Ternary alkali stannosilicate glasses: a Mossbauer and neutron diffraction study

Neutron diffraction and Mossbauer spectroscopic measurements have been performed on four series of ternary alkali stannosilicate glasses of nominal composition (SnO0.5-x (M2O)(x) (SiO2)(0.5) with 0 less than or equal to x less than or equal to 0.2, where the modifier cations were M = Li, Na, K and Rb. The data show that the tin is predominantly three co-ordinate and that the length of the Sn-O bond and the O-Sn-O angle decrease with increasing modifier concentration x. This reduction increases with increasing size of the modifier cation, and is opposite in sign to the macroscopic molar volume which increases with modifier content. The Sn-119 Mossbauer spectra of these samples showed that most of the tin is in the Sn2+ state and that the isomer 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 with a contraction of the 5p electron orbitals of the tin atoms and an increase in the symmetry of the Ligand environment as modifier ions are added.