JP2010086666A - Oxide superconducting wire and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve on magnetic field characteristics of an ReBCO superconductor having different characteristics at a high magnetic field. <P>SOLUTION: On a biaxially oriented metal base plate 11, a first intermediate layer 12a made of Ce<SB>2</SB>Zr<SB>2</SB>O<SB>7</SB>by an MOD method and a second intermediate layer 12b made of CeO<SB>2</SB>by a PLD method are laminated, on which, a superconducting layer 13 made by a TFA-MOD method is laminated. The superconducting layer 13 has a 3-layer structure with a film thickness of 1.1 μm sequentially laminating a first superconducting layer 13a made of YBa<SB>1.5</SB>Cu<SB>3</SB>O<SB>y</SB>, a second superconducting layer 13b made of SmBa<SB>1.5</SB>Cu<SB>3</SB>O<SB>y</SB>, and a third superconducting layer 13c made of YBa<SB>2.0</SB>Cu<SB>3</SB>O<SB>y</SB>. Jc of the superconducting wire 10 shows a value each of [3.46×10<SP>4</SP>A/cm<SP>2</SP>]<SB>OT</SB>in a self-magnetic field (77K), and [0.83×10<SP>4</SP>A/cm<SP>2</SP>]<SB>3T</SB>in an outside magnetic field (B//c axis, 77K) of 3T. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a superconducting magnet, a superconducting cable, a superconducting energy storage device, an oxide superconducting wire useful for a superconducting power device such as an electric motor or a transformer, and more particularly to improvement of a superconducting wire suitable for the MOD method and a method for manufacturing the same. .

Oxide superconductors have a higher critical temperature (Tc) than conventional metal-based superconductors such as Nb ₃ Sn and Nb ₃ Al, and superconducting applications such as power cables, transformers, motors, and power storage systems. Since it can be operated at liquid nitrogen temperature, research into making it into wire has been vigorously conducted.

  In order to apply the oxide superconductor to the above-mentioned field, it is necessary to produce a long wire having a high critical current density (Jc) and a high critical current (Ic) value, In order to obtain the above, it is necessary to form an oxide superconductor on a metal substrate from the viewpoint of strength and flexibility. In addition, an Ic value of about 500 A / cm (77 K, in a self-magnetic field) is required to enable use at a practical level equivalent to a conventional metal superconductor.

Among oxide superconductors, ReBa ₂ Cu ₃ O _y (where y = 6.2 to 7 and Re is Y, Yb, Tm, Er, Ho, Dy, Gd, Eu, Sm, Nd or This represents at least one element selected from La. Hereinafter referred to as ReBCO.) Since oxide superconductors are excellent in magnetic field characteristics, they are expected to be used as next-generation superconducting materials. .

  The crystal system of this ReBCO oxide superconductor is orthorhombic, the lengths of the three sides of the x-axis, y-axis and z-axis are different, and the three angles of the unit cell are slightly different, so twins are formed. There exists a problem that it is easy to make the wire material easily compared with a Bi-type superconductor. In addition, since the superconducting properties of the ReBCO oxide superconductor change depending on the crystal orientation, it is necessary to improve the in-plane orientation in order to improve Jc. Are significantly affected by the orientation and surface smoothness of the intermediate layer and the oriented metal substrate. In order to improve the in-plane orientation of the ReBCO oxide superconductor, it is necessary to form the oxide superconductor on a tape-like substrate. For this reason, the oxide superconductor is formed on the substrate having a high in-plane orientation. A film forming process for epitaxially growing is used.

  In this case, in order to improve Jc, the c-axis of the oxide superconductor is oriented perpendicular to the plate surface of the substrate, and the a-axis (or b-axis) is oriented in-plane parallel to the substrate surface, It is necessary to maintain the superconducting state quantum connectivity well, and for this reason, one or more intermediate layers with improved in-plane orientation and orientation are formed on a metal substrate having high in-plane orientation, By using the crystal lattice of the intermediate layer as a template, the in-plane orientation degree and orientation of the crystal of the superconducting layer have been improved, and further, the surface protection of the superconducting layer and the improvement of electrical contact and overcurrent A structure in which a stabilizing layer of silver or the like that plays a role as a protection circuit is laminated on the superconducting layer is employed.

  At present, tape-like ReBCO oxide superconducting wires are manufactured by various method processes such as PLD (Pulsed Laser Deposition), MOCVD (Metal Organic Chemical Vapor Deposition), The MOD (Metal Organic Deposition) method is known.

