Mechanisms of Pressure-Induced Phase Transitions by Real-Time Laue Diffraction

Abstract

Synchrotron X-ray radiation Laue diffraction is a widely used diagnostic technique for characterizing the microstructure of materials. An exciting feature of this technique is that comparable numbers of reflections can be measured several orders of magnitude faster than using monochromatic methods. This makes polychromatic beam diffraction a powerful tool for time-resolved microstructural studies, critical for understanding pressure-induced phase transition mechanisms, by in situ and in operando measurements. The current status of this technique, including experimental routines and data analysis, is presented along with some case studies. The new experimental setup at the High-Pressure Collaborative Access Team (HPCAT) facility at the Advanced Photon Source, specifically dedicated for in situ and in operando microstructural studies by Laue diffraction under high pressure, is presented.

Nontrivial nanostructure, stress relaxation mechanisms, and crystallography for pressure-induced Si-I → Si-II phase transformation

“…In reality, the defect-free Si-I should transform to Si-II at 18.3 GPa, when the first phonon instability in the first principle calculations is observed 9 . Then the observed PT pressure in the current experiment, ~13 GPa (see Supplementary Material), which matches the typically reported pressures 3 , 5 – 10 , is lower than 18.3 GPa by a factor of 1.41. Thus, a typical nucleation event in the experiment should occur at a single dislocation, consistent with low dislocation density in our Si-I sample.…”

“…High pressure diffraction experiments have been conducted using experimental setup available at 16 BMB beamline of Advanced Photon Source 3 . Incident polychromatic beam, with the highest X-ray energy limit about 90 keV, reached the sample through one of the diamonds while the diffracted beams reached Perkin Elmer area detector, positioned at about 600 mm from the sample and tilted vertically by , through the other diamond.…”

“…For phases that do not exist in the stress-free state, including Si-II, in situ measurements are vital and essential in studying high-pressure PTs. High pressure Laue diffraction is a powerful tool to investigate microstructure evolution across PT in situ 3 – 5 , however, a broader application of this powerful experimental capability also requires a strong collaboration with modeling and theory work. Martensitic PT from Si-I to Si-II occurring at 12–14 GPa is studied broadly 3 , 5 – 10 .…”

“…High pressure Laue diffraction is a powerful tool to investigate microstructure evolution across PT in situ 3 – 5 , however, a broader application of this powerful experimental capability also requires a strong collaboration with modeling and theory work. Martensitic PT from Si-I to Si-II occurring at 12–14 GPa is studied broadly 3 , 5 – 10 . Si-I/Si-II interface is observed but not uniquely indexed with diffraction, and twining in Si-II is mentioned hypothetically by Popov et al 5 .…”

Pressure-Induced Phase Transformations

“…Another article focused on recent developments of experimental techniques is the one of Popov et al [10]. This review is devoted to synchrotron X-ray radiation Laue diffraction, a widely used diagnostic technique for characterizing the microstructure of materials.…”