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

The Zn environments in six zirconium borosilicate glasses were characterize d using X-ray absorption spectroscopy (XAS). The Zn environment is of inter est because the addition of ZnO to borosilicate glass produces beneficial e ffects on certain bulk physical properties that are important in the produc tion and long-term storage of radioactive waste glasses. Zn XAS data and an alyses show that all glass samples investigated contain Zn++ surrounded by four oxygens in tetrahedral coordination. with most likely, Si second neare st neighbors. The Zn environments are essentially invariant in all of the g lass samples investigated, despite significant differences in glass chemist ry and sample homogeneity. The results indicate that tetrahedral Zn in thes e glasses takes on the role of a weakly bonded network former. As ZnO is ad ded to a silicate glass, Zn tetrahedra most likely link to silicate tetrahe dra, decrease the volume of voids between linked tetrahedra, and restrict d iffusion of large ions. These inferences concur with observations that leac h rates are reduced for zirconium borosilicate glass as ZnO is added. (C) 2 000 Elsevier Science B.V. All rights reserved.