NMR evidence for Co-Al-Co molecular groups trapped in cages of Co4A113

We present the results of Al-27 nuclear magnetic resonance (NMR) experiments on the phase Co4Al13, These results are compared to a recent structure model [I], which demonstrates a unique bonding for Al atoms in the Co-Al-Co molecular groups. In our measurement, two Al-27 signals were identified. The first one originates from Al atoms forming cages. The second signal corresponds to Al sites with exceptionally large almost axially symmetric quadrupole coupling. This finding is in perfect agreement with isolated Co-Al-Co molecular groups in accordance to Ref. [1]. (C) 2008 Elsevier B.V. All rights reserved