JP5701253B2 - Oxide superconducting wire and method for producing the same - Google Patents
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/60—Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment
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- Superconductors And Manufacturing Methods Therefor (AREA)
- Inorganic Compounds Of Heavy Metals (AREA)
Description
本発明は、酸化物超電導線材およびその製造方法に関する。 The present invention relates to an oxide superconducting wire and a method for producing the same.
ＲＥ−１２３系の酸化物超電導体（ＲＥＢａ２Ｃｕ３Ｏ７−Ｘ：ＲＥはＹを含む希土類元素）は、液体窒素温度で超電導性を示し、電流損失が低いため、実用上極めて有望な素材とされており、これを線材に加工して電力供給用の導体あるいは電磁コイル等として使用することが要望されている。この酸化物超電導線材の一例構造として、機械的強度の高いテープ状の金属製の基材を用い、その表面にイオンビームアシスト成膜法（ＩＢＡＤ法）により結晶配向性の良好な中間層を形成し、該中間層の表面に成膜法により酸化物超電導層を形成し、その表面にＡｇなどの良導電材料からなる保護層を形成し、さらに該保護層の表面にＣｕの金属箔などの安定化層を備えた酸化物超電導線材が知られている。 An RE-123-based oxide superconductor (REBa 2 Cu 3 O 7-X : RE is a rare earth element including Y) exhibits superconductivity at a liquid nitrogen temperature and has a low current loss. Therefore, it is an extremely promising material for practical use. It is desired to process this into a wire and use it as a power supply conductor or electromagnetic coil. As an example of the structure of this oxide superconducting wire, a tape-shaped metal substrate with high mechanical strength is used, and an intermediate layer with good crystal orientation is formed on its surface by ion beam assisted film formation (IBAD method). Then, an oxide superconducting layer is formed on the surface of the intermediate layer by a film forming method, a protective layer made of a highly conductive material such as Ag is formed on the surface, and a Cu metal foil or the like is further formed on the surface of the protective layer. An oxide superconducting wire having a stabilizing layer is known.
保護層及び安定化層を形成するのは、酸化物超電導層に通電している際、外乱などにより超電導状態から常電導状態に転移する虞があり、この場合に電流を安定化層に分流させるバイパスとしての機能を得るためである。 The protective layer and the stabilization layer are formed when there is a risk of transition from the superconducting state to the normal conducting state due to a disturbance or the like when the oxide superconducting layer is energized. In this case, the current is divided into the stabilizing layer. This is to obtain a function as a bypass.
ところで、このような酸化物超電導線材を製造する際、酸化物超電導層を形成した後、線材外周もしくは酸化物超電導層を覆うように、Ａｇからなる保護層を形成し、その後、酸素雰囲気中において酸素アニール処理を行うのが一般的である（例えば、特許文献１参照）。
ここで、酸素アニール処理を行う理由は、成膜直後の酸化物超電導層は酸素が不足した結晶構造となっているため、酸素を供給して結晶構造を整えるためである。
また、保護層としてＡｇ層を使用するのは、Ａｇ層は、常温では酸素を非透過、高温では酸素を透過する性質があるため、Ａｇ層を介し酸素アニール処理を行うことで酸化物超電導層へ酸素を安定的に供給することが可能なことによる。更に、Ａｇ層は、酸化物超電導層との接触抵抗（界面抵抗）が低いため酸化物超電導層の電流を分流させるバイパスとして適していること、酸化物超電導層と化学反応を起こし難い性質があるという利点を有している。
By the way, when manufacturing such an oxide superconducting wire, after forming the oxide superconducting layer, a protective layer made of Ag is formed so as to cover the outer periphery of the wire or the oxide superconducting layer, and then in an oxygen atmosphere. An oxygen annealing process is generally performed (see, for example, Patent Document 1).
Here, the reason for performing the oxygen annealing treatment is to adjust the crystal structure by supplying oxygen because the oxide superconducting layer immediately after film formation has a crystal structure lacking oxygen.
In addition, the Ag layer is used as the protective layer because the Ag layer has the property of not transmitting oxygen at room temperature and transmitting oxygen at high temperature. Therefore, by performing oxygen annealing treatment through the Ag layer, the oxide superconducting layer is used. This is because it is possible to supply oxygen stably. Furthermore, since the Ag layer has a low contact resistance (interface resistance) with the oxide superconducting layer, it is suitable as a bypass for diverting the current of the oxide superconducting layer, and has a property that hardly causes a chemical reaction with the oxide superconducting layer. Has the advantage.
Ａｇの保護層は、従来、１０μｍ程度の厚さで成膜されているが、Ａｇは比較的高価であるため、Ａｇの保護層を更に薄膜化することが求められている。
しかしながら、本発明者らの研究の結果、Ａｇの保護層を薄膜化すると、酸素アニール処理に際し、厚膜の場合には発生しなかった問題を発生することがわかった。すなわち、常温下でスパッタ法により成膜されたＡｇの保護層は、アモルファス構造をなしており、均一な膜厚を有している。しかし、このＡｇの保護層を酸素アニール処理すると、酸素アニール時の熱処理温度で、Ａｇの再結晶化による凝集が顕著となり、Ａｇの保護層に空孔が発生し、その下に存在する酸化物超電導層が露出してしまうことが判明した。
The protective layer of Ag is conventionally formed with a thickness of about 10 μm. However, since Ag is relatively expensive, it is required to further reduce the thickness of the protective layer of Ag.
However, as a result of the study by the present inventors, it has been found that when the protective layer of Ag is thinned, the oxygen annealing treatment causes a problem that did not occur in the case of a thick film. That is, the protective layer of Ag formed by sputtering at room temperature has an amorphous structure and a uniform film thickness. However, when this Ag protective layer is subjected to oxygen annealing treatment, aggregation due to recrystallization of Ag becomes prominent at the heat treatment temperature at the time of oxygen annealing, and voids are generated in the Ag protective layer, and the oxide present thereunder It was found that the superconducting layer was exposed.
酸化物超電導層が部分的に露出すると、この露出した部分から酸素が抜け出て酸化物超電導層の結晶構造が変化し、超電導特性が低下するおそれが生じる。また、Ａｇの保護層上にＣｕ等の安定化層を半田付けした場合、半田と酸化物超電導層との反応によって超電導特性が低下する問題が生じる。さらに、Ａｇの保護層上にＣｕの安定化層をめっき法によって形成する場合、酸性であるめっき液と酸化物超電導層が接触するため、酸化物超電導層が腐食し、超電導特性の劣化を引き起こすおそれがある。このため、Ａｇの保護層を従来よりも薄膜化するには、このようなＡｇの凝集に対し対策を講じることが必要となる。 When the oxide superconducting layer is partially exposed, oxygen escapes from the exposed portion, the crystal structure of the oxide superconducting layer changes, and the superconducting characteristics may be deteriorated. Further, when a stabilizing layer such as Cu is soldered on the protective layer of Ag, there arises a problem that the superconducting characteristics are lowered due to the reaction between the solder and the oxide superconducting layer. Furthermore, when a Cu stabilization layer is formed on the Ag protective layer by plating, the oxide superconducting layer is corroded because the acidic plating solution and the oxide superconducting layer are in contact with each other, causing deterioration of superconducting properties. There is a fear. For this reason, in order to make the protective layer of Ag thinner than before, it is necessary to take measures against such aggregation of Ag.
本発明は、このような従来の実情に鑑みてなされたものであり、保護層を薄膜化した場合であっても、酸素アニール処理による保護層からの酸化物超電導層の露出を抑えることができ、超電導特性に優れるとともに、保護層の上方に安定化層を半田付けすることができる酸化物超電導線材およびその製造方法を提供することを目的とする。 The present invention has been made in view of such a conventional situation, and even when the protective layer is thinned, the exposure of the oxide superconducting layer from the protective layer by the oxygen annealing treatment can be suppressed. An object of the present invention is to provide an oxide superconducting wire that is excellent in superconducting properties and that can be soldered with a stabilization layer above a protective layer, and a method for manufacturing the same.
