Structural investigation of alkali aluminoborosilicate glass containing MoO3 for vitrification of nuclear waste

Molybdenum poses challenges due to its low solubility and propensity for undesirable crystallization in nuclear waste glasses. An increased concentration of MoO3 promotes the formation of crystalline phases within the glass matrix, potentially compromising the long-term stability of nuclear waste glasses. This study explored the impact of incorporating various alkali cations into Mo-containing aluminoborosilicate glasses, employing various spectroscopies. We found that incorporating larger alkali cations promotes a more polymerized silicate network, consequently reducing the crystallization tendency. Spectroscopic analysis suggests the structural modification of Mo units with the incorporation of larger alkali cations, presenting two potential structural adjustments. Both scenarios facilitate the direct linkage of Mo units to the silicate network (Mo-O-Si), in alignment with Pauling's stability rule. The formation of Mo-O-Si bonds not only improves the solubility of Mo in glass but also prevents the crystallization of Mo-containing phases by inhibiting the formation of nucleation seeds, MoO42- entities.