High-T[sub(c)] Coated Conductors

Coated conductors consist of a thin coat of superconductor laid down on a

supporting substrate and buffer layer (Figure 12.1). The coating can be several

micrometers thick. The buffer layer, which is between the substrate and the

superconductor, has highly textured crystallites, and the superconductor takes

this texture when it is deposited on the buffer layer. The texture is "biaxial" as

opposed to the "uniaxial" texture of typical B S C C O superconductors. 1 Thus the

properties of the superconductor are like those of a single crystal, i.e. the crystals are

sufficiently wel I aligned that the grain boundaries offer little resistance to electrical

current. Two methods have been used to produce the oriented buffer layer: the

I B A D a p p r o a c h 2 - 4 which is an ion beam assisted vapor deposition process on

an untextured substrate, and the R A B i T S approach 5 which starts by producing a

textured metallic substrate, obtained by rolling deformation and heat treatment. The

conductor is made in the form of strips with the c axis of the crystals perpendicular

to the plain of the strip. The most common superconducting material which is used

is YiBa?Cu307_,5 ( Y B C O ) . Similar materials with thallium also show promise.