JP4203582B2 - RE-Ba-Cu-O-based oxide superconducting bulk material manufacturing method and apparatus - Google Patents

Description

を計算することによって得られる。材料設置面の中心の強度で規格化すると直径に沿った輻射の相対的な強度比はヒーターの材料設置位置から上部までの高さをａ、直径をｈとすると、各ａとｈの比に対して図２のように計算される。
【００２０】
ここで製造する材料の直径をＲとすると、この材料を製造する場合に適した炉体形状と製造材料の形状と設置位置との関係は以下のようにすると対流や伝熱による影響と相まって、適切な輻射強度分布を与えて、材料中の温度勾配を適切にすることが出来ることが確認された。
【００２１】
ａ／ｈが０．５以下では材料中の温度勾配が大きくなりすぎて材料端部付近での結晶成長に長時間を要してしまい、３以上では対流等を防ぐ効果があるが、実質的にコストが多くかかる。Ｒ／ｈは０．０５以下だとコスト的に悪く、０．７以上だと材料中の温度勾配が大きくなりすぎて材料端部付近での結晶成長に長時間を要してしまう。
【００２２】
またヒーターの内径の面積をＳ_h 、製造する材料の表面積をＳ_R とすると、Ｓ_R ／Ｓ_h は０．００２５以下ではコスト的に悪く、０．４９以上だと材料中の温度勾配が大きくなりすぎて材料端部付近での結晶成長に長時間を要してしまう。
【００２３】
以上は円柱状のヒーターの場合の例であるが、ヒーターが直方体や楕円柱等の場合にも、直方体の場合には各辺の平均を、楕円柱の場合には長軸と短軸との平均をｈとすればほぼ同様の結果が得られる。なお、炉体内部における材料設置位置からヒーター下部までの長さをｂとするとｂ／ｈはａ／ｈと同程度の範囲であることが望ましい。永久磁石との磁気反発力を利用したシステムに利用する場合、超電導体に加わる外部磁場は０．３Ｔ程度となるため、０．３Ｔ以上の保持磁束密度能を有する面積が広いとシステムの大型化・高効率化が可能となる。
【００２４】
なお、Ｐｔは、超電導体を形成するための原料混合体を作製する処理を行う際に、白金坩堝などから混入することがあるが、これは０．０５〜５ｗｔ％の範囲で含まれていると２１１相が微細になり高特性を示すことが確認されている。また、Ｐｔ、Ｐｄ、Ｒｕ、Ｒｈ、Ｉｒ、Ｏｓ、Ｒｅ、Ｃｅの金属もしくは化合物粉末を０．０５〜５ｗｔ％の範囲で添加しても同様に高特性を示すことが確認されている。
【００２５】
さらにＡｇが結晶中に微細に分散するとマイクロクラックが減少し、磁気特性、機械強度、耐水性が向上する。この際、１ｗｔ％より下ではその効果は低く、６０ｗｔ％より多いと超電導電流が流れにくくなり特性が低下してしまう。また、溶融工程は、比較的低酸素濃度の１０^-3〜２×１０^-1％の範囲で行なうとＲＥ元素との相互置換量が最適化され、つまり、一般式ＲＥ_1+P Ｂａ_2+q Ｃｕ₃ Ｏ_7-x で表される結晶相中のｐ，ｑが−０．２〜０．２の範囲となり、高磁場下における臨界電流密度特性が向上する。
【００２６】
【発明の実施の形態】
（実施例１）
この実施例は、溶融結晶化装置の上部ヒーターの高さをａ、内径をｈ、横断面積をＳ_h 、円板状の原料混合体の径をＲ、表面積をＳ_R とした場合に、ａ／ｈ＝１．２５、Ｒ／ｈ＝０．４５、Ｓ_R ／Ｓ_h=＝０．２０として原料混合体の成形体の中心（種結晶が接触する点；基準点）が低温側となるように外側（基準点から遠ざかる方向）に向かって０．２℃／ｃｍの温度勾配を加えて大型のＹ系酸化物超電導体結晶を製造する例である。
【００２７】
Ｙ₂ Ｏ₃ 、ＢａＣＯ₃ 、ＣｕＯの各原料粉末をＹ：Ｂａ：Ｃｕ＝１８：２４：３４になるように秤量した後、ＢａＣＯ₃ 、ＣｕＯのみを８８０℃で３０時間焼成してＢａＣｕＯ₂ とＣｕＯの仮焼粉を得た（モル比でＢａＣｕＯ₂ ：ＣｕＯ＝２４：１０）。この仮焼粉とあらかじめ秤量しておいたＹ₂ Ｏ₃ と更に全体に対して０．５ｗｔ％Ｐｔ粉末を加えて混合して８８０℃で再度焼成してＹＢａ₂ Ｃｕ₃ Ｏ_x 相とＹ₂ ＢａＣｕＯ₅ 相およびＰｔの混合粉とし、その後平均粒径約１０μｍに粉砕した。次にこの仮焼粉を直径１８０ｍｍ厚さ３０ｍｍのデイスク状に金型を用いて０．７ton ／ｃｍ² で一軸プレス成形し、さらにこの成形体を２ton ／ｃｍ² の圧力を加えてＣＩＰして成形体を作製した。
【００２８】
次に、上記原料混合体の成形体を溶融結晶化装置によって溶融結晶化する。図１は溶融結晶化装置の概略構成を示す図である。図１において、この溶融結晶化装置は、円筒状の上部ヒーター１と下部ヒーター２とから構成されている。上部ヒーター１及び下部ヒーター２の内部には巻線タイプのヒーター線１１及び２１がそれぞれ埋め込まれている。また、上部ヒーターの上部は上蓋１２によって塞がれ、下部ヒーター２の下部は底蓋２２によって塞がれている。上蓋１２には種結晶挿入孔１３が設けられ、この挿入孔１３には着脱自在な蓋体１４が設けられている。上部ヒーター１と下部ヒーター２との境界部には、原料混合体の成形体３０を載置するための支持板３が設けられている。
【００２９】
ここで、前試験として成形体３０に加わる温度分布を成形体中に熱電対を図３のように中心及び中心から外側に30mm間隔で挿入して測温した。成形体は支持板３上にアルミナ基板にのせてヒーター内部の中央に載置した。図１においてヒーター内径ｈは40cm、上部ヒーター１及び下部ヒーター２はその高さａ及びｂが共に50cmである。なお、このように、ヒーターを２つ上下にかさねた炉体を一般に２ゾーン型ヒーターという。熱電対を上下共円筒状の各ヒーターの中心で材料設置位置から上に15cmと下に15cmの位置に設置し、各々上下のヒーターの制御に用いた。次に、上下の熱電対の温度が1000℃となるように加熱した。この時成形体に設置した熱電対の温度はそれぞれ中心から外側に向かって1000℃、1000.5℃、1001.1℃と中心から外側に向かって約0.2 ℃／ｃｍの温度勾配を有していた。
【００３０】
次に、別の熱電対を挿入していない成形体を同形状の炉体の中心付近に設置し、上下ヒーター１，２の温度を共に1100℃となるように炉体を加熱し20分保持して成形体を半溶融状態にした。その後、上部ヒーターを1010℃、下部ヒーターを1050℃に30分で降温して成形体の上下に約2 ℃／ｃｍの温度勾配を加えた。次に、予め溶融法で作製しておいたＹ_1.8 （Ｂａ_0.75Ｓｒ_0.25）_2.4 Ｃｕ_3.4 Ｏ_x 組成の種結晶を成長方向がｃ軸と平行になるように成形体３０の上部中心に接触させる。そこから０．５℃／ｈｒの速度で上部ヒーター１を1000℃、下部ヒーター２を1040℃にまで降温した後500 時間温度保持し、種結晶から径方向の結晶成長を進めた。その後、上部ヒーター１を930 ℃、下部ヒーター２を970 ℃にまで70時間で降温し、そこから室温まで100 時間かけて徐冷することによって結晶化を行った。
【００３１】
作製した試料は焼き縮みのために直径１５０ｍｍ 、厚さ２５ｍｍのディスク状となっていた。結晶化した試料はガス置換を行える炉の中に設置される。まず、ロータリーポンプで１３．３Ｐａまで炉内を排気した後、酸素ガスを流し込んで酸素分圧が９５％以上である大気圧の酸素雰囲気にする。その後も０．５Ｌ／ｍｉｎの流量で酸素ガスを炉内に流しながら、室温から４５０℃まで１０時間で昇温し、４５０℃から２５０℃まで２００時間かけて徐冷し、２５０℃から室温まで１０時間で降温させることにより超電導体材料を製造した。
【００３２】
得られた材料を切断して断面を走査型電子顕微鏡で観察したところ、ＹＢａ₂ Ｃｕ₃ Ｏ_7-x 相（１２３相）中に0.1 〜30μｍ程度のＹ₂ ＢａＣｕＯ₅ 相（２１１相）が微細に分散していた。また、背面反射ラウエ法により中心付近を5mm 間隔で３点、材料端部付近を90度づつずらして４箇所、同じく5mm 間隔で３点測定したところ、種結晶を反映していずれの部分もｃ軸に配向し、それぞれの部分における３点間の方位のズレはどれも測定誤差範囲以下の１°以下であり、各部分間の方位のズレは５°以下である１６８ｃｍ² にわたって実質的に単結晶状の材料が得られた。
【００３３】
この材料から約2.8 ×2.8 ×2mm （ｃ軸方向の厚さが2mm ）の単一結晶粒を切り出し、臨界電流密度を測定したところ１［Ｔ］の磁場中で１．５×１０⁴ Ａ／ｃｍ² であった。
【００３４】
次に、この超電導体に外部磁場0.5Tを加えながら室温から温度77K まで冷却し、その後磁場を取り去って超電導体中に捕捉される磁束密度を測定した。測定はホール素子をＸＹステージに取り付けて超電導体表面から約0.1mm の距離で超電導体表面に沿って移動させ、ディスク状材料の軸方向の磁束密度分布を測定したところ図４のように約４７ｃｍ² 程度の広い範囲に渡って0.3 Ｔ以上の捕捉磁束密度が得られていた。
【００３５】
さらに、これらをロードセルの先端に取り付けた直径39.2mm、内径16mm、厚さ49mmのNd-Fe-B 系磁石（表面最大磁束密度 0.53T）を用いてオートグラフによって各々超電導体との磁気反発力を測定した。まず、リング磁石の軸方向とディスク状超電導体の軸方向がほぼ一致するように磁石を超電導体から300mm 離して設置する。超電導体を液体窒素中に漬けて温度77K に冷却した後、磁石を軸方向に沿って速度5mm/min で超電導体に近づける。超電導体と磁石との間隔が0.1mm となるまで磁石を近づけて、この時発生する反発力を測定した。超電導体と磁石との間隔が0.1mm のときの磁気反発力18kg・f と高い値が得られた。
【００３６】
（実施例２）
この実施例は、溶融結晶化装置の上部ヒーターの高さをａ、内径をｈ、横断面積をＳ_h 、円板状の原料混合体の径をＲ、表面積をＳ_R とした場合に、ａ／ｈ＝１．２５、Ｒ／ｈ＝０．３８、Ｓ_R ／Ｓ_h=＝０．１５として原料混合体の成形体の中心（種結晶が接触する点；基準点）が低温側となるように外側（基準点から遠ざかる方向）に向かって０．２℃／ｃｍの温度勾配を加えて大型のＳｍ系酸化物超電導体結晶を製造する例である。
【００３７】
Ｓｍ₂ Ｏ₃ 、ＢａＣＯ₃ 、ＣｕＯの各原料粉末をＳｍ：Ｂａ：Ｃｕ＝１８：２４：３４になるように秤量した後、ＢａＣＯ₃ 、ＣｕＯのみを880 ℃で30時間焼成してＢａＣｕＯ₂ とＣｕＯの仮焼粉を得た（モル比でＢａＣｕＯ₂ ：ＣｕＯ＝２４：１０）。この仮焼粉とあらかじめ秤量しておいたＳｍ₂ Ｏ₃ と更に全体に対して０．５ｗｔ％のPt粉末と１０ｗｔ％のAg粉末を加えて混合して880 ℃で再度焼成してＳｍＢａ₂ Ｃｕ₃ Ｏx 相とＳｍ₂ ＢａＣｕＯ₅ 相およびPt，Agの混合粉とし、その後平均粒径約10μm に粉砕した。次にこの仮焼粉を直径115mm 、厚さ30mmのデイスク状に金型を用いて0.7ton／ｃｍ² で一軸プレス成形し、さらにこの成形体を2ton／ｃｍ² の圧力を加えてCIP して成形体を作製した。
【００３８】
次に、上記原料混合体の成形体を溶融結晶化装置によって溶融結晶化する。ここで、前試験として、成形体３０に加わる温度分布を成形体中に熱電対を図３のように中心及び中心から外側に20mm間隔で挿入して測温した。成形体はアルミナ基板からなる支持板３上の中央に載置した。図１においてヒーター内径ｈは30cm、上部ヒーター１及び下部ヒーター２はその高さａ及びｂが共に37.5cmである。熱電対を上下共円筒ヒーターの中心で材料設置位置から上に15cmと下に15cmの位置に設置し、各々上下のヒーターの制御に用いた。次に、上下の熱電対の温度が1000℃となるように加熱した。この時成形体に設置した熱電対の温度はそれぞれ中心から外側に向かって1000℃、1000.4℃、1000.8℃と中心から外側に向かって約0.2 ℃／ｃｍの温度勾配を有していた。
【００３９】
次に、別の熱電対を挿入していない成形体を雰囲気置換が出来る容器に入れられた同形状の炉体の中心付近に設置した。炉内をロータリーポンプで１３．３Ｐａまで排気した後、Ｏ_２１％、Ａｒ９９％の混合ガスを流し込み大気圧にした。その後も同様の混合ガスを流しながら以下の行程を行った。上下ヒーターの温度を共に１１００℃となるように炉体を加熱し２０分保持して成形体を半溶融状態にした後、上部ヒーター１を９８０℃、下部ヒーター２を１０２０℃に３０分で降温して成形体の上下に約２℃／ｃｍの温度勾配を加えた。
【００４０】
次に、予め溶融法で作製しておいた銀を含まないＳｍ_1.8 Ｂａ_2.4 Ｃｕ_3.4 Ｏ_x 組成の種結晶を成長方向がｃ軸と平行になるように成形体の上部に接触させる。そこから０．５℃／ｈｒの速度で上部ヒーターを970 ℃、下部ヒーターを1010℃にまで降温した後150 時間温度保持し、種結晶から径方向の結晶成長を進めた。その後、上部ヒーターを900 ℃、下部ヒーターを940 ℃にまで70時間で降温し、そこから室温まで100 時間かけて徐冷することによって結晶化を行った。
【００４１】
作製した試料は焼き縮みのために直径１００ｍｍ厚さ２５ｍｍのディスク状となっていた。結晶化した試料はガス置換を行える炉の中に設置される。まず、ロータリーポンプで１３．３Ｐａまで炉内を排気した後、酸素ガスを流し込んで酸素分圧が９５％以上である大気圧の酸素雰囲気にする。その後も０．５Ｌ／ｍｉｎの流量で酸素ガスを炉内に流しながら、室温から４５０℃まで１０時間で昇温し、４５０℃から２５０℃まで２００時間かけて徐冷し、２５０℃から室温まで１０時間で降温させることにより超電導体材料を製造した。
【００４２】
得られた材料を切断して断面を走査型電子顕微鏡で観察したところ、Ｓｍ_1+p Ｂａ_2+q Ｃｕ₃ Ｏ_7-x 相中に0.1 〜30μm 程度のＳｍ_2+r Ｂａ_1+s ＣｕＯ₅ 相が微細に分散していた。ここで、p,q,r,s はそれぞれ-0.2〜0.2 までの値を取る相が主に存在していた。また、背面反射ラウエ法により中心付近を5mm 間隔で３点、材料端部付近を90度づつずらして４箇所同じく5mm 間隔で３点測定したところ、種結晶を反映していずれの部分もｃ軸に配向し、それぞれの部分における３点間の方位のズレはどれも測定誤差範囲以下の１°以下であり、各部分間の方位のズレは３°以下である７５ｃｍ² にわたって実質的に単結晶状の材料が得られた。
【００４３】
