JP4105881B2

JP4105881B2 - Large superconducting intermediates and large superconductors and their fabrication methods

Info

Publication number: JP4105881B2
Application number: JP2002088010A
Authority: JP
Inventors: 充澤村; 芳生平野
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2002-03-27
Filing date: 2002-03-27
Publication date: 2008-06-25
Anticipated expiration: 2022-03-27
Also published as: JP2003277188A

Description

【０００１】
【発明の属する技術分野】
本発明は、 90K級の臨界温度を有する希土類系酸化物超電導体の大型材料及びその製造法に関する。
【０００２】
【従来の技術】
従来、本発明が対象とするREBa₂Cu₃O_x系超電導バルク材料の製法としては、Quench and Melt Growth法(特許登録第1869884号及び特許登録第2556401号)で代表されるような溶融法が挙げられる。この方法は、RE₂BaCuO₅相又は RE₄Ba₂Cu₂O₁₀相と、Ba-Cu-Oを主成分とした液相が共存する温度領域まで一旦昇温し、 REBa₂Cu₃O_xが生成する包晶温度直上迄冷却し、その温度から徐冷を行うことにより結晶成長させ、核生成と結晶方位の制御を行ない、大型のバルク材を得る方法である。この製法を用いることによって、臨界電流密度（超電導特性の一つで、単位断面積あたりに流せる電流密度）が高く、比較的大型の超電導材料を得ることができる。
【０００３】
一方、大型材料作製に複数個の種結晶を用い、各々の種結晶から結晶成長させる方法は、個々の種結晶から結晶成長すべき領域が狭くなるため、比較的短期間で結晶成長が実現できる特徴をもつ。特に、特開 2001-322897号公報の方法は、従来の複数個の種結晶を用いた方法で課題となっていた「各々の種結晶から結晶成長した領域間に排斥された偏析相」の除去を実現し、結果として各々の種結晶から結晶成長した領域間の超電導特性が改善され、全体としてより均一な超電導特性が得られる特徴をもつ。
【０００４】
上記方法を用いることで、より広い面積で、かつ均一な超電導特性をもつ試料製造が可能となったが、サイズが大きい分、希望形状への加工の際等に超電導材料中に割れが入りやすくなる等の問題があった。RE-Ba-Cu-O超電導材料自体の材料強度はセラミックス材料の中では強い方ではなく、強度改善のためAg元素を添加する方法も知られているが、Ag元素添加のみでは大型材料での強度改善は十分ではなかった。
【０００５】
これに対して、他の強度の高い材料との組み合わせ、つまり強度の高い構造支持材料と超電導材料の複合材料化が考えられる。先述のような希望形状への加工時に入る割れ等を回避するには、結晶成長直後において既に強度の高い構造支持材料と複合化されている必要があり、このために結晶成長処理時に超電導前駆体と構造支持材料とを同時に投入する方法が考えられる。しかし、この場合RE-Ba-Cu-O超電導材料は、上記結晶成長時に1000℃前後の高温状態になり、Ba元素やCu元素の酸化物が液相として存在するため、反応性が高く、単純な組み合わせでは構造支持材料と反応し、構造支持材料の構成元素がRE-Ba-Cu-O超電導材料へ拡散することで、超電導転移温度や臨界電流密度が低下する等の問題があった。
【０００６】
【発明が解決しようとする課題】
本発明は、複数の種結晶を用いて結晶成長させ、結果としてより広い面積でかつ均一な超電導特性をもつ大型超電導バルク材料において、超電導転移温度や臨界電流密度等の超電導特性を劣化させることなく強度の高いセラミックス材料との複合化された構造支持材付き大型超電導バルク材料及びその製造方法を提供することにある。
【０００７】
【課題を解決するための手段】
本発明は、上記の問題を解決するために、少なくとも 123相包晶温度(Tp)が異なる３種類以上の酸化物超電導体で構成し、多結晶酸化物セラミックスと最も低い Tpを有する酸化物超電導層とが一部反応し、強固に固着しても、中間(最も高いTpより低く、かつ最も低いTpよりも高い)の Tpをもつ酸化物超電導層には構造支持材料の構成元素が拡散せず、その超電導特性 (超電導転移温度や臨界電流密度)には影響しない点と、特開2001-322897号公報の方法を発展させて、構造支持材料との間に最もTpの低い超電導層を配することで超電導転移温度や臨界電流密度等の超電導特性を劣化させることなく、強度の高いセラミックス材料との複合化された構造支持材付き大型超電導バルク材料を得る手段を講じたものである。
【０００８】
本発明の第１の特徴は、REBa₂Cu₃O_x（REはYを含む希土類元素の１種類又はその組み合わせ）系超電導中間体であって、REBa₂Cu₃O_x相（123相）中に非超電導相が微細に分散した組織を有する123相の包晶温度(Tp)が異なる複数の酸化物超電導体層をTpの順に立体的に少なくとも３層を積層した構造を有し、最も高いTpを有する酸化物超電導層上に２個以上の種結晶が載置され、少なくとも前記高Tp酸化物超電導層に排斥相を含有し、室温から800℃までの平均線膨張係数が10ppm/℃以上20ppm/℃以下である多結晶酸化物セラミックスが最も低いTpを有する酸化物超電導層の下面と固着した構造を特徴とする大型超電導中間体である。
【０００９】
本発明での非超電導相とは、母相である REBa₂Cu₃O_x(123)相中に微細分散したRE₂BaCuO₅相又はRE₄Ba₂Cu₂O₁₀相等のことを指す。また、REBa₂Cu₃O_x相(123相)の包晶温度(Tp)が異なる123相とは、RE組成を変化させることで123相の包晶温度(Tp)を変化させ、Tpの異なる組成粉末で構成された酸化物超電導体を指す。また、立体的に積層した構造とは、層状に積層した場合や、同心円状に構成された場合、もしくはこの組み合わせを指す。
【００１０】
本発明の第２の特徴は、多結晶酸化物セラミックスの主成分が、MgO多結晶材料であることを特徴とする上記第１の大型超電導中間体である。主成分がMgO多結晶材料であるとは、多結晶酸化物セラミックス中にMgOが90％以上存在する材料を意味する。
【００１１】
本発明の第３の特徴は、前記最も低いTpを有する酸化物超電導層にYb元素が含まれることを特徴とする上記第１又は第２のいずれかの大型超電導中間体である。本発明の第４の特徴は、前記積層体が1〜30質量％のAg元素を含有する酸化物超電導体層を少なくとも１層積層してなる上記第１〜第３のいずれかの大型超電導中間体である。
【００１２】
本発明の第５の特徴は、前記積層体が、0.001〜2.0質量％のRh元素、0.05〜5.0質量％のPt元素、又は0.05〜10.0質量％のCe元素の内の少なくとも１つの元素を含有する酸化物超電導体層を少なくとも１層積層してなる上記第１〜第４のいずれかの大型超電導中間体である。本発明の第６の特徴は、上記第１〜第５のいずれかに記載の大型超電導中間体の種結晶及び排斥相を含有する酸化物超電導層を切除し、酸素富化熱処理をしてなることを特徴とする大型超電導体である。
【００１３】
本発明の第７の特徴は、REBa₂Cu₃O_x（REはYを含む希土類元素の１種類又はその組み合わせ）系超電導体を構成するRE、Ba及びCu成分を含む原料成型体を加熱し、最高温度が該成型体のREBa₂Cu₃O_x相（123相）の包晶温度（Tp）以上とした後、冷却することにより123相中に非超電導相が微細に分散した酸化物超電導中間体を作製する方法であって、123相のTpが異なる原料成型体をTpの順に立体的に少なくとも３層を積層した原料成型積層体とし、室温から800℃までの平均線膨張係数が10ppm/℃以上20ppm/℃以下である多結晶酸化物セラミックスの上に最も低いTpを有する原料成型積層体とが接するように載置し、さらに最も高いTpを有する原料成型積層体上に複数個の種結晶を載置してから、前記原料成型積層体を熱処理することを特徴とした酸化物超電導中間体の作製方法である。
【００１４】
本発明の第８の特徴は、前記多結晶酸化物セラミックスの主成分が、MgO多結晶材料であることを特徴とする上記第７の大型超電導中間体の作製方法である。
【００１５】
本発明の第９の特徴は、前記最も低いTpを有する酸化物超電導原料成型体にYb元素が含まれることを特徴とする上記第７又は第８のいずれかの大型超電導中間体の作製方法である。本発明の第１０の特徴は、前記積層体に1〜30質量％のAg元素を含有する酸化物超電導原料成型体を少なくとも１層積層している上記第７〜第９のいずれかの大型超電導中間体の作製方法である。
【００１６】
本発明の第１１の特徴は、前記原料成型積層体が、0.001〜2.0質量％のRh元素、0.05〜5.0質量％のPt元素、又は0.05〜10.0質量％のCe元素の内の少なくとも１つの元素を含有する原料成型体を少なくとも１層積層している上記第７〜第１０のいずれかの大型超電導中間体の作製方法である。
【００１７】
本発明の第１２の特徴は、上記第７〜１１の作製方法から得られた大型超電導中間体から種結晶及び排斥相を含有する酸化物超電導体層を切除した後、酸素富化処理することを特徴とする大型超電導体の作製方法である。
【００１８】
【発明の実施の形態】
本発明は、複数の種結晶を用いて結晶成長させ、結果として、より広い面積でかつ均一な超電導特性をもつ大型超電導バルク材料において、超電導転移温度や臨界電流密度等の超電導特性を劣化させることなく、強度の高いセラミックス材料との複合化された構造支持材付き大型超電導バルク材料及びその製造方法である。本発明のポイントは、特開 2001-322897号公報の方法を発展させて、大型超電導バルク材料と構造支持材料との間に最もTpの低い超電導層を用いる点にある。以下、この点について詳細に説明する。
【００１９】
構造支持材料の上に、特開 2001-322897号公報における原料成型積層体を載置し、結晶成長処置を行なった場合、結晶成長時に1000℃前後の高温下に曝されるため、超電導層と構造支持材料との界面で反応が生じ、結果として超電導層に不純物元素が混入し、超電導転移温度や臨界電流密度等の超電導特性を劣化させてしまうことが散発していた。
【００２０】
一方、本発明方法では、図１のように少なくとも Tpの異なる3層で構成された酸化物超電導体を用いるが、最も低いTpをもつ層の厚みを適当な厚み (100μm以上が好ましい)をもたせることで、最も低い Tpをもつ層は構造支持材料と反応しても、中間(最も高いTpより低く、最も低いTpよりも高い)のTpをもつ層への不純物元素混入は極めて低減させることができる。つまり、最も低いTpをもつ層は中間のTpをもつ層の不純物元素混入を防ぐ層として利用することになる。加えて超電導材料としての機能は中間のTpをもつ層が担うため、最も低いTpをもつ層は結晶成長させる必要は必ずしもなく、多結晶化してもかまわない。また、構造支持材料との接着との観点から、最も低いTpをもつ層の密度は高い方が好ましい。例えば、原料成型積層体として、最も低いTpをもつ層、中間のTpをもつ層及び最も高いTpをもつ層の３層を一体成型し、その後静水圧印加したものを、構造支持材に載置し、結晶成長処理を行なうことで、結晶成長後は最も低いTpをもつ層は高い密度を有し、かつ構造支持材料との密着も図られる。
【００２１】
