Domain structures and plasticity of ferroelastic materials: Case of rare earth sesquioxides and YBa2Cu3O7

Abstract Domain structures and the number of different orientation variants for ferroelastic materials are studied here for different cases and with different degrees of approximation. The special case of YBa 2 Cu 3 O 7 is discussed. The dissociation into two twins of rotation interfaces occurring in the 3 mF 2m transitions of Sm 2 O 3 or Nd 2 O 3 leading to star patterns is studied in detail. The plasticity due to mechanical twinning of ferroelastic materials is also studied with the problem of twin intersections and of microtwinning. Conditions for twin intersections are given which are more general than the previous conditions given by Cahn, which are shown to be too restrictive. The problems of brittleness and of annealing in these materials are also studied.