  Among these, the MOD method thermally decomposes a metal organic acid salt (or organometallic compound), and after applying a solution in which an organic compound containing a metal component constituting a superconductor is uniformly dissolved on a substrate, This is a method of forming a thin film on a substrate by performing decomposition and crystallization heat treatment. Since it is a non-vacuum process, it can be formed at high speed at a low cost and a high Jc can be obtained. It has an advantage suitable for manufacturing a tape-shaped oxide superconducting wire.

  In the MOD method, when a metal organic acid salt that is a starting material is thermally decomposed, a carbonate of an alkaline earth metal (Ba or the like) is usually generated. An oxide superconductor by a solid-phase reaction via this carbonate. The formation of this requires high-temperature heat treatment at 800 ° C. or higher. Further, when the film thickness is increased, nucleation for crystal growth occurs also from a part other than the substrate interface, so it is difficult to control the crystal growth rate. As a result, the in-plane orientation is excellent, that is, high. There is a problem that it is difficult to obtain a superconducting film having Jc.

  In order to solve the above-mentioned problem in the MOD method, as a method for forming a ReBCO superconductor without passing through a carbonate, an organic acid salt containing fluorine (for example, TFA salt: trifluoroacetate) is used as a starting material, In recent years, a method of obtaining a superconductor through the decomposition of fluoride by performing heat treatment under the control of the partial pressure of water vapor in a water vapor atmosphere has been vigorously performed (see, for example, Patent Documents 1 and 2).

  In the TFA-MOD method using TFA salt as a starting material, HF is generated at the interface where superconducting film grows while generating HF gas by the reaction between the amorphous precursor containing fluorine obtained after calcining of the coating film and water vapor. By forming the resulting liquid phase, the superconductor grows epitaxially from the substrate interface. In this case, since the decomposition rate of fluoride can be controlled by the partial pressure of water vapor during the heat treatment, the crystal growth rate of the superconductor can be controlled, and as a result, a superconducting film having excellent in-plane orientation can be produced. In this method, the ReBCO superconductor can be epitaxially grown from the upper surface of the substrate through the intermediate layer at a relatively low temperature.

The YBa ₂ Cu ₃ O _z (hereinafter referred to as YBCO) superconducting wire produced by the above MOD method has a relatively low firing temperature, and is based on the reaction with CeO ₂ well known as an alignment intermediate layer during firing. Since the generation of BaCeO ₃ is suppressed, various studies of YBCO superconducting wires by the TFA-MOD method have been conducted, and the temperature lower than the heat treatment temperature for superconductor generation between the calcination heat treatment and the heat treatment for superconductor generation. It is also known that it is effective in preventing cracks by discharging the residual organic component or residual fluoride in the calcination before reaching the crystallization temperature by performing an intermediate heat treatment in (see, for example, Patent Document 3). .)

Conventionally, in the TFA-MOD method described above, a raw material solution having a molar ratio of Re: Ba: Cu = 1: 2: 3, such as a YBCO oxide superconductor, can be made thicker and subjected to a high-speed calcining process. In order to achieve this, a TFA salt of Y and Ba as a starting material and a naphthenate salt of Cu were mixed in an organic solvent at a molar ratio of Y: Ba: Cu = 1: 2: 3, and calcined. Although a large amount of HF gas is suppressed in the process, in order to produce an oxide superconductor, heat treatment must be performed at a firing temperature of 750 ° C. or higher, and the produced oxide superconducting layer and intermediate layer are As a result of the reaction, BaCeO ₃ is generated at the interface, and it takes a long time to discharge the F element to the outside of the film. As a result, this discharge becomes insufficient and the Ic value is lowered. Furthermore, there is a problem that Jc decreases as the thickness of the superconducting layer increases, and only an Ic value lower than expected can be obtained.

In particular, when a method using a batch-type heat treatment furnace is employed for firing to produce an oxide superconductor, a long wire formed with a calcined film is wound on a drum, and the predetermined length is set in an electric furnace. Although the heat treatment is performed according to the heat treatment pattern, it is necessary to efficiently discharge the harmful gas (for example, HF gas at the time of manufacturing the YBCO superconductor) generated to the outside of the furnace because the reaction gas is generated. That is, the heat treatment of the ReBCO oxide superconductor is performed in a water vapor atmosphere, and the HF gas is generated by the reaction of F of BaF ₂ and H ₂ O in the calcined film to be discharged out of the film. If the HF gas is not quickly discharged out of the furnace, the concentration of HF gas at the interface of the calcined film disappears and the reaction is suppressed. As a result, the crystal growth rate is affected by the concentration of HF gas.

