Nanoscale Room-Temperature Na Dynamics in Layered Ruthenates Na1RuO3 and Na1.5RuO3.

Understanding the atomic-scale ionic motion and transport in layered transition-metal oxides is essential for elucidating structural stability and electronic behaviour in complex systems. Here, we investigate nanoscale Na dynamics in Na1RuO3 and Na1.5RuO3 using room-temperature ab initiomolecular dynamics at the r2SCAN + U level. While Na mobility plays a key role in local coordination, its nanoscale mechanism remains nuanced and unexplored. Our simulations show that Na ions undergo pervasive rattling, with Na1.5RuO3 enabling exploration of larger volumes and exhibiting incipient migration compared to the more confined behaviour in Na1RuO3. In addition, oxygen's contribution to redox capacity decreases from 43% to 24% with increasing Na content. These nanoscale insights demonstrate that tuning the local ionic environment governs charge compensation and dynamical response in ruthenate frameworks, with direct implications for the design of Na-ion battery cathodes.