Al-Doped Zinc Oxide Nanocomposites with Enhanced Thermoelectric Properties

ZnO is a promising high figure-of-merit (ZT) thermoelectric material for power harvesting from heat due to its high melting point, high electrical conductivity sigma, and Seebeck coefficient alpha, but its practical use is limited by a high lattice thermal conductivity kappa(L). Here, we report Al-containing ZnO nanocomposites with up to a factor of 20 lower kappa(L) than non-nanostructured ZnO, while retaining bulklike alpha and sigma. We show that enhanced phonon scattering promoted by Al-induced grain refinement and ZnAl2O4 nanoprecipitates presages ultralow kappa similar to 2 Wm(-1) K-1 at 1000 K The high a alpha similar to -300 mu VK-1 and high alpha similar to 1-10(4) Omega(-1) m(-1) result from an offsetting of the nanostructuring-induced mobility decrease by high, and nondegenerate, carrier concentrations obtained via excitation from shallow Al donor states. The resultant ZT similar to 0.44 at 1000 K is 50% higher than that for the best non-nanostructured counterpart material at the same temperature and holds promise for engineering advanced oxide-based high-ZT thermoelectrics for applications.