Understanding the Enhancement of Ionic Transport in Heterogeneously Doped Zirconia by Heterointerface Engineering

Zirconia-based ceramics have been the most promising oxide electrolyte material with high ionic conductivity for solid oxide fuel cell (SOFC) applications. Even though yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ) are typically used for the SOFC at high temperatures, their performance is not optimal at operating temperatures with respect to their ionic conductivity and stability. The literature has focused largely on ionic diffusion dynamics in bulk YSZ and ScSZ, whereas their heterogeneously doped alloy and heterolayered superlattices are less investigated. In this work, using molecular dynamics simulations and diffusion dynamics analysis, we examine and consider five main mechanisms that may contribute to the enhancement of the overall ionic conductivity of these doped zirconia, namely, the influence of cation size, concentration, distribution, the crystal orientation and direction, and lastly, the degree of atomic roughness at the interface in the heterolayered structures. Our results support that heterointerface engineering at the atomic scale greatly reduces local lattice distortions (commonly seen in the bulk phases) while inducing an in-plane strain and thus leading to an overall enhancement of the ionic conductivity and stability for SOFC applications.