WO2016002061A1 - Thermoelectric conversion material, thermoelectric conversion element, thermoelectric conversion module, and method for manufacturing thermoelectric conversion material - Google Patents

Thermoelectric conversion material, thermoelectric conversion element, thermoelectric conversion module, and method for manufacturing thermoelectric conversion material Download PDF

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WO2016002061A1
WO2016002061A1 PCT/JP2014/067855 JP2014067855W WO2016002061A1 WO 2016002061 A1 WO2016002061 A1 WO 2016002061A1 JP 2014067855 W JP2014067855 W JP 2014067855W WO 2016002061 A1 WO2016002061 A1 WO 2016002061A1
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thermoelectric conversion
conversion material
phase
particles
interface
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PCT/JP2014/067855
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French (fr)
Japanese (ja)
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拓也 青柳
内藤　孝
一宗 児玉
正 藤枝
高橋　研
大郊 高松
尚平 寺田
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株式会社日立製作所
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/34—Sputtering
    • 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
    • H10N10/855—Thermoelectric active materials comprising inorganic compositions comprising compounds containing boron, carbon, oxygen or nitrogen
    • 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
    • H10N10/857—Thermoelectric active materials comprising compositions changing continuously or discontinuously inside the material

Definitions

  • the present invention relates to a thermoelectric conversion material, a thermoelectric conversion element, a thermoelectric conversion module, and a method for manufacturing a thermoelectric conversion material.
  • thermoelectric conversion material is based on the Seebeck effect in which a voltage is generated when two kinds of substances are joined to cause a temperature difference between both ends. So far, thermoelectric conversion materials made of Bi 2 Te 3 and the like have been developed and put into practical use. However, the inclusion of rare metals and toxic metals and low conversion efficiency are problems for diffusion.
  • thermoelectric conversion material As an approach for improving the conversion efficiency, it has been theoretically shown that the conversion efficiency is improved by making the thermoelectric conversion material nano-sized as compared with the bulk thermoelectric conversion material.
  • figure of merit Z generally used as an index of the thermoelectric conversion material is defined by the following formula (1).
  • the thermal conductivity ⁇ is reduced by effectively scattering phonons by nano-sizing.
  • the Seebeck coefficient S is improved by changing the density of states due to the quantum effect that appears when the thermoelectric conversion material is reduced to the quantum size.
  • the latter is expected to be particularly effective for improving performance, but the characteristics also change depending on the dimensionality of the thermoelectric conversion material. For example, it is predicted that characteristics are improved in a one-dimensional material (nanowire) than in a two-dimensional material (superlattice thin film).
  • thermoelectric conversion material in which a glass member is filled with a thermoelectric conversion material and then drawn into a nanowire is disclosed (see Patent Document 1).
  • thermoelectric conversion material described in Patent Document 1 has room for improvement in conversion efficiency.
  • an object of the present invention is made in view of the above problems, and is to provide a nanocomposite thermoelectric conversion material having excellent conversion efficiency.
  • thermoelectric conversion material having excellent conversion efficiency
  • thermoelectric conversion material which concerns on embodiment of this invention. It is a schematic diagram of an example of the nanocomposite thermoelectric conversion material which concerns on embodiment of this invention. It is a schematic diagram of an example of the nanocomposite thermoelectric conversion material which concerns on embodiment of this invention. It is a schematic diagram of an example of the nanocomposite thermoelectric conversion element which concerns on embodiment of this invention.
  • 1 is an example of a structure of a ⁇ -type thermoelectric conversion module according to an embodiment of the present invention. It is a TEM image of the nanocomposite thermoelectric conversion material which concerns on embodiment of this invention. It is an AFM image (phase difference mapping figure) of the nanocomposite thermoelectric conversion material concerning the embodiment of the present invention. It is a cross-sectional structure of the nanocomposite thermoelectric conversion material which concerns on embodiment of this invention. It is a STEM (ZC) image of the nanocomposite thermoelectric conversion material which concerns on embodiment of this invention.
  • thermoelectric conversion material 100 has at least two phases, ie, a first phase that forms particles and a second phase that surrounds the interface of the particles, and these are combined in a nano size (several nm to several tens of nm). It is a composite thermoelectric conversion material.
  • the melting point of the second phase surrounding the interface is lower than the melting point of the first phase forming the particles.
  • the first phase that forms the particles and the second phase that surrounds the interface of the particles are either the thermoelectric conversion phase 101 or the barrier phase 102.
  • the barrier phase 102 means a phase that has a higher electrical resistance than the thermoelectric conversion phase 101 and serves as a barrier that hinders the movement of electrons.
  • FIG. 1 shows a schematic diagram of the nanocomposite thermoelectric conversion material 100 when the melting point of the thermoelectric conversion phase 101 is higher than that of the barrier phase 102.
  • a plurality of thermoelectric conversion phases 101 forming columnar crystals are spread in a direction perpendicular to the major axis direction, and a barrier phase 102 is provided between the wall surfaces of the columnar crystals to form a thin-film thermoelectric conversion material 100.
  • the barrier phase 102 exists between the thermoelectric conversion phases 101, when using as a thermoelectric conversion material, it is necessary to form a temperature difference in the vertical direction (long axis direction of the columnar crystal) as shown in the figure. There is.
  • FIG. 2 shows a schematic diagram of the nanocomposite thermoelectric conversion material 100 when the melting point of the thermoelectric conversion phase 101 is lower than that of the barrier phase 102.
  • the thermoelectric conversion phase 101 forms an interface phase surrounding the columnar crystal. Therefore, when used as a thermoelectric conversion material, in addition to the temperature difference in the vertical direction as in FIG. 1, the thermoelectric conversion material can be used regardless of whether the temperature difference is formed in either the left-right direction (the minor axis direction of the columnar crystal) It is possible to use.
  • FIGS. 1 and 2 The structure of FIGS. 1 and 2 is illustrated such that the columnar crystals extend linearly in the vertical direction for convenience, but in this embodiment, the first phase forming the particles has a temperature gradient. It suffices to leave two areas necessary for the second phase and surround the interface with the second phase except for the two areas. Even if the first phase and the second phase are not linear and have an intricate structure, the same effect can be exhibited.
  • thermoelectric conversion phase 101 and the barrier phase 102 are composited with a size of 10 nm or less.
  • the quantum size effect is easily exhibited when the particle size in the direction in which the temperature difference occurs when used as the thermoelectric conversion material is 10 nm or less, and the second phase surrounding the particle interface.
  • the thickness of the second phase between the first phase and the first phase is 10 nm or less, whereby the quantum size effect is easily exhibited and the Seebeck coefficient can be improved.
  • the material forming the barrier phase 102 is desirably amorphous. This is because it becomes easy to scatter phonons by becoming amorphous, and thermal conductivity can be lowered.
  • a phase separation phenomenon As a result, a nano-sized composite thermoelectric conversion material can be produced, and the size can be controlled to a size of 10 nm or less by adjusting the composition, heat treatment conditions, and the like.
  • thermoelectric conversion material of this embodiment It is desirable to use a sputtering method as a method for manufacturing the thermoelectric conversion material of this embodiment.
  • a sputtering method By simultaneously sputtering the target including the element group forming the first phase and the target including the element group forming the second phase, a phase separation phenomenon occurs, and the thermoelectric conversion material of this embodiment can be manufactured. .
  • the first phase and the second homology are not mixed with each other.
  • a structure is formed by a worker.
