JP6635581B2 - Skutterudite thermoelectric semiconductor doped with silicon and tellurium, method for producing the same, and thermoelectric power generation element using the same - Google Patents
Skutterudite thermoelectric semiconductor doped with silicon and tellurium, method for producing the same, and thermoelectric power generation element using the same Download PDFInfo
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- 239000004065 semiconductor Substances 0.000 title claims description 77
- 238000004519 manufacturing process Methods 0.000 title claims description 17
- 229910052710 silicon Inorganic materials 0.000 title claims description 14
- 239000010703 silicon Substances 0.000 title claims description 5
- 229910052714 tellurium Inorganic materials 0.000 title description 11
- 238000010248 power generation Methods 0.000 title description 5
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 title description 2
- 238000000137 annealing Methods 0.000 claims description 31
- 238000010304 firing Methods 0.000 claims description 24
- 239000000203 mixture Substances 0.000 claims description 24
- 229910018989 CoSb Inorganic materials 0.000 claims description 15
- 230000007704 transition Effects 0.000 claims description 13
- 239000002994 raw material Substances 0.000 claims description 10
- 229910052725 zinc Inorganic materials 0.000 claims description 8
- 229910052759 nickel Inorganic materials 0.000 claims description 6
- 238000000034 method Methods 0.000 claims description 5
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 4
- 229910052742 iron Inorganic materials 0.000 claims description 4
- -1 antimontelluride Chemical compound 0.000 claims description 3
- UFIKNOKSPUOOCL-UHFFFAOYSA-N antimony;cobalt Chemical compound [Sb]#[Co] UFIKNOKSPUOOCL-UHFFFAOYSA-N 0.000 claims description 3
- 229910017052 cobalt Inorganic materials 0.000 claims description 3
- 239000010941 cobalt Substances 0.000 claims description 3
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 3
- 229910021332 silicide Inorganic materials 0.000 claims description 3
- FVBUAEGBCNSCDD-UHFFFAOYSA-N silicide(4-) Chemical compound [Si-4] FVBUAEGBCNSCDD-UHFFFAOYSA-N 0.000 claims description 3
- CXXKWLMXEDWEJW-UHFFFAOYSA-N tellanylidenecobalt Chemical compound [Te]=[Co] CXXKWLMXEDWEJW-UHFFFAOYSA-N 0.000 claims description 3
- XSOKHXFFCGXDJZ-UHFFFAOYSA-N telluride(2-) Chemical compound [Te-2] XSOKHXFFCGXDJZ-UHFFFAOYSA-N 0.000 claims description 3
- 238000010298 pulverizing process Methods 0.000 claims description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 23
- 150000002910 rare earth metals Chemical group 0.000 description 12
- 150000001875 compounds Chemical class 0.000 description 8
- 238000005259 measurement Methods 0.000 description 8
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- 238000006467 substitution reaction Methods 0.000 description 3
- 239000002918 waste heat Substances 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 229910052787 antimony Inorganic materials 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 238000003786 synthesis reaction Methods 0.000 description 2
- 229910020630 Co Ni Inorganic materials 0.000 description 1
- 238000003991 Rietveld refinement Methods 0.000 description 1
- 230000005678 Seebeck effect Effects 0.000 description 1
- 230000005535 acoustic phonon Effects 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
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Description
本発明は、スクッテルダイト（skutterudite）化合物からなる熱電半導体に関し、とりわけその原子籠状構造への二重ドーピングによって、通常の高性能化メカニズムの一つである籠状構造の空間内への希土類原子挿入によるラットリング（rattling）に頼ることなく、希土類なしで高い熱電性能を実現した熱電半導体に関する。本発明は更にそのような希土類を含まない高性能なスクッテルダイト熱電半導体の製造方法及びそれを用いた熱電発電素子にも関する。 The present invention relates to a thermoelectric semiconductor comprising a skutterudite compound, and more particularly to a rare earth element in the space of a cage structure, which is one of the usual high-performance mechanisms, by means of double doping of the atomic cage structure. The present invention relates to a thermoelectric semiconductor that achieves high thermoelectric performance without relying on rare earth elements without relying on rattling by atomic insertion. The present invention further relates to a method for producing such a high-performance skutterudite thermoelectric semiconductor containing no rare earth element and a thermoelectric power generation element using the same.
従来、熱電半導体については、現代社会で効率的にエネルギーを使用するために盛んな材料研究が行われており、信頼性の高い静かな冷却装置や発電機に使用するための大きな需要が築かれた。 In the past, active research has been conducted on thermoelectric semiconductors in order to efficiently use energy in modern society, and there has been a great demand for reliable and quiet cooling devices and generators. Was.
また、廃熱回収の分野においては、世界での省エネルギーが進んだ我が国でも、一次供給エネルギーの約３／４が熱エネルギーとして廃棄されているのが現状である。そのような社会情勢で、熱電発電素子は熱エネルギーを回収して有用な電気エネルギーに直接変換できる唯一の固体素子として注目される。しかし、このような発電に用いるには希少で高価で資源が特定地域に偏在している傾向のある希土類元素を含まないで素子を形成することが望ましい場合が多い。 Also, in the field of waste heat recovery, even in Japan, where energy conservation has progressed in the world, about 3/4 of the primary supply energy is currently discarded as heat energy. In such a social situation, a thermoelectric power generation element is attracting attention as the only solid-state element that can recover heat energy and directly convert it into useful electric energy. However, it is often desirable to form an element without using a rare earth element that is rare, expensive, and has a tendency for resources to be unevenly distributed in a specific area for use in such power generation.