この材料から約2.8 ×2.8 ×2mm(ｃ軸方向の厚さが2mm)の単一結晶粒を切り出し、臨界電流密度を測定したところ1[T]の磁場中で2.0 ×１０⁴ Ａ／ｃｍ² であった。
【００４４】
次に、この超電導体に外部磁場0.5Tを加えながら室温から温度77K まで冷却し、その後磁場を取り去って超電導体中に捕捉される磁束密度を測定した。測定はホール素子をＸＹステージに取り付けて超電導体表面から約0.1mm の距離で超電導体表面に沿って移動させ、ディスク状材料の軸方向の磁束密度分布を測定したところ図５のように約１５ｃｍ² 程度の広い範囲に渡って0.3 Ｔ以上の捕捉磁束密度が得られていた。
【００４５】
さらに、これらをロードセルの先端に取り付けた直径39.2mm、内径16mm、厚さ49mmのNd-Fe-B 系磁石( 表面最大磁束密度 0.53T) を用いてオートグラフによって各々超電導体との磁気反発力を測定した。まず、リング磁石の軸方向とディスク状超電導体の軸方向がほぼ一致するように磁石を超電導体から300mm 離して設置する。超電導体を液体窒素中に漬けて温度77K に冷却した後、磁石を軸方向に沿って速度5mm/min で超電導体に近づける。超電導体と磁石との間隔が0.1mm となるまで磁石を近づけて、この時発生する反発力を測定した。超電導体と磁石との間隔が0.1mm のときの磁気反発力18kg・f と高い値が得られた。
【００４６】
（実施例３）
この実施例は、溶融結晶化装置の上部ヒーターの高さをａ、内径をｈ、横断面積をＳ_h 、円板状の原料混合体の径をＲ、表面積をＳ_R とした場合に、ａ／ｈ＝１．２５、Ｒ／ｈ＝０．３８、Ｓ_R ／Ｓ_h=＝０．１５として原料混合体の成形体の中心（種結晶が接触する点；基準点）が低温側となるように外側（基準点から遠ざかる方向）に向かって０．２℃／ｃｍの温度勾配を加えて大型のＮｄ系酸化物超電導体結晶を製造する例である。
【００４７】
Ｎｄ₂ Ｏ₃ 、ＢａＣＯ₃ 、ＣｕＯの各原料粉末をＮｄ：Ｂａ：Ｃｕ＝１６：２３：３３になるように秤量した後、ＢａＣＯ₃ 、ＣｕＯのみを880 ℃で30時間焼成してＢａＣｕＯ₂ とＣｕＯの仮焼粉を得た（モル比でＢａＣｕＯ₂ ：ＣｕＯ＝２３：１０）。この仮焼粉とあらかじめ秤量しておいたＮｄ₂ Ｏ₃ と更に全体に対して0.5wt%のPt粉末と20wt% のAg粉末を加えて混合して880 ℃で再度焼成してＮｄＢａ2 Ｃｕ3 Ｏx 相とＮｄ₄ Ｂａ₂ Ｃｕ₂ Ｏ₁₀相およびPt,Ag の混合粉とし、その後平均粒径約10μm に粉砕した。次にこの仮焼粉を直径115mm 厚さ30mmのデイスク状に金型を用いて0.7ton／ｃｍ² で一軸プレス成形し、さらにこの成形体を2ton／ｃｍ² の圧力を加えてCIP して成形体を作製した。
【００４８】
次に、上記原料混合体の成形体を溶融結晶化装置によって溶融結晶化する。この実施例では、溶融結晶化装置として、図６に示したように、実施例１，２における溶融結晶化装置の下部ヒーター２の下に同様なヒーター２ａを付け加えた、いわゆる３ゾーンヒーターを用いる。ヒーターの内径は、実施例１，２と同じである。各ヒーターの高さ（筒長さ）は375mm である。原料混合体の成形体を載置する支持板３は上側の２つのヒーターの境界部に設けた。
【００４９】
ここで、前試験として、成形体３０に加わる温度分布を成形体中に熱電対を図３のように中心及び中心から外側に20mm間隔で挿入して測温した。成形体はアルミナ基板からなる支持板３上の中央に載置した。熱電対は上下共円筒ヒーターの中心で材料設置位置から上に15cmと下に15cmの位置に設置し、各々上下のヒーターの制御に用いた。次に、上下の熱電対の温度が1000℃となるように加熱した。この時成形体に設置した熱電対の温度はそれぞれ中心から外側に向かって1000℃、1000.4℃、1000.8℃と中心から外側に向かって約0.2 ℃／ｃｍの温度勾配を有していた。
【００５０】
次に別の熱電対を挿入していない成形体を雰囲気置換が出来る容器に入れられた同形状の炉体の中心付近に設置した。炉内をロータリーポンプで１３．３Ｐａまで排気した後、Ｏ_２１％、Ａｒ９９％の混合ガスを流し込み大気圧にした。その後も同様の混合ガスを流しながら以下の行程を行った。上下ヒーターの温度を共に１１００℃となるように 炉体を加熱し２０分保持して成形体を半溶融状態にした後、上部ヒーターを９９０℃、下部ヒーターを１０３０℃に３０分で降温して成形体の上下に約２℃／ｃｍの温度勾配を加えた。
【００５１】
次に、予め溶融法で作製しておいた銀を含まないＮｄ_1.8 Ｂａ_2.4 Ｃｕ_3.4 Ｏ_x 組成の種結晶を成長方向がｃ軸と平行になるように成形体の上部に接触させる。そこから0.5 ℃/hr の速度で上部ヒーターを980 ℃、下部ヒーターを1020℃にまで降温した後150 時間温度保持し、種結晶から径方向の結晶成長を進めた。その後、上部ヒーターを910 ℃、下部ヒーターを950 ℃にまで70時間で降温し、そこから室温まで100 時間かけて徐冷することによって結晶化を行った。作製した試料は焼き縮みのために直径100mm 厚さ25mmのディスク状となっていた。結晶化した試料はガス置換を行える炉の中に設置される。
【００５２】
まず、ロータリーポンプで１３．３Ｐａまで炉内を排気した後、酸素ガスを流し込んで酸素分圧が９５％以上である大気圧の酸素雰囲気にする。その後も０．５Ｌ／ｍｉｎの流量で酸素ガスを炉内に流しながら、室温から７００℃まで１０時間で昇温し、８０時間保持した後４５０℃まで１００時間で降温し、４５０℃から２５０℃まで２００時間かけて徐冷し、２５０℃から室温まで１０時間で降温させることにより超電導体材料を製造した。
【００５３】
得られた材料を切断して断面を走査型電子顕微鏡で観察したところ、得られた材料を切断して断面を走査型電子顕微鏡で観察したところ、Ｎｄ_1+p Ｂａ_2+q Ｃｕ₃ Ｏ_7-x 相中に0.1 〜30μm 程度のＮｄ_4+r Ｂａ_2+s ＣｕＯ₅ 相が微細に分散していた。ここで、p,q,r,s はそれぞれ-0.2〜0.2 までの値を取る相が主に存在していた。また、背面反射ラウエ法により中心付近を5mm 間隔で３点、材料端部付近を90度づつずらして４箇所同じく5mm 間隔で３点測定したところ、種結晶を反映していずれの部分もc 軸に配向し、それぞれの部分における３点間の方位のズレはどれも測定誤差範囲以下の１°以下であり、各部分間の方位のズレは３°以下である７５ｃｍ² にわたって実質的に単結晶状の材料が得られた。
【００５４】
この材料から約2.8 ×2.8 ×2mm(ｃ軸方向の厚さが2mm)の単一結晶粒を切り出し、臨界電流密度を測定したところ1[T]の磁場中で1.9 ×１０⁴ Ａ／ｃｍ² であった。
【００５５】
さらに、これらをロードセルの先端に取り付けた直径39.2mm、内径16mm、厚さ49mmのNd-Fe-B 系磁石（表面最大磁束密度 0.53T）を用いてオートグラフによって各々超電導体との磁気反発力を測定した。まず、リング磁石の軸方向とディスク状超電導体の軸方向がほぼ一致するように磁石を超電導体から300mm 離して設置する。超電導体を液体窒素中に漬けて温度77K に冷却した後、磁石を軸方向に沿って速度5mm/min で超電導体に近づける。超電導体と磁石との間隔が0.1mm となるまで磁石を近づけて、この時発生する反発力を測定した。超電導体と磁石との間隔が0.1mm のときの磁気反発力17kg・f と高い値が得られた。
【００５６】
（比較例１）
この比較例は、溶融結晶化装置の上部ヒーターの高さをａ、内径をｈ、横断面積をＳ_h 、円板状の原料混合体の径をＲ、表面積をＳ_R とした場合に、ａ／ｈ＝１．０、Ｒ／ｈ＝０．７２、Ｓ_R ／Ｓ_h ＝０．５２として原料混合体の成形体の中心（種結晶が接触する点；基準点）が低温側となるように外側（基準点から遠ざかる方向）に向かって０．５℃／ｃｍの温度勾配を加えて大型のＹ系酸化物超電導体結晶を製造する例である。
【００５７】
Ｙ₂ Ｏ₃ 、ＢａＣＯ₃ 、ＣｕＯの各原料粉末をY:Ba:Cu=18:24:34になるように秤量した後、ＢａＣＯ₃ 、ＣｕＯのみを880 ℃で30時間焼成してＢａＣｕＯ₂ とＣｕＯの仮焼粉を得た（モル比でＢａＣｕＯ₂ ：ＣｕＯ＝２４：１０）。この仮焼粉とあらかじめ秤量しておいたＹ₂ Ｏ₃ と更に全体に対して0.5wt%のPt粉末を加えて混合して880 ℃で再度焼成してＹＢａ₂ Ｃｕ₃ Ｏ_x 相とＹ₂ ＢａＣｕＯ₅ 相およびPtの混合粉とし、その後平均粒径約10μm に粉砕した。次にこの仮焼粉を直径180mm 、厚さ30mmのデイスク状に金型を用いて0.7ton／ｃｍ² で一軸プレス成形し、さらにこの成形体を2ton/cm2の圧力を加えてCIP して成形体を作製した。
【００５８】
ここで、前試験として成形体に加わる温度分布を成形体中に熱電対を図３のように中心及び中心から外側に30mm間隔で挿入して測温した。この成形体をアルミナ基板上にのせて、図１に示されるヒーター内径ｈが25cm、高さａが25cmである２ゾーン型ヒーターの炉体のほぼ中央に設置した。熱電対は上下共円筒ヒーターの中心で材料設置位置から上に15cmと下に15cmの位置に設置し、各々上下のヒーターの制御に用いた。次に、上下の熱電対の温度が1000℃となるように加熱した。この時成形体に設置した熱電対の温度はそれぞれ中心から外側に向かって1000℃、1001.5℃、1003.1℃と中心から外側に向かって約0.5 ℃/cm の温度勾配を有していた。
【００５９】
次に別の熱電対を挿入していない成形体を同形状の炉体の中心付近に設置し、上下ヒーターの温度を共に1100℃となるように炉体を加熱し20分保持して成形体を半溶融状態にした。その後、上部ヒーターを1010℃、下部ヒーターを1050℃に30分で降温して成形体の上下に約2 ℃/cm の温度勾配を加えた。
【００６０】
次に、予め溶融法で作製しておいたＹ_1.8 （Ｂａ_0.75Ｓｒ_0.25）_2.4 Ｃｕ_3.4 Ｏ_x 組成の種結晶を成長方向がｃ軸と平行になるように成形体の上部に接触させる。そこから0.5 ℃/hr の速度で上部ヒーターを1000℃、下部ヒーターを1040℃にまで降温した後500 時間温度保持し、種結晶から径方向の結晶成長を進めた。その後、上部ヒーターを930 ℃、下部ヒーターを970 ℃にまで70時間で降温し、そこから室温まで100 時間かけて徐冷することによって結晶化を行った。作製した試料は焼き縮みのために直径150mm 厚さ25mmのディスク状となっていた。
【００６１】
結晶化した試料はガス置換を行える炉の中に設置される。まず、ロータリーポンプで１３．３Ｐａまで炉内を排気した後、酸素ガスを流し込んで酸素分圧が９５％以上である大気圧の酸素雰囲気にする。その後も０．５Ｌ／ｍｉｎの流量で酸素ガスを炉内に流しながら、室温から４５０℃まで１０時間で昇温し、４５０℃から２５０℃まで２００ 時間かけて徐冷し、２５０℃から室温まで１０時間で降温させることにより超電導体材料を製造した。
【００６２】
得られた材料を切断して断面を走査型電子顕微鏡で観察したところ、ＹＢａ₂ Ｃｕ₃ Ｏ_7-x 相（１２３相）中に0.1 〜30μｍ程度のＹ₂ ＢａＣｕＯ₅ 相（２１１相対）が微細に分散していた。また、背面反射ラウエ法により中心付近を5mm 間隔で３点、材料端部付近を90度づつずらして４箇所同じく5mm 間隔で３点測定したところ、中心付近では種結晶を反映していずれの部分もｃ軸に配向し、３点間の方位のズレは測定誤差範囲以下の１°以下であったが、結晶の成長が途中で止まってしまったために材料端部付近では異方位の核発生が起こり、各部分間の方位のズレが１０°〜４０°程度である多結晶体となっていた。
【００６３】
この材料から約2.8 ×2.8 ×2mm （ｃ軸方向の厚さが2mm ）の単一結晶粒を切り出し、 臨界電流密度を測定したところ1[T]の磁場中で1.0 ×１０⁴ Ａ／ｃｍ² であった。
【００６４】
次に、この超電導体に外部磁場0.5Tを加えながら室温から温度77K まで冷却し、 その後磁場を取り去って超電導体中に捕捉される磁束密度を測定した。測定はホール素子をXYステージに取り付けて超電導体表面から約0.1mm の距離で超電導体表面に沿って移動させ、ディスク状材料の軸方向の磁束密度分布を測定したところ図７のように結晶方位の異なる部分から磁束の漏れが発生し０．３Ｔ以上の捕捉磁束密度能を有する部分がなかった。
【００６５】
さらに、これらをロードセルの先端に取り付けた直径39.2mm、内径16mm、厚さ49mmのNd-Fe-B 系磁石（表面最大磁束密度 0.53T）を用いてオートグラフによって各々超電導体との磁気反発力を測定した。まず、リング磁石の軸方向とディスク状超電導体の軸方向がほぼ一致するように磁石を超電導体から300mm 離して設置する。超電導体を液体窒素中に漬けて温度77K に冷却した後、磁石を軸方向に沿って速度5mm/min で超電導体に近づける。超電導体と磁石との間隔が0.1mm となるまで磁石を近づけて、この時発生する反発力を測定した。超電導体と磁石との間隔が0.1mm のときの磁気反発力12kg・f と低かった。
【００６６】
（比較例２）
この比較例は、溶融結晶化装置の上部ヒーターの高さをａ、内径をｈ、横断面積をＳ_h 、円板状の原料混合体の径をＲ、表面積をＳ_R とした場合に、ａ／ｈ＝０．３３、Ｒ／ｈ＝０．６、Ｓ_R ／Ｓ_h ＝０．３６として原料混合体の成形体の中心（種結晶が接触する点；基準点）が低温側となるように外側（基準点から遠ざかる方向）に向かって１．０℃／ｃｍの温度勾配を加えて大型のＹ系酸化物超電導体結晶を製造する例である。
【００６７】
Ｙ₂ Ｏ₃ 、ＢａＣＯ₃ 、ＣｕＯの各原料粉末をY:Ba:Cu=18:24:34になるように秤量した後、ＢａＣＯ₃ 、ＣｕＯのみを880 ℃で30時間焼成してＢａＣｕＯ₂ とＣｕＯの仮焼粉を得た（モル比でＢａＣｕＯ₂ ：ＣｕＯ２４：１０）。この仮焼粉とあらかじめ秤量しておいたＹ₂ Ｏ₃ と更に全体に対して0.5wt%のPt粉末を加えて混合して880 ℃で再度焼成してＹＢａ₂ Ｃｕ₃ Ｏ_x 相とＹ₂ ＢａＣｕＯ₅ 相およびPtの混合粉とし、その後平均粒径約10μm に粉砕した。次にこの仮焼粉を直径180mm 、厚さ30mmのデイスク状に金型を用いて0.7ton／ｃｍ² で一軸プレス成形し、さらにこの成形体を2ton／ｃｍ² の圧力を加えてCIP して成形体を作製した。
