JP5087447B2 - Oxide superconducting wire and manufacturing method of oxide superconducting wire - Google Patents

Description

  The present invention relates to an oxide superconducting wire and a method for manufacturing an oxide superconducting wire.

  Conventionally, a YBaCuO-based rare earth oxide superconductor is known as an oxide superconductor having a critical temperature (TC) exceeding a liquid nitrogen temperature (about 77 K). Various studies have been conducted to apply these oxide superconductors to various superconducting applications such as power transport, superconducting magnets, and superconducting devices. As one method for producing such an oxide superconductor, a method of forming an oxide superconducting thin film on the surface of a substrate by a film forming means such as chemical vapor deposition (CVD) is known. It is known that the oxide superconducting layer formed by this film forming means has a larger critical current density (Jc) than a superconductor obtained by processing a bulk material and has excellent superconducting characteristics. The CVD method is attracting attention as a means that can form a thicker film in a shorter time than a film forming means such as sputtering.

  However, a superconducting wire using a rare earth oxide superconductor thin film exhibits a high critical current density when the superconducting thin film is thin, but the critical current density decreases as the thickness of the superconducting thin film increases.

  In order to prevent the critical current density from decreasing as the film thickness of the superconducting thin film increases, conventionally, the film temperature of the superconducting thin film is controlled by increasing the temperature as the film thickness increases. Measures such as high temperature are taken. However, since this method performs temperature control, there is a problem that there are limitations depending on the method and equipment that can be applied.

An object of the present invention is to provide an oxide superconducting wire capable of suppressing a decrease in critical current density without increasing the temperature even when the thickness of the superconducting thin film is increased.
Another object of the present invention is to provide an oxide superconducting wire manufacturing method capable of suppressing a decrease in critical current density without increasing the temperature even when the thickness of the superconducting thin film increases. .

In order to solve the above problems, the oxide superconducting wire of the present invention includes a base material, an intermediate layer laminated on the base material, and a rare earth oxide superconductor RE-Ba- laminated on the intermediate layer. Superconductivity including a thin film layer made of Cu-O (wherein RE is selected from one or more rare earth elements (La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Y and Yb)) In the thin film wire, the thin film layer is characterized in that the Ba composition ratio decreases and the rare earth element composition ratio relatively increases as the distance from the intermediate layer increases.
The oxide superconducting wire of the present invention includes a base material, an intermediate layer laminated on the base material, and a rare-earth oxide superconductor RE-Ba-Cu-O laminated on the intermediate layer (wherein RE is a superconducting thin film wire comprising a thin film layer comprising a rare earth element (selected from one or more of La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Y, and Yb). As the distance from the intermediate layer increases, the composition ratio of Ba and Cu decreases, and the composition ratio of the rare earth element relatively increases.

The method for producing an oxide superconducting wire according to the present invention includes a rare earth oxide superconductor RE-Ba-Cu-O (wherein RE is a rare earth element) by an MOCVD method on an intermediate layer laminated on a substrate. In the method of manufacturing a superconducting thin film wire in which a thin film layer made of La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Y, and Yb) is selected from one or two or more) is laminated. When the film is formed, the composition ratio of Ba is decreased and the composition ratio of the rare earth element is relatively increased as the film thickness increases.
In addition, the method for producing an oxide superconducting wire according to the present invention includes a rare earth-based oxide superconductor RE-Ba-Cu-O (wherein RE is a rare earth) by an MOCVD method on an intermediate layer laminated on a substrate. In the method for producing an oxide superconducting wire in which a thin film layer made of an element (selected from one or more selected from La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Y and Yb) is laminated, When forming a thin film layer, the composition ratio of Ba and Cu is decreased and the composition ratio of the rare earth element is relatively increased as the film thickness increases.

According to the oxide superconducting wire of the present invention, when the composition ratio of Ba , or both Ba and Cu is decreased according to the film thickness during production, the composition ratio of the rare earth element is relatively increased, and the rare earth element is increased. As a result, the pinning effect of fixing the magnetic flux is obtained and the generation of precipitates is suppressed. As a result, in the oxide superconducting wire according to the first aspect of the present invention, even when the thickness of the superconducting thin film is increased, the decrease in critical current density can be suppressed without increasing the temperature.

According to the oxide superconducting wire manufacturing method of the present invention, when the composition ratio of Ba or both Ba and Cu is decreased according to the film thickness, the composition ratio of the rare earth element is relatively increased. Elemental oxides are interspersed, so that a pinning effect for fixing the magnetic flux is obtained, and generation of precipitates is suppressed. As a result, in the method for manufacturing an oxide superconducting wire according to the fifth aspect of the present invention, even when the thickness of the superconducting thin film is increased, the decrease in critical current density can be suppressed without increasing the temperature.

Hereinafter, an oxide superconducting wire according to an embodiment of the present invention and a manufacturing method thereof will be described.
As for the base material of the oxide superconducting wire of this embodiment, Hastelloy (registered trademark), silver, platinum, stainless steel, etc. can be mentioned as the material, and the long tape, plate material, etc. are mentioned as the shape. be able to. The thickness of the substrate is preferably about 50 μm to 1 mm (for example, 100 μm), but is not limited to this value.

