In situ 3D observations of a core–shell volume transition in an Ni 3 Fe nanocrystal using Bragg coherent X-ray diffraction imaging

Abstracts of the 33rd European Crystallography Meeting, 23-27 August 2022International audienceCoherent X-ray Diffraction Imaging (CDI) [1] allows for the in situ 3D mapping of the structural changes during phase transitions and chemical reactions, with a fair spatial resolution of the order of magnitude of 10 nm [2]. Using this technique in multi-Bragg conditions (Bragg CDI on multiple reflections), it was possible to follow the structural evolution (change in morphology, variation of the displacement and strain fields) as a function of temperature in a 300 nm Ni3Fe nanocrystal. During this volume transition, which happens between 500°C and 600°C, a core-shell structure is progressively observed with two distinct lattice parameters (difference of 0.39%, corresponding to two different Ni:Fe ratios), leading to highly strained and coherent domains. A rounding of the particle is also observed, with a disappearing of the initial facets. Static molecular calculations (LAMMPS) of different systems, such as faceted and core-shellnanoparticles, complete this work and allow for the confirmation of a core-shell structure. This study shows the perfect ability of modern phase retrieval methods to reconstruct highly strained systems such as core-shell nanoparticles