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 σ, and Seebeck coefficient α, but its practical use is limited by a high lattice thermal conductivity κL. Here, we report Al-containing ZnO nanocomposites with up to a factor of 20 lower κL than non-nanostructured ZnO, while retaining bulklike α and σ. We show that enhanced phonon scattering promoted by Al-induced grain refinement and ZnAl2O4 nanoprecipitates presages ultralow κ 2 Wm −1 K–1 at 1000 K. The high α −300 μV K–1 and high σ 1–104 Ω–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 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.