Arash Yavari

California Institute of Technology



Atomic Structure of Ferroelectric Domain Walls

Ferroelectrics are polar crystals in which spontaneous polarization can be switched by applying an external applied electric field or mechanical loads. These materials are technologically important and have applications in microactuators and microsensors. Electromechanical response of ferroelectrics is highly affected by the evolution of defects. The most important defects in ferroelectrics are believed to be ferroelectric domain walls, which are two-dimensional defects. Very little is known about the structure of domain walls in the nano-scale. This seminar is on harmonic and anharmonic lattice static modeling of ferroelectric domain walls in tetragonal BaTiO3. We start from an effective potential that is derived from quantum mechanics ab-initio calculations and construct the governing equations of the multi-lattice about an unrelaxed reference configuration. This work is different from previous similar lattice static calculations in the sense that it is more systematic and does not start from force constants (that respect all the symmetries of the lattice) and can consider any number of nearest neighbor interactions. In this formulation of lattice statics, the stiffness coefficients are directly derived from the given atomic potential and geometry of the problem. There are subtleties in calculating forces, which are defined in terms of conditionally convergent lattice sums, and stiffness matrices. These issues and also the solution procedure will be explained in detail.  Some numerical results for structures of 180o and 90o domain walls will be presented.