上記課題を解決するため、本発明の酸化物超電導線材は、基材と、該基材の上方に設けられた中間層と酸化物超電導層とＡｇの保護層とを備えた酸化物超電導線材であって、前記保護層は、前記酸化物超電導層上に形成した保護層に対しＡｇの再結晶温度以上で酸素アニール処理が施されて形成され、前記保護層に含まれるＡｇ結晶粒の最大結晶粒径が、前記酸素アニール処理後の保護層の膜厚平均の１．２５倍以下であることを特徴とする。
保護層に含まれるＡｇ結晶粒の最大結晶粒径が酸素アニール処理後の保護層の膜厚平均の１．２５倍以下であるということは、酸素アニール処理の過程でＡｇの再結晶による凝集が抑えられており、Ａｇ結晶粒同士の間にＡｇが残存していること、すなわち、保護層の空孔率が低く、保護層が酸化物超電導層の表面を全面的に覆っていることを意味している。このため、保護層における最大結晶粒径が前記範囲の酸化物超電導線材は、保護層の膜厚を従来より薄くした場合であっても、酸化物超電導層の保護層側の表面を保護層により覆うことができる。このため、酸化物超電導層が保護層から露出することによる不都合、すなわち、酸化物超電導層から酸素が脱離することによる超電導特性の低下が無く、安定化層の半田付け不良を生じることがなく、めっき液による酸化物超電導層の腐食の問題を回避しつつ、コストの低減を図ることが可能となる。
In order to solve the above problems, an oxide superconducting wire according to the present invention is an oxide superconducting wire comprising a base material, an intermediate layer provided above the base material, an oxide superconducting layer, and an Ag protective layer. The protective layer is formed by subjecting the protective layer formed on the oxide superconducting layer to an oxygen annealing treatment at a temperature equal to or higher than the recrystallization temperature of Ag, and forming a maximum crystal of Ag crystal grains contained in the protective layer. The particle size is 1.25 times or less of the average film thickness of the protective layer after the oxygen annealing treatment.
The maximum crystal grain size of the Ag crystal grains contained in the protective layer is 1.25 times or less the average film thickness of the protective layer after the oxygen annealing treatment, which means that aggregation due to recrystallization of Ag occurs during the oxygen annealing treatment. Means that Ag remains between the Ag crystal grains, that is, the porosity of the protective layer is low, and the protective layer covers the entire surface of the oxide superconducting layer. doing. For this reason, the oxide superconducting wire having a maximum crystal grain size in the above-mentioned range in the protective layer can protect the surface of the oxide superconducting layer on the protective layer side even when the protective layer is made thinner. Can be covered. For this reason, there is no inconvenience due to the oxide superconducting layer being exposed from the protective layer, that is, there is no deterioration in superconducting characteristics due to the desorption of oxygen from the oxide superconducting layer, and no soldering failure of the stabilization layer occurs. It is possible to reduce the cost while avoiding the problem of corrosion of the oxide superconducting layer due to the plating solution.
本発明において、前記酸素アニール処理後の酸化物超電導層上の保護層に、膜厚６μｍ以下の部分を有していても良い。
この場合、酸素アニール処理の過程で、酸化物超電導層上の保護層において膜厚６μｍ以下の部分があった場合、Ａｇの再結晶による凝集を抑制でき、酸化物超電導層上の保護層に空孔がほとんど形成されていない保護層を提供することができる。
In the present invention, the protective layer on the oxide superconducting layer after the oxygen annealing treatment may have a portion with a thickness of 6 μm or less.
In this case, if there is a portion having a thickness of 6 μm or less in the protective layer on the oxide superconducting layer during the oxygen annealing process, aggregation due to recrystallization of Ag can be suppressed, and the protective layer on the oxide superconducting layer is empty. It is possible to provide a protective layer in which almost no pores are formed.
本発明の酸化物超電導線材の製造方法は、基材の上方に中間層と酸化物超電導層を形成した後、酸化物超電導層上にＡｇの保護層を成膜法により形成する工程と、前記保護層に、Ａｇが再結晶する温度で酸素アニール処理を行うことにより、Ａｇの再結晶粒を含む保護層を形成する工程とを有し、前記アニール処理を２５０℃以上、３００℃以下で行うことにより、前記酸素アニール処理前の保護層に含まれるＡｇ結晶粒の最大結晶粒径を前記酸素アニール処理前の保護層の膜厚平均の１．２５倍以下とすることを特徴とする。
本発明の酸化物超電導線材の製造方法によれば、保護層の酸素アニール処理を比較的低い温度で行うため、酸素アニール処理に伴うＡｇの再結晶化に伴う凝集を抑え、空孔率の低い保護層を得ることができる。これにより、酸化物超電導層の保護層側の表面を従来より薄い保護層により確実に覆うことができるため、保護層から酸化物超電導層が露出することによる不都合を解消できる。
即ち、酸化物超電導層から酸素が脱離することによる超電導特性の低下が無く、安定化層の半田付け不良が無く、めっき液による酸化物超電導層の腐食の問題を回避することが可能となる。
さらに、酸素アニール処理温度の下限を２５０℃と規定していることにより、酸化物超電導層に十分に酸素を供給することができる。これにより、酸化物超電導層の超電導特性を確実に向上させるとともに、酸化物超電導層と保護層との界面抵抗を低減することが可能となる。
The method for producing an oxide superconducting wire according to the present invention comprises forming an intermediate layer and an oxide superconducting layer above a base material, and then forming an Ag protective layer on the oxide superconducting layer by a film forming method, Forming a protective layer containing Ag recrystallized grains by performing an oxygen annealing process on the protective layer at a temperature at which Ag recrystallizes, and the annealing process is performed at 250 ° C. or higher and 300 ° C. or lower. Thus, the maximum crystal grain size of the Ag crystal grains contained in the protective layer before the oxygen annealing treatment is made 1.25 times or less the average film thickness of the protective layer before the oxygen annealing treatment.
According to the method for manufacturing an oxide superconducting wire of the present invention, the oxygen annealing treatment of the protective layer is performed at a relatively low temperature, so that aggregation due to recrystallization of Ag accompanying the oxygen annealing treatment is suppressed and the porosity is low. A protective layer can be obtained. As a result, the surface of the oxide superconducting layer on the protective layer side can be reliably covered with a protective layer thinner than the conventional one, so that the inconvenience due to the oxide superconducting layer being exposed from the protective layer can be eliminated.
That is, there is no deterioration in superconducting characteristics due to oxygen desorption from the oxide superconducting layer, no soldering failure of the stabilization layer, and it is possible to avoid the problem of corrosion of the oxide superconducting layer due to the plating solution. .
Furthermore, by setting the lower limit of the oxygen annealing treatment temperature to 250 ° C., oxygen can be sufficiently supplied to the oxide superconducting layer. As a result, the superconducting properties of the oxide superconducting layer can be reliably improved, and the interface resistance between the oxide superconducting layer and the protective layer can be reduced.
本発明において、前記酸素アニール処理の時間を９００分以上とすることが好ましい。
この場合、酸素アニールの処理温度が比較的低い場合でも、酸化物超電導層に十分な酸素を供給することができ、酸化物超電導層が保護層から露出するのを防止しつつ、酸化物超電導層の超電導特性を確実に向上させることが可能となる。
In the present invention, the oxygen annealing treatment time is preferably 900 minutes or longer.
In this case, even when the treatment temperature of the oxygen annealing is relatively low, sufficient oxygen can be supplied to the oxide superconducting layer, and the oxide superconducting layer is prevented from being exposed from the protective layer. It becomes possible to improve the superconducting properties of the.
本発明の酸化物超電導線材は、保護層に含まれるＡｇ結晶粒の最大結晶粒径を酸素アニール処理前の保護層の膜厚平均の１．２５倍以下としたので、酸素アニール処理の過程で生じるＡｇの再結晶化による凝集が抑えられており、Ａｇ結晶粒同士の間にＡｇが残存していること、すなわち、保護層の空孔率が低く、保護層が酸化物超電導層の表面をほぼ全面的に覆っている構造を提供できる。
即ち、本発明の酸化物超電導線材は、保護層の膜厚が薄い場合であっても、酸化物超電導層の保護層側の表面を保護層により覆うことができる。このため、酸化物超電導層が保護層から露出することによる不都合がない酸化物超電導線材、即ち、酸化物超電導層から酸素が脱離することによる超電導特性の低下が無く、安定化層の半田付け不良が無く、めっき液による酸化物超電導層の腐食の問題を回避しつつ、コストの低減を図ることが可能な酸化物超電導線材を提供できる。
In the oxide superconducting wire of the present invention, the maximum crystal grain size of the Ag crystal grains contained in the protective layer is 1.25 times or less of the average thickness of the protective layer before the oxygen annealing treatment. Aggregation caused by recrystallization of Ag is suppressed, Ag remains between Ag crystal grains, that is, the porosity of the protective layer is low, and the protective layer covers the surface of the oxide superconducting layer. A structure covering almost the whole surface can be provided.
