WO2013108661A1 - Thermoelectric material - Google Patents
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- WO2013108661A1 WO2013108661A1 PCT/JP2013/050097 JP2013050097W WO2013108661A1 WO 2013108661 A1 WO2013108661 A1 WO 2013108661A1 JP 2013050097 W JP2013050097 W JP 2013050097W WO 2013108661 A1 WO2013108661 A1 WO 2013108661A1
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- 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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Definitions
- the present invention relates to a thermoelectric material having good thermoelectric conversion performance even in a temperature region above room temperature.
- Thermoelectric conversion refers to the mutual conversion of thermal energy and electrical energy using the Seebeck effect or Peltier effect. If thermoelectric conversion is used, it is possible to generate an endothermic phenomenon or an exothermic phenomenon by taking out electric power from the heat flow using the Seebeck effect or by passing an electric current through the material using the Peltier effect. Since thermoelectric conversion is direct conversion, no extra waste is discharged during energy conversion, exhaust heat can be used effectively, and there are no moving parts such as motors and turbines, so maintenance is free. It has the advantages such as.
- thermoelectric conversion materials include Bi—Te, Mg—Si, Fe—Si, Si—Ge, Pb—Te, Fe—V—Al, chalcogenide, and skutter.
- thermoelectric materials that can be used in the room temperature range that has been put to practical use, Bi-Te, etc. This is limited to degenerate semiconductors with high mobility.
- a performance index Z (unit K ⁇ 1 ) or a dimensionless performance index ZT is used for performance evaluation of a thermoelectric material (thermoelectric conversion element).
- S represents the Seebeck coefficient
- ⁇ represents electrical conductivity
- ⁇ represents thermal conductivity.
- the dimensionless figure of merit ZT is a value obtained by multiplying the figure of merit Z by the absolute temperature T. The higher the figure of merit Z or the dimensionless figure of merit ZT, the higher the thermoelectric conversion performance. Therefore, in order to obtain good thermoelectric conversion performance, it is most effective that the Seebeck coefficient S and the electrical conductivity ⁇ are high and the thermal conductivity ⁇ is low.
- thermoelectric materials are described in, for example, “Figure ofmerit quaternary (Sb 0.75 Bi 0.25 ) 2-x In x Te 3 single crystals”, C. Drasar, A. Hovorkova, P. Lostak, H. Kong, C.-P. Li, and C. Uher, JOURNAL OF APPLIED PHYSICS 104, 023701, p1-4, 2008 (hereinafter referred to as literature).
- thermoelectric material of this document is represented by (Bi 0.25 Sb 0.75 ) 2-x In x Te 3 , and when the In composition ratio x is 0.03 or 0.05, 0 to 300 K ( ⁇ 273 It is said that the figure of merit Z is improved at a temperature of ⁇ 27 ° C. (FIG. 5 of the literature).
- thermoelectric materials are sometimes used in a temperature range from room temperature (about 20 ° C.) to about 200 ° C. (473 K), a figure of merit in a temperature range of 300 K or higher is also important.
- FIG. 4 As shown in FIG. 4, since the thermal conductivity ⁇ is reduced, it has been found that substituting part of Bi with In is effective for improving the figure of merit Z or the dimensionless figure of merit ZT.
- FIG. 2 when the amount of substitution of In is large, the electrical conductivity ⁇ also tends to decrease, so that the improvement effect of the performance index Z or the dimensionless performance index ZT decreases.
- x is 0.15 ⁇ 0.25
- y is 0.75 ⁇ 0.85
- x + y 1
- z is 0.006 to 0.02
- A is In, Ge, Sn, Al, or Ga. That is, in the Bi—Te-based basic composition represented by Bi 2 Te 3, most of Bi is substituted with Sb, and further, it is slightly substituted with another element A such as In. And by making the substitution amount with Sb and element A within this range, the figure of merit Z or the dimensionless figure of merit ZT can be reliably improved not only below 300K but also in the temperature range of 300K or more, and above room temperature.
- thermoelectric material having good thermoelectric conversion performance.
- element A in the composition formula In is most preferable.
- “A1 to a2” indicating a numerical range means a range including the lower limit and the upper limit. Therefore, it is “a1 or more and a2 or less” when expressed accurately.
- thermoelectric material It is a schematic diagram which shows the crystal structure of a Bi-Te type thermoelectric material. It is a graph which shows the change of thermal conductivity (kappa) and electrical resistance value (rho) accompanying the fluctuation
- thermoelectric material of the present invention is a Bi—Te based semiconductor.
