JP2013089882A

JP2013089882A - Thermoelectric conversion material

Info

Publication number: JP2013089882A
Application number: JP2011231196A
Authority: JP
Inventors: Yoichi Nishino; 洋一西野; Yuko Tamada; 裕子玉田
Original assignee: Nagoya Institute of Technology NUC
Current assignee: Nagoya Institute of Technology NUC
Priority date: 2011-10-21
Filing date: 2011-10-21
Publication date: 2013-05-13

Abstract

PROBLEM TO BE SOLVED: To provide an FeVal-based thermoelectric conversion material allowing a small environmental load, a low cost, and a large thermoelectric conversion performance index.SOLUTION: P-type and n-type thermoelectric conversion materials having a chemical composition ratio of Fe and V being adjusted with an adjustment amount n relative to a basic structure of FeVal and comprising a compound with some constituent elements replaced by other elements are adjusted in the range of an adjustment amount allowing improved thermoelectric conversion efficiency compared with a compound having a chemical composition ratio of Fe and V being not adjusted with an adjustment amount n and in the range of the total valence electron number.

Description

本発明は熱電変換材料に関する。 The present invention relates to a thermoelectric conversion material.

熱エネルギーを電気エネルギーに変換する材料として熱電変換材料がある。この熱電変換材料はｎ型又はｐ型の二種類に大別される。ｎ型の熱電変換材料とｐ型の熱電変換材料とを電気的に直列、熱的に並列となるよう交互に配置、結線すれば、熱電変換素子が得られる。この熱電変換素子の両面間に温度差を与えれば、発電を行うことが可能となる。また、熱電変換素子の両端子間に電圧を印加すれば、両面間に温度差が発生する。 There is a thermoelectric conversion material as a material that converts thermal energy into electric energy. This thermoelectric conversion material is roughly classified into two types, n-type and p-type. A thermoelectric conversion element can be obtained by alternately arranging and connecting n-type thermoelectric conversion materials and p-type thermoelectric conversion materials so as to be electrically in series and thermally parallel. If a temperature difference is given between both surfaces of the thermoelectric conversion element, power generation can be performed. Moreover, if a voltage is applied between the both terminals of a thermoelectric conversion element, a temperature difference will generate | occur | produce between both surfaces.

一般的な熱電変換材料としてＢｉ−Ｔｅ系金属間化合物があり、これは高いゼーベック係数を有し、比較的良好な発電効率を有することから広く用いられている（非特許文献１）。また、他の一般的な熱電変換材料としてＰｂ−Ｔｅ系金属間化合物や、Ｚｎ−Ｓｂ系金属間化合物があり、金属間化合物以外の熱電変換材料として、酸化物系の熱電変換材料がある（非特許文献１）。 As a general thermoelectric conversion material, there is a Bi-Te-based intermetallic compound, which is widely used because it has a high Seebeck coefficient and relatively good power generation efficiency (Non-patent Document 1). Further, as other general thermoelectric conversion materials, there are Pb—Te-based intermetallic compounds and Zn—Sb-based intermetallic compounds, and as thermoelectric conversion materials other than intermetallic compounds, there are oxide-based thermoelectric conversion materials ( Non-patent document 1).

また、本願発明者らは特許文献１記載の熱電変換材料を提案した。この熱電変換材料は、ホイスラー合金型の結晶構造をもち、化学式当たりの総価電子数が２４である基本構造Ｆｅ₂ＶＡｌに対し、化学組成比を調整したり、構成元素の一部を他の元素で置換したりし、化学式当たりの総価電子数を制御したものである。 The inventors of the present application have proposed a thermoelectric conversion material described in Patent Document 1. This thermoelectric conversion material has a Heusler alloy type crystal structure, and the chemical composition ratio is adjusted with respect to the basic structure Fe ₂ VAl having a total number of valence electrons of 24 per chemical formula. The total number of valence electrons per chemical formula is controlled by substituting with elements.

また、発明者らは特許文献２記載の熱電変換材料も提案した。この熱電変換材料は、Ｆｅ₂ＶＡｌの基本構造に対し、構成元素の一部を他の元素で置換するとともに、置換する元素の原子量等を制御したものである。 The inventors have also proposed a thermoelectric conversion material described in Patent Document 2. This thermoelectric conversion material is obtained by substituting a part of the constituent element with another element and controlling the atomic weight of the element to be substituted with respect to the basic structure of Fe ₂ VAl.

これらの提案に係る熱電変換材料は、化学量論組成のＦｅ₂ＶＡｌにおける構成元素の一部をほかの元素で置換した場合には，総価電子数が２４超でｎ型、２４未満でｐ型となる（特許文献２の図１３）。例えば、総価電子数が２４超となるｎ型のＦｅ₂Ｖ（Ａｌ_1-αＭ_α）（Ｍ＝Ｓｉ、Ｇｅ又はＳｎ、０＜α＜１）は、ゼーベック係数が約−１２０μＶ／Ｋの高い絶対値を示す（特許文献１、２、非特許文献２）。一方、総価電子数が２４未満となるｐ型のＦｅ₂（Ｖ_1-αＭ_α）Ａｌ（Ｍ＝Ｔｉ、０＜α＜１）は、ゼーベック係数が約＋８０μＶ／Ｋである（特許文献１、２、非特許文献３）。 The thermoelectric conversion materials according to these proposals have a total valence electron number of more than 24, n-type, and less than 24 p when the constituent elements in the stoichiometric composition of Fe ₂ VAl are replaced with other elements. It becomes a mold (FIG. 13 of Patent Document 2). For example, n-type Fe ₂ V (Al _1−α M _α ) (M = Si, Ge or Sn, 0 <α <1) having a total valence electron number exceeding 24 has a Seebeck coefficient of about −120 μV / K. The high absolute value is shown (patent documents 1, 2, nonpatent literature 2). On the other hand, p-type Fe ₂ (V _1−α M _α ) Al (M = Ti, 0 <α <1) having a total valence electron number of less than 24 has a Seebeck coefficient of about +80 μV / K (patent document) 1, 2, Non-Patent Document 3).

また、熱電変換材料として、より良好な発電効率の熱電変換材料が望まれている。このため、発明者らは、特許文献３において、Ｆｅ₂ＶＡｌの基本構造に対し、Ｆｅ及びＶのそれぞれ少なくとも一部を他の元素で置換した熱電変換材料を提案した。 Moreover, a thermoelectric conversion material with better power generation efficiency is desired as the thermoelectric conversion material. For this reason, the inventors have proposed a thermoelectric conversion material in which at least a part of each of Fe and V is substituted with another element for the basic structure of Fe ₂ VAl in Patent Document 3.

この熱電変換材料においては、Ｆｅに替えて置換する他の元素がＭ₁である場合には、元素Ｍ₁が周期表における第４〜６周期の７〜１０族からなる群から選ばれ、Ｖに替えて置換する他の元素がＭ₂である場合には、元素Ｍ₂が周期表における第４〜６周期の４〜６族からなる群から選ばれる。また、この熱電変換材料は、元素Ｍ₁及び元素Ｍ₂の置換量は、一般式（Ｆｅ_1-αＭ_1α）₂（Ｖ_1-βＭ_2β）Ａｌを満たす０＜α＜１及び０＜β＜１の範囲内で調整される。さらに、この熱電変換材料は、化学式当たりの総価電子数が２４未満になるようにしてｐ型に制御され、２４を超えるようにしてｎ型に制御される。例えば、Ｍ₁がＩｒ、Ｍ₂がＴｉの熱電変換材料は、ゼーベック係数が約＋９０μＶ／Ｋであり、Ｍ₂をＴｉとして置換しただけの熱電変換材料よりも、出力因子及び性能指数が向上する。 In this thermoelectric conversion material, when the other element that replaces Fe is M ₁ , the element M ₁ is selected from the group consisting of groups 7 to 10 of the 4th to 6th periods in the periodic table, and V When the other element to be substituted in place of is M ₂ , the element M ₂ is selected from the group consisting of groups 4 to 6 of the 4th to 6th periods in the periodic table. Further, in this thermoelectric conversion material, the substitution amount of the element M ₁ and the element M ₂ is 0 <α <1 and 0 <where the general formula (Fe _1-α M _1α ) ₂ (V _1-β M _2β ) Al is satisfied. Adjustment is made within the range of β <1. Furthermore, this thermoelectric conversion material is controlled to be p-type so that the total number of valence electrons per chemical formula is less than 24, and is controlled to be n-type so as to exceed 24. For example, a thermoelectric conversion material in which M ₁ is Ir and M ₂ is Ti has a Seebeck coefficient of about +90 μV / K, and the output factor and the figure of merit are improved as compared with a thermoelectric conversion material in which M ₂ is simply replaced with Ti. .

ＷＯ２００３/０１９６８１WO2003 / 019681 特開２００４−２５３６１８号公報Japanese Patent Laid-Open No. 2004-253618 ＷＯ２００７/１０８１７６WO2007 / 108176

「新教科書シリーズ熱電変換−基礎と応用−」９６〜９７頁、裳華房（２００５）坂田亮編"New Textbook Series Thermoelectric Conversion-Fundamentals and Applications-" pp. 96-97, Hanafusa (2005) Ryo Sakata 「擬ギャップ系ホイスラー化合物の熱電特性」まてりあ第４４巻第８号（２００５）６４８〜６５３頁、西野洋一著"Thermoelectric properties of pseudogap-type Heusler compounds" Materia 44, No. 8 (2005) pp. 648-653, Yoichi Nishino 「擬ギャップ系Ｆｅ2ＶＡｌ合金の熱電特性に及ぼす元素置換効果」日本金属学会誌第６６巻第７号（２００２）７６７〜７７１頁、松浦仁・西野洋一・水谷宇一郎・浅野滋著"Element substitution effect on thermoelectric properties of pseudogap Fe2VA1 alloy" Journal of the Japan Institute of Metals, Vol. 66, No. 7 (2002), pp. 767-771, Hitoshi Matsuura, Yoichi Nishino, Yuichiro Mizutani, Shigeru Asano

ところで、自動車や自動二輪車のエンジン、家庭用燃料電池やガスコージェネレーション等の廃熱を利用する発電装置に熱電変換材料を応用するためには、その熱電変換材料が良好な発電効率を発揮するだけでなく、環境に対する負荷が小さく、さらに耐酸化性や機械的強度も高いことが必要である。 By the way, in order to apply thermoelectric conversion materials to power generation devices that use waste heat, such as automobile engines, motorcycle engines, household fuel cells, and gas cogeneration, the thermoelectric conversion materials only exhibit good power generation efficiency. It is also necessary that the load on the environment is small and that the oxidation resistance and mechanical strength are also high.

上記したＢｉ−Ｔｅ系金属間化合物からなる熱電変換材料は、室温付近で大きなゼーベック係数を示すことが知られている。しかし、構成元素であるＢｉやＴｅが高価な金属であるため、高コストとなるだけでなく、ｎ型の熱電変換材料を形成する際にはＳｅが添加されるが、ＳｅやＴｅは毒性を有するため、この熱電変換材料は環境に対する負荷も大きなものとなる。さらに、Ｂｉ−Ｔｅ系金属間化合物からなる熱電変換材料は、耐酸化性や機械的強度が低いことなどから、現実の５００〜７００Ｋなどの中温域の廃熱への応用を想定した場合には耐久性を保証するための高度な周辺技術が必要となる。このため、Ｂｉ−Ｔｅ系金属間化合物の中温域廃熱への応用は困難である。
また、上記したＰｂ−Ｔｅ系金属間化合物も、Ｂｉ−Ｔｅ系金属間化合物と同様に構成元素であるＰｂは人体にとって有害有毒であり、また地球環境の観点からも、Ｐｂ−Ｔｅ系金属間化合物の使用は好ましくない。 It is known that a thermoelectric conversion material composed of the above-described Bi—Te intermetallic compound exhibits a large Seebeck coefficient near room temperature. However, since Bi and Te, which are constituent elements, are expensive metals, not only the cost is increased, but Se is added when forming an n-type thermoelectric conversion material, but Se and Te are toxic. Therefore, this thermoelectric conversion material also has a large environmental load. Furthermore, thermoelectric conversion materials made of Bi-Te based intermetallic compounds have low oxidation resistance and mechanical strength, and therefore, when applied to actual waste heat in the middle temperature range such as 500 to 700K. Advanced peripheral technology is required to guarantee durability. For this reason, it is difficult to apply Bi-Te based intermetallic compounds to intermediate temperature waste heat.
Further, in the Pb-Te intermetallic compound described above, the constituent element Pb is harmful to the human body as well as the Bi-Te intermetallic compound. From the viewpoint of the global environment, the Pb-Te intermetallic compound is also used. The use of compounds is not preferred.

