JPH0218321A - La-ba-ca-cu oxide superconductor - Google Patents

Abstract

PURPOSE:To provide a superconductor hardly undergoing deterioration in the superconducting characteristics by heating temp., having a high critical temp. and causing sharp superconduction transition in a wide heating temp. range by specifying the molar ratios of La:Ba:Ca:Cu. CONSTITUTION:The molar ratios of La:Ba:Ca:Cu in an La-Ba-Ca-Cu oxide superconductor are regulated to 1:1:1:3 or about 1:1:1:3. This superconductor has a high critical temp. and very stable superconducting characteristics independently of heating temp. and can be produced by mixing and sintering oxides or salts of the constituent elements. CaCO3 or CaO is preferably used as starting material for Ca and the mixture is preferably heated to >=900 deg.C.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an L a -B a -Ca-Cu oxide superconductor. More specifically, the present invention provides a La-based oxide superconductor that has a high critical temperature, improves the instability of superconducting properties due to heating temperature, and maintains a sharp superconducting transition even when the heating temperature is within a wide range. Excellent L a -B with high stability that can cause
This invention relates to an a-Ca-Cu oxide superconductor.

(Background technology) Conventionally, La-based oxide superconductors include Lat, s
214 type represented by 5ro2Cuba and LaBa
2Cu, 07-F type 123 is becoming known. 21
For Type 4, the critical temperature is around 40°C, and for Type 123, the critical temperature is on the order of 70°C. These L
A-based oxide superconductors have the disadvantage that their specific resistance and critical temperature vary greatly depending on the heating temperature, and when putting these unstable oxide superconductors into practical use in the future, it is necessary to At present, there are many problems that must be overcome. For example, when making wires from oxide superconductors, there are issues regarding critical current, or 3f! The issue of physical property values, which are extremely unstable depending on conditions, will be an important issue for practical application.

The above-mentioned La-based oxide superconductor is no exception;
Excellent L a B a 2 system with high critical temperature
Even in Cu s O7-7, the heating temperature is 1050″C
However, if the heating temperature exceeds even slightly 1050°C, the superconducting properties deteriorate significantly. This deterioration of superconducting properties due to heating temperature is not only observed in La-based oxide superconductors, but also in Y-based, Bi-based, and TI-based oxide superconductors that have been discovered so far. Deterioration of properties occurs.

(Object of the invention) This invention was made in view of the above circumstances,
It improves the deterioration of superconducting properties due to heating temperature of conventional La-based oxide superconductors, has a high critical temperature, and is highly stable, capable of causing a sharp superconducting transition even at a wide range of heating temperatures. La-Ba-Ca with excellent properties
-Cu oxide superconductor.

(Disclosure of the invention) In order to achieve the above object, the present invention
, characterized in that the molar ratio of Ca and Cu is 1:1:1:3 or something similar thereto, or a
-Ba-Ca-Cu oxide superconductor is provided.

In addition, in this invention, especially raw materials (:, a C
The present invention also provides a La-Ba-Ca-Cu oxide superconductor which is produced by blending Os or CaO and heating to 900°C or higher.

Among the La-based oxide superconductors known so far, L a B a 2Cu l Ot-y has a higher critical temperature than YBa2C
It has a perovskite structure similar to u and 07-y, but its superconducting properties are extremely unstable with respect to heating temperature. Although research has been conducted to stabilize the superconducting properties of L a B at Cu s O□-7, such stabilization has not yet been achieved.

For example, the divalent ion Ba20 is converted into the equivalent 3r2
A method of substituting with + was attempted, but the critical temperature of LaBa5rCus 07-F obtained by this method was lower than that of LaBa2Cult-.
Two types of superconducting phases occur in 5rCuOy-y.

In contrast, this invention was completed as a result of intensive studies aimed at stabilizing the superconducting properties of La Ba 2 Cu s 07-y, which has a high critical temperature among La-based oxide superconductors. It is something.

In other words, by mixing Ca into the La-Ba-Cu oxide superconductor, the correlation between resistivity and temperature change shows a metallic deformation and a sharp superconductor even within a wide heating temperature range. The critical temperatures of the La-Ba-Ca-Cu oxide superconductors that caused conduction transition and were produced at each heating temperature were 74 or higher, which is an extremely high critical temperature for a La-based oxide superconductor. , and the critical temperature difference between each superconductor was within a few degrees, which is an extremely good result.

