JP2014010978A - Thin film superconducting wire rod and production method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film superconducting wire rod having a higher Ic than that of a conventional art, and a production method of the same.SOLUTION: A production method of a rare earth based thin film superconducting wire rod includes: a superconducting layer forming process that forms a rare earth based thin film superconducting layer on an oriented metal substrate by using a physical vapor deposition method; and an oxygen anneal process in which the rare earth based thin film superconducting layer is performed by oxygen anneal, and in the production method of the rare earth based thin film superconducting wire rod, a high temperature low oxygen anneal process in which a rare earth based thin film superconducting layer formed by the superconducting layer forming process is performed by anneal under a high temperature low oxygen atmosphere at a temperature of 600-1,000°C and of an Oconcentration of at most 1,000 ppm, is included between the superconducting layer forming process and the oxygen anneal process. The rare earth based thin film superconducting wire rod is produced by using the production method of the rare earth based thin film superconducting wire rod.

Description

  The present invention relates to a thin film superconducting wire, and more particularly to a rare earth thin film superconducting wire and a method for producing the same.

  Since the discovery of high-temperature superconductors that have superconductivity at the temperature of liquid nitrogen, development of high-temperature superconducting wires aimed at application to power devices such as cables, current limiters, and magnets has been actively conducted. In particular, a thin film superconducting wire in which a thin film of a rare earth oxide superconducting layer is formed on a substrate has attracted attention.

Such a rare earth-based thin film superconducting wire generally includes a biaxially oriented metal substrate made of a Ni (nickel) alloy or the like, and CeO ₂ (cerium oxide), YSZ (yttria stabilized zirconia), An oxide layer such as Y ₂ O ₃ (yttrium oxide) is formed by sputtering or the like, and further, an oxide superconductor represented by REBCO (REBa ₂ Cu ₃ O _7-δ : RE is a rare earth) It is produced by forming a rare earth-based oxide superconducting layer made of, for example.

  As a specific manufacturing method, a so-called physical vapor deposition method is generally used in which a rare earth oxide superconductor is vapor-deposited on the surface of a substrate to continuously form a rare earth oxide superconductor layer. (For example, Patent Document 1).

  As such a physical vapor deposition method, for example, by converging and irradiating a laser beam on a target, the superconducting thin film material on the target surface is peeled off and decomposed to generate a plasma called a plume, which faces the target. There is a PLD method (Pulse Laser Deposition), in which a superconducting thin film material in a generated plume is vapor-deposited and deposited on a tape-like base material arranged in the form of a tape-like base material. A thin film superconducting wire is manufactured by continuously forming a superconducting layer on the surface of the superconducting layer.

JP 07-037444 A

  However, it cannot be said that the thin film superconducting wire produced by the conventional physical vapor deposition has sufficient high Ic suitable for the above-mentioned use, and further improvement of Ic is demanded.

  Then, this invention makes it a subject to provide the thin film superconducting wire which has higher Ic compared with the past, and its manufacturing method.

  As a result of intensive studies, the present inventor has found that the above-described problems can be solved by the invention shown below, and has completed the present invention. Hereinafter, each claim will be described.

The invention described in claim 1
A superconducting layer forming step for forming a rare earth-based thin film superconducting layer on an oriented metal substrate using a physical vapor deposition method, and an oxygen annealing step for subjecting the rare earth-based thin film superconducting layer to oxygen annealing are provided. A rare earth-based thin film superconducting wire manufacturing method,
Between the superconducting layer forming step and the oxygen annealing step, the rare earth-based thin film superconducting layer formed by the superconducting layer forming step is heated to a high temperature and low oxygen atmosphere at a temperature of 600 to 1000 ° C. and an O ₂ concentration of 1000 ppm or less. A method for producing a rare earth-based thin film superconducting wire characterized by being provided with a high-temperature low-oxygen annealing step for annealing at a low temperature.

  The inventor has a superconducting layer forming step of forming a rare earth-based thin film superconducting layer on an oriented metal substrate using a physical vapor deposition method, and an oxygen annealing step of subjecting the formed thin film superconducting layer to oxygen annealing. A conventional thin-film superconducting wire manufacturing method in which oxygen annealing is performed after forming the superconducting layer is provided by providing a high-temperature and low-oxygen annealing step in which the thin film superconducting layer is annealed in a high-temperature and low-oxygen atmosphere. It was found that a thin film superconducting wire having a higher Ic can be obtained as compared with the case of the above.

