Strain Evolution in Nanocrystals under High Pressure Tracked with Bragg Coherent X-ray Diffraction Imaging

Understanding stress accommodation at the atomic scale in nanocrystals is essential for operation in extreme environments. We use high-pressure Bragg Coherent Diffraction Imaging (BCDI) in a diamond anvil cell (DAC) to track three-dimensional strain and defects in individual platinum nanoparticles. The particle hosts an interfacial Shockley partial dislocation up to 2.7 GPa, followed at 5.0 GPa by nucleation of a dense dislocation network accompanied by anisotropic Bragg peak broadening, which later relaxes, indicating plasticity. Upon partial unloading, the interfacial partial reappears and transforms into a perfect dislocation that propagates into the crystal via cross-slip; additional glide events occur, while at 6.7 GPa anisotropic broadening re-emerges. Elastic finite-element modeling predicts shear stress concentrations near the particle-substrate interface, whereas nucleation is observed near the particle top surface. These results show that high-pressure BCDI captures dislocation activity and links reciprocal- and real-space signatures of plasticity in nanocrystals.