- thermoelectric materials currently in practical use, it has excellent thermoelectric conversion performance in the low temperature range of room temperature (about 20 ° C) to 200 ° C, and has a high performance index Z or dimensionless performance index ZT. Because it can be expected.
- the basic composition of a Bi—Te based semiconductor is Bi2Te3.
- a part of the Bi site is replaced by Sb and other elements.
- the Bi abundance x is greater than 0.15 and the Sb abundance y is less than 0.75, the electrical conductivity ⁇ decreases as the carrier concentration decreases, and the figure of merit Z or dimensionless figure of merit ZT cannot be effectively improved.
- the amount of In is less than 0.006, the effect of reducing the thermal conductivity ⁇ cannot be obtained accurately.
- the amount of In exceeds 0.02, the electric conductivity ⁇ tends to decrease.
- x is preferably 0.15 to 0.2 and y is preferably 0.8 to 0.85.
- z is preferably 0.01 to 0.02.
- In is preferable.
- Bi-Te thermoelectric materials are classified as trigonal, but the unit cell has a crystal structure as shown in FIG. 1 and can be regarded as equivalent to a hexagonal system.
- most of Bi is replaced with Sb, and the Bi / Sb site is further replaced with a small amount of In.
- the carrier concentration of the semiconductor increases, and the decrease in electrical conductivity ⁇ can be suppressed.
- the figure of merit Z or the dimensionless figure of merit ZT of the thermoelectric material can be reliably improved. The reason is not clear, but it is considered that a part of Sb substituting most of Bi enters a Te defect by a small amount of In substitution.
- the Te site may be replaced with other elements such as N, P, As, Sb, Bi, C, Si, Ge, Sn, Pb, B, Al, Ga, or Tl. it can.
- thermoelectric material ingot is obtained by a single crystal method or a melting method. From the viewpoint of productivity, the melting method is preferred. For example, a thermoelectric material ingot alloyed by high-frequency melting, arc melting, or the like after mixing each raw material powder to have a predetermined composition can be obtained. Next, the obtained thermoelectric material ingot is pulverized, classified as necessary, and sintered into a predetermined shape to obtain a nanocomposite thermoelectric material (thermoelectric conversion element).
- the average particle diameter of the thermoelectric material powder is preferably as small as possible. This is because the smaller the particle size of the thermoelectric material powder before sintering, the finer the crystal grain size of the matrix after sintering, which is effective in reducing the thermal conductivity ⁇ .
- the average particle diameter of the thermoelectric material powder before sintering is pulverized to 30 ⁇ m or less, preferably 10 ⁇ m or less, more preferably 5 ⁇ m or less.
- the coarse crushing of the thermoelectric material ingot can be performed by a jaw crusher, a hammer, a stamp mill, a rotor mill, a pin mill, a cutter mill, a coffee mill, a mortar or the like.
- the fine pulverization after the coarse pulverization can be performed by a rotating ball mill, a vibration ball mill, a planetary ball mill, a wet mill, a jet mill or the like.
- a normal pressure sintering method a pressure sintering method, a hot press sintering method, a high temperature isostatic pressing (HIP) sintering method, or the like can be employed.
- HIP high temperature isostatic pressing
- SPS spark plasma sintering
- a powder filled in a hollow cylindrical mold (die) is pressed from above and below by two upper and lower pressing members (punch) in a vacuum environment (inert atmosphere).
- thermoelectric material ingot was coarsely pulverized in a mortar and sintered by SPS at 400 ° C. and 40 MPa for 10 minutes to obtain a nanocomposite thermoelectric material sample.
- the electrical resistance ⁇ , Seebeck coefficient S, carrier concentration n, and thermal conductivity ⁇ of each sample were measured at 30 ° C. (303 K), and the tendency of each physical property depending on the amount of In substitution was examined.
- the electrical resistance ⁇ and Seebeck coefficient S were measured using a thermoelectric property evaluation apparatus (ZEM, manufactured by ULVAC).
- the carrier concentration n was measured using a Hall effect measuring device (Toyo Technica, ResiTest 8300).
- the thermal conductivity ⁇ was measured using a laser flash device (manufactured by ULVAC, TC-7000).
- the value of the carrier concentration n in each sample is shown in Table 1, the tendency of electric resistance ⁇ and thermal conductivity ⁇ is shown in FIG. 2, and the tendency of the obtained dimensionless figure of merit ZT is shown in FIG.
