UC Berkeley

This dissertation details the synthesis and characterization of compressively strained epitaxially grown bismuth ferrite thin films in an effort to improve their piezoelectric properties with the goal of finding a viable lead-free alternative to lead zirconate titanate. It is found that under compressive epitaxial strain a morphotropic phase boundary, the hallmark of high performance piezoelectrics, is stabilized in this material. The structural characterization of these films reveals complex mixed-phase morphologies whereby nearly energetically degenerate monoclinically distorted tetragonal and rhombohedral ferroelectric phases coexist with apparent crystallographically coherent interfaces. This mixed phase morphology is found to be responsive to perturbations both via mechanical indentation and an applied electric field, whereby a reversible phase transition is observed in the films. Electrical characterization of these films indicates a pronounced increase in their piezoelectric and ferroelectric properties.