JP2506892B2 - Oxide superconducting material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an oxide superconducting material.

2. Description of the Related Art In recent years, YBaCuO-based materials have been reported as superconducting materials, and various test studies have been conducted. As a result, it has been known that this material is very unstable and has a big defect that the difference between the starting temperature and the completion temperature of the superconducting state is large. In addition, since it uses a large amount of rare earth elements, it has an economically unstable element that the price is high and it is easily affected by market fluctuations. Improvements in all of these are desired.

Even more recently, new SrBiCuO-based materials have been reported. However, the details of these are currently unknown.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention provides a material having no problem in temperature difference, stability, and economical efficiency as described above.

Means for Solving the Problems ABiCuO (A contains at least one element of alkaline earth group)
A / Bi / Cu atomic ratio is 5/5/4, 6/4/5, 4/2/3, 6/3/4, 9/6
/ 5 is contained in a range surrounded by each point, contains at least a phase of 3/2/2, and as A, an element having an ionic radius larger than 1 angstrom and an element having a smaller ion radius are mixed.

Action Rare earth elements and alkaline earth elements that cause instability are not contained in large amounts in an unstable form, so corrosion by water does not occur. Further, it is presumed that the solid solution range is wide, which is considered to be due to the fact that it does not contain much impurity phase, which also contributes to stability. Furthermore, this seems to be useful for reducing the above-mentioned temperature difference. It is presumed that excellent characteristics are obtained because an appropriate inter-element distance is realized by first mixing an alkaline earth element with an ionic radius of 1 angstrom or more and the following.

Furthermore, as is apparent, it does not contain expensive rare earth elements, which are unstable, and it has excellent economic efficiency.

Example When a general recent YBaCuO-based material was supplemented, a transition temperature of about 90 was found to be obtained even with the optimum composition of so-called 123 (Y / Ba / Cu ratio). Although it was K, it was shown that the above-mentioned temperature difference was about 10 degrees and was very large.
It was also shown that if the composition was changed slightly, an impurity phase was generated and the characteristics changed.

On the other hand, according to the study by the present inventors, the new material has stable and excellent characteristics as shown below.

An oxide containing Bi, Cu and at least one or more members from each group of Mg, Ca having an ionic radius of 1 Å or less and a group of Sr, Ba having an ionic radius larger than that, and an oxide containing Bi, Cu have a ratio A
/ Bi / Cu was weighed so that it was approximately 3/2/2, and then uniformly mixed, then calcined at 800 to 850 degrees, further pulverized and molded, and then fired at 850 degrees. The results obtained are shown in Table 1.

In Table 1, the transition temperature is an intermediate value between the temperature at the inflection point (extrapolation point) on the resistance temperature curve indicating the start point of superconductivity and the end point temperature at which the resistance becomes zero. The temperature difference indicates the temperature difference between the starting point and the ending point. In the table, composition 14
All of the samples other than the sample of 1 are mixed with an element having an ionic radius of an alkaline earth element of 1 angstrom or less and a larger element. Further, as is clear from the sample data of the compositions 1 to 5 and 9 to 13 in the table, all of them except the compositions 9 and 13 have a single phase, and the temperature difference is 10 degrees or less (particularly composition 1
-5, 10, and 11 are excellent in that the temperature difference is 5 degrees or less. Composition 9
And 13 became a double phase, so the temperature difference was about 10 degrees), and the transition temperature was stable at about 80 to 85 degrees K (in the sample of composition 13, the X-ray diffraction results show that Thus, a sample containing a large amount of 3/2/2 phase exhibits a temperature of about 77 degrees K. However, even a sample having the same composition may exhibit a temperature of about 100 degrees K with a small amount of 3/2/2 phase.) It has been shown.

Furthermore, by mixing the elements of the above two groups as shown in the samples of compositions 9 and 13 in the same table, in the case of the combination of elements belonging to a single group as shown in the sample of composition 14 in the table, the transition temperature It is shown that those with 20 to 30 degrees K are around 80 degrees K. Further high temperature and high humidity (60 degrees 60%)
In a moisture resistance test that was left for 1 month, the so-called YBaCu-based material turned white and collapsed considerably, whereas this material only had the composition 8, 9, 13 and 14 in the table and the surface was It was shown to be very stable with only a slight whitening. As you can see from Table 1, basically composition 2,
It is shown that it is particularly excellent in the range surrounded by 3, 4, 5, and 9. In addition, the materials in which alkaline earth elements are replaced, such as 11, 12, and 13, also show good characteristics.

In addition, the result of X-ray analysis shows that a phase consisting of a single 3/2/2 composition ratio in a fairly wide range (currently under investigation, the lattice constant is a = 15.3 angstrom, b = c = 22.9 angstrom square Crystal and surface, and combined with the results of transmission electron microscopy, it is presumed to be composed of a pseudolattice superlattice with a unit cell of 5.4 angstroms.). However, with respect to the compositions 6 and 7 in Table 1, a phenomenon was observed in which the characteristics such as the critical temperature and the temperature difference varied considerably even when the same composition ratio was prepared.

Advantageous Effects of the Invention According to the present invention, it is possible to provide a material having excellent moisture resistance, a wide solid solution range, and a small temperature difference and excellent stability reproducibility, and is widely applied to superconducting equipment. obtain.

Claims (1)

(57) [Claims] 1. A constituent element mainly composed of ABiCuO (A includes at least one element of alkaline earth elements), and the atomic ratio of A / Bi / Cu is 5/5/4, 6/4. / 5, 4/2/3,
It is characterized by containing at least a phase consisting of 3/2/2 within the range surrounded by the points 6/3/4 and 9/6/5, and the element with an ionic radius larger than 1 angstrom as A and that An oxide superconducting material, characterized in that the following elements are mixed.