That is, the oxide superconducting wire of the present invention can cover the protective layer side surface of the oxide superconducting layer with the protective layer even when the protective layer is thin. For this reason, there is no inconvenience due to the oxide superconducting layer being exposed from the protective layer, that is, the superconducting characteristics are not deteriorated due to the desorption of oxygen from the oxide superconducting layer, and the stabilization layer is soldered It is possible to provide an oxide superconducting wire that is free from defects and can reduce the cost while avoiding the problem of corrosion of the oxide superconducting layer due to the plating solution.
＜酸化物超電導線材＞
以下、本発明に係る酸化物超電導線材の実施形態について図面に基づいて説明するが、本発明は係る実施形態に限定されるものではない。
図１は本発明に係る実施形態の酸化物超電導線材１を模式的に示す概略断面図である。
この実施形態の酸化物超電導線材１は、テープ状の基材２の上方に、下地層３と配向層４とキャップ層５からなる中間層が形成され、その上方に酸化物超電導層６と保護層７と金属安定化層８がこの順に積層されてなる。さらに、この酸化物超電導線材１の周面を絶縁被覆層９が覆っている。
<Oxide superconducting wire>
Hereinafter, embodiments of the oxide superconducting wire according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments.
FIG. 1 is a schematic cross-sectional view schematically showing an oxide superconducting wire 1 according to an embodiment of the present invention.
In the oxide superconducting wire 1 of this embodiment, an intermediate layer composed of a base layer 3, an alignment layer 4, and a cap layer 5 is formed above a tape-shaped substrate 2, and the oxide superconducting layer 6 and a protective layer are formed thereon. The layer 7 and the metal stabilizing layer 8 are laminated in this order. Furthermore, the insulating coating layer 9 covers the peripheral surface of the oxide superconducting wire 1.
基材２は、長尺のケーブルとするためにテープ状であることが好ましく、耐熱性の金属からなるものが好ましい。各種耐熱性金属の中でもニッケル合金が好ましく、市販品であれば、ハステロイ（米国ヘインズ社製商品名）が好適であり、モリブデン、クロム、鉄、コバルト等の成分量が異なる、ハステロイＢ、Ｃ、Ｇ、Ｎ、Ｗ等のいずれの種類も使用できる。また、基材２として、ニッケル合金に集合組織を導入した配向Ｎｉ−Ｗ合金テープ基材等を使用することもできる。
基材２の厚みは、目的に応じて適宜調整すれば良く、通常は、１０〜５００μｍの範囲とすることができる。
The base material 2 is preferably in the form of a tape to make a long cable, and is preferably made of a heat-resistant metal. Among various refractory metals, nickel alloys are preferable, and if it is a commercial product, Hastelloy (trade name, manufactured by Haynes, USA) is suitable, and has different amounts of components such as molybdenum, chromium, iron, cobalt, Hastelloy B, C, Any kind of G, N, W, etc. can be used. Further, as the base material 2, an oriented Ni—W alloy tape base material in which a texture is introduced into a nickel alloy can be used.
What is necessary is just to adjust the thickness of the base material 2 suitably according to the objective, Usually, it can be set as the range of 10-500 micrometers.
下地層３は、以下に説明する拡散防止層とベッド層の複層構造又は、これらのうちどちらか１層からなる構造とすることができる。
下地層３として設けられる拡散防止層は、通常、構成元素拡散を防止する目的又はその上に形成される他の層の膜質を改善する目的で形成される。下地層３として拡散防止層を設ける場合、該拡散防止層は、窒化ケイ素（Ｓｉ３Ｎ４）、酸化アルミニウム（Ａｌ２Ｏ３、「アルミナ」とも呼ぶ）又はＧＺＯ（Ｇｄ２Ｚｒ２Ｏ７）等から構成される単層構造又は複層構造の層であることが好ましい。
前記拡散防止層の厚みは特に制限されず、例えば１０〜４００ｎｍとすることができる。拡散防止層の厚みが１０ｎｍ未満となると、拡散防止層のみでは基材２の構成元素の拡散を十分に防止できなくなる虞がある。一方、拡散防止層の厚みが４００ｎｍを超えると、拡散防止層の内部応力が増大し、これにより、他の層を含めて全体が基材２から剥離しやすくなる虞がある。また、拡散防止層の結晶性は特に問われないので、通常のスパッタ法等の成膜法により形成すれば良い。
The underlayer 3 can have a multi-layer structure of a diffusion preventing layer and a bed layer, which will be described below, or a structure composed of one of these layers.
The diffusion preventing layer provided as the underlayer 3 is usually formed for the purpose of preventing the diffusion of the constituent elements or improving the film quality of other layers formed thereon. When a diffusion prevention layer is provided as the underlayer 3, the diffusion prevention layer is formed of silicon nitride (Si 3 N 4 ), aluminum oxide (Al 2 O 3 , also referred to as “alumina”), or GZO (Gd 2 Zr 2 O 7 ). It is preferable that the layer has a single-layer structure or a multi-layer structure composed of the like.
The thickness in particular of the said diffusion prevention layer is not restrict | limited, For example, it can be 10-400 nm. When the thickness of the diffusion preventing layer is less than 10 nm, there is a possibility that the diffusion of the constituent elements of the substrate 2 cannot be sufficiently prevented only by the diffusion preventing layer. On the other hand, when the thickness of the diffusion preventing layer exceeds 400 nm, the internal stress of the diffusion preventing layer increases, and there is a possibility that the whole including the other layers is easily peeled off from the substrate 2. Further, since the crystallinity of the diffusion preventing layer is not particularly limited, it may be formed by a film forming method such as a normal sputtering method.
下地層３として設けられるベッド層は、通常、界面反応性を低減する目的又はその上に配される膜の配向性を得る目的で形成される。下地層３としてベッド層を設ける場合、該ベッド層は、耐熱性の高い材料で形成されることが好ましい。このような材料としては、例えば、Ｙ２Ｏ３、Ｅｒ２Ｏ３、ＣｅＯ２、Ｄｙ２Ｏ３、Ｅｒ２Ｏ３、Ｅｕ２Ｏ３、Ｈｏ２Ｏ３、Ｌａ２Ｏ３などの希土類酸化物が挙げられる。その層構造は単層構造でも良いし複層構造でも良い。
前記ベッド層の厚みは特に制限されず、例えば１０〜１００ｎｍとすることができる。
また、ベッド層の結晶性は特に問われないので、通常のスパッタ法等の成膜法により形成すれば良い。
なお、下地層３は拡散防止層とベッド層の２層構造でも、これらのどちらかからなる単層構造でも良く、場合によっては下地層３を省いても良い。下地層３を省く場合は、基材２上に直接、以下に説明する配向層４が形成される。
The bed layer provided as the underlayer 3 is usually formed for the purpose of reducing the interfacial reactivity or obtaining the orientation of the film disposed thereon. When a bed layer is provided as the foundation layer 3, the bed layer is preferably formed of a material having high heat resistance. Examples of such materials include rare earth oxidation such as Y 2 O 3 , Er 2 O 3 , CeO 2 , Dy 2 O 3, Er 2 O 3 , Eu 2 O 3 , Ho 2 O 3 , and La 2 O 3. Things. The layer structure may be a single layer structure or a multilayer structure.
The thickness of the bed layer is not particularly limited, and can be, for example, 10 to 100 nm.
Further, since the crystallinity of the bed layer is not particularly limited, it may be formed by a film forming method such as a normal sputtering method.
The underlayer 3 may be a two-layer structure including a diffusion prevention layer and a bed layer, or may be a single layer structure made of either of these layers. In some cases, the underlayer 3 may be omitted. When the base layer 3 is omitted, an alignment layer 4 described below is formed directly on the substrate 2.
配向層４は、酸化物超電導層６の結晶配向性を制御するバッファー層として機能し、酸化物超電導層６と格子整合性の良い金属酸化物からなるものであることが好ましい。また、配向層４は、ＩＢＡＤ法（イオンビームアシスト蒸着法）によって形成されたものであることが好ましい。ＩＢＡＤ法によって形成された配向層は配向性に優れる。
配向層４の好ましい材料としては、例えば、Ｇｄ２Ｚｒ２Ｏ７、ＭｇＯ、ＺｒＯ２−Ｙ２Ｏ３（ＹＳＺ）、ＳｒＴｉＯ３、ＣｅＯ２、Ｙ２Ｏ３、Ａｌ２Ｏ３、Ｇｄ２Ｏ３、Ｚｒ２Ｏ３、Ｈｏ２Ｏ３、Ｎｄ２Ｏ３等の金属酸化物が挙げられる。配向層４は、単層でも良いし、複層構造でも良い。
The alignment layer 4 functions as a buffer layer for controlling the crystal orientation of the oxide superconducting layer 6 and is preferably made of a metal oxide having good lattice matching with the oxide superconducting layer 6. The alignment layer 4 is preferably formed by IBAD (ion beam assisted vapor deposition). An alignment layer formed by the IBAD method is excellent in alignment.
