The Structure and Dynamics of Fundamental Glasses by Neutron Scattering Techniques

Abstract

The method of isotope substitution in neutron spectroscopy is introduced to measurefor the rst time the partial vibrational density of states of two network glass formingsystems, namely GeSe2 at temperatures of 5, 20 and 292 K and GeO2 at a temperatureof 10 K. This work included the development of a new data analysis procedure involvingcorrections for e.g. beam attenuation, multiple scattering and multiple phonon scattering.The measurements were made using the MARI and MERLIN spectrometers at theISIS pulsed neutron source where measurements of the elastic lines were used to helpdeduce the mean squared atomic displacements and Debye-Waller factors. In the caseof GeSe2, the latter were found as a function of temperature between 10 and 280 K.The results for GeSe2 glass at temperatures of 5, 20, and 292 K were found to be ingood agreement, proving the ecacy of the data correction procedure. For both GeSe2and GeO2, the results were interpreted with the aid of molecular dynamics simulationsto identify the energies corresponding to rocking, bending and stretching motions.The method of in situ high pressure neutron diraction was developed using doubletoroid sintered diamond anvils in a Paris-Edinburgh press to measure, for the rsttime, reliable diraction patterns for GeO2, SiO2 and B2O3 glasses at pressures up to17.5 GPa. The total pair distribution functions were obtained, allowing the nearestneighbour Ge-O, Si-O or B-O coordination numbers and bond distances to be calculated.The glass networks collapse by two principal mechanisms. The rst mechanism,at lower pressures, involves a rearrangement of the structural motifs on an intermediaterange length scale. The second mechanism, above thresholds in pressure of 5, 20 and9 GPa for GeO2, SiO2 and B2O3, respectively, involves a change in the nature of thestructural motifs.

Date of Award	21 Nov 2012
Original language	English
Awarding Institution	University of Bath
Supervisor	Philip Salmon (Supervisor)