JP3683395B2 - Calcinated powder and polycrystal for Bi-based high-temperature superconductor - Google Patents
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Description
【０００１】
【発明の属する技術分野】
この出願の発明は、Ｂｉ系高温相超電導体用の仮焼粉とこの仮焼粉より得られる高Ｊｃ高温相超電導体多結晶体に関するものである。
【０００２】
【従来の技術とその課題】
Ｂｉ系酸化物高温超電導体については、Ｔｃ（臨界温度）が１００Ｋレベルの高温相結晶体と、８０Ｋレベルの低温相結晶体があることが知られており、前者の高温相結晶体は、その成分組成が（Ｂｉ，Ｐｂ）2 Ｓｒ2 Ｃａ2 Ｃｕ3 Ｏx として標準化して表わされる２２２３相の結晶からなり、一方、低温相結晶体は、Ｂｉ2 Ｓｒ2 Ｃａ1 Ｃｕ2 Ｏx として標準化して表わされる２２１２相の結晶からなることが明らかにされている。
【０００３】
これらＢｉ系超電導体のうち、前者の高温２２２３相超電導体については、線材化が難しく、Ｊｃ（臨界電流密度）が低いという問題点を解消すべく、その実用化について精力的に検討が進められており、たとえばこれまでにも、短い試料ではあるが、Ａｇシース法により、Ｊｃ≧６０，０００Ａ／ｃｍ2 の特性を有するものが実現されたと報告されている。
【０００４】
しかしながら、大きな期待にもかかわらず、２２２３高温相超電導体のＪｃは、一般的な焼結法では一桁低い１，０００〜２，５００Ａ／ｃｍ2 レベルにとどまっているのが現状であり、この点についての抜本的で大幅な特性改善が望まれているところである。
このような問題の解決には、製造工程の改善がなによりも考慮され、焼結のための原料粉の扱いも見直されるべきと考えられる。実際、たとえば、「粉体及び粉末冶金」３５（１９８８）、Ｐ１０２０、または「粉体及び粉末冶金」３９（１９９２）、Ｐ３７８には、原料粉を焼結して超電導焼結体を製造するさいに、中間圧縮工程を挿入するとＣ軸配向組織の形成と高密度化により臨界電流密度が大きく向上すると報告されている。また、焼結に適用する原料粉（仮焼粉）の状態を示す評価手段として、ＸＲＤ図、ＴＧ−ＤＴＡ図を用いることは一般的に行われている。例えば、Jpn. J.Appl.Phys.,２８（１９８９），Ｌ２１９６には、酸素分圧や、示差熱分析の昇温速度によってＤＴＡ吸熱曲線の形状が変化することが報告されている。
【０００５】
しかし、焼結に適用する原料粉（仮焼粉）の状態が超電導焼結体の臨界電流密度に及ぼす影響については報告例は少なく、充分に解析されていない。
そこで、この出願の発明は、以上のとおりの従来技術の限界を克服し、焼結に適用する原料粉（仮焼粉）に着目することで、Ｂｉ系酸化物高温相超電導体のＪｃ（臨界電流密度）を大幅に向上させるための新しい技術的手段を提供することを課題としている。
【０００６】
【課題を解決するための手段】
この出願の発明は、上記の課題を解決するものとして、焼結法に適用するためのＢｉ系酸化物高温２２２３相超電導体の焼結体用仮焼粉であって、全体組成は焼結体と実質的に同一であり、かつ、大気中、最高温度７２０〜８００℃で仮焼されていて、結晶形態は主成分のＢｉ−２２１２相結晶に超伝導相以外の不純物酸化物相あるいはＢｉ−２２０１相が取り込まれることなく均一に分散し、ＤＴＡ吸熱ピークとして、８６０〜８７５℃に頂点を持つ低温側吸熱ピークと、８７５〜８９０℃に頂点を持つ高温側吸熱ピークとが表われることを特徴とするＢｉ系高温相超電導体用の仮焼粉（請求項１）と、焼結法に適用するためのＢｉ系酸化物高温２２２３相超電導体の焼結体用仮焼粉であって、全体組成は焼結体と実質的に同一であり、かつ、大気中、最高温度８００〜８４０℃で仮焼されていて、結晶形態はＢｉ−２２１２相結晶あるいはＢｉ−２２２３相結晶に超伝導相以外の不純物酸化物相が均一に取り込まれて分散し、ＤＴＡ吸熱ピークとして、８７５〜８９０℃に頂点を持つ吸熱ピークのみが表われることを特徴とするＢｉ系高温相超電導体用の仮焼粉（請求項２）を提供する。また、この出願の発明は、上記の仮焼粉について、成分組成が次式（１）
【０００７】
【化３】
（式中の元素数は次の値を示す。
１．２０≦ａ≦２．５０
０≦ｂ≦０．８０
１．２０≦ｃ≦３．００
１．２０≦ｄ≦３．００
９．００≦ｘ≦１０．００）
で表わされるＢｉ系酸化物高温相超電導体の焼結体製造用の仮焼粉であって、全体組成は前記式（１）と実質的に同一であり、かつ、次式（２）
【０００９】
【化４】
（式中の元素数は次の値を示す。
１．５０≦ａ≦２．５０
０≦ｂ≦０．０５
１．５０≦ｃ≦２．５０
０．５０≦ｄ≦１．５０
７．００≦ｘ≦８．００）
で表わされる成分組成の結晶とそれ以外のＢｉ，Ｐｂ，Ｓｒ，ＣａおよびＣｕの元素の１種以上のものの酸化物とを含有することを特徴とするＢｉ系高温相超電導体用の仮焼粉（請求項３）をも提供する。
