Local motifs in GeS$_2$-Ga$_2$S$_3$ glasses

TL;DR

This study investigates the local atomic structure of GeS$_2$-Ga$_2$S$_3$ glasses using advanced spectroscopic and modeling techniques, revealing details about coordination and bonding that challenge traditional chemical ordering assumptions.

Contribution

It provides new insights into the local motifs and bonding environment in GeS$_2$-Ga$_2$S$_3$ glasses through combined experimental and computational analysis.

Findings

Ga has a coordination number close to four.

Ga bonds to S and Ga, violating chemical ordering.

About 30% of Ge atoms are involved in edge-shared tetrahedra.

Abstract

The structure of (GeS$_2$)$_{0.75}$(Ga$_2$S$_3$)$_{0.25}$ and (GeS$_2$)$_{0.83}$(Ga$_2$S$_3$)$_{0.17}$ glasses was investigated by Raman scattering, high energy X-ray diffraction and extended X-ray absorption fine structure (EXAFS) measurements at the Ga and Ge K-edges. The reverse Monte Carlo simulation technique (RMC) was used to obtain structural models compatible with diffraction and EXAFS datasets. It was found that the coordination number of Ga is close to four. While Ge atoms have only S neighbors, Ga binds to S as well as to Ga atoms showing a violation of chemical ordering in GeS$_2$-Ga$_2$S$_3$ glasses. Analysis of the corner- and edge-sharing between [GeS$_{4/2}$] units revealed that about 30% of germanium atoms participate in the edge-shared tetrahedra.