JP2008305918A - Thermoelectric conversion element and manufacturing method therefor - Google Patents
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- 238000006243 chemical reaction Methods 0.000 title claims abstract description 93
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 12
- 239000000463 material Substances 0.000 claims abstract description 72
- 239000002245 particle Substances 0.000 claims abstract description 36
- 239000002994 raw material Substances 0.000 claims abstract description 11
- 150000003839 salts Chemical class 0.000 claims abstract description 11
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 10
- 238000005245 sintering Methods 0.000 claims abstract description 8
- 238000010438 heat treatment Methods 0.000 claims abstract 2
- 238000000034 method Methods 0.000 claims description 7
- FAPDDOBMIUGHIN-UHFFFAOYSA-K antimony trichloride Chemical compound Cl[Sb](Cl)Cl FAPDDOBMIUGHIN-UHFFFAOYSA-K 0.000 claims description 4
- GVPFVAHMJGGAJG-UHFFFAOYSA-L cobalt dichloride Chemical compound [Cl-].[Cl-].[Co+2] GVPFVAHMJGGAJG-UHFFFAOYSA-L 0.000 claims description 4
- 239000012279 sodium borohydride Substances 0.000 claims description 2
- 229910000033 sodium borohydride Inorganic materials 0.000 claims description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims 1
- JHXKRIRFYBPWGE-UHFFFAOYSA-K bismuth chloride Chemical compound Cl[Bi](Cl)Cl JHXKRIRFYBPWGE-UHFFFAOYSA-K 0.000 claims 1
- 229910052714 tellurium Inorganic materials 0.000 claims 1
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 claims 1
- 230000007423 decrease Effects 0.000 abstract description 8
- 239000013078 crystal Substances 0.000 abstract description 5
- 238000000151 deposition Methods 0.000 abstract description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 12
- 239000000243 solution Substances 0.000 description 12
- 229910018989 CoSb Inorganic materials 0.000 description 5
- 150000002500 ions Chemical class 0.000 description 5
- 230000000694 effects Effects 0.000 description 4
- 239000006227 byproduct Substances 0.000 description 3
- 239000000969 carrier Substances 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- OAKJQQAXSVQMHS-UHFFFAOYSA-N Hydrazine Chemical compound NN OAKJQQAXSVQMHS-UHFFFAOYSA-N 0.000 description 2
- 229910021586 Nickel(II) chloride Inorganic materials 0.000 description 2
- 229910002665 PbTe Inorganic materials 0.000 description 2
- 229910000577 Silicon-germanium Inorganic materials 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 238000003917 TEM image Methods 0.000 description 2
- 230000005611 electricity Effects 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- QMMRZOWCJAIUJA-UHFFFAOYSA-L nickel dichloride Chemical compound Cl[Ni]Cl QMMRZOWCJAIUJA-UHFFFAOYSA-L 0.000 description 2
- OCGWQDWYSQAFTO-UHFFFAOYSA-N tellanylidenelead Chemical compound [Pb]=[Te] OCGWQDWYSQAFTO-UHFFFAOYSA-N 0.000 description 2
- 229910019001 CoSi Inorganic materials 0.000 description 1
- 229910019018 Mg 2 Si Inorganic materials 0.000 description 1
- 229910019021 Mg 2 Sn Inorganic materials 0.000 description 1
- 230000005678 Seebeck effect Effects 0.000 description 1
- 239000012298 atmosphere Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 238000001027 hydrothermal synthesis Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 239000012266 salt solution Substances 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C11/00—Alloys based on lead
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C12/00—Alloys based on antimony or bismuth
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C23/00—Alloys based on magnesium
-
- 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
- H10N10/80—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
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- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Manufacture Of Metal Powder And Suspensions Thereof (AREA)
- Powder Metallurgy (AREA)
Abstract
Description
本発明は、熱を電気に又は電気を熱に変換する熱電変換素子及びその製造方法に関する。 The present invention relates to a thermoelectric conversion element that converts heat into electricity or electricity into heat, and a manufacturing method thereof.
