Structural studies using synchrotron X-ray powder diffraction and other techniques

Chapter 1 gives an introduction to X-ray and neutron powder diffraction and the use of these techniques for crystal structure determination and refinement. The Rietveld structure refinement method is described and examples of different methods of structure determination from powder diffraction data are given. The techniques of EXAFS and Mossbauer spectroscopy, which were used to provide additional structural information, are also introduced. Chapter 2 describes the different radiation sources and experimental techniques used in this work. Chapter 3 describes a structural study of magnetite, Fe₃O₄, below the Verwey phase transition (~120 K). The P:2/c structure of Fe₃O₄ at 60 K has been refined with lattice parameters of a= 5.9412(3) Å, b = 5.9290(3) Å, c = 16.789(1) Å and β = 90.196^\circ. A variable temperature study of the Fe₃O₄ lattice parameters between 2-280 K shows this transition is first-order. An EXAFS study between 80-270 K shows that there is no significant change in the average Fe-0 distance in Fe₃O₄ around the transition. Chapter 4 describes a structural study on a material related to magnetite, Fe₂OBO₃. Two phase transitions have been found for this material. The first of these is due to magnetic ordering and takes place at -155 K. The second is due to charge ordering and takes place at 315 K, this is a structural (P2₁/c $\Longleftrightarrow$ Pnma) transition. Chapter 5 describes a resonant scattering experiment done on CsI. Resonant scattering parameters have been refined from synchrotron X-ray powder diffraction data collected at room ' temperature ,md al -+ K close to the Cs and I K-edges. The refined f parameters are -6.2(2) e/atorn (Cs. A = 0.3453 A), -9.0(1) e/atom (I. A = 0.374105 A.) and -6.2(2) e/atom (I, 4 K, A = 0.37367 Å). Chapter 6 describes the ab initio structure determination of 4-(2'3'4'-trifluorophenyl)-1235 dithiadiazolyl (C₇S₂N₂F₃H₂ P2 /n, a = 11.543(4) Å, b = 20.666(8) Å, c = 7.045(2) Å and β = 100.35(4)) using synchrotron X-ray powder diffraction data. A global optimisation method was used to provide a starting model for Rietveld refinement.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

1999

Author dc:creator

• Bell, Anthony Martin Thomas

Licence

• https://www.repository.cam.ac.uk/bitstreams/6060bccc-9e6c-4b22-8345-53c9365bbcb8/download
• http://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.41650

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/294545