JP5565652B2 - Superconducting element - Google Patents
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Description
本発明は、導電性材料と超電導材料と絶縁材料によって構成される電導素子に関する。 The present invention relates to a conductive element including a conductive material, a superconducting material, and an insulating material.
ＭｇＢ２の細線が超電導特性を発現することは、特許文献１に示されるように従来より知られている事実である。しかしながら、特許文献１の発明の詳細な説明に記載されているように、従来行われてきたＭｇＢ２ナノ細線に関する評価は、その磁気的性質に限定されてきた。電流を通すことにより、ＭｇＢ２ナノ細線がどのような挙動を示すかについては、全く明らかにされていない。
また特許文献２にも、ＭｇＢ２ナノ細線の超電導特性として磁化測定データが示されているのみである。 これらの知見は、ＭｇＢ２ナノ細線を、特許文献３、４に示されるような超電導素子に使用することを想定しているものと思われる。
これら従来技術では、超電導体自身は、その電流の流れ方向に長いものであるとの概念のもとに作られたものである。
It is a fact conventionally known that the fine wire of MgB 2 develops superconducting properties as shown in Patent Document 1. However, as described in the detailed description of the invention of Patent Document 1, the conventional evaluation on MgB 2 nanowires has been limited to its magnetic properties. It has not been clarified at all how MgB 2 nanowires behave by passing an electric current.
Patent Document 2 also shows only magnetization measurement data as the superconducting characteristics of MgB 2 nanowires. These findings seem to assume that MgB 2 nanowires are used in superconducting elements as shown in Patent Documents 3 and 4.
In these prior arts, the superconductor itself is made based on the concept that it is long in the direction of current flow.
本発明は、このような従来の概念では想起し得なかった構造を持つ超電導デバイスを提供するものである。 The present invention provides a superconducting device having a structure which cannot be conceived by such a conventional concept.
発明１の超電導素子は、導電性材料と超電導材料と絶縁材料とからなる超電導素子であって、前記導電性材料からなる導電部材と、この表面を被覆する前記絶縁材料からなる被覆層と、この被覆層中に埋め込まれている前記超電導材料であって、幹より多数の枝が分岐されてなる樹木状のナノ細線からなり、前記ナノ細線の前記幹の一端が前記導電部材に電気的に接続され、他端が前記被覆層中に埋没されてなることを特徴とする。
発明２は、発明１の超電導素子において、前記超電導材料がＭｇＢ２であり、前記絶縁材料がＭｇＯであることを特徴とする。
The superconducting element of the invention 1 is a superconducting element comprising a conductive material, a superconducting material, and an insulating material, the conductive member comprising the conductive material, the coating layer comprising the insulating material covering the surface, the embedded in the coating layer a superconducting material consists dendritic nanowires multiple branches from the stem is formed by branched, electrically to one end of the conductive member of said stem of said nanowire It is connected and the other end is buried in the coating layer.
Invention 2, in the superconducting device of the invention 1, wherein the superconducting material is MgB 2, wherein said insulating material is MgO.
本発明の超電導素子では、超電導細線の方向性に関係なく、前記導電性材料への通電特性に、前記ナノ細線の一次元性を反映した超電導特性を発現させることができた。
具体的には、転移幅１ Ｋ以下の鋭い超電導転移を示すことが可能である。
ナノ細線への磁束線の侵入が抑えられる結果、見掛け上極めて高い臨界電流密度を示す。
そして、本発明の素子は、導電性部材へ電気配線を施すだけで、ナノ細線の一次元超電導性を反映した電流輸送特性を得ることができるため、一次元超電導デバイス用の素子として高い利用価値を備えている。
また、その製造についても、化学的な合成法を用いることで、本発明の主要な構造を形成することができるので、従来のようなナノ成型技術に伴う問題を生じることなく、複雑なナノ構造を得ることが出来得る。
In the superconducting element of the present invention, the superconducting characteristics reflecting the one-dimensionality of the nanowires can be expressed in the current-carrying characteristics to the conductive material regardless of the directionality of the superconducting wires.
Specifically, it is possible to show a sharp superconducting transition having a transition width of 1 K or less.
As a result of suppressing the penetration of magnetic flux lines into the nanowires, it appears to have an extremely high critical current density.
The element of the present invention can obtain current transport characteristics reflecting the one-dimensional superconductivity of the nanowire simply by applying electrical wiring to the conductive member, and thus has high utility value as an element for a one-dimensional superconducting device. It has.
