JP5397500B2 - Nanocomposite thermoelectric conversion material and method for producing the same - Google Patents
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Description
本発明は、熱電変換材料マトリクス中にナノサイズのフォノン散乱粒子が分散したナノコンポジット熱電変換材料およびその製造方法に関する。 The present invention relates to a nanocomposite thermoelectric conversion material in which nano-sized phonon scattering particles are dispersed in a thermoelectric conversion material matrix and a method for producing the same.
熱電変換材料は、２つの基本的な熱電効果であるゼーベック（Seebeck）効果及びペルチェ（Peltier）効果に基づき、熱エネルギと電気エネルギとの直接変換を行なうエネルギ材料である。 The thermoelectric conversion material is an energy material that performs direct conversion between thermal energy and electric energy based on two basic thermoelectric effects, the Seebeck effect and the Peltier effect.
熱電変換材料を用いた熱電発電デバイスは、従来の発電技術に比べて、構造は簡単で、堅牢かつ耐久性が高く、可動部材は存在せず、マイクロ化が容易であり、メンテナンス不要で信頼性が高く、寿命が長く、騒音は発生せず、汚染も発生せず、低温の廃熱を利用可能であるといった多くの利点がある。 Thermoelectric power generation devices using thermoelectric conversion materials have a simple structure, robustness, high durability, no moving parts, easy microfabrication, no maintenance, and reliability compared to conventional power generation technology There are many advantages such as high life, long life, no noise, no pollution and low temperature waste heat can be used.
熱電変換材料を用いた熱電冷却デバイスも、従来の圧縮冷却技術に比べて、フロン不要で汚染は発生せず、小型化は容易で、可動部材は存在せず、騒音も発生しないなどの利点がある。 Compared to conventional compression cooling technology, thermoelectric cooling devices using thermoelectric conversion materials do not require chlorofluorocarbon, do not cause contamination, are easily downsized, have no moving parts, and do not generate noise. is there.
そのため、特に近年のエネルギ問題や環境問題の重大化に伴い、航空・宇宙、国防建設、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方面などの広範な用途への実用化が期待されている。 Therefore, especially in recent years, energy and environmental issues have become more serious, such as aviation / space, national defense construction, geological and meteorological observation, medical hygiene, microelectronics, etc. Is expected to be put to practical use for a wide range of applications.
熱電変換材料の性能を評価する指数として、パワーファクターＰ＝Ｓ2σおよび無次元性能指数ＺＴ＝（Ｓ2σ／κ）Ｔが用いられている。ここで、Ｓ：ゼーベック係数、σ：導電率、κ：熱伝導率、Ｔ：絶対温度である。すなわち、良好な熱電特性を得るには、ゼーベック係数Ｓおよび導電率σが高く、熱伝導率κが低いことが必要である。 As an index for evaluating the performance of the thermoelectric conversion material, a power factor P = S 2 σ and a dimensionless performance index ZT = (S 2 σ / κ) T are used. Here, S: Seebeck coefficient, σ: conductivity, κ: thermal conductivity, T: absolute temperature. That is, in order to obtain good thermoelectric properties, it is necessary that the Seebeck coefficient S and the electrical conductivity σ are high and the thermal conductivity κ is low.
熱伝導率κを低減するためには、熱伝導の担い手の一つであるフォノンを散乱させることが有効であり、熱電変換材料マトリクス中にフォノン散乱用の粒子が分散したコンポジット熱電変換材料が提唱されている。 In order to reduce the thermal conductivity κ, it is effective to scatter phonons, one of the players in heat conduction, and a composite thermoelectric conversion material in which phonon scattering particles are dispersed in a thermoelectric conversion material matrix is proposed. Has been.
特許文献１には、ＢｉＴｅ系熱電半導体の粒界または粒内に、化学量論組成に対して過剰濃度のＴｅを含むＴｅリッチ相を偏析させ、それに起因する結晶格子の歪により熱伝導率を低下させることが開示されている。 In Patent Document 1, a Te-rich phase containing an excessive concentration of Te with respect to the stoichiometric composition is segregated in the grain boundary or grain of the BiTe-based thermoelectric semiconductor, and the thermal conductivity is increased by distortion of the crystal lattice resulting therefrom. It is disclosed to reduce.
しかし、偏析Ｔｅリッチ相がミクロンオーダーのサイズであるため、熱伝導率の低下が僅かしかなく、熱電変換性能を大きく向上させることはできなかった。この技術では、合成を溶融金属から行なっており、粒子サイズを更に小さくすることはできない。 However, since the segregated Te-rich phase has a micron-order size, there was only a slight decrease in thermal conductivity, and the thermoelectric conversion performance could not be greatly improved. In this technique, the synthesis is performed from molten metal, and the particle size cannot be further reduced.
