Thesis (M.S.)--University of Texas at El Paso, 2007. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (Ph. D.)--Michigan State University. Dept. of Chemistry, 2006. / Title from PDF t.p. (viewed on June 19, 2009) Includes bibliographical references. Also issued in print.

Thesis (M.S.)--Michigan State University. Materials Science and Engineering, 2008. / Title from PDF t.p. (viewed on Aug. 7, 2009) Includes bibliographical references (p. 151-159). Also issued in print.

Thesis (Ph. D.)--University of Oregon, 2005. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 110-113). Also available for download via the World Wide Web; free to University of Oregon users.

The main focus of this work is on exploratory investigation of thermoelectric (TE) materials. Thermoelectric devices are solid-state devices that convert thermal energy from a temperature gradient into electrical energy (Seebeck effect), or convert electrical energy into a temperature gradient (Peltier effect). Modifying existing materials and finding new materials with proper thermoelectric properties are the two approaches considered in this research. Good thermoelectric materials are usually narrow band gap semiconductors with large Seebeck coefficient, reasonably high electrical conductivity and low thermal conductivity. Early transition metal antimonides and arsenides, with unique structural features were chosen for finding high performance TE materials. During the investigation of group four antimonides, a series of new ternaries, ZrSiδSb2-δ, ZrGeδSb2-δ and HfGeδSb2-δ was developed. Single crystal X-ray diffraction was used for crystal structure determination, and energy depressives X-ray analysis (EDX) was used for compositional analysis. Metallic properties of these compounds were predicted by electronic structure calculations and confirmed by physical property measurements. It was revealed that Mo3Sb7 turns semiconducting by partial Sb/Te exchange. Similarly, isostructural Re3As7 was modified to become semiconducting by partial Ge/As exchange. Crystal structures were determined by single crystal X-ray and powder X-ray diffraction utilizing Rietveld method. Electronic structures were determined by using the LMTO method and confirmed the semiconducting properties of these ternary compounds. Physical property measurements showed exceptional TE properties for these compounds. It was also confirmed by the X-ray single crystal analysis that it is possible to intercalate different cations with the proper size into the existing cubic voids of the structure. The effect of cation intercalation on physical properties of these compounds were investigated and revealed the enhancement of transport properties as a result of this intercalation.

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Increasing efforts have been put into research about thermoelectric materials for the last few decades, especially recently, faced with the crucial demand for new energy and energy savings. Among the potential candidates for new generation thermoelectric materials are the intermetallic clathrates. Clathrates are cage-structured materials with guest atoms enclosed. Previous studies have shown lower thermal conductivities compared with many other bulk compounds, and it is believed that guest atom vibration modes are the reason for such thermal behaviors. Several models, including the Einstein oscillator and soft potential models, have been used to explain the guest motion. However the characterization of the anharmonic oscillating motion can be a challenge. In this work, Nuclear Magnetic Resonance (NMR), heat capacity and transport measurements have been used to study several clathrate systems, especially the well- known type-I Ba8Ga16Sn30, which has been reported to have one of the lowest thermal conductivities for bulk compounds. In this material the strong anharmonic rattling behavior was investigated and analyzed according to a double well potential model, yielding good agreement with the experimental results. Furthermore, the resistivity and heat capacity results were studied and analyzed according to the influence of the anharmonic contribution. This offered a way to connect the NMR, transport and heat capacity properties, providing an advantageous way to study strongly anharmonic systems. In further work, several related intermetallic materials were examined for their structure, motion and NMR properties. Dynamical and electrical behaviors were investigated by studying the magnetic and quadrupole NMR spin-lattice relaxation. Type-VIII Ba8Ga16Sn30 exhibits an enhanced dynamics-related term at low temperature, but no rattling response as observed for the type-I structure. Type-I Ba8In16Ge30 was compared with the type-I Ba8Ga16Sn30 because their cage structures are similar. No strong anharmonic contribution was found in the NMR T1 behavior of Ba8In16Ge30, however the T2 showed behavior characteristic of atomic motion. In all cases, the magnetic relaxation was used to characterize the electron structures, and n- type Ba8Ga16Ge30 exhibited a spin-lattice relaxation behavior which is characteristic of impurity band structures near the Fermi surface. Also, a series of Ba8CuxGe46-x clathrates were investigated and showed much more insulating like behavior. In related work, the layered BaGa4 and BaGa3Sn have shown interesting NMR spin-spin relaxation behavior that indicates atomic fluctuations. This is similar to the situation found in type-I Ba8In16Ge30. The influence of atomic motion on the NMR and also the atomic structures of these alloys is further discussed in this work.

Thesis (M.S.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (December 20, 2006) Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Thesis (Ph. D. in Interdisciplinary Materials Science)--Vanderbilt University, Aug. 2007. / Title from title screen. Includes bibliographical references.