Multiscale properties of disordered ferroics and glasses

"Functional materials" are of basic importance for modern technology of the 21th century. They represent organic or inorganic materials which respond very sensitively to changes of external conditions such as temperature, electric or magnetic field, mechanical stress, optical radiation, etc. Ferroics belong to this class of materials. Phase Transitions are important in this context, since they often lead to enhancement of functionality. "Structural materials" are mainly important for their - in many cases outstanding - mechanical properties as is the case e.g. in metallic glasses or nanostructured metal alloys. Since most materials phenomena are of cooperative nature, they depend strongly upon the size of the system and are affected by the presence of surfaces and interfaces. A major challenge therefore is the multiscale nature of many phenomena, which requires detailed understanding of how structures at different length scales interact and influence each other over different time scales. This will require considerable effort in experiment, modelling and analytic theory. In the present project we will therefore bring together experiments, computer simulations and theory to solve fundamental questions concerning the role of heterogeneities at various length and time scales on the thermodynamic and dynamic properties of multi/ ferroic and glass forming materials. We are targeting on the following major aims: 1. Study the influence of confinement on glass freezing and ferroic phase transitions 2. Investigate domains and elastic manifolds, like e.g. domain walls in random media 3. Explore possible relations between glass freezing, domain freezing and ferroic relaxors The project will be run in cooperation with scientific Institutes in England, Switzerland, Germany, Slovenia, Czech Republic and Austria. Many of the findings of the project are expected to have eminent implications for a basis of novel functional and structural materials with superior properties.

Functional materials are organic or inorganic materials responding sensitively to external fields like temperature, electric or magnetic field, pressure, etc. Ferroic materials are very interesting in this context, since phase transitions often lead to enhancement of functionality and their properties can be efficiently tuned, making them first class candidates for technological applications as sensors, actuators, etc. Of course most of these ferroic materials contain defects in the form of impurities, dislocations, domains and domain boundaries, phase fronts and other microstructures on various length scales and with different distributions. The macroscopic properties of such materials are strongly dependent on the interactions operating on various length- and time scales. Within the present project we have investigated how these structures at different length scales interact and influence each other over various time scales. A highlight in this respect was the discovery of a nano- structured glass like material that showed interesting crackling noise behaviour under slow uniaxial compression. Using acoustic emission and height drop measurements of nano- structured Vycor and Gelsil we could show, that such materials behave under very slow uniaxial compression in a very similar way as our earth crust does, when tectonic plates movement induces earthquakes. These unexpected findings demonstrate, that earthquake laws are valid from the nanometre scale up to the kilometre scale, implying that we can now study the statistics of earthquakes in the lab. This work has gained considerable interest. Other problems studied within the present project concerned the influence of spatial confinement on the properties of ferroic phase transitions and glass transitions, the dynamic behaviour of domains and domain walls in disordered systems, as well as the exploration of possible relations between glass freezing, domain freezing and ferroic relaxors. The project was run in cooperation with scientific institutes in England, Switzerland, Germany, Slovenia, Czech Republic and Austria. The results have been published in renowned international journals and will have eminent implications for a basis of novel functional and structural materials with superior properties.