Tuning Ionic Conductivity in Fluorite Gd-Doped CeO₂-Bixbyite RE₂O₃ (RE = Y and Sm) Multilayer Thin Films by Controlling Interfacial Strain

Interfacial strain in heteroepitaxial oxide thin films is a powerful tool for discovering properties and recognizing the potential of materials performance. Particularly, facilitating ion conduction by interfacial strain in oxide multilayer thin films has always been seen to be a highly promising route to this goal. However, the effect of interfacial strain on ion transport properties is still controversial due to the difficulty in deconvoluting the strain contribution from other interfacial phenomena, such as space charge effects. Here, we show that interfacial strain can effectively tune the ionic conductivity by successfully growing multilayer thin films composed of an ionic conductor Gd-doped CeO₂ (GDC) and an insulator RE₂O₃ (RE = Y and Sm). In contrast to compressively strained GDC-Y₂O₃ multilayer films, tensile strained GDC-Sm₂O₃ multilayer films demonstrate the enhanced ionic conductivity of GDC, which is attributed to the increased concentration of oxygen vacancies. In addition, we demonstrate that increasing the number of interfaces has no impact on the further enhancement of the ionic conductivity in GDC-Sm₂O₃ multilayer films. Our findings demonstrate the unambiguous role of interfacial strain on ion conduction of oxides and provide insights into the rational design of fast ion conductors through interface engineering.