一方、RE-Ba-Cu-O超電導材料は、大きな熱膨張係数(REがYの場合、ab軸方向で13ppm/℃前後) をもつため、構造支持材料もほぼ同程度の熱膨張係数である必要がある。該超電導材料に比べて大幅に異なる熱膨張係数をもつ構造支持材料を用いた場合、結晶成長時の 900℃〜1100℃程度の高温から室温まで冷却する際に、界面で熱収縮の差による引張応力もしくは圧縮応力が該超電導材料に働き、割れ等の亀裂を誘発する原因となる。該超電導材料は引張条件よりも圧縮条件の方が強度(例えば３点曲げ強度)は高い。そのため、構造支持材料の熱膨張係数が該超電導材料の熱膨張係数に比べて幾分大きくても、冷却時に該超電導材料へ圧縮応力が働くケースであることから、割れ等を誘発しにくい。このような理由から、熱収縮が働く主な温度領域(室温(20℃)から800℃)で線膨張係数が10ppm/℃から20ppm/℃の範囲に限定している。このような構造支持材料としては、MgOや安定化ZrO₂等が挙げられる。特に、緻密な MgO多結晶材料は、安価で軽く、熱膨張係数も約13ppm/℃とRE-Ba-Cu-O超電導材料に近い値をもつ点で優れており、構造支持材料に適している。
【００２２】
また、熱収縮による発生応力は最も低いTpを有する酸化物超電導層が固化し、構造支持材料と固着する温度Tpと室温との差に比例することから、最も低いTpを有する酸化物超電導層にYb元素(Tp=910±10℃)を用いることで、Tpを効果的に低く押さえ、構造支持材料と固着する温度も低温化させることで、結果として熱収縮差による発生応力を低く押さえることができる。
【００２３】
更に、超電導材料にAg元素を含有させることで添加量に応じて酸化物超電導体自体の強度向上が図れ、亀裂等を抑制する効果がある。Ag元素添加量は 1〜30質量％の範囲であって、これにより強度向上の効果が発揮できる。また、熱処理時にAg元素は各酸化物超電導層内を拡散しやすく、Ag元素の濃度によりTpも変化するため、安定した結晶成長を得るためには各酸化物超電導層へのAg元素添加量は、各層とも同一質量%であることが望ましい。
【００２４】
また、Rh、Pt、Ce元素の添加について、以下に説明する。これらの元素は、母相であるREBa₂Cu₃O_x(123)相中にRE₂BaCuO₅相又はRE₄Ba₂Cu₂O₁₀相を微細分散させ、超電導特性の１つである臨界電流密度を向上させる効果がある。添加の量はそれぞれ、RE₂BaCuO₅相又は RE₄Ba₂Cu₂O₁₀相の微細化に効果が現れ始める濃度から、これ以上添加しても効果があがらない濃度で限定しており、これによって超電導体内により大きな電流密度を流すことが可能になる。即ち、添加効果が得られる量が、Rh元素で0.001〜2.0質量％、Pt元素で0.05〜5.0質量％、Ce元素で 0.05〜10.0質量％である。また、各元素の拡散を考慮すると、各酸化物超電導層への元素添加量は、各層とも同一質量％であることが望ましいが、最も低いTpをもつ層は結晶成長させる必要が必ずしもないことから、当該層のみに安価なCe元素を用いることもできる。
【００２５】
また、本方法では、複数の種結晶を用いるため、最も高いTpをもつ層には、各種結晶から成長した結晶成長領域間に Ba-Cu-O化合物、Cu-O化合物、もしくは偏析したRE₂BaCuO₅相又は RE₄Ba₂Cu₂O₁₀相等の非超電導相が排斥される。この非超電導層は、各種結晶から成長した結晶成長領域間の超電導結合を著しく阻害し、その領域間を通過して流れる超電導電流も著しく低下する。そのため、結晶成長処理後に上記排斥相が析出する超電導層をあらかじめ切除し、その後該超電導中間体に酸素富化処理することで各種結晶から成長した結晶成長領域間を通過して流れる超電導電流の大幅な低下をすることなく、より均一な超電導特性をもつ材料を得ることができる。
【００２６】
また、各超電導層の厚みに関して、以下に述べる。結晶成長後結晶成長時の高温下においては、各Tpの異なる超電導層の拡散が生じる。そのため、拡散した領域の一部ではTpが同一になる領域が生じる。それゆえ厚みの下限に関しては、各Tpが異なる超電導層として残存できる厚みが好ましい。例えば、RE成分を変えることでTpを変えた場合、各超電導層は100μm程度が下限として好ましい。また、各超電導層の厚みの比率としては、本発明の請求項６もしくは１２のように、最終的に排斥相の生じた領域を切除することを考慮して、切除する超電導層の合計厚みが、切除後残存する超電導層の合計厚みを超えないことが好ましい。
【００２７】
【実施例】
（実施例１）
Dy₂O₃、BaO₂、CuOの各原料粉体を各元素のモル比(Dy:Ba:Cu)が(13:17:24)になるように混合し、さらにこの混合粉に 0.5質量％のPt元素を添加し、混合した原料粉末を作製した。これを 900℃で酸素気流中で仮焼した。これを粉体１−Ａとする。また、Dy₂O₃、Ho₂O₃、BaO₂、CuOの各原料粉体を各元素のモル比(Dy:Ho:Ba:Cu)が(6.5:6.5:17:24)になるように混合し、さらにこの混合粉に0.5質量％のPt元素を添加し、混合した原料粉末を作製した。これを 900℃で酸素気流中で仮焼した。これを粉体１−Ｂとする。更に、Yb₂O₃、BaO₂、CuOの各原料粉体を各元素のモル比 (Yb:Ba:Cu)が(13:17:24)になるように混合し、さらにこの混合粉に1.0質量％のCe元素を酸化物として添加し、混合した原料粉末を作製した。これを850℃で酸素気流中で仮焼した。これを粉体１−Ｃとする。さらにSm₂O₃、BaO₂、CuOの各原料粉体を各元素のモル比 (Sm:Ba:Cu)が(13:17:24)になるように混合し、さらにこの混合粉に1.0質量％の Ce元素を酸化物として添加し、混合した原料粉末を作製した。これを 920℃で酸素気流中で仮焼した。これを粉体１−Ｄとする。
【００２８】
次に粉体１−Ａ、１−Ｂ、１−Ｃを用いて、図２−ａのように成型体を作製し、2ton/cm²で、直径54mm、厚さ20mmの円柱状前駆体を作製した。この前駆体に3mm角で厚み1mmのSm_0.7Nd_0.3Ba₂Cu₃O_x系超電導体種結晶を図２−ｂのように配置し、アルミナ板上に粉体1-Dを60mm角、厚さ8mm程度に敷き詰め、その上に構造支持材として50mm角で厚み4mmの緻密質で純度99％のMgO板を置き、更にその上に該円柱状前駆体を載置した。これを大気中で 1045℃まで10時間で昇温し、4時間保持したのち、1010℃に2時間で降温した。その後、980℃まで 100時間かけて徐冷し、結晶成長を行ない、24時間かけて室温まで冷却した。この熱処理によって、円柱状前駆体の直径は46mmに収縮し、かつ50mm角の構造支持材に固着していることを確認した。
【００２９】
得られた超電導バルク材料には割れ等の亀裂は見られなかった。その後、種結晶と粉体１−Ａで構成された層を切り取り、酸素気流中を 450℃まで24時間で昇温し、400℃まで100時間かけて徐冷した後、10時間かけて室温まで降温した。
上記の酸素富化処理を行なった超電導バルク材料を 77Kにおいて磁場中冷却し、外部磁界を取り除いた後、補足磁束密度を測定したところ、最高0.8Tの良好な値が得られた。
【００３０】
（実施例２）
Gd₂O₃、BaO₂、CuOの各原料粉体を各元素のモル比(Gd:Ba:Cu)が(12:18:26)になるように混合し、さらにこの混合粉に 0.5質量％のPt元素を添加し、混合した原料粉末を作製した。これを 900℃で酸素気流中で仮焼して得られた粉体に、10質量％のAg₂O粉を添加した。これを粉体２−Ａとする。また、Dy₂O₃、Gd₂O₃、BaO₂、CuOの各原料粉体を各元素のモル比 (Dy:Gd:Ba:Cu)が(6:6:18:26)になるように混合し、さらにこの混合粉に 0.5質量％のPt元素を添加し、混合した原料粉末を作製した。これを900℃で酸素気流中で仮焼して得られた粉体に、10質量％のAg₂O粉を添加した。これを粉体２−Ｂとする。更に、Yb₂O₃、BaO₂、CuOの各原料粉体を各元素のモル比(Yb:Ba:Cu)が(12:18:26)になるように混合し、さらにこの混合粉に 0.5質量％のPt元素を酸化物として添加し、混合した原料粉末を作製した。これを850℃で酸素気流中で仮焼して得られた粉体に、10質量％の Ag₂O粉を添加した。これと粉体２−ＢとのRE元素のモル比が等量になるよう秤量し、混合して得られた粉体を２−Ｃとする。
【００３１】
次に、粉体２−Ａ、２−Ｂ、２−Ｃを用いて、図３−ａのように成型体を作製し、2ton/cm²で、縦27mm、横77mm、厚さ15mmの角柱状前駆体を作製した。この前駆体に3mm角で厚み1mmのSm_0.7Nd_0.3Ba₂Cu₃O_x系超電導体種結晶を図３−ｂのように配置し、アルミナ板上にアルミナ粉体を 60mm角、厚さ8mm程度に敷き詰め、その上に構造支持材として縦30mm、横80mmで厚み4mmの緻密質で純度99％のMgO板を置き、更にその上に該角柱状前駆体を載置した。これを大気中で1058℃まで10時間で昇温し、2時間保持したのち、1010℃に2時間で降温した。その後、結晶成長のため 980℃まで100時間かけて徐冷し、870℃まで50時間かけて冷却し、24時間かけて室温まで冷却した。
【００３２】
得られた超電導バルク材料には割れ等の亀裂は見られなかった。その後、種結晶と粉体２−Ａで構成された層を切り取り、酸素気流中を 400℃まで24時間で昇温し、400℃で100時間維持した後、10時間かけて室温まで降温した。
上記の酸素富化処理を行なった超電導バルク材料を 77Kにおいて磁場中冷却し、外部磁界を取り除いた後、補足磁束密度を測定したところ、最高0.6Tの良好な値が得られた。
【００３３】
【発明の効果】
本発明により、広い面積でかつ均一な超電導特性をもち、割れ等の亀裂の入りにくい強度の高いセラミックス材料との複合化された構造支持材付き大型超電導バルク材料が実現できる効果が得られた。
【図面の簡単な説明】
【図１】本発明の構成図の一例
【図２】実施例１に使用した超電導体の概略図
（ａ）実施例１で使用した成型体の概略図
（ｂ）実施例１で使用した種結晶の配置図
【図３】実施例２に使用した超電導体の概略図
（ａ）実施例２で使用した成型体の概略図
（ｂ）実施例２で使用した種結晶の配置図[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a large-scale material of a rare earth oxide superconductor having a critical temperature of 90K class and a method for producing the same.
[0002]
[Prior art]
Conventionally, as a method for producing a REBa ₂ Cu ₃ O _x- based superconducting bulk material targeted by the present invention, a melting method represented by the Quench and Melt Growth method (patent registration No. 1869884 and patent registration No. 2556401) is used. Can be mentioned. In this method, the temperature is raised once to a temperature range in which the RE ₂ BaCuO ₅ phase or the RE ₄ Ba ₂ Cu ₂ O ₁₀ phase and the liquid phase mainly composed of Ba-Cu-O coexist, and the REBa ₂ Cu ₃ O _x The crystal is grown to a temperature just above the peritectic temperature, and is gradually cooled from that temperature, and nucleation and crystal orientation are controlled to obtain a large bulk material. By using this manufacturing method, it is possible to obtain a superconducting material having a high critical current density (one of the superconducting characteristics and a current density that can be flown per unit cross-sectional area) and a relatively large size.
