Free electron to electride transition in dense liquid potassium

At high pressures, simple metals such as potassium have a rich phase diagram including an insulating electride in which electrons localized, anionic character. Measurements the liquid shown transition between two states, but experimental challenges prevented detailed thermodynamic measurements. Using example, we present numerical evidence that liquid–liquid is continuous transformation from free electron to behaviour. We show manifests anomalous diffusivity, thermal expansion, speed of sound, coordination number, reflectivity and heat capacity across wide range pressures. The abnormalities stem significant change local electronic ionic structure. Although primarily pressure-induced phenomenon, there also expansion anomaly. By establishing nature high-pressure phase, resolve long-standing mystery how can be denser than close-packed solid. Our work relevant for properties all alkali metal liquids. Alkali at pressures difficult study detail. Numerical calculations now suggest higher-pressure state liquid, behave like localized anions.