Using atomic scale X-ray photon correlation spectroscopy to study atomic diffusion in alkali borate glasses

Despite ever-increasing efforts in research, only little is known about the structure and dynamics of glasses and especially the mechanisms of diffusion of glasses on the atomic level are far from being understood. Diffusion studies of solids focused on macroscopic methods like tracer diffusion. With the advent of atomic scale X-ray correlation spectroscopy (aXPCS) the dynamics of crystals and glasses became experimentally accessible. aXPCS is able to provide the temporal and spatial resolution required for diffusion studies on the atomic scale in solids.

Alkali borate glasses belong to the better understood glasses in terms of the structure. Due to their interesting properties as fast ion conductors they are an interesting candidate for diffusion studies. Diffusion experiments on two rubidium borate glasses with different concentrations were performed showing large discrepancies in the diffusivities and a clear dependence on the scattering angle. First promising results from fits to several jump models were obtained.

Supplementary total scattering experiments were performed to obtain the structure factor and the pair distribution functions. Both quantities provide information about structural correlations and are needed for comparison with computer simulations and models. Additional computer simulations can give insight into structural details otherwise not accessible.

This work was founded by the Austrian Science Fund (FWF): P28232-N36.

Results of the aXPCS experiment for the low alkali content sample measured at 20K. Inverse correlation times are plotted over wave vector transfer q. Coloured lines are fits using several jump models.