Structural Stability and Emergent Phases in Oxygen Deficient Complex Transition Metal Oxides

This dissertation is a theoretical and computational examination of structural, electronic and magnetic properties of complex transition metal oxide structures. Our work is motivated by experimental observations that transition metal oxides manifest novel properties at surfaces and interfaces that are absent in bulk, and that there exist competing ground states driven by off-stoichiometry, oxygen vacancy and reduction of symmetry. We examine these properties using density functional theory (DFT) within the spin-generalized gradient approximation (Spin-GGA) along with the application of a Hubbard U (GGA + U). We present our detailed results for the following systems: oxygen deficient strontium titanate surface, strontium ruthenate interfaced with ruthenium metal inclusions, and ytterbium titanate with Yb "stuffing". In the course of our work, we cover materials with 3d, 4d and 4f band characters, each of which have different band masses, electron-electron correlations and spin-orbit coupling (SOC) strength. We investigate the role of surface termination, oxygen vacancy doping and cation "stuffing" defects in these metal-oxides and show the emergence of novel properties consistent with experimentally acquired information and possible applications. We conclude by presenting implications for further work.