Examples of preferable materials for the alignment layer 4 include Gd 2 Zr 2 O 7 , MgO, ZrO 2 —Y 2 O 3 (YSZ), SrTiO 3 , CeO 2 , Y 2 O 3 , Al 2 O 3 , Gd 2 O. 3 , metal oxides such as Zr 2 O 3 , Ho 2 O 3 , and Nd 2 O 3 . The alignment layer 4 may be a single layer or a multilayer structure.
キャップ層５は好ましい材料として、例えば、ＣｅＯ２、Ｙ２Ｏ３、Ａｌ２Ｏ３、Ｇｄ２Ｏ３、Ｚｒ２Ｏ３、Ｈｏ２Ｏ３、Ｎｄ２Ｏ３等が挙げられる。キャップ層５の材料がＣｅＯ２である場合、キャップ層５は、Ｃｅの一部が他の金属原子又は金属イオン（Ｍ）で置換されたＣｅ−Ｍ−Ｏ系酸化物を含んでいても良い。ＣｅＯ２からなるキャップ層５の膜厚は、５０ｎｍ以上であればよいが、単結晶と同程度の十分な配向性を得るには１００ｎｍ以上が好ましい。但し、厚すぎると結晶配向性が悪くなる場合があるので、５０〜５０００ｎｍの範囲とすることが好ましい。 As the cap layer 5 are preferred materials, for example, CeO 2, Y 2 O 3 , Al 2 O 3, Gd 2 O 3, Zr 2 O 3, Ho 2 O 3, Nd 2 O 3 and the like. When the material of the cap layer 5 is CeO 2 , the cap layer 5 may include a Ce—M—O-based oxide in which part of Ce is substituted with another metal atom or metal ion (M). . The thickness of the cap layer 5 made of CeO 2 may be 50 nm or more, but is preferably 100 nm or more in order to obtain sufficient orientation similar to that of a single crystal. However, since crystal orientation may deteriorate if it is too thick, the thickness is preferably in the range of 50 to 5000 nm.
酸化物超電導層６は、公知の酸化物超電導体に使用されている材料を広く適用することができ、例えばＲｅＢａ２Ｃｕ３Ｏ７−ｘ（ＲｅはＹ、Ｌａ、Ｎｄ、Ｓｍ、Ｅｒ、Ｇｄ等の希土類元素を表す。）の化学式で表されるものが好ましい。より具体的には、Ｙ１２３（ＹＢａ２Ｃｕ３Ｏ７−ｘ）又はＧｄ１２３（ＧｄＢａ２Ｃｕ３Ｏ７−ｘ）が好適なものとして例示できる。前記キャップ層５の上に成膜された酸化物超電導層６は優れた結晶配向性を有し、優れた超電導特性を示す。
酸化物超電導層６の厚みは、５００〜５０００ｎｍ程度が好ましく、均一な厚みであることが好ましい。
For the oxide superconducting layer 6, materials widely used for known oxide superconductors can be widely applied. For example, ReBa 2 Cu 3 O 7-x (Re is Y, La, Nd, Sm, Er, Gd Represents a rare earth element, etc.). More particularly, Y123 (YBa 2 Cu 3 O 7-x) or Gd123 (GdBa 2 Cu 3 O 7 -x) can be exemplified as a preferable. The oxide superconducting layer 6 formed on the cap layer 5 has excellent crystal orientation and exhibits excellent superconducting properties.
The thickness of the oxide superconducting layer 6 is preferably about 500 to 5000 nm, and preferably has a uniform thickness.
保護層７は、酸化物超電導層６の表面（上面と側面）を覆うように、即ち、酸化物超電導層６上を覆うように形成されていて、Ａｇからなる。特に保護層７をスパッタ法などの成膜法により形成した場合、酸化物超電導層６の上面と側面に主体として成膜されるが、更に、保護層７を構成するべきＡｇ粒子の成膜時の回り込みにより、基材２と下地層３と配向層４とキャップ層５と酸化物超電導層６を含む線材の側面や底面側にも薄く形成される。
本実施形態の保護層７は、後述するように、スパッタ法などの物理的蒸着法によって、アモルファス構造の保護層として形成された後、酸素雰囲気中で熱処理（酸素アニール処理）されて多結晶体とされている。酸素アニール処理は、酸化物超電導層６の結晶に酸素を供給して、その結晶構造を整え、超電導特性を向上させる処理である。
ここで、例えば常温下でスパッタ法によって成膜された酸素アニール処理前の保護層は、アモルファス構造をなしており、略均一な膜厚を有している。この保護層に９０℃以上の温度で酸素アニール処理を施すと、Ａｇが再結晶化して凝集する。このとき、再結晶化したＡｇ結晶粒同士の間では、Ａｇが周囲に拡散すること（Ａｇの凝集が進行すること）によって徐々に厚さが薄くなり、さらにＡｇの凝集が進行すると空孔が形成されて酸化物超電導層６の上面が露出してしまう。なお、アモルファス構造の保護層を酸素アニール処理に伴い再結晶化させたとしても酸化物超電導層上に存在する保護層７の膜厚の平均（平均膜厚）に変化は生じない。
The protective layer 7 is formed to cover the surface (upper surface and side surface) of the oxide superconducting layer 6, that is, to cover the oxide superconducting layer 6, and is made of Ag. In particular, when the protective layer 7 is formed by a film forming method such as a sputtering method, it is formed mainly on the upper surface and the side surface of the oxide superconducting layer 6. Further, when the Ag particles to form the protective layer 7 are formed. Is thinly formed on the side surface and the bottom surface side of the wire including the base material 2, the base layer 3, the alignment layer 4, the cap layer 5, and the oxide superconducting layer 6.
As will be described later, the protective layer 7 of the present embodiment is formed as a protective layer having an amorphous structure by a physical vapor deposition method such as a sputtering method, and is then heat-treated (oxygen annealing treatment) in an oxygen atmosphere. It is said that. The oxygen annealing treatment is a treatment for improving the superconducting characteristics by supplying oxygen to the crystal of the oxide superconducting layer 6 to adjust its crystal structure.
Here, for example, the protective layer before the oxygen annealing process formed by sputtering at room temperature has an amorphous structure and has a substantially uniform film thickness. When this protective layer is subjected to oxygen annealing at a temperature of 90 ° C. or higher, Ag recrystallizes and aggregates. At this time, between the recrystallized Ag crystal grains, the thickness gradually decreases as Ag diffuses to the surroundings (Ag aggregation progresses). As a result, the upper surface of the oxide superconducting layer 6 is exposed. Note that even if the protective layer having an amorphous structure is recrystallized along with the oxygen annealing treatment, the average thickness (average film thickness) of the protective layer 7 existing on the oxide superconducting layer does not change.
これに対して、本発明の酸化物超電導線材１では、酸素アニール処理後の多結晶体としての保護層７に含まれるＡｇ結晶粒の最大結晶粒径が、酸素アニール処理後の保護層の膜厚平均の１．２５倍以下とされている。
保護層７に含まれるＡｇ結晶粒の最大結晶粒径がこのような範囲であるならば、保護層の酸素アニール処理の過程でＡｇの再結晶化による凝集が抑えられており、Ａｇ結晶粒同士の間にＡｇの結晶粒が残存していること、すなわち、保護層７の空孔率が低く、保護層７が酸化物超電導層６の表面（上面＋側面）をほぼ全面的に覆っていることを意味している。このため、酸化物超電導線材１は、保護層７の膜厚が従来用いられていた１０μｍより薄い場合であっても、酸化物超電導層６の表面を保護層７により覆うことができる。即ち、酸化物超電導層６の表面が保護層７から露出することによる不都合を解消できる。即ち、酸化物超電導層６から酸素が脱離することによる超電導特性の低下を無くし、金属安定化層８の半田付け不良を無くし、めっき液による酸化物超電導層６の腐食の問題を回避しながら、コストの低減を図ることが可能となる。
On the other hand, in the oxide superconducting wire 1 of the present invention, the maximum crystal grain size of the Ag crystal grains contained in the protective layer 7 as a polycrystal after the oxygen annealing treatment is such that the film of the protective layer after the oxygen annealing treatment. The thickness average is 1.25 times or less.
