Diffusion of rubidium ion in pure silver chloride crystals

The diffusion of 86 Rb in AgCl has been measured in the temperature range 184-448 degrees C by a tracer-sectioning technique. The transport of Rb + is found to proceed by a vacancy mechanism. The temperature dependence of the diffusivity follows a linear Arrhenius law with parameters D 0 =(1.10 -0.37 +0.56 )*10 2 cm 2 s -1 and H=1.20+or-0.02 eV. The data fail to exhibit the continuous positive curvature which is expected on the basis of a non-linear decrease in the Gibbs free energy for Frenkel defect formation with the increase of temperature. It is possible that a strain-induced and temperature-dependent binding energy between the oversized solute ion and a neighbouring vacancy washes out the expected curvature. When the diffusion results of other alkali ions are compared together with the diffusion of Rb + in AgCl, it seems likely that the temperature dependence of the motion energy is also to be considered along with those of the formation and solute-vacancy association.