スクッテルダイト化合物は、非特許文献１、２に示されるように、中高温域できわめて高い熱電性能を示す系として知られている。しかしながら、その高性能のメカニズムは、原子の籠状構造の空間内に希土類原子やＢａを挿入することで、その希土類原子やＢａが非特許文献３に示されるように、ラットリングと呼ばれる現象を起こして、周波数の低いアインシュタイン振動子として作用し、熱を伝番する音響フォノンを散乱して熱伝導率を下げることにあった。そのため、高性能のスクッテルダイト熱電材料は構成元素に元素戦略的に望ましくない希土類原子や酸化に対してきわめて敏感なＢａを含むことが不可欠であった。更には、Ｂａだけでなく、希土類元素を含む材料は耐酸化性が低いため、高温環境下で使用されることが前提の熱電半導体としては、希土類の使用を回避できれば好都合である。また、スクッテルダイト化合物に関しては、挿入原子ではなく、非特許文献４に示されるように、Ｓｂの置換ドープもＴｅなど様々行われたが、籠状構造の空間内への挿入原子無しで十分大きな性能指数ＺＴを達成できるような材料は得られていない。そして、Ｓｉの置換ドープ、ましてやＳｉを含む他の元素の二重ドープに成功した例も報告されていない。 As shown in Non-Patent Documents 1 and 2, skutterudite compounds are known as systems exhibiting extremely high thermoelectric performance in a medium to high temperature range. However, the mechanism of the high performance is to insert a rare earth atom or Ba into the space of the cage structure of the atom, and the rare earth atom or Ba causes a phenomenon called ratling as shown in Non-Patent Document 3. It wakes up and acts as a low-frequency Einstein oscillator, scatters acoustic phonons that transmit heat, and lowers the thermal conductivity. For this reason, it is essential that the high-performance skutterudite thermoelectric material contains a rare-earth element that is elementally undesirable in elemental elements and Ba that is extremely sensitive to oxidation. Furthermore, since a material containing a rare earth element in addition to Ba has low oxidation resistance, it is convenient if the use of a rare earth can be avoided as a thermoelectric semiconductor that is assumed to be used in a high-temperature environment. Regarding the skutterudite compound, instead of insertion atoms, various substitution doping of Sb, such as Te, was performed as shown in Non-Patent Document 4, but it was sufficient without insertion atoms into the cage-shaped structure space. No material capable of achieving a large figure of merit ZT has been obtained. Further, there has been no report on a case in which the substitution doping of Si and the double doping of other elements including Si have been successful.
本発明の課題は、上述の従来の問題点を解消し、スクッテルダイトからなる化合物に対しケイ素（Ｓｉ）とテルル（Ｔｅ）とを同時にドープすることにより希土類フリーの高性能熱電半導体を提供すること、更にはそのようなスクッテルダイト熱電半導体を利用した熱電発電素子を提供することにある。 An object of the present invention is to solve the above-mentioned conventional problems and to provide a rare earth-free high-performance thermoelectric semiconductor by simultaneously doping silicon (Si) and tellurium (Te) into a skutterudite compound. Another object of the present invention is to provide a thermoelectric element using such a skutterudite thermoelectric semiconductor.
本発明の一側面によれば、以下の組成を有するスクッテルダイト熱電半導体が与えられる。
ＣｏＳｂ３−ｘ−ｙＳｉｘＴｅｙ（ここで、０．００３＜ｘ＜０．２５、０．０２５＜ｙ＜０．４０）
ここで、０．０２５＜ｘ＜０であってよい。
また、Ｃｏの一部を遷移元素で置換してよい。
また、前記遷移元素はＮｉまたはＺｎであり、Ｃｏの０〜７．５原子％が置換されていてよい。
また、前記遷移元素はＦｅであり、Ｃｏの０〜１５原子％が置換されていてよい。
また、０．０２５＜ｙ＜０．２５であってよい。
また、内部に空孔を含んでよい。
また、前記空孔のうちの８０％のもののサイズは１〜１５μｍの範囲であってよい。
また、相対密度が８２〜９２％の範囲であってよい。
また、熱電性能指数が１．２以上であってよい。
本発明の他の側面によれば、ｎ型熱電半導体として上記何れかのスクッテルダイト熱電半導体を使用した熱電発電素子が与えられる。
本発明の更に他の側面によれば、Ｃｏ源、Ｓｂ源、Ｓｉ源及びＴｅ源を混合した原料混合物を準備し、前記原料混合物を焼成するステップを有する、以下の組成を有するスクッテルダイト熱電半導体の製造方法が与えられる。
ＣｏＳｂ３−ｘ−ｙＳｉｘＴｅｙ（ここで、０．００３＜ｘ＜０．２５、０．０２５＜ｙ＜０．４０）
ここで、０．０２５＜ｘ＜０．２５であってよい。
また、前記Ｃｏ源、Ｓｂ源、Ｓｉ源及びＴｅ源の少なくとも一つは当該元素の単体であってよい。
また、前記Ｃｏ源、Ｓｂ源、Ｓｉ源及びＴｅ源はコバルトアンチモン化合物、コバルトシリサイド、コバルトテルライド、アンチモンテルライド及びシリコンテルライドからなる群から選択された少なくとも一つを含んでよい。
また、更にＮｉ、Ｚｎ、Ｆｅ等の遷移元素を含む遷移元素源を前記原料混合物に含み、前記ＣｏＳｂ３−ｘ−ｙＳｉｘＴｅｙ中のＣｏの一部を前記遷移元素で置換してよい。
また、０．０２５＜ｙ＜０．２５であってよい。
また、前記焼成は真空または不活性雰囲気中にて５５０℃〜１１５０℃の温度範囲で行ってよい。
また、前記焼成は１時間以上行ってよい。
また、前記焼成後、粉砕して再度焼成を行う追加焼成を少なくとも１回行ってよい。
また、前記焼成または前記追加焼成の後、アニーリングを行ってよい。
また、前記アニーリングは５５０℃〜７５０℃の温度範囲で行ってよい。
また、前記アニーリングは１時間〜１５時間の範囲で行ってよい。
According to one aspect of the present invention, a skutterudite thermoelectric semiconductor having the following composition is provided.