If the maximum crystal grain size of the Ag crystal grains contained in the protective layer 7 is within such a range, aggregation due to recrystallization of Ag is suppressed in the course of the oxygen annealing treatment of the protective layer. In other words, Ag crystal grains remain, that is, the porosity of the protective layer 7 is low, and the protective layer 7 almost entirely covers the surface (upper surface + side surface) of the oxide superconducting layer 6. It means that. For this reason, the oxide superconducting wire 1 can cover the surface of the oxide superconducting layer 6 with the protective layer 7 even when the thickness of the protective layer 7 is thinner than 10 μm which has been conventionally used. That is, inconvenience due to the surface of the oxide superconducting layer 6 being exposed from the protective layer 7 can be eliminated. That is, the superconducting property is not deteriorated due to the desorption of oxygen from the oxide superconducting layer 6, the soldering failure of the metal stabilizing layer 8 is eliminated, and the problem of corrosion of the oxide superconducting layer 6 due to the plating solution is avoided. It becomes possible to reduce the cost.
酸化物超電導層６の表面（上面＋側面）を覆っている酸素アニール処理後の保護層７の膜厚は、特に限定されないが、６μｍ以下を望ましくは採用することができ、１．４μｍ以上、６μｍ以下であるのが好ましく、２μｍ以上、６μｍ以下であることがより好ましい。酸素アニール処理後の保護層の膜厚が１．４μｍより薄いと、酸素アニール処理の温度と時間によっては、Ａｇの再結晶化による凝集により、保護層７に空孔が形成される確率が増加し、酸化物超電導層６の表面が露出する確率が高くなる。また、酸素アニール処理前の保護層７の膜厚が６μｍより厚いと、Ａｇは高価であるため、酸化物超電導線材１がコスト高になる傾向となるため薄い方が望ましい。
後述する製造方法により、膜厚１．４〜６μｍのアモルファス構造の保護層を常温スパッタ法により形成し、この保護層に後述する温度範囲で酸素アニール処理を施すならば、Ａｇの再結晶粒の集合体である多結晶体の保護層７において、ほぼ空孔を生じていない緻密な保護層７を設けた酸化物超電導線材１を提供できる。
なお、成膜法により保護層７を形成した場合、基材２、下地層３、配向層４、キャップ層５の側面側にもＡｇ粒子が回り込んでＡｇの薄い層が形成され、基材２の裏面側にもＡｇの薄い層が形成されるが、本発明で問題とするのは、酸化物超電導層６の上面と側面を覆う保護層７の部分であるので、他の層の側面や基材２の裏面側に形成されるＡｇの層はいずれの厚さであっても差し支えない。上述の厚さ範囲でも良いし、上述の範囲から外れていても問題とはしない。
The film thickness of the protective layer 7 after the oxygen annealing treatment that covers the surface (upper surface + side surface) of the oxide superconducting layer 6 is not particularly limited, but 6 μm or less can be desirably employed, and 1.4 μm or more, It is preferably 6 μm or less, and more preferably 2 μm or more and 6 μm or less. If the thickness of the protective layer after the oxygen annealing treatment is thinner than 1.4 μm, the probability that voids are formed in the protective layer 7 due to aggregation due to recrystallization of Ag increases depending on the temperature and time of the oxygen annealing treatment. In addition, the probability that the surface of the oxide superconducting layer 6 is exposed increases. In addition, when the thickness of the protective layer 7 before the oxygen annealing treatment is thicker than 6 μm, Ag is expensive, and the oxide superconducting wire 1 tends to be costly.
If a protective layer having an amorphous structure with a film thickness of 1.4 to 6 μm is formed by a room temperature sputtering method by a manufacturing method described later, and oxygen annealing treatment is performed on the protective layer in a temperature range described later, the recrystallized grains of Ag It is possible to provide the oxide superconducting wire 1 provided with the dense protective layer 7 that is substantially free of voids in the polycrystalline protective layer 7 that is an aggregate.
When the protective layer 7 is formed by a film forming method, Ag particles wrap around the side surfaces of the base material 2, the base layer 3, the alignment layer 4, and the cap layer 5 to form a thin layer of Ag. A thin layer of Ag is also formed on the back surface side of 2, but the problem in the present invention is the portion of the protective layer 7 that covers the upper surface and the side surface of the oxide superconducting layer 6, so that the side surface of the other layer In addition, the thickness of the Ag layer formed on the back side of the substrate 2 may be any thickness. The above-mentioned thickness range may be used, and even if it is outside the above-mentioned range, there is no problem.
Ａｇの保護層７は、酸化物超電導層６との反応性が低く、また酸化物超電導層６との界面抵抗が低いため、酸化物超電導層６の電流を分流するバイパスとして良好な機能を発揮する。さらに、Ａｇの保護層７は、その上に形成される金属安定化層８又は半田との密着性が良好であり、Ａｇを保護層７の材料として用いることにより、保護層７の表面に金属安定化層８を密着性よく形成することが可能となる。 Since the protective layer 7 of Ag has low reactivity with the oxide superconducting layer 6 and low interfacial resistance with the oxide superconducting layer 6, it exhibits a good function as a bypass for diverting the current of the oxide superconducting layer 6. To do. Further, the protective layer 7 of Ag has good adhesion to the metal stabilizing layer 8 or solder formed thereon, and by using Ag as a material for the protective layer 7, a metal is formed on the surface of the protective layer 7. It becomes possible to form the stabilization layer 8 with good adhesion.
金属安定化層８は、良導電性の金属の箔やめっき層等からなり、酸化物超電導層６が超電導状態から常電導状態に遷移しようとした時、保護層７とともに酸化物超電導層６の電流を転流させるバイパスとして機能する。
金属安定化層８を構成する金属材料は、良伝導性のＣｕやＣｕ合金が望ましいが、酸化物超電導線材１を超電導限流器に使用する場合、金属安定化層８は高抵抗の金属材料であることが好ましく、例えばＮｉ−Ｃｒ等のＮｉ系合金などからなる。
The metal stabilizing layer 8 is made of a highly conductive metal foil, a plating layer, or the like. When the oxide superconducting layer 6 attempts to transition from the superconducting state to the normal conducting state, the protective layer 7 and the oxide superconducting layer 6 It functions as a bypass that commutates current.
The metal material constituting the metal stabilization layer 8 is preferably a highly conductive Cu or Cu alloy. However, when the oxide superconducting wire 1 is used in a superconducting current limiter, the metal stabilization layer 8 is a high resistance metal material. Preferably, it is made of, for example, a Ni-based alloy such as Ni—Cr.
金属安定化層８の厚みは特に限定されないが、１０μｍ〜５００μｍであることが好ましく、２０μｍ〜３００μｍであることがより好ましい。
金属安定化層８の厚みが上記範囲の下限値以上であると、酸化物超電導層６及び保護層７を外乱などから物理的に保護すると共に、製造時や使用時にピンホールや破れが生じること防止できる。
金属安定化層８の厚みが上記範囲の上限値以下であると、金属安定化層８の剛性が過度に高くなることを防ぎ、使用時の応力によって保護層７から金属安定化層８が剥離することを抑制できる。金属安定化層８の剛性が高くなり過ぎると、曲げや捻りなどの外力が加わった際に、金属安定化層８の変形度と保護層７の変形度が大きく解離して、金属安定化層８が保護層７から剥離し易くなる場合がある。
Although the thickness of the metal stabilization layer 8 is not specifically limited, It is preferable that they are 10 micrometers-500 micrometers, and it is more preferable that they are 20 micrometers-300 micrometers.
When the thickness of the metal stabilizing layer 8 is equal to or more than the lower limit of the above range, the oxide superconducting layer 6 and the protective layer 7 are physically protected from disturbances and the like, and pinholes and tears occur during manufacture and use. Can be prevented.
If the thickness of the metal stabilization layer 8 is not more than the upper limit of the above range, the metal stabilization layer 8 is prevented from becoming too rigid, and the metal stabilization layer 8 is peeled off from the protective layer 7 due to stress during use. Can be suppressed. If the rigidity of the metal stabilizing layer 8 becomes excessively high, the degree of deformation of the metal stabilizing layer 8 and the degree of deformation of the protective layer 7 are largely dissociated when an external force such as bending or twisting is applied. 8 may easily peel from the protective layer 7.
