JP2009283372A - Oxide superconductor introducing artificial pin and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide superconductor capable of improving critical current characteristics at a magnetic field and restraining deterioration of critical current density at a non-magnetic field and having suitable critical current characteristics; and to provide a simple method of manufacturing the same. <P>SOLUTION: The oxide superconductor 1 has a base body 2 and an oxide superconducting layer 5 formed on one surface of the base body. The oxide superconducting layer is made of a superconductive material of a RE123 system, and is a laminate of a first superconductive film 3 including no impurities and a second superconductive film 4 including impurities. The laminate has at least an interface between the first superconductive film and the second superconductive film. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention has been developed for application to superconducting power cables, superconducting magnets, superconducting energy storage devices, superconducting power generation devices, medical MRI devices, superconducting current leads, and the like. The present invention relates to a superconducting conductor and a method for manufacturing the same.

The RE123-based superconducting conductor is widely known as a high-temperature superconducting conductor that exhibits good critical current characteristics even at a liquid nitrogen temperature (77 K). Here, the RE123-based superconducting conductor is expressed by a composition formula “RE ₁ Ba ₂ Cu ₃ O _y ”, and “RE” means a superconducting conductor composed of rare earth elements such as Y, Gd, and Sm.
In general, a superconducting conductor formed using a pure RE123-based superconducting material so as to have good crystal orientation exhibits high critical current characteristics under no magnetic field. However, the pure RE123-based superconducting conductor has a problem that the critical current characteristic is rapidly deteriorated under a high magnetic field.
As a solution, attempts have been made to introduce a pinning center for pinning magnetic flux in the superconducting layer.

As a method for improving the critical current density, for example, Patent Document 1 discloses a method in which a plurality of RE123-based superconducting layers and ferromagnetic metal layers are alternately laminated so that the ferromagnetic metal layer acts as a pinning center. It has been.
For example, in Patent Document 2, an oxide superconducting part having a different crystal orientation or a heterogeneous part made of a material that does not exhibit superconductivity is formed between each of a plurality of oxide superconducting layers in which crystal grains are c-axis oriented. Thus, it is described that an oxide superconducting conductor having a high critical current density can be obtained even in a magnetic field.
Further, for example, in Patent Document 3, critical current characteristics are obtained even when the film thickness is increased by stacking a plurality of oxide superconducting layers having different stacking fault amounts by forming films under different oxygen partial pressures and temperature conditions. Has been proposed to form a thin film having a high critical current value in a magnetic field.
For the RE123 melt-solidified bulk body, for example, Patent Document 4 describes that the critical current characteristics are improved by adding Pt to Rh and introducing a non-superconducting phase such as BaCeO ₃ as a pinning center.
However, when the superconducting layer is originally formed, strict control of the film forming conditions is required, and the superconducting laminate is formed by changing the film forming conditions such as the configuration of the introduced gas, the oxygen partial pressure, and the substrate temperature. However, there is a problem that the critical current characteristics are greatly deteriorated or become unstable due to deviation from the optimum film forming conditions.

On the other hand, as a simpler manufacturing method for introducing the pinning center, for example, in Non-Patent Documents 1 and 2, a pulse laser deposition method is used, and an impurity phase such as BaZrO ₃ or Y ₂ O ₃ is added to the target in advance. Thus, an attempt to introduce these finely into a superconducting thin film crystal has been proposed. In this method, the shape of crystal grains in the superconducting layer differs depending on the type of impurity phase, and the pinning force can be controlled.
However, as the impurity phase is generally added up to a certain amount, the critical current characteristic under a magnetic field improves, but there is a problem that the characteristic under no magnetic field deteriorates conversely.
JP-A-63-318014 JP-A-4-154604 JP-A-2005-116408 JP 2006-62896 A 2007 Spring Cryogenic Engineering Proceedings, 132P Spring 2007 Low Temperature Engineering Proceedings, 133P

The present invention has been made in view of the above circumstances, and can improve the critical current characteristics under a magnetic field and can suppress the decrease in the critical current density under no magnetic field. It is a first object to provide an oxide superconducting conductor.
In addition, a second object of the present invention is to provide a method for producing an oxide superconducting conductor that can easily form the above-described oxide superconducting conductor having good critical current characteristics with good reproducibility.