また、上記したＺｎ−Ｓｂ系金属間化合物は、特にｐ型半導体であるＺｎＳｂはゼーベック係数が＋２００μＶ／Ｋと高く、かつ電気抵抗も低いことから古くから熱電半導体として研究されてきた。しかし、材料として低強度かつ低靱性であることから、モジュールへの組み込みを考えると機械的特性を相当に改善しないと実用化は困難であるため、結果的に熱電変換素子の製造コストの高騰化を招来する。 In addition, the Zn—Sb-based intermetallic compounds described above have been studied as thermoelectric semiconductors for a long time since ZnSb, which is a p-type semiconductor, has a high Seebeck coefficient of +200 μV / K and low electrical resistance. However, because it has low strength and low toughness as a material, it is difficult to put it into practical use unless the mechanical properties are significantly improved when considering the incorporation into modules. As a result, the manufacturing cost of thermoelectric conversion elements increases. Invite

また、酸化物系の熱電変換材料は、１０００Ｋ付近の高温域で高いゼーベック係数を示すという利点を有している。しかし、酸化物系の熱電変換材料は、Ｂｉ―Ｔｅ系熱電変換材料と同様、脆くて加工が困難であるという性質を有する。このため、酸化物系の熱電変換材料を用いて熱電変換素子を製造した場合、やはり切断のための削り代が必要になるとともに、切断時においてインゴットが割れやすく、歩留まりが非常に悪く、熱電変換素子の製造コストの高騰化を招来する。 In addition, the oxide-based thermoelectric conversion material has an advantage of exhibiting a high Seebeck coefficient in a high temperature region around 1000K. However, the oxide-based thermoelectric conversion material, like the Bi—Te-based thermoelectric conversion material, has the property of being brittle and difficult to process. For this reason, when a thermoelectric conversion element is manufactured using an oxide-based thermoelectric conversion material, a cutting allowance for cutting is still necessary, and the ingot is easily broken at the time of cutting, and the yield is very poor. This leads to an increase in device manufacturing costs.

一方、特許文献１−３に記載のＦｅ₂ＶＡｌ系熱電変換材料は、Ｆｅ、Ｖ、Ａｌの比較的安価な元素からなり、また、各元素は毒性を有さない点で、Ｂｉ−Ｔｅ系金属間化合物やＰｂ−Ｔｅ系金属間化合物よりも優れた熱電変換材料である。また、特許文献１−３に記載の通り、基本構造であるＦｅ₂ＶＡｌは、半導体と金属との間に位置づけされる半金属であることから、半導体、酸化物よりも靱性が高く機械的特性に優れている。したがって、特許文献１−３に記載のＦｅ₂ＶＡｌ系熱電変換材料は、Ｚｎ−Ｓｂ系金属間化合物や酸化物系の熱電変換材料よりも、機械的特性が優れた熱電変換材料である。 On the other hand, the Fe ₂ VAl-based thermoelectric conversion material described in Patent Documents 1-3 is composed of relatively inexpensive elements such as Fe, V, and Al, and each element has no toxicity, and is Bi-Te-based. It is a thermoelectric conversion material superior to intermetallic compounds and Pb—Te-based intermetallic compounds. In addition, as described in Patent Documents 1-3, Fe ₂ VAl, which is a basic structure, is a semimetal positioned between a semiconductor and a metal, and thus has higher toughness and higher mechanical properties than semiconductors and oxides. Is excellent. Therefore, the Fe ₂ VAl-based thermoelectric conversion material described in Patent Documents 1-3 is a thermoelectric conversion material having superior mechanical characteristics as compared to Zn—Sb-based intermetallic compounds and oxide-based thermoelectric conversion materials.

ただし、特許文献２の比較試験で記載のように、Ｆｅ₂ＶＡｌの基本構造に対し、３元素の組成比を調整することなく、構成元素の一部を他の元素で置換したものは、ゼーベック係数と置換量の関係は置換する元素の種類によって、置換量に対する変化の仕方は異なっているが、総価電子数で整理したとき、ゼーベック係数は置換する元素の種類によらず，１本のマスターカーブで記述できるような変化の仕方になっている。このため，置換する元素の種類を選択することにより、ゼーベック係数の符号を制御することができるために、ｐ型とｎ型の熱電変換材料を作製することが可能にはなるが、置換する元素の種類を選択するだけでゼーベック係数の絶対値を大幅に増大させることは困難となる。 However, as described in the comparative test of Patent Document 2, a part of the constituent elements replaced with another element without adjusting the composition ratio of the three elements with respect to the basic structure of Fe ₂ VAl is Seebeck The relationship between the coefficient and the amount of substitution varies depending on the type of element to be replaced, but the manner of change with respect to the amount of substitution differs, but when organized by the total number of valence electrons, the Seebeck coefficient is independent of the type of element to be substituted. It is a way of change that can be described by a master curve. For this reason, since the sign of the Seebeck coefficient can be controlled by selecting the type of element to be replaced, it is possible to produce p-type and n-type thermoelectric conversion materials. It is difficult to greatly increase the absolute value of the Seebeck coefficient simply by selecting the type of the.

このため、特許文献１に記載のＦｅ_２−ｎＶ_１＋ｎ（Ａｌ_１−ｙＳｉ_ｙ）のように、Ｆｅ₂ＶＡｌの基本構造に対して、ＦｅとＶの化学組成比を調整量ｎで調整するとともに、Ａｌの少なくとも一部をＳｉで置換した熱電変換材料を用いれば、Ａｌの少なくとも一部をＳｉで置換しただけの熱電変換材料と比べ、ゼーベック係数はさらに増加しており、良好な発電効率が発揮されることが望まれる。
しかし、ＦｅとＶの化学組成比を調整量ｎで調整する特許文献１の化合物は、良好な発電効率が発揮される調整量の範囲が開示されておらず、しかもｎ型のみならずｐ型についても特許文献１〜３に記載の調整量で調整していない化合物よりも良好な発電効率が発揮される熱電変換材料が求められる。 Therefore, as in the described in Patent Document _{_{1 Fe 2-n V 1 +}} n (Al 1-y Si y), the basic structure of Fe ₂ VAl, adjusted by the adjustment amount n the chemical composition ratio of Fe and V In addition, if a thermoelectric conversion material in which at least a part of Al is replaced with Si is used, the Seebeck coefficient is further increased as compared with a thermoelectric conversion material in which at least a part of Al is replaced with Si, and good power generation is achieved. It is desired that efficiency be exhibited.
However, the compound of Patent Document 1 that adjusts the chemical composition ratio of Fe and V by the adjustment amount n does not disclose the range of the adjustment amount that exhibits good power generation efficiency, and is not only n-type but also p-type. Also, there is a need for a thermoelectric conversion material that exhibits better power generation efficiency than a compound that is not adjusted with the adjustment amounts described in Patent Documents 1 to 3.

本発明は、上記従来の実情に鑑みてなされたものであって、Ｆｅ₂ＶＡｌの基本構造に対して、ＦｅとＶの化学組成比を調整量ｎで調整するとともに、構成元素の一部を他の元素で置換した化合物からなり、特許文献１に記載のＦｅとＶを調整量ｎで調整するとともに、Ａｌの少なくとも一部をＳｉで置換した化合物と比較して、良好な発電効率が発揮される熱電変換材料を提供することを解決すべき課題としている。また、本発明は、Ｆｅ₂ＶＡｌの基本構造に対して、ＦｅとＶの化学組成比を調整量ｎで調整するとともに、構成元素の一部を他の元素で置換した化合物からなり、ＦｅとＶの化学組成比を調整量ｎで調整していない化合物と比較して熱電変換効率が向上し得る調整量の範囲並びに総価電子数の範囲に制御されているp型及びｎ型の熱電変換材料を提供することを他の解決すべき課題としている。 The present invention has been made in view of the above-described conventional situation, and with respect to the basic structure of Fe ₂ VAl, the chemical composition ratio of Fe and V is adjusted by an adjustment amount n, and a part of the constituent elements is adjusted. It is composed of a compound substituted with other elements, and Fe and V described in Patent Document 1 are adjusted with an adjustment amount n, and excellent power generation efficiency is exhibited as compared with a compound in which at least a part of Al is substituted with Si. It is set as the problem which should be solved to provide the thermoelectric conversion material. Further, the present invention comprises a compound in which the chemical composition ratio of Fe and V is adjusted with an adjustment amount n with respect to the basic structure of Fe ₂ VAl, and a part of the constituent elements is substituted with another element, and Fe and V P-type and n-type thermoelectric conversions in which the range of the adjustment amount and the total number of valence electrons are controlled so that the thermoelectric conversion efficiency can be improved as compared with a compound in which the chemical composition ratio of V is not adjusted by the adjustment amount n Providing materials is another issue to be solved.

発明者らが先の出願（特許文献１）で確認したように、ホイスラー合金型の結晶構造をもつＦｅ₂ＶＡｌの基本構造は化学式当たりの総価電子数が２４である。すなわち原子当たりの平均電子濃度が２４／４＝６である場合、この熱電変換材料は、フェルミ準位に鋭い擬ギャップをもつ。そして、この基本構造に対し、基本構造のＦｅ及びＶの化学組成比を調整し，さらに構成元素の一部をほかの元素で置換することにより化学式当たりの総価電子数を制御すれば、フェルミ準位を擬ギャップの中心からシフトさせることができ、ゼーベック係数の符号や大きさを変化させ得る。 As the inventors have confirmed in a previous application (Patent Document 1), the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure has 24 total valence electrons per chemical formula. That is, when the average electron concentration per atom is 24/4 = 6, the thermoelectric conversion material has a sharp pseudogap at the Fermi level. If the chemical composition ratio of Fe and V of the basic structure is adjusted with respect to this basic structure, and the total number of valence electrons per chemical formula is controlled by substituting some of the constituent elements with other elements, Fermi The level can be shifted from the center of the pseudogap, and the sign and magnitude of the Seebeck coefficient can be changed.

今回、発明者らは、Ｆｅ₂ＶＡｌの基本構造に対して、Ｆｅ及びＶの化学組成比を特定の範囲内の調整量で調整し、さらに構成元素の一部をほかの元素で置換した場合に、Ｆｅ及びＶの化学組成比を調整していない化合物に対して元素置換した場合と比較して、ゼーベック係数の絶対値を大幅に増大させることができることを見出し、本願発明を完成させるに至った。そしてＦｅ₂ＶＡｌの基本構造に対して元素置換した場合の総価電子数は、ｐ型の場合は２４未満、一方ｎ型の場合は２４超であり、２４を中心としているのに対して、本願発明のｐ型あるいはｎ型の熱電変換材料の総価電子数は２４を中心とした分布とならず、基本構造の総価電子数とは異なることを見出した。 This time, the inventors adjusted the chemical composition ratio of Fe and V to the basic structure of Fe ₂ VAl by an adjustment amount within a specific range, and further replaced some of the constituent elements with other elements. In addition, it was found that the absolute value of the Seebeck coefficient can be greatly increased compared to the case where element substitution is performed on a compound whose chemical composition ratio of Fe and V is not adjusted, and the present invention has been completed. It was. The total number of valence electrons when element substitution is performed on the basic structure of Fe ₂ VAl is less than 24 in the case of p-type, while it is more than 24 in the case of n-type. It has been found that the total valence electrons of the p-type or n-type thermoelectric conversion material of the present invention do not have a distribution centered at 24, and are different from the total valence electrons of the basic structure.

