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XPS, Chalcogenides, XANES, Spectroscopy

Rudyk, Brent W.

Supervisor and department: Mar, Arthur Chemistry

Examining committee member and department: Rivard, Eric Chemistry McDermott, Mark Chemistry Veinot, Jonathan Chemistry Ivey, Douglas Chemical and Materials Engineering Bieringer, Mario Chemistry at University of Manitoba

Department: Department of Chemistry

Specialization:

Date accepted: 2013-11-28T16:14:03Z

Graduation date: 2014-06

Degree: Doctor of Philosophy

Degree level: Doctoral

Abstract: Several series of quaternary chalcogenides were synthesized by high temperature reactions and their crystal structures were determined by X-ray diffraction methods. Differences in electronic structure were examined by X-ray photoelectron spectroscopy XPS and X-ray absorption near-edge spectroscopy XANES. For some of these compounds, magnetic properties were also measured. New non-centrosymmetric quaternary chalcogenides RE3MM-Ch7 RE = La–Er; M = Fe, Co, Ni; M- = Ga, In; Ch = S, Se were synthesized and characterized. Their structure consists of isolated 1D chains of M-centred octahedra and M-centred tetrahedra. Shifts in the XPS and XANES spectra support the assignment of valence states consistent with the charge balanced formulation RE+33M2+M-3+Ch2-7. On proceeding from the sulphides RE3MM-S7 to the selenides RE3MM-Se7, the M-Ch bonds show increased covalent character. The Co 2p spectrum of La3CoInS7 exhibits asymmetric line broadening suggestive of electronic delocalization. The RE substitution affects the c-a ratios, which are the largest observed to date for compounds with this structure type, but does not drastically modify the electronic structure. Magnetic measurements indicated predominantly paramagnetic behaviour for most members, but antiferromagnetic ordering at low temperatures is suggested for a few members. The electronic structures of candidates for p-type transparent oxide semiconductors LaCuOCh Ch = S, Se, Te were investigated using XPS and XANES. The observation of large XPS binding energy shifts and the analysis of Cu M-edge XANES spectra supports the valence states in the formulation La3+Cu+O2-Ch2-. Subtle changes in the fine structure of La 3d core-lines provide evidence for the occurrence of interlayer interactions, namely that charge transfer takes place from the insulating and highly ionic LaO layer to the semiconducting and more covalent CuCh layer. This phenomenon was further probed in the solid solution LaCuOSe1-xTex, in which further evidence for interlayer charge transfer was found; intralayer Cu-to-Ch charge transfer within the CuCh layer becomes more pronounced upon substitution with more electronegative chalcogen atoms. Through a comparison of chalcogenide binding energy shifts, a new electronegativity value for Se, intermediate between S and Te, was proposed.

Language: English

DOI: doi:10.7939-R3V698K01

Rights: Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.





Autor: Rudyk, Brent W.

Fuente: https://era.library.ualberta.ca/



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