Cation tracer diffusion in the thermoelectric materials Cu3Mo6Se8 and “β-Zn4Sb3”

The diffusion of radioactive tracers, Ag-110m diffusing in Cu3Mo6Se8 and Zn-65 diffusing in “β-Zn4Sb3”, was experimentally studied. Tracer concentration profiles were generated by diffusion-annealing samples in argon atmospheres containing 1–2% H2. 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 “β-Zn4Sb3”. The temperatures investigated were between about 195 and 900 °C for Cu3Mo6Se8 and between about 195 and 475 °C for “β-Zn4Sb3”. It was found that the diffusion of Ag in Cu3Mo6Se8 and of Zn in “β-Zn4Sb3” is very fast, with tracer diffusion coefficients on the order of 10− 5 to 10− 6 cm2/s in the temperature ranges considered. The temperature dependencies of the tracer diffusion coefficients denoted above can be described by using Arrhenius-type relations. The values determined for activation energies are 18.70 ± 0.95 kJ/mol for the tracer diffusion of Ag-110m in Cu3Mo6Se8 and 11.07 ± 0.95 kJ/mol for the tracer diffusion of Zn-65 in “β-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 α-Agl.