Ionic transport in AgI‐HgS‐As2S3 glasses: Critical percolation and modifier‐controlled domains

Abstract

AbstractElectrical measurements, dc and ac, show that (AgI)x(HgS)0.5‐x/2(As2S3)0.5‐x/2 glasses, 0.0 ≤ x ≤ 0.6, exhibit drastic changes in ionic conductivity σi 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, xc ≈ 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 σi. The ion transport parameters depend on the host network connectivity, represented by the average coordination number <n0>, via the critical fictive temperature T0; the calculated T0 value is comparable to the glass transition temperature for the glassy (HgS)0.5(As2S3)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 (AgI2/2S2/2)n chains in the silver iodide content range 0.2 < x ≤ 0.5, and from 2D layers (Ag3/3I3/3)n or 3D mixed tetrahedral subnetwork (AgI3/3S1/2) in the range x > 0.5.