【００１１】
そして、さらにこの出願の発明は、以上の仮焼粉が焼結されてなるＢｉ系酸化物高温相超電導体の多結晶体であって、Ｊｃ（臨界電流密度）≧９０００Ａ／ｃｍ2 の特性を有することを特徴とするＢｉ系高温相超電導体の多結晶体（請求項４）も提供する。
【００１２】
【発明の実施の形態】
この出願の発明は、上記のとおりの特徴を持つものであるが、発明者による詳細な検討の結果導かれた新しい知見に基づいて完成されている。
発明は、この知見に留意することにより様々な形態として実施することができる。
【００１３】
すなわち、まず、一般に焼結法によるＢｉ系２２２３相焼結体は、多結晶体であるがために結晶粒界が多く存在し、粒界間の弱結合により超電導電流が阻害され臨界電流密度（Ｊｃ）が最大で２，５００Ａ／ｃｍ2 程度しか得られていなかったが、同じ多結晶体でありながら、Ａｇシース線材ではＪｃ数万Ａ／ｃｍ2 以上得られている。このことから、粒界の性状を改善する事により多結晶体であっても現状の値から大きく改善することができると考えられることから、発明者は、焼結する前の段階における仮焼粉に着目し、様々な要因を検討している。
【００１４】
仮焼粉の一般的製造プロセスは、たとえば図１に示すことができ、また、多結晶体の製造プロセスは、たとえば図２に示すことができるが、高Ｊｃが得られる多結晶体とするには、仮焼粉を大気中で焼結する際にＢｉ系２２２３相が成長しやすく、粒界間に不純物が出来るだけ存在しないような、仮焼の段階での適切な結晶形態とその割合があると考えられる。また、Ｂｉ系２２２３相はＢｉ−２２１２相とＣａ2ＰｂＯ4，ＣｕＯなどの超電導相以外の酸化物が反応して成長することが知られている。そこで理想的な仮焼粉は、Ｂｉ−２２１２相結晶にＣａ2ＰｂＯ4，ＣｕＯなどの超電導相以外の不純物酸化物相あるいはＢｉ−２２０１相が均一に分散されていることが望ましいことがわかる。
【００１５】
このような超電導相と不純物相あるいはＢｉ−２２０１相の分散状態を熱分析のＴＧ−ＤＴＡ（熱重量−示差熱分析装置）を用いることで判断できることが見出されている。たとえば、高温相の結晶と実質的に同じ成分組成に原料を調整し、最高温度７００℃で仮焼すると２２０１相の結晶ができ、さらに温度を上昇して７２０℃〜８００℃の最高温度で仮焼するとＢｉ−２２１２相結晶とＣａ2 ＰｂＯ4 ，ＣｕＯなどの超電導相以外の不純物相とＢｉ−２２０１相となる。粉砕を行い、再度同条件で仮焼することにより主成分のＢｉ−２２１２相結晶にＣａ2 ＰｂＯ4 ，ＣｕＯなどの超電導相以外の不純物相あるいはＢｉ−２２０１相が取り込まれることなく均一に分散している状態となる。そのとき所定の条件で測定すると図３▲１▼のＤＴＡ曲線となる。この曲線の特徴は８６０℃〜８７５℃に頂点を持つ低温側吸熱ピークと８７５℃〜８９０℃に頂点を持つ高温側吸熱ピークの２つの吸熱ピークを持つことにある。
【００１６】
また、最高温度８００℃にて仮焼し、粉砕を行い再度同条件で仮焼すると、やはりＢｉ−２２１２相結晶とＣａ2 ＰｂＯ4 ，ＣｕＯなどの超電導相以外の不純物相あるいはＢｉ−２２０１相の結晶形態であるが、その主成分のＢｉ−２２１２相結晶にＣａ2 ＰｂＯ4 ，ＣｕＯなどの超電導相以外の不純物相が一部取り込まれて分散している状態となる。そのとき所定の条件で図３▲２▼のＤＴＡ曲線となる。この曲線の特徴は、前述の８６０℃〜８７５℃に頂点を持つ低温側吸熱ピークが高温側にシフトし、その曲線が前述の８７５℃〜８９０℃に頂点を持つ高温側吸熱曲線と一部重なっていることにある。
【００１７】
最高温度８００℃〜８４０℃にて仮焼すると、Ｂｉ−２２１２相結晶とＣａ2 ＰｂＯ4 ，ＣｕＯなどの超電導相以外の不純物相の結晶、Ｂｉ−２２２３相の結晶の混相状態となるが、そのＢｉ−２２１２相結晶、あるいはＢｉ−２２２３相の結晶にＣａ2 ＰｂＯ4 ，ＣｕＯなどの超電導相以外の不純物相が均一に取り込まれて分散している状態となる。そのとき所定の条件で図３▲３▼のＤＴＡ曲線となる。この曲線の特徴は、前述の低温側吸熱ピークが無くなり、８７５℃〜８９０℃に頂点を持つ一つの吸熱ピークのみということにある。
【００１８】
最高温度８４０℃〜融点以下にて仮焼するとＢｉ−２２１２相結晶とＣａ2 ＰｂＯ4 ，ＣｕＯなどの超電導相以外の不純物相の結晶、Ｂｉ−２２２３相の結晶の混相状態となるが、Ｂｉ−２２２３相が主成分となる。そのため多結晶焼結体を作成時に高温相が成長するところは少なく、結果的にＢｉ−２２２３相になりきらない部分が残り、高Ｊｃが得られなくなる。そのときのＤＴＡ曲線は、所定の測定条件で、図３▲３▼となる。この曲線の特徴は、前述の低温側吸熱ピークが無くなり、８７５℃〜８９０℃に頂点を持つ一つの吸熱ピークのみということにある。
【００１９】