  That is, as described above, in the case of a method for manufacturing a thin film superconducting wire using a conventional physical vapor deposition method, oxygen annealing is performed as it is on the thin film superconducting layer formed using the physical vapor deposition method. However, the physical vapor deposition method is a method of evaporating the superconducting thin film material from the target and depositing it on the substrate, so that the formed thin film superconducting layer has many voids and it is difficult to form a smooth surface. Met.

  In addition, physical vapor deposition such as PLD is a method for growing columnar crystal grains in a relatively short time compared with chemical film formation such as MOD or CVD. It was difficult to form sufficient bonds.

  For this reason, when oxygen annealing is performed as it is, the superconductor crystal grains take in oxygen and try to align them, but cracks occur in places where the bonding of the crystal grains is weak, so a smooth surface state cannot be obtained, Ic cannot be fully improved.

  On the other hand, when the high-temperature low-oxygen annealing under predetermined conditions is performed on the thin film superconducting layer in advance before the oxygen annealing as in the invention of the present claim, the rearrangement of crystal grains and It has been found that the occurrence of cracks as described above is suppressed by coarsening and diffusion bonding between grains, a smooth surface state can be obtained, and crystal grain bonds can be sufficiently formed. As a result, a higher Ic can be obtained while the thin film superconducting layer has the same thickness. In addition, when a thin film superconducting layer having a smooth surface state is formed, the thin film superconducting layer can be easily laminated, so that Ic can be further improved.

Specifically, the high temperature and low oxygen annealing is performed in a high temperature and low oxygen atmosphere at a temperature of 600 to 1000 ° C. and an O ₂ concentration of 1000 ppm or less.

  When the temperature is too low, the phase transition of the superconductor crystal grains does not occur, and when it is too high, the superconductor crystal grains may be decomposed. In addition, in order to produce crystal flow and crystal grain bonding for smoothing and suppressing cracks in a physically vapor-deposited thin film superconducting layer, a heat treatment temperature exceeding 1000 ° C. is required. A diffusion reaction with the substrate metal layer may occur, and problems such as a significant decrease in critical current and critical temperature may occur.

When the O ₂ concentration is too high, it is difficult to sufficiently form crystal grain bonds in the thin film superconducting layer in the temperature range of 600 to 1000 ° C. On the other hand, in the region of 1000 ° C. or higher, crystal grain bonding is possible even when the O ₂ concentration is high. In this case, however, a composition shift occurs in order to exhibit superconducting characteristics, and the optimal crystal form is decomposed. Arise.

The invention described in claim 2
In the superconducting layer forming step, the rare earth-based thin film superconducting layer is formed on a base material comprising a metal substrate having biaxial crystal orientation and an intermediate layer formed thereon. The method for producing a rare earth thin film superconducting wire according to claim 1.

  By forming a rare earth-based thin film superconducting layer on a base material composed of a metal substrate having biaxial crystal orientation and an intermediate layer formed thereon, sufficiently c-axis oriented crystal grains are grown. be able to.

The invention according to claim 3
A rare earth-based thin film superconducting layer is further formed on the rare earth-based thin film superconducting layer formed in the superconducting layer forming step using a fluorine-free MOD method, and then the high-temperature low-oxygen by the high-temperature low-oxygen annealing step is performed. The method for producing a rare earth-based thin film superconducting wire according to claim 1 or 2, wherein annealing is performed.

  In the present invention, as described above, the surface state of the rare earth-based thin film superconducting layer formed using physical vapor deposition can be made smoother. An earth-based thin film superconducting layer can be laminated, and Ic can be further improved.

The invention according to claim 4
A rare earth thin film superconducting wire manufactured using the method of manufacturing a rare earth thin film superconducting wire according to any one of claims 1 to 3.

  By using each of the above rare earth-based thin film superconducting wire manufacturing methods, a thin film superconducting wire having a higher Ic can be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the thin film superconducting wire which has higher Ic compared with the past, and its manufacturing method can be provided.

