Tin valence and local environments in silicate glasses as determined from X-ray absorption spectroscopy

X-ray absorption spectroscopy (XAS) was used to characterize the tin (Sn) environments in four borosilicate glass nuclear waste formulations, two silicate float glasses, and three potassium aluminosilicate glasses. Sn K-edge XAS data of most glasses investigated indicate Sn4+O6 units with average Sn–O distances near 2.03 Å. XAS data for a float glass fabricated under reducing conditions show a mixture of Sn4+O6 and Sn2+O4 sites. XAS data for three glasses indicate Sn–Sn distances ranging from 3.43 to 3.53 Å, that suggest Sn4+O6 units linking with each other, while the 4.96 Å Sn–Sn distance for one waste glass suggests clustering of unlinked Sn4+O6 units.