[0003]
On the other hand, the method of using a plurality of seed crystals for large-sized material fabrication and crystal growth from each seed crystal can realize crystal growth in a relatively short period of time because the area for crystal growth from each seed crystal becomes narrow. Has characteristics. In particular, the method disclosed in Japanese Patent Laid-Open No. 2001-322897 eliminates the “segregation phase rejected between the crystal growth regions from each seed crystal”, which has been a problem in the conventional method using a plurality of seed crystals. As a result, the superconducting characteristics between the regions grown from each seed crystal are improved, and as a whole, more uniform superconducting characteristics can be obtained.
[0004]
By using the above method, it was possible to produce a sample with a larger area and uniform superconducting properties. However, because of the large size, cracks tend to occur in the superconducting material when processing into the desired shape. There was a problem of becoming. The strength of the RE-Ba-Cu-O superconducting material itself is not strong among ceramic materials, and a method of adding Ag element to improve the strength is also known. Strength improvement was not enough.
[0005]
On the other hand, a combination with other high-strength materials, that is, a composite material of a high-strength structural support material and a superconducting material can be considered. In order to avoid cracks and the like that occur during processing into the desired shape as described above, it is necessary to have already been combined with a strong structural support material immediately after crystal growth. For this reason, a superconducting precursor is used during crystal growth processing. And a structure supporting material can be simultaneously introduced. However, in this case, the RE-Ba-Cu-O superconducting material is in a high temperature state of around 1000 ° C. during the crystal growth, and the oxide of Ba element or Cu element exists in the liquid phase. In such a combination, there is a problem that the superconducting transition temperature and the critical current density are lowered by reacting with the structural support material and diffusing the constituent elements of the structural support material into the RE-Ba-Cu-O superconducting material.
[0006]
[Problems to be solved by the invention]
The present invention grows a crystal using a plurality of seed crystals, and as a result, in a large superconducting bulk material having a larger area and uniform superconducting characteristics, without degrading superconducting characteristics such as superconducting transition temperature and critical current density. An object of the present invention is to provide a large-scale superconducting bulk material with a structural support compounded with a high-strength ceramic material and a method for producing the same.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention is composed of at least three types of oxide superconductors having different 123 phase peritectic temperatures (Tp), polycrystalline oxide ceramics, and oxide superconductor having the lowest Tp. Even if the layer partially reacts and adheres firmly, the constituent elements of the structural support material diffuse into the oxide superconducting layer with an intermediate Tp (lower than the highest Tp and higher than the lowest Tp). However, the superconducting properties (superconducting transition temperature and critical current density) are not affected, and the method disclosed in Japanese Patent Laid-Open No. 2001-322897 has been developed to provide a superconducting layer with the lowest Tp between the structural support materials. Thus, a means for obtaining a large superconducting bulk material with a structural support combined with a high-strength ceramic material without degrading the superconducting properties such as the superconducting transition temperature and critical current density is provided.
[0008]
The first feature of the present invention is a REBa ₂ Cu ₃ O _x (RE is a rare earth element containing Y or a combination thereof) -based superconducting intermediate, which is in the REBa ₂ Cu ₃ O _x phase (123 phase). It has a structure in which a plurality of oxide superconductor layers with different peritectic temperatures (Tp) of 123 phase having a structure in which the non-superconducting phase is finely dispersed are stacked in a three-dimensional order in the order of Tp. Two or more seed crystals are placed on the oxide superconducting layer having Tp, and at least the high Tp oxide superconducting layer contains an exclusion phase, and the average linear expansion coefficient from room temperature to 800 ° C is 10 ppm / ° C or more. A large-scale superconducting intermediate characterized by a structure in which a polycrystalline oxide ceramic of 20 ppm / ° C. or less is fixed to the lower surface of an oxide superconducting layer having the lowest Tp.
