Growth of heteroepitaxial single crystal lead magnesium niobate-lead titanate thin films on r-plane sapphire substrates

The research reported in this dissertation investigates approaches to grow heteroepitaxial (001) Lead Magnesium Niobate-Lead Titanate (PMN-PT) perovskite thin films on highly mismatched commercial (102) Sapphire substrates. A hetero epitaxial buffer layer stack consisting of (001) YBa2Cu3O 7 / (001)c SrRuO3 / (001) YBa2Cu3O 7 / (001) CeO2 was used to promote epitaxial (001) PMN-PT perovskite films. In general, achieving growth of PMN-PT perovskite thin films is challenging due to the poor thermodynamic stability of the desired perovskite phase when compared to the stable functionally unresponsive pyrochlore phase. In addition to this challenge there exists large differences in crystal structure and lattice constant values (∼ 15% lattice mismatch) between the (001) PMN-PT cubic perovskite and the r-plane Al2O3 growth surface that would preclude growth of single crystal (001) PMN-PT perovskite directly on the (102) Al2O3 growth surface.;The overriding hypothesis that is being investigated in this dissertation is that the phase, orientation, epitaxy and crystallinity of Lead based perovskite films grown on highly mismatched commercial substrates can be controlled by using a specific set of buffer layers that mitigate the overall lattice and crystal structure mismatch. In addition to the overriding hypothesis, other sub-hypotheses that are essential for enabling growth of the oxide buffer layers with the desired in-plane epitaxy, out of plane orientation and surface roughness have been proposed and tested.;A confocal ultra high vacuum RF magnetron sputtering growth system is used to deposit the PMN-PT thin film and the multilayer oxide heterostructures. In addition, post growth techniques such as slow furnace annealing and rapid thermal annealing are employed to bring about improvements in the as grown film crystallinity and to investigate stabilization of the perovskite PMN-PT phase. The important growth conditions, substrate morphologies, growth surfaces and post growth processes necessary for engineering the desired orientation, phase, crystallinity, in plane epitaxy and surface roughness of perovskite PMN-PT thin films and the thin film buffer oxide layers are examined in detail.;The results of the hypotheses are verified by performing structural characterization on the PMN-PT films and buffer layers using a high resolution X-ray diffractometer. The surface morphology of the films is assessed by an atomic force microscope. The film thicknesses are measured using Pendellosung fringe spacing, X-ray reflectivity, as well as contact profilometry (in the case of thick films).;A 300 nm thick epitaxial (001) PMN-PT perovskite film with a (001) PMN-PT rocking curve FWHM of 0.75° and a surface roughness of 8.6 nm RMS (10mum by 10mum scan area) is grown on buffered (102) Al2 O3 substrates for the first time.