Point defect formation and migration in Ga stabilised δ-Pu

Abstract

The energetics of point defects in Ga stabilised δ-Pu are investigated through calculations of formation energies, migration pathways and through on-the-fly kinetic Monte Carlo (OTF-KMC) calculations. Using the Modified Embedded Atom Method as the interatomic potential, defect formation energies are found to depend greatly on both the specie of the defect and the surrounding local environment. Ga vacancies are found to have considerably larger formation energies than Pu vacancies, due to the change in the nearest neighbour Pu–Ga ordering. Point vacancy and point interstitial migration involving Ga atoms or Pu atoms in regions close to substitutional Ga, results in much higher energy barriers than for migration in pure Pu. OTF-KMC calculations show that this leads to defect migration pathways confined to areas of high Pu concentration, with the degree of confinement dependent on the location and ordering of the substitutional Ga. Vacancy migration takes place only through displacing Pu atoms and split Ga interstitials become almost instantaneously substitutional, displacing a Pu atom. The results indicate that the presence of Ga within the Pu matrix has a significant effect on the recovery of point defects.