  In order to solve the above problems, an oxide superconducting conductor according to claim 1 of the present invention includes a base and an oxide superconducting layer formed on one surface of the base, and the oxide superconducting layer includes: It is a laminate of a RE123-based superconducting material and includes a first superconducting film that does not contain impurities and a second superconducting film that contains impurities, and the laminated body includes the first superconducting film and the second superconducting film. An oxide superconducting conductor comprising at least an interface.

  An oxide superconducting conductor according to claim 2 of the present invention is characterized in that, in claim 1, the laminate includes at least a configuration in which the second superconducting film is stacked on the first superconducting film. .

  An oxide superconducting conductor according to claim 3 of the present invention is characterized in that, in claim 2, the multilayer body includes a plurality of the interfaces.

According to a fourth aspect of the present invention, there is provided a method of manufacturing an oxide superconducting conductor comprising: a RE123-based superconducting material on one surface of a substrate; a first superconducting film containing no impurities; a second superconducting film containing impurities; And a manufacturing method for forming an oxide superconducting layer having at least an interface between the first superconducting film and the second superconducting film, wherein the oxide superconducting layer is formed by a pulse laser deposition method. As a base material for the first superconducting film, an RE ₁ Ba ₂ Cu ₃ O _y target that does not contain impurities, and as a base material for the second superconducting film, an RE ₁ Ba ₂ Cu ₃ mixed with an impurity phase is used. An O _y target is used.

  The oxide superconducting conductor according to the present invention (Claim 1) is a laminate of an RE123-based superconducting material containing no impurities and a second superconducting film containing impurities as an oxide superconducting layer. By using a structure having at least the interface between the first superconducting film and the second superconducting film, in addition to the impurity phase in the second superconducting film, crystal grain boundaries due to lattice mismatch at the interface are also pinning centers. Therefore, a stable pinning effect can be obtained, and the critical current density under a magnetic field can be improved. Further, the presence of the first superconducting film can suppress a decrease in critical current density under no magnetic field. Therefore, the present invention contributes to the provision of an oxide superconductor having good critical current characteristics.

  The method for manufacturing an oxide superconducting conductor according to the present invention (Claim 4) is the same superconducting material based on RE123, wherein the oxide superconducting layer, which is a laminate of the first superconducting film and the second superconducting film, is used. By using a target that does not contain impurities and a target that contains impurities, and forming by pulse laser vapor deposition, stable film formation can be performed without removing optimum film formation conditions. Therefore, according to the present invention, there can be obtained a production method capable of easily forming an oxide superconductor having good critical current characteristics with good reproducibility.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view showing an embodiment of the oxide superconducting conductor of the present invention. The oxide superconducting conductor 1 according to this embodiment has a structure in which an oxide superconducting laminate 5 is provided on one surface of a base 2, and the oxide superconducting laminate 5 is composed of the same RE123-based superconducting material. The first superconducting film 3 containing no impurities and the second superconducting film 4 containing impurities are formed.

As the substrate 2, a tape-shaped substrate made of a metal material having sufficient mechanical strength, heat resistance, and oxidation resistance as a substrate for the oxide superconductor 1 is generally used, such as Hastelloy. Alternatively, a substrate having an intermediate layer provided on the surface of the tape-shaped substrate may be used as the substrate 2. The length, width, and thickness of the substrate 2 can be appropriately set according to the use of the oxide superconducting conductor 1 to be manufactured.
The oxide superconducting laminate 5 is all formed by a pulse laser deposition method. As a base material for the first superconducting film 3, an RE ₁ Ba ₂ Cu ₃ O _y target containing no impurities is used as the second superconducting film. As the base material for 4, for example, a RE ₁ Ba ₂ Cu ₃ O _y target mixed with ZrO ₂ as an impurity phase is used.

