JP3529576B2 - Thermoelectric material and method for manufacturing the same - Google Patents
Thermoelectric material and method for manufacturing the sameInfo
- Publication number
- JP3529576B2 JP3529576B2 JP04358797A JP4358797A JP3529576B2 JP 3529576 B2 JP3529576 B2 JP 3529576B2 JP 04358797 A JP04358797 A JP 04358797A JP 4358797 A JP4358797 A JP 4358797A JP 3529576 B2 JP3529576 B2 JP 3529576B2
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- Prior art keywords
- ultrafine particles
- thermoelectric material
- particles
- inert
- thermoelectric
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Description
【０００１】[0001]
【発明の属する技術分野】本発明は、熱電変換装置に利
用する熱電材料に関する。更に詳述すると、本発明は熱
電材料の組成の改良に関する。TECHNICAL FIELD The present invention relates to a thermoelectric material used for a thermoelectric conversion device. More specifically, the present invention relates to improving the composition of thermoelectric materials.
【０００２】[0002]
【従来の技術】熱電材料の電気的性能は性能指数Ｚによ
り示される。この性能指数Ｚは、数式１に示すように材
料の熱伝導率κ，電気抵抗率ρ，ゼーベック係数αの３
つの物性値で決定される。The electrical performance of thermoelectric materials is indicated by the figure of merit Z. This figure of merit Z is, as shown in Equation 1, 3 of the thermal conductivity κ of the material, the electrical resistivity ρ, and the Seebeck coefficient α.
Determined by one physical property value.
【０００３】[0003]
【数１】Ｚ＝α2／（ρ×κ）
この性能指数Ｚが大きいほど熱電材料として高性能であ
る。このため、性能指数Ｚを向上させる手段の１つとし
て材料の熱伝導率κを低減することが望まれる。すなわ
ち、熱電材料は温度差により発電するものなので、熱伝
導率κが低い程、温度差を生じ易いということになる。## EQU1 ## Z = α 2 / (ρ × κ) The larger the figure of merit Z, the higher the performance as a thermoelectric material. Therefore, it is desired to reduce the thermal conductivity κ of the material as one of means for improving the figure of merit Z. That is, since the thermoelectric material generates electricity by the temperature difference, the lower the thermal conductivity κ, the more easily the temperature difference occurs.
【０００４】材料の熱伝導率κを低減するために、熱電
材料の出発原料の粒子に熱電材料の母材と反応しない粒
径数ｎｍ〜数十ｎｍの超微粒子（不活性超微粒子）を添
加することがある。これにより、不活性超微粒子が熱電
材料における熱伝導の主要因であるフォノンを散乱させ
て、熱伝導率κを低減することができる。In order to reduce the thermal conductivity κ of the material, ultrafine particles (inert ultrafine particles) having a particle size of several nm to several tens nm which do not react with the base material of the thermoelectric material are added to the particles of the starting material of the thermoelectric material. I have something to do. As a result, the inert ultrafine particles scatter phonons, which are the main cause of heat conduction in the thermoelectric material, and the thermal conductivity κ can be reduced.
【０００５】そこで、従来の熱電材料は、粒径１μｍ〜
数十μｍ（多くの場合には数十μｍオーダ）程度の熱電
材料の粒子を出発原料として用い、これに上述の不活性
超微粒子を添加してから合金化し、更にこれを所定形状
に成形してから２〜３時間加熱・焼結することによって
作製されている。Therefore, the conventional thermoelectric material has a particle size of 1 μm to
Particles of a thermoelectric material of about several tens of μm (often on the order of several tens of μm) are used as a starting material, and the above-mentioned inert ultrafine particles are added to the starting alloy, which is then alloyed and further formed into a predetermined shape. After that, it is produced by heating and sintering for 2 to 3 hours.
【０００６】[0006]
【発明が解決しようとする課題】しかしながら、従来の
熱電材料では、図３に示すように不活性超微粒子１０２
が偏在することによって、不活性超微粒子１０２による
フォノンの散乱効果よりも不活性超微粒子１０２の偏在
による電気抵抗率等の他の物性値の悪化が起こり、熱電
材料の性能向上が妨げられている。However, in the conventional thermoelectric material, as shown in FIG. 3, the inert ultrafine particles 102 are used.
Uneven distribution causes deterioration of other physical property values such as electrical resistivity due to uneven distribution of the inactive ultrafine particles 102 rather than the scattering effect of phonons by the inactive ultrafine particles 102, which hinders the performance improvement of the thermoelectric material. .
【０００７】不活性超微粒子１０２が偏在する原因は、
出発原料の粒子１０１の粒径と不活性超微粒子１０２の
粒径比（出発原料の粒径／不活性超微粒子の粒径）が大
きかったためと考えられる。すなわち、出発原料の粒子
１０１の粒径は小さくても１μｍ程度はあるので、焼結
前の状態で出発原料の粒子１０１と不活性超微粒子１０
２との粒径比は少なくとも１００程度になる。このた
め、この巨大な出発原料の粒子１０１の粒子と微小な不
活性超微粒子１０２とを混合すると、図３に示すように
出発原料の粒子１０１同士が接触すると共に粒子１０１
間の隙間に不活性超微粒子１０２が存在する状態、即ち
不活性超微粒子１０２が偏在した状態となってしまう。The cause of uneven distribution of the inert ultrafine particles 102 is
It is considered that this was because the particle size ratio of the starting material particles 101 and the particle size of the inert ultrafine particles 102 (particle size of the starting material / particle size of the inert ultrafine particles) was large. That is, since the particle size of the starting material particles 101 is about 1 μm at the smallest, the particle size of the starting material particles 101 and the inert ultrafine particles 10 in the state before sintering are small.