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Abstract
A thermoelectric material represented by the compositional formula (BixSby)2-zAzTe3, wherein x is 0.15 to 0.25, y is 0.75 to 0.85, x+y = 1, z is 0.006 to 0.02, and A is any one of In, Ge, Sn, Al and Ga. In one embodiment, A in the compositional formula is In.
Description
本発明は、室温以上の温度領域においても良好な熱電変換性能を有する熱電材料に関する。
The present invention relates to a thermoelectric material having good thermoelectric conversion performance even in a temperature region above room temperature.
熱電変換とは、ゼーベック効果やペルチェ効果を利用して、熱エネルギーと電気エネルギーとを相互に変換することをいう。熱電変換を利用すれば、ゼーベック効果を用いて熱流から電力を取り出したり、ペルチェ効果を用いて材料に電流を流すことで、吸熱現象や発熱現象を起こしたりすることが可能である。熱電変換は直接変換であるため、エネルギー変換の際に余分な廃棄物を排出しない、排熱の有効利用が可能である、及びモータやタービンなどのような可動部がないためメンテナンスフリーである、などの利点を有している。
Thermoelectric conversion refers to the mutual conversion of thermal energy and electrical energy using the Seebeck effect or Peltier effect. If thermoelectric conversion is used, it is possible to generate an endothermic phenomenon or an exothermic phenomenon by taking out electric power from the heat flow using the Seebeck effect or by passing an electric current through the material using the Peltier effect. Since thermoelectric conversion is direct conversion, no extra waste is discharged during energy conversion, exhaust heat can be used effectively, and there are no moving parts such as motors and turbines, so maintenance is free. It has the advantages such as.
現在では、上記利点を利用して、センサー素子や光素子、ＬＳＩ基板などの半導体回路、レーザダイオード等の精密温度制御が要求される分野や、冷蔵庫、ワインセラー、自動車などにも利用されている。さらに、近年のエネルギー問題や環境問題の重大化に伴い、航空、宇宙、建設、地質及び気象観測、医療衛生、マイクロ電子などの領域や、石油化工、冶金、電力工業における廃熱利用など広範な用途への実用化も期待されている。なお、このような熱電変換用の材料としては、Ｂｉ－Ｔｅ系，Ｍｇ－Ｓｉ系，Ｆｅ－Ｓｉ系，Ｓｉ－Ｇｅ系，Ｐｂ－Ｔｅ系，Ｆｅ－Ｖ－Ａｌ系，カルコゲナイド系，スクッテルダイト系，フィルドスクッテルダイト系，炭化ホウ素系などの半導体やセラミックの開発が進められているが、これまでに実用化されている室温域において使用可能な熱電材料としては、Ｂｉ－Ｔｅ系等のような高移動度の縮退半導体に限られている。
Currently, using the above advantages, it is also used in fields that require precise temperature control such as sensor elements, optical elements, semiconductor circuits such as LSI substrates, laser diodes, refrigerators, wine cellars, automobiles, etc. . In addition, with the recent seriousness of energy and environmental problems, a wide range of areas such as aviation, space, construction, geology and meteorological observation, medical hygiene, microelectronics, and waste heat utilization in the petrochemical, metallurgy, and power industries It is also expected to be put to practical use. Such thermoelectric conversion materials include Bi—Te, Mg—Si, Fe—Si, Si—Ge, Pb—Te, Fe—V—Al, chalcogenide, and skutter. Development of semiconductors and ceramics such as dieto, filled skutterudite, and boron carbide is underway. As thermoelectric materials that can be used in the room temperature range that has been put to practical use, Bi-Te, etc. This is limited to degenerate semiconductors with high mobility.
熱電材料（熱電変換素子）の性能評価には、性能指数Ｚ（単位Ｋ－１）や無次元性能指数ＺＴが使用される。性能指数Ｚは、Ｚ＝Ｓ２σ／κの式により求められる。なお、Ｓはゼーベック係数を、σは電気伝導率を、κは熱伝導率をそれぞれ示す。無次元性能指数ＺＴは、性能指数Ｚに絶対温度Ｔを掛けた値である。性能指数Ｚないし無次元性能指数ＺＴが高いほど、熱電変換性能が高いことになる。そこで、良好な熱電変換性能を得るには、ゼーベック係数Ｓおよび電気伝導率σが高く、且つ熱伝導率κが低いことが最も効果的である。
A performance index Z (unit K −1 ) or a dimensionless performance index ZT is used for performance evaluation of a thermoelectric material (thermoelectric conversion element). The figure of merit Z is determined by the equation Z = S 2 σ / κ. S represents the Seebeck coefficient, σ represents electrical conductivity, and κ represents thermal conductivity. The dimensionless figure of merit ZT is a value obtained by multiplying the figure of merit Z by the absolute temperature T. The higher the figure of merit Z or the dimensionless figure of merit ZT, the higher the thermoelectric conversion performance. Therefore, in order to obtain good thermoelectric conversion performance, it is most effective that the Seebeck coefficient S and the electrical conductivity σ are high and the thermal conductivity κ is low.
