JP2008130291A - Superconductor film and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a superconductor film high in critical current density Jc, and small in magnetic field angle dependency. <P>SOLUTION: In the superconductor film, columnar crystals each formed of a normally-conductive material containing Ba and intermittently arranged in the film thickness direction are formed in a superconductor layer formed of a superconductive material represented by general formula REBa<SB>2</SB>Cu<SB>3</SB>O<SB>x</SB>, where RE is at least one kind of element within rare-earth elements excluding Pr and Ce, and 6.5<x<7.1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a superconductor film that can be used in the field of superconducting wires or superconducting devices, and a method for manufacturing the same.

  Oxide superconductors typified by the Y-Ba-Cu-O system exhibit a critical temperature Tc higher than that of liquid nitrogen, and are expected to be applied to the fields of superconducting wires and superconducting devices. However, in order to apply such an oxide superconductor to these fields, the critical current density Jc of the oxide superconductor is improved, and a pinning point for stopping the movement of the quantized magnetic flux in the oxide superconductor is set. It is necessary to prevent the decrease of the critical current density Jc in the magnetic field by introducing it.

  In particular, in the Y-Ba-Cu-O-based oxide superconductor, the critical current density Jc is maximized when a magnetic field parallel to the a axis is applied due to the anisotropy of superconducting properties (strong crystal anisotropy). The critical current density Jc monotonously decreases as the angle formed between the a-axis and the applied magnetic field increases, and the critical current density Jc is minimized when a magnetic field parallel to the c-axis is applied. Therefore, various studies have been made on the introduction of a pinning point into a superconductor in order to improve the critical current density Jc when a magnetic field parallel to the c-axis is applied.

One of them, in Y-Ba-Cu-O based oxide superconductor film is composed of BaZrO ₃ is a normal conducting material, the nanorods extending in the thickness direction form a plurality of pinning points the nanorods There is a superconductor film (see Non-Patent Documents 1 and 2). It is known that this superconductor film has a high critical current density Jc due to the BaZrO ₃ nanorods formed therein acting as a strong pinning center.

M.M. MUKAIDA, T.M. HORIDE, R.M. KITA, S. HORI, A. ICHINOSE, Y.M. YOSHIDA, O.I. MIURA, K.M. MATSUMOTO, K.M. YAMADA, N.A. MORI: Jpn. J. et al. Appl. Phys. 44 (2005) L952. J. et al. L. Macmanus-Driscoll, S.M. R. Foltyn, W.M. X. Jia, A .; Serquis, B.M. Maiorov, L.M. Cival, M.M. E. Hawley, M .; P. Maley, D.M. E. Peterson: Nature Materials 3 (2004) 439.

  However, while the superconductor film described above has a high critical current density Jc, the critical current density Jc has a strong dependence (magnetic field angle dependence) on the direction of application of the magnetic field, so that a superconducting wire or a superconducting device is used. There was a problem that could not be applied. Specifically, since the characteristics of the superconducting wire and the superconducting device are determined by the lowest critical current density Jc under the environment in which they are used, the superconducting film having a high critical current density Jc at a predetermined magnetic field angle is used. Even if it has a low critical current density Jc at a magnetic field angle other than that angle, it could not be applied to a superconducting wire or a superconducting device.

  In view of the circumstances described above, an object of the present invention is to provide a superconductor film having a high critical current density Jc and low magnetic field angle dependency.

A first aspect of the present invention that solves the above problems is a general formula REBa ₂ Cu ₃ O _X (wherein RE is at least one element of rare earth elements excluding Pr and Ce, and 6.5 < X <7.1)), a superconducting layer made of a superconducting material is made of a normal conducting material containing Ba, and columnar crystals arranged intermittently in the film thickness direction are formed. It is in the superconductor film.

  In the first aspect, it is possible to provide a superconductor film having a high critical current density Jc and a small magnetic field angle dependency.

  According to a second aspect of the present invention, the weight ratio of the superconducting material to the material constituting the columnar crystal is in the range of 99.5: 0.5 to 70.0: 30.0. The superconductor film according to the first aspect is provided.

  In the second aspect, it is possible to provide a superconductor film that has a smaller magnetic field angle dependency.

  A third aspect of the present invention is the superconductor film according to the first or second aspect, wherein the length of the columnar crystal in the axial direction is in the range of 5 to 200 nm.

