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Planar defects in off-stoichiometric, Nb-rich NbFe2 Laves phase

Deviations from the ideal, stoichiometric composition of tcp (tetrahedrally close-packed) intermetallic phases as, e.g., Laves phases can be partially compensated by point defects like antisite atoms or vacancies, but also planar defects may offer an opportunity to accommodate excess atoms.

In cooperation with the group Advanced Transmission Electron Microscopy (Christian Liebscher), various types of such planar faults in a Nb-rich off-stoichiometric NbFe2 Laves phase are investigated by HRSTEM (high resolution scanning transmission electron microscopy) and accompanied by ab initio calculations (performed by the CM department). Interestingly, all types of observed planar faults contain structural motifs, which are characteristic for the crystal structure of the µ phase Nb6Fe7 that occurs at higher Nb contents in the binary system; see Fig. 1 for an example.

Fig. 1: Atomically resolved STEM image of a C14-type, Nb-rich NbFe2 Laves phase revealing an extended, coherent planar defect containing structural motifs marked by red arrows that are characteristic for the crystal structure of the Fe-Nb µ phase. For better visualization of the characteristic atomic arrangement in the planar defect, on the right side a magnified sketch of the structure is shown containing as an example a planar defect with two rows of the µ phase structural motifs.

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