Chemical diffusion in β-Ag2Te

Abstract

The chemical diffusion coefficient D̃ of β-Ag2+δTe was obtained within its homogeneity range between 110°C and 140°C from galvanostatic polarization experiments using a symmetric solid-state electrochemical cell with ionic electrodes and ionic probes. The composition of the sample was varied in situ with high stoichiometric resolution by means of the coulometric titration technique. D̃ shows a maximum around δ=2.5·10−4. The phase width ranges from approximately δ=4·10−4 to δ=−15·10−4 between 110°C and 140°C. This behavior of D̃ is similar to that of the medium temperature α phases of Ag2Te, although the absolute values of D̃ are three orders of magnitude lower than those of α′-Ag2Te at 160°C or of α-Ag2Te at 300°C. The ionic conductivity of β-Ag2Te at 140°C (as obtained with the same experimental technique) is constant within the whole homogeneity range with values around σi=6·10−3 S cm−1.