The ion-irradiation tolerance of the pyrochlore to fluorite Ho_(x)Yb_(2-x)TiO₅ and Er₂TiO₅ compounds: A TEM comparative study using both in-situ and bulk ex-situ irradiation approaches

We refine the crystal structures of a systematic series of compounds with the general composition Ho_(x)Yb_(2-x)TiO₅ (x = 2, 1.6, 1.2, 1, 0.8, 0.4, 0) and Er₂TiO₅ and find a transition from defect-pyrochlore to defect-fluorite structure with increasing ytterbium content, decreasing lanthanide radius. Short-range structure modulations consisting of pyrochlore-like nano-domains are systematically characterised using transmission electron microscopy. We test the Kr²⁺ 1 MeV ion-irradiation response of Ho₂TiO₅, HoYbTiO₅, Yb₂TiO₅, and Er₂TiO₅, via the crystalline to amorphous transition observed by using the in-situ TEM approach. The critical dose of amorphisation, D_c, was measured at various temperatures and used to calculate the critical temperature for maintaining crystallinity, T_c. A trend of lower T_c values with decreasing lanthanide radius is found. We describe a new approach for determining T_c values using cross-sectional TEM analysis of ex-situ bulk irradiated, 1 MeV Se⁺, samples; Ho₂TiO₅, HoYbTiO₅ and Yb₂TiO₅. The results of D_c and T_c values using the two approaches vary; however the trends across the sample system remain the same.