JP2875684B2 - Method for producing coarse crystals of RE-based superconducting oxide - Google Patents

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

[0002]

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

[0003] Taking a Y-based oxide superconducting material as an example, the following process has conventionally been employed for producing a coarse crystal. Note that FIG. 4 is a part of a phase diagram of the Y—Ba—Cu—O system, in which YBa ₂ Cu ₃ O _y shown shows superconductivity and is called a 123 phase.

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

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

[0006] The alloy is rapidly cooled from a semi-molten state to a structure in which Y ₂ O ₃ is precipitated.

[0007] Pulverization produces a powder (called a precursor).

[0008] The above precursor is molded, and once Y ₂ BaCuO ₅
(The non-superconducting phase called the 211 phase) and the liquid phase (Fig. 4
(B) point), and then slowly cooled to grow the crystal coarsely.

The reason for passing through the above steps is to finely disperse the 211 phase in the crystals of the 123 phase. In this process, the above four steps are necessary until the precursor is obtained. It is.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide an
An object of the present invention is to simplify a precursor manufacturing process which is a preliminary process when manufacturing a coarse crystal of a system superconducting oxide.

[0011]

The gist of the present invention is to provide a method for producing coarse crystals of RE-based superconducting oxide comprising the following steps.

(1) The raw materials are blended so as to have a predetermined composition, and in a low oxygen partial pressure atmosphere having an oxygen partial pressure of 10 ⁻³ Torr or less.
Heat at a temperature of 800 to 1000 ° C for 1 hour or more and calcine.

(2) The calcined product is pulverized into a precursor.

(3) The above precursor is molded, heated rapidly to the coexistence region of the 211 phase and the liquid phase, and then gradually cooled to grow the crystal coarsely.

[0015]

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

The reason why the calcining atmosphere is an atmosphere having an oxygen partial pressure of 10 ⁻³ Torr. Or less is that if the oxygen partial pressure is higher than this, coarse 123 phase crystals are generated during the calcining, This is because in the subsequent semi-solid treatment step, the 123 phase remains without being completely decomposed into the 211 phase and the liquid phase and acts as a nucleus during slow cooling, and the 123 phase of the final structure becomes fine. Also, the temperature of calcination
The reason for setting the temperature to 800 to 1000 ° C. is that calcination at a temperature lower than 800 ° C. results in the formation of a 123 phase, and a temperature higher than 1000 ° C. results in a semi-molten state.

The step (3) of growing the crystal grains coarsely includes:
It is not substantially different from the conventional process (the above process).
In this step, the crystal is grown and coarsened by gradually cooling from a semi-molten state where the solute is easily diffused.

[0018]

EXAMPLE Y ₂ O ₃ , BaCO ₃ and CuO were used as raw materials, and these were blended 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
Under reduced pressure of rr., it was calcined at 900 ° C. for 12 hours, and pulverized to obtain a precursor.

Each of the above precursors was formed into a diameter of 20 mm and a height of 5 mm, and the temperature was raised to 1000 ° C. in 1 hour, then raised to 1120 ° C. in 2 hours, and maintained at this temperature for 0.5 hour. Thereafter, the mixture was cooled to 1000 ° C. in 0.2 hours, gradually cooled to 800 ° C. in 200 hours, and then cooled in a furnace to room temperature.
The heat pattern for this process is shown in FIG.

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

First, the crystal phase contained in the precursor obtained by the first method and the second method is examined by X-ray diffraction, and then the crystal size of the 123 phase after the crystal growth treatment is determined by using a macro microscope. Examined.

FIG. 2 shows the X-ray diffraction pattern of the precursor (a)
Is based on the first method (the method of the present invention), and (b) is based on the second method (the method of the comparative example). (a) As is clear from the figure, the precursor obtained by the method of the present invention was
Cu ₂ O ₂ is the main phase and does not contain the 123 phase. On the other hand, the precursor obtained by the second method is a single phase having almost 123 phases. These crystal grains are considered to have grown 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 (Example of the present invention), and (b) is the one using the precursor obtained by the second method (Comparative Example). In the former, only one crystal on the surface is observed. On the other hand, the latter has many crystals. That is, the former crystal grains 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 crystal, and the average of those was taken to show the atomic ratio based on Ba. As shown, the matrix has 123 phases and the granular crystals are 211
Phase. Such a structure exerts a so-called pinning effect that suppresses the movement of the magnetic flux into which the fine 211 phase enters, and is therefore particularly desirable 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 method.

[Brief description of the 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. 3 (a) is a macrostructure after coarsening of crystal grains by the method of the present invention, and (b) is a macrostructure after coarsening treatment of the precursor of the comparative example. is there.

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

──────────────────────────────────────────────────続 き Continuing on the front page (73) Patent holder 000000044 Asahi Glass Co., Ltd. 2-1-2-2 Marunouchi, Chiyoda-ku, Tokyo (73) Patent holder 000173784 Railway Technical Research Institute 2-chome Mitsumachi, Kokubunji-shi, Tokyo 8 No. 38 (73) Patent holder 000000099 Ishikawajima-Harima Heavy Industries Co., Ltd. 2-2-1 Otemachi, Chiyoda-ku, Tokyo (72) Inventor Teruo Izumi 1-1-14 Shinonome, Koto-ku, Tokyo Foundation law International Superconductivity Industry Technology Research Center, Superconductivity Engineering Research Laboratory (72) Inventor, Daisuke Otsu 1-14-3, Shinonome, Koto-ku, Tokyo Foundation: International Superconductivity Technology Research Center, Superconductivity Research Laboratory (72) Inventor: Yoji Yamada Koto-ku, Tokyo 1-14-3 Shinonome Foundation International Research Institute of Superconducting Technology, Superconducting Engineering Laboratory (72 ) Inventor Yuichi Nakamura 1-14-3 Shinonome, Koto-ku, Tokyo Foundation International Research Institute for Superconducting Technology, Superconductivity Engineering Laboratory (72) Inventor Kengo Ishige 1-14-1 Shinonome, Koto-ku, Tokyo Foundation International Kokusai Superconductivity Inside the Superconductivity Engineering Research Center, Industrial Technology Research Center (72) Inventor, Mr. Atsushi Shiohara 1-1-14 Shinonome, Koto-ku, Tokyo Foundation International Research Institute for Superconductivity Technology, Superconductivity Research Laboratory (56) References JP-A-5-24825 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C30B 28/00-35/00 C01G 1/00 C01G 3/00 ZAA CA (STN) WPI (DIALOG)

Claims (1)

(57) [Claims] A raw material is blended so as to have a predetermined composition, and has a partial pressure of oxygen of less than 10 ^-3 Torr.
The material is calcined by heating to a temperature of 1000 ° C. for 1 hour or more, and the obtained calcined material is pulverized into a precursor.
A method for producing a coarse crystal of an RE-based superconducting oxide, characterized by rapidly heating to a coexistence region of a 211 phase and a liquid phase, and then gradually cooling the crystal to grow the crystal.