The only Landau-type model for antiferroelectric phase transitions was proposed by Kittel, in which two interpenetrating sublattices with opposite polarizations of equal amplitude were assumed. The theory, however, did not include any mechanism to specify the relative spatial positions of the two sublattices, and therefore could not address the cell doubling during antiferroelectric phase transitions. We propose a Landau-Ginzburg-type model based on microscopic symmetry and group theory, which can, without having to assume sublattices, account for all aspects of antiferroelectric states, including local dipole orientation and cell doubling. The average of these dipoles naturally leads to the Kittel model. The inclusion of gradient terms in the free energy allows the modeling of multidomain structures and domain walls in antiferroelectric states.

• Received 15 February 2000

DOI:https://doi.org/10.1103/PhysRevB.62.818