Award Date

8-2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Physics

Department

Physics and Astronomy

First Committee Member

John Farley, Chair

Second Committee Member

Allen Johnson

Third Committee Member

Michael Pravica

Fourth Committee Member

Oliver Tschauner

Graduate Faculty Representative

Clemens Heske

Number of Pages

155

Abstract

Solid solution spinel oxides of composition MgxNi1−xCr2O4, NiFexCr2−xO4, and FexCr3−xO4 were synthesized and characterized using x-ray diffraction and Raman spectroscopy. Frequencies of the Raman-active modes are tracked as the metal cations within the spinel lattice are exchanged. This gives information about the dependence of the lattice vibrations on the tetrahedral and octahedral cations. The highest-frequency Raman-active mode, A1g, is unaffected by substitution of the divalent tetrahedral cation, whereas the lower frequency vibrations are more strongly affected by substitution of the tetrahedral cation. The change in wavenumber of many phonons is nonlinear upon cation exchange. All detected modes of MgxNi1−xCr2O4 and FexCr3−xO4 exhibit one-mode behavior. Additional modes are detected in the NiFexCr2−xO4 series due to cation inversion of the spinel lattice.

Results from the FexCr3−xO4 spinels are then applied to identifying the corrosion layers of three stainless steel samples exposed to lead-bismuth eutectic in a high temperature, oxygen-controlled environment. The Raman spectrum of the outer corrosion layer in all steels is identified as Fe3O4. The wavenumber of the A1g mode for the inner corrosion layer indicates an iron chromium spinel oxide. Micro-Raman spectroscopy proves capable of determining structural and compositional differences between complex corrosion layers of stainless steels.

Keywords

Artificial minerals; Crystal lattices; Raman spectroscopy; Spinel; Spinel group; Vibration; Vibrational

Disciplines

Condensed Matter Physics | Materials Science and Engineering | Mineral Physics | Physics

Language

English


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