Pressure-induced variations of medium-range order in B2O3 glasses

Lead-borate glasses manifest unique structure with lead oxide composition owing to their dual role of modifier and former. The medium-range signature from the first sharp diffraction peak (FSDP) in lead-borates exhibits substantial correlations due to the presence of superstructural units. Pressure plays an important role in altering bonding characteristics and hence structure in materials. To understand pressure-induced changes in the medium-range order (MRO) in lead-borate glasses, we have carried out high pressure X-ray diffraction studies in the FSDP region of these glasses up to 25 GPa. Two clear peaks, q0 and q1 are observed in all the modified glasses, below and above the position of the FSDP in pure B2O3 glass. This shows that lead oxide alters the FSDP and causes changes in the network structure at the MRO. q1 exhibits an increase under compression, resulting in a reduction in correlation lengths for all glass compositions. The initial steep decrease is accompanied by a lower rate of reduction at higher pressures. This shows that correlations arising from structural voids in the boron matrix exhibit similar decrease for various lead oxide compositions.