Connecting structure and dynamics in glass forming materials by photon correlation spectroscopy

Dynamic light scattering in network-forming sodium ultraphosphate liquids near the glass transition

“…5, we plot the nonergodic level observed near T g for our ultraphosphate samples along with values reported previously 14 for other glass-forming liquids including two network-forming oxides ͑B 2 O 3 and As 2 O 3 ͒ and several molecular liquids ͑orthoterphenyl, salol, and 0.4Ca͑NO 3 ͒ 2 -0.6KNO 3 as well as values observed for a hard-sphere liquid in molecular-dynamics simulations. In the previous study, 14 we highlighted the interesting correlation between the nonergodic level and the inverse fragility ͑as depicted by the dashed line͒; a correlation that is congruent with a similar correlation 13,36,37 reported for the Debye-Waller factor of the solid phase. The implication of this correlation is that as fragility increases, a greater portion of the structure decays in the form of fast, localized relaxations with the partition between fast and slow decays approaching about 50% in the high fragility limit.…”

Viscoelastic relaxation in molten phosphorus pentoxide using photon correlation spectroscopy

“…This value is identical to that reported 14 for SiO 2 and GeO 2 and only slightly more fragile than As 2 O 3 ͑m Ϸ 18± 2͒. 8,9 These fragility values are near the m = 16 limit 14 for strong glass formers, and their nearly Arrhenius-type temperature dependence would suggest that viscous flow occurs predominantly through a tear and repair process. By comparison, the two metaphosphate liquids possess a polymeric structure consisting of PO 3 chains that are more weakly cross linked by alkali-metal ions.…”

“…9 All measurements were performed at a 90°scattering angle and only the vertically polarized scattering was analyzed owing to the abnormally low scattering intensity. In our experience 7,9,19 with other oxide liquids ͑B 2 O 3 and As 2 O 3 ͒ a distinct beam of scattered light was visible to the naked eye and could be confidently separated from stray parasitic elastic scattering. This was not the case for P 2 O 5 and as a result of its weak scattering ͑I S ͒ relative to the parasitic elastic light ͑I LO ͒, only heterodyne detection could be achieved.…”

“…No attempt was made to determine either I S or I LO and so the actual amplitude of S q ͑t͒, the so-called nonergodic level, 9 could not be estimated.…”

Glass‐Forming Dynamics of Aluminophosphate Melts Studied by Photon Correlation Spectroscopy

“…This is partly due to the refractory temperatures at which such melts must be studied and is particularly unfortunate as these network‐forming liquids are most suitable to the sort of two‐state bond model developed by Angell and Rao and it would be instructive to better assess the validity of such models. For these reasons, our research group has endeavored in the past few years to apply dynamic light scattering to study variety of oxide glasses . In our most recent study of sodium phosphates, we examined how the fragility increases with the addition of sodium oxide to P 2 O 5 .…”