Chemical evolution effects on phase and microstructure of [CsxBay] [Ti2y+x3+Ti8-2y-x4+]O16 ceramic waste forms for radioactive cesium immobilization

The effects of fission product transmutation on the structural stability of ceramic waste forms are a critical concern due to the changes of valence and ionic size, which can impair the stability of the host matrices. In this study, [CsxBay] [Ti2y+x3+Ti8-2y-x4+]O-16 (0.3 <= x, y <= 0.75) ceramics were designed and successfully synthesized to immobilized Cs-137 and its daughter product Ba-137. The evolution of phase and microstructure of the hollandite-ceramic waste forms were investigated by the substitution of Ba2+ into the Cs+ site and the incorporation of Ti3+ for charge compensation. The results show that the prepared hollandite ceramics exhibit excellent capacity to accommodate Cs+ and Ba2+ in its lattice while retaining a stable crystalline structure with a compact microstructure. Additionally, all elements of Cs, Ba, Ti and O homogeneously distributed in the sintered hollandite ceramics. These results further indicate that hollandite ceramics are a promising candidate for selective and durable immobilization of radioactive cesium. (C) 2019 Elsevier B.V. All rights reserved.