CoSb 3-x-y Si x Te y ( where, 0.003 <x <0.25,0.025 <y <0.40)
Here, 0.025 <x <0 may be satisfied.
Further, a part of Co may be replaced with a transition element.
The transition element is Ni or Zn, and 0 to 7.5 atomic% of Co may be substituted.
The transition element is Fe, and 0 to 15 atomic% of Co may be substituted.
Further, the relationship may be 0.025 <y <0.25.
Further, a void may be included inside.
The size of 80% of the holes may be in the range of 1 to 15 μm.
Further, the relative density may be in the range of 82 to 92%.
The thermoelectric figure of merit may be 1.2 or more.
According to another aspect of the present invention, there is provided a thermoelectric power generation element using any of the above skutterudite thermoelectric semiconductors as an n-type thermoelectric semiconductor.
According to yet another aspect of the present invention, there is provided a skutterudite thermoelectric having the following composition, comprising the steps of: preparing a raw material mixture obtained by mixing a Co source, a Sb source, a Si source, and a Te source, and firing the raw material mixture. A method of manufacturing a semiconductor is provided.
CoSb 3-x-y Si x Te y ( where, 0.003 <x <0.25,0.025 <y <0.40)
Here, 0.025 <x <0.25 may be satisfied.
At least one of the Co source, the Sb source, the Si source, and the Te source may be a simple substance of the element.
In addition, the Co source, the Sb source, the Si source and the Te source may include at least one selected from the group consisting of a cobalt antimony compound, cobalt silicide, cobalt telluride, antimontelluride, and silicon telluride.
Further, a transition element source containing a transition element such as Ni, Zn, or Fe may be further included in the raw material mixture, and part of Co in the CoSb 3-xy Si x T y may be replaced with the transition element. .
Further, the relationship may be 0.025 <y <0.25.
The firing may be performed in a vacuum or in an inert atmosphere at a temperature in the range of 550 ° C to 1150 ° C.
Further, the firing may be performed for one hour or more.
Further, after the firing, additional firing in which pulverization is performed and firing is performed again may be performed at least once.
After the firing or the additional firing, annealing may be performed.
Further, the annealing may be performed at a temperature in a range of 550 ° C. to 750 ° C.
Further, the annealing may be performed for a period of 1 hour to 15 hours.
本発明によれば、高い熱電性能を有する希土類を含まないスクッテルダイト熱電半導体を提供することができる。 ADVANTAGE OF THE INVENTION According to this invention, the skutterudite thermoelectric semiconductor which does not contain the rare earth which has high thermoelectric performance can be provided.
本発明によれば、ＳｉとＴｅとが共にドープされたスクッテルダイト化合物からなるｎ型熱電半導体が与えられる。この熱電半導体は下式に示す組成を有する立方晶系である。
ＣｏＳｂ３−ｘ−ｙＳｉｘＴｅｙ
（ここで、０．００３＜ｘ＜０．２５かつ０．０２５＜ｙ＜０．４０、好ましくは０．０２５＜ｘ＜０．２５、更に好ましくは０．０２５＜ｙ＜０．２５）
According to the present invention, there is provided an n-type thermoelectric semiconductor comprising a skutterudite compound doped with both Si and Te. This thermoelectric semiconductor is a cubic system having a composition shown by the following formula.
CoSb 3-x-y Si x Te y
(Here, 0.003 <x <0.25 and 0.025 <y <0.40, preferably 0.025 <x <0.25, more preferably 0.025 <y <0.25)
この熱電半導体はスクッテルダイトからなる化合物にＳｉとＴｅとを共にドープしたものである。リートベルト解析と各種の測定結果等から、スクッテルダイトの籠状構造に対してＳｉとＴｅとを共にドープした構造であると考えられる。そして、この構造により、非特許文献１にあるような通常の高性能化メカニズムの一つである籠状構造の空間内への希土類原子挿入によるラットリングに頼ることなく、導電率を比較的損なわず効果的に籠状構造内に熱伝導率を低減する乱れを導入することができ、そのため、本発明の熱電半導体においては、上述の二重ドーピングを行うことで、希土類や酸化に対してきわめて敏感なＢａを含まないにも関わらず高熱電性能が得られるという効果が発現すると考えるのが合理的である。また、希土類元素やＢａを含有している材料は酸化し易いという問題もあるが、本発明の熱電半導体は希土類やＢａを使用しないため、この面でも有利である。 This thermoelectric semiconductor is obtained by doping a compound of skutterudite with both Si and Te. From Rietveld analysis and various measurement results, it is considered that the cage structure of skutterudite is a structure in which both Si and Te are doped. With this structure, the conductivity is relatively impaired without relying on rattling by inserting rare earth atoms into the space of the cage-like structure, which is one of the usual high-performance mechanisms as described in Non-Patent Document 1. In addition, it is possible to effectively introduce turbulence that reduces the thermal conductivity in the cage structure, and therefore, in the thermoelectric semiconductor of the present invention, by performing the above-described double doping, the rare-earth element and oxidation can be extremely prevented. It is reasonable to think that the effect of obtaining high thermoelectric performance despite not containing sensitive Ba is exhibited. Further, there is a problem that a material containing a rare earth element or Ba is easily oxidized. However, the thermoelectric semiconductor of the present invention does not use a rare earth element or Ba, and thus is advantageous in this aspect.
