JP2928311B2 - Manufacturing method of oxide superconductor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an oxide superconductor, and particularly to easily produce an yttrium-based oxide superconductor having excellent properties by improving the orientation. The improvement of the method.

[Prior Art] As a method for synthesizing an oxide superconductor, a method using a raw material powder such as an oxide or a carbonate produced by a solid-state reaction method is known. This method, for example, _{Y 2 O 3, BaCO 3,} C after the raw material powder of _U O such molded and then mixed in predetermined proportions, heat-treated (123) phase (Y: Ba: Cu = 1 : 2 : 3 compound phase, the same shall apply hereinafter), but the density of the sintered body is small, there are many grain boundaries, and there is a problem in the uniformity and orientation of the composition. There is a problem that characteristics such as current density (Jc) are low.

As a method to solve these problems, QMG method (quench
and melt growth process: Jpn.J.Appl.Phys., Vol.28, N
o.7,1989), MTG method (melt textured growth process)
There is known a method utilizing a peritectic reaction in a partial melting region called a so-called peritectic reaction.

In the above-mentioned QMG method, in order to obtain a structure in which the (211) phase is finely dispersed in the liquid phase (L), [Y ₂ O ₃ + L] at a higher temperature is used.
By quenching from the region, a finely dispersed structure of Y ₂ O ₃ was obtained, which was reheated to the [(211) phase + L] region and then gradually cooled under a temperature gradient. By heating the YBCO sintered body to the partial melting zone and gradually cooling it under a high temperature gradient,
1) The phase is changed to a superconducting phase, that is, a (123) phase, using a peritectic reaction.

In the above method, the superconducting phase is divided into the (211) phase and the liquid phase (L).
Y ₂ O ₃ in the liquid phase to develop by peritectic reaction with
And (211) phase must be dispersed as finely and uniformly as possible.

[Problems to be Solved by the Invention] In these methods, a structure having a dense structure in which crystal grains are grown large and with few grain boundaries can be obtained, but the Y ₂ O ₃ or (211) phase is added to the melt. It is necessary to raise the melting temperature and lengthen the melting time in order to uniformly disperse, and therefore, there is a problem that reaction and segregation with the material of the container such as a crucible or the like and the base material are easily caused. Furthermore, there is a disadvantage that a high temperature gradient is formed in order to cause directional solidification, and a very long heat treatment is required. Therefore, the method cannot be applied substantially to a long floc.

The present invention has been made to solve the above-described problem, and Y ₂ O _{3 is formed} by rapid melting and solidification by a laser beam.
A method for easily producing an oxide superconductor having excellent orientation by dispersing finely divided crystals and subsequently performing heat treatment at a temperature at which the (123) phase and / or (211) phase coexists with the liquid phase. The purpose is to provide.

[Means for Solving the Problems] In order to achieve the above object, a method for producing an oxide superconductor of the present invention uses an yttrium-based oxide superconducting material (hereinafter, referred to as an yttrium-based superconducting material).
By irradiating a laser beam on a thin film, a molded body, or a flocculent body made of a substance containing the element constituting the substance or a substance containing the element constituting the substance, the laser beam is scanned, and the irradiated portion is rapidly melted and solidified. After the Y ₂ O ₃ crystal forms a finely dispersed solidified portion, the (123) phase and / or (21)
1) A heat treatment is performed at a temperature at which a phase and a liquid phase coexist to grow a crystal in the scanning direction.

The Y-based superconducting material in the present invention is mainly composed of the Y-Ba-Cu-O-based (123) phase, while the material containing the element constituting the Y-based superconducting material is approximately Y, Ba, and Cu. Although it is included at a ratio of 1: 2: 3, in any case, it is sufficient that the material is formed of a substance that forms a superconductor by final heat treatment.

The composition of these substances can be shifted from the above composition ratio to some extent. That is, according to the Y-system state diagram, [(21
The (123) phase can be generated from the (1) phase + L] with a wide range of composition of Y. Therefore, when the (211) phase or the like remains, the above composition ratio is appropriately shifted. For example, (123) phase: (211) phase = 1: 0.3 (weight ratio)
It is. In this case, since the remaining (211) phase and the like function as a pinning center, the characteristics are improved.

