Femtosecond diffraction studies of solid and liquid phase changes in shock-compressed bismuth

M G Gorman,E Granados,A L Coleman,C A Bolme,M I Mcmahon,E Galtier,C Sanloup,R S Mcwilliams,S Rothman,A E Gleason,D E Fratanduono,J H Eggert,R F Smith,D Mcgonegle,R Briggs,J S Wark,G W Collins,M Śliwa,H J Lee

doi:10.1038/s41598-018-35260-3

Abstract

Bismuth has long been a prototypical system for investigating phase transformations and melting at high pressure. Despite decades of experimental study, however, the lattice-level response of Bi to rapid (shock) compression and the relationship between structures occurring dynamically and those observed during slow (static) compression, are still not clearly understood. We have determined the structural response of shock-compressed Bi to 68 GPa using femtosecond X-ray diffraction, thereby revealing the phase transition sequence and equation-of-state in unprecedented detail for the first time. We show that shocked-Bi exhibits a marked departure from equilibrium behavior - the incommensurate Bi-III phase is not observed, but rather a new metastable phase, and the Bi-V phase is formed at significantly lower pressures compared to static compression studies. We also directly measure structural changes in a shocked liquid for the first time. These observations reveal new behaviour in the solid and liquid phases of a shocked material and give important insights into the validity of comparing static and dynamic datasets.

Highlights

When compressed and heated, materials frequently undergo phase transitions associated with atomic structural changes to denser crystalline or amorphous forms
The first solid-solid transformation is determined to occur at 2.5 GPa (Fig. 2a(ii)) and the Bragg reflections from the new phase fit very well to the structure of Bi-II, with refined lattice parameters in excellent agreement with previous diamond anvil cell (DAC) studies of Bi-II at the same pressure[1] (See Fig. S3)
The shock compression behavior of Bi observed via X-ray diffraction differs from that reported from previous studies both in terms of the phases observed and conditions achieved

Summary

Introduction

Materials frequently undergo phase transitions associated with atomic structural changes to denser crystalline or amorphous (e.g. liquid) forms Such high-pressure transformations, and the properties of the high-pressure phases, can be studied using X-ray diffraction on statically-compressed samples[1,2], and, more recently, using rapid, or dynamic, compression coupled to powerful X-ray sources[3,4,5,6]. The densities of the high-pressure phases observed in the shock experiments are at considerable odds with those obtained in the static compression studies, with discrepancies as large as 5% at only ~5 GPa, and gradual density changes are seen[11], suggestive of mixed-phase regions As a result, it is not at all clear whether the complex structures observed in static compression studies on the timescales of seconds or minutes, such as incommensurate Bi-III, are the same as those that form in nanoseconds or microseconds under shock compression. The improved data quality and extended angular range that have since become available[5] allow for structural studies of shocked liquids for the first time

Methods

Results

Conclusion