It is a SEM photograph of the oxide superconducting layer surface in a comparative example. 2 is a SEM photograph of the surface of an oxide superconducting layer in Example 1. 4 is a SEM photograph of the surface of an oxide superconducting layer in Example 2. It is a figure which shows the XRD measurement result of a comparative example and Examples 1, 2.

  Hereinafter, the present invention will be specifically described based on embodiments.

1. Preparation of metal substrate First, a biaxially oriented metal substrate is prepared, and an intermediate layer is formed thereon, thereby preparing a metal substrate.

  As the biaxially oriented metal substrate, an IBAD base material, a Ni—W alloy base material, a clad type metal substrate material based on SUS or the like can be used.

As the intermediate layer, in general, CeO ₂ , YSZ, Y ₂ O ₃ , stabilized zirconia, BaZrO ₃ (barium zirconate), LaAlO ₃ (lanthanum aluminate), Gd ₂ Zr ₂ O ₇ , SmGdO ₃ , RE ₂ O ₃ (RE: Y, lanthanoid), etc., and usually an intermediate layer having a three-layer structure formed in the order of seed layer / diffusion prevention layer / crystal lattice matching layer from the metal substrate side. Provided. As a forming method, a sputtering method is usually used.

2. Formation of Thin Film Superconducting Layer by Physical Vapor Deposition Next, a thin film superconducting layer made of a rare earth oxide superconductor is formed on a metal substrate using a physical vapor deposition method such as a PLD method. As a forming method, a method similar to the conventional method is employed.

Specific examples of the rare earth-based oxide superconductor include an oxide superconductor represented by REBCO (REBa ₂ Cu ₃ O _7-δ : RE is a rare earth). (Y), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), holmium (Ho), ytterbium (Yb), and the like.

  Examples of the physical vapor deposition method include a sputtering method, a vacuum vapor deposition method, and an ion plating method in addition to the PLD method described above.

3. High-temperature and low-oxygen annealing In the production of oxide superconducting thin film wires by conventional physical vapor deposition, as described above, oxygen annealing is performed as it is after the formation of the thin film superconducting layer. In the present invention, however, oxygen annealing is performed. First, high-temperature and low-oxygen annealing is first performed in a high-temperature and low-oxygen atmosphere at a temperature of 600 to 1000 ° C. and an O ₂ concentration of 1000 ppm or less.

  By performing high temperature and low oxygen annealing in a high temperature and low oxygen atmosphere, as described above, the bonding of crystal grains is improved, and a smooth surface state can be obtained.

  The time for performing the high temperature low oxygen annealing is appropriately set in consideration of the thickness of the thin film superconducting layer formed by physical vapor deposition.

4). Oxygen annealing Next, oxygen annealing is performed on the thin film superconducting layer as in the conventional case. At this time, in this embodiment, since the bonding of crystal grains is improved, oxygen can be more sufficiently taken in oxygen annealing, and Ic can be further improved.

  Hereinafter, the present invention will be described in more detail by way of examples in which a rare earth thin film superconducting layer is formed using the PLD method.

(Comparative example)
First, after forming a thin film superconducting layer using the PLD method, a rare earth thin film superconducting wire of a comparative example was manufactured based on a conventional manufacturing method in which oxygen annealing is performed as it is.

1. Preparation of metal base material As a metal base material, a NiW alloy-based biaxially oriented substrate (thickness 120 μm × width 30 mm × length 250 m) is prepared, and a Y ₂ O ₃ seed layer (thickness) is formed thereon by sputtering. 70 nm) / YSZ diffusion prevention layer (thickness 200 nm) / CeO ₂ crystal lattice matching layer (thickness 120 nm) in this order, an intermediate layer having a three-layer structure was formed to form a metal substrate.

2. Formation of Thin Film Superconducting Layer by PLD Method A GdBCO superconducting layer having a thickness of 2.8 μm was formed by using the PLD method on the intermediate layer of the metal substrate produced as described above.

The film forming conditions in the PLD method were as follows.
Laser: Kr-F excimer laser
Frequency: 250Hz
Output: 1J
Wavelength: 248nm
Oxygen atmosphere: 20 Pa
Target: GdBCO

3. Oxygen annealing Finally, after holding at 550 ° C. for 120 minutes in an atmosphere with an O ₂ concentration of 98%, the furnace was cooled to room temperature over 20 hours (oxygen annealing) to obtain a rare earth thin film superconducting wire as a comparative example. It was.

