Free volume evolution in chalcogenide glasses as probed by PAL spectroscopy

•Enhanced void sizes in chalcogenide glasses as compared with molecular polymers.•Modified τ2–R equation to account for free-volume evolution in glassy As–S/Se.•Voids of ~ 2 Å radius cannot be responsible for positron trapping in As2S3 glass.

A newly modified correlation equation between defect-related positron lifetime τ2 (ns) determined within two-state trapping model and corresponding radius of free-volume defects R (Å) in a full non-linear formτ2=0.285⋅1−RR+5.50+12π⋅sin2πRR+5.50−1or in a simplified linear formτ2=0.212⋅(1+0.244⋅R).τ2=0.212⋅1+0.244⋅R.is proposed to account for compositional trends in free volume evolution of chalcogenide compounds like binary As–S/Se glasses. Specific chemical environment of voids possessing an effective negative charge owing to difference in the electronegativities of atoms forming covalent chemical bonds belonging to neighboring network polyhedrons is shown to play a decisive role in this correlation, leading to larger open volumes than would be attributed to the same positron lifetimes in a typical polymer material.