熱電変換材料は、熱エネルギーと電気エネルギーを相互に変換することができる材料であり、熱電冷却素子や熱電発電素子として利用される熱電変換素子を構成する材料である。この熱電変換材料はゼーベック効果を利用して熱電変換を行うものであるが、その熱電変換性能は、性能指数ＺＴと呼ばれる下式（１）で表される。
ＺＴ＝α2σＴ／κ （１）
（上式中、αはゼーベック係数を、σは電気伝導率を、κは熱伝導率を、そしてＴは測定温度を示す）
The thermoelectric conversion material is a material that can mutually convert heat energy and electric energy, and is a material that constitutes a thermoelectric conversion element used as a thermoelectric cooling element or a thermoelectric power generation element. This thermoelectric conversion material performs thermoelectric conversion using the Seebeck effect, and the thermoelectric conversion performance is represented by the following formula (1) called a figure of merit ZT.
ZT = α 2 σT / κ (1)
(Where α is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the measured temperature)
上記式（１）から明らかなように、熱電変換材料の熱電変換性能を高めるためには、用いる材料のゼーベック係数α及び電気伝導率σを大きくし、熱伝導率κを小さくすればよいことがわかる。ここで材料の熱伝導率κを小さくするために、熱電変換材料を微細化することが提案されている（例えば非特許文献１参照）。すなわち、熱電変換材料粒子を微細化することにより、この微細な粒子の界面において熱電変換材料における熱伝導の主要因であるフォノンを散乱させて、熱伝導率κを低減することができる。 As apparent from the above formula (1), in order to improve the thermoelectric conversion performance of the thermoelectric conversion material, it is necessary to increase the Seebeck coefficient α and the electric conductivity σ of the material to be used and to decrease the thermal conductivity κ. Recognize. Here, in order to reduce the thermal conductivity κ of the material, it has been proposed to miniaturize the thermoelectric conversion material (see, for example, Non-Patent Document 1). That is, by miniaturizing the thermoelectric conversion material particles, the phonons that are the main factor of heat conduction in the thermoelectric conversion material can be scattered at the interface between the fine particles, thereby reducing the thermal conductivity κ.
上記開示技術では、熱電変換材料を構成する金属の酸化物を２５０〜３５０℃において熱処理し、さらに３５０〜４５０℃において合金化しているため、最終熱電変換素子における結晶粒の粒径は１５０〜２５０ｎｍと粗大化している。粒子の粒径がこのように粗大化していると、粒界におけるフォノン散乱は不十分であり、熱伝導率低減効果は不十分であると考えられ、性能向上も不十分である。 In the above disclosed technique, the metal oxide constituting the thermoelectric conversion material is heat-treated at 250 to 350 ° C., and further alloyed at 350 to 450 ° C., so the crystal grain size in the final thermoelectric conversion element is 150 to 250 nm. It has become coarse. When the particle size of the particles is thus increased, phonon scattering at the grain boundary is insufficient, the effect of reducing thermal conductivity is considered insufficient, and the performance improvement is also insufficient.
そこで本発明では、上記従来の問題を解決し、優れた性能指数を有する熱電変換素子及びその製造方法を提供することを目的とする。 Therefore, an object of the present invention is to solve the above conventional problems and provide a thermoelectric conversion element having an excellent figure of merit and a method for manufacturing the thermoelectric conversion element.
上記課題を解決するために１番目の発明によれば、熱電変換材料を構成する元素の塩を含む溶液を調製した後、この溶液を、還元剤を含む溶液に滴下して熱電変換材料の原料粒子を析出させ、加熱処理し、次いで焼結する工程を含む、熱電変換熱電素子の製造方法が提供される。 In order to solve the above-mentioned problem, according to the first invention, after preparing a solution containing a salt of an element constituting the thermoelectric conversion material, this solution is dropped into a solution containing a reducing agent, and the raw material of the thermoelectric conversion material There is provided a method for producing a thermoelectric conversion thermoelectric element, comprising the steps of depositing particles, heat-treating, and then sintering.
本発明によれば、熱電変換材料を構成する元素の塩を含む溶液を、還元剤を含む溶液に滴下することにより、平均粒径が１０〜１００ｎｍである熱電変換材料の原料粒子を析出させ、この原料粒子を加熱処理し、焼結することにより、平均粒径が１０〜１００ｎｍである熱電変換材料の結晶粒子からなる熱電変換素子を得ることができ、十分な粒界におけるフォノン散乱を示し、熱伝導率低減を低減させ、性能指数ＺＴを向上させることができる。 According to the present invention, by dropping a solution containing a salt of an element constituting the thermoelectric conversion material into a solution containing a reducing agent, the raw material particles of the thermoelectric conversion material having an average particle size of 10 to 100 nm are precipitated, By heat-treating and sintering the raw material particles, a thermoelectric conversion element composed of crystal particles of a thermoelectric conversion material having an average particle size of 10 to 100 nm can be obtained, and exhibits phonon scattering at a sufficient grain boundary, The reduction in thermal conductivity can be reduced and the figure of merit ZT can be improved.
