Date of Award
Master of Science (MS)
John E. Greedan
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.
The lithium spinels LiM2O4 (M = V, Ti) were investigated for chemical lithium insertion and magnetic properties of their lithiated end products. These products, of formula LiM2O4, take on a rock salt structure but maintain the pyrochlore sublattice of the M3+ cations, a configuration that is subject to strong geometric magnetic frustration.
Several synthetic pathways for LiV2O4 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 V2O3 and a mixture of LiVO3 and Li3VO4 was the most reliable at generating a chemically pure product. The lithiated rock salt Li2V2O4 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.
The investigation of LiTi2O4 and Li2Ti2O4 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 LiTi2O4, a partially lithiated sample was completely returned to a pure spinel within a few weeks.
Investigation of the Jahn-Teller distorted spinel NiRh2O4 revealed the phase NixRh2.xO3.δ, which is related to the structure of orthorhombic Rh2O3(III). Magnetic properties of the new compound are unclear due to overlapping magnetic susceptibility with the spinel.
Mitchell, Jonathan Everett, "Synthesis and Magnetic Properties of Spinel-Based Transition Metal Oxides" (2009). Open Access Dissertations and Theses. Paper 4174.
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