Functional Interfaces in Ferroeleastic Materials

Functional interfaces, such as multiferroic twin boundaries in passive matrices, may be the next major step towards device fabrication where functionality of materials is not related to bulk properties but to interfacial properties. Eminent examples are superconducting interfaces in insulating matrices, ferroelectric twin boundaries in non-polar materials and defect accumulation together with the nucleation of dislocations in alloys. In the latter case, the superplastic properties are destroyed by the pinning of dislocations attached to martensitic twin boundaries. As functionalities are strongly located in a sample one obtains high density memory devices and rapid response times as required in electronic materials. Simultaneously, most functional interfaces remain very mobile and are shifted by strain. The materials remain soft. The softness is not a continuous function of the interface movement, however. It will be shown that the soft elastic response to external stress contains a large 'jerky' component, i.e. samples will display acoustic emission and irreversible deformation.