Three-dimensional imaging of dislocation dynamics during the hydriding phase transformation

• Published in: Nature materials Vol. 16; no. 5; pp. 565 - 571
• Main Authors: Ulvestad, A., Welland, M. J., Cha, W., Liu, Y., Kim, J. W., Harder, R., Maxey, E., Clark, J. N., Highland, M. J., You, H., Zapol, P., Hruszkewycz, S. O., Stephenson, G. B.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.05.2017; Nature Publishing Group
• Subjects: 639/301/119/2795; 639/301/357/354; Biomaterials; Condensed Matter Physics; Crystal defects; Crystallography; Dislocations; Hydrogen; Imaging; MATERIALS SCIENCE; Morphology; Nanotechnology; Nucleation; Optical and Electronic Materials; Palladium; Particle physics; Particle size; Phase boundaries; Phase transformations; X-rays
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/nmat4842

Crystallographic imperfections significantly alter material properties and their response to external stimuli, including solute-induced phase transformations. Despite recent progress in imaging defects using electron and X-ray techniques, in situ three-dimensional imaging of defect dynamics remains challenging. Here, we use Bragg coherent diffractive imaging to image defects during the hydriding phase transformation of palladium nanocrystals. During constant-pressure experiments we observe that the phase transformation begins after dislocation nucleation close to the phase boundary in particles larger than 300 nm. The three-dimensional phase morphology suggests that the hydrogen-rich phase is more similar to a spherical cap on the hydrogen-poor phase than to the core–shell model commonly assumed. We substantiate this using three-dimensional phase field modelling, demonstrating how phase morphology affects the critical size for dislocation nucleation. Our results reveal how particle size and phase morphology affects transformations in the PdH system. Coherent diffractive imaging during hydriding of palladium nanocrystals reveals that phase nucleation begins after dislocation nucleation at the phase boundary for large particles. The hydrogen-rich phase resembles a spherical cap.