JP2747438B2 - Oxide superconducting material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide superconducting material.

[0002]

2. Description of the Related Art In recent years, YBaCuO-based materials have been reported as superconducting materials. Various tests and researches have been conducted on this YBaCuO-based material.

[0003]

As a result, it has been known that this material is very unstable and has significant drawbacks such as a large difference between the onset temperature and the completion temperature of the superconducting state. In addition, there are economically unstable factors such as high prices for rare earth elements and susceptibility to market fluctuations. Improvements are desired for all of these.

[0004] More recently, a new SrBiCuO-based material has been reported. However, the details of these are currently unknown.

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

[0006]

Means for Solving the Problems The main constituent elements are ABiCuO (A contains at least one element composed of an alkaline earth), and the ratio of A / Bi / Cu is 3/2/2. It contains at least a crystal phase and a crystal phase composed mainly of constituent elements of ACuO, and forms a structure in which these layers are stacked in multiple layers.

Further, it is composed of constituent elements mainly composed of ABiCuO (A contains at least one element composed of an alkaline earth group), and the ratio of A / Bi / Cu is 3/2 /
2 and A / Cu ratio of 1 mainly with ACuO
/ 2 and at least two crystalline phases, and they are laminated in multiple layers.

Further, it is composed of a constituent element mainly composed of ABiCuO (A contains at least one element composed of an alkaline earth group), and the ratio of A / Bi / Cu is 3/2 /
2 and A / Cu ratio of 1 mainly with ACuO
/ 2 at least, and is precipitated in fine particles constituting the material in a state of being laminated in multiple layers.

[0009]

[Function] It does not contain a large amount of rare earth elements or alkaline earth elements which cause instability and is stable, so that erosion or the like by water does not occur. Further, the solid solution range of each of the two crystal phases is presumed to be considerably wide, and it is thought that the solid solution hardly contains an impurity phase, which is also considered to contribute to stability. It is also believed that this has helped to reduce the temperature difference described above. Although the reason at present is not well understood, it is presumed that two points at which an unusual phenomenon occurs at the interface between the two crystal phases are responsible for the improvement of the superconducting transition temperature.

[0010] Furthermore, as is apparent from the fact that it does not contain any expensive supply of unstable unstable rare earth elements, it is also excellent in economical efficiency.

[0011]

EXAMPLE When a supplementary test was conducted on a general recent YBaCuO-based material, according to the study of the present inventors, the transition temperature was found to be the optimum composition of the contract 123 (Y / Ba / Cu ratio). Although it was about 90 degrees K, the above temperature difference was about 10 degrees, indicating that it was very large, and it was also shown that if the composition was slightly changed, an impurity phase was formed and the characteristics were changed.

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

M having an ion radius of 1 angstrom or less
g, Ca and a larger ionic radius of Sr,
At least one or more oxides from a group of Ba and an oxide containing Bi and Cu are weighed so that the ratio of the three becomes 3/2/2.
Next, they were mixed uniformly. This is calcined at 800 to 850 ° C and pulverized, and this is used as a raw material for the former. Next, similarly, the three components are blended so that the ratio becomes 1/0/2, and after mixing, the mixture is calcined at 800 to 850 ° C. and pulverized to obtain a second raw material.
Materials of various compositions were prepared by mixing the raw materials of Koto. After mixing well, calcining at 800 to 850 degrees, further pulverizing and molding, and then firing at 850 degrees for 6 hours, followed by 82 hours.
It was kept at 0 ° and was cooled at 50 ° / hour. The results obtained are shown in Table 1.

[0014]

[Table 1]

