X-ray photo-induced atomic motion in Phase Change Materials and conventional covalent chalcogenide glasses

Irene Festi; Antoine Cornet; Tomoki Fujita; Jens Moesggard; Alberto Ronca; Jie Shen; Michael Sprung; Shuai Wei; Fabian Westermeier; Raphael Escalier; Andrea Piarristeguy; Giacomo Baldi; Beatrice Ruta

arXiv · 2601.02550

X-ray photo-induced atomic motion in Phase Change Materials and conventional covalent chalcogenide glasses

Irene Festi·Antoine Cornet·Tomoki Fujita·Jens Moesggard·Alberto Ronca·Jie Shen·Michael Sprung·Shuai Wei·Fabian Westermeier·Raphael Escalier·Andrea Piarristeguy·Giacomo Baldi·Beatrice Ruta

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Abstract

X-ray Photon Correlation Spectroscopy (XPCS) enables direct access to atomic-scale dynamics in disordered materials, revealing both spontaneous and X-ray-induced relaxation processes. Here, we study two compositionally similar alloy glasses near their glass transition temperatures: the phase change material (PCM) Ge15Sb85 and the non-PCM alloy Ge15Te85. Both exhibit X-ray induced atomic motion, yet with markedly different responses. Ge15Sb85 undergoes an immediate transition to a photo-induced yielding state, characterised by stationary dynamics governed solely by the absorbed dose. In contrast, Ge15Te85 shows a progressive slowing-down of the relaxation process, accompanied by a crossover from compressed to stretched exponential decay in the density autocorrelation functions. This behaviour is consistent with the emergence of liquid-like collective motion as supported by de Gennes narrowing in the wave-vector dependence of the dynamics at length scales comparable with the first sharp diffraction peak. Unlike Ge15Sb85, this alloy does not reach a stationary regime within experimental timescales, implying that the yielding transition occurs only after thousands of seconds with the available dose rate. Its response is also temperature dependent: at lower temperatures, the dynamics reflects intrinsic stress relaxation processes, whereas at higher temperatures becomes dose-controlled. These findings demonstrate that the dynamical response to X-ray excitation is not determined solely by chemical composition or bonding character, but results from the interplay between irradiation effects and structural relaxation pathways.

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Irene Festi, Antoine Cornet, Tomoki Fujita, Jens Moesggard, Alberto Ronca, Jie Shen, Michael Sprung, Shuai Wei, Fabian Westermeier, Raphael Escalier, Andrea Piarristeguy, Giacomo Baldi, Beatrice Ruta. 2026-01-05. X-ray photo-induced atomic motion in Phase Change Materials and conventional covalent chalcogenide glasses. https://arxiv.org/abs/2601.02550

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