WO2014126211A1 - N-type thermoelectric conversion material, thermoelectric conversion component, and manufacturing method for n-type thermoelectric conversion material - Google Patents

N-type thermoelectric conversion material, thermoelectric conversion component, and manufacturing method for n-type thermoelectric conversion material Download PDF

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WO2014126211A1
WO2014126211A1 PCT/JP2014/053512 JP2014053512W WO2014126211A1 WO 2014126211 A1 WO2014126211 A1 WO 2014126211A1 JP 2014053512 W JP2014053512 W JP 2014053512W WO 2014126211 A1 WO2014126211 A1 WO 2014126211A1
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thermoelectric conversion
conversion material
type thermoelectric
nanotubes
nanowires
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PCT/JP2014/053512
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French (fr)
Japanese (ja)
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斐之 野々口
壯 河合
剛児 足羽
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国立大学法人奈良先端科学技術大学院大学
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/80—Constructional details
    • H10N10/85—Thermoelectric active materials
    • H10N10/851—Thermoelectric active materials comprising inorganic compositions
    • H10N10/852—Thermoelectric active materials comprising inorganic compositions comprising tellurium, selenium or sulfur
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/01—Manufacture or treatment
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/10—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects operating with only the Peltier or Seebeck effects
    • H10N10/17—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects operating with only the Peltier or Seebeck effects characterised by the structure or configuration of the cell or thermocouple forming the device

Definitions

  • the present invention relates to an n-type thermoelectric conversion material in which nanowires or nanotubes are woven into a nonwoven fabric, a thermoelectric conversion element including the thermoelectric conversion material, and a method for producing the n-type thermoelectric conversion material.
  • thermoelectric conversion element generates power by utilizing a potential difference generated in a substance due to a temperature difference.
  • industrial waste heat such as industrial furnaces.
  • thermoelectric conversion materials have attracted attention as one of CO 2 -free power generation technologies for obtaining power from natural renewable energy and exhaust heat.
  • the thermoelectric conversion material is closely_contact
  • thermoelectric conversion materials are mainly bulk solid materials as shown in FIG. Since the bulk solid material cannot provide flexibility, it cannot be brought into close contact with a heat source, which is disadvantageous from the viewpoint of heat transfer.
  • Non-Patent Document 1 describes a conductive polymer film formed by doping iodine into a phenylene vinylene copolymer containing a dialkoxyphenylene unit.
  • Non-Patent Document 2 describes that poly (3,4-ethylenedioxythiophene) (PEDOT) is used as the conductive polymer.
  • PEDOT poly (3,4-ethylenedioxythiophene)
  • Non-Patent Document 3 describes a composite material using a composite of PEDOT and poly (styrene sulfonic acid) (PEDOT: PSS) and carbon nanotubes.
  • Non-Patent Document 4 describes a thermoelectric module using a composite material of a carbon nanotube and a fluoropolymer.
  • Non-Patent Document 5 describes that a composite material obtained by mixing a transition metal dichalcogenide and a carbon-based material is formed into a film shape.
  • Non-Patent Documents 1 to 5 provide a material having a certain degree of flexibility or a material having thermoelectric conversion characteristics, but sufficient thermoelectric conversion characteristics and flexibility for practical use. It is not compatible with sex.
  • ZT Dimensionless figure of merit
  • ZT can be cited as an index for evaluating the characteristics of thermoelectric conversion materials. It can be said that the larger the ZT, the better the thermoelectric conversion characteristics.
  • ZT is desirably 1 or more, but it is difficult to realize. Therefore, it is first required to realize a ZT of about 0.1.
  • ZT is calculated
  • the absolute value of the Seebeck coefficient and the electrical conductivity are preferably larger, and the thermal conductivity is preferably smaller.
  • the conductive polymer film described in Non-Patent Document 1 has a thermal conductivity of 0.25 to 0.80 W / mK, and a dimensionless figure of merit ZT at 313 K of about 0.006 to 0.09. is there.
  • a thermoelectric conversion material having a lower thermal conductivity and a higher ZT.
  • ZT may be about 0.25 depending on conditions, but ZT is likely to vary depending on the degree of oxidation. That is, the technique described in Non-Patent Document 2 is sensitive to environmental changes and requires precise adjustment for use. Therefore, the technique described in Non-Patent Document 2 cannot be said to have stable thermoelectric conversion characteristics.
  • Non-Patent Document 3 rubber is included to give flexibility. Since rubber is an insulator, the Seebeck effect and conductivity are greatly reduced. Therefore, in the technique described in Non-Patent Document 3, ZT at room temperature is a low value of about 0.02.
  • Non-Patent Documents 4 and 5 have not yet achieved sufficient thermoelectric conversion characteristics and flexibility.
  • Non-Patent Documents 1 to 5 all relate to p-type thermoelectric conversion materials. No n-type thermoelectric conversion material having both flexibility and excellent thermoelectric conversion characteristics is disclosed.
  • the present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a thermoelectric conversion material that is lightweight and flexible and has excellent n-type thermoelectric conversion characteristics.
  • thermoelectric conversion material As a result of intensive studies to solve the above-mentioned problems, the present inventors have surprisingly been able to integrate light-weight and flexible and excellent thermoelectric conversion characteristics by integrating nanowires or nanotubes made of a narrow gap semiconductor in a nonwoven fabric shape. It was originally found that an n-type thermoelectric conversion material provided with The present invention has been completed based on new findings uniquely found by the present inventors, and includes the following inventions.
  • the n-type thermoelectric conversion material according to the present invention is characterized in that nanowires or nanotubes made of a narrow gap semiconductor are integrated and formed in a nonwoven fabric in order to solve the above-described problems.
  • the method for producing an n-type thermoelectric conversion material according to the present invention adds a metal salt to a solvent in which a metal acid salt or a metal oxide is dissolved.
  • a step of forming a nanowire or a nanotube comprising: and a step of accumulating the nanowire or the nanotube in a nonwoven fabric.
  • the n-type thermoelectric conversion material according to the present invention has a configuration in which nanowires or nanotubes made of a narrow gap semiconductor are integrated in a nonwoven fabric shape.
  • thermoelectric conversion material that is lightweight and flexible and has excellent thermoelectric conversion characteristics.
  • (A)-(c) is a figure which shows the n-type thermoelectric conversion material produced in Example 1 of this invention
  • (d)-(f) is the n-type thermoelectric produced in Example 2 of this invention. It is a figure which shows conversion material. It is a figure which shows the change of the Seebeck coefficient by the temperature in Example 1 and 2 of this invention. It is a figure which shows the change of the dimensionless figure of merit ZT by the temperature in Example 1 and 2 of this invention.
  • (A)-(d) is a figure which shows the n-type thermoelectric conversion material manufactured in Example 3 of this invention.
  • (A) contains 1% by weight of single-walled carbon nanotubes (SWNT), (b) contains 5% by weight of SWNTs, and (c) and (d) contain 10% by weight of SWNTs. Show the case. It is a figure which shows the change of the electrical conductivity by content of SWNT in Example 3 and 4 of this invention. It is a figure which shows the change of the dimensionless figure of merit ZT by the content of SWNT in Examples 3 and 4 of the present invention. It is a figure which shows the conventional thermoelectric conversion element.
  • thermoelectric conversion characteristic a characteristic of a thermoelectric conversion material
  • ZT is calculated
  • thermoelectric conversion material The larger the ZT, the better the thermoelectric conversion material. From formula (1), it can be seen that in order to obtain a large ZT, it is preferable that the absolute value and the conductivity of the Seebeck coefficient are large. When two different materials are connected and a temperature difference is provided, a thermoelectromotive force is generated between the materials. The phenomenon that generates this thermoelectromotive force is called Seebeck effect. The Seebeck coefficient is used to represent this thermoelectromotive force. The larger the absolute value of the Seebeck coefficient, the greater the thermoelectromotive force.
  • thermoelectric conversion material uses a temperature difference.
  • the thermal conductivity is large, the temperature in the material is easily uniform, and a temperature difference is hardly generated.
  • required from the Seebeck coefficient in Formula (1) and electrical conductivity can be represented with the power factor P, as shown in the following formula (2).
  • the power factor P is large.
  • thermoelectric conversion characteristics means that ZT is equal to or higher than that of a thermoelectric conversion material having at least conventional flexibility.
  • the n-type thermoelectric conversion material according to the present invention is formed by integrating nanowires or nanotubes in a nonwoven fabric shape.
  • a non-woven structure is formed so that nanowires or nanowires are entangled with each other.
  • flexibility can be provided to a thermoelectric conversion material by nanowire or a nanotube sliding each other.
  • FIGS. 1 and 2 are views showing the appearance of an n-type thermoelectric conversion material 1 according to an embodiment of the present invention.
  • the n-type thermoelectric conversion material 1 can be easily deformed. Therefore, the n-type thermoelectric conversion material according to the present invention is excellent in workability.
  • the n-type thermoelectric conversion material according to the present invention can be affixed to silicon or plastic having a complicated shape, and can be deformed according to the shape of the human body.
  • the n-type thermoelectric conversion material according to the present invention can be stored in the shape of a deformed state.
  • the shape of the n-type thermoelectric conversion material according to the present invention is not particularly limited, and may be, for example, a circle or a quadrangle. Further, the size of the n-type thermoelectric conversion material according to the present invention is not particularly limited, and may be appropriately determined depending on the application.
  • the n-type thermoelectric conversion material according to the present invention has a large number of voids due to the nonwoven fabric structure. Therefore, the n-type thermoelectric conversion material according to the present invention is lightweight. Furthermore, due to the large number of voids, the n-type thermoelectric conversion material according to the present invention exhibits a lower thermal conductivity than the bulk state.
  • the nanowire means a fine fibrous substance that is filled in the center and is not hollow.
  • the nanotube means a fine fibrous substance that is hollow.
  • the size of the nanowire and the nanotube is not particularly limited, but may be, for example, 0.5 ⁇ m or more and 1000 ⁇ m or less in length. Further, the diameter of the nanowire and the nanotube may be 1 nm or more and 1000 nm or less.
  • the nanowire may be described as “NW” and the nanotube as “NT”.
  • the nanowire or the nanotube is made of a narrow gap semiconductor.
  • a narrow gap semiconductor refers to a semiconductor having a small band gap.
  • the narrow gap semiconductor preferably has a band cap of 0.01 eV or more and 1.0 eV or less. In a semiconductor with a small band gap, carriers are easily excited by small thermal energy. Therefore, if a narrow gap semiconductor is used, a usable thermoelectric conversion material can be obtained even at a low temperature.
  • the narrow gap semiconductor is preferably a compound containing Te, Se, or both.
  • the compound preferably contains at least one of Te and Se.
  • the narrow gap semiconductor is preferably a compound containing Bi.
  • Preferred examples of the narrow gap semiconductor include Bi 2 Te 3 , Bi 2 Se 3 , and Bi 2 Se x Te 3-x (0 ⁇ x ⁇ 3). According to the above configuration, it is possible to provide a thermoelectric conversion material exhibiting excellent thermoelectric conversion characteristics even at a relatively low temperature (for example, 200 to 580 K). In addition, it is known that the said substance will show the property as a narrow gap semiconductor in a bulk state.
  • the n-type thermoelectric conversion material according to the present invention has a large absolute value of the Seebeck coefficient due to the narrow gap semiconductor and a low thermal conductivity due to the non-woven structure. Therefore, the n-type thermoelectric conversion material according to the present invention exhibits excellent thermoelectric conversion characteristics due to the interaction between the use of a narrow gap semiconductor and the non-woven fabric structure.
  • the n-type thermoelectric conversion material according to the present invention is lightweight and flexible due to the nonwoven fabric structure. Therefore, the n-type thermoelectric conversion material according to the present invention is lightweight and flexible and exhibits excellent thermoelectric conversion characteristics. The above has been uniquely found by the present inventors.
  • thermoelectric conversion material according to the present invention can be confirmed to be an n-type thermoelectric conversion material because the Seebeck coefficient is a negative value.
  • An n-type thermoelectric conversion material that is lightweight and flexible and has excellent thermoelectric conversion characteristics can be realized for the first time by the present invention.
  • the nanowires or the nanotubes may be integrated together with the carbon nanotubes in a non-woven shape. That is, the nanowire or the nanotube may have a non-woven structure so as to be entangled with the carbon nanotube.
  • the mechanical strength of the thermoelectric conversion material can be increased.
  • electrical conductivity can be improved. That is, the power factor of the thermoelectric conversion material can be improved.
  • the absolute value of the Seebeck coefficient may be small. Accordingly, the content of the carbon nanotubes may be appropriately determined in consideration of a balance such as Seebeck coefficient, conductivity, mechanical strength, and the like.
  • the content of the carbon nanotube may be, for example, 1% by weight or more and 90% by weight or less, or 1% by weight or more and 20% by weight or less, when the formed thermoelectric conversion material is 100% by weight. Although it is good, it is preferably 1% by weight or more and 10% by weight or less.
  • the carbon nanotube may be a single-walled carbon nanotube or a multi-walled carbon nanotube, but a single-walled carbon nanotube (hereinafter also referred to as SWNT) is particularly preferable. According to the said structure, the outstanding elasticity and intensity
  • thermoelectric conversion element includes the n-type thermoelectric conversion material according to the present invention. Therefore, the thermoelectric conversion element according to the present invention is lightweight and has excellent thermoelectric conversion characteristics. Moreover, since the n-type thermoelectric conversion material according to the present invention has flexibility and excellent workability, it is possible to manufacture thermoelectric conversion elements having various shapes.
  • thermoelectric conversion element according to the present invention can be realized by combining the n-type thermoelectric conversion material according to the present invention and the p-type thermoelectric conversion material. Although it does not specifically limit as a p-type thermoelectric conversion material combined with the n-type thermoelectric conversion material which concerns on this invention, For example, a well-known p-type thermoelectric conversion material can be used.