  • the presence of the second phase surrounding the grain boundary of the first phase suppresses the crystal growth of the first phase in the in-plane direction of the thin film. Thus, it is possible to grow upward (long axis direction) while maintaining a substantially constant area.
  • thermoelectric conversion phase 101 for example, a material having generally good characteristics as a thermoelectric conversion material such as Bi, Bi 2 Te 3 , PbTe, NaCoO 2 , Ca 3 Co 4 O 9 , Si, or SiGe can be used.
  • a material having generally good characteristics as a thermoelectric conversion material such as Bi, Bi 2 Te 3 , PbTe, NaCoO 2 , Ca 3 Co 4 O 9 , Si, or SiGe can be used.
  • Bi has a long Fermi wavelength, so that it is easy to obtain the quantum size effect, and the effect obtained when nano-sized is large.
  • This Bi is preferably doped with a minute amount of Te, Sb or the like in order to control the carrier concentration.
  • the barrier phase 102 is not particularly limited as long as it has a higher electrical resistance than the thermoelectric conversion phase 101 and does not form a solid solution with the thermoelectric conversion phase 101.
  • An oxide is preferable because amorphization can be promoted by using a network forming compound such as silicon, phosphorus, germanium, or boron.
  • a network forming compound such as silicon, phosphorus, germanium, or boron.
  • the glass transition temperature at which the bonds between elements begin to break can be used as an index for changing the melting point.
  • FIG. 3 shows an example of a thermoelectric conversion element 300 using the thermoelectric conversion material 100 of the present embodiment.
  • a thermoelectric conversion element When used as a thermoelectric conversion element, it is necessary to form a temperature difference, so that a width of at least several tens of ⁇ m to several mm is required in the temperature difference direction. Since it takes time to reach a sufficient thickness, the thermoelectric conversion material 100 of this embodiment formed by the sputtering method forms a temperature difference in the vertical direction in the structure shown in FIGS.
  • a metal film 301 may be formed between the thermoelectric conversion materials 100 and stacked as shown in FIG. Thereby, disorder of crystal orientation etc. can also be corrected.
  • FIG. 4 shows an example of a ⁇ -type thermoelectric conversion module 400 manufactured using the thermoelectric conversion material of the present embodiment.
  • the thermoelectric conversion module 400 is a device that can generate a heat generating part and a heat absorbing part by taking out electricity using a temperature difference between a high temperature part and a low temperature part, or by flowing electricity.
  • the thermoelectric conversion module 400 is formed by joining P-type and N-type thermoelectric conversion elements 300 to upper and lower extraction electrodes 401 formed on an insulating substrate 402.
  • a temperature difference can be formed by attaching one side of the insulating substrate to a heat source or the like and water-cooling or air-cooling the one side to generate electric power.
  • the structure of the thermoelectric conversion module is not particularly limited to this, and various forms are conceivable.
  • Table 1 shows the studied target compositions.
  • the production of the Co 3 O 4 thermoelectric conversion material was performed under the following conditions using an RF magnetron sputtering method.
  • a mixed film having a target composition shown in Table 1 was formed to a thickness of about 1 ⁇ m.
  • the sputtering conditions were an Ar flow rate: 40 sccm, an O 2 flow rate: 10 sccm, a discharge pressure of 0.7 Pa, and an input power of 1 kW using an RF power source.
  • the film formation was performed at 300 ° C.
  • FIG. 5 shows a TEM image when A-7 is observed from the upper surface as an example.
  • a Co 3 O 4 phase 501 that is a nanocrystal having an average particle diameter of 13 nm was surrounded by a Co—Si—O-based SiO 2 phase 502 that is an amorphous phase having a thickness of about 1-2 nm.
  • Table 1 also shows the evaluation results of thermal conductivity. Evaluation of the thermal conductivity of the produced sample was performed by depositing Mo on the upper surface of the thin film and using the pulsed light heating thermoreflectance method.
  • x is higher than the thermal conductivity of Sample A-1, x is equal to 0.9 or more and less than 1.0 times, ⁇ is 0.6 or more and less than 0.9 times Is shown as ⁇ , and less than 0.6 times is shown as ⁇ . From Table 1, it was found that the samples A-2 to A-10 all showed thermal conductivity less than 0.9 times that of the sample A-1 as a comparative example. This is because phonon scattering occurs at the interface between Co 3 O 4 and SiO 2 , resulting in a decrease in thermal conductivity. Therefore, it has been found that the characteristics as a thermoelectric conversion material are improved by taking the structure as shown in FIG.
  • the melting point will be considered.
  • Co 3 O 4 does not have a melting point and oxygen is desorbed at 895 ° C. and decomposes into CoO.
  • the ease of cation diffusion is important.
  • Comparison is made at a melting point of 1933 ° C. for CoO and 1600 ° C. for SiO 2 melting point. In this case, it can be seen that the relationship of the melting point of the particle> the melting point of the particle interface is established.
  • Co—Si—O based amorphous Co is contained in SiO 2 , but even if Co is contained, the melting point at the particle interface does not increase, and Is thought to be maintained.
  • the Seebeck coefficient was improved, and when the thickness was reduced to 5 nm, the Seebeck coefficient was improved about 4 times. Therefore, in the samples of A-9 and A-10 in this example, the Co 3 O 4 crystals are reduced to 10 nm or less, so that the Seebeck coefficient is improved and the characteristics as a thermoelectric conversion material are improved. Conceivable.
  • Example 1 ⁇ Preparation of Na x CoO 2 Thermoelectric Conversion Material> Eight NaCO 3 chips (10 ⁇ ) were placed on the A-3 sputter target used in Example 1, and a thin film having a thickness of about 200 nm was formed in the same manner as in Example 1. When X-ray diffraction of this thin film was performed, a diffraction peak of only Na x CoO 2 was obtained. Further, when TEM observation was performed in the same manner, 17 nm Na x CoO 2 crystals were obtained. Thus, as in Example 1, excellent thermoelectric conversion characteristics were exhibited by a decrease in thermal conductivity due to phonon scattering. Can be expected.
  • ZnO was used as a target material, five SiO 2 chips (10 mm square) were arranged on the target, and a thin film was formed by RF sputtering in the same manner as in Example 1.
  • the experimental conditions were the same except that the temperature of the substrate was 400 ° C.
  • the XRD analysis of the produced thin film was implemented, it became clear that a ZnO crystal and an amorphous phase existed.
  • tissue equivalent to FIG. 1 was formed.
  • ZnO was a columnar crystal as in Example 1, and the interface portion was amorphous SiO 2 . Since the melting point of ZnO is 1975 ° C., it can be seen that the relationship between the melting point of the particles> the melting point of the particle interface is the same as in Example 1.
  • thermoelectric characteristics can be expected also in this case.
  • Si was used as a target material, four Bi chips (5 ⁇ ) were arranged on the target, and DC magnetron sputtering was performed under the following conditions.
  • a sputtering condition a thin film having a thickness of about 200 nm was formed on a glass substrate using a DC power source with an Ar flow rate of 50 sccm, a discharge pressure of 0.7 Pa, and an input power of 0.3 kW.
  • FIG. 6 shows an AFM phase difference mapping diagram
  • FIG. 7 shows a TEM image of a thin film cross section.
  • Bi having a low hardness is a portion having a large phase difference delay.
  • 602 was the crystalline Si phase (melting point: 1414 ° C.)
  • 601 was the Bi phase (melting point: 271.5 ° C.)
  • the relationship of the melting point of the particle> the melting point of the particle interface was established. I understand that.
