Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – Coating
Reexamination Certificate
1999-06-04
2001-04-17
Kopec, Mark (Department: 1751)
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
Coating
C505S475000, C505S731000, C505S732000, C505S816000
Reexamination Certificate
active
06218341
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a high temperature superconductor. More specifically, it relates to a superconductor usable at the temperature of liquid nitrogen or a higher temperature, and a superconductor usable at the temperature of liquid nitrogen or a higher temperature, being low in anisotropy, and having a high critical current density, and a process for their preparation.
2. Description of the Prior Art
Known copper oxide superconductors having superconducting transition temperatures, Tc's, of 110K or more are Tl and Hg type copper oxide superconductors. These copper oxide superconductors have high Tc values, but they contain harmful and rare elements such as Tl or Hg. Thus, they posed marked problems, such as the necessity for anti-pollution measures, the need for cost reduction, and difficulty in securing such rare resources.
With those conventional superconductors, let the coherence length in the intrafacial direction of the CuO
2
plane (ab plane) in its crystal structure be &xgr;
ab
, the coherence length in a direction perpendicular to the CuO
2
plane (c-axis direction) be &xgr;
c
, and the anisotropy &ggr; of the superconducting properties be expressed as &xgr;
ab
/&xgr;
c
. Then, &ggr;=5 for the composition YBa
2
Cu
3
O
7
-y with the lowest anisotropy, and this value was considerably high. Thus, those conventional oxide superconductors have had short coherence lengths in the c-axis direction perpendicular to the CuO
2
plane, which, in turn, have made critical current densities under high temperature, high magnetic field conditions small. These facts have been an obstacle to their practical use.
SUMMARY OF THE INVENTION
This invention has been accomplished in the light of the foregoing situations, and is aimed at resolving the aforementioned harmfulness, high anisotropy of superconducting properties, short coherence lengths, and decreases in current densities under high magnetic field conditions.
In other words, an object of the present invention is to provide a high temperature superconductor free from harmful elements or low in their content, and having a superconducting transition temperature, Tc, of 110 K or more.
Another object of the present invention is to provide a high temperature superconductor having, in addition to the above-described advantages, a large coherence length in the c-axis direction, a high current density under a high magnetic field, and low anisotropy.
Still another object of the present invention is to provide a process for preparing such high temperature superconductors.
To solve the aforementioned problems, the present invention uses an oxide of the alkaline earth metal element Ba, Sr or Ca with copper as a matrix, and adds a monovalent alkali metal element or Cu, Ag or Au, or divalent Cu, Hg, Pb or Cd, or trivalent Y or lanthanum elements for introduction of a carrier to form a layered copper oxide, thereby realizing a high temperature superconductor having a superconducting transition temperature, Tc, of 110 K or more.
The present invention also uses an oxide of the alkaline earth metal element Ba, Sr or Ca with copper as a matrix, and adds various elements for introduction of a carrier and stabilization of the structure to form a layered copper oxide with as short a c-axis as possible, thereby realizing a low anisotropy, high temperature superconductor having a superconducting transition temperature, Tc, of 110 K or more, and low anisotropy of superconducting properties.
The above-mentioned high temperature superconductor or low anisotropy, high temperature superconductor is prepared by use of a non-equilibrium method such as high pressure synthesis, hot pressing, HIP (high temperature isostatic processing), sputtering or laser abrasion. The target in sputtering may be either a sintered material of the same composition as a film to be produced, or those targets for the respective elements which are to be laminated for atomic layers. Sputtering or laser abrasion is performed, for example, using an SrTiO
3
(100 plane) substrate at a substrate temperature of 300 to 600° C. and an oxygen partial pressure of 0.001 to 1 Torr.
