Comparative ab initio study of point defect energies and atom migration profiles in the L12-ordered intermetallic compounds Ni3Al, Ni3Ga, Pt3Ga, Pt3ln

Formation energies of antisite defects and vacancies were derived for the Ll2-ordered intermetallics Ni3Al, Ni3Ga, Pt3Ga, and Pt3In by a supercell ab initio approach. A thermodynamical treatment of point-like defects was then used for the calculation of temperature-dependent defect properties. For all compounds antisite formation requires less energy than vacancy formation, the difference being larger (by 1.2 - 2 eV) for the Ni compounds than for the Pt compounds (by ?0.7-1.1 eV). Some of the tendencies observed can be made plausible by arguments of atom size and relative rigidity of the lattice. Energy profiles for atom jumps were calculated by statically displacing the jumping atom and relaxing the surrounding neighbours. The influence of variable atomic neighbourhoods on the migration barrier and the stability of the initial and final states were studied by systematically exchanging nearest and next nearest neighbour atoms.