Beware Phantom Phases! Guidelines for Identifying the Structure of Buried Precipitates

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Abstract
High-resolution scanning transmission electron microscopy images of nanoparticles embedded in a crystalline matrix can be easily misinterpreted, leading to proposed crystal structures that are incorrect and phases that do not exist, or ”Phantom Phases”. This is illustrated here through the case of low-dimensional precipitates buried in an aluminium matrix, as commonly observed in high-strength aluminium alloys. Guidelines for testing proposed structural models and avoiding such pitfalls are provided, incorporating the use of electron diffraction and simulations. Other benefits of this approach are also presented, such as identifying deeply buried particles and accurately mapping nanostructures.