Comment on ``45Sc Spectroscopy of Solids: Interpretation of Quadrupole Interaction Parameters and Chemical Shifts''

D. RICHARD; E.L. MUÑOZ; T. BUTZ; L.A. ERRICO; M. RENTERÍA

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Lugar: Washington DC; Año: 2011 vol. 115 p. 17621 - 17622

1932-7447

In Ref. 1, .M. D. Alba et al. applied MAS-NMR technique (using 45Sc as a probe-atom) to study the nuclear quadrupole interaction of 45Sc in X2-Sc2SiO5, C-Sc2Si2O7, and in scandium sesquioxide (Sc2O3). In order to obtain a simple model that links the local symmetry around the probes with the observed hyperfine parameters, the authors have compared experimental quadrupole parameters with electrostatic calculations. In particular, they showed that point-charge calculations (PCM) can approximate the electric field gradient (EFG) tensor to a sufficiently good level in order to assign their NMR hyperfine interactions. Discrepancies between the predicted EFGs and the experimental values were attributed to unreliable determination of the structures.In conclusion, hyperfine interactions, and in particular the EFG, constitute a very sensitive tool to investigate the local environment of probe nuclei. In a well-defined single-phase crystal with known lattice structure the interpretation of such measurements is usually not too difficult. But, in more complicated cases like systems with   impurities (being them the hyperfine tracers or other impurity atoms), point defects, multi-phase samples or systems with more than one crystallographic site, the interpretation of multiple interactions is by no means straightforward. In these cases, arguments based on point charge summations or symmetry considerations may fail, and lead to erroneous conclusions. To unravel these complex cases, a realistic theory which models different structural and electronic scenarios is needed.