Experimental results were presented which showed that, at about 500C, Ag could be mobile on SnO2 and other oxide surfaces. Because the migrating species appeared to be Ag+, both diffusion and electrically assisted migration occurred. This movement was made visible, in the form of tiny Ag droplets on the glass surface, by the presence of methanol vapor in the ambient air. No migration at all occurred in the absence of O. It was concluded that the movement required the continuous or dynamic conversion of Ag ions into Ag2O and back again; due to the presence of both oxidizing and reducing agents. It was shown that it was possible to measure the diffusion coefficient and the electrical mobility coefficient by analyzing the temporal evolution of a circular front of Ag droplets. Typical values for a roughened glass surface at 500C were a mobility of 4.2 x 10-5cm2/Vs and a diffusivity of 1.2 x 10-5cm2/s. Similar values were found for the electrical mobility on a smooth SnO2 surface.

W.M.Sears, D.A.Love: Journal of Applied Physics, 1995, 77[6], 2407-14