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Title: Modelling the structural and vibrational properties of amorphous materials
Author: Christie, J. K.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2006
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The thesis describes modelling studies of amorphous, or non-crystalline, materials. It is split into two parts: modelling the vibrational behaviour of amorphous materials, and modelling their atomic structure. A recurring theme is representing amorphous materials as disordered crystals, and exploring to what extent this is a realistic representation. Adding force-constant and positional disorder to a diamond crystal lattice allows some, but not all, of the features of the vibrational spectrum of a realistic amorphous silicon model to be reproduced. Various properties of realistic amorphous silicon models are then examined: localization, scaling of the width of the spectral density with wavevector, and the boson peak. The medium-range structure of certain amorphous materials is shown to be well reproduced by the simple method of adding positional disorder into the structures of their crystalline counterparts. In particular, the wavevector of the first sharp diffraction peak in amorphous silicon and vitreous silica can be predicted. Further, the medium-range atomic structure of very high-density amorphous (VHDA) ice can be predicted by combining certain disordered crystalline ice phases. The best-fit phase fractions of these crystalline phases are very close to those observed in the experimental recrystallization of VHDA ice. Finally, connections between the structures of the high-pressure amorphous phases of silicon and ice are explored.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available