  • the crystal and the interface portion have a shape that is intertwined in the film thickness direction.
  • thermoelectric conversion phase is mainly the Bi phase 601 at the interface, but the particle size of Bi is as small as about 3 to 10 nm. It seems that there is also an improvement in the Seebeck coefficient due to.
  • SiO 2 was used as a target material, eight Bi chips (5 ⁇ ) were arranged on the target, and RF magnetron sputtering was performed under the following conditions.
  • sputtering conditions a thin film having a thickness of about 200 nm was formed on a glass substrate using an RF power source with an Ar flow rate of 50 sccm, a discharge pressure of 0.7 Pa, and an input power of 0.35 kW.
  • the microstructure of the produced thin film was analyzed using STEM.
  • a STEM ZC image is shown in FIG. From this, 801 is the crystalline SiO 2 phase (melting point: 1600 ° C.) and 802 is the Bi phase (melting point: 271.5 ° C.), so the relationship of the melting point of the particle> the melting point of the particle interface is established. I understand that When the thermal conductivity of this sample was measured in the same manner as in Example 1, it was 0.45 times that of the Bi thin film.
  • 100 Thermoelectric conversion material
  • 101 Thermoelectric conversion phase
  • 102 Barrier phase
  • 300 Thermoelectric conversion element
  • 301 Metal layer
  • 400 Thermoelectric conversion module
  • 401 Extraction electrode
  • 402 Insulating substrate
  • 501 Co 3 O 4- phase
  • 502 SiO 2 phase
  • 602 Si phase

Abstract

　A thermoelectric conversion material provided with particles and a phase surrounding the particle interfaces, the particles and the phase being combined at a nanosize level; wherein the thermoelectric conversion material is characterized in that the phase surrounding the particle interfaces being has a lower melting point than that of the particles. A method for manufacturing a thermoelectric conversion material, which is characterized in that a plurality of types of targets are sputtered to form particles containing an element that is contained within one of the targets, and a phase surrounding the particle interfaces containing an element that is contained within another one of the targets; the particles and phase surrounding the particle interfaces forming a thin film.

Description

熱電変換材料、熱電変換素子、熱電変換モジュール、熱電変換材料の製造方法Thermoelectric conversion material, thermoelectric conversion element, thermoelectric conversion module, and method of manufacturing thermoelectric conversion material
　本発明は、熱電変換材料、熱電変換素子、熱電変換モジュール、熱電変換材料の製造方法に関する。 The present invention relates to a thermoelectric conversion material, a thermoelectric conversion element, a thermoelectric conversion module, and a method for manufacturing a thermoelectric conversion material.
　熱電変換材料は、２種類の物質を接合させて両端に温度差を生じさせると電圧が発生するゼーベック効果が基本になっている。これまでにＢｉ2Ｔｅ3等からなる熱電変換材料が開発され、実用化されているが、希少金属や有害金属を含むことや変換効率が低いことが普及への課題となっている。 The thermoelectric conversion material is based on the Seebeck effect in which a voltage is generated when two kinds of substances are joined to cause a temperature difference between both ends. So far, thermoelectric conversion materials made of Bi 2 Te 3 and the like have been developed and put into practical use. However, the inclusion of rare metals and toxic metals and low conversion efficiency are problems for diffusion.
　この変換効率を向上させるためのアプローチとして、熱電変換材料をナノサイズ化することでバルク状態の熱電変換材料に比べて変換効率が向上することが理論的に示されている。ここで、熱電変換材料の指標として一般的に使用される性能指数Ｚは以下の式（１）によって定義されている。 As an approach for improving the conversion efficiency, it has been theoretically shown that the conversion efficiency is improved by making the thermoelectric conversion material nano-sized as compared with the bulk thermoelectric conversion material. Here, the figure of merit Z generally used as an index of the thermoelectric conversion material is defined by the following formula (1).
　Ｚ＝Ｓ2×σ／κ　　（１）
　ナノサイズ化することにより性能が向上する理由は２つある。１つは、ナノサイズ化することによってフォノンを効果的に散乱することにより熱伝導率κが低減するためである。もう１つは、熱電変換材料が量子サイズまで小さくなったときに発現する量子効果によって状態密度が変化することによりゼーベック係数Ｓが向上するためである。後者は性能向上のために特に効果が大きいことが予測されているが、特性は熱電変換材料の次元数によっても変化する。例えば、２次元化した材料（超格子薄膜）よりも１次元化した材料（ナノワイヤ）の方が特性は向上することが予測されている。 Z = S 2 × σ / κ (1)
There are two reasons why the performance is improved by the nano-size. One is that the thermal conductivity κ is reduced by effectively scattering phonons by nano-sizing. The other is that the Seebeck coefficient S is improved by changing the density of states due to the quantum effect that appears when the thermoelectric conversion material is reduced to the quantum size. The latter is expected to be particularly effective for improving performance, but the characteristics also change depending on the dimensionality of the thermoelectric conversion material. For example, it is predicted that characteristics are improved in a one-dimensional material (nanowire) than in a two-dimensional material (superlattice thin film).
　例えば、ガラス部材の中に熱電変換材料を充填し、その後延伸してナノワイヤ化された熱電変換材料が公開されている（特許文献１参照）。 For example, a thermoelectric conversion material in which a glass member is filled with a thermoelectric conversion material and then drawn into a nanowire is disclosed (see Patent Document 1).
特開２０１０－８０５２１号公報JP 2010-80521 A
　しかし、特許文献１に記載のナノコンポジット熱電変換材料は、変換効率に改良の余地がある。 However, the nanocomposite thermoelectric conversion material described in Patent Document 1 has room for improvement in conversion efficiency.
　そこで本発明の目的は、上記問題に鑑みてなされたものであり、変換効率の優れたナノコンポジット熱電変換材料を提供することにある。 Therefore, an object of the present invention is made in view of the above problems, and is to provide a nanocomposite thermoelectric conversion material having excellent conversion efficiency.
　上記目的は、例えば特許請求の範囲に記載された発明により達成される。 The above object is achieved, for example, by the invention described in the claims.
　本発明によれば、変換効率の優れたナノコンポジット熱電変換材料を提供することができる。 According to the present invention, a nanocomposite thermoelectric conversion material having excellent conversion efficiency can be provided.
本発明の実施形態に係るナノコンポジット熱電変換材料の一例の模式図である。It is a schematic diagram of an example of the nanocomposite thermoelectric conversion material which concerns on embodiment of this invention. 本発明の実施形態に係るナノコンポジット熱電変換材料の一例の模式図である。It is a schematic diagram of an example of the nanocomposite thermoelectric conversion material which concerns on embodiment of this invention. 本発明の実施形態に係るナノコンポジット熱電変換素子の一例の模式図である。It is a schematic diagram of an example of the nanocomposite thermoelectric conversion element which concerns on embodiment of this invention. 本発明の実施形態に係るπ型熱電変換モジュールの構造の一例である。1 is an example of a structure of a π-type thermoelectric conversion module according to an embodiment of the present invention. 本発明の実施形態に係るナノコンポジット熱電変換材料のＴＥＭ像である。It is a TEM image of the nanocomposite thermoelectric conversion material which concerns on embodiment of this invention. 本発明の実施形態に係るナノコンポジット熱電変換材料のＡＦＭ像（位相差マッピング図）である。It is an AFM image (phase difference mapping figure) of the nanocomposite thermoelectric conversion material concerning the embodiment of the present invention. 本発明の実施形態に係るナノコンポジット熱電変換材料の断面構造である。It is a cross-sectional structure of the nanocomposite thermoelectric conversion material which concerns on embodiment of this invention. 本発明の実施形態に係るナノコンポジット熱電変換材料のＳＴＥＭ（ＺＣ）像である。It is a STEM (ZC) image of the nanocomposite thermoelectric conversion material which concerns on embodiment of this invention.
