Structure of tin phosphate glasses by neutron and X-ray diffraction

Neutron and X-ray diffraction experiments with large ranges of scattering vector, up to Qmax of 400 nm−1 and 250 nm−1, respectively, were performed on (SnO)x(P2O5)1-x glasses with 0.5 ≤ x ≤ 0.7, and the structural parameters of the P[sbnd]O and Sn[sbnd]O polyhedra were determined. The fraction of P–NBO (non-bridging oxygen) bonds increases systematically at the expense of the P–BO (bridging oxygen) bonds with SnO additions. The Sn[sbnd]O coordination number decreases in a predictable way from four at the metaphosphate composition (x = 0.5) to about three at the diphosphate composition (x = 0.67). The structural units are assumed to be SnO4 trigonal bipyramids and SnO3 trigonal pyramids with the lone-pair of Sn(II) electrons occupying one of the corners, similar to those in related crystal structures. For all glasses up to x = 0.67, the SnOz pyramids and PO4 tetrahedra form a continuous network with P[sbnd]O[sbnd]P and P[sbnd]O[sbnd]Sn bonds and the Sn[sbnd]O polyhedra do not share oxygen neighbors. From comparisons of the compositional dependences of the Sn[sbnd]O and Zn[sbnd]O coordination numbers and the respective number densities of atoms in the binary tin and zinc phosphate glasses, it is presumed that the Sn[sbnd]O coordination increases further with NSnO > 4 in the ultraphosphate range (x < 0.5). © 2019 The Author(s)