そして、以上の仮焼粉の組成構成、結晶の混晶状態、並びにＤＴＡ吸熱ピークとＪｃ（臨界電流密度）との対応関係からは、Ｂｉ系２２２３相多結晶体で高い臨界電流密度を得るには、焼結する前の段階における仮焼粉がＢｉ系２２２３相の結晶と実質的に同じ成分組成を有し、Ｂｉ−２２１２相の結晶が主成分となり、Ｂｉ，Ｐｂ，Ｓｒ，ＣａまたはＣｕの１種以上の酸化物から実質的になるものであり、主成分のＢｉ−２２１２相の結晶に取り込まれることなくその他の酸化物が均一に分散しているためＤＴＡの吸熱ピークが所定の測定条件で図３▲１▼の特徴を持つものであればよいことがわかる。また、その仮焼条件は、最高温度７２０℃〜８００℃望ましくは７４０℃〜７８０℃であり、さらにその焼成時間は固相反応の開始に最低必要な０．１時間以上であればよいが、あまり長いと外部からのコンタミネーションが懸念されるため、最長でも３００時間とするが、望ましくは１時間〜１００時間である。
【００２０】
あるいは、仮焼粉は、Ｂｉ−２２１２相の結晶が主成分となり、Ｂｉ，Ｐｂ，Ｓｒ，ＣａまたはＣｕの１種以上の酸化物から実質的になるものであり、主成分のＢｉ−２２１２相の結晶にその他の酸化物が均一に取り込まれているためＤＴＡの吸熱ピークが所定の測定条件で図３▲３▼の特徴を持つものであればよいことがわかる。また、その仮焼条件が最高温度８００℃〜８４０℃望ましくは８０５℃〜８３０℃であり、さらにその焼成時間は上記と同様の理由により０．１時間〜３００時間望ましくは１時間〜１００時間である。
【００２１】
そこで、この出願の発明の仮焼粉では、前記のとおり、ＤＴＡ吸熱ピークとして、８６０〜８７５℃に頂点を持つ低温側吸熱ピークと８７５〜８９０℃に頂点を持つ高温側吸熱ピークとが表われるもので、特に、最高温度７２０〜８００℃、望ましくは７４０〜７８０℃で、上記と同様の理由により０．１〜３００時間、望ましくは１〜１００時間仮焼されてなるものであること、あるいは、ＤＴＡ吸熱ピークとして、８７５〜８９０℃のみに頂点を持つ吸熱ピークが表われるもので、特に、最高温度８００〜８４０℃、望ましくは８０５〜８３０℃で、上記と同様の理由により０．１〜３００時間、望ましくは１〜１００時間仮焼されてなるものであることを特徴としている。
【００２２】
また、この発明の仮焼粉は、成分組成が式（１）で表わされるＢｉ系酸化物高温相超電導体の焼結体製造用の仮焼粉であって、全体組成は前記式（１）と実質的に同一であり、式（２）で表わされる成分組成の結晶とそれ以外のＢｉ，Ｐｂ，Ｓｒ，ＣａおよびＣｕの元素の１種以上のものの酸化物とを含有することを適当としている。
【００２３】
式（１）（２）における元素数は、各々Ｃｕを３および２として標準化した時のものである。そしてこの元素数の上下限の範囲は、高温相超電導体の焼結体としての多結晶体を得るために望ましいものである。
なお、前記の「実質的に同一」との規定は、不可避的要因（不純物の混入等）を除いて同一であることを意味している。
【００２４】
仮焼粉の製造プロセスについては、図１のような一般的なものとして適宜に考慮される。また、この発明のＪｃ≧９０００Ａ／ｃｍ2 の特性の多結晶体の製造も図２のような一般的なものとして適宜に考慮される。
また、前記のＤＴＡ吸熱ピークについても、その測定は通常の手法によるものとして考慮される。
【００２５】
以下、実施例を示し、さらに詳しくこの発明の実施の形態について例示説明する。もちろん、この発明は以下の例により何ら限定されることはない。
【００２６】
【実施例】
以下の実施例においては次の諸条件が共通して採用されている。
ＴＧ−ＤＴＡ（熱重量−示差熱分析）装置は、マックサイエンス製２０００型を用いた。
測定条件は、７００℃〜９２０℃で２℃／ｍｉｎの昇温速度、試料充填量は内容積０．１ｃｃのアルミナ容器に２０ｍｇ、乾燥Ａｉｒ雰囲気で行った。
【００２７】
１軸成形条件としては、１．０〜５．０Ｔｏｎ／ｃｍ2 のプレス成形を行った。
中間圧縮はＣＩＰ装置を用い１〜３Ｔｏｎ／ｃｍ2 の圧力をかけ、必要に応じて数回行った。
焼結条件は、温度８２０〜８６０℃、雰囲気は大気である。
【００２８】
Ｊｃ測定にあたっては、上記プロセスにて得られた多結晶体を短冊状に切り出し、電極を作成して測定用試料とした。この試料を４端子通電法にてＪｃを測定した。
実施例１
所要の原料を、酸化物組成がＢｉ1.85Ｐｂ0.35Ｓｒ1.90Ｃａ2.05Ｃｕ3.05ＯX となるように調整し、圧粉体を形成してこれを仮焼した。
【００２９】
仮焼は乾燥空気中７６０℃で１０時間行った。粉砕は極性有機溶媒と非極性有機溶媒５：１００（重量比）の混合液を溶媒に用いて、Ｚｒボールを使用しての湿式粉砕により行った。粉砕は、平均粒子径が２．０μｍ以下になるまで行った。粉砕後の乾燥は減圧乾燥法で密閉系で行い大気中の水分やカーボンが吸着しないようにした。再び仮焼を乾燥空気中７６０℃で１０時間行い仮焼粉を得た。平均粒径は２．５μｍ以下であり、ＸＲＤにて確認したところＢｉ−２２１２相Ｂｉ−２２０１相及びＣａ2 ＰｂＯ4 ，ＣｕＯなどの超電導相以外の不純物相からなっていた。また、ＴＧ−ＤＴＡ測定を行ったところ、８６５℃と８８３℃の頂点を持つ吸熱ピークが確認された。この時の仮焼粉の炭素含有量は１８０ｐｐｍであった。この仮焼粉を用いて、前記焼結条件に沿って、以下の条件で焼結体を作製した。
