JP2007021670A - Core shell type nano particle and thermoelectric conversion material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermoelectric conversion material, exhibiting high thermoelectric conversion performance and having excellent mass-productivity, and to provide a core shell type nano particle used in the thermoelectric conversion material. <P>SOLUTION: This core shell type nano particle includes a core part and a shell part covering the core material. The component material of the shell part is InSb, and the component material of the core part has a higher melting point than that of InSb which is the component material of the shell part. Thus, the above object is achieved by providing the above particle of the invention. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to core-shell type nanoparticles and thermoelectric conversion materials used for thermoelectric conversion elements and the like.

Thermoelectric conversion materials used for thermoelectric conversion elements are required to have high conversion efficiency of heat energy into electric energy, and the following performance is required. (1) The voltage generated when the temperature difference is given is preferably large, and the thermoelectromotive force per 1 K of the temperature difference is required to be large. (2) If the electric resistance is large when current flows, energy is lost due to Joule heat. Therefore, it is preferable that the electric resistance is small. (3) Since thermal energy that should be converted into electrical energy escapes as heat when thermal conduction occurs, it is better that the thermal conductivity is small. From the above, the characteristics of the thermoelectric conversion material are governed by the value represented by the following formula (i) called the figure of merit Z.
Z = S ² · σ / k (i)
Here, S is the thermoelectromotive force, σ is the conductivity, and k is the thermal conductivity. A material having a larger value of the figure of merit Z is a more excellent thermoelectric conversion material.

  In recent years, as one of attempts to improve the performance of thermoelectric conversion materials, research on dispersing fine particles in thermoelectric conversion materials has been conducted. When materials with high mobility such as skutterudite compounds and SiGe are used as thermoelectric conversion materials, these materials contribute to performance improvement due to their high conductivity σ, while the figure of merit Z is determined because of their high thermal conductivity k. Although it could not be increased, by dispersing fine particles in such a thermoelectric conversion material, phonons are scattered by the fine particles, so that the thermal conductivity k can be reduced and the performance can be improved. It can be done.

For example, Non-Patent Document 1 proposes a thermoelectric conversion material in which FeSb ₂ fine particles are introduced into a skutterudite compound matrix by a mechanical alloying process up to a molar ratio of 40%. Size of FeSb ₂ fine particles was submicron order, the performance index in the range of 600K~800K is towards the system introduced FeSb ₂ particles have been shown to be greater than the system without introducing FeSb ₂ particles. However, at 500K or less, the performance improvement due to the introduction of FeSb ₂ fine particles was not shown.

  Non-Patent Document 2 introduces fleurite (mixture of C60: 90% and C70: 10%) with a particle size of 0.7 nm into SiGe alloy (Ge: 20 atm%) up to 1 wt% by mechanical alloying treatment. did. However, the dispersibility of fluorite is not mentioned, and no performance improvement was shown. It is considered that the main reason why the performance is not improved is that although the thermal conductivity k decreases due to the introduction of fine particles, the electrical conductivity σ also decreases.

  Further, Non-Patent Document 3 proposes a method for improving performance by using a PbTe / PbSeTe-based quantum dot superlattice. In this quantum dot superlattice, PbTe and PbSeTe (mixing molar ratio Pb: Se: Te = 1.00: 0.98: 0.02, hereinafter omitted) are obtained by a molecular beam epitaxy method. It is manufactured by alternately laminating, using the fact that the PbSeTe film formed on PbTe changes from a thin film immediately after film formation into particles due to lattice mismatch with PbTe over time. is there. Quantum having a structure in which PbSeTe fine particles (quantum dots) are regularly dispersed in PbTe by further forming PbTe so as to cover the PbSeTe particles changed into particles on the PbTe film, and again forming PbSeTe. A dot superlattice is obtained. The size of the PbSeTe fine particles was 30 nm or less, and within the range of 300K to 500K, the system in which the PbSeTe fine particles were introduced into PbTe showed a performance index that was 7 to 13 times larger than the system without the introduction. This is considered to be due to the fact that the quantum effect contributes to the performance improvement in addition to the effect of phonon scattering described above. This theory is described in detail in Non-Patent Document 4. In general, the size at which the quantum effect appears is 100 nm or less.

  However, since the quantum dot superlattice is produced by alternately stacking PbTe and PbSeTe in a vacuum system by the molecular beam epitaxy method as described above, there is a problem that it takes a lot of work. Each layer has a thickness of about 10 nm and needs to be 10 μm or more for use as a thermoelectric conversion material. Therefore, each layer must be laminated at least 500 layers, which is not suitable for mass production.

On the other hand, although not a system in which fine particles are dispersed in a thermoelectric conversion material, Non-Patent Document 5 proposes a method of coating SiO ₂ fine particles with a skutterudite compound. This is a method of coating SiO ₂ fine particles having a particle diameter of 300 nm with a thickness of 10 to 60 nm by sputtering, and further coating CoSb ₃ which is one kind of skutterudite compound thereon. This CoSb ₃ is formed by coating the precursor on gold and then firing by reduction. However, this method uses SiO ₂ fine particles as a mere support, and does not describe the phonon scattering effect by the SiO ₂ fine particles. Further, since a reducing gas is used when reducing the CoSb ₃ precursor, there is a problem that the inside of the precursor may not be sufficiently reduced.

J. Applied Physics, 88, p.3484-3489 (2000) Materials Science and Engineering, B41, p.280-288 (1996) 18th International Conference on Thermoelectrics, p.280-284 (1999) Phys. Rev. B, 47, p.16631 (1993) Nanostructured Films and Coatings, p.149-156 (2000)

  The main object of the present invention is to provide a thermoelectric conversion material that exhibits high thermoelectric conversion performance and is excellent in mass productivity, and to provide core-shell type nanoparticles used for the thermoelectric conversion material and the like. is there.

  In order to achieve the above object, the present invention provides a core-shell type nanoparticle having a core part and a shell part covering the core part, wherein the constituent material of the shell part is InSb, Provided is a core-shell nanoparticle characterized in that the constituent material has a melting point higher than that of InSb which is a constituent material of the shell portion.

  In the present invention, since the melting point of the constituent material of the core part is higher than InSb which is the constituent material of the shell part, for example, the core-shell type nanoparticle of the present invention is compression-molded to produce a core-shell structure described later When the component material of the shell part is melted and the shell parts of the adjacent core-shell type nanoparticles are bonded to each other, the constituent material of the core part is not melted and can maintain an independent core part, As a result, a thermoelectric conversion material having excellent thermoelectric conversion performance can be obtained.

  Moreover, in the said invention, it is preferable that the said shell part and the said core part are phase-separated. This is because when different functions are imparted to the core portion and the shell portion, if these are phase-separated, the respective functions can be exhibited more efficiently.

  The present invention also provides a core-shell nanoparticle dispersion characterized by containing the core-shell nanoparticle and a dispersion medium.

  In the present invention, handling property and storage stability can be improved by dispersing the core-shell type nanoparticles in a dispersion medium to obtain a core-shell type nanoparticle dispersion, as compared with the case of the core-shell type nanoparticles alone.

  The present invention is also a thermoelectric conversion material comprising a core-shell structure having a plurality of core portions and a coupling shell portion covering the core portions, wherein the plurality of core portions are independent of each other and the coupling A thermoelectric conversion characterized in that the shell part is continuous, the constituent material of the joint shell part is InSb, and the melting point of the constituent material of the core part is higher than InSb which is the constituent material of the joint shell part Provide material.

  In the present invention, a plurality of core portions are independent from each other in the core-shell structure and are finely dispersed. Therefore, when electricity and heat are conducted through the core-shell structure, the core portion causes the phonon. Is scattered, the thermal conductivity can be reduced, and the performance of thermoelectric conversion can be improved. Moreover, since the core-shell structure in the present invention can be produced, for example, by compression molding the core-shell type nanoparticles, it has an advantage that it is suitable for mass production as compared with the production of the quantum dot superlattice described above.

  The present invention also includes a core part preparation step in which a core part is formed using a material having a melting point higher than that of InSb, and the core part is coated with InSb by a hot soap method to form a shell part. A thermoelectric conversion material comprising: a shell part preparation step to be formed; a removal step of removing an organic substance adhering to the shell part; and a compression molding step of compression-molding core-shell type nanoparticles from which the organic substance has been removed. A manufacturing method is provided.

  In this invention, by performing the said process, the thermoelectric conversion material which shows the performance of high thermoelectric conversion and was excellent in mass productivity can be obtained.

