Dynamic light scattering study of the non-exponential α-relaxation in sodium germanate glass melts

Photon correlation spectroscopy is used to measure the dynamic structure factor in a series of network-forming sodium germanate glass melts at temperatures near but above the glass transition. In addition to the primary α -relaxation, a slower diffusive process is identified with the diffusion of mobile Na cations within the oxide network. Along with determination of the glass transition temperature and fragility index, the non-exponentiality of the α -relaxation is characterized and compared with previous studies in sodium phosphate and sodium borate melts. A key result found here is a temperature-dependent stretching exponent which uniformly approaches a universal value of β = 0.5 in all three oxide systems as the glass transition is approached.