The diffusion of radioactive tracers, Ag-110m diffusing in Cu3Mo6Se8 and Zn-65 diffusing in "beta-Zn4Sb3", was experimentally studied. Tracer concentration profiles were generated by diffusion -annealing samples in argon atmosphere containing 1-2% H-2. The corresponding residual radioactivity profiles were measured and analyzed to determine tracer diffusion coefficients of Ag-110m diffusing in Cu3Mo6Se8 and of Zn-65 diffusing in "beta-Zn4Sb3''. The temperatures investigated were between about 195 and 900 degrees C and between about 195 and 475 degrees C for "beta-Zn4Sb3". It was found that the diffusion of Ag in Cu3Mo6Se8 and of Zn in "beta-Zn4Sb3" is very fast, with tracer diffusion coefficients on the order of 10(-5) to 10(-6) cm(2)/s in the temperature ranges considered. The temperature dependencies of the tracer diffusion coefficients denoted above can be describedby using Arrhenius-type relations. The values determined for activation energies are 18.70 +/- 0.95 kJ/mol for the tracer diffusion of Zn-65 in "beta-Zn4Sb3". These values are comparable to the very low activation energy of 9.16 kJ/mol observed for the diffusion of Ag in the fast ion conductor alpha-Agl. (c) 2007 Elsevier B.V. All rights reserved.