すなわち、請求項１に記載の発明は、ホイスラー合金型の結晶構造をもち、化学式当たりの総価電子数が２４であるＦｅ_２ＶＡｌの基本構造に対し、化学組成比の調整量ｘ並びに基本構造のＡｌに替えて置換する元素Ｄの置換量ｙが一般式Ｆｅ_２−ｘＶ_１+ｘ（Ａｌ_１−ｙＤ_ｙ）を満たす０．０２≦ｘ≦０．０８の範囲内で調整量ｘを選択する熱電変換材料において、Ａｌに替えて置換する他の元素がＤである場合には、元素Ｄが周期表における第３〜６周期の１４〜１６族からなる群から選ばれた元素であり、化学式当たりの総価電子数を、２３．７を超え、２４．１以下になるようにしてｎ型に制御することを特徴とする。
請求項２に記載の発明は、ホイスラー合金型の結晶構造をもち、化学式当たりの総価電子数が２４であるＦｅ_２ＶＡｌの基本構造に対し、化学組成比の調整量ｘ並びに基本構造のＶに替えて置換する元素Ｎの置換量ｙが一般式Ｆｅ_２−ｘ（Ｖ_{１+ｘ−ｙ}Ｎ_ｙ）Ａｌを満たす０．０２≦ｘ≦０．０８の範囲内で調整量ｘを選択する熱電変換材料において、Ｖに替えて置換する他の元素がＮである場合には、元素Ｎが周期表における第４〜６周期の６族からなる群から選ばれた元素であり、化学式当たりの総価電子数を、２３．７を超え、２４．１以下になるようにしてｎ型に制御することを特徴とする。
請求項３に記載の発明は、ホイスラー合金型の結晶構造をもち、化学式当たりの総価電子数が２４であるＦｅ_２ＶＡｌの基本構造に対し、化学組成比の調整量ｘ並びに基本構造のＶに替えて置換する元素Ｎの置換量ｙが一般式Ｆｅ_２−ｘ（Ｖ_{１+ｘ−ｙ}Ｎ_ｙ）Ａｌを満たす−０．０７≦ｘ＜０の範囲内で調整量ｘを選択する熱電変換材料において、Ｖに替えて置換する他の元素がＮである場合には、元素Ｎが周期表における第４〜６周期の４族からなる群から選ばれた元素であり、化学式当たりの総価電子数を、２４を超え、２４．３以下になるようにしてｐ型に制御することを特徴とする。
請求項４に記載の発明は、ホイスラー合金型の結晶構造をもち、化学式当たりの総価電子数が２４であるＦｅ_２ＶＡｌの基本構造に対し、化学組成比の調整量ｘ並びに基本構造のＦｅに替えて置換する元素Ｍの置換量ｙ及びＶに替えて置換する元素Ｔａの置換量ｚが一般式（Ｆｅ_{２−ｘ−ｙ}Ｍ_ｙ）（Ｖ_{１+ｘ−ｚ}Ｔａ_ｚ）Ａｌを満たす０．０２≦ｘ≦０．０８の範囲内で調整量ｘを選択する熱電変換材料において、Ｆｅに替えて置換する他の元素がＭである場合には、元素Ｍが周期表における第４〜６周期の９族及び１０族からなる群から選ばれた元素であり、化学式当たりの総価電子数を、２３．７を超え、２４．１以下になるようにしてｎ型に制御することを特徴とする。
請求項５に記載の発明は、ホイスラー合金型の結晶構造をもち、化学式当たりの総価電子数が２４であるＦｅ_２ＶＡｌの基本構造に対し、化学組成比の調整量ｘ並びに基本構造のＦｅに替えて置換する元素Ｍの置換量ｙが一般式（Ｆｅ_{２−ｘ−ｙ}Ｍ_ｙ）Ｖ_１+ｘＡｌを満たす０．０２≦ｘ≦０．０８の範囲内で調整量ｘを選択する熱電変換材料において、Ｆｅに替えて置換する他の元素がＭである場合には、元素Ｍが周期表における第４〜６周期の９族及び１０族からなる群から選ばれた元素であり、化学式当たりの総価電子数を、２３．７を超え、２４．１以下になるようにしてｎ型に制御することを特徴とする。
請求項６に記載の発明は、ホイスラー合金型の結晶構造をもち、化学式当たりの総価電子数が２４であるＦｅ_２ＶＡｌの基本構造に対し、化学組成比の調整量ｘ並びに基本構造のＶに替えて置換する元素Ｎの置換量ｙ及びＶに替えて置換する元素Ｔａの置換量ｚが一般式Ｆｅ_２−ｘ（Ｖ_{１+ｘ−ｙ−ｚ}Ｎ_ｙＴａ_ｚ）Ａｌを満たす０．０２≦ｘ≦０．０８の範囲内で調整量ｘを選択する熱電変換材料において、Ｖに替えて置換する他の元素がＮである場合には、元素Ｎが周期表における第４〜６周期の６族からなる群から選ばれた元素であり、化学式当たりの総価電子数を、２３．７を超え、２４．１以下になるようにしてｎ型に制御することを特徴とする。
請求項７に記載の発明は、ホイスラー合金型の結晶構造をもち、化学式当たりの総価電子数が２４であるＦｅ_２ＶＡｌの基本構造に対し、化学組成比の調整量ｘ並びに基本構造のＶに替えて置換する元素Ｎの置換量ｙ及びＶに替えて置換する元素Ｔａの置換量ｚが一般式Ｆｅ_２−ｘ（Ｖ_{１+ｘ−ｙ−ｚ}Ｎ_ｙＴａ_ｚ）Ａｌを満たす−０．０７≦ｘ＜０の範囲内で調整量ｘを選択する熱電変換材料において、
Ｖに替えて置換する他の元素がＮである場合には、元素Ｎが周期表における第４〜６周期の４族からなる群から選ばれた元素であり、化学式当たりの総価電子数を、２４を超え、２４．３以下になるようにしてｐ型に制御することを特徴とする。 That is, the invention described in claim 1 has a chemical composition ratio adjustment amount x and a basic structure with respect to a basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total valence electron number of 24 per chemical formula. The substitution amount x of the element D that substitutes for Al in the range of 0.02 ≦ x ≦ 0.08 satisfying the general formula Fe _2-x V _{1 + x} (Al _1-y D _y ) In the thermoelectric conversion material for selecting, when the other element substituted for Al is D, the element D is an element selected from the group consisting of groups 14 to 16 of the 3rd to 6th periods in the periodic table And the total number of valence electrons per chemical formula is controlled to be n-type so that it exceeds 23.7 and is 24.1 or less.
The invention according to claim 2 has an adjustment amount x of the chemical composition ratio and V of the basic structure with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and having 24 total valence electrons per chemical formula. The adjustment amount x is selected within the range of 0.02 ≦ x ≦ 0.08 where the substitution amount y of the element N to be replaced with satisfies the general formula Fe _2-x (V _{1 + xy} N _y ) Al. In the thermoelectric conversion material, when the other element to be substituted in place of V is N, the element N is an element selected from the group consisting of Group 6 of the 4th to 6th periods in the periodic table, and per chemical formula The total number of valence electrons is controlled to be n-type so as to exceed 23.7 and not more than 24.1.
The invention according to claim 3 has an adjustment amount x of the chemical composition ratio and V of the basic structure with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total valence electron number of 24 per chemical formula. In which the substitution amount y of the element N to be replaced with satisfies the general formula Fe _2-x (V _{1 + xy} N _y ) Al and the adjustment amount x is selected within a range of −0.07 ≦ x <0. In the conversion material, when the other element to be substituted in place of V is N, the element N is an element selected from the group consisting of groups 4 to 6 in the periodic table, and the total per chemical formula The p-type is controlled so that the number of valence electrons is more than 24 and 24.3 or less.
The invention according to claim 4 has an adjustment amount x of the chemical composition ratio and Fe of the basic structure with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total valence electron number of 24 per chemical formula. The substitution amount y of the element M to be substituted instead of and the substitution amount z of the element Ta to substitute instead of V satisfy the general formula (Fe _2−x− M _y ) (V _{1 + x−z} Ta _z ) Al In the thermoelectric conversion material in which the adjustment amount x is selected within the range of 0.02 ≦ x ≦ 0.08, when the other element to be substituted in place of Fe is M, the element M is the fourth to fourth in the periodic table. It is an element selected from the group consisting of Group 9 and Group 10 in 6 cycles, and the total valence electrons per chemical formula is controlled to be n-type so as to exceed 23.7 and not more than 24.1 Features.
The invention according to claim 5 has an adjustment amount x of the chemical composition ratio and Fe of the basic structure with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total valence electron number of 24 per chemical formula. The adjustment amount x is selected within a range of 0.02 ≦ x ≦ 0.08 where the substitution amount y of the element M to be substituted satisfies the general formula (Fe _2- _{xy My} ) V _{1 + x} Al. In the thermoelectric conversion material, when the other element to be substituted in place of Fe is M, the element M is an element selected from the group consisting of groups 9 and 10 of the 4th to 6th periods in the periodic table, The total number of valence electrons per chemical formula is controlled to be n-type so as to be over 23.7 and below 24.1.
The invention according to claim 6 has a chemical composition ratio adjustment amount x and a basic structure V with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total valence electron number of 24 per chemical formula. The substitution amount y of the element N substituted for V and the substitution amount z of the element Ta substituted for V _{satisfy the} general formula Fe _2-x (V _{1 + x−yZ} N _y Ta _z ) Al In the thermoelectric conversion material in which the adjustment amount x is selected within the range of 02 ≦ x ≦ 0.08, when the other element to be substituted in place of V is N, the element N is the fourth to sixth periods in the periodic table. The total number of valence electrons per chemical formula is controlled to be n-type so as to be more than 23.7 and not more than 24.1.
The invention according to claim 7 has an adjustment amount x of the chemical composition ratio and V of the basic structure with respect to the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total number of valence electrons of 24 per chemical formula. The substitution amount y of the element N substituted for V and the substitution amount z of the element Ta substituted for V satisfies the general formula Fe _2-x (V _{1 + x−yz} N _y Ta _z ) Al−0 In the thermoelectric conversion material in which the adjustment amount x is selected within the range of .07 ≦ x <0,
When the other element substituted for V is N, the element N is an element selected from the group consisting of Group 4 of the 4th to 6th periods in the periodic table, and the total number of valence electrons per chemical formula is , 24, and 24.3 or less, and the p-type control is performed.

