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 hulk superconductor materials by this process.
1. A seed crystal for the fabrication of a superconductor, the seed crystal grown from a rare-earth oxide having the basic formula X w Z t Ba x Cu y O z ;
where X 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.
2. A seed crystal according to claim 1 , 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.
3. A seed crystal according to claim 1 , in which
t is in the range 0.01 to 2.
4. A seed crystal according to claim 3 , 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.
5. A seed crystal according to claim 1 , in which the addition of the dopant does not alter the crystal structure of at least a matrix portion of the crystal.
6. A seed crystal according to claim 1 , when used in the fabrication of a rare-earth copper-oxide superconductor.
7. A seed crystal according to claim 1 , grown under an oxygen-rich or pure oxygen atmosphere.
8. A rare-earth oxide material having the basic formula (RE) w Z t Ba x Cu y O z ;
where (RE) comprises at least one of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu;
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 material contains less than 40% w/w/of Mg.
9. A material according to claim 8 , in which
t is in the range 0.01 to 2.
10. A material according to claim 9 , 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.
11. A material according to claim 8 , in which the addition of the dopant does not alter the crystal structure of at least a matrix portion of the crystal.
12. A seed crystal grown from a material according to claim 8 , preferably grown in an oxygen-rich, or pure oxygen, atmosphere.