Details of Grant 

EPSRC Reference:	GR/K24215/01
Title:	NEW TECHNIQUES FOR HIGH-PRESSURE DIFFRACTION STUDIES OF STRUCTURES AND TRANSITIONS AT SRS
Principal Investigator:	Nelmes, Professor RJ
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Department:	Sch of Physics and Astronomy
Organisation:	University of Edinburgh
Scheme:	Standard Research (Pre-FEC)
Starts:	01 April 1995	Ends:	31 March 1998	Value (£):	198,148
EPSRC Research Topic Classifications:	Condensed Matter Physics Materials Characterisation
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Summary on Grant Application Form
High pressure structure determination by powder-diffraction techniques has been transformed recently by the introduction of the image-plate area detector. This advance has opened up the possibility of full Rietveld refinement of crystal structures at high pressure for the first time. We have developed an image-plate system of currently unrivalled sensitivity at SRS Daresbury. With this facility we have obtained a wealth of entirely new information on II-VI, III-V and group IV semiconductors over the past two years. It seems that a whole new structural systematics is emerging that will transform this area of research and stimulate a large amount of new theoretical work. However, fully satisfactory results have not been obtained so far in a significant number of cases due to pronounced preferred orientation (PO) effects. It has become apparent that it is essential to determine the PO distribution completely separately from structure solution and refinement. We have completed the successful development of techniques and models to achieve this in simple cases. We now need to make extensive studies of more complex distributions and other microstructural effects, and construct new beamline equipment to allow for routine measurement of sample texture. These techniques will be applied to a further major programme to complete the present studies of the core semiconductor systems to 20GPa, and then to pursue the systematics to 'ultimate' high pressure phases in the 50-100GPa range, including new work on other II-VI and III-V systems.
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