NMR determined interactions in CaB6-structured metal hexaborides: Correlation with structure and properties.

The nuclear quadrupole coupling constant at the boron site, in a series of sixteen isomorphous metal hexaborides with the CaB6 structure, is shown to vary as a function of lattice parameter, metal ion size, and metal ion valence. The NMR data in the literature are comprehensively reviewed and some reanalysed. Electric field gradient (EFG) values derived from experiment are compared with those calculated using first principles density functional theory. Boron EFG values are used as an indicator of the metal-boron bonding and are correlated to cohesive properties, including asymptotic bulk hardness values and melting temperature, to examine the efficacy of NMR aiding materials properties optimisation.