Critical comments on speculations with open and closed “free-volume defects … in ion-conducting Ag/AgI-As2S3 glasses …”

Microstructure model proposed by T. Kavetskyy et al. [T. Kavetskyy, J. Borc, P. Petkov, K. Kolev, T. Petkova, Solid State Ionics 183 (2011) 16] to explain positron annihilation experiments in glassy (As2S3)0.85Ag0.15 and (As2S3)0.85(AgI)0.15 is shown to be completely inconsistent with realistic structural observations for ion-conducting chalcogenide glasses of the above systems. This speculation arises from incorrect acceptance of compositional trends in annihilation modes treated within two-state positron trapping model under a condition of changes possible in both defect-free bulk and defect-related annihilation channels.