Towards Oxygen Ion Conductor Designs Based on Lattice Dynamics

The existing oxygen ion conductors exhibit insufficient conductivity for practical applications in solid oxide electrochemical cells. To design oxygen ion conductors with higher conductivities at lower temperatures, a deeper understanding of the processes governing ionic conductivity is needed. This understanding is crucial to identify new chemistries with superior conductivities. In pursuit of this goal, the Arrhenius law emphasizes the importance of decreasing activation energy and increasing the pre-exponential factor for enhancing oxygen ion conductivity. However, a major obstacle lies in the lack of understanding surrounding the compensation law, where reducing activation energy is typically associated with decreasing the pre-exponential factor. This limitation hampers progress in designing improved oxygen ion conductors.<br/>In this presentation, we discuss designs of oxygen ion conductors with low activation energies and high pre-exponential factors. Specifically, we establish a correlation between pre-exponential factors and changes in lattice dynamics that occur during oxygen migration from equilibrium to the transition state. Variations in the order of magnitude of pre-exponential factor values across oxides with the perovskite and fluorite structures are attributed to changes in vibrational properties, such as the vibrational entropy of migration. By utilizing density functional theory simulations, we gain atomic-scale insights into these vibrational property changes and investigate their coupling with the electronic structure and activation energy. Our new findings and proposed descriptors hold great potential for accelerating the discovery of new oxygen ion conductors through machine learning and high-throughput virtual screening (HTVS). By leveraging the growing approaches of computation-aided designs, the next generation of oxygen ion conductors can be developed to catalyze the clean energy transition.