第１実施形態の酸化物超電導線材１の外周は、絶縁被覆層９で被覆されている。絶縁被覆層９は、絶縁テープを巻き回して形成されたものでも良いし、絶縁性樹脂がコーティングされたものでも良い。絶縁被覆層９は、必ずしも設けられていなくても良いが、本発明に係る酸化物超電導線材１を保護する。前記絶縁テープ及び絶縁性樹脂の材料は特に制限されず、例えばポリイミド樹脂等の公知の材料を適用できる。絶縁被覆層９の厚みも特に制限されず、用途に応じて適宜調整すれば良く、例えば１００μｍ〜１ｍｍとすることができる。 The outer periphery of the oxide superconducting wire 1 according to the first embodiment is covered with an insulating coating layer 9. The insulating coating layer 9 may be formed by winding an insulating tape, or may be coated with an insulating resin. The insulating coating layer 9 is not necessarily provided, but protects the oxide superconducting wire 1 according to the present invention. The material of the insulating tape and the insulating resin is not particularly limited, and a known material such as a polyimide resin can be applied. The thickness of the insulating coating layer 9 is not particularly limited, and may be appropriately adjusted according to the application, and may be set to, for example, 100 μm to 1 mm.
保護層７上に金属安定化層８を半田により接合する場合、従来公知の半田を用いることができる。半田として、例えば、Ｓｎ、あるいは、Ｓｎ−Ａｇ系合金、Ｓｎ−Ｂｉ系合金、Ｓｎ−Ｃｕ系合金、Ｓｎ−Ｚｎ系合金などの鉛フリー半田、Ｐｂ−Ｓｎ系合金半田、共晶半田、低温半田などが挙げられ、これらの半田を１種または２種以上組み合わせて使用することができる。これらの中でも、酸化物超電導線材１を必要以上に加熱しないことを重視するならば、融点が３００℃以下の半田を用いることが好ましい。 When the metal stabilizing layer 8 is joined to the protective layer 7 with solder, a conventionally known solder can be used. As the solder, for example, Sn or Sn-Ag alloy, Sn-Bi alloy, Sn-Cu alloy, Sn-Zn alloy or other lead-free solder, Pb-Sn alloy solder, eutectic solder, low temperature A solder etc. are mentioned, These solders can be used 1 type or in combination of 2 or more types. Among these, if importance is attached to not heating the oxide superconducting wire 1 more than necessary, it is preferable to use solder having a melting point of 300 ° C. or lower.
＜酸化物超電導線材の製造方法＞
以下に、本発明に係る酸化物超電導線材１の製造方法について説明する。
まず、基材２の上方に下地層３と配向層４とキャップ層５からなる中間層及び酸化物超電導層６を形成する。
基材２の上に下地層３を形成する場合は、イオンビームスパッタ法等の公知の成膜方法を適用できる。
下地層３の上に、ＩＢＡＤ法によって配向層４を形成する方法としては、例えばターゲットにイオンビームを照射して、ターゲットの構成粒子を基材２上に飛来させて堆積させるとともに、基材２に対し所定の入射角度でアシスト用のイオンビームを照射する方法が挙げられる。この方法は公知のイオンビームアシストスパッタ装置で実現できる。この方法により結晶配向性の良好な配向層４を得ることができる。
<Oxide superconducting wire manufacturing method>
Below, the manufacturing method of the oxide superconducting wire 1 which concerns on this invention is demonstrated.
First, an intermediate layer composed of a base layer 3, an alignment layer 4, and a cap layer 5 and an oxide superconducting layer 6 are formed above the substrate 2.
In the case of forming the underlayer 3 on the substrate 2, a known film forming method such as an ion beam sputtering method can be applied.
As a method of forming the alignment layer 4 on the underlayer 3 by the IBAD method, for example, the target is irradiated with an ion beam so that the constituent particles of the target fly on the substrate 2 and are deposited. In contrast, there is a method of irradiating an assist ion beam at a predetermined incident angle. This method can be realized by a known ion beam assisted sputtering apparatus. By this method, the alignment layer 4 having good crystal orientation can be obtained.
続いて、キャップ層５及び酸化物超電導層６をＰＬＤ法（パルスレーザー蒸着法）などの成膜法により形成する。良好な配向性を有するキャップ層５上に酸化物超電導層６を形成すると、酸化物超電導層６もキャップ層５の配向性に整合するように結晶化する。
従って得られた酸化物超電導層６は、結晶粒界における量子的結合性に優れ、結晶粒界における超電導特性の劣化が殆どないので、基材２の長さ方向に電気を流し易くなり、十分に高い臨界電流が得られ、優れた超電導性を発揮する。
Subsequently, the cap layer 5 and the oxide superconducting layer 6 are formed by a film forming method such as a PLD method (pulse laser deposition method). When the oxide superconducting layer 6 is formed on the cap layer 5 having good orientation, the oxide superconducting layer 6 is also crystallized so as to match the orientation of the cap layer 5.
Therefore, the obtained oxide superconducting layer 6 is excellent in quantum connectivity at the crystal grain boundary, and hardly deteriorates in the superconducting characteristics at the crystal grain boundary. High critical current is obtained, and excellent superconductivity is exhibited.
次に、酸化物超電導層６の上面を覆うように、Ａｇの保護層を成膜法により形成する。
Ａｇの保護層は、Ａｇのターゲットを用い、常温スパッタリングにより形成できる。常温スパッタにより、アモルファス構造のＡｇの保護層を形成できる。
続いて、前記保護層を備えた酸化物超電導層６を酸素雰囲気下で加熱する処理（酸素アニール処理）を行う。酸素アニール処理を行うことによって、酸化物超電導層６に酸素を供給して、その結晶構造を整え、超電導特性を向上させる。
本発明では、この酸素アニール処理の温度を望ましくは２５０℃以上、３００℃以下の範囲に規定する。これにより、酸素アニール処理の過程で、Ａｇの再結晶化による凝集が抑えられ、酸化物超電導層６の表面が保護層７から露出することを抑えることができる。
Next, an Ag protective layer is formed by a film forming method so as to cover the upper surface of the oxide superconducting layer 6.
The protective layer of Ag can be formed by room temperature sputtering using an Ag target. An amorphous protective layer of Ag can be formed by room temperature sputtering.
Subsequently, a treatment (oxygen annealing treatment) is performed in which the oxide superconducting layer 6 provided with the protective layer is heated in an oxygen atmosphere. By performing the oxygen annealing treatment, oxygen is supplied to the oxide superconducting layer 6 to adjust its crystal structure and improve the superconducting characteristics.
In the present invention, the temperature of the oxygen annealing treatment is desirably set in a range of 250 ° C. or higher and 300 ° C. or lower. Thereby, in the course of the oxygen annealing treatment, aggregation due to recrystallization of Ag is suppressed, and exposure of the surface of the oxide superconducting layer 6 from the protective layer 7 can be suppressed.
即ち、保護層に比較的高い温度（４００〜５００℃）で酸素アニール処理を施すと、その熱によってＡｇが酸化物超電導層６の表面において再結晶化することで凝集する。このとき、再結晶化したＡｇ結晶粒同士の間では、Ａｇが周囲に拡散することにより徐々に厚さが薄くなり、保護層が薄い場合は部分的に空孔が形成されて酸化物超電導層６の上面が露出してしまうおそれがある。なお、Ａｇの保護層が１０μｍ以上の膜厚の場合、Ａｇの再結晶粒の大きさに対し、十分な膜厚があるので、空孔の生成は起こり難いが、Ａｇの保護層の膜厚が１０μｍ以下になって６μｍ程度になると空孔が生成され易くなり、膜厚５μｍ以下では空孔がより生成しやすくなる。 That is, when oxygen annealing treatment is performed on the protective layer at a relatively high temperature (400 to 500 ° C.), Ag is aggregated by recrystallization on the surface of the oxide superconducting layer 6 due to the heat. At this time, between the recrystallized Ag crystal grains, the thickness gradually decreases as Ag diffuses to the periphery, and when the protective layer is thin, vacancies are partially formed and the oxide superconducting layer 6 may be exposed. When the Ag protective layer has a thickness of 10 μm or more, there is a sufficient film thickness with respect to the size of the recrystallized grains of Ag. When the thickness becomes 10 μm or less and becomes about 6 μm, vacancies are easily generated, and when the film thickness is 5 μm or less, vacancies are more easily generated.