【００３０】
プレス成型：直径２０φｍｍ、厚さ１ｍｍの円盤状圧粉体に３．０Ｔｏｎ／ｃｍ2
焼結：８５０℃＊５０時間（大気中）
中間圧縮：ＣＩＰ法で３．０Ｔｏｎ／ｃｍ2
こうして得られた試料を短冊状に切り出し、Ａｇ電極を作製し、４端子通電法により７７Ｋで臨界電流密度Ｊｃを測定したところ、１０，５００Ａ／ｃｍ2 の値が得られた。
実施例２
実施例１において仮焼粉作製時に仮焼温度を８２０℃とした以外は、同様な方法でＪｃ測定用試料を作製した。ＸＲＤにて確認したところ仮焼粉はＢｉ−２２２３相、Ｂｉ−２２１２相及びＣａ2 ＰｂＯ4 ，ＣｕＯなどの超電導相以外の不純物相からなっており、Ｂｉ−２２２３相の割合は５％であった。ＴＧ−ＤＴＡ測定を行ったところ、８８３℃の頂点を持つ吸熱ピークが確認された。この時の仮焼粉の炭素含有量は１６０ｐｐｍであった。この試料のＪｃは、９，０００Ａ／ｃｍ2 の値を示した。
実施例３
実施例１において得られた仮焼粉を銀シースに充填し外径が約２ｍｍになるまで線引きを行った。その後電気炉にて簡単な熱処理を行い、テープ厚が０．２ｍｍ程度になるまで圧延を行い、その後８４０℃前後で２５〜１００時間焼成を行う。この圧延と焼成を数回繰り返し試料を作製した。こうして得られた試料のＪｃは、２０，０００Ａ／ｃｍ2 の値を示した。
実施例４
実施例１において作製した仮焼粉と同じ条件で作製した仮焼粉を、有機溶剤及び有機バインダーにより合成した有機ビヒクルと重量比３：１でそれぞれ混合し、三本ロールにより均一分散させ、超電導ペーストを得た。このペーストを用い、スクリーン印刷法により銀基板上に膜厚５０μｍのペースト厚膜を作製し、８５０℃×５０時間の熱処理を行って試料を作製した。この試料のＪｃは、１１，２００Ａ／ｃｍ2 の値を示した。
比較例１
実施例１において仮焼粉作製時に仮焼温度を８００℃とした以外は、同様な方法でＪｃ測定用試料を作製した。Ｂｉ−２２１２相及びＣａ2 ＰｂＯ4 ，ＣｕＯなどの超電導相以外の不純物相からなっており、またＴＧ−ＤＴＡ測定を行ったところ、８７５℃と８８５℃に頂点を持つ吸熱ピークが確認された。この時の仮焼粉の炭素含有量は１９０ｐｐｍであった。この試料のＪｃは、５，０００Ａ／ｃｍ2 の値を示した。
比較例２
実施例１において仮焼粉作製時に仮焼温度を７００℃とした以外は、同様な方法でＪｃ測定用試料を作製した。Ｂｉ−２２０１相・Ｂｉ−２１２２相及びＣａ2 ＰｂＯ4 ，ＣｕＯなどの超電導相以外の不純物相からなっていて、その主成分は、Ｂｉ−２２０１相であった。また、ＴＧ−ＤＴＡ測定を行ったところ、８３０〜８９０℃に４つの吸熱ピークが確認された。この時の仮焼粉の炭素含有量は３８０ｐｐｍであった。この試料のＪｃは、１，５００Ａ／ｃｍ2 の値を示した。
比較例３
実施例１において仮焼粉作製時に仮焼温度を８５０℃とした以外は、同様な方法でＪｃ測定用試料を作製した。Ｂｉ−２２２３相、Ｂｉ−２２１２相及びＣａ2 ＰｂＯ4 ，ＣｕＯなどの超電導相以外の不純物相からなっていて、その主成分は、Ｂｉ−２２２３相であり、割合は９０％であった。また、ＴＧ−ＤＴＡ測定を行ったところ、８８４℃にのみ吸熱ピークが確認された。この時の仮焼粉の炭素含有量は１８０ｐｐｍであった。この試料のＪｃは、１，０００Ａ／ｃｍ2 の値を示した。
比較例４
比較例１で得られた仮焼粉を用い、焼結時の焼結温度を８３０℃とした以外は、実施例１と同じ手法で焼結体を作製した。この試料のＪｃを測定したところ、８００Ａ／ｃｍ2 の値しか得られなかった。
比較例５
比較例３で得られた仮焼粉を用いた以外は、実施例３と同一条件にて銀テープを作製した。この試料のＪｃを測定したところ、８，５００Ａ／ｃｍ2 の値しか得られなかった。
比較例６
比較例３で得られた仮焼粉を用いた以外は、実施例４と同一条件にてペースト厚膜を作製した。この試料のＪｃを測定したところ、４，３００Ａ／ｃｍ2 の値しか得られなかった。
【００３１】
【発明の効果】
以上詳しく説明したとおり、この出願の発明により、Ａｇシース等の手段を採用することなしに、焼結によって、Ｊｃ（臨界電流密度）の高いＢｉ系高温相超電導体が提供されることになる。
【図面の簡単な説明】
【図１】仮焼粉の製造プロセスを示した工程図である。
【図２】焼結多結晶体の製造プロセスを示した工程図である。
【図３】ＤＴＡ吸熱ピークを示した図である。[0001]
BACKGROUND OF THE INVENTION
The invention of this application relates to a calcined powder for a Bi-based high-temperature phase superconductor and a high Jc high-temperature phase superconductor polycrystal obtained from the calcined powder.