【００６８】
ここで、前試験として成形体に加わる温度分布を成形体中に熱電対を図３のように中心及び中心から外側に30mm間隔で挿入して測温した。この成形体をアルミナ基板にのせて、図１に示される装置の上部ヒーター１の内部中央の上部から下に１０ｃｍのところに配置した。この時のヒーター内径ｈは30cm、高さａは37.5cmである。熱電対を上下共円筒ヒーターの中心で材料設置位置から上に15cmと下に15cmの位置に設置し、各々上下のヒーターの制御に用いた。次に、上下の熱電対の温度が1000℃となるように加熱した。この時成形体に設置した熱電対の温度はそれぞれ中心から外側に向かって996 ℃、998.5 ℃、1002℃と中心から外側に向かって約1.0 ℃/cm の温度勾配を有していた。
【００６９】
次に別の熱電対を挿入していない成形体を同形状の炉体の同位置に設置し、上下ヒーターの温度を共に1100℃となるように炉体を加熱し20分保持して成形体を半溶融状態にした。その後、上部ヒーターを1046℃、下部ヒーターを1086℃に30分で降温して成形体の上下に約2 ℃/cm の温度勾配を加えた。次に、予め溶融法で作製しておいたＹ_1.8 （Ｂａ_0.75Ｓｒ_0.25）_2.4 Ｃｕ_3.4 Ｏ_x 組成の種結晶を成長方向がｃ軸と平行になるように成形体の上部に接触させる。
【００７０】
そこから0.5 ℃/hr の速度で上部ヒーターを1036℃、下部ヒーターを1076℃にまで降温した後500 時間温度保持し、種結晶から径方向の結晶成長を進めた。その後、上部ヒーターを966 ℃、下部ヒーターを1006℃にまで70時間で降温し、そこから室温まで100 時間かけて徐冷することによって結晶化を行った。作製した試料は焼き縮みのために直径150mm 、厚さ25mmのディスク状となっていた。
【００７１】
結晶化した試料はガス置換を行える炉の中に設置される。まず、ロータリーポンプで１３．３Ｐａまで炉内を排気した後、酸素ガスを流し込んで酸素分圧が９５％以上である大気圧の酸素雰囲気にする。その後も０．５Ｌ／ｍｉｎの流量で酸素ガスを炉内に流しながら、室温から４５０℃まで１０時間で昇温し、４５０℃から２５０℃まで２００時間かけて徐冷し、２５０℃から室温まで１０時間で降温させることにより超電導体材料を製造した。
【００７２】
得られた材料を切断して断面を走査型電子顕微鏡で観察したところ、ＹＢａ₂ Ｃｕ₃ Ｏ_7-x 相中に0.1 〜30μm 程度のＹ₂ ＢａＣｕＯ₅ 相が微細に分散していた。また、背面反射ラウエ法により中心付近を5mm 間隔で３点、材料端部付近を90度づつずらして４箇所同じく5mm 間隔で３点測定したところ、種結晶直下の2 ×2cm 角程度までは種結晶を反映していずれの部分もｃ軸に配向し、３点間の方位のズレは測定誤差範囲以下の１°以下であったが、他からの核発生が多数起こり各部分間の方位のズレが１０°〜４０°程度であって多結晶体となっていた。
【００７３】
この材料から約2.8 ×2.8 ×2mm(c 軸方向の厚さが2mm)の単一結晶粒を切り出し、臨界電流密度を測定したところ1[T]の磁場中で0.9 ×１０⁴ Ａ／ｃｍ² であった。
【００７４】
次に、この超電導体に外部磁場0.5Tを加えながら室温から温度77K まで冷却し、その後磁場を取り去って超電導体中に捕捉される磁束密度を測定した。測定はホール素子をXYステージに取り付けて超電導体表面から約0.1mm の距離で超電導体表面に沿って移動させ、ディスク状材料の軸方向の磁束密度分布を測定したところ図８のように結晶方位の異なる部分から磁束の漏れが発生０．３Ｔ以上の捕捉磁束密度能を有する部分が５ｃｍ² 程度まばらに存在する程度であった。
【００７５】
さらに、これらをロードセルの先端に取り付けた直径39.2mm、内径16mm、厚さ49mmのNd-Fe-B 系磁石（表面最大磁束密度 0.53T）を用いてオートグラフによって各々超電導体との磁気反発力を測定した。まず、リング磁石の軸方向とディスク状超電導体の軸方向がほぼ一致するように磁石を超電導体から300mm 離して設置する。超電導体を液体窒素中に漬けて温度77K に冷却した後、磁石を軸方向に沿って速度5mm/min で超電導体に近づける。超電導体と磁石との間隔が0.1mm となるまで磁石を近づけて、この時発生する反発力を測定した。超電導体と磁石との間隔が0.1mm のときの磁気反発力11kg・f と低かった。
【００７６】
【発明の効果】
以上詳述したように、本発明は、溶融結晶化装置の上部ヒーターの高さをａ、内径をｈ、横断面積をＳ_h 、円板状の原料混合体の径をＲ、表面積をＳ_R とした場合に、０．５≦ａ／ｈ、Ｒ／ｈ≦０．７、Ｓ_R ／Ｓ_h ≦０．４９のいずれか１以上の条件を満たすようにして、原料混合体の成形体の中心（種結晶が接触する点；基準点）が低温側となるように外側（基準点から遠ざかる方向）に向かって０．０１〜０．４℃／ｃｍの温度勾配を形成させて溶融結晶化を行なうことによって、結晶方向の揃った大型のＲＥーＢａーＣｕーＯ系酸化物超電導バルク材を得ること可能にしたものである。
【図面の簡単な説明】
【図１】本発明の実施例にかかる溶融結晶化装置の概略構成を示す図である。
【図２】図１の溶融結晶化装置のヒーターの形状と輻射の関係を計算した結果である。
【図３】原料混合体の成形体内部の温度分布を測定するための手法を示す図である。
【図４】実施例１で製造された酸化物超電導バルク材の捕捉磁束密度能を示す図である。
【図５】実施例２で製造された酸化物超電導バルク材の捕捉磁束密度能を示す図である。
【図６】実施例３で用いた溶融結晶化装置の概略構成を示す図である。
【図７】比較例１で製造された酸化物超電導バルク材の捕捉磁束密度能を示す図である。
【図８】比較例で製造された酸化物超電導バルク材の捕捉磁束密度能を示す図である。
【符号の説明】
１…上部ヒーター、２…下部ヒーター、３…支持板、１１，２１…ヒーター線、１２…上蓋、１３…種結晶挿入孔、１４…蓋体、２２…底蓋、３０…原料混合体の成形体。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a RE-Ba-Cu-O-based oxide superconducting bulk material excellent in electrical characteristics, magnetic characteristics, mechanical strength and environmental resistance used for current leads, magnetic bearings, magnetic shields, bulk magnets, and the like. It relates to a method and a device.
[0002]
[Prior art]
While heating and melting a raw material mixture containing an RE compound (RE is one or more rare earth metal elements including Y), a Ba compound and a Cu compound above the melting point temperature of the raw material mixture, applying a temperature gradient As a method for producing a RE-Ba-Cu-O-based oxide superconductor by performing a slow cooling step to grow a crystal, for example, a method described in JP-A-5-9059 is known. In the method described in this publication, an RE compound, a Ba compound and a Cu compound are mixed and fired at a predetermined ratio, the obtained fired powder is pulverized, molded, melted, and slowly cooled in a temperature gradient. This is a method for producing a RE-Ba-Cu-O-based oxide superconductor having a high critical current density by performing a crystallization process.
[0003]
[Problems to be solved by the invention]
By the way, in general, oxide superconductors have poor thermal conductivity compared to metals, and when crystallizing after melting and producing large oriented crystals with good reproducibility, the radiation applied to the sample is controlled to control the crystal. It is necessary to control the origin generation. However, the influence of the heater shape for producing the oxide superconductor crystal on the produced crystal has not been clarified so far, and it has been difficult to produce a large oriented crystal with good reproducibility.
[0004]
The present invention has been made under the above-mentioned background, and can provide a RE-Ba-Cu-O-based oxide superconducting bulk material excellent in electrical characteristics, magnetic characteristics, mechanical strength, and environmental resistance. An object of the present invention is to provide a RE-Ba-Cu-O-based oxide superconducting bulk material and a method and apparatus for producing the same.
[0005]
[Means for Solving the Problems]
As means for solving the above-mentioned problems, the first invention provides:
In the RE-Ba-Cu-O-based oxide superconducting bulk material,
The crystal plane of any region of the surface of the bulk material or the cut plane that appears when the bulk material is cut at an arbitrary plane is an oriented crystal plane whose orientation deviation between adjacent crystals is ± 5 ° or less And the area is 75 cm. ² A RE-Ba-Cu-O-based oxide superconducting bulk material characterized by having the above.
[0006]
The second invention is
In the RE-Ba-Cu-O-based oxide superconducting bulk material,
15 cm in the region of the surface of the bulk material or the cut surface that appears when the bulk material is cut by an arbitrary surface. ² A RE-Ba-Cu-O-based oxide superconducting bulk material having a trapped magnetic flux density capability of 0.3 T or more over the above range.
[0007]
The third invention is
In the RE-Ba-Cu-O-based oxide superconducting bulk material,
The crystal plane of any region of the surface of the bulk material or the cut plane that appears when the bulk material is cut at an arbitrary plane is an oriented crystal plane whose orientation deviation between adjacent crystals is ± 5 ° or less And the area is 75 cm. ² With the above,