[0009]
The non-superconducting phase in the present invention refers to the RE ₂ BaCuO ₅ phase or the RE ₄ Ba ₂ Cu ₂ O ₁₀ phase finely dispersed in the REBa ₂ Cu ₃ O _x (123) phase that is the parent phase. In addition, the REBa ₂ Cu ₃ O _x phase (123 phase) has a different peritectic temperature (Tp), and the 123 phase has a different Tp by changing the RE composition to change the peritectic temperature (Tp) of the 123 phase. It refers to an oxide superconductor composed of a composition powder. The three-dimensionally stacked structure refers to a case where layers are stacked, a case where they are configured concentrically, or a combination thereof.
[0010]
The second feature of the present invention is the first large superconducting intermediate described above, wherein the main component of the polycrystalline oxide ceramic is an MgO polycrystalline material. The main component being a MgO polycrystalline material means a material in which MgO is present in a polycrystalline oxide ceramic in an amount of 90% or more.
[0011]
A third feature of the present invention is the large superconducting intermediate according to any one of the first and second features, wherein the oxide superconducting layer having the lowest Tp contains a Yb element. According to a fourth feature of the present invention, any one of the first to third large superconducting intermediates, wherein the laminate is formed by laminating at least one oxide superconductor layer containing 1 to 30% by mass of Ag element. Is the body.
[0012]
According to a fifth feature of the present invention, the laminate contains at least one element selected from 0.001 to 2.0 mass% Rh element, 0.05 to 5.0 mass% Pt element, or 0.05 to 10.0 mass% Ce element. Any one of the first to fourth large superconducting intermediates obtained by laminating at least one oxide superconductor layer. A sixth feature of the present invention is that the oxide superconducting layer containing the seed crystal and the exclusion phase of the large superconducting intermediate according to any one of the first to fifth aspects is cut out and subjected to an oxygen-enriched heat treatment. It is a large-sized superconductor characterized by this.
[0013]
The seventh feature of the present invention is that a raw material molded body containing RE, Ba, and Cu components constituting a REBa ₂ Cu ₃ O _x (RE is one of rare earth elements including Y or a combination thereof) series superconductor is heated. , Oxide superconductivity in which the non-superconducting phase is finely dispersed in the 123 phase by cooling after the maximum temperature is higher than the peritectic temperature (Tp) of the REBa ₂ Cu ₃ O _x phase (123 phase) of the molded body A method for producing an intermediate, which is a raw material molded body in which at least three layers are three-dimensionally laminated in the order of Tp, with a raw material molded body having different 123 phase Tp, and an average linear expansion coefficient from room temperature to 800 ° C. is 10 ppm. It is placed on the polycrystalline oxide ceramics having a temperature of 20 ppm / ° C. or less so that the raw molded laminate having the lowest Tp is in contact with each other, and a plurality of the raw molded laminate having the highest Tp An oxide superconductor characterized by heat-treating the raw material molded laminate after placing a seed crystal. A manufacturing method of the intermediate.
[0014]
The eighth feature of the present invention is the seventh method for producing a large superconducting intermediate, wherein the main component of the polycrystalline oxide ceramic is an MgO polycrystalline material.
[0015]
According to a ninth feature of the present invention, in the method for producing a large-scale superconducting intermediate according to any one of the seventh and eighth aspects, the oxide superconducting raw material molded body having the lowest Tp contains a Yb element. is there. The tenth feature of the present invention is that the superconducting material according to any one of the seventh to ninth aspects, wherein at least one oxide superconducting material molded body containing 1 to 30% by mass of Ag element is laminated on the laminate. This is a method for producing an intermediate.
[0016]
According to an eleventh feature of the present invention, the raw molded laminate is at least one element selected from 0.001 to 2.0 mass% Rh element, 0.05 to 5.0 mass% Pt element, or 0.05 to 10.0 mass% Ce element. Is a method for producing a large-scale superconducting intermediate according to any one of the seventh to tenth embodiments, wherein at least one layer of a raw material-molded body containing bismuth is laminated.
[0017]
