Evidence of a dissolution-precipitation mechanism in hydrothermal synthesis of barium titanate powders

In our study of the system barium hydroxide-titanium tetraisopropoxide-wate r-isopropanol between 85 and 150 degrees C, we have observed the following evidence of a mechanism by dissolution-precipitation: (1) when varying the water/isopropanol ratio in synthesis at 150 degrees C, the grain size of ba rium titanate decreases when the amount of alcohol increases, i.e. when the solubility of the precursors decreases, (2) TEM observations of incomplete ly reacted powders showed that the grains are either amorphous or entirely crystalline BaTiO3, which means that homogeneous nucleation and growth is o ccurring instead of heterogeneous nucleation; (3) high resolution TEM obser vations of fully reacted powders revealed the presence of necks between par ticles. These three experimental observations in rite same reaction system provide strong evidence of dissolution-precipitation as the primary reactio n mechanism. (C) 1999 Elsevier Science Limited. All rights reserved.