Oxide superconductor and manufacturing method thereof via HIP an

Details Oxide superconductor and manufacturing method thereof via HIP an Oxide superconductor and manufacturing method thereof via HIP an

1992-07-08

1994-06-07

Walsh, Donald P.

Superconductor technology: apparatus, material, process

High temperature , per se

Copper containing

505725, 505742, 505491, H01B 1200, B22F 314

Patent

active

053187458

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a method of manufacturing an oxide superconductor, and more particularly to a method of manufacturing an oxide superconductor having a composition expressed by formula La.sub.2-X Sr.sub.X CaCu.sub.2 O.sub.6 (O<x.ltoreq.0.6).


BACKGROUND ART

One of oxide superconductors having compositions expressed by formula La.sub.2-X Sr.sub.X CaCu.sub.2 O.sub.6, which has a composition of La.sub.1.6 Sr.sub.0.4 CaCu.sub.2 O.sub.6, is manufactured by a known method. In the method, predetermined raw materials such as nitrate, oxalate, and oxide are mixed to form a mixture having a predetermined composition, and then the mixture is preliminarily burned in a flow of oxygen at 900.degree. C. for 40 hours. Thereafter, the mixture is sintered in the same atmosphere at 925.degree. C. for 72 hours. The resultant sintered body is received in a cooled quartz tube, and then sealed in an airtight manner. This tube is heated at 970.degree. C., thereby making a pressurized atmosphere of 20 atm (i.e., 2 MPa) by using thermal expansion of oxygen condensed at the time of cooling the tube. The sintered body is kept in the pressurized atmosphere for 48 hours, and then is cooled at 850.degree. C., 750.degree. C., 650.degree. C. and 500.degree. C., successively, in units of five hours. Through these steps, a superconductor having a critical temperature of 50K or more is obtained (see R. J. Cava, Nature Vol. 345 (1990), pp. 602-604).
In the above-described method of manufacturing a superconductor, only a single manufacturing condition is disclosed, under which steps from the preliminary burning to the treatment in a pressurized atmosphere are performed. Further, the composition which the method can make superconductive is limited to La.sub.1.6 Sr.sub.0.4 CaCu.sub.2 O.sub.6, and hence any other composition (i.e., wherein the value of the Sr content x differs from that of the former composition) cannot have superconductivity.
In addition, in a case where a superconductive ceramic is produced by the above method, at least as long as 223 hours are required for performing the steps from the preliminary burning to the treatment in a pressurized atmosphere. Also, since a quartz tube is used for receiving a sintered body in an airtight manner, a batch of composite is greatly limited. Since the treatments are performed under only a single manufacturing condition, temperatures and pressures must be controlled with accuracy.


DISCLOSURE OF INVENTION

This invention has been made to solve the above problems, and provides a method of manufacturing, at a temperature and under a pressure within respective wide ranges, a superconductor from an oxide, which has a composition expressed by formula La.sub.2-X Sr.sub.X CaCu.sub.2 O.sub.6 and falling within a wide range of 0<X.ltoreq.0.6, thereby shortening the manufacturing time and increasing the amount of products.
The method of the invention which is for manufacturing an oxide superconductor having a composition expressed by formula La.sub.2-X Sr.sub.X CaCu.sub.2 O.sub.6 (0<X.ltoreq.0.6), comprising the steps of: preliminarily burning a raw powder having a desired composition, and sintering the powder to obtain a sintered body; and subjecting the sintered body to hot isostatic pressing at a temperature falling within a range of from 940.degree.-1600.degree. C. under a total pressure of 10 MPa or more and an oxygen partial pressure of 2 MPa or more. This method provides an oxide superconductor having a composition expressed by formula La.sub.2-X Sr.sub.X CaCu.sub.2 O.sub.6 (0<X.ltoreq.0.6), containing Ca.ltoreq.0.25 and Sr.ltoreq.0.15 in 2a sites, and La.ltoreq.0.2 and Sr.ltoreq.0.2 in 4e sites, and having a superconductive critical temperature of 50K or more. The reason why X is limited to a value satisfying 0<X.ltoreq.0.6 will be explained. If X= 0, that is, if the invention is applied to an oxide having a composition of La.sub.2 CaCu.sub.2 O.sub.6, the oxide will not provide superconductivity. Similarly, if X<0.6, i.e., if the invention is applie

REFERENCES:
Hoi et al "Superconductivity & Its Applications", (1988), Elsevier Science Publishing Co., Ltd., B. C. Hendrix et al, Hot Isostatic Pressing (HIP) of Oxide Superconductors, pp. 94-99.
Japanese Journal of Applied Physics, vol. 29, No. 9, (1990), pp. L1632-L1634, K. Kinoshita et al, "Preparation & Superconducting Properties of La.sub.2-x (Ca.sub.1-y Sr.sub.y).sub.1+x Cu.sub.2 O.sub.6-x/2+.delta. ", pp. L1632-L1634.
Sakurai et al., Physica 174, (1991), 187.
Nature, vol. 345, No. 6276 (1990), R. J. Cava et al Superconductivity at 60K in La.sub.2-x Srx Ca Cu.sub.2 O.sub.6 : the simplest double-layer cuprate:, pp. 602-604.
"Hot Isostatic Pressing (HIP) for the Densification of Oxide Superconductors," Tien et al. MRS: High Temperature Superconductors II, Apr. 1988.

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