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 κ(L). Here, we report Al-containing ZnO nanocomposites with up to a factor of 20 lower κ(L) than non-nanostructured ZnO, while retaining bulklike α and σ. We show that enhanced phonon scattering promoted by Al-induced grain refinement and ZnAl(2)O(4) nanoprecipitates presages ultralow κ ∼ 2 Wm( -1) K(-1) at 1000 K. The high α∼ -300 μV K(-1) and high σ ∼ 1-10(4) 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.

In this work, we demonstrate the use of high performance nanostructured PbTe-based materials in high conversion efficiency thermoelectric modules.

To grow the thermoelectric market, the module development must be at par with the advancements in the materials development. In this work, we successfully bridge the two by developing high-ZT (1.9) PbTe-based thermoelectric material and using this material in thermoelectric module development, leading to a record high efficiency of 12%. The ZT was enhanced through nanostructuring and engineered doping. The high-efficiency module will pave the way for many new opportunities for thermoelectric power generation in commercial applications.

The thermoelectric performance of room temperature Ag₂Se was greatly enhanced by stabilizing the crystal structure and eliminating metastability.

Many monumental breakthroughs in p-type PbTe thermoelectrics are driven by optimizing a Pb 0.98 Na 0.02 Te matrix. However, recent works found that x > 0.02 in Pb 1−x Na x Te further improves the thermoelectric figure of merit, zT, despite being above the expected Na solubility limit. We explain the origins of improved performance from excess Na doping through computation and experiments on Pb 1−x Na x Te with 0.01 ≤ x ≤ 0.04. High temperature X-ray diffraction and Hall carrier concentration measurements show enhanced Na solubility at high temperatures when x > 0.02 but no improvement in carrier concentration, indicating that Na is entering the lattice but is electrically compensated by high intrinsic defect concentrations. The higher Na concentration leads to band convergence between the light L and heavy Σ valence bands in PbTe, suppressing bipolar conduction and increasing the Seebeck coefficient. This results in a high temperature zT nearing 2 for Pb 0.96 Na 0.04 Te, ∼25% higher than traditionally reported values for pristine PbTe-Na. Further, we apply a phase diagram approach to explain the origins of increased solubility from excess Na doping and offer strategies for repeatable synthesis of high zT Na-doped materials. A starting matrix of simple, high performing Pb 0.96 Na 0.04 Te synthesized following our guidelines may be superior to Pb 0.98 Na 0.02 Te for continued zT optimization in p-type PbTe materials.