Mixed-metal oxide nanopowders for structural and photonic applications

This dissertation uses liquid feed flame spray pyrolysis (LF-FSP) to synthesize and process mixed-metal nano oxides with well-defined structural and photonic properties. LF-FSP combusts a metal oxide precursor solution and oxygen aerosol to produce nanoparticles with the same metal ratio as the precursor solution. The ability to tailor compositions and morphologies of the resultant nanopowders through the use of multiple liquid based metal-oxide precursors lends itself to combinatorial studies of composition and morphology, which is highly useful in property optimization.; We first chose to investigate the effects of different aluminum oxide precursors on the morphology of the resulting alumina nanoparticles. This study showed that the metal ligand strongly influences the particle morphology based on the mechanisms of ligand decomposition. We successfully applied flame spray pyrolysis for the first time to synthesize combinatorially MgO:Al 2O3 with MgO concentrations in the range 0.005--50 mol%. The investigation provide a complete picture of the physical phase structure and associated native defect content over the full concentration range allowed by thermodynamics, but controlled by kinetics resulting in novel metastable phase formation and optimization the novel UV emission behavior.; To demonstrate how the choice of ligand depends on the desired property, two different ceria ligands were used to alter the ceria doping mechanism of the alumina nanoparticles. The use of combustible, cerium propionate increased in the theta-alumina phase stability through increased dopant homogeneity and nano-domain development compared to the nitrite derived nanopowder. While the inorganic, cerium nitrate appears to favor Ce3+ in the Ce3+/4+ redox couple providing novel incoherent lasing.; Previous combinatorial upconversion emission studies on co-doped yttria (Y0.86Yb0.11Er0.03)2O3 provided nanopowders that could be densified to give the first example of a submicron transparent upconversion ceramic sintered at 1400°C with unprecedented dopant concentrations of > 10 mol% allowing new photonic application to be realized. In addition, these sintering studies demonstrated the exceptional sinterability of LF-FSP powders.; In toto, this dissertation demonstrates many experimental firsts that have only been predicted previously; including, the furthest extension of the magnesium spinel phase field, incoherent lasing, submicron transparent upconversion ceramics and reduced sintering parameters due to unaggregated nanocrystalline powders.