Vacancy formation in Ni and Ni(Ge)

Vacancy formation in Ni and Ni(1 at% Ge) was studied under thermal equilibrium conditions using positron annihilation Doppler-broadening. A monovacancy formation enthalpy of 1.8 +- 0.1 eV was determined for pure Ni; combining this result with those from previous tracer self-diffusion measurements, a monovacancy migration enthalpy of 1.1 +- 0.1 eV was also deduced. An effective vacancy formation enthalpy of 1.4 eV was found for Ni(1 at% Ge). Using a model to simulate the free and bound-vacancy ensemble in the alloy, a value of 0.7 eV was obtained for the formation enthalpy of Ge-bound vacancies. The results are compared with previous theoretical and experimental results. (author)