Short range order and topology of binary Ge-S glasses

TL;DR

This study investigates the short-range order and topology of Ge-S glasses across a broad composition range using neutron diffraction, X-ray diffraction, and EXAFS, revealing structural details consistent with the chemically ordered network model.

Contribution

It provides comprehensive experimental and simulation analysis of Ge-S glasses, confirming the applicability of the chemically ordered network model and detailing the bonding preferences and ring structures.

Findings

Ge and S atoms follow the Mott-rule in all glasses.

Ge-S bonds are predominant; S-S bonds appear only in S-rich glasses.

Ge-Ge bonds are necessary in Ge-rich compositions.

Abstract

Short range order and topology of Ge$_x$S$_{100-x}$ glasses over a broad composition range (20 $\le$ x $\le$ 42 in at%) was investigated by neutron diffraction, X-ray diffraction, and Ge K-edge extended X-ray absorption fine structure (EXAFS) measurements. The experimental data sets were fitted simultaneously in the framework of the reverse Monte Carlo simulation method. It was found that both constituents (Ge and S) satisfy the Mott-rule in all investigated glasses: Ge and S atoms have 4 and 2 neighbours, respectively. The structure of these glasses can be described with the chemically ordered network model: Ge-S bonds are preferred, S-S bonds are present only in S-rich glasses. Dedicated simulations showed that Ge-Ge bonds are necessary in Ge-rich glasses. Connections between Ge atoms (such as edge-sharing GeS$_{4/2}$ tetrahedra) in stoichiometric and S-rich glasses were analysed. The frequency of primitive rings was also calculated.