Photon correlation spectroscopy study of slow relaxation in alkali germanate and phosphate germanate glass melts
The study of relaxation dynamics in network-forming oxide glass melts has been a long-standing challenge in condensed matter physics, owing in large part to the scarcity of experimental data compared to the wealth of studies conducted on molecular liquids and organic polymers. Over the past two decades, a series of photon correlation spectroscopy (PCS) investigations carried out by Dr.Sidebottom and colleagues at Creighton University have worked to fill this data gap by systematically probing the α-relaxation in a variety of alkali-modified network-forming oxides, beginning with sodium phosphate, then extending to sodium aluminophosphate, sodium borate, and sodium germanate glass melts. These studies revealed a compelling and consistent picture: the fragility of a network-forming glass melt is governed primarilyby the average bridging oxygen bond density of the oxide network, which in turn is controlled by the amount and type of alkali oxide added. A particularly striking finding from the sodium germanate study was the detection of a secondary slow relaxation process in addition to the primary α-relaxation, attributed to the diffusive motion of mobile sodium ions within the oxide network. This unexpected observation raised important new questions about the generality of this slow relaxation process across different glass-forming systems and motivated the investigations presented in this thesis. I report results in which photon correlation spectroscopy is used to identify and characterize the origin of a secondary slow relaxation process observed in both alkali germanate glass systems and in mixed phosphate-germanate glass systems.
Diffusivity, Dynamic light scattering, Germanate, Glass oxides, Photon correlation soectroscopy, Secondary relaxation
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