Degree Type

Dissertation

Date of Award

1990

Degree Name

Doctor of Philosophy

Department

Physics and Astronomy

First Advisor

David W. Lynch

Abstract

Optical properties and electronic structures of disordered Ag[subscript]1-xIn[subscript]x (x = 0.0, 0.04, 0.08, 0.12) and Ni[subscript]1-xCu[subscript]x(x = 0.0, 0.1, 0.3, 0.4) alloys and ordered AuGa[subscript]2, PtGa[subscript]2, [beta][superscript]'-NiAl, [beta][superscript]'-CoAl, CeSn[subscript]3, and LaSn[subscript]3 have been studied. The complex dielectric functions have been determined for Ag[subscript]1-xIn[subscript]x,Ni[subscript]1-xCu[subscript]x,AuGa[subscript]2, and PtGa[subscript]2 in the 1.2-5.5 eV region and for CeSn[subscript]3 and LaSn[subscript]3 in the 1.5-4.5 eV region using spectroscopic ellipsometry. Self-consistent relativistic band calculations using the linearized-augmented-plane-wave method have been performed for AuGa[subscript]2, PtGa[subscript]2,[beta][superscript]'-CoAl, CeSn[subscript]3, and LaSn[subscript]3 to interpret the experimental optical spectra. In Ag[subscript]1-xIn[subscript]x, the intraband scattering rate increases with increasing In concentration in the low-energy region (<3.5 eV). As the In concentration increases, the onset energy of the L[subscript]3→ L[subscript]sp2'(E[subscript]F) transitions, 4.03 eV for pure Ag, shifts to higher energies, while that of the L[subscript]sp2'(E[subscript]F) → L[subscript]1 transitions, 3.87 eV for pure Ag, shifts to lower energies. This is only partly attributable to the rise of the Fermi level E[subscript]F caused by an increase in the average number of electrons per atom due to the In solute and to the narrowing of the Ag 4d-bands. The L[subscript]1-band may also lower as In is added. In Ni[subscript]1-xCu[subscript]x, the 4.7-eV edge (from transitions between the s-d-hybridized bands well below E[subscript]F and the s-p-like bands above E[subscript]F, e.g., X[subscript]1→ X[subscript]sp4') shifts to higher energies, while the 1.5-eV edge (from transitions between a p-like band below E[subscript]F and a d-band above E[subscript]F, e.g., L[subscript]sp2' → L[subscript]3) remains at the same energy as the Cu concentration increases. A structure grows in the (2-3)-eV region as Cu is added, and it is interpreted as being due to transitions between the localized Cu subbands. For AuGa[subscript]2 and PtGa[subscript]2, both compounds show interband absorption at low photon energies (<1.3 eV). The interband absorption for AuGa[subscript]2 is strong at about 2 eV while that for PtGa[subscript]2 shows a broad structure in the range 2.5-4.5 eV, with a shoulder at 3.3 eV. The observed interband features in the imaginary parts of the complex dielectric functions [epsilon][subscript]2 can be interpreted in terms of band calculational results. For [beta][superscript]'-NiAl and CoAl all of the structures found in the optical spectra of both compounds involve states with some Ni/Co d-character in both the initial and the final states of the transitions. A self-energy correction for the excitation spectrum has been used for [beta][superscript]'-CoAl to improve the agreement. The optical conductivities of CeSn[subscript]3 and LaSn[subscript]3 show structures due to interband absorption at about 2 and 3 eV, which are mostly due to transitions between band-like Ce/La d- and f-states. The larger strengths of the structures in CeSn[subscript]3 than in LaSn[subscript]3 may be due to the existence of more f-character near E[subscript]F in CeSn[subscript]3 than in LaSn[subscript]3.

DOI

https://doi.org/10.31274/rtd-180813-12214

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Kwang Joo Kim

Language

en

Proquest ID

AAI9110519

File Format

application/pdf

File Size

118 pages

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