Relaxation dynamics in borate glass formers probed by photon correlation at the microscopic and macroscopic length scale

X-ray photon correlation is used to probe the dynamics of the strong glass former boron trioxide and of a series of alkali borate glasses, (M₂O)_x(B₂O₃)_1-x where M is the alkali modifier (M=Li, Na and K). The decay times τ of the obtained correlation functions in B₂O₃ are consistent with visible light scattering results and independent of the incoming beam intensity in the undercooled liquid phase; are instead temperature independent and show a definite dependence on the X-ray beam intensity in the glass [1]. We are therefore witnessing an atomic dynamics induced by the X-ray beam, similarly to what recently observed in silica and germania [2]. Furthermore, we clearly demonstrate that the value of τ is related to absorption by investigating a series of alkali borate glass with the same molar ratio and as a function of the alkali modifier. Finally, we highlight the role played by the structure in the X-ray induced dynamics by studying a series of lithium borate glasses with different molar ratios, and by investigating the wave vector dependence. Despite the observed dynamics is clearly intensity dependent, we obtain very interesting information on glasses not available with other experimental techniques.

[1] B. Ruta et al., Hard X-rays as pump and probe of atomic motion in oxide glasses. https://arxiv.org/abs/1610.09236 (2016)

[2] G. Pintori et al., “Collective dynamics induced in glasses by the absorption of X-ray photons” (to be submitted).