Crystallinity and stoichiometry of nano-structured sol-gel-derived BaTiO3 monolithic gels

The crystallization behavior and stoichiometric changes of barium titanium alkoxide-derived monolithic gels prepared by the sol-gel process using a high-concentration Ba,Ti precursor solution (0.8 mol/L) were investigated during aging at room temperature, Crystallization of the gels (which were amorphous, per X-ray diffraction analysis immediately after gelation) into the BaTiO3 perovskite phase increased during aging and was associated with significant shrinkage of the gels, Crystallization reached a value of similar to 82% by the final stage of shrinkage, assuming the degree of crystallization of a gel treated at 600 degrees C to be 100%. The stoichiometry of the gels (Ba/Ti molar ratio) also changed considerably during aging, as estimated by the concentrations of Ba and Ti that remained in the expelled liquid resulting from syneresis at any time during the aging process, Deviation in the Ba/Ti ratio of the precursor solution ranged from 0.015 at the initial stage of shrinkage to 0.003 at the final stage, a value determined by inductively coupled plasma atomic emission spectroscopy, The present study demonstrates the great advantage of using high-concentration precursor solutions of barium titanium alkoxides, rather than lo cv-concentration solutions, to obtain BaTiO3 gel monoliths with high density and crystallinity and little stoichiometric deviation, by sol-gel processing at room temperature.