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Solid state NMR chemical shifts as an alternative to diffraction data in the determination of SIC polytypic structures

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dc.contributor.author Guo, Degi. en_US
dc.date.accessioned 2009-07-09T18:42:58Z
dc.date.available 2009-07-09T18:42:58Z
dc.date.issued 1988-07-09T18:42:58Z
dc.identifier.uri http://hdl.handle.net/10464/2062
dc.description.abstract Silicon carbide, which has many polytypic modifications of a very simple and very symmetric structure, is an excellent model system for exploring, the relationship between chemical shift, long-range dipolar shielding, and crystal structure in network solids. A simple McConnell equation treatment of bond anisotropy effects in a poly type predicts chemical shifts for silicon and carbon sites which agree well with the experiment, provided that contributions from bonds up to 100 A are included in the calculation. The calculated chemical shifts depend on three factors: the layer stacking sequence, electrical centre of gravity, and the spacings between silicon and carbon layers. The assignment of peaks to lattice sites is proved possible for three polytypes (6H, 15R, and 3C). The fact that the calculated chemical shifts are very sensitive to layer spacings provides us a potential way to detennine and refine a crystal structure. In this work, the layer spacings of 6H SiC have been calculated and are within X-ray standard deviations. Under this premise, the layer spacings of 15R have been detennined. 29Si and 13C single crystal nmr studies of 6H SiC polytype indicate that all silicons and carbons are magnetically anisotropic. The relationship between a magnetic shielding tensor component and layer spacings has been derived. The comparisons between experimental and semi-empirical chemical shielding tensor components indicate that the paramagnetic shielding of silicon should be included in the single crystal chemical shift calculation. en_US
dc.language.iso eng en_US
dc.publisher Brock University en_US
dc.subject Silicon carbide. en_US
dc.subject Nuclear magnetic resonance. en_US
dc.subject Diffraction. en_US
dc.subject Solid state chemistry. en_US
dc.title Solid state NMR chemical shifts as an alternative to diffraction data in the determination of SIC polytypic structures en_US
dc.type Electronic Thesis or Dissertation en_US
dc.degree.name M.Sc. Chemistry en_US
dc.degree.level Masters en_US
dc.contributor.department Department of Chemistry en_US
dc.degree.discipline Faculty of Mathematics and Science en_US


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