Point Defects in B2 Intermetallic Compounds

We are applying perturbed angular correlations (PAC) to study point defects near 111In probes in ordered B2 alloys. Systems studied include NiAl, CoAl, FeAl, CoGa and PdIn Ten different point defect configurations have been observed in annealed, quenched or mechanically-milled samples. The present status of this work is summarized. Systematics of hyperfine interactions of vacancy defects are then examined. It is found that quadrupole interactions due to first-shell transition-metal vacancies vary in good approximation as the reciprocal cube of the lattice-parameter. Quadrupole interactions due to configurations of two first-shell vacancies exhibit deviations from predictions of a simple point-charge model, which can be explained by small amounts of local lattice relaxation of the probe atom toward the vacancies, of order 0.02 nm. ____________________________________