High temperature superconductors having planar magnetic flux pinning centers and methods for making the same
Superconductor wires or layers having improved properties and methods for making the same are described. The superconducting layer includes a rare earth element-alkaline earth element-transition metal oxide having an average stacking fault density that is greater than about 0.01 nm −1 , wherein two or more rare earth cations form the rare earth element. To form the superconductor layer of the present invention, a layer having a rare earth element-alkaline earth element-transition metal oxide substantially in a first crystal structure can be provided to a substrate where two or more rare earth cations form the rare earth element. The layer can then be heated at a temperature that is greater than 550° C. under oxidizing conditions to form a high-temperature superconducting layer substantially in a second crystal structure.
1. A method for forming a superconducting layer, the method comprising:
providing on a substrate a layer comprising a rare earth element (RE)-alkaline earth-transition metal oxide substantially in a first crystal structure, the RE comprising two or more rare earth cations; and
heating the layer at a temperature that is greater than 550° C. under oxidizing conditions to form a high-temperature superconducting (HTS) layer substantially in a second crystal structure,
wherein the HTS material has an average stacking fault density that is greater than about 0.01 nm −1 and comprises a stoichiometric excess amount of the transition metal element.
2. The method as claimed in claim 1 , wherein RE is selected from the group consisting of yttrium, scandium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and mixtures thereof.
3. The method as claimed in claim 1 , wherein the layer comprises (RE)Ba 2 Cu 3 O 7 -y, at least one of the RE being yttrium.
4. The method as claimed in claim 3 , wherein RE is selected from the group consisting of yttrium, scandium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, and mixtures thereof.
5. The method as claimed in claim 3 , wherein the first crystal structure is the tetragonal phase and the second crystal phase is the orthorhombic phase.
6. The method as claimed in claim 3 , wherein the stacking fault comprises YBa 2 Cu 4 O 8 -y type intergrowths.
7. The method as claimed in claim 1 , wherein the HTS material comprises a stoichiometric excess amount of at least one RE.
8. The method as claimed in claim 7 , wherein layer comprising a rare earth element (RE)-alkaline earth element-transition metal oxide substantially in a first crystal structure comprises nanosized precipitates incorporating a rare earth element.
9. The method as claimed in claim 7 , wherein the HTS material has a critical current density ratio, (Ic:H//ab)/(Ic:H//c), of at least 1.8, the ratio being the critical current density measured with magnetic field parallel to the ab-plane of the second crystal structure (Ic:H//ab) and the critical current density measured with magnetic field parallel to the c-axis of the second crystal structure (Ic:H//c).
10. The method as claimed in claim 1 , wherein the HTS material has a critical current density ratio, (Ic:H//ab)/(Ic:H//c), from about 1.2 to about 4, the ratio being the critical current density measured with magnetic field parallel to the ab-plane of the second crystal structure (Ic:H//ab) and the critical current density measured with magnetic field parallel to the c-axis of the second crystal structure (Ic:H//c).
11. The method as claimed in claim 1 , wherein the transition metal element is copper.
12. The method as claimed in claim 1 , wherein the HTS material has an average stacking fault density that is from about 0.015 nm −1 to about 0.085 −1 .
13. The method as claimed in claim 1 , wherein the heating the layer is carried out at a temperature not exceeding 1000° C.
14. The method as claimed in claim 1 , wherein the oxidizing condition comprises a substantially pure dry oxygen gas.
15. The method as claimed in claim 1 , wherein the substrate comprises nickel, silver, copper, zinc, aluminum, iron, chromium, vanadium, palladium, molybdenum, alloys thereof, and mixtures thereof.
16. The method as claimed in claim 1 , wherein the substrate is biaxially textured.
17. The method as claimed in claim 1 , wherein at least one buffer layer which comprises a metal oxide is disposed between the substrate and the layer comprising a rare earth element (RE)-alkaline earth-transition metal oxide.
18. The method as claimed in claim 17 , wherein the at least one buffer layer comprises LaAlO 3 , Y 2 O 3 , CeO 2 , or yttria-stabilized zirconia (YSZ).
