Pressure- driven electronegativity inversion in alkali liquids

CX Han and HX Zong and XD Ding and J Sun and GJ Ackland, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 122, e2424701122 (2025).

DOI: 10.1073/pnas.2424701122

Liquid-liquid phase transitions (LLPTs) are typically characterized as two-state systems, where transitions occur between two distinct liquid phases driven by local structural rearrangements. In this study, we observed a continuous LLPT with an inversion of electronegativity in a K-Rb binary alloy. This uniquely exhibits a three-state system behavior. The transition, induced by pressure-driven reordering of electronic orbital energies, progresses through a sequence from s-metal to electride to ti-metal, accompanied by a valence reversal: Potassium transitions from a negative to a positive valence, while rubidium undergoes the opposite shift. This process is marked by two successive anomalies in the alloy's optical, thermodynamic, and dynamic properties over a broad pressure range. The observation of similar LLPT phenomena in other alkali and alkaline earth metal liquids suggests that this three-state system mechanism may provide broader insights into the nature of continuous phase transitions.

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