Superconducting composition Tl.sub.2 Ba.sub.2 CuO.sub.6+x and process for manufacture

DETAILED DESCRIPTION OF THE INVENTION The superconducting compositions of this invention comprises a crystalline phase with the formula Tl.
sub.
2 Ba.
sub.
2 CuO.
sub.
6+x wherein x is from 0 to about 0.
5.
The superconducting composition can be prepared by the following process.
Quantities of the oxide reactants Tl.
sub.
2 O.
sub.
3, BaO.
sub.
2 and CuO are chosen with the atomic ratio of Tl:Ba:Cu of a:b:1, wherein a and b are each about 1/2-2, and are mixed, for example, by grinding them together in a mortar.
The mixed powder may then be heated directly or it can be first formed into a pellet or other shaped object and then heated.
The crystalline phase of this invention is produced only when the atmosphere in which the reactants are heated is carefully controlled.
One way to control the atmosphere is to place the reactants in a tube made of a non-reacting metal such as gold and then seal the tube by welding it shut.
The sealed tube is then placed in a furnace and heated at about 850.
degree.
C.
to about 900.
degree.
C.
for about 3 to about 12 hours.
The power to the furnace is then turned off and the tube is permitted to cool in the furnace to ambient temperature, about 20.
degree.
C.
The tube is then removed from the furnace and opened and the product comprised of the black crystalline phase recovered.
The compositions prepared in this manner exhibit the onset of superconductivity above 90 K.
In order to produce a composition of this invention that is substantially single phase it is desirable to react quantities of the oxide reactants Tl.
sub.
2 O.
sub.
3, BaO.
sub.
2 and CuO chosen with the atomic ratio of Tl:Ba:Cu of 2:2:1.
The composition has less material of phases other than Tl.
sub.
2 Ba.
sub.
2 CuO.
sub.
6+x as the ratio of Tl:Ba:Cu nears the stoichiometric ratio 2:2:1.
In order to produce single crystals with at least 2 dimensions greater than a millimeter it is desirable to have excess CuO present and it is therefore desirable to have a and b as defined above in connection with the Tl:Ba:Cu ratio to be each less than 2