Crystal growth upon firing of hydrous transition metal oxide gels can be effectively inhibited by replacing the surface hydroxyl group before firing with another functional group that does not condense and that can produce small, secondary-phase particles that restrict advancing of grain boundaries at elevated temperatures. Accordingly, fully crystallized SnO(2), TiO(2), and ZrO(2) materials with mean crystallite sizes of approximately 20, 50, and 15 angstroms, respectively, were synthesized by replacing the hydroxyl group with methyl siloxyl before firing at 500 degrees C. An ultrasensitive SnO(2)-based chemical sensor resulting from the microstructural miniaturization was demonstrated.