15 cm in the region of the surface of the bulk material or the cut surface that appears when the bulk material is cut by an arbitrary surface. ² A RE-Ba-Cu-O-based oxide superconducting bulk material having a trapped magnetic flux density capability of 0.3 T or more over the above range.
[0008]
The fourth invention is:
Molten crystals in a temperature range higher than the melting point of the raw material mixture are formed into a molded body of the raw material mixture containing an RE compound (RE is one or more rare earth metal elements including Y), a Ba compound and a Cu compound. In a method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material, which includes a process including a crystallization step to produce a RE-Ba-Cu-O-based oxide superconducting bulk material,
The melt crystallization step is performed by forming a temperature gradient of 0.01 to 0.4 ° C./cm in a direction away from a reference point to be a starting point of crystallization in the molded body of the raw material mixture. This is a method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material.
[0009]
The fifth invention is:
Molten crystals in a temperature range higher than the melting point of the raw material mixture are formed into a molded body of the raw material mixture containing an RE compound (RE is one or more rare earth metal elements including Y), a Ba compound and a Cu compound. In a method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material, which includes a process including a crystallization step to produce a RE-Ba-Cu-O-based oxide superconducting bulk material,
The melt crystallization step is performed by arranging the molded body of the raw material mixture in a heater having a cylindrical shape, an elliptical cylinder shape, a rectangular parallelepiped shape or the like,
The heater has a portion extending up and down from the position where the raw material mixture is arranged, and at least the height of the upper heater extended at the top from the position where the raw material mixture is arranged. When the heater height is a and the heater diameter is h (in the case of an ellipse, the average of the long axis and the short axis, and in the case of a rectangular parallelepiped, the average of the two vertical and horizontal sides is h), 0.5 ≦ a / h In this way, the RE-Ba-Cu-O-based oxide superconducting bulk material is produced by melt crystallization.
[0010]
The sixth invention is:
Molten crystals in a temperature range higher than the melting point of the raw material mixture are formed into a molded body of the raw material mixture containing an RE compound (RE is one or more rare earth metal elements including Y), a Ba compound and a Cu compound. In a method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material, which includes a process including a crystallization step to produce a RE-Ba-Cu-O-based oxide superconducting bulk material,
The melt crystallization step is performed by arranging the molded body of the raw material mixture in a heater having a cylindrical shape, an elliptical cylinder shape, a rectangular parallelepiped shape or the like,
The heater has a portion that is vertically extended from the position where the raw material mixture is disposed,
The molded body of the raw material mixture has a disk shape, an elliptical plate shape, a cylindrical shape, a rectangular parallelepiped shape or a shape similar to these,
The diameter of the compact of the raw material mixture (the average of the long axis and the short axis in the case of an ellipse, the average of the two sides in the case of a rectangular parallelepiped) is R, and the heater diameter (the long axis and the short axis in the case of an ellipse) RE-Ba-Cu-O-based oxidation characterized in that melt crystallization is performed so that R / h≤0.7, where h is an average or an average of two sides in the case of a rectangular parallelepiped) This is a method for manufacturing a superconducting bulk material.
[0011]
The seventh invention
Molten crystals in a temperature range higher than the melting point of the raw material mixture are formed into a molded body of the raw material mixture containing an RE compound (RE is one or more rare earth metal elements including Y), a Ba compound and a Cu compound. In a method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material, which includes a process including a crystallization step to produce a RE-Ba-Cu-O-based oxide superconducting bulk material,
The melt crystallization step is performed by arranging the molded body of the raw material mixture in a heater having a cylindrical shape, an elliptical cylinder shape, a rectangular parallelepiped shape or the like,
The heater has a portion that is vertically extended from the position where the raw material mixture is disposed,
The molded body of the raw material mixture has a disk shape, an elliptical plate shape, a cylindrical shape, a rectangular parallelepiped shape or a shape similar to these,
The area of the cut surface when the heater is cut along a plane parallel to the arrangement surface of the molded body is S. _R And the area of the cut surface when the molded body of the raw material mixture is cut along a plane parallel to the arrangement surface of the molded body. _h S _R / S _h It is a method for producing an oxide superconducting bulk material, wherein melt crystallization is performed so that ≦ 0.49.
[0012]
The eighth invention
In the method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material according to any one of the fourth to seventh inventions,
The raw material mixture further contains 0.05 to 5 wt% of Pt, Pd, Ru, Rh, Ir, Os, Re, Ce, or one or more of these compounds (in the case of a compound, only the metal). (RE-Ba-Cu-O-based oxide superconducting bulk material manufacturing method, characterized in that it is added).
[0013]
The ninth invention
In the method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material according to any one of the fourth to eighth inventions,
A RE-Ba-Cu-O-based oxide superconducting bulk material characterized by further adding 1 to 60 wt% of Ag metal or compound (in the case of a compound, indicated by the element weight of Ag only) to the raw material mixture. It is a manufacturing method.