That is, the high temperature superconductor according to the present invention is characterized by having a composition expressed as the following formula (1)
MAe
2
Ca
x−1
Cu
x
O
y
where M is at least one member selected from the group consisting of monovalent ions of Cu, Ag and Au, divalent ions of Cu, Hg and Pb, and trivalent Ions of Tl, Bi, Y and lanthanide elements, Hg or Tl does not exist singly, Ae is at least one of Ba and Sr, x=1 to 10, and y=2x to 2x+4,
having a layered crystal structure, and having a superconducting transition temperature, Tc, of 110 K or more.
The high temperature superconductor according to the present invention is characterized by having a composition expressed as the following formula (2)
(M,Ae)
3
Ae′
x−1
Cu
x
O
y
where M is at least one member selected from the group consisting of monovalent ions of Cu, Ag and Au, divalent ions of Cu, Hg and Pb, and trivalent ions of Tl, Bi, Y and lanthanide elements, Hg or Tl does not exist singly, Ae is a mixture of Ba and Sr, Ae′ is a mixture of Ba, Sr and Ca, x=1 to 10, and y=2x to 2x+4,
having a layered crystal structure, and having a superconducting transition temperature, Tc, of 110 K or more.
The low anisotropy, high temperature superconductor of the present invention is characterized by having a composition expressed as the following formula (3)
Cu
1−z
M
z
Ae
2
Ca
x−1
Cu
x
O
y
where M is at least one member selected from the group consisting of monovalent ions of Li, Na, K, Rb, Cs, Ag and Au, divalent ions of Hg, Cd and Pb, trivalent ions of Tl, Bi, Y and lanthanide elements, and polyvalent ions of Cr, Mn, Fe, Co, Ni, Mo, Tc, Ru, Rh, Pd, W, Re, Os, Ir and Pt, Ae is at least one of Ba, Sr and Ba
1−w
Sr
w
, x=1 to 10, and y=2x+1 to 2x+4, z=0 to 0.5, and w=0 to 1.0,
having a layered crystal structure, and having a superconducting transition temperature, Tc, of 110 K or more, and by being constituted such that when letting &xgr;
ab
denote the coherence length in the intrafacial direction of the CuO
2
plane (ab plane) in the crystal structure, and &xgr;
c
the coherence length in a direction perpendicular to the CuO
2
plane (c-axis direction), the anisotropy &ggr; of the superconducting properties, expressed as &xgr;
ab
/&xgr;
c
, is 5 or less.
In the formula (3), it is preferred that Ae is Ba, z=0 to 0.3, and x=2 to 6. Further preferably, the low anisotropy, high temperature superconductor has a composition expressed substantially as CuBa
2
Ca
3
Cu
4
O
12−n
where n=0 to 4.
In the formula (3), it is also preferred that M is Re, Ae is Ba, and x=2 to 6. Further preferably, the low anisotropy, high temperature superconductor has a composition expressed substantially as (Cu,Re)Ba
2
Ca
3
Cu
4
O
12−n
where n=0 to 4.
In the formula (3), it is also preferred that M is Ag, Ae is Ba, and x=2 to 6. Further preferably, the low anisotropy, high temperature superconductor has a composition expressed substantially as (Cu,Ag)Ba
2
Ca
3
Cu
4
O
12−n
where n=0 to 4.
In the formula (3), it is also preferred that M is Ag, Ae is Sr, and x=2 to 6. Further preferably, the low anisotropy, high temperature superconductor has a composition expressed substantially as AgSr
2
Ca
3
Cu
4
O
12−n
where n=0 to 4.
The process of the present invention is a process for preparing the above-described high temperature superconductor or low anisotropy, high temperature superconductor, which comprises mixing the starting powders to form a mixture of a desired composition, and subjecting the powder mixture to a high pressure, high temperature synthesis involving a pressure of 100 kg/cm
2
to 100,000 kg/cm
2
, and a temperature of 300 to 1,300° C.
In the above process, the starting powders may be powders formed by pulv
Hirabayashi Masayuki
Ihara Hideo
Iyo Akira
Agency of Industrial Science and Technology
Frank Robert J.
Kopec Mark
Venable
Wells Ashley J.
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