Nanoscale behavior of ferroelectric domains in perovskite thin films

Controlling the polarization of ferroelectrics plays an increasingly important role in many technological devices including ferroelectric memory, tunable communication filters, and vibrational energy scavengers. To advance the development of ferroelectric devices, we must improve our understanding of the complex internal domain structure of ferroelectric materials. Because these domains are only 50-500 nm wide, they have historically been difficult to probe.;This dissertation demonstrates how nanoscale ferroelectric domain configurations can be tailored in epitaxial perovskite thin films by controlling the electromechanical boundary conditions of the film. Epitaxial films of BiFeO3 and Pb(Zr,Ti)O3 were used as model systems because the latter is a mainstay in piezoelectric sensing and actuating applications and the former is a promising Pb-free magnetoelectric-ferroelectric with large polarization, strong piezoelectricity, and multiple ferroelastic domain wall variants.;The as-grown domain structures of epitaxial BiFeO3 films deposited on (001)-oriented SrTiO3 substrates were investigated using piezoelectric force microscopy. The equilibrium ground state consists of alternating domain stripes consisting of only two ferroelastic variants, separated by 71° domain walls. Selective activation of 71° and 109° ferroelastic switching---which is important for magnetoelectric applications ---was achieved by controlling the strength of the applied electric field. A similar behavior was found in BiFeO3 films deposited on (110)-oriented SrTiO 3.;The novel characterization technique of planar electrode piezoelectric force microscopy is introduced as a non-destructive method for viewing nanoscale domains at intermediate stages of the poling process. This apparatus was used to selectively enable 109° or 71° reversible rotation of the 71° domain stripes in BiFeO3 films. Domain stripe rotation was then used to achieve magnetoelectric switching of a permanent magnet, and also to modulate the photo-electric effect in BiFeO3 domain walls.;A novel concept for harnessing electricity from ferroelastic domain wall motion is applied to vibrational energy scavenging. Methods for imaging domains while deforming the Pb(Zr,Ti)O3 or BiFeO3 film with a micromachined cantilever and magnetic actuation or by three-point bending are presented. Reverse polarized domains in BiFeO3 were found to grow under compressive strain by 180° domain wall motion that maintains the equilibrium 71° domain stripes.