Ultrafine tttanate powders produced via a precursor-modified sol-gel method

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Abstract
Ultrafine titanate powders were produced by a sol-gel process in which the reaction rates in the precursor solutions were modified with β-diketonates. The amount of the β-diketonate was varied to control the crystallite size and the crystallization behavior of the titanate powders. The crystallite size, crystallinity, and crystalline structures of the titanate powders were studied using x-ray diffractometry. For PbTiO3, it was found that the crystallite size decreases and the crystallite density increases with increasing amount of β-diketone modification. Our results suggest that the β-diketone modification reduces the size of the structural units in the gel network resulting in smaller crystallite size and more nucleation sites in the powders produced. For BaTiO3, powders crystallized into cubic phase rather than tetragonal phase. The cubic powders can be converted to tetragonal phase by heating to 1100°C if barium hydroxide is used as a precursor. On the other hand, if barium acetate is used as a precursor, powders stay as cubic even heat treated at 1100°C. Therefore, a sintering temperature below 1000° C is required to maintain the cubic phase of BaTiO3. In contrast to the PbTiO3 system, the addition of β-diketone in the precursor solutions of BaTiO3 has no significant effect on the crystallite size of the produced powders. The lack of a significant effect of β-diketone in BaTiO3 is probably due to the already slow hydrolysis-condensation rate of barium hydroxide/titanium isopropoxide system compared to that of lead acetate/titanium isopropoxide system. Fùrther reduction in the reaction rate in the barium titanate system probably does not make any significant difference in the structure of the xerogel and the powders derived from it.