  In the present invention, when the core-shell structure is produced using the core-shell type nanoparticles, when electricity and heat are conducted through the core-shell structure, phonons are scattered by the core portion that exists independently. Therefore, the thermal conductivity can be reduced and the performance of thermoelectric conversion can be improved. Moreover, since the said core-shell structure can be produced by compression-molding the said core-shell type nanoparticle, there exists an effect that it is suitable for mass production.

  Hereinafter, the core-shell nanoparticle, the core-shell nanoparticle dispersion, the thermoelectric conversion material, and the method for producing the thermoelectric conversion material of the present invention will be described.

A. Core-shell type nanoparticles First, the core-shell type nanoparticles of the present invention will be described. The core-shell nanoparticle of the present invention is a core-shell nanoparticle having a core part and a shell part covering the core part, wherein the constituent material of the shell part is InSb, and the constituent material of the core part is The melting point is higher than InSb which is a constituent material of the shell part.

  In the present invention, since the melting point of the constituent material of the core part is higher than InSb which is the constituent material of the shell part, for example, the core-shell type nanoparticle of the present invention is compression-molded to produce a core-shell structure described later When the component material of the shell part is melted and the shell parts of the adjacent core-shell type nanoparticles are bonded to each other, the constituent material of the core part is not melted and can maintain an independent core part, As a result, a thermoelectric conversion material having excellent thermoelectric conversion performance can be obtained.

Next, the core-shell type nanoparticles of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of the core-shell nanoparticle of the present invention. In FIG. 1, a core-shell nanoparticle 3 has a core part 1 using a material having a melting point higher than that of InSb, and a shell part 2 covering the core part 1 and using InSb.
Hereinafter, each configuration of the core-shell nanoparticle of the present invention will be described.

1. Shell Part First, the shell part used in the present invention will be described. The shell portion used in the present invention covers a core portion described later, and uses InSb as a constituent material of the shell portion.

In the present invention, “InSb” used as a constituent material of the shell portion includes not only InSb but also InSb doped with other elements. When other elements are doped, for example, the conductivity of the shell portion can be improved. As an example of such doping, for example, for InSb, Group 6 elements such as S, Se, Te, etc .; Group 12 elements such as Zn, Cd, Hg; Cr, Mn, Fe, Co, Ni, Examples include those obtained by doping a Group 3 to Group 11 transition element such as Cu; Specifically, In _x Zn _(1-x) Sb (where x = 0.01 to 0.1) can be given. As the doping method, a method generally used in the semiconductor field after forming the core-shell type nanoparticles can be applied. For example, thermal diffusion is applied. Alternatively, doping may be performed by adding a doping element or a precursor containing a doping element when core-shell type nanoparticles are produced by a hot soap method described later.

  In addition, the thickness of the shell portion varies depending on the use of the core-shell nanoparticle, but the core-shell nanoparticle of the present invention is used for the core-shell structure described in “C. Thermoelectric conversion material” described later. Is preferably in the range of 1 nm to 100 nm, more preferably in the range of 1 nm to 70 nm, and particularly preferably in the range of 2 nm to 50 nm. This is because if the film thickness is too thin, electrons are not sufficiently conducted, and the conductivity may be reduced to deteriorate the performance. On the contrary, if the thickness is too thick, it may be difficult to obtain the phonon scattering effect by the core. Here, the thickness of the shell portion refers to, for example, the thickness indicated by n in FIG.

  The thickness of the shell part is obtained by subtracting the particle diameter of the fine particles forming only the core part from the particle diameter of the fine particles formed up to the shell part and dividing by 2. As for the particle size of each fine particle, 20 or more fine particles are present from an image obtained by using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) of the core-shell nanoparticle of the present invention. The region to be confirmed is selected, the particle diameter is measured for all the fine particles in this region, and the average value is obtained. However, the part where the focus is blurred is excluded from the measurement target.

2. Core part Next, the core part used for this invention is demonstrated. The core part used for this invention is coat | covered by the said shell part, Comprising: The melting | fusing point of the constituent material of the said core part is a thing higher than InSb which is the constituent material of the said shell part. Moreover, the core part used for this invention is normally comprised from core part microparticles | fine-particles.

  In the present invention, the melting point of the constituent material of the core part is not particularly limited as long as it is higher than InSb which is the constituent material of the shell part, but the melting point of the constituent material of the core part, The difference from the melting point of InSb is preferably 50 ° C. or higher, more preferably 100 ° C. or higher, and particularly preferably 200 ° C. or higher. When a core-shell type nanoparticle having a difference in melting point between the core part and the shell part is compression-molded to produce a core-shell structure to be described later, the constituent material of the shell part melts and the shell of the adjacent core-shell type nanoparticle This is because the constituent materials of the core portion are not melted while the core portions are bonded to each other, and independent core portions can be maintained. As a result, a thermoelectric conversion material having excellent thermoelectric conversion performance can be obtained. In addition, the melting point of the material constituting the core part is preferably in the range of 550 ° C. to 5000 ° C., more preferably in the range of 1050 ° C. to 4000 ° C. When the size of the core part fine particles constituting the core part is 1 μm or less, the melting point of the core part fine particles may be lower than the original melting point of the material. The melting point originally possessed shall be indicated.

Examples of the material constituting the core part include inorganic oxides such as SiO ₂ , Al ₂ O ₃ , and ZnO, inorganic sulfides such as MnS, CdS, and ZnS, and inorganic nitrides such as BN and Si ₃ N ₄ . , Au, Cu, U, Mn, Sm, Be, Gd, Tb, Si, Ni, Co, Dy, Y, Er, Fe, Sc, Pd, Ti, Th, Pt, Zr, Cr, V, Rh, Hf , B, Ru, Ir, Nb, Mo, Os, Ta, Re, W, etc., materials containing at least one of the above elements, NiSi, FeSi, TiSi inorganic silicides, SiC, Inorganic carbides such as MoC, carbon, CB _{4 and the} like can be mentioned.

  Further, the average particle size of the core part fine particles varies depending on the use of the core-shell nanoparticle, but the core-shell nanoparticle of the present invention is the core-shell structure described in “C. Thermoelectric conversion material” described later. In the case of using for, it is preferable that the size is such that phonons can be effectively scattered. Specifically, it is preferably in the range of 0.3 nm to 100 nm, more preferably in the range of 1 nm to 70 nm, and particularly preferably in the range of 2 nm to 50 nm.

  In addition, the said average particle diameter has 20 or more core parts from the image obtained using the scanning electron microscope (SEM) or transmission electron microscope (TEM) of the core-shell type | mold nanoparticle of this invention. It is set as the value obtained by selecting the area | region where it is confirmed, measuring particle size about all the core parts in this area | region, and calculating | requiring an average value. However, the core portion with a blurred focus is excluded from the measurement target.

3. Core-shell type nanoparticles The core-shell type nanoparticles of the present invention have the shell part and the core part. Among these, in the present invention, it is preferable that the core part and the shell part are phase-separated. This is because when different functions are imparted to the core portion and the shell portion, if these are phase-separated, the respective functions can be exhibited more efficiently. For example, when the core-shell nanoparticle of the present invention is used for a core-shell structure of a thermoelectric conversion material to be described later, the core part has a function of scattering phonons, and the shell part has a function of conducting electrons. If the core part and the shell part are phase-separated, each function can be exhibited more effectively.

  In the present invention, whether or not the core portion and the shell portion are phase-separated can be determined from the result of two-dimensional mapping of elements obtained by measurement with a scanning transmission electron microscope (STEM). . Specifically, the core-shell type nanoparticles are measured using STEM, and the state where there is a region having 10% or more of the constituent elements of the core portion is obtained from the result of the obtained two-dimensional mapping. And the shell part are defined as being in a state of phase separation. Note that the above percentage is the value obtained by standardizing the value obtained by subtracting the background intensity from the intensity near the center of the nanoparticle to 100% in the constituent elements of the core part. However, the standardization and the calculation of the percentage are limited to the case where there is a significant difference in strength in the vicinity of the center of the nanoparticle with respect to the background in the constituent elements of the core part. In the present invention, the core part is usually in a crystalline or amorphous state, but when the core part is in a crystalline state, analysis by X-ray diffraction analysis (XRD) is possible. Therefore, in the present invention, when the peak of the constituent material of the core part is detected by XRD measurement, the core part and the shell part can be phase-separated.

  Further, the average particle diameter of the core-shell type nanoparticles of the present invention is not particularly limited, but is, for example, in the range of 2 nm to 200 nm, particularly in the range of 3 nm to 100 nm, particularly in the range of 5 nm to 50 nm. It is preferable. This is because a product having an average particle size that is too small is difficult to produce. On the other hand, if the average particle size is too large, the surface area per unit weight (specific surface area) becomes small, and the desired effect may not be obtained.

