Landau Theory of Domain Patterns in Ferroelastics

Abstract

Domain patterns in several classes of ferroelastics are studied using a Landau expansion in the strains and their derivatives. Examination of the local rotation, the non-order-parameter strains and the local energy density reveals the wedge and other disclinations responsible for the complexity of the patterns in (1) tetragonal-orthorhombic materials, and (2) hexagonal-orthorhombic and related materials. At temperatures where the parent phase is unstable and so has negative stiffness, simulations of hexagonal-orthorhombic systems yield pockets where the order parameter is much reduced; if the parent phase exists experimentally under these conditions, it might give rise to extreme damping. For cubic-tetragonal materials, perturbing the parent phase at a temperature well below its stability limit gives an inhomogeneous noncompact product.