JPH02257525A - Manufacture of oxide superconductor - Google Patents

Abstract

PURPOSE:To prevent the critical current density of an oxide superconductor from lowering by causing a low viscous material or solution to penetrate into cracks generated through an oxide layer re-crystallized or crystallized, and applying laser beam for re-crystallization or crystallization. CONSTITUTION:A film of an oxide superconducting material 2 e.g. of Y Ba Cu O is formed on an yttrium stabilized zilconia base 1. The film is then irradiated with laser beam to re-crystallize or crystallize the material 2. Thereafter, a solution 4 of naphthene acid yttrium, naphtene acid barium and naphthene acid copper is applied on the outside of the material 2, and the material 2 is irradiated with laser beam to form a crystallized layer 5. Lowering of critical current density is thus prevented that may be caused by cracks liable to form through the oxide superconductor, and the mechanical stability of the oxide superconductor is enhanced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an oxide superconductor, and in particular, a method for manufacturing an oxide superconductor that can prevent deterioration of superconducting properties due to the occurrence of cracks. Regarding.

[Prior Art] In recent years, the development of oxide superconducting materials has progressed at a remarkable speed, and the use of superconducting materials such as La-based, Y-based, old thread, and TI-based materials has become promising.

However, these materials have anisotropy in their superconducting properties, that is, there are significant differences in properties depending on the crystal orientation, and simply molding and sintering the raw material powder obtained by normal synthesis methods only yields materials with random crystal orientation. Because it is not possible to
There is a problem in that electrical and magnetic properties that reach a practical level cannot be obtained.

As a method to solve the above problem, an attempt has been made to increase crystal orientation by melting an oxide superconducting material and moving this melt relatively in an electric furnace with a temperature gradient to grow crystals. ing.

Furthermore, attempts have been made to improve crystal orientation by forming a floating zone in a superconductor, such as a linear superconductor, and melting and solidifying the superconductor.

However, in the former melting temperature gradient crystallization method, there is a limit to the setting of the temperature gradient, and it is impossible to form a large gradient in the furnace by heat conduction, so it has the disadvantage that it is difficult to control the crystal orientation. .

On the other hand, in the latter method using a floating zone, only a phase that stably crystallizes from the liquid 10 can be obtained, and
It has the disadvantage that its growth rate is extremely slow, ranging from several marks to several 1 ml/hr. In particular, in this method, Y-Ba-
In the case of Cu-0-based oxides, melting-recrystallization produces a Y2 BaCu0x phase, which is an insulating material, but has a fatal drawback in that a Y11a2 CuOx phase, which is a superconducting material, is not produced.

A method using a laser beam is being considered as a method to solve these difficulties. When an oxide superconducting material is recrystallized or crystallized by this method, extremely dense crystals are obtained due to growth from the liquid phase and rapid solidification.

[Problems to be Solved by the Invention] However, in the case of laser heating, there is a problem in that distortion is likely to occur between the recrystallized or crystallized layer due to heating and the unfused portion, resulting in large racks.

Furthermore, since the temperature is extremely high, cracks may occur due to differences in coefficient of thermal expansion with the substrate, differences in thermal expansion due to crystal orientation, or phase transitions due to the entry and exit of oxygen.

One possible way to remove the above cracks is to reheat immediately after laser irradiation, but this method reduces the recrystallization and crystallization effects based on the steep temperature gradient, which is an advantage of laser heating, and as a result, reduce its properties.

The present invention has been made to solve the above-mentioned difficulties.
It is an object of the present invention to provide a method for preventing deterioration of superconducting properties due to cracks generated in an oxide superconductor by laser irradiation.

[Means for Solving the Problems] In order to achieve the above object, the method for manufacturing an oxide superconductor of the present invention includes applying a laser beam to an oxide superconducting material or a raw material containing an element constituting the oxide superconducting material. After recrystallizing or crystallizing the substance by irradiation, the outer side thereof is coated with a low-viscosity substance or solution that produces an oxide superconducting substance by melting and solidification, and then the coating layer is formed by irradiating with a laser beam. is recrystallized or crystallized.