In addition, since the main structure of the present invention can be formed by using a chemical synthesis method for the production, complicated nanostructures can be produced without causing problems associated with conventional nano-molding techniques. Can be obtained.
本明細書に記載の参考文献からも明らかな通り、本発明に用いられる材料としては、下記実施例のものに限らず各種のものが知られており、これらより適宜して、実施例に示す構造と同様な構造を有さしめることに何らの問題はない。
また、その形状を板状、リボン状あるいは線状とすることも可能である。
As is clear from the references described in the present specification, the materials used in the present invention are not limited to those in the following examples, and various materials are known. There is no problem in having a structure similar to the structure.
Further, the shape can be a plate, a ribbon or a line.
塩化マグネシウム（ＭｇＣｌ２、９９．９％、高純度化学）、塩化カリウム（ＫＣｌ、９９％、高純度化学）、塩化ナトリウム（ＮａＣｌ、９９ ％、Ａｌｄｒｉｃｈ）、およびホウ酸マグネシウム（ＭｇＢ２Ｏ４、キシダ化学）を表1に示す割合で混合して、高純度アルゴンガス（９９．９９９９ ％）気流下、６００ ℃に加熱し、溶融塩（１）とする。機械攪拌により、常に溶融塩組成の均一性を保つ。
一方、表面酸化被膜を除去した純鉄板（幅１０ｍｍ×厚さ０．５ｍｍ）を飽和ホウ酸水溶液に浸潤後、大気中で十分に乾燥させて導電部材を生成する。
この導電部材を、太さ１ｍｍのグラファイト棒とともに、前記溶融塩中に挿入する。グラファイト棒を正極、鉄基板を負極として、表1の電着条件で処理することにより、導電部材の表面に絶縁性被膜を形成した。導電部材を溶融塩から取り出し、メタノール洗浄を行うと、その表面は、表1に示す厚さの黒色電着膜（絶縁性被膜）によって被覆されていた。
そして、下記する分析結果から、その絶縁性被膜内には、表1に示すような超電導ナノ細線が形成されていた。
Magnesium chloride (MgCl 2, 99.9%, Pure Chemical), potassium chloride (KCl, 99%, high purity chemical), sodium chloride (NaCl, 99%, Aldrich), and magnesium borate (MgB 2 O 4, (Kida Chemical) is mixed at the ratio shown in Table 1 and heated to 600 ° C. in a stream of high-purity argon gas (99.9999%) to obtain a molten salt (1). Uniformity of the molten salt composition is always maintained by mechanical stirring.
On the other hand, a pure iron plate (width 10 mm × thickness 0.5 mm) from which the surface oxide film has been removed is infiltrated into a saturated boric acid aqueous solution and then sufficiently dried in the air to produce a conductive member.
This conductive member is inserted into the molten salt together with a graphite rod having a thickness of 1 mm. By treating the graphite rod as the positive electrode and the iron substrate as the negative electrode under the electrodeposition conditions shown in Table 1, an insulating film was formed on the surface of the conductive member. When the conductive member was taken out of the molten salt and washed with methanol, the surface was covered with a black electrodeposition film (insulating film) having a thickness shown in Table 1.
From the analysis results described below, superconducting nanowires as shown in Table 1 were formed in the insulating coating.
絶縁性被膜層によって被覆された導電部材表面から得られたＸ線回折（ＸＲＤ）の結果を示す（図１）。
導電材料である鉄の回折ピーク以外に、ＭｇＯに帰属される複数の回折ピークが認められる。一方、ＭｇＢ２ １０１回折のピークが、ＭｇＯ ２００回折ピークの肩として観察される。
絶縁性被膜層は、主相のＭｇＯと、副相のＭｇＢ２（体積分率 ＜２０％）によって構成されていることが分かる。
図２の導電部材表面から剥離した絶縁性被膜層の透過電子顕微鏡（ＴＥＭ）像と、図3の導電部材表面に平行に切断した絶縁性被膜層の横断面のTEM像から、以下の事実が明らかとなった。
中間的なコントラストを持つ不定形相（Ａ相）と共に、低いコントラストを持つ幹の太さ約１×102ｎｍの樹木状のナノ細線が多数並立する組織（Ｂ相）が認められる。
電子線回折（ＴＥＤ）観測の結果、ＡおよびＢ相はそれぞれ、単相ＭｇＯおよび単相ＭｇＢ２に帰属された。
ＴＥＤの回折点の鋭さから、ＭｇＢ２ナノ細線は高い結晶性を備えているものと結論される。
絶縁性被膜層は、ナノ細線状のＭｇＢ２相と、バルク状のＭｇＯ相（以後、ＭｇＯマトリックスと呼ぶ）とが混じり合った、特殊なナノ構造を備えていることが分かる。
その結果を模式的に図5に示す。
The result of X-ray diffraction (XRD) obtained from the surface of the conductive member covered with the insulating coating layer is shown (FIG. 1).
