The diffusion of 86Rb was studied at temperatures of between 184 and 448C by using a tracer-sectioning technique. It was found that the migration of Rb+ occurred via a vacancy mechanism. The temperature dependence of the diffusivity obeyed an Arrhenius relationship of the form:

D (cm2/s) = 110 exp[-1.20(eV)/kT]

The data did not exhibit the continuous positive curvature which was expected on the basis of a non-linear decrease in the Gibbs free energy for Frenkel defect formation with increasing temperature. It was suggested that a strain-induced and temperature-dependent binding energy between the oversized solute ion and a neighboring vacancy washed out the expected curvature. It was proposed that motion energy should be accounted for, as well as the energies of formation and solute-vacancy association.

Diffusion of Rubidium Ion in Pure Silver Chloride Crystals. P.A.Cardegna, A.L.Laskar: Journal of Physics - C, 1983, 16[11], 2075-86