  In addition, the average particle diameter indicates that 20 or more core-shell nanoparticles are present from an image obtained by using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) of core-shell nanoparticles. Is selected, a particle size is measured for all core-shell nanoparticles in this region, and an average value is obtained. However, core-shell nanoparticles with a blurred focus are excluded from the measurement target. In addition, when the core-shell type nanoparticles are not spherical but have a rod-like shape, for example, the maximum diameter and the minimum diameter are measured for each particle, and the average value is taken as the average particle diameter.

  In addition, the ratio between the particle size of the core part and the thickness of the shell part in the core-shell nanoparticle used in the present invention varies depending on the use of the core-shell nanoparticle. When used in the core-shell structure described in “C. Thermoelectric conversion material” described later, the ratio is preferably such that electrons and heat can be conducted and phonons can be scattered by the core. Specifically, the ratio between the particle size of the core part and the thickness of the shell part is preferably in the range of 1:10 to 10: 1, more preferably in the range of 1: 7 to 7: 1. In particular, it is preferably within a range of 1: 5 to 5: 1. This is because the thermal conductivity can be effectively reduced when the ratio of the core portion to the shell portion is within the above range.

  The core-shell type nanoparticles of the present invention are preferably dispersed independently. In addition, it can confirm that the said core-shell type nanoparticle is disperse | distributing independently by observing using a transmission electron microscope (TEM). For example, as shown in the TEM photograph of FIG. 2, the core-shell nanoparticles are said to be dispersed independently if the particles do not overlap. On the other hand, although it is not a core-shell type nanoparticle, for example, Adv. Mater., 13, p.145-148 (2001) Fig. 2. a-b TEM photograph or Can. J. Chem., 79, p.127 -130 (2001), as shown in the TEM photographs of Fig. 2. a to c, particles are said to be secondary agglomerated if they are superposed.

  Moreover, it is preferable that the core-shell type nanoparticles of the present invention can be dispersed in a dispersion medium. Here, “dispersible in a dispersion medium” means that the core-shell nanoparticles themselves exist as fine particles and can be dispersed in a predetermined dispersion medium. The dispersion medium is the same as that described in “B. Core-shell type nanoparticle dispersion liquid”, and the description thereof is omitted here.

  The core-shell type nanoparticles of the present invention preferably have an organic compound having one or more hydrophilic groups and a hydrophobic group attached to the surface of one molecule. This is because the aggregation of the core-shell type nanoparticles can be prevented by attaching a predetermined organic compound to the surface of the core-shell type nanoparticles. Note that the surface of the core-shell nanoparticle means the surface of the shell portion of the core-shell nanoparticle. As described above, InSb is used as a constituent material of the shell portion in the present invention.

  On the other hand, in the case where the core-shell type nanoparticles do not have a predetermined organic compound attached to the surface, the aggregation of the core-shell type nanoparticles is prevented by adding the predetermined organic compound when dispersed in the dispersion medium. It becomes possible.

  The predetermined organic compound attached to the surface of the core-shell nanoparticle in the present invention is not particularly limited as long as it has one or more hydrophilic groups and a hydrophobic group in one molecule. An organic compound in which a hydrophilic group is bonded to one end or both ends of a hydrophobic group is preferable.

  Examples of the hydrophobic group include aliphatic hydrocarbon groups having 4 or more carbon atoms; aromatic hydrocarbon groups such as phenyl group and naphthyl group; heterocyclic groups such as pyridyl group, pyrrole group and thiophene group; . The hydrophobic group may be a residue of these groups.

  Among the above, the hydrophobic group is preferably an aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be linear or cyclic, but is preferably linear. Further, the chain-like aliphatic hydrocarbon group may be linear or branched. Furthermore, the aliphatic hydrocarbon group may be unsaturated or saturated.

  As the carbon number of such a chain-like aliphatic hydrocarbon group, the straight chain carbon number excluding the normally branched carbon is within the range of 6 to 30, more preferably within the range of 8 to 20. It is.

  The hydrophilic group is not particularly limited as long as it is a functional group that can be attached to the surface of the core-shell nanoparticle. For example, a carboxyl group, an amino group, a hydroxyl group, a thiol group, an aldehyde group, a sulfonic acid group, an amide group , Sulfonamide group, phosphoric acid group, phosphinic acid group, P═O group and the like. Among these, the hydrophilic group is preferably a carboxyl group, an amino group or a hydroxyl group. This is because a carboxyl group, an amino group, or a hydroxyl group generally has a high affinity for a metal. Moreover, it is because the organic compound which has these hydrophilic groups is easy to acquire.

  Specifically, an organic compound that is coordinated to InSb, which is a constituent material of the shell portion of the core-shell nanoparticle, in the dispersion medium and stabilized is used as the predetermined organic compound. Examples of such organic compounds include aminoalkanes such as octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine; higher fatty acids such as palmitic acid, stearic acid, and oleic acid; higher alcohols; Etc. can be mentioned as preferred. This is because the hydrophilic group of the predetermined organic compound is preferably an amino group, a carboxyl group, or a hydroxyl group as described above.

  The higher alcohols preferably have one or more long-chain alkyl groups and two or more hydroxyl groups in one molecule, and examples thereof include long-chain alkyl-1,2-diols. As described later in “4. Method for producing core-shell type nanoparticles”, when synthesizing core-shell type nanoparticles by the hot soap method, when antimony alkoxide is used as the shell portion precursor, long-chain alkyl- This is because antimony alkoxide can be stabilized by using 1,2-diol or the like.

  The above-mentioned organic compounds may be attached to the surface of the core-shell nanoparticle alone, or a plurality of types may be attached. The amount of the organic compound attached to the core-shell nanoparticle is not particularly limited.

  Further, the predetermined organic compound only needs to be attached to the surface of the core-shell nanoparticle, and the “attachment” here may include the case where the predetermined organic compound is adsorbed to the surface of the core-shell nanoparticle. This includes cases where coordination is performed.

  In addition, it is confirmed that the core-shell type nanoparticles are dispersed in a dispersion medium in advance if the predetermined organic compound is attached to the surface of the core-shell type nanoparticles, and the core-shell type nanoparticles are one of surface analysis methods. This can be confirmed by examining that elements corresponding to carbon and hydrophilic groups are contained using X-ray photoelectron spectroscopy (XPS).

  The use of the core-shell nanoparticle of the present invention is not particularly limited, and examples thereof include semiconductor applications such as thermoelectric conversion elements, Hall elements, and photoconductive elements, and nonlinear optical elements.

4). Next, a method for producing core-shell nanoparticles will be described. The method for producing the core-shell type nanoparticles is not particularly limited as long as the above-described core-shell type nanoparticles can be obtained, but in particular, when the core part is covered with the shell part (shell part adjusting step) The liquid phase method is preferably used as a method for forming the shell part. This is because the liquid phase method has an advantage that the composition can be chemically uniform when the constituent components form two or more kinds of compounds. Examples of the liquid phase method include a coprecipitation method, a reverse micelle method, and a hot soap method. Among these, the hot soap method is preferably used in the present invention.

  Here, the hot soap method is a process in which at least one precursor of a target compound is thermally decomposed in a dispersant heated to a high temperature, and as a result, the nucleation and crystal growth of the crystal proceeds by a starting reaction. It is a method to make it. For the purpose of controlling the reaction rate in the process of crystal nucleation and crystal growth, a dispersant having a coordination power suitable for the constituent element of the target compound is used as an essential component constituting the liquid phase medium. . This situation is called the hot soap method because the situation where the dispersant is coordinated to the crystals and stabilized is similar to the situation where the soap molecules stabilize the oil droplets in water.

In the present invention, by using such a hot soap method, the shell portion can be grown around the core portion using the core portion as a nucleus, so that the core portion can be uniformly covered with the shell portion. Has the advantage.
Hereinafter, the manufacturing method of the core-shell type nanoparticles using the hot soap method will be described.

  In the present invention, a method for manufacturing a thermoelectric conversion material using a hot soap method includes a core part preparation step in which a core part is formed using a material having a melting point higher than InSb, and the core part is coated with InSb by a hot soap method. And a shell part preparing step for forming a shell part. Hereinafter, each process in the manufacturing method of such a core-shell type nanoparticle will be described.

(1) Core part preparation process The core part preparation process in this invention is a process of preparing a core part (core part microparticles | fine-particles) using the material whose melting | fusing point is higher than InSb which is a constituent material of a shell part.
The method for forming the core part fine particles used in the present invention is not particularly limited as long as it is a method capable of forming the core part fine particles as described in “2. Core part” described above. Like the method for forming the part, it is preferable to use a liquid phase method, and it is particularly preferable to use a hot soap method. This is because core part fine particles having a narrow particle size distribution can be obtained by using the hot soap method. In addition, the core part fine particles obtained by using the hot soap method have good dispersibility in the shell part precursor containing the constituent elements of the shell part and the dispersant in the shell part preparation step described later. .

