Surface Structural Relaxation Research Articles

Tensile stress-acceleration of the surface structural relaxation of SiO2 optical fibers

Tensile stress-acceleration of the surface structural relaxation of SiO2 optical fibers

Tensile stress-acceleration of the surface structural relaxation of SiO 2 optical fibers

The surface relaxation kinetics of commercial silica optical fibers were studied by measuring the IR band positions in reflection, which are directly correlated with the SiOSi bond angle as well as the fictive temperature of the glass. The silica glass optical fibers were heat-treated at 650°C under 355 torr water vapor pressure and dry nitrogen atmosphere with and without applied stress. It was found that the relaxation kinetics were measurably accelerated by a tensile stress in the presence of water vapor.

Surface and bulk structural relaxation kinetics of silica glass

The structural relaxation kinetics of a silica glass were measured by following the IR structural band positions, which are directly correlated with the average Si–O–Si bond angle as well as with the fictive temperature of the glass, as a function of heat-treatment time, temperature and the water vapor pressure. Both surface relaxation and bulk relaxation kinetics were determined by measuring the IR reflection and absorption band positions, respectively. The surface relaxation was much faster than the bulk relaxation and had a smaller activation energy. Also, both relaxation kinetics were faster in the presence of water vapor. The apparent bulk relaxation time determined from the IR absorption band shift was a composite relaxation time consisting of both the relaxation time of the water-catalyzed near surface layer and the true bulk relaxation time of the glass interior which is unaffected by water vapor. The true bulk relaxation time was evaluated and found to have an activation energy consistent with that of the viscous flow.

Surface Structural Properties of Crystallines-Triazine: A Computational Investigation

Abstract This paper considers the surface structural properties and crystal morphology of crystalline s-triazine. A key feature of the computational approach adopted is the consideration of surface structural relaxation of the uppermost section of the crystal and the use of non-rigid molecules. Crystal morphologies calculated on the basis of surface energies and attachment energies are considered.

Computational investigation of surface structural relaxation in crystalline urea

The effects of surface structural relaxation on the energetic and morphological properties of crystalline urea have been investigated. Specifically, the {001}, {110}, {200}, {101}, {111} and {[graphic ommitted]} surfaces have been considered. Upon relaxation of the cleaved surfaces, significant perturbations in the positions and internal geometries of the molecules (compared with the corresponding positions in the bulk crystal structure) are observed. Interestingly, the {[graphic ommitted]} surface has a lower surface energy than the {111} surface, and thus a polar morphology is predicted. The predicted crystal shape is compared with that observed experimentally (for crystals grown by deposition from the vapour phase), and reasons for discrepancies between the calculated and experimental morphologies are discussed.

Interrelationship between Densification, Crystallization, and Chemical Evolution in Sol‐Gel Titania Thin Films

The mechanisms contributing to densification during non‐isothermal heat treatments in sol‐gel titania films have been studied. At low temperatures, shrinkage is attributed to condensation reactions between hydroxyls located primarily within the oxide skeleton. At higher temperatures, densification is due to both continued condensation between surface hydroxyls and structural relaxation. Shrinkage stops when films attain a level of crystallinity corresponding to the percolation threshold. At conventional rates, densification is delayed by faster heating; however, at very fast heating rates provided by rapid thermal annealing (8000°C/min), condensation is highly arrested and densification is faster. Similarly, the onset of crystallization increases with conventional heating rates, but crosses over to a lower temperature with rapid thermal annealing.