The twelfth feature of the present invention is that an oxygen superconducting layer containing a seed crystal and a waste phase is excised from the large superconducting intermediate obtained from the seventh to eleventh fabrication methods, and then oxygen-enriched. This is a method for producing a large superconductor characterized by the following.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The present invention grows crystals using a plurality of seed crystals, and as a result, deteriorates the superconducting properties such as the superconducting transition temperature and critical current density in a large superconducting bulk material having a larger area and uniform superconducting properties. And a large superconducting bulk material with a structural support compounded with a high-strength ceramic material and a method for producing the same. The point of the present invention is that the method disclosed in Japanese Patent Laid-Open No. 2001-322897 is developed to use a superconducting layer having the lowest Tp between a large superconducting bulk material and a structural support material. Hereinafter, this point will be described in detail.
[0019]
When the raw material molded laminate in JP 2001-322897 A is placed on a structural support material and subjected to crystal growth treatment, it is exposed to a high temperature around 1000 ° C. during crystal growth. A reaction occurred at the interface with the structural support material, and as a result, impurity elements were mixed in the superconducting layer, resulting in sporadic deterioration of superconducting properties such as superconducting transition temperature and critical current density.
[0020]
On the other hand, in the method of the present invention, an oxide superconductor composed of at least three layers having different Tp as shown in FIG. 1 is used, but the layer having the lowest Tp has an appropriate thickness (preferably 100 μm or more). Thus, even if the layer with the lowest Tp reacts with the structural support material, the contamination of the impurity element into the layer with the intermediate Tp (lower than the highest Tp and higher than the lowest Tp) can be greatly reduced. it can. That is, the layer having the lowest Tp is used as a layer that prevents the impurity element from being mixed in the layer having the intermediate Tp. In addition, since the layer having the intermediate Tp functions as a superconducting material, the layer having the lowest Tp does not necessarily need to be crystal-grown and may be polycrystallized. From the viewpoint of adhesion to the structural support material, the density of the layer having the lowest Tp is preferably higher. For example, as a raw material molded laminate, three layers of a layer having the lowest Tp, a layer having an intermediate Tp, and a layer having the highest Tp are integrally molded, and then applied with hydrostatic pressure, and then placed on the structural support material By performing the crystal growth treatment, the layer having the lowest Tp after the crystal growth has a high density and can be adhered to the structural support material.
[0021]
On the other hand, RE-Ba-Cu-O superconducting material has a large coefficient of thermal expansion (around 13 ppm / ° C in the ab axis direction when RE is Y), so the structural support material also has a similar coefficient of thermal expansion. There is a need. When a structural support material having a coefficient of thermal expansion significantly different from that of the superconducting material is used, when cooling from a high temperature of about 900 ° C. to 1100 ° C. during crystal growth to room temperature, tensile stress due to the difference in thermal shrinkage at the interface Stress or compressive stress acts on the superconducting material and causes cracks such as cracks. The superconducting material has higher strength (for example, three-point bending strength) under compression than under tension. Therefore, even if the thermal expansion coefficient of the structural support material is somewhat larger than the thermal expansion coefficient of the superconducting material, it is difficult to induce cracks and the like because the compressive stress acts on the superconducting material during cooling. For these reasons, the linear expansion coefficient is limited to the range of 10 ppm / ° C. to 20 ppm / ° C. in the main temperature range where thermal shrinkage works (room temperature (20 ° C.) to 800 ° C.). Examples of such a structural support material include MgO and stabilized ZrO ₂ . In particular, dense MgO polycrystalline material is excellent in that it is inexpensive and light, and its thermal expansion coefficient is about 13ppm / ° C, which is close to that of RE-Ba-Cu-O superconducting material, and is suitable as a structural support material. .
[0022]
In addition, since the oxide superconducting layer with the lowest Tp solidifies due to heat shrinkage and is proportional to the difference between the temperature Tp to be fixed to the structural support material and room temperature, the oxide superconducting layer with the lowest Tp By using Yb element (Tp = 910 ± 10 ℃), Tp can be effectively kept low, and the temperature at which it adheres to the structural support material can also be lowered, resulting in low generation stress due to thermal shrinkage difference. it can.
[0023]
