Domain structures in epitaxial ferroelastic films near and far from the phase transition

We consider two generic cases of proper ferroelastic phase transitions in t hin epitaxial films. The domain structure, which forms at these transitions , is similar to either a(1)/a(2)/a(1)/a(2) or c/a/c/a structures in ferroel ectric perovskites. We find the form of the inhomogeneously strained state ("strain wave"). which appears at the transition and then evolves into the domain structure. The parameters of the domain structures are also calculat ed and compared with the parameters of the "strain wave". There is no criti cal thickness for the existence of the domain pattern, when the "extrinsic" (not related to the phase transition) misfit is absent. When the extrinsic misfit exceeds some critical value., there occurs a topological phase tran sition between the polydomain and monodomain states. (C) 2001 Elsevier Scie nce B.V. All rights reserved.