In order to form core part fine particles using such a hot soap method, a method of heating a dispersant and injecting a core part precursor containing the constituent elements of the core part into the heated dispersant is used. it can.
Hereinafter, a method for forming core fine particles using such a hot soap method will be described.

  The core part precursor used in the present invention is not particularly limited as long as it contains the constituent elements of the core part described above and can form the core part fine particles. For example, in order to form Mo fine particles, a compound containing Mo may be used as the core portion precursor, and specifically, those described in Chem. Mater., 13, p1008-1014 (2001) may be used. it can. For example, molybdenum hexacarbonyl, molybdenyl acetylacetonate, etc. are used. In addition, for example, in order to form ZnS fine particles, a compound containing ZnS may be used as the core portion precursor. Specifically, the compounds described in Chem. Commun., P1849-1850 (1998) or the like are used. Can be used. For example, diethyldithiocarbamic acid ginxolt, bis- (ethylhexyl) dithiocarbamic acid ginxolt, etc. are used. Further, when two or more core part precursors are used, the mixing ratio may be set based on, for example, the stoichiometric ratio of the target compound.

  Moreover, it is preferable that the said core part precursor is a liquid form for the reason of the simplicity on manufacture operation. If the core part precursor itself is liquid at room temperature, it can be used as it is, but if necessary, it may be dissolved or dispersed in a suitable organic solvent. Examples of such organic solvents include alkanes such as n-hexane, n-heptane, n-octane, isooctane, nonane and decane, aromatic hydrocarbons such as benzene, toluene, xylene and naphthalene, diphenyl ether, di (n- Octyl) ethers, ethers, chloroform, dichloromethane, dichloroethane, monochlorobenzene, dichlorobenzene and other halogenated hydrocarbons, n-hexylamine, n-octylamine, tri (n-hexyl) amine, tri (n-octyl) amine And the like, or compounds used in the dispersant described later. Among these, alkanes such as n-hexane, n-heptane, n-octane, and isooctane, or trialkylphosphines such as tributylphosphine, trihexylphosphine, and trioctylphosphine, and ethers are preferably used.

  Further, when at least one of the core part precursors is a gas, it is introduced by dissolving in the organic solvent or dispersant by bubbling or the like, or in the reaction liquid phase into which other core part precursors are injected. Gas can also be introduced directly.

  The dispersant used in the present invention is not particularly limited as long as it is a substance that coordinates and stabilizes in microcrystals in a high-temperature liquid phase, and examples thereof include tributylphosphine, trihexylphosphine, and trioctylphosphine. Organic phosphorus compounds such as trialkylphosphines, tributylphosphine oxide, trihexylphosphine oxide, trioctylphosphine oxide, tridecylphosphine oxide, ω such as octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, etc. -Tertiary amines such as aminoalkanes, tri (n-hexyl) amine, tri (n-octyl) amine, organic nitrogen compounds such as nitrogen-containing aromatic compounds such as pyridine, lutidine, collidine, and quinoline, dibutyl sulfide Dialkyl sulfoxides, dialkyl sulfoxides such as dimethyl sulfoxide and dibutyl sulfoxide, organic sulfur compounds such as sulfur-containing aromatic compounds such as thiophene, higher fatty acids such as palmitic acid, stearic acid and oleic acid, and 1-adamantanecarboxylic acid It is done. Among these, trialkylphosphines such as tributylphosphine and trioctylphosphine, trialkylphosphine oxides such as tributylphosphine oxide and trioctylphosphine oxide, ω having 12 or more carbon atoms such as dodecylamine, hexadecylamine and octadecylamine. -Compounds containing a nitrogen atom or a phosphorus atom in the molecular structure such as aminoalkanes are preferably used. More preferable compounds include compounds having a carbon-phosphorus single bond such as trialkylphosphines such as tributylphosphine and trioctylphosphine, and trialkylphosphine oxides such as tributylphosphine oxide and trioctylphosphine oxide. In particular, trialkylphosphine oxides such as trioctylphosphine oxide are preferably used. These dispersants may be used alone or as a mixture of a plurality of types as necessary.

  Furthermore, the dispersant is an appropriate organic solvent (for example, aromatic hydrocarbons such as toluene, xylene, naphthalene, etc., long chain alkanes such as octane, decane, dodecane, octadecane, diphenyl ether, di (n-octyl) ether, tetrahydrofuran. Etc., and may be diluted with an ether such as a halogenated hydrocarbon).

  The heating temperature of the dispersant is not particularly limited as long as it is a temperature at which the dispersant and the core part precursor are melted. . Moreover, it is preferable that this heating temperature is relatively high. Since the core part precursor injected into the dispersant is decomposed all at once by setting it to a high temperature, a large number of nuclei are generated at once, making it easier to obtain core part fine particles having a relatively small particle size. is there.

  Further, the method for injecting the core part precursor into the heated dispersant is not particularly limited as long as the core part fine particles can be formed. Further, the core part precursor is preferably injected once in a short time if possible to obtain core part fine particles having a relatively small particle diameter. When it is desired to increase the particle size, the injection may be performed a plurality of times or continuously.

  The reaction temperature at the time of forming the core part fine particles after injecting the core part precursor into the heated dispersant is a temperature at which the dispersant and the core part precursor are melted or dissolved in an organic solvent, and The temperature is not particularly limited as long as crystal growth occurs, and is usually 150 ° C. or higher although it varies depending on pressure conditions and the like.

  As described above, after the core part fine particles are formed by injecting the core part precursor into the dispersant, the core part fine particles are usually separated from the dispersant. Examples of the separation method include sedimentation separation methods such as centrifugation, flotation separation, and foam separation, filtration methods such as cake filtration and clarification filtration, and compression methods. In the present invention, among the above, centrifugation is preferably used. However, the core fine particles obtained after the separation operation are often obtained as a mixture with a small amount of a dispersant.

  In the case of the separation described above, when the core fine particles are extremely small in size so that the core fine particles are difficult to settle, acetonitrile, methanol, ethanol, n-propyl alcohol, Alcohols having 1 to 4 carbon atoms such as isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, secondary butyl alcohol, and tertiary butyl alcohol; aldehydes having 1 to 4 carbon atoms such as formaldehyde, acetaldehyde, acrolein, and crotonaldehyde; C3-C5 ketones such as acetone, methyl ethyl ketone and diethyl ketone, C2-C4 ethers such as dimethyl ether, methyl ethyl ether, diethyl ether and tetrahydrofuran, methylamine, dimethylamine, trimethylamine and dimethyl It can be used an additive such as an organic nitrogen-containing compound having 1 to 4 carbon atoms such as formamide. Among these, water or alcohols such as methanol and ethanol are preferably used. The additives described above may be used alone or in combination of two or more.

  The core part fine particles are usually formed in an atmosphere of an inert gas such as argon gas or nitrogen gas.

(2) Shell part preparation process Next, the shell part preparation process in this invention is demonstrated. The shell part preparation step in the present invention is a step of forming a shell part by coating the core part with InSb by a hot soap method. Specifically, the dispersant is heated, and the core part fine particles and the shell part precursor containing the constituent elements of the shell part are injected into the heated dispersant, and the core part is covered with the shell part. This is a step of forming mold nanoparticles.

  The shell part precursor used in the present invention is not particularly limited as long as it contains the constituent elements of the shell part described above and can coat the core part fine particles. In the present invention, since the core part fine particles are coated with InSb, a compound containing In and a compound containing Sb may be used as the shell part precursor. As the compound containing In, an organometallic compound containing In can be used, and examples thereof include indium acetylacetonate, indium acetate, cyclopentadienyl indium, indium alkoxide, and indium chloride. Further, as the compound containing Sb, an organometallic compound containing Sb can be used, and examples thereof include Sb alkoxide, antimony acetate, triphenylantimony, trimethylsilylantimony, and the like. In addition, when two or more kinds of shell part precursors are used in this way, the mixing ratio may be set based on, for example, the stoichiometric ratio of the target compound.

  Moreover, it is preferable that the said shell part precursor is a liquid form for the reason of the simplicity on manufacture operation. If the shell part precursor itself is liquid at room temperature, it can be used as it is, but if necessary, it may be used by dissolving or dispersing in a suitable organic solvent. Examples of such organic solvents include alkanes such as n-hexane, n-heptane, n-octane, isooctane, nonane, and decane, aromatic hydrocarbons such as benzene, toluene, xylene, and naphthalene, or the above-described dispersants. Examples include compounds used. Among these, alkanes such as n-hexane, n-heptane, n-octane, and isooctane, or trialkylphosphines such as tributylphosphine, trihexylphosphine, and trioctylphosphine, and ethers are preferably used.

