TRENDS IN PRECURSOR DESIGN FOR CONVENTIONAL AND AEROSOL-ASSISTED CVD OF HIGH-T-C SUPERCONDUCTORS

Conventional MOCVD techniques require molecules displaying volatility and constant vapor pressure, Metal oxide precursors, i.e., beta-diketo nates, or classical or functionalized metal alkoxides are mostly solid s, The various approaches used to tailor volatility are discussed with barium derivatives as an example, The relationships between sublimati on temperature and molecular weight suggest that volatility can be opt imized on the basis of molecular weight, Aerosol-assisted CVD (AACVD) can use a larger range of precursors since volatility is no longer cru cial, The solvent is an undesired ballast in a CVD process, High solub ility of the precursors in the selected solvent is thus desirable, 'St ability' here includes the absence of precipitation which would change the stoichiometry of the feed solution for multicomponent oxides, Pre cipitation is often promoted by hydrolysis; stability toward moisture is thus desirable. The use of mixtures of precursors based on differen t ligands (beta-diketonates, beta-ketoesterates, alkoxides) can lead t o ligand exchange reactions giving homometallic species, sometimes of low solubility, or mixed-metal species by self-assembly, thus improvin g solubility and stability toward moisture. These aspects are illustra ted in compositions related to high-T-c superconductors, Novel copper, yttrium, cerum(IV), barium-copper, yttrium-copper and praseodynium-co pper species are reported. (C) 1998 John Wiley & Sons, Ltd.