Local structure of solid Rb at megabar pressures

Year: 2015

Authors: De Panfilis S., Gorelli F., Santoro M., Ulivi L., Gregoryanz E., Irifune T., Shinmei T., Kantor I., Mathon O., S. Pascarelli S.

Autors Affiliation: Ist Italiano Tecnol, Ctr Life Nano Sci IIT Sapienza, I-00161 Rome, Italy; INO CNR, I-50019 Florence, Italy; LENS, I-50019 Florence, Italy; ISC CNR, I-50019 Florence, Italy; Univ Edinburgh, Sch Phys & Astron, Ctr Sci Extreme Condit, Edinburgh EH9 3JZ, Midlothian, Scotland; Ehime Univ, Geodynam Res Ctr, Matsuyama, Ehime 7908577, Japan; European Synchrotron Radiat Facil, F-38043 Grenoble, France.

Abstract: We have investigated the local and electronic structure of solid rubidium by means of x-ray absorption spectroscopy up to 101.0 GPa, thus doubling the maximum investigated experimental pressure. This study confirms the predicted stability of phase VI and was completed by the combination of two pivotal instrumental solutions. On one side, we made use of nanocrystalline diamond anvils, which, contrary to the more commonly used single crystal diamond anvils, do not generate sharp Bragg peaks (glitches) at specific energies that spoil the weak fine structure oscillations in the x-ray absorption cross section. Second, we exploited the performance of a state-of-the-art x-ray focussing device yielding a beam spot size of 5 x 5 mu m(2), spatially stable over the entire energy scan. An advanced data analysis protocol was implemented to extract the pressure dependence of the structural parameters in phase VI of solid Rb from 51.2 GPa up to the highest pressure. A continuous reduction of the nearest neighbour distances was observed, reaching about 6% over the probed pressure range. We also discuss a phenomenological model based on the Einstein approximation to describe the pressure behaviour of the mean-square relative displacement. Within this simplified scheme, we estimate the Gruneisen parameter for this high pressure Rb phase to be in the 1.3-1.5 interval. (C) 2015 AIP Publishing LLC.

Journal/Review: JOURNAL OF CHEMICAL PHYSICS

Volume: 142 (21)      Pages from: 214503-1  to: 214503-6

KeyWords: Ray-absorption-spectroscopy; Body Distribution-functions; Gruneisen-parameter; Condensed Matter; Polycrystalline Diamond; Fine-structure; Rubidium
DOI: 10.1063/1.4921894

Citations: 10
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