The particle size ratio with 2 is at least about 100. Therefore, when the particles of the huge starting material particles 101 and the minute inert ultrafine particles 102 are mixed, the starting material particles 101 come into contact with each other as shown in FIG.
This results in a state in which the inert ultrafine particles 102 are present in the gap between them, that is, a state in which the inert ultrafine particles 102 are unevenly distributed.
【０００８】さらに、この状態で２〜３時間かけて焼結
される間に、隣り合って接触する出発原料の粒子１０１
同士が一体化して結晶粒になって成長する。このとき、
不活性超微粒子１０２が分散されることはないので、焼
結後の熱電材料は巨大な結晶粒の隙間に微小な不活性超
微粒子１０２が位置した状態、即ち不活性超微粒子１０
２が偏在した状態となってしまう。これにより、フォノ
ンの散乱による熱伝導率κの低減よりも電気抵抗率ρや
ゼーベック係数αの悪化の方が上回ってしまい、熱電材
料の熱伝導率κが低減しても熱電材料の性能指数Ｚの向
上を図ることができなかった。Further, while being sintered in this state for 2 to 3 hours, the particles 101 of the starting material which come into contact with each other next to each other
They are integrated with each other to form crystal grains and grow. At this time,
Since the inert ultrafine particles 102 are not dispersed, the thermoelectric material after sintering is in a state where the minute inert ultrafine particles 102 are located in the gaps between the huge crystal grains, that is, the inert ultrafine particles 10
2 will be unevenly distributed. As a result, the deterioration of the electrical resistivity ρ and the Seebeck coefficient α exceeds the reduction of the thermal conductivity κ due to the scattering of phonons, and even if the thermal conductivity κ of the thermoelectric material is reduced, the figure of merit Z of the thermoelectric material is reduced. Could not be improved.
【０００９】ところで、一部の不活性超微粒子１０２’
が、隣り合う出発原料の粒子１０１’，１０１’に挟ま
れてこれらの粒子１０１’，１０１’同士の接触を妨害
することがある。この場合、焼結の際にこれらの粒子１
０１’，１０１’同士の結晶化がなされないので、母材
の粒子の成長を抑制することができる。すなわち、不活
性超微粒子１０２は母材の粒子の成長を抑制するピン止
め効果的な働きをすることがある。By the way, some of the inert ultrafine particles 102 '.
However, the particles 101 ′ and 101 ′ of the starting material may be sandwiched between adjacent particles of the starting material to prevent contact between the particles 101 ′ and 101 ′. In this case, these particles 1
Since 01 'and 101' are not crystallized, the growth of the base material particles can be suppressed. That is, the inert ultrafine particles 102 may function as a pinning effect that suppresses the growth of the base material particles.
【００１０】しかし、出発原料の粒子１０１と不活性超
微粒子１０２との粒径比は少なくとも１００程度はある
ので、これら出発原料の粒子１０１と不活性超微粒子１
０２とを混合した場合に不活性超微粒子１０２が出発原
料の粒子１０１同士の間に挟まれることはほとんどな
い。このため、不活性超微粒子１０２がピン止め効果的
な働きをして熱電材料の結晶成長を抑制する効果が得ら
れない。However, since the particle size ratio between the starting material particles 101 and the inert ultrafine particles 102 is at least about 100, these starting material particles 101 and the inert ultrafine particles 1 are used.
When mixed with 02, the inert ultrafine particles 102 are hardly sandwiched between the particles 101 of the starting material. For this reason, the inert ultrafine particles 102 cannot effectively prevent the crystal growth of the thermoelectric material due to the pinning effect.
【００１１】さらに、この状態で焼結される際は、大部
分の出発原料の粒子１０１は隣り合う粒子１０１に接し
て結晶化し易くなっているので、焼結後の熱電材料の母
材の粒子は大きくなってしまう。Further, when sintered in this state, most of the starting material particles 101 are in contact with the adjacent particles 101 and are likely to be crystallized, so that the particles of the base material of the thermoelectric material after sintering are easy to crystallize. Will grow.
【００１２】これにより、結晶粒が極めて大きく成長す
ることから、結晶粒界の増加による熱電材料中でのフォ
ノンの散乱を十分に促進することができず、熱電材料の
熱伝導率κを低減することが困難であった。As a result, the crystal grains grow extremely large, so that the scattering of phonons in the thermoelectric material due to the increase of crystal grain boundaries cannot be sufficiently promoted, and the thermal conductivity κ of the thermoelectric material is reduced. Was difficult.
【００１３】そこで、本発明は、熱電材料の電気抵抗率
ρやゼーベック係数αの劣化による性能指数Ｚの低下量
よりも熱伝導率κの低減による性能指数Ｚの増加量を大
きくすることにより性能指数Ｚの向上を図ることができ
る熱電材料及びその製造方法を提供することを目的とす
る。Therefore, according to the present invention, the performance is increased by increasing the increase amount of the performance index Z due to the decrease of the thermal conductivity κ rather than the decrease amount of the performance index Z due to the deterioration of the electrical resistivity ρ and the Seebeck coefficient α of the thermoelectric material. An object of the present invention is to provide a thermoelectric material capable of improving the index Z and a manufacturing method thereof.
