Nuclear quadrupole couplings and polarizability of the oxygen ion in spinel-structure compounds

Abstract

The contributions of monopoles, dipoles and quadrupoles to the electric field gradient at B sites of normal cubic spinels, ZnAl2O4, ZnFe2O4, CoAl2O4, MgAl2O4, CdFe2O4 and WNa2O4 have been calculated. From a comparison with experimental results, a coherent range of variation of the dipole polarizability of the oxygen ion, between 0.5 and 1.5 AA3, is determined. The variation seems to be due to an evolution of the dipole polarizability with the ionic radius of the oxygen ion. Effects of covalency are also discussed.