Irradiation damage in Gd2Ti2O7single crystals: Ballistic versus ionization processes

Abstract

The structural transformations induced in Gd${}_{2}$Ti${}_{2}$O${}_{7}$ single crystals irradiated at high energies (870-MeV Xe), where ionization processes (electronic stopping) dominate, and at low energies (4-MeV Au), where ballistic processes (nuclear stopping) dominate, have been studied via the combination of Rutherford backscattering spectrometry and channeling (RBS/C), Raman spectroscopy, and transmission electron microscopy (TEM) experiments. At high energy, amorphization occurs directly in individual ion tracks from the extreme electronic-energy deposition, and full amorphization results from the overlapping of these tracks as described by a direct impact model. The track diameters lie in the range 6--9 nm. At low energy, amorphization occurs via indirect processes, driven by ballistic nuclear energy deposition from the ions, that is accounted for in the framework of both direct-impact/defect-stimulated and multi-step damage accumulation models. The ion fluence for total amorphization of the irradiated layer is much higher at low energy (0.5 ion nm${}^{\ensuremath{-}2}$) than at high energy (0.05 ion nm${}^{\ensuremath{-}2}$), consistent with the nuclear stopping at low energy (5.2 keV/nm) compared to the electronic stopping at high energy (29 keV/nm).