  • thermoelectric conversion element according to the present invention since the thermoelectric conversion element according to the present invention has excellent thermoelectric conversion characteristics, environmental power generation such as geothermal power generation, industrial waste heat such as pipes and electric furnaces, and waste of equipment such as vehicle bodies, engine peripheral equipment, and air conditioning equipment Can be used for heat utilization. Moreover, since the thermoelectric conversion element according to the present invention is lightweight and has excellent thermoelectric conversion characteristics, it can be used for power supplies for emergencies, disasters, and medical use. Furthermore, since the thermoelectric conversion element according to the present invention is lightweight and flexible and has excellent thermoelectric conversion characteristics, it can be used as a power source for small devices such as portable devices, wearable devices, and flexible devices. Examples of the small device include a mobile phone, a wrist watch, and a cardiac pacemaker.
  • thermoelectric conversion material A method for producing the n-type thermoelectric conversion material according to the present invention will be described below. In addition, detailed description is abbreviate
  • the method for producing an n-type thermoelectric conversion material according to the present invention includes a step of adding a metal salt to a solvent in which a metal acid salt or metal oxide is dissolved to form nanowires or nanotubes made of a narrow gap semiconductor. It is out.
  • the narrow gap semiconductor originating in the said metal acid salt or the said metal oxide, and the said metal salt can be formed. Therefore, as described above, the Seebeck coefficient in the n-type thermoelectric conversion material obtained by the manufacturing method can be improved due to the narrow gap semiconductor.
  • the metal acid salt or the metal oxide preferably contains Te or Se.
  • the metal acid salt includes Na 2 O 3 Te, Na 2 O 3 Se, Ka 2 O 3 Te, Ka 2 O 3 Se, MgO 3 Te, MgO 3 Se, CaO 3 Te, and CaO 3 Se.
  • H 2 O 3 Te, H 2 O 3 Se, H 6 TeO 6 or H 6 SeO 6 is preferred.
  • the metal oxide, TeO 2, SeO 2, TeO 3, SeO 3, Te is preferably 2 O 5 or Se 2 O 5. According to the said structure, the narrow gap semiconductor obtained can be made into the compound containing Te or Se.
  • the resulting narrow gap semiconductor is a compound containing both Te and Se. It can be.
  • the said metal salt contains Bi.
  • the counter ion for Bi is not particularly limited, but may be, for example, Cl ⁇ , Br ⁇ , I ⁇ , NO 3 ⁇ , SO 4 2 ⁇ , SCN ⁇ . According to the said structure, the narrow gap semiconductor obtained can be made into the compound containing Bi.
  • the obtained narrow gap semiconductor is represented by Bi 2 Te 3 , Bi 2 Se 3 or Bi 2 Se.
  • x Te 3-x (0 ⁇ x ⁇ 3) may be satisfied.
  • the molar ratio of the metal salt or the metal oxide and the metal salt used is preferably 3: 2.
  • a nanowire when the metal acid salt is used, a nanowire can be formed. Further, in the above process, when the metal oxide is used, a nanotube can be formed. Therefore, according to the said structure, a nanowire and a nanotube can be selectively formed by using a metal acid salt and a metal oxide properly. This has been uniquely found by the inventor.
  • the metal acid salt, the metal oxide, and the metal salt are relatively inexpensive, although depending on the type. Therefore, the manufacturing method of the n-type thermoelectric conversion material according to the present invention can reduce the cost as compared with the conventional technique using PEDOT or the like.
  • the method for producing an n-type thermoelectric conversion material according to the present invention is preferably performed as a one-pot reaction.
  • a waste liquid does not arise and the fall of the yield of nanowire or a nanotube can also be prevented.
  • cleaning of a container is also unnecessary.
  • the usage-amount of a solvent can also be suppressed.
  • the solvent used in the above step is (a) having a boiling point of 160 ° C. or higher, (b) showing weak reducing ability, and (c) showing excellent solubility in metal salts. It preferably has at least one or more properties, and more preferably has all the properties (a) to (c).
  • the solvent include polyols (ethylene glycol, diethylene glycol, triethylene glycol, etc.), alkyl amines (oleyl amine, etc.), and alkyl phosphines (trioctyl phosphine, etc.).
  • the reaction temperature in the above step may be appropriately determined according to the metal acid salt, metal oxide, metal salt and solvent to be used, but is preferably 50 ° C. or higher and 250 ° C. or lower, and 140 ° C. or higher and 200 ° C. or lower. More preferably.
  • the method for producing an n-type thermoelectric conversion material according to the present invention includes a step of accumulating the nanowires or the nanotubes in a nonwoven fabric shape.
  • thermoelectric conversion material in which the nanowires or the nanotubes are accumulated in a nonwoven fabric can be produced. Therefore, the thermoelectric conversion material obtained by the manufacturing method due to the non-woven structure as described above can be a lightweight and flexible thermoelectric conversion material having a low thermal conductivity.
  • the method for accumulating the nanowire or the nanotube in a nonwoven fabric is not particularly limited.
  • the nanowire or the nanotube is obtained by filtering or spraying a solvent containing the nanowire or the nanotube, or by electrospinning.
  • the method of accumulating on a support body is mentioned. Among these, the method of filtering the solvent is preferable from the viewpoint of easy implementation.
  • a filter such as a porous membrane can be used.
  • the solvent can be filtered using a filter, and the nanowire or the nanotube can be accumulated on the filter.
  • the diameter of the pores of the porous membrane is preferably 5 ⁇ m or less because most of the nanowires or nanotubes have a length of about 5 ⁇ m or more, and more preferably 0.5 ⁇ m or less from the viewpoint of the recovery rate. From a practical viewpoint, it is more preferably 0.2 ⁇ m or less.
  • the method for producing an n-type thermoelectric conversion material according to the present invention includes a step of adding carbon nanotubes to a solvent containing the nanowires or nanotubes before the step of accumulating the nanowires or nanotubes in a nonwoven fabric shape. You may go out.
  • stacked and formed in the nonwoven fabric shape with the carbon nanotube can be manufactured.
  • the carbon nanotube is preferably a single-walled carbon nanotube as described above.
  • the thermoelectric conversion material in which the said carbon nanotube was contained uniformly can be manufactured.
  • the present invention can also be configured as follows.
  • the n-type thermoelectric conversion material according to the present invention is characterized in that nanowires or nanotubes made of a narrow gap semiconductor are integrated and formed in a nonwoven fabric in order to solve the above-described problems.
  • the n-type thermoelectric conversion material according to the present invention has a large absolute value of the Seebeck coefficient due to the narrow gap semiconductor. Furthermore, since the nonwoven fabric-like structure has a large number of voids, the thermal conductivity is small. Therefore, an n-type thermoelectric conversion material having a large dimensionless figure of merit ZT and exhibiting excellent thermoelectric conversion characteristics can be provided.
  • thermoelectric conversion material according to the present invention is formed into a nonwoven fabric, it has flexibility and is lightweight.
  • thermoelectric conversion material that is lightweight and flexible and has excellent thermoelectric conversion characteristics.
  • the narrow gap semiconductor is preferably a compound containing at least one of Te and Se.
  • the narrow gap semiconductor is preferably a compound containing Bi.
  • the narrow gap semiconductor is preferably Bi 2 Te 3 , Bi 2 Se 3 , or Bi 2 Se x Te 3-x .
  • the nanowires or nanotubes may be integrated in a nonwoven fabric together with carbon nanotubes.
  • thermoelectric conversion element according to the present invention is characterized by including the n-type thermoelectric conversion material according to the present invention.
  • a method for producing an n-type thermoelectric conversion material according to the present invention comprises a narrow gap semiconductor by adding a metal salt to a solvent in which a metal acid salt or metal oxide is dissolved.
  • the method includes a step of forming nanowires or nanotubes, and a step of accumulating the nanowires or nanotubes in a nonwoven fabric.
  • a nanowire or a nanotube made of a narrow gap semiconductor can be obtained as a reaction product of the metal salt or the metal oxide and the metal salt. Therefore, an n-type thermoelectric conversion material having a large absolute value of the Seebeck coefficient can be obtained.
  • an n-type thermoelectric conversion material formed by accumulating the nanowires or the nanotubes in a nonwoven fabric shape can be obtained. Therefore, it is possible to obtain an n-type thermoelectric conversion material that has a low thermal conductivity and is lightweight and flexible due to the non-woven fabric structure.
  • thermoelectric conversion material that is lightweight and flexible and has excellent thermoelectric conversion characteristics can be provided.
  • the metal acid salt or the metal oxide preferably contains Te or Se.
  • the metal salt is preferably Bi.
  • the metal acid salt includes Na 2 O 3 Te, Na 2 O 3 Se, Ka 2 O 3 Te, Ka 2 O 3 Se, MgO 3 Te, MgO 3. Se, CaO 3 Te, CaO 3 Se, H 2 O 3 Te, H 2 O 3 Se, H 6 TeO 6 or H 6 SeO 6 are preferred.
  • the metal oxide is preferably TeO 2 , SeO 2 , TeO 3 , SeO 3 , Te 2 O 5 or Se 2 O 5 .
  • the method for producing an n-type thermoelectric conversion material according to the present invention includes a step of adding carbon nanotubes to a solvent containing the nanowires or nanotubes before the step of accumulating the nanowires or nanotubes in a nonwoven fabric shape. Also good.
  • the nanowires or nanotubes are nonwoven fabric-like by filtering the solvent containing the nanowires or the nanotubes. It is preferable to make it accumulate.
  • Example 1 Bi 2 Te 3 nanowires were fabricated by the manufacturing method shown in FIG. As shown in FIG. 3 (a), a 50 mL three-necked flask was charged with 332.4 mg (1.5 mmol) Na 2 O 3 Te, 0.5 g polyvinylpyrrolidone, 0.3 g NaOH and 10 mL ethylene. Glycol was added and degassed for 15 minutes at room temperature, followed by N 2 substitution. Let the liquid obtained at the said process be a solution (A).
  • the nanowire was purified.
  • the obtained Bi 2 Te 3 nanowires were dispersed with ethanol, and suction filtration was performed using a membrane filter.
  • the membrane filter had a pore diameter of 0.2 ⁇ m.
  • a thermoelectric conversion material in which Bi 2 Te 3 nanowires were accumulated in a nonwoven fabric was obtained by the suction filtration.
  • thermoelectric conversion material was easily oxidized in the air and the thermoelectric performance was impaired, it reduced before each physical property measurement.
  • FIG. 4 shows the reduction method.
  • Example 2 In FIG. 3A, the starting material Na 2 O 3 Te was replaced with 239.4 mg of TeO 2 to produce Bi 2 Te 3 nanotubes.
  • a thermoelectric conversion material in which Bi 2 Te 3 nanotubes were accumulated in a non-woven fabric was produced using the same method as in Example 1 except that TeO 2 was used.
  • FIG. 5 (a) shows the result of observing the nanowire obtained in Example 1 at 150,000 times by SEM
  • FIG. 5 (b) shows the nanotube obtained in Example 2. The result observed by SEM at 100,000 times is shown. The center of the nanowire is filled, while the center of the nanotube is hollow.
  • thermoelectric conversion material obtained in Example 1 has shown the external appearance of the thermoelectric conversion material obtained in Example 1.
  • FIG. Moreover, (b) and (c) of FIG. 6 have shown the result of having observed the thermoelectric conversion material obtained in Example 1 by SEM.
  • FIG. 6D shows the appearance of the thermoelectric conversion material obtained in Example 2.
  • (e) and (f) of FIG. 6 have shown the result of having observed the thermoelectric conversion material obtained in Example 2 by SEM.
  • (b) and (e) of FIG. 6 are the results of observation at 5,000 times
  • (c) and (f) of FIG. 6 are the results of observation at 25,000 times.
  • the thermoelectric conversion materials obtained in Examples 1 and 2 were substantially circular and both had a diameter of about 16 mm. In any of Examples 1 and 2, it can be seen that the obtained thermoelectric conversion material has a non-woven structure and has a large number of voids.
  • thermoelectric conversion material For the thermoelectric conversion materials obtained in Examples 1 and 2, Seebeck coefficient, conductivity, and thermal conductivity were measured. Moreover, ZT was calculated
  • the Seebeck coefficient was measured using a Seebeck effect measuring apparatus (MMR, SB-100).
  • the conductivity was measured using a four-probe method (Mitsubishi Chemical Analytech, Loresta GP).
  • the thermal conductivity was measured using a thermal diffusivity / thermal conductivity measuring device (ai-Phase Mobile 1u).
  • FIG. 7 is a graph showing changes in Seebeck coefficient with temperature in Examples 1 and 2.
  • Example 1 compared with Example 2, the absolute value of the Seebeck coefficient was about 20% larger.
  • the Seebeck coefficient at 310 K was ⁇ 124 ⁇ V / K in Example 1, and ⁇ 101 ⁇ V / K in Example 2. These values were comparable to the values shown for bulk Bi 2 Te 3 (about 200 ⁇ V / K).
  • the Seebeck coefficient is a negative value, it can be seen that the thermoelectric conversion materials of Examples 1 and 2 are n-type thermoelectric conversion materials.
  • FIG. 8 is a diagram showing changes in ZT due to temperature in Examples 1 and 2 of the present invention.
  • the ZT of Example 1 was larger than the ZT of Example 2.
  • Example 1 showed ZT exceeding 0.1 at 350K or more.
  • ZT was 0.06 at 310K
  • ZT was 0.16 at 450K.
  • ZT was 0.026 at 310K
  • ZT was 0.07 at 450K. Therefore, in Examples 1 and 2, it was found that ZT was equal to or higher than that of conventional thermoelectric conversion materials (for example, the film described in Non-Patent Document 1 has a ZT at 313 K of 0.006 to 0.09. ).
  • the thermoelectric conversion material of Example 1 shows the more excellent thermoelectric conversion characteristic compared with the thermoelectric conversion material of Example 2.
  • FIG. 1 shows the more excellent thermoelectric conversion characteristic compared with the thermoelectric conversion material of Example 2.
  • Example 1 The typical values of conductivity and thermal conductivity are listed below.
  • the conductivity at 310K was 290 S / m, and the thermal conductivity was 0.023 W / mK.
