JP4094238B2 - Method for producing acicular crystals of high-temperature superconducting oxide - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、超伝導エレクトロニクス素子を実現するために不可欠な、高温超伝導酸化物の欠陥のほとんどない結晶、すなわち完全結晶に近い針状結晶の製造方法に関するものである。
【０００２】
【従来の技術】
高温超伝導酸化物の単結晶は、導電層と非導電層が交互に積層した結晶構造をもち、各層間が固有ジョセフソン結合している。近年、この固有ジョセフソン効果を用いた単結晶スイッチング素子が提案されている。この新しい単結晶スイッチング素子は、従来のジョセフソン結合よりほぼ１／１００に小型化でき、スイッチング速度も１００倍程度速く、動作周波数はＴＨｚ（テラヘルツ）の高周波が期待されている。また、現在、Ｂｉ2 Ｓｒ2 Ｃａ1 Ｃｕ2 Ｏx （Ｘ：８〜９）針状結晶を用いて作製したサブミクロン結晶素子において、電子対が一個づつ通過する超伝導単電子トンネル現象が起こることが明らかにされている。この現象を起こすには、液体ヘリウム温度（４．２Ｋ）で作動する必要があるが、結晶のユニットセルの積層数を１０００程度にすると、液体窒素温度（７７Ｋ）で作動する超伝導単電子対素子が実現できるものと予想されている。
【０００３】
しかし、これらの素子の実現には、無欠陥もしくは欠陥の極めて少ない単結晶が要求される。現在のところ、針状結晶が最も性能がよく、開発・研究には、主にＢｉ2 Ｓｒ2 Ｃａ1 Ｃｕ2 Ｏx （Ｂｉ２２１２相）針状結晶が使用されている。しかし、現在作製されるＢｉ２２１２相針状結晶は、均一なＢｉ２２１２相の単相ではなく、わずかにＢｉ2 Ｓｒ2 Ｃａ2 Ｃｕ3 Ｏx （Ｂｉ２２２３相）が混在しているため、それが特性に悪い影響を与えている。さらに、超伝導の担い手であるキャリア数を制御できないという問題も抱えている。このような不均一な針状結晶が製造される原因は、その製造の仕方に強く依存している。現在行われている製造方法は、Ａｌを含有した試料を完全に溶融したのち、超急冷して非晶質化し、それを後熱処理して針状結晶を育成するというものである。この完全非晶質化が針状結晶の育成に不可欠である。しかし、その際の仕込み組成がＢｉ２２１２相組成よりもかなり異っており、さらに成長状態は後熱処理中の酸素気流に極めて敏感である。このように限られた条件下でのみ針状結晶の育成が可能であるため、上述のような不均一さが生ずる。
【０００４】
【発明が解決しようとする課題】
上記したように、高温超伝導酸化物Ｂｉ2 Ｓｒ2 Ｃａ1 Ｃｕ2 Ｏx （Ｂｉ２２１２相）の欠陥のない針状結晶の製造方法を確立し、高品位針状結晶を作製することが現在理論的に提案されているが、未だ実現していない。
【０００５】
そこで、Ｂｉ２２１２相の欠陥のない均一な針状結晶の製造方法を提供し、それにより、超伝導エレクトロニクス素子実用化への道を拓くことが望まれている。
【０００６】
本発明は、上記状況に鑑みて、超伝導デバイス素子の実現に不可欠な欠陥の極めて少ない高温超伝導酸化物Ｂｉ2 Ｓｒ2 Ｃａ1 Ｃｕ2 Ｏx の針状結晶の製造方法を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明は、上記目的を達成するために、
〔１〕高温超伝導酸化物の針状結晶の製造方法において、高温超伝導酸化物Ｂｉ2 Ｓｒ2 Ｃａ1 Ｃｕ2 Ｏx （Ｂｉ２２１２相）の針状結晶を育成するために各原料粉末を所定の組成に配合し、その融点を低くする元素を０．１〜１．０モル比組成含有する圧粉成形体を、２０〜１００％酸素雰囲気中、８３０〜９００℃で部分溶融法によって熱処理し、溶融・急冷非晶質化を経ないで、前記圧粉成形体から前記高温超伝導酸化物Ｂｉ 2 Ｓｒ 2 Ｃａ 1 Ｃｕ 2 Ｏ x の針状結晶を育成することを特徴とする。