特許文献２には、熱電変換材料のマトリクス中に、フォノンの平均自由行程以下かつキャリアの平均自由行程以上でナノサイズのフォノン散乱粒子を分散させることが開示されている。ｐＨ調整セラミック粉末分散液に熱電材料前駆体溶液を混合して還元することも開示されている。 Patent Document 2 discloses that nano-sized phonon scattering particles are dispersed in a matrix of a thermoelectric conversion material with a mean free path of phonons or less and a mean free path of carriers or more. It is also disclosed that a thermoelectric material precursor solution is mixed with a pH-adjusted ceramic powder dispersion for reduction.
特許文献３には、熱電変換材料のマトリクス中にナノサイズのフォノン散乱粒子としてセラミック粒子を分散させることが開示されている。 Patent Document 3 discloses that ceramic particles are dispersed as nano-sized phonon scattering particles in a matrix of a thermoelectric conversion material.
特許文献４には、熱電変換材料のマトリクス中にナノサイズのフォノン散乱粒子として金属粒子を分散させることが開示されている。 Patent Document 4 discloses that metal particles are dispersed as nano-sized phonon scattering particles in a matrix of a thermoelectric conversion material.
特許文献２、３、４の技術は、フォノン散乱粒子をナノサイズとすることにより、ミクロンサイズの粒子に対して顕著に熱伝導率を低下させ、熱電変換性能を大きく向上させることができたが、更に熱伝導率を低下させる余地が残されていた。 Although the techniques of Patent Documents 2, 3, and 4 can make the phonon scattering particles nano-sized, the thermal conductivity is remarkably lowered with respect to micron-sized particles, and the thermoelectric conversion performance can be greatly improved. Furthermore, there is still room for lowering the thermal conductivity.
本発明は、ナノサイズのフォノン散乱粒子による熱伝導率の低減効果を更に高めて大幅に熱電変換性能を高めたナノコンポジット熱電変換材料およびその製造方法を提供することを目的とする。 An object of the present invention is to provide a nanocomposite thermoelectric conversion material that further enhances the effect of reducing thermal conductivity by nano-sized phonon scattering particles and greatly improves thermoelectric conversion performance, and a method for producing the same.
上記の目的を達成するために、本発明のナノコンポジット熱電変換材料は、
熱電変換材料のマトリクス中にナノサイズのフォノン散乱粒子を分散させたナノコンポジット熱電変換材料において、
マトリクスが多結晶組織からなり、結晶粒とは異なる組成の結晶粒界相が存在し、結晶粒内および結晶粒界相内に同一種類のフォノン散乱粒子が分散していることを特徴とする。
In order to achieve the above object, the nanocomposite thermoelectric conversion material of the present invention comprises:
In a nanocomposite thermoelectric conversion material in which nano-sized phonon scattering particles are dispersed in a matrix of thermoelectric conversion material,
The matrix has a polycrystalline structure, a crystal grain boundary phase having a composition different from that of the crystal grains exists, and the same kind of phonon scattering particles are dispersed in the crystal grains and the crystal grain boundary phase.
上記の目的を達成するために、本発明のナノコンポジット熱電変換材料の製造方法は、
熱電変換材料のマトリクス中にナノサイズのフォノン散乱粒子を分散させたナノコンポジット熱電変換材料の製造方法において、
熱電変換材料の各構成元素の塩を溶解させ、かつ、フォノン散乱粒子を分散させた原料溶液を調製する第１工程、
上記原料溶液に還元剤を滴下して、上記フォノン散乱粒子の表面に上記熱電変換材料の各構成元素を析出させてスラリーを形成する第２工程、
上記スラリーを水熱処理して、相対的に高融点の高融点合金相と低融点の低融点合金相とから成るマトリクス前駆体中に上記フォノン散乱粒子が分散した複合体を形成する第３工程、
上記複合体を焼結して、多結晶マトリクス中に上記フォノン散乱粒子が分散した焼結体を形成する第４工程、および
上記焼結体を熱処理することにより、該焼結体の結晶粒界において上記低融点合金相のみを選択的に溶融させ、生成した低融点溶融相中に近傍の上記フォノン散乱粒子を取り込ませ、上記低融点合金相中に該フォノン散乱粒子が分散した複合体としての粒界相を形成する第５工程、
を含むことを特徴とする。
In order to achieve the above object, a method for producing a nanocomposite thermoelectric conversion material of the present invention comprises:
In a method for producing a nanocomposite thermoelectric conversion material in which nano-sized phonon scattering particles are dispersed in a matrix of a thermoelectric conversion material,
A first step of preparing a raw material solution in which the salt of each constituent element of the thermoelectric conversion material is dissolved and the phonon scattering particles are dispersed;
A second step in which a reducing agent is dropped into the raw material solution to deposit a constituent element of the thermoelectric conversion material on the surface of the phonon scattering particles to form a slurry;
The slurry was hydrothermally treated, third step of relatively high melting point of the phonon scattering particles in the body during the ejection before matrix of a refractory alloy phase and a low melting point of the low melting point alloy phase to form a complex dispersed ,
A fourth step in which the composite is sintered to form a sintered body in which the phonon scattering particles are dispersed in a polycrystalline matrix; and the sintered body is subjected to a heat treatment, whereby grain boundaries of the sintered body are formed. As a composite in which only the low melting point alloy phase is selectively melted, the phonon scattering particles in the vicinity are taken into the generated low melting point melt phase, and the phonon scattering particles are dispersed in the low melting point alloy phase. A fifth step of forming a grain boundary phase;
It is characterized by including.