[0002]
[Prior art and its problems]
Regarding Bi-based oxide high-temperature superconductors, it is known that there are high-temperature phase crystals with a Tc (critical temperature) of 100K level and low-temperature phase crystals with an 80K level. The composition is composed of 2223 phase crystals expressed as standardized as (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O x , while the low-temperature phase crystal is standardized as Bi 2 Sr 2 Ca 1 Cu 2 O x . It is clarified that it consists of 2212-phase crystals expressed as follows.
[0003]
Among these Bi-based superconductors, the former high-temperature 2223-phase superconductor is vigorously studied for practical use in order to solve the problems that it is difficult to make a wire and the Jc (critical current density) is low. For example, it has been reported so far that a sample having a characteristic of Jc ≧ 60,000 A / cm 2 has been realized by the Ag sheath method although it is a short sample.
[0004]
However, in spite of high expectations, the Jc of the 2223 high-temperature superconductor remains at the 1,000 to 2,500 A / cm 2 level, which is an order of magnitude lower in the general sintering method. A drastic and drastic improvement in characteristics is desired.
In order to solve such problems, it is considered that the improvement of the manufacturing process is taken into consideration, and the handling of the raw material powder for sintering should be reviewed. Actually, for example, in “Powder and Powder Metallurgy” 35 (1988), P1020, or “Powder and Powder Metallurgy” 39 (1992), P378, raw powder is sintered to produce a superconducting sintered body. In addition, it is reported that the insertion of an intermediate compression step greatly improves the critical current density due to the formation and densification of the C-axis oriented structure. Moreover, using an XRD figure and a TG-DTA figure as an evaluation means which shows the state of the raw material powder (calcined powder) applied to sintering is generally performed. For example, Jpn. J. Appl. Phys., 28 (1989), L2196 reports that the shape of the DTA endothermic curve changes depending on the oxygen partial pressure and the temperature increase rate of differential thermal analysis.
[0005]
However, there are few reports on the influence of the state of the raw material powder (calcined powder) applied to the sintering on the critical current density of the superconducting sintered body, and it has not been fully analyzed.
Therefore, the invention of this application overcomes the limitations of the prior art as described above, and focuses on the raw material powder (calcined powder) applied to sintering, so that the Jc (criticality) of Bi-based oxide high-temperature phase superconductor can be obtained. It is an object to provide a new technical means for greatly improving current density.
[0006]
[Means for Solving the Problems]
The invention of this application is a calcined powder for a sintered body of a Bi-based oxide high-temperature 2223 phase superconductor to be applied to a sintering method in order to solve the above-mentioned problems, and the overall composition is a sintered body And is calcined at a maximum temperature of 720 to 800 ° C. in the atmosphere , and the crystal form is an impurity oxide phase other than the superconducting phase or Bi− The 2201 phase is uniformly dispersed without being taken in , and as a DTA endothermic peak, a low temperature side endothermic peak having a peak at 860 to 875 ° C. and a high temperature side endothermic peak having a peak at 875 to 890 ° C. appear. A calcined powder for a Bi-based high-temperature phase superconductor (Claim 1) and a calcined powder for a sintered body of a Bi-based oxide high-temperature 2223-phase superconductor for application to a sintering method, the composition is substantially identical to the sintered body, or , In the air, it has been calcined at a maximum temperature of from 800 to 840 ° C., the crystalline form impurities oxide phases other than the superconducting phase is dispersed is incorporated uniformly into Bi-2212 phase crystal or Bi-2223 phase crystal, Only the endothermic peak having an apex at 875 to 890 ° C. appears as a DTA endothermic peak. In addition, the invention of this application is such that the component composition of the calcined powder is the following formula (1)
[0007]
[Chemical 3]
(The number of elements in the formula shows the following values.
1.20 ≦ a ≦ 2.50
0 ≦ b ≦ 0.80
1.20 ≦ c ≦ 3.00
1.20 ≦ d ≦ 3.00
9.00 ≦ x ≦ 10.00)
A calcined powder for producing a sintered body of a Bi-based oxide high-temperature phase superconductor represented by the following formula, wherein the overall composition is substantially the same as the above formula (1), and the following formula (2)
[0009]
[Formula 4]
(The number of elements in the formula shows the following values.
1.50 ≦ a ≦ 2.50
0 ≦ b ≦ 0.05
1.50 ≦ c ≦ 2.50
0.50 ≦ d ≦ 1.50
7.00 ≦ x ≦ 8.00)
And a calcined powder for a Bi-based high-temperature superconductor, characterized in that it contains a crystal having a component composition represented by formula (II) and an oxide of one or more other elements of Bi, Pb, Sr, Ca and Cu. (Claim 3 ) is also provided.
[0011]
Further, the invention of this application is a polycrystalline body of a Bi-based oxide high-temperature phase superconductor obtained by sintering the above calcined powder, and has a characteristic of Jc (critical current density) ≧ 9000 A / cm 2 . The present invention also provides a polycrystalline body of a Bi-based high-temperature phase superconductor (claim 4 ).
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The invention of this application has the characteristics as described above, but has been completed based on new findings derived as a result of detailed examination by the inventors.
The invention can be implemented in various forms by paying attention to this finding.
[0013]
That is, first, in general Bi-based 2223 phase sintered body by sintering method, polycrystal is the crystal grain boundaries often exist for critical current density superconducting current is inhibited by the weak coupling between the grain boundary ( Jc) was only obtained at a maximum of about 2,500 A / cm 2 , but the Ag sheath wire has a Jc of several tens of thousands A / cm 2 even though it is the same polycrystal . From this, it is considered that even if it is a polycrystalline body by improving the properties of the grain boundary, it can be greatly improved from the current value. We are studying various factors.