【００１４】[0014]
【課題を解決するための手段】かかる目的を達成するた
め、請求項１の熱電材料は、出発原料を超微粒子とし、
それに母材と反応しない不活性な超微粒子を均一に分布
する状態に添加して焼結して成るようにしている。ここ
で、本明細書中において「超微粒子」とは粒径数ｎｍ〜
数十ｎｍ程度の粒子をいう。In order to achieve the above object, the thermoelectric material according to claim 1 uses ultrafine particles as a starting material,
In addition, inert ultrafine particles that do not react with the base material are added in a uniformly distributed state and sintered. Here, in the present specification, the "ultrafine particles" have a particle diameter of several nm to
It refers to particles of about several tens of nm.
【００１５】したがって、請求項１の熱電材料によれ
ば、出発原料と不活性超微粒子とのいずれもが超微粒子
で粒径比がほぼ１の同等の大きさとなる。このため、不
活性超微粒子が熱電材料の母材全体に分散し易くなり出
発原料の粒子間に存在する確率が高くなるので、母材の
粒子同士の結晶化を防止することになる。すなわち、不
活性超微粒子が母材の粒子の結晶化に対してピン止め効
果的に作用して結晶粒の成長を抑制する。これにより、
結晶粒を細かくして結晶粒界を増やすことができる。Therefore, according to the thermoelectric material of the first aspect, both the starting material and the inert ultrafine particles are ultrafine particles and have a particle size ratio of about 1 and an equivalent size. For this reason, the inert ultrafine particles are easily dispersed throughout the matrix of the thermoelectric material, and the probability that they exist between the particles of the starting material is increased, so that the crystallization of the particles of the matrix is prevented. That is, the inert ultrafine particles act effectively by pinning the crystallization of the particles of the base material to suppress the growth of the crystal particles. This allows
The grain boundaries can be increased by making the crystal grains finer.
【００１６】しかも、熱電材料の出発原料と不活性超微
粒子とはほぼ同等の大きさであるため、不活性超微粒子
は図１に示すように熱電材料中に偏在することなく均一
に分布して存在することになる。このため、熱電材料の
結晶粒界の増加と不活性超微粒子の均一添加によるフォ
ノンの散乱によって、熱伝導率以外の電気抵抗率やゼー
ベック係数の劣化による性能指数の低下量よりも熱伝導
率の低減による性能指数の増大量を大きくすることがで
き、熱電材料の性能を向上することができる。Moreover, since the starting material of the thermoelectric material and the inert ultrafine particles have almost the same size, the inert ultrafine particles are uniformly distributed in the thermoelectric material without being unevenly distributed as shown in FIG. Will exist. Therefore, due to the increase of crystal grain boundaries of the thermoelectric material and the scattering of phonons due to the uniform addition of the inert ultrafine particles, the thermal conductivity is lower than the decrease in the figure of merit due to the deterioration of the electrical resistivity other than the thermal conductivity and the Seebeck coefficient. The amount of increase in the figure of merit due to the reduction can be increased, and the performance of the thermoelectric material can be improved.
【００１７】また、請求項２の熱電材料の製造方法は、
超微粒子の熱電材料の出発原料に母材と反応しない不活
性な超微粒子を添加して混合して焼結するようにしてい
る。したがって、熱電材料の結晶粒と不活性超微粒子の
大きさとが共に超微粒子で近似した大きさであるため、
出発原料の超微粒子に対して不活性超微粒子は偏在する
ことなく均一に分布して存在することになる。そして、
出発原料が超微粒子であるので、不活性超微粒子が出発
原料の粒子間に存在する確率が高くなり出発原料の結晶
化に対してピン止め効果的に作用して結晶粒の成長を抑
制する。このため、結晶粒を細かくでき、尚かつ不活性
超微粒子の均一添加によりフォノンの散乱が効果的に促
進されて熱伝導率が低減した熱電材料を製造することが
できる。The method of manufacturing a thermoelectric material according to claim 2 is
Inert ultrafine particles that do not react with the base material are added to the starting material of the ultrafine particle thermoelectric material and mixed and sintered. Therefore, since the crystal grains of the thermoelectric material and the size of the inert ultrafine particles are similar to those of the ultrafine particles,
The inert ultrafine particles are uniformly distributed without being unevenly distributed with respect to the ultrafine particles of the starting material. And
Since the starting material is ultrafine particles, the probability that inert ultrafine particles are present between the particles of the starting material is high, and pinning effect is exerted on the crystallization of the starting material to suppress the growth of the crystal particles. Therefore, it is possible to manufacture a thermoelectric material in which the crystal grains can be made fine, and the phonon scattering is effectively promoted by the uniform addition of the inert ultrafine particles to reduce the thermal conductivity.
