Ionic transport in AgI‐HgS‐As 2 S 3 glasses: Critical percolation and modifier‐controlled domains

Electrical measurements, dc and ac , show that (AgI) x (HgS) 0.5‐ x /2 (As 2 S 3 ) 0.5‐ x /2 glasses, 0.0 ≤  x  ≤   0.6, exhibit drastic changes in ionic conductivity σ i with silver iodide additions. The ionic transport increases by 13 orders of magnitude with increasing silver content from ~0.002 to ~23 at.%, and the activation energy decreases from 1.05 to 0.35 eV . Two distinctly different ion transport regimes above the percolation threshold concentration, x c ≈ 30 ppm, were distinguished. The critical percolation regime at low silver content (≤ 2‐5 at.% Ag) is characterized by a random distribution of silver‐related entities and obeys a power‐law composition dependence of σ i . The ion transport parameters depend on the host network connectivity, represented by the average coordination number , via the critical fictive temperature T 0 ; the calculated T 0 value is comparable to the glass transition temperature for the glassy (HgS) 0.5 (As 2 S 3 ) 0.5 host matrix. In contrast, in the modifier‐controlled domain, the silver‐related entities are nonrandomly distributed. The high Ag + ionic mobility results from interconnected tetrahedral (AgI 2/2 S 2/2 ) n chains in the silver iodide content range 0.2 <  x  ≤   0.5, and from 2D layers (Ag 3/3 I 3/3 ) n or 3D mixed tetrahedral subnetwork (AgI 3/3 S 1/2 ) in the range x  >   0.5.