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

在高压下，钾等简单金属具有丰富的相图，包括绝缘电子化物相，其中电子具有局部的阴离子特性。液相测量显示两种状态之间的转变，但实验挑战阻碍了详细的热力学测量。以钾为例，我们提供了数值证据表明液-液转变是从自由电子到电子化物行为的连续转变。我们表明，这种转变表现为在广泛的压力范围内的异常扩散率、热膨胀、声速、配位数、反射率和热容量。异常源于局部电子和离子结构的显着变化。虽然主要是压力引起的现象，还有一个热膨胀异常。通过建立高压液相的电化物性质，我们解决了长期以来液体如何比密堆积固体更致密的谜团。我们的工作与所有碱金属液体的高压热力学性质有关。