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 com- positions. 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. (author)