Interfaces in quasicrystals: problems and prospects

We propose to discuss the importance of unified 6D description for understanding the geometrical aspects of interfaces in quasicrystalline and its related phases. These will in particular be presented in relation to the icosahedrally related phases. However, the viewpoints adopted will be sufficiently general to help discuss interfaces in any quasiperiodic systems. The consequence of 6D homophase/heterophase interfaces on 3D physical space will be considered by taking examples. These include RAs/IQC, IQC/DQC interfaces apart from the hypertwin and antiphase domain boundaries. It will be shown that such a description does not promise to solve the problems of energetics of interfaces in these systems. It will be concluded that 3D and hypercrystal structural description need to supplement each other for unravelling the underlying mechanism of growth of a particular interface during processing of these materials. The importance of HREM studies in understanding the interface structures in aperiodic systems will be clearly brought out.