JPH02239102A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To produce the oxide superconductor having high c-axis orientation by irradiating an oxide superconducting material with laser beam whose energy distribution in the direction perpendicular to the scanning direction is made higher from the center toward both sides. CONSTITUTION:The thin film (sample) 1 of an oxide superconductor formed on a substrate 2 is irradiated with laser beam 3 almost at a perpendicular angle and scanned in direction of the arrow A, and the irradiated part 1a is heated and melted. As the laser beam 3 moves, the part is cooled from the rear and crystallized. Two round beams formed by using two laser sources 10, mirrors 11 and 12 and a prism 13 are used as the laser beam 3. The irradiation of the beam 3 is carried out at a specified interval in the X-X' direction perpendicular to the scanning direction A. The temp. distribution of the sample 1 has a gradient rising from the center of the beam 3 toward both ends in the direction perpendicular to the scanning direction. Consequently, the crystal orientation can be easily controlled.

Description

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

[Prior Art] It has been known that oxide superconductors have properties that vary greatly depending on crystal orientation and are anisotropic. In particular, the C@ direction is a plane (a
, b plane) The electrical resistance value is much larger than that in the inward direction. Therefore, it is desired to increase the C-axis orientation of the crystal so that the current path is in the a and b planes in order to improve the critical current density and the critical magnetic field.

By the way, in normal synthesis methods, especially sintered bodies (bulk)
In this case, since the crystal orientation is random, both the electrical and magnetic properties do not reach a practical level.

One way to increase the conformality of a crystal is to melt an oxide superconductor and recrystallize it in an electric furnace with a temperature gradient while creating a temperature gradient. It is known that the larger the temperature gradient, the more neatly the conformation of the crystal aligns.
In electric furnaces, the temperature tends to be uniform due to heat conduction, and it is impossible to create a steep temperature gradient, making it difficult to control orientation. In addition, an attempt was made to irradiate an oxide superconducting material with laser light, locally heat it, melt it in a band, and then move it (scan) to create a temperature gradient in the scanning direction and sequentially crystallize the irradiated area. However, in this case, the temperature is highest at the center of the irradiated area, so a temperature gradient is created radially from this center, and even though the laser beam is scanned in one direction, the orientation of the crystal is not uniform. Not aligned in direction. Therefore, there was a problem that the orientation could not be controlled.

Furthermore, YBCO-based oxide superconductors generally have an insulating so-called 211 structure (YJ
aCuOs-m), and a superconducting 123 structure (YBa2Cu.O, -z) could not be formed. [Problems to be Solved by the Invention] As described above, it has been difficult to obtain an oxide superconductor with excellent C-axis orientation using conventional methods. It is an object of the present invention to solve these conventional drawbacks and provide a method for manufacturing an oxide superconductor that enables unidirectional solidification of crystals and, as a result, has a high C-axis orientation.

[Means for Solving the Problems] In order to achieve such an object, the method for producing an oxide superconductor of the present invention involves applying a laser beam to an oxide superconducting substance or a substance that produces an oxide superconducting substance by melting and sintering. When scanning light and crystallizing an oxide superconducting material or the above-mentioned material after zone melting or semi-melting, a laser light whose energy distribution in the direction perpendicular to the scanning direction increases from the center toward both ends is used as the laser light. It is characterized by

[Function] According to the present invention, it is possible to form a steep temperature gradient aligned in the scanning direction on the sample. Oxide superconductors can be created. [Example] Hereinafter, an example 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, sample I for producing an oxide superconductor (hereinafter referred to as the sample) is a thin film formed on a long substrate 2, and the sample 1 is irradiated with laser light 3 almost at right angles. By scanning in the eight directions of the arrows, the irradiated portion 1a is heated and melted, and as the laser beam 8 moves, it is cooled from behind and crystallized. Here, 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 becomes an oxide superconducting material by melting and sintering is, for example, Y, Ba, Superconducting materials such as Cu oxides made into pellets using the solid phase method, coating films of superconducting solutions using metal alkoxides and other organic/metallic compounds and inorganic compounds, and raw material powders and organic materials created using the doctor blade method. A thick film of a slurry of a solution consisting of a binder, etc. is used. 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 zone melting by laser is small and cracks are less likely to occur.

Further, 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 laser scattering method using an excimer laser, a VD method, a spray virolysis method, etc. are used.

The substrate 2 may be either a plate-shaped body or a tape, and may be a metal substrate such as silver or zirconium, or a metal substrate with magnesium oxide, 1-rea stabilized zirconia (YSZ), etc. Either a substrate provided with a buffer layer such as strontium titanate, or an insulating substrate such as magnesium oxide or YSZ can be used. However, if a metal substrate is used as the substrate, the substrate 2 should be forcibly cooled after laser irradiation to prevent a reaction between the substrate surface and the sample 1, and also to prevent radial thermal diffusion from occurring during cooling. There is a need.

