JPH061697A - Method for producing coarse crystal of RE-based superconducting oxide - Google Patents

Abstract

(57) [Summary] [Objective] When a coarse crystal of an RE-based superconducting oxide is produced, the precursor production step, which is a preliminary step thereof, is simplified. [Structure] A method for producing coarse crystals of an RE-based superconducting oxide, which comprises the following steps. (1) Blend the raw materials so that they have the specified composition, and adjust the oxygen partial pressure.
Calcination is performed by heating at a temperature of 800 to 1000 ° C. for 1 hour or more in a low oxygen partial pressure atmosphere of 10 ⁻³ Torr. Or less. (2) The calcined product is crushed to obtain a precursor. (3) The above precursor is molded, and once rapidly heated to the coexistence region of the 211 phase and the liquid phase, and then slowly cooled to grow the crystal coarsely. [Effect] The calcination powder used in the conventional precursor manufacturing process
The two steps of heating in the coexisting region of ₂ O ₃ and liquid phase to a semi-molten state and then quenching are not required.

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 a coarse crystal of a RE superconducting oxide, for example, a Y-Ba-Cu-O superconducting material.

[0002]

2. Description of the Related Art In RE-based superconducting oxides, crystal grain boundaries impede the superconducting current, so that the crystal grains must be as coarse as possible in order to produce a high-performance superconductor required for practical use. It

Taking a Y-based oxide superconducting material as an example, the following processes (1) to (3) have been conventionally used for producing coarse crystals thereof. Note that FIG. 4 is a part of the phase diagram of the Y—Ba—Cu—O system, and YBa ₂ Cu ₃ O _y shown in the figure shows superconductivity, which is called the 123 phase.

Raw materials (Y ₂ O ₃ , BaCO ₃ , CuO) are converted into Y: Ba:
It is blended so that the ratio of Cu is about 1: 2: 3, and calcined in air.

The obtained calcined powder is heated to a coexisting region of Y ₂ O ₃ and a liquid phase (point (a) in FIG. 4) to be in a semi-molten state.

A semi-molten state is rapidly cooled to a structure in which Y ₂ O ₃ is precipitated.

Grind to make a powder (called a precursor).

[0008] The above precursor was molded and once Y ₂ BaCuO ₅
(Coexistence region of non-superconducting phase called 211 phase) and liquid phase (Fig. 4
(Point (b)) is rapidly heated, and then slowly cooled to grow crystals coarsely.

The reason for passing through the above steps is to finely disperse the 211 phase in the 123 phase crystal, but this process requires four steps from the above to the step of obtaining the precursor. Is.

[0010]

DISCLOSURE OF THE INVENTION The object of the present invention is RE
The purpose is to simplify the precursor manufacturing process, which is a preliminary process when manufacturing coarse crystals of a superconducting oxide.

[0011]

SUMMARY OF THE INVENTION The gist of the present invention is a method for producing coarse crystals of an RE-based superconducting oxide, which comprises the following steps.

(1) The raw materials are blended so as to have a predetermined composition, and the oxygen partial pressure is kept under a low oxygen partial pressure atmosphere of 10 ^-3 Torr. Or less.
Calcination is performed by heating at a temperature of 800 to 1000 ° C for 1 hour or more.

(2) The calcined product is crushed to obtain a precursor.

(3) The above-mentioned precursor is molded, once rapidly heated to a coexisting region of the 211 phase and the liquid phase, and then slowly cooled to grow the crystal coarsely.

[0015]

As described above, in the method of the present invention, calcination is performed in an atmosphere having an oxygen partial pressure of 10 ^-3 Torr. Or less, that is, an atmosphere in which the oxygen partial pressure is extremely low. This makes it possible to prevent the formation of the 123 phase in the precursor, which is mainly the 211 phase.
It consists of BaCu ₂ O ₂ .

The calcination atmosphere is set to have an oxygen partial pressure of 10 ^-3 Torr. Or less. If the oxygen partial pressure is higher than this, coarse 123-phase crystals are generated during calcination, This is because the 123 phase cannot be completely decomposed into the 211 phase and the liquid phase in the subsequent step of semi-melting treatment and remains as a core during the slow cooling, and the 123 phase of the final structure becomes fine. In addition, the temperature of calcination
The reason why the temperature is set to 800 to 1000 ° C is that the 123 phase is generated by calcination at a temperature lower than 800 ° C, and it becomes a semi-molten state at a temperature higher than 1000 ° C.

The step (3) of coarsely growing the crystal grains is
It is substantially the same as the conventional process (the process described above).
In this step, crystals are grown and coarsened by gradually cooling from a semi-molten state where the solute is easily diffused.

[0018]

[Examples] Y ₂ O ₃ , BaCO ₃ and CuO were used as raw materials, and these were compounded so that Y: Ba: Cu = 1.2: 2.1: 3.1.
A precursor was prepared by the following two methods.

