Degree Type

Dissertation

Date of Award

2003

Degree Name

Doctor of Philosophy

Department

Materials Science and Engineering

First Advisor

Steve W. Martin

Abstract

The glass forming range of the Ag2S + B 2S3 + GeS2 ternary system was investigated and a wide range of ternary glasses were obtained. The thermal properties of these thioborogermanate glasses were studied by DSC and TMA. The Raman, IR and NMR spectroscopy were used to explore the short-range order structure of the binary (Ag-B) and (Ag-Ge) and ternary (Ag-B-Ge) glasses. The Raman and NMR studies show that Ag2S goes into the GeS2 subnetwork to form pyrothiogermanate groups before going to the B2S3 subnetwork. In doing so, it is suggested that [B10S186- ] superstructure exist in Ag2S + B2S3 and Ag2S + B2S3 + GeS2 glasses. From these observations, a structural model for these glasses has been developed and proposed.;Fast Ion Conducting (FIC) glasses of composition xAg2S + (1-x)[0.5B 2S3 + 0.5GeS2] have been studied using neutron scattering to investigate their short-range order structure and intermediate range order structure. The total correlation functions T(r) were fitted with Gaussian functions and the bond length and coordination numbers of Ge-S, Ag-S and Ag-Ag correlations are determined. It is found that the Ag2S + B2S3 + GeS2 glasses are composed of a B 2S3 network containing [B10S18 6-] superstructure and an over-doped GeS4/2 network. The existence of boron superstructure contributes to the high mobility and conductivity of Ag ions. The temperature and composition dependence of Ag-Ag correlation supports that Ag ion interaction is a factor that cannot be ignored at relatively high temperature and could explain the origin of the non-Arrhenius behavior.;Conductivity measurements of zAgI + (1-z)[xAg2S + (1-x)(0.67B 2S3 + 0.33GeS2)] fast ion conducting glasses were performed to explore the non-Arrhenius behavior above room temperature. A distinct non-Arrhenius deviation is observed that causes the dc conductivity to be lower than the expected values. Ion Trapping Model has been used to describe the non-Arrhenius conductivity and fit the experimental data. It is found that the model is able to accurately reproduce the non-Arrhenius temperature dependence of the conductivity of these optimized fast ion conducting glasses. The model has only one independently adjustable parameter and it provides a physical picture of the cause of non-Arrhenius deviation.

DOI

https://doi.org/10.31274/rtd-180813-13135

Publisher

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

Copyright Owner

Qiang Mei

Language

en

Proquest ID

AAI3085931

File Format

application/pdf

File Size

138 pages

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