simonmartinclarkresearchsite - Amorphous structure solution

A comparative study of the atomic structures of Ge-doped As₄S₃ and P₄Se₃molecular glasses

B. Kalkan, C.J. Benmore, B.G. Aitken, S. Sen and S.M. Clark, J. Non-Cryst. Solids 514 83-89 (2019).

The structures of pseudo-binary P-Se and As-S 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 P-Se glass displays significantly higher intermolecular connectivity via P-Se-Ge linkages, consistent with the significantly higher glass transition temperature and lower fragility of this liquid compared to its As-S 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 P-Se glass compared to the Ge-doped As-S glass.

Fig 1. Total structure factors, S(Q), for (a) GPS and (b) GAS calculated from our X-ray scattering data (thick gray bars) compared to values given by our EPSR simulations.

Fig 2. Partial structure factors for GPS and GAS calculated from EPSR simulations. The gray vertical lines indicate the positions of FSDP and principal peak in total structure factor.

Fig 3. Total pair distribution functions, G(r), for (a) GPS and (b) GAS calculated from our EPSR simulations (solid black lines) compared with values calculated from our experimental data (gray thick bars).

Fig 4. Partial pair distribution functions for: (a) Ge-Se and Ge-S, (b) P-P and As-As, (c) P-Se and As-S, and (d) Se-Se and S-S determined from the EPSR simulations.

Fig 5. The nearest-neighbor coordination numbers calculated from our EPSR simulations.

Fig 6. Bond angle distribution functions obtained from our EPSR simulations. All bond angle distribution functions, except the Se-Se-Se and S-S-S distributions, were calculated by including neighbors separated by less than 2.9 Å. For the Se-Se-Se and S-S-S distributions neighboring atoms are defined to be in the range of 2.5 Å < r < 4.5 Å.

Fig 7. Structural motifs found in GAS and GPS together with their corresponding peaks in the bond angle distribution functions.

Fig 9. A schematic representation of the major structural components found in (a) GPS and (b) GAS glass. Their relative concentrations are only approximate.