Ｂｉ－Ｔｅ系熱電材料の性能指数Ｚないし無次元性能指数ＺＴを向上させるには、Ｂｉ２Ｔｅ３からなる基本組成において、Ｂｉサイトを他の元素で一部置換することが有効であることが知られている。このような熱電材料は、例えば"Figure ofmerit quaternary (Sb0.75Bi0.25)2-xInxTe3single crystals", C. Drasar, A. Hovorkova, P. Lostak, H. Kong, C.-P. Li,and C. Uher, JOURNAL OF APPLIED PHYSICS 104, 023701, p1-4, 2008（以下文献という）にて提案されている。この文献の熱電材料は（Ｂｉ０．２５Ｓｂ０．７５）２－ｘＩｎｘＴｅ３で表され、Ｉｎの組成比ｘが０．０３または０．０５の場合に、０～３００Ｋ（－２７３～２７℃）の温度において性能指数Ｚが向上するとされている（文献のＦＩＧ．５）。
In order to improve the figure of merit Z or the dimensionless figure of merit ZT of a Bi-Te-based thermoelectric material, it is effective to partially substitute Bi sites with other elements in the basic composition composed of Bi 2 Te 3. Are known. Such thermoelectric materials are described in, for example, “Figure ofmerit quaternary (Sb 0.75 Bi 0.25 ) 2-x In x Te 3 single crystals”, C. Drasar, A. Hovorkova, P. Lostak, H. Kong, C.-P. Li, and C. Uher, JOURNAL OF APPLIED PHYSICS 104, 023701, p1-4, 2008 (hereinafter referred to as literature). The thermoelectric material of this document is represented by (Bi 0.25 Sb 0.75 ) 2-x In x Te 3 , and when the In composition ratio x is 0.03 or 0.05, 0 to 300 K (−273 It is said that the figure of merit Z is improved at a temperature of ˜27 ° C. (FIG. 5 of the literature).
上記文献では０～３００Ｋの温度領域における性能指数Ｚの向上効果しか確認されておらず、３００Ｋ以上の温度領域においても良好な性能指数が得られるかは不明である。熱電材料は、室温（約２０℃）域から２００℃（４７３Ｋ）程度の温度範囲において使用されることがあるため、３００Ｋ以上の温度領域における性能指数も重要である。
In the above document, only the improvement effect of the figure of merit Z in the temperature range of 0 to 300K has been confirmed, and it is unclear whether a good figure of merit can be obtained even in the temperature range of 300K or higher. Since thermoelectric materials are sometimes used in a temperature range from room temperature (about 20 ° C.) to about 200 ° C. (473 K), a figure of merit in a temperature range of 300 K or higher is also important.
また、Ｂｉの一部をＩｎで置換すると、同文献のＦＩＧ．４に示されるように熱伝導率κが低減するため、性能指数Ｚないし無次元性能指数ＺＴの向上にはＢｉの一部をＩｎで置換することが有効であることがわかっている。しかし、同文献のＦＩＧ．２に示されるようにＩｎの置換量が多いと、電気伝導率σも低下してしまう傾向があり、したがって性能指数Ｚないし無次元性能指数ＺＴの向上効果が低下してしまう。
Also, if a part of Bi is replaced with In, FIG. As shown in FIG. 4, since the thermal conductivity κ is reduced, it has been found that substituting part of Bi with In is effective for improving the figure of merit Z or the dimensionless figure of merit ZT. However, FIG. As shown in FIG. 2, when the amount of substitution of In is large, the electrical conductivity σ also tends to decrease, so that the improvement effect of the performance index Z or the dimensionless performance index ZT decreases.