また、この熱電半導体ＣｏＳｂ３−ｘ−ｙＳｉｘＴｅｙはＳｉとＴｅとの組み合わせの結果、原子結合が適度に弱くなるために、例えば５５０℃〜７５０℃のアニーリングによって容易に適度な空孔を有する試料が作成でき、電気伝導をそれほど損なわずに、熱伝導率の一層大きな低減が可能となる。従って、本発明の熱電半導体において、アニーリングによりさらなる高性能化を実現することができ、具体的には１．２以上の熱電性能指数ＺＴを達成できた（図６参照。ここで、グラフ中の水平の破線がＺＴ＝１．２を示す）。 Also, the thermoelectric semiconductor CoSb 3-x-y Si x Te y is the result of a combination of Si and Te, for atomic bond is moderately weak, for example, easily moderate pores by the annealing of 550 ° C. to 750 ° C. Can be prepared, and the thermal conductivity can be further reduced without significantly impairing the electrical conductivity. Therefore, in the thermoelectric semiconductor of the present invention, higher performance can be realized by annealing, and more specifically, a thermoelectric performance index ZT of 1.2 or more can be achieved (see FIG. 6, where the graph in the graph is used). The horizontal dashed line indicates ZT = 1.2).
本発明の希土類を含まない高性能スクッテルダイト熱電半導体の製造に当たっては、先ず、組成がＣｏＳｂ３−ｘ−ｙＳｉｘＴｅｙ（原料組成）となるように原料を混合する。原料は、Ｃｏ、Ｓｂ、Ｓｉ及びＴｅのそれぞれ単体としてもよいし、あるいは出発原料としてコバルトアンチモン化合物、コバルトシリサイド、コバルトテルライド、アンチモンテルライド、シリコンテルライド等を使用してもよい。追加の実施例の結果まで考えれば、０．００３＜ｘ＜０．２５かつ０．０２５＜ｙ＜０．４０とすることが好ましく、更に好ましくは０．０２５＜ｘ＜０．より一層好ましくは０．０２５＜ｙ＜０．２５とする。ｘが０．００３以下あるいはｙが０．０２５以下である場合には高い熱電性能が得られない。また、ｘが０．２５以上の場合においては、その製造過程で不純物としてＳｉ等の第二相が現れ、粉末試料（つまり、所望の構造を有するスクッテルダイト化合物）の収率が悪くなる。また、ｙに関しては、０．４０以上だと、Ｓｂ２Ｔｅ３等の第二相が現れ、粉末試料（つまり、所望の構造を有するスクッテルダイト化合物）の収率が悪くなる。 In the manufacture of high-performance skutterudite thermoelectric semiconductor which does not include the rare earth of the present invention, first, the composition is mixed raw material so that the CoSb 3-x-y Si x Te y ( raw material composition). The raw material may be each of Co, Sb, Si, and Te alone, or a cobalt antimony compound, cobalt silicide, cobalt telluride, antimontelluride, silicon telluride, or the like may be used as a starting material. Considering the results of the additional examples, it is preferable that 0.003 <x <0.25 and 0.025 <y <0.40, more preferably 0.025 <x <0. Still more preferably, 0.025 <y <0.25. When x is 0.003 or less or y is 0.025 or less, high thermoelectric performance cannot be obtained. When x is 0.25 or more, a second phase such as Si appears as an impurity in the manufacturing process, and the yield of a powder sample (that is, a skutterudite compound having a desired structure) deteriorates. When y is 0.40 or more, a second phase such as Sb 2 Te 3 appears, and the yield of a powder sample (that is, a skutterudite compound having a desired structure) deteriorates.
この混合物を真空またはアルゴンなどの不活性雰囲気中にて焼成する。焼成温度は５５０℃〜１１５０℃であり、１時間以上焼成することが好ましい。更に長時間焼成を行っても問題はないが、時間と消費電力の浪費となる。例えば１００時間超等の技術常識を外れた長時間の焼成は無意味である。繰り返しの焼成（ここでは焼成後に粉砕するというサイクルを繰り返す）やアニーリングによって、特にＳｉがスクッテルダイト構造中により良好に取り込まれてＳｂを置換するので、ドーピングを更に完全に達成できるようにするという点で、これらの処理を行うことが好ましい。また、アニーリングにより、本発明の熱電半導体中に空孔を形成することで、導電率の大きな変化を伴うことなく熱伝導率を低下させることができる。アニール前の試料は相対密度が９５％〜９７％で、図８右側のように、空孔が少ない状態である。アニーリングによって図８左側のように顕著な空孔が形成された。全空孔の８０％のサイズが１〜５０μｍの範囲に入り、アニーリング後の相対密度は好ましくは８２〜９２％である。このアニーリングは１時間以上行うことが望ましい。これより短時間では熱電性能の向上は達成できない。また、アニーリングによる熱電性能の向上は１０時間程度でほぼ飽和し、１５時間まで延長した場合でも更なる性能向上はほとんど見られなかった。従って、１０時間を大きく超えるアニーリングを行うことはあまり意味がない。 The mixture is fired in a vacuum or an inert atmosphere such as argon. The firing temperature is 550 ° C. to 1150 ° C., and it is preferable that the firing be performed for 1 hour or more. There is no problem even if the firing is performed for a long time, but it wastes time and power consumption. For example, baking for a long time out of common technical knowledge, such as over 100 hours, is meaningless. Repeated firing (here a cycle of crushing after firing) or annealing allows the doping to be more fully achieved, especially since Si is better incorporated into the skutterudite structure and replaces Sb. In this respect, it is preferable to perform these processes. In addition, by forming holes in the thermoelectric semiconductor of the present invention by annealing, the thermal conductivity can be reduced without a large change in conductivity. The sample before annealing has a relative density of 95% to 97% and has few vacancies as shown on the right side of FIG. As shown in the left side of FIG. 8, remarkable holes were formed by annealing. The size of 80% of all the holes is in the range of 1 to 50 μm, and the relative density after annealing is preferably 82 to 92%. This annealing is preferably performed for one hour or more. An improvement in thermoelectric performance cannot be achieved in a shorter time. Further, the improvement of the thermoelectric performance due to the annealing was almost saturated in about 10 hours, and even when the performance was extended to 15 hours, further improvement in the performance was hardly observed. Therefore, it is not very meaningful to perform annealing for much longer than 10 hours.