  • Example 2 the conductivity at 310K was 240 S / m, and the thermal conductivity was 0.029 W / mK. Therefore, in Examples 1 and 2, it can be seen that the thermal conductivity is smaller than that of the conventional thermoelectric conversion material (for example, the film described in Non-Patent Document 1 has a thermal conductivity of 0.25 to 313K). 0.80 W / mK). This also shows that the thermoelectric conversion material which concerns on this invention has the thermoelectric conversion characteristic excellent compared with the conventional thermoelectric conversion material.
  • thermoelectric conversion material was prepared in the same manner as in Example 1 except that SWNT dispersed in DMSO was added to Bi 2 Te 3 nanowires dispersed in ethanol before suction filtration using a membrane filter. Was made.
  • the SWNT content was varied between 0 and 10% by weight.
  • content of SWNT is a value when the obtained thermoelectric conversion material is 100 weight%.
  • Example 4 Thermoelectric conversion material in the same manner as in Example 2 except that SWNT dispersed in DMSO was added to Bi 2 Te 3 nanotubes dispersed in ethanol before suction filtration using a membrane filter. was made. The SWNT content was varied between 0 and 10% by weight. In addition, content of SWNT is a value when the obtained thermoelectric conversion material is 100 weight%.
  • thermoelectric conversion materials show the results of observing the thermoelectric conversion material obtained in Example 3 with an SEM.
  • A shows a case where 1 wt% SWNT is contained
  • (b) shows a case containing 5 wt% SWNT
  • (c) and (d) show a case containing 10 wt% SWNT.
  • (a) to (c) are the results of observation at 300 times
  • (d) are the results of observation at 100,000 times.
  • the white part in the figure is SWNT and the black part is nanowire.
  • thermoelectric conversion material ⁇ Characteristics of thermoelectric conversion material>
  • the Seebeck coefficient, conductivity, and thermal conductivity were measured for the thermoelectric conversion materials obtained in Examples 3 and 4.
  • ZT was calculated
  • the temperature was fixed at 310K.
  • FIG. 10 is a diagram showing a change in conductivity depending on the SWNT content ( ⁇ SWNT ) in Examples 3 and 4. In both Examples 3 and 4, increasing the SWNT content increased the conductivity.
  • FIG. 11 is a graph showing changes in ZT depending on the SWNT content ( ⁇ SWNT ) in Examples 3 and 4 of the present invention.
  • ZT decreased compared to the case where SWNT was not included.
  • ZT increased compared to the case where SWNT was not included.
  • ZT equal to or higher than that of a conventional thermoelectric conversion material (for example, a film described in Non-Patent Document 1) was shown.
  • the present invention can be used for, for example, energy harvesting, emergency / disaster power supplies, medical power supplies, small equipment power supplies, and industrial waste heat applications.
  • thermoelectric conversion material 1 ... n-type thermoelectric conversion material

Abstract

An n-type thermoelectric conversion material that has both excellent thermoelectric conversion characteristics and flexibility and that is lightweight is provided. This n-type thermoelectric conversion material is created by integrating nanowires or nanotubes of narrow-gap semiconductor into the form of a nonwoven fabric.

Description

ｎ型熱電変換材料および熱電変換素子、ならびにｎ型熱電変換材料の製造方法N-type thermoelectric conversion material, thermoelectric conversion element, and method for producing n-type thermoelectric conversion material
　本発明はナノワイヤまたはナノチューブを不織布状に織り込んだｎ型熱電変換材料、および該熱電変換材料を含んだ熱電変換素子、ならびに該ｎ型熱電変換材料の製造方法に関する。 The present invention relates to an n-type thermoelectric conversion material in which nanowires or nanotubes are woven into a nonwoven fabric, a thermoelectric conversion element including the thermoelectric conversion material, and a method for producing the n-type thermoelectric conversion material.
　熱電変換素子とは、温度差によって物質内に生じる電位差を利用することにより、発電を行うものである。従来は、工業炉等の産業廃熱の有効利用を目指して、その開発が進められてきた。近年、環境発電への要請が高まりつつあるため、自然再生可能エネルギーや排熱から電力を得るものであるＣＯ２フリーの発電技術の一つとして、熱電変換材料が注目されている。また一方で、緊急時用、災害時用または医療用の電源として利用するために、小型かつ軽量な熱電変換材料が求められている。また、上記熱電変換材料をウェアラブルデバイスまたはポータブルデバイス等に適用する場合、熱電変換材料を体の形状に沿って密着させ、熱源として体温を利用できることが好ましい。そのため、柔軟性を有する熱電変換材料も求められていた。そこで、屋根、壁、変電所等の産業廃熱および生活廃熱による中低温で動作する柔軟かつ軽量な熱電変換材料の実現が待たれている。 A thermoelectric conversion element generates power by utilizing a potential difference generated in a substance due to a temperature difference. Conventionally, the development has been advanced with the aim of effectively using industrial waste heat such as industrial furnaces. In recent years, demand for energy harvesting has been increasing, and thermoelectric conversion materials have attracted attention as one of CO 2 -free power generation technologies for obtaining power from natural renewable energy and exhaust heat. On the other hand, there is a need for a small and lightweight thermoelectric conversion material for use as an emergency, disaster or medical power source. Moreover, when applying the said thermoelectric conversion material to a wearable device, a portable device, etc., it is preferable that the thermoelectric conversion material is closely_contact | adhered along the shape of a body, and body temperature can be utilized as a heat source. Therefore, a thermoelectric conversion material having flexibility has also been demanded. Therefore, realization of a flexible and lightweight thermoelectric conversion material that operates at medium and low temperatures due to industrial waste heat and domestic waste heat such as roofs, walls, and substations is awaited.
　しかしながら、従来開発されてきた熱電変換材料は、主に図１２に示すようなバルク状の固体材料であった。当該バルク状の固体材料では柔軟性が得られないことから、熱源に密着させることができず、熱伝達の観点から不利である。 However, conventionally developed thermoelectric conversion materials are mainly bulk solid materials as shown in FIG. Since the bulk solid material cannot provide flexibility, it cannot be brought into close contact with a heat source, which is disadvantageous from the viewpoint of heat transfer.
　そこで、柔軟性に関する問題を解決するために、導電性高分子やカーボンナノチューブからなる熱電変換材料が検討されている。例えば、非特許文献１には、ジアルコキシフェニレン単位を含むフェニレンビニレン共重合体にヨウ素をドープすることによって形成されている導電性高分子のフィルムが記載されている。また、非特許文献２には、導電性高分子として、ポリ（３，４－エチレンジオキシチオフェン）（ＰＥＤＯＴ）を利用することが記載されている。 Therefore, in order to solve the problem relating to flexibility, thermoelectric conversion materials composed of conductive polymers and carbon nanotubes have been studied. For example, Non-Patent Document 1 describes a conductive polymer film formed by doping iodine into a phenylene vinylene copolymer containing a dialkoxyphenylene unit. Non-Patent Document 2 describes that poly (3,4-ethylenedioxythiophene) (PEDOT) is used as the conductive polymer.
　さらに非特許文献３には、ＰＥＤＯＴおよびポリ（スチレンスルホン酸）の複合体（ＰＥＤＯＴ：ＰＳＳ）とカーボンナノチューブとを利用した複合材料が記載されている。非特許文献４には、カーボンナノチューブとフッ素ポリマーとの複合材料を使用した熱電モジュールが記載されている。非特許文献５には、遷移金属ジカルコゲナイドと炭素系材料とを混合した複合材料をフィルム状に成形することが記載されている。 Further, Non-Patent Document 3 describes a composite material using a composite of PEDOT and poly (styrene sulfonic acid) (PEDOT: PSS) and carbon nanotubes. Non-Patent Document 4 describes a thermoelectric module using a composite material of a carbon nanotube and a fluoropolymer. Non-Patent Document 5 describes that a composite material obtained by mixing a transition metal dichalcogenide and a carbon-based material is formed into a film shape.
　しかしながら、上述のような従来技術は、熱電変換特性と柔軟性とを両立できていないという問題がある。具体的には、非特許文献１～５に記載の技術は、ある程度の柔軟性を有する材料または熱電変換特性を有する材料を提供しているが、実用化するために十分な熱電変換特性と柔軟性とを両立できていない。 However, the conventional techniques as described above have a problem that thermoelectric conversion characteristics and flexibility are not compatible. Specifically, the techniques described in Non-Patent Documents 1 to 5 provide a material having a certain degree of flexibility or a material having thermoelectric conversion characteristics, but sufficient thermoelectric conversion characteristics and flexibility for practical use. It is not compatible with sex.
　熱電変換材料の特性を評価する指標として、無次元性能指数ＺＴが挙げられる。ＺＴが大きいほど、良好な熱電変換特性を有するといえる。熱電変換素子の実用化のためには、ＺＴが１以上であることが望ましいとされているが、実現は難しい。そこで、まずＺＴが０．１程度のものを実現することが求められている。なお、詳しくは後述するが、ＺＴはゼーベック係数、導電率および熱伝導率から求められるものである。ここで、ゼーベック係数の絶対値および導電率はより大きいほうが好ましく、熱伝導率はより小さいほうが好ましい。 Dimensionless figure of merit ZT can be cited as an index for evaluating the characteristics of thermoelectric conversion materials. It can be said that the larger the ZT, the better the thermoelectric conversion characteristics. For practical use of thermoelectric conversion elements, ZT is desirably 1 or more, but it is difficult to realize. Therefore, it is first required to realize a ZT of about 0.1. In addition, although mentioned later in detail, ZT is calculated | required from Seebeck coefficient, electrical conductivity, and thermal conductivity. Here, the absolute value of the Seebeck coefficient and the electrical conductivity are preferably larger, and the thermal conductivity is preferably smaller.
　例えば、非特許文献１に記載の導電性高分子のフィルムは、熱伝導率が０．２５～０．８０Ｗ／ｍＫであり、３１３Ｋにおける無次元性能指数ＺＴが約０．００６～０．０９である。実用化のためには、熱伝導率がさらに小さく、ＺＴがさらに大きい熱電変換材料とする必要がある。 For example, the conductive polymer film described in Non-Patent Document 1 has a thermal conductivity of 0.25 to 0.80 W / mK, and a dimensionless figure of merit ZT at 313 K of about 0.006 to 0.09. is there. For practical use, it is necessary to use a thermoelectric conversion material having a lower thermal conductivity and a higher ZT.
　また、非特許文献２に記載の技術は、条件によってはＺＴが０．２５程度を示す場合もあるが、酸化の程度によってＺＴが変動しやすい。つまり、非特許文献２に記載の技術は環境変化に敏感であり、利用のためには緻密な調整が必要となる。よって、非特許文献２に記載の技術は、安定した熱電変換特性を有するとは言えない。 Further, according to the technique described in Non-Patent Document 2, ZT may be about 0.25 depending on conditions, but ZT is likely to vary depending on the degree of oxidation. That is, the technique described in Non-Patent Document 2 is sensitive to environmental changes and requires precise adjustment for use. Therefore, the technique described in Non-Patent Document 2 cannot be said to have stable thermoelectric conversion characteristics.
　非特許文献３に記載の技術では、柔軟性を付与するためにゴムが含まれている。ゴムは絶縁体であるため、ゼーベック効果および導電率を大きく低減させる。そのため、非特許文献３に記載の技術では、室温におけるＺＴは０．０２程度と低い値となっている。 In the technique described in Non-Patent Document 3, rubber is included to give flexibility. Since rubber is an insulator, the Seebeck effect and conductivity are greatly reduced. Therefore, in the technique described in Non-Patent Document 3, ZT at room temperature is a low value of about 0.02.
　また、非特許文献４および５に記載の技術においても、十分な熱電変換特性と柔軟性とを実現するには至っていない。 Also, the techniques described in Non-Patent Documents 4 and 5 have not yet achieved sufficient thermoelectric conversion characteristics and flexibility.
　また、非特許文献１～５に記載の技術は、いずれもｐ型熱電変換材料に関するものである。柔軟性と優れた熱電変換特性とを兼ね備えたｎ型熱電変換材料については、何ら開示されていない。 The techniques described in Non-Patent Documents 1 to 5 all relate to p-type thermoelectric conversion materials. No n-type thermoelectric conversion material having both flexibility and excellent thermoelectric conversion characteristics is disclosed.
　本発明は、上記従来の問題点に鑑みてなされたものであって、その目的は、軽量かつ柔軟であるとともに優れたｎ型熱電変換特性を備えた熱電変換材料を提供することにある。 The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a thermoelectric conversion material that is lightweight and flexible and has excellent n-type thermoelectric conversion characteristics.
　本発明者らは上記課題を解決するために鋭意検討した結果、驚くべきことに、ナローギャップ半導体からなるナノワイヤまたはナノチューブを不織布状に集積することによって、軽量かつ柔軟であるとともに優れた熱電変換特性を備えたｎ型熱電変換材料を実現できるということを独自に見出した。本発明は、本発明者らが独自に見出した新規知見によって完成されたものであり、以下の発明を包含する。 As a result of intensive studies to solve the above-mentioned problems, the present inventors have surprisingly been able to integrate light-weight and flexible and excellent thermoelectric conversion characteristics by integrating nanowires or nanotubes made of a narrow gap semiconductor in a nonwoven fabric shape. It was originally found that an n-type thermoelectric conversion material provided with The present invention has been completed based on new findings uniquely found by the present inventors, and includes the following inventions.
　すなわち、本発明に係るｎ型熱電変換材料は、上記の課題を解決するために、ナローギャップ半導体からなるナノワイヤまたはナノチューブが不織布状に集積して形成されていることを特徴としている。 That is, the n-type thermoelectric conversion material according to the present invention is characterized in that nanowires or nanotubes made of a narrow gap semiconductor are integrated and formed in a nonwoven fabric in order to solve the above-described problems.