Furthermore, by containing an Ag element in the superconducting material, the strength of the oxide superconductor itself can be improved according to the added amount, and there is an effect of suppressing cracks and the like. The addition amount of Ag element is in the range of 1 to 30% by mass, and thereby the effect of improving the strength can be exhibited. In addition, Ag element easily diffuses in each oxide superconducting layer during heat treatment, and Tp also changes depending on the concentration of Ag element. Therefore, in order to obtain stable crystal growth, the amount of Ag element added to each oxide superconducting layer is It is desirable that each layer has the same mass%.
[0024]
The addition of Rh, Pt and Ce elements will be described below. These elements are the critical current, which is one of the superconducting properties, by finely dispersing the RE ₂ BaCuO ₅ phase or the RE ₄ Ba ₂ Cu ₂ O ₁₀ phase in the REBa ₂ Cu ₃ O _x (123) phase that is the parent phase. There is an effect of improving the density. The amount of addition is limited from the concentration at which the effect of refinement of the RE ₂ BaCuO ₅ phase or RE ₄ Ba ₂ Cu ₂ O ₁₀ phase starts to appear, and the concentration at which no further effect is obtained. This allows a larger current density to flow in the superconductor. That is, the amount by which the effect of addition is obtained is 0.001 to 2.0 mass% for the Rh element, 0.05 to 5.0 mass% for the Pt element, and 0.05 to 10.0 mass% for the Ce element. Also, considering the diffusion of each element, the amount of element added to each oxide superconducting layer is preferably the same mass% in each layer, but the layer having the lowest Tp does not necessarily need to be crystal-grown. An inexpensive Ce element can be used only for the layer.
[0025]
In addition, since a plurality of seed crystals are used in this method, the layer having the highest Tp has a Ba—Cu—O compound, a Cu—O compound, or segregated RE ₂ between crystal growth regions grown from various crystals. Non-superconducting phases such as BaCuO ₅ phase or RE ₄ Ba ₂ Cu ₂ O ₁₀ phase are excluded. This non-superconducting layer significantly hinders superconducting coupling between crystal growth regions grown from various crystals, and the superconducting current flowing through the regions also decreases significantly. For this reason, the superconducting layer on which the above exclusion phase is deposited after the crystal growth treatment is excised in advance, and then the superconducting intermediate is subjected to oxygen enrichment treatment to greatly increase the superconducting current flowing through the crystal growth regions grown from various crystals. A material having more uniform superconducting characteristics can be obtained without causing a significant decrease.
[0026]
The thickness of each superconducting layer will be described below. Under the high temperature during crystal growth after crystal growth, diffusion of superconducting layers having different Tp occurs. Therefore, a region where Tp is the same is generated in a part of the diffused region. Therefore, regarding the lower limit of the thickness, a thickness that allows each Tp to remain as a different superconducting layer is preferable. For example, when Tp is changed by changing the RE component, each superconducting layer preferably has a lower limit of about 100 μm. Further, as the ratio of the thickness of each superconducting layer, the total thickness of the superconducting layer to be excised is determined in consideration of the excision of the region in which the exclusion phase is finally produced, as in claim 6 or 12 of the present invention. The total thickness of the superconducting layer remaining after the excision is preferably not exceeded.
[0027]
【Example】
(Example 1)
Each raw material powder of Dy ₂ O ₃ , BaO ₂ , and CuO is mixed so that the molar ratio of each element (Dy: Ba: Cu) is (13:17:24), and 0.5% by mass is further added to this mixed powder. The Pt element was added and mixed raw material powders were produced. This was calcined at 900 ° C. in an oxygen stream. This is designated as Powder 1-A. In addition, each raw material powder of Dy ₂ O ₃ , Ho ₂ O ₃ , BaO ₂ , and CuO is adjusted so that the molar ratio of each element (Dy: Ho: Ba: Cu) is (6.5: 6.5: 17: 24). Further, 0.5% by mass of Pt element was added to the mixed powder to prepare a mixed raw material powder. This was calcined at 900 ° C. in an oxygen stream. This is designated as Powder 1-B. Furthermore, each raw material powder of Yb ₂ O ₃ , BaO ₂ , CuO was mixed so that the molar ratio of each element (Yb: Ba: Cu) was (13:17:24). A mass powder of Ce element was added as an oxide to produce a mixed raw material powder. This was calcined at 850 ° C. in an oxygen stream. This is designated as Powder 1-C. Furthermore, each raw material powder of Sm ₂ O ₃ , BaO ₂ and CuO was mixed so that the molar ratio of each element (Sm: Ba: Cu) was (13:17:24), and 1.0 mass was further added to this mixed powder. % Ce element was added as an oxide to prepare a mixed raw material powder. This was calcined at 920 ° C. in an oxygen stream. This is designated as Powder 1-D.
[0028]