実施例１の熱電変換材料（Ｆｅ_１．９５Ｖ_１．０５（Ａｌ_１―ｙＳｉ_ｙ）（ｙ＝０、０．０３、０．０５、０．１０））に係り、温度とゼーベック係数との関係を示すグラフである。In relation to the thermoelectric conversion material of Example 1 (Fe _1.95 V _1.05 (Al _1-y Si _y ) (y = 0, 0.03, 0.05, 0.10)), the temperature, the Seebeck coefficient, It is a graph which shows the relationship. 実施例１の熱電変換材料（Ｆｅ_１．９５Ｖ_１．０５（Ａｌ_１―ｙＳｉ_ｙ）（ｙ＝０、０．０３、０．０５、０．１０））に係り、温度と電気抵抗率との関係を示すグラフである。In relation to the thermoelectric conversion material (Fe _1.95 V _1.05 (Al _1-y Si _y ) (y = 0, 0.03, 0.05, 0.10)) of Example 1, temperature and electrical resistivity It is a graph which shows the relationship. 実施例１の熱電変換材料（Ｆｅ_２−ｘＶ_１+ｘ（Ａｌ_１―ｙＳｉ_ｙ）（ｘ＝−０．０７、 −０．０４、０．０２、０．０５、０．０８）（ｙ＝０、０．０１、０．０３、０．０５、０．０７、０．１０））及び比較例１の熱電変換材料（Ｆｅ_２Ｖ（Ａｌ_１―ｙＳｉ_ｙ）（ｙ＝０，０．０３、０．０５、０．１０））に係り、Ｓｉ組成と３００Ｋにおけるゼーベック係数との関係を示すグラフである。Thermoelectric conversion material of Example _{_{1 (Fe 2-x V 1}} + x (Al 1-y Si y) (x = -0.07, -0.04,0.02,0.05,0.08) ( y = 0, 0.01, 0.03, 0.05, 0.07, 0.10)) and the thermoelectric conversion material of Comparative Example 1 (Fe ₂ V (Al _1-y Si _y ) (y = 0, 0.03, 0.05, 0.10)), and is a graph showing the relationship between the Si composition and the Seebeck coefficient at 300K. 実施例２の熱電変換材料（Ｆｅ_2．０４（Ｖ_{０．９６−ｙ}Ｔｉ_ｙ）Ａｌ（ｙ＝０、０．０１、０．０３、０．０５、０．１０））に係り、温度とゼーベック係数との関係を示すグラフである。The thermoelectric conversion material of Example 2 (Fe _2.04 (V _0.96-y Ti _y ) Al (y = 0, 0.01, 0.03, 0.05, 0.10)), It is a graph which shows the relationship with a Seebeck coefficient. 実施例２の熱電変換材料（（Ｆｅ_2．０４（Ｖ_{０．９６−ｙ}Ｔｉ_ｙ）Ａｌ（ｙ＝０、０．０１、０．０３、０．０５、０．１０））に係り、温度と電気抵抗率との関係を示すグラフである。The thermoelectric conversion material of Example 2 ((Fe _2.04 (V _0.96-y Ti _y ) Al (y = 0, 0.01, 0.03, 0.05, 0.10))), temperature It is a graph which shows the relationship between and electrical resistivity. 実施例２の熱電変換材料（Ｆｅ_２−ｘ（Ｖ_{１+ｘ−ｙ}Ｔｉ_ｙ）Ａｌ（ｘ＝−０．０７、 −０．０４、０．０２、０．０５）（ｙ＝０、０．０１、０．０２，０．０３、０．０５、０．１０））及び比較例２の熱電変換材料（Ｆｅ_２（Ｖ_１−ｙＴｉ_ｙ）Ａｌ（ｙ＝０、０．０１、０．０２，０．０３、０．０５、０．１０））に係り、Ｔｉ組成と３００Ｋにおけるゼーベック係数との関係を示すグラフである。Thermoelectric conversion material of Example 2 (Fe _2−x (V _{1 + xy} Ti _y ) Al (x = −0.07, −0.04, 0.02, 0.05) (y = 0, 0 0.01, 0.02, 0.03, 0.05, 0.10)) and the thermoelectric conversion material of Comparative Example 2 (Fe ₂ (V _1-y Ti _y ) Al (y = 0, 0.01, ₀ ) .02, 0.03, 0.05, 0.10)), and is a graph showing the relationship between the Ti composition and the Seebeck coefficient at 300K. 実施例１の熱電変換材料（Ｆｅ_１．９８Ｖ_１．０２（Ａｌ_０．９０Ｓｉ_０．１０）），比較例１の熱電変換材料（Ｆｅ_２Ｖ（Ａｌ_０．９０Ｓｉ_０．１０）），実施例２の熱電変換材料（Ｆｅ_2．０４（Ｖ_０．８６Ｔｉ_０．１０）Ａｌ）及び比較例２の熱電変換材料（Ｆｅ₂（Ｖ_０．９０Ｔｉ_０．１０）Ａｌ）に係り、温度と出力因子との関係を示すグラフである。Thermoelectric conversion material of Example 1 (Fe _1.98 V _1.02 (Al _0.90 Si _0.10 )), Thermoelectric conversion material of Comparative Example 1 (Fe ₂ V (Al _0.90 Si _0.10 )) The thermoelectric conversion material of Example 2 (Fe _2.04 (V _0.86 Ti _0.10 ) Al) and the thermoelectric conversion material of Comparative Example 2 (Fe ₂ (V _0.90 Ti _0.10 ) Al). It is a graph which shows the relationship between temperature and an output factor. 実施例３の熱電変換材料（（Ｆｅ_{１．９５−ｙ}Ｉｒ_ｙ）（Ｖ_０．９５Ｔａ_０．１０）Ａｌ（ｙ＝０、０．０３、０．０５、０．１０））に係り、温度とゼーベック係数との関係を示すグラフである。The thermoelectric conversion material of Example 3 ((Fe _1.95-y Ir _y ) (V _0.95 Ta _0.10 ) Al (y = 0, 0.03, 0.05, _0.10 )), It is a graph which shows the relationship between temperature and a Seebeck coefficient. 実施例３の熱電変換材料（（Ｆｅ_{１．９５−ｙ}Ｉｒ_ｙ）（Ｖ_０．９５Ｔａ_０．１０）Ａｌ（ｙ＝０、０．０３、０．０５、０．１０））に係り、温度と電気抵抗率との関係を示すグラフである。The thermoelectric conversion material of Example 3 ((Fe _1.95-y Ir _y ) (V _0.95 Ta _0.10 ) Al (y = 0, 0.03, 0.05, _0.10 )), It is a graph which shows the relationship between temperature and an electrical resistivity. 実施例３の熱電変換材料（（Ｆｅ_{２−ｘ−ｙ}Ｉｒ_ｙ）（Ｖ_{０．９０+ｘ}Ｔａ_０．１０）Ａｌ（ｘ＝０．０２、０．０５））に係り、Ｉｒ組成と３００Ｋにおける熱伝導率との関係を示すグラフである。It relates to the thermoelectric conversion material of Example 3 ((Fe _2−x−y Ir _y ) (V _{0.90 + x} Ta _0.10 ) Al (x = 0.02, 0.05)), Ir composition and 300K It is a graph which shows the relationship with the heat conductivity in. 実施例３の熱電変換材料（Ｆｅ_{１．９８−ｙ}Ｉｒ_ｙ）（Ｖ_０．９２Ｔａ_０．１０）Ａｌと実施例４の熱電変換材料（Ｆｅ_{１．９８−ｙ}Ｉｒ_ｙ）Ｖ_１．０２Ａｌに係り、Ｉｒ組成と３００Ｋにおける性能指数との関係を示すグラフである。Thermoelectric conversion material (Fe _1.98-y Ir _y ) (V _0.92 Ta _0.10 ) Al of Example 3 and thermoelectric conversion material (Fe _1.98-y Ir _y ) V _{1.02 of} Example 4 It is a graph which shows the relationship between Ir composition and a figure of merit in 300K concerning Al. 実施例１の熱電変換材料（Ｆｅ_２−ｘＶ_１+ｘ（Ａｌ_１―ｙＳｉ_ｙ）、実施例２の熱電変換材料（Ｆｅ_２−ｘ（Ｖ_{１+ｘ−ｙ}Ｔｉ_ｙ）Ａｌ、実施例３の熱電変換材料（（Ｆｅ_{２−ｘ−ｙ}Ｉｒ_ｙ）（Ｖ_{０．９０+ｘ}Ｔａ_０．１０）Ａｌ、実施例４の熱電変換材料（（Ｆｅ_{１．９８−ｙ}Ｉｒ_ｙ）Ｖ_１．０２Ａｌ）、実施例５の熱電変換材料（Ｆｅ_２−ｘ（Ｖ_{１+ｘ−ｙ}Ｍｏ_ｙ）Ａｌ、実施例６の熱電変換材料（Ｆｅ_２−ｘ（Ｖ_{０．９０+ｘ−ｙ}Ｔｉ_ｙＴａ_０．１０）Ａｌ、比較例１の熱電変換材料（Ｆｅ_２Ｖ（Ａｌ_１―ｙＳｉ_ｙ）、比較例２の熱電変換材料（Ｆｅ_２（Ｖ_１−ｙＴｉ_ｙ）Ａｌ、比較例３の熱電変換材料（Ｆｅ_２−ｙＩｒ_ｙ）ＶＡｌ及び比較例４の熱電変換材料（Ｆｅ_２（Ｖ_１−ｙＭｏ_ｙ）Ａｌに係り、総価電子数と３００Ｋにおけるゼーベック係数との関係を示すグラフである。Thermoelectric conversion material of Example 1 (Fe2 _-xV1 _{+ x} (Al1 _- _ySiy ), Thermoelectric conversion material of Example 2 (Fe2 _-x (V1 ₊ _xyTiy ) Al, Implementation Thermoelectric conversion material of Example 3 ((Fe _2-xy Ir _y ) (V _{0.90 + x} Ta _0.10 ) Al, Thermoelectric conversion material of Example 4 ((Fe _1.98-y Ir _y ) V _1.02 Al), thermoelectric conversion material of Example 5 (Fe _2-x (V _{1 + xy} Mo _y ) Al, thermoelectric conversion material of Example 6 (Fe _2-x (V _{0.90 + x− y} Ti _y Ta _0.10 ) Al, thermoelectric conversion material of Comparative Example 1 (Fe ₂ V (Al _1-y Si _y ), thermoelectric conversion material of Comparative Example 2 (Fe ₂ (V _1-y Ti _y ) Al), thermoelectric conversion material of Comparative example _{_{3 (Fe 2-y Ir y}} ) VAl and thermoelectric conversion material of Comparative example _{_{4 (Fe 2 (V 1-}} y Mo y) a It relates to a graph showing the relationship between the Seebeck coefficient in the total number of valence electrons and 300K.

本発明の熱電変換材料は、例えば以下の製造方法により製造され得る。この製造方法は、上記熱電変換材料を製造可能な元素と構成比率とを有する原料混合物を用意する第１工程と、該原料混合物を真空中又は不活性ガス中において溶融又は気化及び固化し、熱電変換材料を得る第２工程とを有する。 The thermoelectric conversion material of the present invention can be produced, for example, by the following production method. This manufacturing method includes a first step of preparing a raw material mixture having an element capable of manufacturing the thermoelectric conversion material and a composition ratio, and melting or vaporizing and solidifying the raw material mixture in a vacuum or an inert gas, A second step of obtaining a conversion material.

この製造方法で上記熱電変換材料を製造すれば、得られる熱電変換材料のゼーベック係数が比較的高くなる。このため、この製造方法によれば、廃熱回収効率が高く、環境汚染のおそれも少ない熱電変換材料を低廉に製造できる。 If the said thermoelectric conversion material is manufactured with this manufacturing method, the Seebeck coefficient of the thermoelectric conversion material obtained will become comparatively high. For this reason, according to this manufacturing method, a thermoelectric conversion material with high waste heat recovery efficiency and less risk of environmental pollution can be manufactured at low cost.