本発明のナノコンポジット熱電変換材料は、多結晶体である熱電変換材料マトリックスの結晶粒内だけでなく結晶粒界相にもフォノン散乱粒子を分散させたことにより、フォノン散乱効果が大幅に高まるので、熱伝導率が大きく低下し、それによって極めて高い熱電変換性能が得られる。 In the nanocomposite thermoelectric conversion material of the present invention, the phonon scattering effect is greatly enhanced by dispersing the phonon scattering particles not only within the crystal grains of the polycrystalline thermoelectric conversion material matrix but also in the grain boundary phase. , The thermal conductivity is greatly reduced, thereby obtaining extremely high thermoelectric conversion performance.
本発明のナノコンポジット熱電変換材料の製造方法は、相対的な高融点相と低融点相とが混在した多結晶マトリックスを持つ焼結体の結晶粒界において低融点相のみを選択的に溶融させると、結晶粒界に形成された融解相中に周囲に存在するフォノン散乱粒子が取り込まれるので、熱電変換材料の結晶粒内のみでなく結晶粒界相にもフォノン散乱粒子を分散させることができ、高い熱電変換性能を実現できる。 The method for producing a nanocomposite thermoelectric conversion material of the present invention selectively melts only a low melting point phase at a grain boundary of a sintered body having a polycrystalline matrix in which a relative high melting point phase and a low melting point phase are mixed. Since the phonon scattering particles present in the surroundings are taken into the melt phase formed at the grain boundaries, the phonon scattering particles can be dispersed not only in the crystal grains of the thermoelectric conversion material but also in the grain boundary phase. High thermoelectric conversion performance can be realized.
図１を参照して、本発明のナノコンポジット熱電変換材料の組織を説明する。 The structure of the nanocomposite thermoelectric conversion material of the present invention will be described with reference to FIG.
図１（１）の模式的に示すように、本発明のナノコンポジット熱電変換材料１は多結晶体であり、結晶粒１０と結晶粒界相１２とから成るマトリックス中にフォノン散乱粒子１４が分散している。フォノン散乱粒子１４は、結晶粒１０内および結晶粒界相１２内でフォノンを散乱する。更に、図１（２）に粒界付近を拡大して模式的に示すように、フォノンＰは、粒界相１２内のフォノン散乱粒子１４で散乱されるのに加えて、結晶粒１０と粒界相１２との界面でも散乱される。すなわち、粒界相の存在しない従来のナノコンポジット熱電変換材料では、フォノンは粒内のフォノン散乱粒子により散乱されるだけであったが、本発明のナノコンポジット熱電変換材料では、これに加えて粒界相内のフォノン散乱粒子と結晶粒／粒界相界面によっても散乱される、三重の散乱作用を受ける。 As schematically shown in FIG. 1 (1), the nanocomposite thermoelectric conversion material 1 of the present invention is a polycrystal, and phonon scattering particles 14 are dispersed in a matrix composed of crystal grains 10 and grain boundary phases 12. doing. The phonon scattering particles 14 scatter phonons in the crystal grains 10 and the grain boundary phase 12. Further, as schematically shown in FIG. 1B by enlarging the vicinity of the grain boundary, the phonon P is scattered by the phonon scattering particles 14 in the grain boundary phase 12, and in addition to the crystal grains 10 and the grains. It is also scattered at the interface with the field phase 12. That is, in the conventional nanocomposite thermoelectric conversion material having no grain boundary phase, phonons are only scattered by the phonon scattering particles in the grains, but in the nanocomposite thermoelectric conversion material of the present invention, in addition to this, It undergoes a triple scattering action that is also scattered by the phonon scattering particles in the field phase and the grain / grain boundary phase interface.
本発明のナノコンポジット熱電変換材料は、多結晶体である熱電変換材料マトリクスの結晶粒内と結晶粒界相内に同一種類のフォノン散乱粒子が分散している。 In the nanocomposite thermoelectric conversion material of the present invention, the same type of phonon scattering particles are dispersed in the crystal grains and the grain boundary phase of the polyelectric thermoelectric conversion material matrix.
本発明の第１の実施形態においては、フォノン散乱粒子は原料溶液中に分散していたものが結晶粒内と結晶境界相内とに分散する。 In the first embodiment of the present invention, the phonon scattering particles dispersed in the raw material solution are dispersed in the crystal grains and in the crystal boundary phase.