[0014]
The tenth invention is
In the method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material according to any one of the fourth to ninth inventions,
In the melt crystallization step, the oxygen partial pressure is 10 ^-3 ~ 2x10 ^-1 % Is a method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material characterized by performing melt crystallization in the range of%.
[0015]
The eleventh invention is
Molten crystals in a temperature range higher than the melting point of the raw material mixture are formed into a molded body of the raw material mixture containing an RE compound (RE is one or more rare earth metal elements including Y), a Ba compound and a Cu compound. In a RE-Ba-Cu-O-based oxide superconducting bulk material manufacturing apparatus for manufacturing a RE-Ba-Cu-O-based oxide superconducting bulk material by performing a process including a crystallization step,
The melt crystallization step is performed by arranging the molded body of the raw material mixture in a heater having a cylindrical shape, an elliptical cylinder shape, a rectangular parallelepiped shape or the like,
The heater has a portion extending up and down from the position where the raw material mixture is arranged, and at least the height of the upper heater extended at the top from the position where the raw material mixture is arranged. When the heater height is a and the heater diameter is h (in the case of an ellipse, the average of the long axis and the short axis, and in the case of a rectangular parallelepiped, the average of the two vertical and horizontal sides is h), 0.5 ≦ a / h The RE-Ba-Cu-O-based oxide superconducting bulk material manufacturing apparatus is characterized in that melt crystallization is performed as described above.
[0016]
In general, a heater used for crystal growth is a cylindrical type or a similar shape. RE ₂ BaCuO _Five REBa through peritectic reaction from the partially molten state of phase (211 phase) and liquid ₂ Cu _Three O _7-x When this material is produced by crystallizing the phase (123 phase), the pre-formed shape can be maintained with some shrinkage because it is in a partially molten state. Therefore, unlike a metal crystal or the like, if it is previously formed into a plate shape such as a cylinder or a rectangular parallelepiped and melted and crystallized, the subsequent process can be easily performed and the portion to be cut off can be reduced, thereby reducing the cost.
[0017]
In the growth of such a plate-like large oriented crystal, it is possible to produce a large crystal with high reproducibility by performing horizontal growth radially from the seed crystal in the first stage and then performing vertical growth. . When this horizontal growth is performed, it is desirable that the horizontal heat applied to the material be smooth so that the temperature gradient in the vicinity of the material is 1 ° C./cm or less. If there is a large temperature difference in the horizontal direction, for example, nucleation of crystals from other than the seed crystal occurs in the low temperature portion, resulting in a polycrystal, or crystal growth stops in the high temperature portion.
[0018]
The temperature distribution in the furnace when manufacturing this material is about the horizontal direction of the material, and if there is a small temperature gradient toward the outside so that the temperature near the center on which the seed crystal is placed is low, disordered nucleation occurs. It can be suppressed. At that time, if the temperature gradient is 0.01 ° C./cm or less, the effect is small, and if it is 0.4 ° C./cm or more, it takes a long time to grow the crystal of the material, which increases the cost.
[0019]
In addition, it has been found that the following conditions are appropriate as a heating method in producing this material. For example, in the case of heating with a wire heater, heat transfer to the material includes radiation, convection, heat transfer from the substrate, etc. Of these, regarding radiation, the case of using a cylindrical heater as shown in FIG. If the intensity of radiation from the heater to the material installation surface ignores reflection, a small part of the heater is d _A1 , D _A2 Q is the radiant heat flux per unit time and unit time injected from _A2 Where r is the length of the straight line connecting them, and θ is the angle formed by the straight line r and the perpendicular of the heater.
[Expression 1]

Is obtained by calculating When normalized by the intensity at the center of the material installation surface, the relative intensity ratio of radiation along the diameter is a ratio of a to h, where a is the height from the material installation position to the top of the heater and h is the diameter. On the other hand, it is calculated as shown in FIG.
[0020]
If the diameter of the material to be manufactured here is R, the relationship between the furnace body shape suitable for manufacturing this material, the shape of the manufactured material, and the installation position is coupled with the influence of convection and heat transfer as follows, It was confirmed that the temperature gradient in the material can be made appropriate by giving an appropriate radiation intensity distribution.
[0021]
If a / h is 0.5 or less, the temperature gradient in the material becomes too large, and it takes a long time for crystal growth near the edge of the material. If it is 3 or more, there is an effect of preventing convection. Costs a lot. If R / h is 0.05 or less, the cost is poor, and if it is 0.7 or more, the temperature gradient in the material becomes too large, and it takes a long time for crystal growth near the edge of the material.
[0022]
The area of the inner diameter of the heater is S _h The surface area of the material to be manufactured is S _R Then, S _R / S _h Is less than 0.0025 in terms of cost, and if it is 0.49 or more, the temperature gradient in the material becomes too large, and it takes a long time for crystal growth near the end of the material.
[0023]
The above is an example in the case of a cylindrical heater, but even when the heater is a rectangular parallelepiped or an elliptical cylinder, the average of each side in the case of a rectangular parallelepiped, the long axis and the short axis in the case of an elliptical cylinder If the average is h, almost the same result can be obtained. In addition, when the length from the material installation position inside the furnace body to the lower part of the heater is b, it is desirable that b / h is in the same range as a / h. When used in a system using magnetic repulsion with a permanent magnet, the external magnetic field applied to the superconductor is about 0.3 T. Therefore, if the area having a holding magnetic flux density capacity of 0.3 T or more is large, the system becomes large.・ High efficiency can be achieved.
[0024]
In addition, Pt may be mixed from a platinum crucible or the like when performing a process for producing a raw material mixture for forming a superconductor, but this is included in a range of 0.05 to 5 wt%. It has been confirmed that the 211 phase becomes fine and exhibits high characteristics. Further, it has been confirmed that even when a metal or compound powder of Pt, Pd, Ru, Rh, Ir, Os, Re, and Ce is added in a range of 0.05 to 5 wt%, high characteristics are similarly exhibited.
[0025]
Further, when Ag is finely dispersed in the crystal, microcracks are reduced and magnetic properties, mechanical strength, and water resistance are improved. In this case, the effect is low below 1 wt%, and if it exceeds 60 wt%, the superconducting current hardly flows and the characteristics are deteriorated. Also, the melting process is performed at a relatively low oxygen concentration of 10 ^-3 ~ 2x10 ^-1 %, The amount of mutual substitution with the RE element is optimized, that is, the general formula RE _{1 + P} Ba _{2 + q} Cu _Three O _7-x In the crystal phase represented by the formula, p and q are in the range of −0.2 to 0.2, and the critical current density characteristics under a high magnetic field are improved.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
In this example, the height of the upper heater of the melt crystallizer is a, the inner diameter is h, and the cross-sectional area is S. _h The diameter of the disc-shaped raw material mixture is R, and the surface area is S _R Where a / h = 1.25, R / h = 0.45, S _R / S _{h =} = 0.20, the temperature of 0.2 ° C./cm toward the outside (in the direction away from the reference point) so that the center of the compact of the raw material mixture (the point where the seed crystal contacts; the reference point) is on the low temperature side This is an example of manufacturing a large Y-based oxide superconductor crystal by applying a gradient.
[0027]
Y ₂ O _Three , BaCO _Three , CuO raw powders were weighed so that Y: Ba: Cu = 18: 24: 34, and then BaCO. _Three BaCuO by firing only CuO at 880 ° C. for 30 hours ₂ And CuO calcined powder was obtained (in terms of molar ratio BaCuO ₂ : CuO = 24: 10). Y pre-weighed with this calcined powder ₂ O _Three Furthermore, 0.5 wt% Pt powder is added to the whole and mixed, and then fired again at 880 ° C., YBa ₂ Cu _Three O _x Phase and Y ₂ BaCuO _Five A mixed powder of the phase and Pt was obtained, and then pulverized to an average particle size of about 10 μm. Next, this calcined powder is 0.7 ton / cm using a mold in a disk shape with a diameter of 180 mm and a thickness of 30 mm. ² Uniaxially press-molded with 2 ton / cm ² A molded product was produced by applying CIP and applying CIP.
[0028]
Next, the molded body of the raw material mixture is melt crystallized by a melt crystallizer. FIG. 1 is a diagram showing a schematic configuration of a melt crystallization apparatus. In FIG. 1, the melt crystallization apparatus includes a cylindrical upper heater 1 and a lower heater 2. Winding type heater wires 11 and 21 are embedded in the upper heater 1 and the lower heater 2, respectively. Further, the upper portion of the upper heater is closed by the upper lid 12, and the lower portion of the lower heater 2 is closed by the bottom lid 22. A seed crystal insertion hole 13 is provided in the upper lid 12, and a detachable lid body 14 is provided in the insertion hole 13. At the boundary between the upper heater 1 and the lower heater 2, a support plate 3 for placing a raw material mixture compact 30 is provided.
[0029]
Here, as a pre-test, the temperature distribution applied to the molded body 30 was measured by inserting thermocouples into the molded body at the center and from the center to the outside at 30 mm intervals as shown in FIG. The compact was placed on the support plate 3 on an alumina substrate and placed in the center of the heater. In FIG. 1, the inner diameter h of the heater is 40 cm, and the heights a and b of the upper heater 1 and the lower heater 2 are both 50 cm. Note that a furnace body in which two heaters are held up and down as described above is generally called a two-zone heater. A thermocouple was installed at the center of each of the upper and lower co-cylindrical heaters at 15 cm above and 15 cm below from the material installation position, and was used to control the upper and lower heaters. Next, it heated so that the temperature of an upper and lower thermocouple might be set to 1000 degreeC. At this time, the temperature of the thermocouple installed on the molded body had a temperature gradient of 1000 ° C., 1000.5 ° C., and 1001.1 ° C. from the center to the outside and about 0.2 ° C./cm from the center to the outside.
[0030]
Next, a molded body with no other thermocouple inserted is placed near the center of the same shaped furnace body, and the furnace body is heated so that the temperature of the upper and lower heaters 1 and 2 is both 1100 ° C. and held for 20 minutes. Thus, the molded body was made into a semi-molten state. Thereafter, the temperature of the upper heater was lowered to 1010 ° C. and the lower heater was lowered to 1050 ° C. in 30 minutes, and a temperature gradient of about 2 ° C./cm was applied above and below the compact. Next, Y prepared in advance by the melting method _1.8 (Ba _0.75 Sr _0.25 ) _2.4 Cu _3.4 O _x The seed crystal of the composition is brought into contact with the upper center of the molded body 30 so that the growth direction is parallel to the c-axis. Then, the temperature of the upper heater 1 was lowered to 1000 ° C. and the lower heater 2 to 1040 ° C. at a rate of 0.5 ° C./hr, and the temperature was maintained for 500 hours, and crystal growth in the radial direction from the seed crystal was advanced. Then, crystallization was performed by lowering the temperature of the upper heater 1 to 930 ° C. and the lower heater 2 to 970 ° C. in 70 hours and then gradually cooling to room temperature over 100 hours.
[0031]
The produced sample was disk-shaped with a diameter of 150 mm and a thickness of 25 mm due to shrinkage. The crystallized sample is placed in a furnace capable of gas replacement. First, with a rotary pump 13.3Pa After evacuating the inside of the furnace, oxygen gas is flowed into an oxygen atmosphere at atmospheric pressure with an oxygen partial pressure of 95% or more. Then, while flowing oxygen gas at a flow rate of 0.5 L / min, the temperature was raised from room temperature to 450 ° C. over 10 hours, gradually cooled from 450 ° C. to 250 ° C. over 200 hours, and from 250 ° C. to room temperature. A superconductor material was manufactured by lowering the temperature in 10 hours.