第２工程としては、例えば、原料混合物を真空中や不活性ガス中において溶解させた後で冷却する方法を採用することができる。ｎ型の熱電変換材料又はｐ型の熱電変換材料を可及的に小さな粒径の粉体の集合体とするためには、まず、原料混合物をアーク溶解等により溶解した後に固化することによりインゴットを作製し、これを不活性ガス又は窒素ガス雰囲気中で機械的に粉砕してほぼ均粒の粉体を得る方法、溶湯粉化（アトマイズ）やガスアトマイズ法によってほぼ均粒の粉体を得る方法、メカニカルアロイング法により不活性ガス又は窒素ガス雰囲気中で原料混合物の圧着と破断を繰り返すことによってほぼ均粒の粉体を得る方法等を採用することができる。そして、こうして得られた粉体を真空中のホットプレス法、ＨＩＰ（熱間等方圧成形）法、放電プラズマ焼結法、パルス通電法等により焼結することが可能である。ＨＩＰ法により粉体を焼結する場合、例えば８００°Ｃで１５０ＭＰａのアルゴンガスにより圧縮成形と焼結とを同時に進行させ、真密度で固化を行うことができる。また、擬ＨＩＰ法によれば成形プレスを利用して安価に真密度固化を行うことができる。また、ｎ型の熱電変換材料又はｐ型の熱電変換材料を可及的に小さな粒径の結晶粒の集合体とするためには、熱間圧延等の歪加工を行ったり、溶融した原料を急冷したりすること等により結晶粒を小さくする方法を採用することができる。 As a 2nd process, the method of cooling, after melt | dissolving a raw material mixture in a vacuum or an inert gas is employable, for example. In order to make an n-type thermoelectric conversion material or a p-type thermoelectric conversion material as an aggregate of powders having as small a particle size as possible, first, the raw material mixture is melted by arc melting or the like and then solidified. A method for obtaining a substantially uniform powder by mechanically pulverizing it in an inert gas or nitrogen gas atmosphere, and a method for obtaining a substantially uniform powder by molten metal atomization or gas atomization. Further, a method of obtaining a substantially uniform powder by repeatedly pressing and breaking the raw material mixture in an inert gas or nitrogen gas atmosphere by a mechanical alloying method can be employed. The powder thus obtained can be sintered by a hot press method in a vacuum, a HIP (hot isostatic pressing) method, a discharge plasma sintering method, a pulse current method or the like. When the powder is sintered by the HIP method, for example, compression molding and sintering can be simultaneously performed with an argon gas of 150 MPa at 800 ° C. to solidify at a true density. Further, according to the pseudo-HIP method, the true density can be solidified at low cost by using a molding press. In addition, in order to make an n-type thermoelectric conversion material or a p-type thermoelectric conversion material as an aggregate of crystal grains having a particle size as small as possible, strain processing such as hot rolling is performed, or a molten raw material is used. A method of reducing the crystal grains by rapid cooling or the like can be employed.

本発明の熱電変換材料により熱電変換素子を製造することが可能である。こうして得られる熱電変換素子は、ゼーベック係数の符号が正の上記熱電変換材料がｐ型としての挙動を示し、ゼーベック係数の符号が負の上記熱電変換材料がｎ型としての挙動を示す。これらの熱電変換素子は、熱電変換効率が高く、製造コストの低廉化が可能であり、環境汚染のおそれが少ない。 It is possible to manufacture a thermoelectric conversion element with the thermoelectric conversion material of the present invention. In the thermoelectric conversion element thus obtained, the thermoelectric conversion material having a positive sign of the Seebeck coefficient exhibits a behavior as a p-type, and the thermoelectric conversion material having a negative sign of the Seebeck coefficient exhibits a behavior as an n-type. These thermoelectric conversion elements have high thermoelectric conversion efficiency, can be manufactured at low cost, and are less likely to cause environmental pollution.

［実施例１〜６］
実施例１〜６の熱電変換材料は、基本構造のＦｅ₂ＶＡｌに対し、一般式Ｆｅ_2―ｘＶ_1+ｘＡｌの調整量ｘが−０．０７≦x≦０．０８の範囲内で選択されており、さらに構成元素の一部が他の元素で置換されている。 [Examples 1 to 6]
In the thermoelectric conversion materials of Examples 1 to 6, the adjustment amount x of the general formula Fe _2−x V _{1 + x} Al is within the range of −0.07 ≦ x ≦ 0.08 with respect to Fe ₂ VAl having the basic structure. In addition, some of the constituent elements are replaced with other elements.

Ｆｅ₂ＶＡｌの基本構造の化学式当たりの総価電子数は、以下の計算により２４である。つまり、Ｆｅの価電子数は４ｓ軌道の２と３ｄ軌道の６との合計８に係数２を乗じた１６である。また、Ｖの価電子数は４ｓ軌道の２と３ｄ軌道の３との合計５である。また、Ａｌの価電子数は３ｓ軌道の２と３ｐ軌道の１との合計３である。これらＦｅ、Ｖ及びＡｌの価電子数の合計２４が基本構造の化学式当たりの総価電子数である。 The total number of valence electrons per chemical formula of the basic structure of Fe ₂ VAl is 24 by the following calculation. That is, the number of valence electrons of Fe is 16, which is obtained by multiplying a total of 8 of 2 of the 4s orbit and 6 of the 3d orbit by the coefficient 2. Further, the number of valence electrons of V is a total of 5, 2 of 4s orbitals and 3 of 3d orbitals. Further, the number of valence electrons of Al is 3 in total, 2 of 3s orbitals and 1 of 3p orbitals. The total number of valence electrons 24 of Fe, V and Al is the total number of valence electrons per chemical formula of the basic structure.

この基本構造に対し、一般式Ｆｅ_2―ｘＶ_1+ｘＡｌで表される化合物において、０＜ｘ≦０．０８とすることで、総価電子数は２４未満となり、ｎ型熱電変換材料となる。また、−０．０７≦ｘ＜０とすることで、総価電子数は２４を超え、ｐ型熱電変換材料となる。 With respect to this basic structure, in the compound represented by the general formula Fe _2−x V _{1 + x} Al, by setting 0 <x ≦ 0.08, the total number of valence electrons becomes less than 24, and the n-type thermoelectric conversion material It becomes. Further, by setting −0.07 ≦ x <0, the total number of valence electrons exceeds 24, and a p-type thermoelectric conversion material is obtained.

この熱電変換材料は以下のように製造される。まず、上記組成条件を満たすように、Ｆｅ、Ｖ及びＡｌの３種類の元素を秤量した。これら元素をアルゴンアークを用いて溶解し、ボタン状のインゴットを作製した。均質なインゴットを得るため、得られたインゴットを再溶解した。この再溶解を２回以上行い、均質なインゴットを得た。溶解前後での重量変化は０．１％以内であるため、溶解による組成の変化は無視できる程度であると仮定した。 This thermoelectric conversion material is manufactured as follows. First, three kinds of elements of Fe, V, and Al were weighed so as to satisfy the above composition condition. These elements were melted using an argon arc to produce a button-like ingot. In order to obtain a homogeneous ingot, the obtained ingot was redissolved. This re-dissolution was performed twice or more to obtain a homogeneous ingot. Since the change in weight before and after dissolution is within 0.1%, it was assumed that the change in composition due to dissolution was negligible.

作製したインゴットに対し、５×１０^-3Ｐａ以下の高真空中で１２７３Ｋ×４８ｈｒの均質化処理を行い、短冊状、粉末及びブロック状の各測定形状に成型した。この後、真空中で１２７３Ｋ×１ｈｒの歪取処理と、６７３Ｋ×４ｈｒの規則化処理とを行った。こうして、実施例１〜６の熱電変換材料を得た。なお、実施例１、２の熱電変換材料は、ＦｅとＶとの間の組成比をわずかに調整するだけで、総価電子数を基本構造の２４からずらしたものである。ここで、化学量論組成からの組成比の調整量が小さいほど、固溶体の形態が維持され、化学量論組成からの組成比の調整量が大きいと、析出物が生成し、構成元素の全てが固溶体の形態で存在しなくなる。
このため、実施例１〜６の熱電変換材料は、調整量が小さいので、基本構造が維持されている。 The produced ingot was homogenized at 1273 K × 48 hr in a high vacuum of 5 × 10 ⁻³ Pa or less, and molded into strips, powders and blocks. Thereafter, a distortion removing process of 1273 K × 1 hr and a regularizing process of 673 K × 4 hr were performed in a vacuum. Thus, thermoelectric conversion materials of Examples 1 to 6 were obtained. The thermoelectric conversion materials of Examples 1 and 2 are obtained by shifting the total number of valence electrons from 24 of the basic structure by slightly adjusting the composition ratio between Fe and V. Here, the smaller the adjustment amount of the composition ratio from the stoichiometric composition, the more the form of the solid solution is maintained.When the adjustment amount of the composition ratio from the stoichiometric composition is large, precipitates are generated and all of the constituent elements are formed. No longer exists in the form of a solid solution.
For this reason, since the adjustment amount of the thermoelectric conversion materials of Examples 1 to 6 is small, the basic structure is maintained.

［比較例１〜４］
比較例１〜４の熱電変換材料は、基本構造のＦｅ₂ＶＡｌに対し、構成元素の一部を他の元素で置換したものである。 [Comparative Examples 1-4]
The thermoelectric conversion materials of Comparative Examples 1 to 4 are obtained by substituting a part of the constituent elements with other elements for the basic structure Fe ₂ VAl.

［評価方法］
実施例１〜６および比較例１〜４の熱電変換材料について、以下の評価を行った。 [Evaluation method]
The following evaluation was performed about the thermoelectric conversion material of Examples 1-6 and Comparative Examples 1-4.

（Ｘ線回折）

各材料の構造を決定するため、上記方法で作製した粉末を用い、Ｘ線回折を行った。評価にはＣｕＫα線を用いた。これらはＦｅを含む合金系であるため、バックグラウンドを除去する目的でモノクロメータを用いた。この結果、作製した材料はすべてホイスラー構造を有していた。
(X-ray diffraction)

In order to determine the structure of each material, X-ray diffraction was performed using the powder produced by the above method. CuKα rays were used for the evaluation. Since these are alloy systems containing Fe, a monochromator was used for the purpose of removing the background. As a result, all the produced materials had a Heusler structure.

（ゼーベック係数の測定）

０．５×０．５×５．０ｍｍ³の試験片を用い、ＭＭＲ−Technologies社製「ＳＢ−１００」にて、ゼーベック係数Ｓ（μＶ／Ｋ）を１００Ｋ〜４００Ｋの温度範囲で測定した。
(Measurement of Seebeck coefficient)

Using a test piece of 0.5 × 0.5 × 5.0 mm ³ , the Seebeck coefficient S (μV / K) was measured in a temperature range of 100K to 400K with “SB-100” manufactured by MMR-Technologies.

（電気抵抗率の測定）
１×１×１５ｍｍ³の短冊状試料を用い、直流四端子法にて電気抵抗率ρ（μΩｃｍ）を測定した。測定温度範囲は液体Ｈｅ温度（４．２Ｋ）から８００Ｋまでである。４．２Ｋから室温までは自然昇温して測定を行った。室温から８００Ｋまでは、電気炉を用い、５×１０^-3Ｐａ以下の真空雰囲気中で０．０５Ｋ／秒で昇温して測定を行った。 (Measurement of electrical resistivity)
An electrical resistivity ρ (μΩcm) was measured by a DC four-terminal method using a 1 × 1 × 15 mm ³ strip sample. The measurement temperature range is from liquid He temperature (4.2K) to 800K. From 4.2K to room temperature, the temperature was naturally raised and measured. From room temperature to 800 K, an electric furnace was used and the temperature was increased at 0.05 K / second in a vacuum atmosphere of 5 × 10 ⁻³ Pa or less and measurement was performed.

（熱伝導率の測定）
各熱電変換材料を炭化ケイ素の切断刃によって切断して３．５×３．５×４．０（ｍｍ^３）の角柱状の試験片とする。そして、４×１０^−４Ｐａの真空中において、熱流法による定常比較測定法を用いて各試験片の熱伝導率κ（Ｗ／ｍＫ）を測定する。 (Measurement of thermal conductivity)
Each thermoelectric conversion material is cut with a silicon carbide cutting blade to obtain a 3.5 × 3.5 × 4.0 (mm ³ ) prismatic test piece. Then, in a vacuum of 4 × 10 ⁻⁴ Pa, the thermal conductivity κ (W / mK) of each test piece is measured using a stationary comparative measurement method using a heat flow method.

（出力因子と性能指数）
熱電変換材料を評価する指数として、出力因子：Ｐ＝Ｓ²／ρ及び性能指数：Ｚ＝Ｓ²／（ρκ）が挙げられる。ここで、Ｓはゼーベック係数、ρは電気抵抗率、κは熱伝導率である。これらの値は上記の各測定値とし、出力因子Ｐ（１０^-3Ｗ／ｍＫ²）及び性能指数Ｚ（１０^-４／Ｋ）を求めた。 (Output factor and figure of merit)
As an index for evaluating the thermoelectric conversion material, there are an output factor: P = S ² / ρ and a performance index: Z = S ² / (ρκ). Here, S is the Seebeck coefficient, ρ is the electrical resistivity, and κ is the thermal conductivity. These values were taken as the above measured values, and the output factor P (10 ⁻³ W / mK ² ) and the figure of merit Z (10 ⁻⁴ / K) were determined.

