The vacancy formation enthalpy in Ni determined by positron annihilation

The monovacancy formation enthalpy, Hsub(1v)sup(F), was determined for Ni using the Doppler broadening technique. The 58Co positron source was ion implanted in Ni of 99.995 wt% purity. A 103Ru γ-ray line (497 keV) was recorded simultaneously with the positron annihilation 511 keV line, and was used in stabilising the data. Measurements were performed on three similar Ni samples, which were annealed in an ultra-high vacuum chamber (10-8-10-9 Torr) at approximately 300C below their melting point for at least two hours prior to the in situ measurements. For one of the samples, a comparison was made of Hsub(1v)sup(F) = 1.8 +- 0.1 eV was determined from the present data. This result is compared with previous positron annihilation and quenching results for Ni. In addition, a value for the monovacancy migration enthalpy, Hsub(1v)sup(M) = 1.1 +- 0.1 eV, has been deduced from a comparison of the present Hsub(1v)sup(F) measurement with previous self-diffusion results. (author)