【０００８】
〔２〕高温超伝導酸化物の針状結晶の製造方法において、高温超伝導酸化物Ｂｉ 2 Ｓｒ 2 Ｃａ 1 Ｃｕ 2 Ｏ x の針状結晶を育成するためにＢｉが１．５〜４．０、Ｓｒが１．５〜３．０、Ｃａが１．０〜４．０、Ｃｕが０．５〜４．０、Ｔｅが０．１〜１．０モル比組成の酸化物の圧粉成形体を２０〜１００％酸素雰囲気中、８３０〜９００℃で部分溶融法によって熱処理し、溶融・急冷非晶質化を経ないで、前記圧粉成形体から高温超伝導酸化物Ｂｉ2 Ｓｒ2 Ｃａ1 Ｃｕ2 Ｏx （Ｂｉ２２１２相）の針状結晶を育成することを特徴とする。
【０００９】
【発明の実施の形態】
以下、本発明の実施の形態について詳細に説明する。
【００１０】
本願発明者は、高温超伝導酸化物Ｂｉ2 Ｓｒ2 Ｃａ1 Ｃｕ2 Ｏx （Ｂｉ２２１２相）の針状結晶を育成するための仕込み組成に、その融点を低くするＴｅ，Ｇｅ，Ｖなどの酸化物を含有させることにより、溶融・急冷非晶質化を経ない独自の方法、すなわち、圧粉成形体を酸素雰囲気中で部分溶融熱処理し、この成形体から直接Ｂｉ２２１２相の針状結晶を作製することに成功した。従来と異なるこの方法は、Ｂｉ２２１２単相の針状結晶が作製できるとともに、均一な組成でキャリア濃度も制御でき、従来の欠点を克服することができた。
【００１１】
以下、その詳細について説明する。
【００１２】
（１）母相の融点を低くする効果
Ｂｉ２２１２相の針状結晶は、この高温超伝導酸化物と仕込み組成の母相との融点の差が大きいほど成長が促進されることを見いだした。そこで、母相の融点を低くする元素Ｔｅ，Ｇｅ，Ｖなどの酸化物を仕込み組成に含有させることが極めて有効である。Ｂｉ２２１２単相の針状結晶は、母相の融点を低くする元素がモル比で０．１〜１．０含有された場合において成長する。特に、Ｔｅの含有が針状結晶の成長促進に最も効果的である。また、融点を低くする酸化物の複合含有においても、針状結晶が成長する。それでいて育成した針状結晶には、母相の融点を低くする元素が含まれていない。
【００１３】
（２）熱処理雰囲気について
Ｂｉ２２１２相の針状結晶は、２０〜１００％酸素雰囲気において成長し、酸素割合７０％以上で長さ１０ｍｍ以上が育成できる。
【００１４】
（３）熱処理温度について
Ｂｉ２２１２相の針状結晶は、８３０〜９００℃で通常の部分溶融法において成長し、そのサイズ・長さは、母相の部分溶融温度直下での長時間保持によって最も大きくなる。ここで、長時間保持温度は、部分溶融温度より約１０℃低く、針状結晶は保持時間とともに長くなる。
【００１５】
（４）仕込み組成について
Ｂｉ２２１２相の針状結晶は、その組成より広い範囲の仕込み組成で成長する。すなわち、酸化物仕込み組成でＢｉが１．５〜４．０、Ｓｒが１．５〜３．０、Ｃａが１．０〜４．０、Ｃｕが０．５〜４．０、Ｔｅが０．１〜１．０のモル比範囲においてＢｉ２２１２単相の針状結晶が育成できる。
〔実施例〕
（１）融点を低くする効果
表１には、Ｂｉ２２１２相の針状結晶を育成するための仕込み組成に母相の融点を低くする元素の例、Ｔｅ，Ｇｅ，Ｖのモル比組成と針状結晶の長さを示す。
【００１６】
【表１】
ここで、Ｂｉ2 Ｏ3 ，ＳｒＣＯ3 ，ＣａＣＯ3 ，ＣｕＯ，ＴｅＯ2 ，ＧｅＯ2 ，Ｖ2 Ｏ5 の原料粉末を所定の組成に配合・混合し、２０％（大気）の酸素雰囲気中７６０〜８２０℃で１０時間仮焼したものを圧粉成形し、圧粉成形体：直径φ１５ｍｍ、厚さ２ｍｍにした。各成形体は、２０％（大気）の酸素雰囲気中、８６０℃で１５分部分溶融し、その後８５０℃で１００時間保持の熱処理を行った。この部分溶融熱処理はＢｉ２２１２相の生成に通常用いられている方法で、部分溶融温度は、２０％酸素雰囲気中で８８５℃、１００％酸素雰囲気中で９００℃近傍である。以後の結果からもＴｅ，Ｇｅ，Ｖの含有によって融点が低くなっていることが明らかである。
【００１８】
はじめに、Ｂｉ２２１２相の針状結晶の育成に不可欠な母相の融点を低くする元素含有の効果を明らかにする。母相の融点を低くする元素を含有する全ての成形体は、針状結晶の成長が観察され、それらの長さは、上記表１に示した通りである。