実施例１の熱電変換材料（Ｆｅ_１．９５Ｖ_１．０５（Ａｌ_１―ｙＳｉ_ｙ）（ｙ＝０、０．０３、０．０５、０．１０））について、温度とゼーベック係数との関係を図１に示し、温度と電気抵抗率との関係を図２に示す。また、実施例１の熱電変換材料（Ｆｅ_２−ｘＶ_１+ｘ（Ａｌ_１―ｙＳｉ_ｙ）（ｘ＝−０．０７、 −０．０４、０．０２、０．０５、０．０８）（ｙ＝０、０．０１、０．０３、０．０５、０．０７、０．１０））及び比較例１の熱電変換材料（Ｆｅ_２Ｖ（Ａｌ_１―ｙＳｉ_ｙ）（ｙ＝０，０．０３、０．０５、０．１０））について、Ｓｉ組成と３００Ｋにおけるゼーベック係数との関係を図３に示す。 Regarding the thermoelectric conversion material of Example 1 (Fe _1.95 V _1.05 (Al _1-y Si _y ) (y = 0, 0.03, 0.05, 0.10)), the temperature and Seebeck coefficient The relationship is shown in FIG. 1, and the relationship between temperature and electrical resistivity is shown in FIG. Further, the thermoelectric conversion material of Example 1 (Fe _2-x V _{1 + x} (Al _1-y Si _y ) (x = −0.07, −0.04, 0.02, 0.05, 0.08) ) (Y = 0, 0.01, 0.03, 0.05, 0.07, 0.10)) and the thermoelectric conversion material of Comparative Example 1 (Fe ₂ V (Al _1-y Si _y ) (y = (0, 0.03, 0.05, 0.10)), the relationship between the Si composition and the Seebeck coefficient at 300K is shown in FIG.

図１より、実施例１の熱電変換材料は、Ｓｉの添加量が０．０３でゼーベック係数の絶対値が３００Ｋ付近で最大の１８０μＶ／Ｋになっている。また，さらにＳｉの添加量が増加するとゼーベック係数の絶対値は減少している。また、図２に示すように、実施例１の熱電変換材料は、Ｓｉの添加量が増加するに従って、５００Ｋ以下の電気抵抗率が減少することがわかる。とくにｙ＝０．１０となる熱電変換材料は、４．２Ｋでの電気抵抗率が約３００μΩｃｍと低い値を示しており、また、５００Ｋ以下では温度上昇に伴って電気抵抗率が上昇し，半導体的なものから金属的な挙動を示した。また、図３に示すように、実施例１の熱電変換材料は、化学組成比の調整量ｘ＝０．０２〜０．０８の範囲ではＳｉ組成によらずゼーベック係数の符号が負となり，ｎ型であることがわかる。さらに、比較例１の熱電変換材料と比較して、すべてのＳｉ組成において３００Ｋにおけるゼーベック係数の絶対値が大きくなっている。中でも，ｘ＝０．０５となる熱電変換材料は最大のゼーベック係数になっている。なお、実施例１ではＡｌをＳｉにより置換したが、Ｇｅ、Ｓｎ、あるいはＰによる置換でもよい。 As shown in FIG. 1, the thermoelectric conversion material of Example 1 has an Si addition amount of 0.03 and an absolute value of the Seebeck coefficient of 180 μV / K which is the maximum around 300K. Further, the absolute value of the Seebeck coefficient decreases as the addition amount of Si further increases. In addition, as shown in FIG. 2, it can be seen that the thermoelectric conversion material of Example 1 has an electric resistivity of 500 K or less that decreases as the amount of Si added increases. In particular, the thermoelectric conversion material with y = 0.10 shows a low electrical resistivity of about 300 μΩcm at 4.2 K, and the electrical resistivity increases with increasing temperature below 500 K, and the semiconductor It showed a metallic behavior from a typical one. As shown in FIG. 3, the thermoelectric conversion material of Example 1 has a negative sign of the Seebeck coefficient regardless of the Si composition in the range of the chemical composition ratio adjustment amount x = 0.02 to 0.08, and n It turns out that it is a type. Furthermore, compared with the thermoelectric conversion material of Comparative Example 1, the absolute value of the Seebeck coefficient at 300 K is increased in all Si compositions. Among them, the thermoelectric conversion material in which x = 0.05 has the maximum Seebeck coefficient. In Example 1, Al was replaced by Si, but it may be replaced by Ge, Sn, or P.

実施例２の熱電変換材料（Ｆｅ_2．０４（Ｖ_{０．９６−ｙ}Ｔｉ_ｙ）Ａｌ（ｙ＝０、０．０１、０．０３、０．０５、０．１０））について、温度とゼーベック係数との関係を図４に示し、温度と電気抵抗率との関係を図５に示す。また、実施例２の熱電変換材料（Ｆｅ_２−ｘ（Ｖ_{１+ｘ−ｙ}Ｔｉ_ｙ）Ａｌ（ｘ＝−０．０４、 −０．０７、０．０２、０．０５）（ｙ＝０、０．０１、０．０２，０．０３、０．０５、０．１０））及び比較例２の熱電変換材料（Ｆｅ_２（Ｖ_１−ｙＴｉ_ｙ）Ａｌ（ｙ＝０、０．０１、０．０２，０．０３、０．０５、０．１０））について、Ｔｉ組成と３００Ｋにおけるゼーベック係数との関係を図６に示す。なお、実施例２ではＶをＴｉにより置換したが、Ｚｒによる置換でもよい。 Regarding the thermoelectric conversion material of Example 2 (Fe _2.04 (V _0.96-y Ti _y ) Al (y = 0, 0.01, 0.03, 0.05, 0.10)), the temperature and Seebeck FIG. 4 shows the relationship with the coefficient, and FIG. 5 shows the relationship between the temperature and the electrical resistivity. Further, the thermoelectric conversion material of Example 2 (Fe _2−x (V _{1 + xy} Ti _y ) Al (x = −0.04, −0.07, 0.02, 0.05) (y = 0) , 0.01, 0.02, 0.03, 0.05, 0.10)) and the thermoelectric conversion material of Comparative Example 2 (Fe ₂ (V _1-y Ti _y ) Al (y = 0, 0.01) , 0.02, 0.03, 0.05, 0.10)), the relationship between the Ti composition and the Seebeck coefficient at 300K is shown in FIG. In Example 2, V is substituted with Ti, but Zr may be substituted.

図４より、実施例２の熱電変換材料は、Ｔｉの添加量が０．０３でゼーベック係数の絶対値が３００Ｋ付近で最大の１１０μＶ／Ｋになっている。また，さらにＴｉの添加量が増加するとゼーベック係数の絶対値は減少している。また、図５に示すように、実施例２の熱電変換材料は、Ｔｉの添加量が増加するに従って、７００Ｋ以下の電気抵抗率が減少することがわかる。とくにｙ＝０．１０となる熱電変換材料は、４．２Ｋでの電気抵抗率が約１３０μΩｃｍと低い値を示しており、また、８００Ｋ以下では温度上昇に伴って電気抵抗率が上昇し，半導体的なものから金属的な挙動を示した。また、図６に示すように、実施例２の熱電変換材料は、化学組成比の調整量ｘ＝−０．０７〜０の範囲ではＴｉ組成によらずゼーベック係数の符号が正となり，ｐ型であることがわかる。さらに、比較例２の熱電変換材料と比較して、ｘ＝−０．０４と−０．０７となる熱電変換材料はすべてのＴｉ組成において３００Ｋにおけるゼーベック係数の絶対値が大きくなっている。中でも，ｘ＝−０．０４となる熱電変換材料はＴｉ組成ｙが０．０３のときに最大のゼーベック係数になっている。 As shown in FIG. 4, the thermoelectric conversion material of Example 2 has a maximum addition amount of 110 μV / K around 300 K with an addition amount of Ti of 0.03 and a Seebeck coefficient. Further, the absolute value of the Seebeck coefficient decreases as the addition amount of Ti further increases. Further, as shown in FIG. 5, it can be seen that the thermoelectric conversion material of Example 2 has an electrical resistivity of 700 K or less that decreases as the addition amount of Ti increases. In particular, the thermoelectric conversion material with y = 0.10 shows a low electric resistivity of about 130 μΩcm at 4.2 K, and the electric resistivity increases with increasing temperature below 800 K, and the semiconductor It showed a metallic behavior from a typical one. Further, as shown in FIG. 6, the thermoelectric conversion material of Example 2 has a positive sign of the Seebeck coefficient regardless of the Ti composition in the range of the chemical composition ratio adjustment amount x = −0.07 to 0, and is p-type. It can be seen that it is. Furthermore, as compared with the thermoelectric conversion material of Comparative Example 2, the thermoelectric conversion materials having x = −0.04 and −0.07 have a large Seebeck coefficient at 300 K in all Ti compositions. Among them, the thermoelectric conversion material in which x = −0.04 has the maximum Seebeck coefficient when the Ti composition y is 0.03.

実施例１の熱電変換材料（Ｆｅ_１．９８Ｖ_１．０２（Ａｌ_０．９０Ｓｉ_０．１０））と比較例１の熱電変換材料（Ｆｅ_２Ｖ（Ａｌ_０．９０Ｓｉ_０．１０）），及び実施例２の熱電変換材料（Ｆｅ_2．０４（Ｖ_０．８６Ｔｉ_０．１０）Ａｌ）と比較例２の熱電変換材料（Ｆｅ₂（Ｖ_０．９０Ｔｉ_０．１０）Ａｌ）について、出力因子の温度依存性を求めた。この結果を図７に示す。 Thermoelectric conversion material of Example 1 (Fe _1.98 V _1.02 (Al _0.90 Si _0.10 )) and thermoelectric conversion material of Comparative Example 1 (Fe ₂ V (Al _0.90 Si _0.10 )) , And the thermoelectric conversion material (Fe _2.04 (V _0.86 Ti _0.10 ) Al) of Example 2 and the thermoelectric conversion material (Fe ₂ (V _0.90 Ti _0.10 ) Al) of Comparative Example 2 The temperature dependence of the output factor was obtained. The result is shown in FIG.

図７より、実施例１の熱電変換材料の出力因子は３００Ｋで７×１０⁻³Ｗ／ｍＫ^２達しており，同じＳｉ組成となる比較例１の熱電変換材料よりも大きいことがわかる。さらに、従来の代表的な熱電変換材料であるＢｉ−Ｔｅ系ｎ型熱電変換材料の出力因子の代表値４．５×１０⁻³Ｗ／ｍＫ^２を上回る大きさである。一方，実施例２の熱電変換材料はｐ型であるが，最大４×１０⁻³Ｗ／ｍＫ^２に達しており、同じＴｉ組成となる比較例２の熱電変換材料よりも大きいことがわかる。さらに、従来の代表的な熱電変換材料であるＢｉ−Ｔｅ系ｐ型熱電変換材料の出力因子の代表値３×１０⁻³Ｗ／ｍＫ^２を上回る大きさである。 FIG. 7 shows that the output factor of the thermoelectric conversion material of Example 1 reaches 7 × 10 ⁻³ W / mK ^{2 at} 300 K, which is larger than the thermoelectric conversion material of Comparative Example 1 having the same Si composition. Furthermore, it is the magnitude | size exceeding the typical value 4.5 * 10 < ^-3 > W / mK < ² > of the output factor of the conventional typical thermoelectric conversion material Bi-Te type n-type thermoelectric conversion material. On the other hand, although the thermoelectric conversion material of Example 2 is p-type, it reaches a maximum of 4 × 10 ⁻³ W / mK ² , which is larger than the thermoelectric conversion material of Comparative Example 2 having the same Ti composition. Furthermore, it is the magnitude | size exceeding the typical value 3 * 10 < ^-3 > W / mK < ² > of the output factor of the Bi-Te type p-type thermoelectric conversion material which is a conventional typical thermoelectric conversion material.

