Evidence for 6-Coordinated Zirconium in Inactive Nuclear Waste Glasses

In inactive glasses used as models for French nuclear waste forms, Zr K‐ and L2,3‐edge X‐ray absorption spectroscopy spectra indicate that Zr is only 6‐coordinated, with d(Zr‐O) distances of 2.08 ± 0.01 Å and with a small radial disorder. Beyond, the first coordination shell, next‐nearest Si neighbors occur at about 3.4 Å. These distances exclude the presence of [7]Zr and/or [8]Zr and suggest [6]Zr‐O‐Si angles close to 130°, indicating corner‐shared ZrO6 and SiO4 polyhedra. This structural configuration is similar to those observed in some crystalline zirconosilicates and is in agreement with the stability of Zr in borosilicate melts and glasses.