Radiation-modified structure of Ge25Sb15S60 and Ge35Sb5S60 glasses

Abstract

Atomic structures of Ge 25 Sb 15 S 60 and Ge 35 Sb 5 S 60 glasses are investigated in the ␥-irradiated and annealed after ␥-irradiation states by means of high-energy synchrotron x-ray diffraction technique. The first sharp diffraction peak ͑FSDP͒ is detected at around 1.1 Å −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 ␥-irradiated and annealed states. The peaks in the pair distribution functions observed between 2 and 4 Å 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 4/2 tetrahedra, and S-S and/or Ge-Ge second neighbor correlations in the corner-shared GeS 4/2 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.

Long-term radiation-induced optical darkening effects in chalcogenide glasses

“…Thus, when the radiation-induced structural changes in ChGs occur towards the disordering on the MRO scale and no changes or ordering on the SRO scale, the non-defective mechanism in the frame of the distortion model and any other models (if exist), resulting in a final structural configuration without charged defects, is dominant. On the other hand, the established for Ge-S based glasses the long-term radiation-induced structural changes in DBAL data [2,11,14], when the FSDP remains practically unchanged [2] or its intensity can be something higher [16] and peak is probably something narrower upon γ-irradiation, have been interpreted within the defective CTD model, involving atomic rearrangements directly in the first coordination shells (first-nearest-neighbor atomic correlations), that is, on the SRO scale. The unobservable changes in the FSDP and/or the FSDP sharping and narrowing means that no changes or increasing the MRO structural correlation length and, consequently, a stable MRO structure and/or rise of ordering on the MRO scale take place.…”

“…It has been suggested that the non-defective mechanism within the distortion model for g-As 2 S 3 and the defective mechanism within the coordination topological defects (CTDs) model for g-Ge 15.8 As 21 S 63.2 took place [11,14], since the latter CTD model has been evidently verified using Raman spectroscopy studies, employing the differential representation of depolarized Raman spectra [13]. The CTD approach used for g-Ge 15.8 As 21 S 63.2 or (As 2 S 3 ) 0.4 (GeS 2 ) 0.6 alloy with the dominant Ge-S subsystem seems to be valid for major Ge-S based chalcogenides (see, for example, [15][16][17]). …”

Radiation/annealing-induced structural changes in GexAs40-xS60 glasses as revealed from high-energy synchrotron X-ray diffraction measurements

“…(a) The total structure factors S(Q) for the samples of the investigated Ge x As 40-x S 60 system in -irradiated (the curves for -irradiated state is shifted (+1) for clarity) and annealed after -irradiation states; and (b) the first sharp diffraction peak (FSDP) in -irradiated and annealed after -irradiation states. difference is notably larger than the total experimental error of the structure factor, which is estimated to be below 1% in the low Q-part of S(Q) as shown in [18]. glasses, both in the -irradiated and annealed after -irradiation states.…”

“…A maximum at r = 3.55-3.60 Å reflects the second coordination sphere. Also, a hump at r = 2.99 Å is observed on g(r) of all the investigated samples in the second coordination shell like to the samples of Ge x Sb 40-x S 60 with x = 25 and 35 [18]. But due to the risk that this hump may come from the termination effect, we will not analyze this hump in further consideration.…”

“…Therefore, the experimental error should be minimized for correct investigation of such phenomena. In the present study, like in the case of glasses [18], all XRD experiments were carried out within a couple of hours; the specimens were of the same thickness; they were fixed in a holder moving horizontally, providing practically identical sample adjustment during measurements. The samples were positioned in the holder at the same position to be measured first as -irradiated and than as annealed after -irradiation.…”