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Title: Pressure-induced structural and electronic effects in solids
Author: Crain, Jason
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1993
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A series of detailed experimental and computational studies on aspects of pressure-induced phase transitions in solids is described. The emphasis is on the nature of such transitions in tetrahedral semiconductors. It is found that the materials investigated exhibit previously unreported and very complex behaviour which is related to the structural transition. New high-pressure diffraction evidence suggests that the crystallographic structures of several III-V semiconductors are not in agreement with those suggested either by prior experimentation or total energy calculation. The high-pressure structures determined in this work are generally of lower symmetry than previously believed and in at least one case of much greater complexity. It is also argued that phase-transition-induced defects are created at the transition in many of these materials and that the transition may be sensitive to either the concentration or mobility of such defects. The development and implementation of a simple new x-ray detection method has allowed for the observation of these subtle processes for the first time. To a certain degree, these novel aspects of previously well-studied transitions are now amenable to theoretical and computational treatment through the advances made in modern computer technology and parallel algorithms. As a result, new ab-initio local density functional investigations of structural stability and possible transition routes in one of these materials have been performed and the results are in good agreement with observation. Also the issue of defects has been treated by Car-Parrinello-type pseudopotential calculations on defect energies. It is found, among other things that the defect formation energies are relatively low and that structural relaxation under the influence of Hellmann-Feynman forces is necessary in order to obtain accurate values of such energies. The remainder of the thesis is devoted to an exploration of pressure-induced metastable forms of group IV and III-V semiconductors. These studies unite and compare results from image plate experiments, ab-initio pseudopotential calculations as well as empirical calculations using pair potentials and are applied in an attempt to make speculations as to the relative structural stability of these phases at finite temperature.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available