Ferroelastic phase transitions in crystals of finite size

The dependence of the correlation radius of the order parameter on plate thickness is studied for ferroelastic phase transitions. It is shown that, under certain conditions, the strictional relation between the order parameter and the lattice deformation leading to, instead of a homogeneous phase at the transition point, leads to the emergence of a spatially modulated structure in the plane of the plate, its wave vector depending on the constant of interaction between the order parameter and elastic deformation, as well as on plate thickness.