TITLE:
Reverse Monte Carlo Modeling of the Rigidity Percolation Threshold in GexSe1-x Glassy Networks
AUTHORS:
Moneeb T. M. Shatnawi
KEYWORDS:
Chalcogenide Glasses, Rigidity Percolation, Reverse Monte Carlo Modeling, Atomic Pair Distribution Function (PDF), GexSe1-x Glasses
JOURNAL NAME:
New Journal of Glass and Ceramics,
Vol.5 No.3,
June
26,
2015
ABSTRACT: Based on Maxwell’s constraint counting theory, rigidity percolation in GexSe1-x glasses occurs
when the mean coordination number reaches the value of 2.4. This corresponds to Ge0.20Se0.80 glass. At this composition, the number of constraints experienced by an atom equals the number of
degrees of freedom in three dimensions. Hence, at this composition, the network changes from a
floppy phase to a rigid phase, and rigidity starts to percolate. In this work, we use reverse Monte
Carlo (RMC) modeling to model the structure of Ge0.20Se0.80 glass by simulating its experimental
total atomic pair distribution function (PDF) obtained via high energy synchrotron radiation. A
three-dimensional configuration of 2836 atoms was obtained, from which we extracted the partial
atomic pair distribution functions associated with Ge-Ge, Ge-Se and Se-Se real space correlations
that are hard to extract experimentally from total scattering methods. Bond angle distributions,
coordination numbers, mean coordination numbers and the number of floppy modes were also
extracted and discussed. More structural insights about network topology at this composition
were illustrated. The results indicate that in Ge0.20Se0.80 glass, Ge atoms break up and cross-link
the Se chain structure, and form structural units that are four-fold coordinated (the GeSe4 tetrahedra).
These tetrahedra form the basic building block and are connected via shared Se atoms or
short Se chains. The extent of the intermediate ranged oscillations in real space (as extracted from
the width of the first sharp diffraction peak) was found to be around 19.6 ?. The bonding schemes
in this glass are consistent with the so-called “8-N” rule and can be interpreted in terms of a chemically
ordered network model.