A technique for measuring thermal vacancy concentrations in stoichiometric FeAl

A technique for measuring thermal vacancy concentrations in FeAl is described. The densities of specimens quenched from different temperatures (to freeze in the thermal vacancies) were obtained from room temperature lattice parameter and bulk density measurements. The two sets of density data were extrapolated to a quenching temperature of 0 K and adjusted to match at that temperature. From the adjusted density values the vacancy concentrations were calculated as a function of temperature. The vacancy formation enthalpy for stoichiometric FeAl was found to be (0.51±0.14) eV. A comparison with published experimental and theoretical formation enthalpies showed considerable uncertainty in measuring and interpreting the formation energy. As a result, the formation energy for thermal vacancies in stoichiometric FeAl is believed to be somewhere between 0.5 and 0.8 eV.