Superconductor fabrication
A seed crystal for the fabrication of a superconductor is grown from a rare-earth oxide having the basic formula X w Z t Ba x Cu y O z , X comprising at least one rare-earth element and Z being a dopant which raises the peritectic decomposition temperature (T p ) of the oxide. In a preferred embodiment, the dopant is Mg. Use of this rare-earth oxide material for seed crystals increases the temperature at which cold-seeding can be performed and thus enables the growth of a wider range of bulk superconductor materials by this process.
1. A method of fabricating a superconductor of predetermined grain orientation comprising the steps of;
selecting a superconductor material;
selecting a seed crystal grown from a rare-earth oxide having the basic formula (RE) w Z t Ba x Cu y O z ;
where (RE) comprises at least one rare earth element;
where w is in the range 1 to 4, x is in the range 1 to 6, y is in the range 1 to 6 and z is in the range 3 to 20; and
Z is a dopant which raises the peritectic decomposition temperature (T p ) of the oxide, in which Z comprises Mg and in which the rare-earth oxide contains less than 40% w/w of Mg; and,
arranging the seed crystal in contact with the superconductor material in a desired crystallographic orientation such that, during processing, grain growth in the superconductor material is initiated in a predetermined orientation.
2. A method according to claim 1 in which the superconductor material comprises a rare-earth barium copper oxide of the general formula X a Ba b Cu c O d ;
where X comprises at least one rare-earth element.
3. A method according to claim 2 , in which
X comprises at least one of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
4. A method according to claim 2 , in which;
a is in the range 1 to 4,
b is in the range 1 to 6,
c is in the range 1 to 6, and
d is in the range 3 to 20.
5. A method according to claim 4 , in which a is in the range 1 to 3.
6. A method according to claim 4 , in which b is in the range 2 to 4.
7. A method according to claim 4 , in which c is in the range 1 to 3.
8. A method according to claim 4 , in which d is in the range 6 to 8.
9. A method according to claim 1 in which the selected seed crystal has a higher melting point than the selected superconductor material.
10. A method according to claim 1 , in which the selected seed material is iso-structural with the selected superconductor material.
11. A method according to claim 1 , in which the superconductor material comprises excess Ba, enabling processing of the superconductor material in air.
12. A superconductor fabricated by a method according to claim 1 .
13. A method according to claim 1 , in which (RE) comprises at least one of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
14. A method according to claim 1 , in which t is in the range of 0.01 to 2.
15. A method according to claim 1 , in which
w is in the range 1 to 3, and/or
x is in the range 2 to 4, and/or
y is in the range 2 to 6, and/or
z is in the range 6 to 8, and/or
t is in the range 0.5 to 1.