Ternary alkali stannosilicate glasses: a Mossbauer and neutron diffractionstudy

Neutron diffraction and Mossbauer spectroscopic measurements have been perf ormed on four series of ternary alkali stannosilicate glasses of nominal co mposition (SnO0.5-x (M2O)(x) (SiO2)(0.5) with 0 less than or equal to x les s than or equal to 0.2, where the modifier cations were M = Li, Na, K and R b. The data show that the tin is predominantly three co-ordinate and that t he length of the Sn-O bond and the O-Sn-O angle decrease with increasing mo difier concentration x. This reduction increases with increasing size of th e modifier cation, and is opposite in sign to the macroscopic molar volume which increases with modifier content. The Sn-119 Mossbauer spectra of thes e samples showed that most of the tin is in the Sn2+ state and that the iso mer shift and quadrupole splitting vary approximately linearly with the Sn- O bond length and O-Sn-O bond angle for each series. This is consistent wit h a contraction of the 5p electron orbitals of the tin atoms and an increas e in the symmetry of the Ligand environment as modifier ions are added.