JPH0397621A - Oxide superconductor and production thereof - Google Patents

Abstract

PURPOSE:To increase superconducting critical temp. and to reduce sintering temp. by substituting a specified alkali metal for part of Tl in a Tl-Ba-Ca-Cu oxide superconductor. CONSTITUTION:This oxide superconductor has a basic compsn. obtd. by partially substituting at least one kind of alkali metal (A) selected among K, Rb and Cs for Tl and represented by a formula (Tl1-yAy)mBa2-Can-1CunOx (where m is 1 or 2 and n is 1, 2 or 3). When this oxide superconductor is produced by sintering, a compd. of at least one kind of alkali metal selected among K, Rb and Cs is added at the time of mixing starting materials. This oxide superconductor has >125K critical temp. (Tc).

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to oxide superconductors used in Josephson devices, linear motors, etc. :
u IIOX (m=1.2, n=1.2.
3) A group of oxide high temperature superconductors represented by T l
sI3 atc arc u10x has the highest Tc of 125K among the existing oxides.These oxides have C
uO. ! = Multilayer structure force in which CaO is alternately stacked (Ba.
Even if a layered structure is formed through the O layer and the Tl2Os layer,
In Figure 4, an index representing the structure is also written for each structural diagram.For example, in Figure (f), 2223 has 2 Tl layers, 2 Ba layers, and C
This indicates that the a layer is 2 and the Cu layer is 3. It is generally believed that superconducting current flows in the CuO plane in these oxides, and as shown in the table, the number of CuO layers n
The larger the value, the higher the critical temperature Tc (t Table Critical temperature (K) of TlJaeCa++-+CunO+t) The larger the number of meters of the tOs layer, the higher the Tc. The current highest Tc is only 125K, and in order to put it into practical use at the actual liquid nitrogen temperature (77K), a slightly higher critical temperature is required. and ideally T
A thallium-based oxide with the highest Tc at present has a very complex phase diagram near its calcination temperature of 900°C, which is 125K or more.
Although it is difficult to burn out only the phase with Tc of
Since it is difficult to control the assembly, a simpler burning method has been awaited, and the present invention aims to solve the problems. Means for Solving the Problems The present invention provides a method that makes it easier to put it into practical use, and provides a simpler method for producing a single phase compared to the conventional method. Now, as a means to solve the above problems, the conventional Tl
sBapCan-+CunCl+(m=1.2,
n=1. 2. The present invention provides a material in which T1 of the oxide represented by 3) is partially replaced with an alkali metal such as K, Rb, or Cs, and a manufacturing method in which an alkali metal element is added when mixing raw materials during annealing. .

The critical temperature of a functional high-temperature superconductor is determined by the number of CuO layers as well as the nature of the oxide layers that sandwich the CuO layers.
When Tl is partially substituted with a monovalent alkali metal as in the present invention, compared to when no substitution is made, 1) Holes are more easily provided to the CuO layer.

2) The Tl*O* layer becomes more electrically positive.

Therefore, it is possible to raise the critical temperature, albeit slightly, and when an alkali metal is included in the structure, the melting point of the oxide generally decreases, making it possible to lower the sintering temperature.As a result, T] In this example, well-dried Tl*0*, CaaCuOs, BaCu02 powder was used as the raw material for the thallium-based oxide. Added nitrates of alkali metals and mixed them Calculated at 600 degrees for 2 hours or chemically analyzed to confirm that they did not contain nitrates Mixed these raw material powders used for Hon-yakkai in a predetermined ratio L , 400kg
This raw material powder pellet, which was formed into pellets using a press pressure of w/cm2, was wrapped in gold foil and baked in a vacuum-sealed L'K air furnace in a quartz tube at 6 different temperatures from 800 to 900 degrees for 24 hours. The alkali metal elements used were K, Rb, and Cs1. After cooling, the quartz tube was destroyed in a dry box and a superconducting property evaluation test was conducted. The results when 50% of various alkali metals were replaced. As shown in Figure 1,
Also, regarding K, we conducted many tests by changing the amount of K added and the burning time.We obtained knowledge about the optimal amount of alkali added and burning time.Figure 2 shows the results of Q when the amount of K replaced is changed.
Also, Fig. 3 shows the change in Tc when the firing time is changed.
As is clear from the results shown in Figure 1, where the temperature is below 0-6 Ωcm, when K, Rb, and Cs are added, the critical temperature increases by 3 to 10 degrees Celsius compared to conventional thallium-based oxide superconductors. It was found that the optimum incineration temperature was 900 to 910 °C for conventional thallium-based oxides that do not contain alkali metals, whereas the optimum firing temperature was 1,82
The temperature has dropped significantly from 0℃ to 860℃.9 Na, Li
These effects were not observed in the case of t. :O This is thought to be because if too much alkali metal is added, the oxide cannot maintain its original superconducting structure.
Furthermore, according to the results of powder X-ray diffraction conducted by varying the firing time, it was confirmed that a single layer was formed after about 20 hours, and when combined with the results shown in FIG. It was found that the method requires a short sintering time and that the instability of the assembly due to the dissipation of Tl203 etc. is reduced.4 Effects of the Invention According to the present invention, Tc oxidation exceeding Tel25K of the conventional Tl-based superconductor can be achieved. Since it is possible to obtain a physical superconductor, it will greatly contribute to the practical application of superconducting material devices.It will also make it easier to burn the material, so the manufacturing benefits will be immeasurable (1)

[Brief explanation of drawings]

Figure 1 shows the relationship between Tc and firing temperature of type K alkali metal additive; Figure 2 shows the relationship between the addition amount and critical temperature when K is added; Figure 3 shows the relationship between firing time and critical temperature. Figure 4 is a diagram of the crystal structure of a thallium-based oxide superconductor.

Claims (2)

[Claims] (1) An oxide superconductor represented by the basic composition formula ▲ Numerical formula, chemical formula, table, etc. available ▼ in which at least one alkali metal A among K, Rb, and Cs partially substitutes Tl. (2) In firing the oxide superconductor according to claim 1,
A method for producing an oxide superconductor, which comprises adding at least one kind of alkali metal compound among K, Rb, and Cs during mixing of raw materials.