Optimizing interfacial transport properties of InO ₂ single atomic layers in In ₂ O ₃ (ZnO) ₄ natural superlattices for enhanced high temperature thermoelectrics

In₂O₃(ZnO)_k 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 In₂O₃(ZnO)₄ 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 InO₂ 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 k_BT above the Fermi level. The interfacial thermal (Kapitza) resistance of the InO₂ 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 In₂O₃(ZnO)₄. 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.