Lone-pair distribution and plumbite network formation in high lead silicate glass, 80PbO20SiO2Electronic supplementary information (ESI) available: Full experimental details: X-ray diffraction; neutron diffraction; EDX measurements. Total scattering formalism. Neutron and X-ray diffraction from a vitreous SiO2 standard. Additional EPSR modelling results: partial pair interference functions; low Q neutron and X-ray distinct scattering functions; coordination number histograms; oxygen speciation w

For the first time a detailed structural model has been determined which shows how the lone-pairs of electrons are arranged relative to each other in a glass network containing lone-pair cations. High energy X-ray and neutron diffraction patterns of a very high lead content silicate glass (80PbO20SiO 2 ) have been used to build three-dimensional models using empirical potential structure refinement. Coordination number and bond angle distributions reveal structural similarity to crystalline Pb 11 Si 3 O 17 and - and -PbO, and therefore strong evidence for a plumbite glass network built from pyramidal [PbO m ] polyhedra ( m 34), with stereochemically active lone-pairs, although with greater disorder in the first coordination shell of lead compared to the first coordination shell of silicon. The oxygen atoms are coordinated predominantly to four cations. Explicit introduction of lone-pair entities into some models leads to modification of the local Pb environment, whilst still allowing for reproduction of the measured diffraction patterns, thus demonstrating the non-uniqueness of the solutions. Nonetheless, the models share many features with crystalline Pb 11 Si 3 O 17 , including the OPbO bond angle distribution, which is more highly structured than reported for lower Pb content glasses using reverse Monte Carlo techniques. The lone-pair separation of 2.85 in the model glasses compares favourably with that estimated in -PbO as 2.88 , and these lone-pairs organise to create voids in the glass, just as they create channels in Pb 11 Si 3 O 17 and interlayer spaces in the PbO polymorphs. The structure of a lead silicate glass, 80PbO20SiO 2 , with extremely high lead content is studied by high energy X-ray and neutron diffraction, and empirical structural modelling, in order to reveal details of the plumbite based glass network and electron lone-pair distribution.