【００１９】
次いで、母相の融点を低くする元素が針状結晶成長に有効な組成は、０．１〜１．０モル比であり、特に０．５モル比において０．１および１．０モル比より針状結晶が長く成長した。このモル比は、母相の融点を低くする元素の種類によって変わることはない。さらに、複合含有においても、針状結晶が成長する。しかし、これらを含有しない成形体では、針状結晶の成長が観察されなかった。
【００２０】
（２）酸素雰囲気について
表２には、仕込み組成酸化物Ｂｉ2 Ｓｒ2 Ｃａ2 Ｃｕ2 Ｔｅ0.5 Ｏx 成形体の熱処理条件の酸素割合、部分溶融温度と針状結晶長さについて示す。Ｂｉ２２１２相の針状結晶は、２０〜１００％酸素雰囲気において成長し、酸素割合７０％以上で長さ１０ｍｍ以上が育成できる。
【００２１】
【表２】
（３）熱処理温度について
Ｂｉ２２１２相の針状結晶は、８３０〜９００℃部分溶融、部分溶融温度より１０℃低温度での保持において成長し、そのサイズ・長さは、表１，表２から明らかなように母相の部分溶融温度直下での保持によって最も大きくなる。
【００２３】
（４）仕込み組成について
Ｂｉ２２１２相の針状結晶は、その組成より広い範囲の仕込み組成で成長する。表３には、ＣａとＣｕのモル比を変えた種々の仕込み組成範囲について育成した針状結晶の長さを示す。
【００２４】
【表３】
ここで、熱処理条件は、１００％酸素雰囲気、８８５℃部分溶融、８７５℃１００時間保持である。Ｂｉ２２１２相のＣａモル比１〜３において長さ１０ｍｍ以上の針状結晶が育成できる。しかし、このモル比が１以下になるとＢｉ２２０１相の針状結晶になり好ましくない。これは、Ｂｉ２２１２相を構成する他の元素についても同様である。すなわち、Ｂｉが１．５〜４．０、Ｓｒが１．５〜３．０、Ｃａが１．０〜４．０、Ｃｕが０．５〜４．０、Ｔｅが０．１〜１．０のモル比範囲においてＢｉ２２１２単相の針状結晶が育成できる。
【００２６】
また、育成された針状結晶は、Ｘ線回折法、電子線マイクロアナライザー、エネルギー分散スペクトロメーターで調べたところ、針状結晶は、全てＢｉ２２１２相の単結晶で、母相の融点を低くする元素Ｔｅ，Ｇｅ，Ｖを含有していなかった。
【００２７】
なお、本発明は上記実施例に限定されるものではなく、本発明の趣旨に基づいて種々の変形が可能であり、これらを本発明の範囲から排除するものではない。
【００２８】
【発明の効果】
以上、詳細に説明したように、本発明によれば、以下のような効果を奏することができる。
【００２９】
（Ａ）Ｂｉ−Ｓｒ−Ｃａ−Ｃｕ−Ｏからなる仕込組織に、その融点を低くするＴｅ，Ｇｅ，Ｖ等の酸化物を含有させた圧粉成形体を、酸素雰囲気中で部分溶融、熱処理してＢｉ２２１２針状単結晶を作製する。この方法は、従来の溶融・急冷非晶質化の工程を経ないため工程が簡単であると共に、仕込組成がＢｉ２２１２組成に極めて近く、質の良い、均一な組成の単結晶を作製できると共に、キャリア濃度も制御できるため、従来のものに比べて一桁大きい臨界電流密度Ｊｃを持つものを製造することができる。
【００３０】
（Ｂ）上記（Ａ）により、超伝導エレクトロニクス素子の開発に貢献することができる。すなわち、これまで不可能な領域であった高周波・高速スイッチング素子が実現され、とくに情報関連技術にブレークスルーをもたらす。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a crystal having almost no defects of a high-temperature superconducting oxide, that is, a needle-like crystal close to a perfect crystal, which is indispensable for realizing a superconducting electronic device.
