Electric-field gradients in ionic gadolinium compounds

The calculation of the electric-field gradients (EFG's) in a number of ionic gadolinium compounds is considered. The lattice EFG's at the sites of Gd3+ ions have been evaluated by means of a point-charge model. Comparison of the results with quadrupole-splitting data yields a value of - 75 +- 2 for the Sternheimer antishielding factor γ infinity for the Gd3+ ion. The accuracy of the lattice EFG's is discussed in terms of uncertainties in the structural parameters, the assumption of complete ionicity and the omission of ionic polarisabilities. (author)