Compositional anomalies in Se-rich As-Se glass-forming system as revealed from positron annihilation lifetime spectroscopy and ab initio cluster modeling

Abstract

Positron annihilation lifetime spectroscopy in high-measurements statistics supported by ab initio quantum chemical modeling developed within cation-interlinking network cluster approach were used to examine compositional peculiarities of free-volume evolution in Se-rich As-Se glasses. Existence of some anomalies in the studied glasses observed as jump in the defect-related positron lifetime near average coordination Z≈2.33 and strong growing trend approaching Z=2.40 is justified. These features correspond to evolution of glassy network due to free-volume elements based on solid angle free of bond charge associated with Se atoms in a vicinity of heteropolar chemical bonds. The results are explained within structural models of optimized network of As-Se glasses composed of AsSe3/2 pyramids interlinked by variable-length Se-chains.