  In order to suppress the reaction between the oxide superconductor layer and the intermediate layer due to the generation of the HF gas and to obtain an oxide superconductor having a high Ic value, it is effective to reduce the fluorine compound, and the thickness of the superconductor layer. In order to prevent the deterioration of superconducting characteristics accompanying film formation, it is effective to use a raw material solution with a reduced Ba concentration.

  That is, the decrease in Jc accompanying the increase in the thickness of the superconducting layer and the Ic value lower than the expected value are caused by the reaction between the oxide superconducting layer and the intermediate layer, the generation of cracks due to the increase in the thickness, and the electrical properties of the grain boundaries. Based on the knowledge that it is caused by the decrease in bonding properties, the present applicant suppresses the generation of such HF gas and the reaction between the oxide superconducting layer and the intermediate layer, as well as the generation of cracks and the electrical property of the grain boundaries. A method for producing a thick-film tape-shaped Re-based superconductor having a high Jc and Ic value by removing or suppressing the cause of the decrease in connectivity has been filed earlier (see, for example, Patent Document 4). .

According to the knowledge at this time, by making the molar ratio of Ba smaller than the standard molar ratio, generation of HF gas and segregation of Ba are suppressed, and precipitation of Ba-based impurities at the crystal grain boundary is suppressed. As a result, the occurrence of cracks is suppressed, and the electrical connectivity between crystal grains is improved and Jc defined by the energization current is improved. By reducing the molar ratio of Ba, magnetic flux pinning points Y ₂ Cu ₂ O ₅ , CuO and Y ₂ O ₃ are formed, the magnetic field characteristics are improved, and the superconducting layer is formed by the TFA-MOD method. Thus, it is possible to easily manufacture a tape-shaped Re-based superconductor having a uniform thick film at high speed and excellent in superconducting characteristics.

For example, by using a solution mixed in an organic solvent at a molar ratio of Re: Ba: Cu = 1: 1.5: 3, a crystallization heat treatment temperature becomes possible at 700 ° C. or higher, and YBa _{1 having} a film thickness of 1.5 μm. An Ic value of 340 A / cm was obtained at a crystallization heat treatment temperature of 750 ° C. with a _.5 Cu ₃ O _y superconductor.

However, the YBCO superconducting wire manufactured by the TFA-MOD method improves the grain boundary characteristics and crystallinity of the superconductor by controlling the composition of the solution, and the self magnetic field Jc, that is, Jc at 77K, 0T (Tesla). However, Jc decreases as the external magnetic field increases. On the other hand, GdBCO and SmBCO superconducting wire using Gd or Sm instead of Y have a relatively large Jc in the magnetic field than YBCO, but the reaction temperature at the time of forming the superconducting layer is higher than that of YBCO superconductor, and CeO. The reaction with ₂ becomes very large, and the reaction between ReBCO and CeO ₂ results in the formation of a very thick BaCeO ₃ layer.

For example, in the case of a YBCO superconductor, Jc of the superconducting film by the TFA-MOD method has a high value of about 7 MA / cm ² when the external magnetic field B (B // c axis, 77K) is 0T, but 1000 A at about 8T. It decreases to a value of about / cm ² . On the other hand, in the case of a GdBCO superconductor, the external magnetic field B (B // c axis, 77K) is 2.9 MA / cm ² at 0T, which is lower than YBCO, but at about 8T, it has a value of about 10000 A / cm ² . Further, the external magnetic field dependence of Jc of the ReBCO superconductor varies depending on the type of Re element. For example, in the case of a YBCO superconductor in a bulk body, the Jc value decreases as the external magnetic field increases, but GdBCO, SmBCO and In the case of the NdBCO superconductor, there is a peak value where Jc increases as the external magnetic field increases. For example, it is known that the external magnetic field has a higher Jc value than the YBCO superconductor in the range of about 1 to 5T. .

No. 2004-100182 JP 2004-171841 A JP 2007-165153 A JP 2008-050190 A

  As described above, since the ReBCO superconductor has a large magnetic field dependency, there is a problem that the characteristics of the ReBCO superconductor having a high Jc in the self-magnetic field cannot be sufficiently exhibited in a high magnetic field region, There is a problem that high Jc cannot be expected outside the magnetic field region. For this reason, in order to obtain an Ic value above a certain level in a high magnetic field region, it is necessary to improve the Ic value by increasing the thickness and to introduce a pinning point in the superconducting film.

  The present invention has been made to solve the above-described problems, and provides an oxide superconducting wire excellent in superconducting characteristics by improving the magnetic field characteristics of a ReBCO superconductor having different characteristics in a high magnetic field region, and a method for manufacturing the same. The purpose is to do.

