The irradiation effects of Gd ₂Hf ₂O ₇ and Gd ₂Ti ₂O ₇

In this report, we present dramatically different behavior between isostructural Gd ₂Hf ₂O ₇ and Gd ₂Ti ₂O ₇ pyrochlore using 400 keV Ne ²⁺ irradiation under cryogenic conditions (∼77 K), in which the lattice volume of the irradiated layer of Gd ₂Ti ₂O ₇ increased with ion fluence up to 1 × 10 ¹⁵ ions/cm ², whereas, the lattice volume of the irradiated layer of Gd ₂Hf ₂O ₇ decreased with increasing fluence from 1 × 10 ¹⁵ to 6 × 10 ¹⁶ ions/cm ². The cation radius ratio r _A/r _B, the bond-type of A-O and B-O bonds, the order-to-disorder transition energy of Gd ₂Hf ₂O ₇ and Gd ₂Ti ₂O ₇, temperature-composition (T-C) phase diagrams of HfO ₂-Gd ₂O ₃ and TiO ₂-Gd ₂O ₃ mixtures were used to explain the response of Gd ₂Hf ₂O ₇ and Gd ₂Ti ₂O ₇ to ion irradiation-induced structure transformation.