As an example, the critical current characteristic of the superconducting thin film when the oxide superconducting laminate 5 is formed by laminating the first superconducting film 3 and the second superconducting film 4 in various orders by a pulse laser deposition method. It was measured. The configuration used for the experiment is shown below.
An IBAD intermediate layer made of Gd ₂ Zr ₂ O _{7 having a} thickness of 1 μm was formed on the surface of a tape substrate made of Hastelloy having a thickness of 100 μm by the IBAD method, and the thickness was formed on the IBAD intermediate layer by a pulse laser deposition method. A 1 μm CeO ₂ intermediate layer is formed, an RE123-based oxide superconducting layer is formed on the CeO ₂ intermediate layer by pulse laser deposition, and an Ag sputtered layer having a thickness of 10 μm is further formed on the oxide superconducting layer. The oxide superconducting tape was produced by forming a film.
For the formation of the oxide superconducting layer, a RE ₁ Ba ₂ Cu ₃ O _y target or a RE ₁ Ba ₂ Cu ₃ O _y target mixed with ₂ mol% of ZrO ₂ as an impurity phase is used, and the temperature is 820 ° C. and the pressure is Film formation and lamination were performed by irradiating excimer laser light at 90 Pa.

The critical current characteristics under liquid nitrogen temperature (77K) were measured, the magnetic field application angle dependence of the critical current density Jc under a 3T magnetic field is shown in FIG. 2, and the critical current Ic and critical current density Jc under no magnetic field are shown in FIG. Expressed in
Here, the first superconducting film 3 containing no impurities is represented as an N layer, and the second superconducting film 4 containing impurities is represented as a P layer, which are arranged in the order of lamination from the surface of the substrate 2 and represented by symbols. For example, when a N-layer is formed on the surface of the substrate 2, an N-layer is further formed on the surface of the N-layer, and a P-layer is formed on the surface of the N-layer to form a three-layer laminate, the notation is NNP To do.
From FIG. 2, the critical current density Jc is 2 in the laminated body PPP composed of the second superconducting film 4 in all three layers as compared with the laminated body NNN composed of the first superconducting film 3 in all three layers. The result is more than twice as high, and it can be seen that the artificial pin was simply introduced simply by using the target containing the impurity phase. However, as shown in FIG. 3, the critical current density Jc of the stacked body PPP is lowered in the absence of a magnetic field.
Therefore, when one of the three layers of the multilayer NNN is replaced with the second superconducting film 4 and mixed and laminated (laminate NNP, NPN, PNN), as shown in FIGS. 2 and 3, the critical current density Jc Depending on the laminated structure, the critical current density Jc can be improved under a magnetic field, and the reduction of the critical current density Jc under a non-magnetic field can be suppressed.

According to the structure of the oxide superconducting conductor 1 of the present invention, in addition to the impurity phase present in the second superconducting film 4, crystal grains due to lattice mismatch at the interface between the first superconducting film 3 and the second superconducting film 4. Since the field also functions as a pinning center, a stable pinning effect can be obtained, and the critical current density under a magnetic field can be improved. Further, the presence of the first superconducting film 3 can suppress the decrease in the critical current density in the absence of a magnetic field, and thus an oxide superconducting conductor having good critical current characteristics can be obtained.
At this time, the film thickness and the number of laminated layers of the first superconducting film 3 and the second superconducting film 4 can be arbitrarily set.

Furthermore, in the oxide superconducting conductor 1 of the present invention, the oxide superconducting laminate 5 preferably includes at least a configuration in which the second superconducting film 4 is stacked on the first superconducting film 3.
2 and 3, it can be seen that the stacked bodies NPN and NNP including at least the configuration in which the P layer is stacked on the N layer can obtain better critical current characteristics than the stacked body PNN.

  Further, the oxide superconducting laminate 5 preferably has a structure (NPN) in which the second superconducting film 4 is sandwiched between the first superconducting films 3. This increases the contact area at the interface between the first superconducting film 3 and the second superconducting film 4 and increases the pinning effect due to the lattice crystal grain boundary at the interface, resulting in a more stable structure and high reproducibility and high critical current characteristics. Can be maintained.