本発明の第２の実施形態においては、マトリクスを構成する熱電変換材料の構成元素のうち少なくとも１種を過飽和に原料溶液中に溶解させ、水熱処理中に析出させて、付加的な第２のフォノン散乱粒子とし、これも同様に結晶粒内と結晶粒界相内とに分散する。これによりフォノン散乱作用が更に高まる。この実施形態においては、フォノン散乱粒子と第２のフォノン散乱粒子が粒界相内で数ｎｍの間隔になり、大きな界面粗さとして作用し、更にフォノン散乱作用を高める。 In the second embodiment of the present invention, at least one of the constituent elements of the thermoelectric conversion material constituting the matrix is dissolved in the raw material solution in a supersaturated state, and is precipitated during the hydrothermal treatment, so that the additional second Phonon scattering particles are also dispersed in the crystal grains and the grain boundary phase. This further increases the phonon scattering effect. In this embodiment, the phonon scattering particles and the second phonon scattering particles are spaced by a few nanometers in the grain boundary phase and act as a large interface roughness, further enhancing the phonon scattering effect.
本発明のナノコンポジット熱電変換材料において、マトリクスの結晶粒径は１００ｎｍ以下のナノサイズであることが望ましい。 In the nanocomposite thermoelectric conversion material of the present invention, the crystal grain size of the matrix is desirably 100 nm or less.
結晶粒界相は、ナノコンポジット熱電変換材料の導電性を良好に確保するために、導電相でなくてはならない。 The grain boundary phase must be a conductive phase in order to ensure good conductivity of the nanocomposite thermoelectric conversion material.
また、結晶粒界相は、結晶粒径に対して十分に薄くなくてはならない。典型的には、１００ｎｍ以下の結晶粒径に対して、結晶粒界相の厚さは１〜１０ｎｍ程度であることが望ましい。 The crystal grain boundary phase must be sufficiently thin with respect to the crystal grain size. Typically, for a crystal grain size of 100 nm or less, the thickness of the grain boundary phase is desirably about 1 to 10 nm.
結晶粒内に分散するフォノン散乱粒子は１〜１００ｎｍ程度、結晶粒界相内に分散するフォノン散乱粒子は１〜１０ｎｍ程度であることが望ましい。 The phonon scattering particles dispersed in the crystal grains are desirably about 1 to 100 nm, and the phonon scattering particles dispersed in the crystal grain boundary phase are desirably about 1 to 10 nm.
本発明のナノコンポジット熱電変換材料に用いる組成系は特に限定する必要はないが、望ましい組成系としては、(Ｂｉ，Ｓｂ)２(Ｔｅ，Ｓｅ)３系、ＣｏＳｂ３系、ＰｂＴｅ系、ＳｉＧｅ系、ＭｇＳｉ系などが挙げられる。これら以外にも下記の組成系が考えられる。 Although the composition system used for the nanocomposite thermoelectric conversion material of the present invention is not particularly limited, preferred composition systems include (Bi, Sb) 2 (Te, Se) 3 system, CoSb 3 system, PbTe system, SiGe system , MgSi type and the like. In addition to these, the following composition systems are conceivable.
ＴｉＮｉＳｎ系、ＺｒＮｉＳｎ系等のハーフホイスラー合金。 Half-Heusler alloys such as TiNiSn and ZrNiSn.
本発明の望ましい実施形態により、(Ｂｉ，Ｓｂ)２Ｔｅ３熱電変換材料のマトリクス中に、フォノン散乱粒子としてＳｉＯ２と、第２のフォノン散乱粒子としてＳｂ２Ｏ３が分散しているナノコンポジット熱電変換材料を作製した。条件および手順は以下のとおりであった。 According to a preferred embodiment of the present invention, a nanocomposite in which SiO 2 as phonon scattering particles and Sb 2 O 3 as second phonon scattering particles are dispersed in a matrix of (Bi, Sb) 2 Te 3 thermoelectric conversion material. A thermoelectric conversion material was produced. Conditions and procedures were as follows.
図２に、製造工程に伴う内部構造の変遷を順次模式的に示す。 In FIG. 2, the transition of the internal structure accompanying a manufacturing process is typically shown sequentially.
また図３に、原料溶液の調製工程（第１工程）と還元処理工程（第２工程）を示す。 FIG. 3 shows a raw material solution preparation step (first step) and a reduction treatment step (second step).
まず第１工程として、１００ｍｌのエタノールに、熱電変換材料の構成元素Ｂｉ，Ｔｅ，Ｓｂの塩として塩化ビスマス（ＢｉＣｌ３）０．４ｇ、塩化テルル（ＴｅＣｌ４）２．５６ｇ、塩化アンチモン（ＳｂＣｌ３）１．４７ｇを溶解してエタノール溶液を作成し、この溶液中にフォノン散乱粒子としてＳｉＯ２粉末１４（平均粒径：５ｎｍ）を分散させ、原料溶液とした（図２（Ａ））。ここで、塩化アンチモンは、熱電変換材料(Ｂｉ，Ｓｂ)２Ｔｅ３マトリクスに対して室温で過飽和なＳｂとなる過剰量とした。 First, as a first step, 100 g of ethanol, 0.4 g of bismuth chloride (BiCl 3 ) as a salt of the constituent elements Bi, Te, and Sb of thermoelectric conversion material, 2.56 g of tellurium chloride (TeCl 4 ), antimony chloride (SbCl 3) 1.47 g was dissolved to prepare an ethanol solution, and SiO 2 powder 14 (average particle size: 5 nm) was dispersed as phonon scattering particles in this solution to obtain a raw material solution (FIG. 2A). Here, the antimony chloride was used as an excessive amount that becomes Sb supersaturated at room temperature with respect to the thermoelectric conversion material (Bi, Sb) 2 Te 3 matrix.
