Atomic level structure of Ge-Sb-S glasses: chemical short range order and long Sb-S bonds

TL;DR

This study reveals the atomic structure of Ge-Sb-S glasses, showing a chemically ordered network with specific Ge-S and Sb-S bonds, and identifies longer Sb-S bonds indicating more complex local environments.

Contribution

The paper provides detailed atomic-scale structural models of Ge-Sb-S glasses using combined diffraction, EXAFS, and Raman data, highlighting the presence of longer Sb-S bonds and their implications.

Findings

Ge and S atoms have 4 and 2 nearest neighbors

Ge-S and Sb-S bonds are predominant in the structure

Longer Sb-S bonds suggest Sb atoms with more than 3 S neighbors

Abstract

The structure of Ge$_{20}$Sb$_{10}$S$_{70}$, Ge$_{23}$Sb$_{12}$S$_{65}$ and Ge$_{26}$Sb$_{13}$S$_{61}$ glasses was investigated by neutron diffraction (ND), X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) measurements at the Ge and Sb K-edges as well as Raman scattering. For each composition, large scale structural models were obtained by fitting simultaneously diffraction and EXAFS data sets in the framework of the reverse Monte Carlo (RMC) simulation technique. Ge and S atoms have 4 and 2 nearest neighbors, respectively. The structure of these glasses can be described by the chemically ordered network model: Ge-S and Sb-S bonds are always preferred. These two bond types adequately describe the structure of the stoichiometric glass while S-S bonds can also be found in the S-rich composition. Raman scattering data show the presence of Ge-Ge, Ge-Sb and Sb-Sb bonds in the S-deficient glass but only Ge-Sb bonds are needed to fit diffraction and EXAFS datasets. A significant part of the Sb-S pairs has 0.3-0.4 {\AA} longer bond distance than the usually accepted covalent bond length (~2.45 {\AA}). From this observation it was inferred that a part of Sb atoms have more than 3 S neighbors.