実施例３の熱電変換材料（（Ｆｅ_{１．９５−ｙ}Ｉｒ_ｙ）（Ｖ_０．９５Ｔａ_０．１０）Ａｌ（ｙ＝０、０．０３、０．０５、０．１０））について，温度とゼーベック係数との関係を図８に示し、温度と電気抵抗率の関係を図９に示す。 Regarding the thermoelectric conversion material ((Fe _1.95-y Ir _y ) (V _0.95 Ta _0.10 ) Al (y = 0, 0.03, 0.05, _0.10 )) of Example 3, the temperature 8 and FIG. 9 show the relationship between the temperature and the electrical resistivity.

図８より，ＦｅとＶの化学組成比を調整してＶの一部をＴａで置換した熱電変換材料は、Ｆｅの一部をＩｒで置換していないときに，ゼーベック係数は負で２００Ｋにおいて−２００μＶ／Ｋという大きな値になっていることがわかる。また，Ｉｒ組成の増加に伴ってゼーベック係数の絶対値は減少している。また、図９に示すように、ＦｅとＶの化学組成比を調整してＶの一部をＴａで置換した熱電変換材料において、低温で大きな電気抵抗率を示すとともに、半導体的な負の温度依存性が現われている。しかし、Ｉｒ置換量の増加とともに４００Ｋ以下の電気抵抗率は急激に減少しており、ｙ＝０．１０では金属的な温度依存性を示す。 FIG. 8 shows that the thermoelectric conversion material in which the chemical composition ratio of Fe and V is adjusted and a part of V is substituted with Ta has a negative Seebeck coefficient at 200 K when a part of Fe is not substituted with Ir. It can be seen that the value is as large as −200 μV / K. In addition, the absolute value of the Seebeck coefficient decreases as the Ir composition increases. In addition, as shown in FIG. 9, in the thermoelectric conversion material in which the chemical composition ratio of Fe and V is adjusted and a part of V is replaced with Ta, a large electrical resistivity is exhibited at a low temperature and a semiconductor negative temperature is obtained. Dependence appears. However, the electrical resistivity of 400K or less rapidly decreases with the increase of the Ir substitution amount, and shows metallic temperature dependence at y = 0.10.

実施例３の熱電変換材料（（Ｆｅ_{２−ｘ−ｙ}Ｉｒ_ｙ）（Ｖ_{０．９０+ｘ}Ｔａ_０．１０）Ａｌ（ｘ＝０．０２、０．０５））について、Ｉｒ組成と３００Ｋにおける熱伝導率との関係を図１０に示す。 Regarding the thermoelectric conversion material of Example 3 ((Fe _2−xy Ir _y ) (V _{0.90 + x} Ta _0.10 ) Al (x = 0.02, 0.05)), the Ir composition and 300K The relationship with thermal conductivity is shown in FIG.

基本構造（置換量ｙ＝０）である実施例３の熱電変換材料は、すでにＶをＴａで１０％置換しているので、３００Ｋにおいて１０．５Ｗ／ｍＫという比較的小さい値になっている。ところが、FeをＩｒで置換すると、熱伝導率は著しく減少している。特に、ｙ＝０．１０の置換量において、調整量ｘに関わらず６．５Ｗ／ｍＫまで減少している。したがって、原子量の大きい元素で置換することにより、熱伝導率の減少は顕著になることがわかる。 The thermoelectric conversion material of Example 3 having a basic structure (substitution amount y = 0) has a relatively small value of 10.5 W / mK at 300 K because V is already substituted by 10% with Ta. However, when Fe is replaced with Ir, the thermal conductivity is remarkably reduced. In particular, at the substitution amount of y = 0.10, the value decreases to 6.5 W / mK regardless of the adjustment amount x. Therefore, it can be seen that the decrease in thermal conductivity becomes significant by substitution with an element having a large atomic weight.

また、熱伝導率はキャリアによる成分と格子振動による成分の和であることが知られている。Ｗｉｅｄｅｍａｎｎ−Ｆｒａｎｚ則を用いて図９の電気抵抗率からキャリアによる熱伝導率を見積もると、図１０に示した全体の熱伝導率の３分の１から半分程度と比較的大きいことがわかる。したがって、実施例３の熱電変換材料においては熱伝導率に対する格子振動とキャリアによる寄与が同程度であり、原子量の大きい元素による置換は、格子振動による熱伝導率を大幅に低減するうえで有効である。このため、実施例３の熱電変換材料を用いれば、熱伝導率が小さく、ひいては熱電変換の性能に優れた熱電変換素子を得られることがわかる。すなわち、ＦｅをＩｒで置換すると、ゼーベック係数の絶対値が小さくなるが、電気抵抗率および熱伝導率が顕著に小さくなり、結果として性能指数が大きくなる。ＦｅのＩｒによる置換量ｙが０．１０以上で特に好ましい。なお、実施例３ではＦｅをＩｒにより置換したが、Ｐｄ，Ｃｏ，あるいはＮｉでもよい。 Further, it is known that the thermal conductivity is the sum of a component due to carriers and a component due to lattice vibration. When the thermal conductivity due to carriers is estimated from the electrical resistivity of FIG. 9 using the Wiedemann-Franz rule, it can be seen that the overall thermal conductivity shown in FIG. Therefore, in the thermoelectric conversion material of Example 3, the contribution of the lattice vibration and the carrier to the thermal conductivity is about the same, and substitution with an element having a large atomic weight is effective in significantly reducing the thermal conductivity due to the lattice vibration. is there. For this reason, if the thermoelectric conversion material of Example 3 is used, it turns out that a heat conductivity is small and by extension the thermoelectric conversion element excellent in the performance of thermoelectric conversion can be obtained. That is, when Fe is replaced with Ir, the absolute value of the Seebeck coefficient is reduced, but the electrical resistivity and thermal conductivity are significantly reduced, resulting in an increase in the figure of merit. The substitution amount y of Fe by Ir is particularly preferably 0.10 or more. In Example 3, Fe was replaced with Ir, but Pd, Co, or Ni may be used.

実施例３の熱電変換材料（Ｆｅ_{１．９８−ｙ}Ｉｒ_ｙ）（Ｖ_０．９２Ｔａ_０．１０）Ａｌと実施例４の熱電変換材料（Ｆｅ_{１．９８−ｙ}Ｉｒ_ｙ）Ｖ_１．０２Ａｌについて、Ｉｒ組成と３００Ｋにおける性能指数との関係を図１１に示す。 Thermoelectric conversion material (Fe _1.98-y Ir _y ) (V _0.92 Ta _0.10 ) Al of Example 3 and thermoelectric conversion material (Fe _1.98-y Ir _y ) V _{1.02 of} Example 4 FIG. 11 shows the relationship between the Ir composition and the figure of merit at 300 K for Al.

図１１より、Ｆｅの一部をＩｒで置換することで性能指数は大幅に増加することがわかる。特に、予めＶを１０％のＴａで置換した実施例３の熱電変換材料では性能指数の増加が顕著であり，Ｉｒ組成ｙ＝０．１５において１×１０^−３／Ｋに達している。Ｉｒによる置換だけでなく、Ｔａで同時置換することによりの性能指数が大きくなっており、原子量の大きい元素で置換した熱電変換材料を用いて熱電変換素子を製造した場合、大きな性能指数を示す熱電変換素子が得られることがわかる。 From FIG. 11, it can be seen that the figure of merit is greatly increased by replacing part of Fe with Ir. In particular, in the thermoelectric conversion material of Example 3 in which V was previously substituted with 10% Ta, the figure of merit increased remarkably, and reached 1 × 10 ⁻³ / K at an Ir composition y = 0.15. The figure of merit due to simultaneous substitution with Ta as well as substitution with Ir is large, and when a thermoelectric conversion element is manufactured using a thermoelectric conversion material substituted with an element having a large atomic weight, a thermoelectric characteristic exhibiting a large figure of merit is shown. It can be seen that a conversion element is obtained.

さらに、実施例４として熱電変換材料（Ｆｅ_{２−ｘ−ｙ}Ｉｒ_ｙ）Ｖ_１＋ｘＡｌ（ｘ＝−０．０４、０．０２、０．０５）、実施例５として熱電変換材料（Ｆｅ_２−ｘ（Ｖ_{１+ｘ−ｙ}Ｍｏ_ｙ）Ａｌ（ｘ＝−０．０４、０．０２）、および実施例６として熱電変換材料Ｆｅ_２−ｘ（Ｖ_{０．９０+ｘ−ｙ}Ｔｉ_ｙＴａ_０．１０）Ａｌ（ｘ＝−０．０４）の３００Ｋにおけるゼーベック係数を測定した。 Further, as Example 4, a thermoelectric conversion material (Fe _2-xy Ir _y ) V _{1 + x} Al (x = −0.04, 0.02, 0.05), and as Example 5, a thermoelectric conversion material (Fe _{2− x} (V _{1 + xy} Mo _y ) Al (x = −0.04, 0.02), and thermoelectric conversion material Fe _2-x (V _{0.90 + xy} Ti _y Ta ₀ as Example 6) _.10 ) The Seebeck coefficient of Al (x = −0.04) at 300 K was measured.

実施例１の熱電変換材料Ｆｅ_２−ｘＶ_１+ｘ（Ａｌ_１―ｙＳｉ_ｙ）と、実施例２の熱電変換材料Ｆｅ_２−ｘ（Ｖ_{１+ｘ−ｙ}Ｔｉ_ｙ）Ａｌと、実施例３の熱電変換材料（Ｆｅ_{２−ｘ−ｙ}Ｉｒ_ｙ）（Ｖ_{０．９０+ｘ}Ｔａ_０．１０）Ａｌと、実施例４の熱電変換材料（Ｆｅ_{２−ｘ−ｙ}Ｉｒ_ｙ）Ｖ_１＋ｘＡｌと、実施例５の熱電変換材料Ｆｅ_２−ｘ（Ｖ_{１+ｘ−ｙ}Ｍｏ_ｙ）Ａｌと、実施例６の熱電変換材料Ｆｅ_２−ｘ（Ｖ_{０．９０+ｘ−ｙ}Ｔｉ_ｙＴａ_０．１０）Ａｌ、以上６種類の実施例と、比較例１の熱電変換材料Ｆｅ_２Ｖ（Ａｌ_１―ｙＳｉ_ｙ）と、比較例２の熱電変換材料Ｆｅ_２（Ｖ_１−ｙＴｉ_ｙ）Ａｌと、比較例３の熱電変換材料（Ｆｅ_２−ｙＩｒ_ｙ）ＶＡｌと、比較例４の熱電変換材料Ｆｅ_２（Ｖ_１−ｙＭｏ_ｙ）Ａｌ、以上４種類の比較例について、３００Ｋにおけるゼーベック係数（μＶ／Ｋ）と総価電子数との関係を求める。結果を図１２に示す。なお、実施例および比較例の各試料の組成を表１に記載する。 Thermoelectric conversion material Fe _2-x V _{1 + x} (Al _1-y Si _y ) of Example 1, thermoelectric conversion material Fe _2-x (V _{1 + xy} T _y ) Al of Example 2, and implementation Thermoelectric conversion material (Fe _2-xy Ir _y ) (V _{0.90 + x} Ta _0.10 ) Al of Example 3 and thermoelectric conversion material (Fe _2-xy Ir _y ) V _{1 + x of} Example 4 Al and thermoelectric conversion materials _{Fe 2-x} of example _{5 (V 1 + x-y} Mo y) Al and thermoelectric conversion materials _Fe _2-x of example _{6 (V 0.90 + x-y} Ti y Ta _0.10 ) Al, the above six examples, the thermoelectric conversion material Fe ₂ V (Al _1-y Si _y ) of Comparative Example 1, and the thermoelectric conversion material Fe ₂ (V _1-y Ti _y ) of Comparative Example 2 ) Al, thermoelectric conversion material (Fe _2-y Ir _y ) VAl of Comparative Example 3, and thermoelectric conversion material Fe ₂ (V _{1-y of} Comparative Example 4) Mo _y ) Al, and the relationship between the Seebeck coefficient (μV / K) at 300 K and the total number of valence electrons is determined for the above four comparative examples. The results are shown in FIG. In addition, Table 1 describes the compositions of the samples of the examples and comparative examples.

