Sintering behavior of partially crystallized barium titanate monolithic xerogels with different nano-crystalline structure

The densification behavior of partially crystallized barium titanate (BaTiO3) monolithic xerogels prepared by a high concentration sol-gel method with different degree of hydrolysis was examined as a function of sintering temperature. The structural evolution of the xerogels during thermal treatment has been monitored by nitrogen adsorption/desorption porosimetry, XRD, TG/DTA, TEM, and SEM measurements. Sintering behavior of the xerogels can be significantly influenced by their initial microstructure that was affected by the content of water used for hydrolysis. Density change with sintering temperature was different between xerogels with different degrees of hydrolysis. Hydrolysis water content is H2O/Ba molar ratio, denoted as rw. Xerogels with rw=5.0, having a lower porosity and smaller pore size with less agglomerated particles, were sintered to form ceramics with a relative density of about 97% at a temperature of 1100 °C, whereas this was only 83% for xerogels with rw=5.7 having relatively larger pore volume and pore size. The average pore size of the xerogels increased with increasing sintering temperature up to 700 °C. For temperatures over 700 °C, it continued to increase for xerogels with rw=5.7, but it fell for xerogels with rw=5.0 due to rapid densification. Microstructural changes of the xerogels are discussed as a function of heat treatment temperature.