[0014]
The general manufacturing process of the calcined powder can be shown, for example, in FIG. 1, and the manufacturing process of the polycrystalline body can be shown, for example, in FIG. When the calcined powder is sintered in the air , the Bi-based 2223 phase is likely to grow, and the appropriate crystal form and the ratio at the calcining stage are such that impurities are not present between the grain boundaries as much as possible. It is believed that there is. Further, it is known that the Bi-based 2223 phase grows by the reaction of the Bi-2212 phase and oxides other than the superconducting phase such as Ca 2 PbO 4 and CuO. Therefore, it can be seen that an ideal calcined powder desirably has an impurity oxide phase other than a superconducting phase such as Ca 2 PbO 4 or CuO or a Bi-2201 phase uniformly dispersed in a Bi-2212 phase crystal.
[0015]
It has been found that the dispersion state of such a superconducting phase and impurity phase or Bi-2201 phase can be judged by using a thermal analysis TG-DTA (thermogravimetric-differential thermal analyzer). For example, if the raw material is adjusted to a composition substantially the same as that of a high-temperature phase crystal and calcined at a maximum temperature of 700 ° C., a 2201 phase crystal is formed, and the temperature is further increased to a temporary temperature of 720 ° C. to 800 ° C. When baked, Bi-2212 phase crystals and impurity phases other than the superconducting phase, such as Ca 2 PbO 4 and CuO, and Bi-2201 phases are formed. By pulverizing and calcining again under the same conditions, the main component Bi-2212 phase crystal is uniformly dispersed without incorporating an impurity phase other than the superconducting phase such as Ca 2 PbO 4 , CuO or the Bi-2201 phase. It will be in the state. At that time, when measured under predetermined conditions, the DTA curve shown in FIG. The characteristic of this curve is that it has two endothermic peaks, a low temperature side endothermic peak having a peak at 860 ° C. to 875 ° C. and a high temperature side endothermic peak having a peak at 875 ° C. to 890 ° C.
[0016]
In addition, when calcined at the maximum temperature of 800 ° C., pulverized and calcined again under the same conditions, an impurity phase other than the superconducting phase such as Bi-2212 phase crystal and Ca 2 PbO 4 , CuO or Bi-2201 phase Although it is in a crystal form, a part of the impurity phase other than the superconducting phase such as Ca 2 PbO 4 or CuO is taken in and dispersed in the Bi-2212 phase crystal as its main component. At that time, the DTA curve shown in FIG. The characteristic of this curve is that the low temperature side endothermic peak having the peak at 860 ° C. to 875 ° C. shifts to the high temperature side, and the curve partially overlaps with the high temperature side endothermic curve having the peak at 875 ° C. to 890 ° C. There is in being.
[0017]
When calcined at a maximum temperature of 800 ° C. to 840 ° C., a Bi-2212 phase crystal, a crystal of an impurity phase other than a superconducting phase such as Ca 2 PbO 4 , CuO, and a Bi-2223 phase crystal are mixed. Impurity phases other than the superconducting phase such as Ca 2 PbO 4 and CuO are uniformly taken in and dispersed in the Bi-2212 phase crystal or Bi-2223 phase crystal. At that time, the DTA curve shown in FIG. The characteristic of this curve is that the above-mentioned low-temperature side endothermic peak disappears and only one endothermic peak having a peak at 875 ° C. to 890 ° C. is present.
[0018]
When calcined at a maximum temperature of 840 ° C. to a melting point or lower, a Bi-2212 phase crystal, a crystal of an impurity phase other than a superconducting phase such as Ca 2 PbO 4 , CuO, and a Bi-2223 phase crystal are mixed, but Bi− The 2223 phase is the main component. For this reason, there are few places where the high-temperature phase grows at the time of producing the polycrystalline sintered body, and as a result, a portion that cannot be the Bi-2223 phase remains, and high Jc cannot be obtained. The DTA curve at that time is as shown in FIG. The characteristic of this curve is that the above-mentioned low-temperature side endothermic peak disappears and only one endothermic peak having a peak at 875 ° C. to 890 ° C. is present.
[0019]
From the above-mentioned composition of the calcined powder, the mixed crystal state of the crystal, and the correspondence between the DTA endothermic peak and Jc (critical current density), a Bi 2223 phase polycrystal has a high critical current density. In the pre-sintering stage, the calcined powder has substantially the same composition as the Bi-based 2223 phase crystal, the Bi-2212 phase crystal is the main component, and Bi, Pb, Sr, Ca or Cu. The DTA endothermic peak is a predetermined measurement because the other oxides are uniformly dispersed without being incorporated into the main component Bi-2212 phase crystal. It can be seen that any condition having the characteristics shown in FIG. The calcining conditions are a maximum temperature of 720 ° C. to 800 ° C., preferably 740 ° C. to 780 ° C., and the firing time may be at least 0.1 hour required for the start of the solid phase reaction, If it is too long, there is a concern about contamination from the outside, so the maximum is 300 hours, but it is preferably 1 to 100 hours.
[0020]
Alternatively, the calcined powder is mainly composed of a Bi-2212 phase crystal, and is substantially composed of one or more oxides of Bi, Pb, Sr, Ca, or Cu. Since other oxides are uniformly incorporated into the crystal, it can be understood that the endothermic peak of DTA only needs to have the characteristics shown in FIG. Further, the calcining conditions are a maximum temperature of 800 ° C. to 840 ° C., preferably 805 ° C. to 830 ° C., and the firing time is 0.1 to 300 hours, preferably 1 to 100 hours for the same reason as described above. is there.
