Cluster modeling of quasi‐adaptive phases in vitreous germanium selenides

Abstract

The developed cluster modeling approach based on ab‐initio calculations with RHF/6‐311G* basis set testifies absence of intermediate optimally‐constrained phase in binary Gex Se100‐x system within 20 ≤ x < 26 domain. It is shown, that character “outrigger raft” carcass is conserved for all glass compositions within expected reversibility window. Thus, the structure of binary Gex Se100‐x glasses can be described in terms of “chains crossing” model in case of x < 12, mixed “chains crossing” and “outrigger raft” models in case of 12 ≤ x < 20 and modified “outrigger raft” model in case of x ≥ 20. The expected reversibility window in binary Gex Se100‐x glasses is shown to be only quasi‐adaptive phase, based on “outrigger raft” structural motive with two edge‐ and four corner‐sharing tetrahedra interconnected by optimally‐constrained Ge‐Se‐Se‐Ge bridges with extra Se atoms in ring‐like configurations replaced Se‐Se dimers. The results of quantum mechanics modeling are confirmed well by high‐resolution X‐ray photoelectron spectroscopy measurements in this system. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Pseudo‐self‐organized topological phases in glassy selenides for IR photonics

“…The performed quantum mechanics calculations show that all glass compositions of binary Ge x Se 100-x system within 20<x<28 range are more energetically preferable in the atomic configurations, which involve two Se atoms incorporated between separate outrigger raft NFC as optimally-constrained ≡Ge-Se-Se-Ge≡ inter-cluster bridges (Fig. 2b) [26]. Other Se atoms, which do not participate in the backbone connectivity, form Se-rich fragments attached to a place I in Fig.…”

“…2b possesses n c =3 in a global sense. All the rest glasses in the range of expected reversibility window (20≤x≤25) [14] [26]), which form a so-called pseudo-selforganized phase. Thus, our modelling shows that there is no structural signature for intermediate phase in this binary glass system in terms of global optimally-constrained network in good agreement with [18].…”

“…Therefore, with increase in Se content, the structural evolution of binary Ge x Se 100-x system occurs keeping optimally-constrained inter-cluster bridges (≡Ge-Se-Se-Ge≡) and Se atoms in ring-like fragments at the place of Se-Se dimers. The x=21.5 composition is the last one in our set of NFC used for modelling where this tendency is still fully preserved [26]. According to the above scheme of structural evolution, only one glass composition Ge 21.5 Se 78.5 shown in Fig.…”

“…2a) [25]. This so-called outrigger raft structural motive was used as a basic NFC for our quantum mechanical modelling [26]. With increase in Se content, additional Se atoms can be attached to these NFC instead of Se-Se dimers (place I in Fig.…”

“…So, in view of the above consideration the onset of self-organized phase in this system should occur near Ge 20 Se 80 glass. According to our quantum mechanics calculations with outrigger raft structural unit as a basic motive of Ge x Se 100-x glass backbone within 20<x<28 compositional range [26], only Ge 21.5 Se 78.5 glass (Fig. 2b) possesses n c =3 in a global sense.…”