Example 1
Before performing oxygen annealing on the GdBCO superconducting layer formed by the PLD method in the same manner as in the comparative example, it was held at 800 ° C. for 120 minutes in an atmosphere with an O ₂ concentration of 100 ppm and then taken to 500 ° C. over 1 hour. Then, the furnace was cooled and subjected to high temperature and low oxygen annealing. Thereafter, oxygen annealing was performed under the same conditions as in the comparative example, and the rare earth thin film superconducting wire of Example 1 was obtained.

(Example 2)
A FF-MOD solution having a YBCO composition was applied using a die coat on a GdBCO superconducting layer formed by the PLD method in the same manner as in the comparative example, and then 505 in an atmosphere having an O ₂ concentration of 100% and a dew point of 19 ° C. Pre-baking was carried out by maintaining at 120 ° C. for 120 minutes. Thereafter, holding at 680 ° C. for 45 minutes and 850 ° C. for 30 minutes in an atmosphere with an O ₂ concentration of 100 ppm, quenching to 500 ° C. over 1 hour, followed by firing, and a 0.6 μm thick FF-MOD superconducting layer (YBCO superconducting layer) was formed. Thereafter, high-temperature and low-oxygen annealing was performed under the same conditions as in Example 1, and further, oxygen annealing was performed under the same conditions as in the comparative example to obtain the rare earth thin film superconducting wire of Example 2.

(Evaluation of crystallinity)
In order to evaluate the crystallinity of the GdBCO superconducting layer, the in-plane orientations of Examples 1 and 2 and the comparative example before oxygen annealing were measured using X-ray diffraction (θ-2θ scan method and pole figure method). did. In addition, the in-plane orientation in the biaxially oriented substrate and the metal substrate was also measured. The measurement results are shown in Table 1.

  Moreover, the surface SEM photograph of a comparative example and Example 1, 2 was image | photographed, and the smoothness of the surface was observed. The SEM photograph in the comparative example is shown in FIG. 1, the SEM photograph in Example 1 is shown in FIG. 2, and the SEM photograph in Example 2 is shown in FIG.

  And the XRD measurement of the comparative example and Examples 1 and 2 was performed. The results are shown in FIG.

(Evaluation of superconducting properties)
Ic after oxygen annealing of Comparative Example and Examples 1 and 2 was measured by the 4-terminal method (77.3K, under self-magnetic field). The results are shown in Table 1.

  From Table 1, it can be seen that ΔΦ is reduced by performing high temperature low oxygen annealing, and the in-plane orientation is improved. It can also be seen that Ic is significantly increased by performing high temperature low oxygen annealing.

  Further, from the comparison between FIG. 1 (Comparative Example) and FIG. 2 (Example 1), the high-temperature low oxygen annealing improves the bonding of crystal grains in the superconducting layer in FIG. It has a smooth surface state, and the formation trace of crystal growth is recognized by high temperature low oxygen annealing. Furthermore, in FIG. 3 (Example 2), it can be seen that the epitaxial growth is performed on the superconducting layer by the PLD method by the FF-MOD method.

  And as shown in FIG. 4, compared with a comparative example, all of Example 1 and Example 2 show that there is no change in the peak intensity of a superconducting layer, and crystallinity is maintained. This indicates that the superconducting layer is maintained without being destroyed even when the high temperature low oxygen annealing is performed.

Furthermore, in Examples 1 and 2, the NiO ₂ peak at 2θ = 37 ° and the GdBCO (005) peak at 2θ = 38 ° are clearly separated, and by annealing the thin film superconducting layer, It can be seen that oxygen is sufficiently taken in and the crystal lattice shrinks, and the GdBCO (005) peak shifts to the right.

(Example 3)
Similar to Example 1, before performing oxygen annealing on the GdBCO superconducting layer formed by using the PLD method, 500 ° C., 600 ° C., 700 ° C., 800 ° C., 900 ° C. in an atmosphere of 100 ppm O ₂ concentration. , 1000 ° C., 1100 ° C., and 1200 ° C. for 90 minutes, followed by furnace cooling to 500 ° C. over 1 hour and high-temperature low oxygen annealing. Thereafter, oxygen annealing was performed under the same conditions as in the comparative example, and the rare earth thin film superconducting wire of Example 3 was obtained.

