Ternary alkali stannosilicate glasses: a Mössbauer and neutron diffraction study

Neutron diffraction and Mössbauer spectroscopic measurements have been performed on four series of ternary alkali stannosilicate glasses of nominal composition (SnO_0.5-x (M₂ O)_x (SiO₂ )_0.5with 0x 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 ¹¹⁹ Sn Mössbauer 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.