110Ag tracer diffusion study of percolation transition in Ag 2S–As 2S 3 glasses

Abstract

Silver tracer diffusion study of homogeneous Ag 2S–As 2S 3 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 x c≈3×10 −3 at.% Ag, the diffusion coefficients D Ag and activation energy E d do not depend on the silver content and similar to those in pure As 2S 3; the silver ion transport number t Ag + 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 ( t Ag + >0.8), the ionic conductivity σ i( x) and diffusion coefficients D Ag( x) exhibit a power-law composition dependence: σ i ∝ x t and D Ag ∝ x t−1 with temperature-dependent power-law exponent t ∝ T 0/ T. (iii) At x>15 at.% Ag, a well-known rather exponential increase of σ i( x) and D Ag( x) is observed with strongly correlated Ag + ion motion.