In the present invention, the irradiation part can be heated to the melting point or higher by the short-time irradiation part of the laser beam, and after the beam passes, self-cooling can be rapidly performed by heat diffusion to the surroundings.

As a result, a solidified body in which Y ₂ O ₃ is finely and uniformly dispersed can be obtained. Further, since the treatment time is extremely short, a continuous process becomes possible, and the present invention can be applied to a long cotton-like body which cannot be dealt with by the melting method.

In the above heat treatment at a temperature where the (123) phase and / or (211) phase and the liquid phase coexist, the Y ₂ O ₃ is finely and uniformly dispersed by rapid melting and solidification after irradiation. Therefore, the treatment can be performed at a lower temperature than the QMG method, and the treatment can be performed at 1050 ° C. or less. The treatment is preferably performed in an oxidizing atmosphere.

[Action] In the present invention, Y ₂ O ₃ is converted by laser beam irradiation.
Since BaCuO ₂ , an amorphous phase or a solidified part finely dispersed in microcrystals is formed thinner on the irradiated surface, (12
3) By heat treatment at a temperature at which the phase and / or the (211) phase and the liquid phase coexist, a structure in which crystals have grown in the scanning direction can be obtained. When the (123) phase is generated, its (ab) plane grows in the scanning direction and easily grows parallel to the irradiation plane.
As a result, a high orientation structure is obtained, and characteristics such as Jc are improved. In addition, since there is no adverse effect even if it reacts with the base material other than the solidified portion, it is possible to prevent deterioration of the characteristics due to mixing of impurities.

[Examples] Hereinafter, examples of the present invention and comparative examples will be described.

Example 1 YBa ₂ C on YSZ (yttrium-stabilized zirconia) substrate
u ₃ O _x powder (average particle diameter φ10μm) 75wt% and an organic binder, i.e., ethyl cellulose 2.5 wt%, terpineol 7.5 wt%, dibutyl phthalate 12.5 wt%, were mixed butyl carbitol acetate 2.5 wt% superconducting Paste 3
After printing to a thickness of 00 μm by a method similar to screen printing to form a film body, heat treatment was performed at 950 ° C. × 1 hour to remove the binder and form a powder temporary sintered body.

A 10 W output YAG laser was applied to this pre-sintered body, and the irradiation area was φ40.
Irradiation was performed at 0 μm at a scanning speed of 10 mm / sec. By the irradiation of the laser beam, the depth of the solidified zone formed on the pre-sintered body after melting was 200 μm.

FIG. 2 shows the results of measuring the solidified portion by XRD (X-ray diffraction). As is clear from this figure,
Y ₂ O ₃ forms the main peak, and the elemental analysis by X-ray microanalyzer shows that the distributions of Y, Ba, and Cu are almost the same. Therefore, it is estimated that no peak appears.

In the membrane containing the coagulation zone obtained as described above,
A heat treatment was performed in an oxygen atmosphere at a partial melting temperature of 1000 ° C., which is estimated to be a coexistence region of [(123) phase + (211) phase + L], in an oxygen atmosphere to produce a superconductor.

As a result of observing the crystal structure of the above-described superconductor, it was found that crystal grains were largely grown on the plate in the laser scanning direction in the solidification zone.

In addition, its critical temperature (Tc) and critical current density (Jc: a
t77K), Tc = 89K, Jc = 750A / cm ² (OT)
And 5000 A / cm ² (0.2 T). FIG. 1 shows the magnetization curve of this superconductor.

Example 2 The membrane containing the coagulation zone obtained in Example 1 was added with [(21
1) The partial melting temperature of 102, which is estimated to be the coexistence region of phase + L]
A heat treatment was performed at 0 ° C. for 1 hour in an oxygen atmosphere to produce a superconductor.

As a result of observing the crystal structure of the above-mentioned superconductor, it was found that the grain boundaries were not clearly observed, but that the (123) phase had grown into a composite structure in which the (211) phase and Y ₂ O ₃ were dispersed. Was done.

Also, as a result of measuring its Tc and Jc (at77K), Tc
= 90K, Jc = 13000A / cm ² (OT) and 10,000A / cm ² (0.2
The value of T) was obtained.

