JPH02129027A - Oxide superconductor composition and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title composition with low content of toxic Tl, capable of continuously controlling its superconductivity transition temperature and also giving sharp superconductivity transition by mutually mixing each powder of Tl2O3, BaO, CaO, Y2O3 and CuO at specified ratio followed by press forming and then by heat treatment of the resulting form at specified temperature. CONSTITUTION:Each powder of Tl2O3, BaO, CaO, Y2O3 and CuO is weighed so as to result in a composition ratio of the formula (0.1<=x<=0.8) followed by mutual mixing. The resultant mixture is then put to press forming followed by heat treatment of the resulting form at 875-915 deg.C, thus obtaining the objective oxide superconductor composition of the formula. This composition can continuously control its superconductivity transition temperature through controlling the x value and also gives sharp superconductivity transition; therefore, being suitable in the form of e.g., a thermosensor. Wrapping the press form with a gold leaf in sintering will further improve the superconducting characteristics of said composition.

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 B1-3r-Ca-Cu-
0 series, 120 grade Tl-Ba-Ca-Cu-○ 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.

(Problems to be Solved by the Invention) The following two problems are to be solved by the present invention.

First of all, TI-based superconductors, the current amount of which is known to have a high superconducting transition temperature Tc, are difficult to handle because their main constituent element T1 is highly toxic. . However, for example, in T12Ba2Ca2Cu301o, which is known to have a Tc of 120,
Approximately 40% of the total weight is occupied by the T1 element, and great care is required in the preparation of the substance. If Tc
If the TI content can be reduced without lowering the TI content, the risks associated with the manufacturing work can be reduced, and the rare element T1 can also be saved.

Second, Tc is inherent to a substance and always remains approximately constant 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 it were possible to obtain a material whose total volume undergoes a sharp superconducting transition at a given temperature, it would open up many applications, including temperature sensors.

Therefore, the object of the present invention is to provide an oxide superconductor composition that reduces the T1 content in a Tl-based superconductor compared to conventional ones and exhibits a sharp superconducting transition at any temperature below 116°C, and an oxide superconductor composition thereof. The object of the present invention is to provide a manufacturing method.

(Means for solving the problems) The present invention provides TIBaz (Cat-xYx) 3cu40y
With the composition formula 0.1≦x≦0.8, from 875℃
Tc can be changed continuously by sintering at 915°C. The Tl content is about half that of the conventional one,
It has also been discovered that the properties of the composition can be further improved by wrapping the press-formed body with gold foil during sintering.

(Function) The conventional superconductor T12Ba2Ca2Cu3010 has 1
It transitions to superconductivity at around 20 years old. Of the total weight of this composition, 36% is the weight of T1. However, for example, TlBa
The composition 2(Cao9Y0.1)3 Cu4Oy is 1
No. 14 shows a sharp superconducting transition, but the weight of Tl is only 19% of the total weight. As the value of X increases, the transition temperature decreases, but the sharpness of the transition remains unchanged, and it was confirmed that approximately 80% of the total volume is in a superconducting state after the transition.

(Example) The present invention will be specifically described below with reference to Examples. Thallium oxide (T120) with a purity of 99.9% or more is used as a starting material.
3), barium oxide (Bad), calcium oxide (Ca
b), yttrium oxide (Y2O2), cupric oxide (C
ub), and each was weighed so as to have the blending ratio shown in Table 1. Next, after mixing the weighed ingredients thoroughly in a mortar,
A pressed body of 5 mm x 10 mm x 1 mm was created by pressing. This pressed body was wrapped in gold foil and placed in an oxygen atmosphere for 87 days.
Sintering was performed at 5°C to 915°C for 3 to 10 hours.

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 zero. If the press-formed body is fired without being wrapped in gold foil, T1 disappears during firing, resulting in a compositional deviation and a slight decrease in volume fraction. Regarding the range of X, if X is less than 0.1, the superconducting properties hardly change, and therefore it is inappropriate for the purpose of the present invention, which uses Tc for control. Moreover, if X exceeds 0.8, superconductivity will not be exhibited from room temperature to 462K, which is not practical. Regarding the sintering temperature, if the temperature is lower than 875°C, TlBa2(Ca1-xYx)Cu20° or TlBa2(Ca1-xYx)Cu20°, which has a shorter crystal period than this composition,
2(Ca1-xYx)2Cu30. Since a mixture with Tc is formed, the volume fraction exhibiting Tc of 100 or more becomes low. Moreover, when the temperature exceeds 910° C., decomposition occurs and the volume fraction decreases.

Table 1 (Effects of the Invention) The composition of the present invention has a lower T1 content than conventional materials, and even if Tc is continuously changed depending on the value of X, it exhibits a sharp superconducting transition. It is extremely practical.

Claims (2)

[Claims] 1. Tl_1Ba_2(Ca_1_-_xY_x)_3
An oxide superconductor composition expressed as Cu_4O_y, characterized in that the oxide superconductor composition is in the range of 0.1≦x≦0.8. 2. Tl_2O_3, BaO, CaO, Y_2O_3,
A method for producing an oxide superconductor composition, which comprises mixing CuO powder to have the composition set forth in claim 1, press-molding, and then heat-treating at a temperature range of 875°C to 915°C. .