これに対して、本発明では、保護層の酸素アニール処理を３００℃以下の比較的低い温度で行うため、当該処理に伴うＡｇの再結晶化による凝集をできる限り抑制し、空孔率の低い保護層７を得ることができる。これにより、酸化物超電導層６の表面を保護層７により覆うことができるため、保護層７から酸化物超電導層６が露出することによる不都合を解消できる。
即ち、酸化物超電導層６から酸素が脱離することによる超電導特性の低下が無くなり、金属安定化層８の半田付け不良が無くなり、めっき液による酸化物超電導層６の腐食の問題を回避することが可能となる。
ただし、酸素アニール処理時の加熱温度が２５０℃未満である場合は、酸化物超電導層６に供給される酸素が不足し、その超電導特性を十分に向上させることができず、また、酸化物超電導層６と保護層７との界面抵抗も高くなる。このため、本発明では、酸素アニール処理温度の下限を２５０℃に規定することが好ましい。
On the other hand, in the present invention, since the oxygen annealing treatment of the protective layer is performed at a relatively low temperature of 300 ° C. or lower, aggregation due to recrystallization of Ag accompanying the treatment is suppressed as much as possible, and the porosity is low. The protective layer 7 can be obtained. Thereby, since the surface of the oxide superconducting layer 6 can be covered with the protective layer 7, inconvenience due to the oxide superconducting layer 6 being exposed from the protective layer 7 can be solved.
That is, the superconducting characteristics are not deteriorated due to the desorption of oxygen from the oxide superconducting layer 6, the soldering failure of the metal stabilizing layer 8 is eliminated, and the problem of corrosion of the oxide superconducting layer 6 due to the plating solution is avoided. Is possible.
However, when the heating temperature at the time of the oxygen annealing treatment is less than 250 ° C., oxygen supplied to the oxide superconducting layer 6 is insufficient, and the superconducting characteristics cannot be sufficiently improved. The interface resistance between the layer 6 and the protective layer 7 is also increased. For this reason, in this invention, it is preferable to prescribe | regulate the minimum of oxygen annealing process temperature to 250 degreeC.
また、２５０℃以上、３００℃以下で行う酸素アニール処理の時間は、６００分以上であることが好ましく、９００分以上であることがより好ましい。これにより、酸素アニール処理の温度が比較的低い場合でも、酸化物超電導層６に十分な酸素を供給することができ、保護層７に空孔が生成することを抑えつつ、酸化物超電導層６の超電導特性を確実に向上させ、酸化物超電導層６と保護層７との界面抵抗を低減させることが可能となる。
次に、保護層７にハンダ層付きの金属安定化層８を貼り合せて加熱ロール圧着するなどの方法により金属安定化層８を保護層７の上に形成する。或いは、公知のめっき法により保護層７上にめっき層からなる金属安定化層８を形成しても良い。
The time for the oxygen annealing treatment performed at 250 ° C. or more and 300 ° C. or less is preferably 600 minutes or more, and more preferably 900 minutes or more. Thereby, even when the temperature of the oxygen annealing treatment is relatively low, sufficient oxygen can be supplied to the oxide superconducting layer 6, and the generation of vacancies in the protective layer 7 can be suppressed, and the oxide superconducting layer 6. Thus, it is possible to improve the superconducting characteristics and reduce the interface resistance between the oxide superconducting layer 6 and the protective layer 7.
Next, the metal stabilizing layer 8 is formed on the protective layer 7 by a method such as bonding the metal stabilizing layer 8 with a solder layer to the protective layer 7 and press-bonding with a heating roll. Or you may form the metal stabilization layer 8 which consists of a plating layer on the protective layer 7 with a well-known plating method.
以上説明のように製造された酸化物超電導線材１は、酸化物超電導層６上に成膜した酸素アニール処理前の保護層での状態はアモルファス層であっても、酸素アニール処理することでＡｇの再結晶化が進行し、Ａｇの再結晶粒の集合体となる保護層７について、空孔のほぼ無い保護層７として酸化物超電導層６の表面を覆うことができる。
このため、保護層７での最大結晶粒径が酸素アニール処理前の保護層の膜厚平均の１．２５倍以内である保護層７を備えた酸化物超電導線材１は、保護層７の膜厚を６μｍ以下などのように、従来よりも薄くした場合であっても、酸化物超電導層６の表面を保護層７により確実に覆うことができる。このため、酸化物超電導層６が保護層７から露出することによる不都合、すなわち、酸化物超電導層６から酸素が脱離することによる超電導特性の低下が無く、金属安定化層８の半田付け不良を生じることがなく、めっき液による酸化物超電導層６の腐食の問題を回避しつつ、コストの低減を図ることが可能となる。
The oxide superconducting wire 1 manufactured as described above is obtained by performing the oxygen annealing treatment even if the protective layer before the oxygen annealing treatment formed on the oxide superconducting layer 6 is in an amorphous layer. Thus, the surface of the oxide superconducting layer 6 can be covered as the protective layer 7 having almost no voids in the protective layer 7 which is an aggregate of Ag recrystallized grains.
Therefore, the oxide superconducting wire 1 including the protective layer 7 having the maximum crystal grain size in the protective layer 7 within 1.25 times the average thickness of the protective layer before the oxygen annealing treatment is the film of the protective layer 7. Even when the thickness is made thinner than conventional, such as 6 μm or less, the surface of the oxide superconducting layer 6 can be reliably covered with the protective layer 7. For this reason, there is no inconvenience due to the oxide superconducting layer 6 being exposed from the protective layer 7, that is, there is no deterioration in superconducting characteristics due to the desorption of oxygen from the oxide superconducting layer 6, and poor soldering of the metal stabilization layer 8 Thus, it is possible to reduce the cost while avoiding the problem of corrosion of the oxide superconducting layer 6 caused by the plating solution.
ハステロイＣ−２７６（米国ヘインズ社商品名：表面粗さＲａ≒５ｎｍ）からなる幅１０ｍｍ、厚み１００μｍ、長さ１０００ｍｍのテープ状の基材本体上に、下地層であるＡｌ２Ｏ３の拡散防止層（厚み１００ｎｍ）と、下地層であるＹ２Ｏ３のベッド層（厚み２５ｎｍ）と、ＩＢＡＤ法で形成したＭｇＯの配向層（厚み１０ｎｍ）と、ＰＬＤ法で形成したＣｅＯ２のキャップ層（厚み３００ｎｍ）からなる中間層と、ＰＬＤ法によるＧｄＢａ２Ｃｕ３Ｏ７−ｘで示される組成の酸化物超電導層（厚み２μｍ）を、この順で積層した。
次に、Ａｇ板をターゲットとして用いた常温ＤＣスパッタ法により、酸化物超電導層の上面を覆うようにＡｇの保護層（厚み２μｍ）を成膜した。
続いて、保護層を形成したテープ状の基材を、酸素含有雰囲気とした加熱炉内に収容し、以下の表１に示す温度および時間で酸素アニール処理し、２６時間炉冷した後、加熱炉から取り出した。以上の工程により、酸化物超電導線材を得た。
Prevention of diffusion of Al 2 O 3 as a base layer on a tape-shaped base body having a width of 10 mm, a thickness of 100 μm, and a length of 1000 mm made of Hastelloy C-276 (trade name: surface roughness Ra≈5 nm). Layer (thickness 100 nm), Y 2 O 3 bed layer (thickness 25 nm) as an underlayer, MgO alignment layer (thickness 10 nm) formed by IBAD method, and CeO 2 cap layer (by PLD method) An intermediate layer having a thickness of 300 nm) and an oxide superconducting layer (thickness: 2 μm) having a composition represented by GdBa 2 Cu 3 O 7-x by the PLD method were stacked in this order.
Next, an Ag protective layer (thickness: 2 μm) was formed so as to cover the upper surface of the oxide superconducting layer by room temperature DC sputtering using an Ag plate as a target.
Subsequently, the tape-shaped substrate on which the protective layer was formed was housed in a heating furnace having an oxygen-containing atmosphere, subjected to oxygen annealing treatment at the temperature and time shown in Table 1 below, cooled in the furnace for 26 hours, and then heated. Removed from the furnace. The oxide superconducting wire was obtained by the above process.
Ａｇの保護層の厚みを６μｍとし、以下の表１に示す温度および時間で酸素アニール処理を行うこと以外は、前述と同様の工程により、酸化物超電導線材を得た。 An oxide superconducting wire was obtained by the same process as described above except that the thickness of the protective layer of Ag was 6 μm and the oxygen annealing treatment was performed at the temperature and time shown in Table 1 below.