本発明のひとつの観点からは、（ＢｉｘＳｂｙ）２－ｚＡｚＴｅ３の組成式で表され、ｘが０．１５～０．２５、ｙが０．７５～０．８５、ｘ＋ｙ＝１、ｚが０．００６～０．０２、ＡがＩｎ，Ｇｅ，Ｓｎ，Ａｌ，又はＧａである熱電材料が得られる。すなわち、Ｂｉ２Ｔｅ３で表されるＢｉ－Ｔｅ系の基本組成において、Ｂｉの大半がＳｂで置換され、そのうえでさらにＩｎなどの他の元素Ａでも僅かに置換されている。そして、Ｓｂ及び元素Ａによる置換量をこの上記範囲とすることで、３００Ｋ未満はもちろん、３００Ｋ以上の温度領域においても確実に性能指数Ｚないし無次元性能指数ＺＴを向上することができ、室温以上においても良好な熱電変換性能を有する熱電材料となる。上記組成式中の元素Ａとしては、Ｉｎが最も好適である。なお数値範囲を示す「ａ１～ａ２」とは、その下限及び上限を含む範囲を意味する。したがって、正確に表せば「ａ１以上ａ２以下」となる。
From one aspect of the present invention, (Bi x Sb y) 2 -z A z expressed by a composition formula of Te 3, x is 0.15 ~ 0.25, y is 0.75 ~ 0.85, x + y = 1, z is 0.006 to 0.02, and A is In, Ge, Sn, Al, or Ga. That is, in the Bi—Te-based basic composition represented by Bi 2 Te 3, most of Bi is substituted with Sb, and further, it is slightly substituted with another element A such as In. And by making the substitution amount with Sb and element A within this range, the figure of merit Z or the dimensionless figure of merit ZT can be reliably improved not only below 300K but also in the temperature range of 300K or more, and above room temperature. Is a thermoelectric material having good thermoelectric conversion performance. As the element A in the composition formula, In is most preferable. “A1 to a2” indicating a numerical range means a range including the lower limit and the upper limit. Therefore, it is “a1 or more and a2 or less” when expressed accurately.
以下に、本発明の実施形態について詳細に説明する。本発明の熱電材料は、Ｂｉ－Ｔｅ系の半導体である。現在実用化されている熱電材料の中でも、室温（約２０℃）～２００℃程度の低温域において優れた熱電変換性能を本来的に有しており、高い性能指数Ｚないし無次元性能指数ＺＴを期待できるからである。
Hereinafter, embodiments of the present invention will be described in detail. The thermoelectric material of the present invention is a Bi—Te based semiconductor. Among the thermoelectric materials currently in practical use, it has excellent thermoelectric conversion performance in the low temperature range of room temperature (about 20 ° C) to 200 ° C, and has a high performance index Z or dimensionless performance index ZT. Because it can be expected.
Ｂｉ－Ｔｅ系半導体の基本組成はＢｉ２Ｔｅ３となるが、本発明ではＢｉサイトの一部をＳｂ及び他の元素によって置換している。具体的には、（ＢｉｘＳｂｙ）２－ｚＡｚＴｅ３の組成式で表され、ここでｘが０．１５～０．２５、ｙが０．７５～０．８５、ｘ＋ｙ＝１、ｚが０．００６～０．０２、ＡがＩｎ，Ｇｅ，Ｓｎ，Ａｌ，又はＧａである。Ｂｉ，Ｓｂ，Ｉｎのうちいずれか１つでもこの範囲を外れていると、良好な熱電変換性能を担保できなくなる。特に、Ｂｉの存在量ｘが０．１５超でＳｂの存在量ｙが０．７５未満であると、キャリア濃度の低下に伴い電気伝導率σが低下して、性能指数Ｚないし無次元性能指数ＺＴを効果的に向上できなくなる。Ｉｎの存在量が０．００６未満では、熱伝導率κの低減効果を的確に得られない。一方、Ｉｎの存在量が０．０２を超えると、電気伝導率σが低下してしまう傾向にある。ｘとｙとの関係は、ｘを０．１５～０．２、且つｙを０．８～０．８５とするのが好ましい。ｚは０．０１～０．０２が好ましい。他の元素Ａとしては、Ｉｎが好ましい。
The basic composition of a Bi—Te based semiconductor is Bi2Te3. In the present invention, a part of the Bi site is replaced by Sb and other elements. Specifically, (Bi x Sb y) 2 -z A z Te is represented by 3 of formula, wherein x is 0.15 ~ 0.25, y is 0.75 ~ 0.85, x + y = 1 , Z is 0.006 to 0.02, and A is In, Ge, Sn, Al, or Ga. If any one of Bi, Sb, and In is out of this range, good thermoelectric conversion performance cannot be ensured. In particular, if the Bi abundance x is greater than 0.15 and the Sb abundance y is less than 0.75, the electrical conductivity σ decreases as the carrier concentration decreases, and the figure of merit Z or dimensionless figure of merit ZT cannot be effectively improved. If the amount of In is less than 0.006, the effect of reducing the thermal conductivity κ cannot be obtained accurately. On the other hand, when the amount of In exceeds 0.02, the electric conductivity σ tends to decrease. As for the relationship between x and y, x is preferably 0.15 to 0.2 and y is preferably 0.8 to 0.85. z is preferably 0.01 to 0.02. As the other element A, In is preferable.