In order to solve the above problem, an oxide superconducting wire according to the present invention is an oxide superconducting wire in which an oxide superconducting layer is formed on a substrate via one or more intermediate layers. Represents ReBa _x Cu ₃ O _y (Re represents at least one element selected from Y, Yb, Tm, Er, Ho, Dy, Gd, Eu, Sm, Nd or La, and x ≦ 2 and y = 6.2 to 7. The same applies hereinafter.) The type and / or composition of the Re element forming each superconducting layer adjacent to each other is formed by stacking a plurality of superconducting layers made of superconductors. It is a thing.

The oxide superconducting layer has a superconducting layer made of a YBa _x Cu ₃ O _y superconductor formed on the intermediate layer, or the Re element of the ReBa _x Cu ₃ O _y superconductor formed on the intermediate layer. It is preferable to have a superconducting layer containing at least Y therein. In this case, the characteristics of the YBa _x Cu ₃ O _y superconductor can be maintained and the high magnetic field characteristics can be improved.

The molar ratio of the Ba element in the ReBa _x Cu ₃ O superconductor is preferably in the range of 1.3 ≦ x ≦ 2.0, and more preferably in the range of 1.3 ≦ x ≦ 1.8. . This is because the superconducting characteristics are lowered as the molar ratio of Ba exceeds 2.0, and similarly the superconducting characteristics are lowered as the molar ratio of Ba is less than 1.3. In this case, by changing the molar ratio of the Ba element within the range of 1.3 ≦ x ≦ 1.8, the generation of HF gas and the segregation of Ba described above are suppressed, and the Ba base at the grain boundary is suppressed. As a result of suppressing the precipitation of impurities, the generation of cracks can be suppressed, the electrical connectivity between crystal grains can be improved and Jc can be improved, and at the same time, the molar ratio of Ba can be reduced, Magnetic field characteristics are improved as a result of the formation of Y ₂ Cu ₂ O ₅ , CuO and Y ₂ O ₃ which are magnetic flux pinning points. The above-described effect of reducing the molar ratio of Ba is clarified by the above-mentioned Patent Document 4 by the present applicant.

  Furthermore, in the above invention, in order to enable thickening of the oxide superconducting layer and high-speed calcination process, the oxide superconducting layer is formed by the MOD method, in particular, the TFA-MOD method using TFA salt as a starting material. It is preferable that it is formed by.

The oxide superconducting wire according to the present invention described above includes a step of applying a heat treatment after applying a ReBa _x Cu ₃ O _y superconductor raw material solution on a substrate via one or more intermediate layers by the MOD method. In the method of manufacturing an oxide superconducting wire by repeatedly forming a plurality of calcined films and then performing a crystallization heat treatment, the type and / or composition of the Re element constituting each calcined film is set at least partially. It can manufacture by making it differ in a fired film, It is preferable to form a calcined film especially by TFA-MOD method. The number of some calcined films and other calcined films having different types and / or compositions of the Re element is not particularly limited. What is necessary is just to comprise so that the kind and / or composition of Re element which comprise each adjacent superconducting layer may differ after final crystallization heat processing.

In this case, the calcined film on the intermediate layer is preferably formed of a precursor of YBa _x Cu ₃ O _y superconductor or a precursor of ReBa _x Cu ₃ O _y superconductor containing at least Y in the Re element. .

In the production of the above oxide superconducting wire, the crystallization heat treatment is carried out at a pressure of P _total = 1 to 760 Torr, a water vapor partial pressure of P _H2O = 1 to 7.5% and a maximum temperature of T _max = 700 to 800 ° C. It is given within the range.

  As the substrate in the present invention, Hastelloy (registered trademark), highly heat-resistant non-oriented metal such as stainless steel, Ni or one or more elements (W, Mo, Cr, Fe, Cu, V, Sn or Zn). A biaxially oriented metal substrate manufactured by cold rolling a Ni-based alloy or Cu or a Cu-based alloy with one or more elements added thereto at a predetermined temperature and then subjecting it to an orientation heat treatment at a predetermined temperature. Further, since the alignment metal region only needs to be on the side in contact with the intermediate layer, a metal substrate having a two-layer or multilayer structure in which an alignment metal substrate and a non-alignment metal substrate such as stainless steel are bonded to each other can also be used. In any case, a biaxially oriented intermediate layer may be formed on the metal substrate.

  Further, as a composite substrate in which an intermediate layer is formed on a polycrystalline substrate, a composite substrate manufactured by an IBAD (Ion Beam Assisted Deposition) method can be used.

