In-situ x-ray diffraction of bismuth loaded to 4.4 GPa via shock reverberation

Static and dynamic high-pressure studies of bismuth have yielded conflicting phase diagrams, especially regarding the existence of the incommensurate host-guest Bi-III phase. Prior shock compression experiments may not have provided adequate loading conditions (stemming from uncertainties in the bismuth equation of state) and/or may not have provided sufficient loading duration to enable bismuth to transition to Bi-III. To drastically reduce loading condition uncertainties and to monitor phase transition kinetics for more than a few ns, we performed in-situ x-ray diffraction measurements of bismuth subjected to shock reverberation loading up to 4.4 GPa at the Dynamic Compression Sector of Argonne National Laboratory's Advanced Photon Source. Machine learning-informed molecular dynamics analysis and traditional Rietveld refinement of collected diffraction patterns indicate that, under steady loading conditions commensurate with Bi-III, bismuth exhibits a mixed state that evolves over 100s of ns.