In addition to the diffraction peak of iron, which is a conductive material, a plurality of diffraction peaks attributed to MgO are observed. On the other hand, the MgB 2 101 diffraction peak is observed as the shoulder of the MgO 200 diffraction peak.
It can be seen that the insulating coating layer is composed of the main phase MgO and the subphase MgB 2 (volume fraction <20%).
From the transmission electron microscope (TEM) image of the insulating coating layer peeled off from the surface of the conductive member in FIG. 2 and the TEM image of the cross section of the insulating coating layer cut parallel to the surface of the conductive member in FIG. It became clear.
Along with an amorphous phase (A phase) having an intermediate contrast, a structure (B phase) in which a large number of dendritic nanowires having a low contrast and a trunk thickness of about 1 × 10 2 nm are juxtaposed is observed.
As a result of electron beam diffraction (TED) observation, the A and B phases were assigned to single-phase MgO and single-phase MgB 2 , respectively.
From the sharpness of the TED diffraction point, it is concluded that MgB 2 nanowires have high crystallinity.
It can be seen that the insulating coating layer has a special nanostructure in which nanowire-like MgB 2 phase and bulk MgO phase (hereinafter referred to as MgO matrix) are mixed.
The result is schematically shown in FIG.
絶縁性被膜層を導電部材表面平行に切断・薄片化し、断面ＴＥＭ試料を作製した。絶縁性被膜層横断面の高分解能ＴＥＭ像を示す図３において、画面中央、１００ｎｍ２程度の多角形領域に、周囲のＭｇＯ（２００）原子列像に埋め込まれる形で、ＭｇＢ２（００１）原子列像が認められる。これは、基板表面垂直に伸長したＭｇＢ２ナノ細線の垂直断面像と見做すことができる。
導電部材表面に垂直に切断した電着膜断面に対し、電子線プローブマイクロアナライザ （ＥＰＭＡ）を用い、ホウ素の空間分布マッピングを行った結果をしめす図４では、ＭｇＯマトリックス中に埋め込まれたＭｇＢ２ナノ細線が、導電部材表面に垂直な方向に伸びる樹枝状構造として観察されている。
上記結果を総合して、導電部材表面に対して垂直に伸長した超電導ＭｇＢ２ナノ細線が、絶縁体ＭｇＯ内部に埋め込まれた形態を持つ、金属・超電導・絶縁体複合材料であると結論できる。（図５）。
The insulating coating layer was cut and sliced in parallel with the surface of the conductive member to prepare a cross-sectional TEM sample. In FIG. 3 showing a high-resolution TEM image of a cross-section of the insulating coating layer, MgB 2 (001) atoms are embedded in the surrounding MgO (200) atomic sequence image in the polygonal region of about 100 nm 2 at the center of the screen. A row image is recognized. This can be regarded as a vertical cross-sectional image of MgB 2 nanowires extending perpendicular to the substrate surface.
FIG. 4 shows the result of spatial distribution mapping of boron using an electron beam probe microanalyzer (EPMA) on the cross section of the electrodeposited film cut perpendicular to the surface of the conductive member. In FIG. 4, MgB 2 embedded in an MgO matrix is shown. Nanowires are observed as dendritic structures extending in a direction perpendicular to the surface of the conductive member.
By summing up the above results, it can be concluded that the superconducting MgB 2 nanowires extending perpendicularly to the surface of the conductive member are a metal / superconducting / insulator composite material having a form embedded in the insulator MgO. (FIG. 5).
