Bragg Coherent Imaging of nanoprecipitates: role of superstructure reflections

TL;DR

This paper demonstrates how Bragg coherent diffraction imaging (BCDI) can accurately characterize strain fields in nanoprecipitates and ordered phases within alloys and nanoparticles, highlighting its potential for advanced materials analysis.

Contribution

The study shows the effectiveness of BCDI in retrieving strain distributions in ordered nanoprecipitates, including partially ordered phases, and assesses its applicability to complex systems with multiple precipitates.

Findings

BCDI accurately retrieves strain fields in single nanoprecipitates.

The technique effectively characterizes partially ordered phases with inhomogeneous strains.

BCDI is suitable for studying systems with many precipitates, especially with new synchrotron sources.

Abstract

Coherent precipitation of ordered phases is responsible for providing exceptional high temperature mechanical properties in a wide range of compositionally complex alloys (CCAs). Ordered phases are also essential to enhance the magnetic or catalytic properties of alloyed nanoparticles. The present work aims at demonstrating the relevance of Bragg coherent diffraction imaging (BCDI) to study bulk and thin film samples or isolated nanoparticles containing coherent nanoprecipitates / ordered phases. Crystals of a few tens of nanometres are modelled with realistic interatomic potentials and relaxed after introduction of coherent ordered nanoprecipitates. Diffraction patterns from fundamental and superstructure reflections are calculated in the kinematic approximation and used as input to retrieve the strain fields using algorithmic inversion. We first tackle the case of single nanoprecipitates and show that the strain field distribution from the ordered phase is retrieved very accurately. Then, we investigate the influence of the order parameter S on the strain field retrieved from the superstructure reflections and evidence that a very accurate strain distribution can be retrieved for partially ordered phases with large and inhomogeneous strains. In a subsequent section, we evaluate the relevance of BCDI for the study of systems containing many precipitates and demonstrate that the technique is relevant for such systems. Finally, we discuss the experimental feasibility of using BCDI to image ordered phases, in the light of the new possibilities offered by the 4 th generation synchrotron sources.