JPH02255529A - Oxide superconductor composition and production thereof - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductor compsn. causing quick superconductivity transition at an arbitrary temp. of >=40K by using an oxide having a specified compsn. contg. Tl, Ba, La and Cu. CONSTITUTION:This oxide superconductor compsn. is represented by a general formula TlBa1+xLa1-xCuOy (where -0.2<=x<=0.6) and is produced as follows: powders of Tl2O3, RaO, La2O3 and CuO are mixed so as to prepare a mixture having a compsn. represented by the general formula and the mixture is press- molded and heat-treated at 800-910 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to oxide superconducting materials used in various superconducting application devices and superconducting elements.

(Prior Art) Superconducting materials currently in practical use include metal/alloy superconducting materials and compound superconducting materials.

Superconducting materials are used to make electronic devices such as Josephson elements and coils for superconducting magnets, and are particularly useful for 5QUID and precision measurement that utilize the high sensitivity, high precision, and low noise properties of Josephson junctions. In addition to applications in electronic computers, Josephson junctions are expected to have applications that focus on their high-speed response and low power consumption.

It is desired that the superconducting transition temperature Tc of the superconducting material is as high as possible, but La-Ba-Cu with a Tc of 30
Since the discovery of -0-based oxide superconductors, Ba-Y
-Cu-0 series, 110 grade B1-8r-Ca-Cu-
0 series, 120 grade Tl-Ba-Ca-Cu-0 series, etc. have been discovered one after another. The discovery of a material with a Tc that far exceeds the temperature of liquid nitrogen has raised expectations for its use as a practical material.

(To be solved by the invention) The superconducting transition temperature Tc is unique to a substance, and is always a substantially constant value when no magnetic field is applied. Changing the composition ratio of the constituent elements apparently lowers the superconducting transition temperature, but this is because the volume fraction that transitions to superconductivity decreases and the transition slows down. If we can obtain a material whose total volume undergoes a sharp superconducting transition at a given temperature, it will open up many applications, including temperature sensors.

Therefore, an object of the present invention is to provide an oxide superconductor composition that exhibits a sharp superconducting transition at any temperature below 40°C, and a method for producing the same.

(Means for Solving the Problems) The present invention has a composition formula of TlBa1.4-xLal-xCuOy and a composition of 10, 2≦x0.6 at 800°C to 91°C.
It was discovered that Tc can be changed continuously by sintering at 0°C, and that the properties of the composition can be further improved by wrapping the press-formed body with gold foil during sintering.

(Function) For example, the compositions TlBa1.3Lao and 7CuOy exhibit a sharp superconducting transition at 39°C, and the composition TlBa1.1La□0gcuoy exhibits a sharp superconducting transition at 30°C, and after the transition, almost the entire area becomes superconducting. It was confirmed that

(Example) The present invention will be specifically described below with reference to Examples. Thallium oxide (Ti2O) with a purity of 99.9% or more is used as a starting material.
3), barium oxide (Bad), lanthanum oxide (La2)
03) and cupric oxide (Cub) were used, and each was weighed so as to have the compounding ratio shown in Table 1. Next, mix the weighed ingredients thoroughly in a mortar and press to make 5mm x 10mm.
A press body with a size of 1 mm was created. This pressed body was fired at 800°C to 910°C for 1 to 10 hours in an oxygen atmosphere. Some samples were wrapped in gold foil and fired.

The resistivity and superconducting volume fraction of the sintered bodies in the range shown in Table 1 were measured to evaluate the superconducting properties.

Resistivity measurement was performed by a DC 4-terminal method. The electrodes were sputtered with gold, and the leads were attached using tin-plated copper wire.

The superconducting volume fraction was determined by AC magnetic susceptibility measurement.

AC magnetic susceptibility was measured by placing a sample in a coil and measuring the change in L of the coil. The volume fraction was calculated by setting ΔL at 4.2K of lead having the same volume and shape as 100. Resistance measurements were carried out from room temperature to the temperature at which resistance becomes 0, and magnetic susceptibility measurements were carried out from room temperature to 4.2K.

Table 1 shows the blending ratio and the proportion of the superconducting phase at the critical temperature of 4.2 at which the resistance becomes O. If the press-formed body is fired without being wrapped in gold foil, TI disappears during firing, resulting in a compositional deviation and a slight decrease in volume fraction. Regarding the range of X, a range where X is less than -0.2 and where X is greater than 0.6 is inappropriate for the purpose of the present invention because superconductivity is not exhibited from room temperature to 4.2K. 80 for sintering temperature
If the temperature is below 0°C, the reaction will not proceed and excellent superconducting properties will not be obtained. Moreover, when the temperature exceeds 910° C., decomposition occurs and the volume fraction decreases.

Table 1 (Effects of the Invention) As shown in Table 1, the composition of the present invention continuously changes Tc depending on the value of It has a high value.

Claims (2)

[Claims] (1) TlBa_1_+_xLa_1_-_xCuO_
An oxide superconductor composition characterized in that, when expressed as y, it is in the range -0.2≦x≦0.6. (2) Tl_2O_3, BaO, La_2O_3, Cu
Production of an oxide superconductor composition characterized in that O powder is mixed to have the composition described in claim 1, press-molded, and then heat-treated in a temperature range of 800°C to 910°C. Method.