　また、上記の課題を解決するために、本発明に係るｎ型熱電変換材料の製造方法は、金属酸塩または金属酸化物が溶解している溶媒に対して、金属塩を加え、ナローギャップ半導体からなるナノワイヤまたはナノチューブを形成する工程と、上記ナノワイヤまたは上記ナノチューブを不織布状に集積させる工程と、を含んでいることを特徴としている。 In addition, in order to solve the above-described problem, the method for producing an n-type thermoelectric conversion material according to the present invention adds a metal salt to a solvent in which a metal acid salt or a metal oxide is dissolved. A step of forming a nanowire or a nanotube comprising: and a step of accumulating the nanowire or the nanotube in a nonwoven fabric.
　本発明に係るｎ型熱電変換材料は、ナローギャップ半導体からなるナノワイヤまたはナノチューブが不織布状に集積して形成されている構成である。 The n-type thermoelectric conversion material according to the present invention has a configuration in which nanowires or nanotubes made of a narrow gap semiconductor are integrated in a nonwoven fabric shape.
　それゆえ、軽量かつ柔軟であるとともに優れた熱電変換特性を備えたｎ型熱電変換材料を提供することができる。 Therefore, it is possible to provide an n-type thermoelectric conversion material that is lightweight and flexible and has excellent thermoelectric conversion characteristics.
本発明の一実施形態に係るｎ型熱電変換材料の外観を示す図である。It is a figure which shows the external appearance of the n-type thermoelectric conversion material which concerns on one Embodiment of this invention. 本発明の一実施形態に係るｎ型熱電変換材料の外観を示す図である。It is a figure which shows the external appearance of the n-type thermoelectric conversion material which concerns on one Embodiment of this invention. 本発明の実施例におけるｎ型熱電変換材料の製造方法を示す概略図である。It is the schematic which shows the manufacturing method of the n-type thermoelectric conversion material in the Example of this invention. 本発明の実施例におけるｎ型熱電変換材料の製造方法を示す概略図である。It is the schematic which shows the manufacturing method of the n-type thermoelectric conversion material in the Example of this invention. （ａ）は、本発明の実施例１において作製されたナノワイヤを示す図であり、（ｂ）は本発明の実施例２において作製されたナノチューブを示す図である。(A) is a figure which shows the nanowire produced in Example 1 of this invention, (b) is a figure which shows the nanotube produced in Example 2 of this invention. （ａ）～（ｃ）は本発明の実施例１において作製されたｎ型熱電変換材料を示す図であり、（ｄ）～（ｆ）は本発明の実施例２において作製されたｎ型熱電変換材料を示す図である。(A)-(c) is a figure which shows the n-type thermoelectric conversion material produced in Example 1 of this invention, (d)-(f) is the n-type thermoelectric produced in Example 2 of this invention. It is a figure which shows conversion material. 本発明の実施例１および２における温度によるゼーベック係数の変化を示す図である。It is a figure which shows the change of the Seebeck coefficient by the temperature in Example 1 and 2 of this invention. 本発明の実施例１および２における温度による無次元性能指数ＺＴの変化を示す図である。It is a figure which shows the change of the dimensionless figure of merit ZT by the temperature in Example 1 and 2 of this invention. （ａ）～（ｄ）は、本発明の実施例３において製造されたｎ型熱電変換材料を示す図である。（ａ）は単層カーボンナノチューブ（ＳＷＮＴ）を１重量％含んでいる場合、（ｂ）はＳＷＮＴを５重量％含んでいる場合、（ｃ）および（ｄ）はＳＷＮＴを１０重量％含んでいる場合を示す。(A)-(d) is a figure which shows the n-type thermoelectric conversion material manufactured in Example 3 of this invention. (A) contains 1% by weight of single-walled carbon nanotubes (SWNT), (b) contains 5% by weight of SWNTs, and (c) and (d) contain 10% by weight of SWNTs. Show the case. 本発明の実施例３および４におけるＳＷＮＴの含有量による導電率の変化を示す図である。It is a figure which shows the change of the electrical conductivity by content of SWNT in Example 3 and 4 of this invention. 本発明の実施例３および４におけるＳＷＮＴの含有量による無次元性能指数ＺＴの変化を示す図である。It is a figure which shows the change of the dimensionless figure of merit ZT by the content of SWNT in Examples 3 and 4 of the present invention. 従来型の熱電変換素子を示す図である。It is a figure which shows the conventional thermoelectric conversion element.
　以下、本発明の実施の形態の一例について詳細に説明するが、本発明は、これらに限定されない。 Hereinafter, an example of an embodiment of the present invention will be described in detail, but the present invention is not limited thereto.
　〔熱電変換特性に関する指標〕
　本発明の実施の形態の説明に当たり、まず、熱電変換材料の特性（本明細書において「熱電変換特性」とも称する）を表す指標について説明する。熱電変換材料の特性を評価する指標として、無次元性能指数ＺＴが挙げられる。ＺＴは以下の式（１）によって求められる。 [Indicators for thermoelectric conversion characteristics]
In the description of the embodiment of the present invention, first, an index representing a characteristic of a thermoelectric conversion material (also referred to as “thermoelectric conversion characteristic” in this specification) will be described. As an index for evaluating the characteristics of the thermoelectric conversion material, there is a dimensionless figure of merit ZT. ZT is calculated | required by the following formula | equation (1).
　ＺＴ＝Ｓ２σＴ／κ　　　　　　（１）
　式（１）中で、Ｓはゼーベック係数、σは導電率、Ｔは温度、κは熱伝導率を示す。 ZT = S 2 σT / κ (1)
In the formula (1), S is the Seebeck coefficient, σ is the conductivity, T is the temperature, and κ is the thermal conductivity.
　ＺＴが大きいほど、優れた熱電変換材料であることを表している。式（１）から、大きいＺＴを得るためには、ゼーベック係数の絶対値および導電率は大きいほうが好ましいことがわかる。２つの異なる物質を接続し、温度差を設けると当該物質間に熱起電力が生じる。この熱起電力を生じる現象をゼーベック効果という。ゼーベック係数はこの熱起電力を表すものとして用いられる。ゼーベック係数の絶対値が大きいほど、熱起電力が大きいことを表す。 The larger the ZT, the better the thermoelectric conversion material. From formula (1), it can be seen that in order to obtain a large ZT, it is preferable that the absolute value and the conductivity of the Seebeck coefficient are large. When two different materials are connected and a temperature difference is provided, a thermoelectromotive force is generated between the materials. The phenomenon that generates this thermoelectromotive force is called Seebeck effect. The Seebeck coefficient is used to represent this thermoelectromotive force. The larger the absolute value of the Seebeck coefficient, the greater the thermoelectromotive force.
　また、式（１）から、大きいＺＴを得るためには、熱伝導率は小さいほうが好ましいことがわかる。このことは熱電変換材料が温度差を利用するものであることに対応している。熱伝導率が大きい場合、物質中の温度が容易に均一になってしまい、温度差を生じにくい。 Also, from formula (1), it can be seen that a smaller thermal conductivity is preferable in order to obtain a large ZT. This corresponds to the fact that the thermoelectric conversion material uses a temperature difference. When the thermal conductivity is large, the temperature in the material is easily uniform, and a temperature difference is hardly generated.
　なお、式（１）中のゼーベック係数および導電率から求められる値は、下記式（２）で示すようにパワーファクターＰと表すことができる。上述のように、ゼーベック係数の絶対値および導電率は大きいほうが好ましいため、パワーファクターも大きいことが好ましい。 In addition, the value calculated | required from the Seebeck coefficient in Formula (1) and electrical conductivity can be represented with the power factor P, as shown in the following formula (2). As described above, since it is preferable that the absolute value and conductivity of the Seebeck coefficient are large, it is also preferable that the power factor is large.
　Ｐ＝Ｓ２σ　　　　　　　　（２）
　本明細書において、「優れた熱電変換特性を備える」とは、少なくとも従来型の柔軟性を有する熱電変換材料と同等またはそれを上回るＺＴを示すことを意味する。 P = S 2 σ (2)
In the present specification, “having excellent thermoelectric conversion characteristics” means that ZT is equal to or higher than that of a thermoelectric conversion material having at least conventional flexibility.
　〔ｎ型熱電変換材料〕
　本発明に係るｎ型熱電変換材料は、ナノワイヤまたはナノチューブが不織布状に集積して形成されている。換言すれば、本発明に係るｎ型熱電変換材料では、ナノワイヤまたはナノワイヤ同士が互いに絡み合うように不織布状の構造を形成している。上記構成によれば、ナノワイヤまたはナノチューブ同士が滑り合うことによって、熱電変換材料に柔軟性を付与することができる。 [N-type thermoelectric conversion material]
The n-type thermoelectric conversion material according to the present invention is formed by integrating nanowires or nanotubes in a nonwoven fabric shape. In other words, in the n-type thermoelectric conversion material according to the present invention, a non-woven structure is formed so that nanowires or nanowires are entangled with each other. According to the said structure, a softness | flexibility can be provided to a thermoelectric conversion material by nanowire or a nanotube sliding each other.
　図１および２は、本発明の一実施形態に係るｎ型熱電変換材料１の外観を示す図である。図１および２に示すように、ｎ型熱電変換材料１は容易に変形させることができる。そのため、本発明に係るｎ型熱電変換材料は加工性に優れている。例えば、本発明に係るｎ型熱電変換材料は複雑な形状のシリコンまたはプラスチックに貼り付けることも可能であり、人間の体の形状に合わせて変形させることも可能である。また、本発明に係るｎ型熱電変換材料は、変形させた状態で形状記憶させることも可能である。 1 and 2 are views showing the appearance of an n-type thermoelectric conversion material 1 according to an embodiment of the present invention. As shown in FIGS. 1 and 2, the n-type thermoelectric conversion material 1 can be easily deformed. Therefore, the n-type thermoelectric conversion material according to the present invention is excellent in workability. For example, the n-type thermoelectric conversion material according to the present invention can be affixed to silicon or plastic having a complicated shape, and can be deformed according to the shape of the human body. In addition, the n-type thermoelectric conversion material according to the present invention can be stored in the shape of a deformed state.
　本発明に係るｎ型熱電変換材料の形状は特に限定されず、例えば円形、四角形等であってもよい。また、本発明に係るｎ型熱電変換材料の大きさも特に限定されず、用途によって適宜決定すればよい。 The shape of the n-type thermoelectric conversion material according to the present invention is not particularly limited, and may be, for example, a circle or a quadrangle. Further, the size of the n-type thermoelectric conversion material according to the present invention is not particularly limited, and may be appropriately determined depending on the application.
　また、本発明に係るｎ型熱電変換材料は、不織布状の構造に起因して多数の空隙を有している。そのため、本発明に係るｎ型熱電変換材料は、軽量である。さらに、上記多数の空隙に起因して、本発明に係るｎ型熱電変換材料は、バルクの状態に比べて低い熱伝導率を示す。 Further, the n-type thermoelectric conversion material according to the present invention has a large number of voids due to the nonwoven fabric structure. Therefore, the n-type thermoelectric conversion material according to the present invention is lightweight. Furthermore, due to the large number of voids, the n-type thermoelectric conversion material according to the present invention exhibits a lower thermal conductivity than the bulk state.
　なお、本明細書において、ナノワイヤとは、微小な繊維状の物質であって、中心が充填されており、中空ではない物質を意味する。また、本明細書において、ナノチューブとは、中空である微小な繊維状の物質を意味する。ナノワイヤおよびナノチューブの大きさは特に限定されないが、例えば長さが０．５μｍ以上１０００μｍ以下であってもよい。また、ナノワイヤおよびナノチューブの直径は１ｎｍ以上１０００ｎｍ以下であってもよい。なお、本明細書において、ナノワイヤを「ＮＷ」、ナノチューブを「ＮＴ」と記載する場合もある。 Note that in this specification, the nanowire means a fine fibrous substance that is filled in the center and is not hollow. Further, in this specification, the nanotube means a fine fibrous substance that is hollow. The size of the nanowire and the nanotube is not particularly limited, but may be, for example, 0.5 μm or more and 1000 μm or less in length. Further, the diameter of the nanowire and the nanotube may be 1 nm or more and 1000 nm or less. In this specification, the nanowire may be described as “NW” and the nanotube as “NT”.
　上記ナノワイヤまたは上記ナノチューブは、ナローギャップ半導体からなる。本明細書において、ナローギャップ半導体とは、バンドギャップが小さい半導体を指す。上記ナローギャップ半導体は、特にバンドキャップが０．０１ｅＶ以上１．０ｅＶ以下であることが好ましい。バンドギャップが小さい半導体においては、小さな熱エネルギーによって容易にキャリアが励起される。よって、ナローギャップ半導体を使用すれば、低温であっても利用可能な熱電変換材料を得ることができる。 The nanowire or the nanotube is made of a narrow gap semiconductor. In this specification, a narrow gap semiconductor refers to a semiconductor having a small band gap. The narrow gap semiconductor preferably has a band cap of 0.01 eV or more and 1.0 eV or less. In a semiconductor with a small band gap, carriers are easily excited by small thermal energy. Therefore, if a narrow gap semiconductor is used, a usable thermoelectric conversion material can be obtained even at a low temperature.
　上記ナローギャップ半導体は、Ｔｅ、Ｓｅ、またはその両方を含んでいる化合物が好ましい。換言すれば、上記化合物は、ＴｅおよびＳｅの少なくとも一方を含んでいることが好ましい。また、上記ナローギャップ半導体は、Ｂｉを含んでいる化合物が好ましい。上記ナローギャップ半導体として好ましい例としては、Ｂｉ２Ｔｅ３、Ｂｉ２Ｓｅ３、またはＢｉ２ＳｅｘＴｅ３－ｘ（０＜ｘ＜３）が挙げられる。上記構成によれば、比較的低い温度（例えば２００～５８０Ｋ）においても、優れた熱電変換特性を示す熱電変換材料を提供することができる。なお、上記物質は、バルクの状態でナローギャップ半導体としての性質を示すことが知られている。 The narrow gap semiconductor is preferably a compound containing Te, Se, or both. In other words, the compound preferably contains at least one of Te and Se. The narrow gap semiconductor is preferably a compound containing Bi. Preferred examples of the narrow gap semiconductor include Bi 2 Te 3 , Bi 2 Se 3 , and Bi 2 Se x Te 3-x (0 <x <3). According to the above configuration, it is possible to provide a thermoelectric conversion material exhibiting excellent thermoelectric conversion characteristics even at a relatively low temperature (for example, 200 to 580 K). In addition, it is known that the said substance will show the property as a narrow gap semiconductor in a bulk state.
