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

Abstract

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.

Atomistic modeling and analysis of hydride phase transformation in palladium nanoparticles

“…While the behavior of Pd-H is well-understood in the bulk, the phase transformation dynamics within nanostructured Pd-H systems remains an active area of research [7,10,11,12,13,14,15,16,17,18]. In this regard, a few recent experiments suggest that in nanosized particles, the phase transformation is driven by the propagation of an atomistically sharp phase boundary at a speed as low as 1 nm/s.…”

“…For example, by scanning transmission electron microscopy (STEM), Narayan et al observed the propagation of a sharp α/β phase boundary in individual Pd nanocubes with edge lengths between 20 nm and 40 nm [16]. Using coherent X-ray diffractive imaging, Ulvestad et al measured the evolution of strain within individual Pd nanocubes between 60 nm and 100 nm, which also indicates a sharp α/β phase transformation [14,17]. Beyond the overall transformation mechanism, other unresolved issues include the morphology of the phase boundary [11,16,17], the effect of particle shape and lattice orientation [12], and the interaction of phase boundary with preexisting defects [15].…”

Accurate, rapid identification of dislocation lines in coherent diffractive imaging via a min-max optimization formulation

“…In materials, crystallographic imperfections such as dislocations often dictate performance and properties. For example, dislocation cores can act as fast diffusion sites [1][2][3][4], mitigate strain and plasticity during structural phase transformations [5][6][7], and govern crystal growth [8][9][10]. Increasingly, Bragg coherent x-ray diffractive imaging (BCDI) is being utilized at synchrotron and x-ray free electron laser [11,12] sources to address this challenge of understanding and optimizing materials properties via tuning of lattice distortions by nondestructively imaging the 3D lattice distortion field under in situ and operando conditions [13][14][15][16][17][18][19].…”

Performance evaluation of Bragg coherent diffraction imaging

“…The complete strain tensor field can be obtained by measuring projection components on multiple non-coplanar scattering vectors [5]. This unique capability to access displacement field in nanocrystals finds wide applications, especially in investigating morphology and displacement evolutions under varying external conditions, such as chemically derived stress [6][7][8], temperature introduced strain [9], dislocation propagation during crystal growth [10,11], laser pulse induced lattice dynamics [12,13], radiation damage on protein crystals [14,15], static pressure driven strain [16,17], lattice defects during battery charging [18][19][20], as well as ion-implantation-induced strains [21]. Bragg CDI has also been further developed to integrate with lateral scans for enlarged field of view [22][23][24][25][26][27][28].…”