Dynamical Crossover at the Liquid-Liquid Transformation of a Compressed Molten Alkali Metal

Year: 2013

Authors: Bryk T., De Panfilis S., Gorelli F. A., Gregoryanz E., Krisch M., Ruocco G., Santoro M., Scopigno T., Seitsonen A. P.

Autors Affiliation: Dipartimento di Fisica, Università di Roma “Sapienza”, I-00185 Roma, Italy;
Institute for Condensed Matter Physics of NASU, UA-79011 Lviv, Ukraine;
Centre for Life Nano Science IIT@Sapienza, Istituto Italiano di Tecnologia, I-00161 Roma, Italy

European Laboratory for Non Linear Spectroscopy, I-50019 Sesto Fiorentino, Firenze, Italy

IPCF-CNR, c/o Università di Roma “Sapienza”, I-00185 Roma, Italy

Centre for Science at Extreme Conditions and School of Physics and Astronomy,
University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom

European Synchrotron Research Facility, F-38043 Grenoble, France

IFAC-CNR, I-50019 Sesto Fiorentino, Italy

Institute for Physical Chemistry, University of Zurich, CH-8057 Zurich, Switzerland

Abstract: Density-driven phase transformations are a known phenomenon in liquids. Pressure-driven transitions from an open low-density to a higher-density close-packed structure were observed for a number of systems. Here, we show a less intuitive, inverse behavior. We investigated the electronic, atomic, and dynamic structures of liquid Rb along an isothermal line at 573 K, at 1.2-27.4 GPa, by means of ab initio molecular dynamics simulations and inelastic x-ray scattering experiments. The excellent agreement of the simulations with experimental data performed up to 6.6 GPa validates the overall approach. Above 12.5 GPa, the breakdown of the nearly-free-electron model drives a transition of the pure liquid metal towards a less metallic, denser liquid, whose first coordination shell is less compact. Our study unveils the interplay between electronic, structural, and dynamic degrees of freedom along this liquid-liquid phase transition. In view of its electronic nature, we believe that this behavior is general for the first group elements, thus shedding new light into the high-pressure properties of alkali metals.

Journal/Review: PHYSICAL REVIEW LETTERS

Volume: 111 (7)      Pages from: 077801  to: 077801

More Information: The supercomputer allocation time within the CINECA project \”Dynamics and thermodynamics of compressed liquid metals studied with ab initio molecular dynamics\” is gratefully acknowledged. The calculations have been performed using the ab initio total-energy and molecular dynamics program VASP (Vienna ab initio simulation program) developed at the Institute fur Materialphysik of the Universitat Wien [42,43]. We acknowledge the helpful technical assistance of the European Synchrotron Radiation Facility staff during the IXS experimental campaign. T.S. has received funding from the European Research Council under the European Community\’s Seventh Framework Program (FP7/20072013)/ERC Grant Agreement FEMTOSCOPY No. 207916.
KeyWords: high pressure physics; alkali metals; liquid state; inelastic x-ray scattering; ab initio molecular dynamics
DOI: 10.1103/PhysRevLett.111.077801

Citations: 24
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