Thermoelectric Property Studies of Nanostructured Bulk Materials: Si1-xGex, In4Se3-x, and Zn4Sb3

Thesis advisor: Zhifeng RenThermoelectric materials have attracted a lot of research interests because of their promising applications in solid-state cooling and power generation. The low ZTs of the current available thermoelectric materials have restricted the device efficiency, and thus the wide application of the thermoelectric technique. We propose a nanocomposite approach to improve ZT by reducing lattice thermal conductivity. The nanocomposite approach was first applied to n-type Si. Since there is no point defect scattering from Ge in pure Si, hence it provides an opportunity to study the scattering of grain boundaries. We found that the thermal conductivity is reduced by a factor of 10 in nanostructured Si in comparison with bulk crystalline Si. By adding 5 at% Ge, the thermal conductivity is further reduced by a factor of 2, thereby leading to a thermoelectric figure of merit 0.95 for Si95Ge5, similar to that of large grained Si80Ge20 alloys. Moreover, thermoelectric properties of In4Se3-x and Zn4Sb3 were investigated. Extremely low thermal conductivity values of 0.41 and 0.69 Wm-1K-1 were obtained in In4Se2.2 and Zn4Sb3 nanocomposites respectively, leading to peak ZTs of 1 and 1.3.Thesis (PhD) — Boston College, 2011.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Physics