Ｂｉ－Ｔｅ系の熱電材料は三方晶系に分類されるが、単位格子は図１に示すような結晶構造であり、六方晶系と等価とみなせる。そして、本発明ではＢｉの大半をＳｂで置換したうえで、さらに微量のＩｎによってＢｉ／Ｓｂサイトを置換している。これにより、半導体のキャリア濃度が増加し、電気伝導率σの低下を抑制することができる。延いては、熱電材料の性能指数Ｚないし無次元性能指数ＺＴを確実に向上することができる。その理由は定かではないが、微量のＩｎ置換によって、Ｂｉの大半を置換しているＳｂの一部がＴｅの欠陥に進入するためと考えられる。
Bi-Te thermoelectric materials are classified as trigonal, but the unit cell has a crystal structure as shown in FIG. 1 and can be regarded as equivalent to a hexagonal system. In the present invention, most of Bi is replaced with Sb, and the Bi / Sb site is further replaced with a small amount of In. As a result, the carrier concentration of the semiconductor increases, and the decrease in electrical conductivity σ can be suppressed. As a result, the figure of merit Z or the dimensionless figure of merit ZT of the thermoelectric material can be reliably improved. The reason is not clear, but it is considered that a part of Sb substituting most of Bi enters a Te defect by a small amount of In substitution.
なお、この種の熱電材料は、ＴｅサイトをＮ，Ｐ，Ａｓ，Ｓｂ，Ｂｉ，Ｃ，Ｓｉ，Ｇｅ，Ｓｎ，Ｐｂ，Ｂ，Ａｌ，Ｇａ，又はＴｌ等の他の元素によって置換することもできる。
In this type of thermoelectric material, the Te site may be replaced with other elements such as N, P, As, Sb, Bi, C, Si, Ge, Sn, Pb, B, Al, Ga, or Tl. it can.
本発明の熱電材料の製造方法は特に限定されることはなく、従来から公知の方法であればよい。先ず、単結晶法や溶製法などによって熱電材料インゴットを得る。生産性の観点からは、溶製法が好ましい。例えば、各原料粉末を所定の組成となるように混合してから、高周波溶解やアーク溶解などによって合金化された熱電材料インゴットを得ることができる。次いで、得られた熱電材料インゴットを粉砕し、必要に応じて分級してから所定形状に焼結してナノコンポジット化された熱電材料（熱電変換素子）を得ることができる。
The method for producing the thermoelectric material of the present invention is not particularly limited and may be any conventionally known method. First, a thermoelectric material ingot is obtained by a single crystal method or a melting method. From the viewpoint of productivity, the melting method is preferred. For example, a thermoelectric material ingot alloyed by high-frequency melting, arc melting, or the like after mixing each raw material powder to have a predetermined composition can be obtained. Next, the obtained thermoelectric material ingot is pulverized, classified as necessary, and sintered into a predetermined shape to obtain a nanocomposite thermoelectric material (thermoelectric conversion element).
