X-ray induced temperature dependent amorphous-amorphous transitions in the GeO2 glass

Glasses are non-equilibrium materials whose structure and dynamics can be strongly modified by external perturbations such as ionizing radiation. This thesis investigates the effects of intense X-ray irradiation on vitreous germanium dioxide (v-GeO₂), a prototypical strong oxide glass, by combining X-ray photon correlation spectroscopy (XPCS), X-ray diffraction (XRD), and inelastic X-ray scattering (IXS). The results demonstrate that intense X-rays induce atomic dynamics and structural transformations in v-GeO₂ far below the glass transition temperature. The induced dynamics evolves with absorbed dose toward a stationary state whose properties depend on the irradiation temperature. Structural measurements reveal increased density fluctuations and reduced medium-range order, indicating a radiation-induced rejuvenation of the glass toward higher fictive-temperature states. To investigate these phenomena, novel XPCS data-analysis methodologies were developed, including the multi-tau two-time-correlation (MTTTC) approach and advanced detector corrections, enabling reliable measurements over extended timescales and low-signal conditions. Finally, the combination of XPCS and IXS measurements allows the non-ergodicity factor and density fluctuations to be studied across a broad frequency range, providing new insight into the microscopic mechanisms governing irradiation-induced amorphous-amorphous transitions in oxide glasses.