57Co impurity-interstitial configurations in NbMo alloys observed by Mössbauer spectroscopy

Lattice defects in NbMo⁵⁷Co alloys produced by neutron irradiation at 4.6 K and by cold working were investigated by Mössbauer spectroscopy. On isochronal annealing up to about 100 K, trapping of two different types of mobile interstitials at the⁵⁷Co probe atoms was observed as additional lines in the spectra. These are characterized by centre shifts of +0.44 mm/s and +0.41 mm/s relative to⁵⁷Co on substitutional lattice sites and by large quadrupole splittings of 1.50 mm/s. Above 640 K, vacancy trapping was observed. With the onset of recrystallization, dislocation pinning was found in both the neutron irradiated and the cold worked sample.