Composition dependence of chemical diffusion coefficient and ionic conductivity of α'-and α-Ag2Te
Abstract The chemical diffusion coefficient and the ionic conductivity of Ag2Te have been measured simultaneously with high stoichiometric resolution between 160 and 300°C as a function of composition by a recently developed polarization technique. The composition of the system was varied by coulometric titration employing AgI as solid ionic conductor. The results indicate the existence of two structurally cationic-disordered, mixed conducting phases of α-Ag2Te with narrow homogeneity ranges and high ionic conductivities. Between 160 and 220°C the chemical diffusion coefficient of α′-Ag2Te shows a distinct maximum at the inflexion point of the coulometric titration curve with values between 0.02 and 0.35 cm2s−1. At temperatures between 260 and 350°C a monotonically decreasing function of the chemical diffusion coefficient could be observed for α-Ag2Te. For both phases, the ionic conductivity was found to be almost independent of the silver activity showing rather high values between 1.0 and 1.6 S cm−1.