Abstract
Free-volume evolution processes in As2Se3 glasses connected with subsequent stages of their modification (Ga-codoping, Te-modification, and Pr3+-doping) are studied employing positron annihilation lifetime (PAL) spectroscopy. Ga-codoping and rare-earth (RE)-doping effects are considered within the formal valence shell model, assuming fourfold coordination for metallic co-dopants. The PAL response on Ga-codoping in As2Se3 glass is associated with an increase in the defect-related positron lifetime τ2 and a decrease in the I2 intensity, meaning agglomeration of the PAL-responsible voids. The effect of Te-modification (in order to lower the phonon energy) testifies in favor of the stretching fragmentation process in the void structure resulting in essentially enhanced positron trapping rate in free-volume defects κd. Under the subsequent stage of Pr3+-doping, free volume space is changed due to void agglomeration resulting in 10 % decrease in the positron trapping rate. This effect is ascribed to the competitive occupation of positron preferential annihilation sites in the glass by RE dopants.
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