Download or read book Synthesis, Characterization, and Transport Properties of Zintl Phases for Thermoelectric Applications written by Christopher James Perez and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermoelectric generators (TEG) convert heat directly into electricity without moving parts resulting in extremely rugged devices that are used in locations with restricted access such as deep space. There is also a need to use thermoelectric generators for waste heat reclamation in applications such as power plants or cars where efficiencies can be improved with TEGs. The efficiency of TEGs is directly dependent on zT, the thermoelectric material's figure of merit. zT, is defined by the material's Seebeck coefficient (S), temperature (T), electrical resistivity (p), and thermal conductivity (K), zT= (S2 T)/pK. Designing materials with higher zT provides for the fabrication of higher power density thermoelectric devices. These devices enable deep space missions by providing power to more experiments over a longer time span and capture of waste heat to improve the overall efficiency of power plants and cars, thereby reducing the reliance on fossil fuels. Zintl phases display inherently low thermal conductivity due to complex crystal structures and electronic tunability due to a wide range of chemical substitutions. The first project described in this dissertation is the synthesis, characterization, and thermoelectric properties of a material in the Zintl phase family of compounds, the type-I clathrate K8E8Ge38 (E = Al, Ga, In). The primary goal of this research was to improve on the earth abundant K8Al8Si38 material by replacing Si with the larger element with more diffuse orbitals for bonding, Ge, to improve zT by reducing electrical resistivity. K8Al8Ge38 showed a 46-fold reduction in resistivity leading to a 10-fold improvement in zT. K8Al8Ge38 decomposes at 550 °C and may be ideal for waste heat recovery applications after additional optimization. Another Zintl compound of interest is Yb14MgSb11 which has a higher operational zT than the current state of the art material in development by NASA for the next generation radioisotope thermoelectric generator (RTG), Yb14MnSb11, due to an ultra low thermal conductivity arising from its large complex unit cell. The next projects focus on the design and materials optimization of Yb14MgSb11 as a high temperature candidate p-type material in NASA's RTG. Yb14MgSb11 composites (1 - 8 vol %) with iron were prepared via mechanical milling and reactive spark plasma sintering (SPS) to improve mechanical properties. The result were samples which demonstrated crack arresting at iron inclusions and an increase in all elastic moduli which should help the material survive longer under the large axial compression materials experience in an RTG. Additionally, these iron micron-sized inclusions systematically reduce resistivity without significantly reducing Seebeck coefficient leading to a 40% improvement in thermoelectric power factor, which is a measure of the power density a material can deliver and provides a route for tuning the electrical resistivity of Yb14MgSb11. A follow up study was performed employing FeSb2 as the source for iron. SEM shows using this atomic source of iron leads to inclusions that are in part in the nanodomain (