Point Defects in Intermetallic Compounds

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9313702 Collins Concentrations of point defects in highly-ordered intermetallic compounds are detected with atomic-scale resolution using perturbed angular correlations (PAC), a gamma-ray spectroscopy capable of differentiating clearly between defects. An objective is to identify equilibrium and deformation-induced defects in a variety of compounds. Equilibrium (thermal) defect formation enthalpies and defect concentrations are determined from measured site fractions of probe-defect complexes using a methodology developed during previous studies. Deformation-induced defects are compared to thermal defects and the concentrations estimated from site fractions of probe atoms using PAC and Mossbauer techniques. A second objective is to examine the microstructural evolution of materials subjected to high energy mechanical milling. Defects in volume sites and probe sites at grain boundaries and surfaces are monitored. The effect of the defects on destabilizing equilibrium phases is assessed. %%% The material defects under study here affect phase stability and diffusion in advanced materials used in a variety of applications. ***