In addition, although the measurement result is not obtained in Example 3, it is estimated that it is comparable to Examples 1 and 2.

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

  Referring 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 the comparative example, and is 2.0 or more over 700K to 850K. I understand that. In particular, it can be seen that Example 1 shows a maximum value of 2.5 at 720K, compared to 1.76 of the maximum value (810K) of the comparative example. In addition, since the measurement result of thermal conductivity is not obtained in Example 3, the dimensionless thermoelectric figure of merit ZT is not calculated, but it is estimated to be approximately the same as in Examples 1 and 2.

  This is because the crystal lattice of the substrate and the crystal lattice of Ge-Na nanoprecipitates of various sizes and shapes are partially or fully crystallographically aligned, thus affecting electron transport. On the other hand, the Ge—Na nanoprecipitates effectively scatter phonons, which is considered to increase the dimensionless thermoelectric figure of merit 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 the base material containing PbTe, C, Si, Sn. A nanoprecipitate containing at least one element M selected from the group consisting of:

  The thermoelectric conversion material according to the second embodiment is an N-type thermoelectric conversion material, and is at least one selected from chlorine (Cl), bromine (Br), and iodine (I) that are group 17 elements serving as donors. One element (hereinafter referred to as “X”) may be included.

Thermoelectric conversion material according to the second embodiment, for example, represented by the composition formula _{Pb 1-x M x Te 1} -z X z. Here, x represents the atomic ratio of the element M with respect 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. x is more preferably 0.002 or more and 0.012 or less, and particularly preferably x is 0.007 or more and 0.010 or less.

  z represents the atomic ratio of donor X with respect to the total amount of Te and donor X, and z is preferably larger than 0 and not larger than 0.01. z is more preferably 0.002 or more and 0.006 or less, and particularly preferably z is 0.004.

  In the composition of the thermoelectric conversion material described above, the element M is particularly preferably 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 the same element M as in the first embodiment is the same. It is thought that the nanoprecipitate has the same action and effect with respect to the PbTe substrate by containing the amount. As a result, a high dimensionless thermoelectric figure of merit ZT similar to that of the first embodiment can be achieved, and an N-type thermoelectric conversion material that exhibits stable characteristics can be realized because it does not include a material that easily deteriorates.

A method for producing a thermoelectric conversion material according to the second embodiment of the present invention will be described. In the step (S110) of preparing the material of the flowchart of FIG. 4 showing the method for producing the thermoelectric conversion material according to the first embodiment, the method for producing the thermoelectric conversion material according to the second embodiment, instead of the element A, As a donor, at least one element (X) selected from Group 17 elements (Cl, Br, I) is added. The addition of the element X is, for example, an addition of a group 17 element (Cl, Br, I) alone or a group 17 element (Cl, Br, I) containing Te, Pb, and an element M. Starting compounds such as PbCl ₂ , PbBr ₂ , and PbI ₂ . Except this, it is the same as the manufacturing method of the thermoelectric conversion material which concerns on 1st Embodiment, The description is abbreviate | omitted. The formulation in the step of preparing the material is prepared with 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 not greater than 0.01, more preferably not less than 0.002 and not greater than 0.006, and particularly preferably z is 0.004. preferable.

  According to the method for producing a thermoelectric conversion material according to the second embodiment, from the group consisting of lead (Pb), tellurium (Te), carbon (C), silicon (Si), germanium (Ge), and tin (Sn). By heating and dissolving at least one selected element M and a dopant element X as a donor, or a compound of element X and either Pb, Te, or element M, a nanostructure containing elements M and X A PbTe-based thermoelectric conversion material having precipitates is obtained. Since a material that easily deteriorates is not used, it is easy to handle, and the obtained thermoelectric conversion material has stable characteristics.

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

  Referring to FIG. 10, a thermoelectric power generation module 10 according to an 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. Each electrode has an electrode 30 in contact with one side, an electrode 41 in contact with the other side of the P-type thermoelectric conversion element 21, and an electrode 42 in contact with 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 include the thermoelectric conversion material of the second embodiment described above, or may include 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 brings the high-temperature body into contact with the electrode 30 and the low-temperature body into contact with the electrodes 41, 42, so that the carriers of the P-type thermoelectric conversion element 21 and N-type thermoelectric conversion element 22 that are in contact with the electrode 30 The concentrations (hole concentration and electron concentration, respectively) increase, and the carriers diffuse to the electrodes 41 and 42 side, respectively. As a result, 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, thereby generating a positive voltage at the electrode 42 with respect to the electrode 41. As a result, power generation is possible.

  According to the present embodiment, the P-type thermoelectric conversion element 21 has the thermoelectric conversion material of the first embodiment, so that the thermoelectric power generation module 10 having stable power generation performance with stable characteristics can be realized. Further, since the N-type thermoelectric conversion element 22 includes 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, higher power generation performance with stable characteristics. The thermoelectric power generation module 10 can be realized.

