Chemical diffusion in β-Ag2Te

The chemical diffusion coefficient (D) over tilde of beta -Ag-2 Te+delta was obtained within its homogeneity range between 110 degreesC and 140 degreesC 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. D shows a maximum around delta = 2.5 10(-4). The phase width ranges from approximately delta = 4.10(-4) to delta = - 15.10(-4) between 110 degreesC and 140 degreesC. This behavior of D is similar to that of the medium temperature a phases of Ag2Te, although the absolute values of (D) over tilde are three orders of magnitude lower than those of alpha ' -Ag2Te at 160 degreesC or of alpha -Ag2Te at 300 degreesC. The ionic conductivity of beta -Ag2Te at 140 degreesC (as obtained with the same experimental technique) is constant within the whole homogeneity range with values around sigma (1) = 6.10(-3) S cm(-1). (C) 2001 Elsevier Science B.V. All rights reserved.