JPH01257159A - Oxide superconducting material - Google Patents

Abstract

PURPOSE:To form an oxide superconducting material exhibiting superconducting characteristics even when oxygen is not satisfactorily absorbed in the material during sintering, by providing a specified compsn. CONSTITUTION:This oxide superconducting material has a compsn. represented by a formula CaxR1-xBa2Cu3O7-delta (where R is at least one kind of metal selected among Y and lanthanoids, 0.4<x<0.6 and 0<delta<1). The superconducting material may be obtd. by uniformly mixing compds. of the constituent elements such as oxides, salts or alkoxides in a prescribed ratio, drying and sintering the mixture. At this time, in order to allow a solid phase reaction to proceed satisfactorily, the powdery mixture is preferably press-molded and sintered in the form of pellets. The pref. sintering temp. is 920-940 deg.C. It is not especially required to slowly cool the sintered material and this material may be rapidly cooled by putting in liq. nitrogen after calcining.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to oxide superconducting materials used in various superconducting application devices, superconducting elements, and the like.

[Conventional technology]

YB is a substance that has recently attracted attention as a superconducting material.
a2Cu307-. 5 (0<δ<7). Although this substance has a high critical temperature (Tc), it absorbs and releases oxygen significantly at temperatures above 300°C, and has a compositional formula of Y.
Ba2Cu30. In the case of −δ, δ>o, the one on the left is a tetragonal system, and it is known that it does not exhibit superconducting properties. Therefore, when sintering the substance, it is necessary to sinter it at 900° C. to qtio° C. and then slowly cool it at a cooling rate of generally about 50° C./h to absorb enough oxygen.

On the other hand, when superconducting materials are used in magnets and coils, they are required to have a high current density due to the usage conditions, and to achieve this, it is necessary to have a densely packed state in which the particles are in sufficient contact with each other. However, when the sintered body becomes dense, it becomes difficult to absorb enough oxygen into the interior of the sintered body during the slow cooling process.

[Problem to be solved by the invention]

Therefore, the present inventors have conducted intensive studies on oxide superconducting materials that exhibit superconducting properties even without sufficient absorption of oxygen during the sintering process, and as a result, have arrived at the present invention.

[Failure to solve the problem]

That is, the gist of the present invention is the composition formula CaXR, -xBa2Cu, O, -6 (wherein R represents at least seven metals selected from yttrium and lanthanoids).

X is Q, lI<X<0.6, preferably o, qs≦X≦
o,! represents the number of rs, and δ represents the number of 0 × δ ×/. ) exists in oxide superconducting materials shown in

Specifically, for example, Cax (y, -, Ery), -XB
a2Cu307-δ, CaX(Y, -yYby), -x
Ba2Cu30,4 (where X is 0, Da<x<
0. The number O, y represents the number 0≦y≦7, and δ represents the number Okuδku/, respectively. ) etc.

Carbonates, hydroxides, nitrates, sulfates, oxalates, chlorides, alkoxides, etc. of the respective elements can be used as the lanthanide compounds, calcium compounds, barium compounds, and copper compounds that are raw materials. The weighed compounds of each element are prepared by, for example, powder mixing method, wet co-precipitation method,
Mixing is performed by a conventionally known method aiming at uniform mixing, such as a wet evaporation to dryness method or 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 press-molded into pellets and fired.

The molding pressure in pressure molding may be any pressure that can provide a compacted powder state that allows the powder to be handled.

For sintering, a raw powder compact may be used, but in order to improve the uniformity of the sample, a calcination step for about 70 hours at goθ~qoo°C may be performed, followed by pulverization, molding, and main firing. . The sintering temperature is between 900°C and 940°C, preferably 9
The range is from 0°C to qlIo°C. A sintering time of 7 hours or more is sufficient, but desirably a time of S or more is required.

There is no particular need to slowly cool the fired material; for example, it may be placed in liquid nitrogen after firing to rapidly cool it. In other words, in the present invention, it is not necessary to slowly cool the material after firing to absorb enough oxygen. An oxide superconducting material exhibiting conductive properties is obtained. Moreover, the cooling time after firing can be significantly shortened. Further, it is possible to achieve a high degree of densification and obtain a high current density.

〔Example〕

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to the following examples as long as they do not go beyond the gist of the invention.

Example/ Purity of each? 9.9% or more of reagent was used.

Each powder of yttrium oxide (Y2O2), calcium carbonate (CaCO3), barium carbonate (BaCO3), and copper oxide (CuO) was prepared at an atomic ratio of Y: Ca: Ba: Cu with θ, j-: 0. After weighing so that k: 2: 3 was obtained, the mixture was uniformly mixed by a wet mixing method using an agate mortar. After drying this/at a pressure of t/z2, the diameter is reduced to Otm.
Pressure molded to φ, thickness/*3 m, then 9'l in air
Calcined at 0° C. for 20 hours. After firing, the sample was placed in liquid nitrogen and rapidly cooled.

The composition of the obtained oxide superconducting material was Cao, 5Yo, 5Ba2Cu30. −δ was □
Tc onset ('K) and Tc end ('
K) values are shown in Table 1.

FIG. 7 shows the temperature change in electrical resistance of the obtained oxide superconducting material.

Comparative Example/An oxide material was produced in exactly the same manner as in Example/, except that each reagent was weighed so that the composition was YBa2Cu307-δ. Tc onset ('K) and T
The values of c end (°K) are shown in Table 1.

FIG. 2 shows the temperature change in electrical resistance of the obtained YBa2Cu307-δ.

As is clear from FIGS. 1 and 2, conventional Tc=9
YBa2Cu30, which is said to be of grade 0. If δ is rapidly cooled after firing, it will freeze due to the lack of oxygen at high temperatures, so it does not exhibit superconductivity. However, in the present invention, Cao-, Yo
, 5Ba2Cu, O,-,5, although the Tc onset and Tc end decrease, they exhibit superconductivity even when the oxygen supply is small due to rapid cooling.

Examples 3 and Comparative Examples 2 to 7 Oxide materials were produced in exactly the same manner as in Examples except that each sample was weighed to have the composition shown in Table 1. Tc onset ('K) and Tc end (
'K) values are shown in Table 1.

Table 7 [Effects of the Invention] According to the present invention, it is possible to obtain a material exhibiting superconductivity even when the material is rapidly cooled from a high temperature, so that the oxygen absorption time due to cooling can be shortened in the manufacturing process. Further, the superconducting material of the present invention can be made into a wire to be used as a coil for a magnet, or made into a thin film to be used as a superconducting device such as a 5QUID.

[Brief explanation of the drawing]

Figure 1 shows Cao, Yo, Ba2C obtained in Example/
u30. FIG. 3 is a diagram showing the resistivity-temperature characteristics of δ. Figure 2 shows YBa2Cu307-δ obtained in Comparative Example/
FIG. 3 is a diagram showing the resistivity temperature characteristics of Applicant: Mitsubishi Chemical Industries, Ltd. Agent: Patent Attorney Hase - Others/Names

Claims (1)

[Claims] (1) Composition formula Ca_xR_1_-_xBa_2Cu_3O_7_-_
δ (wherein R represents at least one metal selected from yttrium and lanthanoids, x represents a number of 0.4<x<0.6, and δ represents 0<
Represents a number where δ<1. ) is an oxide superconducting material.