＜評価＞
実施例および比較例で作製した酸化物超電導線材について、走査型電子顕微鏡を用いて表面の組織写真を撮影し、該写真を画像解析することによってＡｇ保護層の空孔率（酸化物超電導層露出率）を測定した。また、７７ＫでのＡｇ保護層と酸化物超電導層との界面抵抗および磁化測定装置（ＴＨＥＶＡ社製）による臨界電流（Ｉｃ）を測定した。その結果を表２に示す。また、実施例４および比較例２で作製した酸化物超電導線材について、走査型電子顕微鏡による組織表面の拡大写真を図２、図３にそれぞれ示す。
<Evaluation>
For the oxide superconducting wires produced in the examples and comparative examples, a surface structure photograph was taken using a scanning electron microscope, and the porosity of the Ag protective layer (exposure of the oxide superconducting layer was exposed by analyzing the photograph). Rate). Further, the interface resistance between the Ag protective layer and the oxide superconducting layer at 77K and the critical current (Ic) by a magnetization measuring device (manufactured by THEVA) were measured. The results are shown in Table 2. Moreover, about the oxide superconducting wire produced in Example 4 and Comparative Example 2, enlarged photographs of the structure surface by a scanning electron microscope are shown in FIGS. 2 and 3, respectively.
表２に示すように、Ａｇ結晶粒の最大結晶粒径が２．５μｍ以下（酸素アニール処理前の保護層の膜厚平均の１．２５倍以下）の保護層（実施例１〜実施例９）は、いずれも、Ａｇ結晶粒の最大結晶粒径が２．５μｍを超える保護層（比較例１〜比較例３）に比べて、空孔率がはるかに小さい値となっている。また、このうち特に、酸素アニールの処理温度を２５０℃以上、３００℃以下とした実施例４〜実施例９の酸化物超電導線材は、界面抵抗が低く、臨界電流Ｉｃが高い値となっている。
更に、酸素アニール処理の時間を９００分とした実施例４、実施例９の酸化物超電導線材は、臨界電流Ｉｃが最も優れた値となっており、優れた超電導特性が得られる。
これらのことから、保護層に含まれるＡｇ結晶粒の最大結晶粒径を規定することにより、保護層の膜厚を２μｍと薄くしながら、空孔率の小さい保護層を得ることができた。更に、酸素アニール処理の温度を２５０℃以上、３００℃以下とした上に、時間を９００分以上に規定することにより、超電導特性に優れ、酸化物超電導層と保護層との界面抵抗が低く、より安価に生産できる酸化物超電導線材を実現できることがわかった。
As shown in Table 2, the protective layer (Examples 1 to 9) having a maximum crystal grain size of Ag crystal grains of 2.5 μm or less (1.25 times or less of the average thickness of the protective layer before the oxygen annealing treatment). ) Has a much smaller porosity than the protective layers (Comparative Examples 1 to 3) in which the maximum crystal grain size of Ag crystal grains exceeds 2.5 μm. Of these, in particular, the oxide superconducting wires of Examples 4 to 9 in which the oxygen annealing treatment temperature is 250 ° C. or higher and 300 ° C. or lower have low interface resistance and high critical current Ic. .
Furthermore, the oxide superconducting wires of Example 4 and Example 9 in which the oxygen annealing treatment time is 900 minutes have the most excellent critical current Ic, and excellent superconducting characteristics can be obtained.
From these facts, by defining the maximum crystal grain size of Ag crystal grains contained in the protective layer, it was possible to obtain a protective layer with a low porosity while reducing the thickness of the protective layer to 2 μm. Furthermore, by setting the temperature of the oxygen annealing treatment to 250 ° C. or more and 300 ° C. or less and defining the time to 900 minutes or more, the superconducting properties are excellent, and the interface resistance between the oxide superconducting layer and the protective layer is low, It was found that an oxide superconducting wire that can be produced at a lower cost can be realized.
なお、アモルファスの保護層からＡｇの結晶粒が成長する場合、保護層における粒径の大小は酸素アニール時の温度による影響が支配的である。このため、酸素アニール処理前の保護層の空孔率は表２に示す膜厚２μｍの場合に対し、仮に、膜厚４μｍ、５μｍの保護層を用いた場合の方が低い空孔率となる。よって、空孔率に関し、実施例１〜９の試料を見て低い空孔率が得られていることから、２μｍより膜厚の大きな保護層、例えば、２〜６μｍの保護層を用いた場合に表２の試料と同じ条件で酸素アニールするならば、いずれも低い空孔率の保護層を得られることが分かる。
また、表２の実施例１〜７の試料が１．３〜１．９μｍのＡｇ結晶粒径であることから鑑み、実施例１〜７の各試料に適用した条件で製造することで、膜厚２μｍよりも薄い膜厚、例えば、１．５μｍまでの膜厚の酸素アニール処理前の保護層であっても、低い空孔率、低い界面抵抗、高いＩｃ値を示す酸化物超電導線材を製造可能であることも分かる。
これらの結果から鑑み、表２に示す酸素アニール処理前の保護層の膜厚２μｍの試料と６μｍの試料の結果から総合的に考察すると、膜厚１．５μｍ以上、６μｍ以下の範囲の保護層を用い、表２に示す試料と同等の酸素アニール条件で処理することで、空孔率の小さいＡｇの保護層を確実に得ることができことが明かである。また、酸素アニール条件を選択することで、空孔率が小さく、界面抵抗が小さいＡｇの保護層を得られることが分かり、更に条件を選択することで、空孔率が小さく、界面抵抗が小さく、かつ、臨界電流が高いＡｇの保護層を製造できることもわかる。
When Ag crystal grains grow from the amorphous protective layer, the influence of the temperature during oxygen annealing is dominant on the size of the grain size in the protective layer. For this reason, the porosity of the protective layer before the oxygen annealing treatment is lower when the protective layer having a film thickness of 4 μm and 5 μm is used than when the film thickness is 2 μm shown in Table 2. . Therefore, regarding the porosity, a low porosity was obtained by looking at the samples of Examples 1 to 9, and thus a protective layer having a thickness greater than 2 μm, for example, a protective layer having a thickness of 2 to 6 μm was used. In addition, it can be seen that a protective layer having a low porosity can be obtained if oxygen annealing is performed under the same conditions as the samples in Table 2.
Moreover, in view of the fact that the samples of Examples 1 to 7 in Table 2 have an Ag crystal grain size of 1.3 to 1.9 μm, the film was manufactured under the conditions applied to each sample of Examples 1 to 7. Produces oxide superconducting wires that exhibit low porosity, low interface resistance, and high Ic value even for protective layers with a thickness of less than 2 μm, for example, up to 1.5 μm before oxygen annealing. You can see that it is possible.
In view of these results, the protective layers in the range of 1.5 μm or more and 6 μm or less in thickness are considered from the results of the samples of 2 μm and 6 μm in thickness of the protective layer before oxygen annealing shown in Table 2. It is clear that an Ag protective layer having a low porosity can be obtained with certainty by processing under oxygen annealing conditions equivalent to those of the samples shown in Table 2. It can also be seen that by selecting the oxygen annealing conditions, an Ag protective layer having a low porosity and a low interface resistance can be obtained, and by selecting the conditions further, the porosity is low and the interface resistance is low. It can also be seen that an Ag protective layer having a high critical current can be produced.
本発明は、例えば酸化物超電導送電線や超電導マグネット用のコイル巻線に利用することができる酸化物超電導線材を提供する。 The present invention provides an oxide superconducting wire that can be used for, for example, an oxide superconducting power transmission line or a coil winding for a superconducting magnet.
１…酸化物超電導線材、２…基材、３…下地層、４…配向層、５…キャップ層、６…酸化物超電導層、７…保護層、８…金属安定化層、９…絶縁被覆層。 DESCRIPTION OF SYMBOLS 1 ... Oxide superconducting wire, 2 ... Base material, 3 ... Underlayer, 4 ... Orientation layer, 5 ... Cap layer, 6 ... Oxide superconducting layer, 7 ... Protective layer, 8 ... Metal stabilization layer, 9 ... Insulation coating layer.
Claims (5)
前記保護層は、前記酸化物超電導層上に形成した保護層に対しＡｇの再結晶温度以上で酸素アニール処理が施されて形成され、前記酸素アニール処理後の保護層に含まれるＡｇ結晶粒の最大結晶粒径が、前記酸素アニール処理後の保護層の膜厚平均の１．２５倍以下であることを特徴とする酸化物超電導線材。 An oxide superconducting wire comprising a base material, an intermediate layer provided above the base material, an oxide superconducting layer, and an Ag protective layer,
The protective layer is formed by subjecting the protective layer formed on the oxide superconducting layer to an oxygen annealing treatment at a temperature equal to or higher than the recrystallization temperature of Ag, and forming Ag crystal grains contained in the protective layer after the oxygen annealing treatment. An oxide superconducting wire, wherein the maximum crystal grain size is 1.25 times or less of the average thickness of the protective layer after the oxygen annealing treatment.
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