Effect of rare-earth doping on the free-volume structure of Ga-modified Te20As30Se50 glass

Abstract

By exploring the positron–electron annihilation technique in positron lifetime measuring mode, it is shown that principal rare-earth (RE) induced structural reconfiguration in Ga-codoped TAS-235 glass (that is a glassy Te₂₀As₂₉Ga₁Se₅₀ alloy) is related to occupation of intrinsic free-volume voids by embedded RE ions tightly connected with Ga-based tetrahedrons via strong covalent RE-Se/Te–Ga links. A gradual decrease in the intensity of the second component of two-term decomposed lifetime spectra of annihilating positrons accompanied with a detectable increase in the defect-related positron lifetime (thus inducing essentially a depressed rate in positron trapping) is evidenced by the example of Pr³⁺ ions added homogeneously to Te₂₀As₂₉Ga₁Se₅₀ glass in the amount of 500 ppmw. Observed changes in positron lifetime spectra are explained in terms of the competitive contribution of different occupancy positions in Ga-codoped glass available for RE ions and trapped positrons.