  In the third aspect, it is possible to provide a superconductor film having a higher critical current density Jc and a smaller magnetic field angle dependency.

  A fourth aspect of the present invention is the superconductor film according to any one of the first to third aspects, wherein a distance in the film thickness direction between the columnar crystals is in a range of 5 to 200 nm. .

According to a fifth aspect of the present invention, in the first to fourth aspects, the columnar crystal is composed of any one of BaZrO ₃ , BaWO ₄ , BaNb ₂ O ₆ , BaSnO ₃ , BaHfO ₃ , or BaTiO ₃ . It exists in the superconductor film | membrane as described in any one aspect.

  In the fifth aspect, it is possible to provide a superconductor film having a higher critical current density Jc and a smaller magnetic field angle dependency.

In a sixth aspect of the present invention, the superconductor layer is composed of YBa ₂ Cu ₃ O _X (wherein 6.5 <X <7.1), and the columnar crystal is composed of BaZrO ₃ . The superconductor film according to any one of the first to fifth aspects is characterized in that.

  In the sixth aspect, it is possible to provide a superconductor film having a higher critical current density Jc and a smaller magnetic field angle dependency.

According to a seventh aspect of the present invention, there is provided a general formula REBa ₂ Cu ₃ O _X (wherein RE is at least one element of rare earth elements excluding Pr and Ce, and 6.5 <X <7.1). And forming a first superconductor layer using a physical vapor deposition method using a first target composed of a substance represented by a normal conductive substance containing Ba, and a general formula REBa ₂ Cu ₃ O _X (wherein RE is at least one element of rare earth elements excluding Pr and Ce, and 6.5 <X <7.1). Forming a second superconductor layer using a physical vapor deposition method using a second target, and repeating the steps alternately to form the first superconductor layer and the second superconductor layer. A superconductor film manufacturing method characterized by alternately laminating superconductor layers That.

  In the seventh aspect, a superconductor film having a high critical current density Jc and a small magnetic field angle dependency can be produced.

  In an eighth aspect of the present invention, each of the first target and the second target includes a region made of a substance constituting the first target and a region made of the substance constituting the second target. The method of manufacturing a superconductor film according to the seventh aspect, wherein the superconductor film is formed by dividing the film into two.

  In the eighth aspect, a superconductor film can be easily produced.

  According to the superconductor film and the manufacturing method thereof according to the present invention, it is possible to provide a superconductor film having a high critical current density Jc and a small magnetic field angle dependency.

  Hereinafter, the best mode for carrying out the present invention will be described. The description of the present embodiment is an exemplification, and the present invention is not limited to the following description.

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing a superconductor film according to Embodiment 1 of the present invention. As shown in FIG. 1, the superconductor film 1 according to the present embodiment is formed on a substrate 100, and columnar crystals 20 arranged intermittently in the film thickness direction are formed in a superconductor layer 10 made of a superconducting material. A plurality are formed. That is, the superconductor film 1 is formed with a plurality of columnar crystals 20 in which a long columnar crystal extending from the surface of the substrate 100 to the surface of the superconductor layer 10 is cut a plurality of times in the superconductor layer 10 made of a superconducting material. Has been.

Examples of the substrate 100 include perovskite crystals such as SrTiO ₃ and LaAlO ₃ , rock salt crystals such as MgO and NiO, spinel crystals such as MgAl ₂ O ₄ , YSZ (yttria-stabilized zirconia), and CeO ₂ . Fluorite-type crystal, rare earth c-type crystal, biquare type crystal and metal substrate (Ni-based alloy substrate made of Ni, Ni-Cr, Ni-W, etc., Cu-based synthetic substrate made of Cu, Cu-Ni, etc., Fe- An Fe-based synthetic substrate made of Si, stainless steel, or the like can be used.

The superconducting material constituting the superconductor layer 10 includes a general formula REBa ₂ Cu ₃ O _X (wherein RE is at least one element of rare earth elements excluding Pr and Ce, and 6.5 <X < 7.1), YBa ₂ Cu ₃ O _X , ErBa ₂ Cu ₃ O _X , and GdBa ₂ Cu ₃ O _X are preferable.

