Cation Tracer Diffusion in the Thermoelectric Materials Cu₃Mo₆Se₈ and “β-Zn₄Sb₃”

Eric Chalfin, Hongxia Lu and Rüdiger Dieckmann

Department of Materials Science and Engineering, Cornell University, Bard Hall, Ithaca, NY 14853-1501, U.S.A.

Abstract

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 Cu₃Mo₆Se₈and of Zn-65 diffusing in “β-Zn₄Sb₃”. The temperatures investigated were between about 195 and 900 °C for Cu₃Mo₆Se₈and between about 195 and 475 °C for “β-Zn₄Sb₃”. It was found that the diffusion of Ag in Cu₃Mo₆Se₈and 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 Cu₃Mo₆Se₈and 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-AgI.

Arrhenius plots of tracer diffusion coefficients: a) for Ag-110m diffusing in Cu₃Mo₆Se₈ and b) for Zn-65 diffusing in “β-Zn₄Sb₃”.

Solid State Ionics, 178 (5-6) [2007] 447-456, article available at http://dx.doi.org/10.1016/j.ssi.2007.01.026

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