Relaxation dynamics induced in oxide glasses by the absorption of hard X-ray photons
(University of Trento)
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.
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