Simple-to-Complex Transformation in Liquid Rubidium

Abstract

We investigated the atomic structure of liquid Rb along an isothermal path at 573 K, up to 23 GPa, by X-ray diffraction measurements. By raising the pressure, we observed a liquid-liquid transformation from a simple metallic liquid to a complex one. The transition occurs at 7.5 ± 1 GPa which is slightly above the first maximum of the T-P melting line. This transformation is traced back to the density-induced hybridization of highest electronic orbitals leading to the accumulation of valence electrons between Rb atoms and to the formation of interstitial atomic shells, a behavior that Rb shares with Cs and is likely to be common to all alkali metals.

Kosterlitz-Thouless-type caging-uncaging transition in a quasi-one-dimensional hard disk system

“…We see a notable drift of k max towards smaller values as ρ decreases. In disordered systems, where the structural transition takes place, k max (ρ) has different slopes on two sides of the transition [23]. The plot 2π/k max versus l is of this kind.…”

High-pressure vibrational properties of dense rubidium

“…GPa, alkali metals exhibit complex low-symmetry crystalline phases, whose existence is bound to the density-driven change of character of the valence electron from the s-type to states of higher angular momentum, namely s-p and s-d transition for light, Li and Na, and heavy, K, Rb and Cs, elements, respectively. Similarly, density-driven simple-tocomplex phase transitions were also observed in the liquid state for Cs and Rb 1,2,3 , due to the change of character of the valence electron. Interestingly, the high pressure, low symmetry crystalline phases of these systems allow a rich Raman activity, whose experimental observation has been so far limited to the light alkali metals 4,5,6 .…”

“…Having successfully performed Raman spectroscopy measurements on light alkalis 5,6 , we have decided to study the vibrational properties of a heavier alkali Rb, aiming to investigate the change of character of the valence electron by comparing to the light alkali metals. The structural properties of Rb under pressure, along with the phase diagram of this elemental system (figure 1), were extensively investigated both in the solid and the liquid state 7,8,9,10,11,12,13,14,15,16,17,18,19,2,20,3 . The knowledge of structural properties and equation of state are necessary requirements for the quantitative interpretation of vibrational properties we aim to investigate.…”

“…(Color on line) High-pressure phase diagram of Rb13,14,16,15,17,18,20,3 . The dashed line is a hypothetical phase boundary passing through the only single melting point observed along an isotherm decompression at 573 K. The high temperature extensions of the solid-solid phase transitions are also hypothetical, as these phase transitions have only been investigated at room temperature.…”

Rubidium at Extreme Conditions

“…I will describe recent X-ray diffraction (XRD), Raman spectroscopy and Inelastic X-ray Scattering (IXS) studies on liquid and solid Rubidium at extreme pressures, up to several tens of GPa. XRD and IXS data in diamond anvil cells (DACs) consistently show a liquid−liquid transformation from a simple metallic liquid to a complex one, occurring at 6.5-8.5 GPa, which is slightly above the first maximum of the T−P melting line [1,2]. This transformation is traced back to the density-induced hybridization of highest electronic orbitals (s-d transition) leading to the accumulation of valence electrons between Rb atoms and to the formation of interstitial atomic shells, a behavior that Rb shares with Cs and is likely to be common to all alkali metals.…”