Understanding and controlling thermal and mechanical stability in nanoscale metal-oxide systems

Nanoscale metal-oxide systems exhibit desirable characteristics that are attractive for many applications. In order to access these properties, it is necessary to understand and tune the atomic-scale crystal structure and nanoscale architecture to produce metastable states that do not normally exist in bulk forms under ambient conditions. These states are formed by controlling the size and thermal stability of the nanoscale structure. In addition to controlling thermal stability, understanding mechanical stability in nanoscale metal oxides is essential, as optimum materials should remain robust and intact. This dissertation addresses the control of thermal stability in zirconia nanoparticles and ordered mesoporous titania films, and complements this knowledge by examining the mechanical stability of nanoperiodic silica/polymer composite films.; To better understand the phase stability and mechanical stability of nanoscale metal-oxide systems, the rearrangements that produce and alter these materials must be thoroughly examined. The first part of this dissertation explores the thermal stability of amorphous and crystalline zirconia nanoparticles by changing the interfacial chemistry through a core/shell motif. After synthesizing and coating the particles with a thin alumina shell, the transition temperatures and kinetic barriers for amorphous zirconia crystallization, tetragonal zirconia grain growth, and formation of monoclinic zirconia are found to be drastically altered. In a related system, kinetic analysis is used to examine coupled rearrangements in nanoperiodic titania/polymer composite films. As the initially-amorphous wall structure crystallizes, the ordering of the polymer domains can deteriorate to produce a random porous material. By understanding and controlling the kinetics of the crystallization process, a semiconducting thin film with order on both atomic and nanometer length scales can be achieved. Lastly, the effects of nanoscale architecture on the mechanical stability of silica/polymer composite films are probed by imparting uniaxial strain along two different dimensions in an anisotropic hexagonal architecture. These films show anisotropy in their tensile behavior that indicates nanoscale metal-oxide structures can be ordered to produce materials with tunable stiffness and elasticity.