WFD-1 Self organized structures in ferroelastic and co-elastic systems Ekhard K.H. Salje Cambridge University, Downing Street, Cambridge CB2 3EQ, UK 　　　　　Self organized mesoscopic structures in ferroelastic materials display as basic 　　　　　excitation mobile twin walls. These twin walls form hierarchical structures with 　　　　　needles and corner domains (level 1), combs, zig-zag domains, multiple junctions 　　　　　(level 2), and tweed and tartan structures (level 3). Walls and segments can easily be 　　　　　modified chemically and ,sometimes, structurally so that they can be used as 　　　　　templates for the fabrication of electronic devises (e.g. superconducting wall patterns 　　　　　in insulating matrices for the formation of arrays of Josephson junctions). 　　　　　　In co-elastic structures the elastic degrees of freedom couple with order parameters 　　　　　with different physical properties and, often, different symmetries. This disallows for 　　　　　the formation of switchable domain patterns. Instead more complex patterns emerge, 　　　　　often related to incommensurate phases (e.g. in quartz). In case of Dauphine twin 　　　　　walls in quartz, it is shown that transport along the crystallographic c-axis is reduced 　　　　　rather than enhanced while transport in the perpendicular directions is highly 　　　　　anisotropic. It is argued that ions such as Li(+) are more mobile in the 　　　　　incommensurate structure while their activation energy changes dramatically between 　　　　　the two commensurate structures. 　　　　　The tutorial is structured as follows: 　　　　　・ I will introduce the non-linear elastic response in ferroelastic systems, based on 　　　　　　mobile domain walls. 　　　　　・ The concept of wall trajectories and junction formation is introduced. 　　　　　・ Modification of patterns close to surfaces are discussed. 　　　　　・ It is demonstrated that the self energy of oxygen vacancies (as example) is 　　　　　　drastically reduced inside wall patterns, simultaneously transport and confinement 　　　　　　are enhanced. 　　　　　・ The dynamical response of wall structures under external elastic forces is 　　　　　　demonstrated. 　　　　　Reading Materials: 　　　　　Salje, E.K.H. (1993) 　　　　　　　　　　Phase transitions in ferroelastic and co-elastic crystals, 　　　　　　　　　　Cambridge University Press 1993, ISBN 0521429366 　　　　　Harrison, R. J., Redfern, S. A. T. , Buckley, A., and Salje, E. K. H. (2004) 　　　　　　　　　　Application of real-time, stroboscopic x-ray diffraction with dynamical 　　　　　　　　　　mechanical analysis to characterize the motion of ferroelastic domain walls 　　　　　　　　　　Journal of Applied Physics 95,1706-1717 　　　　　Lee, W. T., Salje, E. K. H., Bismayer, U. (2003) 　　　　　　　　　　Domain wall diffusion and domain wall softening Journal of Physics: Condensed 　　　　　　　　　　Matter Volume: 15, 1353-1366 　　　　　Calleja, M., Dove, M. T., Salje, E. K. H. (2003) 　　　　　　　　　　Trapping of oxygen vacancies on twin walls of CaTiO3: a computer simulation 　　　　　　　　　　study, Journal of Physics: Condensed Matter, 15, 2301-2307 　　　　　Conti, S., Salje, E. K. H. (2001) 　　　　　　　　　　Surface structure of ferroelastic domain walls: a continuum elasticity approach 　　　　　　　　　　Journal of Physics: Condensed Matter, 13, L847-L854 　　　　　Calleja, M.,Dove, M. T., Salje, E. K. H. (2001) 　　　　　　　　　　Anisotropic ionic transport in quartz: the effect of twin boundaries 　　　　　　　　　　Journal of Physics: Condensed Matter, 13, 9445-9454 　　　　　Salje, E. K. H. (2000) 　　　　　　　　　　Ferroelasticity, Contemporary Physics, 41, 79-91 　　　　　Aird, A., Salje, E. K. H. (1998) 　　　　　　　　　　Sheet superconductivity in twin walls: experimental evidence of WO3-x 　　　　　　　　　　Journal of Physics: Condensed Matter, 10, L377-L380 　　　　　Salje, E. K. H., Ishibashi, Y. (1996) 　　　　　　　　　　Mesoscopic structures in ferroelastic crystals: needle twins and right-angled 　　　　　　　　　　domains 　　　　　　　　　　Journal of Physics: Condensed Matter, 8, 1-19