Ion velocity effect governs damage annealing process in defective KTaO₃

Abstract

Effects of electronic to nuclear energy losses (Se/Sn) ratio on damage evolution in defective KTaO3 have been investigated by irradiating pre-damaged single crystal KTaO3 with intermediate energy O ions (6 MeV, 8 MeV and 12 MeV) at 300 K. By exploring these processes in pre-damaged KTaO3 containing a fractional disorder level of 0.35, the results demonstrate the occurrence of a precursory stage of damage production before the onset of damage annealing process in defective KTaO3 that decreases with O ion energy. The observed ionization-induced annealing process by ion channeling analysis has been further mirrored by high resolution transmission electron microscopy analysis. In addition, the reduction of disorder level is accompanied by the broadening of the disorder profiles into greater depth with increasing ion fluence, and enhanced migration is observed with decreasing O ion energy. Since Se (~ 3.0 keV nm-1) is nearly constant at all 3 ion energies, the difference in behavior is due to the so-called “velocity effect”: the lower ion velocity below the Bragg peak yields a confined spread of the electron cascade and hence an increased energy deposition density. The inelastic thermal spike calculation has further confirmed the existence of a velocity effect, not previously reported in KTaO3 or very scarcely reported in other materials for which the existence of ionization-induced annealing has been reported.