[0002]
[Prior art]
A single crystal of a high-temperature superconducting oxide has a crystal structure in which conductive layers and non-conductive layers are alternately stacked, and each layer has an intrinsic Josephson bond. In recent years, single crystal switching elements using the intrinsic Josephson effect have been proposed. This new single crystal switching element can be reduced in size to about 1/100 of the conventional Josephson coupling, the switching speed is about 100 times faster, and the operating frequency is expected to be a high frequency of THz (terahertz). In addition, superconducting single-electron tunneling phenomenon in which electron pairs pass one by one occurs in a submicron crystal device manufactured using Bi 2 Sr 2 Ca 1 Cu 2 O x (X: 8 to 9) needle-like crystals. It has been made clear. In order to cause this phenomenon, it is necessary to operate at a liquid helium temperature (4.2K). However, when the number of crystal unit cells stacked is about 1000, a superconducting single electron pair operating at a liquid nitrogen temperature (77K). It is expected that the device can be realized.
[0003]
However, realization of these elements requires single crystals with no defects or very few defects. At present, acicular crystals have the best performance, and Bi 2 Sr 2 Ca 1 Cu 2 O x (Bi 2212 phase) acicular crystals are mainly used for development and research. However, the presently produced Bi2212 phase needle-like crystal is not a uniform single phase of Bi2212 phase, but a slight amount of Bi 2 Sr 2 Ca 2 Cu 3 O x (Bi2223 phase) is mixed. It has a bad influence. In addition, there is a problem that the number of carriers that are responsible for superconductivity cannot be controlled. The reason why such non-uniform acicular crystals are produced depends strongly on the production method. The manufacturing method currently performed is to melt a sample containing Al completely, and then rapidly cool it to make it amorphous and post-heat-treat it to grow needle crystals. This complete amorphization is indispensable for growing acicular crystals. However, the charged composition at that time is considerably different from that of the Bi2212 phase composition, and the growth state is extremely sensitive to the oxygen flow during post-heat treatment. Since acicular crystals can be grown only under such limited conditions, the above-described non-uniformity occurs.
[0004]
[Problems to be solved by the invention]
As described above, the present theory is to establish a method for producing acicular crystals having no defects in the high-temperature superconducting oxide Bi 2 Sr 2 Ca 1 Cu 2 O x (Bi 2212 phase) and to produce high-quality acicular crystals. Has been proposed, but not yet realized.
[0005]
Therefore, it is desired to provide a method for producing uniform acicular crystals free from defects in the Bi2212 phase, thereby opening up the way to the practical application of superconducting electronics elements.
[0006]
In view of the above situation, the present invention provides a method for producing acicular crystals of a high-temperature superconducting oxide Bi 2 Sr 2 Ca 1 Cu 2 O x with extremely few defects essential for realizing a superconducting device element. Objective.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides
[1] In the method for producing acicular crystals of a high-temperature superconducting oxide , each raw material powder is predetermined in order to grow acicular crystals of the high-temperature superconducting oxide Bi 2 Sr 2 Ca 1 Cu 2 O x (Bi2212 phase). incorporated into the composition, heat treatment of the green compact the element to lower the melting point containing 0.1 to 1.0 molar ratio composition in 20-100% oxygen atmosphere, the part content melting method at 830 to 900 ° C. and, without going through melt-quenching amorphized, characterized by growing a needle crystal of the high-temperature superconducting oxide Bi 2 Sr 2 Ca 1 Cu 2 O x from the green compact.
