Preparation of transparent, partially-crystallized BaTiO3 monolithic xerogels by sol-gel processing

Transparent, partially-crystallized nanostructured barium titanate (BaTiO3) monolithic xerogels (dried at 90 degrees C) have been successfully synthes ized via hydrolysis of Ba, Ti alkoxide precursor solutions in a concentrati on range of greater than or equal to 1.0 mol/l with addition of water with a molar ratio of H2O/Ba greater than or equal to 6.3. Transparent monolithi c xerogels obtained from a precursor solution of 1.0 mol/l remained transpa rent even after firing at 500 degrees C in oxygen, although the degree of t heir transparency was considerably decreased. Firing at temperatures above 500 degrees C yielded translucent ceramics of BaTiO3, and ultimately, firin g above 600 degrees C resulted in normal opaque ceramic bodies. Those obtai ned from a more concentrated precursor solution of 1.2 mol/l were, on the o ther hand, still transparent after firing at 600 degrees C in oxygen, and t urned opaque at 700 degrees C. The results demonstrate that the materials r etained their transparency even after pyrolysis of organic compounds involv ing exothermic oxidation at temperatures in the range of 200 to 400 degrees C. The densification behavior of transparent BaTiO3 monolithic xerogels ob tained was found to be excellent; for example, those derived from a 1.0 mol /l precursor solution could be sintered to form monolithic BaTiO3 ceramics with a relative sintered density of about 94% and an average grain size of approximate to 1 mu m by firing at 1100 degrees C for 2 h in oxygen.