[0032]
The obtained material was cut and the cross section was observed with a scanning electron microscope. ₂ Cu _Three O _7-x Y of about 0.1-30 μm in the phase (123 phase) ₂ BaCuO _Five The phase (211 phase) was finely dispersed. In addition, the back reflection Laue method was used to measure 3 points near the center at 5mm intervals, 4 points around the edge of the material by 90 degrees, and 3 points at 5mm intervals. The orientation deviation between the three points in each part is less than 1 ° below the measurement error range, and the orientation deviation between each part is less than 5 °. ² A substantially single crystalline material was obtained over
[0033]
A single crystal grain of about 2.8 × 2.8 × 2 mm (thickness in the c-axis direction is 2 mm) was cut out from this material, and the critical current density was measured to find 1.5 × 10 in a magnetic field of 1 [T]. ^Four A / cm ² Met.
[0034]
Next, while applying an external magnetic field of 0.5 T to this superconductor, it was cooled from room temperature to a temperature of 77 K, and then the magnetic field was removed to measure the magnetic flux density trapped in the superconductor. In the measurement, the Hall element was attached to the XY stage, moved along the superconductor surface at a distance of about 0.1 mm from the superconductor surface, and the magnetic flux density distribution in the axial direction of the disk-shaped material was measured. As shown in FIG. ² A trapped magnetic flux density of 0.3 T or more was obtained over a wide range.
[0035]
Furthermore, magnetic repulsive force with each superconductor by autograph using Nd-Fe-B magnet (maximum surface magnetic flux density 0.53T) of diameter 39.2mm, inner diameter 16mm, thickness 49mm attached to the tip of load cell. Was measured. First, the magnet is placed 300 mm away from the superconductor so that the axial direction of the ring magnet and the axial direction of the disk-shaped superconductor substantially coincide. After the superconductor is immersed in liquid nitrogen and cooled to a temperature of 77K, the magnet is moved close to the superconductor along the axial direction at a speed of 5 mm / min. The magnets were brought close to each other until the distance between the superconductor and the magnet became 0.1 mm, and the repulsive force generated at this time was measured. A high value of 18 kg · f was obtained when the distance between the superconductor and the magnet was 0.1 mm.
[0036]
(Example 2)
In this example, the height of the upper heater of the melt crystallizer is a, the inner diameter is h, and the cross-sectional area is S. _h The diameter of the disc-shaped raw material mixture is R, and the surface area is S _R Where a / h = 1.25, R / h = 0.38, S _R / S _{h =} = 0.15, 0.2 ° C / cm toward the outside (in the direction away from the reference point) so that the center of the compact of the raw material mixture (the point where the seed crystal contacts; the reference point) is on the low temperature side This is an example of manufacturing a large Sm-based oxide superconductor crystal by applying a gradient.
[0037]
Sm ₂ O _Three , BaCO _Three , CuO raw powders were weighed so that Sm: Ba: Cu = 18: 24: 34, and then BaCO _Three BaCuO by firing only CuO at 880 ° C. for 30 hours ₂ And CuO calcined powder was obtained (in terms of molar ratio BaCuO ₂ : CuO = 24: 10). Sm previously weighed with this calcined powder ₂ O _Three Further, 0.5 wt% Pt powder and 10 wt% Ag powder are added to the whole, mixed and fired again at 880 ° C. to obtain SmBa. ₂ Cu _Three Ox phase and Sm ₂ BaCuO _Five A mixed powder of phase, Pt, and Ag was pulverized to an average particle size of about 10 μm. Next, this calcined powder is 0.7 ton / cm using a die in a disk shape with a diameter of 115 mm and a thickness of 30 mm. ² Uniaxially press-molded with 2 ton / cm ² A molded body was produced by applying CIP under the pressure of.
[0038]
Next, the molded body of the raw material mixture is melt crystallized by a melt crystallizer. Here, as a pre-test, the temperature distribution applied to the molded body 30 was measured by inserting thermocouples into the molded body at intervals of 20 mm from the center and from the center to the outside as shown in FIG. The molded body was placed at the center on the support plate 3 made of an alumina substrate. In FIG. 1, the inner diameter h of the heater is 30 cm, and the heights a and b of the upper heater 1 and the lower heater 2 are both 37.5 cm. A thermocouple was installed in the center of the upper and lower cylindrical heaters at a position 15 cm above and 15 cm below the material installation position, and each was used to control the upper and lower heaters. Next, it heated so that the temperature of an upper and lower thermocouple might be set to 1000 degreeC. At this time, the temperature of the thermocouple installed in the compact had a temperature gradient of 1000 ° C., 1000.4 ° C., and 1000.8 ° C. from the center to the outside and about 0.2 ° C./cm from the center to the outside.
[0039]
Next, a molded body into which another thermocouple was not inserted was placed in the vicinity of the center of the same-shaped furnace body placed in a container capable of atmosphere replacement. A rotary pump in the furnace 13.3Pa After exhausting to 0 ₂ A mixed gas of 1% and Ar 99% was poured into the atmospheric pressure. Thereafter, the following process was performed while flowing the same mixed gas. The furnace body was heated so that the temperature of the upper and lower heaters was both 1100 ° C. and held for 20 minutes to bring the molded body into a semi-molten state. Then, a temperature gradient of about 2 ° C./cm was applied above and below the molded body.
[0040]
Next, Sm containing no silver prepared in advance by a melting method _1.8 Ba _2.4 Cu _3.4 O _x The seed crystal of the composition is brought into contact with the upper part of the compact so that the growth direction is parallel to the c-axis. Thereafter, the temperature of the upper heater was lowered to 970 ° C. and the lower heater to 1010 ° C. at a rate of 0.5 ° C./hr, and the temperature was maintained for 150 hours. Thereafter, crystallization was performed by lowering the temperature of the upper heater to 900 ° C. and the lower heater to 940 ° C. in 70 hours, and then gradually cooling to room temperature over 100 hours.
[0041]
The produced sample was disk-shaped with a diameter of 100 mm and a thickness of 25 mm due to shrinkage. The crystallized sample is placed in a furnace capable of gas replacement. First, with a rotary pump 13.3Pa After evacuating the inside of the furnace, oxygen gas is flowed into an oxygen atmosphere at atmospheric pressure with an oxygen partial pressure of 95% or more. Then, while flowing oxygen gas at a flow rate of 0.5 L / min, the temperature was raised from room temperature to 450 ° C. over 10 hours, gradually cooled from 450 ° C. to 250 ° C. over 200 hours, and from 250 ° C. to room temperature. A superconductor material was manufactured by lowering the temperature in 10 hours.
[0042]
The obtained material was cut and the cross section was observed with a scanning electron microscope. _{1 + p} Ba _{2 + q} Cu _Three O _7-x Sm of about 0.1-30μm in the phase _{2 + r} Ba _{1 + s} CuO _Five The phase was finely dispersed. Here, p, q, r, and s mainly existed phases having values of -0.2 to 0.2, respectively. In addition, the back reflection Laue method was used to measure 3 points near the center at 5mm intervals and 4 points at the same 5mm intervals by shifting the vicinity of the material edge by 90 degrees. The misalignment between the three points in each part is 1 ° or less below the measurement error range, and the misalignment between the parts is 3 ° or less. ² A substantially single crystalline material was obtained over
[0043]
A single crystal grain of about 2.8 x 2.8 x 2 mm (c-axis direction thickness: 2 mm) was cut out from this material, and the critical current density was measured to find 2.0 x 10 in a magnetic field of 1 [T]. ^Four A / cm ² Met.
[0044]
Next, while applying an external magnetic field of 0.5 T to this superconductor, it was cooled from room temperature to a temperature of 77 K, and then the magnetic field was removed to measure the magnetic flux density trapped in the superconductor. In the measurement, the Hall element was attached to the XY stage and moved along the superconductor surface at a distance of about 0.1 mm from the superconductor surface, and the magnetic flux density distribution in the axial direction of the disk-shaped material was measured. As shown in FIG. ² A trapped magnetic flux density of 0.3 T or more was obtained over a wide range.
[0045]
Furthermore, magnetic repulsive force with each superconductor by autograph using Nd-Fe-B magnet (surface maximum magnetic flux density 0.53T) of diameter 39.2mm, inner diameter 16mm, thickness 49mm attached to the tip of load cell. Was measured. First, the magnet is placed 300 mm away from the superconductor so that the axial direction of the ring magnet and the axial direction of the disk-shaped superconductor substantially coincide. After the superconductor is immersed in liquid nitrogen and cooled to a temperature of 77K, the magnet is moved close to the superconductor along the axial direction at a speed of 5 mm / min. The magnets were brought close to each other until the distance between the superconductor and the magnet became 0.1 mm, and the repulsive force generated at this time was measured. A high value of 18 kg · f was obtained when the distance between the superconductor and the magnet was 0.1 mm.
[0046]
(Example 3)
In this example, the height of the upper heater of the melt crystallizer is a, the inner diameter is h, and the cross-sectional area is S. _h The diameter of the disc-shaped raw material mixture is R, and the surface area is S _R Where a / h = 1.25, R / h = 0.38, S _R / S _{h =} = 0.15, 0.2 ° C / cm toward the outside (in the direction away from the reference point) so that the center of the compact of the raw material mixture (the point where the seed crystal contacts; the reference point) is on the low temperature side This is an example of manufacturing a large Nd-based oxide superconductor crystal by applying a gradient.
[0047]
Nd ₂ O _Three , BaCO _Three , CuO raw powders were weighed so that Nd: Ba: Cu = 16: 23: 33, then BaCO _Three BaCuO by firing only CuO at 880 ° C. for 30 hours ₂ And CuO calcined powder was obtained (in terms of molar ratio BaCuO ₂ : CuO = 23: 10). This calcined powder and Nd weighed in advance ₂ O _Three Furthermore, 0.5 wt% Pt powder and 20 wt% Ag powder are added to the whole, mixed, fired again at 880 ° C., and NdBa2 Cu3 Ox phase and Nd _Four Ba ₂ Cu ₂ O _Ten A mixed powder of phase, Pt, and Ag was pulverized to an average particle size of about 10 μm. Next, this calcined powder is formed into a disk shape with a diameter of 115 mm and a thickness of 30 mm using a mold to 0.7 ton / cm ² Uniaxially press-molded with 2 ton / cm ² A molded body was produced by applying CIP under the pressure of.
[0048]
Next, the molded body of the raw material mixture is melt crystallized by a melt crystallizer. In this embodiment, as shown in FIG. 6, a so-called three-zone heater in which a similar heater 2a is added below the lower heater 2 of the melt crystallization apparatus in Embodiments 1 and 2, as shown in FIG. . The inner diameter of the heater is the same as in Examples 1 and 2. The height (cylinder length) of each heater is 375 mm. The support plate 3 on which the raw material mixture compact was placed was provided at the boundary between the two upper heaters.
[0049]
Here, as a pre-test, the temperature distribution applied to the molded body 30 was measured by inserting thermocouples into the molded body at intervals of 20 mm from the center and from the center to the outside as shown in FIG. The molded body was placed at the center on the support plate 3 made of an alumina substrate. A thermocouple was installed at the center of the upper and lower cylindrical heaters at a position 15 cm above and 15 cm below the material installation position, and each was used to control the upper and lower heaters. Next, it heated so that the temperature of an upper and lower thermocouple might be set to 1000 degreeC. At this time, the temperature of the thermocouple installed in the compact had a temperature gradient of 1000 ° C., 1000.4 ° C., and 1000.8 ° C. from the center to the outside and about 0.2 ° C./cm from the center to the outside.
