Positron annihilation lifetime spectroscopy as experimental probe of free volume concepts in network glasses

Positron annihilation lifetime spectroscopy (PALS) is tested for use as an alternative experimental probe of free volume concepts in network chalcogenide glasses. PALS measurements are carried out within binary As-Se and ternary GeAs(Sb)-S systems on the examples of g-As2Se3 and samples from stoichiometric As(Sb)(2)S-3-GeS2 and nonstoichiometric As(Sb)(2)S-3-Ge2S3 cross sections. The effect of high energy gamma-irradiation on PALS parameters is studied for ternary glass compositions. The role of induced defect related positron traps in annihilation processes is illustrated. The correlations between nanovoid sizes obtained from PALS, Monte Carlo simulation and first sharp diffraction peak (FSDP) measurements in the framework of Elliott's model are established on the example of g-As2Se3, in order to study the nanovoid topology in the real glass structure. It is shown that nanovoids with average radius of 2.9 angstrom, being effective traps for positrons with 0.37 ns defect related lifetime, are also detected within nanovoid distribution data obtained from Monte Carlo simulation. Suggesting that this group of nanovoids is responsible for the void based origin of FSDP, the analytical relationship between FSDP position and nanovoid diameter is proposed for layer like As2X3-type structures.