[0008]
[2] In the method for producing acicular crystals of high-temperature superconducting oxide , Bi is 1.5 to 4.0 in order to grow acicular crystals of high-temperature superconducting oxide Bi 2 Sr 2 Ca 1 Cu 2 O x. , Sr is 1.5 to 3.0, Ca is 1.0 to 4.0, Cu is 0.5 to 4.0, and Te is 0.1 to 1.0 molar ratio composition oxide compacting 20-100% oxygen atmosphere body was heat-treated by parts partial melting method at eight hundred and thirty to nine hundred ° C., without going through melt-quenching amorphization, the high-temperature superconducting oxide from powder compact Bi 2 Sr 2 A needle crystal of Ca 1 Cu 2 O x (Bi 2212 phase) is grown.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0010]
The inventor of the present application added Te, Ge, V, etc., which lowers the melting point to a charged composition for growing needle-like crystals of the high-temperature superconducting oxide Bi 2 Sr 2 Ca 1 Cu 2 O x (Bi 2212 phase). A unique method that does not go through melting / quenching and amorphization by containing a product, that is, a compacted compact is partially melt-treated in an oxygen atmosphere, and Bi2212 phase needle crystals are produced directly from this compact. Succeeded in doing. This method, which is different from the conventional method, can produce Bi2212 single-phase needle-like crystals and can control the carrier concentration with a uniform composition, thus overcoming the conventional drawbacks.
[0011]
The details will be described below.
[0012]
(1) Effect of lowering the melting point of the parent phase It was found that the growth of the needle-like crystals of the Bi2212 phase was promoted as the melting point difference between the high-temperature superconducting oxide and the parent phase of the charged composition increased. Therefore, it is very effective to add an oxide such as elements Te, Ge, and V that lowers the melting point of the matrix to the charged composition. Bi2212 single-phase needle crystals grow when an element that lowers the melting point of the parent phase is contained in a molar ratio of 0.1 to 1.0. In particular, the inclusion of Te is most effective in promoting the growth of needle crystals. In addition, acicular crystals grow even in the case of complex inclusion of oxides that lower the melting point. Nevertheless, the grown acicular crystal does not contain an element that lowers the melting point of the parent phase.
[0013]
(2) Heat treatment atmosphere Bi2212 phase needle crystals grow in an oxygen atmosphere of 20 to 100%, and can grow up to a length of 10 mm or more at an oxygen ratio of 70% or more.
[0014]
(3) Heat treatment temperature The Bi2212 phase acicular crystal grows at 830 to 900 ° C. in a normal partial melting method, and its size and length are the largest by holding for a long time just below the partial melting temperature of the parent phase. Become. Here, the long-time holding temperature is about 10 ° C. lower than the partial melting temperature, and the acicular crystals become longer with the holding time.
[0015]
(4) About charge composition The needle-like crystal of Bi2212 phase grows with a charge composition in a wider range than the composition. That is, Bi is 1.5 to 4.0, Sr is 1.5 to 3.0, Ca is 1.0 to 4.0, Cu is 0.5 to 4.0, and Te is 0 in an oxide charging composition. Bi2212 single phase acicular crystals can be grown in a molar ratio range of 0.1 to 1.0.
〔Example〕
(1) Effect of lowering the melting point Table 1 shows examples of elements that lower the melting point of the parent phase in the preparation composition for growing needle-like crystals of the Bi2212 phase, the molar ratio composition of Te, Ge, and V and the needle shape. Indicates the length of the crystal.
[0016]
[Table 1]
Here, raw material powders of Bi 2 O 3 , SrCO 3 , CaCO 3 , CuO, TeO 2 , GeO 2 , and V 2 O 5 are blended and mixed in a predetermined composition, and 760 to 60% in an oxygen atmosphere of 20% (atmosphere). What was calcined at 820 ° C. for 10 hours was compacted to obtain a compacted compact: diameter φ15 mm, thickness 2 mm. Each molded body was partially melted at 860 ° C. for 15 minutes in a 20% (atmosphere) oxygen atmosphere, and then heat-treated at 850 ° C. for 100 hours. This partial melting heat treatment is a method usually used for producing the Bi2212 phase, and the partial melting temperatures are 885 ° C. in a 20% oxygen atmosphere and about 900 ° C. in a 100% oxygen atmosphere. From the subsequent results, it is clear that the melting point is lowered by the inclusion of Te, Ge, V.
