Thesis (Ph. D.)--Michigan State University. Dept. of Physics and Astronomy, 2006. / Title from PDF t.p. (viewed on June 19, 2009) Includes bibliographical references (p. 90-98). Also issued in print.

Thesis (Ph. D.) -- California Institute of Technology, 2010. / Title from home page (viewed 05/26/10). Advisor and committee chair names found in the thesis' metadata record in the digital repository. Includes bibliographical references.

The thermal conductivity of thin Germanane (GeH) layers was measured using suspended micro-devices with integrated heaters and thermometers. The thermal contact resistance of the GeH samples suspended on the measurement devices was determined from the measured thermal resistance values of samples with different suspended lengths. The room-temperature thermal conductivity of the GeH samples was observed to be 0.6-1.0 Wm⁻¹K⁻¹. This low thermal conductivity is attributed to phonon scattering by defects and grain boundaries in the layered materials, including scattering caused by gangling bonds associated with missing Hydrogen atoms between adjacent layers. / text

Thesis (Ph. D.)--University of Oregon, 2000. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 91-93). Also available for download via the World Wide Web; free to University of Oregon users.

Since the beginning of the industrial revolution in the late 18th century, there's an abrupt increase in need for energy and resources. Despite of advantages it offers, waste heat or energy generated by machines or vehicles exhaust is evolved into the surrounding atmosphere, resulting in the evolution of the Greenhouse effect. With rampant global warming, thermoelectricity - an environmentally benign technology that recovers waste heat and converts it directly into useful electricity or vice versa - has gradually become an interesting topic for researchers. Regardless, it has yet to be widely commercialised mainly due to its inferior energy conversion efficiency to the conventional power generators and cooling devices. The aim of this project was to explore ways of enhancing the efficiency of thermoelectric materials. NaC0204 is one of the state-of-the-art p-type thermoelectric materials to date due to its superior thermoelectric properties and stability at elevated temperatures. As a result of its layered structure, NaC0204 is highly anisotropic in thermoelectric properties. Literatures revealed that the thermoelectric properties along the in-plane direction are superior to that along the out-of-plane direction, which emphasise the significance of texture. In this work, the texturing mechanisms and the texturing process as a function of sintering duration were studied in detail and the synthesis procedure of highly textured NaC0204-; materials was optimized. The results indicate that the extent of texture increased with increasing process duration and then reached the maximum when the materials were sintered at 900??C for 12 hrs. The texturing kinetics obeys an exponential relationship, suggesting that the texturing processing is dominated by self-diffusion mechanism. The experimental evidence also shows that the extent of texture decreased when the annealing time exceeded 12 hrs. The mechanisms of such deterioration were highly due to the nature of grain growth in ceramics. Given that the Co ions in NaxC020 4-; have different valence between 3+ and 3.48+ depending on the Na content and have spins, it is expected that oxygen vacancies formed in the lattice would cause charge-spin interaction, which would have a profound effect on the thermoelectric properties. As part of current study, the oxygenation kinetics and possible mechanisms were investigated. Room temperature X-ray diffraction study shows a decrease in FWHM and a certain left shift of spectra for the oxygenated samples, suggesting an increase in d-spacing and lattice distortion as a result of oxygen deficiency. The extent of oxygen saturation increased with decreasing annealing temperature. The high oxygenation flux in the first three hours of annealing was possibly due to lower energy requirement for oxygen to occupy its vacant sites than that to interstitially occupy a site. These experimental results could be used to further study the oxygen dependence of thermoelectric performance. Moreover, the investigation of temperature effects on lattice structure of NaC02O4-; with/without oxygenation was carried out to understand oxygen contribution to the lattice structure and also thermal expansion behaviours. Refined high temperature XRD results revealed that lattice parameter a decreased and c increased over the temperature range investigated after oxygenation due to Coulomb interaction between the constituent ions. Linear thermal expansion coefficient along the a- b-axis direction is circa 1.105 x 10-5K-1 for the sample before oxygenation and 1.06 x 10-5K-1 after oxygenation. An almost three-fold increase was observed for the thermal expansion coefficient along the c-axis direction for the samples before and after oxygenation, suggesting that higher oxygen concentration suppresses the thermal expansion coefficient in all directions.

Thesis (M.S.)--Rochester Institute of Technology, 2009. / Typescript. Includes bibliographical references (leaves 96-98).

Thesis (M.S.)--Bowling Green State University, 2008. / Document formatted into pages; contains viii, 32 p. : ill. Includes bibliographical references.

Thesis (Ph. D.)--Northeastern University, 2008. / Title from title page (viewed May 21, 2009). Graduate School of Engineering, Dept. of Mechanical and Industrial Engineering. Includes bibliographical references (p. 184-186).

Thesis (M.Sc.Eng.) / Despite of recent success in achieving the figure of merit ZT > 1 based on the nanoscale patterned thermoelectric structures, there have been few stable n-type materials with attractive thermoelectric responses for high temperature applications at T > 800K. In this thesis, we applied the first-principles density functional theory (DFT) calculations to probe the structure and thermoelectric properties relationship of a comprehensive series of perovskite materials. The density of states (DOS), Seebeck coefficient S, electric conductivity σ, and electronic contribution of the thermal conductivity Ke were obtained directly from the first-principles DFT calculations. In particular, Lanthanum (La), Gadolinium (Gd), Samarium (Sm), Yttrium (Y) doped MU+2093SrU+2081U+208BU+2093TiOU+2083 and Niobium (Nb) doped SrNbyTi1-yOU+2083 and doubly doped LaU+2093SrU+2081U+208BU+2093NbyTi1-yOU+2083 systems were studied. The change of the power factor S^2σ corresponding to the different dopant concentration had a good agreement with the experimental data. Our computed power factors S^2σ as a function of the dopant con- centration agree well with the available experimental data, and at the same time provide new insights for the optimal compositions. In the low doping region (x U+003E 12:5%), gadolinium and niobium are the best candidates of perovskite thermoelectric materials while at high doping level (x U+003E 25%), lanthanum and yttrium are the best options. In the case of doubly doped perovskites LaU+2093SrU+2081U+208BU+2093NbyTi1-yOU+2083, our calculations predict that the x= 12.5% and y= 12.5% is the best choice.

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, ZrSi??Sb2-??, ZrGe??Sb2-?? and HfGe??Sb2-?? 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.