　以上のように、本発明に係るｎ型熱電変換材料は、ナローギャップ半導体に起因してゼーベック係数の絶対値が大きく、不織布状の構造に起因して熱伝導率が小さい。よって、本発明に係るｎ型熱電変換材料は、ナローギャップ半導体を使用していることと不織布状の構造であることとの相互作用によって、優れた熱電変換特性を示す。また、本発明に係るｎ型熱電変換材料は、不織布状の構造に起因して、軽量かつ柔軟である。従って、本発明に係るｎ型熱電変換材料は、軽量かつ柔軟であるとともに優れた熱電変換特性を示す。以上のことは、本発明者らが独自に見出したものである。 As described above, the n-type thermoelectric conversion material according to the present invention has a large absolute value of the Seebeck coefficient due to the narrow gap semiconductor and a low thermal conductivity due to the non-woven structure. Therefore, the n-type thermoelectric conversion material according to the present invention exhibits excellent thermoelectric conversion characteristics due to the interaction between the use of a narrow gap semiconductor and the non-woven fabric structure. In addition, the n-type thermoelectric conversion material according to the present invention is lightweight and flexible due to the nonwoven fabric structure. Therefore, the n-type thermoelectric conversion material according to the present invention is lightweight and flexible and exhibits excellent thermoelectric conversion characteristics. The above has been uniquely found by the present inventors.
　本発明に係る熱電変換材料は、ゼーベック係数が負の値となることからｎ型熱電変換材料であることが確認できる。軽量かつ柔軟であるとともに、優れた熱電変換特性を備えたｎ型熱電変換材料は、本発明によって初めて実現できるものである。 The thermoelectric conversion material according to the present invention can be confirmed to be an n-type thermoelectric conversion material because the Seebeck coefficient is a negative value. An n-type thermoelectric conversion material that is lightweight and flexible and has excellent thermoelectric conversion characteristics can be realized for the first time by the present invention.
　また、上記ナノワイヤまたは上記ナノチューブは、カーボンナノチューブとともに不織布状に集積されていてもよい。つまり、上記ナノワイヤまたは上記ナノチューブは、カーボンナノチューブと絡み合うように不織布状の構造を形成していてもよい。上記構成によれば、熱電変換材料の機械的強度を高めることができる。また、上記構成によれば、導電率を向上させることができる。つまり、熱電変換材料のパワーファクターを向上させることができる。 Further, the nanowires or the nanotubes may be integrated together with the carbon nanotubes in a non-woven shape. That is, the nanowire or the nanotube may have a non-woven structure so as to be entangled with the carbon nanotube. According to the above configuration, the mechanical strength of the thermoelectric conversion material can be increased. Moreover, according to the said structure, electrical conductivity can be improved. That is, the power factor of the thermoelectric conversion material can be improved.
　なお、上記カーボンナノチューブを使用した場合、ゼーベック係数の絶対値が小さくなる場合もある。従って、上記カーボンナノチューブの含有量は、ゼーベック係数、導電率、機械的強度等のバランスを考慮して、適宜決定すればよい。上記カーボンナノチューブの含有量は、形成された熱電変換材料を１００重量％とした場合に、例えば１重量％以上９０重量％以下であってもよく、１重量％以上２０重量％以下であってもよいが、１重量％以上１０重量％以下であることが好ましい。 When using the above carbon nanotube, the absolute value of the Seebeck coefficient may be small. Accordingly, the content of the carbon nanotubes may be appropriately determined in consideration of a balance such as Seebeck coefficient, conductivity, mechanical strength, and the like. The content of the carbon nanotube may be, for example, 1% by weight or more and 90% by weight or less, or 1% by weight or more and 20% by weight or less, when the formed thermoelectric conversion material is 100% by weight. Although it is good, it is preferably 1% by weight or more and 10% by weight or less.
　上記カーボンナノチューブは、単層カーボンナノチューブであってもよく、多層カーボンナノチューブであってもよいが、単層カーボンナノチューブ（以下、ＳＷＮＴとも称する）が特に好ましい。上記構成によれば、熱電変換材料に対して、優れた弾性および強度を付与することができる。 The carbon nanotube may be a single-walled carbon nanotube or a multi-walled carbon nanotube, but a single-walled carbon nanotube (hereinafter also referred to as SWNT) is particularly preferable. According to the said structure, the outstanding elasticity and intensity | strength can be provided with respect to the thermoelectric conversion material.
　〔熱電変換素子〕
　本発明に係る熱電変換素子は、本発明に係るｎ型熱電変換材料を備えている。そのため、本発明に係る熱電変換素子は、軽量であるとともに、優れた熱電変換特性を備えている。また、本発明に係るｎ型熱電変換材料は柔軟性を有しており、加工性に優れているため、様々な形状の熱電変換素子を製造することができる。 [Thermoelectric conversion element]
The thermoelectric conversion element according to the present invention includes the n-type thermoelectric conversion material according to the present invention. Therefore, the thermoelectric conversion element according to the present invention is lightweight and has excellent thermoelectric conversion characteristics. Moreover, since the n-type thermoelectric conversion material according to the present invention has flexibility and excellent workability, it is possible to manufacture thermoelectric conversion elements having various shapes.
　本発明に係る熱電変換素子は、本発明に係るｎ型熱電変換材料と、ｐ型熱電変換材料とを組み合わせることで実現できる。本発明に係るｎ型熱電変換材料と組み合わせるｐ型熱電変換材料としては、特に限定されないが、例えば公知のｐ型熱電変換材料を用いることができる。 The thermoelectric conversion element according to the present invention can be realized by combining the n-type thermoelectric conversion material according to the present invention and the p-type thermoelectric conversion material. Although it does not specifically limit as a p-type thermoelectric conversion material combined with the n-type thermoelectric conversion material which concerns on this invention, For example, a well-known p-type thermoelectric conversion material can be used.
　例えば、本発明に係る熱電変換素子は優れた熱電変換特性を有するため、地熱発電等の環境発電、ならびに配管および電気炉等の工業廃熱、ならびに車体、エンジン周辺機器、空調設備等の機器廃熱の利用に適用することができる。また、本発明に係る熱電変換素子は軽量かつ優れた熱電変換特性を有するため、緊急時用、災害時用および医療用の電源に利用することができる。さらに、本発明に係る熱電変換素子は、軽量かつ柔軟性を有し、優れた熱電変換特性を有するため、ポータブルデバイス、ウェアラブルデバイス、フレキシブルデバイス等の小型機器の電源に利用することができる。当該小型機器としては、例えば、携帯電話、腕時計、心臓ペースメーカー等が挙げられる。 For example, since the thermoelectric conversion element according to the present invention has excellent thermoelectric conversion characteristics, environmental power generation such as geothermal power generation, industrial waste heat such as pipes and electric furnaces, and waste of equipment such as vehicle bodies, engine peripheral equipment, and air conditioning equipment Can be used for heat utilization. Moreover, since the thermoelectric conversion element according to the present invention is lightweight and has excellent thermoelectric conversion characteristics, it can be used for power supplies for emergencies, disasters, and medical use. Furthermore, since the thermoelectric conversion element according to the present invention is lightweight and flexible and has excellent thermoelectric conversion characteristics, it can be used as a power source for small devices such as portable devices, wearable devices, and flexible devices. Examples of the small device include a mobile phone, a wrist watch, and a cardiac pacemaker.
　〔ｎ型熱電変換材料の製造方法〕
　本発明に係るｎ型熱電変換材料の製造方法を以下に説明する。なお、前述の〔ｎ型熱電変換材料〕および〔熱電変換素子〕において既に説明した構成については、詳細な説明は省略する。 [Method for producing n-type thermoelectric conversion material]
A method for producing the n-type thermoelectric conversion material according to the present invention will be described below. In addition, detailed description is abbreviate | omitted about the structure already demonstrated in the above-mentioned [n-type thermoelectric conversion material] and [thermoelectric conversion element].
　本発明に係るｎ型熱電変換材料の製造方法は、金属酸塩または金属酸化物が溶解している溶媒に対して、金属塩を加え、ナローギャップ半導体からなるナノワイヤまたはナノチューブを形成する工程を含んでいる。上記構成によれば、上記金属酸塩または上記金属酸化物と上記金属塩とに由来するナローギャップ半導体を形成することができる。よって、上述のように上記ナローギャップ半導体に起因して、当該製造方法によって得られたｎ型熱電変換材料におけるゼーベック係数を向上させることができる。 The method for producing an n-type thermoelectric conversion material according to the present invention includes a step of adding a metal salt to a solvent in which a metal acid salt or metal oxide is dissolved to form nanowires or nanotubes made of a narrow gap semiconductor. It is out. According to the said structure, the narrow gap semiconductor originating in the said metal acid salt or the said metal oxide, and the said metal salt can be formed. Therefore, as described above, the Seebeck coefficient in the n-type thermoelectric conversion material obtained by the manufacturing method can be improved due to the narrow gap semiconductor.
　金属酸塩または上記金属酸化物はＴｅまたはＳｅを含んでいることが好ましい。具体的には、上記金属酸塩は、Ｎａ２Ｏ３Ｔｅ、Ｎａ２Ｏ３Ｓｅ、Ｋａ２Ｏ３Ｔｅ、Ｋａ２Ｏ３Ｓｅ、ＭｇＯ３Ｔｅ、ＭｇＯ３Ｓｅ、ＣａＯ３Ｔｅ、ＣａＯ３Ｓｅ、Ｈ２Ｏ３Ｔｅ、Ｈ２Ｏ３Ｓｅ、Ｈ６ＴｅＯ６またはＨ６ＳｅＯ６であることが好ましい。また、上記金属酸化物は、ＴｅＯ２、ＳｅＯ２、ＴｅＯ３、ＳｅＯ３、Ｔｅ２Ｏ５またはＳｅ２Ｏ５であることが好ましい。上記構成によれば、得られるナローギャップ半導体をＴｅまたはＳｅを含んでいる化合物とすることができる。また、Ｔｅを含んでいる金属酸塩または金属酸化物と、Ｓｅを含んでいる金属酸塩または金属酸化物とを使用すれば、得られるナローギャップ半導体をＴｅおよびＳｅの両方を含んでいる化合物とすることができる。 The metal acid salt or the metal oxide preferably contains Te or Se. Specifically, the metal acid salt includes Na 2 O 3 Te, Na 2 O 3 Se, Ka 2 O 3 Te, Ka 2 O 3 Se, MgO 3 Te, MgO 3 Se, CaO 3 Te, and CaO 3 Se. H 2 O 3 Te, H 2 O 3 Se, H 6 TeO 6 or H 6 SeO 6 is preferred. Also, the metal oxide, TeO 2, SeO 2, TeO 3, SeO 3, Te is preferably 2 O 5 or Se 2 O 5. According to the said structure, the narrow gap semiconductor obtained can be made into the compound containing Te or Se. In addition, if a metal acid salt or metal oxide containing Te and a metal acid salt or metal oxide containing Se are used, the resulting narrow gap semiconductor is a compound containing both Te and Se. It can be.
　また、上記金属塩はＢｉを含んでいることが好ましい。上記金属塩において、上記Ｂｉに対するカウンターイオンは特に限定されないが、例えば、Ｃｌ－、Ｂｒ－、Ｉ－、ＮＯ３ －、ＳＯ４ ２－、ＳＣＮ－であってもよい。上記構成によれば、得られるナローギャップ半導体を、Ｂｉを含んでいる化合物とすることができる。 Moreover, it is preferable that the said metal salt contains Bi. In the metal salt, the counter ion for Bi is not particularly limited, but may be, for example, Cl − , Br − , I − , NO 3 − , SO 4 2− , SCN − . According to the said structure, the narrow gap semiconductor obtained can be made into the compound containing Bi.
　つまり、ＴｅまたはＳｅを含んでいる金属酸塩または金属酸化物と、Ｂｉを含んでいる金属塩とを使用した場合、得られるナローギャップ半導体をＢｉ２Ｔｅ３、Ｂｉ２Ｓｅ３またはＢｉ２ＳｅｘＴｅ３－ｘ（０＜ｘ＜３）とすることができる。また、化学量論比を正確にするため、上記金属酸塩または上記金属酸化物と上記金属塩とは、使用するモル比を３：２とすることが好ましい。 That is, when a metal salt or metal oxide containing Te or Se and a metal salt containing Bi are used, the obtained narrow gap semiconductor is represented by Bi 2 Te 3 , Bi 2 Se 3 or Bi 2 Se. x Te 3-x (0 <x <3) may be satisfied. In order to make the stoichiometric ratio accurate, the molar ratio of the metal salt or the metal oxide and the metal salt used is preferably 3: 2.
　なお、上記工程において、上記金属酸塩を用いた場合、ナノワイヤを形成することができる。また、上記工程において、上記金属酸化物を用いた場合、ナノチューブを形成することができる。よって、上記構成によれば、金属酸塩および金属酸化物を使い分けることによって、ナノワイヤおよびナノチューブを選択的に形成することができる。このことは、本発明者によって独自に見出されたことである。 In the above process, when the metal acid salt is used, a nanowire can be formed. Further, in the above process, when the metal oxide is used, a nanotube can be formed. Therefore, according to the said structure, a nanowire and a nanotube can be selectively formed by using a metal acid salt and a metal oxide properly. This has been uniquely found by the inventor.
　また、上記金属酸塩、上記金属酸化物および上記金属塩は、その種類にもよるが、比較的安価である。よって、本発明に係るｎ型熱電変換材料の製造方法は、ＰＥＤＯＴ等を使用する従来技術に比べて、コストを低減することができる。 Further, the metal acid salt, the metal oxide, and the metal salt are relatively inexpensive, although depending on the type. Therefore, the manufacturing method of the n-type thermoelectric conversion material according to the present invention can reduce the cost as compared with the conventional technique using PEDOT or the like.
