Migration Of Intrinsic Defects Research Articles

Intrinsic defect migration in Be12Ti

Be12Ti is a leading candidate neutron-multiplier material for fusion breeder blankets; yet the evolution of the crystal defects under irradiation is poorly understood. Here, the migration of intrinsic defects in tetragonal Be12Ti was predicted using atomic scale computer simulation. Transport of titanium and beryllium through the interstitial, interstitialcy and vacancy-mediated models was considered, along with the migration of divacancy clusters, previously identified as important to the defect chemistry of Be12Ti. It was found that titanium defects exhibit much higher migration energies than beryllium for most migration pathways, leading to a dramatic difference in the self-diffusivity of the two species. Both beryllium vacancy and interstitial diffusion is close to isotropic with vacancy transport exhibiting the highest self-diffusion coefficient. Migration of beryllium di-vacancies is also isotropic with activation energy equal to that of isolated vacancies. The titanium interstitial exhibits significantly lower migration energy than its vacancy (1.00 eV and 6.75 eV respectively), with both mechanisms strongly anisotropic: the activation energy for [001] migration is at least 5 eV lower than other directions. Even the more exotic mixed titanium beryllium vacancy migration exhibits a much higher migration energy than [001] titanium interstitial transport. The framework used for predicting defect transport kinetics, including vacancy-mediated, interstitial and interstitialcy mechanisms, can be applied to any complex-structured intermetallic compound.

Creation and Migration of Intrinsic Defects in Si‐Doped Diamond Produced Using Microwave Plasma Chemical Vapor Deposition

In this study, low temperature micro‐photoluminescence technology is used to investigate the development and migration of intrinsic defects in Si‐doped diamond. The results demonstrate that NV and Si‐V luminescence are weakened due to the recombination of self‐interstitials created by electron irradiation in diamond. After annealing at high temperatures, interstitial‐related centers disappear and the vacancy migrate significant distances to isolated N and Si atoms for conversion into NV and Si‐V centers.

Interconnection of defect entropies and enthalpies in BaF2 revisited

Here, we investigate the following key prediction of a thermodynamical model that interrelates the defect parameters with the bulk elastic and expansivity data: for various defect processes in a given matrix material, a proportionality exists between defect entropies and enthalpies. The investigation is focused on BaF2 for which ab initio calculations within density functional theory and the generalized-gradient approximation have been recently made as far as the formation and migration of intrinsic defects are concerned, as well as for the elastic constants. Four defect processes have been studied in BaF2: anion Frenkel formation, fluorine vacancy migration, fluorine interstitial motion and electrical relaxation associated with a single tetravalent uranium. For these processes, the entropies and enthalpies vary by almost two orders of magnitude and reveal a proportionality between them. We find that this proportionality is solely governed by the bulk elasticity and expansivity data, which conforms to the aforementioned thermodynamical model.

First-principles investigation of intrinsic defects and (N, O) impurity atom stimulated Al vacancy in Ti2AlC

We use first-principles calculations to study the energetics of intrinsic defects in Ti2AlC and the effect of N or O impurity atoms on the generation of Al vacancies. The insertion of impurity atoms lowers the vacancy formation energy of its neighboring Al. The formation of Al vacancies is related to the experimental observations of growth of AlN or Al2O3 nanowires and nanofibers on the surface of Ti2AlC. Since the growth of these nanostructures is controlled by the generation and migration of intrinsic defects, we propose that a tunable method for synthesis of such nanostructures is possible by controlling impurities.

Correlation of microstructure and strength during stage III annealing of irradiated vanadium

Abstract The microstructure of Vanadium irradiated to a fluence of 1.0 × 1019 n/cm2 E < 1 MeV at a temperature of 55 °C was quantitatively analyzed after irradiation and post-irradiation annealing and correlated with changes in the strength as determined from microhardness measurements. Radiation anneal hardening during Stage III annealing was not accompanied by a change in the size or number of defect aggregates. It is shown that the strength changes and migration kinetics of Stage III are consistent with the migration of oxygen and/or carbon to the defect aggregates. It is suggested that the simultaneous observation of no growth of defect aggregates and radiation anneal hardening in Stage III can be used to differentiate between impurity migration and intrinsic defect migration.