Next, using powders 1-A, 1-B, and 1-C, a molded body was prepared as shown in FIG. 2A, and a cylindrical precursor having a diameter of 54 mm and a thickness of 20 mm at ² ton / cm ² was obtained. Produced. The precursor 3mm angle _{_{_{_{Sm 0.7 Nd 0.3 Ba 2 Cu 3}}}} O x superconductor seed crystal thickness 1mm at the place as shown in FIG. 2-b, 60 mm square powder 1-D on alumina plate, thickness A 50 mm square and 4 mm thick dense MgO plate having a purity of 99% was placed thereon as a structural support material, and the columnar precursor was placed thereon. The temperature was raised to 1045 ° C. in the atmosphere in 10 hours, held for 4 hours, and then lowered to 1010 ° C. in 2 hours. Thereafter, the mixture was gradually cooled to 980 ° C. over 100 hours, crystal growth was performed, and the mixture was cooled to room temperature over 24 hours. By this heat treatment, it was confirmed that the diameter of the cylindrical precursor was reduced to 46 mm and fixed to a 50 mm square structural support material.
[0029]
Cracks such as cracks were not observed in the obtained superconducting bulk material. Thereafter, the layer composed of the seed crystal and the powder 1-A is cut out, heated in an oxygen stream to 450 ° C. over 24 hours, gradually cooled down to 400 ° C. over 100 hours, and then over 10 hours to room temperature. The temperature dropped.
When the superconducting bulk material subjected to the above oxygen enrichment treatment was cooled in a magnetic field at 77 K, the external magnetic field was removed, and the supplementary magnetic flux density was measured, a good value of 0.8 T at maximum was obtained.
[0030]
(Example 2)
Each raw material powder of Gd ₂ O ₃ , BaO ₂ , and CuO is mixed so that the molar ratio of each element (Gd: Ba: Cu) is (12:18:26), and 0.5% by mass is further added to this mixed powder. The Pt element was added and mixed raw material powders were produced. 10% by mass of Ag ₂ O powder was added to the powder obtained by calcining this in an oxygen stream at 900 ° C. This is designated as Powder 2-A. In addition, each raw material powder of Dy ₂ O ₃ , Gd ₂ O ₃ , BaO ₂ , and CuO is adjusted so that the molar ratio of each element (Dy: Gd: Ba: Cu) is (6: 6: 18: 26). Further, 0.5% by mass of Pt element was added to the mixed powder to produce a mixed raw material powder. 10% by mass of Ag ₂ O powder was added to the powder obtained by calcining this in an oxygen stream at 900 ° C. This is designated as Powder 2-B. Furthermore, each raw material powder of Yb ₂ O ₃ , BaO ₂ and CuO was mixed so that the molar ratio of each element (Yb: Ba: Cu) was (12:18:26), and 0.5% was further added to this mixed powder. A mass powder of Pt element was added as an oxide to produce a mixed raw material powder. 10% by mass of Ag ₂ O powder was added to the powder obtained by calcining this in an oxygen stream at 850 ° C. Weigh this so that the molar ratio of the RE element to the powder 2-B is equal, and let the powder obtained by mixing be 2-C.
[0031]
Next, using powders 2-A, 2-B, and 2-C, a molded body is produced as shown in FIG. 3-a, and the corner is ² ton / cm ² and is 27 mm long, 77 mm wide, and 15 mm thick. A columnar precursor was prepared. A Sm _0.7 Nd _0.3 Ba ₂ Cu ₃ O _x based superconductor seed crystal of 3 mm square and 1 mm thickness is placed on this precursor as shown in FIG. 3B, and alumina powder is 60 mm square and 8 mm thick on the alumina plate. A dense MgO plate having a thickness of 30 mm, a width of 80 mm, and a thickness of 4 mm as a structural support material was placed thereon, and the prismatic precursor was placed thereon. The temperature was raised to 1058 ° C. in the atmosphere in 10 hours, held for 2 hours, and then lowered to 1010 ° C. in 2 hours. Then, it was gradually cooled to 980 ° C. over 100 hours for crystal growth, cooled to 870 ° C. over 50 hours, and cooled to room temperature over 24 hours.
[0032]
Cracks such as cracks were not observed in the obtained superconducting bulk material. Thereafter, the layer composed of the seed crystal and the powder 2-A was cut out, heated in the oxygen stream to 400 ° C. in 24 hours, maintained at 400 ° C. for 100 hours, and then cooled to room temperature over 10 hours.
When the superconducting bulk material subjected to the above oxygen enrichment treatment was cooled in a magnetic field at 77 K, the external magnetic field was removed, and the supplementary magnetic flux density was measured, a good value of up to 0.6 T was obtained.
[0033]
【The invention's effect】
According to the present invention, a large superconducting bulk material with a structural support material combined with a high-strength ceramic material having a large area and uniform superconducting characteristics and being difficult to crack can be obtained.
[Brief description of the drawings]
FIG. 1 is an example of a configuration diagram of the present invention. FIG. 2 is a schematic diagram of a superconductor used in Example 1. (a) Schematic diagram of a molded body used in Example 1. (b) Species used in Example 1. 3 is a schematic diagram of a superconductor used in Example 2. (a) Schematic diagram of a molded body used in Example 2. (b) Arrangement of seed crystal used in Example 2.

