Nanocluster-driven topology as a unifying parameter of physical properties in chalcogenide glasses

Abstract

Amorphous chalcogenide glasses exhibit a wide spectrum of anomalous physical properties, including nonlinear optical response, the boson peak in the low-frequency spectra, non-Debye low-temperature thermal conductivity, complex dielectric relaxation, and pronounced photoinduced structural transformations. Despite decades of research, these phenomena are typically treated independently, and a unified microscopic interpretation remains lacking. In this report, a unified framework based on nanocluster-driven topology is proposed. Within this approach, chalcogenide systems such as As–S, Ge–S, and Ge–As–S are considered as structurally heterogeneous media composed of interacting nanoclusters forming medium-range order. These nanoclusters are built from fundamental structural units (AsS₃/SGe₃ pyramids and GeS₄ tetrahedra) and include “rigid”,“soft” and “defect” ring-like configurations; chain-like and branched-like with closed ends, and cage-like configurations. Their topology, connectivity, and spatial distribution define the effective structure of the glass. A key concept of the model is the presence of "keystone nanoclusters" [1,2] acting as topological organizing centers that determine the rigidity and stability of the network . Spectroscopic evidence supports this framework. Raman studies of glassy GeS₂ demonstrate the coexistence of nanoclusters related to both α- and β-GeS₂ crystalline phases , indicating mixed medium-range ordering.