Investigation of Electron Irradiation Induced Amorphous to Crystalline Phase Transformations in Nanostructured Ceramics
Creators: name: Keninger, Nathaniel John
Publisher: name: Purdue University Graduate School
Year: 2024
Subjects: classificationCode: 340301
subject: Inorganic materials (incl. nanomaterials)
classificationCode: 340307
subject: Structure and dynamics of materials
classificationCode: 340702
subject: Radiation and matter

description: The effects of electron irradiation induced amorphous-to-crystalline (a-to-c) phase transformations were investigated for 5 different nanostructured ceramic materials. Nanoporous Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub> nanotubes, ZrO<sub>2</sub> nanotubes, nanoporous Nb<sub>2</sub>O<sub>5</sub>, and nanoporous Ta<sub>2</sub>O<sub>5</sub> were analyzed <i>in situ </i>using transmission 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 transmission 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, intermediate, and concentrated beam conditions and 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, where the electron beam was spread to an area of 30-80μm<sup>2</sup>, with low electron flux consistently observed little to no a-to-c phase transformations, even over longer time scales. Intermediate beam experiments, where the electron beam was spread to an area of .08-.03μm<sup>2</sup>, observed consistent a-to-c phase transformation across all materials, though at varying rates and producing crystallites of various sizes between materials. Concentrated beam experiments, where the electron beam was spread to an area of .003μm<sup>2</sup>, consistently observed rapid a-to-c phase transformation, and also consistently produced larger crystallites compared to intermediate beam experiment counterparts. Comparison between materials showed a trend in susceptibility of crystallization under electron irradiation, with Nb<sub>2</sub>O<sub>5</sub> as the least susceptible to electron irradiation induced crystallization, followed by Ta<sub>2</sub>O<sub>5</sub>, then TiO<sub>2</sub>, then ZrO<sub>2</sub>, and Al<sub>2</sub>O<sub>3</sub> as the most susceptible to electron irradiation induced crystallization. The area of observed crystalline phases was fairly consistent with some outliers within each experiment, though varied both with material and beam concentration. Both production and dissipation of crystalline phases were observed. Dissipation of crystalline phases into amorphous phases appeared to be loosely correlated to the size of the grain within the material. Multiple material properties from literature were compared against the trend observed between materials, though no individual material property showed clear or consistent alignment with the experimental trend observed.