The intermediate layer laminated on the substrate can include Gd—Zr oxide (GZO: Gd ₂ Zr ₂ O ₇ ) as the first intermediate layer, but is not limited to GZO. The first intermediate layer is formed by laminating a thin film layer of a rare earth element of a ceramic material on a base material made of a metal material, so that the thermal expansion coefficient of the base material and the ceramic material is relaxed and the lattice constant of the crystal is different. Is provided in order to alleviate the above and further control the crystal orientation of the thin film layer. The formation of the first intermediate layer can be performed by an IBAD method (ion beam assist method). The thickness of the first intermediate layer may be about 1 μm, but is not limited to this.

A second intermediate layer may be provided between the first intermediate layer and the thin film layer. The second intermediate layer can be formed by, for example, a pulse laser deposition method (PLD method). Examples of the compound forming the second intermediate layer include CeO ₂ , but the compound is not limited and may be other than CeO ₂ .

When CeO ₂ is formed as the second intermediate layer on the first intermediate layer made of GZO, the crystal orientation of the first intermediate layer can be made particularly good as that of a single crystal. The combination is not limited to this example combination. For example, a stacked structure of MgO layer, YSZ (yttrium-stabilized zirconia) and CeO _{2, and} a stacked structure of Y ₂ O ₃ , YSZ and CeO ₂ are also known as stacked structures for controlling crystal orientation. May be used. In addition, an underlayer for orientation control as another generally known oxide superconducting layer may be used as a substrate using a single layer structure or a multilayer structure.

A thin film layer is formed on the first intermediate layer or the second intermediate layer. The thin film layer is made of a rare earth oxide superconductor RE-Ba-Cu-O (wherein RE is one of rare earth elements (La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Y and Yb) or 2 or more types are selected). The thin film layer is formed to have a thickness of several μm by MOCVD (metal organic chemical vapor deposition). As a raw material of the thin film layer of this embodiment, a metal complex, specifically, a THF (tetrahydrofuran) solution of Y (DMP) ₃ , Ba (DMP) ₂ , Cu (DMP) ₂ complex is used, and the temperature is 800 ° C. to 930 ° C. In this range, the film is formed at a constant film formation temperature. DMP is dipivaloylmethanato. The thin film layer is epitaxially grown in a form that matches the crystal orientation of the first or second intermediate layer at the time of film formation, the crystal orientation of the thin film layer becomes good, and excellent superconducting characteristics are obtained.

  The characteristic of the present invention is that as the thin film layer is separated from the intermediate layer, the composition ratio of at least one of Ba and Cu decreases, and the composition ratio of the rare earth element relatively increases. It is that. A decrease in the composition ratio of at least one of Ba and Cu means that as the distance from the intermediate layer increases, the composition ratio of Ba decreases and the composition ratio of the rare earth element relatively increases. Alternatively, as the distance from the intermediate layer increases, the composition ratio of Cu may decrease and the composition ratio of the rare earth element may relatively increase. Alternatively, as the distance from the intermediate layer increases, the composition ratio of Ba and Cu may both decrease and the composition ratio of the rare earth element may relatively increase. As described above, when the composition ratio of at least one of Ba and Cu is reduced according to the film thickness during manufacturing, the composition ratio of the rare earth element relatively increases as the film thickness increases, and the oxide of the rare earth element As a result, the pinning effect for fixing the magnetic flux is obtained and the generation of precipitates is suppressed.

  In addition, a characteristic of the present invention is that the film formation temperature is not controlled and the MOCVD method is performed using the raw material at a constant temperature. Therefore, no device for temperature control is required.

  Moreover, it is preferable to laminate | stack a stabilization layer on a thin film layer. The stabilization layer is formed for the purpose of preventing normal conduction transition, such as normal conduction buds when energized to the thin film layer, or when the invading magnetic flux moves and tries to generate heat. It is preferable that a highly conductive metal material layer having a low electrical resistance is in contact with the thin film layer. Specifically, it is preferable to use Ag or an Ag alloy as a constituent material of the stabilization layer. The thickness is preferably about several tens of μm.

Hereinafter, Examples 1 to 3 and Comparative Examples 1 and 2 will be described.
The oxide superconducting wires of each Example and Comparative Example were manufactured as follows.
(Film formation method)
A Gd-Zr oxide (GZO) is formed as a first intermediate layer by IBAD method on Hastelloy tape (thickness 100 μm, width 10 mm) as a base material, and CeO ₂ is formed as a second intermediate layer by PLD method. The obtained substrate was used for forming a thin film layer. The GZO layer and the CeO2 layer have thicknesses of about 1 μm and 0.5 μm, respectively.

A thin film layer made of a rare earth oxide superconductor uses a THF (tetrahydrofuran) solution of Y (DPM) ₃ , Ba (DPM) ₂ , Cu (DPM) ₂ complex as a raw material, and uses a hot wall type CVD apparatus. The film was formed while moving the substrate at a film formation temperature of 800 to 930 ° C. Orientation was evaluated by X-ray diffraction and X-ray polar figures. The Ic (critical current) measurement was carried out in liquid nitrogen by the direct current four-terminal method after coating the superconducting layer with an Ag layer and annealing in oxygen, and the Ic definition was 1 μV / cm.

