HRTEM study of track evolution in 120-MeV U irradiated Gd2Ti2O7

High Resolution Scanning Transmission Electron Microscopy (HRTEM) experiments were performed on Gd2Ti2O7 pyrochlore irradiated with 120-MeV U ions. A judicious choice of irradiation energy, sample preparation (using Focused Ion Beam) and analytical technique (HRTEM) allowed us to visualize the complete evolution of tracks from the surface of samples down to depths exceeding the projected range of irradiating ions. Such features as variation of track diameters, changes in track directions and discontinuous segments of tracks were clearly documented at various depths. By using two different Scanning Transmission Electron Microscopy (STEM) imaging modes: High- and Low-Angle Annular Dark Field imaging (HAADF and LAADF), it was possible to observe the radial substructure of tracks composed of an amorphous core surrounded by a damaged and strained crystalline envelope.