図１２において、比較例１〜４の熱電変換材料のように化学組成比を調整量ｘで調整しない場合（ｘ＝０）、基本構造のＦｅ_２ＶＡｌの総価電子数は２４．０であり、元素置換によって総価電子数が２４．０未満になる場合も、総価電子数が２４．０超になる場合も、ゼーベック係数の絶対値は大幅に増大している。このようなゼーベック係数の変化は総価電子数が２４．０となる近傍において特に顕著である。また、比較例１、３及び４の熱電変換材料は、総価電子数が２４．０超となっており、ゼーベック係数はすべて負の値になることから、ｎ型の熱電変換特性を示すことがわかる。一方、比較例２の熱電変換材料では、総価電子数が２４．０未満となっており、ゼーベック係数はすべて正の値になることから、ｐ型の熱電変換特性を示すことがわかる。 In FIG. 12, when the chemical composition ratio is not adjusted by the adjustment amount x (x = 0) as in the thermoelectric conversion materials of Comparative Examples 1 to 4, the total valence electron number of the basic structure Fe ₂ VAl is 24.0. The absolute value of the Seebeck coefficient is greatly increased both when the total valence electron number becomes less than 24.0 due to element substitution and when the total valence electron number exceeds 24.0. Such a change in the Seebeck coefficient is particularly remarkable in the vicinity where the total number of valence electrons is 24.0. Further, the thermoelectric conversion materials of Comparative Examples 1, 3, and 4 have a total valence electron number exceeding 24.0, and all Seebeck coefficients are negative values, and therefore show n-type thermoelectric conversion characteristics. I understand. On the other hand, the thermoelectric conversion material of Comparative Example 2 has a total valence electron number of less than 24.0, and all Seebeck coefficients are positive values, indicating that p-type thermoelectric conversion characteristics are exhibited.

図１２のように総価電子数で整理したとき、ゼーベック係数は置換する元素の種類によらず、１本のマスターカーブで記述できるような変化の仕方になっている。このため、本発明で明らかにしたように、置換する元素の種類を選択することにより、擬ギャップ内のフェルミ準位のエネルギー位置を最適化することが可能であり、ひいてはゼーベック係数の符号を制御することができるために、基本構造のＦｅ_２ＶＡｌをベースとしてｐ型とｎ型の熱電変換材料を作製することが可能になるだけでなく、ゼーベック係数の絶対値を大幅に増大することによって、優れた熱電特性を発揮できる熱電変換材料を製造することが可能となる。 When organized by the total number of valence electrons as shown in FIG. 12, the Seebeck coefficient changes in such a way that it can be described by one master curve regardless of the type of element to be replaced. For this reason, as clarified in the present invention, it is possible to optimize the energy position of the Fermi level in the pseudogap by selecting the type of element to be replaced, and thus control the sign of the Seebeck coefficient. In addition to making it possible to fabricate p-type and n-type thermoelectric conversion materials based on the basic structure Fe ₂ VAl, by greatly increasing the absolute value of the Seebeck coefficient, A thermoelectric conversion material that can exhibit excellent thermoelectric properties can be produced.

図１２において、実施例１〜６の熱電変換材料のように化学組成比を調整量ｘで調整した場合、ｘ＝０．０２〜０．０８ではマスターカーブは総価電子数が２４以下の方に向かってシフトしており、しかも調整量が大きいほど大きくシフトしている。一方、ｘ＝−０．０４と−０．０７ではマスターカーブは総価電子数が２４以上の方に向かってシフトしており，しかも調整量の絶対値が大きいほど大きくシフトしている。ここで、ゼーベック係数が負となるｎ型の熱電変換材料は、調整量ｘが正の値のときに絶対値が大きく増大していることがわかる。具体的には調整量ｘが０＜ｘ≦０．０８の範囲内で優れた熱電特性を発揮できるｎ型熱電変換材料を製造することが可能となる。一方、ゼーベック係数が正となるｐ型の熱電変換材料は、調整量ｘが負の値のときに絶対値が大きく増大していることがわかる。具体的には調整量ｘが−０．０７≦ｘ＜０の範囲内で優れた熱電特性を発揮できるｐ型熱電変換材料を製造することが可能となる。 In FIG. 12, when the chemical composition ratio is adjusted by the adjustment amount x as in the thermoelectric conversion materials of Examples 1 to 6, the master curve has a total valence electron number of 24 or less at x = 0.02 to 0.08. Further, the shift is larger as the adjustment amount is larger. On the other hand, at x = −0.04 and −0.07, the master curve shifts toward the total valence electron number of 24 or more, and the master curve shifts larger as the absolute value of the adjustment amount increases. Here, it is understood that the absolute value of the n-type thermoelectric conversion material having a negative Seebeck coefficient greatly increases when the adjustment amount x is a positive value. Specifically, it is possible to produce an n-type thermoelectric conversion material that can exhibit excellent thermoelectric characteristics when the adjustment amount x is in the range of 0 <x ≦ 0.08. On the other hand, the p-type thermoelectric conversion material having a positive Seebeck coefficient has a large increase in absolute value when the adjustment amount x is a negative value. Specifically, it is possible to manufacture a p-type thermoelectric conversion material that can exhibit excellent thermoelectric characteristics when the adjustment amount x is within a range of −0.07 ≦ x <0.

また、実施例1〜６の熱電変換材料からｐ型とｎ型を選択した１組又は実施例１〜６の熱電変換材料と公知の他の熱電変換材料との組み合わせによって、熱電変換素子を製造することができる。実施例1〜６の熱電変換材料は汎用の金属を用いて安価に製造可能であるため、これらの熱電変換素子の製造コストも低廉である。さらに、実施例1〜６の熱電変換材料が毒性の極めて弱い成分のみで構成されるため、これらの熱電変換素子は環境汚染の原因となる恐れも少ない。 Moreover, a thermoelectric conversion element is manufactured by one set which selected p-type and n-type from the thermoelectric conversion material of Examples 1-6, or the combination of the thermoelectric conversion material of Examples 1-6 and other well-known thermoelectric conversion materials. can do. Since the thermoelectric conversion materials of Examples 1 to 6 can be manufactured at low cost using a general-purpose metal, the manufacturing cost of these thermoelectric conversion elements is also low. Furthermore, since the thermoelectric conversion materials of Examples 1 to 6 are composed of only extremely toxic components, these thermoelectric conversion elements are less likely to cause environmental pollution.

本発明は、自動車や自動二輪車のエンジン、家庭用燃料電池やガスコージェネレーション等、中温域の廃熱を利用して発電装置等に利用可能である。

INDUSTRIAL APPLICABILITY The present invention can be used for a power generation device or the like using waste heat in an intermediate temperature range, such as an engine of a car or a motorcycle, a household fuel cell or a gas cogeneration.

Claims

For the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total number of valence electrons of 24 per chemical formula, the chemical composition ratio adjustment amount x and the substitution of element D that replaces the basic structure Al In the thermoelectric conversion material in which the adjustment amount x is selected within the range of 0.02 ≦ x ≦ 0.08 where the amount y satisfies the general formula Fe _2−x V _{1 + x} (Al _1−y D _y ), it is replaced with Al. When the other element to be substituted is D, the element D is an element selected from the group consisting of groups 14 to 16 of the third to sixth periods in the periodic table, and the total number of valence electrons per chemical formula is A thermoelectric conversion material which is controlled to be n-type so as to exceed 23.7 and not more than 24.1.

Substitution of element N which replaces the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total number of valence electrons of 24 per chemical formula in place of the adjustment amount x of the chemical composition ratio and V of the basic structure In the thermoelectric conversion material in which the adjustment amount x is selected in the range of 0.02 ≦ x ≦ 0.08 where the amount y satisfies the general formula Fe _2-x (V _{1 + xy} N _y ) Al, When the other element to be substituted is N, the element N is an element selected from the group consisting of Group 6 of the 4th to 6th periods in the periodic table, and the total number of valence electrons per chemical formula is 23.7. And a n-type thermoelectric conversion material that is controlled to be 24.1 or less.

Substitution of element N which replaces the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total number of valence electrons of 24 per chemical formula in place of the adjustment amount x of the chemical composition ratio and V of the basic structure In the thermoelectric conversion material in which the adjustment amount x is selected within the range of −0.07 ≦ x <0 where the amount y satisfies the general formula Fe _2-x (V _{1 + xy} N _y ) Al, substitution is performed for V When the other element is N, the element N is an element selected from the group consisting of Group 4 of the 4th to 6th periods in the periodic table, and the total number of valence electrons per chemical formula exceeds 24, A thermoelectric conversion material which is controlled to be p-type so as to be 24.3 or less.

For the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total number of valence electrons of 24 per chemical formula, the chemical composition ratio adjustment amount x and the substitution of the element M substituted for the basic structure Fe The substitution amount z of the element Ta to be substituted in place of the amounts y and V satisfies 0.02 ≦ x ≦ 0.08 satisfying the general formula (Fe _2−x− M _y ) (V _{1 + x−z} Ta _z ) Al. In the thermoelectric conversion material in which the adjustment amount x is selected within the above range, when the other element to be substituted for Fe is M, the element M is from the 9th and 10th groups of the 4th to 6th periods in the periodic table. A thermoelectric conversion material, which is an element selected from the group consisting of, and is controlled to be n-type so that the total number of valence electrons per chemical formula exceeds 23.7 and is 24.1 or less.

For the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total number of valence electrons of 24 per chemical formula, the chemical composition ratio adjustment amount x and the substitution of the element M substituted for the basic structure Fe In the thermoelectric conversion material in which the adjustment amount x is selected within the range of 0.02 ≦ x ≦ 0.08 where the amount y satisfies the general formula (Fe _2−xy M _y ) V _{1 + x} Al, instead of Fe When the other element to be substituted is M, the element M is an element selected from the group consisting of groups 9 and 10 of the 4th to 6th periods in the periodic table, and the total number of valence electrons per chemical formula is 23 A thermoelectric conversion material that is controlled to be n-type so as to exceed .7 and not more than 24.1.

Substitution of element N which replaces the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total number of valence electrons of 24 per chemical formula in place of the adjustment amount x of the chemical composition ratio and V of the basic structure The range of 0.02 ≦ x ≦ 0.08 where the substitution amount z of the element Ta to be substituted in place of the amounts y and V satisfies the general formula Fe _2-x (V _{1 + x−yZ} N _y Ta _z ) Al In the thermoelectric conversion material in which the adjustment amount x is selected, when the other element to be substituted in place of V is N, the element N is selected from the group consisting of Group 6 of the 4th to 6th periods in the periodic table. A thermoelectric conversion material characterized in that the total number of valence electrons per chemical formula is controlled to be n-type so as to be more than 23.7 and not more than 24.1.

Substitution of element N which replaces the basic structure of Fe ₂ VAl having a Heusler alloy type crystal structure and a total number of valence electrons of 24 per chemical formula in place of the adjustment amount x of the chemical composition ratio and V of the basic structure In the range of −0.07 ≦ x <0, the substitution amount z of the element Ta to be substituted in place of the amounts y and V satisfies the general formula Fe _2-x (V _{1 + x−yz} N _y Ta _z ) Al. In the thermoelectric conversion material for selecting the adjustment amount x in the above, when the other element to be substituted in place of V is N, the element N is selected from the group consisting of Group 4 of the 4th to 6th periods in the periodic table. A thermoelectric conversion material which is an element and is controlled to be p-type so that the total number of valence electrons per chemical formula exceeds 24 and is 24.3 or less.