次に第２工程として、ＮａＢＨ４２．５ｇを１００ｍｌのエタノールに溶解した還元剤を、上記の原料溶液に滴下した。これにより、ＳｉＯ２粒子１４の表面に熱電変換材料の各構成元素Ｂｉ，Ｔｅ、Ｓｂ（１０＋１２）’が析出したエタノールスラリーが形成された（図２（Ｂ））。これを水５００ｍｌ＋エタノール３００ｍｌでろ過し、その後更にエタノール３００ｍｌでろ過洗浄した。 Next, as a second step, a reducing agent obtained by dissolving 2.5 g of NaBH 4 in 100 ml of ethanol was added dropwise to the raw material solution. As a result, an ethanol slurry was formed in which the constituent elements Bi, Te, and Sb (10 + 12) ′ of the thermoelectric conversion material were deposited on the surface of the SiO 2 particles 14 (FIG. 2B). This was filtered with 500 ml of water + 300 ml of ethanol, and then further washed by filtration with 300 ml of ethanol.
次に第３工程として（図２（Ｃ））、密閉したオートクレーブ中で、２４０℃×２４ｈの水熱処理を行なう。これにより、熱電変換材料の構成元素（１０＋１２）’が相互に拡散し合金化する。ただし、完全に合金化する条件よりは短時間であるため、相対的な高融点合金相と低融点合金相とが混在したマトリクス前駆体（１０＋１２）が生成する。本実施例においては、高融点合金相はＳｂ２Ｔｅ３または(Ｂｉ、Ｓｂ)２Ｔｅ３のＳｂリッチ相であり、低融点合金相はＢｉ２Ｔｅ３または(Ｂｉ、Ｓｂ)２Ｔｅ３のＢｉリッチ相である。マトリクス前駆体（１０＋１２）中には、原料溶液中に分散していたフォノン散乱粒子ＳｉＯ２１４が分散しており、更に、原料溶液中に過剰量溶解させたＳｂが析出し、水熱処理中に酸化してＳｂ２Ｏ３となり第２のフォノン散乱粒子として分散している。生成物はＮ２ガスフロー雰囲気で乾燥させ、粉末として回収した。このとき、約２．１ｇの粉末が回収された。 Next, as a third step (FIG. 2C), hydrothermal treatment at 240 ° C. × 24 h is performed in a closed autoclave. Thereby, the constituent element (10 + 12) ′ of the thermoelectric conversion material is diffused and alloyed. However, completely because more conditions for alloying is short, relative high melting alloy phase and a low melting alloy phase and are mixed matrix Precursor (10 + 12) is produced. In this example, the high melting point alloy phase is Sb 2 Te 3 or (Bi, Sb) 2 Te 3 Sb rich phase, and the low melting point alloy phase is Bi 2 Te 3 or (Bi, Sb) 2 Te 3 . Bi rich phase. During matrix Precursor (10 + 12), the phonon scattering particles SiO 2 14 which has been dispersed in the raw material solution is dispersed, further, the raw material solution excess dissolved Sb precipitates were in, in the hydrothermal treatment Oxidized into Sb 2 O 3 and dispersed as second phonon scattering particles. The product was dried in an N 2 gas flow atmosphere and recovered as a powder. At this time, about 2.1 g of powder was recovered.
更に第４工程として、上記粉末に３５０℃×５秒でＳＰＳ焼結を行い、焼結体を得た（図２（Ｃ））。 Furthermore, as a fourth step, the powder was subjected to SPS sintering at 350 ° C. for 5 seconds to obtain a sintered body (FIG. 2C).
最後に第５工程として、焼結体にＮ２雰囲気中で４００℃×２４ｈのアニールを施した。これにより、まず図２（Ｄ）に示すように、結晶粒界で低融点合金相（Ｂｉ２Ｔｅ３または(Ｂｉ、Ｓｂ)２Ｔｅ３のＢｉリッチ相）のみが選択的に溶融する。アニールの条件は、低融点合金相のみが融解するように選択する。 Finally, as a fifth step, the sintered body was annealed at 400 ° C. × 24 h in an N 2 atmosphere. As a result, first, as shown in FIG. 2D, only the low melting point alloy phase (Bi 2 Te 3 or (Bi, Sb) 2 Te 3 Bi-rich phase) is selectively melted at the grain boundaries. The annealing conditions are selected so that only the low melting point alloy phase melts.
その際、低融点溶融層１２’中には、結晶粒内に分散していたフォノン散乱粒子ＳｉＯ２１４および第２のフォノン散乱粒子Ｓｂ２Ｏ３が取り込まれ、低融点合金相から成る粒界相１２中に分散する（図２（Ｅ））。 At this time, the phonon scattering particles SiO 2 14 and the second phonon scattering particles Sb 2 O 3 dispersed in the crystal grains are taken into the low melting point molten layer 12 ′, and the grain boundary composed of the low melting point alloy phase is taken. Disperse in the phase 12 (FIG. 2E).