Claims

REBa ₂ Cu ₃ O _x (RE is one or a combination of rare earth elements including Y) based superconducting intermediate, and non-superconducting phase is finely dispersed in REBa ₂ Cu ₃ O _x phase (123 phase) It has a structure in which a plurality of oxide superconductor layers with different peritectic temperatures (Tp) of 123 phase having a structure are three-dimensionally laminated in the order of Tp, on the oxide superconductor layer having the highest Tp. Polycrystalline oxidation in which two or more seed crystals are placed, and at least the high Tp oxide superconducting layer contains an exclusion phase, and the average linear expansion coefficient from room temperature to 800 ° C is 10 ppm / ° C to 20 ppm / ° C Large superconducting intermediate characterized by a structure in which the ceramics adhere to the lower surface of the oxide superconducting layer having the lowest Tp.

2. The large superconducting intermediate according to claim 1, wherein a main component of the polycrystalline oxide ceramic is an MgO polycrystalline material.

The large-sized superconducting intermediate according to claim 1, wherein the oxide superconducting layer having the lowest Tp contains a Yb element.

The large-sized superconducting intermediate according to any one of claims 1 to 3, wherein the laminate is formed by laminating at least one oxide superconductor layer containing 1 to 30% by mass of Ag element. .

The laminated body includes at least one oxide superconductor layer containing at least one element selected from 0.001 to 2.0 mass% Rh element, 0.05 to 5.0 mass% Pt element, or 0.05 to 10.0 mass% Ce element. The large superconducting intermediate according to any one of claims 1 to 4, wherein the large superconducting intermediate is formed by laminating layers.

The large-sized superconducting intermediate according to any one of claims 1 to 5, wherein the large-sized superconducting intermediate seed crystal and the oxide superconducting layer containing the excluded phase are excised and then subjected to an oxygen-enriched heat treatment. Superconductor.

REBa ₂ Cu ₃ O _x (one kind of rare earth elements including Y or a combination thereof) The raw material molded body containing RE, Ba and Cu components constituting the superconductor is heated, and the maximum temperature is the REBa ₂ Cu of the molded body. A method for producing an oxide superconducting intermediate in which a non-superconducting phase is finely dispersed in a 123 phase by cooling after the peritectic temperature (Tp) of the ₃ O _x phase (123 phase) is reached. A raw material molded body having a different phase Tp is formed into a raw material molded laminated body in which at least three layers are three-dimensionally laminated in the order of Tp, and an average linear expansion coefficient from room temperature to 800 ° C. is 10 ppm / ° C. to 20 ppm / ° C. The raw material molding laminate having the lowest Tp is placed on the oxide ceramic so as to be in contact therewith, and a plurality of seed crystals are placed on the raw material molding laminate having the highest Tp, and then the raw material molding is performed. A method for producing a large superconducting intermediate, characterized by heat-treating a laminate.

The method for producing a large superconducting intermediate according to claim 7, wherein a main component of the polycrystalline oxide ceramic is an MgO polycrystalline material.

The method for producing a large-scale superconducting intermediate according to claim 7 or 8, wherein the oxide superconducting raw material molded body having the lowest Tp contains a Yb element.

The large superconducting intermediate according to any one of claims 7 to 9, wherein at least one oxide superconducting raw material compact containing 1 to 30% by mass of Ag element is laminated on the laminated body. How to make a body.

The raw material molded laminate includes at least one raw material molded body containing at least one element of 0.001 to 2.0 mass% Rh element, 0.05 to 5.0 mass% Pt element, or 0.05 to 10.0 mass% Ce element. The method for producing a large superconducting intermediate according to any one of claims 7 to 10, wherein layers are laminated.

Oxygen enrichment treatment is performed after excising the oxide superconductor layer containing the seed crystal and the exclusion phase from the oxide superconducting intermediate obtained from the manufacturing method according to any one of claims 7 to 11. A method for producing a large superconductor characterized by the above.