  The eight samples prepared in Example 3 were evaluated for crystallinity (in-plane orientation) and Ic (77.3K under self-magnetic field) by the same method as in Example 1.

  The results are shown in Table 2. In Table 2, the results of the comparative examples in Table 1 are also shown.

  From Table 2, it can be seen that ΔΦ is smaller than that of the comparative example and the crystallinity (in-plane orientation) is improved by performing high temperature low oxygen annealing in the temperature range of 600 ° C. to 1000 ° C. . It can also be seen that Ic is improved.

  However, it can be seen that at temperatures exceeding 1000 ° C., the crystallinity decreases and Ic also decreases significantly. On the other hand, at temperatures below 600 ° C., the effect of low oxygen annealing is not observed, and it can be seen that both the crystallinity and Ic remain the same as those of the comparative example.

Example 4
As in Example 2, after applying a FF-MOD solution having a YBCO composition on a GdBCO superconducting layer formed by using the PLD method using a die coat, in an atmosphere having an O ₂ concentration of 100% and a dew point of 19 ° C. And calcination was performed at 505 ° C. for 120 minutes. Thereafter, holding at 680 ° C. for 45 minutes and 850 ° C. for 30 minutes in an atmosphere with an O ₂ concentration of 100 ppm, quenching to 500 ° C. over 1 hour, followed by firing, and a 0.6 μm thick FF-MOD superconducting layer (YBCO superconducting layer) was formed. Then, after holding at 850 ° C. for 90 minutes in each O ₂ concentration atmosphere of 50 ppm, 100 ppm, 200 ppm, 500 ppm, 1000 ppm, 2000 ppm and 5000 ppm, the furnace was cooled to 500 ° C. over 1 hour, and high temperature low oxygen annealing was performed. gave. Thereafter, oxygen annealing was performed under the same conditions as in Example 1 to obtain a rare earth thin film superconducting wire of Example 4.

  Seven types of samples produced in Example 4 were evaluated for crystallinity (in-plane orientation) and Ic (77.3K, under self-magnetic field) by the same method as in Example 1. The results are shown in Table 3.

  From Table 3, the oxygen concentration range of 100 ppm to 1000 ppm is markedly improved by high temperature and low oxygen annealing, and among these, the oxygen concentration region of 100 ppm to 500 ppm improves crystallinity and Ic is particularly high. It can be seen that it has improved. In particular, in this example, the optimum region for the oxygen concentration was found under the condition of holding at 850 ° C. for 90 minutes. It was.

  While the present invention has been described based on the embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the above-described embodiment within the same and equivalent scope as the present invention.

Claims (4)

A superconducting layer forming step for forming a rare earth-based thin film superconducting layer on an oriented metal substrate using a physical vapor deposition method, and an oxygen annealing step for subjecting the rare earth-based thin film superconducting layer to oxygen annealing are provided. A rare earth-based thin film superconducting wire manufacturing method,
Between the superconducting layer forming step and the oxygen annealing step, the rare earth-based thin film superconducting layer formed by the superconducting layer forming step is heated to a high temperature and low oxygen atmosphere at a temperature of 600 to 1000 ° C. and an O ₂ concentration of 1000 ppm or less. A method for producing a rare earth-based thin film superconducting wire, characterized in that a high-temperature low-oxygen annealing step for annealing is provided.   In the superconducting layer forming step, the rare earth-based thin film superconducting layer is formed on a base material comprising a metal substrate having biaxial crystal orientation and an intermediate layer formed thereon. The method for producing a rare earth thin film superconducting wire according to claim 1.   A rare earth-based thin film superconducting layer is further formed on the rare earth-based thin film superconducting layer formed in the superconducting layer forming step using a fluorine-free MOD method, and then the high-temperature low-oxygen by the high-temperature low-oxygen annealing step The method for producing a rare earth-based thin film superconducting wire according to claim 1 or 2, wherein annealing is performed.   A rare earth thin film superconducting wire manufactured using the method of manufacturing a rare earth thin film superconducting wire according to any one of claims 1 to 3.