まず、性能指数ＺＴと熱電変換材料の組織構成との関係について、図１を参照しながら詳細に説明する。図１に示すように、熱電変換材料の組織寸法が、フォノンの平均自由行程の長さを起点にこれよりも小さくなるにつれて、熱電変換材料の熱伝導率κは徐々に減少する。したがって、組織寸法がフォノンの平均自由行程よりも小さくなるように設計すると、性能指数ＺＴが向上する。 First, the relationship between the figure of merit ZT and the structure of the thermoelectric conversion material will be described in detail with reference to FIG. As shown in FIG. 1, the thermal conductivity κ of the thermoelectric conversion material gradually decreases as the structure size of the thermoelectric conversion material becomes smaller than the starting length of the phonon mean free path. Therefore, the figure of merit ZT is improved when the structure size is designed to be smaller than the mean free path of phonons.
一方、熱電変換材料の組織寸法がフォノンの平均自由行程を起点にこれより小さくなっても、熱電変換材料の電気伝導率σは減少せず、概ねキャリアの平均自由行程以下の粒径となった場合に減少する。このように、熱伝導率κが減少し始める熱電変換材料の組織寸法と、電気伝導率σが減少し始める熱電変換材料の組織寸法とが異なることを利用し、電気伝導性の減少率よりも熱伝導率κの減少率が大きい熱電変換材料の組織寸法となるように、熱電変換材料の少なくとも一部の組織寸法をキャリアの平均自由行程以上フォノンの平均自由行程以下とすることで、上記式（１）で表される性能指数ＺＴをよりいっそう高めることができる。 On the other hand, even if the structure size of the thermoelectric conversion material is smaller than the average free path of phonons, the electrical conductivity σ of the thermoelectric conversion material does not decrease, and the particle size is generally less than the average free path of carriers. Decrease in case. Thus, using the fact that the structural dimension of the thermoelectric conversion material where the thermal conductivity κ begins to decrease and the structural dimension of the thermoelectric conversion material where the electrical conductivity σ begins to decrease are different from each other, By setting the structure size of at least a part of the thermoelectric conversion material to be equal to or more than the average free path of carriers and equal to or less than the average free path of phonons so that the structure size of the thermoelectric conversion material has a large reduction rate of the thermal conductivity κ The figure of merit ZT represented by (1) can be further increased.
ここで、熱電変換材料の組織寸法を規定するのは、熱電変換材料を構成する粒子の粒径である。そこで、本発明の方法によれば、熱電変換材料を構成する粒子の少なくとも一部の粒径を熱電変換材料のフォノンの平均自由行程以下としている。熱電変換材料を構成する粒子の粒径を熱電変換材料のフォノンの平均自由行程以下とすることで、粒界におけるフォノン散乱を示し、熱伝導率低減を低減させ、性能指数ＺＴを向上させることができる。 Here, it is the particle size of the particles constituting the thermoelectric conversion material that defines the tissue size of the thermoelectric conversion material. Therefore, according to the method of the present invention, the particle size of at least a part of the particles constituting the thermoelectric conversion material is set to be equal to or less than the mean free path of phonons of the thermoelectric conversion material. By setting the particle size of the particles constituting the thermoelectric conversion material to be equal to or less than the mean free path of phonons of the thermoelectric conversion material, phonon scattering at the grain boundary can be shown, thermal conductivity reduction can be reduced, and the figure of merit ZT can be improved. it can.
平均自由行程（ＭＦＰ）は、以下の式を用いて計算される。
キャリアＭＦＰ＝（移動度×有効質量×キャリア速度）／電荷素量
フォノンＭＦＰ＝３×格子熱伝導率／比熱／音速
上式において、各々の値は文献値と温度特性の近似式から換算し、比熱のみ実測値を用いる。
The mean free path (MFP) is calculated using the following formula:
Carrier MFP = (mobility × effective mass × carrier velocity) / elementary charge phonon MFP = 3 × lattice thermal conductivity / specific heat / sound velocity In the above equation, each value is converted from the literature value and the approximate equation of the temperature characteristic, Only measured values are used for specific heat.