  In addition, about a dispersing agent, since it is the same as that of what was described in the item of the said core part preparation process, description here is abbreviate | omitted.

  The heating temperature of the dispersant is not particularly limited as long as it is a temperature at which the dispersant and the shell part precursor are melted or dissolved in an organic solvent. 60 ° C. or higher.

  The method for injecting the core part fine particles and the shell part precursor into the heated dispersant is not particularly limited as long as the core part can be coated with the shell part. For example, the core part fine particles and the shell part precursor may be injected at the same time, or the core part fine particles may be injected first. However, in the present invention, after the core part fine particles are injected, the shell part precursor is gradually added. It is preferable to inject. This is because, if the shell portion precursor is injected first or a large amount is injected at once, nucleation by the shell portion precursor occurs, and fine particles composed only of the shell portion may be formed.

  After injecting the core part fine particles and the shell part precursor into the heated dispersant, the reaction temperature when the core part is coated with the shell part is such that the dispersant and the shell part precursor are melted or dissolved in an organic solvent. It is not particularly limited as long as it is a temperature at which crystal growth of the constituent material of the shell portion occurs, and it is usually 100 ° C. or higher although it varies depending on pressure conditions and the like.

  As described above, after the core-shell type nanoparticles are formed by covering the core part with the shell part, the core-shell type nanoparticles are usually separated from the dispersant. Examples of the separation method include sedimentation separation methods such as centrifugation, flotation separation, and foam separation, filtration methods such as cake filtration and clarification filtration, and compression methods. In the present invention, among the above, centrifugation is preferably used.

  In the above-described separation, if the core-shell nanoparticles are difficult to settle due to the extremely small size of the core-shell nanoparticles, an additive can be used to improve the sedimentation property. In addition, since it is the same as that of what was described in the item of the said core part preparation process about an additive, description here is abbreviate | omitted.

  Moreover, this process is normally performed in the atmosphere of inert gas, such as argon gas and nitrogen gas.

  In the present invention, classification may be performed when obtaining core-shell type nanoparticles having a uniform particle diameter. As a method for classifying core-shell nanoparticles according to the size of the particle size, for example, a mixed solvent of a parent solvent having a high affinity and a poor solvent having a low affinity for the core-shell nanoparticles is used. By changing the ratio with the solvent, the particle diameter of the precipitated core-shell nanoparticles can be controlled. This utilizes the phenomenon that core-shell type nanoparticles with a larger particle size precipitate as the ratio of the parent solvent / poor solvent increases, and that the core-shell type nanoparticles with a smaller particle size also precipitate when the above ratio decreases. It is. Specifically, first, a small amount of a poor solvent is added to a dispersion obtained by dispersing core-shell nanoparticles in a parent solvent to precipitate only core-shell nanoparticles having a large particle size. The precipitate is separated by centrifugation or the like to obtain core-shell type nanoparticles having a large particle size. Next, a poor solvent is further added to the dispersion liquid after centrifugation, and core-shell nanoparticles having a smaller particle diameter than the previously precipitated core-shell nanoparticles are precipitated. The precipitate is separated by centrifugation or the like to obtain core-shell type nanoparticles having a smaller particle size than the previously precipitated core-shell type nanoparticles. Thus, classification can be performed by repeating the addition of the poor solvent and the operation of centrifugation.

  Examples of the parent solvent used for classification include the dispersion media described in the section “B. Core-shell type nanoparticle dispersion liquid”. Moreover, as a poor solvent, the additive used in order to improve the sedimentation property of the core-shell type nanoparticle mentioned above is mentioned.

  Furthermore, in this invention, the dispersing agent adhering to the surface of a core-shell type nanoparticle can be substituted with another organic compound. In this case, a large amount of the dispersant adhering to the surface of the core-shell nanoparticles can be obtained by heating while mixing a large amount of other organic compounds to be substituted with the core-shell nanoparticles in an inert gas atmosphere. Is replaced by other organic compounds present in The amount of the other organic compound to be substituted may be 5 times or more by weight with respect to the core-shell type nanoparticles. The heating time is usually 1 to 48 hours.

  Moreover, in this invention, the core-shell type nanoparticle which the dispersion agent has adhered to the surface can be removed by heating the core-shell type nanoparticle which has the dispersion agent adhered to the surface, and the surface can also be obtained. In this case, a dispersant may be added in order to disperse the core-shell type nanoparticles in the dispersion medium. Thereby, the core-shell type nanoparticles are in an independently dispersed state in the dispersion medium.

  Furthermore, in the present invention, when producing core-shell type nanoparticles having a shell portion of InSb doped with a trace amount of element, when the dispersant is heated, a trace amount of a predetermined element or its element is added to the dispersant. Add containing compound. Alternatively, a trace amount of a predetermined element or a compound containing the element may be added to the precursor.

  The core-shell type nanoparticles having InSb doped with a trace amount of element as a shell part are useful as a semiconductor forming material because they can be both an n-type semiconductor forming material and a p-type semiconductor forming material depending on the type of element. The compound containing a predetermined element to be added varies depending on the kind of element to be doped. However, when preparing core-shell type nanoparticles that are n-type semiconductor forming materials, for example, a tributylphosphine solution of Se or Te, diisopropyl telluride , Tellurium alkoxide and the like are used. On the other hand, when producing core-shell type nanoparticles to be a p-type semiconductor forming material, for example, zinc acetate, cobalt carbonyl, cadmium chloride or the like is used as a compound containing a predetermined element to be added.

B. Core-shell nanoparticle dispersion Next, the core-shell nanoparticle dispersion of the present invention will be described. The core-shell type nanoparticle dispersion of the present invention is characterized by containing core-shell type nanoparticles and a dispersion medium.

In the present invention, handling property and storage stability can be improved by dispersing the core-shell type nanoparticles in a dispersion medium to obtain a core-shell type nanoparticle dispersion, as compared with the case of the core-shell type nanoparticles alone.
Hereinafter, each configuration of the core-shell nanoparticle dispersion of the present invention will be described.

1. Core-shell type nanoparticles The core-shell type nanoparticles used in the present invention may be the same as those described in the above section “A. Core-shell type nanoparticles”. In particular, in the present invention, the core-shell type nanoparticles are preferably those in which an organic compound having one or more hydrophilic groups and a hydrophobic group in one molecule is attached to the surface. This is because such an organic compound adheres to the surface, thereby effectively preventing aggregation of the core-shell type nanoparticles.

  On the other hand, when a predetermined organic compound is not attached to the surface of the core-shell nanoparticle, the core-shell nanoparticle is aggregated by adding the predetermined organic compound when the core-shell nanoparticle dispersion is used. It becomes possible to prevent.

  Further, the content of the core-shell nanoparticle in the core-shell nanoparticle dispersion is not particularly limited, but is preferably an amount capable of maintaining the independent dispersion state of the core-shell nanoparticle. . Specifically, the content of the core-shell type nanoparticles is preferably 10% by weight or less, more preferably 5% by weight or less, and most preferably 1% by weight or less in the core-shell type nanoparticle dispersion. The lower limit is 0.01% by weight or more, preferably 0.05% by weight or more.

2. Next, the dispersion medium used in the present invention will be described. The dispersion medium used in the present invention is not particularly limited as long as it can disperse the core-shell nanoparticles, but the core-shell nanoparticles have a predetermined organic compound attached to the surface. Or when a predetermined organic compound is added to the core-shell type nanoparticle dispersion, it is preferable to select appropriately according to the type of the predetermined organic compound.

  For example, when the predetermined organic compound has a hydrophilic group and a hydrophobic group in one molecule, and the hydrophilic group is bonded to one end of the hydrophobic group, the dispersion medium preferably has a low polarity. This is because the hydrophilic group of the organic compound interacts with the core-shell nanoparticle, and the organic compound is attached to the core-shell nanoparticle with the hydrophilic group inside (core-shell nanoparticle side) and the hydrophobic group outside. Because it is assumed. For this reason, the surface of the core-shell nanoparticle is in a state of being covered with a hydrophobic group. Therefore, if the dispersion medium has a low polarity, it is easy to interact with the hydrophobic group, and the core-shell type nanoparticles covered with the hydrophobic group are easily dispersed independently.

