JP2596964B2 - Oxide superconducting material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an oxide superconducting material used for various superconducting applied devices and superconducting elements.

[Conventional technology]

YB is a substance that has recently attracted attention as a superconducting material.
a ₂ Cu ₃ O _{7- δ} (0 <δ <1). Although this substance has a high critical temperature (Tc), it absorbs and releases oxygen significantly at a temperature of 300 ° C or higher, and becomes tetragonal when the composition formula Y ₁ Ba ₂ Cu ₃ O _{7- δ} is δ> 0.5, It is known that it does not show superconducting properties. Therefore, when sintering the material, 90
After firing at 0 ° C. to 940 ° C., it is generally necessary to gradually cool at a rate of about 50 ° C./h to absorb oxygen sufficiently.

On the other hand, when a superconducting material is used for a magnet or a coil, it is required to have a high current density due to use conditions, and for that purpose, it is necessary to form a densely packed state in which grains are in good contact with each other. However, when densified, it is difficult to sufficiently absorb oxygen to the inside of the sintered body during the slow cooling process.

[Problems to be solved by the invention]

The inventors of the present invention have conducted intensive studies on oxide superconducting materials that exhibit superconducting properties without sufficiently absorbing oxygen during the sintering process, and as a result, have reached the present invention.

[Means for Solving the Problems] That is, the gist of the present invention is a composition formula of Ca _x R _{1 -x} Ba ₂ Cu ₃ O _{7- δ} (where R is at least one metal selected from yttrium and lanthanoids) X is 0.4 <x <0.
6, preferably a number satisfying 0.45 ≦ x ≦ 0.55, and δ is 0 <
represents a number of δ <1. ) In the oxide superconducting material.

Specifically, for example, Ca _x (Y _1-y Er _y ) _1-x Ba ₂ Cu ₃ O _{7- δ} , Ca
_x (Y _1-y Y _b ) _1-x Ba ₂ Cu ₃ O _{7- δ} (where x is a number of 0.4 <x <0.6, y is a number of 0 ≦ y ≦ 1, and δ is 0 <δ < 1 represents a number).

Lanthanoid compounds, calcium compounds,
As the barium compound and the copper compound, carbonates, hydroxides, nitrates, sulfates, oxalates, chlorides, alkoxides and the like of the respective elements can be used. The weighed compound of each element is mixed by a conventionally known method for uniform mixing, such as a powder mixing method, a wet coprecipitation method, a wet evaporation to dryness method, and an alkoxide method.
The resulting mixture is dried and then fired.

At this time, in order to make the solid-phase reaction more sufficient, it is preferable that the powder is molded under pressure, pelletized, and fired.

The molding pressure in the pressure molding may be any pressure as long as a powder state that can handle the powder can be obtained.

For sintering, a green compact may be used, but in order to improve the uniformity of the sample, a calcination step of about 800 to 900 ° C. for about 10 hours may be performed, followed by pulverization, molding, and final firing. . The sintering temperature is between 900 ° C and 960 ° C, preferably between 920 ° C and 940 ° C
It is in the range of ° C. A sintering time of 1 hour or more is sufficient, but preferably 5 hours or more.

The calcined material does not need to be gradually cooled, and may be quenched, for example, by placing it in liquid nitrogen after calcining.

That is, in the present invention, an oxide superconducting material which exhibits superconductivity even if the oxygen is not sufficiently absorbed by slow cooling after firing is obtained. Further, the cooling time after firing can be greatly reduced. Further, it is highly densified, and a high current density can be obtained.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples as long as the gist is not exceeded.

Example 1 Reagents each having a purity of 99.9% or more were used.

Yttrium oxide (Y ₂ O ₃ ) Calcium carbonate (CaCO ₃ ) Barium carbonate (BaCO ₃ ) Copper oxide (CuO) powder should be 0.5: 0.5: 2: 3 in atomic ratio of Y: Ca: Ba: Cu And then uniformly mixed by a wet mixing method using an agate mortar. This pressure after drying 1t / cm ² diameter 20 mm.phi,
It was pressed to a thickness of 1.5 mm and then fired in air at 940 ° C. for 20 hours. After firing, the sample was placed in liquid nitrogen and quenched.

The composition of the obtained oxide superconducting material is Ca _0.5 Y _0.5 Ba ₂ Cu ₃ O
_{7- δ} . The values of Tconser (ΔK) and Tcend (ΔK) are shown in Table 1.

FIG. 1 shows the temperature change of the electric resistance of the obtained oxide superconducting material.

Comparative Example 1 An oxide material was produced in exactly the same manner as in Example 1, except that each reagent was weighed so that the composition became YBa ₂ Cu ₃ O _{7- δ} . Table 1 shows the values of Tc onset (゜ K) and Tc end (゜ K).

FIG. 2 shows the temperature change of the electric resistance of the obtained YBa ₂ Cu ₃ O _{7- δ} .

As is clear from FIGS. 1 and 2, the conventional Tc = 90
YBa ₂ Cu ₃ O _{7- δ} , which is said to be K-class, does not exhibit superconductivity because it freezes with insufficient oxygen at high temperatures when quenched after firing. However, in the present invention Ca _0.5 Y _0.5 Ba ₂ Cu ₃ O _{7- δ}
Although the onset of Tc and the end of Tc decrease, superconductivity is exhibited even with a small supply of oxygen due to rapid cooling.

Examples 2 to 3 and Comparative Examples 2 to 7 An oxide material was produced in exactly the same manner as in Example 1 except that each sample was weighed so as to have the composition shown in Table 1. Table 1 shows the values of Tc onset (゜ K) and Tc end (゜ K).

[Effects of the Invention] According to the present invention, a material exhibiting superconductivity can be obtained even from a material quenched from a high temperature, so that the oxygen absorption time by cooling in the manufacturing process can be reduced.
Further, the superconducting material of the present invention can be used as a coil for a magnet by being made into a wire or a superconducting device such as a SQUID by being made thin.

[Brief description of the drawings]

FIG. 1 is a diagram showing the resistivity-temperature characteristics of Ca _0.5 Y _0.5 Ba ₂ Cu ₃ O _{7- δ} obtained in Example 1. FIG. 2 is a diagram showing the resistivity-temperature characteristics of YBa ₂ Cu ₃ O _{7- δ} obtained in Comparative Example 1.

Continuation of the front page (56) References Japanese Journal of Applied Physics Part2 Letters, Vol. 26 No. 5 May 1987 L 665-L667

Claims (1)

(57) [Claims] A composition formula Ca _x R _1-x Ba ₂ Cu ₃ O _{7- δ} (wherein R represents at least one metal selected from yttrium and lanthanoids; x is 0.4 <x <0.6
And δ represents a number of 0 <δ <1. ) An oxide superconducting material represented by