Relaxation dynamics induced in oxide glasses by the absorption of hard X-ray photons

by Dr Giulio Monaco (University of Trento)

Tuesday 10 Dec 2019, 13:15 → 14:15 Europe/Berlin

109 (25b)

X-ray photon correlation spectroscopy (XPCS) is an established tool to probe the slow dynamics in soft matter and in glass-forming liquids close to the structural arrest [1]. Recently, it has been demonstrated that it can also be used to probe a peculiar dynamic process in glasses which is induced by the X-ray beam and leaves the structure unaffected [2]. We will discuss in some detail this X-ray induced dynamics here. Specifically, XPCS is used to probe the slow dynamics of the glass-former B2O3 across the glass transition [3]. In the undercooled liquid phase, the decay times of the measured correlation functions are consistent with visible light scattering results and independent of the incoming flux; in the glass they are instead temperature independent and show a definite dependence on the X-ray flux. This dependence can be exploited to obtain information on the volume, Va, occupied by the atoms that move in the glass following an X-ray absorption event. The length scale derived in this way, of the order of the nanometer, is very close to that reported for the dynamical heterogeneities, suggesting a connection between these two quantities. Moreover, we also discuss this X-ray induced effect in a series of borate glasses (M2O)x (B2O3)1-x, where M is the alkali modifier and x its molar ratio. We show that the x-dependence of the volume Va can be exploited to provide structural information at the medium range order length scale, an information notoriously difficult to obtain with diffuse scattering measurements. [1] G. Grübel, A. Madsen and A. Robert, Soft-Matter Characterization (Berlin, Springer, 2008). [2] B. Ruta, F. Zontone, Y. Chuskin, G. Baldi, G. Pintori, G. Monaco, B. Rufflé and W. Kob, Sci. Rep. 7, 3962 (2017). [3] G. Pintori, G. Baldi, B. Ruta and G. Monaco, Phys. Rev. B 99, 224206 (2019).