  The dispersion medium having a low polarity is not particularly limited as long as it is a nonpolar solvent. For example, the solubility parameter described in “Solvent Handbook” (Shozo Asahara et al., Kodansha) p. 34: δ is less than 10 A solvent is preferred. Specifically, aliphatic hydrocarbons such as pentane, cyclopentane, hexane, cyclohexane, octane, isooctane; aromatic hydrocarbons such as benzene, toluene, xylene; dichloromethane, carbon tetrachloride, chloroform, 1,2-dichloroethane, Halogenated hydrocarbons such as propyl chloride, chlorobenzene, bromobenzene and methyl iodide; ethers such as diethyl ether, diisopropyl ether, tetrahydrofuran and dioxane; esters such as ethyl acetate and methyl benzoate; ketones such as acetone and methyl ethyl ketone Amines such as triethylamine and propylamine; diethyl sulfide; or a mixture thereof. Among these, toluene, chloroform, hexane and the like are preferably used.

  For example, when a predetermined organic compound has a hydrophilic group and a hydrophobic group in one molecule, and the hydrophilic group is bonded to both ends of the hydrophobic group, the dispersion medium is preferably highly polar. This is because the hydrophilic group on one side of the organic compound interacts with the core-shell type nanoparticles, and the organic compound has the hydrophilic group on one side inside (the core-shell type nanoparticle side) and the hydrophilic group on the other side through the hydrophobic group. This is because it is assumed that they are attached to the core-shell type nanoparticles on the outside. For this reason, the surface of the core-shell nanoparticle is in a state covered with a hydrophilic group. Therefore, if the dispersion medium has a high polarity, it is easy to interact with the hydrophilic group, and the core-shell type nanoparticles covered with the hydrophilic group are easily dispersed independently.

  The dispersion medium having high polarity is not particularly limited as long as it is a polar solvent. For example, a solvent having a solubility parameter: δ of 10 or more described in “Solvent Handbook” (Terzo Asahara et al., Kodansha) p.34 Is preferred. Specifically, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butyl alcohol, phenol, 1,2-ethanediol; formamide, N, N-dimethyl Amides such as formamide and N, N-dimethylacetamide; nitro group-containing compounds such as nitromethane and nitrobenzene; nitrile group-containing compounds such as acetonitrile, 1,3-dicyanopropane and benzonitrile; pyridine; propylene carbonate; 2-aminoethanol Water; acetic acid; or a mixture thereof. Among these, N, N-dimethylformamide, 2-propanol and acetonitrile are preferably used.

3. Dispersibility improver The core-shell nanoparticle dispersion of the present invention may contain a dispersibility improver in order to improve the dispersibility of the core-shell nanoparticles. As such a dispersibility improver, aminoalkanes, higher fatty acids, higher alcohols and the like described in the above section “A. Core-shell type nanoparticles” can be used.

4). Core-shell type nanoparticle dispersion liquid The core-shell type nanoparticle dispersion liquid of the present invention contains the core-shell type nanoparticle and a dispersion medium. The core-shell nanoparticle dispersion of the present invention is not particularly limited as long as it contains the core-shell nanoparticle and the dispersion medium, and the core-shell nanoparticle may be dispersed in the dispersion medium and settled. You may do it.

  In particular, in the present invention, the core-shell type nanoparticles are preferably dispersed independently in the dispersion medium. Here, “the core-shell nanoparticles are dispersed independently in the dispersion medium” means that the core-shell nanoparticles do not settle in the dispersion medium for more than 1 hour at the operating temperature of the core-shell nanoparticle dispersion. . In the present invention, it is more preferable not to settle for 6 hours or more, particularly 12 hours or more. In addition, said time is the value which measured time until putting a core-shell type nanoparticle dispersion liquid in a transparent container, leaving still in a horizontal place, and visually recognizing precipitation at the bottom part of a container. Moreover, as said operating temperature, when apply | coating or patterning a core-shell type nanoparticle dispersion liquid, it is in the range of 0 to 40 degreeC normally, for example.

  Thus, if the core-shell type nanoparticles are independently dispersed in the dispersion medium and do not settle for a predetermined time, for example, when the semiconductor is formed by applying the core-shell type nanoparticle dispersion of the present invention. , It has the advantage that a uniform coating film can be obtained. In particular, it is advantageous when patterning a semiconductor by an ink jet method or a printing method. Further, since the semiconductor can be patterned by an ink-jet method or a printing method, patterning becomes easier and the manufacturing process can be simplified as compared with the case of a conventional lithography method.

  In addition, when the core-shell nanoparticle of the core-shell nanoparticle dispersion of the present invention is precipitated in a dispersion medium, the core-shell nanoparticle is dispersed in the dispersion medium by further diluting with the dispersion immediately before use. Can be dispersed independently. Moreover, when using a core-shell type nanoparticle dispersion liquid, a core-shell type nanoparticle can be independently dispersed in a dispersion medium by adding a predetermined organic compound. Therefore, the same effects as those obtained by independently dispersing the above-described core-shell type nanoparticles in the dispersion medium can be obtained.

  The use of the core-shell nanoparticle dispersion of the present invention is not particularly limited, and examples thereof include semiconductor applications such as thermoelectric conversion elements, Hall elements, and photoconductive elements, and non-linear optical element applications. be able to.

C. Thermoelectric Conversion Material Next, the thermoelectric conversion material of the present invention will be described. The thermoelectric conversion material of the present invention is a thermoelectric conversion material composed of a core-shell structure having a plurality of core portions and a coupling shell portion covering the core portions, wherein the plurality of core portions are independent from each other, The bond shell portion is continuous, and further, the constituent material of the bond shell portion is InSb, and the melting point of the constituent material of the core portion is higher than InSb that is the constituent material of the bond shell portion. .

  In the present invention, a plurality of core portions are independent from each other in the core-shell structure and are finely dispersed. Therefore, when electricity and heat are conducted through the core-shell structure, the core portion causes the phonon. Is scattered, the thermal conductivity can be reduced, and the performance of thermoelectric conversion can be improved. Moreover, since the core-shell structure in the present invention can be produced, for example, by compression molding the core-shell type nanoparticles, it has an advantage that it is suitable for mass production as compared with the production of the quantum dot superlattice described above.

  Next, the thermoelectric conversion material of the present invention will be described with reference to the drawings. FIG. 3 is a schematic cross-sectional view showing an example of a core-shell structure constituting the thermoelectric conversion material of the present invention. In FIG. 3, the core-shell structure 5 includes a plurality of core portions 1 and a coupling shell portion 4 that covers the core portions 1. The plurality of core portions 1 are independent from each other and are dispersed in the core-shell structure 5. On the other hand, the connecting shell portion 4 is not independent but continuous. Further, InSb is used as a constituent material of the bonding shell portion 4, and a material having a melting point higher than that of InSb is used as a constituent material of the core portion 1.

  In the present invention, the connection shell portion is continuous means that, for example, there is no interface inside the connection shell portion 4 as shown in FIG. Is included because the conductivity of electrons moving through the coupling shell portion 4 is improved, and even if there is a part, discontinuous or independent part, it is included in the term “continuous” in the present invention. Is. Here, the presence of the interface means, for example, a state in which the bonding shell portions 4 covering the adjacent core portions 1 are not bonded to each other as shown in FIG.

  In the present invention, as shown in FIG. 3, since the core portion 1 is finely dispersed in the core shell structure 5, when electricity and heat are conducted through the core shell structure 5, Since the phonons are scattered by the core portion 1 and move as indicated by the arrow P, it is difficult for heat to be conducted and the thermal conductivity can be reduced. On the other hand, since the electrons can move in the coupling shell portion 4 as shown by the arrow E with almost no scattering due to the continuation of the coupling shell portion 4, the conductivity is greatly reduced. Absent. In addition, when the thickness of the coupling shell portion 4 that is a path of electrons and phonons is 100 nm or less where the quantum effect appears, the figure of merit Z may be improved by the quantum effect. Therefore, in the present invention, the performance of thermoelectric conversion can be improved.

  Moreover, since the core-shell structure in the present invention can be produced by compression molding the core-shell nanoparticle described in the above-mentioned “A. Core-shell nanoparticle”, as described later, In comparison, it has the advantage of being suitable for mass production.

In addition, when the core-shell structure in the present invention is produced, for example, by compression molding the above-mentioned core-shell type nanoparticles, the shell part of the core-shell type nanoparticles is fused and bonded. Part.
Hereinafter, such a core-shell structure will be described.

  The core-shell structure used in the present invention has a plurality of core portions and a coupling shell portion that covers the core portions. Further, the plurality of core parts are independent from each other, and the bonding shell part is continuous, and InSb is used as a constituent material of the binding shell part, and a material having a higher melting point than InSb as a constituent material of the core part Is used.

