Award Date

5-1-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Committee Member

Andrew Cornelius

Second Committee Member

Yusheng Zhao

Third Committee Member

Leonard Zane

Fourth Committee Member

Stanislav Sinogeikin

Fifth Committee Member

Hartmut Schneider

Sixth Committee Member

Wanda Taylor

Number of Pages

201

Abstract

Even though mullite occurs rarely in nature, it is perhaps one of the most important phases in both traditional and advanced ceramics. Existing and emerging applications of mullite and mullite-type materials include: high-temperature composites, aerospace materials, ballistic shielding for military applications and even non-linear optical materials. There are many uncertainties regarding the basic physical properties of mullite-type materials, particularly in terms of their high-pressure structural stability and mechanical behavior that are important to address for emerging applications of mullites as engineering materials. This work is the first reported comprehensive investigation of the high –pressure structural behavior of several different mullites and synthetic mullite-type oxides. The materials investigated are representatives of different structural and chemistry branches of the mullite family. The goal is to elucidate how the most fundamental building blocks of mullite oxides accommodate high pressure compression. Mullites and mullite-type oxides are investigated at extreme pressures using synchrotron x-ray diffraction and laser Raman spectroscopy. These experiments enable the extraction of the materials’ structure and its modifications in a function of increasing pressure: deformation of polyhedra, phase transitions, formation and breaking of bonds. The experimental techniques used here are ideally suited to provide a synergical interplay in the study of oxides under high-pressure conditions: Raman spectroscopy is a technique for investigating short range order phenomena while x-ray diffraction accesses structural changes occurring at the long range order. The following phenomena are discussed: phase transitions, equations of state, pressure-driven amorphization, and the very rare effect of negative linear compressibility. The unprecedented discovery of negative linear compressibility in mullite-type oxides presented here opens the door to military applications as incompressible optical materials.

Keywords

Ceramics; Diamond anvil cell; High pressure (Science); Laser Raman spectroscopy; Mullite – Mechanical properties; PbAlBO4; PbFeBO4; Synchrotrons; X-ray diffraction

Disciplines

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

Language

English

Available for download on Thursday, May 31, 2018


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