　本発明に係るｎ型熱電変換材料の製造方法は、ワンポット反応として行うことが好ましい。上記構成によれば、廃液が生じることがなく、ナノワイヤまたはナノチューブの収率の低下も防ぐことができる。また、上記構成によれば、容器の洗浄も不要である。さらに、上記構成によれば、溶媒の使用量も抑えることができる。 The method for producing an n-type thermoelectric conversion material according to the present invention is preferably performed as a one-pot reaction. According to the said structure, a waste liquid does not arise and the fall of the yield of nanowire or a nanotube can also be prevented. Moreover, according to the said structure, the washing | cleaning of a container is also unnecessary. Furthermore, according to the said structure, the usage-amount of a solvent can also be suppressed.
　上記工程において使用される溶媒は、（ａ）１６０℃以上の沸点を有すること、（ｂ）弱還元性を示すこと、および（ｃ）金属塩に対し優れた溶解性を示すこと、のうちの少なくとも１つ以上の性質を有することが好ましく、（ａ）～（ｃ）の性質を全て備えていることがより好ましい。上記溶媒としては、例えば、ポリオール（エチレングリコール、ジエチレングリコール、トリエチレングリコール等）、アルキルアミン（オレイルアミン等）、アルキルホスフィン（トリオクチルホスフィン等）が挙げられる。酸化された場合に、ポリオールはアルデヒドやカルボン酸に、アミンはヒドロキシルアミン、オキシム、ニトロソ化合物、ニトロ化合物に、ホスフィンはホスフィンオキシドに変換される。よって、上記溶媒は還元性を有している。 The solvent used in the above step is (a) having a boiling point of 160 ° C. or higher, (b) showing weak reducing ability, and (c) showing excellent solubility in metal salts. It preferably has at least one or more properties, and more preferably has all the properties (a) to (c). Examples of the solvent include polyols (ethylene glycol, diethylene glycol, triethylene glycol, etc.), alkyl amines (oleyl amine, etc.), and alkyl phosphines (trioctyl phosphine, etc.). When oxidized, polyols are converted to aldehydes and carboxylic acids, amines are converted to hydroxylamines, oximes, nitroso compounds, nitro compounds, and phosphines to phosphine oxides. Therefore, the solvent has reducibility.
　上記工程における反応温度は、使用する金属酸塩、金属酸化物、金属塩および溶媒に応じて適宜決定すればよいが、５０℃以上２５０℃以下であることが好ましく、１４０℃以上２００℃以下であることがより好ましい。 The reaction temperature in the above step may be appropriately determined according to the metal acid salt, metal oxide, metal salt and solvent to be used, but is preferably 50 ° C. or higher and 250 ° C. or lower, and 140 ° C. or higher and 200 ° C. or lower. More preferably.
　さらに、本発明に係るｎ型熱電変換材料の製造方法は、上記ナノワイヤまたは上記ナノチューブを不織布状に集積させる工程を含んでいる。 Furthermore, the method for producing an n-type thermoelectric conversion material according to the present invention includes a step of accumulating the nanowires or the nanotubes in a nonwoven fabric shape.
　上記構成によれば、上記ナノワイヤまたは上記ナノチューブが不織布状に集積して形成されている熱電変換材料を作製することができる。よって、上述のように不織布状の構造に起因して、当該製造方法によって得られた熱電変換材料を、熱伝導率が小さく、軽量かつ柔軟な熱電変換材料とすることができる。 According to the above-described configuration, a thermoelectric conversion material in which the nanowires or the nanotubes are accumulated in a nonwoven fabric can be produced. Therefore, the thermoelectric conversion material obtained by the manufacturing method due to the non-woven structure as described above can be a lightweight and flexible thermoelectric conversion material having a low thermal conductivity.
　上記ナノワイヤまたは上記ナノチューブを不織布状に集積する方法は特に限定されず、例えば、上記ナノワイヤまたは上記ナノチューブを含んでいる溶媒を濾過もしくはスプレー塗布する方法、またはエレクトロスピニング法によって、上記ナノワイヤまたは上記ナノチューブを支持体上に集積させる方法が挙げられる。中でも、簡便に実施できるという観点からは、上記溶媒を濾過する方法が好ましい。 The method for accumulating the nanowire or the nanotube in a nonwoven fabric is not particularly limited. For example, the nanowire or the nanotube is obtained by filtering or spraying a solvent containing the nanowire or the nanotube, or by electrospinning. The method of accumulating on a support body is mentioned. Among these, the method of filtering the solvent is preferable from the viewpoint of easy implementation.
　上記溶媒を濾過する方法には、多孔性膜等のフィルターを用いることができる。フィルターを用いて上記溶媒を濾過し、当該フィルター上に上記ナノワイヤまたは上記ナノチューブを集積させることができる。上記多孔性膜の孔の直径は、ナノワイヤまたはナノチューブの多くが約５μｍ以上の長さであることから、５μｍ以下であることが好ましく、回収率の観点から０．５μｍ以下であることがより好ましく、実用的な観点から０．２μｍ以下であることがさらに好ましい。 For the method of filtering the solvent, a filter such as a porous membrane can be used. The solvent can be filtered using a filter, and the nanowire or the nanotube can be accumulated on the filter. The diameter of the pores of the porous membrane is preferably 5 μm or less because most of the nanowires or nanotubes have a length of about 5 μm or more, and more preferably 0.5 μm or less from the viewpoint of the recovery rate. From a practical viewpoint, it is more preferably 0.2 μm or less.
　また、本発明に係るｎ型熱電変換材料の製造方法は、上記ナノワイヤまたはナノチューブを不織布状に集積させる工程の前に、上記ナノワイヤまたはナノチューブを含んでいる溶媒に対してカーボンナノチューブを加える工程を含んでいてもよい。上記構成によれば、上記ナノワイヤまたは上記ナノチューブが、カーボンナノチューブとともに不織布状に集積されて形成されている熱電変換材料を製造できる。上記カーボンナノチューブは、前述のように単層カーボンナノチューブであることが好ましい。また、上記カーボンナノチューブを加える場合、超音波を用いて上記カーボンナノチューブを溶媒中に分散させておくことが好ましい。上記構成によれば、上記カーボンナノチューブが均一に含まれた熱電変換材料を製造することができる。 Further, the method for producing an n-type thermoelectric conversion material according to the present invention includes a step of adding carbon nanotubes to a solvent containing the nanowires or nanotubes before the step of accumulating the nanowires or nanotubes in a nonwoven fabric shape. You may go out. According to the said structure, the thermoelectric conversion material in which the said nanowire or the said nanotube is integrated | stacked and formed in the nonwoven fabric shape with the carbon nanotube can be manufactured. The carbon nanotube is preferably a single-walled carbon nanotube as described above. Moreover, when adding the said carbon nanotube, it is preferable to disperse | distribute the said carbon nanotube in a solvent using an ultrasonic wave. According to the said structure, the thermoelectric conversion material in which the said carbon nanotube was contained uniformly can be manufactured.
　本発明は上述した各実施形態に限定されるものではなく、請求項に示した範囲で種々の変更が可能であり、異なる実施形態にそれぞれ開示された技術的手段を適宜組み合わせて得られる実施形態についても本発明の技術的範囲に含まれる。 The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.
　本発明は、以下のように構成することも可能である。 The present invention can also be configured as follows.
　すなわち、本発明に係るｎ型熱電変換材料は、上記の課題を解決するために、ナローギャップ半導体からなるナノワイヤまたはナノチューブが不織布状に集積して形成されていることを特徴としている。 That is, the n-type thermoelectric conversion material according to the present invention is characterized in that nanowires or nanotubes made of a narrow gap semiconductor are integrated and formed in a nonwoven fabric in order to solve the above-described problems.
　上記構成によれば、本発明に係るｎ型熱電変換材料は、ナローギャップ半導体に起因してゼーベック係数の絶対値が大きい。さらに、不織布状構造は多数の空隙を有しているため、熱伝導率が小さい。よって、無次元性能指数ＺＴが大きく、優れた熱電変換特性を示すｎ型熱電変換材料を提供することができる。 According to the above configuration, the n-type thermoelectric conversion material according to the present invention has a large absolute value of the Seebeck coefficient due to the narrow gap semiconductor. Furthermore, since the nonwoven fabric-like structure has a large number of voids, the thermal conductivity is small. Therefore, an n-type thermoelectric conversion material having a large dimensionless figure of merit ZT and exhibiting excellent thermoelectric conversion characteristics can be provided.
　また、本発明に係るｎ型熱電変換材料は、不織布状に成形されているため、柔軟性を有しているとともに軽量である。 Further, since the n-type thermoelectric conversion material according to the present invention is formed into a nonwoven fabric, it has flexibility and is lightweight.
　よって、上記構成によれば、軽量かつ柔軟であるとともに優れた熱電変換特性を備えた熱電変換材料を提供することができる。 Therefore, according to the above configuration, it is possible to provide a thermoelectric conversion material that is lightweight and flexible and has excellent thermoelectric conversion characteristics.
　本発明に係るｎ型熱電変換材料では、上記ナローギャップ半導体は、ＴｅおよびＳｅの少なくとも一方を含んでいる化合物であることが好ましい。 In the n-type thermoelectric conversion material according to the present invention, the narrow gap semiconductor is preferably a compound containing at least one of Te and Se.
　本発明に係るｎ型熱電変換材料では、上記ナローギャップ半導体は、Ｂｉを含んでいる化合物であることが好ましい。 In the n-type thermoelectric conversion material according to the present invention, the narrow gap semiconductor is preferably a compound containing Bi.
　本発明に係るｎ型熱電変換材料では、上記ナローギャップ半導体は、Ｂｉ２Ｔｅ３、Ｂｉ２Ｓｅ３、またはＢｉ２ＳｅｘＴｅ３－ｘであることが好ましい。ただし０＜ｘ＜３とする。 In the n-type thermoelectric conversion material according to the present invention, the narrow gap semiconductor is preferably Bi 2 Te 3 , Bi 2 Se 3 , or Bi 2 Se x Te 3-x . However, 0 <x <3.
　本発明に係るｎ型熱電変換材料では、上記ナノワイヤまたはナノチューブは、カーボンナノチューブとともに不織布状に集積されていてもよい。 In the n-type thermoelectric conversion material according to the present invention, the nanowires or nanotubes may be integrated in a nonwoven fabric together with carbon nanotubes.
　上記の課題を解決するために、本発明に係る熱電変換素子は、本発明に係るｎ型熱電変換材料を含んでいることを特徴としている。 In order to solve the above-described problems, the thermoelectric conversion element according to the present invention is characterized by including the n-type thermoelectric conversion material according to the present invention.
　上記の課題を解決するために、本発明に係るｎ型熱電変換材料の製造方法は、金属酸塩または金属酸化物が溶解している溶媒に対して、金属塩を加え、ナローギャップ半導体からなるナノワイヤまたはナノチューブを形成する工程と、上記ナノワイヤまたは上記ナノチューブを不織布状に集積させる工程と、を含んでいることを特徴としている。 In order to solve the above problems, a method for producing an n-type thermoelectric conversion material according to the present invention comprises a narrow gap semiconductor by adding a metal salt to a solvent in which a metal acid salt or metal oxide is dissolved. The method includes a step of forming nanowires or nanotubes, and a step of accumulating the nanowires or nanotubes in a nonwoven fabric.
　上記構成によれば、上記金属酸塩または上記金属酸化物と上記金属塩との反応産物として、ナローギャップ半導体からなるナノワイヤまたはナノチューブを得ることができる。よって、ゼーベック係数の絶対値が大きいｎ型熱電変換材料を得ることができる。 According to the above configuration, a nanowire or a nanotube made of a narrow gap semiconductor can be obtained as a reaction product of the metal salt or the metal oxide and the metal salt. Therefore, an n-type thermoelectric conversion material having a large absolute value of the Seebeck coefficient can be obtained.
　また、上記構成によれば、上記ナノワイヤまたは上記ナノチューブが不織布状に集積して形成されたｎ型熱電変換材料を得ることができる。よって、不織布状の構造に起因して熱伝導率が小さく、軽量かつ柔軟であるｎ型熱電変換材料を得ることができる。 Further, according to the above configuration, an n-type thermoelectric conversion material formed by accumulating the nanowires or the nanotubes in a nonwoven fabric shape can be obtained. Therefore, it is possible to obtain an n-type thermoelectric conversion material that has a low thermal conductivity and is lightweight and flexible due to the non-woven fabric structure.
　従って、上記構成によれば、軽量かつ柔軟であるとともに優れた熱電変換特性を備えたｎ型熱電変換材料を提供することができる。 Therefore, according to the above configuration, an n-type thermoelectric conversion material that is lightweight and flexible and has excellent thermoelectric conversion characteristics can be provided.
　本発明に係るｎ型熱電変換材料の製造方法では、上記金属酸塩または上記金属酸化物はＴｅまたはＳｅを含んでいることが好ましい。 In the method for producing an n-type thermoelectric conversion material according to the present invention, the metal acid salt or the metal oxide preferably contains Te or Se.
　本発明に係るｎ型熱電変換材料の製造方法では、上記金属塩はＢｉであることが好ましい。 In the method for producing an n-type thermoelectric conversion material according to the present invention, the metal salt is preferably Bi.
　本発明に係るｎ型熱電変換材料の製造方法では、上記金属酸塩は、Ｎａ２Ｏ３Ｔｅ、Ｎａ２Ｏ３Ｓｅ、Ｋａ２Ｏ３Ｔｅ、Ｋａ２Ｏ３Ｓｅ、ＭｇＯ３Ｔｅ、ＭｇＯ３Ｓｅ、ＣａＯ３Ｔｅ、ＣａＯ３Ｓｅ、Ｈ２Ｏ３Ｔｅ、Ｈ２Ｏ３Ｓｅ、Ｈ６ＴｅＯ６またはＨ６ＳｅＯ６であることが好ましい。 In the method for producing an n-type thermoelectric conversion material according to the present invention, the metal acid salt includes Na 2 O 3 Te, Na 2 O 3 Se, Ka 2 O 3 Te, Ka 2 O 3 Se, MgO 3 Te, MgO 3. Se, CaO 3 Te, CaO 3 Se, H 2 O 3 Te, H 2 O 3 Se, H 6 TeO 6 or H 6 SeO 6 are preferred.