First method (example of the present invention): Absolute pressure 10 ^-3 To
It was calcined at 900 ° C. for 12 hours under reduced pressure of rr. and pulverized to obtain a precursor.

Each of the above precursors was molded to a diameter of 20 mm and a height of 5 mm, heated to 1000 ° C. in 1 hour, heated to 1120 ° C. in 2 hours, and kept at this temperature for 0.5 hour. After that, it was cooled to 1000 ° C in 0.2 hours, and then gradually cooled to 800 ° C in 200 hours, and then cooled to room temperature by furnace cooling.
The heat pattern for this process is shown in FIG.

Second method (comparative example): 900 ° C. in air
It was heated for 12 hours, calcined and pulverized to obtain a precursor. The subsequent grain coarsening treatment is the same as in the first method.

First, the crystal phases contained in the precursors obtained by the first method and the second method were investigated by X-ray diffraction, and then the crystal size of the 123 phase after the crystal growth treatment was examined by using a macro microscope. Examined.

FIG. 2 is an X-ray diffraction pattern of the precursor (a)
Is according to the first method (method of the present invention), and (b) is according to the second method (comparative example method). As is clear from the figure (a), the precursor obtained by the method of the present invention is 211 phase and Ba
Cu ₂ O ₂ is the main phase, and the 123 phase is not included. On the other hand, the precursor obtained by the second method is a single phase of approximately 123 phases. It is considered that these crystal grains grow during the calcination for 12 hours.

FIG. 3 shows a macrostructure after crystal growth treatment of each precursor. (a) is the one using the precursor obtained by the first method (invention example), and (b) is the one using the precursor obtained by the second method (comparative example). In the former, only one crystal is observed on the surface. On the other hand, many crystals are found in the latter. That is, the crystal grains of the former are significantly larger than those of the latter.

Table 1 shows that the crystal shown in FIG.
It is a result of composition analysis by MA. Five points were analyzed for the matrix and three points were analyzed for the granular crystals, and the average thereof was taken to show the atomic ratio based on Ba. As shown, the matrix is 123-phase and the granular crystals are 211-phase.
It is a phase. Such a structure exhibits a so-called pinning effect that suppresses the movement of the magnetic flux into which the fine 211 phase enters, and is therefore desirable especially when used as a superconducting material in a high magnetic field.

[0026]

[Table 1]

[0027]

According to the method of the present invention, coarse 123 phase crystals can be obtained by a much simpler process than the conventional methods.

[Brief description of drawings]

FIG. 1 is a heat pattern showing an example of the method of the present invention.

FIG. 2 (a) is an X-ray diffraction pattern of a precursor obtained by the method of the present invention, and (b) is an X-ray diffraction pattern of a precursor obtained in a comparative example.

FIG. 3A is a macrostructure after coarsening of crystal grains by the method of the present invention, and FIG. 3B is a macrostructure after coarsening treatment of crystal grains to a precursor of a comparative example. is there.

FIG. 4 is a part of a phase diagram of the Y-Ba-Cu-O system.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 000000044 Asahi Glass Co., Ltd. 2 1-2 Marunouchi, Chiyoda-ku, Tokyo (71) Applicant 000173784 2-8 Mitsumachi, Kokubunji-shi, Tokyo 38 (71) Applicant 000000099 Ishikawajima Harima Heavy Industries Co., Ltd. 2-2-1 Otemachi, Chiyoda-ku, Tokyo (72) Inventor Teruo Izumi 1-14-3 Shinonome, Koto-ku, Tokyo Superconducting Industrial Technology Research Center Inside the Institute of Electrical Engineering (72) Inventor Ogai Otsu 1-14-3 Shinonome, Koto-ku, Tokyo Inside the Superconducting Engineering Research Center, International Superconductivity Technology Center (72) Inventor Yoji Yamada Shinonome, Koto-ku, Tokyo 1-14-3 International Superconductivity Industrial Technology Research Center Superconductivity Research Institute (72) Invention Yuichi Nakamura 1-14-3 Shinonome, Koto-ku, Tokyo International Superconductivity Industrial Technology Research Center Superconductivity Engineering Laboratory (72) Inventor Kengo Ishige 1-14-3 Shinonome, Koto-ku, Tokyo International Superconductivity Industrial Technology Research Foundation Inside the Center for Superconductivity Engineering (72) Inventor Yuru Shiobara 1-14-3 Shinonome, Koto-ku, Tokyo International Superconducting Technology Research Center Superconducting Institute of Technology

Claims (1)

[Claims] 1. A raw material is blended so as to have a predetermined composition, and the oxygen partial pressure is 800 to 800 in a low oxygen partial pressure atmosphere of 10 ^-3 Torr. Or less.
The mixture is heated to a temperature of 1000 ° C. for 1 hour or more to be calcined, and the calcined product obtained is crushed into a precursor, and the precursor is molded.
A method for producing coarse crystals of a RE-based superconducting oxide, which comprises rapidly heating to a coexisting region of a 211 phase and a liquid phase and then gradually cooling to grow crystals.