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Title: Preferred orientation modelling in high-pressure powder diffraction applied to structural studies of semiconductors
Author: Wright, Nicholas George
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1994
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This thesis presents a new technique which makes use of the ability of area detectors, such as image-plates, to record simultaneously data from crystallites in many different orientations to model texture from samples under pressure. Experimental methods have been developed to allow data to be collected of sufficient quality to allow preferred orientation of the sample to be accurately modelled. A new preferred orientation model is presented that describes the effect of preferred orientation on the whole 2-D powder pattern and is suitable for the transmission geometry used in high-pressure angle-dispersive diffraction. Techniques are developed which make use of the new model and the 2-D character of the effect of preferred orientation on the powder pattern to de-correlate the effects of texture and structure on the powder pattern. The model and these techniques are tested against diffraction data collected from a wide range of sample orientations from a sample of known texture. The techniques are applied to a study of the crystal structures of three high-pressure phases of the II-VI semiconductor HgTe. A detailed study of the crystal structure of the cinnabar phase of HgTe is presented, which shows the structure to be different from the prototype HgS cinnabar, with coordination much closer to 4-fold. Results on the pressure dependence of the structure are presented and discussed in relation to the transformation upon further pressure increase to the NaCl structure. A structural study of the previously unsolved HgTe phase IV is presented. This phase, which forms with particularly severe preferred orientation, is found to be an orthorhombic distortion of the NaCl structure. Also presented is a short study of HgTe phase V, which is observed to occur above 29 GPa and to have a disordered b.c.c. structure.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available