Mixed metallo-organic precursor systems

Abstract

Solution processing of functional oxides often starts with rather complex precursor systems consisting of metal alkoxides, carboxylates and/or nitrates dissolved, mixed and reacted (modified) in different solvents. Precursor systems of main functional perovskite groups are reviewed in this chapter. The breakthrough was achieved in mid-1980s, when the 2-methoxyethanol route was developed for processing of Pb(Zr,Ti)O3-based films, in which this ether alcohol is used as the solvent, acetates as the A-site and alkoxides as the B-site ion sources. Two other very popular routes are the diol-route, in which 1,3-propanediol is used as the solvent, and the so-called inverse-mixing-order route, in which the B-site cations are mixed first and the A-site source is added afterwards. In the alkali metals-based systems, such as Li(Nb,Ta)O3, (K,Na)(Nb,Ta)O3, and Na0.5Bi0.5TiO3, several methods have been developed in which different starting metallo-organic compounds have been used as the A-site metal sources, while mainly alkoxides have been employed as the B-site precursors. A variety of solvents can be used, such as methanol, ethanol, 2-methoxyethanol, 1,3-propanediol, as well as modifiers, for instance acetic acid, acetylacetone, and polyvinylpyrrolidone. Even water has been employed in some systems. The chapter concludes with the review of (Ba,Sr)TiO3-based precursor systems, mainly involving A-site carboxylates and stabilized Ti-alkoxides mixed in one of the above mentioned solvents.