Based on this knowledge, further investigation was conducted and La.

A La-Ba-Ca-Cu oxide superconductor made of Ba, Ca, and Cu having the same or similar molar ratio of 1:1:1:3 has a high critical temperature and is a highly stable superconductor. The present invention was completed based on the discovery that the present invention has the following characteristics.

The La-Ba-Ca-Cu oxide superconductive S body of this invention is
It can be manufactured by mixing and sintering oxides of each element and various salts.

Particularly preferably, it is produced by blending CaCO5 or CaO as a raw material and heating it to 900°C or higher.

The molar ratio of La, Ba, Ca and Cu is 1:1:1:3
The composition shall be the same or similar to this.

(Examples 1 to 4) The molar ratio of La, Ba, Ca and Cu is 1:1:1=3
La2o1, BaCO5 so that.

Ca COs and CuO were weighed, pulverized and mixed in an agate pot, calcined in oxygen at 900° C. for 10 hours, and further pulverized and mixed. After molding into berets, it is divided into four types of samples, each of which is heated at approximately 900°C to 1050°C in an oxygen stream.
℃ for 10 hours at approximately 50 degree intervals. Thereafter, it was gradually cooled at a temperature decreasing rate of -80°C/hr.

Each oxide superconductor having a composition of LaBaCaCu5Oa with a molar ratio of La, Ba, Ca and Cu of 1:1:1:3 produced at temperatures of 890°C, 950°C, 1ooo°C and 1050°C. The specific resistance was measured. Figure 1 shows the results.

As is clear from this Figure 1, the heating temperature is approximately 900℃.
Even though the resistivity varies over a wide range from °C to 1050 °C, the temperature change in resistivity is metallic in all samples, and moreover, a sharp superconducting transition occurs. Moreover, even in this wide range of heating temperatures, the critical temperature of each oxide superconductor having the composition of LaBaCaCu50y is as high as 74 degrees, and the temperature difference is only a few degrees at most. As is clear from the comparison with the comparative example described below, La-Ba-Ca-Cu oxide superconductor has an extremely high critical temperature and is highly stable against heating temperature. I was able to get a body.

FIG. 2 shows, as a comparative example, a conventional L a B a2 Cu s 07-11 oxide superconductor produced by heat treatment under the same heating conditions and the same slow cooling conditions as in Examples 1 to 4. This figure shows the correlation between the specific resistance of the oxide superconductor and the temperature change.

As is clear from Fig. 2, for those heat-treated at 1050°C, the temperature change in resistivity is metallic, showing a relatively sharp superconducting transition, and the critical temperature is around 70°C. However, in those heat-treated at temperatures other than 1050° C., the temperature change in resistivity becomes semiconductor-like, and the critical temperature is also significantly lowered, resulting in deterioration of superconducting properties.

Of course, the present invention is not limited to the examples shown above, and even if a similar composition and appropriate raw material are used, La-Ba-C which has a similar high critical temperature and high stability can be used.
An a-Cu oxide superconductor can be obtained.

(Effects of the Invention) As explained in detail above, the present invention makes it possible to obtain a La-Ba-Ca-Cu oxide superconductor that has a high critical temperature and is extremely stable against heating temperatures. can. This can greatly contribute to the practical application of La-based oxide superconductors.

[Brief explanation of the drawing]

FIG. 1 is a correlation diagram illustrating the temperature change in resistivity of LaBaCaCuO, an oxide superconductor of the present invention. FIG. 2 is a correlation diagram showing a temperature change in resistivity of a conventional LaBa2Cus 07-7 oxide superconductor. Figure 1

Claims (2)

[Claims] (1) The molar ratio of La, Ba, Ca and Cu is 1:1:
A La-Ba-Ca-Cu oxide superconductor characterized by a ratio of 1:3 or something similar thereto. (2) Add CaCO_3 or CaO to the raw materials and
The La-Ba-Ca-Cu oxide superconductor according to claim 1, which is produced by heat treatment at 0°C or higher.