Low-temperature processing of (Pb, La)(Zr, Ti)O-3 thick films os alumina substrates

Lantanum-modified lead zirconate titanate (Pb0.88La0.08Zr0.65Ti0.35O3, PLZT 8/65/35) thick films of final thickness 35 mum were processed on alumina s ubstrates by screen-printing and sintering at 900 degreesC. Bulk ceramics o f the same composition were prepared under identical conditions. In order t o identify the influence of the PbO-based liquid phase on the densification of the PLZT thick films, two compositions were chosen, the stoichiometric composition and a composition with an excess of 6 mol % PbO. The latter dev eloped a liquid phase upon heating to 900 degreesC. The heat treatment was performed in a PbO-rich atmosphere determined by the equilibrium pressure o f the PbO vapor phase above PbZrO3/PbO. Densification, microstructure, chemical homogeneity and electrical properti es of the bulk ceramics and thick films are reported and discussed. There i s a significant difference in the densification of bulk ceramics and thick films. While the former strongly depend on the presence of an excess of PbO at the onset of densification, the latter are only slightly dependent on t he starting stoichiometry. It has been generally accepted that bulk densifi cation depends on the amount of liquid phase whereas according to our resul ts only a minimal amount of liquid phase is required for densification unde r constrained conditions. This also happens in samples with the stoichiomet ric composition due to the capillary condensation of supersaturated PbO vap or that further reacts with the alumina substrate.