【００１８】また、請求項３の熱電材料の製造方法で
は、出発原料と不活性超微粒子とを放電プラズマ焼結に
より焼結するようにしている。この場合、短時間に大き
なエネルギーを投入することが可能であることから焼結
時間を短くして焼結中の結晶粒の成長を抑制して緻密な
結晶粒、例えば１μｍ未満の結晶粒の焼結体を得ること
ができる。また、超微粒子は活性が高いため、超微粒子
よりも大きい粒子の焼結温度よりも低い温度での焼結が
可能となるので、結晶粒の成長を抑えることができる。
この結果、結晶粒をより一層細かくできるため、粒界部
分の増加によりフォノンの散乱が十分に促進されて熱伝
導率が低減した熱電材料を製造することができる。Further, in the method for manufacturing a thermoelectric material according to the third aspect, the starting material and the inert ultrafine particles are sintered by spark plasma sintering. In this case, since it is possible to apply a large amount of energy in a short time, the sintering time is shortened to suppress the growth of crystal grains during sintering and to fire dense crystal grains, for example, crystal grains of less than 1 μm. You can get a unity. Further, since the ultrafine particles have high activity, it becomes possible to sinter at a temperature lower than the sintering temperature of particles larger than the ultrafine particles, so that the growth of crystal grains can be suppressed.
As a result, since the crystal grains can be made finer, the thermoelectric material in which the phonon scattering is sufficiently promoted by the increase in the grain boundary portion and the thermal conductivity is reduced can be manufactured.
【００１９】さらに、請求項４の熱電材料の製造方法で
は、出発原料と不活性超微粒子とをメカニカルアローイ
ング法により混合している。この場合、出発原料が不活
性超微粒子を含んだ状態で均一な合金になるので、不活
性超微粒子が熱電材料中に偏在することなく均一に分布
して存在するようになる。これにより、フォノンが十分
に散乱されて熱伝導率が低い熱電材料を製造することが
できる。Further, in the method for producing a thermoelectric material according to the fourth aspect, the starting material and the inert ultrafine particles are mixed by a mechanical arrowing method. In this case, since the starting material becomes a uniform alloy in the state of containing the inert ultrafine particles, the inert ultrafine particles are uniformly distributed in the thermoelectric material without being unevenly distributed. This makes it possible to produce a thermoelectric material having a low thermal conductivity in which phonons are sufficiently scattered.
【００２０】[0020]
【発明の実施の形態】以下、本発明の構成を図面に示す
実施の形態の一例に基づいて詳細に説明する。熱電材料
は、出発原料を超微粒子とし、それに母材と反応しない
超微粒子である不活性超微粒子を均一に分布する状態に
添加して焼結して成るようにしている。すなわち、熱電
材料１は、図１に示すように、超微粒子の結晶粒２とそ
れに均一に分布する状態に添加された超微粒子の不活性
超微粒子３とから成る。本実施形態では、出発原料とし
てビスマス・Ｂｉ，テルル・Ｔｅ，アンチモン・Ｓｂ，
セレン・Ｓｅの超微粒子を使用して合金化された結晶粒
２が用いられる。また、不活性超微粒子３としてはＢＮ
の超微粒子を使用している。このため、この熱電材料１
はＢＮの超微粒子を含んだビスマス−テルル系の焼結体
とされている。BEST MODE FOR CARRYING OUT THE INVENTION The structure of the present invention will be described below in detail based on an example of an embodiment shown in the drawings. The thermoelectric material is formed by using ultrafine particles as a starting material, and adding inactive ultrafine particles that are ultrafine particles that do not react with the base material in a uniformly distributed state and sinter them. That is, as shown in FIG. 1, the thermoelectric material 1 is composed of crystal grains 2 of ultrafine particles and inert ultrafine particles 3 of ultrafine particles added to the crystal grains 2 in a uniformly distributed state. In this embodiment, the starting materials are bismuth / Bi, tellurium / Te, antimony / Sb,
Crystal grains 2 alloyed with ultrafine particles of selenium / Se are used. Further, as the inert ultrafine particles 3, BN is used.
Uses ultrafine particles. Therefore, this thermoelectric material 1
Is a bismuth-tellurium-based sintered body containing ultrafine BN particles.
【００２１】この熱電材料１を製造する手順を図２に示
すフローチャートに基づいて説明する。本実施形態で
は、熱電材料１を製造する手順は出発原料及び不活性超
微粒子３から合金の微粉末を合成する粉末合成工程（ス
テップ１０〜１２）とこの微粉末を焼結する焼結工程
（ステップ１３〜１４）との２工程から成るものであ
る。The procedure for producing the thermoelectric material 1 will be described with reference to the flow chart shown in FIG. In the present embodiment, the procedure for manufacturing the thermoelectric material 1 is a powder synthesizing step (steps 10 to 12) for synthesizing fine powder of an alloy from the starting raw material and the inert ultrafine particles 3 and a sintering step (sintering the fine powder). It is composed of two processes including steps 13 to 14).
【００２２】粉末合成工程では、出発原料として単体の
Ｂｉ，Ｔｅ，Ｓｂ，Ｓｅの超微粒子と不活性超微粒子と
してのＢＮの超微粒子とを用意する（ステップ１０）。
これらの超微粒子の粒径は０．０１μｍ程度である。こ
れらの超微粒子をグローブボックス内に入れて混合粉砕
機を用いてメカニカルアローイング法により摩砕，混合
する（ステップ１１）。これにより、Ｂｉ，Ｔｅ，Ｓ
ｂ，Ｓｅが合金化して、Ｂｉ−Ｔｅ−Ｓｂ−Ｓｅ系の合
金粒子あるいはＢｉ−Ｔｅ−Ｓｂ系の合金粒子と不活性
超微粒子とが、例えば合金粒子数個と不活性超微粒子１
個の割合で結合した微粉体を構成する（ステップ１
２）。この微粉体の粒径は０．１μｍ程度となる。ま
た、合金粒子としては、例えば（Ｂｉ2Ｔｅ3）90（Ｓｂ
2Ｔｅ3）5（Ｓｂ2Ｓｅ3）5のｎ型熱電材料の合金粒子
や、（Ｓｂ2Ｔｅ3）70（Ｂｉ2Ｔｅ3）30のｐ型熱電材料
の合金粒子が作られる。合金粒子の組成はこれらのもの
に限定されないことは言うまでもない。In the powder synthesizing process, simple particles of Bi, Te, Sb and Se as starting materials and ultrafine particles of BN as inert ultrafine particles are prepared (step 10).
