Thermal Kharkiv Seminars: "Heat Capacity and Thermal Conductivity of Solids at Low Temperatures"
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The effect of intense x-ray beams on oxide glasses unveiled by means of photon correlation spectroscopy
dr Erica Affinelli
University of Trento
The slow relaxations processes in amorphous systems can be captured by means of X-ray Photon Correlation Spectroscopy (XPCS). The technique probes the density fluctuations by exploiting the coherent portion of the synchrotron beam. XPCS measurements on oxide glasses have revealed the presence of a faster than expected atomic relaxation that has been recognized as an induced dynamics, where the x-ray beam is pumping and probing at the same time the atomic displacements [1]. The dynamics is intermittent and it has been attributed to the presence of a local force field which stimulates the release of stresses via bond ruptures and atomic rearrangements[2].
The work that I will present and a novel article on the argument have contributed to clarify the idea that the artificial dynamics induced by the x-ray beam evolves during the exposure to the x-ray radiation [3]. At low exposure times, the phenomenon is reversible, and the structure is mildly affected. Conversely, the dynamics and the structure are modified when high x-ray doses are delivered to those oxide glasses. In these cases indeed, the motion evolves with the release of stresses through radiolytic events where the bond ruptures are promoted by localization of free-electrons. The saturation of the effect is reached when the system undergoes a transformation towards a new amorphous state, called fully irradiated glass. Interestingly, the process is similar to the metamictization process observed in ceramic materials in which they transform to a new amorphous state under the effect of nuclear or ionising radiation [4-6]. Differently from those irradiation methods, the XPCS experiments allow to follow the dynamics of transformation. I will show how the final amorphous state shows an induced dynamics with features similar to the one of the supercooled liquid and how the transformation can be envisioned as an evolution in the potential energy landscape.
[1] B. Ruta, F. Zontone, et al, Sci. Rep. 7, 3962 (2017).
[2] L. Cipelletti, S. Manley, RC Ball & DA Weitz, Phys. Rev. Lett., 84, 10 (2000).
[3] A. Martinelli, F. Caporaletti, et al, Phys. Rev. X, 13, 4 (2023).
[4] M. F. Thorpe & P. M. Duxbury. Rigidity theory and applications. Springer Science & Business Media, 2006.
[5] B. Ruta, Y. Chushkin et al, Phys. Rev. Lett., 109, 16 (2012).
[6] B. Ruta, G. Baldi, et al, Nat. Comm, 5, 1 (2014).
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