45Sc Solid State NMR Spectroscopy – A Complementary Tool to X-ray Crystallography for Structure Determination of Intermetallic Com-pounds
Résumé
45Sc solid state NMR is a useful complementary tool to x-ray crystallographyfor structure determination. The recent developments in the field of intermetallic scandium compounds are reviewed. The structural topics concern defect formation, structural disorder, superstructure formation, as well as the detection of multiple scandium sites. To address questions of this kind, high-resolution 45Sc NMR techniques have been established as a new structural tool for the quantification of the local coordination scan-dium environments and the detailed characterization of their internal NMR interaction parameters. Owing to the moderately sized nuclear electric quadrupole moment of 45Sc, the magic-angle spinning spectra are affected both by first- and second-order quadrupo-lar perturbations, which can be analyzed and quantified by fast magic angle spinning, assisted by lineshape simulations. The resolution can be further improved by correlating triple quantum (TQ) with single quantum coherences. Using this 2D NMR methodol-ogy, the effects of magnetic shielding and second-order quadrupolar perturbations on the MAS NMR lineshape cn be separated, enabling a more precise experimental characteri-zation of electric field gradients present at the 45Sc nuclei. Structure validation includes the precise measurement of these parameters and comparison with quantum mechani-cally calculated values based on the atomic positions. In this regard, satisfactory results have been obtained using the WIEN2k programme.
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