Preparation of La1−zSrzCo1−yFeyO3−x thin films, membranes, and coatings on dense and porous substrates

Abstract

A modified Pechini process has been successfully developed for preparation of thin films of La1−zSrzCo1−yFeyO3−x (LSCF) on both dense and porous substrates. Results indicatc that the most important processing parameter is the ratio of the polymerization/complexation agent to metal ions. Ceramic films derived from solutions with a relatively low ratio of citric acid to metal ions are usually cracked, while films derived from solutions with a relatively high ratio are crack-free and uniform. The use of ethylenediamine as an additional chelating agent further improves film quality, especially the adhesion and uniformity of the films. A single coating of solution typically yields a ceramic film of thickness about 0.4 μm, and thicker films can be prepared by application of successive coatings. For deposition of thin-film membranes on a porous substrate, however, it is necessary to modify the surface of the porous substrate in order to prevent solution from infiltrating into the pores due to capillary force, and to prevent oxide films from cracking due to surface roughness. The application of an intermediate polymer film to the surfaces of porous substrates has effectively overcome the problems and has resulted in uniform, nonporous membranes of LSCF on porous substrates. Successful deposition of thin-film ceramic membranes on porous substrates is important to fabrication of various ionic and micro-ionic devices based on ceramic thin films.