なお、上で本発明のスクッテルダイト熱電半導体の組成をＣｏＳｂ３−ｘ−ｙＳｉｘＴｅｙとしたが、Ｃｏの一部をＮｉ、Ｚｎ、Ｆｅ等の遷移元素で置換してもほぼ同等な熱電性能が得られる。この場合、Ｎｉ及びＺｎはＣｏの最大７．５原子％を置換でき、またＦｅはＣｏの最大１５％を置換できることが判った。すなわち、本発明のスクッテルダイト熱電半導体の組成式は以下のように更に一般化することができる。
（Ｃｏ１−ｚ，Ｔｚ）Ｓｂ３−ｘ−ｙＳｉｘＴｅｙ
（ここで、０．００３＜ｘ＜０．２５、０．０２５＜ｙ＜０．４０（好ましくは０．０２５＜ｘ＜０．２５、一層好ましくは０．０２５＜ｙ＜０．２５）、０≦ｚ≦０．１５、ＴはＮｉ、Ｚｎ、Ｆｅ等の遷移元素）
Although the composition of the skutterudite thermoelectric semiconductor of the present invention above was CoSb 3-x-y Si x Te y, almost be partially substituted Co Ni, Zn, a transition element such as Fe equivalent Thermoelectric performance is obtained. In this case, it was found that Ni and Zn could replace up to 7.5 at% of Co, and Fe could replace up to 15% of Co. That is, the composition formula of the skutterudite thermoelectric semiconductor of the present invention can be further generalized as follows.
(Co 1-z, T z ) Sb 3-x-y Si x Te y
(Here, 0.003 <x <0.25, 0.025 <y <0.40 (preferably 0.025 <x <0.25, more preferably 0.025 <y <0.25), 0 ≦ z ≦ 0.15, T is a transition element such as Ni, Zn, Fe)
上述した本発明のｎ型のスクッテルダイト熱電半導体を使用することにより、従来は不可能とされていた廃棄熱からのエネルギー回収が可能になる。具体的には、これら両熱電半導体を使用して、これに限定する意図はないが、例えば図１３に概念的に示す構造の熱電発電素子を構成することができる（特許文献３の熱電発電素子も参照されたい）。 By using the n-type skutterudite thermoelectric semiconductor of the present invention described above, it is possible to recover energy from waste heat, which was conventionally impossible. Specifically, there is no intention to use these two thermoelectric semiconductors, but a thermoelectric generator having a structure conceptually shown in FIG. 13 can be configured (for example, a thermoelectric generator of Patent Document 3). See also
図１３において、熱電発電素子３１の構成は、低温となる側の電極３５に、例えば半田等によって熱電材料チップであるｎ型半導体３２が接合され、ｎ型半導体３２の反対側の端部と高温となる側の電極３４とが同じく半田等によって接合されるようになっている。さらに同じ高温側電極３４と熱電材料チップであるｐ型半導体３３とが接合され、ｐ型半導体３３の反対側の端部は別のｎ型半導体３２が接合された別の低温側電極３５に接合されている。このような構成にすることによって電気的に直列した接続が完成する。 In FIG. 13, the configuration of the thermoelectric generation element 31 is such that the n-type semiconductor 32 which is a thermoelectric material chip is joined to the electrode 35 on the low-temperature side by, for example, soldering, and the end on the opposite side of the n-type semiconductor 32 and And the electrode 34 on the other side is also joined by solder or the like. Further, the same high-temperature side electrode 34 is joined to a p-type semiconductor 33 which is a thermoelectric material chip, and the opposite end of the p-type semiconductor 33 is joined to another low-temperature side electrode 35 to which another n-type semiconductor 32 is joined. Have been. With such a configuration, the electrical series connection is completed.
電極３４が高温、電極３５がそれに較べて低温となるような環境に熱電発電素子３１を設置して端部の電極を電気回路等に接続すると、ゼーベック効果によって電圧が発生し、矢印で示すように、電極３５→ｎ型半導体３２→電極３４→ｐ型半導体３３と電流が流れる。つまり、ｎ型半導体３２内の電子が高温の電極３４から熱エネルギーを得て低温の電極３５へ移動してそこで熱エネルギーを放出し、それに対してｐ型半導体の正孔が高温の電極３４から熱エネルギーを得て低温の電極３５へ移動してそこで熱エネルギーを放出するという原理によって電流が流れる。 When the thermoelectric power generating element 31 is installed in an environment where the electrode 34 is at a high temperature and the electrode 35 is at a lower temperature, and the electrodes at the ends are connected to an electric circuit or the like, a voltage is generated by the Seebeck effect, as indicated by an arrow. Then, a current flows through the electrode 35 → the n-type semiconductor 32 → the electrode 34 → the p-type semiconductor 33. That is, the electrons in the n-type semiconductor 32 obtain thermal energy from the high-temperature electrode 34, move to the low-temperature electrode 35, and release the thermal energy there. A current flows according to the principle that heat energy is obtained, moves to the low-temperature electrode 35, and releases the heat energy there.
