Structural Nature of Boson Peak and Low‐Temperature Heat Excess in As2S3 Glass

Abstract

Comparative analysis of experimentally measured Raman spectra of crystalline (c), glassy (g), and powdered c‐As2S3 samples is performed based on vibrational modes of As6S6+6/2 ring‐like nanoclusters being fully (“rigid”) or partially (“soft”) interconnected with the glassy matrix, calculated using density functional theory (DFT). Although good agreement is found in the 100–500 cm−1 spectral range, the DFT simulations show additional super‐low frequency modes of “soft” rings at wavenumbers being significantly lower than the “rigid” ring's vibrational band at 26 cm−1. Broadening of the relatively narrow low‐frequency band of “rigid” clusters is found to be dependent on the number of interconnections of “soft” clusters with the glassy matrix, demonstrating mixing of “rigid” and “soft” vibrations in the boson peak region of g‐As2S3. In addition, the shift of the super‐low frequency Raman modes of “soft” nanoclusters and equivalent characteristic temperature are found to be nonlinearly dependent on the number of interconnections. Comparison with experimental Raman spectroscopic and heat capacity data indicates that the main contribution of both the LF Raman intensity and the low‐temperature anomaly of specific heat at 5.3 K comes from “soft” clusters with four and two interconnections.