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

Abstract

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 PO and SnO 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 SnO 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 POP and POSn bonds and the SnO polyhedra do not share oxygen neighbors. From comparisons of the compositional dependences of the SnO and ZnO coordination numbers and the respective number densities of atoms in the binary tin and zinc phosphate glasses, it is presumed that the SnO coordination increases further with NSnO > 4 in the ultraphosphate range (x < 0.5).