このような構造を有する熱電発電素子中のｎ型半導体３２として、本発明により提供されるところの、例えば実施例で例示するようなｎ型のスクッテルダイト熱電半導体を用いることで、従来以上に良好な熱回収が可能となる。 By using an n-type skutterudite thermoelectric semiconductor provided by the present invention, for example, as exemplified in the examples, as the n-type semiconductor 32 in the thermoelectric power generating element having such a structure, Good heat recovery becomes possible.
以下では実施例により本発明をさらに詳細に説明するが、この実施例はあくまで本発明の理解を助けるためにここに挙げたものであり、本発明をこれに限定するものでないことを理解しなければならない。 Hereinafter, the present invention will be described in more detail with reference to Examples. However, it should be understood that these Examples are merely provided to assist understanding of the present invention, and do not limit the present invention. Must.
下式の組成から出発して希土類を含まないスクッテルダイト熱電半導体を合成し、その特性を評価した。
ＣｏＳｂ３−ｘ−ｙＳｉｘＴｅｙ
（ここで、０．０２５＜ｘ＜０．２５、０．０２５＜ｙ＜０．４０）
Starting from the composition of the following formula, a skutterudite thermoelectric semiconductor containing no rare earth was synthesized and its characteristics were evaluated.
CoSb 3-x-y Si x Te y
(Here, 0.025 <x <0.25, 0.025 <y <0.40)
製造に当たっては、目的物質を構成する各元素の単体（Ｃｏ、Ｓｂ、Ｓｉ及びＴｅ）の粉末を混合した混合物をプレス成型（ＣＩＰ）し、石英管に内包して真空中にて焼成を行った。この真空中での焼成は１０５０℃にて５時間行った。その後は、８００ｏＣまで冷やし２時間保持したあとは６００ｏＣまで冷やして１５時間保持したあと室温まで自然冷却した。このプロセスは相の合成には必須ではないが、これによってより均一な良い試料が得られた。得られた試料を粉砕し、上記の成形・加熱・反応プロセスをもう一度行った。上記ｘとｙの範囲内の各種の原料組成で、かつ上記温度範囲内の各種の温度、各種の処理条件の組合せの下で合成を行い、その結果、ＣｏＳｂ３−ｘ−ｙＳｉｘＴｅｙ（試料番号２ＡＫ０６２、（ｘ，ｙ）＝（０．１７５，０．０７５）；試料番号３ＡＫ１２９、（ｘ，ｙ）＝（０．０７５，０．１７５））の試料が得られた。また、上述したところの、Ｃｏの一部（ここでは１．２５％）のＮｉによる置換を行った試料（試料番号２ＡＫ０９２）、及びＴｅを試料番号３ＡＫ１２９よりも増加させた試料（試料番号２ＡＫ０９１、（ｘ，ｙ）＝（０．０７５，０．３００））も実施例の一部として作製し、その測定結果も示した。なお、比較例としてのＳｉのみをドープしたｙ＝０（ｘ＝０．１２５）の試料（試料番号２ＡＫ０８２）及びＴｅのみをドープしたｘ＝０、ｙ＝０．１７５の試料（試料番号２ＡＫ０９５）についての結果も示した。以下の表に、上記実施例及び比較例の試料番号と組成をまとめて示す。 In the production, a mixture obtained by mixing powders of simple substances (Co, Sb, Si, and Te) of each element constituting the target substance was press-molded (CIP), enclosed in a quartz tube, and fired in a vacuum. . This firing in vacuum was performed at 1050 ° C. for 5 hours. After that, it was cooled to 800 ° C., kept for 2 hours, cooled to 600 ° C., kept for 15 hours, and then naturally cooled to room temperature. Although this process is not essential for the synthesis of the phase, it resulted in a better and more uniform sample. The obtained sample was pulverized, and the above-described molding, heating and reaction processes were performed again. The synthesis is carried out under various raw material compositions within the above-mentioned ranges of x and y, under various temperatures within the above-mentioned temperature range, and under a combination of various processing conditions. As a result, CoSb 3-xy Si x Te y (Sample No. 2AK062, (x, y) = (0.175, 0.075); Sample No. 3AK129, (x, y) = (0.075, 0.175)) were obtained. Further, as described above, a sample in which a part of Co (here, 1.25%) was replaced with Ni (sample number 2AK092), and a sample in which Te was increased from sample number 3AK129 (sample number 2AK091, (X, y) = (0.075, 0.300)) was also produced as a part of the example, and the measurement results are also shown. As a comparative example, a sample of y = 0 (x = 0.125) doped only with Si (sample number 2AK082) and a sample of x = 0 and y = 0.175 doped only with Te (sample number 2AK095) Are also shown. The following table summarizes the sample numbers and compositions of the above Examples and Comparative Examples.