[0050]
Next, a molded body into which another thermocouple was not inserted was placed in the vicinity of the center of the furnace body of the same shape placed in a container capable of atmosphere replacement. A rotary pump in the furnace 13.3Pa After exhausting to 0 ₂ A mixed gas of 1% and Ar 99% was poured into the atmospheric pressure. Thereafter, the following process was performed while flowing the same mixed gas. The furnace body was heated so that the temperature of the upper and lower heaters was both 1100 ° C. and held for 20 minutes to bring the molded body into a semi-molten state. A temperature gradient of about 2 ° C./cm was applied above and below the molded body.
[0051]
Next, Nd that does not contain silver prepared in advance by a melting method _1.8 Ba _2.4 Cu _3.4 O _x The seed crystal of the composition is brought into contact with the upper part of the compact so that the growth direction is parallel to the c-axis. Thereafter, the temperature of the upper heater was lowered to 980 ° C. and the lower heater to 1020 ° C. at a rate of 0.5 ° C./hr, and the temperature was maintained for 150 hours to proceed crystal growth from the seed crystal in the radial direction. Thereafter, crystallization was performed by lowering the temperature of the upper heater to 910 ° C. and the lower heater to 950 ° C. in 70 hours and then gradually cooling to room temperature over 100 hours. The prepared sample was disc-shaped with a diameter of 100 mm and a thickness of 25 mm due to shrinkage. The crystallized sample is placed in a furnace capable of gas replacement.
[0052]
First, with a rotary pump 13.3Pa After evacuating the inside of the furnace, oxygen gas is flowed into an oxygen atmosphere at atmospheric pressure with an oxygen partial pressure of 95% or more. Thereafter, while flowing oxygen gas at a flow rate of 0.5 L / min, the temperature was raised from room temperature to 700 ° C. in 10 hours, held for 80 hours, then lowered to 450 ° C. in 100 hours, and from 450 ° C. to 250 ° C. The superconductor material was manufactured by gradually cooling to 200 hours until the temperature was lowered from 250 ° C. to room temperature in 10 hours.
[0053]
When the obtained material was cut and the cross section was observed with a scanning electron microscope, the obtained material was cut and the cross section was observed with a scanning electron microscope. _{1 + p} Ba _{2 + q} Cu _Three O _7-x Nd of about 0.1-30 μm in the phase _{4 + r} Ba _{2 + s} CuO _Five The phase was finely dispersed. Here, p, q, r, and s mainly existed phases having values of -0.2 to 0.2, respectively. In addition, the back reflection Laue method was used to measure three points near the center at 5mm intervals and three points near the edge of the material by 90 degrees, and three points at the same 5mm intervals. The misalignment between the three points in each part is 1 ° or less below the measurement error range, and the misalignment between the parts is 3 ° or less. ² A substantially single crystalline material was obtained over
[0054]
A single crystal grain of about 2.8 x 2.8 x 2mm (c-axis direction thickness 2mm) was cut out from this material, and the critical current density was measured to find 1.9 x 10 in a magnetic field of 1 [T]. ^Four A / cm ² Met.
[0055]
Furthermore, magnetic repulsive force with each superconductor by autograph using Nd-Fe-B magnet (maximum surface magnetic flux density 0.53T) of diameter 39.2mm, inner diameter 16mm, thickness 49mm attached to the tip of load cell. Was measured. First, the magnet is placed 300 mm away from the superconductor so that the axial direction of the ring magnet and the axial direction of the disk-shaped superconductor substantially coincide. After the superconductor is immersed in liquid nitrogen and cooled to a temperature of 77K, the magnet is moved close to the superconductor along the axial direction at a speed of 5 mm / min. The magnets were brought close to each other until the distance between the superconductor and the magnet became 0.1 mm, and the repulsive force generated at this time was measured. A magnetic repulsion force of 17 kg · f was obtained when the distance between the superconductor and the magnet was 0.1 mm.
[0056]
(Comparative Example 1)
In this comparative example, the height of the upper heater of the melt crystallizer is a, the inner diameter is h, and the cross-sectional area is S. _h The diameter of the disc-shaped raw material mixture is R, and the surface area is S _R Where a / h = 1.0, R / h = 0.72, S _R / S _h = 0.52 at a temperature of 0.5 ° C / cm toward the outside (in the direction away from the reference point) so that the center of the compact of the raw material mixture (the point where the seed crystal contacts; the reference point) is on the low temperature side This is an example of manufacturing a large Y-based oxide superconductor crystal by applying a gradient.
[0057]
Y ₂ O _Three , BaCO _Three After weighing each raw material powder of CuO so that Y: Ba: Cu = 18: 24: 34, BaCO _Three BaCuO by firing only CuO at 880 ° C. for 30 hours ₂ And CuO calcined powder was obtained (in terms of molar ratio BaCuO ₂ : CuO = 24: 10). Y pre-weighed with this calcined powder ₂ O _Three Then add 0.5 wt% Pt powder to the whole, mix and baked again at 880 ° C. ₂ Cu _Three O _x Phase and Y ₂ BaCuO _Five A mixed powder of phase and Pt was formed and then pulverized to an average particle size of about 10 μm. Next, this calcined powder is 0.7 ton / cm by using a mold in a disk shape with a diameter of 180 mm and a thickness of 30 mm. ² The compact was then uniaxially press-molded and CIP was performed by applying a pressure of 2 ton / cm 2 to produce a compact.
[0058]
Here, as a pre-test, the temperature distribution applied to the molded body was measured by inserting thermocouples into the molded body at the center and from the center to the outside at 30 mm intervals as shown in FIG. This molded body was placed on an alumina substrate and installed in the approximate center of the furnace body of a two-zone heater having a heater inner diameter h of 25 cm and a height a of 25 cm shown in FIG. A thermocouple was installed at the center of the upper and lower cylindrical heaters at a position 15 cm above and 15 cm below the material installation position, and each was used to control the upper and lower heaters. Next, it heated so that the temperature of an upper and lower thermocouple might be set to 1000 degreeC. At this time, the temperature of the thermocouple installed in the molded body had a temperature gradient of 1000 ° C., 1001.5 ° C., and 1003.1 ° C. from the center to the outside and about 0.5 ° C./cm 2 from the center to the outside.
[0059]
Next, a molded body without another thermocouple inserted is placed near the center of the furnace body of the same shape, and the furnace body is heated so that the temperature of the upper and lower heaters is both 1100 ° C. and held for 20 minutes. Was in a semi-molten state. Thereafter, the temperature of the upper heater was lowered to 1010 ° C. and the lower heater to 1050 ° C. in 30 minutes, and a temperature gradient of about 2 ° C./cm 2 was added to the top and bottom of the compact.
[0060]
Next, Y prepared in advance by the melting method _1.8 (Ba _0.75 Sr _0.25 ) _2.4 Cu _3.4 O _x The seed crystal of the composition is brought into contact with the upper part of the compact so that the growth direction is parallel to the c-axis. From there, the temperature of the upper heater was lowered to 1000 ° C. and the lower heater to 1040 ° C. at a rate of 0.5 ° C./hr. Thereafter, crystallization was performed by lowering the temperature of the upper heater to 930 ° C. and the lower heater to 970 ° C. in 70 hours and then gradually cooling to room temperature over 100 hours. The prepared sample was disk-shaped with a diameter of 150 mm and a thickness of 25 mm due to shrinkage.
[0061]
The crystallized sample is placed in a furnace capable of gas replacement. First, with a rotary pump 13.3Pa After evacuating the inside of the furnace, oxygen gas is flowed into an oxygen atmosphere at atmospheric pressure with an oxygen partial pressure of 95% or more. After that, while flowing oxygen gas at a flow rate of 0.5 L / min, the temperature was raised from room temperature to 450 ° C. over 10 hours, gradually cooled from 450 ° C. to 250 ° C. over 200 hours, and from 250 ° C. to room temperature. A superconductor material was manufactured by lowering the temperature in 10 hours.
[0062]
The obtained material was cut and the cross section was observed with a scanning electron microscope. ₂ Cu _Three O _7-x Y of about 0.1-30 μm in the phase (123 phase) ₂ BaCuO _Five The phase (211 relative) was finely dispersed. In addition, the back reflection Laue method was used to measure three points near the center at 5mm intervals and four points at the same distance from the end of the material by 90 degrees, and three points at the same 5mm intervals. The orientation misalignment between the three points was 1 ° or less, which is less than the measurement error range, but the crystal growth stopped midway, so that the nucleation of different orientations occurred near the edge of the material. Occurred, and a misalignment between the portions was a polycrystal having a degree of about 10 ° to 40 °.
[0063]
A single crystal grain of about 2.8 x 2.8 x 2mm (thickness in the c-axis direction is 2mm) was cut out from this material, and the critical current density was measured to find 1.0 x 10 in a magnetic field of 1 [T]. ^Four A / cm ² Met.
[0064]
Next, the superconductor was cooled from room temperature to a temperature of 77K while applying an external magnetic field of 0.5T, and then the magnetic flux was removed and the magnetic flux density trapped in the superconductor was measured. The measurement was performed by attaching the Hall element to the XY stage and moving it along the superconductor surface at a distance of about 0.1 mm from the superconductor surface, and measuring the magnetic flux density distribution in the axial direction of the disk-shaped material, as shown in FIG. Magnetic flux leakage occurred from different parts of the magnetic field, and there was no part having a trapped magnetic flux density capability of 0.3 T or more.
[0065]
Furthermore, magnetic repulsive force with each superconductor by autograph using Nd-Fe-B magnet (maximum surface magnetic flux density 0.53T) of diameter 39.2mm, inner diameter 16mm, thickness 49mm attached to the tip of load cell. Was measured. First, the magnet is placed 300 mm away from the superconductor so that the axial direction of the ring magnet and the axial direction of the disk-shaped superconductor substantially coincide. After the superconductor is immersed in liquid nitrogen and cooled to a temperature of 77K, the magnet is moved close to the superconductor along the axial direction at a speed of 5 mm / min. The magnets were brought close to each other until the distance between the superconductor and the magnet became 0.1 mm, and the repulsive force generated at this time was measured. The magnetic repulsion force was as low as 12 kg · f when the distance between the superconductor and the magnet was 0.1 mm.
[0066]
(Comparative Example 2)
In this comparative example, the height of the upper heater of the melt crystallizer is a, the inner diameter is h, and the cross-sectional area is S. _h The diameter of the disc-shaped raw material mixture is R, and the surface area is S _R Where a / h = 0.33, R / h = 0.6, S _R / S _h = 0.36, the temperature of 1.0 ° C./cm toward the outside (in the direction away from the reference point) so that the center of the compact of the raw material mixture (the point where the seed crystal contacts; the reference point) is on the low temperature side This is an example of manufacturing a large Y-based oxide superconductor crystal by applying a gradient.
[0067]
Y ₂ O _Three , BaCO _Three After weighing each raw material powder of CuO so that Y: Ba: Cu = 18: 24: 34, BaCO _Three BaCuO by firing only CuO at 880 ° C. for 30 hours ₂ And CuO calcined powder was obtained (in terms of molar ratio BaCuO ₂ : CuO 24:10). Y pre-weighed with this calcined powder ₂ O _Three Then add 0.5 wt% Pt powder to the whole, mix and baked again at 880 ° C. ₂ Cu _Three O _x Phase and Y ₂ BaCuO _Five A mixed powder of phase and Pt was formed and then pulverized to an average particle size of about 10 μm. Next, this calcined powder is 0.7 ton / cm by using a mold in a disk shape with a diameter of 180 mm and a thickness of 30 mm. ² Uniaxially press-molded with 2 ton / cm ² A molded body was produced by applying CIP under the pressure of.