The oxide superconducting material in the present invention is not particularly limited, and for example, La-Ba-Cu-0 system, La-3r-Ca
-Cu-0 series, Y-Ba-Cu-0 series, B1-9r-C
Examples include a-Cu-0 type oxides, Tl-Ba-Ca-Cu-0 type oxides, and the like.

In addition, raw materials containing elements constituting oxide superconducting materials include oxides, carbonates, and nitrates containing these elements, and metal salts other than alkali salts such as fatty acids, resin acids, and naphthenic acids, that is, metals. A molded body made of soap or the like or a coating film formed on a substrate is used.

Further, as the superconducting material, a film formed on a substrate by vapor deposition, sputtering, CVD, etc. can also be used.

On the other hand, as the low-viscosity substance or solution to be coated on the outside of the recrystallized or crystallized layer after laser irradiation, a substance containing the elements constituting the above-mentioned oxide superconducting substance or superconducting powder is prepared using a solvent, etc. It is used in the form of a solution with a viscosity of . The viscosity of this solution is reduced to such an extent that it sufficiently fills the cracks, and is coated sufficiently thinly on the underlying recrystallized or crystallized layer.

The laser beam in the present invention is Ar, YAG 5CO
It is formed by a CW (continuous) laser of the order of 2, and the laser beam irradiation of the coating layer has a sufficiently low power so as not to affect the underlying oxide superconducting material.

For example, a beam with a diameter of about 20 to 50 μm is used and moved at a scanning speed of 1-10 cm/sec.

In this case, in order to obtain crystals oriented in the scanning direction, it is preferable to use twin beams, triple beams, slit beams, etc. to form a large temperature gradient in the scanning direction.

[Operation] With the above configuration, a low viscosity substance or solution penetrates into the cracks generated in the recrystallized or crystallized oxide layer and is recrystallized or crystallized by laser irradiation, so that critical Along with improving current density, mechanical stability can also be increased.

[Example] As shown in FIG. 2, a film of ynco-based superconducting material 2 is formed to a thickness of 2 μm on a yttrium-stabilized zirconia substrate 1, and a 2-layer film with an output of 10 v, a beam radius of 50 μm, and a beam focal length of 100 μm is formed. Recrystallization was performed by irradiation using a regular YAG laser beam (twin beam) at a scanning speed of 10 cm/sec. Superconducting material 2' obtained in this way
The orientation of the a-b axis is good, and its critical current density J
The value of c (external magnetic field OT.

77 (same as 1 or less) was 103 A/c-. However, as a result of observing this oxide layer with an SEM, the third
As shown in the figure, it was observed that many fine racks 3 were generated on the surface. Next, as shown in FIG. 4, on the surface of the above oxide superconductor, yttrium naphthenate, barium naphthenate, copper naphthenate (Y:Ba:C
u = l:2:3) solution 4 to a thickness of 0.2. cza
A crystallized layer 5 was formed on the surface as shown in FIG. 1 by applying a laser beam at an output of 3 V and a scanning speed of 10 c+n/see. As a result, the critical current density is 10”~
IO'A/Cl rose to 112.

[Effects of the Invention] As described above, according to the present invention, it is possible to prevent a decrease in critical current density due to cracks that are likely to occur in an oxide superconductor, and to improve its mechanical stability.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a superconductor obtained by the method of the present invention, Fig. 2 is a cross-sectional view showing a state in which an oxide layer is formed on a substrate, and Figs. FIG. 3 is a cross-sectional view of a state in which a solution has been applied and a state in which a solution has been applied and after laser beam irradiation.

Claims (1)

[Claims] After recrystallizing or crystallizing the material by irradiating the oxide superconducting material or the raw material containing the elements constituting the oxide superconducting material with a laser beam, melting,
A method for producing an oxide superconductor, which comprises coating a low-viscosity substance or solution that produces an oxide superconductor by solidification, and then recrystallizing or crystallizing the coating layer by irradiating with a laser beam.