45Sc NMR spectroscopy and first-principles calculation on the symmetry of ScO6 polyhedra in BaO–Sc2O3-based oxides
The correlation between the local structure and the electric-field gradient at the Sc site in ScO6 polyhedra in Sc2O3, Ba3Sc4O9 and BaSc2O4 was investigated by means of 45Sc NMR spectroscopy and DFT calculations. The electric-field gradient at the nucleus as determined experimentally and by calculations is compared using the quadrupolar coupling constant, CQ, around chemically and crystallographically distinct Sc sites in Sc-containing compounds. With CQ as the NMR parameter, the results obtained from the DFT calculation were in good agreement with the NMR measurements. The increase in the CQ values with the standard deviation of the O–O bond length surrounding Sc indicates that CQ is affected by the distribution of the six nearest neighboring O atoms around Sc. This study suggests that CQ plays an important role as an indicator of the local structure around ions, and that a combined complementary approach using both NMR spectroscopy and DFT calculation can be used along with diffraction techniques to provide a detailed understanding of crystal structures.