　以下、本発明の実施形態について、図面を参照しながら説明する。なお、本発明はここで取り上げた実施形態に限定されることはなく、要旨を変更しない範囲で適宜組み合わせや改良が可能である。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to embodiment taken up here, A combination and improvement are possible suitably in the range which does not change a summary.
　図１及び図２は、本実施形態に係る熱電変換材料の模式図である。熱電変換材料１００には、粒子を形成する第１相と、粒子の界面を取り囲む第２相の少なくとも２相が存在し、これらがナノサイズ（数ｎｍ～数十ｎｍ）で複合化されたナノコンポジット熱電変換材料である。また、粒子を形成する第１相の融点よりも、その界面を取り囲む第２相の融点が低いことが特徴である。粒子を形成する第１相と、粒子の界面を取り囲む第２相が、熱電変換相１０１およびバリア相１０２のどちらかとなる。ここで、バリア相１０２とは熱電変換相１０１よりも電気抵抗が高く、電子の移動を阻害する障壁となる相のことを意味する。 1 and 2 are schematic views of the thermoelectric conversion material according to the present embodiment. The thermoelectric conversion material 100 has at least two phases, ie, a first phase that forms particles and a second phase that surrounds the interface of the particles, and these are combined in a nano size (several nm to several tens of nm). It is a composite thermoelectric conversion material. In addition, the melting point of the second phase surrounding the interface is lower than the melting point of the first phase forming the particles. The first phase that forms the particles and the second phase that surrounds the interface of the particles are either the thermoelectric conversion phase 101 or the barrier phase 102. Here, the barrier phase 102 means a phase that has a higher electrical resistance than the thermoelectric conversion phase 101 and serves as a barrier that hinders the movement of electrons.
　図１には、熱電変換相１０１の融点がバリア相１０２よりも高い場合のナノコンポジット熱電変換材料１００の模式図を示す。図１の場合には、柱状結晶を形成した複数の熱電変換相１０１が長軸方向と直交する方向に敷き詰められ、柱状結晶の壁面間にバリア相１０２を設けて薄膜状の熱電変換材料１００を形成している。熱電変換相１０１間にはバリア相１０２が存在するため、熱電変換材料として使用する場合には図中に示すように上下方向（柱状結晶の長軸方向）に温度差を形成して使用する必要がある。 FIG. 1 shows a schematic diagram of the nanocomposite thermoelectric conversion material 100 when the melting point of the thermoelectric conversion phase 101 is higher than that of the barrier phase 102. In the case of FIG. 1, a plurality of thermoelectric conversion phases 101 forming columnar crystals are spread in a direction perpendicular to the major axis direction, and a barrier phase 102 is provided between the wall surfaces of the columnar crystals to form a thin-film thermoelectric conversion material 100. Forming. Since the barrier phase 102 exists between the thermoelectric conversion phases 101, when using as a thermoelectric conversion material, it is necessary to form a temperature difference in the vertical direction (long axis direction of the columnar crystal) as shown in the figure. There is.
　図２には、熱電変換相１０１の融点がバリア相１０２よりも低い場合のナノコンポジット熱電変換材料１００の模式図を示す。図２の場合には、熱電変換相１０１が柱状結晶を取り囲む界面相を形成する。そのため、熱電変換材料として使用する場合には、図１と同様に上下方向の温度差に加えて、左右方向（柱状結晶の短軸方向）のどちらに温度差を形成しても熱電変換材料として使用することが可能である。 FIG. 2 shows a schematic diagram of the nanocomposite thermoelectric conversion material 100 when the melting point of the thermoelectric conversion phase 101 is lower than that of the barrier phase 102. In the case of FIG. 2, the thermoelectric conversion phase 101 forms an interface phase surrounding the columnar crystal. Therefore, when used as a thermoelectric conversion material, in addition to the temperature difference in the vertical direction as in FIG. 1, the thermoelectric conversion material can be used regardless of whether the temperature difference is formed in either the left-right direction (the minor axis direction of the columnar crystal) It is possible to use.
　図１および図２の構造は、便宜的に柱状結晶が上下方向に直線的に伸びているように図示したが、本実施形態においては粒子を形成する第１相が、温度の傾斜をつけるために必要な領域を２箇所残し、その２箇所以外を第２相に界面を取り囲まれていれば良い。第１相と第２相が直線的でなく、入り組んだ構造となっていても同様の効果を発揮できる。 The structure of FIGS. 1 and 2 is illustrated such that the columnar crystals extend linearly in the vertical direction for convenience, but in this embodiment, the first phase forming the particles has a temperature gradient. It suffices to leave two areas necessary for the second phase and surround the interface with the second phase except for the two areas. Even if the first phase and the second phase are not linear and have an intricate structure, the same effect can be exhibited.
　また、本実施形態のナノコンポジット熱電変換材料１００において、熱電変換相１０１とバリア相１０２はどちらも１０ｎｍ以下の大きさで複合されていることが望ましい。粒子を形成する第１相の場合は、熱電変換材料としての使用時に温度差が生じる方向の粒径が１０ｎｍ以下になることで量子サイズ効果が発現しやすくなり、粒子の界面を取り囲む第２相の場合は、第１相と第１相との間の第２相の厚さが１０ｎｍ以下になることで量子サイズ効果が発現しやすくなり、ゼーベック係数を向上できるためである。さらに、バリア相１０２を形成する材料は非晶質であることが望ましい。これは、非晶質になることでフォノンを散乱しやすくなり、熱伝導率を低下させることができるためである。 Moreover, in the nanocomposite thermoelectric conversion material 100 of this embodiment, it is desirable that both the thermoelectric conversion phase 101 and the barrier phase 102 are composited with a size of 10 nm or less. In the case of the first phase forming the particles, the quantum size effect is easily exhibited when the particle size in the direction in which the temperature difference occurs when used as the thermoelectric conversion material is 10 nm or less, and the second phase surrounding the particle interface. In this case, the thickness of the second phase between the first phase and the first phase is 10 nm or less, whereby the quantum size effect is easily exhibited and the Seebeck coefficient can be improved. Further, the material forming the barrier phase 102 is desirably amorphous. This is because it becomes easy to scatter phonons by becoming amorphous, and thermal conductivity can be lowered.
　上記構造を達成するための手段としては、相分離現象を用いることが望ましい。これにより、ｎｍサイズのコンポジット熱電変換材料を作製することができ、さらに組成や熱処理条件等を調整することによって１０ｎｍ以下のサイズまで大きさを制御することが可能となる。 It is desirable to use a phase separation phenomenon as a means for achieving the above structure. As a result, a nano-sized composite thermoelectric conversion material can be produced, and the size can be controlled to a size of 10 nm or less by adjusting the composition, heat treatment conditions, and the like.
