JPH01201026A - Oxide superconducting material - Google Patents

Abstract

PURPOSE:To obtain the title material outstanding in temperature difference, stability and economy, predominant in alkaline earth element-Bi-Cu-O, by further incorporating specific two kinds of crystal phase laminated in tiers. CONSTITUTION:The objective material constituted mainly of ABiCuO (A is at least one kind of alkaline earth element), incorporated with at least two kinds of crystal phase laminated in tiers (one of said crystal phases being such that the atom. ratio A/Bi/Cu is ca. 3/2/2, and the other being predominant in ACuO with the atom. ratio A/Cu of ca. 1/2). Also, great quantities of such rare earth elements and alkaline earth elements as to cause instability in the final superconducting material are not present in said material thus protecting said material from erosion or the like due to water. Furthermore, the range capable of being solid solution for each of said two kinds of crystal phase is estimated to be fairly broad, and impurity phases are virtually absent, thus probably contributing, in part, to the stability of the final superconducting material.

Description

[Detailed description of the invention] Industrial applications The present invention relates to oxide superconducting materials.

Conventional technology In recent years, YBaCuO-based materials have been reported as superconducting materials.
Various experimental studies are being conducted. As a result, it has become known that this material is very unstable and has major drawbacks such as a large difference between the starting temperature and the completion temperature of superconducting state. Furthermore, because it uses a large amount of rare earth elements, it is economically unstable due to its low price (easily affected by market fluctuations). Improvements are needed in all of these areas.

Furthermore, very recently, new materials based on 5rBiCuO have been reported. However, details regarding these are currently unknown.

Problems to be Solved by the Invention It is an object of the present invention to provide a material that does not have the above-mentioned problems in temperature difference, stability, and economical efficiency.

Means for Solving the Problems A crystal consisting mainly of constituent elements ABiCuO (A contains at least one or more elements of the alkaline earth group) and further having an A/Bi/Cu ratio of approximately 3/2/2. phase and constituent elements mainly consisting of ACuO, A/
It contains at least a crystal phase with a Cu ratio of approximately 1/2, and these are laminated in multiple layers.

In addition, it is mainly composed of constituent elements ABiCuO (A contains at least one kind of element of the alkaline earth group), and furthermore, the ratio of A / Bi / Cu is approximately 3/2.
The material contains at least a crystal phase consisting of A/2 and a crystal phase consisting of constituent elements mainly consisting of ACuO and having an A/Cu ratio of approximately 1/2, and is laminated in multiple layers in the fine particles constituting the material. Let it precipitate.

It does not contain large amounts of rare earth elements or alkaline earth elements, which can cause operational instability, and is stable, so it will not be eroded by water. Furthermore, it is estimated that the solid solution range of each of the above-mentioned two crystal phases is quite wide, and this may be because it contains almost no impurity phase, which also seems to be helpful for stability. Furthermore, this seems to be helpful in reducing the temperature difference mentioned above. At present, the reasons are good (I don't know, but it is presumed that something peculiar is occurring at the interface between the two crystal phases mentioned above) that are responsible for the increase in the superconducting transition temperature.

Furthermore, it is also excellent in economical efficiency as it does not contain any rare earth elements that are expensive and unstable in supply.

Example When conducting additional tests on common recent YBaCuO-based materials, we found that even with the so-called optimal composition of 123 (Y/Ba/CLl ratio), the transition temperature was approximately 90. degree I (but the temperature difference mentioned above is about 10
It was shown that the degree of oxidation is very large, and that if the composition is slightly changed, an impurity phase is generated and the characteristics change.

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

A group of MgCa having an ionic radius of 1 angstrom or less, at least one member from the group of Sr and Ba, Bi, and C.
The oxides containing u were weighed so that the ratio of the three was approximately 3/2/2, and then uniformly mixed. This is used as the raw material for the former. Next, the ratio of the three ingredients is similarly blended to 110/2, and it is used as raw material O.