The laser beam 3 includes two laser sources lO as shown in FIG.
Two parallel round beams (hereinafter referred to as twin beams) formed by an optical device using mirrors 11, 12 and prisms 13 are used. As shown in FIG. 3, this twin beam 3 is
' The beams are irradiated at predetermined intervals in the direction. In these twin beams, the focal point of each round beam has the highest energy, so if the focal distance is made equal to or slightly smaller than the beam diameter, the energy distribution on the line connecting each focal point will be from the center to both sides (focal point). It gets higher towards. Therefore, the temperature distribution of the sample 1 heated by such a twin beam is as follows in the direction perpendicular to the scanning direction.
As shown in the figure, there is a temperature gradient in which the temperature increases from the center of the twin beam toward both ends. Note that if the interval is much larger than the beam diameter, sufficient energy cannot be obtained to melt the sample at the center. Such twin beam laser light varies depending on the film thickness of the sample, but normally, for example, in the case of a YAG laser, one with an output of 5 W or more 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 a 17 laser with the above laser beam output, a beam radius of 50 μI, and a beam focal distance of 100 μl, it is approximately IO cm/sec.

Note that a so-called M-type beam may be used instead of the twin beam. The M-type beam is produced by dividing a laser beam with a normal energy distribution as shown in Fig. 5(a) by a double prism 14 shown in Fig. 5(b), and dividing it into two ends as shown in Fig. 5(C). It is a laser beam with high energy. Like the twin beam, this M-type beam has an energy distribution with a gradient such that the temperature increases from the center toward both sides.

The region of the sample 1 that is heated and melted by the irradiation with the laser beam 3 having such an energy distribution generates a temperature gradient in the direction of movement due to the relative movement of the laser beam, and begins to cool down sequentially from the rear and crystallizes. do. At this time, since the central part of the twin beam is cooled more preferentially than the opposite ends, the temperature gradient caused by cooling in the region between the focal points of the beam (the area indicated by the single-pointed button in Figure 1) is approximately equal to the direction of movement. become parallel. Since crystallization progresses in one direction along this temperature gradient, crystals are formed in this region that are substantially single-phase and uniaxially oriented in the scanning direction, and furthermore, the C-axis is oriented perpendicularly to the substrate.

Note that it is preferable that the zone melting using the laser described above be performed under the control of atmospheric pressure such as oxygen. It is desirable to perform heat treatment in advance using a preheating source such as a halogen lamp prior to laser irradiation in order to prevent evaporation and foaming of the material as well as to prevent cracks from occurring due to recrystallization.

A twin beam with an output of 5 W, a beam radius of 50 μm, and a beam spacing of 100 μm was used on a long thin film of YBCO superconducting material with a thickness of 1 μ1 and a width of 200 μm, and a scanning speed of 10 μm.
It was irradiated at cm/sec and recrystallized.

The state of the a-axis (or b-axis) orientation in the recrystallization phase, the possibility of its control, and the critical current density J at the external magnetic field O
The value of c(^/cm2) is calculated using a single beam (one round beam) (Comparative Example 1) and a temperature gradient of 30
The results were compared with those obtained when melting and crystallizing in a furnace at .degree. C./cm (Comparative Example 2). The results are shown in Table 1.Also, it is possible to form a material component surface gradient due to rapid heating by a laser, and it is possible to easily control the crystal direction and to produce an oxide superconductor having high conformation.

As is clear from Table 1, by using twin beams with temperature distribution according to the present invention, the a-axis (or b-axis
The arrangement and controllability of the axis) are significantly improved. Furthermore, the critical current density Jc can be one or two orders of magnitude higher than that of the conventional method.

[Brief explanation of drawings]

Figure 1 shows the method for producing an oxide superconductor according to the present invention.
Fig. 2 is a schematic diagram of a laser beam generator with a specific light intensity distribution, and Figs. 3 and 4 respectively show the heating area of the laser beam and its temperature distribution. FIG. 5 is a diagram showing another example of laser light having a specific light intensity distribution. [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, a laser having a specific temperature distribution is used as a heat source for melting the sample, and the laser is applied to the sample. On the other hand, since we scanned at high speed, a steep temperature 1 uniform in the scanning direction was formed on the sample...Oxide superconducting material (sample)
, 2...Substrate, 3...Laser light, A...Scanning direction. 3 Ray light 1a Figure 1 Figure 2 Figure 4

Claims (1)

[Claims] 1) When crystallizing the oxide superconducting material or the substance by scanning a laser beam on an oxide superconducting substance or a substance that generates an oxide superconducting substance by melting and sintering, the laser beam is used in a direction perpendicular to the scanning direction. A method for manufacturing an oxide superconductor, characterized by using a laser beam whose energy distribution increases from the center toward both ends.