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

  Referring to FIG. 11, a Peltier cooler 50 according to an 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. Electrode 30 in contact with one side of each of the electrodes, electrode 41 in contact with the other side of P-type thermoelectric conversion element 21, electrode 42 in contact with the other side of N-type thermoelectric conversion element 22, and electrodes 41, 42 And a power supply unit 60 that applies a positive voltage to the electrode 41 and a negative voltage to the electrode 42. Note that the P-type thermoelectric conversion element 21, the N-type thermoelectric conversion element 22, and the electrodes 30, 41, 42 are the same as those shown in FIG. .

  The power supply unit 60 is not particularly limited as long as a sufficient current can be supplied by a DC voltage source.

  In the Peltier cooler 50, the current supplied from the power supply unit 60 flows in order from the electrode 42 to the N-type thermoelectric conversion element 22, the electrode 30, the P-type thermoelectric conversion element 21, and the electrode 41. In the P-type thermoelectric conversion element 21, holes absorb energy on the electrode 30 side and release energy on the electrode 41 side. In the N-type thermoelectric conversion element 22, electrons absorb energy on the electrode 30 side and the electrode 42. The object to be cooled can be cooled by releasing energy on the side.

  According to the present embodiment, the P-type thermoelectric conversion element 21 includes the thermoelectric conversion material of the first embodiment, whereby the Peltier 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 Peltier cooler 50 having stable characteristics and high cooling capacity can be realized. In addition, 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, stable cooling characteristics and higher cooling capacity are achieved. A Peltier cooler 50 can be realized.

  The preferred embodiment of the present invention has been described in detail above, but 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. Is possible. Needless to say, the thermoelectric conversion material, the manufacturing method thereof, and the thermoelectric power generation module of the present invention can be applied to various heat sources such as automobiles, thermal power plants, data centers, and the like. Needless to say, the Peltier cooler of the present invention can cool various objects.

In addition, the following additional notes are disclosed regarding the above description.
(Appendix 1) A thermoelectric conversion material,
A substrate comprising PbTe;
A nanoprecipitate comprising at least one element (M) selected from the group consisting of C, Si, Ge and Sn in the substrate;
The thermoelectric conversion material comprising:
(Additional remark 2) The said thermoelectric conversion material is a thermoelectric conversion material of Additional remark 1 containing at least 1 element (A) selected from the group which consists of a 1st group element, a 11th group element, and a 13th group element.
(Supplementary Note 3) The thermoelectric conversion material is represented by the composition formula of _{Pb 1-xy A y M x} Te, x and y, Pb, the total amount of M and A, respectively M, the atomic ratio of A The thermoelectric conversion material according to supplementary note 2, wherein x is greater than 0 and 0.015 or less, and y is greater than 0 and 0.1 or less.
(Additional remark 4) The thermoelectric conversion material of Additional remark 3 whose said x is 0.002 or more and 0.012 or less.
(Additional remark 5) The thermoelectric conversion material of Additional remark 3 whose said x is 0.007 or more and 0.010 or less.
(Appendix 6) The thermoelectric conversion material according to any one of appendices 3 to 5, wherein A is Na and y is 0.04.
(Appendix 7) The thermoelectric conversion material according to any one of appendices 1 to 6, wherein M is Ge.
(Supplementary Note 8) thermal conductivity, over the 700K to 900 K, is less than or equal 1.3WK ^-1 m ^-1, the thermoelectric conversion material as claimed in any one of Appendices 1-7.
(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 over 700 to 850K.
(Additional remark 10) The said nano precipitate is a thermoelectric conversion material as described in any one of additional marks 1-9 whose particle size is 2 nm-1 micrometer.
(Additional remark 11) The said thermoelectric conversion material is a thermoelectric conversion material of Additional remark 1 containing the at least 1 element (X) selected from the 17th group element.
(Supplementary Note 12) The thermoelectric conversion material is represented by the composition formula of _{Pb 1-x M x Te 1} -z X z, x represents an atomic ratio of M based on the total amount of Pb and M, x is 0 The thermoelectric conversion material according to appendix 11, wherein z is an atomic ratio of X with respect to the total amount of Te and X, and z is greater than 0 and not greater than 0.01.
(Additional remark 13) The thermoelectric conversion material of Additional remark 12 whose said z is 0.002 or more and 0.006 or less.
(Additional remark 14) The thermoelectric conversion material of Additional remark 12 whose said z is 0.004.
(Supplementary note 15) The thermoelectric conversion material according to any one of Supplementary notes 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 the 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.
(Additional remark 18) The said nano precipitate is a thermoelectric conversion material as described in any one of Additional remarks 11-17 whose particle size is 2 nm-1 micrometer.
(Supplementary note 19) A method for producing a thermoelectric conversion material,
Providing a material comprising Pb, Te, and at least one element (M) selected from the group consisting of C, Si, Ge, and Sn;
Heating and dissolving the prepared material in vacuum to obtain a material containing nanoprecipitates containing M;
The said manufacturing method containing.
(Supplementary note 20) In the step of preparing,
The manufacturing method according to appendix 19, wherein the material is prepared at a molar ratio of Te: Pb: M = 1: 1−x: x, and x is greater than 0 and not more than 0.015.
(Supplementary note 21) The manufacturing method according to supplementary note 20, wherein the x is 0.002 or more and 0.012 or less.
(Supplementary note 22) The method according to supplementary note 20, wherein x is 0.005 or more and 0.010 or less.
(Supplementary Note 23) In the preparing step, the material further includes at least one element (A) selected from the group consisting of a Group 1 element, a Group 11 element, and a Group 13 element,
It is prepared at a molar ratio of Te: Pb: M: A = 1: 1−xy: x: y, and y is greater than 0 and 0.1 or less, and any one of appendices 20 to 22 Manufacturing method.
(Supplementary Note 24) In the preparing step, the material further includes at least one element (X) selected from Group 17 elements, Te: Pb: M: X = 1-z: 1-x: x : The preparation method according to any one of appendices 20 to 22, wherein the preparation is performed at a molar ratio of z, and z is greater than 0 and 0.01 or less.
(Additional remark 25) The manufacturing method as described in any one of additional marks 19-24 which heats the said material to the temperature of 1207K or more in the said melt | dissolving step.
(Supplementary Note 26) The material obtained by the dissolving step is pulverized into a powder and sintered under pressure;
The production method according to any one of appendices 19 to 25, further including:
(Additional remark 27) A thermoelectric power generation module provided with the thermoelectric conversion element which has the thermoelectric conversion material as described in any one of Additional remarks 1-18.
(Additional remark 28) A thermoelectric power generation module provided with the P-type thermoelectric conversion element which has the thermoelectric conversion material as described in any one of Additional remarks 2-10.
(Additional remark 29) A thermoelectric power generation module provided with the N type thermoelectric conversion element which has the thermoelectric conversion material as described in any one of Additional remarks 11-18.
(Additional remark 30) A Peltier cooler provided with the thermoelectric conversion element which has the thermoelectric conversion material as described in any one of Additional remarks 1-18.
(Additional remark 31) A Peltier cooler provided with the P-type thermoelectric conversion element which has the thermoelectric conversion material as described in any one of Additional remarks 2-10.
(Additional remark 32) A Peltier cooler provided with the N type thermoelectric conversion element which has the thermoelectric conversion material as described in any one of Additional remarks 11-18.