　本実施形態の熱電変換材料の製造方法としては、スパッタ法を用いることが望ましい。第１相を形成する元素群を含むターゲットと第２相を形成する元素群を含むターゲットとを同時にスパッタすることで、相分離現象が生じ、本実施形態の熱電変換材料を作製することができる。スパッタした際の元素の基板表面での拡散しやすさ（すなわち各相の融点）の違いを利用することによって、第１相と第２相とがあまり混ざらずに第１相同士、第２相同士で構造物を形成する。また、本実施形態においては、第１相の粒界を取り囲む第２相の存在によって、薄膜の面内方向への第１相の結晶成長が抑制されるため、第１相の柱状結晶面内でほぼ一定の面積を維持しながら、上方（長軸方向）に成長することが可能となる。 It is desirable to use a sputtering method as a method for manufacturing the thermoelectric conversion material of this embodiment. By simultaneously sputtering the target including the element group forming the first phase and the target including the element group forming the second phase, a phase separation phenomenon occurs, and the thermoelectric conversion material of this embodiment can be manufactured. . By utilizing the difference in easiness of diffusion of elements on the substrate surface when sputtering (ie, melting point of each phase), the first phase and the second homology are not mixed with each other. A structure is formed by a worker. In the present embodiment, the presence of the second phase surrounding the grain boundary of the first phase suppresses the crystal growth of the first phase in the in-plane direction of the thin film. Thus, it is possible to grow upward (long axis direction) while maintaining a substantially constant area.
　本実施形態におけるナノコンポジット熱電変換材料の第１相と第２相の組み合わせは、平衡状態で分離する物質同士であることが求められる。これによって相分離が誘発され、本実施形態のナノコンポジット熱電変換材料が形成できる。したがって、それ以外は特に限定されるところではない。熱電変換相１０１には、例えばＢｉ、Ｂｉ2Ｔｅ3、ＰｂＴｅ、ＮａＣｏＯ2、Ｃａ3Ｃｏ4Ｏ9、Ｓｉ、ＳｉＧｅなど一般的に熱電変換材料として特性が良好な材料を使用することができる。この中でも特にＢｉを使用することが望ましい。この理由は、Ｂｉは、フェルミ波長が長いために量子サイズ効果を得やすく、ナノサイズ化したときに得られる効果が大きいためである。このＢｉには、キャリア濃度をコントロールするために微小のＴｅやＳｂなどのドーピングがされることが望ましい。 The combination of the first phase and the second phase of the nanocomposite thermoelectric conversion material in the present embodiment is required to be substances that separate in an equilibrium state. This induces phase separation, and the nanocomposite thermoelectric conversion material of this embodiment can be formed. Therefore, other than that, there is no particular limitation. For the thermoelectric conversion phase 101, for example, a material having generally good characteristics as a thermoelectric conversion material such as Bi, Bi 2 Te 3 , PbTe, NaCoO 2 , Ca 3 Co 4 O 9 , Si, or SiGe can be used. Among these, it is particularly preferable to use Bi. This is because Bi has a long Fermi wavelength, so that it is easy to obtain the quantum size effect, and the effect obtained when nano-sized is large. This Bi is preferably doped with a minute amount of Te, Sb or the like in order to control the carrier concentration.
　バリア相１０２は、電気抵抗が熱電変換相１０１よりも高く、熱電変換相１０１と固溶体を形成したりしない化合物であれば特に限定されるものではない。ただし、熱伝導率が低いものの観点から非晶質（ガラス）を形成しやすい元素群から選択することが望ましい。酸化物であれば、シリコン、リン、ゲルマニウム、ホウ素などネットワーク形成化合物を用いることによって、非晶質化を促進させることができるために望ましい。ガラスの場合、上記で示したような明確な融点というものは存在しないが、ガラスの場合には元素同士の結合が切れ始めるガラス転移する温度を融点の変わりの指標として用いることができる。 The barrier phase 102 is not particularly limited as long as it has a higher electrical resistance than the thermoelectric conversion phase 101 and does not form a solid solution with the thermoelectric conversion phase 101. However, it is desirable to select from the group of elements that easily form amorphous (glass) from the viewpoint of low thermal conductivity. An oxide is preferable because amorphization can be promoted by using a network forming compound such as silicon, phosphorus, germanium, or boron. In the case of glass, there is no clear melting point as described above, but in the case of glass, the glass transition temperature at which the bonds between elements begin to break can be used as an index for changing the melting point.
　図３には、本実施形態の熱電変換材料１００を用いた熱電変換素子３００の一例を示す。熱電変換素子として使用する場合には、温度差を形成する必要があるために温度差方向に少なくとも数１０μｍから数ｍｍ程度の幅が必要となる。スパッタ法で形成される本実施形態の熱電変換材料１００は充分な厚さに達するのに時間がかかるので、図１や図２に示した構造のうち、上下方向に温度差を形成して熱電変換材料１００を使用する場合には、図３に示すように熱電変換材料１００間に金属膜３０１を形成して積層して使用することもできる。これにより、結晶配向の乱れなどを補正することもできる。 FIG. 3 shows an example of a thermoelectric conversion element 300 using the thermoelectric conversion material 100 of the present embodiment. When used as a thermoelectric conversion element, it is necessary to form a temperature difference, so that a width of at least several tens of μm to several mm is required in the temperature difference direction. Since it takes time to reach a sufficient thickness, the thermoelectric conversion material 100 of this embodiment formed by the sputtering method forms a temperature difference in the vertical direction in the structure shown in FIGS. When the conversion material 100 is used, a metal film 301 may be formed between the thermoelectric conversion materials 100 and stacked as shown in FIG. Thereby, disorder of crystal orientation etc. can also be corrected.
　図４には、本実施形態の熱電変換材料を用いて作製したπ型熱電変換モジュール４００の一例を示す。熱電変換モジュール４００は、高温部と低温部の温度差を利用して電気を取り出す、もしくは電気を流すことにより発熱部と吸熱部を発生させることを可能とするデバイスである。図４に示すように熱電変換モジュール４００は、Ｐ型とＮ型の熱電変換素子３００が絶縁性基板４０２に形成された上下の取り出し電極４０１に接合されることで形成される。この絶縁性基板の片側を熱源等に貼り付け、片側を水冷や空冷することによって温度差を形成し、発電することができる。ただし、熱電変換モジュールの構造は、特にこれに限定されるところではなく、様々な形態が考えられる。 FIG. 4 shows an example of a π-type thermoelectric conversion module 400 manufactured using the thermoelectric conversion material of the present embodiment. The thermoelectric conversion module 400 is a device that can generate a heat generating part and a heat absorbing part by taking out electricity using a temperature difference between a high temperature part and a low temperature part, or by flowing electricity. As shown in FIG. 4, the thermoelectric conversion module 400 is formed by joining P-type and N-type thermoelectric conversion elements 300 to upper and lower extraction electrodes 401 formed on an insulating substrate 402. A temperature difference can be formed by attaching one side of the insulating substrate to a heat source or the like and water-cooling or air-cooling the one side to generate electric power. However, the structure of the thermoelectric conversion module is not particularly limited to this, and various forms are conceivable.
　以下、実施例を用いて更に詳細に説明する。ただし、本発明は、ここで取り上げた実施例の記載に限定されることはなく、適宜組み合わせてもよい。 Hereinafter, further detailed description will be given using examples. However, the present invention is not limited to the description of the embodiments taken up here, and may be combined as appropriate.
