Domain structure and phase boundaries in ferroelastics

The unique ability of ferroic crystals to break up on domains, which can be switched under the influence of external fields or their combinations attracted the investigator's attention for many years. The present article sums up the results of our work devoted to the investigations of the domain structure of ferroelastic crystals and formulates the principal problems the further solution of which is necessary for clarification of characteristic properties of domain structure of ferroic crystals. The article includes sections on 1. Symmetry approach, 2. Real domain structure, 3. Forbidden domain walls, 4. Switching processes, 5. Phase boundaries.