Local environment of Zn in zirconium borosilicate glasses determined by X-ray absorption spectroscopy

The Zn environments in six zirconium borosilicate glasses were characterized using X-ray absorption spectroscopy (XAS). The Zn environment is of interest because the addition of ZnO to borosilicate glass produces beneficial effects on certain bulk physical properties that are important in the production and long-term storage of radioactive waste glasses. Zn XAS data and analyses show that all glass samples investigated contain Zn++ surrounded by four oxygens in tetrahedral coordination, with most likely, Si second nearest neighbors. The Zn environments are essentially invariant in all of the glass samples investigated, despite significant differences in glass chemistry and sample homogeneity. The results indicate that tetrahedral Zn in these glasses takes on the role of a weakly bonded network former. As ZnO is added to a silicate glass, Zn tetrahedra most likely link to silicate tetrahedra, decrease the volume of voids between linked tetrahedra, and restrict diffusion of large ions. These inferences concur with observations that leach rates are reduced for zirconium borosilicate glass as ZnO is added.