title: Network-Forming Nanoclusters in Binary As-S/Se Glasses: From Ab Initio Quantum Chemical Modeling to Experimental Evidences.
abstract: Network-forming As2(S/Se)mnanoclusters are employed to recognize expected variations in a vicinity of some remarkable compositions in binary As-Se/S glassy systems accepted as signatures of optimally constrained intermediate topological phases in earlier temperature-modulated differential scanning calorimetry experiments. The ab initio quantum chemical calculations performed using the cation-interlinking network cluster approach show similar oscillating character in tendency to local chemical decomposition but obvious step-like behavior in preference to global phase separation on boundary chemical compounds (pure chalcogen and stoichiometric arsenic chalcogenides). The onsets of stability are defined for chalcogen-rich glasses, these being connected with As2Se5(Z = 2.29) and As2S6(Z = 2.25) nanoclusters for As-Se and As-S glasses, respectively. The physical aging effects result preferentially from global phase separation in As-S glass system due to high localization of covalent bonding and local demixing on neighboring As2Sem+1and As2Sem-1nanoclusters in As-Se system. These nanoclusters well explain the lower limits of reversibility windows in temperature-modulated differential scanning calorimetry, but they cannot be accepted as signatures of topological phase transitions in respect to the rigidity theory.
authors.affiliation: Institute of Physics of Jan Dlugosz University of Czestochowa, Al. Armii Krajowej 13/15, 42-200, Czestochowa, Poland. malgorzatahyla@yahoo.com.|Lviv Scientific-Research Institute of Materials of Scientific Research Company "Carat", Stryjska str. 202, Lviv, 79031, Ukraine. malgorzatahyla@yahoo.com.
authors.forename: M
authors.initials: M
authors.lastname: Hyla
keywords: Ab initio calculation; Chalcogenide glasses; Nanocluster; Reversibility window