[0021]
Therefore, in the calcined powder of the invention of this application, as described above, as the DTA endothermic peak, a low temperature side endothermic peak having a peak at 860 to 875 ° C. and a high temperature side endothermic peak having a peak at 875 to 890 ° C. appear. In particular, the maximum temperature is 720 to 800 ° C., preferably 740 to 780 ° C., and is calcined for 0.1 to 300 hours, preferably 1 to 100 hours, for the same reason as above, or , An endothermic peak having an apex only at 875-890 ° C. appears as the DTA endothermic peak, particularly at a maximum temperature of 800-840 ° C., preferably 805-830 ° C. It is characterized by being calcined for 300 hours, preferably 1 to 100 hours.
[0022]
The calcined powder of the present invention is a calcined powder for producing a sintered body of a Bi-based oxide high-temperature phase superconductor whose component composition is represented by the formula (1), and the overall composition is the formula (1). And containing a crystal having a component composition represented by the formula (2) and an oxide of one or more other elements of Bi, Pb, Sr, Ca and Cu. Yes.
[0023]
The numbers of elements in the formulas (1) and (2) are those when standardized with Cu of 3 and 2, respectively. The upper and lower limits of the number of elements are desirable for obtaining a polycrystalline body as a sintered body of a high-temperature phase superconductor.
The above-mentioned definition “substantially the same” means that it is the same except for inevitable factors (mixing of impurities, etc.).
[0024]
About the manufacturing process of calcining powder, it considers suitably as a general thing like FIG. In addition, the production of a polycrystal having a characteristic of Jc ≧ 9000 A / cm 2 according to the present invention is appropriately considered as a general one as shown in FIG.
In addition, the measurement of the DTA endothermic peak is considered to be based on a normal method.
[0025]
Hereinafter, examples will be shown, and the embodiments of the present invention will be described in detail. Of course, the present invention is not limited to the following examples.
[0026]
【Example】
In the following embodiments, the following conditions are commonly adopted.
As a TG-DTA (thermogravimetric-differential thermal analysis) apparatus, a 2000 model manufactured by Mac Science was used.
The measurement conditions were 700 ° C. to 920 ° C., a temperature increase rate of 2 ° C./min, and the sample filling amount was 20 mg in an alumina container with an internal volume of 0.1 cc in a dry Air atmosphere.
[0027]
As uniaxial molding conditions, 1.0 to 5.0 Ton / cm 2 of press molding was performed.
Intermediate compression was performed several times as required using a CIP device, applying a pressure of 1 to 3 Ton / cm 2 .
The sintering conditions are a temperature of 820 to 860 ° C., and the atmosphere is air.
[0028]
In the Jc measurement, the polycrystalline body obtained by the above process was cut into a strip shape, and an electrode was prepared as a measurement sample. This sample was measured for Jc by the 4-terminal energization method.
Example 1
The required raw materials were adjusted so that the oxide composition was Bi 1.85 Pb 0.35 Sr 1.90 Ca 2.05 Cu 3.05 O x , a green compact was formed, and this was calcined.
[0029]
The calcination was performed in dry air at 760 ° C. for 10 hours. The pulverization was performed by wet pulverization using Zr balls using a mixed liquid of a polar organic solvent and a nonpolar organic solvent 5: 100 (weight ratio) as a solvent. The pulverization was performed until the average particle size became 2.0 μm or less. Drying after pulverization was performed in a closed system by a reduced pressure drying method so that moisture and carbon in the atmosphere were not adsorbed. Calcination was again performed at 760 ° C. for 10 hours in dry air to obtain a calcined powder. The average particle size was 2.5 μm or less, and as confirmed by XRD, it consisted of impurity phases other than the superconducting phase such as Bi-2212 phase Bi-2201 phase and Ca 2 PbO 4 , CuO. Moreover, when TG-DTA measurement was performed, the endothermic peak which has the peak of 865 degreeC and 883 degreeC was confirmed. The carbon content of the calcined powder at this time was 180 ppm. Using this calcined powder, a sintered body was produced under the following conditions in accordance with the sintering conditions.
[0030]
Press molding: 3.0 Ton / cm 2 on a disk-shaped green compact with a diameter of 20 mm and a thickness of 1 mm
Sintering: 850 ° C. * 50 hours (in air)
Intermediate compression: 3.0 Ton / cm 2 by CIP method
The sample thus obtained was cut into a strip shape, an Ag electrode was prepared, and the critical current density Jc was measured at 77 K by a four-terminal energization method. A value of 10,500 A / cm 2 was obtained.
Example 2
A sample for Jc measurement was produced in the same manner as in Example 1 except that the calcining temperature was set to 820 ° C. when the calcined powder was produced. As confirmed by XRD, the calcined powder is composed of impurity phases other than the superconducting phase such as Bi-2223 phase, Bi-2212 phase and Ca 2 PbO 4 , CuO, and the ratio of Bi-2223 phase is 5%. It was. When TG-DTA measurement was performed, an endothermic peak having an apex of 883 ° C. was confirmed. The carbon content of the calcined powder at this time was 160 ppm. Jc of this sample showed a value of 9,000 A / cm 2 .
Example 3
The calcined powder obtained in Example 1 was filled in a silver sheath and drawn until the outer diameter was about 2 mm. Thereafter, simple heat treatment is performed in an electric furnace, rolling is performed until the tape thickness is about 0.2 mm, and then baking is performed at around 840 ° C. for 25 to 100 hours. This rolling and firing were repeated several times to prepare a sample. The Jc of the sample thus obtained showed a value of 20,000 A / cm 2 .
