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Title: Structural studies into AM(_2)O(_7) framework materials and parametric Rietveld refinement
Author: Stinton, Graham William
ISNI:       0000 0001 3485 8329
Awarding Body: Durham University
Current Institution: Durham University
Date of Award: 2006
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This thesis investigates the structural properties of the AM2O7 family of materials, many of which show interesting thermal expansion properties and remarkably complex structures. It also develops Parametric Rietveld refinement, a method of extracting more information from multi-condition powder diffraction data. Chapter 1 reviews the relevant literature. Chapter 2 describes the equipment and analytic techniques used in the work. Chapter 3 describes Parametric Rietveld refinement, which aims to fit a single, evolving structural model to a series of diffraction data collected as a function of time, temperature, pressure or other external variable. This can lead to a number of benefits over conventional, sequential Rietveld refinement: it can increase the precision of refined parameters; allow physically realistic models to be applied during data analysis; and allow 'non-crystallographic’ quantities, such as temperature or rate constants, to be refined directly from diffraction data. Chapter 4 presents a full structure solution of ZrP(_2)O(_7) at room temperature from powder diffraction data. This involved developing a method for combining Rietveld refinement, restraints and simulated annealing. Despite 136 unique atoms and close-to metrically cubic symmetry, the true structure of this orthorhombic material can be refined to a high degree of precision. Chapter 5 is an investigation into the structures and thermal expansion of two AM(_2)O(_7) species, pseudo-cubic SnP(_2)O(_7) and GeP(_2)o(_7). A full structure solution of the room temperature phase of SnP(_2)O(_7) is presented. Two higher temperature phases of SnP(_2)O(_7) and the low temperature phase of GeP(_2)o(_7) are also analysed. Variable temperature data for both materials are presented. Chapter 6 describes the synthesis and characterisation via powder diffraction of solid-state solutions of the general formula Zr(_x)Sn(_1-x)P(_2)o(_7). The variation of properties across the series is investigated both at room temperature and upon heating.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available