　本発明に係るｎ型熱電変換材料の製造方法では、上記金属酸化物は、ＴｅＯ２、ＳｅＯ２、ＴｅＯ３、ＳｅＯ３、Ｔｅ２Ｏ５またはＳｅ２Ｏ５であることが好ましい。 In the method for producing an n-type thermoelectric conversion material according to the present invention, the metal oxide is preferably TeO 2 , SeO 2 , TeO 3 , SeO 3 , Te 2 O 5 or Se 2 O 5 .
　本発明に係るｎ型熱電変換材料の製造方法は、上記ナノワイヤまたはナノチューブを不織布状に集積させる工程の前に、上記ナノワイヤまたはナノチューブを含んでいる溶媒に対してカーボンナノチューブを加える工程を含んでいてもよい。 The method for producing an n-type thermoelectric conversion material according to the present invention includes a step of adding carbon nanotubes to a solvent containing the nanowires or nanotubes before the step of accumulating the nanowires or nanotubes in a nonwoven fabric shape. Also good.
　本発明に係るｎ型熱電変換材料の製造方法は、上記ナノワイヤまたはナノチューブを不織布状に集積させる工程において、上記ナノワイヤまたは上記ナノチューブを含んでいる溶媒を濾過することによって、上記ナノワイヤまたはナノチューブを不織布状に集積させることが好ましい。 In the method for producing an n-type thermoelectric conversion material according to the present invention, in the step of accumulating the nanowires or nanotubes in a nonwoven fabric shape, the nanowires or nanotubes are nonwoven fabric-like by filtering the solvent containing the nanowires or the nanotubes. It is preferable to make it accumulate.
　以下に本発明の実施例を説明するが、本発明の趣旨を逸脱しない限り、本発明はこれら実施例に限定されるものではない。 Examples of the present invention will be described below, but the present invention is not limited to these examples unless departing from the spirit of the present invention.
　〔実施例１および２〕
　＜実施例１＞
　図３に示す製造方法によって、Ｂｉ２Ｔｅ３のナノワイヤを作製した。図３の（ａ）に示すように、５０ｍＬの三つ口フラスコに、３３２．４ｍｇ（１．５ｍｍｏｌ）のＮａ２Ｏ３Ｔｅ、０．５ｇのポリビニルピロリドン、０．３ｇのＮａＯＨおよび１０ｍＬのエチレングリコールを加えて室温で１５分間脱気し、Ｎ２置換した。当該工程にて得られた液を溶液（Ａ）とする。さらに、サンプル管中に４０９．２ｍｇ（１ｍｍｏｌ）のＢｉ（ＮＯ３）３・５Ｈ２Ｏおよび２．５ｍＬのエチレングリコールを加え、超音波照射して十分に溶かした後、Ｎ２置換した。当該工程にて得られた液を溶液（Ｂ）とする。溶液（Ａ）を１６０℃まで昇温し、ヒドラジン一水和物０．５ｍＬを加え１０分間加熱還元した。このとき溶液（Ａ）は薄いオレンジ色から濃青色に変化した。１０分後、溶液（Ｂ）を溶液（Ａ）にインジェクションし、さらに１時間撹拌した。このとき得られた溶液は濃青色から黒色に変化した。溶液（Ａ）と溶液（Ｂ）とを混合して得られた溶液を溶液（Ｃ）とする。１時間後、加熱を止めて室温に戻るまで窒素雰囲気下で溶液（Ｃ）を撹拌した。 [Examples 1 and 2]
<Example 1>
Bi 2 Te 3 nanowires were fabricated by the manufacturing method shown in FIG. As shown in FIG. 3 (a), a 50 mL three-necked flask was charged with 332.4 mg (1.5 mmol) Na 2 O 3 Te, 0.5 g polyvinylpyrrolidone, 0.3 g NaOH and 10 mL ethylene. Glycol was added and degassed for 15 minutes at room temperature, followed by N 2 substitution. Let the liquid obtained at the said process be a solution (A). Further, 409.2 mg (1 mmol) of Bi (NO 3 ) 3 .5H 2 O and 2.5 mL of ethylene glycol were added to the sample tube, and the mixture was sufficiently dissolved by sonication, followed by N 2 substitution. Let the liquid obtained at the said process be a solution (B). The temperature of the solution (A) was raised to 160 ° C., 0.5 mL of hydrazine monohydrate was added, and the mixture was reduced by heating for 10 minutes. At this time, the solution (A) changed from light orange to dark blue. After 10 minutes, the solution (B) was injected into the solution (A) and further stirred for 1 hour. The solution obtained at this time changed from dark blue to black. Let the solution obtained by mixing a solution (A) and a solution (B) be a solution (C). After 1 hour, the solution (C) was stirred under a nitrogen atmosphere until the heating was stopped and the temperature returned to room temperature.
　次に、図３の（ｂ）に示すように、ナノワイヤの精製を行った。室温まで冷ました溶液（Ｃ）を、ヒドラジン一水和物：エタノール＝１：１０の溶液８０ｍＬに加え、３０分間８０℃で加熱撹拌した。３０分後加熱を止め、遠心分離（１００００ｇ，１０ｍｉｎ）を行い、上澄みを除去し、沈殿をエタノールで再分散させた。この遠心分離による余剰な配位子の洗浄を計３回行い、Ｂｉ２Ｔｅ３ナノワイヤを得た。 Next, as shown in FIG. 3B, the nanowire was purified. The solution (C) cooled to room temperature was added to 80 mL of a solution of hydrazine monohydrate: ethanol = 1: 10, and heated and stirred at 80 ° C. for 30 minutes. After 30 minutes, heating was stopped, centrifugation (10000 g, 10 min) was performed, the supernatant was removed, and the precipitate was redispersed with ethanol. The excess ligand was washed by this centrifugation three times in total to obtain Bi 2 Te 3 nanowires.
　得られたＢｉ２Ｔｅ３ナノワイヤをエタノールで分散させ、メンブレンフィルターを用いて吸引濾過を行った。上記メンブレンフィルターの孔の直径０．２μｍであった。上記吸引濾過によって、Ｂｉ２Ｔｅ３ナノワイヤが不織布状に集積した熱電変換材料が得られた。 The obtained Bi 2 Te 3 nanowires were dispersed with ethanol, and suction filtration was performed using a membrane filter. The membrane filter had a pore diameter of 0.2 μm. A thermoelectric conversion material in which Bi 2 Te 3 nanowires were accumulated in a nonwoven fabric was obtained by the suction filtration.
　なお、得られた熱電変換材料は、空気中で容易に酸化され、その熱電性能が損なわれてしまうため、各物性測定前に還元を行った。図４に還元方法を示す。メンブレンフィルター上に付着した熱電変換材料を、ヒドラジン一水和物：エタノール＝１：１０の溶液中で８０℃、３０分間還元し、エタノールで数回洗浄した。このとき、熱電変換材料をメンブレンフィルターからゆっくり丁寧に剥がし、濾紙で挟んでから８０℃で真空乾燥した。熱電変換材料の物性測定を行う前は、必ずこの還元プロセスを行った。 In addition, since the obtained thermoelectric conversion material was easily oxidized in the air and the thermoelectric performance was impaired, it reduced before each physical property measurement. FIG. 4 shows the reduction method. The thermoelectric conversion material attached on the membrane filter was reduced in a solution of hydrazine monohydrate: ethanol = 1: 10 at 80 ° C. for 30 minutes and washed several times with ethanol. At this time, the thermoelectric conversion material was slowly and carefully peeled off from the membrane filter, sandwiched between filter papers, and vacuum-dried at 80 ° C. This reduction process was always performed before measuring the physical properties of the thermoelectric conversion material.
　＜実施例２＞
　図３の（ａ）において、出発物質であるＮａ２Ｏ３Ｔｅを２３９．４ｍｇのＴｅＯ２に置き換えて、Ｂｉ２Ｔｅ３ナノチューブを作製した。ＴｅＯ２を使用すること以外は実施例１と同じ方法を用いて、Ｂｉ２Ｔｅ３ナノチューブが不織布状に集積した熱電変換材料を作製した。 <Example 2>
In FIG. 3A, the starting material Na 2 O 3 Te was replaced with 239.4 mg of TeO 2 to produce Bi 2 Te 3 nanotubes. A thermoelectric conversion material in which Bi 2 Te 3 nanotubes were accumulated in a non-woven fabric was produced using the same method as in Example 1 except that TeO 2 was used.
　＜熱電変換材料の観察＞
　図５の（ａ）は、実施例１において得られたナノワイヤをＳＥＭによって１５０，０００倍にて観察した結果を示しており、図５の（ｂ）は、実施例２において得られたナノチューブをＳＥＭによって１００，０００倍にて観察した結果を示している。ナノワイヤの中心は充填されており、一方、ナノチューブの中心は中空である。 <Observation of thermoelectric conversion materials>
FIG. 5 (a) shows the result of observing the nanowire obtained in Example 1 at 150,000 times by SEM, and FIG. 5 (b) shows the nanotube obtained in Example 2. The result observed by SEM at 100,000 times is shown. The center of the nanowire is filled, while the center of the nanotube is hollow.
　図６の（ａ）は、実施例１において得られた熱電変換材料の外観を示している。また、図６の（ｂ）および（ｃ）は、実施例１において得られた熱電変換材料をＳＥＭによって観察した結果を示している。図６の（ｄ）は、実施例２において得られた熱電変換材料の外観を示している。また、図６の（ｅ）および（ｆ）は、実施例２に得られた熱電変換材料をＳＥＭによって観察した結果を示している。なお、図６の（ｂ）および（ｅ）は、５，０００倍にて観察した結果であり、図６の（ｃ）および（ｆ）は２５，０００倍にて観察した結果である。実施例１および２において得られた熱電変換材料は略円形であり、その直径は、ともに約１６ｍｍであった。実施例１および２のいずれにおいても、得られた熱電変換材料が不織布状の構造を有しており、多数の空隙を有していることがわかる。 (A) of FIG. 6 has shown the external appearance of the thermoelectric conversion material obtained in Example 1. FIG. Moreover, (b) and (c) of FIG. 6 have shown the result of having observed the thermoelectric conversion material obtained in Example 1 by SEM. FIG. 6D shows the appearance of the thermoelectric conversion material obtained in Example 2. Moreover, (e) and (f) of FIG. 6 have shown the result of having observed the thermoelectric conversion material obtained in Example 2 by SEM. In addition, (b) and (e) of FIG. 6 are the results of observation at 5,000 times, and (c) and (f) of FIG. 6 are the results of observation at 25,000 times. The thermoelectric conversion materials obtained in Examples 1 and 2 were substantially circular and both had a diameter of about 16 mm. In any of Examples 1 and 2, it can be seen that the obtained thermoelectric conversion material has a non-woven structure and has a large number of voids.
　＜熱電変換材料の特性＞
　実施例１および２において得られた熱電変換材料に関して、ゼーベック係数、導電率および熱伝導率を測定した。また、得られたゼーベック係数、導電率および熱伝導率からＺＴを求めた。ゼーベック係数はゼーベック効果測定装置（ＭＭＲ社、ＳＢ－１００）を用いて測定した。導電率は４探針法（三菱化学アナリテック、ロレスタＧＰ）を用いて測定した。熱伝導率は熱拡散率・熱伝導率測定装置（ａｉ－Ｐｈａｓｅ　Ｍｏｂｉｌｅ　１ｕ）を用いて測定した。 <Characteristics of thermoelectric conversion material>
For the thermoelectric conversion materials obtained in Examples 1 and 2, Seebeck coefficient, conductivity, and thermal conductivity were measured. Moreover, ZT was calculated | required from the obtained Seebeck coefficient, electrical conductivity, and thermal conductivity. The Seebeck coefficient was measured using a Seebeck effect measuring apparatus (MMR, SB-100). The conductivity was measured using a four-probe method (Mitsubishi Chemical Analytech, Loresta GP). The thermal conductivity was measured using a thermal diffusivity / thermal conductivity measuring device (ai-Phase Mobile 1u).
　図７は、実施例１および２における温度によるゼーベック係数の変化を示す図である。実施例１では、実施例２に比べて、ゼーベック係数の絶対値が約２０％大きかった。例えば、３１０Ｋにおけるゼーベック係数は、実施例１では－１２４μＶ／Ｋ、実施例２では－１０１μＶ／Ｋであった。これらの値は、バルクのＢｉ２Ｔｅ３において示される値（約２００μＶ／Ｋ）と比べても遜色ない値であった。また、ゼーベック係数が負の値であることから、実施例１および２の熱電変換材料はｎ型熱電変換材料であることがわかる。 FIG. 7 is a graph showing changes in Seebeck coefficient with temperature in Examples 1 and 2. In Example 1, compared with Example 2, the absolute value of the Seebeck coefficient was about 20% larger. For example, the Seebeck coefficient at 310 K was −124 μV / K in Example 1, and −101 μV / K in Example 2. These values were comparable to the values shown for bulk Bi 2 Te 3 (about 200 μV / K). Moreover, since the Seebeck coefficient is a negative value, it can be seen that the thermoelectric conversion materials of Examples 1 and 2 are n-type thermoelectric conversion materials.
