Cathodic Codeposition of Alloys and Polymetallic Compositions - the HTSC Precursors

2 Cathodic Codeposition of Alloys and Polymetallic Compositions - the HTSC Precursors 

Both crystalline [168] and amorphous [169] alloys are considered as precursors in the preparation of HTSC films. Atomic-level uniformity of the component distribution in metallurgical alloys can be achieved. One more type of metal precursor, the oxidation of which gives good results under relatively mild conditions, are multilayer polymetallic coatings with nanometer-thick layers [170], Similar compositions are also the most frequently used type of precursors in the technology of semiconductors [171]. 

The codeposition of metals from electrolytes of complex compositions is well established for a large number of systems [172]. In such systems, the chemical and/or 

The main features of studies on this topic are summarized in Table 3. Because deposition of active metals in protic media is always accompanied by the hydrogen evolution, it is common to use substrates with a high hydrogen overpotential, to optimize solution pH, or to operate in aprotic solvents. Thus precursors of bismuth and thallium-based HTSCs are prepared most advantageously in aqueous media, while it is preferable to deposit Y-Ba-Cu and related compositions from organic media. In the latter case, traces of water can substantially spoil the coating quality 

In most work on deposition of precursors from aqueous solutions, the products were analyzed only after annealing. The possibility cannot be excluded of the presence in the deposits not only of metals (and even instead of them) but also of the corresponding hydroxides which are deposited on the surface as a result of a local pH 

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