This IBAD composite substrate is formed by depositing YSZ or Gd ₂ Zr ₂ O ₇ on a non-magnetic high-strength tape-like Ni-based polycrystalline substrate made of Hastelloy (registered trademark) C276 or the like by a laser vapor deposition method (PLD method). The CeO ₂ intermediate layer is formed on the intermediate layer by the PLD method. In the IBAD method, an intermediate layer in which the crystal grain size is fine and densely oriented is formed on a polycrystalline substrate by performing deposition while irradiating an ion beam from a certain angle direction with respect to the normal of the substrate surface. The formation of this highly oriented intermediate layer has the advantage that the reaction with the elements constituting the superconducting layer can be suppressed (see, for example, JP-A-4-329867 and JP-A-4-33195). ).

According to the present invention, the ReBa _x Cu ₃ O _y superconductor laminated via the intermediate layer on the substrate is made different in the kind and / or composition of the Re element constituting each adjacent superconducting layer. The magnetic field characteristics of the ReBCO superconductor having different characteristics in the magnetic field region can be improved.

FIG. 3 shows a cross section perpendicular to the axial direction of the oxide superconducting wire of the present invention. The oxide superconducting wire 30 has an intermediate layer 32 and a superconducting layer 33 on a substrate 31 made of a Ni—W alloy or the like. Are sequentially stacked. The intermediate layer 32 has, for example, a two-layer structure in which a first intermediate layer made of Ce—Zr—O oxide and a _second intermediate layer made of CeO ₂ oxide are sequentially stacked. The intermediate layer 32 is formed on the substrate 31. The formed composite substrate is formed by, for example, the above-described MOD method or PLD method. For example, Ce ₂ Zr ₂ O ₇ is deposited as a first intermediate layer on a Ni—W alloy substrate by a MOD method, and CeO ₂ is deposited thereon as a second intermediate layer by a PLD method. Is done. Instead of this substrate, a non-magnetic high-strength tape-like Ni-based polycrystalline substrate such as Hastelloy (registered trademark) C276 can be used.

On the other hand, the superconducting layer 33 includes a first superconducting layer 33a made of (Re-1) Ba _x1 Cu ₃ O _y , a second superconducting layer 33b made of (Re-2) Ba _x2 Cu ₃ O _y, and (Re- 3) It has a three-layer structure consisting of the third superconducting layer 33c made of Ba _x3 Cu ₃ O _y , where (Re-1), (Re-2) and (Re-3) are Y, At least one element selected from Yb, Tm, Er, Ho, Dy, Gd, Eu, Sm, Nd or La is shown, and the type and / or composition of the Re element is different. That is, (Re-1), (Re-2), and (Re-3) are each composed of, for example, Y, Sm, and Nd, or are composed of Y, (Y + Sm), and (Y + Nd), or (Re -1), (Re-2) and (Re-3) elements are composed of one or more identical Re elements and the compositions thereof are different. In the first, second and third superconducting layers 33a, 33b and 33c, the molar ratios x1, x2 and x3 of Ba are within the range of 1.3 ≦ x ≦ 2.0, particularly as described above. , 1.3 ≦ x ≦ 1.8, and the molar ratio may be the same or different. Further, the first, second, and third superconducting layers 33a, 33b, and 33c are each subjected to crystallization heat treatment after forming a single or plural calcined films that finally form the superconducting layer. It is formed.

  FIG. 4 shows a cross section perpendicular to the axial direction of another oxide superconducting wire of the present invention. In FIG. 4, the same parts as those in FIG. 3 are denoted by the same reference numerals, and (Re-1) and (Re -2) and x1 and x2 are used in the same meaning as in FIG.

4A, an oxide superconducting wire 40 has a structure in which an intermediate layer 32 and a superconducting layer 43 are sequentially laminated on a substrate 31, and the superconducting layer 43 is composed of (Re-1) Ba _x1 Cu ₃ O. having a two-layer structure consisting of the first superconducting layer 43a and _{(Re-2) Ba x2 Cu} 3 consisting _{O y} second superconducting layer 43b made of _y.

4B, the oxide superconducting wire 50 has a structure in which an intermediate layer 32 and a superconducting layer 53 are sequentially laminated on a substrate 31, and the superconducting layer 53 is composed of (Re-1) Ba _x1 Cu. ₃ O first superconducting _{where y} consisting layer 53a and _{(Re-2) Ba x2 Cu} 3 O y over the two-layer structure consisting of the second superconducting layer 53b made of a first superconducting layer and a third of the same composition A superconducting layer 53c is laminated. In this case, the Ba molar ratio of the first and second superconducting layers can be varied.