　図８は、本発明の実施例１および２における温度によるＺＴの変化を示す図である。実施例１のＺＴは、実施例２のＺＴに比べて大きかった。特に実施例１では、３５０Ｋ以上にて０．１を上回るＺＴを示した。具体的には、実施例１では、３１０ＫにおいてＺＴは０．０６、４５０ＫにおいてＺＴは０．１６であった。また、実施例２では、３１０ＫにおいてＺＴは０．０２６、４５０ＫにおいてＺＴは０．０７であった。よって、実施例１および２では、従来の熱電変換材料と同等またはそれ以上のＺＴを示すことがわかった（例えば、非特許文献１に記載のフィルムは３１３ＫにおけるＺＴが０．００６～０．０９）。なお、実施例１の熱電変換材料は、実施例２の熱電変換材料に比べて、より優れた熱電変換特性を示すことがわかった。 FIG. 8 is a diagram showing changes in ZT due to temperature in Examples 1 and 2 of the present invention. The ZT of Example 1 was larger than the ZT of Example 2. In particular, Example 1 showed ZT exceeding 0.1 at 350K or more. Specifically, in Example 1, ZT was 0.06 at 310K, and ZT was 0.16 at 450K. In Example 2, ZT was 0.026 at 310K and ZT was 0.07 at 450K. Therefore, in Examples 1 and 2, it was found that ZT was equal to or higher than that of conventional thermoelectric conversion materials (for example, the film described in Non-Patent Document 1 has a ZT at 313 K of 0.006 to 0.09. ). In addition, it turned out that the thermoelectric conversion material of Example 1 shows the more excellent thermoelectric conversion characteristic compared with the thermoelectric conversion material of Example 2. FIG.
　なお、導電率および熱伝導率の代表的な値を以下に挙げる。実施例１では、３１０Ｋにおける導電率は２９０Ｓ／ｍ、熱伝導率は０．０２３Ｗ／ｍＫであった。また実施例２では、３１０Ｋにおける導電率は２４０Ｓ／ｍ、熱伝導率は０．０２９Ｗ／ｍＫであった。よって、実施例１および２では、従来の熱電変換材料に比べて、より小さい熱伝導率を示すことがわかる（例えば、非特許文献１に記載のフィルムは３１３Ｋにおける熱伝導率が０．２５～０．８０Ｗ／ｍＫ）。このことからも、本発明に係る熱電変換材料が、従来の熱電変換材料に比べて優れた熱電変換特性を有することがわかる。 The typical values of conductivity and thermal conductivity are listed below. In Example 1, the conductivity at 310K was 290 S / m, and the thermal conductivity was 0.023 W / mK. In Example 2, the conductivity at 310K was 240 S / m, and the thermal conductivity was 0.029 W / mK. Therefore, in Examples 1 and 2, it can be seen that the thermal conductivity is smaller than that of the conventional thermoelectric conversion material (for example, the film described in Non-Patent Document 1 has a thermal conductivity of 0.25 to 313K). 0.80 W / mK). This also shows that the thermoelectric conversion material which concerns on this invention has the thermoelectric conversion characteristic excellent compared with the conventional thermoelectric conversion material.
　〔実施例３および４〕
　＜実施例３＞
　メンブレンフィルターを用いて吸引濾過を行う前に、エタノール中に分散したＢｉ２Ｔｅ３ナノワイヤに対し、ＤＭＳＯ中に分散させたＳＷＮＴを加えたこと以外は、実施例１と同様の方法で熱電変換材料を作製した。ＳＷＮＴの含有量は０～１０重量％の間で変化させた。なお、ＳＷＮＴの含有量は、得られた熱電変換材料を１００重量％とした場合の値である。 [Examples 3 and 4]
<Example 3>
A thermoelectric conversion material was prepared in the same manner as in Example 1 except that SWNT dispersed in DMSO was added to Bi 2 Te 3 nanowires dispersed in ethanol before suction filtration using a membrane filter. Was made. The SWNT content was varied between 0 and 10% by weight. In addition, content of SWNT is a value when the obtained thermoelectric conversion material is 100 weight%.
　＜実施例４＞
　メンブレンフィルターを用いて吸引濾過を行う前に、エタノール中に分散したＢｉ２Ｔｅ３ナノチューブに対し、ＤＭＳＯ中に分散させたＳＷＮＴを加えたこと以外は、実施例２と同様の方法で熱電変換材料を作製した。ＳＷＮＴの含有量は０～１０重量％の間で変化させた。なお、ＳＷＮＴの含有量は、得られた熱電変換材料を１００重量％とした場合の値である。 <Example 4>
Thermoelectric conversion material in the same manner as in Example 2 except that SWNT dispersed in DMSO was added to Bi 2 Te 3 nanotubes dispersed in ethanol before suction filtration using a membrane filter. Was made. The SWNT content was varied between 0 and 10% by weight. In addition, content of SWNT is a value when the obtained thermoelectric conversion material is 100 weight%.
　＜熱電変換材料の観察＞
　図９の（ａ）～（ｄ）は、実施例３において得られた熱電変換材料をＳＥＭによって観察した結果を示している。（ａ）はＳＷＮＴを１重量％含んでいる場合、（ｂ）はＳＷＮＴを５重量％含んでいる場合、（ｃ）および（ｄ）はＳＷＮＴを１０重量％含んでいる場合を示す。なお、（ａ）～（ｃ）は３００倍にて観察した結果であり、（ｄ）は１００，０００倍にて観察した結果である。図中の白い部分がＳＷＮＴ、黒い部分がナノワイヤである。 <Observation of thermoelectric conversion materials>
9A to 9D show the results of observing the thermoelectric conversion material obtained in Example 3 with an SEM. (A) shows a case where 1 wt% SWNT is contained, (b) shows a case containing 5 wt% SWNT, and (c) and (d) show a case containing 10 wt% SWNT. Note that (a) to (c) are the results of observation at 300 times, and (d) are the results of observation at 100,000 times. The white part in the figure is SWNT and the black part is nanowire.
　＜熱電変換材料の特性＞
　実施例１および２と同様に、実施例３および４において得られた熱電変換材料に関しても、ゼーベック係数、導電率および熱伝導率を測定した。また、得られたゼーベック係数、導電率および熱伝導率からＺＴを求めた。なお、上記測定において、温度は３１０Ｋに固定した。 <Characteristics of thermoelectric conversion material>
As in Examples 1 and 2, the Seebeck coefficient, conductivity, and thermal conductivity were measured for the thermoelectric conversion materials obtained in Examples 3 and 4. Moreover, ZT was calculated | required from the obtained Seebeck coefficient, electrical conductivity, and thermal conductivity. In the above measurement, the temperature was fixed at 310K.
　図１０は、実施例３および４におけるＳＷＮＴの含有量（ΦＳＷＮＴ）による導電率の変化を示す図である。実施例３および４のいずれにおいても、ＳＷＮＴの含有量を増加させると、導電率が上昇した。 FIG. 10 is a diagram showing a change in conductivity depending on the SWNT content (Φ SWNT ) in Examples 3 and 4. In both Examples 3 and 4, increasing the SWNT content increased the conductivity.
　図１１は、本発明の実施例３および４におけるＳＷＮＴの含有量（ΦＳＷＮＴ）によるＺＴの変化を示す図である。実施例３においては、ＳＷＮＴを含む場合は、ＳＷＮＴを含まない場合に比べてＺＴが減少したが、実施例４においてはＳＷＮＴを含む場合、ＳＷＮＴを含まない場合に比べてＺＴが増加した。いずれにせよ、実施例３および４では、従来の熱電変換材料（例えば、非特許文献１に記載のフィルム）と同等またはそれ以上のＺＴを示した。 FIG. 11 is a graph showing changes in ZT depending on the SWNT content (Φ SWNT ) in Examples 3 and 4 of the present invention. In Example 3, when SWNT was included, ZT decreased compared to the case where SWNT was not included. However, in Example 4, when SWNT was included, ZT increased compared to the case where SWNT was not included. In any case, in Examples 3 and 4, ZT equal to or higher than that of a conventional thermoelectric conversion material (for example, a film described in Non-Patent Document 1) was shown.
　本発明は、例えば環境発電、緊急・災害時用電源、医療電源、小型機器電源、工業廃熱用途に利用することができる。 The present invention can be used for, for example, energy harvesting, emergency / disaster power supplies, medical power supplies, small equipment power supplies, and industrial waste heat applications.
　１　・・・ｎ型熱電変換材料 1 ... n-type thermoelectric conversion material

Claims (13)

  1. 　ナローギャップ半導体からなるナノワイヤまたはナノチューブが不織布状に集積して形成されていることを特徴とするｎ型熱電変換材料。 An n-type thermoelectric conversion material characterized in that nanowires or nanotubes made of a narrow gap semiconductor are integrated in a nonwoven fabric.
  2. 　上記ナローギャップ半導体は、ＴｅおよびＳｅの少なくとも一方を含んでいる化合物であることを特徴とする請求項１に記載のｎ型熱電変換材料。 The n-type thermoelectric conversion material according to claim 1, wherein the narrow gap semiconductor is a compound containing at least one of Te and Se.
  3. 　上記ナローギャップ半導体は、Ｂｉを含んでいる化合物であることを特徴とする請求項１または２に記載のｎ型熱電変換材料。 The n-type thermoelectric conversion material according to claim 1 or 2, wherein the narrow gap semiconductor is a compound containing Bi.
  4. 　上記ナローギャップ半導体は、Ｂｉ２Ｔｅ３、Ｂｉ２Ｓｅ３、またはＢｉ２ＳｅｘＴｅ３－ｘ（０＜ｘ＜３）であることを特徴とする請求項１～３のいずれか１項に記載のｎ型熱電変換材料。 4. The narrow gap semiconductor according to claim 1, wherein the narrow gap semiconductor is Bi 2 Te 3 , Bi 2 Se 3 , or Bi 2 Se x Te 3-x (0 <x <3). The n-type thermoelectric conversion material described.
  5. 　上記ナノワイヤまたは上記ナノチューブは、カーボンナノチューブとともに不織布状に集積されていることを特徴とする請求項１～４のいずれか１項に記載のｎ型熱電変換材料。 5. The n-type thermoelectric conversion material according to claim 1, wherein the nanowires or the nanotubes are accumulated together with carbon nanotubes in a nonwoven fabric shape.
  6. 　請求項１～５のいずれか１項に記載のｎ型熱電変換材料を含んでいることを特徴とする熱電変換素子。 A thermoelectric conversion element comprising the n-type thermoelectric conversion material according to any one of claims 1 to 5.
  7. 　金属酸塩または金属酸化物が溶解している溶媒に対して、金属塩を加え、ナローギャップ半導体からなるナノワイヤまたはナノチューブを形成する工程と、
    　上記ナノワイヤまたは上記ナノチューブを不織布状に集積させる工程と、を含んでいることを特徴とするｎ型熱電変換材料の製造方法。     Adding a metal salt to a solvent in which the metal salt or metal oxide is dissolved to form nanowires or nanotubes made of a narrow gap semiconductor; and
    And a step of accumulating the nanowires or the nanotubes in a non-woven fabric shape, and a method for producing an n-type thermoelectric conversion material.
  8. 　上記金属酸塩または上記金属酸化物はＴｅまたはＳｅを含んでいることを特徴とする請求項７に記載のｎ型熱電変換材料の製造方法。 The method for producing an n-type thermoelectric conversion material according to claim 7, wherein the metal acid salt or the metal oxide contains Te or Se.
  9. 　上記金属塩はＢｉを含んでいることを特徴とする請求項７または８に記載のｎ型熱電変換材料の製造方法。 The method for producing an n-type thermoelectric conversion material according to claim 7 or 8, wherein the metal salt contains Bi.
  10. 　上記金属酸塩は、Ｎａ２Ｏ３Ｔｅ、Ｎａ２Ｏ３Ｓｅ、Ｋａ２Ｏ３Ｔｅ、Ｋａ２Ｏ３Ｓｅ、ＭｇＯ３Ｔｅ、ＭｇＯ３Ｓｅ、ＣａＯ３Ｔｅ、ＣａＯ３Ｓｅ、Ｈ２Ｏ３Ｔｅ、Ｈ２Ｏ３Ｓｅ、Ｈ６ＴｅＯ６またはＨ６ＳｅＯ６であることを特徴とする請求項７～９のいずれか１項に記載のｎ型熱電変換材料の製造方法。 The metal acid salt is Na 2 O 3 Te, Na 2 O 3 Se, Ka 2 O 3 Te, Ka 2 O 3 Se, MgO 3 Te, MgO 3 Se, CaO 3 Te, CaO 3 Se, H 2 O 3 10. The method for producing an n-type thermoelectric conversion material according to claim 7, wherein the method is Te, H 2 O 3 Se, H 6 TeO 6, or H 6 SeO 6 .
  11. 　上記金属酸化物は、ＴｅＯ２、ＳｅＯ２、ＴｅＯ３、ＳｅＯ３、Ｔｅ２Ｏ５またはＳｅ２Ｏ５であることを特徴とする請求項７～９のいずれか１項に記載のｎ型熱電変換材料の製造方法。 10. The n-type thermoelectric according to claim 7, wherein the metal oxide is TeO 2 , SeO 2 , TeO 3 , SeO 3 , Te 2 O 5 or Se 2 O 5. A method for producing a conversion material.
  12. 　上記ナノワイヤまたはナノチューブを不織布状に集積させる工程の前に、上記ナノワイヤまたはナノチューブを含んでいる溶媒に対してカーボンナノチューブを加える工程を含んでいることを特徴とする請求項７～１１のいずれか１項に記載のｎ型熱電変換材料の製造方法。 The method according to any one of claims 7 to 11, further comprising a step of adding carbon nanotubes to a solvent containing the nanowires or nanotubes before the step of accumulating the nanowires or nanotubes in a nonwoven fabric shape. A method for producing the n-type thermoelectric conversion material according to Item.
  13. 　上記ナノワイヤまたはナノチューブを不織布状に集積させる工程において、上記ナノワイヤまたは上記ナノチューブを含んでいる溶媒を濾過することによって、上記ナノワイヤまたはナノチューブを不織布状に集積させることを特徴とする請求項７～１２のいずれか１項に記載のｎ型熱電変換材料の製造方法。 13. The step of accumulating the nanowires or nanotubes in a nonwoven fabric form, wherein the nanowires or nanotubes are accumulated in a nonwoven fabric shape by filtering a solvent containing the nanowires or the nanotubes. The manufacturing method of the n-type thermoelectric conversion material of any one of Claims 1.
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