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Thursday, June 28, 2007
11:00 AM - 12:00 PM
CNLS Conference Room (TA-3, Bldg 1690)

Colloquium

Ferroelastic twin boundaries as super-highways for ionic transport

Ekhard Salje
University of Cambridge, UK

Ferroelastic phase transitions generate twin structures which can be tailored by subtle application of boundary conditions, local stresses and, in case of multiferroics, by electric fields. It was found that ionic transport along such twin boundaries is often enhanced (e.g. in WO3, CaTiO3) or reduced (quartz). The geometrical reason for changes in the transport coefficient is not the ferroelastic shear but the stretching of the lattice inside the boundaries. This indicates the important role of domain wall 'engineering' where secondary order parameters dominate the physical and chemical behaviour of the walls. A typical example is the chemical turnstile where transport can be switched on and off by weak elastic forces. The non-linear elastic problem of intersections of walls with surfaces (the entry point for transport) is discussed. The dynamics of wall movements under external stresses shows that fast movements are often related to the formation and retraction of needle domain rather than the sideways movement of twin walls. Results from 3-point bending experiments and computer simulation are compared.

Host: Avadh Saxena, T-11