19. The method as claimed in claim 17 , wherein the at least one buffer layer is an epitaxial buffer layer.
20. The method as claimed in claim 1 , wherein the layer in the first crystal structure is obtained by decomposing a layer comprising an oxyfluoride.
21. The method as claimed in claim 20 , wherein the layer comprising an oxyfluoride further comprises a metal fluoride.
22. The method as claimed in claim 21 , wherein the metal fluoride comprises barium fluoride.
23. A superconducting wire comprising:
a substrate having a superconducting layer disposed thereon, the superconducting layer comprising a rare earth element (RE)-alkaline earth element-transition metal oxide having an average stacking fault density that is greater than about 0.01 nm −1 , wherein RE comprises two or more rare earth cations and the superconducting layer comprises a stoichiometric excess amount of the transition metal element.
24. The superconducting wire as claimed in claim 23 , wherein RE is selected from the group consisting of yttrium, scandium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and mixtures thereof.
25. The superconducting wire as claimed in claim 23 , wherein the layer comprises (RE)Ba 2 2Cu 3 O 7-y , at least one RE being yttrium.
26. The superconducting wire as claimed in claim 25 , wherein RE is selected from the group consisting of yttrium, scandium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, and mixtures thereof.
27. The superconducting wire as claimed in claim 25 , wherein the superconducting material is substantially in an orthorhombic phase.
28. The superconducting wire as claimed in claim 25 , wherein the stacking fault comprises YBa 2 Cu 4 O 8-y type intergrowths.
29. The superconducting wire as claimed in claim 23 , further comprising a stoichiometric excess amount of at least one RE.
30. The superconducting wire as claimed in claim 29 , wherein the stoichiometric excess amount of at least one RE forms nanosized precipitates.
31. The superconducting wire as claimed in claim 30 , said superconducting wire having a critical current density ratio of at least 1.8, the ratio being the critical current density measured with magnetic field parallel to the ab-plane of the second crystal structure (Ic:H//ab) and the critical current density measured with magnetic field parallel to the c-axis of the second crystal structure (Ic:H//c).
32. The superconducting wire as claimed in claim 23 , said superconducting wire having a critical current density ratio from about 1.2 to about 4, the ratio being the critical current density measured with magnetic field parallel to the ab-plane of the second crystal structure (Ic:H//ab) and the critical current density measured with magnetic field parallel to the c-axis of the second crystal structure (Ic:H//c).
33. The superconducting wire as claimed in claim 23 , wherein the transition metal element is copper.
34. The superconducting wire as claimed in claim 23 , said superconducting wire having an average stacking fault density that is from about 0.015 nm −1 to about 0.085 nm −1 .
35. The superconducting wire as claimed in claim 23 , wherein the substrate comprises nickel, silver, copper, zinc, aluminum, iron, chromium, vanadium, palladium, molybdenum, alloys thereof, and mixtures thereof.
36. The superconducting wire as claimed in claim 23 , wherein the substrate is biaxially textured.
37. The superconducting wire as claimed in claim 23 , further comprising at least one buffer layer comprising a metal oxide disposed between the substrate and the superconducting layer.
38. The superconducting wire as claimed in claim 37 , wherein the at least one buffer layer comprises LaAlO 3 , Y 2 O 3 , CeO 2 , or yttria-stabilized zirconia (YSZ).
39. The superconducting wire as claimed in claim 37 , wherein the at least one buffer layer is an epitaxial buffer layer.
40. A superconducting layer produced by
providing a layer comprising a rare earth element (RE)-alkaline earth element transition metal oxide substantially in a first crystal structure;
heating the layer at a temperature that is greater than 550° C. under oxidizing conditions to form a high-temperature superconducting (HTS) material substantially in a second crystal structure; wherein
the RE comprises two or more rare earth cations; and
the HTS material has an average stacking fault density that is greater than about 0.01 nm −1 and comprises a stoichiometric excess amount of the transition metal element.