Multi-scale Dynamics of Twinning in Ferroic Materials
Doron Shilo (Technion - IIT), Eilon Faran (Technion - IIT)
From Atomistics to Reality: Spanning Scales in Simulations and Experiments Symposium B
Mon 4:20 - 5:40
CIT 227
This talk presents combined theoretical and experimental approaches for studying twinning processes at different spatial and temporal scales. First, we present a modeling approach based on Discrete Twin Boundary Dynamics, which is similar to the Discrete Dislocation Dynamics approach, but more simple and straightforward. This modeling approach is based on knowledge of the kinetic relations between the twin boundary velocity and the electro/magneto/mechanical driving force. For this purpose, we developed a unique experimental method for measuring kinetic relations of discrete twin boundaries by tracking the distance they pass during an application of a tunable magnetic or electric pulse with a rectangular shape and µsec-scale duration. The obtained results demonstrate two significantly different kinetic relations, viscous type and thermally activated type, which are valid in different ranges of the driving force. Further, we present analytical models taking into account the barriers for twin boundary motion and the mechanisms for overcoming them. It is shown that all kinetic relations are governed by several nanoscale properties of the twin boundary such as the crystal lattice barrier (similarly to the Peierls barrier) and the energy of twinning dislocations. Fittings of the models to measured kinetic relations allow the extraction of these nanoscale properties. We then present analytical models which relate the crystal lattice barrier and the energy of twinning dislocations to the thickness and energy of twin boundaries. Measurements of the latter properties by means of AFM and TEM are then presented and discussed. Finally, the necessity for atomistic simulations in order to relate the above mentioned nanoscale properties to atomic concentrations is discussed.