JPH02258695A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain the title superconductor with its crystal unidirectionally orientatively solidified and crystal phase uniformity improved in its width direction by forming an oxide superconducting film on a laser beam-transmissive base and by irradiating both the surfaces of the base and the film with laser beams to effect melting the film followed by cooling and crystallizing said film. CONSTITUTION:A thin film 1 consisting of an oxide superconducting substance or a substance capable of forming the same by melting and sintering is formed on a base 2 consisting of a high-melting, optically transparent material (pref. zirconium oxide or yttrium-stabilized zirconium). Thence, both the surfaces of the film 1 and the base 2 are irradiated with laser beams 3; during the process, a scanning is made in the arrow A direction to heat and melt the irradiated zone 1a, and as the laser beams 3 move, the melted zone is cooled and recrystallized, thus obtaining the objective oxide superconductor. When the surface of the thin film 1, i.e., the opposite side to the base 2 is provided with a protective film made of a high-melting, transparent material similar to the base, evaporation of the sample from the surface heated by the laser beams can be protected.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for manufacturing oxide superconductors such as YBCO-based or Bi-based oxide superconductors, and particularly relates to a method for producing oxide superconductors that enable unidirectional solidification of crystals. It is related to the manufacturing method.

[Prior Art and Problems to be Solved by the Invention] It has been known that oxide superconductors have properties that vary greatly depending on crystal orientation and are anisotropic. In particular, the electrical resistance value in the vertical direction (C axis) of the crystal is much larger than in the horizontal plane (Jl, b plane), and the characteristics of oxide superconductors are a,
It is thought that the structure of the b-plane is dominant.

By the way, in normal synthesis methods, especially sintered bodies (bulk)
In the case of , the crystal orientation is random, so both the electrical and magnetic properties have not reached a practical level.

As a method of increasing crystal orientation, there is a method of melting an oxide superconductor and recrystallizing it by moving it relatively in an electric furnace having a temperature gradient. It is known that the larger the temperature gradient, the more aligned the crystal orientation is in one direction, but in an electric furnace, the temperature is easily equalized by heat conduction, making it impossible to form a steep temperature gradient. Controlling sexuality is difficult.

In addition, attempts have been made to irradiate oxide superconducting materials with laser light to locally heat and melt it, and then move (scan) it to form a temperature gradient in the scanning direction and sequentially crystallize the irradiated areas. There is. In particular, when a laser beam having a specific light intensity pattern is used, crystals oriented in the scanning direction are obtained.

However, oxide superconducting materials and their raw materials generally have low thermal conductivity, and only the area near the surface irradiated with laser light is heated, with a large temperature gradient in the direction of laser light irradiation (thickness direction). occurs. Therefore, even if oriented crystals are obtained in the vicinity of the irradiated surface, the thickness thereof is so thin that it is difficult to obtain desired characteristics. Furthermore, the temperature gradient in the thickness direction not only creates non-uniform crystals in the thickness direction, but also may impede orientation of the crystals in the scanning direction of the laser beam in the vicinity of the surface. Furthermore, since the surface side irradiated with laser light becomes extremely high temperature, in the case of a Bi-based superconducting material, there is a problem that the constituent materials, mainly PB, evaporate.

[Object of the Invention] The present invention has been made in view of the above-mentioned conventional difficulties, and provides an oxide superconductor in which unidirectional crystal orientation solidification is possible, and in particular the uniformity of the crystal phase in the thickness direction is improved. The purpose is to provide a manufacturing method for.

[Means for Solving the Problems] In order to achieve such objects, according to the method for producing an oxide superconductor of the present invention, an oxide superconductor or a molten
A substrate that is transparent to laser light as a substrate in irradiating a substance that generates an oxide superconducting substance by sintering with a laser beam, melting the oxide superconducting substance or the substance, and then cooling and crystallizing the substance. In this method, laser light is irradiated from both sides of the substrate and sample.

Furthermore, according to the method for producing an oxide superconductor of the present invention, a transparent substrate is used as the substrate, and a protective film having a high melting point and transparent to laser light is provided on the surface opposite to the surface of the sample facing the substrate. The laser beam is irradiated from both sides of the substrate and sample.

[Embodiments of the Invention] Hereinafter, an embodiment of the method for producing an oxide superconductor according to the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, the sample 1 is a thin film formed on a long substrate 2, and by scanning in the direction of arrow A while irradiating the sample 1 with laser light 3 from both sides, the irradiated area 1a
is heated and melted, and as the laser beam 3 moves, it is cooled from behind and recrystallized.

