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, C_Q, around chemically and crystallographically distinct Sc sites in Sc-containing compounds. With C_Q as the NMR parameter, the results obtained from the DFT calculation were in good agreement with the NMR measurements. The increase in the C_Q values with the standard deviation of the O-O bond length surrounding Sc indicates that C_Q is affected by the distribution of the six nearest neighboring O atoms around Sc. This study suggests that C_Q 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.