The experimentally observed temperature dependence of the quartic coefficients in the Landau-Devonshire expansion for BaTiO_3 is naturally accounted for within a proper fluctuation model. It is explained, in particular, why one of the quartic coefficients varies with temperature above T_c while the second is constant. The tetragonal phase in BaTiO_3 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. Certain conclusions concerning the temperature dependence of the sextic Landau-Devonshire coefficients are also made.
@article{arxiv.cond-mat/0202341,
title = {Fluctuations and Landau-Devonshire expansion for barium titanate},
author = {A. I. Sokolov and A. K. Tagantsev},
journal= {arXiv preprint arXiv:cond-mat/0202341},
year = {2009}
}
Comments
Minor changes, 1 reference added, published version