A review was presented of positron lifetime spectroscopic studies of high-temperature thermal vacancy formation in intermetallic compounds. In the case of Fe3Al, a low effective vacancy formation enthalpy of 1.18eV was found, giving rise to a high thermal equilibrium vacancy concentration of 0.066 at the melting point; as in B2 intermetallic compounds. Differences in vacancy formation behavior were attributed to the differing lattice structures and bonding characteristics. A tentative comparison with self-diffusion data suggested that an effective vacancy migration enthalpy of 1.58eV applied in the case of Fe3Al. This contrasted with the situation in pure metals, where the formation enthalpy was greater than, or equal to, the migration enthalpy.

Thermal Formation of Vacancies in Intermetallic Compounds. H.E.Schaefer, R.Würschum, J.Bub: Materials Science Forum, 1992, 105-110, 439-50