110Ag tracer diffusion study of percolation transition in Ag2S–As2S3 glasses

Silver tracer diffusion study of homogeneous Ag2S–As2S3 glasses has been realised over an extremely wide composition range covering nearly five orders of magnitude in the silver concentration from 4×10−4% (4 ppm) to 33.3 at.% Ag. Three characteristic composition domains with drastically different ion transport properties have been found. (i) Below the percolation threshold at xc≈3×10−3 at.% Ag, the diffusion coefficients DAg and activation energy Ed do not depend on the silver content and similar to those in pure As2S3; the silver ion transport number tAg+ is 0.10–0.14. (ii) In the critical region just above the percolation threshold (x=0.012–1.2 at.% Ag), the glasses are nearly pure Ag+ ion conductors (tAg+>0.8), the ionic conductivity σi(x) and diffusion coefficients DAg(x) exhibit a power-law composition dependence: σi ∝ xt and DAg ∝ xt−1 with temperature-dependent power-law exponent t ∝ T0/T. (iii) At x>15 at.% Ag, a well-known rather exponential increase of σi(x) and DAg(x) is observed with strongly correlated Ag+ ion motion.