Characterization of irradiation defects using positron annihilation spectroscopy in γ-NiSb and δ-Ni 2Si intermetallic phases

Abstract

γ-NiSb and δ-Ni 2Si phases were studied using positron annihilation spectroscopy after electron irradiation at 20 K ( E = 3 MeV; dose, about 5 × 10 18 e − cm −2). Isochronal spectra of the τ m positron average lifetime and of the Doppler broadening parameter R showed the same evolution for both compounds studied. Recombination of mobile interstitials with vacancies for NiSb occurred between 100 and 250 K although nickel vacancy migration occurred at approximately 400 K and formed dislocation loops. Mobile interstitials and vacancies recombined at a temperature as low as 77 K for Ni 2Si and were accompanied by the formation of three-dimensional mixed clusters from 325 K. At about 400 K, the less stable clusters evaporated, although recovery was still incomplete at 700 K. In addition, a study of the positron lifetime variation as a function of measuring temperature made it possible to characterize the two- or three-dimensional nature of the clusters formed during annealing.