JPH05193934A - Production of oxide superconductor member - Google Patents

Abstract

PURPOSE:To perfectly orient the C axis of the crystal of an oxide superconductor and to improve its critical current density in the process of heat-treating a precursor having the same composition as the oxide superconductor formed on a substrate by grading the temp. of heat treatment. CONSTITUTION:The temp. gradient of 0.1-100 deg.C/mum is imparted vertically to the thickness direction of the precursor in heat treatment. For example, when a target consists of Bi2Sr2Ca1Cu2Ox, etc., the precursor for the oxide superconductor having about 10mum thickness is formed on a silver polycrystal substrate 3 by a laser-beam abrasion device. The substrate 3 is heated to 895 deg.C and the surface of the precursor to 885 deg.C, and the substrate and precursor are slowly cooled respectively to 875 deg.C and 865 deg.C at the rate of 2 deg.C/hr, held at the temps. for 20hr and then cooled to room temp. to form an oxide superconductor 7 on the substrate 3. A temp. gradient of 1 deg.C/mum is imparted vertically to the thickness direction of the precursor in this way in the heat treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide superconductor member, and more particularly to an oxide superconductor member having an improved oxide superconducting crystal structure and improved critical current density (Jc) characteristics. It relates to a manufacturing method.

[0002]

2. Description of the Related Art An oxide superconductor member obtained by a thick film method and a thin film method comprises a substrate as a base material, an oxide superconducting conductor provided on the substrate via an intermediate layer,
It is composed of a protective layer provided on the surface of the oxide superconducting conductor. The intermediate layer and the protective layer are provided as necessary. The intermediate layer prevents deterioration of superconducting properties due to element diffusion between the oxide superconducting conductor and the substrate, and matches the lattice constant and the thermal expansion coefficient. Further, the protective layer insulates each other when forming a coil by overlapping, and also plays a role of reinforcement and a stabilizing material of the oxide superconducting conductor.

When synthesizing an oxide superconducting conductor on a substrate or an intermediate layer, a precursor having the same composition as that of the oxide superconducting conductor is formed on the surface of the substrate or the intermediate layer to adjust the chemical composition. After that, a post-heat treatment of 400 to 1100 ° C is performed to synthesize by crystallization and adjustment of oxygen concentration, or a substrate heated to 400 to 1100 ° C or an oxide superconducting conductor is directly synthesized on the intermediate layer. Method (method of simultaneously adjusting crystallization and oxygen concentration: Superconducting Materials Research Group,
The 6th Symposium Proceedings 1988, 3-1) has been adopted.

When the oxide superconducting conductor is synthesized on the substrate or the intermediate layer by the above method, not only when the substrate or the intermediate layer is a ceramic single crystal (001) but also in other cases, the C plane is parallel to the substrate surface. It has the characteristic of growing, and an oxide superconducting conductor having a C-axis oriented crystal structure can be easily obtained.

[0005]

However, when the crystal structure of the oxide superconductor member obtained by the above method was evaluated by X-ray analysis, it was found that the oxide superconductor on the substrate was C-axis oriented as a whole. However, the presence of peaks on other crystal planes other than (00l) was observed, and when attention was paid to individual crystal grains, the substrate surface was tilted from several degrees to several tens of degrees, and the complete C-axis was observed. Orientation is not obtained. Therefore, the bondability between the crystal grains deteriorates, and the critical current density value (Jc value) of the oxide superconductor member becomes low.

Therefore, an object of the present invention is to provide a method for producing an oxide superconductor member which can obtain a perfect C-axis orientation as a crystal structure of an oxide superconductor and can improve the critical current density value. Is.

[0007]

In view of the above problems, the present invention provides a perfect C-axis orientation as a crystal structure of an oxide superconducting conductor and improves the critical current density value. It is intended to provide a method for producing an oxide superconductor member in which a heat treatment is performed with a temperature gradient of 0.1 to 100 ° C./μm perpendicular to the direction.

When the temperature gradient is less than 0.1 ° C./μm, there is no effect of the temperature gradient, and nucleation of crystals occurs randomly in the thickness direction of the precursor, degrading the C-axis orientation, and If the temperature gradient exceeds 100 ° C./μm, the temperature difference between the substrate and the precursor becomes too large, and proper crystal growth cannot be expected.

[0009]

As described above, when the heat treatment is performed with a temperature gradient of 0.1 to 100 ° C./μm perpendicular to the thickness direction of the precursor, the thermal gradient is generated between the substrate and the precursor. Therefore, the crystal growth of the precursor occurs along the surface of the substrate having a high temperature, and the crystal structure of the oxide superconducting conductor is a single C-axis oriented film, and the crystallinity can be improved. Therefore, the critical current density (Jc) value can be improved.

[0010]

EXAMPLES The method for producing an oxide superconductor member of the present invention will be described in detail below.