ここで、Ｃｏ0.94Ｎｉ0.06Ｓｂ3及びＣｏＳｂ3について計算したキャリアＭＦＰとフォノンＭＦＰの結果を以下に示す。 Here, the results of the carrier MFP and the phonon MFP calculated for Co 0.94 Ni 0.06 Sb 3 and CoSb 3 are shown below.
このように、キャリアＭＦＰ及びフォノンＭＦＰは材料及び温度によってきまる。本発明によって得られる熱電変換素子においては、少なくとも一部の組織寸法が、熱電変換材料のパワーファクター（α2σ）が最高出力時のフォノンの平均自由行程以下であればよい。ＣｏＳｂ3系は４００℃においてパワーファクター（α2σ）が最高出力を示すので、４００℃時のフォノンの平均自由行程以下であればよい。 As described above, the carrier MFP and the phonon MFP are determined by the material and the temperature. In the thermoelectric conversion element obtained by the present invention, it is sufficient that at least some of the structural dimensions are equal to or less than the phonon mean free path at the time when the power factor (α 2 σ) of the thermoelectric conversion material is the maximum output. Since the power factor (α 2 σ) shows the maximum output at 400 ° C. in the CoSb 3 system, it may be equal to or less than the phonon mean free path at 400 ° C.
このような熱電変換素子を製造するため、本発明においては、まず熱電変換材料を構成する元素の塩を含む溶液を調製する。 In order to produce such a thermoelectric conversion element, in the present invention, first, a solution containing a salt of an element constituting the thermoelectric conversion material is prepared.
形成しようとする熱電変換材料はＰ型であってもＮ型であってもよい。Ｐ型熱電変換材料の材質としては特に制限なく、例えば、Ｂｉ2Ｔｅ3系、ＰｂＴｅ系、Ｚｎ4Ｓｂ3系、ＣｏＳｂ3系、ハーフホイスラー系、フルホイスラー系、ＳｉＧｅ系などを用いることができる。Ｎ型熱電変換材料の材質としても特に制限なく公知の材料を適用することができ、例えば、Ｂｉ2Ｔｅ3系、ＰｂＴｅ系、Ｚｎ4Ｓｂ3系、ＣｏＳｂ3系、ハーフホイスラー系、フルホイスラー系、ＳｉＧｅ系、Ｍｇ2Ｓｉ系、Ｍｇ2Ｓｎ系、ＣｏＳｉ系などを用いることができる。 The thermoelectric conversion material to be formed may be P-type or N-type. The material of the P-type thermoelectric conversion material is not particularly limited, and for example, Bi 2 Te 3 system, PbTe system, Zn 4 Sb 3 system, CoSb 3 system, half-Heusler system, full Heusler system, SiGe system, etc. can be used. . As the material of the N-type thermoelectric conversion material, a known material can be applied without particular limitation. For example, Bi 2 Te 3 system, PbTe system, Zn 4 Sb 3 system, CoSb 3 system, half-Heusler system, full Heusler system SiGe, Mg 2 Si, Mg 2 Sn, CoSi, or the like can be used.
本発明において形成する熱電変換材料は、出力因子が１ｍＷ／Ｋ2よりも大きいことが好ましく、２ｍＷ／Ｋ2以上であることがより好ましく、３ｍＷ／Ｋ2以上であることが更に好ましい。出力因子が１ｍＷ／Ｋ2以下の場合には、あまり大きな性能向上が期待できない。また、熱電変換材料の熱伝導率κは、５Ｗ／ｍＫよりも大きいことが好ましく、７Ｗ／ｍＫ以上であることがより好ましく、１０Ｗ／ｍＫ以上であることが更に好ましい。熱伝導率κが５Ｗ／ｍＫよりも大きい場合に、特に本発明の効果が著しく呈される。つまり、熱電変換材料の組織寸法について本発明に規定するナノオーダーで制御を行った場合の効果は、熱伝導率κが大きい熱電変換材料を用いるほど熱伝導率κの低下が著しくなる傾向にあり、特に熱伝導率κが５Ｗ／ｍＫよりも大きい熱電変換材料を用いた場合に、熱伝導率κの減少効果が大きく現れる。 Thermoelectric conversion material forming the present invention, it is preferable power factor is greater than 1 mW / K 2, more preferably 2 mW / K 2 or more, more preferably 3 mW / K 2 or more. When the output factor is 1 mW / K 2 or less, a great performance improvement cannot be expected. Further, the thermal conductivity κ of the thermoelectric conversion material is preferably larger than 5 W / mK, more preferably 7 W / mK or more, and further preferably 10 W / mK or more. When the thermal conductivity κ is larger than 5 W / mK, the effect of the present invention is particularly remarkable. In other words, the effect of controlling the microstructure dimensions of the thermoelectric conversion material at the nano-order specified in the present invention tends to decrease the thermal conductivity κ more significantly as the thermoelectric conversion material having a higher thermal conductivity κ is used. In particular, when a thermoelectric conversion material having a thermal conductivity κ greater than 5 W / mK is used, the effect of reducing the thermal conductivity κ is significant.