The manufacturing method of the oxide superconducting conductor according to the present embodiment is a method of forming the oxide superconducting laminate 5 on one surface of the substrate, and all uses a pulse laser deposition method and does not contain impurities RE ₁ Ba. which comprises using a _{2 Cu 3 O y RE 1 Ba} 2 Cu 3 O y targets as a target and impurity phases example by mixing ZrO _2. As a result, in the production of oxide superconducting thin films that require strict film formation conditions, an oxide superconductor having good critical current characteristics stably while maintaining optimum film formation conditions can be easily reproduced with good reproducibility. Can be formed.

As an embodiment of the present invention, a shape such as an oxide superconducting tape as shown in FIG. On the surface of the Hastelloy tape substrate 11, an oxide (for example, an IBAD method) IBAD intermediate layer 12 made of Gd ₂ Zr ₂ O _7), the IBAD CeO ₂ intermediate layer 13 to the surface by pulsed laser deposition of the intermediate layer 12, the RE123-based by pulsed laser deposition on the surface of the CeO ₂ intermediate layer 13 An oxide superconducting layer 14 and an Ag sputtered layer 15 are formed on the oxide superconducting layer 14, and a stabilized metal tape made of Cu or the like or a high resistance tape 16 such as Ni-Cr is bonded together by solder. Structure.
The oxide superconducting conductor of the present invention can control critical current characteristics under no magnetic field or (or) magnetic field by changing the number of layers and the order of stacking the first superconducting film 3 and the second superconducting film 4. Furthermore, various superconducting wires can be produced by selecting the film thickness of the Ag sputter layer 15 and the selection of the stabilized metal tape or the high-resistance tape 16.

  In the present invention, an oxide superconducting layer formed on a substrate is efficiently artificially laminated by stacking an RE123-based superconducting film containing no impurities and an RE123-based superconducting film containing impurities so as to have an interface. Can be used for oxide superconducting conductors that can improve characteristics under a magnetic field and suppress deterioration of characteristics under no magnetic field, and the production thereof. For example, a small and high-power magnetic field The generation source can be expected to be applied to various devices including superconducting magnets.

Sectional drawing which shows an example of the oxide superconductor of one Embodiment which concerns on this invention. The graph showing the relationship between the stacking order of an oxide superconducting layer and the critical current density under a magnetic field. The graph showing the relationship between the lamination | stacking order of an oxide superconducting layer, and the critical current density under a non-magnetic field. The principal part perspective view which shows one Embodiment of the oxide superconducting tape which concerns on this invention.

Explanation of symbols

1, 10 oxide superconducting conductor, 2 substrate, 3 first superconducting film, 4 second superconducting film, 5 oxide superconducting layer (laminated body), 11 Hastelloy tape base material, 12 IBAD intermediate layer, 13 CeO ₂ intermediate layer 14 Oxide superconducting layer, 15 Ag sputter layer, 16 Stabilized metal tape or high resistance tape.

Claims (4)

A substrate and an oxide superconducting layer formed on one surface of the substrate, the oxide superconducting layer being made of a RE123-based superconducting material, a first superconducting film containing no impurities, and a second superconducting film containing impurities. A laminate with a superconducting film,
The laminated body includes at least an interface between the first superconducting film and the second superconducting film.   The oxide superconducting conductor according to claim 1, wherein the stacked body includes at least a configuration in which the second superconducting film is stacked on the first superconducting film.   The oxide superconducting conductor according to claim 2, wherein the multilayer body includes a plurality of the interfaces. A laminated body of a first superconducting film containing an impurity and a second superconducting film made of an RE123-based superconducting material and a second superconducting film containing an impurity on one surface of the substrate, the first superconducting film and the second superconducting film A method of forming an oxide superconducting layer having at least an interface with
The oxide superconducting layers are all formed by a pulse laser deposition method. As a base material for the first superconducting film, an RE ₁ Ba ₂ Cu ₃ O _y target containing no impurities is used, and a base material for the second superconducting film is used. As a manufacturing method of an oxide superconducting conductor using an RE ₁ Ba ₂ Cu ₃ O _y target mixed with an impurity phase.

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