The particle size of these ultrafine particles is about 0.01 μm. These ultrafine particles are put in a glove box and ground and mixed by a mechanical arrowing method using a mixing and grinding machine (step 11). As a result, Bi, Te, S
b and Se are alloyed to form Bi-Te-Sb-Se alloy particles or Bi-Te-Sb alloy particles and inert ultrafine particles, for example, several alloy particles and inert ultrafine particles 1
Fine powders are combined at a ratio of individual particles (Step 1)
2). The particle size of this fine powder is about 0.1 μm. The alloy particles include, for example, (Bi 2 Te 3 ) 90 (Sb
Alloy particles of n-type thermoelectric material of 2 Te 3 ) 5 (Sb 2 Se 3 ) 5 and alloy particles of p-type thermoelectric material of (Sb 2 Te 3 ) 70 (Bi 2 Te 3 ) 30 are produced. It goes without saying that the composition of the alloy particles is not limited to these.
【００２３】そして、焼結工程では、このＢｉ−Ｔｅ−
Ｓｂ−Ｓｅ系の微粉体を放電プラズマ焼結加工法により
焼結する（ステップ１３）。具体的には、例えば住石放
電プラズマ焼結装置（住友石炭鉱業株式会社製）により
焼結を行う。これにより、Ｂｉ−Ｔｅ系焼結体を得るこ
とができる（ステップ１４）。このＢｉ−Ｔｅ系焼結体
が熱電材料１として使用される。Then, in the sintering step, this Bi-Te-
Sb-Se based fine powder is sintered by a spark plasma sintering method (step 13). Specifically, for example, it is sintered by a Sumiishi discharge plasma sintering device (manufactured by Sumitomo Coal Mining Co., Ltd.). Thereby, a Bi-Te based sintered body can be obtained (step 14). This Bi—Te based sintered body is used as the thermoelectric material 1.
【００２４】したがって、この手順により製造された熱
電材料１は、出発原料と不活性超微粒子３とのいずれも
が超微粒子で同等の大きさとなるので、出発原料の大き
さを基準とすると不活性超微粒子３は結晶粒２に対して
偏在することなく分散して均一に分布する。このため、
熱電材料１中でフォノンが十分に散乱されて熱伝導率を
低減させることができる。また、不活性超微粒子３は均
一に分布されているので、熱伝導率以外の電気抵抗率や
ゼーベック係数の劣化による性能指数の低下量よりも熱
伝導率の低減による性能指数の増加量を大きくして性能
指数を増加させることができる。Therefore, in the thermoelectric material 1 produced by this procedure, both the starting material and the inactive ultrafine particles 3 are ultrafine particles and have the same size. The ultrafine particles 3 are dispersed and uniformly distributed without being unevenly distributed with respect to the crystal grains 2. For this reason,
Phonons are sufficiently scattered in the thermoelectric material 1 to reduce the thermal conductivity. In addition, since the inert ultrafine particles 3 are uniformly distributed, the amount of increase in the figure of merit due to the reduction of the thermal conductivity is larger than the amount of decrease in the figure of merit due to the deterioration of the electrical resistivity other than the thermal conductivity and the Seebeck coefficient. Therefore, the figure of merit can be increased.
【００２５】ここで、熱電材料１中のフォノンは、不活
性超微粒子３の粒径よりも大きい波長について散乱され
る。例えば、不活性超微粒子３の粒径が４ｎｍであれば
４ｎｍ以上の波長のフォノンが散乱されることになる。
そして、フォノンの波長は０．４ｎｍ以上であり、４ｎ
ｍ程度のものが最も多い。したがって、本実施形態では
不活性超微粒子３として大きさの小さいＢＮを使用して
いるので、フォノンの波長成分のうち最も多い４ｎｍ程
度の部分を効率的に散乱することができる。これによ
り、熱電材料１の熱伝導率を十分に低減させることがで
きる。Here, the phonons in the thermoelectric material 1 are scattered at a wavelength larger than the particle size of the inert ultrafine particles 3. For example, if the particle diameter of the inert ultrafine particles 3 is 4 nm, phonons having a wavelength of 4 nm or more will be scattered.
The phonon wavelength is 0.4 nm or more, and 4n
Most are about m. Therefore, in the present embodiment, since BN having a small size is used as the inert ultrafine particles 3, it is possible to efficiently scatter a portion of about 4 nm, which is the largest phonon wavelength component. Thereby, the thermal conductivity of the thermoelectric material 1 can be sufficiently reduced.