Next, the substance constituting the columnar crystal 20 is not particularly limited as long as it is a normal conductive substance containing Ba, but BaZrO ₃ , BaWO ₄ , BaNb ₂ O ₆ , BaSnO ₃ , BaHfO ₃ , and BaTiO ₃ are preferable, and BaZrO. ₃ , BaWO ₄ , BaNb ₂ O ₆ and BaSnO ₃ are more preferable, and BaZrO ₃ is particularly preferable.

  The weight ratio between the superconducting substance and the substance constituting the columnar crystal 20 is not particularly limited, but is preferably in the range of 99.5: 0.5 to 70.0: 30.0. By adjusting the weight ratio between the superconducting material and the material constituting the columnar crystal 20, a superconductor film having a desired critical current density Jc and magnetic field angle dependency can be produced. When the weight ratio of the material constituting the columnar crystal 20 to the superconducting material is smaller than 0.5 / 99.5, the critical current density Jc of the superconductor film 1 is lowered. Further, when the weight ratio of the material constituting the columnar crystal 20 to the superconducting material is larger than 30.0 / 70.0, the superconductivity of the superconductor film 1 is lowered.

  The length L in the axial direction of the columnar crystal 20 is not particularly limited, but is preferably in the range of 5 to 200 nm. By adjusting the length L of the columnar crystal 20, the superconductor film 1 having a desired magnetic field angle dependency can be produced. When the length L of the columnar crystal 20 is smaller than 5 nm, the critical current density Jc of the superconductor film 1 is lowered. Moreover, when the length L of the columnar crystal 20 is greater than 200 nm, the magnetic field angle dependency of the superconductor film 1 increases.

  Further, the distance D between the columnar crystals 20 is not particularly limited, but a range of 5 to 200 nm is preferable. By adjusting the distance D between the columnar crystals 20, the superconductor film 1 having a desired magnetic field angle dependency can be produced. If the distance D between the columnar crystals 20 is smaller than 5 nm, the magnetic field angle dependency of the superconductor film 1 increases. Further, when the distance D between the columnar crystals 20 becomes larger than 200 nm, the critical current density Jc of the superconductor film 1 similarly decreases.

  By configuring the superconductor film 1 as described above, it is possible to provide the superconductor film 1 having a high critical current density Jc and a small magnetic field angle dependency.

  Next, a method for manufacturing the above-described superconductor film 1 will be described. As a method of manufacturing the superconductor film 1 described above, as shown in FIG. 2, physical using a first target composed of the above-described superconducting material and a material constituting the columnar crystal 20 on the substrate 100. Forming a first superconductor layer using a physical vapor deposition method and a physical vapor deposition method using a second target composed only of the superconducting material described above. There is no particular limitation as long as the first superconductor layer and the second superconductor layer can be alternately stacked by repeating these steps alternately. Examples of physical vapor deposition used in this method include pulse laser vapor deposition (PLD), sputtering, and vacuum vapor deposition.

  Specifically, for example, a first target obtained by mixing and sintering a superconducting substance and a substance constituting a columnar crystal at a predetermined ratio and a second target made of only the superconducting substance are prepared, and these targets are prepared. Is installed in a pulsed laser deposition apparatus.

  Then, the first superconductor layer 10a and the superconductor layer 10b described above are formed on the substrate 100 as described later while heating the substrate 100 attached in the pulse laser deposition apparatus in a reduced-pressure oxygen atmosphere. Are alternately stacked.

  First, by using the first target as the target, as shown in FIG. 3A, the first superconductor layer 10a in which a plurality of columnar crystals extending in the film direction are formed on the substrate 100 is produced. . Next, by using the second target as the target, as shown in FIG. 3B, the second superconductor layer 10b is formed on the first superconductor layer 10a. Further, by using the first target as a target, as shown in FIG. 3C, the first superconductor layer 10a is further formed on the second superconductor layer 10b. Then, by repeating these steps a plurality of times alternately, the superconductor film 1 as shown in FIG. 1 can be formed.

  That is, the first superconductor layer 10a in which the columnar crystal 20 extending in the film thickness direction is formed in the superconductor layer made of the superconducting material and the second superconductor layer 10b made only of the superconducting material are formed on the substrate 100. As shown in FIG. 1, the superconductor film 1 in which the columnar crystals 20 arranged intermittently in the film thickness direction are formed in the superconductor layer 10 can be formed. It is not clear why the columnar crystal 20 is due to internal stress, but the columnar crystal 20 formed on the first superconductor layer 10a on the substrate 100 and the first superconductor layer 10a above the columnar crystal 20a The formed columnar crystals 20 are formed so as to be aligned in the film thickness direction.

