Relaxation dynamics induced in oxide glasses by the absorption of hard X-ray photons
by Dr. Giulio Monaco (University of Trento)
Tuesday, December 10, 2019 from to (Europe/Berlin)
at 25b ( 109 )
at 25b ( 109 )
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 . 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 . 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 . 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.  G. Grübel, A. Madsen and A. Robert, Soft-Matter Characterization (Berlin, Springer, 2008).  B. Ruta, F. Zontone, Y. Chuskin, G. Baldi, G. Pintori, G. Monaco, B. Rufflé and W. Kob, Sci. Rep. 7, 3962 (2017).  G. Pintori, G. Baldi, B. Ruta and G. Monaco, Phys. Rev. B 99, 224206 (2019).