導電部材に電流・電圧端子を取り付け、四端子法によって電気輸送特性を評価した。
電気抵抗率の温度依存性を示す図６より、３４Ｋにおいて、ＭｇＢ２ナノ細線の超電導転移に伴う鋭い（遷移温度＜１Ｋ）電気抵抗率の温度変化が認められる。ＭｇＢ２ナノ細線は、導電部材と高い電気的導通を保っていることが分かる。
有限磁場下での超電導臨界電流測定結果を示す図７では、５Ｋおよび２０Ｋそれぞれの測定温度において、絶縁性被膜層全体の臨界電流密度として、１×１０５Ａｃｍ−２および４×１０４Ａｃｍ−２という値が得られた。絶縁性被膜層中のＭｇＢ２相の体積分率の低さ（＜２０％）を考慮すると、ＭｇＢ２ナノ細線は全体として、極めて高い臨界電流密度（＞５×１０５Ａｃｍ−２ ＠５ Ｋ；＞２×１０５Ａｃｍ−２＠２０ Ｋ）を備えていることが分かる。
A current / voltage terminal was attached to the conductive member, and the electrotransport characteristics were evaluated by a four-terminal method.
From FIG. 6 showing the temperature dependency of the electrical resistivity, a sharp (transition temperature <1K) temperature change of the electrical resistivity accompanying the superconducting transition of the MgB 2 nanowire is observed at 34K. It can be seen that the MgB 2 nanowire maintains high electrical continuity with the conductive member.
In FIG. 7 showing the results of superconducting critical current measurement under a finite magnetic field, 1 × 10 5 Acm −2 and 4 × 10 4 Acm − are obtained as critical current densities of the entire insulating coating layer at measurement temperatures of 5K and 20K, respectively. A value of 2 was obtained. Considering the low volume fraction (<20%) of the MgB 2 phase in the insulating coating layer, the MgB 2 nanowires as a whole have a very high critical current density (> 5 × 10 5 Acm −2 @ 5 K > 2 × 10 5 Acm −2 @ 20 K).
図１は、電着膜表面から得られたＸＲＤ測定結果であり、ピーク位置に対応する面指数を記す。挿入図は、ＭｇＯ ２００反射近傍の拡大図である。
図２は、剥離電着膜のＴＥＭ像。挿入図Ａ・Ｂはそれぞれ、ＴＥＭ像中Ａ・Ｂで示した部分から得られたＴＥＤ像である。挿入図中に、回折点に対応する面指数を記す。
図３は、基板表面平行に切断した電着膜の断面ＴＥＭ像。収束イオン線（ＦＩＢ）を用い、超高真空下で切断・成形作業を行った。試料厚さは ＜ ５０ ｎｍである。
図４は、基板表面垂直に切断した電着膜の断面ＥＰＭＡ像。ホウ素の特性Ｘ線を用い、元素マッピングを行った。
図６は、材料全体の電気抵抗率の温度依存性。電流端子、電圧端子ともに、金属基板に取り付けられた。測定電流の方向は、金属基板表面に平行である。
図７は、電着膜全体の臨界電流密度の磁場依存性。電流端子、電圧端子ともに、金属基板に取り付けられた。測定電流方向は金属基板表面に平行、磁場の方向は、金属基板表面に垂直である。臨界電流密度は、測定された臨界電流を、電着膜の厚みと幅で割ることによって求められた。
FIG. 1 is an XRD measurement result obtained from the electrodeposited film surface, and shows a surface index corresponding to the peak position. The inset is an enlarged view of the vicinity of the MgO 200 reflection.
FIG. 2 is a TEM image of the peeled electrodeposition film. Insets A and B are TED images obtained from portions indicated by A and B in the TEM image, respectively. In the inset, the surface index corresponding to the diffraction point is noted.
FIG. 3 is a cross-sectional TEM image of the electrodeposition film cut parallel to the substrate surface. Using a focused ion beam (FIB), cutting and forming operations were performed under ultra-high vacuum. The sample thickness is <50 nm.
FIG. 4 is a cross-sectional EPMA image of the electrodeposition film cut perpendicular to the substrate surface. Elemental mapping was performed using characteristic X-rays of boron.
FIG. 6 shows the temperature dependence of the electrical resistivity of the entire material. Both current and voltage terminals were attached to a metal substrate. The direction of the measurement current is parallel to the metal substrate surface.
FIG. 7 shows the magnetic field dependence of the critical current density of the entire electrodeposited film. Both current and voltage terminals were attached to a metal substrate. The measurement current direction is parallel to the metal substrate surface, and the magnetic field direction is perpendicular to the metal substrate surface. The critical current density was determined by dividing the measured critical current by the thickness and width of the electrodeposited film.
Claims (2)
A superconducting element according to claim 1, wherein the superconducting material is MgB 2, superconducting device, wherein the insulation material is MgO.
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