Ph.D. Defense
Understanding the high-pressure behavior of transport properties has
been a driving force in the study of materials under extreme
conditions for well over a century being pioneered by P.W. Bridgman in
the early 20th century. Research dedicated to the study of these
properties leads to a variety of important applications: exploration
of insulator to semi-conductor to metal structural and electronic
phase transitions, correlation of structural phase transitions and the
electronic properties along phase boundaries, testing validity of
theoretical models, understanding the effects of chemical pressure,
among a slew of other applications. This work has designed and
developed a specialized sample cell assembly for use with a
Paris-Edinburgh press capable of performing high-pressure and
high-temperature (HP-HT) electrical resistance, Seebeck coefficient,
thermal conductivity measurements alongside energy-dispersive X-ray
diffraction and X-ray radiography imagining up to 6 GPa and 500°C to
fully characterize the electrical, thermal, and structural properties
of materials simultaneously at extreme conditions. This system has
been installed at Argonne National Laboratory at the Advanced Photon
Source at the Sector 16 BM-B beamline of the High-Pressure
Collaborative Access Team and is now available to general users as a
measurement technique. Application of this system has been applied to
thermoelectric materials: PbTe, SnTe, TiCoSb, and
TiNiSn. Thermoelectric materials provide a valuable means of
converting waste heat into useful electrical energy and studying their
HP-HT properties allows a better understanding and identification of
greater efficiency through tuning of transport properties. The
detailed discussion of the design and development of this system
alongside the important results on the thermoelectric materials
mentioned will be presented in this dissertation.