＜Ｃｏ3Ｏ4系熱電変換材料の作製＞
　表１は、検討したターゲット組成を示したものである。Ｃｏ3Ｏ4熱電変換材料の作製は、ＲＦマグネトロンスパッタリング法を用いて以下の条件で実施した。サファイヤ基板上に、表１に示すターゲット組成の混合膜を約１μｍ形成した。スパッタ条件は、ＲＦ電源を用いてＡｒ流量：４０ｓｃｃｍ、Ｏ2流量：１０ｓｃｃｍ、放電圧力０．７Ｐａ、投入電力１ｋＷとした。また、成膜は３００℃にて実施した。 <Preparation of Co 3 O 4 -based thermoelectric conversion material>
Table 1 shows the studied target compositions. The production of the Co 3 O 4 thermoelectric conversion material was performed under the following conditions using an RF magnetron sputtering method. On the sapphire substrate, a mixed film having a target composition shown in Table 1 was formed to a thickness of about 1 μm. The sputtering conditions were an Ar flow rate: 40 sccm, an O 2 flow rate: 10 sccm, a discharge pressure of 0.7 Pa, and an input power of 1 kW using an RF power source. The film formation was performed at 300 ° C.
　得られた薄膜のＸ線回折を実施したところ、いずれの試料もＣｏ3Ｏ4のピークのみが観察されたことから、ＳｉＯ2やＴｉＯ2は非晶質で存在することが判明した。作製した薄膜の微細構造をＴＥＭにて確認したところ、Ａ－２からＡ－１０のサンプルはいずれも図１のような構造を形成していた。図５にその一例としてＡ－７を上面から観察した際のＴＥＭ像を示す。平均粒径１３ｎｍのナノ結晶であるＣｏ3Ｏ4相５０１が、約１－２ｎｍの厚さの非晶質相であるＣｏ－Ｓｉ―Ｏ系のＳｉＯ2相５０２に取り囲まれていた。一方でＡ－１のサンプルは、膜厚が厚くなるにしたがって、粒径が大きく成長しており、ナノサイズの構造を維持することができていなかった。これは、バリア相となる他のターゲットが存在しなかったことにより、薄膜の面内方向におけるＣｏ3Ｏ4の結晶の成長を制限することができなかったためと考えられる。表１に、算出した平均粒径を示す。 When X-ray diffraction was performed on the obtained thin film, only the peak of Co 3 O 4 was observed in any sample, and it was found that SiO 2 and TiO 2 existed in an amorphous state. When the microstructure of the produced thin film was confirmed by TEM, all of the samples A-2 to A-10 had a structure as shown in FIG. FIG. 5 shows a TEM image when A-7 is observed from the upper surface as an example. A Co 3 O 4 phase 501 that is a nanocrystal having an average particle diameter of 13 nm was surrounded by a Co—Si—O-based SiO 2 phase 502 that is an amorphous phase having a thickness of about 1-2 nm. On the other hand, the sample of A-1 grew larger in size as the film thickness increased, and the nano-sized structure could not be maintained. This is presumably because the growth of Co 3 O 4 crystals in the in-plane direction of the thin film could not be restricted due to the absence of another target serving as a barrier phase. Table 1 shows the calculated average particle diameter.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　また、表１には熱伝導率の評価結果も示した。作製したサンプルの熱伝導率の評価は、薄膜の上面にＭｏを成膜し、パルス光加熱サーモリフレクタンス法を用いて実施した。表１において、サンプルＡ－１の熱伝導率よりも高くなったものを×、０．９以上１．０倍未満の同等であったものを△、０．６以上０．９倍未満のものを○、０．６倍未満のものを◎として示した。表１より、Ａ－２からＡ－１０のサンプルはいずれも比較例であるＡ－１のサンプルの０．９倍未満の熱伝導率を示すことが判明した。これは、Ｃｏ3Ｏ4とＳｉＯ2の界面にてフォノン散乱が生じるため、熱伝導率が低下したためである。したがって、図２のような構造をとることで、熱電変換材料としての特性が向上することが分かった。 Table 1 also shows the evaluation results of thermal conductivity. Evaluation of the thermal conductivity of the produced sample was performed by depositing Mo on the upper surface of the thin film and using the pulsed light heating thermoreflectance method. In Table 1, x is higher than the thermal conductivity of Sample A-1, x is equal to 0.9 or more and less than 1.0 times, Δ is 0.6 or more and less than 0.9 times Is shown as ○, and less than 0.6 times is shown as ◎. From Table 1, it was found that the samples A-2 to A-10 all showed thermal conductivity less than 0.9 times that of the sample A-1 as a comparative example. This is because phonon scattering occurs at the interface between Co 3 O 4 and SiO 2 , resulting in a decrease in thermal conductivity. Therefore, it has been found that the characteristics as a thermoelectric conversion material are improved by taking the structure as shown in FIG.
　ここで、融点に関して考察する。Ｃｏ3Ｏ4には融点がなく８９５℃で酸素が脱離してＣｏＯに分解するが、このような微細構造を形成するときは、カチオンの拡散のしやすさが重要となるので、分解後のＣｏＯの融点１９３３℃とＳｉＯ2融点１６００℃で比較する。この場合、粒子の融点＞粒子界面の融点の関係になっていることが分かる。また、上述したようにＣｏ－Ｓｉ－Ｏ系の非晶質に関してはＳｉＯ2にＣｏが含有されているが、Ｃｏが含有されても粒子界面の融点が上昇することはなく、先の関係性は維持されると考えられる。 Here, the melting point will be considered. Co 3 O 4 does not have a melting point and oxygen is desorbed at 895 ° C. and decomposes into CoO. When such a fine structure is formed, the ease of cation diffusion is important. Comparison is made at a melting point of 1933 ° C. for CoO and 1600 ° C. for SiO 2 melting point. In this case, it can be seen that the relationship of the melting point of the particle> the melting point of the particle interface is established. As described above, regarding Co—Si—O based amorphous, Co is contained in SiO 2 , but even if Co is contained, the melting point at the particle interface does not increase, and Is thought to be maintained.
　さらに、ゼーベック係数が向上するかどうかの検討を行った。ただし、上記のような薄膜の膜厚方向に温度差をかけたときのゼーベック係数を直接計測することは難しいため、間接的にどのくらいのサイズまで粒径を小さくすることで量子サイズ効果によるゼーベック係数向上効果が得られるのかを薄膜の面内方向に温度差を形成することで代用実験した。代用実験はサファイヤ基板の上にＣｏ3Ｏ4単体の薄膜を薄く形成し、薄膜の面内方向に温度差を形成することでＣｏ3Ｏ4における量子サイズ効果によるゼーベック係数向上効果が発現する臨界粒径を測定した。その結果、薄膜の厚みが１０ｎｍ以下になるとゼーベック係数の向上が見られ、５ｎｍまで薄くした際にはゼーベック係数が４倍程度に向上することが分かった。したがって、本実施例におけるＡ－９やＡ－１０のサンプルはＣｏ3Ｏ4の結晶が１０ｎｍ以下まで小さくなっているために、ゼーベック係数が向上し、熱電変換材料としての特性が向上することが考えられる。 In addition, we examined whether the Seebeck coefficient would improve. However, since it is difficult to directly measure the Seebeck coefficient when a temperature difference is applied in the film thickness direction as described above, the size of the Seebeck coefficient due to the quantum size effect can be reduced indirectly by decreasing the particle size. A substitution experiment was conducted by forming a temperature difference in the in-plane direction of the thin film to see if the improvement effect was obtained. In the substitution experiment, a thin Co 3 O 4 thin film is formed on a sapphire substrate, and a temperature difference is formed in the in-plane direction of the thin film, so that the Seebeck coefficient improvement effect due to the quantum size effect in Co 3 O 4 appears. The particle size was measured. As a result, it was found that when the thickness of the thin film was 10 nm or less, the Seebeck coefficient was improved, and when the thickness was reduced to 5 nm, the Seebeck coefficient was improved about 4 times. Therefore, in the samples of A-9 and A-10 in this example, the Co 3 O 4 crystals are reduced to 10 nm or less, so that the Seebeck coefficient is improved and the characteristics as a thermoelectric conversion material are improved. Conceivable.