DESCRIPTION OF SYMBOLS 10 Thermoelectric power generation module 21 P type thermoelectric conversion element 22 N type thermoelectric conversion element 30, 41, 42 Electrode 50 Peltier cooler 60 Power supply part

Claims (15)

A thermoelectric conversion material,
A substrate comprising PbTe;
A nanoprecipitate comprising at least one element (M) selected from the group consisting of C, Si, Ge and Sn in the substrate;
The thermoelectric conversion material comprising:   The thermoelectric conversion material according to claim 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. The thermoelectric conversion material is represented by a composition formula of Pb _1-xy A _y M _x Te, and x and y represent the atomic ratio of M and A with respect to the total amount of Pb, M, and A, respectively. The thermoelectric conversion material according to claim 2, wherein y is greater than 0 and 0.015 or less, and y is greater than 0 and 0.1 or less.   The thermoelectric conversion material according to claim 3, wherein the x is 0.002 or more and 0.012 or less.   The thermoelectric conversion material according to claim 1, wherein M is Ge. 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 over 700K to 900K.   The thermoelectric conversion material according to any one of claims 1 to 6, wherein the dimensionless thermoelectric figure of merit ZT is 2.0 or more over 700 to 850K.   The thermoelectric conversion material according to claim 1, wherein the thermoelectric conversion material contains at least one element (X) selected from Group 17 elements. The thermoelectric conversion material is represented by a composition formula of Pb _1-x M _x Te _1-z X _z , x represents an atomic ratio of M with respect to the total amount of Pb and M, and x is greater than 0 and 0 9. The thermoelectric conversion material according to claim 8, wherein z is an atomic ratio of X with respect to the total amount of Te and X, and z is greater than 0 and not greater than 0.01.   The thermoelectric conversion material according to claim 1, wherein the nanoprecipitate has a particle size of 2 nm to 1 μm. A method for producing a thermoelectric conversion material,
Providing a material comprising Pb, Te, and at least one element (M) selected from the group consisting of C, Si, Ge, and Sn;
Heating and dissolving the prepared material in vacuum to obtain a material containing nanoprecipitates containing M;
The said manufacturing method containing. In the preparing step,
The manufacturing method according to claim 11, wherein the material is prepared at a molar ratio of Te: Pb: M = 1: 1−x: x, and x is greater than 0 and equal to or less than 0.015. In the preparing step, the material further includes at least one element (A) selected from the group consisting of Group 1 elements, Group 11 elements and Group 13 elements,
The production method according to claim 11 or 12, wherein the preparation is performed at a molar ratio of Te: Pb: M: A = 1: 1-xy: x: y, and y is greater than 0 and 0.1 or less.   A thermoelectric power generation module comprising a thermoelectric conversion element comprising the thermoelectric conversion material according to claim 1. A Peltier cooler provided with the thermoelectric conversion element which has the thermoelectric conversion material as described in any one of Claims 1-10.

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