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.

晶体学缺陷极大地改变了材料特性及其对外部刺激的响应，包括溶质诱导的相变。尽管在使用电子和X射线技术，成像缺陷最近进展原位缺陷动力学的三维成像仍然具有挑战性。在这里，我们使用布拉格相干衍射成像来成像钯纳米晶体的氢化相变过程中的缺陷。在恒压实验中，我们观察到在大于300 nm的粒子中，位错成核接近相边界后，相变开始。三维相形态表明，富氢相与贫氢相上的球形帽盖相比，通常与核-壳模型更相似。我们使用三维相场建模对此进行了证实，证明了相形态如何影响位错成核的临界尺寸。我们的结果揭示了粒径和相形态如何影响PdH系统中的转变。