Ginzburg-Landau-type theory of antiphase boundaries in polytwinned structures

The conventional Ginzburg-Landau theory of interphase boundaries is generalized to values of order parameters that are not small, with application to polytwinned structures characteristic of cubic-tetragonal-type phase transitions. Explicit expressions for the structure and energy of antiphase boundaries via the functions entering the free-energy functional are given. A peculiar dependence of equilibrium orientations of antiphase boundaries on the interaction type is predicted, and it qualitatively agrees with the available experimental data.