JPH07102970B2 - Oxide superconductor composition and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an oxide superconducting material used in various superconducting application devices and superconducting elements.

(Prior Art) Materials that are currently in practical use as superconducting materials include metal / alloy-based superconducting materials and compound superconducting materials.
Superconducting materials are used to make electronic devices such as Shosefson elements and coils for superconducting magnets, and especially for SQUID and precision measurement utilizing the high sensitivity, high accuracy, and low noise of Josephson junctions. In addition to applications, it is expected to be applied to electronic computers that focus on the high-speed response and low power consumption of Josephson junctions.

The superconducting transition temperature Tc of the superconducting material is desired to be as high as possible, but since the discovery of the La-Ba-Cu-O-based oxide superconductor having a Tc of 30K, 90K-class Ba-Y-Cu- O type, 110K
Grade Bi-Sr-Ca-Cu-O system, 120K grade Tl-Ba-Ca-Cu-
O-types have been discovered one after another. The discovery of materials with Tc well above the liquid nitrogen temperature has further raised expectations as practical materials.

(Problems to be Solved by the Invention) The superconducting transition temperature Tc is unique to a substance and has a substantially constant value when no magnetic field is applied. When the composition ratio of the constituent elements is changed, the superconducting transition temperature apparently decreases, but this is because the volume fraction of transition to superconductivity decreases and the transition slows down. If we can obtain a substance that undergoes a superconducting transition with a sharp total volume at any temperature, we can open 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 an arbitrary temperature of 40 K or less, and a method for producing the same.

(Means for Solving Problems) The present invention has a composition formula of TlBa _{1 + x} La _1-x CuOy of −0.2 ≦ x0.6.
Tc can be continuously changed by sintering the composition of 800 ° C. to 910 ° C., and the properties of the composition can be further improved by wrapping the press-molded body with gold foil during sintering. It is something I found.

(Function) For example, the composition of TlBa _1.3 La _0.7 CuOy is 39 K, and the composition of TlBa _1.1 La
_{It was} confirmed that the composition of _0.9 CuOy showed a sharp superconducting transition at 30 K, and almost the entire volume was in the superconducting state after the transition.

(Example) The present invention will be specifically described with reference to the following examples. As a starting material, thallium oxide (Tl ₂ O ₃ ), barium oxide (BaO), lanthanum oxide (La ₂ O ₃ ) with a purity of 99.9% or more, second oxide
Copper (CuO) was used and weighed so that the compounding ratios shown in Table 1 were obtained. Next, the weighed materials were thoroughly mixed in a mortar and then pressed to prepare a pressed body of 5 mm × 10 mm × 1 mm. This pressed body is heated at 800 ° C to 910 ° C in an oxygen atmosphere for 1 hour.
Baked for ~ 10 hours. Some samples were wrapped in gold foil and fired.

The resistivity and the superconductor integral ratio of the sintered body within the range of Table 1 were measured to evaluate the superconducting property.

The resistivity was measured by the DC 4-terminal method. Gold was attached to the electrode by a sputtering method, and a tin-plated copper wire was used as a lead.

The superconductor volume fraction was determined by measuring the AC magnetic susceptibility.

The AC susceptibility was measured by putting a sample in the coil and measuring the change in L of the coil. The volume fraction was calculated assuming that ΔL of lead having the same volume and the same shape at 4.2K is 100. The resistance was measured from room temperature to the temperature at which the resistance became zero, and the magnetic susceptibility was measured from room temperature to 4.2K.

Table 1 shows the composition ratio and the ratio of the superconducting phase at the critical temperature of 4.2K at which the resistance becomes zero. When the press-molded body is fired without being wrapped with gold foil, Tl disappears during firing, resulting in compositional deviation and a slight decrease in volume fraction. For the range of x, x
Is less than -0.2 and x is greater than 0.6, superconductivity is not exhibited from room temperature to 4.2K, which is unsuitable for the purpose of the present invention. If the sintering temperature is less than 800 ° C, the reaction does not proceed and excellent superconducting properties cannot be obtained. Further, when the temperature exceeds 910 ° C, decomposition occurs, so that the volume fraction decreases.

(Effects of the invention) As shown in Table 1, the composition of the present invention continuously changes Tc depending on the value of x and exhibits a sharp superconducting transition.
It is a very practical material as a superconducting material.

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Claims (2)

[Claims] 1. When expressed as TlBa _{1 + x} La _1-x CuOy, −0.
An oxide superconductor composition characterized by being in the range of 2 ≦ x ≦ 0.6. 2. Tl ₂ O ₃ , BaO, La ₂ O ₃ and CuO powders are mixed so as to have the composition described in claim 1, press-molded, and then the temperature range from 800 ° C. to 910 ° C. A method for producing an oxide superconductor composition, which comprises heat-treating.