Perturbative studies of perovskite thin films

The perovskite system exhibits a variety of interesting and useful physical properties and has attracted significant issue in part due to potential applications but largely due to the fundamental study of the mechanisms responsible for its diverse properties. This dissertation will demonstrate the exploration of two materials in the perovskite family through careful perturbation of model systems. I shall first provide a general overview of the creation of model perovskite systems in thin film form and present data confirming the high quality nature of these films and the ability to fabricate devices suitable for characterizing relevant electrical and magnetic properties. Having created a model perovskite system I shall then study the fundamental physics of the system through mechanical and chemical perturbations.; This approach has been applied to two perovskite systems, the ferroelectric lead titanate, PbTiO₃, and the mixed valence manganite La _0.67Ca_0.33MnO₃. In the first case, I explore perturbations to the model pyroelectric system chemically through the introduction of vacancies by careful variation of processing conditions. I find that such a perturbation leads to a significant enhancement in the materials pyroelectric response relative to the unperturbed state. In the manganite system, I follow another approach and mechanically perturb the system through the formation of an ultrahigh strain state which has been realized through a novel epitaxial SrTiO ₃ buffered silicon approach. The large thermal expansion mismatch causes the large biaxial strain-controlled evolution of a multiphase state seemingly responsible for creating a disconnect between the transport transitions and the ferromagnetic transition, and the observation of the most peculiar onset of a positive magnetoresistance in the vicinity of room temperature in stark contrast to typical properties of the unperturbed state.; I shall demonstrate throughout the course of this work a parallel trend of the results of the perturbative approach in these two uniquely interesting materials within the perovskite system. This work will highlight the role of defects and careful control of strain to induce novel phases within each respective system. These phases in turn show the onset of new and significantly altered properties from typical properties of the model system.