Formation and Stability of Ferroelectric BaTi2O5

Volume 93 Issue 1, Pages 295 – 300

Na Zhu, Anthony R. West
Published Online: Nov 23 2009 6:56PM

DOI: 10.1111/j.1551-2916.2009.03393.x

ABSTRACT
BaTi₂O₅
(BT₂) is thermodynamically stable over a very
narrow temperature range between 1220° and 1230°C: a modification to the
BaO–TiO₂ phase diagram is proposed. This
thermodynamic stability was shown by constructing a time–temperature
transformation diagram for the decomposition of BT₂.
Once formed, BT₂ appears to be stable
indefinitely at 1220°–1230°C; at higher temperatures, the decomposition
rate increases with temperature; at lower temperatures, the
decomposition rate increases with decreasing temperature and passes
through a maximum at ∼1200°C; below ∼1150°C, BT₂
has long-lived kinetic stability. Kinetic considerations show a
nucleation and growth mechanism for decomposition, with a nucleation
induction period that is very temperature dependent. BT₂
can be prepared by various routes, including solid-state reaction of
oxides below ∼1100°C; because it is metastable at all temperatures other
than 1220°–1230°C, its formation is an example of Ostwald’s rule of
successive reactions. Discrepancies in the literature concerning the
reported stability range of BT₂ can be explained
by the complex dependence on temperature and time of both its formation
and decomposition, for both of which, the nucleation stage is rate
limiting.

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