Award Date

5-1-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Committee Member

Ashkan Salamat

Second Committee Member

David Shelton

Third Committee Member

Andrew Cornelius

Fourth Committee Member

Paul Forster

Number of Pages

132

Abstract

The ability to access a vast region of the pressure-temperature landscape using energy density tuning enables exotic states of matter to be probed. A well documented method for such exploration, under static conditions, is the use of the laser-heated diamond anvil cell (LH-DAC), accessing a combination of high pressure (>300 GPa) and high temperature (>5000 K). This thesis presents our development of direct CO2 laser heating techniques to study a series of wide band gap insulators, La2Sn2O7, ZrO2, and CeO2, under high pressure conditions. The lasing frequency of CO2 lasers is such that these wide band gap materials absorb the light directly through anharmonic polariton-phonon scattering processes in the material.

In the early stages of our high pressure-temperature laboratory development, a study on the pyrochlore La2Sn2O7 was done using CO2 laser-heating. This study investigated the pressure induced amorphization, and the production of a high pressure phase through laser annealing of La2Sn2O7. This study however was carried out with a lack of in situ diagnostics, a common shortcoming for all experiments prior to this thesis. This thesis reports a series of developments for instrumentation that enabled an ensemble of in situ measurements that are used to investigate wide band gap oxides, such as La2Sn2O7, ZrO2, and CeO2.

Three Raman systems were built in the UNLV laboratory. In addition, a series of CO2 laser heating systems were built. Two dedicated laser heating systems were developed for in situ measurements at Argonne National Laboratory's Advanced Photon Source using synchrotron techniques that allow temporal and spatial resolved diagnostics. These are currently installed at sector 16-IDB for in situ x-ray diffraction, and at 16-BMD for in situ x-ray absorption spectroscopy. In addition, an in-house dedicated system was developed for CO2 laser-heating system, coupled with in situ Raman spectroscopy. A series of techniques were developed and implemented in these systems, such as power stabilization, pyrometry, on-axis laser-heating, mode scrambling, and peak scaling.

Finally, the Clausius-Clapeyron slope of ceria (CeO2) under high pressure and temperature is mapped using in situ Raman spectroscopy to determine both phase and temperature information.

Keywords

CeO2; Claussius-Clapeyron relation; High Pressure; La2Sn2O7; Laser heating

Disciplines

Condensed Matter Physics | Optics

File Format

pdf

File Size

23.4 MB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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