Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-11-26
2003-03-25
Dunn, Tom (Department: 1725)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S930000, C505S237000, C505S238000
Reexamination Certificate
active
06537689
ABSTRACT:
BACKGROUND OF THE INVENTION
Multi-layer articles can be used in a variety of applications. For example, superconductors, including oxide superconductors, can be formed of multi-layer articles. Typically, such superconductors include a layer of superconductor material and a layer, commonly referred to as a substrate, which can enhance the mechanical strength of the multi-layer article.
Generally, in addition to enhancing the strength of the multi-layer superconductor, the substrate should exhibit certain other properties. For example, the substrate should have a low Curie temperature so that the substrate is not ferromagnetic at the superconductor's application temperature. Furthermore, chemical species within the substrate should not be able to diffuse into the layer of superconductor material, and the coefficient of thermal expansion of the substrate should be about the same as the superconductor material. Moreover, if the substrate is used for an oxide superconductor, the substrate material should be relatively resistant to oxidation.
For some materials, such as yttrium-barium-copper-oxide (YBCO), the ability of the material to provide high transport current in its superconducting state depends upon the crystallographic orientation of the material. For example, such a material can exhibit a relatively high critical current density (J
c
) when the surface of the material is biaxially textured.
As used herein, “biaxially textured” refers to a surface for which the crystal grains are in close alignment with a direction in the plane of the surface. One type of biaxially textured surface is a cube textured surface, in which the crystal grains are also in close alignment with a direction perpendicular to the surface. Examples of cube textured surfaces include the (100)[001] and (100)[011] surfaces, and an example of a biaxially textured surface is the (113)[211] surface.
For certain multi-layer superconductors, the layer of superconductor material is an epitaxial layer. As used herein, “epitaxial layer” refers to a layer of material whose crystallographic orientation is directly related to the crystallographic orientation of the surface of a layer of material onto which the epitaxial layer is deposited. For example, for a multi-layer superconductor having an epitaxial layer of superconductor material deposited onto a substrate, the crystallographic orientation of the layer of superconductor material is directly related to the crystallographic orientation of the substrate. Thus, in addition to the above-discussed properties of a substrate, it can be also desirable for a substrate to have a biaxially textured surface or a cube textured surface.
Some substrates do not readily exhibit all the above-noted features, so one or more intermediate layers, commonly referred to as buffer layers, can be disposed between the substrate and the superconductor layer. The buffer layer(s) can be more resistant to oxidation than the substrate, and reduce the diffusion of chemical species between the substrate and the superconductor layer. Moreover, the buffer layer(s) can have a coefficient of thermal expansion that is well matched with the superconductor material.
One type of buffer layer, commonly referred to as a seed layer, is the buffer layer that is formed on the surface of the substrate. Another type of buffer layer, commonly referred to as a cap layer, is the buffer layer on which the superconductor material is formed. A further type of layer, commonly referred to as a barrier layer, is typically a relatively thick layer and acts to substantially reduce diffusion of constituents from the substrate into the superconductor material. In some embodiments, a multi-layer superconductor article contains a seed layer, a cap layer and a barrier layer. In certain embodiments, a multi-layer superconductor article contains a buffer layer that serves as the seed layer, the barrier layer and the cap layer.
Typically, a buffer layer is an epitaxial layer, so its crystallographic orientation is directly related to the crystallographic orientation of the surface onto which the buffer layer is deposited. For example, in a multi-layer superconductor having a substrate, an epitaxial buffer layer and an epitaxial layer of superconductor material, the crystallographic orientation of the surface of the buffer layer is directly related to the crystallographic orientation of the surface of the substrate, and the crystallographic orientation of the layer of superconductor material is directly related to the crystallographic orientation of the surface of the buffer layer. Therefore, the superconducting properties exhibited by a multi-layer superconductor having a buffer layer can depend upon the crystallographic orientation of the buffer layer surface.
The termination plane of a buffer layer can include one or more regions having an undesirable orientation.
SUMMARY OF THE INVENTION
The invention relates to multi-layer articles (e.g., multi-layer superconductors) and methods of making such multi-layer articles.
Typically, the articles have one or more layers (e.g., a substrate, a buffer layer, a superconductor layer) having a termination plane with a relatively high degree of orientation in a desirable direction (e.g., (001)). “Termination plane” of a layer as used herein refers to the plane of the layer that forms an interface with another layer that is formed thereon. These planes can be prepared, for example, by one or more of the processes disclosed herein.
In general, the methods involve conditioning (e.g., by chemical conditioning and/or thermal conditioning) the surface of an underlying layer (e.g., a buffer layer or a superconductor material layer), and then depositing a layer of material (e.g., a superconductor material, a precursor of a superconductor material, a cap material or a buffer layer material), onto the conditioned surface of the underlying layer. The conditioned surface can be relatively atomically flat and/or have a termination plane with a relatively high amount of a desired orientation. A multi-layer superconductor prepared by the methods of the invention can exhibit a relatively high critical current density (J
c
). A multi-layer superconductor prepared by the methods of the invention can be formed into an object having a relatively large surface area, such as a wafer or a tape.
“Chemical conditioning” as used herein refers to a process which uses one or more chemical species (e.g., gas phase chemical species and/or solution phase chemical species) to affect changes in the surface of a material layer, such as a buffer layer or a superconductor material layer.
“Thermal conditioning” as used herein refers to a process which uses elevated temperature, with or without chemical conditioning, to affect changes in the surface of a material layer, such as a buffer layer or a superconductor material layer. Preferably, thermal conditioning occurs in a controlled environment (e.g., temperature and pressure).
In one aspect, the invention features an article that includes a substrate, a layer of a buffer material supported by the termination plane of the substrate, and a layer of a superconductor material disposed on the termination plane of the layer of the buffer material. At least about 25% (e.g., at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%) of the termination plane of the layer of the buffer material is the (001) plane.
In another aspect, the invention features an article that includes a substrate, a layer of a buffer material supported by the termination plane of the substrate, and a layer of a superconductor material disposed on the termination plane of the layer of the buffer material. At most about 75% (e.g., at most about 50%, at most about 25%, at most about 10%, at most about 1%) of the termination plane of the layer of the buffer material comprising the (111) plane.
In a further aspect, the invention features an article that includes a substrate, a
Annavarapu Suresh
Li Qi
Li Xiaoping
Rupich Martin W.
Schoop Urs-Detlev
American Superconductor Corporation
Cooke Colleen P.
Dunn Tom
Fish & Richardson P.C.
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