It is well known that PbO-SiO2 exhibits a wide glass formation composition range, up to 90 mol% PbO. Earlier studies suggest that the existence of PbO3 or PbO4 structural units, which act like network formers, may be the reason for the wide glass formation range but the structure beyond short-range order is still unclear. Here we found that the network formation in the glass is governed by the interplay of SiO4 tetrahedra and PbOx polyhedra (x=3-5, x=4 is major) as a network former while the distribution of other (non-network) units is inhomogeneous. The inhomogeneous distribution of PbOx polyhedra in the 34 mol% PbO glass and that of SiO4 tetrahedra in the 65 mol% PbO glass yield a prepeak at Q<1.5 Å⊃-1, a sign of a characteristic length of the inhomogeneity in the diffraction patterns. Furthermore, PbO-SiO2 glasses contain extraordinarily large amounts of free volume (voids), which cannot be found in conventional binary silicate glasses (network former-network modifier) but only in network-former glasses such as SiO2 glass and in its mixtures with another network former such as GeO2. We classify PbO-SiO2 glass as a "binary network-former glass" with large amounts of free volume.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2010 Oct 29|