The Structure of Lead-Rich PbO-SiO2 Glasses

Oliver L. G. Alderman* & Diane Holland

University of Warwick

Results of a recent neutron diffraction study, performed on the GEM diffractometer at ISIS, are presented. The six xPbO.(100-x)SiO2 (33.3 ≤ x ≤ 80.0 mol.% PbO) glasses were formed by rapid quenching of the melt between twin steel rollers. The resulting vitreous flakes are more highly disordered than glasses quenched conventionally (at 2-3 orders of magnitude more slowly), as evinced by the Q-species distributions extracted by 29Si MAS NMR [1]. The nature of the short range structure about Si atoms is well characterised, whilst the Pb enviromnments are not, with 207Pb NMR yeilding only limited information [2] due to the wide (~4000ppm) featureless lineshapes. Diffraction data, whilst not element specific, can be of great use for short range order determination, and analysis of the neutron total correlation functions has shown that a broad continuum of Pb-O bond lengths exist from about 1.9 to beyond 2.7A. The distribution of the bond lengths suggests the existence of [PbO3] units with 3 equivalent bonds, along with possibly [PbO4], [PbO3+n] and [PbO6] polyhedra. The average Pb-O coordination number is higher than 3, but cannot be uniquely determined from neuton diffraction alone due to the overlap of the longer Pb-O contributions with O-O and Si-Si correlations. [1] S. Feller et al., Journal of Non-Crystalline Solids 356, (2010), 304 [2] F. Fayon et al., Journal of Non-Crystalline Solids 243, (1999), 39