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|Title:||Synthesis and Magnetic Properties of Spinel-Based Transition Metal Oxides|
|Authors:||Mitchell, Everett Jonathan|
|Advisor:||Greedan, John E.|
|Abstract:||<p>Several transition metal oxides were investigated, most based on or derived from the spinel structure. Syntheses included both conventional solid state reactions and chimie douce approaches. The products were characterized by x-ray diffraction, SQUID magnetometry, and in some cases ICP-OES.<br />The lithium spinels LiM<sub>2</sub>O<sub>4</sub> (M = V, Ti) were investigated for chemical lithium insertion and magnetic properties of their lithiated end products. These products, of formula LiM<sub>2</sub>O<sub>4</sub>, take on a rock salt structure but maintain the pyrochlore sublattice of the M<sup>3+ </sup>cations, a configuration that is subject to strong geometric magnetic frustration.</p> <p>Several synthetic pathways for LiV<sub>2</sub>O<sub>4</sub> and were investigated and evaluated based on their consistency in producing a chemically pure product with minimal magnetic defects. Although magnetic purity remained elusive, a ceramic synthesis using V<sub>2</sub>O<sub>3</sub> and a mixture of LiVO<sub>3</sub> and Li<sub>3</sub>VO<sub>4</sub> was the most reliable at generating a chemically pure product. The lithiated rock salt Li<sub>2</sub>V<sub>2</sub>O<sub>4</sub> was found to have sample dependent magnetic susceptibility. No Curie-Weiss region was determined up to 600 K, a good indication that the compound is strongly geometrically frustrated.</p> <p>The investigation of LiTi<sub>2</sub>O<sub>4</sub> and Li<sub>2</sub>Ti<sub>2</sub>O<sub>4 </sub>resulted in the discovery that lithium leaching occurs via lithium-organic phases adsorbed to the particle surfaces during the chimie douce synthesis. While the process occurs in a matter of months for LiTi<sub>2</sub>O<sub>4</sub>, a partially lithiated sample was completely returned to a pure spinel within a few weeks.<br />Investigation of the Jahn-Teller distorted spinel NiRh<sub>2</sub>O<sub>4</sub> revealed the phase Ni<sub>x</sub>Rh<sub>2.x</sub>O<sub>3.δ</sub>, which is related to the structure of orthorhombic Rh<sub>2</sub>O<sub>3</sub>(III). Magnetic properties of the new compound are unclear due to overlapping magnetic susceptibility with the spinel.</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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