Further, in FIG. 4C, the oxide superconducting wire 60 has a structure in which an intermediate layer 32 and a superconducting layer 63 are sequentially laminated on a substrate 31, and the superconducting layer 63 is composed of (Re-1) Ba _x1 Cu. ₃ O first superconducting _{where y} consisting layer 63a and _{(Re-2) Ba x2 Cu} 3 O y the second superconducting layer 63b made of on the superconducting layer laminated two-layer structure, further the same two-layer structure In other words, the four superconducting layers of (Re-1) Ba _x1 Cu ₃ O _y and the fourth superconducting layer 63d of (Re-2) Ba _x2 Cu ₃ O _y are stacked. It has a structure. In this case, the Ba molar ratio of the first and third superconducting layers and / or the second and fourth superconducting layers can be varied.

  Examples of the present invention will be described below.

Example 1
As shown in FIG. 1, an oxide superconducting wire 10 was manufactured by using a composite substrate in which an intermediate layer 12 was deposited on a biaxially oriented metal substrate 11 and laminating a superconducting layer 13 on the composite substrate.

The intermediate layer 12 is obtained by depositing a first intermediate layer 12a made of Ce ₂ Zr ₂ O ₇ by the MOD method and depositing a second intermediate layer 12b made of CeO ₂ on the intermediate layer by the PLD method. The in-plane orientation degree is Δφ = 9 deg. Met.

The superconducting layer 13 is laminated on the composite substrate using the TFA-MOD method, and the first superconducting layer 13a made of YBa _1.5 Cu ₃ O _y and the second made of SmBa _1.5 Cu ₃ O _y . The superconducting layer 13b and the third superconducting layer 13c made of YBa _2.0 Cu ₃ O _y are sequentially stacked.

  The superconducting layer 13 was formed by the following method. First, dip coating a mixed solution in which Y-TFA salt, Ba-TFA salt and Cu naphthenate were mixed in 2-octanone so that the molar ratio of Y: Ba: Cu was 1: 1.5: 3. After coating on a composite substrate using a method, heating to a maximum heating temperature of 380 ° C. in an oxygen gas atmosphere with a water vapor molar fraction of 2.0% and 760 Torr, forming a calcined film by furnace cooling to room temperature, This process was repeated to form a plurality of calcined films of the first superconducting layer. On this calcined film, Sm-TFA salt, Ba-TFA salt and Cu naphthenate were mixed in 2-octanone so that the molar ratio of Sm: Ba: Cu was 1: 1.5: 3. After forming a plurality of calcined films of the second superconducting layer using the solution in the same manner as described above, the Y: TFA salt, Ba-TFA salt and Cu naphthenate were converted to a molar ratio of Y: Ba: Cu. A plurality of calcined films of the third superconducting layer were formed by the same method as described above using a mixed solution mixed in 2-octanone so that the ratio was 1: 2: 3.

  After forming the calcined films of the first, second and third superconducting layers as described above, the maximum heating temperature in an oxygen-argon gas atmosphere having a water vapor partial pressure of less than 7.5% and a furnace pressure of less than 760 Torr. A superconducting layer 13 having a three-layer structure was formed by performing a crystallization heat treatment under a firing condition of 700 to 780 ° C., that is, a heat treatment for generating a superconductor.

The film thickness of the superconducting layer manufactured as described above was 1.1 μm. The result of measuring the Jc of the superconducting wire 10, in self-field ^{(77K) [3.46 × 10 4} ] 0T A / cm 2, 3T of the external magnetic field (B // c-axis, 77K) in [0. 83 × 10 ⁴ ] _3T A / cm ² .

Example 2
A first superconducting layer made of YBa _1.5 Cu ₃ O _y on the composite substrate, NdBa _1.5 Cu, in the same manner as in Example 1, except that the Nd-TFA salt was used instead of the Sm-TFA salt. ₃ was produced O second superconducting layer consisting of _y and _YBa 2.0 _Cu 3 third superconducting wire and the superconducting layers are laminated in consisting of _{O y.}

The film thickness of the superconducting layer manufactured as described above was 1.1 μm. The result of the Jc of the superconducting wire was measured, self-field ^{(77K) [3.31 × 10 4} ] Among 0T A / ^cm 2, 3T of the external magnetic field (B // c-axis, 77K) in [1.33 × 10 ⁴ ] _3T A / cm ² was shown.

