Cu-alkali ion exchange in glass: a model for the copper diffusion based on XAFS experiments

Cu-alkali ion exchange is a suitable way to dope superficial layers of silicate glasses well beyond the Cu solubility limits, with the possibility of controlling nanocluster nucleation and growth by subsequent proper treatments. The ion exchange process gives rise to a peculiar copper distribution, with the possible presence of different oxidation states, namely, Cu+ and Cu2+. The modelization of the copper diffusion process is necessary for defining an effective preparation protocol for the copper-doped composites. In this framework, suitable techniques capable to investigate the local atomic environment of Cu atoms are crucial. With this aim, X-ray absorption fine structure (XAFS) spectroscopy in grazing incidence mode was performed using a synchrotron source on different ion-exchanged samples. Based on the experimental results, a phenomenological model is used to describe the diffusion process.