以上により、図４（１）、（２）にＴＥＭ像を示すように、本発明の望ましい実施形態により、 (Ｂｉ，Ｓｂ)２Ｔｅ３熱電変換材料のマトリクス中に、フォノン散乱粒子としてＳｉＯ２と、第２のフォノン散乱粒子としてＳｂ２Ｏ３が分散しているナノコンポジット熱電変換材料が得られた。 As described above, as shown in FIGS. 4 (1) and 4 (2), according to a preferred embodiment of the present invention, SiO 2 as phonon scattering particles in the matrix of (Bi, Sb) 2 Te 3 thermoelectric conversion material. As a result, a nanocomposite thermoelectric conversion material in which Sb 2 O 3 was dispersed as the second phonon scattering particles was obtained.
結晶粒界に厚さ１〜１０ｎｍの粒界相として(Ｂｉ、Ｓｂ)２Ｔｅ３のＢｉリッチ相が観察される。(Ｂｉ、Ｓｂ)２Ｔｅ３のＢｉリッチ相は導電性である。この粒界相中には粒径１〜１０ｎｍのＳｉＯ２粒子、Ｓｂ２Ｏ３粒子が存在する。結晶粒内にも、粒径１〜１００ｎｍのＳｉＯ２粒子、Ｓｂ２Ｏ３粒子が存在する。ＸＲＤのシェラー法により測定した平均結晶粒径は４１ｎｍであった。 A Bi-rich phase of (Bi, Sb) 2 Te 3 is observed as a grain boundary phase having a thickness of 1 to 10 nm at the crystal grain boundary. The Bi rich phase of (Bi, Sb) 2 Te 3 is conductive. In this grain boundary phase, SiO 2 particles and Sb 2 O 3 particles having a particle diameter of 1 to 10 nm are present. In the crystal grains, there are SiO 2 particles and Sb 2 O 3 particles having a particle diameter of 1 to 100 nm. The average crystal grain size measured by XRD Scherrer method was 41 nm.
〔比較例１〕
工程３の水熱処理の条件を２４０℃×４８ｈとして均一に合金化した以外は実施例１と同様の条件および手順により、実施例１の工程４までを行なって、粒界相は生成させずにナノコンポジット熱電変換材料を作製した。また、第１工程において塩化アンチモン（ＳｂＣｌ３）の配合量はＳｂ量が化学量論値となるように１．２４ｇとし、第３工程において第２のフォノン散乱粒子Ｓｂ２Ｏ３は生成させなかった。すなわち、比較例１は、フォノン散乱粒子としてはＳｉＯ２粒子のみが存在し、かつ粒界相１２は生成しておらず、その他の点では実施例１と同様のナノコンポジット熱電変換材料である。
[Comparative Example 1]
According to the same conditions and procedure as in Example 1 except that the hydrothermal treatment conditions in Step 3 were uniformly 240 ° C. × 48 h, the process up to Step 4 in Example 1 was carried out without generating a grain boundary phase. Nanocomposite thermoelectric conversion materials were prepared. In addition, the blending amount of antimony chloride (SbCl 3 ) in the first step is 1.24 g so that the Sb amount becomes a stoichiometric value, and the second phonon scattering particles Sb 2 O 3 are not generated in the third step. It was. That is, Comparative Example 1 is a nanocomposite thermoelectric conversion material similar to that of Example 1 except that only SiO 2 particles are present as phonon scattering particles and no grain boundary phase 12 is generated.
〔比較例２〕
フォノン散乱粒子としてＳｉＯ２およびＳｂ２Ｏ３を分散させたが、粒界相は生成させないナノコンポジット熱電変換材料を、下記の条件および手順で作製した。すなわち、比較例２は、粒界相が生成していない以外は実施例１と同様のナノコンポジット熱電変換材料である。
[Comparative Example 2]
A nanocomposite thermoelectric conversion material in which SiO 2 and Sb 2 O 3 were dispersed as phonon scattering particles but no grain boundary phase was produced was produced under the following conditions and procedures. That is, Comparative Example 2 is a nanocomposite thermoelectric conversion material similar to Example 1 except that no grain boundary phase is generated.
図５<１>に示すように、原料溶液の配合および還元処理を行なって、ＳｉＯ２粒子の表面にＳｂを析出させてＳｉＯ２／Ｓｂ粒子を作製した。このとき、Ｓｂ層の厚さが数ｎｍになるように析出量を調整した。 As shown in FIG. 5 <1>, perform the blending and reduction of raw materials solution was prepared SiO 2 / Sb particles to precipitate Sb on the surface of the SiO 2 particles. At this time, the amount of precipitation was adjusted so that the thickness of the Sb layer was several nm.
