Nanoionics: Modifying electronic and ionic conductivity through interfacial engineering

Interfacial engineering opens up a new route to tailor the functional properties of electroceramics. Often referred to as nanoionics, the transport properties can be altered by the interplay of strain, space-charge, and... [ view full abstract ]

Interfacial engineering opens up a new route to tailor the functional properties of electroceramics. Often referred to as nanoionics, the transport properties can be altered by the interplay of strain, space-charge, and electro-chemo-mechanical coupling effects at heterogeneous interfaces. In this presentation we will demonstrate two key experimental findings.

First, we demonstrate that the migration barrier in oxygen ion conductors can be modified by lattice strain. In rare-earth substituted CeO₂ thin films, we find that the observed change is in excellent agreement with previous studies, and crucially that the modification is dependent on the size of the dopant cation, showing that defect association plays a substantial role. We rationalise our findings using static force-field simulations, suggesting that the cause is due to a combination of changes in the migration barrier and vacancy-cation configuration.

Second, we show that the charge carrier concentrations in mixed ionic-electronic conductors (MIECs) can by modified at heterogeneous interfaces. Pr substituted CeO₂ (PCO) is an excellent MIEC for fundamental studies as it has been extensively investigated, and the defect chemistry, chemical expansion, and transport properties are well described in the bulk material. We show that in multilayer films of alternating Pr_0.1Ce_0.9O_2-d and SrTiO₃ (STO) layers, the conductivity of the layers shows a dramatic weakening of the pO₂ dependence as the density of the interfaces is increased. This is consistent with a change in the charge carrier concentration due to a lowering of the enthalpy for Pr reduction. This effectively allows PCO to be engineered from a mixed-ionic conductor to a pure ionic conductors at a given oxygen partial pressure.