Controlling Defect Fluorites via Oxidative Charge Ordering in Sc2V1-xMxO5+δ (M = Ti, Cr)

Abstract

The scandium vanadate system contains a diverse family of structures including the bixbyite (s.g. Ia-3), defect fluorite (s.g. Fm-3m), zircon (s.g. I41/amd), and tetragonal-Sc2VO5 (s.g. I-4) structures. Here the structures of the scandium vanadates are determined by charge and size of cations, and oxygen stoichiometry. Consequently, redox chemistry can be used to control the oxidation state of vanadium and navigate between these structures. This thesis focuses on vanadium’s neighbouring elements, titanium and chromium, and investigates if similar chemistry can be conducted as for the scandium vanadates. A series of Sc2V1-xMxO5+δ (M = Ti and Cr) phases were prepared and a detailed structural analysis was conducted including x-ray and neutron diffraction, XANES and DC magnetic susceptibility measurements.

Of particular interest is the tetragonal-Sc2VO5 structure. The vanadium sublattice within the tetragonal structure consists of two distinct crystallographic sites with octahedral and tetrahedral coordination. We show that the octahedral and tetrahedral sites can be individually controlled as demonstrated with the synthesis of tetragosnal-Sc2Ti0.8V0.2O5+δ where Ti4+ and V5+ occupy octahedral and tetrahedral sites, respectively. Notably the vanadium sublattice consists of tetrahedral motifs that are geometrically frustrated. Substitution of paramagnetic chromium into the tetrahedral site provides a route to tune magnetic interactions within the tetragonal I-4 structure.