Understanding Superionic Behavior from First-principles Molecular Dynamics

Superionic materials—solids with liquid-like transport properties—have found widespread use in a variety of applications including fuel cells, switches, sensors, and batteries. However, research into the design and optimization of superionics has been somewhat curtailed by a lack of understanding of the motivations for fast ion conduction in such materials and of the specific atomistic mechanisms involved. First-principles molecular dynamics has proven an excellent tool in this regard, particularly given the complexity and dynamism of the interatomic chemical interactions in such materials. The technique predicts properties directly from quantum mechanics rather than relying on experimental input, which in turn offers unique and unbiased insight into phenomena that defy traditional classification, such as superionicity. I will show how the application of dynamics simulations can reveal the relevant conduction pathways and mechanisms, local sublattice ordering phenomena, and dynamic patterns of chemical bonding and overall bond topology. I will then discuss the impact of our results on understanding the possible structural, chemical, and thermodynamic motivations for superionic behavior.