Superconductor technology: apparatus – material – process – High temperature devices – systems – apparatus – com- ponents,... – Superconductor next to layer containing nonsuperconducting...
Reexamination Certificate
1999-09-27
2004-04-06
Dunn, Tom (Department: 1725)
Superconductor technology: apparatus, material, process
High temperature devices, systems, apparatus, com- ponents,...
Superconductor next to layer containing nonsuperconducting...
C505S237000, C428S701000, C428S702000, C428S930000
Reexamination Certificate
active
06716795
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
(Not Applicable)
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to epitaxial metal oxide buffer layers on metal substrates and articles made therefrom. More specifically, the invention relates to a vacuum process for depositing epitaxial layers of oxides on biaxially-textured metal substrates and superconducting layers on the epitaxial layers, and articles made therefrom.
2. Description of Related Art
Epitaxial metal oxide buffer layers on substrates with crystalline, polycrystalline, or biaxially-textured metal surfaces are potentially useful where an electronically active layer is deposited on the buffer layer. The electronically active layer may be a superconductor, a semiconductor, or a ferroelectric material. For example, a biaxially-textured superconductor article to be used for power transmission lines has a multi-layer composition
10
, as in FIG.
1
.
Such deposited superconductor articles most commonly consist of a biaxially-textured metal surface
12
, a plurality of buffer layers
14
,
16
, and a superconducting layer
18
. The biaxially-textured metal surface
12
, most commonly formed from Cu, Ag, Ni, or Ni alloys, provides support for the superconductor article, and can be fabricated over long lengths and large areas. Epitaxial metal oxide buffer layers
14
,
16
comprise the next layers in the superconductor article. The buffer layers
14
,
16
are commonly formed from Y
2
O
3
or CeO
2
, and serve as chemical barriers between the metal surface
12
and the last layer, which is the superconducting layer
18
.
Current materials research aimed at fabricating improved high-temperature superconductor articles is largely focused on epitaxial growth of high-temperature superconducting layers on biaxially-textured metal surfaces. Superconducting articles with current densities (J
c
) in excess of 0.1 MA/cm
2
at 77 K have been achieved for epitaxial YBa
2
Cu
3
O
7
films on biaxially-textured Ni or Ni-based alloy surfaces with the use of certain epitaxial buffer layer constructs between the metal surface and the superconducting layer. In previous work, the synthesis of high-temperature superconductor layers capable of carrying a high (at least 0.1 MA/cm
2
at 77K) J
c
has required the use of complex, multilayered buffer architectures.
A biaxially-textured article can be defined as a polycrystalline material in which the crystallographic in-plane and out-of-plane grain-to-grain misorientations are small (typically less than 40 degrees) but finite (typically greater than 2 degrees). In order to realize a high-temperature superconducting layer, such as YBa
2
Cu
3
O
7
, possessing a J
c
greater than approximately 0.1 MA/cm
2
at 77K on a biaxially-textured metal substrate, the buffer layer architecture should be epitaxial relative to the metal substrate and crack-free. Most preferably, the grains of the buffer layer should be crystallographically aligned perpendicular to the plane of the metal substrate (c-axis oriented) and parallel to the plane of the metal substrate (a-b alignment).
Formation of superconductor articles with this orientation begins with the selection of the metal surface
12
. The crystallographic orientation of the metal surface
12
is preferably maintained in the buffer layers
14
,
16
and the superconducting layer
18
, to the maximum extent possible. Numerous conventional processes are currently being used to grow buffer layers
14
,
16
on a metal substrate
12
. These processes include vacuum methods, such as pulsed laser deposition, vapor deposition, and sputtering.
