Fluctuations and Landau-Devonshire expansion for barium titanate
A. I. Sokolov, A. K. Tagantsev+
Saint Petersburg Electrotechnical University, St. Petersburg 197376, Russia
+Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
PACS: 77.80.Bh, 77.84.Bw
Abstract
The experimentally observed temperature dependence of
the quartic coefficients in the Landau- Devonshire expansion for
BaTiO3 is naturally accounted for within a proper fluctuation
model. It is explained, in particular, why one of the quartic
coefficients varies with temperature above Tc while the
second is constant. The tetragonal phase in BaTiO3 is argued
to exist essentially due to the thermal fluctuations, while the
true Landau- Devonshire expansion with temperature- independent
coefficients favours the rhombohedral ferroelectric phase.