【００２６】また、この熱電材料１は出発原料が超微粒
子であると共に放電プラズマ焼結法により短時間で焼結
されるので、焼結時の結晶の成長を抑えることができ
る。しかも、不活性超微粒子３が出発原料の結晶化に対
してピン止め効果的に作用するので、結晶粒２の成長が
さらに抑制される。したがって、得られた熱電材料１の
結晶粒２の粒径は最大でも１μｍ未満で緻密なものとな
るので、結晶粒２を細かくできてその粒界部分が増大す
る。ここで、熱電材料１中のフォノンは、結晶粒２の粒
径よりも大きい波長について散乱される。このため、本
実施形態では結晶粒２の粒径が１μｍよりも小さくなる
ので、フォノンの少なくとも１μｍ以上の長波長成分を
散乱させて熱伝導率を低減することができる。Further, since the starting material of the thermoelectric material 1 is ultrafine particles and is sintered in a short time by the discharge plasma sintering method, it is possible to suppress crystal growth during sintering. Moreover, since the inactive ultrafine particles 3 act effectively to pin the crystallization of the starting material, the growth of the crystal grains 2 is further suppressed. Therefore, since the grain size of the obtained crystal grain 2 of the thermoelectric material 1 is less than 1 μm at the maximum, the crystal grain 2 becomes fine and the grain boundary portion increases. Here, the phonons in the thermoelectric material 1 are scattered for wavelengths larger than the grain size of the crystal grains 2. Therefore, in the present embodiment, the grain size of the crystal grain 2 is smaller than 1 μm, so that the long-wavelength component of at least 1 μm or more of phonons can be scattered to reduce the thermal conductivity.
【００２７】なお、上述の実施形態は本発明の好適な実
施の一例ではあるがこれに限定されるものではなく本発
明の要旨を逸脱しない範囲において種々変形実施可能で
ある。例えば、本実施形態では熱電材料１の出発原料と
してはＢｉ，Ｔｅ，Ｓｂ，Ｓｅの単体の超微粒子を使用
しているがこれに限られず、ビスマス−テルル系合金の
超微粒子を使用することもできる。これらの場合も焼結
後の結晶粒２が超微粒子となるので、不活性超微粒子３
を均一に分布させると共に結晶粒２の小さい熱電材料１
を得ることができ、熱電材料１の熱伝導率を低減でき
る。The above-described embodiment is an example of a preferred embodiment of the present invention, but the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention. For example, in the present embodiment, as the starting material for the thermoelectric material 1, ultrafine particles of simple substance of Bi, Te, Sb, Se are used, but the present invention is not limited to this, and ultrafine particles of bismuth-tellurium alloy may be used. it can. In these cases as well, since the crystal grains 2 after sintering become ultrafine particles, the inert ultrafine particles 3
1 having a small grain size and a uniform distribution of
Can be obtained, and the thermal conductivity of the thermoelectric material 1 can be reduced.
【００２８】また、本実施形態では不活性超微粒子３と
してはＢＮの超微粒子を使用しているが、これに限られ
ず、母材と反応しない不活性な超微粒子であれば良く例
えばＳｉ3Ｎ4の超微粒子を使用しても構わない。この場
合もフォノンの短波長成分を散乱させて熱電材料１の熱
伝導率を低減することができる。In this embodiment, BN ultrafine particles are used as the inert ultrafine particles 3, but the present invention is not limited to this, and any inert ultrafine particles that do not react with the base material may be used, such as Si 3 N 2. Ultrafine particles of 4 may be used. Also in this case, the short-wavelength component of phonon can be scattered to reduce the thermal conductivity of the thermoelectric material 1.
【００２９】さらに、本実施形態では熱電材料１の製造
工程の粉末合成工程でＢｉ，Ｔｅ，Ｓｂ，Ｓｅの単体超
微粒子をメカニカルアローイング法で合金化して、これ
で得られた合金の微粉末を焼結しているが、この工程に
は限られない。例えば、別の方法で不活性な超微粒子を
添加し合金化しておき、この合金の微粉末を焼結するよ
うにしても良い。Further, in the present embodiment, in the powder synthesizing step of the manufacturing process of the thermoelectric material 1, the single ultrafine particles of Bi, Te, Sb and Se are alloyed by the mechanical arrowing method, and the fine powder of the alloy obtained by this is obtained. Is sintered, but is not limited to this step. For example, inert ultrafine particles may be added by another method to make an alloy, and fine powder of this alloy may be sintered.
【００３０】また、本実施形態では熱電材料１をＢｉ−
Ｔｅ系のものとしているが、これに限られず熱電材料一
般に適用できると考えられ、酸化物系、例えば酸化イン
ジウムやスクッテルダイト構造の熱電材料，Ｐｂ−Ｔｅ
系，Ｓｉ−Ｇｅ系，Ｆｅ−Ｓｉ系等のものとすることも
できる。In the present embodiment, the thermoelectric material 1 is Bi-
Although it is assumed to be Te-based, it is considered that the invention is not limited to this and is generally applicable to thermoelectric materials, and oxide-based materials such as indium oxide and skutterudite thermoelectric materials, Pb-Te.
A system, a Si-Ge system, a Fe-Si system, or the like can also be used.
