Stability studies of [CsxBay][(Al3+,Ti3+)2y+xTi4+8-2y-x]O16 ceramics for radioactive caesium immobilization

[Cs x Ba y ][(Al 3+ ,Ti 3+ ) 2 y + x Ti 4+ 8-2 y - x ]O 16 (0.4 ≤  x ,  y  ≤ 0.8) ceramics were synthesized to investigate the substitution effects of Ba 2+ for Cs + on the stability of hollandite-ceramic waste forms. It was found that the substitution of Ba 2+ for Cs + in the (Cs,Ba)-hollandite system does not cause substantial variation in the crystallographic phase and microstructure. The normalized release rates of Cs and Ba at 90 °C in deionized water were < 0.005 g m −2 d −1 after 28 days. These results indicate that hollandite ceramics are an ideal host for permanent radioactive caesium disposal.