Optimizing interfacial transport properties of InO single atomic layers in InO(ZnO) natural superlattices for enhanced high temperature thermoelectrics.

InO(ZnO) natural superlattices (where k is an integer), consisting of relatively earth abundant and non-toxic elements with coarsening-resistant nanostructures, are environmentally friendly materials with the potential for high temperature thermoelectric applications. Herein, we report our investigation of the high temperature thermoelectric properties of the InO(ZnO) superlattice bulk polycrystals that were singly and dually doped with Al and Ce. Transport property measurements revealed that Al and Ce did not only enter the ZnO blocks but also modified the InO single atomic layers. The effective electron potential barrier height of the superlattice interfaces can be adjusted by doping, and the optimal value that maximizes the power factor is of the order of kT above the Fermi level. The interfacial thermal (Kapitza) resistance of the InO atomic sheets dramatically increased with doping, primarily accounting for the bulk thermal conductivity reduction. At the optimal crossing of the interfacial thermal resistance and the effective potential barrier height, a maximum ZT of ≈0.22 was achieved at 800 °C in the 1.6 mol% Al-doped superlattice, which was an enhancement of ∼200% over the pristine InO(ZnO). This work provides a new perspective on enhancing the high temperature thermoelectric performance of nanostructured oxides by synergistically optimizing the interfacial phonon and electron transport properties.