【００３１】[0031]
【発明の効果】以上の説明より明らかなように、請求項
１の熱電材料は、出発原料を超微粒子とし、それに母材
と反応しない超微粒子を均一に分布する状態に添加して
焼結して成るようにしているので、不活性超微粒子が出
発原料の結晶化に対してピン止め効果的に作用して結晶
粒の成長を抑制し、結晶粒を細かくして結晶粒界を増や
すことができる。しかも、熱電材料の出発原料と不活性
超微粒子とはほぼ同等の大きさであるため、不活性超微
粒子は熱電材料中に偏在することなく均一に分布して存
在することになる。このため、熱電材料の結晶粒界の増
加と不活性超微粒子の均一添加によるフォノンの散乱で
熱伝導率以外の電気抵抗率やゼーベック係数の劣化によ
る性能指数の低下量よりも熱伝導率の低減による性能指
数の増大量を大きくすることにより、熱電材料の性能指
数の向上を図ることができる。As is clear from the above description, in the thermoelectric material of claim 1, the starting material is ultrafine particles, and ultrafine particles that do not react with the base material are added to the particles in a uniformly distributed state and sintered. Therefore, the inert ultrafine particles can effectively pin the crystallization of the starting material, suppress the growth of crystal grains, and make the crystal grains finer to increase the grain boundaries. it can. Moreover, since the starting material of the thermoelectric material and the inert ultrafine particles have substantially the same size, the inert ultrafine particles are uniformly distributed and exist in the thermoelectric material without being unevenly distributed. For this reason, the thermal conductivity is lower than the amount of decrease in the figure of merit due to the deterioration of the electrical resistivity other than the thermal conductivity and the Seebeck coefficient due to the increase of the grain boundaries of the thermoelectric material and the phonon scattering by the uniform addition of the inert ultrafine particles By increasing the amount of increase in the figure of merit due to, it is possible to improve the figure of merit of the thermoelectric material.
【００３２】また、請求項２の熱電材料の製造方法は、
超微粒子の熱電材料の出発原料に母材と反応しない不活
性な超微粒子を添加して混合して焼結するようにしてい
るので、熱電材料の結晶粒と不活性超微粒子の大きさと
が共に超微粒子で近似した大きさであるため、出発原料
の超微粒子に対して不活性超微粒子は偏在することなく
均一に分布して存在することになる。そして、出発原料
が超微粒子であるので、不活性超微粒子が出発原料の結
晶化に対してピン止め効果的に作用して結晶粒の成長を
抑制する。このため、結晶粒を細かくでき、尚かつ不活
性超微粒子の均一分布によりフォノンの散乱が効果的に
促進されて熱伝導率が低減した熱電材料を製造すること
ができる。The method of manufacturing a thermoelectric material according to claim 2 is
Since inert ultrafine particles that do not react with the base material are added to the starting material of the ultrafine particle thermoelectric material and mixed and sintered, both the crystal grains of the thermoelectric material and the size of the inert ultrafine particles are the same. Since the size is similar to that of the ultrafine particles, the inert ultrafine particles are present in a uniform distribution without being unevenly distributed with respect to the ultrafine particles of the starting material. Further, since the starting material is ultrafine particles, the inert ultrafine particles effectively pin the crystallization of the starting material and suppress the growth of crystal grains. For this reason, it is possible to manufacture a thermoelectric material in which the crystal grains can be made fine, and the phonon scattering is effectively promoted by the uniform distribution of the inert ultrafine particles, and the thermal conductivity is reduced.
【００３３】また、請求項３の熱電材料の製造方法で
は、出発原料と不活性超微粒子とを放電プラズマ焼結に
より焼結するようにしているので、短時間に大きなエネ
ルギーを投入することが可能であることから焼結時間を
短くして焼結中の結晶粒の成長を抑制して緻密な結晶
粒、例えば１μｍ未満の結晶粒の焼結体を得ることがで
きる。また、超微粒子は活性が高いため、超微粒子より
も大きい粒子の焼結温度よりも低い温度での焼結が可能
となるので、結晶粒の成長を抑えることができる。この
結果、結晶粒をより一層細かくできるため、粒界部分の
増加によりフォノンの散乱が十分に促進されて熱伝導率
が低減した熱電材料を製造することができる。Further, in the method for producing a thermoelectric material according to the third aspect, since the starting material and the inert ultrafine particles are sintered by spark plasma sintering, a large amount of energy can be input in a short time. Therefore, it is possible to shorten the sintering time, suppress the growth of crystal grains during sintering, and obtain a dense crystal grain, for example, a sintered body of crystal grains of less than 1 μm. Further, since the ultrafine particles have high activity, it becomes possible to sinter at a temperature lower than the sintering temperature of particles larger than the ultrafine particles, so that the growth of crystal grains can be suppressed. As a result, since the crystal grains can be made finer, the thermoelectric material in which the phonon scattering is sufficiently promoted by the increase in the grain boundary portion and the thermal conductivity is reduced can be manufactured.
【００３４】さらに、請求項４の熱電材料の製造方法で
は、出発原料と不活性超微粒子とをメカニカルアローイ
ング法により混合しているので、出発原料が不活性超微
粒子を含んだ状態で均一な合金になるので、不活性超微
粒子が熱電材料中に偏在することなく均一に分布して存
在するようになる。これにより、フォノンが十分に散乱
されて熱伝導率が低い熱電材料を製造することができ
る。Further, in the method for producing a thermoelectric material according to claim 4, since the starting material and the inert ultrafine particles are mixed by the mechanical alloying method, the starting material is uniformly mixed with the inert ultrafine particles. Since it becomes an alloy, the inert ultrafine particles can be uniformly distributed and present in the thermoelectric material without being unevenly distributed. This makes it possible to produce a thermoelectric material having a low thermal conductivity in which phonons are sufficiently scattered.
