TOWARDS A RIGOROUS DEFINITION OF FERROIC PHASE-TRANSITIONS

Guymont's (Phys. Rev. B (1981), 24, 2647) nondisruption condition is m ade the basis for dividing phase transitions in crystals into nondisru ptive and disruptive categories. Ferroic phase transitions are defined as nondisruptive phase transitions involving a change of point-group symmetry. Prototype symmetry is also defined rigorously in terms of th e nondisruption condition. This approach forms the basis of a comprehe nsive and informative tensor-classification scheme for twinning in cry stals (full details of which are published elsewhere), as also of a cr ystallographic classification of phase transitions.