Degree Type

Dissertation

Date of Award

1984

Degree Name

Doctor of Philosophy

Department

Chemistry

Abstract

The effect of metal atom vacancies on the electronic structure, i.e., the distribution of quantized electron states in the crystalline lattice, and the high temperature thermodynamics of scandium monosulfide are presented in an attempt to understand the stability and bonding of these high temperature compounds;The self-consistent, nonrelativistic band structure calculations, employing the KKR Green's function method, were performed for stoichiometric Sc(,1.00)S and a hypothetical ordered defect compound of composition Sc(,3)S(,4). When metal atom vancancies are introduced, (a) the wavefunctions associated with the sulfur atom near a va- cancy are redistributed, inducing nonbonding p-states and (b) the covalency of the metal-nonmetal bonding interaction is enhanced, resulting in an unchanged scandium valency. Analysis of the charge density suggests that the primary metal-metal bonding interaction is directed through the octahedral faces of the sulfur polyhedron, while a secondary interaction is directed through the edges. Vacancy formation and stabilization is thought to be energetically driven but the exact nature has not been determined;The high temperature vaporization of a scandium rich mono- sulfide was investigated by the mass loss Knudsen effusion method. The homogeneity range was found to extend into the metal-rich region, as far as Sc(,1.14)S, as determined by the rapid decrease in the Sc partial pressure at the start of a run. The activity of ScS in Sc(,0.8065)S(s) was determined to be 0.48 (+OR-) 0.05 and is constant over the temperature interval of 1950 K - 2100 K. The energy required to create approximately 20% scandium vacancies in ScS is 25.0 (+OR-) 1.8 kcal mol('-1) at 298 K. A third-law temperature independent enthalpy of;atomization at 298 K of ScS is 255.7 (+OR-) 2.6 kcal mol('-1) and the enthalpy of formation at 298 K of ScS is -98.7 (+OR-) 2.8 kcal mol('-1); *DOE Report IS-T-1133. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.

DOI

https://doi.org/10.31274/rtd-180813-12009

Publisher

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

Copyright Owner

Jan Fujie Nakahara

Language

en

Proquest ID

AAI8505853

File Format

application/pdf

File Size

101 pages

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