なお、熱電材料粉体を焼結するに際して、熱電材料粉体の平均粒子径はできるだけ小さいことが好ましい。焼結前の熱電材料粉体の粒径が小さいほど、焼結後のマトリックス結晶粒径も微細になることで、熱伝導率κの低減に有効となるからである。具体的には、焼結前の熱電材料粉体の平均粒子径は、３０μｍ以下、好ましくは１０μｍ以下、より好ましくは５μｍ以下に粉砕しておく。また、熱電材料粉体を効率的に微粉末化するためには、微粉砕する前に粗粉砕しておくことが好ましい。熱電材料インゴットの粗粉砕は、ジョークラッシャ、ハンマー、スタンプミル、ロータミル、ピンミル、カッターミル、コーヒーミル，乳鉢などによって行うことができる。粗粉砕後の微粉砕は、回転ボールミル、振動ボールミル、遊星ボールミル、ウェットミル、ジェットミルなどによって行うことができる。
Note that when the thermoelectric material powder is sintered, the average particle diameter of the thermoelectric material powder is preferably as small as possible. This is because the smaller the particle size of the thermoelectric material powder before sintering, the finer the crystal grain size of the matrix after sintering, which is effective in reducing the thermal conductivity κ. Specifically, the average particle diameter of the thermoelectric material powder before sintering is pulverized to 30 μm or less, preferably 10 μm or less, more preferably 5 μm or less. Moreover, in order to efficiently pulverize the thermoelectric material powder, it is preferable to pulverize before pulverizing. The coarse crushing of the thermoelectric material ingot can be performed by a jaw crusher, a hammer, a stamp mill, a rotor mill, a pin mill, a cutter mill, a coffee mill, a mortar or the like. The fine pulverization after the coarse pulverization can be performed by a rotating ball mill, a vibration ball mill, a planetary ball mill, a wet mill, a jet mill or the like.
焼結方法としては、常圧焼結法、加圧焼結法、ホットプレス焼結法、高温等方圧プレス（ＨＩＰ）焼結法などを採用できる。この場合、焼結前に原料粉末を一軸プレス成形、テープ成形法、熱間押し出し法等によって所定形状に成形しておくことも好ましい。また、放電プラズマ焼結（ＳＰＳ）によって焼結することもできる。放電プラズマ焼結とは、真空環境（不活性雰囲気）下において、中空筒状の成形型（ダイス）内に充填された粉体を、上下２つの押圧部材（パンチ）によって上下方向から加圧しながら、当該上下のパンチを電極としてパルス直流電流を流して放電プラズマを発生させることで、粉体内部の渦電流によりジュール熱を生成させ、かつ表面を活性化させることにより、短時間で焼結できる技術である。この場合、従来の焼結法よりも低温度で焼結できる、生産性が高い、焼結体の結晶粒が粗大化し難いなどの特徴がある。なお、熱伝導率κを低減させるためにマトリックス結晶粒を微細化すると、電気伝導率σも低減する傾向にあるので、その場合はホットプレス焼結やＳＰＳが好ましい。これにより、マトリックス結晶粒が配向されて電気伝導率σの低減を抑制できる。
As the sintering method, a normal pressure sintering method, a pressure sintering method, a hot press sintering method, a high temperature isostatic pressing (HIP) sintering method, or the like can be employed. In this case, it is also preferable to form the raw material powder into a predetermined shape by uniaxial press molding, tape molding method, hot extrusion method or the like before sintering. It can also be sintered by spark plasma sintering (SPS). With spark plasma sintering, a powder filled in a hollow cylindrical mold (die) is pressed from above and below by two upper and lower pressing members (punch) in a vacuum environment (inert atmosphere). By generating pulsed DC current using the upper and lower punches as electrodes to generate discharge plasma, Joule heat is generated by eddy current inside the powder and the surface is activated, so that sintering can be performed in a short time. Technology. In this case, there are features such that sintering can be performed at a lower temperature than conventional sintering methods, productivity is high, and crystal grains of the sintered body are difficult to be coarsened. Note that if the matrix crystal grains are refined to reduce the thermal conductivity κ, the electrical conductivity σ also tends to be reduced. In that case, hot press sintering or SPS is preferable. As a result, the matrix crystal grains are oriented, and the reduction in electrical conductivity σ can be suppressed.
Ｂｉ０．３Ｓｂ１．７Ｔｅ３となるようにＢｉ２Ｔｅ３インゴットとＳｂ２Ｔｅ３インゴットを所定量混合し、さらにＩｎが０．００５ｍｏｌ、０．０１ｍｏｌ、０．０２ｍｏｌ、０．０３ｍｏｌ、０．０５ｍｏｌとなるようにそれぞれＩｎ粉末を所定量混合して、電気溶解炉にて合金（熱電材料インゴット）を作製した。次いで、各熱電材料インゴットを乳鉢で粗粉砕し、４００℃、４０ＭＰａで１０分間ＳＰＳにより焼結してナノコンポジット化された熱電材料の試料を得た。
A predetermined amount of Bi 2 Te 3 ingot and Sb 2 Te 3 ingot are mixed so that Bi 0.3 Sb 1.7 Te 3 is obtained, and In is further 0.005 mol, 0.01 mol, 0.02 mol, 0.03 mol, A predetermined amount of each In powder was mixed so as to be 0.05 mol, and an alloy (thermoelectric material ingot) was produced in an electric melting furnace. Next, each thermoelectric material ingot was coarsely pulverized in a mortar and sintered by SPS at 400 ° C. and 40 MPa for 10 minutes to obtain a nanocomposite thermoelectric material sample.