＜ＮａxＣｏＯ2系熱電変換材料の作製＞
　実施例１で使用したＡ－３のスパッタターゲットの上にＮａＣＯ3のチップ（１０φ）を８つ配置し、実施例１と同様にして、約２００ｎｍの薄膜を形成した。この薄膜のＸ線回折を実施したところ、ＮａxＣｏＯ2のみの回折ピークが得られていた。また、同様にＴＥＭ観察を行ったところ、１７ｎｍのＮａxＣｏＯ2の結晶が得られていたことから、実施例１同様に、フォノン散乱による熱伝導率低下によって優れた熱電変換特性を発現することが期待できる。 <Preparation of Na x CoO 2 Thermoelectric Conversion Material>
Eight NaCO 3 chips (10φ) were placed on the A-3 sputter target used in Example 1, and a thin film having a thickness of about 200 nm was formed in the same manner as in Example 1. When X-ray diffraction of this thin film was performed, a diffraction peak of only Na x CoO 2 was obtained. Further, when TEM observation was performed in the same manner, 17 nm Na x CoO 2 crystals were obtained. Thus, as in Example 1, excellent thermoelectric conversion characteristics were exhibited by a decrease in thermal conductivity due to phonon scattering. Can be expected.
＜ＺｎＯ―ＳｉＯ2熱電変換材料の作製＞
　ターゲット材料にＺｎＯを用い、そのターゲットの上にＳｉＯ2のチップ（１０ｍｍ角）を５つ配置し、実施例１と同様にしてＲＦスパッタリング法を用いて薄膜を形成した。このとき、基板の温度は４００℃とした以外は同様の実験条件である。作製した薄膜のＸＲＤ分析を実施したところ、ＺｎＯ結晶と非晶質相が存在することが判明した。また、実施例１と同様にＴＥＭを用いて観察を行ったところ、図１と同等の組織が形成されていることが確認できた。また、この場合には実施例１と同様にＺｎＯが柱状結晶となっており、界面部は非晶質のＳｉＯ2であった。ＺｎＯの融点は１９７５℃であるため、実施例１と同様に粒子の融点＞粒子界面の融点の関係になっていることが分かる。 <Preparation of ZnO-SiO 2 thermoelectric conversion material>
ZnO was used as a target material, five SiO 2 chips (10 mm square) were arranged on the target, and a thin film was formed by RF sputtering in the same manner as in Example 1. At this time, the experimental conditions were the same except that the temperature of the substrate was 400 ° C. When the XRD analysis of the produced thin film was implemented, it became clear that a ZnO crystal and an amorphous phase existed. Moreover, when observing using TEM similarly to Example 1, it has confirmed that the structure | tissue equivalent to FIG. 1 was formed. Further, in this case, ZnO was a columnar crystal as in Example 1, and the interface portion was amorphous SiO 2 . Since the melting point of ZnO is 1975 ° C., it can be seen that the relationship between the melting point of the particles> the melting point of the particle interface is the same as in Example 1.
　作製したサンプルの熱伝導率とＺｎＯ単体で薄膜を成膜したときの熱伝導率を実施例１と同様に測定したところ、作製したサンプルはＺｎＯ単体の０．７倍に低減していることが判明した。従って、この場合にも熱電特性の向上が期待できると考えられる。 When the thermal conductivity of the prepared sample and the thermal conductivity when a thin film was formed with ZnO alone were measured in the same manner as in Example 1, it was found that the prepared sample was reduced to 0.7 times that of ZnO alone. found. Therefore, it is considered that improvement of thermoelectric characteristics can be expected also in this case.
＜Ｂｉ－Ｓｉ熱電変換材料の作製＞
　ターゲット材料にＳｉを用い、そのターゲット上にＢｉのチップ（５φ）を４つ配置し、以下の条件でＤＣマグネトロンスパッタを実施した。スパッタ条件は、ＤＣ電源を用いてＡｒ流量：５０ｓｃｃｍ、放電圧力０．７Ｐａ、投入電力０．３ｋＷとして、ガラス基板上に約２００ｎｍの薄膜を形成した。 <Preparation of Bi-Si thermoelectric conversion material>
Si was used as a target material, four Bi chips (5φ) were arranged on the target, and DC magnetron sputtering was performed under the following conditions. As a sputtering condition, a thin film having a thickness of about 200 nm was formed on a glass substrate using a DC power source with an Ar flow rate of 50 sccm, a discharge pressure of 0.7 Pa, and an input power of 0.3 kW.
　作製した薄膜の微細構造を原子間力顕微鏡（ＡＦＭ）及び断面ＴＥＭによって分析した。図６にＡＦＭの位相差マッピング図を、図７に薄膜断面のＴＥＭ像を示す。位相差マッピング図においては硬度が低いＢｉが位相差遅れの大きい部分となっている。これより、６０２が結晶のＳｉ相（融点：１４１４℃）であり、６０１がＢｉ相（融点：２７１．５℃）となっていたことから、粒子の融点＞粒子界面の融点の関係になっていることが分かる。また図７より結晶と界面部は膜厚方向に入り組んだ形状をしていた。 The microstructure of the prepared thin film was analyzed by an atomic force microscope (AFM) and a cross-sectional TEM. FIG. 6 shows an AFM phase difference mapping diagram, and FIG. 7 shows a TEM image of a thin film cross section. In the phase difference mapping diagram, Bi having a low hardness is a portion having a large phase difference delay. From this, since 602 was the crystalline Si phase (melting point: 1414 ° C.) and 601 was the Bi phase (melting point: 271.5 ° C.), the relationship of the melting point of the particle> the melting point of the particle interface was established. I understand that. Further, as shown in FIG. 7, the crystal and the interface portion have a shape that is intertwined in the film thickness direction.
　このサンプルの熱伝導率を実施例１同様に測定したところ、Ｓｉ単体の薄膜と比較して０．５３倍となっていた。従って、熱電特性の向上が期待できると考えられる。また、本実施例においては熱電変換相は界面部のＢｉ相６０１がメインとなっているが、Ｂｉの粒径は３―１０ｎｍ程度と微小であったことから、実施例１同様に量子サイズ効果によるゼーベック係数の向上も存在すると考えられる。 When the thermal conductivity of this sample was measured in the same manner as in Example 1, it was 0.53 times that of the thin film of Si alone. Therefore, it is considered that improvement of thermoelectric characteristics can be expected. In this embodiment, the thermoelectric conversion phase is mainly the Bi phase 601 at the interface, but the particle size of Bi is as small as about 3 to 10 nm. It seems that there is also an improvement in the Seebeck coefficient due to.
