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X-ray-induced atomic motion in phase-change materials and conventional covalent chalcogenide glasses

I. Festi1,2,*, A. Cornet1, T. Fujita3, J. Moesggard3, A. Ronca1,4, J. Shen1, M. Sprung5, S. Wei3, F. Westermeier5 et al.

R. Escalier6, A. Piarristeguy6, G. Baldi2,†, and B. Ruta1,‡

  • *Contact author: irene.festi@unitn.it
  • †Contact author: giacomo.baldi@unitn.it
  • ‡Contact author: beatrice.ruta@neel.cnrs.fr
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Phys. Rev. B 114, 094207 – Published 25 August, 2026

DOI: https://doi.org/10.1103/d39x-d2hv

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 an x-ray-induced atomic motion, yet with markedly different responses. Ge15Sb85 undergoes an immediate transition to an x-ray-induced yielding state, characterized by stationary dynamics governed solely by the absorbed dose. In contrast, Ge15Te85 shows a progressive slowing down of the x-ray-induced dynamics, accompanied by a crossover from compressed to stretched exponential decay in the density autocorrelation functions. This behavior is consistent with the emergence of liquidlike 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, it 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 internal stress relaxation pathways.

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Phys. Rev. B 114, 094207– Published 25 August, 2026
  • Received 27 August 2025
  • Accepted 24 July 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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