そして、各試料の電気抵抗ρ、ゼーベック係数Ｓ、キャリア濃度ｎ、熱伝導率κを３０℃（３０３Ｋ）にて測定し、Ｉｎ置換量による各物性の傾向を調べた。なお、電気抵抗ρ及びゼーベック係数Ｓは、熱電特性評価装置（アルバック社製、ＺＥＭ）を使用して測定した。キャリア濃度ｎは、ホール効果測定装置（東陽テクニカ社製、ＲｅｓｉＴｅｓｔ８３００）を使用して測定した。熱伝導率κは、レーザーフラッシュ装置（アルバック社製、ＴＣ－７０００）を使用して測定した。各試料におけるキャリア濃度ｎの値を表１に示し、電気抵抗ρ及び熱伝導率κの傾向を図２に示し、求められた無次元性能指数ＺＴの傾向を図３に示す。
Then, the electrical resistance ρ, Seebeck coefficient S, carrier concentration n, and thermal conductivity κ of each sample were measured at 30 ° C. (303 K), and the tendency of each physical property depending on the amount of In substitution was examined. The electrical resistance ρ and Seebeck coefficient S were measured using a thermoelectric property evaluation apparatus (ZEM, manufactured by ULVAC). The carrier concentration n was measured using a Hall effect measuring device (Toyo Technica, ResiTest 8300). The thermal conductivity κ was measured using a laser flash device (manufactured by ULVAC, TC-7000). The value of the carrier concentration n in each sample is shown in Table 1, the tendency of electric resistance ρ and thermal conductivity κ is shown in FIG. 2, and the tendency of the obtained dimensionless figure of merit ZT is shown in FIG.
表１の結果から、Ｉｎの置換量（モル濃度）を増大するにつれて、キャリア濃度が上昇することが確認された。また、図２の結果から、Ｉｎの置換量を増大するにつれて熱伝導率κが低減する反面、電気抵抗ρが上昇、すなわち電気伝導率σが低下することが確認された。そして、図３の結果から、確実に熱電変換性能を向上させるには、Ｉｎの置換量を０．００６～０．０２とすべきことが確認された。
From the results in Table 1, it was confirmed that the carrier concentration increased as the In substitution amount (molar concentration) was increased. From the results of FIG. 2, it was confirmed that the electrical conductivity ρ increased, that is, the electrical conductivity σ decreased, while the thermal conductivity κ decreased as the In substitution amount increased. From the results shown in FIG. 3, it was confirmed that the amount of substitution of In should be 0.006 to 0.02 in order to reliably improve the thermoelectric conversion performance.
Claims (4)
- （ＢｉxＳｂy）2-zＡzＴｅ3の組成式で表され、ｘが０．１５～０．２５、ｙが０．７５～０．８５、ｘ＋ｙ＝１、ｚが０．００６～０．０２であって、ＡがＩｎ，Ｇｅ，Ｓｎ，Ａｌ，Ｇａのいずれかである熱電材料。 (Bi x Sb y) expressed by a composition formula of 2-z A z Te 3, x is 0.15 - 0.25, y is 0.75 ~ 0.85, x + y = 1, z is 0.006 to A thermoelectric material in which A is 0.02, and A is any one of In, Ge, Sn, Al, and Ga.
- 前記組成式中でＡがＩｎである、請求項１に記載の熱電材料。 The thermoelectric material according to claim 1, wherein A is In in the composition formula.
- 前記組成式中でｘが０．１５～０．２、ｙが０．８～０．８５である、請求項１または請求項２に記載の熱電材料。 The thermoelectric material according to claim 1 or 2, wherein x is 0.15 to 0.2 and y is 0.8 to 0.85 in the composition formula.
- 前記組成式中でｚが０．０１～０．０２である、請求項１から請求項３までのいずれか１項に記載の熱電材料。
The thermoelectric material according to any one of claims 1 to 3, wherein z is 0.01 to 0.02 in the composition formula.
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