Here, the sample 1 may be either an oxide superconducting material or a material that produces an oxide superconducting material by melting and sintering, and the latter material that produces an oxide superconducting material by melting and sintering is, for example, YSBa.

Superconducting materials such as Cu oxides made into pellets using the solid phase method, superconductor melt coating films using metal alkoxides and other organic/metallic compounds, and inorganic compounds, and raw material powders and organic materials created using the doctor blade method. It is a thick film of a slurry of a solution consisting of a binder, etc.

It is also possible to employ an amorphous thick film created by immersing the substrate in a high-temperature melt of the oxide superconductor raw material and rapidly cooling it. In this case, the change in density after laser melting is small and cracks are less likely to occur.

Furthermore, as the oxide superconducting material, in addition to those obtained by melting and sintering the above-mentioned materials, those formed on the substrate 2 by a method such as a laser sputtering method using an excimer laser, a CVD method, or a spray pyrolysis method can be used. can.

Further, the substrate 2 is made of an optically transparent material with a high melting point.

Materials for such substrates include titanium oxide, strontium titanate, alumina, magnesia, silicon, zirconium oxide, and yttrium-stabilized zirconium (YS
Z) etc.

In particular, zirconium oxide and YSZ have high oxygen ion conductivity when a voltage is applied, so they are suitable for controlling oxygen inflow and outflow during oxidation annealing, which will be described later.

Laser light 3 uses the same pattern of laser light to target sample 1 and substrate 2.
irradiate from both sides. The laser beam pattern may be a normal round beam, but in order to obtain crystals oriented in the scanning direction, a twin beam 3a1, triple beam 3b or slit beam 3 having a pattern as shown in Fig. 2 is used.
Use c. When using a laser beam having such a specific pattern, it is possible to form a steep temperature gradient in the same direction as the scanning direction as the heated region moves.
Since crystallization proceeds along this temperature gradient, highly oriented crystals are formed.

Moreover, since the laser beam with this pattern is irradiated from both sides of the sample 1, a uniform temperature gradient can be obtained in the thickness direction of the sample 1, and as a result, uniform crystals can be formed in the thickness direction. Furthermore, crystals oriented in the direction of laser movement can be obtained in any thickness direction.

The output of such a laser beam varies depending on the thermal conductivity of the sample, film thickness, etc., but normally, for example, in the case of a YAG laser, an output of several watts to several watts is used. The scanning speed of the laser beam varies depending on the laser beam output and the laser beam diameter, but in the case of twin beams with a beam radius of 50 μm and a beam focus spacing of 100 μm using a laser with the above laser beam output, it is approximately 10 cm/sec.

Note that the above-described laser melting is preferably performed under oxygen pressure control.

In addition, heat treatment is performed using a preheating source such as a halogen lamp prior to laser irradiation in order to prevent material components from evaporating and foaming due to rapid heating by laser, and to prevent cracks from occurring due to recrystallization. It is preferable.

FIG. 3 shows a second embodiment of the method for manufacturing an oxide superconductor of the present invention, in which a transparent protective film 2° is placed on the surface of the sample 1 opposite to the substrate 2 in the first embodiment. It has been established.

Like the substrate 2, this protective film 2' is made of an optically transparent sample with a high melting point, and the same oxide as used for the substrate 2 can be used. The thickness of the protective film 2' is usually equal to or less than that of the substrate 2.

Such a protective film can be provided by a low-temperature process such as a CVD method or a sol-gel method, but a single crystal substrate of the above-mentioned material may be laminated on the sample 1.

The laser beam 3 is irradiated from both sides of the sample 1 via the protective film 2' and the substrate 2. In this case, as described in the first embodiment, a uniform temperature gradient can be obtained in the thickness direction of the sample 1, and evaporation of the sample from the surface heated by the laser can be prevented.

Next, oxygen annealing of the superconducting material recrystallized with orientation as described above will be explained. Since crystals recrystallized by laser melting are very likely to become oxygen-deficient crystals, oxygen annealing is required as a post-treatment. In this case, oxygen annealing must be performed while maintaining the orientation of the crystal. For example: , at relatively low temperatures (Y B C
In the case of O-based materials, heat treatment is performed at 400° C. x lohrs) in a high oxygen pressure atmosphere or in an oxygen stream. Preferably, the fourth
As shown in the figures ((a) and (b)), a laser with a strip pattern 31 is used as a heat source for annealing. The laser for the strip pattern 31 is one having an energy distribution that produces a temperature distribution C in the orientation direction B of the crystal 20 unidirectionally solidified by laser melting.

