Characterization of Local Structures in Layered Niobates Using Solid-State NMR and Rapid Microwave-Assisted Synthesis and Exfoliation of Their Alcohol Grafted Derivative

The research described in this dissertation spans nearly six years and can be broken into three heavily related research projects: 1. Exploration of local structural changes in mixed alkali layered perovskites. 2. Determination of B-site preference in mixed Nb/Ta systems using solid-state NMR 3. Microwave assisted grafting and exfoliation of layered perovskites using long chain alcohols.;Exploration of local structural changes in mixed alkali layered perovskites. A series of three-layered Dion-Jacobson (D-J) RbSrxCa2--xNb3O10 (0 ≤ x ≤ 2) and RbBaxSr2--xNb3O10 (0 ≤ x ≤ 0.8) compounds were synthesized using microwave and molten salt synthetic routes, respectively, and analyzed using powder X-Ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), attenuated total reflectance-infrared spectroscopy (ATR-IR), and wideline uniform rate smooth truncation-quadrupolar Carr-Purcell-Meiboom-Gill (WURST-QCPMG) nuclear magnetic resonance (NMR). An unexpected dichotomy regarding cation distribution was observed with distribution considered homogeneous on a long-range scale and heterogeneous on a local scale.;Determination of B-site preference in mixed Nb/Ta systems using solid-state NMR. D-J phase layered perovskites can readily undergo proton exchange under mild conditions leading to the formation of a solid acid capable of intercalating various organic molecules. The B-site atom in this class of compounds is often Ti4+, Nb5+ , or Ta5+. It has been shown that changing the B-site atom can drastically alter the intercalation behavior and catalytic ability of these materials. While Nb5+ and Ta5+ possess the same charge and approximately equal ionic radii (0.64 A´), Nb is more electronegative than Ta (1.6 vs. 1.5 Pauling Units, respectively) leading to Nb-O bonds being more covalent in character than Ta-O bonds and changes in the energy states of Ta5+ and Nb5+ compounds. As this work shows, in mixed Nb5+/Ta5+ systems, electronegativity is a strong driver of site ordering in D-J niobates.;Microwave assisted grafting and exfoliation of layered perovskites using long chain alcohols. Current grafting methods of layered perovskites involve high pressure heating at 80 to 150 °C for days to weeks, depending on the alcohol involved. The long reaction time involved inhibits the ability to study grafted samples in a timely fashion. This work will present a new microwave assisted grafting technique which decreases reaction time from 17 days to 12 hours. Furthermore, a microwave-sonication based method of exfoliation of grafted niobates in organic solvents was developed, further expanding the capabilities and potential of niobate nanosheets.