A comparative study of the atomic structures of Ge-doped As₄S₃ and P₄Se₃ molecular glasses

The structures of pseudo-binary PSe and AsS glasses with compositions close to the P₄Se₃ and As₄S₃ stoichiometry with a few atom %Ge doping were determined using Monte Carlo simulations constrained by density and x-ray scattering measurements. We find that these glasses consist predominantly of P₄Se₃ and As₄S₃ molecules. The Ge doping results in some important differences between the two glasses. The PSe glass displays significantly higher intermolecular connectivity via PSeGe linkages, consistent with the significantly higher glass transition temperature and lower fragility of this liquid compared to its AsS counterpart. We also speculate that a consequence of this difference in the intermolecular connectivity would be to delay any pressure-induced conversion from a molecular to a network structure for the Ge doped PSe glass compared to the Ge-doped AsS glass.