このような熱電変換材料を構成する元素の塩は例えば、熱電変換材料がＣｏＳｂ3の場合には、塩化コバルトの水和物及び塩化アンチモンを、Ｃｏ1-xＮｉxＳｂ3の場合には、塩化コバルトの水和物、塩化ニッケル及び塩化アンチモンを意味する。そして形成しようとする熱電変換材料の組成を考慮して、用いる熱電変換材料を構成する元素の塩およびその量を選択する。 For example, when the thermoelectric conversion material is CoSb 3 , the salt of an element constituting such a thermoelectric conversion material is a hydrate of cobalt chloride and antimony chloride, and in the case of Co 1-x Ni x Sb 3 , It means hydrated cobalt chloride, nickel chloride and antimony chloride. Then, in consideration of the composition of the thermoelectric conversion material to be formed, the salt of the element constituting the thermoelectric conversion material to be used and the amount thereof are selected.
上記熱電変換材料を構成する元素の塩の溶液の溶媒としては水又はアルコールを用いることができ、エタノールを用いることが好適である。 Water or alcohol can be used as the solvent of the salt solution of the elements constituting the thermoelectric conversion material, and ethanol is preferably used.
こうして上記熱電変換材料を構成する元素の塩の溶液を調製した後、還元剤を含む溶液にこの分散液を滴下する。還元剤としては、熱電変換材料を構成する元素のイオンを還元できるものであればよく、例えばＮａＢＨ4、ヒドラジン等を用いることができる。 Thus, after preparing the solution of the salt of the element which comprises the said thermoelectric conversion material, this dispersion liquid is dripped at the solution containing a reducing agent. The reducing agent may be used as long as it can reduce ions of elements constituting the thermoelectric conversion material may be, for example, NaBH 4, hydrazine and the like.
熱電変換材料を構成する元素の塩を含む分散液中には熱電変換材料の原料イオン、例えばＣｏイオンやＳｂイオンが存在する。従って、還元剤を含む溶液と混合されると、これらのイオンは還元され、熱電変換材料の原料粒子、例えばＣｏ粒子やＳｂ粒子が析出することになる。この還元において、Ｃｏ粒子やＳｂ粒子の他に、副生物、例えばＮａＣｌとＮａＢＯ3が生成する。この副生物を除去するために、濾過を行うことが好ましい。さらに、濾過後、アルコールや水を加えて、副生物を洗い流すことが好適である。 In the dispersion containing the salt of the element constituting the thermoelectric conversion material, raw material ions of the thermoelectric conversion material, such as Co ions and Sb ions, are present. Therefore, when mixed with a solution containing a reducing agent, these ions are reduced, and raw material particles of the thermoelectric conversion material, such as Co particles and Sb particles, are precipitated. In this reduction, in addition to Co particles and Sb particles, by-products such as NaCl and NaBO 3 are generated. Filtration is preferably performed to remove this by-product. Furthermore, after filtration, it is preferable to add alcohol or water to wash away by-products.
次いでこの分散液を加熱処理し、好ましくは水熱処理し、熱電変換材料の原料粒子から熱電変換材料粒子を合成し、必要に応じて洗浄・乾燥した後、一般的な焼結法により、例えば５８０℃においてＳＰＳ焼結することにより、本発明の熱電変換素子が得られる。 The dispersion is then heat-treated, preferably hydrothermally treated, and thermoelectric conversion material particles are synthesized from the raw material particles of the thermoelectric conversion material, washed and dried as necessary, and then subjected to a general sintering method, for example, 580 The thermoelectric conversion element of the present invention can be obtained by performing SPS sintering at ° C.