Comparative Example 1 The provisional sintered body in Example 1 was subjected to 1000 ° C. in an oxygen atmosphere.
A heat treatment was performed for one hour to produce a superconductor.

As a result of observing the crystal structure of the above-mentioned superconductor, no growth of crystal grains was observed, and as a result of measuring Tc and Jc (at 77 K), Tc = 90 K, Jc = 300 A / cm ² (OT) and 50 A
A value of / cm ² (0.2T) was obtained.

Comparative Example 2 A superconductor was manufactured in the same manner as in Comparative Example 1, except that the heat treatment temperature was changed to 1020 ° C.

As a result of observing the crystal structure of the superconductor, although growth of crystal grains was slightly observed, a heterogeneous phase was generated by the decomposition reaction, and its Tc and Jc (at 77K) were measured. Jc = 500A / cm ² (OT) and 100A / cm ²
(0.2T) was obtained.

[Results of the Invention] As described above, according to the method for manufacturing an oxide superconductor of the present invention, (a) a structure in which Y ₂ O ₃ is finely dispersed by rapid melting and solidification by laser beam irradiation; Can be easily obtained, and its dispersion state can be easily controlled by laser output, scanning speed, and the like.

(B) Since Y ₂ O ₃ is finely dispersed, a long-time melting process at a high melting temperature can be omitted.

(C) In addition to being able to omit the above-mentioned melting process, there is no adverse effect on the properties even if it reacts with the base material except in the solidification zone. Problems can be avoided.

(D) Heat treatment at a temperature at which the (123) phase and / or (211) phase and the liquid phase coexist after laser beam irradiation can be performed at a relatively low temperature for a short time, and can be used for directional solidification. It is not necessary to form a high temperature gradient, and it is possible to grow and control large crystal grains having an oriented structure that cannot be obtained by conventional sintering of powder, and it is possible to manufacture a superconductor having excellent characteristics.

(E) Production of long materials is easy.

[Brief description of the drawings]

FIG. 1 shows a magnetization curve of a superconductor obtained by the method of the present invention and a comparative example, and FIG. 2 shows an XRD chart of a solidification zone after laser beam irradiation according to the present invention.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code FI H01B 12/00 ZAA C04B 35/00 ZAAZ (72) Inventor Shigeo Nagaya 2-4-1 Rokuno Atsuta-ku Nagoya-shi, Aichi Prefecture Foundation Nagoya Laboratory, Superconductivity Engineering Laboratory, International Superconducting Technology Research Center (72) Inventor Masamichi Miyajima 2-4-1 Rokuno, Atsuta-ku, Nagoya-shi, Aichi Pref. Laboratory (72) Inventor Izumi Hirabayashi 2-4-1 Rokuno, Atsuta-ku, Nagoya-shi, Aichi Nagoya Lab. 1-10-13 Shinonome International Superconducting Technology Research Center Superconductivity Engineering Inside the laboratory (72) Inventor Shoji Tanaka 1-10-13 Shinonome, Shinonome, Koto-ku, Tokyo Inside the Superconductivity Engineering Laboratory, International Superconducting Technology Research Center (56) References JP-A 1-215963 (JP, A) JP-A-2-196055 (JP, A) JP-A-2-279507 (JP, A) JP-A-3-232706 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01G 1 / 00-57/00 C30B 28/00-35/00 CAS ou-line

Claims (2)

(57) [Claims] 1. A laser beam is applied to a thin film, a molded body, or a floc made of a yttrium-based oxide superconducting substance or a substance containing an element constituting the substance to cause scanning, and the irradiated part is rapidly melted and solidified. After forming a solidified portion in which the Y ₂ O ₃ crystal is finely dispersed, heat treatment is performed at a temperature at which the (123) phase and / or the (211) phase coexists with the liquid phase, and the crystal is formed in the scanning direction. A method for producing an oxide superconductor, comprising: growing an oxide superconductor. 2. The oxide superconductor according to claim 1, wherein the heat treatment at a temperature at which the (123) phase and / or the (211) phase coexists with the liquid phase is performed in an oxidizing atmosphere at 1050 ° C. or lower. Production method.