[0018]
First, the effect of element inclusion to lower the melting point of the parent phase, which is indispensable for the growth of Bi2212 phase needle crystals, will be clarified. In all the compacts containing an element that lowers the melting point of the parent phase, the growth of needle crystals is observed, and the lengths thereof are as shown in Table 1 above.
[0019]
Next, the composition in which the element that lowers the melting point of the matrix phase is effective for acicular crystal growth is 0.1 to 1.0 molar ratio, and more particularly 0.1 and 1.0 molar ratio at 0.5 molar ratio. Needle-like crystals grew longer. This molar ratio does not change depending on the type of element that lowers the melting point of the matrix. Furthermore, needle-like crystals grow even in the composite content. However, no growth of acicular crystals was observed in the compacts not containing these.
[0020]
(2) Oxygen atmosphere Table 2 shows the oxygen ratio, partial melting temperature and needle crystal length of the heat treatment conditions of the charged composition oxide Bi 2 Sr 2 Ca 2 Cu 2 Te 0.5 O x compact. Bi2212 phase acicular crystals grow in an oxygen atmosphere of 20 to 100%, and can grow to a length of 10 mm or more at an oxygen ratio of 70% or more.
[0021]
[Table 2]
(3) Heat treatment temperature The needle-like crystals of Bi2212 phase grew by partial melting at 830 to 900 ° C and holding at 10 ° C lower than the partial melting temperature, and the size and length are apparent from Table 1 and Table 2. Thus, the maximum is obtained by holding the matrix phase just below the partial melting temperature.
[0023]
(4) About charge composition The needle-like crystal of Bi2212 phase grows with a charge composition in a wider range than the composition. Table 3 shows the lengths of the acicular crystals grown for various charged composition ranges with different molar ratios of Ca and Cu.
[0024]
[Table 3]
Here, the heat treatment conditions are 100% oxygen atmosphere, 885 ° C. partial melting, and 875 ° C. holding for 100 hours. Acicular crystals having a length of 10 mm or more can be grown at a Ca molar ratio of 1 to 3 in the Bi2212 phase. However, when the molar ratio is 1 or less, Bi2201 phase acicular crystals are not preferable. The same applies to other elements constituting the Bi2212 phase. That is, Bi is 1.5 to 4.0, Sr is 1.5 to 3.0, Ca is 1.0 to 4.0, Cu is 0.5 to 4.0, and Te is 0.1 to 1. Bi2212 single-phase needle crystals can be grown in a molar ratio range of 0.
[0026]
The grown acicular crystals were examined by an X-ray diffraction method, an electron beam microanalyzer, and an energy dispersive spectrometer. The acicular crystals were all Bi2212 single crystals, and the elements that lower the melting point of the parent phase. Te, Ge, V was not contained.
[0027]
In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and these are not excluded from the scope of the present invention.
[0028]
【The invention's effect】
As described above in detail, according to the present invention, the following effects can be obtained.
[0029]
(A) A powder compact formed by adding an oxide such as Te, Ge, V or the like that lowers its melting point to a charged structure made of Bi—Sr—Ca—Cu—O, partially melted and heat-treated in an oxygen atmosphere. Thus, a Bi2212 needle-like single crystal is produced. This method has a simple process because it does not go through the conventional melting / quenching amorphization process, and the charge composition is very close to the Bi2212 composition, and a single crystal having a high quality and a uniform composition can be produced. Since the carrier concentration can also be controlled, it is possible to manufacture a device having a critical current density Jc that is an order of magnitude larger than the conventional one.
[0030]
(B) The above (A) can contribute to the development of superconducting electronics elements. That is, a high-frequency / high-speed switching element, which has been impossible in the past, is realized, and brings a breakthrough especially to information-related technologies.
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