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.