Mesoscopic Structures in Ferroelastic and Co-Elastic Materials

Phase transitions often lead to the formation of characteristic microstructures. The most common type, namely ferroelastic and co-elastic phase transition, are often dominated by twin patterns. Twin patterns may consists of individual twins, needle domains, combs and tweed patterns with a large variety of bending and, wiggle patterns of twin walls. In this review several characteristic features of mesoscopic twin patterns are described. ” twin walls can be fast diffusion pathways for impurities, the sites of exchange reactions etc.; ” the lattice distortion extends from the centre of the twin walls over several lattice units, the characteristic length W diverges at the transition point of a second order phase transition; ” typical wall energies are several millijoule per square meter; ” the bending of twin walls can relate to the formation of needle domains with characteristic trajectories of the curved walls; ” the intersection of twin walls with surfaces leads to modifications of the surface potential which is expected to influence absorption and diffusion processes.