JPH085672B2 - Method for producing oxide superconductor - Google Patents

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 An object of the present invention is to provide a material that does not have the above-mentioned temperature difference, stability, and economical problems.

Means for Solving the Problem A method for producing an oxide superconductor mainly containing ABiCuO (A includes at least one element of alkaline earth group), wherein an A / Bi / Cu ratio is 3/2. A first crystal phase component consisting of / 2 and a second crystal phase component mainly composed of ACuO are separately prepared, and then these are laminated in multiple layers by sputtering. It is a manufacturing method.

Further, it is a method for producing an oxide superconductor characterized in that an element having an ionic radius of A larger than 1 angstrom and an element having a smaller ionic radius are mixed.

Since it does not contain a large amount of rare earth elements and alkaline earth elements that cause instability, it is stable and does not cause erosion by water. Further, the solid solution range of each of the above-mentioned two crystal phases is presumed to be quite wide, and this is considered to be the reason, but it contains almost no impurity phase, and this also seems to be useful for stability. Furthermore, this seems to be useful for reducing the above-mentioned temperature difference. Although the reason for this is not clear at present, it is presumed that the two points that a peculiar thing occurs at the interface of the above-mentioned two crystal phases are the causes of the improvement of the superconducting transition temperature.

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 additionally tested, the transition temperature was about 90 ° C. according to the study by the present inventors 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 close to 10 degrees and was extremely large, and that the impurity phase was generated and the characteristics fluctuated if the composition was slightly changed.

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

A group of Mg, Ca with an ionic radius of 1 angstrom or less and at least one group of Sr, Ba with an ionic radius larger than that, and an oxide containing Bi, Cu have a ratio of about 3/2/2. Were weighed and then mixed evenly. This is used as a raw material. Next, similarly, the ratio of the three is mixed to 1/0/2 and used as the second raw material. Raw materials of Kotsu were mixed to prepare various compositions. After mixing well, calcination at 800 to 850 degrees, crushing and molding, then firing at 850 degrees for 6 hours, then 8
The temperature was maintained at 20 ° C and the mixture was cooled at 50 ° C / hour. The obtained results 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. The ratios in the table are calculated from the magnetic susceptibility and temperature measurements of the sample. Specifically, the transition temperature (almost equal to the transition temperature) showing the complete diamagnetism (Meissner effect) of the sample is around 80K and from 105 to 115K.
Since there are two types, V1 is obtained by finding the perfect diamagnetic amount (corresponding to the volume) at 95K at the midpoint between them, and V2 is obtained by finding it below 60K, and V1 / V2 x 100 (%) is Ratio ”. In the table, all of the samples other than the sample of composition 9 show the mixture of an element having an ionic radius of an alkaline earth element of 1 angstrom or less and an element having a larger ion radius. Also, as is clear from compositions 1 to 8 in the table, the above temperature differences are all 5 degrees or less, and the transition temperature is 80K (composition 5).
From 05 to 115K (composition 1 to 4, composition 6 to 8), two kinds were mixed, but it was shown to be stable. The table shows high temperature. From the same table, it was clearly confirmed that the ratio of the products having a temperature of 100 degrees K or more was the maximum when the composition ratio was 2/1/2. Further, as can be seen by comparing the results of the samples of compositions 3 and 7 to 9 in the same table, by mixing the elements of the above two groups, the transition temperature is 20 to 30 K in the case of the combination of the elements belonging to the single group. (Sr in Table 9 only Sr) is 105K or more (composition 3 is a combination of Sr and Ca, composition 7 is a combination of (Sr, Ba) and Ca, composition 8 is (Sr, Ba)
And (Ca, Mg) combination). In a moisture resistance test in which the material was left under high temperature and high humidity (60 degrees 60%) for 1 month, the so-called YBaCu-based material turned white and collapsed considerably. Was only slightly whitened, indicating that it was very stable.

In addition, the result of the X-ray analysis shows that a crystal phase consisting of a single 3/2/2 composition ratio in a fairly wide range (currently under study, the lattice constants are a = 15.3 angstrom and b = c = 22.9 angstrom). The surface is described as tetragonal, and when combined with the results of transmission electron microscopy, it is estimated that it is composed of a pseudocubic unit cell of 5.4 angstroms.) And a so-called CaCu ₂ O ₃ crystal phase with a composition of 1/0/2. It was confirmed that they were formed and these particles overlap each other in the particles constituting the sintered body to form a fine thin deposition layer. As mentioned above, composition ratio 2/1 /
The optimum value of 2 corresponds to the fact that these crystal phases become 1/1, and it is presumed that a peculiar thing occurs at the interface between these two crystal phases.

Next, the magnetron sputtering method was used to artificially stack multiple layers. As a target, the above-mentioned raw materials prepared from both raw materials were used, and the thin films were alternately laminated while maintaining the substrate temperature at 550 ° C. in Ar gas containing 4% oxygen. When various layers were formed by changing the thickness of one layer from 200 to 1000 angstroms, an impurity phase having a transition temperature of 80 degrees was observed in some of them, but all showed 100 degrees K or more. Since it is kept at a low temperature, it is estimated that the diffusion between the layers is small. Further, the observation of the cross section by an electron microscope shows that the diffusion is small. It was also confirmed that, as described above, when the thickness ratio was about 1/1, the optimum value was obtained.

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.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunichiro Kawashima 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) , 26 (12) 1987 L2080-2081

Claims (2)

[Claims] 1. A method for producing an oxide superconductor mainly comprising ABiCuO (A includes at least one element of alkaline earth group), wherein A / Bi / Cu ratio is 3/2/2. Consisting of the first
And a second crystal phase component mainly composed of ACuO are separately prepared, and then these are laminated in multiple layers by sputtering, and a method for producing an oxide superconductor. 2. The method for producing an oxide superconductor according to claim 1, wherein elements having an ionic radius of A larger than 1 angstrom and elements having a smaller ionic radius are mixed.