Example 3
The same parts as those in FIG. 1 are denoted by the same reference numerals in FIG. 2, and the Y-TFA salt, Ba-TFA salt and Cu naphthenate are mixed so that the molar ratio of Y: Ba: Cu is 1: 1.5: 3. The first superconducting layer calcined film, Nd-TFA salt, Ba-TFA salt, and Cu naphthenate were mixed on the composite substrate using a mixed solution mixed in a Nd: Ba: Cu molar ratio of 1: 1. Of the second superconducting layer formed on the calcined film of the first superconducting layer by using the mixed solution mixed to be 5: 3, Y-TFA salt, Ba-TFA salt and Cu Calcination of the third superconducting layer formed on the calcined film of the second superconducting layer using a mixed solution in which naphthenate is mixed so that the molar ratio of Y: Ba: Cu is 1: 2: 3 Membrane and Nd-TFA salt, Ba-TFA salt and Cu naphthenate have a Nd: Ba: Cu molar ratio of 1: 2: 3. In the same manner as in Example 1 except that the calcined film of the fourth superconducting layer formed on the calcined film of the third superconducting layer was sequentially formed using the mixed solution so as to be formed on the composite substrate. first superconducting layer 23a consisting of YBa _1.5 Cu ₃ O _y, the second superconducting layer _23b made of _NdBa 1.5 _Cu 3 _{O y,} third superconducting layer 23c made of _YBa 2.0 _Cu 3 _{O y} and _NdBa 2.0 _Cu 3 _{O y} fourth oxide superconducting wire 20 having a superconducting layer 23d stacked consisting produced.

The film thickness of the superconducting layer manufactured as described above was 1.1 μm. The result of the Jc of the superconducting wire 20 was measured, self-field ^{(77K) [2.90 × 10 4} ] Among 0T A / ^cm 2, 3T of the external magnetic field (B // c-axis, 77K) [1 in. 75 × 10 ⁴ ] _3T A / cm ² .

Comparative Example 1
Only a mixed solution in which Y-TFA salt, Ba-TFA salt and Cu naphthenate were mixed in 2-octanone so that the molar ratio of Y: Ba: Cu was 1: 2: 3 was used. In the same manner as in Example 1, a superconducting wire made of YBa _2.0 Cu ₃ O _y was formed on the composite substrate to produce a superconducting wire.

The film thickness of the superconducting layer manufactured as described above was 1.1 μm. As a result of measuring Jc of this superconducting wire, [0.50 × 10 ⁴ ] in a self-magnetic field (77K) [114 × 10 ⁴ ] _0T A / cm ² and 3T in an external magnetic field (B // c axis, 77K). ⁴ ] A value of _3T A / cm ² was shown.

Comparative Example 2
Only the mixed solution in which Sm-TFA salt, Ba-TFA salt and Cu naphthenate were mixed in 2-octanone so that the molar ratio of Sm: Ba: Cu was 1: 2: 3 was used. In the same manner as in Example 1, a superconducting layer made of SmBa _2.0 Cu ₃ O _y was formed on the composite substrate to produce a superconducting wire.

The film thickness of the superconducting layer manufactured as described above was 1.1 μm. As a result of measuring Jc of this superconducting wire, [1.50 × 10 ⁴ ] _0T A / cm ² in a self magnetic field (77K) and [1.50 in an external magnetic field (B // c axis, 77K) of 3T. × 10 ⁴ ] _3T A / cm ² was shown.

Comparative Example 3
Only Nd-TFA salt, Ba-TFA salt and Cu naphthenate were mixed in 2-octanone so that the molar ratio of Nd: Ba: Cu was 1: 2: 3. In the same manner as in Example 1, a superconducting layer made of NdBa _2.0 Cu ₃ O _y was formed on the composite substrate to produce a superconducting wire.

The film thickness of the superconducting layer manufactured as described above was 1.1 μm. The result of the Jc of the superconducting wire was measured, self-field ^{(77K) [1.65 × 10 4} ] Among 0T A / ^cm 2, 3T of the external magnetic field (B // c-axis, 77K) in [4.00 × 10 ⁴ ] _3T A / cm ² was shown.

  As is clear from the results of the above examples and comparative examples, the large magnetic field dependency (Comparative Example 1) in which the high Jc of the YBCO superconductor in the self magnetic field rapidly decreases with the increase of the external magnetic field has a high external magnetic field. By laminating with an Sm-based or Nd-based Re-based superconductor having a high Jc (Examples 1 to 3), it is remarkably improved.

  In addition, SmBCO or NdBCO (Comparative Examples 2 and 3) having a lower Jc than the YBCO superconductor in the self magnetic field is laminated with the YBCO superconductor having the higher Jc in the self magnetic field (Examples 1 to 3). ) Significant improvement.

  According to the present invention, the magnetic field dependence of an oxide superconducting wire suitable for the TFA-MOD method, which is a non-vacuum and low-cost process, can be improved, so that a superconducting magnet, a superconducting transformer, a superconducting power storage device, etc. Application to superconducting equipment is possible.