In Table 1, the transition temperature is an intermediate value between the temperature at the inflection point (extrapolation point) and the temperature at the end point at which zero resistance is reached in the resistance temperature curve indicating the start point of superconductivity. The temperature difference indicates a temperature difference between the start point and the end point. The ratios in the table are calculated from the magnetic susceptibility and temperature measurements of the samples. Specifically, the complete diamagnetism of the sample (Meissner effect)
There are two kinds of transition temperatures (approximately equal to the transition temperature) of around 80K and 105 to 115 ° K, so the complete diamagnetism (corresponding to the volume integral) at 95K at the midpoint between the two is determined as V1, Find it below 60K and use it as V2, V1
/ V2 × 100 (%) was defined as the “ratio”. In the same table, all the samples other than the sample having the composition 9 are those in which an ionic radius of an alkaline earth element is 1 Å or less and a larger element. Further, as is clear from compositions 1 to 8 in the same table, the above-mentioned temperature differences were all as small as 5 ° C. or less, and the transition temperature was 80K (composition 5).
15 ° K (compositions 1 to 4 and compositions 6 to 8) showed that although two types were mixed, they were stable. In the table, those at high temperatures are described. From the same table, it was clearly confirmed that the ratio of the substance having a temperature of 100 ° K or more was maximized 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 above two groups of elements, in the case of a combination of elements belonging to a single group, the transition temperature is 20 to 30. Degree K (composition 9 in the table)
At 105 ° K or higher (Sr only in composition 3)
It is shown that a combination of r and Ca, a composition 7 is a combination of (Sr, Ba) and Ca, and a composition 8 is a combination of (Sr, Ba) and (Ca, Mg). Further, in a moisture resistance test in which the material was left for one month under high temperature and high humidity (60 ° C. 60%), the so-called YBaCu-based material turned white as a whole and collapsed considerably. Is slightly white and very stable.

According to the results of X-ray analysis, a crystal phase composed of a single 3/2/2 composition ratio in a fairly wide range (the lattice constant a is 15.3 angstroms, b = c = 22.9 angstroms tetragonal and superficially described, and when combined with transmission electron microscopy results, is presumed to consist of a unit cell of 5.4 angstroms pseudo-cubic) and a composition of 1/0/2. So-called CaCu ₂ O ₃
It has been confirmed that these crystal phases overlap each other in the particles constituting the sintered body to form a fine thin bent layer. As described above, the optimum at a composition ratio of 2/1/2 corresponds to the fact that these crystal phases become 1/1, and it is estimated that a peculiar thing has occurred at the interface between these two crystal phases. Is done.

Next, a multilayer was artificially laminated by using a magnetron sputtering method. As a target, the above-mentioned materials prepared by using 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% of oxygen. Various layers were formed by changing the thickness of one layer from 200 to 1000 angstroms. As a result, an impurity phase having a transition temperature of 80 ° was partially observed, but all showed an impurity phase of 100 ° K or higher. It is presumed that the diffusion between the layers is small because it is kept at a low temperature. In addition, observation of the cross section with an electron microscope shows that diffusion is small.
It was also confirmed that when the thickness ratio was approximately 1/1 as described above, it was similarly optimum.

[0018]

According to the present invention, it is possible to provide a material having excellent moisture resistance, a wide solid solution range, a small temperature difference, and excellent stability reproducibility. Can be applied.

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI H01B 13/00565 C04B 35/00 ZAAK (72) Inventor Shunichiro Kawashima 1006 Ojidoma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-1-188456 (JP, A) JAPANESE JOURNAL OF APPLIED PHYSICS S, 26 (12) 1987, PP. L2080-2081 "Nikkei Superconducting 1988.2.8", Nikkei McGraw-Hill, February 8, 1988; 1-3 (58) Field surveyed (Int. Cl. ⁶ , DB name) C01G 29/00 ZAA

Claims (4)

(57) [Claims] 1. A crystal phase mainly composed of ABiCuO (A contains at least one element of an alkaline earth group) and further having an A / Bi / Cu ratio of 3/2/2; An oxide superconducting material comprising at least a crystal phase mainly composed of ACuO and having a structure in which these layers are stacked in multiple layers. 2. A crystal phase mainly composed of constituent elements ABiCuO (A contains at least one element composed of an alkaline earth group) and further having an A / Bi / Cu ratio of 3/2/2; An oxide superconducting material comprising at least a crystal phase comprising ACuO as a main component and having an A / Cu ratio of 1/2, and being laminated in multiple layers. 3. An element mainly composed of ABiCuO (A contains at least one element of an alkaline earth group), and the ratio of A / Bi / Cu is 3/2/2.
And a crystal phase consisting of ACuO and at least a crystal phase having an A / Cu ratio of 、, and precipitated in a state of being stacked in multiple layers in fine particles constituting the material. An oxide superconducting material, characterized in that: 4. The oxide superconducting material according to claim 1, wherein an element having an ionic radius of A larger than 1 Å and an element smaller than A are mixed.