Phase evolution in gel-precipitated LaAlO3 ceramics

Lanthanum aluminate ceramic powders could be prepared by a combined gel precipitation process from metal chlorides using ammonia. A slight modification in the conventional gel precipitation technique was carried out by introducing a step of ultrasonication followed by centrifugal washing of the gel. The dried gels produced pure phase lanthanum aluminate powders on calcination at 1100 °C for the combined gel-precipitated powders, and at 600 °C for the washed gel. The phase evolution was studied and it was found that the delay in obtaining monophasic LaAlO₃ in the combined gel-precipitated powder owed to the crystallization of an impure phase LaOCl. This phase was not detected in the washed gel (WG) powders. TEM micrographs showed a uniform morphology for the calcined WG powders, which were in contrast to the irregular particles in the gel-precipitated (GP) powders. The uniform morphology was assigned to the ultrasonic effects during washing of the gel.