NMR evidence for the coexistence of double structure in CaAlSi

With the aim to examine the possible coexistence of double structure in CaAlSi, a comparative study of the as-prepared and annealed samples using Al27 NMR spectroscopy was performed. For the specimen with heat treatment, the NMR powder pattern clearly exhibits two sets of satellite transitions. We associated the narrow one with the AlB2 -type structure, and the other with the BaPtSb type. We further measured the temperature-dependent spin lattice relaxation rate for each individual structure. Results provide an estimate of Al-s Fermi-level density of states Ns (EF) for both phases. We found that the corresponding electronic characteristics are similar in spite of the distinctness in their local electric environments of the Al sites.