Rigidity of the elastic domain structure near the boundary of its existence in thin epitaxial films

We consider an interesting and practically important case of elastic domain structure, which is the analogue of c/a domain pattern with 90$^\circ$ walls in perovskites, and is solvable analytically for arbitrary misfit strain. There is no critical thickness, below which the domain structure cannot exist, when the "extrinsic" misfit is zero and the domains are of equal width. At the boundary of polydomain-monodomain transition the period of the pattern diverges, as does the dynamic stiffness of the domain structure. It is unlikely, therefore, that one can achieve a softness of the dielectric response of the c/a elastic domains in ferroelectric-ferroelastic thin films.