Reply on the “critical comments on speculations with … free-volume defects … in ion-conducting Ag/AgI–As 2 S 3 glasses…” T. Kavetskyy a, ⁎, J. Borc b , P. Petkov c , K. Kolev d , T. Petkova d , V. Tsmots a a Solid State Microelectronics Laboratory, Drohobych Ivan Franko State Pedagogical University, 24 I. Franko Str., 82100 Drohobych, Ukraine b Department of Applied Physics, Lublin University of Technology, 38 Nadbystrzycka Str., 20-618 Lublin, Poland c Thin Films Technology Laboratory, University of Chemical Technology and Metallurgy, 8 Kl. Ohridsky blvd., 1756 Sofia, Bulgaria d Institute of Electrochemistry and Energy Systems, Bulgarian Academy of Sciences, Bl.10 Acad. G. Bonchev Str., 1113 Sofia, Bulgaria abstract article info Article history: Received 22 March 2012 Received in revised form 4 September 2012 Accepted 14 November 2012 Available online 21 January 2013 Keywords: Chalcogenide glasses Ionic conductors Free-volume Positron annihilation Critical comments of Shpotyuk et al. [O. Shpotyuk, J. Filipecki, M. Hyla, A. Ingram, Solid State Ionics 208 (2012) 1] are shown to be inconsistent with the experimental results obtained for a size of free-volume defects in ion-conducting Ag/AgI–As 2 S 3 glasses in view of a new formula for positron lifetime τ 2 versus radius of voids R for R b 5 Å, discovered by Liao et al. [K.-S. Liao, H. Chen, S. Awad, J.-P. Yuan, W.-S. Hung, K.-R. Lee, J.-Y. Lai, C.-C. Hu, Y.C. Jean, Macromolecules 44 (2011) 6818]. In particular, the statement that only voids with volume ~80–100 Å 3 can be effective positron traps with more prolonged lifetimes of τ 2 = 0.35– 0.38 ns is at least inconclusive in terms of a new approach. The experimental results and schematic model reported by Kavetskyy et al. [T. Kavetskyy, J. Borc, P. Petkov, K. Kolev, T. Petkova, Solid State Ionics 183 (2011) 16] are a direct evidence of validity of a newly modified equation for τ 2 -R correlation in the case of inorganic polymeric chalcogenide glasses without orthopositronium component in positron annihilation lifetime spectroscopy. © 2012 Elsevier B.V. All rights reserved. Recently, Shpotyuk et al. [1] critically considered the investigation of free-volume defects and microstructure in ion-conducting Ag/AgI– As 2 S 3 glasses with application of positron annihilation lifetime spec- troscopy (PALS) and load-dependent Vickers microhardness mea- surement techniques [2]. The main discussion topic formulated in [1] is related to the structural network of melt-quenched glassy (g-) (As 2 S 3 ) 0.85 Ag 0.15 . We agree with the authors [1] that the short-range structure of g-(As 2 S 3 ) 0.85 Ag 0.15 is evidently modified in comparison to g-As 2 S 3 . Indeed, Penfold and Salmon [3] showed, using isotopic sub- stitution method in neutron diffraction, applied to two chalcogenide glasses on the (Ag 2 S) x (As 2 S 3 ) 1 -x (0 ≤ x ≤ 1) tie line of the Ag–As–S system, that Ag reacts with S giving rise to AgS 4 and/or AgS 3 polyhedra distributed in the glass network as x is increased from 0.096 to 0.500, while As remains threefold coordinated by S. The glass transition tem- perature decreases rapidly from 206 to 183 °C for small Ag additions (~1 at.%) in the Ag 2 S–As 2 S 3 glassy system [4], indicating a strong de- fragmentation of the host network evidenced also by high-resolution time-of-flight neutron diffraction measurements. Structural studies of (As 0.4 S 0.6 ) 100-x Ag x chalcogenide glasses (x =0, 4, 8, 12 at.%) with high-energy X-ray diffraction, neutron diffraction, extended X-ray ab- sorption fine structure spectroscopy and reverse Monte-Carlo simula- tion method [5] have revealed that addition of Ag to As 2 S 3 mainly results in the formation of Ag–S and As–As bonds in agreement with Ohta's explanation of electrical conduction in As 2 S 3 glasses doped with Ag [6]. Consequently, with addition of Ag the intrinsic structural features are modified including probably a free-volume void structure. It should be noted here that Kavetskyy et al.'s schematic model, pro- posed according to PALS study [2], has presented only the possible modification of free-volume void structure due to expected Ag + migration in the investigated alloys. The Ag + migration in chalcogenide glasses is a well-known phe- nomenon (see, for instance, [7] for review) but, of course, it would be necessary bearing in mind that not all Ag + ions are mobile simul- taneously at low Ag content (~15 at.% in the two Ag/AgI–As 2 S 3 glasses studied [2]). In addition, Ag + ions coming either from AgS n polyhedra or AgI-related clusters appear to be indiscernible in terms of random diffusion in the modified host network. A possible differ- ence between g-(As 2 S 3 ) 0.85 Ag 0.15 and g-(As 2 S 3 ) 0.85 (AgI) 0.15 is that the AgI-based glass is phase-separated and the Ag + ions are confined in AgI-related phase. 129 I-Mössbauer spectroscopy of AgI–Ag 2 S–As 2 S 3 glasses shows a drastic difference in hyperfine interaction parameters for “phase-separated” quasi-binary AgI–As 2 S 3 and homogeneous quasi-ternary AgI–Ag 2 S–As 2 S 3 glasses [8]. Taking all of this mentioned into account and owing to the high sensitivity of positrons to atomic-size defects and their long diffusion length (up to a few hundred nanometers in most materials, allowing a positron to probe about 10 7 atoms before annihilation [9]), we believe that some part of mobile Ag + ions may occupy the voids and thermal- ized positrons cannot be trapped and annihilated in the occupied voids Solid State Ionics 233 (2013) 107–109 ⁎ Corresponding author. Tel.: +380 3244 23257; fax: +380 3244 33332. E-mail address: kavetskyy@yahoo.com (T. Kavetskyy). Contents lists available at SciVerse ScienceDirect Solid State Ionics journal homepage: www.elsevier.com/locate/ssi 0167-2738/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ssi.2012.11.016