  Here, since the superconductor film 1 is formed as described above, the columnar crystal is adjusted by adjusting the thickness of the first superconductor layer 10a according to the method of manufacturing a superconductor film according to this embodiment. The length L of 20 can be adjusted, and the distance D between the columnar crystals 20 can be easily adjusted by adjusting the thickness of the second superconductor layer 10b, resulting in a critical current density. A superconductor film having a high Jc and low magnetic field angle dependency can be produced.

(Other embodiments)
In the first embodiment, the lengths L of the columnar crystals 20 are all the same, but may vary depending on the distance in the film thickness direction from the surface of the substrate 100. That is, as shown in FIG. 4, columnar crystals 20 having different lengths L may be formed in the superconductor layer 10. Such a superconductor film 1A can be easily manufactured by changing the thickness of each of the first superconductor layers 10a described above.

  In the first embodiment, the distances D between the columnar crystals 20 are all the same, but may be different depending on the distance in the film thickness direction from the surface of the substrate 100. That is, the distance D between the columnar crystals 20 in the superconductor layer 10 may be different. Such a superconductor film can be easily manufactured by changing the thickness of each of the second superconductor layers 10b described above.

  Furthermore, in the first embodiment, the first superconductor layer 10a and the second superconductor layer 10b are formed by using two targets (first target and second target), so-called multi-targets. As shown in FIGS. 5A to 5C, mixed targets 200 and 200A each including a portion 210 made of a material having the same composition as the first target and a portion 220 made of a material having the same composition as the second target. , 200B may be used to form the first superconductor layer 10a and the second superconductor layer 10b. In particular, when the mixed targets 200A and 200B shown in FIG. 5B and FIG. 5C are used, by changing the laser irradiation position (the radial distance from the center of the mixed target) of the mixed targets 200A and 200B, It is possible to easily form the first superconductor layer 10a and the second superconductor layer 10b so as to have a desired weight ratio in a wide range. Needless to say, the area ratio between the portion 210 and the portion 220 should be appropriately adjusted according to the thicknesses of the first superconductor layer 10a and the second superconductor layer 10b to be formed.

<Example 1>
YBa ₂ Cu ₃ O _X (6.5 <X <7.1) and BaZrO ₃ are mixed at a weight ratio of 98.5: 1.5 to prepare the target 1, and YBa ₂ Cu ₃ Targets 2 made only of O _X (6.5 <X <7.1) were produced, and these targets were attached to a sputtering apparatus. Then, after the inside of the sputtering apparatus was evacuated to 10 ⁻⁵ Torr, oxygen was introduced, and the substrate 100 was heated to 820 ° C. in an oxygen atmosphere of 200 mTorr, and a superconductor film was produced using the above-described target. .

  FIG. 6 shows an enlarged cross-sectional photograph of the superconductor film obtained by a transmission electron microscope (TEM). Note that a FIB (Focused-Ion Beam) apparatus was used for thinning the superconductor thin film. It can be seen that in the obtained superconductor film, columnar crystals that are intermittently connected in the film thickness direction (c-axis direction) are formed in the superconductor layer. The film thickness of this superconductor film was 300 nm, the length L of the columnar crystals was 50 nm, and the distance D between the columnar crystals was 10 nm.

<Example 2>
A superconductor film was produced in the same manner as in Example 1 except that the length L of each columnar crystal constituting the columnar crystal and the distance D between the columnar crystals were both 10 nm.

  FIG. 7 shows an enlarged cross-sectional photograph of the superconductor film obtained by a transmission electron microscope (TEM). It can be seen that in the obtained superconductor film, columnar crystals that are intermittently connected in the film thickness direction (c-axis direction) are formed in the superconductor layer. The film thickness of this superconductor film was 300 nm, the length L of the columnar crystals was 10 nm, and the distance D between the columnar crystals was 10 nm.

