Anomalous thermophysical properties and electride transition in fcc potassium

Alkali metals undergo an electride transition with excess electrons localized in interstices and acting as anionic interstitial quasi-atoms (ISQs). Less is known about the role of electride transition in changing their thermophysical properties. Here, taking potassium as an example, we investigated the thermodynamic and dynamic properties in the face-centered cubic (fcc) phase region where an electride transition occurs when increasing pressure. With the help of machine-learning-enhanced molecular dynamic simulations and density functional theory calculations, we show property anomalies over a wide pressure range of 10-20 GPa but no accompanying structural transformations. Furthermore, we find that these anomalies in solid potassium are stronger at lower temperatures due to the more electron-localized nature of ISQs. Our findings unveil the rich phenomena in electrides and could deepen our understanding on electride phase transition.