The energies of constitutional and thermal point defects in the L12 phase were calculated using a first-principles local density functional theory method. Relaxed structures and energies, for vacancies and antisites, were calculated by using a plane-wave pseudopotential. The resultant energies were used, within a dilute-solution formalism, to estimate the equilibrium point defect densities as functions of temperature and composition. The first-principles thermodynamic calculations predicted that this material exhibited antisite constitutional defects for both Al-rich and Sc-rich samples. The density of thermal vacancies was found to be very sensitive to the underlying stoichiometry. At 1000K, the Sc sub-lattice vacancy concentration increased by 10 orders of magnitude as the alloy went from Sc-rich to Al-rich. At this temperature, the density of Sc sub-lattice vacancies was expected to be comparable to the concentration of Al antisite defects in Al-rich alloys.

Density of Constitutional and Thermal Point Defects in L12 Al3Sc. C.Woodward, M.Asta, G.Kresse, J.Hafner: Physical Review B, 2001, 63[9], 094103 (6pp)