<Comparative Example 1>
A superconductor film was produced in the same manner as in Example 1 except that only the target 1 was used. FIG. 8 shows an enlarged cross-sectional photograph of the superconductor film obtained by a transmission electron microscope (TEM). In the obtained superconductor film, columnar crystals extending in the film thickness direction are formed in the superconductor layer.

<Test Example 1>
With respect to the superconductor films obtained in Examples 1 and 2 and the superconductor film obtained in Comparative Example 1, the critical current density Jc with respect to the application direction of the magnetic field (magnetic flux density: 3T) was measured. The measurement results of the superconductor films obtained in Examples 1 and 2 and Comparative Example 1 are shown in FIG. In FIG. 9, the application direction of the magnetic field parallel to the film thickness direction is 90 °.

  As shown in FIG. 9, the superconductor film obtained in Examples 1 and 2 has a magnetic field angle compared to the superconductor film obtained in Comparative Example 1 in a region where the direction of application of the magnetic field is not near 90 °. It turns out that the dependency is low. Since the strength of this characteristic varies depending on the strength of the applied magnetic field, this property may appear more prominently depending on the strength of the applied magnetic field.

  Further, it was found that the superconductor films obtained in Examples 1 and 2 had a critical current density Jc comparable to that of the superconductor film obtained in Comparative Example 1.

1 is a schematic cross-sectional view showing a superconductor film according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating a manufacturing process of a superconductor film according to Embodiment 1. FIG. 3 is a diagram illustrating a manufacturing process of a superconductor film according to Embodiment 1. It is a schematic sectional drawing of the superconductor film | membrane which concerns on other embodiment. It is the schematic of the mixing target which concerns on other embodiment. 2 is an enlarged cross-sectional photograph of a superconductor film obtained in Example 1. 4 is an enlarged cross-sectional photograph of a superconductor film obtained in Example 2. 2 is an enlarged cross-sectional photograph of a superconductor film obtained in Comparative Example 1. It is a graph which shows the critical current density Jc with respect to the application direction of the magnetic field of the superconductor film | membrane obtained in Examples 1, 2 and Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1A Superconductor film 10, 10a, 10b Superconductor layer 20 Columnar crystal 100 Substrate 200, 200A, 200B Mixed target 210 Part made of the same composition as the first target 220 From the same composition as the second target Part

Claims (8)

A superconducting material represented by the general formula REBa ₂ Cu ₃ O _X (wherein RE is at least one element of rare earth elements excluding Pr and Ce, and 6.5 <X <7.1) A superconducting film comprising: a superconducting layer made of a normal conducting material containing Ba, and columnar crystals arranged intermittently in the film thickness direction. 2. The superconductor film according to claim 1, wherein a weight ratio between the superconducting material and the material constituting the columnar crystal is in a range of 99.5: 0.5 to 70.0: 30.0. The superconductor film according to claim 1 or 2, wherein the length of the columnar crystal in the axial direction is in the range of 5 to 200 nm. The superconductor film according to any one of claims 1 to 3, wherein a distance in a film thickness direction between the columnar crystals is in a range of 5 to 200 nm. 5. The superconductivity according to claim 1, wherein the columnar crystal is composed of any one of BaZrO ₃ , BaWO ₄ , BaNb ₂ O ₆ , BaSnO ₃ , BaHfO ₃ , and BaTiO _3. Body membrane. The superconductor layer is made of YBa ₂ Cu ₃ O _X (wherein 6.5 <X <7.1), and the columnar crystal is made of BaZrO ₃ . The superconductor film according to any one of 5. A substance represented by the general formula REBa ₂ Cu ₃ O _X (wherein RE is at least one element of rare earth elements excluding Pr and Ce, and 6.5 <X <7.1); Forming a first superconductor layer using a physical vapor deposition method using a first target composed of a normal conductive material containing Ba,
The substance represented by the general formula REBa ₂ Cu ₃ O _X (wherein RE is at least one element of rare earth elements excluding Pr and Ce, and 6.5 <X <7.1) Forming a second superconductor layer using a physical vapor deposition method using a second target composed of: the first superconductor layer and the step by repeating these steps alternately. A method for producing a superconductor film, wherein the second superconductor layer is alternately laminated. The first target and the second target are formed by dividing one target into a region made of a substance constituting the first target and a region made of a substance constituting the second target. The method for producing a superconductor film according to claim 7.

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