The diffusion of Rb+ was measured at temperatures of between 184 and 421C by using radiotracer and serial-sectioning techniques. The results (table 12) could be described by the relationship:

D (cm2/s) = 1.04 x 104 exp[-1.33(eV)/kT]

Assuming that no Coulombic binding existed between the solute ion and the vacancies, the activation enthalpy for the migration of Rb+ ions via a vacancy mechanism could be estimated to be equal to 0.75eV. An expected curvature of the Arrhenius plot was not observed, and this was attributed to the existence of a temperature-dependent elastic binding energy between the oversized Rb+ ion and a neighboring vacancy.

Diffusion of Rubidium Ion in Silver Bromide and Temperature Dependence of Frenkel Formation Energy. P.A.Cardegna, A.L.Laskar: Physical Review B, 1981, 24[2], 530-7

Table 12

Diffusivity of Rb+ in AgBr