It is a cross-sectional view perpendicular to the axial direction showing a specific example of the oxide superconducting wire having a ReBa _x Cu ₃ O _y oxide superconducting layer of the present invention. It is a cross-sectional view perpendicular to the axial direction showing another specific example of the oxide superconducting wire having a ReBa _x Cu ₃ O _y oxide superconducting layer of the present invention. It is a cross-sectional view perpendicular to the axial direction showing an embodiment of the oxide superconducting wire having a ReBa _x Cu ₃ O _y oxide superconducting layer of the present invention. It is a cross-sectional view perpendicular to the axial direction showing another embodiment of the oxide superconducting wire having a ReBa _x Cu ₃ O _y oxide superconducting layer of the present invention.

Explanation of symbols

10, 20 Oxide superconducting wire 11 Oriented metal substrate 12 Intermediate layer 12a First intermediate layer 12b Second intermediate layer 13 Superconducting layer 13a, 23a First superconducting layer 13b, 23b Second superconducting layer 13c, 23c Third Superconducting layer 13c
23d Fourth superconducting layer 30, 40, 50, 60 Oxide superconducting wire 31 Substrate 32 Intermediate layer 33, 43, 53, 63 Superconducting layer 33a, 43a, 53a, 63a First superconducting layer 33b, 43b, 53b, 63b Second superconducting layer 33c Third superconducting layer 53c, 63c Third superconducting layer 63d Fourth superconducting layer

Claims (14)

In an oxide superconducting wire in which an oxide superconducting layer is formed on a substrate via one or more intermediate layers, the oxide superconducting layer is made of ReBa _x Cu ₃ O _y (Re is Y, Yb, Tm). And at least one element selected from Er, Ho, Dy, Gd, Eu, Sm, Nd or La, where x ≦ 2 and y = 6.2 to 7. The same applies hereinafter.) From a superconductor An oxide superconducting wire characterized in that it is formed of a laminate in which a plurality of superconducting layers are laminated and the type and / or composition of the Re element constituting each adjacent superconducting layer is different. The oxide superconducting wire according to claim 1, wherein the oxide superconducting layer has a superconducting layer containing at least Y in the Re element of the ReBa _x Cu ₃ O _y superconductor formed on the intermediate layer. The oxide superconducting wire according to claim 1, wherein the oxide superconducting layer has a superconducting layer made of a YBa _x Cu ₃ O _y superconductor formed on the intermediate layer.   4. The oxide superconducting wire according to claim 1, wherein a molar ratio of the Ba element is in a range of 1.3 ≦ x ≦ 2.0. 5.   5. The oxide superconducting wire according to claim 4, wherein the molar ratio of Ba element is in the range of 1.3 ≦ x ≦ 1.8.   The oxide superconducting wire according to any one of claims 1 to 5, wherein the oxide superconducting layer is formed by a metal organic acid salt deposition method (MOD method).   The oxide superconducting wire according to claim 6, wherein the oxide superconducting layer is formed by a TFA-MOD method using a TFA salt (trifluoroacetate) as a starting material. After a raw solution of ReBa _x Cu ₃ O _y superconductor is applied by MOD method on a substrate through one or more intermediate layers, a plurality of calcined films are formed by repeating a heat treatment step. In the method of manufacturing an oxide superconducting wire by performing a crystallization heat treatment, the type and / or composition of the Re element constituting each calcined film is different in at least a part of the calcined film. A method of manufacturing an oxide superconducting wire. The method for producing an oxide superconducting wire according to claim 8, wherein the calcined film on the intermediate layer is made of a precursor of a ReBa _x Cu ₃ O _y superconductor containing at least Y in the Re element. The method for producing an oxide superconducting wire according to claim 8, wherein the calcined film on the intermediate layer is made of a precursor of a YBa _x Cu ₃ O _y superconductor.   The method for producing an oxide superconducting wire according to any one of claims 8 to 10, wherein a molar ratio of the Ba element is in a range of 1.3? X? 2.0.   The method for producing an oxide superconducting wire according to claim 11, wherein the molar ratio of the Ba element is in the range of 1.3 ≦ x ≦ 1.8.   The method for producing an oxide superconducting wire according to any one of claims 8 to 12, wherein the plurality of calcined films are formed by a TFA-MOD method using a TFA salt as a starting material. The crystallization heat treatment is characterized by being performed within a range of a pressure of P _total = 1 to 760 Torr, a water vapor partial pressure of P _H2O = 1 to 7.5% and a maximum temperature of T _max = 700 to 800 ° C. The method for producing an oxide superconducting wire according to any one of claims 8 to 13.

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