Mechanistic insights into oxygen-ion migration in hexagonal perovskites via autonomous first-principles workflows

Low-temperature oxygen-ion conductors hold the potential to transform sustainable energy storage technologies, but faster conductors are needed. Herein, leveraging high-throughput Density Functional Theory calculations and Nudged Elastic Band workflows, we systematically screen 5400 hexagonal perovskite structures to evaluate oxygen-ion migration via interstitialcy mechanisms. Our findings reveal 29 promising candidate compositions, highlighting systems like Ba₇V₄MoO₂₀ and Sr₇V₄MoO₂₀ as highly viable candidates. Beyond candidate identification, our analysis of the vacancy-mediated single-ion Potential Energy Surface reveals two distinct oxygen-ion migration pathways: conventional ion-hopping and a highly flexible lattice-assisted mechanism. By quantifying structural descriptors, including Continuous Symmetry Measures, local strain, and polyhedral rotation, we establish that the lowest activation barriers correlate with the lattice-assisted pathway. Additionally, we find that this dynamic mechanism is strongly influenced by the size disparity between the A-site cation and the B-site atoms at the interlayer. A larger A-site cation expands the 2D lattice, providing the necessary crystallographic free volume to reduce interlayer friction. By mapping these fundamental structural prerequisites, this study clarifies the polyhedral dynamics of oxygen-deficient environments and provides a quantitative design rule to accelerate the discovery of next-generation solid electrolytes.