【図１】本発明に係る熱電材料の組成を示す模式図であ
る。FIG. 1 is a schematic diagram showing a composition of a thermoelectric material according to the present invention.
【図２】本発明の熱電材料を製造する工程を示すフロー
チャートである。FIG. 2 is a flow chart showing steps for producing the thermoelectric material of the present invention.
【図３】従来の熱電材料の組成を示す模式図である。FIG. 3 is a schematic diagram showing a composition of a conventional thermoelectric material.
１ 熱電材料 ２ 母材の結晶粒 ３ 不活性超微粒子（母材と反応しない超微粒子） 1 Thermoelectric material 2 Base material crystal grains 3 Inert ultrafine particles (ultrafine particles that do not react with the base material)
───────────────────────────────────────────────────── フロントページの続き (58)調査した分野(Int.Cl.7，ＤＢ名) H01L 35/14 H01L 35/34 ─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. 7 , DB name) H01L 35/14 H01L 35/34
Claims (4)
反応しない超微粒子を均一に分布する状態に添加して焼
結して成ることを特徴とする熱電材料。1. A thermoelectric material comprising ultrafine particles as a starting material, to which ultrafine particles which do not react with a base material are added in a uniformly distributed state and sintered.
反応しない超微粒子を添加して混合して焼結することを
特徴とする熱電材料の製造方法。2. A method for producing a thermoelectric material, characterized in that ultrafine particles which do not react with a base material are added to a starting material of an ultrafine particle thermoelectric material, which is mixed and sintered.
結であることを特徴とする請求項２記載の熱電材料の製
造方法。3. The method for producing a thermoelectric material according to claim 2, wherein the sintering is sintering by a discharge plasma sintering method.
よる混合であることを特徴とする請求項２または３記載
の熱電材料の製造方法。4. The method for producing a thermoelectric material according to claim 2, wherein the mixing is a mechanical alloying method.
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| JP04358797A JP3529576B2 (en) | 1997-02-27 | 1997-02-27 | Thermoelectric material and method for manufacturing the same |
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| JP4324999B2 (en) | 1998-11-27 | 2009-09-02 | アイシン精機株式会社 | Thermoelectric semiconductor composition and method for producing the same |
| WO2000054343A1 (en) * | 1999-03-10 | 2000-09-14 | Sumitomo Special Metals Co., Ltd. | Thermoelectric conversion material and method of producing the same |
| CA2331533A1 (en) * | 1999-03-10 | 2000-09-14 | Osamu Yamashita | Thermoelectric conversion material and method of producing the same |
| JP3559962B2 (en) * | 2000-09-04 | 2004-09-02 | 日本航空電子工業株式会社 | Thermoelectric conversion material and method for producing the same |
| US8865995B2 (en) | 2004-10-29 | 2014-10-21 | Trustees Of Boston College | Methods for high figure-of-merit in nanostructured thermoelectric materials |
| US7465871B2 (en) | 2004-10-29 | 2008-12-16 | Massachusetts Institute Of Technology | Nanocomposites with high thermoelectric figures of merit |
| US9865790B2 (en) * | 2004-12-07 | 2018-01-09 | Toyota Motor Engineering & Manufacturing North America, Inc. | Nanostructured bulk thermoelectric material |
| US7309830B2 (en) * | 2005-05-03 | 2007-12-18 | Toyota Motor Engineering & Manufacturing North America, Inc. | Nanostructured bulk thermoelectric material |
| CN104795486A (en) * | 2006-12-01 | 2015-07-22 | 麻省理工学院 | Methods for high figure-of-merit in nanostructured thermoelectric materials |
| CN101681979B (en) | 2007-06-05 | 2012-10-24 | 丰田自动车株式会社 | Thermoelectric conversion element and process for producing the thermoelectric conversion element |
| JP4900061B2 (en) | 2007-06-06 | 2012-03-21 | トヨタ自動車株式会社 | Thermoelectric conversion element and manufacturing method thereof |
| DE102007039060B4 (en) * | 2007-08-17 | 2019-04-25 | Evonik Degussa Gmbh | Thermokraft element or Peltier elements made of sintered nanocrystals of silicon, germanium or silicon-germanium alloys |
| JP4803282B2 (en) | 2009-06-18 | 2011-10-26 | トヨタ自動車株式会社 | Nanocomposite thermoelectric conversion material and method for producing the same |
| DE102012000763A1 (en) * | 2012-01-18 | 2013-07-18 | Emitec Gesellschaft Für Emissionstechnologie Mbh | Semiconductor element and method for producing a tubular thermoelectric module |
| JP6189582B2 (en) * | 2012-04-05 | 2017-08-30 | トヨタ自動車株式会社 | Method for producing nanocomposite thermoelectric conversion material |
| WO2014196233A1 (en) * | 2013-06-04 | 2014-12-11 | 住友電気工業株式会社 | Method for producing nanoparticles, method for producing thermoelectric material, and thermoelectric material |
| EP3196951B1 (en) | 2016-01-21 | 2018-11-14 | Evonik Degussa GmbH | Rational method for the powder metallurgical production of thermoelectric components |
| JP2017216388A (en) * | 2016-06-01 | 2017-12-07 | 住友電気工業株式会社 | Thermoelectric material, thermoelectric device, optical sensor, and method for manufacturing thermoelectric material |
| JP6892786B2 (en) * | 2017-05-10 | 2021-06-23 | 株式会社日立製作所 | Thermoelectric conversion material and thermoelectric conversion module |
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