A hidden low-temperature transformation pathway in compositionally complex materials

Yujiao Li; Elaheh Akbarnejad; Quentin Bizot; Aleksander Kostka; Natalia Pukhareva; Ridha Zerdoumi; Alan Savan; Matous Mrovec; Ralf Drautz; Baptiste Gault; Dierk Raabe; Alfred Ludwig

arXiv · 2608.24357

A hidden low-temperature transformation pathway in compositionally complex materials

Yujiao Li·Elaheh Akbarnejad·Quentin Bizot·Aleksander Kostka·Natalia Pukhareva·Ridha Zerdoumi·Alan Savan·Matous Mrovec·Ralf Drautz·Baptiste Gault·Dierk Raabe·Alfred Ludwig

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Abstract

Most compositionally complex materials (CCMs, frequently referred to as high entropy alloys) are metastable and their attractive properties often belong to kinetically trapped states. However, pathways towards lower-free-energy phase states governing long-term stability, can remain hidden because diffusion-controlled atomic redistribution is too slow to be revealed at experimentally accessible timescales. This blind spot is acute in CCM design: enormous compositional spaces are screened for performance, yet the low-temperature kinetics and the associated transformation pathways determining whether that performance persists are rarely considered in material selection. Here we use defect-rich nanoscale volumes coupled with atom-probe tomography to access and reconstruct the hidden phase-evolution pathway in a metastable Ag24Au20Pd50Pt6 electrocatalyst, without relying on elevated temperatures to accelerate the transformation. By varying microstructural starting state, annealing temperature and time, we reveal precipitation of a Pt-rich phase within the fcc matrix, its coarsening and re-homogenization. The Pt-rich phase recurs after homogenization with delayed kinetic accessibility, while prolonged annealing extends the pathway to 300{\deg}C. Atomistic simulations independently predict the same Pt-rich phase selection. The transformation is accompanied by a 3.7-fold loss of catalytic activity for hydrogen evolution. These results establish hidden phase-evolution pathways as a materials-design variable: resolving them can guide the selection of metastable CCMs not only for their as-synthesized properties, but also for the phase states and associated functionalities they may access over time.

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Yujiao Li, Elaheh Akbarnejad, Quentin Bizot, Aleksander Kostka, Natalia Pukhareva, Ridha Zerdoumi, Alan Savan, Matous Mrovec, Ralf Drautz, Baptiste Gault, Dierk Raabe, Alfred Ludwig. 2026-08-25. A hidden low-temperature transformation pathway in compositionally complex materials. https://arxiv.org/abs/2608.24357

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