＜Ｂｉ－ＳｉＯ2熱電変換材料の作製＞
　ターゲット材料にＳｉＯ2を用い、そのターゲット上にＢｉのチップ（５φ）を８つ配置し、以下の条件でＲＦマグネトロンスパッタを実施した。スパッタ条件は、ＲＦ電源を用いてＡｒ流量：５０ｓｃｃｍ、放電圧力０．７Ｐａ、投入電力０．３５ｋＷとして、ガラス基板上に約２００ｎｍの薄膜を形成した。 <Preparation of Bi-SiO 2 thermoelectric conversion material>
SiO 2 was used as a target material, eight Bi chips (5φ) were arranged on the target, and RF magnetron sputtering was performed under the following conditions. As sputtering conditions, a thin film having a thickness of about 200 nm was formed on a glass substrate using an RF power source with an Ar flow rate of 50 sccm, a discharge pressure of 0.7 Pa, and an input power of 0.35 kW.
　作製した薄膜の微細構造をＳＴＥＭを用いて分析を行った。ＳＴＥＭのＺＣ像を図８に示す。これより、８０１が結晶のＳｉＯ2相（融点：１６００℃）であり、８０２がＢｉ相（融点：２７１．５℃）となっていたことから、粒子の融点＞粒子界面の融点の関係になっていることが分かる。このサンプルの熱伝導度を実施例１同様に測定したところ、Ｂｉ単体の薄膜と比較して０．４５倍となっていた。 The microstructure of the produced thin film was analyzed using STEM. A STEM ZC image is shown in FIG. From this, 801 is the crystalline SiO 2 phase (melting point: 1600 ° C.) and 802 is the Bi phase (melting point: 271.5 ° C.), so the relationship of the melting point of the particle> the melting point of the particle interface is established. I understand that When the thermal conductivity of this sample was measured in the same manner as in Example 1, it was 0.45 times that of the Bi thin film.
　また、ゼーベック係数を測定したところＢｉ単体の薄膜が－４４μＶ／Ｋであったのに対して、作製したサンプルのゼーベック係数は７０μＶ／Ｋとなっており、ＰＮの符号が反転した上に絶対値として向上していることが判明した。 In addition, when the Seebeck coefficient was measured, the thin film of Bi alone was -44 μV / K, whereas the Seebeck coefficient of the prepared sample was 70 μV / K, and the absolute value of the PN sign was reversed. As it turned out to have improved.
１００：熱電変換材料、１０１：熱電変換相、１０２：バリア相、３００：熱電変換素子、３０１：金属層、４００：熱電変換モジュール、４０１：取り出し電極、４０２：絶縁性基板、５０１：Ｃｏ3Ｏ4相、５０２：ＳｉＯ2相、６０１：Ｂｉ相、６０２：Ｓｉ相、８０１：ＳｉＯ2相、８０２：Ｂｉ相 100: Thermoelectric conversion material, 101: Thermoelectric conversion phase, 102: Barrier phase, 300: Thermoelectric conversion element, 301: Metal layer, 400: Thermoelectric conversion module, 401: Extraction electrode, 402: Insulating substrate, 501: Co 3 O 4- phase, 502: SiO 2 phase, 601: Bi phase, 602: Si phase, 801: SiO 2 phase, 802: Bi phase

Claims (15)

  1. 　粒子と、前記粒子の界面を取り囲む相とを備え、これらがナノサイズで複合化された熱電変換材料において、前記粒子の界面を取り囲む相の融点が前記粒子の融点よりも低いことを特徴とする熱電変換材料。 A thermoelectric conversion material comprising a particle and a phase surrounding the interface of the particle, wherein the melting point of the phase surrounding the interface of the particle is lower than the melting point of the particle. Thermoelectric conversion material.
  2. 　請求項１において、前記粒子または前記粒子の界面を取り囲む相のどちらかにＳｉを含むことを特徴とする熱電変換材料。 2. The thermoelectric conversion material according to claim 1, wherein Si is contained in either the particle or the phase surrounding the interface of the particle.
  3. 　請求項１において、前記粒子または前記粒子の界面を取り囲む相のどちらかが非晶質であることを特徴とする熱電変換材料。 2. The thermoelectric conversion material according to claim 1, wherein either the particle or the phase surrounding the interface of the particle is amorphous.
  4. 　請求項１において、前記粒子または前記粒子の界面を取り囲む相の少なくともどちらかが酸化物であることを特徴とする熱電変換材料。 2. The thermoelectric conversion material according to claim 1, wherein at least one of the particles and the phase surrounding the interface of the particles is an oxide.
  5. 　請求項１において、前記粒子の界面を取り囲む相の厚みは、１０ｎｍ以下であることを特徴とする熱電変換材料。 2. The thermoelectric conversion material according to claim 1, wherein the thickness of the phase surrounding the interface of the particles is 10 nm or less.
  6. 　請求項１において、前記粒子が熱電変換相であることを特徴とする熱電変換材料。 The thermoelectric conversion material according to claim 1, wherein the particles are a thermoelectric conversion phase.
  7. 　請求項６において、前記粒子にはＣｏが含まれることを特徴とする熱電変換材料。 7. The thermoelectric conversion material according to claim 6, wherein the particles contain Co.
  8. 　請求項１において、前記粒子の界面を取り囲む相が熱電変換相であることを特徴とする熱電変換材料。 2. The thermoelectric conversion material according to claim 1, wherein the phase surrounding the interface of the particles is a thermoelectric conversion phase.
  9. 　請求項８において、前記粒子の界面を取り囲む相にはＢｉを含むことを特徴とする熱電変換材料。 9. The thermoelectric conversion material according to claim 8, wherein the phase surrounding the interface of the particles contains Bi.
  10. 　請求項９において、前記粒子の界面を取り囲む相はさらにＳｂまたはＴｅを含むことを特徴とする熱電変換材料。 10. The thermoelectric conversion material according to claim 9, wherein the phase surrounding the particle interface further contains Sb or Te.
  11. 　請求項１において、前記粒子はナノサイズの柱状結晶であり、前記粒子の界面を取り囲む相は前記柱状結晶の壁面を取り囲んでいることを特徴とする熱電変換材料。 2. The thermoelectric conversion material according to claim 1, wherein the particles are nano-sized columnar crystals, and a phase surrounding an interface of the particles surrounds a wall surface of the columnar crystals.
  12. 　請求項１において、前記粒子はナノサイズの柱状結晶であり、複数の前記粒子が長軸方向と直交する方向に並べられた薄膜を形成し、前記薄膜の面内方向に温度差が形成された際に発電することを特徴とする熱電変換材料。 2. The particle according to claim 1, wherein the particle is a nano-sized columnar crystal, a thin film in which a plurality of the particles are arranged in a direction orthogonal to a major axis direction is formed, and a temperature difference is formed in an in-plane direction of the thin film. A thermoelectric conversion material characterized by generating electricity at the time.
  13. 　請求項１の熱電変換材料と金属とが積層された構造になっていることを特徴とする熱電変換素子。 A thermoelectric conversion element having a structure in which the thermoelectric conversion material according to claim 1 and a metal are laminated.
  14. 　請求項１の熱電変換材料を用いた熱電変換モジュール。 A thermoelectric conversion module using the thermoelectric conversion material according to claim 1.
  15. 　複数種のターゲットをスパッタすることにより、一の前記ターゲットに含まれる元素を含む粒子と、他の前記ターゲットに含まれる元素を含む前記粒子の界面を取り囲む相とを形成し、前記粒子と前記粒子の界面を取り囲む相とが薄膜を形成することを特徴とする熱電変換材料の製造方法。 By sputtering a plurality of types of targets, particles containing an element contained in one of the targets and a phase surrounding an interface of the particles containing an element contained in another target are formed, and the particles and the particles A method for producing a thermoelectric conversion material, characterized in that a phase surrounding the interface forms a thin film.
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