[0068]
Here, as a pre-test, the temperature distribution applied to the molded body was measured by inserting thermocouples into the molded body at the center and from the center to the outside at 30 mm intervals as shown in FIG. This molded body was placed on an alumina substrate and placed 10 cm below the upper center of the upper heater 1 of the apparatus shown in FIG. At this time, the heater inner diameter h is 30 cm, and the height a is 37.5 cm. A thermocouple was installed in the center of the upper and lower cylindrical heaters at a position 15 cm above and 15 cm below the material installation position, and each was used to control the upper and lower heaters. Next, it heated so that the temperature of an upper and lower thermocouple might be set to 1000 degreeC. At this time, the temperature of the thermocouple installed in the molded body had a temperature gradient of 996 ° C., 998.5 ° C., and 1002 ° C. from the center to the outside and about 1.0 ° C./cm 2 from the center to the outside.
[0069]
Next, a molded body without another thermocouple inserted is installed at the same position in the same shape furnace body, and the furnace body is heated so that the temperature of the upper and lower heaters is both 1100 ° C. and held for 20 minutes. Was in a semi-molten state. Thereafter, the temperature of the upper heater was lowered to 1046 ° C. and the lower heater to 1086 ° C. in 30 minutes, and a temperature gradient of about 2 ° C./cm 2 was added to the top and bottom of the compact. Next, Y prepared in advance by the melting method _1.8 (Ba _0.75 Sr _0.25 ) _2.4 Cu _3.4 O _x The seed crystal of the composition is brought into contact with the upper part of the compact so that the growth direction is parallel to the c-axis.
[0070]
From there, the temperature of the upper heater was lowered to 1036 ° C. and the lower heater to 1076 ° C. at a rate of 0.5 ° C./hr. Thereafter, the temperature of the upper heater was decreased to 966 ° C. and the lower heater to 1006 ° C. in 70 hours, and then gradually cooled to room temperature over 100 hours for crystallization. The produced sample was disk-shaped with a diameter of 150 mm and a thickness of 25 mm due to shrinkage.
[0071]
The crystallized sample is placed in a furnace capable of gas replacement. First, with a rotary pump 13.3Pa After evacuating the inside of the furnace, oxygen gas is flowed into an oxygen atmosphere at atmospheric pressure with an oxygen partial pressure of 95% or more. Then, while flowing oxygen gas at a flow rate of 0.5 L / min, the temperature was raised from room temperature to 450 ° C. over 10 hours, gradually cooled from 450 ° C. to 250 ° C. over 200 hours, and from 250 ° C. to room temperature. A superconductor material was manufactured by lowering the temperature in 10 hours.
[0072]
The obtained material was cut and the cross section was observed with a scanning electron microscope. ₂ Cu _Three O _7-x Y of 0.1-30μm in the phase ₂ BaCuO _Five The phase was finely dispersed. In addition, when the back reflection Laue method was used to measure 3 points near the center at 5mm intervals and 4 points at the same distance from the end of the material by 90 °, 4 points were measured at the same 5mm intervals. Reflecting the crystal, all the parts were oriented along the c-axis, and the misalignment between the three points was 1 ° or less, which is less than the measurement error range. The deviation was about 10 ° to 40 °, and it was a polycrystal.
[0073]
A single crystal grain of about 2.8 x 2.8 x 2mm (c-axis thickness is 2mm) was cut out from this material, and the critical current density was measured to find 0.9 x 10 in a magnetic field of 1 [T]. ^Four A / cm ² Met.
[0074]
Next, while applying an external magnetic field of 0.5 T to this superconductor, it was cooled from room temperature to a temperature of 77 K, and then the magnetic field was removed to measure the magnetic flux density trapped in the superconductor. The measurement was performed by attaching the Hall element to the XY stage and moving it along the superconductor surface at a distance of about 0.1 mm from the superconductor surface, and measuring the axial magnetic flux density distribution of the disk-shaped material. Magnetic flux leaks from different parts of the part. ² It was a sparse degree.
[0075]
Furthermore, magnetic repulsive force with each superconductor by autograph using Nd-Fe-B magnet (maximum surface magnetic flux density 0.53T) of diameter 39.2mm, inner diameter 16mm, thickness 49mm attached to the tip of load cell. Was measured. First, the magnet is placed 300 mm away from the superconductor so that the axial direction of the ring magnet and the axial direction of the disk-shaped superconductor substantially coincide. After the superconductor is immersed in liquid nitrogen and cooled to a temperature of 77K, the magnet is moved close to the superconductor along the axial direction at a speed of 5 mm / min. The magnets were brought close to each other until the distance between the superconductor and the magnet became 0.1 mm, and the repulsive force generated at this time was measured. The magnetic repulsion force was 11 kg · f when the distance between the superconductor and the magnet was 0.1 mm.
[0076]
【The invention's effect】
As described in detail above, the present invention is such that the height of the upper heater of the melt crystallization apparatus is a, the inner diameter is h, and the cross-sectional area is S. _h The diameter of the disc-shaped raw material mixture is R, and the surface area is S _R If 0.5 ≦ a / h, R / h ≦ 0.7, S _R / S _h ≦ 0.49 Any one or more condition of 0.49 is satisfied, and the outer side (the direction away from the reference point) is such that the center (the point where the seed crystal comes into contact; the reference point) of the molded body of the raw material mixture becomes the low temperature side ) To form a large RE-Ba-Cu-O-based oxide superconducting bulk material with a uniform crystal orientation. It is possible to get.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a melt crystallization apparatus according to an embodiment of the present invention.
FIG. 2 is a result of calculating a relationship between a shape of a heater and radiation of the melt crystallizer of FIG. 1;
FIG. 3 is a diagram showing a technique for measuring a temperature distribution inside a molded body of a raw material mixture.
4 is a diagram showing the trapped magnetic flux density capability of the oxide superconducting bulk material manufactured in Example 1. FIG.
5 is a diagram showing the trapped magnetic flux density capability of the oxide superconducting bulk material manufactured in Example 2. FIG.
6 is a diagram showing a schematic configuration of a melt crystallization apparatus used in Example 3. FIG.
7 is a diagram showing the trapped magnetic flux density capability of the oxide superconducting bulk material manufactured in Comparative Example 1. FIG.
FIG. 8 is a diagram showing a trapped magnetic flux density capability of an oxide superconducting bulk material manufactured in a comparative example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Upper heater, 2 ... Lower heater, 3 ... Support plate, 11, 21 ... Heater wire, 12 ... Top cover, 13 ... Seed crystal insertion hole, 14 ... Cover body, 22 ... Bottom cover, 30 ... Molding of raw material mixture body.

Claims (8)

  Molten crystals in a temperature range higher than the melting point of the raw material mixture are formed into a molded body of the raw material mixture containing an RE compound (RE is one or more rare earth metal elements including Y), a Ba compound and a Cu compound. In the method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material by performing a treatment including a crystallization step to produce a RE-Ba-Cu-O-based oxide superconducting bulk material, the melt crystallization step includes the step of A temperature gradient of 0.01 to 0.4 ° C./cm is formed in a direction away from the reference point that should be the starting point of crystallization in the molded body of the raw material mixture so that the temperature increases as the distance from the reference point increases. A process for producing a RE-Ba-Cu-O-based oxide superconducting bulk material, characterized in that   Molten crystals in a temperature range higher than the melting point of the raw material mixture are formed into a molded body of the raw material mixture containing an RE compound (RE is one or more rare earth metal elements including Y), a Ba compound and a Cu compound. In the method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material by performing a process including a crystallization step to produce a RE-Ba-Cu-O-based oxide superconducting bulk material, the melt crystallization step is performed using a cylinder. The raw material mixture molded body is disposed in a heater having a shape, an elliptical cylinder shape, a rectangular parallelepiped shape, or the like, and the heater is vertically moved from the position where the raw material mixture is disposed. It has an extended part, of which the heater height is the height from the position where the raw material mixture of the upper heater extended at least at the top is located, and the heater diameter is h (elliptical) In the case of a rectangular parallelepiped, the average of the two sides in the vertical and horizontal directions is h), and melt crystallization is performed so that 0.5 ≦ a / h. A method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material.   The RE compound (RE is one or more rare earth metal elements including Y), the raw material mixture containing the Ba compound and the Cu compound is melted in a temperature range at least higher than the melting point of the raw material mixture. In the method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material by performing a treatment including a crystallization step to produce a RE-Ba-Cu-O-based oxide superconducting bulk material, the melt crystallization step includes: The raw material mixture molded body is placed in a cylindrical, elliptical cylinder, rectangular parallelepiped or similar shape heater, and the heater is moved up and down from the position where the raw material mixture is placed. The raw material mixture molded body has a disk shape, an elliptical plate shape, a cylindrical shape, a rectangular parallelepiped shape or a shape similar to these, and the raw material mixture Molded body The diameter (average of long and short axes in the case of an ellipse, average of two vertical and horizontal sides in the case of a rectangular parallelepiped) is R, and the heater diameter (the average of the long and short axes in the case of an ellipse, vertical and horizontal in the case of a rectangular parallelepiped) A method for producing an oxide superconducting bulk material, wherein melt crystallization is performed such that R / h ≦ 0.7, where h is an average of two sides. The RE compound (RE is one or more rare earth metal elements including Y), the raw material mixture containing the Ba compound and the Cu compound is melted in a temperature range at least higher than the melting point of the raw material mixture. In the method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material by performing a treatment including a crystallization step to produce a RE-Ba-Cu-O-based oxide superconducting bulk material, the melt crystallization step includes: The raw material mixture molded body is placed in a cylindrical, elliptical cylinder, rectangular parallelepiped or similar shape heater, and the heater is moved up and down from the position where the raw material mixture is placed. The raw material mixture molded body has a disk shape, an elliptical plate shape, a cylindrical shape, a rectangular parallelepiped shape, or a shape similar to these. The composition The area of the cut surface when cut in a plane parallel to the placement surface of the body and S _R, the area of the cut surface when cut in a plane parallel to the placement surface of the molded article molded body of the material mixture S _h In this case, melt crystallization is performed so that S _R / S _h ≦ 0.49. A method for producing an oxide superconducting bulk material. The method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material according to any one of claims 1 to 4 , wherein the raw material mixture is further added to Pt, Pd, Ru, Rh, Ir, Os, Re, A RE-Ba-Cu-O system characterized by adding 0.05 to 5 wt% (in the case of a compound, the element weight of only the metal) of one or two or more of these metals. Manufacturing method of oxide superconducting bulk material. The method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material according to any one of claims 1 to 5 , further comprising 1 to 60 wt% of Ag metal or compound in the raw material mixture (in the case of a compound). A method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material, characterized in that it is added (indicated by the element weight of Ag only). The manufacturing method of claims 1 to RE over Ba over Cu over O-based oxide superconducting bulk material according to any of 6, the melt crystallization process, the oxygen partial pressure ¹⁰ -3 ^~2 × ^{10 -1%} A method for producing a RE-Ba-Cu-O-based oxide superconducting bulk material, characterized in that melt crystallization is performed in the above range.   The RE compound (RE is one or more rare earth metal elements including Y), the raw material mixture containing the Ba compound and the Cu compound is melted in a temperature range at least higher than the melting point of the raw material mixture. In a RE-Ba-Cu-O-based oxide superconducting bulk material manufacturing apparatus for manufacturing a RE-Ba-Cu-O-based oxide superconducting bulk material by performing a treatment including a crystallization step, the melt crystallization step includes: The raw material mixture molded body is placed in a cylindrical, elliptical cylinder, rectangular parallelepiped or similar shape heater, and the heater is moved up and down from the position where the raw material mixture is placed. The height of the heater, which is the height from the position where the raw material mixture of the upper heater extended at least in the upper part is arranged, is a, and the heater diameter is h (elliptical). In the case of (3), the average of the long axis and the short axis, and in the case of a rectangular parallelepiped, the average of the two vertical and horizontal sides is h), and melt crystallization is performed so that 0.5 ≦ a / h. An apparatus for producing a RE-Ba-Cu-O-based oxide superconducting bulk material.

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