M.S. Thesis Presentation by Aurélien Malbec
Friday, May 2, 2003
(Dr. Christopher Lynch, advisor)
"Domain Formation and Evolution in Ferroelectric Materials"
The formation and evolution of domain structures into the grains of ferroelectric ceramics is modeled using energy minimization. The understanding of these phenomena is essential to determine the characteristics, the behavior and the performance of the single crystal as well as the polycrystal. These phenomena are also involved in crack formation and growth.
The formation and evolution of domain structures was studied through the minimization of the energy in a single crystal. Different contributions to the energy were taken into account: the Landau free energy, the Ginzburg free energy, the elastic long-range interaction and the dipole-dipole long-range interaction. The Landau free energy represents the energy wells linked to the stable polarized states of the unit cell below the Curie temperature. The Ginzburg energy gives a penalty for strong gradient of polarization. The elastic and electrostrictive energies were transformed into an elastic long-range interaction. The dipole-dipole long-range energy represents the electric interaction between a dipole and all the others. The phase transition occurring during the cooling below the Curie Temperature was studied using the Time Dependent Ginzburg Landau equations (TDGL).
Two-dimensional numerical simulations of the formation of domain structure occurring during the cubic paraelectric to tetragonal ferroelectric phase transition were performed. The pattern of the domain structure was clearly shown to be linked with the different energies taken into account. In addition, numerical simulations of the evolution of the domain structure at low temperature under simple uniaxial mechanical and electrical loading were performed and discussed.