Synthesis, and/or Structural, Conductivity Investigations of Single and Polycrystalline Fluorides, Ionic Liquids and Conjugated Diynes Using Solid-state Nuclear Magnetic Resonance Spectroscopy and X-ray Diffraction
Boyd, Stephen A.
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One overarching focus of solid-state chemistry has evolved due to the desire to understand the structures and mechanisms underlying conductivity, whether electronic or ionic, and to seek ways toward enhancement and control of those mechanisms and materials. Modern strategies are also shaped by environmental concerns and these concerns have, in turn, influenced the search for synthetic routes which employ more benign methods. The first sections of this dissertation describe adapted and modified reverse-micellar methods, as applied toward the room-temperature synthesis of several different types of binary and lanthanide-doped, monodisperse, nanoparticle (20-40nm), polycrystalline fluorides. Their structures were investigated using Magic-angle Spinning Nuclear Magnetic Resonance (MAS NMR) and X-ray Crystallography. The difficulty of applying these aqueous methods toward nanoparticle lead fluoride (PbF2) was surmounted when a novel crystal, cetyltrimethylammonium hexafluorosilicate monohydrate, was synthesized, its crystal structure solved, and employed as a fluoride delivery mechanism to successfully synthesize both a- and b-phase PbF2. MAS NMR spectroscopy is well-suited as an investigative tool for both crystalline and non-crystalline materials. Two sections of the dissertation deal with two types of compounds in which MAS NMR multinuclear pulse techniques (19F, 7Li, 1H, and 13C) play a critical role in the deduction of structure (conjugated diynes) and conductive behavior as a function of temperature (ionic liquids). The final sections of this dissertation again rely heavily on X-ray crystallography and MAS NMR, as well as Impedance Spectroscopy and EXAFS/XANES via collaborative efforts, to examine fluoride conductivity and temperature-dependent behavior of fluoride materials. The super-Lewis acid, antimony pentafluoride, was used to explore whether morphology affects mobility across grain boundaries when vacancies are artificially induced in both nanoparticles as well as their larger polycrystallite analogs. In a collaborative effort, barium fluoride and calcium fluoride single-crystal heterostructures were grown by the Joachim Maier Group and were used to elucidate the precise mechanisms of observed conductivity enhancement in these heterostructures.