仕込み組成と結果物の組成に大きな差はないと思われる。化学分析によって、例えば３ＡＫ１２９を調べた結果、仕込み組成のＣｏＳｂ２．７５Ｓｉ０．０７５Ｔｅ０．１７５に対して結果物の組成はＣｏＳｂ２．７６±０．０４Ｓｉ０．０５±０．０４Ｔｅ０．１６±０．０４と求められた。 It seems that there is no significant difference between the charge composition and the composition of the resulting product. As a result of examining, for example, 3AK129 by chemical analysis, the composition of the resulting product is CoSb 2.76 ± 0.04 Si 0.05 ± 0.04 with respect to the charged composition of CoSb 2.75 Si 0.075 Te 0.175 . Te was determined to be 0.16 ± 0.04 .
焼成後の試料を用いて、Ｘ線回折パターン、熱電特性等の測定を行った。なお、Ｘ線回折パターン測定以外は、焼成終了後に一度粉砕し、それを熱伝測定のために再度成型した試料で測定を行ったが、この再成型の際に放電プラズマ焼結（ＳＰＳ）を使用した。図１に、ＣｏＳｂ３−ｘ−ｙＳｉｘＴｅｙ（試料番号２ＡＫ０６２、（ｘ，ｙ）＝（０．１７５，０．０７５））のＸ線回折パターンを示す。このＸ線回折パターンに基づき、Rietveldt解析によって、ほぼ単相のスクッテルダイト試料が得られていることを確認した。すなわち、図１中の下部以外の部分には、所々に鋭いピークを有するグラフが２つ、それぞれ淡色及び濃色で描かれている。これらのうち濃色のグラフＹｃａｌｃは、試料がスクッテルタイトの結晶構造を有すると仮定して回折パターンをフィッテングして求めた計算結果のグラフであり、淡色のグラフＹｏｂｓは実際の観測値である。図１から明らかなように両者はほとんど一致し、また図１中の下部に示した両者の差Ｙｏｂｓ−Ｙｃａｌｃが非常に小さいことから、上述の結論が得られた。 Using the fired sample, measurement of an X-ray diffraction pattern, thermoelectric characteristics, and the like was performed. Except for the X-ray diffraction pattern measurement, the sample was crushed once after the completion of calcination, and the measurement was performed on a sample molded again for heat transfer measurement. In this remolding, discharge plasma sintering (SPS) was performed. used. Figure 1, CoSb 3-x-y Si x Te y ( Sample No. 2AK062, (x, y) = (0.175,0.075)) shows the X-ray diffraction pattern of. Based on the X-ray diffraction pattern, it was confirmed by Rietveldt analysis that an almost single-phase skutterudite sample was obtained. That is, two graphs each having a sharp peak in some places other than the lower part in FIG. 1 are drawn in light and dark colors, respectively. Among these, the dark graph Ycalc is a graph of a calculation result obtained by fitting a diffraction pattern assuming that the sample has a skutterite crystal structure, and the light graph Yobs is an actual observed value. . As is clear from FIG. 1, the two almost coincide with each other, and the difference Yobs-Ycalc shown in the lower part of FIG. 1 is very small, so the above conclusion was obtained.
また、図２〜図６にはそれぞれ実施例及び比較例の希土類を含まないスクッテルダイト熱電半導体の導電率、ゼーベック係数、パワーファクター、熱伝導率及び熱電性能指数を示す。これらの図中の左側のグラフはアニーリングを行っていない試料の測定結果を示し、右側のグラフはアニーリング後の試料についての測定結果を示す。このアニーリングの具体的な条件は、再成型して図２〜図６の左側のグラフに示す特性の測定後の試料を真空中で石英管に封入して、６００℃で１５時間の処理を行ったものである。 2 to 6 show the conductivity, the Seebeck coefficient, the power factor, the thermal conductivity, and the thermoelectric figure of merit of the skutterudite thermoelectric semiconductors containing no rare earth of Examples and Comparative Examples, respectively. The graphs on the left side in these figures show the measurement results for the sample that has not been annealed, and the graphs on the right side show the measurement results for the sample after annealing. The specific conditions of this annealing are as follows: the sample after re-molding and measuring the characteristics shown in the left graphs of FIGS. 2 to 6 is sealed in a quartz tube in a vacuum, and treated at 600 ° C. for 15 hours. It is a thing.
図３からわかるように、Ｔｅのドーピングによって電子注入が行われて全温度域でｎ型（ゼーベック係数が負）になっており、また、Ｓｉのみの試料に関しては、Ｓｉのドーピング効果はホール注入であるので、唯一ｐ型を示すことにより、それぞれが籠状構造内のＳｂと置換ドーピングされていることが示唆された。また、Ｓｉのみの試料のアニーリングによって、全温度域で完全にｐ型になっており、アニーリングによって置換ドーピングが促進されたことが分かり、これがＳｉドープの初めての成功例である。また、ＳｉとＴｅの両方のドーピングによって、図２に示す導電率に比べて図５に示す熱伝導率が大きく低減する効果があることも分かる。なお、図２〜図６の右側に示されているアニーリング後の特性から、ＳｉとＴｅの両方のドーピングによってボンディングが弱くなり、その結果、アニーリングによる構造変化を生起させてこのような特性変化をもたらしたことが示唆される。またこのアニーリングにより、図８の左側（アニーリング後）と右側（未アニーリング）との比較からわかるように細孔が形成され、導電率を大きく損なわないが、熱伝導率のさらなる低下（図５）、またこれによる熱電性能指数ＺＴの向上（最大値ＺＴ＝１．２３）（図６）につながっていることが分かる。この効果は他のスクッテルダイトでは報告されたことがなく、ＳｉとＴｅの同時ドーピングにより発現することを本願発明者が初めて見出した。 As can be seen from FIG. 3, electron injection is performed by doping with Te, and becomes n-type (negative Seebeck coefficient) over the entire temperature range. Therefore, by showing only p-type, it was suggested that each was substitutionally doped with Sb in the cage structure. In addition, the annealing of the Si-only sample turned out to be completely p-type in all temperature ranges, and it was found that the substitutional doping was promoted by the annealing. This is the first successful example of Si doping. It can also be seen that the doping of both Si and Te has the effect of significantly reducing the thermal conductivity shown in FIG. 5 as compared to the conductivity shown in FIG. From the characteristics after annealing shown on the right side of FIGS. 2 to 6, the bonding is weakened by doping of both Si and Te, and as a result, a structural change due to annealing is caused to cause such a characteristic change. It is suggested that it did. Further, as can be seen from the comparison between the left side (after annealing) and the right side (unannealed) of FIG. 8, pores are formed by this annealing, and the conductivity is not significantly impaired, but the thermal conductivity is further reduced (FIG. 5). It can be seen that this leads to an improvement in the thermoelectric figure of merit ZT (maximum value ZT = 1.23) (FIG. 6). This effect has not been reported in other skutterudites, and the present inventors have found for the first time that this effect is exhibited by simultaneous doping of Si and Te.
