"Investigation of Electron Irradiation Induced Amorphous to Crystalline Phase Transformations in Nanostructured Ceramics" 

Nathaniel Keninger, MSE MS Candidate 

Advisor: Professor Janelle Wharry

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ABSTRACT

The effects of electron irradiation induced amorphous-to-crystalline (a-to-c) phase transformations were investigated for 5 different nanostructured ceramic materials. Nanoporous Al2O3, TiO2 nanotubes, ZrO2 nanotubes, nanoporous Nb2O5, and nanoporous Ta2O5 were analyzed in situ using tunneling electron microscopy (TEM) techniques, where the imaging 200kV electron beam was used also as an electron irradiation source. TEM techniques for analysis include high-resolution tunneling electron microscopy (HR-TEM), selected area electron diffraction (SAED), and electron energy-loss spectroscopy (EELS). Each material was examined starting from an as-grown amorphous state, with experiments using diffuse 3-5μm diameter, intermediate 160-100nm diameter, and concentrated 30nm diameter beam conditions as well as various durations of irradiation. Flux of irradiating electrons, as controlled by the spread of the electron beam, showed to have considerable and consistent impact on a-to-c phase transformations for all materials. Diffuse beam experiments showed no appreciable a-to-c phase transformation, intermediate beam experiments showed some a-to-c phase transformation, and concentrated beam experiments showed rapid a-to-c phase transformation. Comparison between materials showed a trend in susceptibility of crystallization under electron irradiation, with Nb2O5 as the least susceptible to electron irradiation induced crystallization, followed by Ta2O5, then TiO2, then ZrO2, and Al2O3 as the most susceptible to electron irradiation induced crystallization. The size of observed crystalline phases was fairly consistent with some outliers within each experiment, though varied both with material and beam concentration. Multiple material properties from literature were compared against the trend observed between materials, though no property was found that completely or clearly explained the experimentally observed trend.