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. At this temperature, the diffusivity on pure SiO2 or Pyrex glass powder was very low, but the diffusion constant for MgO or CaO powder which was annealed onto a sand-blasted glass surface was equal to about 0.0001cm2/s. It was suggested that these oxides might be responsible for the movement which was observed on soda-glass surfaces. The activation energy was equal to about 4eV, and seemed to be related to the work function of Ag metal.

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