On the reversibility window in binary As–Se glasses

Physical ageing effects caused by prolonged natural storage are recorded for binary As_xSe_1−x glasses with 0.2x<0.4. Their origin is associated with pure “shrinkage” of under-constrained glass networks. It is shown that only stoichiometric As₂Se₃ composition, which network is formed by a so-called self-organized phase, possesses the ideal non-ageing ability.     

Physical ageing in glassy As–Se induced by above-bandgap photoexposure

Physical ageing induced by above-bandgap photoexposure is studied in As–Se glasses using the differential scanning calorimetry technique. The kinetics of this effect are compared with those caused by natural storage in the dark. Acceleration of physical ageing processes is recorded for Se-rich glasses having more than three Se atoms in their chains.     

Topological controversies in the adaptability concept for glassy germanium selenides

Cluster modelling based on ab-initio calculations testifies lack of intermediate optimally-constrained phase in binary Ge_xSe_100-x system within expected reversibility window (20 ≤ × < 26) in terms of global connectivity. Network of these glasses within 20 ≤ × < 26 compositional range can be composed of over-constrained “outrigger raft” structural motives built of two edge- and four corner-shared GeSe_4/2 tetrahedra interconnected via optimally-constrained ≡ Ge―Se―Se―Ge≡ bridges, extra Se atoms forming ring-like configurations instead of Se―Se dimers.     

Positron annihilation probing of crystallization effects in TAS-235 glass affected by Ga additions

Crystallization effects in Te₂₀As₃₀Se₅₀ glass known also as TAS-235 affected by Ga additions to Ga₂Te₂₀As₂₈Se₅₀ and Ga₅Te₂₀As₂₅Se₅₀ compositions are probed with positron annihilation spectroscopy in the measuring modes exploring positron lifetimes and Doppler broadening of annihilation line. Occurring of cubic-phase Ga₂Se₃ droplets with character nanoscale sizes in partially-crystallized Ga₂Te₂₀As₂₈Se₅₀ alloy is shown to be associated with agglomeration of intrinsic free-volume voids, this process being enhanced over microcrystalline scale in Ga₅Te₂₀As₂₅Se₅₀ alloy. Crystallization changes in the void structure of TAS-235 glass are considered in terms of free-volume evolution under the same principal chemical environment responsible for positron trapping in amorphous and partially crystallized substances.     

A study of reversible gamma-induced structural transformations in vitreous Ge23.5Sb11.8S64.7 by high-resolution X-ray photoelectron spectroscopy

The structural origin of reversible gamma-induced effects in vitreous Ge(23.5)Sb(11.8)S(64.7) has been investigated by high-resolution X-ray photoelectron spectroscopy (XPS). The changes in valence band spectrum from gamma-irradiation suggest a decrease of sulfur lone pair electron concentration accompanied by changes in bonding states of S and Ge. The appearance of additional doublets in the core-level XPS spectra of Ge, Sb, and S atoms for gamma-irradiated sample is described by the formation of over- and under-coordinated charged defect pairs (Ge(3)(-)-S(3)(+)) as a result of radiation treatment. The results verify the switching of Ge-S covalent bonds into S-S bonds as the main microstructural mechanism for gamma-induced optical effects in this glass.     

Radiation-modified structure of Ge25Sb15S60 and Ge35Sb5S60 glasses

Atomic structures of Ge(25)Sb(15)S(60) and Ge(35)Sb(5)S(60) glasses are investigated in the gamma-irradiated and annealed after gamma-irradiation states by means of high-energy synchrotron x-ray diffraction technique. The first sharp diffraction peak (FSDP) is detected at around 1.1 A(-1) in the structure factors of both alloys studied. The FSDP position is found to be stable for radiation/annealing treatment of the samples, while the FSDP intensity shows some changes between gamma-irradiated and annealed states. The peaks in the pair distribution functions observed between 2 and 4 A are related to the Ge-S, Ge-Sb, and Sb-Sb first neighbor correlations and Ge-Ge second neighbor correlations in the edge-shared GeS(42) tetrahedra, and S-S and/or Ge-Ge second neighbor correlations in the corner-shared GeS(42) tetrahedra. Three mechanisms of the radiation-/annealing-induced changes are discussed in the framework of coordination topological defect formation and bond-free solid angle concepts.     

Photoinduced defect formation in chalcogenide vitreous semiconductors

Journal of Applied Spectroscopy -     

Concentration dependence of impurity absorption in chalcogenide glasses of the Ge-Sb-S system

We have investigated the IR spectra of chalcogenide glasses of the triple Ge-Sb-S system in Sb₂S₃-GeS₂ and Sb₂S₃-Ge₂S₃ sections. We have analyzed the specific features of the appearance of intense vibrational bands of absorption of various structural fragments depending on the chemical composition of glasses. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 499–502, July–August, 2000.     

FSDP-related correlations in γ-irradiated chalcogenide semiconductor glasses: The case of glassy arsenic trisulphide g-As2S3 revised

Influence of high-energy γ-irradiation on the FSDP in XRD pattern is investigated at the example of g-As₂S₃. Spectroscopic measurements in the fundamental optical absorption edge regions were used to characterize the value of γ-induced changes through the observed darkening effect. It is concluded that γ-irradiation with ~3 MGy dose does not produce any detectable changes in the FSDP parameters, but leads to the appearance of satellite peaks at the left and right sides of the FSDP. Detailed analysis allows attributing of these peaks to crystalline As₂O₃ and S phases, which appear at the surface of g-As₂S₃ after prolonged γ-irradiation. Some correlations with the value of γ-induced optical changes in g-As₂S₃ were detected only for pre-FSDP.