1. Bonding Shell Part The bonding shell part in the present invention covers a core part to be described later. Further, the bonding shell portion in the present invention is continuous in the core-shell structure, and as described above, it is preferable that there are few interfaces inside the bonding shell portion, and it is particularly preferable that no interface exists inside. .

  In the present invention, “InSb” used as a constituent material of the above-mentioned bonding shell portion includes not only InSb but also InSb doped with other elements. Specifically, since the same material as the constituent material of the shell part described in “A. Core-shell type nanoparticle” can be mentioned, the description here is omitted.

  Further, in the present invention, the thickness of the portion covering the core portion of the coupling shell portion is particularly limited as long as it can conduct electrons and phonons and can exhibit the quantum effect. Although it is not a thing, it is specifically the same as the “thickness of the shell part” described in “A. Core-shell type nanoparticle” above, and therefore, the description thereof is omitted here. In addition, the thickness of the part covering the core part of the said joint shell part means the thickness shown by n 'of FIG. 3, for example.

2. Core part Next, the core part in this invention is demonstrated. The core part in this invention is coat | covered by the said connection shell part, and is mutually independent in a core shell structure. Furthermore, in the present invention, the melting point of the constituent material of the core part is higher than that of InSb, which is the constituent material of the above-mentioned bonded shell part.

  The core parts in the present invention may be any parts as long as they are independent from each other in the core-shell structure, but it is preferable that they are uniformly dispersed. This is because when the core portion is uniformly dispersed in the core-shell structure, phonons can be efficiently scattered and the thermal conductivity can be effectively reduced.

  As the constituent material of the core part used in the present invention, the same material as the constituent material of the core part described in “A. Core-shell type nanoparticles” can be used. Among these, in the present invention, the constituent material of the core part is preferably a material capable of forming an interface with InSb, which is the constituent material of the shell part.

  Further, the average particle diameter of the core part fine particles forming the core part is not particularly limited as long as it is a size capable of effectively scattering phonons. It is preferably within the range of 100 nm, more preferably within the range of 1 nm to 70 nm, and particularly preferably within the range of 2 nm to 50 nm. If the average particle size is too large, a space b generated between the core-shell nanoparticles 3 is large even when the core-shell nanoparticles 3 are arranged without gaps, for example, as shown in FIG. When the material is compressed and molded, the constituent material of the shell portion 2 flows into the space b. For example, as shown in FIG. 5B, the core portion 1 is not covered with the shell portion 2 (joined shell portion 4). This is because c is generated and the core-shell structure cannot be maintained, and there is a possibility that a part having an extremely thin thickness or an extremely hot part may be generated. Further, fine particles having an average particle size smaller than the above range are difficult to produce.

  In addition, the standard deviation of the average particle size of the core fine particles is preferably 20% or less, more preferably 10% or less. This is because if the standard deviation is too large, a large space may be generated between the core-shell nanoparticles as described above before the core-shell nanoparticles are compressed.

3. Core-shell structure The core-shell structure used in the present invention has the above-mentioned joint shell part and the above-mentioned core part. Among these, in the present invention, it is preferable that the core part and the binding shell part are phase-separated. The core part has a function to scatter phonons, and the shell part has a function to conduct electrons. However, if the core part and the shell part are phase-separated, each function can be exhibited more effectively. Because you can. In the present invention, whether or not the core portion and the binding shell portion are phase-separated can be determined from two-dimensional mapping of elements obtained by measurement with a scanning transmission electron microscope (STEM). Since the specific determination method is the same as the content described in the above-mentioned “A. Core-shell type nanoparticle”, description thereof is omitted here.

D. Next, the manufacturing method of the thermoelectric conversion material of this invention is demonstrated. The method for producing a thermoelectric conversion material of the present invention includes a core part preparation step in which a core part is formed using a material having a melting point higher than InSb, and the core part is coated with InSb by a hot soap method to form a shell part. A shell part preparation step for forming core-shell type nanoparticles, a removal step for removing organic substances adhering to the shell part, and a compression molding step for compression molding the core-shell type nanoparticles from which the organic substances have been removed. It is what.

  In this invention, by performing the said process, the thermoelectric conversion material which shows the performance of high thermoelectric conversion and was excellent in mass productivity can be obtained.

In the present invention, the core part preparation step and the shell part preparation step are the same as those described in “A. Core-shell type nanoparticles (4) Method for producing core-shell type nanoparticles” above. Description is omitted. By performing the core part preparation step and the shell part preparation step, the core-shell type nanoparticles described above are obtained.
Hereinafter, the removal process and the compression molding process in the present invention will be described.

1. Removal Step The removal step in the present invention is a step of removing organic substances remaining after the shell part preparation step described above.

  The core-shell type nanoparticles formed in the shell part preparation step are derived from the organometallic compound used for the dispersant, the organic solvent, the core part precursor, and the shell part precursor even after separating from the dispersant as described above. Organic substances, organic solvents, additives, etc. may adhere. This step is performed in order to remove such remaining organic substances and organic substances such as a dispersant.

  In this step, such an organic substance can be removed by thermal decomposition. Reaction conditions such as heating temperature, heating time, and pressure are not particularly limited as long as the organic substances are decomposed and removed. This reaction condition can be determined using, for example, differential thermal analysis (DTA). Usually, it is performed in an inert gas atmosphere such as nitrogen or argon, or in a reduced pressure atmosphere.

2. Next, the compression molding process in the present invention will be described. The compression molding step in the present invention is a step of compression molding core-shell nanoparticles from which organic substances have been removed.

  The method for compression molding the core-shell type nanoparticles is not particularly limited as long as it is a method capable of bonding only the shell portions of the adjacent core-shell type nanoparticles, for example, hot press method or discharge plasma sintering. Law.

  The temperature at which the core-shell type nanoparticles are compression molded is not particularly limited as long as it is a temperature that can melt and bond the constituent materials of the shell part. The shell part is preferably at a temperature at which the shell part can be bonded so that no interface is formed. Further, the melting point of the constituent material of the core part is higher than the melting point of InSb, which is the constituent material of the shell part. In the present invention, the temperature during the compression molding is equal to or higher than the melting point of InSb. It is preferable that it is below the melting point of the constituent material of the part. By performing compression molding in such a temperature range, the shell portion melts and bonds to each other, but the core portion does not melt and can maintain crystallinity, and the core portion and the shell portion (bonded shell portion) are separated. This is because a phase-separated thermoelectric conversion material can be obtained. In addition, since the melting point and the like of the constituent material vary depending on the pressure condition described later, it is preferable to perform compression molding in consideration of the temperature condition and the pressure condition.

  Further, the pressure at the time of compression molding the core-shell type nanoparticles is not particularly limited as long as it is a pressure capable of melting and bonding the constituent materials of the shell part. It is preferable that the pressure is such that the shell portions can be bonded so that no interface is formed.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

Hereinafter, the present invention will be specifically described with reference to examples.
[Example 1]
(Formation of core particles)
Mo fine particles having a particle size of about 4 nm were synthesized by the liquid phase method using the reaction solution shown below.
Dispersant: Hexadecylamine (manufactured by Kanto Chemical Co., Inc.) 0.5 g
Organic solvent: Diphenyl ether (manufactured by Kanto Chemical Co., Inc.) 32 g
Precursor: Molybdenum hexacarbonyl (Kanto Chemical Co., Ltd.) 2g
The above dispersant, organic solvent, and precursor were mixed in a flask, the inside of the flask was replaced with an argon gas atmosphere, the temperature was raised to 250 ° C., and this temperature was maintained for 2.5 hours. Thereafter, the reaction solution was air-cooled, and after cooling to 60 ° C., 40 ml of methanol was added. After the black precipitate was separated from the reaction solution by centrifugation, it was redissolved in chloroform and then reprecipitated by adding methanol to obtain a black powder. The obtained black powder was observed to be spherical with a particle size of about 4 nm by observation with a transmission electron microscope (TEM). Further, it was confirmed by X-ray diffraction (XRD) measurement that a Mo crystal structure was formed.