  In Example 1, the Cu ratio is mainly reduced according to the film thickness, that is, according to the separation distance from the intermediate layer. 1 to 5 show the film thickness dependence of the critical current (Ic) and critical current density (Jc) of Examples 1 to 3 and Comparative Examples 1 and 2, respectively. The vertical axis represents critical current (Ic) and critical current density (Jc), and the horizontal axis represents the film thickness of the thin film layer.

実施例２は、主としてＢａ比を膜厚に応じて、すなわち、中間層からの離間距離に応じて減少させたものである。

In Example 2, the Ba ratio is mainly reduced according to the film thickness, that is, according to the separation distance from the intermediate layer.

実施例３は、主としてＢａ比，Ｃｕ比をともに膜厚に応じて、すなわち、中間層からの離間距離に応じて減少させたものである。

In Example 3, both the Ba ratio and the Cu ratio are mainly reduced according to the film thickness, that is, according to the distance from the intermediate layer.

比較例１は、Ｙ：Ｂａ：Ｃｕ＝１：１．４５〜１．５６：２．９〜３．３で薄膜層を成膜した。

In Comparative Example 1, a thin film layer was formed with Y: Ba: Cu = 1: 1.45 to 1.56: 2.9 to 3.3.

In Comparative Example 2, a thin film layer was formed with Y: Ba: Cu = 1: 1.3 to 1.4: 2.9 to 3.3.
The critical current density thickness of 1μm as shown in FIG. 1-5, in Example 1, 2.3 mA / cm ^2, in Example 2, 2 MA / cm ^2, in Example 3, 2.2 MA / cm whereas obtain a ^2, Comparative example 1, 1 MA / cm ^2, in Comparative example 2, 1.5 MA / cm ² had only.

The critical current density thickness of 1.5μm as shown in FIG. 1-5, in Example 1, 1.6 MA / cm ^2, in Example 2, 1.4 MA / cm ^2, in Example 3, 1 whereas obtain a .7MA / cm ^2, in Comparative example 1, 0.7MA / cm ^2, in Comparative example ^2, 1.1MA / cm 2 had only.

  Thus, in Examples 1 to 3, the composition ratio of at least one of Ba and Cu decreases as the distance of the thin film layer from the intermediate layer (film thickness) increases. It was confirmed that when the composition ratio of the rare earth element was increased, the characteristics of the critical current density were improved as compared with the conventional one.

The chart which shows the dependence of the critical current (Ic) and critical current density (Jc) of Example 1 on the film thickness. The chart which shows the dependence of the critical current (Ic) and critical current density (Jc) of Example 2 on the film thickness. The chart which shows the dependence of the critical current (Ic) and critical current density (Jc) of Example 3 on the film thickness. The chart which shows the dependence of the critical current (Ic) and critical current density (Jc) of Comparative Example 1 on the film thickness. The chart which shows the dependence of the critical current (Ic) and critical current density (Jc) of Comparative Example 1 on the film thickness.

Claims (4)

A base material, an intermediate layer laminated on the base material, and a rare earth oxide superconductor RE-Ba-Cu-O laminated on the intermediate layer (wherein RE is a rare earth element (La, Nd, Sm, In a superconducting thin film wire comprising a thin film layer consisting of Eu, Gd, Dy, Ho, Er, Y and Yb)
The oxide superconducting wire, wherein the thin film layer has a Ba composition ratio that decreases and a rare earth element composition ratio relatively increases as the distance from the intermediate layer increases. A base material, an intermediate layer laminated on the base material, and a rare earth oxide superconductor RE-Ba-Cu-O laminated on the intermediate layer (wherein RE is a rare earth element (La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Y and
And a superconducting thin film wire comprising a thin film layer consisting of one or more selected from Yb)
The thin film layer, the As distance from the intermediate layer is increased, the composition ratio of Ba and Cu are both reduced, relatively rare earth element composition ratio oxides superconducting you characterized by being increased wire.   The rare earth oxide superconductor RE- is applied to the intermediate layer laminated on the base material by MOCVD.
A thin film layer made of Ba-Cu-O (wherein RE is selected from one or more rare earth elements (La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Y and Yb)) In the manufacturing method of the oxide superconducting wire to be laminated,
  A method for producing an oxide superconducting wire, wherein when the thin film layer is formed, the composition ratio of Ba is decreased and the composition ratio of the rare earth element is relatively increased as the film thickness increases. The rare earth oxide superconductor RE- is applied to the intermediate layer laminated on the base material by MOCVD.
A thin film layer made of Ba-Cu-O (wherein RE is selected from one or more rare earth elements (La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Y and Yb)) In the manufacturing method of the oxide superconducting wire to be laminated,
A method of manufacturing an oxide superconducting wire, wherein the composition ratio of Ba and Cu is decreased and the composition ratio of a rare earth element is relatively increased as the film thickness is increased when forming the thin film layer. .

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