Stacking fault defects in hcp cobalt studied by PAC

A study was made of lattice defects in hcp Co metal using the technique of perturbed γ-γ angular correlations. Lattice sites of 111Cd impurities were characterized by their nuclear magnetic dipole and electric quadrupole interaction frequencies, respectively ωL and ωO. The signal for defect-free substitutional Cd impurities was found to have collinear interactions at 77 K, with ωL=438 Mrad/s and ωO=7 Mrad/s. Analysis of measurements after heavy deformation at 100 K and after annealings up to 700 K gave little evidence of thermal trapping of point defects. However, in all spectra measured after deformation, a highly stable defect site with ωL=418 and ωO=12 Mrad/s, and showing collinear interactions, was also observed. It is attributed to a 111Cd probe in stacking fault (SF). Assuming a random distribution of probe atoms and SF's, a SF density of 20% was estimated. (orig.)