FIG. 1 shows a schematic structure of a laser ablation apparatus according to this embodiment. This laser ablation device includes a vacuum chamber 2 having a gas inlet 5 and an exhaust port 6, a target 4 rotatably arranged inside the vacuum chamber 2, a substrate 3 mounted on the target 4, and a target. The laser 1 is emitted toward the laser beam 4.

The vacuum chamber 2 has a structure in which a predetermined degree of vacuum is adjusted through the exhaust port 6 and a predetermined amount of oxygen is introduced through the gas introduction port 5.

The target 4 is, for example, Bi ₂ Sr ₂ C.
a ₁ Cu ₂ O _x or other oxide superconducting material, where A
By irradiating with an rF excimer laser or the like, a precursor of the oxide superconducting conductor is formed on the substrate 3 attached to the upper part.

A method of manufacturing an oxide superconductor member using the above laser ablation device will be described below.

[0015]

Example 1 First, inside the vacuum chamber 2, a width of 5 mm and a length of 1
A silver polycrystalline substrate 3 having a thickness of 0 mm and a thickness of 0.2 mm is attached,
Further, the inside of the vacuum chamber 2 is depressurized to a vacuum degree of 5 × 10 ⁻⁵ Torr, and 0.2 Torr of oxygen is introduced from the gas inlet 5. And pulse energy 1.5 J /
The ArF excimer laser 1 having a frequency of ² cm and a repetition frequency of 40 Hz is rotated by Bi ₂ Sr ₂ Ca ₁ Cu ₂ O.
_{The x} target 4 is irradiated for 1 hour to form a precursor of an oxide superconducting conductor having a thickness of about 10 μm on the silver polycrystalline substrate 3.

Then, the silver polycrystal substrate 3 is heated at 895 ° C. and the surface side of the precursor is heated at 885 ° C., respectively, and at a cooling rate of 2 ° C./h, 875 ° C. and 865 ° C.
After gradually cooling down to 20 ° C., the temperature is lowered to room temperature to form an oxide superconducting conductor on the silver polycrystalline substrate 3. That is, 1 ° C./perpendicular to the thickness direction of the precursor
A heat treatment is performed with a temperature gradient of μm to form an oxide superconducting conductor, and an oxide superconducting member is obtained.

Next, an X-ray analysis of the oxide superconductor member manufactured as described above was performed. As a result, the crystal structure of the oxide superconducting conductor was a low Tc phase (2212 phase) single C-axis oriented film, and although the film thickness was as thick as about 10 μm, its half-value width was 0.2 °. And the crystallinity was very good. Moreover, when the oxide superconductor member was observed with a scanning electron microscope, as shown in FIG. 2, a plate-like texture was confirmed in the oxide superconductor 7 on the substrate 3, and even when observed microscopically. The orientation structure was tilted within 2 degrees with respect to the surface of the substrate 3. The reason for this is that there is a thermal gradient between the substrate and the precursor, so that low-Tc phase crystal growth occurs along the substrate surface where the temperature is high. Furthermore, in order to investigate the superconducting characteristics, the critical current density was measured by a DC four-terminal method in an applied magnetic field of 0T and 4.2K. As a result, the critical current density is 3
It showed excellent superconducting properties of × 10 ⁵ A / cm ² .

[0018]

Comparative Example 1 In the same manner as in Example 1, a precursor of an oxide superconducting conductor was formed on the substrate 3, the whole was heated at a temperature of 895 ° C., and then a cooling rate of 2 ° C./hour was applied. 875 ° C
Was slowly cooled to room temperature, and the temperature was lowered to room temperature for 20 hours to obtain an oxide superconductor member.

Next, an X-ray analysis of the oxide superconductor member produced in this way was carried out. As a result, the crystal structure of the oxide superconductor was a low Tc phase (2212 phase) C-axis oriented film. Its half-width was 0.35 ° and the crystallinity was poor. Further, as a result of observation with a scanning electron microscope, as shown in FIG. 3, a plate-like orientation structure was observed in the oxide superconducting conductor 7, but when observed microscopically, it was several degrees to 3 degrees relative to the substrate surface.
It was tilted about 0 degrees. The reason is that since the substrate 3 and the precursor are heated at the same temperature, nucleation of low Tc phase crystals occurs everywhere in the precursor, and thereafter growth occurs. Furthermore, in order to investigate the superconducting characteristics, the critical current density was measured by a DC four-terminal method in an applied magnetic field of 0T and 4.2K. As a result, the critical current density is 8000 A / cm
^{It was 2} , which was not preferable for superconducting properties.

