Nanoscale Room-Temperature Na Dynamics in Layered Ruthenates Na₁RuO₃ and Na_1.5RuO₃

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 Na_1.5RuO₃ 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 Na_1.5RuO₃ 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.