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Tailoring the Mechanism of the Amorphous-to-Crystalline Phase Transition of PbTiO3 via Kinetically Controlled Hydrolysis.

by Federico A. Rabuffetti and Richard L. Brutchey
A systematic investigation of the effects of hydrolytic conditions on the development of PbTiO3 (PTO) from amorphous metal–organic matrices is reported.

Abstract: Metal–organic matrices were obtained using a novel hydrolytic approach which relies on the kinetically controlled delivery of water vapor at the gas–liquid interface of a Pb–Ti alkoxide precursor. Crystallization was induced via standard thermal treatment and followed using X-ray diffraction, visible Raman spectroscopy, and thermal analysis. It was found that the mechanism of the amorphous-to-crystalline phase transition is controlled by the rate and extent of hydrolysis and polycondensation of the Pb–Ti alkoxide: faster and extended hydrolysis favors an amorphous-to-pyrochlore-to-perovskite transition, whereas slower and less extended hydrolysis favors a direct amorphous-to-perovskite transition. The rate and extent of hydrolysis were found to have a significant impact on the magnitude of the tetragonal distortion of the perovskite unit cell as well. Optimization of hydrolytic conditions allowed for well-crystallized, phase pure, tetragonal PTO to be obtained at temperatures as low as 500 °C via a direct amorphous-to-perovskite phase transition. Differences observed in the mechanism of perovskite phase formation are explained in terms of the differential dependence of the dynamics of lead and titanium atoms on hydrolytic conditions, the former being significantly more affected than the latter. Because long-range redistribution of lead atoms is the rate-determining step of the perovskite phase formation, this finding has implications for the design of metal–organic precursors and hydrolytic approaches targeting the preparation of lead-containing functional perovskite oxides.

Keywords: PbTiO3; vapor diffusion; sol−gel; amorphous; crystalline

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