[0020]

[Embodiment 2] Inside the vacuum chamber 2, a width of 10 mm and a length of 100
A Hastelloy substrate 3 having a thickness of 0 mm and a thickness of 0.5 mm is attached, and further, the inside of the vacuum chamber 2 is depressurized to a vacuum degree of 5 × 10 ⁻⁵ Torr and 0.2 Torr from a gas inlet.
Introduce oxygen. And pulse energy 1.5J
ArF excimer laser 1 having a repetition rate of 10 Hz / cm ² and a repetition frequency of 10 Hz is rotated by Tl ₂ Ba ₂ Ca ₁ Cu ₃
Irradiate the O _x target 4 for 1 hour to obtain the Hastelloy substrate 3
A precursor of an oxide superconducting conductor having a thickness of about 2 μm is formed thereon.

Then, the Hastelloy substrate 3 was heated at 860 ° C. in a Tl ₂ O ₃ atmosphere, and the surface side of the precursor was kept at 8 ° C.
After each heating at 40 ° C., the temperature is kept for 20 hours and the temperature is lowered to room temperature to form an oxide superconducting conductor on the Hastelloy substrate 3. That is, the oxide superconducting conductor is formed by providing a temperature gradient of 10 ° C./μm perpendicular to the thickness direction of the precursor and performing a heat treatment to obtain an oxide superconducting member.

Next, an X-ray analysis of the oxide superconductor member produced in this way was carried out. As a result, the crystal structure of the oxide superconductor became a single C-axis oriented film of high Tc phase (2223 phase). The full width at half maximum was 0.2 ° and the crystallinity was good. In addition, in order to investigate the superconducting characteristics, the critical current density was measured by a DC four-terminal method in an applied magnetic field of 0T and 4.2K. As a result, the critical current density was 1 × 10 ⁵ A / cm ² , showing excellent superconducting properties.

[0023]

COMPARATIVE EXAMPLE 2 In the same manner as in Example 2, a precursor of an oxide superconducting conductor was formed on the Hastelloy substrate 3, and the whole was formed into 8 parts.
It heated at the temperature of 50 degreeC, hold | maintained for 20 hours, and cooled to room temperature.

An X-ray analysis of the oxide superconducting member manufactured as described above revealed that the oxide superconducting conductor had a crystal structure of a high Tc phase (2223 phase) C-axis oriented film.
Its half-width was 0.3 ° and the crystallinity was poor. The critical current density at an applied magnetic field of 0T and 4.2K is 3000A.
/ Cm ² , which was not preferable for superconducting properties.

In the above embodiment, the Bi-based low Tc phase (22
12 phase) and the formation of a Tl-based high Tc phase (2223 phase), other Bi-based high Tc phase (2223 phase) with or without Pb doping, 2201 phase of Tl2 layer system, 2
212 phase, 2234 phase, etc., or Tl1 layer system 1201
Phase, 1212 phase, 1223 phase, 1234 phase, etc., and may be Y—Ba—Cu—O system. Also,
Substrate materials are Au, Pt, P in addition to Ag and Hastelloy.
d, Cu, or alloys thereof, heat-resistant alloys such as Inconel, iron-based alloys such as SUS, or stabilized diniconia (YSZ), MgO, SrTiO ₃ , LaAlO ₃ , L
Ceramics such as aGdO ₃ and semiconductors such as Si can be applied.

Further, in the above embodiment, the precursor is formed on the substrate and then the heat treatment with the temperature gradient is performed. However, when the substrate is heated in advance and the precursor is formed, the temperature gradient is changed. Even if it is turned on, the same effect can be obtained.

Further, the precursor is an ArF excimer laser, an excimer laser such as KrF or XeCl, or YA.
It may be prepared by a G laser, or a vapor phase method such as a vacuum vapor deposition method, a sputtering method or a chemical vapor phase method by optimizing the composition, crystal structure and oxygen content without using a laser ablation method, and It may be prepared by a doctor blade method, a dip coating method, a coating thermal solution method, or a combination thereof.

[0028]

As described above, according to the method for producing an oxide superconductor member of the present invention, a temperature gradient of 0.1 to 100 ° C./μm is applied perpendicularly to the thickness direction of the precursor. Since the heat treatment is performed, perfect C-axis orientation is obtained as the crystal structure of the oxide superconducting conductor, and the critical current density value can be significantly improved.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a laser ablation device used in an embodiment of the present invention.

FIG. 2 is a schematic sectional view showing an oxide superconductor member obtained in this example.

FIG. 3 is a schematic sectional view showing an oxide superconductor member obtained by a comparative example.

[Explanation of symbols]

1 Laser 2 Vacuum Tank 3 Substrate 4 Target 5 Gas Inlet 6 Exhaust 7 Oxide Superconducting Conductor

Claims (1)

[Claims] 1. A method for producing an oxide superconducting member, comprising: forming a precursor having the same composition as that of an oxide superconducting conductor on a substrate; and subjecting the precursor to heat treatment to form an oxide superconducting conductor on the substrate. The method for producing an oxide superconductor member, wherein the heat treatment is performed with a temperature gradient of 0.1 to 100 ° C./μm perpendicular to the thickness direction of the precursor.