In addition to being epitaxial relative to the biaxially-textured metal surface, layers are preferably chemically compatible with both the metal surface superconductor, and mechanically robust so as to prevent microscopic crack formation in the high-temperature superconducting layer and the buffer layers. Prior to the present invention, buffer layers that met these objectives required multilayer combinations of various oxides. For example, CeO
2
has been used to nucleate an epitaxial (001) oriented oxide layer on a biaxially textured (100) Ni surface. A tendency for the CeO
2
layer to crack due to differences in the thermal expansion coefficients of the oxide film and the superconductor layer requires an additional epitaxial yttria-stabilized zirconia (YSZ) buffer layer on the CeO
2
in order to achieve crack-free superconductor articles. In this arrangement, the superior mechanical properties of the YSZ layer circumvent the microcracking problem, and enable the formation of superconducting layers with a high J
c
. The CeO
2
layer serves primarily to nucleate a (001) oriented epitaxial oxide on the metal surface.
Though effective in forming a high J
c
superconductor article, the use of a multilayer buffer architecture, as opposed to a single layer buffer architecture, increases the complexity of the superconductor article fabrication process. Using multiple buffer layers typically requires the use of additional raw materials, as compared to a single buffer layer architecture. In addition, having CeO
2
as the nucleating layer tends to permit the formation of microscopic cracks that can limit the maximum J
c
of the superconductor article.
Epitaxial (001) ZrO
2
, HfO
2
, or related compounds having Ca or a rare earth element grown directly on a biaxially-textured (001) metal surface, such as a Ni or Ni-based alloy substrate, has been an attractive candidate for an improved single layer buffer architecture, as these materials are mechanically-robust oxides. Unfortunately, efforts to grow these epitaxial layers with a (001) orientation directly on such biaxially-textured (001) metal substrates have been unsuccessful. Specifically, such efforts have resulted in an undesirable mixture of (100) and (111) orientations.
Epitaxial ZrO
2
, HfO
2
, or related oxides on crystalline or polycrystalline metal surfaces have potential application in fields other than superconductors. Epitaxial ZrO
2
or HfO
2
on crystalline metal surfaces may prove useful where thin epitaxial layers are needed in electronic applications. Furthermore, epitaxial oxide layers on polycrystalline metal surfaces have potential use in tribological or fuel cell applications where the properties of the metal/oxide interface largely determine material performance. For epitaxy on randomly-oriented polycrystalline metal surfaces, the epitaxial relationship involves a grain-by-grain registry of film and substrate crystallographic orientations.
For further information, refer to the following publications:
1. D. P. Norton, A. Goyal, J. D. Budai, D. K. Christen, D. M. Kroeger, E. D. Specht, Q. He, B. Saffian, M. Paranthaman, C. E. Klabunde, D. F. Lee, B. C. Sales, and F. A. List, “Epitaxial YBa
2
Cu
3
O
7
on Biaxially Textured Nickel (001): An Approach to Superconducting Tapes with High Critical Current Density,”
Science
274, 755 (1996).
2. M. Paranthaman, A. Goyal, F. A. List, E. D. Specht, D. F. Lee, P. M. Martin, Q. He, D. K. Christen, D. P. Norton, J. D. Budai, and D. M. Kroeger, “Growth of Biaxially Textured Buffer Layers on Rolled-Ni Substrates by Electron Beam Evaporation,”
Physica
C 275, 266 (1997).
SUMMARY OF THE INVENTION
The invention relates to an article with an improved buffer layer architecture. An epitaxial article, according to the invention, comprises a substrate having a metal surface, and a single epitaxial layer on the surface of the substrate. The single epitaxial layer comprises at least one of the group consisting of ZrO
2
, HfO
2
, and compounds having at least one of Ca and a rare earth element stabilizing cubic phases of ZrO
2
and/or HfO
2
. The article can also include a superconducting layer deposited on the single epitaxial layer.
A method for preparing an epitaxial article, according to the invention, comprises the steps of providing a substrate with a metal surface, depositing a single epitaxial layer comprising at least one material selected from the group consisting of ZrO
2
, HfO
2
, and compounds hav
Goyal Amit
Norton David P.
Park Chan
Akerman & Senterfitt
Cooke Colleen P
Dunn Tom
UT-Battelle LLC
LandOfFree
Buffer architecture for biaxially textured structures and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Buffer architecture for biaxially textured structures and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Buffer architecture for biaxially textured structures and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3244062