Effect of composition on the behavior of pyrochlores irradiated with swift heavy ions

Abstract A 2 B 2 O 7 pyrochlores (zirconates with A = Gd, Nd, Sm or Eu, and a titanate Gd 2 Ti 2 O 7 ) were irradiated with swift heavy ions in order to investigate the effects of the chemical composition on the structural changes induced by high electronic excitation. XRD results show that the structural modifications induced by irradiation with 119 MeV U ions are strongly dependent on the sample composition: Gd 2 Ti 2 O 7 is readily amorphized, whereas Gd 2 Zr 2 O 7 is transformed into a radiation-resistant anion-deficient fluorite structure. For Sm 2 Zr 2 O 7 , Eu 2 Zr 2 O 7 and Nd 2 Zr 2 O 7 , a more complex behavior is observed since both a pyrochlore–fluorite phase transformation and amorphization occur. The results suggest that an ion track is composed of an amorphous track core surrounded by an anion-deficient fluorite shell. The diameters of different track regions were estimated by using a direct impact mechanism coupled with a single overlap process to fit the transformation build-ups. These diameters depend on the sample composition, the susceptibility to amorphization by high electronic excitation increasing with the cation radius ratio r A / r B .