Structure of Weiss domains in ferroelectric crystals

The structure of Weiss domains in ferroelectric crystals in each of which the polarization vector is constant, is investigated through a new variational principle. The general field equations are obtained and it is shown that in the presence of external electric field the total electric field is also constant in Weiss domains but is usually different from that of the polarization field. Moreover, it is proved that domain walls can only be planar surfaces. Finally the case corresponding to pure polarization fields is also treated and an illustrative problem is considered.