Chemical diffusion coefficient of Ag 1.92Te obtained from galvanostatic polarization measurements

Abstract

Galvanostatic polarization experiments are performed on the asymmetric electrochemical cell Ag|AgI|Ag 1.92Te|Pt in order to determine the chemical diffusion coefficient of Ag y Te (1.912 < y < 1.920) at 160°C as a function of composition, the latter being varied by coulometric titration. As the specimen shows comparable ionic and electronic conductivities (the electronic transport number is around 0.8–0.9), new evaluation formulas are given and applied to determine the chemical diffusion coefficient. Both polarization (switching-on) and depolarization (switching-off) experiments are carried out and the experimental data are evaluated in the range of the short-time behaviour of the diffusion induced polarization process. The chemical diffusion coefficient of Ag 1.92Te decreases slightly with decreasing silver content with typical values around 0.002–0.004 cm 2 s −1.