Recrystallization as the governing mechanism of ion track formation

Abstract

Response of dielectric crystals: MgO, Al 2 O 3 and Y 3 Al 5 O 12 (YAG) to irradiation with 167 MeV Xe ions decelerating in the electronic stopping regime is studied. Comprehensive simulations demonstrated that despite similar ion energy losses and the initial excitation kinetics of the electronic systems and lattices, significant differences occur among final structures of ion tracks in these materials, supported by experiments. No ion tracks appeared in MgO, whereas discontinuous distorted crystalline tracks of ~2 nm in diameter were observed in Al 2 O 3 and continuous amorphous tracks were detected in YAG. These track structures in Al 2 O 3 and YAG were confirmed by high resolution TEM data. The simulations enabled us to identify recrystallization as the dominant mechanism governing formation of detected tracks in these oxides. We analyzed effects of the viscosity in molten state, lattice structure and difference in the kinetics of metallic and oxygen sublattices at the crystallization surface on damage recovery in tracks.

Superionic State in Alumina Produced by Nonthermal Melting

“…We also note that, as reported in the study by Rymzhanov et al, [32] at the front of thermal melting, oxygen sublattice is damaged faster than the aluminum one, suggesting that the superionic state may also be transiently produced.…”

Comprehensive Understanding of Hillocks and Ion Tracks in Ceramics Irradiated with Swift Heavy Ions

“…Two factors that determine the recrystallization process have been proposed; (1) simplicity of lattice structure and (2) the strength of ionic bonding. The previous literature [15] proposed that a simple lattice structure with the smallest number of the peaks in the pair correlation function is in correlation with the recrystallization efficiency. Actually, amorphous ion tracks and hillocks are observed in YIG and GGG that have complicated crystal structure, whereas crystalline ion tracks and hillocks are observed in rather simple structured compounds (CaF 2 , SrF 2 , BaF 2 , and CeO 2 with fluorite structure).…”

“…It has been found that in non-amorphizable ceramics, ion track size is markedly smaller than the size of the melt predicted by the thermal spike models [13,14]. Recent molecular dynamics (MD) simulation has revealed that the small ion tracks in non-amorphizable ceramics are attributable to fast recrystallization after transient melting [15][16][17][18]. It has been pointed out that the ionic nature of atomic bonding in non-amorphizable ceramics may be responsible for such fast recrystallization in non-amorphizable ceramics [9,19].…”

Latent tracks of swift Bi ions in Si3N4

“…To simulate the formation of Bi ion latent tracks a hybrid scheme was applied [7,8] for the coupled kinetics of the excitation and relaxation of the electronic and the atomic sub-systems of a material irradiated with highenergy heavy ions. First, the asymptotic trajectory Monte Carlo code TREKIS [9,10] is used to determine the initial parameters which are characteristic of an excited state of the ensemble of electrons as well as energy transferred to lattice atoms via electron-lattice coupling in an ion track.…”

“…This value is much larger than that obtained from TEM and MD analysis, irrespective of the approach of track size determination. One of possible reasons for this divergence may be the partial recrystallization of the distorted/ disordered lattice, however some investigations have shown that recrystallization does not play significant role in track formation processes in amorphizable materials [8].…”