Square-wave voltammetry and Mössbauer spectroscopy in tin-doped soda-silicate and soda-lime-silicate glasses

Abstract Glasses of the basic compositions x Na 2 O·(100− x )SiO 2 ( x =15, 20, 26 and 33 mol%) and x Na 2 O·10CaO·(90− x )SiO 2 ( x =10, 16, 20 and 26 mol%) doped with 0.25 mol% SnO 2 were studied using square-wave voltammetry in the temperature range from 1000 to 1600 °C. The peak potentials determined by voltammetry were found to decrease linearly with temperature. While the peak potentials of the soda-silicate glasses did not depend on the Na 2 O-content, those measured in the lime containing glasses decreased with increasing Na 2 O-concentration. The Mossbauer spectra of tin-doped soda-lime-silicate glasses showed two signals attributed to Sn 2+ and Sn 4+ . The isomer shift for Sn 2+ decreases with increasing Na 2 O-concentration, while for Sn 4+ the opposite effect was observed. Both, however, can be explained by an increasing covalent character of the Sn–O bonds with increasing sodium concentration. From isomer shifts and quadrupolar interactions it is concluded that Sn 4+ is incorporated in a distorted sixfold coordination with strongly ionic bonds. The redox chemistry of the Sn 2+ /Sn 4+ equilibrium and the incorporation of tin into the silicate network are further discussed.