次に、図５<２>に示すように、図５<１>で作製したＳｉＯ２／Ｓｂ粒子を加えた配合の原料溶液を作製し、これに還元処理を行なって、ＳｉＯ２／Ｓｂ粒子の表面にＢｉ、Ｔｅ、Ｓｂを析出させ、スラリーとした。得られたスラリーを実施例１と同様に２回洗浄を行った。 Next, as shown in FIG. 5 <2>, a raw material solution containing the SiO 2 / Sb particles prepared in FIG. 5 <1> is prepared and subjected to reduction treatment to obtain SiO 2 / Sb particles. Bi, Te, and Sb were deposited on the surface of the resulting slurry. The obtained slurry was washed twice in the same manner as in Example 1.
次に、実施例１の第３工程と同様に水熱処理を行なった。ただし、処理時間は４８ｈとして、全体に均一に合金化させ単相の(Ｂｉ、Ｓｂ)２Ｔｅ３マトリクス前駆体を生成させた。生成物はＮ２ガスフロー雰囲気で乾燥させ、粉末として回収した。このとき、約２．１ｇの粉末が回収された。 Next, hydrothermal treatment was performed in the same manner as in the third step of Example 1. However, as the processing time is 48h, the single-phase evenly alloyed throughout (Bi, Sb) to produce a 2 Te 3 matrix Precursor. The product was dried in an N 2 gas flow atmosphere and recovered as a powder. At this time, about 2.1 g of powder was recovered.
次いで、実施例１の第４工程と同様にＳＰＳ焼結を行なって、比較例２のナノコンポジット熱電変換材料とした。 Subsequently, SPS sintering was performed similarly to the 4th process of Example 1, and it was set as the nanocomposite thermoelectric conversion material of the comparative example 2.
〔従来例〕
下記文献（＊）に開示されている熱電変換材料の特性を従来例として比較に用いた。従来例は、実施例とほぼ等しい組成の熱電変換材料であり、フォノン散乱粒子を用いていない。
（＊：Ｊｏｕｒｎｄ ｏｆ Ｃｒｙｓｔａｌ Ｇｒｏｗｔｈ ２７７（２００３）２５８−２６３．）
[Conventional example]
The characteristics of the thermoelectric conversion material disclosed in the following document (*) were used for comparison as a conventional example. The conventional example is a thermoelectric conversion material having a composition almost equal to that of the example and does not use phonon scattering particles.
(*: Journ of Crystal Growth 277 (2003) 258-263.)
表１に、実施例、比較例１、２、従来例の構成をまとめて示す。 Table 1 summarizes the configurations of the examples, comparative examples 1 and 2, and the conventional example.
＜特性の評価＞
実施例で作製した本発明のナノコンポジット熱電変換材料の特性を評価した結果を図６、図７、図８に示す。図には、比較例１，２および従来例の特性も併せて示す。
<Evaluation of characteristics>
The results of evaluating the characteristics of the nanocomposite thermoelectric conversion material of the present invention produced in the examples are shown in FIGS. 6, 7, and 8. The figure also shows the characteristics of Comparative Examples 1 and 2 and the conventional example.
図６に示すように、これら４者はゼーベック係数がほぼ同じであり、組成、キャリア濃度等がほぼ同じであることが分かる。 As shown in FIG. 6, it can be seen that these four elements have substantially the same Seebeck coefficient, and the composition, carrier concentration, etc. are substantially the same.
図７に示すように、熱伝導率は、フォノン散乱粒子の存在により、実施例および比較例１、２は従来例に比べて劇的に低下しており、特に実施例は、比較例１、２に比べても更に低下している。これは、粒界相自体と粒界相中の２種のフォノン散乱粒子の存在により、熱の散乱界面が大幅に増加したことによると考えられる。 As shown in FIG. 7, the thermal conductivity is drastically lowered in Examples and Comparative Examples 1 and 2 as compared with the conventional example due to the presence of phonon scattering particles. Compared to 2, it is further reduced. This is considered to be due to the fact that the heat scattering interface is greatly increased by the presence of the grain boundary phase itself and the two types of phonon scattering particles in the grain boundary phase.