更に、Ｃｏの一部を遷移金属（ここではＮｉ）で置換しても悪影響はほとんど出ないことも，試料２ＡＫ０９２により確認した。なお、データは省略したが、Ｎｉ以外にＺｎ及びＦｅによる置換についても実験済みであり、同様な結果を得た。また、上述の実施例では真空中での焼成を行ったが、これに限定されるものではなく、不活性雰囲気中での焼成を行ってもよい。例えば、Ａｒ中で６００℃、１時間の焼成を行うことで、ほぼ同等のスクッテルダイト熱電半導体を製造することができた。 Further, it was confirmed by Sample 2AK092 that even if a part of Co was replaced by a transition metal (here, Ni), almost no adverse effect was caused. In addition, although the data was omitted, experiments were also conducted on substitution with Zn and Fe in addition to Ni, and similar results were obtained. In the above-described embodiment, the firing is performed in a vacuum. However, the firing is not limited to this, and the firing may be performed in an inert atmosphere. For example, by performing baking at 600 ° C. for 1 hour in Ar, almost the same skutterudite thermoelectric semiconductor could be manufactured.
［追加の実施例］
本願発明者が更に実験を進めた結果、組成式
ＣｏＳｂ３−ｘ−ｙＳｉｘＴｅｙ
において、ｙの範囲はそのままでｘを０．００３＜ｘ≦０．２５の範囲まで減少させて得られるスクッテルダイト熱電半導体も良好な性能を発揮することを見出した。例として、上記実施例と同じ処理条件で製造したスクッテルダイト熱電半導体ＣｏＳｂ３−ｘ−ｙＳｉｘＴｅｙ（（ｘ，ｙ）＝（０．００５，０．１７５））の熱電的性質を測定した結果である導電率、ゼーベック係数、熱伝導率及び性能指数をそれぞれ図９〜図１２に示す。なお、図９〜図１２に示した値は全てアニーリング前の値である。この実施例の試料に対して上記実施例と同じアニーリングを行うことで、同様な細孔の生成とそれによる熱伝導率の低下が起こり、その結果として当然性能指数が向上する。
[Additional embodiment]
Results by the present inventors have further advanced experiments, composition formula CoSb 3-x-y Si x Te y
It has been found that a skutterudite thermoelectric semiconductor obtained by reducing x to the range of 0.003 <x ≦ 0.25 while maintaining the range of y also exhibits good performance. As an example, the thermoelectric properties of skutterudite was prepared in the same processing conditions as in Example Tel phosphoramidite thermoelectric semiconductor CoSb 3-x-y Si x Te y ((x, y) = (0.005,0.175)) The measured electrical conductivity, Seebeck coefficient, thermal conductivity, and figure of merit are shown in FIGS. 9 to 12, respectively. Note that the values shown in FIGS. 9 to 12 are all values before annealing. By performing the same annealing on the sample of this embodiment as in the above-described embodiment, similar pores are generated and the thermal conductivity is reduced, and consequently the figure of merit is improved.
なお、上に書いたように、試料をＳＰＳ焼結させたが、これは試料を緻密にし、また成型することが目的である。このような成型を行った結果の写真を図７に示す。これにより電気抵抗が下がり、熱電性能が向上する。従って、本発明においてはＳＰＳ焼結は必須のものではないことに注意されたい。 In addition, as described above, the sample was subjected to SPS sintering, but this is for the purpose of making the sample denser and molding. FIG. 7 shows a photograph of the result of such molding. This reduces the electrical resistance and improves the thermoelectric performance. Therefore, it should be noted that SPS sintering is not essential in the present invention.
以上、詳細に説明したように、本発明は、廃熱回収など、産業上大いに利用されることが期待される。 As described in detail above, the present invention is expected to be widely used in industry such as waste heat recovery.
３１：熱電発電素子
３２：ｎ型半導体
３３：ｐ型半導体
３４：電極
３５：電極
31: thermoelectric generator 32: n-type semiconductor 33: p-type semiconductor 34: electrode 35: electrode
Claims (21)
前記原料混合物を焼成するステップを有する、請求項１〜１０のいずれかに記載のスクッテルダイト熱電半導体の製造方法。 Prepare a raw material mixture obtained by mixing a Co source, a Sb source, a Si source and a Te source,
The method for producing a skutterudite thermoelectric semiconductor according to claim 1, further comprising a step of firing the raw material mixture.
21. The method of manufacturing a skutterudite thermoelectric semiconductor according to claim 18 , wherein the annealing is performed in a range of 1 hour to 15 hours.
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