本発明の熱電変換材料の製造方法は、ナノオーダーでの組織寸法（熱電変換材料粒子の粒径）の制御を可能とするものである。すなわち、熱電変換材料を構成する元素の塩を還元することにより、粒径が１０〜１００ｎｍである熱電変換材料の原料粒子を形成し、これから熱電変換材料粒子を調製することにより、熱電変換素子の組織寸法（熱電変換材料粒子の粒径）が、フォノンの平均自由行程以下、好ましくはキャリアの平均自由行程以上フォノンの平均自由行程以下となり、熱電変換素子中のフォノンの散乱が充分に起こり、熱伝導率κを減少させることができる。この結果、式（１）で表される性能指数ＺＴが大きい熱電変換素子となる。このように、本発明の熱電変換素子の製造方法によれば、高い性能指数ＺＴを示す優れた熱電変換素子であって、従来では作製困難であった性能指数ＺＴが２を上回るような熱電変換素子を得ることもできる。 The method for producing a thermoelectric conversion material of the present invention enables control of the tissue size (particle diameter of thermoelectric conversion material particles) on the nano order. That is, by reducing the salt of the element constituting the thermoelectric conversion material, raw material particles of the thermoelectric conversion material having a particle size of 10 to 100 nm are formed, and by preparing thermoelectric conversion material particles therefrom, the thermoelectric conversion element The structure size (particle diameter of the thermoelectric conversion material particles) is not more than the mean free path of phonons, preferably more than the mean free path of carriers and not more than the mean free path of phonons, and sufficient phonon scattering occurs in the thermoelectric conversion element. Conductivity κ can be reduced. As a result, a thermoelectric conversion element having a large figure of merit ZT represented by the formula (1) is obtained. Thus, according to the method for manufacturing a thermoelectric conversion element of the present invention, an excellent thermoelectric conversion element exhibiting a high figure of merit ZT, which has a figure of merit ZT exceeding 2 that has been difficult to produce in the past. An element can also be obtained.
塩化コバルト１．０ｇ及び塩化アンチモン３．０６ｇをエタノール１００ｍＬに加え、溶解させた後、この溶液に塩化ニッケル０．０６４ｇを加え、均一に混合した。この溶液を、水素化ホウ素ナトリウム２．０ｇをエタノール１００ｍＬに溶解させて調製した還元剤溶液に滴下した。次いで、エタノールと水の混合溶液で洗浄することによって不純物を除去した後、２００℃にて４８時間水熱合成を行い、熱電変換材料であるＣｏ0.94Ｎｉ0.06Ｓｂ6化合物を形成した。 After adding 1.0 g of cobalt chloride and 3.06 g of antimony chloride to 100 mL of ethanol and dissolving, 0.064 g of nickel chloride was added to this solution and mixed uniformly. This solution was added dropwise to a reducing agent solution prepared by dissolving 2.0 g of sodium borohydride in 100 mL of ethanol. Next, after removing impurities by washing with a mixed solution of ethanol and water, hydrothermal synthesis was performed at 200 ° C. for 48 hours to form a Co 0.94 Ni 0.06 Sb 6 compound as a thermoelectric conversion material.
その後、不活性ガス雰囲気中でエタノールを蒸発させ、乾燥し、得られた粒子を充填し、６００℃で３０分ＳＰＳ焼結を行い、本発明の熱電変換素子を得た。この素子のＴＥＭ像を図２に示すが、結晶粒サイズは１０〜１００ｎｍであった。この熱電変換素子の熱伝導率をフラッシュ法により測定したところ、１．５Ｗ／ｍ／Ｋであり、従来品（結晶粒サイズ：１５０〜２５０ｎｍ、熱伝導率：３．５Ｗ／ｍ／Ｋ）より６０％低減していた。 Thereafter, ethanol was evaporated in an inert gas atmosphere, dried, the obtained particles were filled, and SPS sintering was performed at 600 ° C. for 30 minutes to obtain the thermoelectric conversion element of the present invention. A TEM image of this device is shown in FIG. 2, and the crystal grain size was 10 to 100 nm. When the thermal conductivity of this thermoelectric conversion element was measured by the flash method, it was 1.5 W / m / K, which is higher than that of the conventional product (crystal grain size: 150 to 250 nm, thermal conductivity: 3.5 W / m / K). It was reduced by 60%.
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