Radiation tolerant ceramics for nuclear waste immobilization: Structure and stability of cesium containing hollandite of the form (Ba,Cs)1.33(Zn,Ti)8O16 and (Ba,Cs)1.33(Ga,Ti)8O16

The radiation damage tolerance of nuclear waste forms is dependent on the material's resistance to defect formation and its ability to accommodate structural distortions that arise from defect creation. This study illustrates how the radiation tolerance of hollandite can be improved thorough compositional control of cesium stoichiometry. A hollandite series with the general form BaxCsyZnx+y/2Ti8-x-y/2O16 (0 < x < 1.33; 0 < y < 1.33) was exposed to heavy ion (Kr2+) irradiation at 27 °C, 100 °C, 200 °C and 300 °C followed by characterization with grazing incidence X-ray diffraction, transmission electron microscopy, and aqueous leaching tests. After exposure to 400 keV or 1 MeV Kr2+ irradiation, hollandite exhibited an onset of amorphization near 0.14 dpa and full amorphization ranging from 0.21 to 0.54 dpa depending on the cesium content. The radiation tolerance increased at elevated temperatures with a critical amorphization temperature between 200 °C and 300 °C. Elemental leaching decreased with increasing cesium content. Irradiated samples exhibited twice the fraction of cesium release compared to pristine samples. Experimental results also showed that cesium release from irradiated samples was at a minimum for the Ba0.33Cs1.00Zn0.83Ti7.17O16 sample.