Example 4
The calcined powder produced under the same conditions as the calcined powder produced in Example 1 was mixed with an organic vehicle synthesized with an organic solvent and an organic binder at a weight ratio of 3: 1 and uniformly dispersed by a three roll, superconductivity A paste was obtained. Using this paste, a paste thick film having a film thickness of 50 μm was produced on a silver substrate by a screen printing method, and a heat treatment was performed at 850 ° C. × 50 hours to produce a sample. Jc of this sample showed a value of 11,200 A / cm 2 .
Comparative Example 1
A sample for Jc measurement was prepared in the same manner as in Example 1 except that the calcining temperature was set to 800 ° C. when the calcined powder was produced. It consists of impurity phases other than the superconducting phase, such as Bi-2212 phase and Ca 2 PbO 4 , CuO. When TG-DTA measurement was performed, endothermic peaks having vertices at 875 ° C. and 885 ° C. were confirmed. The carbon content of the calcined powder at this time was 190 ppm. Jc of this sample showed a value of 5,000 A / cm 2 .
Comparative Example 2
A sample for Jc measurement was prepared in the same manner as in Example 1 except that the calcining temperature was set to 700 ° C. when the calcined powder was produced. It consists of impurity phases other than the superconducting phase such as Bi-2201 phase / Bi-2122 phase and Ca 2 PbO 4 , CuO, and the main component was the Bi-2201 phase. Moreover, when TG-DTA measurement was performed, four endothermic peaks were confirmed at 830 to 890 ° C. The carbon content of the calcined powder at this time was 380 ppm. Jc of this sample showed a value of 1,500 A / cm 2 .
Comparative Example 3
A sample for Jc measurement was produced in the same manner as in Example 1 except that the calcining temperature was set to 850 ° C. when the calcined powder was produced. Bi-2223 phase, consist Bi-2212 phase and Ca 2 PbO 4, impurity phases other than the superconducting phase such as CuO, its main component, a Bi-2223 phase, the proportion was 90%. Moreover, when TG-DTA measurement was performed, the endothermic peak was confirmed only at 884 degreeC. The carbon content of the calcined powder at this time was 180 ppm. Jc of this sample showed a value of 1,000 A / cm 2 .
Comparative Example 4
A sintered body was produced in the same manner as in Example 1 except that the calcined powder obtained in Comparative Example 1 was used and the sintering temperature during sintering was changed to 830 ° C. When Jc of this sample was measured, only a value of 800 A / cm 2 was obtained.
Comparative Example 5
A silver tape was produced under the same conditions as in Example 3 except that the calcined powder obtained in Comparative Example 3 was used. When Jc of this sample was measured, only a value of 8,500 A / cm 2 was obtained.
Comparative Example 6
A paste thick film was produced under the same conditions as in Example 4 except that the calcined powder obtained in Comparative Example 3 was used. When Jc of this sample was measured, only a value of 4,300 A / cm 2 was obtained.
[0031]
【The invention's effect】
As described above in detail, according to the invention of this application, a Bi-based high-temperature phase superconductor having a high Jc (critical current density) is provided by sintering without employing a means such as an Ag sheath.
[Brief description of the drawings]
FIG. 1 is a process diagram showing a process for producing calcined powder.
FIG. 2 is a process diagram showing a manufacturing process of a sintered polycrystalline body.
FIG. 3 is a diagram showing a DTA endothermic peak.
Claims (4)
１．２０≦ａ≦２．５０
０≦ｂ≦０．８０
１．２０≦ｃ≦３．００
１．２０≦ｄ≦３．００
９．００≦ｘ≦１０．００）
で表わされるＢｉ系酸化物高温相超電導体の焼結体製造用の仮焼粉であって、全体組成は前記式（１）と実質的に同一であり、かつ、次式（２）
１．５０≦ａ≦２．５０
０≦ｂ≦０．０５
１．５０≦ｃ≦２．５０
０．５０≦ｄ≦１．５０
７．００≦ｘ≦８．００）
で表わされる成分組成の結晶とそれ以外のＢｉ，Ｐｂ，Ｓｒ，ＣａおよびＣｕの元素の１種以上のものの酸化物とを含有する請求項１または２の仮焼粉。The component composition is the following formula (1)
1.20 ≦ a ≦ 2.50
0 ≦ b ≦ 0.80
1.20 ≦ c ≦ 3.00
1.20 ≦ d ≦ 3.00
9.00 ≦ x ≦ 10.00)
A calcined powder for producing a sintered body of a Bi-based oxide high-temperature phase superconductor represented by the following formula, wherein the overall composition is substantially the same as the above formula (1), and the following formula (2)
1.50 ≦ a ≦ 2.50
0 ≦ b ≦ 0.05
1.50 ≦ c ≦ 2.50
0.50 ≦ d ≦ 1.50
7.00 ≦ x ≦ 8.00)
The calcined powder according to claim 1 or 2, comprising a crystal having a component composition represented by formula (1) and an oxide of at least one of the other elements Bi, Pb, Sr, Ca and Cu.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP30624197A JP3683395B2 (en) | 1997-11-07 | 1997-11-07 | Calcinated powder and polycrystal for Bi-based high-temperature superconductor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP30624197A JP3683395B2 (en) | 1997-11-07 | 1997-11-07 | Calcinated powder and polycrystal for Bi-based high-temperature superconductor |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH11139824A JPH11139824A (en) | 1999-05-25 |
| JP3683395B2 true JP3683395B2 (en) | 2005-08-17 |
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| JP30624197A Expired - Fee Related JP3683395B2 (en) | 1997-11-07 | 1997-11-07 | Calcinated powder and polycrystal for Bi-based high-temperature superconductor |
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| JP (1) | JP3683395B2 (en) |
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|---|---|---|---|---|
| JP2007026773A (en) * | 2005-07-13 | 2007-02-01 | Sumitomo Electric Ind Ltd | Superconducting wire material and manufacturing method thereof |
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