(Coating of core part by shell part)
The reaction field of the hot soap method was composed of the following dispersant and organic solvent.
Dispersant: 1,2-hexadecanediol (manufactured by ALDRICH) 1.2 g
Oleic acid (Kanto Chemical Co., Ltd.) 0.76g
Hexadecylamine (Kanto Chemical Co., Ltd.) 18g
The above dispersant was mixed in a flask, 0.05 g of the Mo fine particles were added to the flask, the inside of the flask was replaced with an argon gas atmosphere, and the temperature was raised to 300 ° C.
Next, the shell portion precursor liquid was composed of the following compounds.
Precursor: Butoxy Sb (manufactured by Amax Co., Ltd.) 0.12 g
Indium acetylacetonate (manufactured by ALDRICH) 0.2g
Dispersant: Octylamine (Tokyo Chemical Industry Co., Ltd.) 0.3g
Organic solvent: dichlorobenzene (manufactured by Kanto Chemical Co., Inc.) 1.0 g
The precursor, dispersant and organic solvent were mixed and dissolved in another container, and then dropped into the flask heated to 300 ° C. over 15 minutes using a syringe.
After the injection of the shell part precursor, the temperature was maintained at 300 ° C. for 20 minutes. Thereafter, the reaction solution was air-cooled, and after cooling to 60 ° C., 50 ml of ethanol was added. The black precipitate was separated from the reaction solution by centrifugation and then washed with a mixed solvent of chloroform / ethanol = 1/2 (volume ratio) to obtain a black powder. The obtained black powder was observed to be spherical with a particle size of about 6 nm by observation with a transmission electron microscope (TEM). Moreover, since the crystal structure of Mo and InSb was formed by X-ray diffraction (XRD) measurement, it was confirmed that core-shell type nanoparticles having Mo as a core part and InSb as a shell part were produced.

(Removal of organic matter)
The black powder was held at 300 ° C. for 2 hours in a reduced-pressure atmosphere to remove remaining organic substances.

(Compression molding)
The black powder from which the organic matter was removed was put in a die having a predetermined shape and molded by a hot press method to obtain a core-shell structure. The hot pressing conditions are a temperature of 350 ° C., a pressure of 630 MPa, a vacuum atmosphere, and 2 hours. The appearance of the core-shell structure after molding was a silver black solid.

[Example 2]
(Formation of core particles)
Rod-shaped ZnS fine particles having a minor axis of about 3 nm and a major axis of 10 to 20 nm were synthesized by a liquid phase method using the following reaction solution.
Dispersant: Hexadecylamine (Kanto Chemical Co., Ltd.) 18g
Precursor: diethyldithiocarbamic acid ginxolt (manufactured by Tokyo Chemical Industry Co., Ltd.) 0.3 g
The above dispersant and precursor were mixed in the flask, the inside of the flask was replaced with an argon gas atmosphere, the temperature was raised to 200 ° C., and this temperature was maintained for 0.5 hour. Thereafter, the reaction solution was air-cooled, and after cooling to 60 ° C., 40 ml of ethanol was added. After the black precipitate was separated from the reaction solution by centrifugation, it was redissolved in chloroform and then reprecipitated by adding ethanol to obtain a black powder. The obtained black powder was observed by a transmission electron microscope (TEM) to be rod-shaped having a minor axis of about 3 nm and a major axis of 10 to 20 nm. Further, it was confirmed by X-ray diffraction (XRD) measurement that a ZnS crystal structure was formed.

(Coating of core part by shell part)
The reaction field of the hot soap method was composed of the following dispersant and organic solvent.
Dispersant: 1,2-hexadecanediol (manufactured by ALDRICH) 1.2 g
Oleic acid (Kanto Chemical Co., Ltd.) 0.4g
Hexadecylamine (Kanto Chemical Co., Ltd.) 18g
The above dispersant was mixed in a flask, 0.1 g of the ZnS fine particles were added to the flask, and the atmosphere in the flask was replaced with an argon gas atmosphere.
Next, the shell portion precursor liquid was composed of the following compounds.
Precursor: Butoxy Sb (manufactured by Amax Co., Ltd.) 0.12 g
Indium acetylacetonate (manufactured by ALDRICH) 0.2g
Dispersant: Octylamine (Tokyo Chemical Industry Co., Ltd.) 0.3g
Organic solvent: dichlorobenzene (manufactured by Kanto Chemical Co., Inc.) 1.0 g
The precursor, dispersant and organic solvent were mixed and dissolved in another container, and then dropped into the flask heated to 300 ° C. over 15 minutes using a syringe.
After the injection of the shell part precursor, the temperature was maintained at 300 ° C. for 20 minutes. Thereafter, the reaction solution was air-cooled, and after cooling to 60 ° C., 50 ml of ethanol was added. The black precipitate was separated from the reaction solution by centrifugation and then washed with a mixed solvent of chloroform / ethanol = 1/2 (volume ratio) to obtain a black powder. The obtained black powder was observed to be spherical with a particle size of about 6 nm by observation with a transmission electron microscope (TEM). Moreover, since the crystal structure of ZnS and InSb was formed by X-ray diffraction (XRD) measurement, it was confirmed that core-shell type nanoparticles having ZnS as a core part and InSb as a shell part were produced.

(Removal of organic matter)
The black powder was held at 300 ° C. for 2 hours in a reduced-pressure atmosphere to remove remaining organic substances.

(Compression molding)
The black powder from which the organic matter was removed was put in a die having a predetermined shape and molded by a hot press method to obtain a core-shell structure. The hot pressing conditions are a temperature of 350 ° C., a pressure of 630 MPa, a vacuum atmosphere, and 2 hours. The appearance of the core-shell structure after molding was a silver black solid.

[Comparative example]
(Formation of fine particles)
In Example 1 described above, except that the Mo fine particles were not added, the fine particles were produced in the same manner as in the Example. As a result, fine particles composed of InSb were obtained. The appearance of the InSb fine particles was a black powder. The black powder was observed to be spherical with a particle size of about 10 nm by observation with a transmission electron microscope (TEM).
(Removal of organic matter)
The black powder was held at 300 ° C. for 2 hours in a reduced-pressure atmosphere to remove remaining organic substances.
(Compression molding)
The black powder from which the organic matter was removed was placed in a die having a predetermined shape and molded by a hot press method. The hot pressing conditions are a temperature of 350 ° C., a pressure of 630 MPa, a vacuum atmosphere, and 2 hours. The appearance after molding was a silver black solid.

[Evaluation]
(Comparison of thermoelectric conversion performance)
100 silver-black solids obtained in Examples 1 and 2 and Comparative Example were cut into cuboids each having a size of 0.5 mm × 0.5 mm × 3 mm. Next, as shown in FIG. 6, the cut out silver-black solid 22 was arranged to produce a thermoelectric conversion element 21. In addition, although the case where the number of the silver black solids 22 is 10 is described in FIG. 6, it is assumed that 100 silver black solids 22 are connected and arranged by repeating the same arrangement as the eight central parts. Here, the alumina substrate 23 is 1 mm thick, and the cut-out silver-black solid 22 is connected in series with a copper wire 24. Reference numeral 25 denotes a light emitting diode incorporating a booster circuit. In producing this thermoelectric element, the silver black solid and the copper wire may be soldered as necessary. Moreover, you may braze an alumina substrate and silver black solid with metals, such as silver, as needed. When 500 K of heat is supplied to the alumina substrate in a room with a room temperature of 300 K, the thermoelectric conversion element composed of the silver black solid of Example 1 or 2 rather than the thermoelectric conversion element composed of the silver black solid of the comparative example The light emitting diode shined brighter.

It is a schematic sectional drawing which shows an example of the core-shell type nanoparticle of this invention. It is a TEM photograph which shows an example of the core-shell type nanoparticle of this invention. It is a schematic sectional drawing which shows an example of the core-shell structure used for this invention. It is a figure for demonstrating a coupling shell part. It is a figure for demonstrating a core part and a shell part (joining shell part). It is a schematic diagram which shows an example of the thermoelectric conversion element using the thermoelectric conversion material of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Core part 2 ... Shell part 3 ... Core-shell type nanoparticle 4 ... Bonding shell part 5 ... Core-shell structure

Claims (5)

  Core-shell type nanoparticles having a core part and a shell part covering the core part, wherein the constituent material of the shell part is InSb, and the melting point of the constituent material of the core part is the constituent material of the shell part A core-shell type nanoparticle characterized by being higher than InSb.   The core-shell type nanoparticles according to claim 1, wherein the shell part and the core part are phase-separated.   A core-shell nanoparticle dispersion liquid comprising the core-shell nanoparticle according to claim 1 or 2 and a dispersion medium.   A thermoelectric conversion material composed of a core-shell structure having a plurality of core parts and a coupling shell part covering the core part, wherein the plurality of core parts are independent from each other, and the coupling shell part is continuous, Further, the thermoelectric conversion material is characterized in that the constituent material of the joint shell portion is InSb, and the melting point of the constituent material of the core portion is higher than InSb which is the constituent material of the joint shell portion. A core part preparing step for forming a core part using a material having a melting point higher than that of InSb, and a shell part preparing process for forming core-shell nanoparticles by coating the core part with InSb by a hot soap method to form a shell part. And a removal step of removing the organic matter adhering to the shell portion, and a compression molding step of compression-molding the core-shell type nanoparticles from which the organic matter has been removed.

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