Materials from A and B were mixed to create products with various compositions. After mixing well, calcining at 800 to 850 degrees, then crushing.
After molding, it was fired at 850 degrees for 6 hours, maintained at 820 degrees, and slowly cooled at 50 degrees/hour. The results obtained are shown in Table 1.

(Leaving space below) Table 1 (Ratio: 2%) As is clear from the table, all the temperature differences mentioned above are small, less than 5 degrees, and there are two types of transition temperatures: one at 80 degrees and one from 105 to 115 degrees. Although mixed, it was shown to be stable. The table shows the high temperature. From the same table, it is clear that the above composition ratio is 2/1/
It was confirmed that the maximum value was reached at 2. Furthermore, it has been shown that by mixing the above two groups of elements, the transition temperature, which would be 20 to 30 degrees when used alone, is increased to 105 degrees or more. Furthermore, under high temperature and high humidity (60
In a moisture resistance test where the product is left at a temperature of 60% for one month, the so-called YBa
In the case of the Cu-based material, the entire surface turned white and collapsed considerably, whereas the surface of this material only slightly turned white, indicating that it is extremely stable.

In addition, the results of analysis using the X-gland show that a crystalline phase consisting of a single composition ratio of 3/2/2 is found in a fairly wide range (the lattice constants are a = 15.3 angostromes, b =
It is superficially described as a tetragonal crystal with c=22.9 angostroms, and when combined with the results of a transmission electron microscope, it is estimated to consist of a pseudocubic crystal with a unit cell of 5.4 angostromes. )
It was confirmed that a so-called crystalline phase of CaCu2O3 having a composition of 110/2 was formed, and these crystal phases overlapped with each other in the particles constituting the sintered body to form a fine thin precipitated layer. As mentioned above, the optimum composition ratio of 2/1/2 corresponds to the reduction of these crystal phases to 1/1, and it is assumed that a unique 11 is generated at the interface of these two crystal phases. be done.

Next, we artificially stacked multiple layers using magnetron sputtering. A target manufactured using the above-mentioned materials A and B alone was used, and each thin film was alternately laminated in an Ar gas containing 4% oxygen while maintaining the substrate temperature at 550 degrees Celsius. When the thickness of one layer was changed from 200 to 1000 angstroms to form a variety of products, some of them had a transition temperature of 80 angstroms.
The physical appearance of screws with degrees was observed, but all were 100 degrees.
We have shown more than that. Since it is kept at a low temperature, it is assumed that the diffusion between the laminated layers is small. Furthermore, the results of cross-sectional observation using an electron microscope also show that the diffusion is small. It was also confirmed that, as mentioned above, when the thickness ratio is approximately 1/1, the thickness is also optimal.

Effects of the Invention According to the present invention, it is possible to provide a material that has excellent moisture resistance, a wide solid solution range, and excellent stability and reproducibility with small temperature differences as described above, and can be applied to a wide range of superconducting devices. can be done.

Claims (3)

[Claims] (1) A crystal phase consisting mainly of constituent elements of ABiCuO (A contains at least one element of the alkaline earth group), and further having an A/Bi/Cu ratio of approximately 3/2/2, and ACuO Consisting of the main constituent elements, A
An oxide superconducting material characterized in that it contains at least a crystal phase having a /Cu ratio of approximately 1/2 and is laminated in multiple layers. (2) A crystal phase consisting mainly of constituent elements of ABiCuO (A contains at least one element of the alkaline earth group), and further having an A/Bi/Cu ratio of approximately 3/2/2, and ACuO Consisting of the main constituent elements, A
An oxide superconducting material characterized in that it contains at least a crystal phase having a /Cu ratio of approximately 1/2, and is precipitated in a multilayered state in fine particles constituting the material. (3) The oxide superconducting material according to claim 1 or 2, wherein an element with an ionic radius of A of 1 angstrom or more and an element with an ionic radius of 1 angstrom or less are mixed.