図８に示すように、無次元性能指数ＺＴは、熱伝導率が大幅に低下したことにより、顕著に向上している。すなわち、ＺＴ値は、フォノン散乱粒子なしの従来例が０．９〜１．０、フォノン散乱粒子がＳｉＯ２のみで粒界相がない比較例１が１．４〜１．５、フォノン散乱粒子がＳｉＯ２とＳｂ２Ｏ３で粒界相がない比較例２が１．５〜１．６であるのに対して、粒界相が存在し、かつ、フォノン散乱粒子がＳｉＯ２とＳｂ２Ｏ３である実施例は２．２〜２．３と顕著に向上している。比較例１と比較例２を比べると、比較例２の方が第２のフォノン散乱粒子であるＳｂ２Ｏ３の存在により特性が向上する。しかし、実施例と比較例２を比較すると、粒界相の存在により特性が大きく向上しており、粒界相の効果の方が大きいことが分かる。従って、データは記載されていないが、第１のフォノン散乱粒子と粒界相のみでも効果があり、それに加えて第２の分散粒子と分散させれば、さらに効果があることが分かる。 As shown in FIG. 8, the dimensionless figure of merit ZT is significantly improved due to the significant decrease in thermal conductivity. That is, the ZT value is 0.9 to 1.0 in the conventional example without the phonon scattering particles, 1.4 to 1.5 in the comparative example 1 in which the phonon scattering particles are only SiO 2 and there is no grain boundary phase, and the phonon scattering particles. Comparative Example 2 having no grain boundary phase with SiO 2 and Sb 2 O 3 is 1.5 to 1.6, whereas a grain boundary phase is present, and phonon scattering particles are SiO 2 and Sb 2. a O 3 is embodiment is remarkably improved as 2.2-2.3. Comparing Comparative Example 1 and Comparative Example 2, the characteristics of Comparative Example 2 are improved due to the presence of Sb 2 O 3 which is the second phonon scattering particle. However, comparing Example and Comparative Example 2, it can be seen that the characteristics are greatly improved due to the presence of the grain boundary phase, and the effect of the grain boundary phase is greater. Therefore, although data is not described, it can be seen that only the first phonon scattering particles and the grain boundary phase are effective, and in addition to that, if the particles are dispersed with the second dispersed particles, it is further effective.
本発明によれば、フォノン散乱粒子を分散させた結晶粒界相を具備したことにより、ナノサイズのフォノン散乱粒子による熱伝導率の低減効果を更に高めて大幅に熱電変換性能を高めたナノコンポジット熱電変換材料およびその製造方法が提供される。 According to the present invention, by providing a grain boundary phase in which phonon scattering particles are dispersed, a nanocomposite that further enhances the effect of reducing thermal conductivity by nano-sized phonon scattering particles and greatly improves thermoelectric conversion performance. A thermoelectric conversion material and a method for producing the same are provided.
Claims (2)
熱電変換材料の各構成元素の塩を溶解させ、かつ、フォノン散乱粒子を分散させた原料溶液を調製する第１工程、
上記原料溶液に還元剤を滴下して、上記フォノン散乱粒子の表面に上記熱電変換材料の各構成元素を析出させてスラリーを形成する第２工程、
上記スラリーを水熱処理して、相対的に高融点の高融点合金相と低融点の低融点合金相とから成るマトリクス前駆体中に上記フォノン散乱粒子が分散した複合体を形成する第３工程、
上記複合体を焼結して、多結晶マトリクス中に上記フォノン散乱粒子が分散した焼結体を形成する第４工程、および
上記焼結体を熱処理することにより、該焼結体の結晶粒界において上記低融点合金相のみを選択的に溶融させ、生成した低融点溶融相中に近傍の上記フォノン散乱粒子を取り込ませ、上記低融点合金相中に該フォノン散乱粒子が分散した複合体としての粒界相を形成する第５工程、
を含むことを特徴とするナノコンポジット熱電変換材料の製造方法。 In a method for producing a nanocomposite thermoelectric conversion material in which nano-sized phonon scattering particles are dispersed in a matrix of a thermoelectric conversion material,
A first step of preparing a raw material solution in which the salt of each constituent element of the thermoelectric conversion material is dissolved and the phonon scattering particles are dispersed;
A second step in which a reducing agent is dropped into the raw material solution to deposit a constituent element of the thermoelectric conversion material on the surface of the phonon scattering particles to form a slurry;
The slurry was hydrothermally treated, third step of relatively high melting point of the phonon scattering particles in the body during the ejection before matrix of a refractory alloy phase and a low melting point of the low melting point alloy phase to form a complex dispersed ,
A fourth step in which the composite is sintered to form a sintered body in which the phonon scattering particles are dispersed in a polycrystalline matrix; and the sintered body is subjected to a heat treatment, whereby grain boundaries of the sintered body are formed. As a composite in which only the low melting point alloy phase is selectively melted, the phonon scattering particles in the vicinity are taken into the generated low melting point melt phase, and the phonon scattering particles are dispersed in the low melting point alloy phase. A fifth step of forming a grain boundary phase;
A method for producing a nanocomposite thermoelectric conversion material, comprising:
上記第１工程において、上記原料溶液に、上記熱電変換材料の各構成元素のうち、少なくとも１種を室温における固溶限に対して過剰量を溶解させ、
上記第３工程において、上記マトリクス前駆体中に上記過剰量の構成元素を析出させて第２のフォノン散乱粒子として分散させ、
上記第５工程において、上記フォノン散乱粒子と共に上記第２のフォノン散乱粒子も分散した上記粒界相を形成する
ことを特徴とするナノコンポジット熱電変換材料の製造方法。 In claim 1,
In the first step, an excess amount of at least one of the constituent elements of the thermoelectric conversion material is dissolved in the raw material solution with respect to a solid solubility limit at room temperature,
In the third step, it is dispersed as a second phonon scattering particles by precipitating the constituent element of the excess body during ejection before the matrix,
The method for producing a nanocomposite thermoelectric conversion material, wherein in the fifth step, the grain boundary phase in which the second phonon scattering particles are dispersed together with the phonon scattering particles is formed.
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