For this reason, a slit laser whose width is wider than the width of the crystal is used as the band laser. The laser power used is smaller than that used for laser melting. This allows heating and oxygen absorption without disturbing the orientation of the crystal.

Oxygen annealing is performed by scanning such a band-shaped laser multiple times in the orientation direction of the crystal under a predetermined oxygen partial pressure to cause the crystal to absorb oxygen. The scanning speed is the same as that for melting and sintering, but under controlled oxygen partial pressure, it is necessary to scan multiple times. For example, when the oxygen partial pressure is 0.2 atm, the voltage is changed about 500 times.

By absorbing oxygen in a band shape with temperature distribution in the crystal orientation direction, the crystal orientation is maintained.
A highly oriented oxide superconductor can be obtained.

Example 1 Thickness 0. ! On a 5mm strontium titanate substrate,
A thin film of YBCO-based superconducting material with a thickness of 1 μm and a width of 200 μm was formed, and such a sample was irradiated from both sides with twin beams with an output of 5 W, a beam radius of 50 μm, and a distance between beam focal points of 100 μm at a scanning speed of 10 am/sec. Recrystallized.

Orientation of the a-b axis of the recrystallization ratio phase, possibility of orientation control, and critical current density J c (A/cr + f) when scanning the same laser beam from one side and crystallizing (Comparative Example 1) compared with. The results are shown in Table 1.

Table 1 (Recrystallization) *External critical OT, 77K (same below) As is clear from Table 1, by scanning the laser from both sides, a
- Excellent b-axis orientation and controllability, and high J
The c value was obtained.

Example 2 A Bi-based superconducting material thin film having a thickness of 1 μm and a width of 200 μm was formed on a strontium titanate substrate having a thickness of 0.5 mm, and the same substrate as the above substrate was closely adhered thereon. Output 5W from both sides of such a sample.

Recrystallization was carried out by irradiation using twin beams with a beam radius of 50 μm and a beam spacing of 100 μm at a scanning speed of I Q cm/sec.

At this time, material evaporation and critical current density Jc (A/c
tri) was compared with the same sample in which no upper substrate was provided and laser scanning was performed only from the upper side (Comparative Example 2).

As a result, the value of Jc is 10'' to 10'A in the former case.
/cm', whereas in the latter it is 10-10'A
/cm'.

Further, in Comparative Example 2, evaporation of the material was observed, whereas in Example 2, there was no evaporation at all, and a superconductor with good orientation could be obtained.

[Effects of the Invention] As is clear from the above examples, according to the method for producing an oxide superconductor according to the present invention, the laser beam that melts the sample is irradiated from both sides of the sample and scanned at high speed. Therefore, it is possible to obtain a crystal that is uniform in the thickness direction of the sample and whose crystal direction is aligned in the scanning direction.

Furthermore, since a transparent protective film is provided on the upper surface of the sample, evaporation of the material can be prevented in the case of a Bi-based superconducting material.

In addition, the orientation of the superconductor formed can be effectively controlled by optimizing the crystal planes of the oxides serving as the substrate and the protective film.

[Brief explanation of drawings]

FIG. 1 shows the first method of manufacturing an oxide superconductor according to the present invention.
FIG. 2 is a plan view showing a laser beam having a specific pattern, FIG. 3 is a plan view showing a second example of the method for producing an oxide superconductor according to the present invention, and FIG. figure(
1A and 2B are diagrams each showing oxygen annealing in the method for producing an oxide superconductor of the present invention. 1... Sample film (oxide superconducting material) 2... Substrate 2''... Protective film 3... Laser light

Claims (1)

[Claims] 1. Oxide superconducting material formed on a substrate or melting
When a sample film made of a substance that generates an oxide superconducting material by sintering is irradiated with a laser beam, and the sample is melted and then cooled and crystallized, the substrate is a substrate that is transparent to the laser beam. A method for manufacturing an oxide superconductor, characterized in that the substrate and the sample are irradiated with laser light from both sides. 2. The oxide superconductor according to claim 1, further comprising a protective film having a high melting point and being transparent to laser light on a surface of the sample opposite to the surface facing the substrate. manufacturing method.