Synthesis and Magnetic Properties of Spinel-Based Transition Metal Oxides

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 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.</p> <p>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.</p> <p>The investigation of LiTi₂O₄ and Li₂Ti₂O₄resulted 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.<br />Investigation of the Jahn-Teller distorted spinel NiRh₂O₄ revealed the phase Ni_xRh_2.xO_3.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.</p>