Electronic Theses and Dissertations

Date of Award

1-1-2020

Document Type

Dissertation

Degree Name

Ph.D. in Physics

First Advisor

Joseph R Gladden

Second Advisor

Likun Zhang

Third Advisor

Nathan Murray

School

University of Mississippi

Relational Format

dissertation/thesis

Abstract

This dissertation primarily focuses on use of resonant ultrasound spectroscopic (RUS) measurements to investigate temperature- and pressure-dependent elastic properties of select materials: porous ceramics, which are used in a wide range of material applications, and thermoelectric tin selenide (SnSe), which is widely studied as an efficient thermoelectric material. RUS experiments were conducted on: ceramics used in LG fuel cells, alumina, zircona and titania, to explore their elastic behavior under the variation of hydrostatic pressure over the low- and high-pressure regimes (0.02 – 800 psi). All the porous ceramics exhibited a reversible material softening mechanism with increasing hydrostatic pressure. The comparison of material stiffening with increasing pressure observed from fully dense ceramics validates the poroelastic behavior of porous ceramics described by Biot’s theory of poroelasticity. The influence of saturated gas type and their physical properties on the above elasticity variation with hydrostatic pressure was analyzed qualitatively as well as quantitatively by using the helium, nitrogen, and argon gas saturation. The observed porous material stiffness with increasing temperature was explained by the partial sintering and microcrack healing mechanisms. Single crystalline SnSe has an orthorhombic Pnma phase that undergoes a displacive phase transition transforming into a Cmcm phase at ~810 K. Temperature dependence of elastic constants (C_ij) of SnSe were measured at elevated temperatures in the range of 295 – 773 K. The measured elastic constants were then used to explain the elastic anisotropic behavior, structural change, and the thermal transportation mechanisms of SnSe at higher temperatures. The occurrence of the phase transition at 803  10 K was analyzed by the temperature-dependent normal mode frequency trends. The validation of the measured elastic constants and derived elastic properties are discussed using the previously reported theoretical and experimental studies.

Available for download on Tuesday, August 31, 2021

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